A chiral methodology was developed in this work enabling for the first time the separation of the four stereo -isomers of the amino acid 4-hydroxyproline (4-Hyp) in the format of capillary... Show moreA chiral methodology was developed in this work enabling for the first time the separation of the four stereo -isomers of the amino acid 4-hydroxyproline (4-Hyp) in the format of capillary electrophoresis (CE). After a screening of different neutral cyclodextrins (CDs) in the electrokinetic chromatography (EKC) mode, methyl-gamma-CD was selected as chiral selector to stereoselectively separate 4-Hyp (previously derivatized with 9-fluorenyl-methyloxycarbonyl chloride (FMOC-Cl)) in a 75 mM phosphate buffer at pH 7.0. The effect of the concentration of the CD, the separation voltage, and the temperature on the chiral separation was investigated. A concentration of 10 mM for methyl-gamma-CD, a voltage of 30 kV, and a temperature of 15 degrees C allowed the separation of the four stereoisomers of 4-Hyp in less than 21 min with resolutions between consecutive peaks of 1.5, 2.7, and 3.6. The injection of individual standard solutions of each stereoisomer enabled peak identification and the methodology was able to detect up to 0.1 % (1.3 x 10-11 mmol) of each stereoisomer. Analytical characteristics of the developed methodology were adequate to be applied to the analysis of nutricosmetic supplements. A good agreement was observed between the content determined for trans-4-L-Hyp and that indicated in the label for the product. No enantiomeric impurities were detected what shows the great potential of this method in the quality control of these products. Show less
Astronomical observations of cold regions in the universe show a rich inventory of ices. Part of these ices may end up on planets like our own, but in that journey they will be exposed to... Show moreAstronomical observations of cold regions in the universe show a rich inventory of ices. Part of these ices may end up on planets like our own, but in that journey they will be exposed to considerable amounts of radiation. As water is the main component of these ices, the optical and photochemical properties of water ice largely determine how the radiation affects the molecules embedded in the ice. In this thesis, water ice is investigated as a host for photochemical reactions. A new laboratory setup is constructed, and two types of molecules are studied: glycine, an amino acid, and triphenylene, a polycyclic aromatic hydrocarbon. The photochemistry upon exposure to ultraviolet radiation is studied using UVvis and infrared spectroscopy. In addition, the optical properties of water ice are constrained in the UV-vis range, resulting in high-resolution optical constants, relevant for all ice-rich environments - from far away in space to our atmosphere. Water itself does not absorb light in this range, but as most organic molecules do, and are destroyed by radiation in this range, this is of high importance for molecules within the ice. Show less
The power of personalized nutrition lies in being able to conduct clinical research on healthy people while capturing metabolic markers sensitive to the impact of environmental and metabolic... Show moreThe power of personalized nutrition lies in being able to conduct clinical research on healthy people while capturing metabolic markers sensitive to the impact of environmental and metabolic stressors (e.g. diet, changing sex hormones and the menstrual cycle). Using clinical biomarkers, metabolomics, and diet interventions with intake analyses, we demonstrated the metabolic impact of vegan and animal diet interventions using fasting plasma analysis after 48 hours and using postprandial plasma analysis after meals and snacks. Sexually dimorphic responses were differentiated using proteomics and pathway analyses in two larger, sex-balanced cohorts. Finally, clinical biomarker and metabolomics analyses identified metabolic subtypes across menstrual cycle phases. Although challenges with integrating –omics technology and nutrition remain, the fundamental information generated from these research studies may provide a foundation for future novel personalized nutrition strategies. Show less
Bergwerff, C.E.; Luman, M.; Blom, H.J.; Oosterlaan, J. 2017
Determining blood concentrations of the amino acids homocysteine, tryptophan, tyrosine and phenylalanine in children is of value in the clinical practice. Over the past decades, the use of blood... Show moreDetermining blood concentrations of the amino acids homocysteine, tryptophan, tyrosine and phenylalanine in children is of value in the clinical practice. Over the past decades, the use of blood spot samples to examine amino acid concentrations is increasing rapidly. In children, the use of blood spot samples is especially of relevance, as this method is much less invasive than venous blood sampling. Currently, no paediatric reference values for amino acids in blood spots are available. The aim of the current study was to establish reference values for blood spot concentrations of total homocysteine, tryptophan, tyrosine and phenylalanine in school-age children. Dried blood spots were obtained in a community sample of 104 healthy children, aged 6–12 years old (52% males). Blood spot concentrations of total homocysteine, tryptophan, tyrosine and phenylalanine were determined by positive electrospray liquid chromatography-tandem mass spectrometry. Parents of participants completed questions regarding demographic characteristics. Our sample consisted of healthy children from various ethnic backgrounds, with varying levels of socioeconomic status, in line with the composition of the Dutch society. Blood spot concentrations of total homocysteine, tryptophan, tyrosine and phenylalanine were similar in males and females, and independent of age. In conclusion, paediatric reference values for blood spot concentrations of total homocysteine, tryptophan, tyrosine and phenylalanine were established, which could be of use in the clinical practice. Show less
The search for organic molecules and traces of life on Mars has been a major topic in planetary science for several decades, and is the future perspective of several missions to Mars. In order to... Show moreThe search for organic molecules and traces of life on Mars has been a major topic in planetary science for several decades, and is the future perspective of several missions to Mars. In order to determine where and what those missions should be looking for, laboratory experiments under simulated Mars conditions have been performed. This thesis describes the effects of simulated martian surface conditions on organic material (amino acids) and living organisms (halophilic archaea). Experiments have been performed to study the stability of thin films of glycine and alanine against UV irradiation under different conditions. Thin films of glycine and alanine have a half-life of 22 ± 5 hours and 3 ± 1 hours, respectively, when extrapolated to Mars-like UV flux levels in vacuum. The presence of a 7 mbar CO2 atmosphere does not affect these destruction rates. Cooling the thin films to 210 K (average Mars temperature) lowers the destruction rate by a factor of 7. The intrinsic amino acid composition of two martian soil analogues, JSC Mars-1 and Salten Skov, has been investigated. The results demonstrated that these analogues are inappropriate for a life-science study in their raw state. Besides amino acids, the response of the halophilic archaea Natronorubrum sp. strain HG-1 to Mars-like conditions, such as low pressure, UV radiation and low temperatures, has been studied. From the results we concluded that this strain would not be a good model organism to survive on the surface of Mars. Show less
