Analytical Chemistry, Mass Spectrometry, Natural Product Chemistry, Food Chemistry, Food Processing, Cocoa, Coffee, Black Tea.
Polyphenols – General Remarks
Polyphenols are only second to carbohydrates the most abundant organic compounds on this planet’s biosphere. So they are important. When life emerged out of water onto land, life adapted to unusual new environmental conditions. This was successfully achieved by the biosynthesis of massive amounts and varieties of phenolic compounds acting primarily as efficient UV light screens, thus protecting fragile life from damaging high energy radiation.
In the course of evolutionary adaptation phenolic compounds have been selected in particular by sessile plant organisms to take over a further series of important tasks as response to environmental stresses. These include the following:
- A structural role in plant cell wall components (lignin or otherwise known as wood is polyphenolic)
- Carbon and energy storage accumulated in photosynthesis
- Defense against herbivores and pest organisms
- Attraction of symbiotic organisms (eg flowering and insect attraction for pollination)
- Many further roles of phenolic secondary metabolites are under discussion including photosensing, UV light harvesting
- Polyphenols play an important role in soil chemistry, since all soil is mainly composed from humic substances, degradation products of plant phenols.
Polyphenols are not only crucial for plants, they are equally of enormous importance to humans, due to the high abundance of these compounds in our diet. Estimation of human daily intake of polyphenols varies greatly but including all structural and non-structural compounds could reach a level of 50 g per human per day.
The tenet “Let food be thy medicine and medicine be thy food” espoused by Hippocrates nearly 2,500 years ago, is receiving renewed interest and forms the basic motivation of our work. In particular, there has been an explosion of consumer interest in the health-enhancing role of specific foods or physiologically-active food components, so-called functional foods. Clearly, all foods are functional, as they provide taste, aroma, or nutritive value. Within the last decade, however, the term functional as it applies to food has adopted a different connotation – that of providing an additional physiological benefit beyond that of meeting basic nutritional needs. Overwhelming evidence from epidemiological studies, human intervention studies, in vivo, in vitro assays, and clinical trial data indicates that a plant-based diet can reduce the risk of chronic disease such as diabetes, cardiovascular disease and cancer. In order to put these findings on a sound scientific basis and to reach a position, in which consumer advice can be given with confidence advances in organic and analytical chemistry is urgently required. We need to identify biologically active compounds in the diet in question, provide structure elucidation of the compounds in question and test their biological activity (both beneficial and adverse) once the compounds are available.
Current work comprises the development of novel methods for structure elucidation using mass spectrometry, isolation and general structure elucidation of dietary natural products, synthesis of selected natural products as reference materials and for biological testing and biological testing of dietary natural products in collaboration with many research collaborators. Furthermore techniques for the characterization of crude complex plant materials using mass spectrometry are developed that take advantage of statistical methods in the interpretation of accurate mass data.
Chlorogenic acids (CGAs) are the most important single class of dietary polyphenols. By definition, chlorogenic acids are esters of quinic acid, most commonly characterized by hydroxycinnamate ester moieties. They are consumed at levels of around 2 g per day per human and show excellent bioavailability (meaning they really end up in the blood) if compared to other polyphenols such as tannins or flavanoids.
CGAs display a wide range of fascinating biological activities including anti-HIV, anti-viral, anti-plasmodic, inhibit glucose transporters or show opioid receptor activity.
Chlorogenic acids are ubiquitous plant secondary metabolites and most dietary plants produce this class of compounds, probably selected in the course of evolution as UV-B screens (providing protection between 300 and 350 nm). The majority of plants produce a large number of different chlorogenic acids, many of them being isomers of one another.
The plant producing the largest quantity of chlorogenic acids both in terms of number of compounds and absolute amounts consumed in the human diet is the coffee plant (more than 100 derivatives characterized so far by our research group, with 10 % of the dry weight in a green coffee bean being CGAs and 200 mg CGAs found in an average cup of coffee).
Chlorogenic Acid Analysis
With most plants producing many difefernt chlorogenic acids (between 20 and 100) many of them being isomers, separation and structural chharacterisation of this class of compounds posed a major challenge only 10 years ago with only a handful of derivatives isolated and characterized.
In 2003 our group jointly with the group of Mike Clifford published a novel method for the identification and structure elucidation of regioisomeric chlorogenic acid derivatives (hydroxycinnamate esters of quinic acid). This method revolutionised chlorogenic acid identification and structure elucidation by introducing a method based on tandem mass spectrometry, allowing assignment of regiochemistry based exclusively on fragment spectra. This tandem MS based methods has been successfully adopted in more than 30 laboratories around the world and can be viewed as the current gold standard method for CGA structure elucidation. Prior to 2003 only fourty different chlorogenic acid derivatives were known in our diet. Since the introduction of our method in 2003 more than 300 novel chlorogenic acid derivatives have been identified in our diet by other research groups and around 200 novel derivatives by our group.
This method has the advantage that CGAs do not need to be isolated but can be identified and their structure elucidated directly from analytical LC-tandem-MS runs, even if present as minor components or as chromatographically close eluting compounds. We observed, that all four regioisomeric mono caffeoylquinic acids and later all six regioisomeric dicaffeoyl quinic acids showed dramatically different tandem mass spectra in the negative ion mode, using an ion trap mass spectrometer (for structures see Figure 1). Due to the diagnostic differences in the tandem MS fragment spectra, a consistent and predictive structure diagnostic hierarchical key for CGA structure elucidation has been established, which allows reliable determination of CGA regiochemistry even for minor component CGAs from tandem MS data exclusively. The basis of these differences in tandem MS spectra was rationalized in terms of different hydrogen bonding arrays found in gas phase ions of regioisomeric CGAs. As a rule of thumb a 1-acyl substituent fragments easier than a 5-acyl substituent and easier than a 3-acyl substituent. A 4-acyl substituent is most difficult to fragment and fragmentation is always accompanied by loss of water. Using this method for the first time aspects of regiochemistry can be assessed using mass spectrometry that lead to an unambiguous and reliable structure assignment.
Coffee makes us severe, and grave, and philosophical. ~ Jonathan Swift
Cofee is the Germans’ favourite drink and worldwide the third most popular beverage. Coffee contains large amount of polyphenolic compounds being on average the largest contributor to human polyphenol intake in the Western World.
Coffee contains as secondary plant metabolites mainly chlorogenic acids (around 200 mg per cup of coffee). In the green coffee bean we have in the last 5 years identified around 80 different chlorogenic acids with another 30 derivatives found in other parts of the plants. Therefore coffee shows the largest variety of different plant secondary metabolites of all plants studied so far. Additionally coffee metabolites are transformed by food processing to produce in the roasting process many more compounds (we estimate at least 200), with so far unknown structure. Current research is addressing the chemistry of coffee roasting including the identification of compounds formed during roasting and their potential health benefits.
Tea Polyphenols (Thearubigins)
There is a lot of poetry in a cup of tea – Ralph Waldo Emerson
Black tea is second to water the most consumed beverage on this planet. Green tea (the leaves of camellia sinensis) contains a series of polyphenols of the flavan-3-ol class (otherwise termed catechins) being responsible for the various health benefits of the beverage. Black tea is produced from the young shots of camellia sinensis by a process called fermentation (enzymatic oxidation). After rolling or crushing of the green tea leaves oxidative enzymes transform the green tea catechins into a material, which has been termed the thearubigins by E.A. H. Roberts 50 years ago. The chemical nature of this material has evaded structure analysis for more than five decades and constitutes one of food chemistry’s greatest enigmas. We have now published work unraveling the nature of this mysterious material and shown that thearubigins are a mixture of around 30 000 different phenolic compounds with molecular weights below 2 000 Da, obtained by a oxidative cascade, in which catechins are oxidized following three distinct mechanisms to form a complex mixture of a diversity never before observed in nature.
Similar to black tea cocoa powder is produced by fermentation from the flavan 3-ols (otherwise known as catechins) from the raw cocoa pods. Green tea and cocoa pods therefore share the same precursors to produce after fermentation mysterious materials of unknown structure. The difference between the two products black tea is i) the selectivity of the oxidase enzyme, ii) the presence of further compounds (eg tea fermentation is carried out in a wet leaf, cocoa fermentation in a dried pod, cocoa contains large amounts of lipids); iii) Cocoa is after fermentation additionally roasted similar to coffee.
Current work is addressing the nature of cocoa polyphenols after fermentation and roasting.
Polyphenols in Other Food and Herbal Remedies
Next to the main topics of investigation already mentioned (coffee, black tea and chocolate) we investigate as well other dietary and herbal plants rich in polyphenols. Here we are driven by curiosity (eg why do certain plants share the same biological activities) or by the curiosity of my co-workers that bring along their favourite plants from all over the world to analyse them.
Recently we have investigated for example the following plants:
Stevia Rebaudiana (a very important plant due to its naturally occurring sweeteners, which will in the near future have a great impact on the way we sweeten things, which contains plenty of chlorogenic acids)
Mate Tea (again a plant full of chlorogenic acids)
Burdock (a popular asian vegetable)
Cistus Incanus (Greek mountain rose with anti-viral properties)
Various asteraceae plants
In order to elucidate the structure of dietary polyphenols and to carry out biological testing we use organic synthesis to obtain authentic reference materials. Therefore we have developed synthetic methods for the synthesis of chlorogenic acids and derivatives. Indeed the combination of analysis and synthesis provides one of the strengths of our research group.
Polyphenols in Food Processing and Metabolism
When looking at the health promoting effects of certain diets, it is unclear whether secondary plant metabolites themselves or products of food processing or metabolism (gut floral metabolism or human metabolism) are responsible for human health benefits. In any case all compounds digested with our diet and arising from our diet need to be evaluated.
Hence current work studies the fate of dietary natural products in food processing and metabolism. Highlights of these works include our work on tea processing (what is black tea) and work on mate roasting.
Scientific progress is achieved by new technologies, new discoveries and new ideas, probably in that order. (Sydney Brenner)
Scientific progress is, like it or not, achieved by new technologies. New technologies provide unprecedented capabilities that change our view of nature and lead to new ideas and concepts.
Mass spectrometry, which dramatically evolved and changed over the last two decades, constitutes in our view a technique that has and will fundamentally change the chemical and life sciences offering powerful capabilities driving future scientific progress. These capabilities in order of importance are:
1. Unsurpassed Resolution
A modern high resolution mass spectrometer can resolve several thousand analytes concomitantly and at the current state of art ultra high resolution instruments are able to resolve up to 100 000 analytes in a single spectrum. This resolution is several orders of magnitude higher than any other spectroscopic or separation technique, providing unprecedented insight into the nature and composition of matter. If we assume that a human organism is made up from around 100 000 different chemical entities, this means that at least in theory all human molecules can be analysed at the same time in a single measurement.
2. Structural Information
MS provides two levels of structural information. Firstly high resolution MS data provide information on molecular formulas (elemental composition) and secondly tandem MS provides via fragmentation further structural information on bond connectivities.
3. Coupling to separation techniques
MS instruments can be routinely interfaced with separation devices including HPLC or GC instrument. Additionally further spectrometers can be interfaced providing for each analyte, multi-dimensional specificity and a multitude of structural information via measurement of retention time UV-VIS absorption and MS data.
MS is one of the most sensitive techniques available to chemists with routine sensitivities in the fmol region. Theoretical consideration predict a maximum sensitivity of around 10 ions, which we might see realized within the next decades.
MS can be used for any type of analyte independent of its size, physical state (gas, solid or liquid) or sensitivity. Modern ionization techniques allow the generation of ions from any analyte imaginable.
6. Speed and Ease of Analysis
MS techniques are relatively easy to use (a few months training is sufficient) are rapid and amenable to high throughput applications.
In our research we use many aspects of modern mass spectrometry to study food, biological systems, environmental samples or synthetic compounds. We try to make the best use out of its unique capabilities and try to identify challenges and find solutions to the challenges to improve the capabilities of this technique to advance scientific progress.
The main challenges in modern mass spectrometry are the following, which we try to address in our research:
1. Interpretation of complex data
As mentioned before, modern high resolution MS is able to routinely provide spectra with tens of thousands of different ions present in a single spectrum. How do we interpret such data? Finding solutions to obtain chemical or biological meaningful information is one of MS most pressing and urgent challenges. We have adopted methods devised in petroleomics to address such complex samples and developed a series of novel data interpretation strategies to extract chemical and biological relevant information from such enormously complex data.
2. Obtaining structural information
We believe that MS is not living up to its full capabilities in chemical structure elucidation. Despite many advances, deriving a full chemical structure from MS data is currently only possible in exceptional circumstances. We believe this can be changed by achieving a better understanding of fragmentation mechanisms and using more sophisticated tandem MS techniques such as energy resolved mass spectrometry. Work in this field will be published soon.
3. Distinction of and unambiguous characterization of isomers
Generally MS is considered to be isomerically blind. Isomers, compounds of identical molecular formula, are generally believed to show if any, only subtle differences in their MS spectra. This is not true. We have shown for a series of regioisomeric compounds (chlorogenic acids, shikimic acid derivatives, carbohydrates) that the use of tandem MS techniques provides a powerful method to distinguish isomeric compounds and even allows a reliable prediction of chemical structure (in most cases even superior to NMR). Current work focuses on extension of these methods and the distinction of stereoisomers by tandem MS.
4. Ion Suppression and Ion Enhancement
If more than one analyte is present in an MS analysis, these analytes compete for ionization, leading to a reduction or enhancement of any number of signals. This effect has been termed ion suppression or enhancement and next to spoiling any quantitation attempts is to the current day poorly understood. Understanding ion enhancement is of utmost importance in complex mixture analysis. If thousands of analytes are present we must know, which ones we can observe and which ones not and what level of quantitative information we can derive from such experiments. We are addressing the problem of ion suppression and have recently shown that such effects can be rationalized on the basis of chemical structure itself.
For quantification in MS authentic reference materials are required, ideally a set of isotopically labeled and unlabeled reference material (because of ion suppression) to allow thorough quantification of analytes. Would it not be great if quantification could be carried out without such a requirement? Current work is addressing this problem trying to find methods that allow reference free MS quantification.
6. Non-covalent interactions
In MS both non-covalently bound and covalently bound species can be analyzed. In several ongoing projects we try to understand the nature of non-covalent interactions in MS to be able to study both interactions in biological systems.
1987-1993: Undergraduate Studies in Chemistry at the University of Würzburg, Germany
1993-1995: Ph.D. with W. A. Schenk, Universität Würzburg Thesis: “Synthesis, Reactivity and Dynamic Behaviour of Rutehnium Sulfine Complexes”
1996/1997: Postdoc with S. Warren at the University of Cambridge, UK
1997/1998: Postdoc with Jeremy Robertson at the University of Oxford, UK
1997/1998: Tutor in organic chemistry at Hertford College and Stanford Centre (Keble College), Oxford, UK
1998-2005: Lecturer in organic chemistry at the University of Surrey, Guildford, UK
2005/2006: Senior Lecturer in organic chemistry at the University of Surrey, Guildford, UK
since 2006: Full Professor of Chemistry at the Jacobs University Bremen
Member of the Society of German Chemists (GDCh)
Fellow of the Royal Society of Chemistry (FRSC)
Member of the Deutsche Hochschulverein (DHV)
Member of the DGMS (Deutsche Gesellschaft für Massenspektroskopie)
President of the Surrey Chemical Society (2001/2006)
Visiting Professor at the Universität des Saarlandes (2000)
Visiting professor (Innovartec Chair for combinatorial chemistry), Universität Regensburg (2001)
Visiting Professor of Chemistry at the Jacobs University Bremen (2006)
Sabbatical at CSIC Rocasolano in Madrid (Spain) with Prof. Juan Davalos (2012)
- Profiling of Regioisomeric Triacylglycerols in Pistachio Nuts by High-Performance Liquid Chromatography-Electrospray Ionization Mass Spectrometry“, Sabzi, F.; Sirbu, D.; Kuhnert, N. J. Food Compos. Anal. 2023, 122. https://doi.org/10.1016/j.jfca.2023.105395.
- “Lignin and Its Pathway-Associated Phytoalexins Modulate Plant Defense against Fungi”, Ninkuu, V.; Yan, J.; Fu, Z.; Yang, T.; Ziemah, J.; Ullrich, M. S.; Kuhnert, N.; Zeng, H.. J. Fungi 2023, 9 (1). https://doi.org/10.3390/jof9010052.
- „PtIV-Containing Hexaplatinate(II) [PtIVPtII 6O6(AsO2(CH3)2)6]2- and Hexapalladate(II) [PtIVPdII6O6AsO.”, Zhang, J.; Bhattacharya, S.; Khsara, B. E.; Nisar, T.; Müller, A. B.; Besora, M.; Poblet, J. M.; Wagner, V.; Kuhnert, N.; Kortz, U. Inorg. Chem. 2023. https://doi.org/10.1021/acs.inorgchem.3c00832.
- “Rationalising the Retro-Diels-Alder Fragmentation Pattern of Viscutins Using Electrospray Interface-Tandem Mass Spectrometry Coupled to Theoretical Modelling.”, Moyo, B.; Novokoza, Y.; Tavengwa, N. T.; Kuhnert, N.; Lobb, K.; Madala, N. E. Rapid Commun. Mass Spectrom. 2023, 37 (15). https://doi.org/10.1002/rcm.9592.
- “ Mixed-Valent Palladium(Iv/Ii)-Oxoanion, [PdIVO6PdII6((CH3)2AsO2)6]2”, Ma, X.; Bhattacharya, S.; Nisar, T.; Müller, A. B.; Wagner, V.; Kuhnert, N.; Kortz, U., Chem. Commun. 2023, 59 (7), 904–907. https://doi.org/10.1039/d2cc05699b.
- “Understanding the fragmentation of glucose” M. Patras, J. Z. Davalos and N. Kuhnert, J. Mass Spectrom. 2023, manuscript accepted, in press.
- “Unbiased and biased chemometric analysis of LC-MS data from human urine following coffee intake”, I. Said, S. Haka, J. Truex, C. heidorn, D. Petrov and N. Kuhnert, , J. Mass Spectrom. 2023, manuscript accepted, in press.
- “Identification of oxygenated triacylglycerols in pistachio nuts” F. Sabzi and N. Kuhnert, Food Res. Int. 2023, manuscript accepted.
- Clifford, M. N.; Kuhnert, N. LC–MS Characterization and Quantification of Known and Unknown (Poly)Phenol Metabolites—Possible Pitfalls and Their Avoidance. Mol. Nutr. Food Res. 2022. https://doi.org/10.1002/mnfr.202101013.
- “A practitioner’s dilemma – Mass Spectrometry-Based Annotation and Identification of Human Plasma and Urinary Polyphenol Metabolites” N. Kuhnert and M. Clifford, Mol. Nutr. Food Res. 2022. https://doi.org/10.1002/mnfr.202100985.
- “Investigating the interaction between dietary polyphenols, the human ACE-2 receptor and the SARS CoV-2 Spike Protein” D. Schmidt, N. Ohl, P. Cotrell and N. Kuhnert, Food Func. 2022, https://doi.org/10.1039/d2fo00394e.
- "Discrete, Cationic Palladium(II)-Oxo Clusters via f-Metal Ion Incorporation and Their Macrocyclic Host-Guest Interactions with Sulfonatocalixarenes", S. Bhattacharya, A. Barba-Bon, T.A. Zewdie, A. Müller, I. A. Rutkowska, V. Wagner, N. Kuhnert, W. Nau and U. Kortz, Angew. Chemie - Int. Ed. 2022. https://doi.org/10.1002/anie.202203114.
- " LC–MS Characterization and Quantification of Known and Unknown (Poly)Phenol Metabolites—Possible Pitfalls and Their Avoidance" N. Kuhnert and M. Clifford, Mol. Nutr. Food Res. 2022. https://doi.org/10.1002/mnfr.202101013.
- "Cocoa Bean Fingerprinting via Correlation Networks", S. Kumar, R. N. d'Souza, M. Corno, M. Ullrich, N. Kuhnert, M.-T. Hütt, npj Sci. Food 2022, 6 (1). https://doi.org/ 10.1038/s41538-021-00120-4.
- “Cocoa origin classifiability through LC-MS data: A statistical approach for large and long-term datasets” S. Kumar, R. N. d’Souza, B. Behrends, N. Kuhnert, M. Ullrich, M.T. Hütt, Food Res. Int. 2021, 140, 109983.
- “Editorial special edition Cocotea 2019: Fifth international conference on coffee, cocoa and tea” N. Kuhnert and M. Ullrich, Food Res. Int. 2021, 143, 10243.
- “Thermal peroxidation of dietary pentapeptides yields N-terminal 1,2 dicarbonyls” M. Bikaki and N. Kuhnert, Frontiers Nutrition, 2021, 8, 663233.
- “Heat induced cleavage of the peptide bond in dietary peptides and proteins in food processing” M. Bikaki, R. Shah, A. Müller and N. Kuhnert, Food Chem. 2021, 357, 129621.
- “HPLC-MS based design of experiments approach on cocoa roasting” P. Andruszkiewicz, R. d’Souza, M. Corno and N. Kuhnert, Food Chem. 2021, 360, 129694.
- “LC-MS based metabolomic approach for the efficient identification and relative quantification of bioavailable polyphenolic metabolites in human urine” I. Said, C. Heidorn, D. Petrov, J. Truex, M. Retta, S.Haka, M. Ullrich and N. Kuhnert, Food Chem. 2021, 364, 130198.
- “Small peptides in cocoa” N. Kuhnert, Sweet Visions, 2, 2021, 2-4.
- “Changes of low molecular weight carbohydrates in kale (Brassica oleraceae) during development and acclimation to cold temperatures determined by chromatographic techniques coupled to mass spectrometry” R. Megias-Perez, C. Hahn, B. Behrends, D. Albach and N. Kuhnert, Food Res. Int. 2020, 127, 108865-108875.
- “Naturstoffe aus Rhododendren als Quelle neuer Antibiotika” Rhodoendron und Immergrün, N. Kuhnert, M. Ullrich, D. Albach, H. Schepker, I. Said, A. Shrestha, A. Rezk und J. Noelzen, 2020, Band 29, 3-14.
- “Monitoring the changes of low molecular weight carbohydrates in cocoa beans during spontaneous fermentation: A chemometric and kinetic approach” R. Megias-Perez, M. Zambrano-Moreno, M. Behrends, M. Corno and N. Kuhnert, Food Res. Int. 2020, 127, 108865-108875.
- “LC-MS/MS based molecular networking approach for the identification of cocoa phenolic metabolites in human urine” I.H. Said, J. Truex, S. Haka, D. Petrov, M. Retta, C. Heidorn and N. uhnert, Food Res. Int. 2020, 128, 109119-109129.
- “Investigating time dependent cocoa bean fermentation by ESI-FT-ICR mass spectrometry” N. Kuhnert. R. N. d’Souza, M. Witt and M. Ullrich, Food Res. Int. 2020, 128, 109209-109219.
- “Classification of Brazilian roasted coffee beans from different geographical origins and farming practices based on chlorogenic acid profiles”, S. Badmos, M. Fu, D. Granato and N. Kuhnert, Food Res. Int. 2020, 134, 109218-109228.
- “Evaluation of carbohydrates and quality parameters in six types of commercial teas by targeted statistical analysis” A. Shevchuk, R. Megias-Perez, Y. Zemedie and N. Kuhnert, Food Res. Int. 2020, 133, 109122.
- “Novel Amadori and Heyns compounds derived from short peptides found in dried cocoa beans” P. Andruszkiewicz, R. N. d’Souza, M. Corno and N. Kuhnert, Food Res. Int. 2020, 133, 109164.
- “Functional changes induced by extrusion during cocoa alkalization” D. Valverde, B. Behrends, É. Pérez-Esteve, N. Kuhnert and J. M. Barat, Food Res. Int. 2020, 136, 109469.
- “Recommendation for standardizing nomenclature for dietary (poly)phenol catabolites” C. D. Kay, M. Clifford, P. Mena, D. del Rio, C. Andres-Lacueva, C. Manach, D. S. Wishart, G. Pereira-Caro, F. Tomas-Barberan, N. Kuhnert, G. Williamson and A. Crozier, Amer. J. Clin. Nutrition, 2020, 00, 1-18.
“Inonenmobilitätsmassenspektrometrie in der Analyse isomerer Lebensmittelinhaltsstoffe” G. H. Yassin and N. Kuhnert, Deutsche Lebensmittelrundschau, 2015, 12, 687-682.
“Differentiation of prototropic ions in regioisomeric caffeoyl quinic acids by electrospray ion mobility mass spectrometry” N. Kuhnert, G. H. Yassin, R. Jaiswal, M. F. Matei and C. Grün, Rapid Commun. Mass Spectrom. 2015, 29, 675-680.
“Photochemical isomerisations of chlorogenic acids in model systems and in agricultural practice” H. Karaköse, R. Jaiswal, S. Deshpande and N. Kuhnert, Food Chem. 2015, 63, 3338-3347.
“Characterization of Microalgal Biocrude Obtained by Hydrothermal Liquefaction of Nannochloropsis salina using Ultra High Resolution APCI Fourier Transform Ion Cyclotron Resonance Mass Spectrometry”, M. M. Sanguinetti, N. Hourani, M. Mathery, M. Witt, L. Thomsen, N. Kuhnert, Rapid Commun. Mass Spectrom., 2015, 1255-1264.
“A model system for the mechanism of black tea thearubigin formation “ G. H. Yassin, J. Koek and N. Kuhnert, Food Chemistry, 2015, 180, 272-279.
“The fascination of black tea chemistry” Deutscher Teeinformationsservice, deutscher Teetrinkerverband, April 2015.
“Profiling and quantitation of phenolics in stevia rebaudiana leaves” H. Karaköse, A. Müller and N. Kuhnert, J. Food Agr. Chem. 2015, 63,9188-9198 .
“Synthesis of tetramethoxy-(tetra-hydrazinecarboxamide) cyclophanes with unexpected conformation, and investigation of their solution-phase recognition of chiral carboxylic guests using time-of-flight and tandem mass spectrometry” H. F. Nour, A. Golon, T. El Malah and N. Kuhnert, , ARCIVOC, 2015, 5, 1-19.
“UHPLC-Q-TOF-MS characterization of leaf extracts of hawthorn (Crataegus)”M. E. Karar and N. Kuhnert, J. Biological Chem. Ther. 2015, 3, 3411-3425.
“A review on Sudanese traditional medicinal plants”, M. E. Karar and N. Kuhnert, Rev. Pharmacognosy 2015, manuscript in press.
“Quantification of microbial uptake of quercetin and its derivatives using an UHPLC-ESI-QTOF mass spectrometry assay”. I.H. Said, R.L. Shah, M.S. Ullrich and N. Kuhnert Food Funct., 2016, 7, 4082-4091.
“Aseptic artificial fermentation of cocoa beans can be fashioned to replicate the peptide profile of commercial cocoa bean fermentations”. W. A. John, N. Kumari, N. L. Böttcher, K. J. Kofi, S. Grimbs, G. Vrancken, R. N. D’Souza, N. Kuhnert, and M. S. Ullrich, Food Research International 2016, 89, 764–772.
“Biochemical fate of vicilin storage protein during fermentation and drying of cocoa beans”. N. Kumari, K. J. Kofi, S. Grimbs, R. N. D’Souza, N. Kuhnert, G. Vrancken, and Ullrich, M. S., Food Research International 2016, 90, 53–65.
“Diversity of kale (brassica oleraceae var. sabellica) Glucosinolate content and phylogenetic relationships”. C. Hahn, A. Müller, D. Albach and N. Kuhnert, Agr. Food Chem., 2016, 64, 3215-3225.
“Polyphenol profile and antibacterial activity of Ziziphus Spinae Christi extracts”, M. E. Karar, M. Ullrich, K. Brix, R. Jaiswal and N. Kuhnert, Omics J. Med. Chem., 2016, 1, 345-356.
“Neuroaminidase inhibition of dietary chlorogenic acids and derivatives – Potential antivirals from dietary sources”, Food Function, 2016, 7, 2052-2059.
“Bioactivity in Rhododendron: A systemic analysis of antimicrobial and cytotoxic activities and their phylogenetic and phytochemical origins”. A. Grimbs, A. Shrestha, A.S. Rezk, S. Grimbs, I. Hakeem Said, H. Schepker, M.T. Hütt, D.C. Albach, K. Brix, N. Kuhnert and M.S. Ullrich. Frontiers in plant science, 2017, 8.
“Origin-based polyphenolic fingerprinting of Theobroma cacao in unfermented and fermented beans”. R. N. D’Souza, S. Grimbs, B. Behrends, H. Bernaert, M. S. Ullrich, and N. Kuhnert, Food Research International 2017, http://dx.doi.org/10.1016/j.foodres.2017.06.007
“Metabolome Comparison of Bioactive and Inactive Rhododendron Extracts and Identification of an Antibacterial Cannabinoid(s) from Rhododendron collettianum”, I. Hakeem Said, A. Grimbs, A. Shrestha, K. Brix, M. Ullrich, N. Kuhnert, Analysis, 2017, http://dx.doi.org/10.1002/pca.2694
“Profiling and quantification of regioisomeric caffeoyl glucoses in Solanaceae vegetables”, M. A. Patras, R. jaiswal, N. Kuhnert, Food Chem. 2017, 237, 659-666.
“Comparison of the polyphenolic profile and antibacterial activity of the leaves, fruits and flowers of Rhododendron ambiguum and Rhododendron cinnabarinum”, A. Shrestha, A.S. Rezk, I. Hakeem Said, V. Glasenapp, R Smith, M.S. Ullrich, H. Schepker, N. Kuhnert, BMC Research Notes, 2017, 10 (1), 297.
“Determination of hydroxycinnamic acids present in Rhododendron species”, A. Shrestha, I. Hakeem Said, N. Thielen, L. Lansing, H. Schepker, N. Kuhnert, Phytochemistry , 2017, 144, 216-225.
“Herbal drugs from Sudan: Traditional uses and phytoconstituents – A review”, M. E. Karar and N. Kuhnert, Pharmacognosy Rev. 2017, 11, 83-103.
“Leaves metabolomic profiling of Musa acuminata accessions using UPLC–QTOF–MS/MS and their antioxidant activity” M. A. Sonibare, I. O. Ayoola, B. Gueye, M. T. Abberton, R. D’Souza, N. Kuhnert J. Food Meas. Char. 2018 12:1093–1106.
“Antibiotika aus Rhododendren” H. Schepker, K. Brix, M. Ullrich and Nikolai Kuhnert, Grüne Forschung, 2018, 42.
“Pilot scale production of antibacterial substances by the marine diatom Phaeodactylum tricornutum Bohlin”, S. Wang, I. Hakeem Said, C. Thorstenson, C. Thomsen, M. S. Ullrich, N. Kuhnert and L. Thomsen, Algae Res. 2018, 32, 112-120.
“Profiling, quantification and classification of cocoa beans based on chemometric analysis of carbohydrates using hydrophilic liquid interaction chromatography coupled to mass spectrometry”, R. Megias-Perez, R. D’Souza, S. Grimbs, H. Bernaert and N. Kuhnert, Food Chem. 2018, 258, 284-294.
“Profiling and quantification of caffeoyl glucoses in berry fruits”, M. A. Patras, R. Jaiswal, G. MacDougal and N. Kuhnert, J. Agr. Food Chem., 2018, 66, 1096-1104.
“Tea and coffee with bacteria –Investigation of uptake of key coffee and tea phenolics by wild type E. coli”, I. Hakeem Said, M. S. Ullrich and N. Kuhnert, Food Res. Int. 2018, 108, 584-594.
“Energy resolved mass spectrometry of chlorogenic acids and direct infusion regioisomer quantification” J. Hernandez, A. Müller, R. Jaiswal, J. Z. Davalos, N. Kuhnert, Phytochem. Anal. 2018, https://doi.org/10.1002/pca.2770.
“Degradation of cocoa proteins into oligopeptides during spontaneous fermentation of cocoa beans” R. N. D’Souza, S. Grimbs, B. Behrends, M. Corno, M. S. Ullrich and N. Kuhnert, Food Res. Int. 2018, 109, 506-516.
“Differentiation of black tea infusions according to origin, processing and botanical varieties using multivariate statistical analysis of LC-MS data”, A. Shevchuk, L. Jayasinghe and N. Kuhnert, Food Res. Int. 2018, 109, 387-402.
“Origin and varietal based proteomic and peptidomic fingerprinting of Theobroma cacao in non-fermented and fermented cocoa beans” N. Kumari, A. Grimbs, R. N. D’Souza, S. K. Verma, M. Corno, N. Kuhnert and M. S. Ullrich, Food Res. Int. 2018, 111, 137-147.
“Characterization of triacylglycerols in unfermented cocoa beans by HPLC-ESI mass spectrometry” D. Sirbu M. Corno M S.Ullrich N. Kuhnert, Food Chem. 2018, 254, 232-240.
“Chemistry, antibacterial effects and bioinformatics of Rhododendron secondary metabolites, I. Hakeem Said, M. S. Ullrich and N. Kuhnert, Rhododendron Int. 2018, article in press.
“Changes in the fucoxanthin production and protein profiles in Cylindrotheca closterium in response to blue light-emitting diode light” S. Wang, S. K. Verma, I. Hakeem Said, L. Thomsen, M. S. Ullrich and N. Kuhnert Microbial Cell Factories 2018 17:110.
“Combined use of gas chromatography and HILIC chromatography coupled to mass spectrometry for the characterization and quantification of unknown carbohydrates in cocoa beans” R. Megias-Perez, A. I. Ruiz-Matute, M. Corno, A. Grimbs and N. Kuhnert, J. Chromat. A. 2019, 135-143.
“Biological activities of Ficus carica latex for potential therapeutics in human Papillomavirus (HPV) related cervical cancers” A. Ghanbari, A. LeGresley, D. Naughton, N. Kuhnert, D. Sirbu and G. H. Ashrafi, Nature Sci. Rep. 2019, 9, 1013-1017.
“Profiling and quantification of carbohydrates in green tea infusions” R. Megias-Perez, Y. Zemedie, A. Shevchuk and N. Kuhnert, Food Chem., 2019, 290, 159-167.
“Thermally-induced formation of taste-active 2,5-diketopiperazines from short-chain peptide precursors in cocoa” P. J. Andruszkiewicz, R. d’Souza, I. Altun, M. Corno and N. Kuhnert, Food Res. Int. 2019, 121, 218-228.
“Thermal degradation of Peptides by decarboxylation and tryptohane oxidation” M. Bikaki and N. Kuhnert, J. Agr. Food Chem. 2019, 67, 7448-7454.
“Comparison and quantification of chlorogenic acids for differentiation of green Robusta and Arabica coffee beans” S. Badmos, S. H. Lee and N. Kuhnert, Food Res. Int. 2019, 126, 108544.
“Experimentally modelling cocoa bean fermentation reveals key factors and their influences” W. A. John, N. L. Böttcher, B. Behrends, M. Corno, R. d’Souza, N. Kuhnert and M. S. Ullrich, Food Chem, 2019, 302, 12535.
“Comparative lipidomic studies of Scenedesmus sp. (Chlorophyceae) and Cylindrotheca closterium (Bacillariophyceae) reveal their differences in lipid production under nitrogen starvation” W. Song, D. Sirbu, L. Thomsen and N. Kuhnert, J. Phycol. 2019, manuscript in press.
On the chemistry of small molecular weight polyphenols in black tea, J. W. Drynan, M. N. Clifford, J. Obuchowicz and N. Kuhnert, Prod. Rep.2010, 27, 417-462. read online
The design and synthesis of deep cavity tetra-acrylato-imine calixarene for the development of static and dynamic combinatorial libraries, N. Kuhnert and A. Le-Gresley, Chem. Res., 2010, 2,61-67.
Repeated oral administration modulates the pharmacokinetic behaviour of the chemopreventive agent phenylethyl isothiocyanate in rats, N. Konsuye, N. Kuhnert, J. Kirkpatrick, L. J. King and C. Ioannides, Nutr. Food Res. 2010, 64, 426-432. read online
How to distinguish feruloyl from isoferuloyl quinic acids by tandem mass spectrometry, R. Jaiswal, M. Matei, S. Deshpande, T. Sovdat, N. Kuhnert, Rapid Commun. Mass Spectrom. 2010, 24, 1575-1582. read online
Profiling the chlorogenic acids and hydroxyl cinnamoylshikimates in mate (ilex paraguayensis), R. Jaiswal, T. Sovdat, N. Kuhnert, Agr. Food Chem. 2010, 58, 5471-5484. read online
Analysis, characterization and pharmacokinetics of dietary hydroxycinnamates, N. Kuhnert, H. Karaköse, R. Jaiswal, Invited review chapter in CRC Handbook of Food Analysis, manuscript in press.
Hierarchical scheme for the identification of 3,4,5 triacyl chlorogenic acids in Robusta green coffee beans,Rapid Commun. Mass Spectrom. 2010, 24, 2283-2294. read online
Profiling the chlorogenic acids of Stevia Rebaudiana by tandem LC-MS, H. Karaköse and N. Kuhnert,Polyphenol Commun. 2010, Vol 1, 544-546. 71.
Analysis of the chlorogenic acids and hydroxycinnamoyl shikimate esters in green tea and mate tea by LC-MSn, R. Jaiswal, T. Sovdat, M. Patras and N. Kuhnert, Polyphenol Commun. 2010, Vol 1, 536-538.
Unravelling the structures of black tea thearubigins, N. Kuhnert, Polyphenol Commun. 2010, Vol 1, 56-58.read online
Profile and Characterization of the Chlorogenic Acids in Green Robusta Coffee Beans by LC-MSn –Identification of Seven New Classes of Compounds, R. Jaiswal, P. Eruchivera, M. A. Patras and N. Kuhnert, Agr. Food Chem.2010, 58, 8722-8737. read online
Unravelling the structure of black tea thearubigins, N. Kuhnert, Biochem. Biophys. 2010, 501, 37-51.
Profiling the Chlorogenic Acids of Rudbeckia hirta, Helianthus tuberosus, Carlina acaulis, and Novae angliae Leaves by LC-MS, R. Jaiswal, S. Deshpande and N. Kuhnert, Phytochem. Anal. Manuscript accepted.read online
On the chemical characterization of black tea thearubigins using mass spectrometry, N. Kuhnert, J. W. Drynan, J. Obuchowicz and M. Clifford, Rapid Commun. Mass Spetrom. Manuscript accepted.
Identification and characterization of five new classes of chlorogenic acids containing aliphatic side chains in Gardenia fructis (Gardenia sativa) by liquid chromatography tandem mass spectrometry, R. Jaiswal, M. N. Clifford and N. Kuhnert, Rapid Commun. Mass Spectrom. manuscript accepted.
Analysis of black tea thearubigins: Evidence for oxidative cascade reactions forming the thearubigins, N. Kuhnert, M. N. Clifford and A. Müller, Food and Function, manuscript accepted 2010.
Identification and characterization of five new classes of chlorogenic acids containing aliphatic side chains in Burdock (Arcticum lappa L.) roots by liquid chromatography tandem mass spectrometry, R. Jaiswal and N. Kuhnert, Food and Function manuscript accepted.read online
Scope and limitations of principal component analysis of high resolution LC-MS data: The analysis of the chlorogenic acid fraction in green coffee beans as a case study, N. Kuhnert, R. Jaiswal, PO. Eruvichera, M. El-Abassy, B. von der Kammer and A. Materny, Anal. Manuscript accepted. read online
Synthesis of Tri-substituted Biaryl Based Trianglimines: Formation of C3-symmetrical and Non-symmetrical Regioisomers, H. F. Nour, M. F. Matei, B. S. Bassil, U. Kortz and N. Kuhnert. Manuscript accepted 2010.read online
Hill Coefficient of dietary polyphenolic enzyme inhibitors: Can beneficial health effects of dietary polyphenols be explained by allosteric enzyme denaturing? N. Kuhnert, F. Dairpoosh, R. Jaiswal, M. Matei, S. Deshpande, A. Golon, H. Nour, H. Karakoese and N. Hourani, Journal of Chemical Biology, 2010 (Submitted). read online
An investigation of the Hydroxycinnamate Profile of Six Galium Plants from the Rubiaceae Family. R. Jaiswal, S. Deshpande and N. Kuhnert. Phytochemical Analysis, 2010, (Submitted).
How to Identify and Discriminate Between the Methyl Quinates of Chlorogenic Acids by Liquid Chromatography/Tandem Mass Spectrometry. R. Jaiswail and N. Kuhnert. Journal of Mass Spectrometry, 2010, (Submitted). read online
Profiling the Hydroxycinnamates of 12 Plants from Asteraceae Family by High–Performance Liquid Chromatography/Tandem Mass Spectrometry. R. Jaiswal, J. Kiprotick and N. Kuhnert. Phytochemistry, 2010, (Submitted).
Identification and Characterization of Two New Classes of Chlorogenic Acids in Arnica (Arnica montana L.) Flowers by High–Performance Liquid Chromatograpghy. R. Jaiswal and N. Kuhnert. Journal of Agricultural and Food Chemistry, 2010, (Submitted).
“Identification and characterization of five new classes of chlorogenic acids containing aliphatic side chains in Burdock (Arcticum lappa L.) roots by liquid chromatography tandem mass spectrometry” R. Jaiswal and N. Kuhnert, Food and Function 2011, 2, 63-71.
“Scope and limitations of principal component analysis of high resolution LC-MS data: The analysis of the chlorogenic acid fraction in green coffee beans as a case study” N. Kuhnert, R. Jaiswal, PO. Eruvichera, M. El-Abassy, B. von der Kammer and A. Materny, Anal. Meth. 2011, 3, 144-155.
“Synthesis of substituted biaryl based trianglimine and trianglamine mecrocycles: Formation of C3symmetrical versus non-symmetrical macrocycles” H. Nour, M. Matei, B. Bassil, U. Kortz, N. Kuhnert, Org. Biomol. Chem. 2011, 9, 3258-3271.
“Characterisation of chlorogenic acids in Galium species” R. Jaiswal, N. Kuhnert, Phytochem. Anal.manuscript accepted.
“Identification of all Regioisomers of Methylquinates by LC-tandem mass spectrometry” R. Jaiswal, N.Kuhnert, J. Mass Spectrom. 2011, 46, 269-281.
“Schwarzer Tee –Der Meister der molekularen Vielfalt”,N. Kuhnert, Laboratory and More, 2011, 124-128.
“Hill coefficients of dietary Polyphenols – Are dietary polyphenols nothing else but allosteric enzyme denaturing agents?”, N. Kuhnert, F. Dairpoosh, H. Nour, N. Hourani, R. Jaiswal, M. Matei, S. Deshpande, A. Golon, H. Karaköse, J. Chem. Biol. 2011, 21, 755-763.
“Profiling the Hydroxycinnamates of 12 Plants from Asteraceae Family by High-Performance Liquid Chromatography/Tandem Mass Spectrometry”, R. Jaiswal, J. Kiprotich, N. Kuhnert, Phytochem.2011, 72, 781-790.
“Profiling the chlorogenic acids in Arnica Montana flowers: Identification of five new classes of aliphatic chlorogenic acids” R. Jaiswal, N. Kuhnert, J. Agr. Food Chem. 2011, 59, 4033-4039.
“Inhibition of DNA Methyltranferase 3a by black tea and coffee phenolics – a potential mechanism for the brain performance enhancing effects of dietary phenols” A. Tulysheva, R. Jaiswal, N. Kuhnert, A. Jeltsch, BMC Biochemistry, 2011, DOI: 10.1186/1471-2091-12-16.
“Characterisation of dehydration products of chlorogenic acids in roasted coffee” M. F. Matei, R. Jaiswal, F. Ullrich and N. Kuhnert, J. Mass Spectrom. 2011, manuscript accepted.
“Assessing the thearubigins from black tea by high resolution MS methods” N. Kuhnert, Deutsche Lebensmittel Rundschau 2011, 107, 388-391.
“Was steckt unter dem Hügel?”N. Kuhnert, Nachr. Chemie und Technik 2011, 866-871.
„Profiling and quantification of the chlorogenic acids in Stevia Rebaudiana”, H. Karaköse, R. Jaiswal, N.Kuhnert, J. Agr. Food Chem. 2011, 59, 10143-10150.
“An analytical method for the discrimination of caffeoyl shikimates and caffeoyl quinides in heat processed food”, N. Kuhnert, M. F. Matei,F. Ullrich, N. Kuhnert, J. Mass Spectrom.2011, 46, 933-942.
“Regioisomere Chlorogensäurederivate- Identifizierung durch Tandem Massenspektrometrie”, N.Kuhnert, Deutsche Lebensmittelrundschau 2011, 107, 521-524.
“Synthesis of novel enantiomerically pure tetra-carbohydrazide cyclophane macrocycles“ H. F. Nour, N. Hourani, Org. Biomol. Chem. 2012, 10, 4381-4389.
“First diastereoselective synthesis of caffeoyl and feruloyl muco-methylquinates” R. Jaiswal, M. H. Dickman,N. Kuhnert, Org. Biomol. Chem. 2012, 10, 5266-5277.
“Chemistry of pyrazolinones and their applications” WH. Wafaa, H. G. El-Gohary, N. Kuhnert, Current Org. Chem. 2012, 3, 373-399.
“Development of a novel direct infusion atmospheric pressure chemical ionization mass spectrometry method for the analysis of heavy hydrocarbons in light shredder waste” N. Hourani, N. Kuhnert, Anal. Meth.2012, 3, 730-735.
“Monitoring stepwise proteolytic degradation of peptides using supramolecular domino tandem assays and mass spectrometry for trypsin and leucine aminopeptidase” G. Ghale, N. Kuhnert, W. M. Nau, Nat. Prod. Commun. 2012, 7, 343-348.
“Black tea – the ultimate master of molecular diversity” Lab and More Int. Ed. Engl. 2012, 465-467.
“Unravelling the chemical composition of caramel”, A. Golon, N. Kuhnert, J. Agr. Food Chem. 2012, 60, 3266-3274.
“Analyse von Karamel durch Domino Tandem Massenspektrometrie” A. Golon, N. Kuhnert, Deutsch.Lebensmittelrundschau 2012, 108, 148-151.
“Identification and characterization of proanthocyanidines of 16 members of the Rhododendron genus (Ericaceae) by tandem LC-MS” R. Jaiswal, L. Jayasinghe, N. Kuhnert, J. Mass Spectrom. 2012, 47, 502-515.
“MALDI-TOF mass spectrometry: avoidance of artifacts and analysis of caffeine precipitated S II thearubigin fraction from 15 commercial black teas” J. W. Drynan, M. N. Clifford, J. Obuchowicz, N. Kuhnert, J. Agr. Food Chem. 2012, 60, 4514-4525.
“Probing the dynamic reversibility of trianglimine formation using real time mass ESI time of flight mass spectrometry” H. F. Nour, A. Lopez-Periago, N. Kuhnert, Rap. Commun. Mass Spectrom. 2012, 26, 1070-1080.
“Raman spectroscopic characterization of different regioisomers of mono acyl and di acyl chlorogenic acids” P. Eravuchira, R. M. El-Abassy, S. Deshpande, N. Kuhnert, A. Materny, Vib. Spectr. 2012, 61, 10-16.
“Polyphenole in Lebensmitteln, Arzneidrogen und industrieller Anwendung”ChemiuZ, 2012, manuscript accepted.
“Understanding the fate of chlorogenic acids in coffee roasting using mass spectrometry based targeted and non-targeted analytical strategies” R. Jaiswal, M. F. Matei, A. Golon, M. Witt, N. Kuhnert, Food Func. 2012,3, 976-984.
“Synthesis of enantiomerically pure tetra carbohydrazide cyclophane macrocycles” H. F. Nour, N. Hourani,N. Kuhnert, Org. Biomol. Chem. 2012, 10, 4381-4389.
“First diastereoselective synthesis of methyl caffeoyl and feruloyl muco quinates” R. Jaiswal, M. H. Dickman, N. Kuhnert, Org. Biomol. Chem. 2012, 10, 5266-5277.
“Investigating the chemical changes of chlorogenic acids during coffee brewing: Conjugate addition of water to the olefinic moiety of chlorogenic acids and their quinides” M. F. Matei, R. Jaiswal, N. Kuhnert, J. Agr. Food Chem. 2012, 60, 12105-12115.
“Lessons from the analysis of complex dietary mixtures by mass spectrometry – understanding the chemistry of black tea thearubigins, coffee melanoidines and caramel”, N. Kuhnert, F. Dairpoosh, A. Golon, G. Yassin and R. Jaiswal, Food and Function, 2013,4, 1130-1147.
“In Garden, Industry Medicine and Food: Polyphenols versatile Plant Ingredients”, N. Kuhnert, Chemie in Uns. Zeit, 2013, 47, 80-91.
“Characterisation of caramel – type thermal decomposition products of monosaccharides including glucose, mannose, galactose, arabinose and ribose using advanced mass spectrometrical methods” A. Golon and Kuhnert, Food Function, Maillard centenary edition, 2013, 4, 1040-1050.
“Analysis of chlorogenic acid lactones and caffeoyl shikimic acids in roasted coffee”, Eng. Food Sci. 2013, 17, 568-576.
“Chemistry inside molecular containers in the gas phase” C. Lee, E. Kalenius, A. I. Lazar, I. Assaf, N. Kuhnert, C. H. Grün, J. Jänis, O. A. Sherman, W. N. Nau, Nature Chemistry, 2013, 4, 376-382.
“One size does not fit all – bacterial cell death by antibiotics cannot be explained by the action of reactive oxygen species”, N. Kuhnert, Chem. Int. Ed. Engl. 2013, 52, 10946-10948.
“Identification of Phenolic Compounds in Plum Fruits (Prunus salicina L. and Prunus domestica L.) by High-Performance Liquid Chromatography/Tandem Mass Spectrometry and Characterization of Varieties by Quantitative Phenolic Fingerprints” R. Jaiswal, H. Karaköse, S. Ruehmann, D. Treutter and N. Kuhnert, Agr. Food Chem. 2013, 61, 1220-1231.
“Synthesis of novel chiral bis-N-substituted-hydrazinecarboxamide receptors and probing their solution-phase recognition to chiral carboxylic guests by ESI-TOF/MS and tandem ESI-MS” H. Nour, A. Golon, T. Islam, M. Fernandez-Lahore, N. Kuhnert, Tetrahedron Lett. 2013, 54, 4139-4142.
- “Identification and Characterization of the Phenolic Glycosides of Lagenaria siceraria Stand. (Bottle Gourd) Fruit by Liquid Chromatography-Tandem Mass Spectrometry” R. Jaiswal, N. Kuhnert, Food Chem. 2014, 62, 1261-1271.
- “Biologische Reststoffbehandlung bei der Autoverwertung” D. Lompe, C. Schubert, J. Warrelmann, A. Groddek, Hewitter, A. Golon and N. Kuhnert, Müll und Abfall, 2014, 14, 259-268.
- “Identification, Characterization, Isolation and Activity Against Escherichia coli of Quince (Cydonia oblonga) Fruit Polyphenols” M. G. Elsadig Karar, D. Pletzer, R. Jaiswal, H. Weingart, N. Kuhnert, Food Res. Int. 2014, 65, 121-129.
- “Which spectroscopic technique allows the best differentiation of coffee varieties: comparing principal component analysis using data derived from CD-, NMR- and IR-spectroscopies and LC-MS in the analysis of the chlorogenic acid fraction in green coffee beans”, S. Deshpande, R. M. El-Abassy, R. Jaiswal, P. Eravuchira, B. von der Kammer, A. Materny and N. Kuhnert, Analytical Methods 2014, 6, 3268-3276.
- “Understanding the dark side of food: analysis of processed food by modern mass spectrometry” N. Kuhnert, New Food 2014, 17, 58-64.
- “ Identification of novel cocoa flavonoids from raw fermented cocoa beans by HPLC-MS “, M. A. Patras, B. Milev, G. Vrancken, Food Res. Int. 2014, 63, 353-359.
- “Fourier transform ion cyclotrone resonance mass spectrometrical analysis of raw fermented cocoa beans from Cameroon and Ivory Coast origin” B. Milev, M. A. Patras, G. Vrancken, N. Kuhnert, Food Res. Int. 2014, 64, 958-962.
- “An Investigation of the complexity of Maillard reaction product profiles from the thermal reaction of amino acids with sucrose using high resolution mass spectrometry”, A. Golon, I. Vockenroth, C. Kropf, N. Kuhnert, Food, 2014, 3, 461-475.
- “Identification of trimeric and tertameric flavan-3-ol derivatives in the SII black tea thearubigin fraction of black tea using ESI-Tandem and MALDI-TOF Mass Spectrometry”, G. H. Yassin, J. Koek, N. Kuhnert, Food Res. Int. 2014, 63, 317-327.
- “Hierarchical key for the identification of all ten regio- and stereoisomers of monocaffeoyl glucose by LC-tandem mass spectrometry”, R. Jaiswal, M. A. Patras, M. Matei, V. Glembockyte, N. Kuhnert, Food Chem. 2014, 62, 9252-9265.
- “Investigation of isomeric flavanol structures in black tea thearubigins using UHPLC coupled to ion mobility mass spectrometry” G. H. Yassin, J. Koek, N. Kuhnert, Mass Spectrom. 2014, manuscript in press.
- “LC-MSn identification and characterization of the phenolic compounds from the fruits of Flacourtia indica (Burm. F.) Merr. and Flacourtia inermis Roxb” A. G. A. W. Alakolanga, A. M. D. A. Siriwardane, N. S. Kumar, L. Jayasinghe, R. Jaiswal and N. Kuhnert, Food Res. Int. 2014, 62, 388-396.
- “Does roasted coffee contain chlorogenic acid lactones and/or caffeoyl shikimates?”, R. Jaiswal, M. F. Matei and N. Kuhnert, Food Res. Int. 2014, 61, 214-227.
- “Investigation of acyl migration in mono- and dicaffeoylquinic acids under aqueous basic, acidic and dry roasting conditions” Chem. 2014, 62, 9160-9170.
- “Identification of Novel Homologous Series of Polyhydroxylated Theasinensins and Theanaphthoquinones in the SII Fraction of Black Tea Thearubigins using ESI /HPLC Tandem Mass Spectrometry” G. H. Yassin, J. Koek, S. Jayaraman and N. Kuhnert, Food Chem. 2014, 62, 9848-9859.
- “Identification and characterization of phenolics of Ilex Glabra (Aquifoliaceae) leaves by liquid chromatography mass spectrometry” R. Jaiswal, A. E. Halabi, M. G. E. Karar and N. Kuhnert, 2014, 106, 141-155.
- “Identification and characterization of phenolics from Ixora coccinea (Rubiaceae) by liquid chromatography multi stage mass spectrometry” R. Jaiswal, M. G. Elsadig Karar, G. H. Abdel, and N. Kuhnert, 2014, 25, 567-576.
- “Investigation of isomeric flavanol structures in black tea thearubigins using ultraperformance liquid chromatography coupled to hybrid quadrupole ion mobility time of flight mass spectrometry” G. H. Yassin, C. Grün, J. Koek and N. Kuhnert, Mass Spectrom. 2014, 49, 1086-1095.
- “Identification, characterization and antimicrobial activity of quince (Cydonia oblongata) fruit polyphenols” M. G. E. Karar, R. Jaiswal and N. Kuhnert, Food Res. Int. 2014, 65, 121-129.
- “Identification and Characterization of Trimeric Proanthocyanidins of Two Members of the Rhododendron Genus (Ericaceae) by Liquid Chromatography Multi‐Stage Mass Spectrometry” R. Jaiswal, M. G. E. Karar and N. Kuhnert. Encyclopedia of Analytical Chemistry. Marietta: Wiley Online Library, 2014.
- “Studies in Natural Products Chemistry” N. Kuhnert, I. Hakeem Said and R. Jaiswal, ed. R. Atta ur, Elsevier, 2014, vol. 42, pp. 305-339.
- “Identification and characterization of chlorogenic acids, chlorogenic acid glycosides and flavonoids from Lonicera Henry L. (Caprifoliaceae) leaves by LC-MSn”. R. Jaiswal, H. Müller, A. Müller, M. G. E. Karar and N. Kuhnert, Phytochem.2014, 108, 252-263.
Discriminating between the six isomers of dicaffeoylquinic acid by LC-MSn, M. Clifford, S. Knight and N. Kuhnert, Agr. Food Chem.2005, 53, 3821-3832. read online
Characterization by LC–MSn of four new classes of chlorogenic acid methyl ethers in green coffee beans: dimethoxycinnamoylquinic acids, diferuloylquinic acids, caffeoyl-dimethoxycinnamoylquinic acids, and feruloyl-dimethoxycinnamoylquinic acids“ M. Clifford, S. Knight and N. Kuhnert, Agr. Food Chem. 2005,53, 3461-3471.
The synthesis and conformational properties of oxygenated trianglimine macrocycles, N. Kuhnert, A. Lopez-Periago and G. M. Rossignolo, Biomol. Chem. 2005, 3, 524-537. read online
The synthesis of static and dynamic combinatorial libraries using deep cavity tetra-formyl calixarenes, N. Kuhnert and A. Le-Gresley, Tetrahedron Lett.2005,46, 2059-2062.
Modulation of hepatic cytochromes P450 and phase II enzymes by dietary doses of sulforaphane in rats: implications for its chemopreventive activity, V. Yoxall, P. Kentish, N. Coldham, N. Kuhnert, M. J Sauer1 and C. Ioannides, J. Cancer. 2005, 1354-1368.read online
On the activation of valerolactam using triflic anhydride, N. Kuhnert, I. Clemens, R. Walsh, Biomol. Chem.2005, 3, 1694 – 1701. read online
Varying the size of the trianglimine cavity-Macrocycles for applications in nanomachines, N. Kuhnert, C. Patel, N. Burzlaff and A. Lopez-Periago, Biomol. Chem.2005, 3, 1911-1921.
Synthesis and capsule formation of tetra-acrylamido calixarenes, N. Kuhnert and A. Le-Gresley, Biomol. Chem. 2005, 3, 2175-2182. read online
Synthesis of chiral non-racemic polyimine macrocycles from cyclocondensation reactions of biaryl and terphenyl based dicarboxaldehydes and 1R, 2R diaminocyclohexane, N. Kuhnert, C. Patel and F. Jami.,Tetrahedron Lett.2005, 46, 7575-7579. read online
Total synthesis of chrysophanol and sennoside C aglycon, N. Kuhnert and H.Y. Molod, Tetrahedron Lett.2005, 46, 7571-7573. read online
Characterisation by LC-MSn of four new classes of chlorogenic acids in green coffee beans: dimethoxycinnamoylquinic acids, diferuloylquinic acids, caffeoyl-dimethoxycinnamoylquinic acids and feruloyl-dimethoxycinnamoylquinic acids, M. N. Clifford, S. Knight, B. Surucu, N. Kuhnert, Agr. Food. Chem. 2006, 54, 1957-1969. read online
Synthesis of diastereomeric trianglamine cyclodextrin  catenanes, N. Kuhnert and B. Tang, Tetrahedron Lett.2006, 47, 2985-2988. read online
Synthesis of enantiomerically pure functionalized trianglamine macrocycles by N-acylation and N-alkylation reactions, N. Kuhnert, D. Goebel, C. Thiele, B. Tang, Tetrahedron Lett.2006, 47, 6915-6918. read online
Characterisation by LC-MSn of four new classes of p-coumaric acid containing diacyl chlorogenic acids in green coffee beans”, M. N. Clifford, S. Marks, S. Knight, N. Kuhnert, Agr. Food Chem. 2006, 54, 4095-4101. read online
The chlorogenic acids of Hemerocallis, M. N. Clifford, W. Wu and N. Kuhnert, Food Chem. 2006, 95, 574-578. read online
Profiling the chlorogenic acids of aster by HPLC-MSn, M. N. Clifford, Z. Wang, N. Kuhnert, Anal. 2006, 17, 384-393. read online
Profiling the chlorogenic acids and other caffeic acid derivatives of herbal chrysanthemum by LC-MSn, M. N. Clifford,W. Wu, J. Kirkpatrick, N. Kuhnert, Agr. Food Chem. 2007, 55, 929-936. read online
Profiling and characterization of galloyl quinic acids by LC-MSn of green tea, tara tannin and tannic acid, M.N. Clifford, S. Stoupi, N. Kuhnert, Agr. Food. Chem.2007, 55, 2797-2807. read online
A structural model for the ion suppression effects of carboxylic acids in negative ESI ion mode, M. N. Clifford, L. Pouquet, V. Lopez, G. Williamson , N. Kuhnert, Commun. Mass Spectr. 2007, 21, 2014-2018. read online
The application of quasi-enantiomeric trianglamine macrocycles as chiral probes for anion recognition in ion trap ESI mass spectrometry, N. Kuhnert, D. Marsh, D. C. Nicolau, Tetrahedron Asymm. 2007, 18, 1648-1654. read online
The synthesis, self-association and chiroselectivity of isotopically labeled trianglamine macrocycles in the ion trap mass spectrometer, N. Kuhnert, A. Le-Gresley, D. C. Nicolau, Labelled Comp. Radiopharm.2007, 50, 1215-1223. read online
The metabolism of 2-amino.3.methylimidazol [4,5] quinoline by precision-cut rat liver slices, N. Arya, N. Kuhnert, C. Ioannides, J. Kirkpatrick, D. Stevenson, Toxicology2007, 240, 185.
The absolute bioavailability and dose dependent pharmacokinetic behaviour of dietary doses of the chemopreventive isothiocyanate sulforaphane in rat, N. Hanlon, N. Coldham, A. Gielbert, M. Sauer, N. Kuhnert, C. Ioannides, British J. Nutrition2008, 99, 559-564. read online
Synthesis of upper rim calixarene carcerands, N. Kuhnert, A. Le-Gresley, Tetrahedron Lett. 2008, 49, 1274-1276. read online
The LC-MSn analysis of cis isomers of chlorogenic acids, N. Kuhnert, M. N. Clifford, Food Chem. 2008, 106, 379-385. read online
Insecticidal activities of Zingiber officinalis and cynbopogon nardus, Z. Abo Elnaga, N. Kuhnert, M. Abdel-Mogib, Pharmacetical Biol. 2009, 47, 27.
Stereo- and Enantioselective Reactions of Organosulfur Compounds Mediated by Transition Metal Complexes, W. A. Schenk, J. Bezler, N. Burzlaff, E. Dombrowski, J. Frisch, N. Kuhnert, I. Reuther, Phosphor Sulfur Silicon Rel. Elem.1994, 95, 367. read it
Stereochemically Controlled Synthesis of Substituted 1,2 Oxathianes, J. Eames, N. Kuhnert, R. V. H. Jones and S: Warren, Tetrahedron Lett. 1998, 39, 1251-1254. read it
Scope and Limitation of [1,4]-S-Benzyl Participation and Debenzylation in the Stereochemically Controlled Synthesis of Substituted Thiolanes, J. Eames, N. Kuhnert, R. V. H. Jones and S, Warren, Tetrahedron Lett.1998,39, 1247-1250. read it
Bis-Trifluoromethansulfonimide in the Catalytic Conjugate Allylation of alpha,beta-Unsaturated Carbonyl Compounds, N. Kuhnert, J. Peverley and J. Robertson, Tetrahedron Lett. 1998, 39, 3215-3216. read it
Kinetic Versus Thermodynamic Control in the Stereospecific Synthesis of Tetrahydro-Pyrans and Furans: Exo Versus Endo Transition States and [1,2] Versus [1,4] Phenylsulfanyl Participation, J. Eames, N. Kuhnert and S. Warren, Synlett 1999,8, 1211-1214.
[1,2]- and [1,4] Phenylsulfanyl Migrations as Alternative Cascade Sequences for the Stereocontrolled Synthesis of Tetrahydrofurans, J. Eames, N. Kuhnert and S. Warren, Synlett 1999, 8, 1215-1218.
Acetylsalicylsäure feiert Ihren 100. Geburtstag, Chemie in unserer Zeit 1999,33, 213-220.
Aspirin, das erfolgreichste Arzneimittel des letzten Jahrtausends, Pharmazie in unserer Zeit 2000, 14, 1-8.
Halfsandwich Ruthenium Complexes of Sulfinic Esters, N. Kuhnert and W. A. Schenk, Naturforsch B 2000, 55, 527 – 535. read online
1282 Chemische Bachelor und Master-Studiengänge in Grossbritannien, N. Kuhnert, Nachrichten aus Chem. und Technik 2000, 11, 1352-1356. read online
Synthesis of 14-C-Labelled Sulforaphane, N. Kuhnert, G. Williamson and B. Holst, Labelled Comp. Radiopharm.2001, 44, 347-355. read online
Synthesis of 3-Chloro-3-Formylpyrrole Derivatives, J. Robertson, N. Kuhnert and Y. Zhao, Heterocycles2000, 53, 2415-2420.
Scope and Limitation of the [1,2]-Alkylsulfanyl (SMe, SEt and SCH2Ph) and Sulfanyl (SH) Migration in the Stereospecific Synthesis of Substituted Tetrahydrofurans, J. Eames, N. Kuhnert and S. Warren, Chem. Soc. Perkin Trans. 12001, 138-143. read online
Highly Diastereoselective Synthesis of Homochiral 1,3-Oxazolidines under Thermodynamic Control Using Focused Microwave Irradiation under Solvent Free Conditions, N. Kuhnert and T. N. Danks, Green Chem.2001, 3, 68-70. read online
Unkonventionell Techniken in der Organischen Synthese, N. Kuhnert, Chemie und Technik 2001(Trendberichte), 306-310. 17.
Microwave Accelerated Synthesis of Cyclopentadienyl Bis-Phosphine Ruthenium Thiolato Complexes Using Focused Microwave Irradiation, N. Kuhnert and T. N. Danks, Chem. Res. (S) 2002, 66-68. read online
Scope and Limitation of [1,4]-S-Benzyl Participation and Debenzylation in the Stereochemically Controlled Synthesis of Substituted Thiolanes, J. Eames, N. Kuhnert and S. Warren, Chem. Soc. Perkin Trans. 1,2001, 1504-1511. read online
Boron-Trifluoride Mediated Synthesis of 2-Deoxy-anthocyanidines including a Total Synthesis of Tricetanidin from Black Tea (Camilla Sinensis), N. Kuhnert, M. Clifford and A.-G. Radenac, Tetrahedron Lett.2001, 42, 9261-9264.
Scope and Limitation of the Heck Reaction of Upper Rim Substituted Tetraiodo Calix-arenes, N. Kuhnert and A. Le-Gresley, Chem. Soc. Perkin Trans. 12001, 3393- 3398. read online
Synthesis, Reactivity, Structure and Dynamic Behaviour of Ruthenium Sulfine Complexes, N. Kuhnert, N. Burzlaff, E. Dombrowski uns W. A. Schenk, Naturforsch B2002, 57, 259-274.
Synthesis of Enantiomerically Pure 42 and 30 Membered Ring Trianglimine and Tranglamine Macrocycles, N. Kuhnert, C. Straßnig and A. M. Lopez-Periago, Tetrahedron Asymm.2002, 13, 123-128.
Synthesis of Chiral Non-Racemic Macrocycles of the Trianglimine and Trianglamine Type, N. Kuhnert und A. Lopez-Periago, Tetrahedron Lett.2002, 43, 3329-3332. read online
Is There a Special Non-Thermal Microwave Effect, N. Kuhnert, Chem. Int. Ed. Engl. 2002, 41, 1863-1866.
Gibt es einen nicht-thermischen Mikrowelleneffekt?, N. Kuhnert, Chem.2002, 114, 1943-1946.read online
Microwave Accelerated Synthesis of Cyclopentadienyl Bis-Phosphine Ruthenium Thiolato Complexes Using Focused Microwave Irradiation, N. Kuhnert and T. N. Danks, Met. Rev. 2002, 46, 140 (abstract).
Stereochemically Controlled Synthesis of Substituted 1,2 Oxathianes, J. Eames, N. Kuhnert and S. Warren, Chem. Soc. Perkin Trans. 12002, 2282-2287. read online
Funktionelle Lebensmittel-Eine Kritische Betrachtung, N. Kuhnert, Chemie und Technik 2002, 50, 142-147. read online
On the Steric Acceleration of Ene Reactions, N. Chooney, N. Kuhnert, P. G. Sammes, G. Smith, R. W. Ward, Chem. Soc. Perkin Trans. 12002, 1999-2006. read online
Hierarchical Scheme for the LC–MSn identification of chlorogenic acids, M. N. Clifford, K. L. Johnston, S. Knight and N. Kuhnert, Agr. Food. Chem.2003, 51, 2900-2911. read online
On the Scope and Limitations of the [3+3] Cyclocondensation Reaction of of Aromatic Dicarbonyl Compounds and 1R, 2R-cyclohexanediamine, N. Kuhnert, A. Lopez-Periago and G. M. Rossignolo, Biomol. Chem.2003, 1, 1157 – 1170. read online
On the Synthesis of Upper Rim Tetraacrylamidocalixarenes and their Dimerisation to Form Molecular Capsules Using Eight Hydrogen Bonds, N. Kuhnert and A. Le-Gresley, Commun.2003, 2426-2427.read online
Detection and Imaging of Vibrationally Labelled Biologically Active Compounds in Living Cells Using Raman Microscopy, N. Kuhnert, A. Thumser, Labl. Comp. Radiopharm.2004, 47, 493-500.
The synthesis of 1,1’,2,2’,3,3’,4,4,’-Octadetero-Sulforaphane, N. Kuhnert and Y. Lu, Labl. Comp. Radiopharm. 2004, 47, 501-507.
A powerful aqueous solvent effect in an intramolecular Diels-Alder cyclisation, N. Kuhnert, P.G. Sammes, G. Smith and R. W. Ward, Chem. Res.2004, 608-610.
- Dr. Robert Lucas [United Kingdom]
- Dr. Adam Le Gresley [United Kingdom]
- Dr. Ana Lopez-Periago [Spain]
- Dr. Giulia Rossignolo [Italy]
- Dr. Hoshiar Molod [Iraq]
- Dr. Rodney Walsh [United Kingdom]
- Dr. Fatemeh Jami [Iran]
- Dr. Warren Drynan [Zimbabwe]
- Dr. Rakesh Jaiswal [India]
- Dr. Birgul Surucu [Turkey]
- Dr. Farnoosh Dairpoosh [Iran]
- Dr. Nadim Hourani [Lebanon]
- Dr. Hany Nour [Egypt]
- Dr. Agnieszka Golon [Poland]
- Dr. Hande Karaköse [Turkey]
- Dr. Sagar Anil Deshpande [India]
- Dr. Mohamed Elsadig [Sudan]
- Dr. Michael Sanguinetti [USA] (joint with Prof. Dr. Laurenz Thomsen)
- Dr. Marius-Febi Matei [Romania]
- Dr. Abhinandan Shrestha [Nepal]
- Dr. Rohan Shah [India]
- Dr. Inamullah Hakeem Said [Afghanistan]
- Dr. Maria Alexandra Patras [Romania]
- Dr. Diana Sirbu [Moldova]
- Dr. Seung-Hun Lee [South Korea]
- Dr. Roberto Megias [Spain]
- Dr. Maria Bikaki [Greece]
- Dr. Pawel Andruszkiewicz [Poland]
- Dr. Anastasiia Shevchuk [Ukraine]
- Dr. Sabur Olarotimi Badmos [Nigeria]
- Dr. Tahira Mussarat [Pakistan]
- Dr. Fariba Sabzi [Iran]
- Dr. Salma Elshami [Egypt]
- Prof. Dr. Edwin Ntakadenzi Madala [South Africa]
- Prof. Dr. Adeola Sonibare [Nigeria]
- Prof. Dr. Lalith Jayasinghe [Sri Lanka]
- Dr. Hiba Ali [Sudan]
- Dr. Zenab [Egypt]
Former Master Students
- Audrey Bergounhou [France]
- Nickolet Ncube [Zimbabwe]
- Joanna Dabrowska [Poland]
- Lucas Lansing [Germany]
- Borislav Milev [Bulgaria]
- Kianoosh Dairpoosh [Iran]
- Awa Rita Diallo [Ivory Coast]
Former Bachelor Students
- Victoria von Glasenapp [Germany]
- Megi Mustafai [Albania]
- Naika Thielen [Germany]
- Rachelle Smith [USA]
- Gediminas Mikutis [Lithuania]
- Viktorija Glembockytė [Lithuania]
- Tina Sovdat [Slovenia]
- Prabal Subedi [Nepal]
- Joseph Kiprotich [Kenya]
- Sanan Eminov [Turkey]
- Fransesco Vivian [Italy]
- Marcus Papmeyer [Germany]
- Warren Andrew [Sri Lanka]
- Selin Gencer [Turkey]
- Irem Altun [Turkey]
- Nicoleta Copaci [Moldova]
- Yeweynwuha Gellaw Zemedie [Ethiopia]
- Nicolescu Vlad-Alexandru [Romania]
- Lingyi Jiao [China]
- Christina Heidorn [Germany]
- Maotian Fu [China]
- Johnathan Douglas Truex [USA]
- Mihella Berhanu Retta [Ethiopia]
- Sara Haka [Albania]
- Dimitar Dimitrov Petrov [Bulgaria]
- Nikesh Chandra Bhardwaj [Germany]
- Tsion Berhane Woldermariam [Ethiopia]
- Argi Pesha [Albania]
- Paula Cotrell [UK]
- Nikolas Ohl [Germany]
- Maryam Mahjoub [Iran]
- Mobinasadat Sharifi [Egypt]
- Sanjeeb Panthi [Nepal]
- Maria Santos [Guatemala]
- Sang Jin [South Korea]
- Mikhael Astorga [Phillipines]
- Munktuul Enkhbat [Mongolia]
- Megan Gurra [Albania]
- Jera Rexhepi [Albania]
- Elena Vide [Albania]
- Yordanos Abeje [Ethiopia]
- George Jabishvili [Georgia]
- Zhibek Konsbayeva [Kazachstan]
- Martinaiden Demaij [Albania]
- Burat Bürgec [Turkey]
- Hiba Mastas [Marocco]
- Yahann Amissah [Ghana]
- Nayana Upadyya [Nepal]
- Hillary Baddoo [Ghana]
- Juan Oviedo [Ecuador]
Currently there are no vacancies for PhD positions in my group.