Influence of water availability on the enzymatic hydrolysis of proteins
Butré, C.I. ; Wierenga, P.A. ; Gruppen, H. - \ 2014
Process Biochemistry 49 (2014)11. - ISSN 1359-5113 - p. 1903 - 1912.
substrate-inhibition - functional-properties - ionic-strength - amino-acid - hydration - nmr - macromolecules - mechanism - kinetics - protease
The overall rate of enzymatic protein hydrolysis decreases with increasing protein concentration (0.1–30% (w/v)) at constant enzyme/substrate ratio. To understand the role of water, the amount of available water was expressed as the ratio between free and bound water and experimentally determined from water activity and T2 relaxation time (NMR) measurements. At low protein concentrations a large excess of water is present (1.5 × 106 water molecules per protein molecule at 0.1% (w/v) whey protein isolate (WPI), but only 3984 at 30% (w/v) WPI. Assuming that 357 molecules of water are needed for full hydration of the protein, these values correspond to a 4280 and 11 times excess of water, showing that at 30% (w/v) WPI the amount of water becomes limited. At the same time, only a small decrease was observed in water activity (1.00–0.997 for 0.1–30% (w/v) WPI), and an increase of bound water measured by NMR (
Rehydration kinetics of freeze-dried carrots
Vergeldt, F.J. ; Dalen, G. van; Duijster, A.J. ; Voda, A. ; Khalloufi, S. ; Vliet, L.J. van; As, H. van; Duynhoven, J.P.M. van; Sman, R.G.M. van der - \ 2014
Innovative Food Science and Emerging Technologies 24 (2014). - ISSN 1466-8564 - p. 40 - 47.
fruits - foods - microstructure - vegetables - quality - impact - nmr
Rehydration kinetics by two modes of imbibition is studied in pieces of freeze-dried winter carrot, after different thermal pre-treatments. Water ingress at room temperature is measured in real time by in situ MRI and NMR relaxometry. Blanched samples rehydrate substantially faster compared to non-blanched samples, independent of their porous microstructure. It is proposed that for non-blanched tissues immobilized sugars result in nearly complete swelling of the solid matrix, hindering the ingress of water through the porous network. Nonblanched carrot pieces frozen at-28 °C rehydrate faster compared to those frozen at-150 °C, due to blocking of smaller pores by swelling. In blanched tissues themobilization of sugars results in amore homogeneous Sugar distribution, leading to less swelling of the solid matrix and allowing fast ingress of water via capillary suction. Industrial relevance: The dried fruits and vegetables that are currently available on the market are a poor compromise between convenience (rehydration kinetics) and sensorial quality. This is a major bottleneck for consumers to “Make the Healthy Choice the Easy Choice” and this also negatively impacts market growth. Currently, rational optimization of drying processes is impeded by lack of insight which structural features determine rehydration kinetics (convenience) and texture (sensorial quality) upon rehydration. We therefore started a program to quantitatively assess and model microstructural features and rehydration behavior of freeze-dried carrots as a model system.
Translational and rotational diffusion of flexible PEG and rigid dendrimer probes in sodium caseinate dispersions and acid gels
Salami, S. ; Rondeau-Mouro, C. ; Barhoum, M. ; Duynhoven, J.P.M. van; Mariette, F. - \ 2014
Biopolymers 101 (2014)9. - ISSN 0006-3525 - p. 959 - 965.
glucono-delta-lactone - hydrodynamic transport-properties - nuclear-magnetic-resonance - polystyrene latex spheres - aqueous polymer-solutions - light-scattering - nmr - suspensions - gelation - microstructure
The dynamics of rigid dendrimer and flexible PEG probes in sodium caseinate dispersions and acid gels, including both translational diffusion and rotational diffusion, were studied by NMR. Above the onset of the close-packing limit (C ~ 10 g/100 g H2O), translational diffusion of the probe depended on its flexibility and on the fluctuations of the matrix chains. The PEG probe diffused more rapidly than the spherical dendrimer probe of corresponding hydrodynamic radius. The greater conformational flexibility of PEG facilitated its motion through the crowded casein matrix. Rotational diffusion was, however, substantially less hindered than the translational diffusion and depended on the local protein–probe friction which became high when the casein concentration increased. The coagulation of the matrix led to the formation of large voids, which resulted in an increase in the translational diffusion of the probes, whereas the rotational diffusion of the probes was retarded in the gel, which could be attributed to the immobilized environment surrounding the probe. Quantitative information from PFG-NMR and SEM micrographs have been combined for characterizing microstructural details in SC acid gels.
H-1-NMR Fingerprinting of Vaccinium vitis-idaea Flavonol Glycosides
Riihinen, K.R. ; Mihaleva, V.V. ; Gödecke, T. ; Soininen, P. ; Laatikainen, R. ; Vervoort, J. ; Lankin, D.C. ; Pauli, G.F. - \ 2013
Phytochemical Analysis 24 (2013)5. - ISSN 0958-0344 - p. 476 - 483.
spectral-analysis - ginkgo-biloba - nmr - purification
Introduction - The fruits of Vaccinium vitis-idaea L. are a valuable source of biologically active flavonoid derivatives. For studies focused on the purification of its quercetin glycosides (QGs) and related glycosides from plants and for the purpose of biological studies, the availability of numeric datasets from computer-assisted 1H iterative full spin analysis (HiFSA), that is, 1H-NMR fingerprinting, can replace and assist the repetitive and tedious two-dimensional NMR identification protocol required for both known and new compounds, respectively. Objective - To fully interpret the complex 1H-NMR fingerprints of eight QGs obtained from the berries of V. vitis-idaea and provide complete and unambiguous signal assignments. Methods - Vaccinium vitis-idaea QGs were purified in a single run by long-bed gel permeation chromatography and identified by comparison with commercially available compounds using LC–MS combining ion-trap and time-of-flight detection and one- or two-dimensional NMR. The HiFSA analysis yielded full sets of 1H chemical shifts and proton–proton coupling constants, allowing for field-independent spectral simulation. Results - Signal assignments were achieved for the reference standards and the QGs that dominated in purified fractions. However, even mixtures of two to three QGs could be fitted using the HiFSA approach. In the case of the overlapped sugar resonances, the initial fitting of the 1H spectra of reference compounds, together with values extracted from the two-dimensional NMR data and literature data, assisted in the process. Conclusion - The HiFSA method revealed for the first time the presence of Q-3-O-ß-glucopyranoside and Q-3-O-ß-glucuronopyranoside in the berries of V. vitis-idaea, and unambiguously confirmed the structures of Q-3-O-[4¿-(3-hydroxy-3-methylglutaroyl)]--rhamnopyranoside, Q-3-O--rhamnopyranoside, Q-3-O-ß-galactopyranoside, Q-3-O--arabinofuranoside, Q-3-O-ß-xylopyranoside and Q-3-O--arabinopyranoside.
Chemodynamics of soft Charged nanoparticles in aquatic media: Fundamental concepts
Town, R.M. ; Buffle, J. ; Duval, J.F.L. ; Leeuwen, H.P. van - \ 2013
The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 117 (2013)33. - ISSN 1089-5639 - p. 7643 - 7654.
metal speciation dynamics - aqueous-solutions - solvent exchange - complexes - relaxation - nmr - ion - approximation - temperature - membranes
Fast and Robust Method To Determine Phenoyl and Acetyl Esters of Polysaccharides by Quantitative 1H NMR
Neumüller, K.G. ; Carvalho de Souza, A. ; Rijn, J. van; Appeldoorn, M.M. ; Streekstra, H. ; Schols, H.A. ; Gruppen, H. - \ 2013
Journal of Agricultural and Food Chemistry 61 (2013)26. - ISSN 0021-8561 - p. 6282 - 6287.
acids - nmr - spectroscopy - extracts
The acetyl (AcE), feruloyl (FE), and p-coumaroyl (pCE) ester contents of different cereal and grass polysaccharides were determined by a quantitative 1H NMR-based method. The repeatability and the robustness of the method were demonstrated by analyzing different plant polysaccharide preparations. Good sensitivity and selectivity for AcE, FE, and pCE were observed. Moreover, an optimized and easy sample preparation allowed for simultaneous quantification of AcE, FE, and pCE. The method is suitable for high-throughput analysis, and it is a good alternative for currently used analytical procedures. A comparison of the method presented to a conventional HPLC-based method showed that the results obtained are in good agreement, whereas the combination of the optimized sample preparation and analysis by the 1H NMR-based methodology results in significantly reduced analysis time.
The podzol hydrosequence of Itaguare (Sao Paulo, Brazil). 2. Soil organic matter chemistry by pyrolysis-gas chromatography / mass spectrometry
Buurman, P. ; Vidal-Torrado, P. ; Millani Lopes, J. - \ 2013
Soil Science Society of America Journal 77 (2013)4. - ISSN 0361-5995 - p. 1307 - 1318.
gc-ms - horizons - gc/ms - micromorphology - fractions - cellulose - nmr
A Late Pleistocene to Holocene hydrosequence of podzols in the coastal plain of São Paulo (Brazil), of which the macromorphology was described previously, was investigated by pyrolysis-gas chromatography/mass spectrometry (GC/ MS). Differences in chemical composition of organic matter (OM) coincided very well with the morphological interpretation of these profiles with respect to drainage conditions, origin of OM, and decomposition. OM in B-horizons of poorly-drained profiles has a signature of dissolved organic matter (DOM), while that of well-drained profiles indicates root-derived material. Bands that, according to their morphology, were attributed to DOM have different signature within the profiles, reflecting DOM origin. The EB horizons of poorly-drained profiles show a selective decay of B-horizon material, resulting in a relative accumulation of aliphatics in poorly drained profiles. In the EB horizons of the well-drained profiles, however, significant amounts of microbial products were accumulated and poly-aromatic compounds were the most stable. This has not been described for temperate podzols. Factor analysis suggests that local differences in vegetation are responsible for about 50% of the total chemical variation in pyrolysates, whereas source, transport, and decomposition in the profile account for the other half. The results underline that OM composition of podzol horizons is strongly dependent on hydrological conditions, resulting in divergent soil organic matter (SOM) properties between soils from different landscape contexts. Nonetheless, there is a comprehensible relation between SOM fingerprints of horizons within one profile. Finally, changes in OM composition at horizon transitions provide insight into the podzolization process.
Seasonal accumulation of major alkaloids in organs of pharmaceutical crop Narcissus Carlton
Lubbe, A. ; Gude, H. ; Verpoorte, R. ; Choi, C.Y. - \ 2013
Phytochemistry 88 (2013). - ISSN 0031-9422 - p. 43 - 53.
amaryllidaceae alkaloids - chlorogenic acid - metabolomic analysis - cancer-cells - galanthamine - apoptosis - root - nmr
Narcissus pseudonarcissus (L.) cv. Carlton is being cultivated as a main source of galanthamine from the bulbs. After galanthamine, haemanthamine and narciclasine are the next most abundant alkaloids in this cultivar. Both these compounds are promising chemical scaffolds for potential anticancer drugs. For further research and drug development, a reliable supply of these compounds will be needed. In this study a field experiment was conducted to investigate the levels of galanthamine, haemanthamine and narciclasine in plants of N. pseudonarcissus cv. Carlton. In a field experiment alkaloids in the bulbs, leaves and roots were analyzed by quantitative 1H NMR to monitor the variations during the growing season. Major primary and secondary metabolites were identified in the various plant parts. Multivariate data analysis was performed on the 1H NMR spectra to investigate how metabolites changed in the plant organs over time. The results show that the leaves have relatively high concentrations of the alkaloids before flowering. The bulbs had lower concentrations of the compounds of interest but would have a higher total yield of alkaloids due to bigger biomass. Narcissus pseudonarcissus cv. Carlton represents a good source of galanthamine, and can potentially be a source of the other major alkaloids depending on choice of organ and harvest time
Gut bacteria-host metabolic interplay during conventionalisation of the mouse germfree colon
Aidy, S. El; Derrien, M.M.N. ; Merrifield, C.A. ; Levenez, F. ; Dore, J. ; Boekschoten, M.V. ; Dekker, J. ; Holmes, E. ; Zoetendal, E.G. ; Baarlen, P. van; Claus, S.P. ; Kleerebezem, M. - \ 2013
ISME Journal 7 (2013). - ISSN 1751-7362 - p. 743 - 755.
colorectal-cancer - polysaccharide utilization - selenomonas-ruminantium - human intestine - immune-system - waste-water - microbiota - mice - mucosa - nmr
The interplay between dietary nutrients, gut microbiota and mammalian host tissues of the gastrointestinal tract is recognised as highly relevant for host health. Combined transcriptome, metabonome and microbial profiling tools were employed to analyse the dynamic responses of germfree mouse colonic mucosa to colonisation by normal mouse microbiota (conventionalisation) at different time-points during 16 days. The colonising microbiota showed a shift from early (days 1 and 2) to later colonisers (days 8 and 16). The dynamic changes in the microbial community were rapidly reflected by the urine metabolic profiles (day 1) and at later stages (day 4 onward) by the colon mucosa transcriptome and metabolic profiles. Correlations of host transcriptomes, metabolite patterns and microbiota composition revealed associations between Bacilli and Proteobacteria, and differential expression of host genes involved in energy and anabolic metabolism. Differential gene expression correlated with scyllo- and myo-inositol, glutamine, glycine and alanine levels in colonic tissues during the time span of conventionalisation. Our combined time-resolved analyses may help to expand the understanding of host-microbe molecular interactions during the microbial establishment
Anomalies in moisture transport during broccoli drying monitored by MRI?
Jin, X. ; Boxtel, A.J.B. van; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Straten, G. van; Boom, R.M. ; Sman, R.G.M. van der - \ 2012
Faraday Discussions 158 (2012). - ISSN 1359-6640 - p. 65 - 75.
viscoelastic behavior - cooking - model - nmr - simulation - carrot - grain - food - meat
Magnetic resonance imaging (MRI) offers unique opportunities to monitor moisture transport during drying or heating of food, which can render unexpected insights. Here, we report about MRI observations made during the drying of broccoli stalks indicating anomalous drying behaviour. In fresh broccoli samples the moisture content in the core of the sample increases during drying, which conflicts with Fickian diffusion. We have put the hypothesis that this increase of moisture is due to the stress diffusion induced by the elastic impermeable skin. Pre-treatments that change skin and bulk elastic properties of broccoli show that our hypothesis of stress-diffusion is plausible.
The impact of freeze-drying on microstructure and rehydration properties of carrot
Voda, A. ; Homan, N. ; Witek, M. ; Duijster, A. ; Dalen, G. van; Sman, R.G.M. van der; Nijsse, J. ; Vliet, L.J. van; As, H. van; Duynhoven, J.P.M. van - \ 2012
Food Research International 49 (2012)2. - ISSN 0963-9969 - p. 687 - 693.
integral-equations - apple tissue - ice crystals - tip radius - frozen - nmr - fruit - crystallization - dehydration - mechanisms
The impact of freeze-drying, blanching and freezing rate pre-treatments on the microstructure and on the rehydration properties of winter carrots were studied by µCT, SEM, MRI and NMR techniques. The freezing rate determines the size of ice crystals being formed that leave pores upon drying. Their average size (determined by µCT) can be predicted in a quantitative manner by considering dendritic growth and freezing rates. Blanching as a pre-treatment, however, did not affect pore size distribution induced by freeze-drying. Upon rehydration of the freeze-dried carrots, PFG NMR and MRI show that cellular compartments were not restored and instead a porous network with permeable barriers is formed. Blanching pre-treatment introduced a less connected and more anisotropic porous network if followed by fast freezing, indicating that more of the native cell wall morphology is preserved.
Structural elucidation and quantification of phenolic conjugates present in human urine after tea intake
Hooft, J.J.J. van der; Vos, R.C.H. de; Mihaleva, V. ; Bino, R.J. ; Ridder, L.O. ; Roo, N. de; Jacobs, D.M. ; Duynhoven, J.P.M. van; Vervoort, J.J.M. - \ 2012
Analytical Chemistry 84 (2012)16. - ISSN 0003-2700 - p. 7263 - 7271.
tandem mass-spectrometry - green tea - black tea - metabolite identification - ellagic acid - metabolomics - polyphenols - nmr - ingestion - phytochemicals
In dietary polyphenol exposure studies, annotation and identification of urinary metabolites present at low (micromolar) concentrations are major obstacles. In order to determine the biological activity of specific components, it is necessary to have the correct structures and the quantification of the polyphenol-derived conjugates present in the human body. We present a procedure for identification and quantification of metabolites and conjugates excreted in human urine after single bolus intake of black or green tea. A combination of a solid phase extraction (SPE) preparation step and two high pressure liquid chromatography (HPLC)-based analytical platforms was used; namely, accurate mass fragmentation (HPLC-FTMSn) and mass-guided SPE-trapping of selected compounds for nuclear magnetic resonance spectroscopy (NMR) measurements (HPLC-TOFMS-SPE-NMR). HPLC-FTMSn analysis led to the annotation of 138 urinary metabolites, including 48 valerolactone and valeric acid conjugates. By combining the results from MSn fragmentation with the one dimensional (1D)-1H-NMR spectra of HPLC-TOFMS-SPE trapped compounds, we elucidated the structures of 36 phenolic conjugates, including the glucuronides of 3’,4’-di, and 3’,4’,5’-trihydroxyphenyl-¿-valerolactone, three urolithin glucuronides, and indole-3-acetic acid glucuronide. We also obtained 26 hours of quantitative excretion profiles for specific valerolactone conjugates. The combination of the HPLC-FTMSn and HPLC-TOFMS-SPE-NMR platforms results in the efficient identification and quantification of low abundant phenolic conjugates down to nanomoles of trapped amounts of metabolite corresponding to micromolar metabolite concentrations in urine
Soil organic matter chemistry changes upon secondary succession in Imperata Grasslands , Indonesia: A pyrolysis - GC/MS study
Yassir, I. ; Buurman, P. - \ 2012
Geoderma 173-174 (2012). - ISSN 0016-7061 - p. 94 - 103.
chromatography-mass-spectrometry - chemical-composition - carbon pool - forest soil - humic acids - land-use - fractions - lignin - nmr - stabilization
The chemical composition of soil organic matter (SOM) following secondary succession in Imperata grassland was investigated by Pyrolysis-Gas Chromatography/Mass Spectrometry (GC/MS). We studied 46 samples from different stages of succession using plots that last burned 3 and 9 years previously, secondary forest (= 15 years), primary forest and Acacia mangium plantation (9 years). During regeneration of Imperata grasslands the chemical composition of SOM changes considerably. Differences between litters and SOM were larger than within SOM, which is mainly due to a rapid degradation of lignin in the soil. Both litter and SOM under Imperata contain larger amounts of carbohydrates and fewer lignin moieties, aliphatics and N-compounds than those under secondary and primary forest. Nevertheless, SOM degradation under grassland is less efficient because of scarcity of N-compounds. SOM decomposition is most advanced under forest, as indicated by lower amounts of plant derived compounds and higher contribution of microbial matter. Decomposition efficiency appears to be related to SOM chemistry, but more to abundance of N-compounds than to that of potentially recalcitrant compounds. C stocks were linked to decomposition efficiency and litter production.
Moisture distribution in broccoli: measurements by MRI hot air drying experiments
Jin, X. ; Sman, R.G.M. van der; Gerkema, E. ; Vergeldt, F.J. ; As, H. van; Boxtel, A.J.B. van - \ 2011
Procedia Food Science 1 (2011). - ISSN 2211-601X - p. 640 - 646.
profiles - nmr - diffusivity - model - food - gel
The internal moisture distribution that arise in food products during drying, is a key factor for the retention of quality attributes. To reveal the course of moisture content in a product, internal moisture profiles in broccoli florets are measured by MRI imaging during drying experiments with controlled air flow and temperature. The 3D images concern a matrix size of 64×64×64 elements. Signal intensity is converted to product moisture content with a linear relationship, while taking a minimum detectable moisture content of 0.3 kg water/ kg dry matter into account. Moisture content as a function of time is presented for a 2D cross sectional area in the middle of a broccoli sample. The average moisture contents for the cross sectional area obtained from the MRI imaging are compared with spatial model simulations for the moisture distribution. In that model the effective diffusion coefficient is based on the Free Volume Theory. This theory has the advantage that the changed mobility of water in the product during drying is taken into account and the theory also predicts the moisture transport in the porous broccoli floret. Key parameters for the Free Volume Theory are estimated by fitting to the experimental MRI results and the effective diffusion coefficient is given as a function of the product water content.
Data-processing strategies for metabolomics studies
Hendriks, M.M.W.B. ; Eeuwijk, F.A. van; Jellema, R.H. ; Westerhuis, J.A. ; Reijmers, T.H. ; Hoefsloot, H.C.J. ; Smilde, A.K. - \ 2011
TrAC : Trends in Analytical Chemistry 30 (2011)10. - ISSN 0165-9936 - p. 1685 - 1698.
principal component analysis - mass-spectrometry - variable selection - optimal-design - models - identification - metabolites - networks - tool - nmr
Metabolomics studies aim at a better understanding of biochemical processes by studying relations between metabolites and between metabolites and other types of information (e.g., sensory and phenotypic features). The objectives of these studies are diverse, but the types of data generated and the methods for extracting information from the data and analysing the data are similar. Besides instrumental analysis tools, various data-analysis tools are needed to extract this relevant information. The entire data-processing workflow is complex and has many steps. For a comprehensive overview, we cover the entire workflow of metabolomics studies, starting from experimental design and sample-size determination to tools that can aid in biological interpretation. We include illustrative examples and discuss the problems that have to be dealt with in data analysis in metabolomics. We also discuss where the challenges are for developing new methods and tailor-made quantitative strategies
Effect of fertilizers on galanthamine and metabolite profiles in narcissus bulbs by 1H NMR
Lubbe, A. ; Choi, Y.H. ; Vreeburg, P.J.M. ; Verpoorte, R. - \ 2011
Journal of Agricultural and Food Chemistry 59 (2011)7. - ISSN 0021-8561 - p. 3155 - 3161.
amaryllidaceae alkaloids - nitrogen-fertilizer - gas-chromatography - nmr - growth - metabolomics - leaves
Narcissus bulbs contain the biologically active alkaloid galanthamine, and Narcissus is being developed as a natural source of the molecule for the pharmaceutical industry. The effect of fertilizer on galanthamine production was investigated in a field study using a 1H nuclear magnetic resonance (NMR) metabolite profiling approach. Galanthamine was quantitated and major metabolites in the bulbs were identified. The application of standard fertilization levels of nitrogen and potassium caused a significant increase in galanthamine as compared to a control. Multivariate data analysis of the 1H NMR data revealed that applying double the standard level of nitrogen fertilizer resulted in production of more amino acids and citric acid cycle intermediates, but not more galanthamine. The results indicated that standard levels of fertilizer currently applied in The Netherlands are sufficient for optimal galanthamine accumulation in the bulbs. This study shows how 1H NMR-based metabolic profiling can provide insight into the response of plant metabolism to agricultural practices.
Comparison of two GM maize varieties with a near-isogenic non-GM variety using transcriptomics, proteomics and metabolomics
Barros, E. ; Lezar, S. ; Anttonen, M.J. ; Dijk, J.P. van; Rohlig, R.M. ; Kok, E.J. ; Engel, K.H. - \ 2010
Plant Biotechnology Journal 8 (2010)4. - ISSN 1467-7644 - p. 436 - 451.
gene-expression - h-1-nmr spectroscopy - safety assessment - food - tool - nmr - hybridization - microarrays - mutants - plants
P>The aim of this study was to evaluate the use of four nontargeted analytical methodologies in the detection of unintended effects that could be derived during genetic manipulation of crops. Three profiling technologies were used to compare the transcriptome, proteome and metabolome of two transgenic maize lines with the respective control line. By comparing the profiles of the two transgenic lines grown in the same location over three growing seasons, we could determine the extent of environmental variation, while the comparison with the control maize line allowed the investigation of effects caused by a difference in genotype. The effect of growing conditions as an additional environmental effect was also evaluated by comparing the Bt-maize line with the control line from plants grown in three different locations in one growing season. The environment was shown to play an important effect in the protein, gene expression and metabolite levels of the maize samples tested where 5 proteins, 65 genes and 15 metabolites were found to be differentially expressed. A distinct separation between the three growing seasons was also found for all the samples grown in one location. Together, these environmental factors caused more variation in the different transcript/protein/metabolite profiles than the different genotypes.
Toxic hazard and chemical analysis of leachates from furfurylated wood
Pilgard, A. ; Treu, A. ; Zeeland, A.N.T. van; Gosselink, R.J.A. ; Westin, M. - \ 2010
Environmental Toxicology and Chemistry 29 (2010)9. - ISSN 0730-7268 - p. 1918 - 1924.
behavioral-responses - alcohol resins - nmr - polymerization - pollutants - chemistry
The furfurylation process is an extensively investigated wood modification process. Furfuryl alcohol molecules penetrate into the wood cell wall and polymerize in situ. This results in a permanent swelling of the wood cell walls. It is unclear whether or not chemical bonds exist between the furfuryl alcohol polymer and the wood. In the present study, five different wood species were used, both hardwoods and softwoods. They were treated with three different furfurylation procedures and leached according to three different leaching methods. The present study shows that, in general, the leachates from furfurylated wood have low toxicity. It also shows that the choice of leaching method is decisive for the outcome of the toxicity results. Earlier studies have shown that leachates from wood treated with furfuryl alcohol prepolymers have higher toxicity to Vibrio fischeri than leachates from wood treated with furfuryl alcohol monomers. This is probably attributable to differences in leaching of chemical compounds. The present study shows that this difference in the toxicity most likely cannot be attributed to maleic acid, furan, furfural, furfuryl alcohol, or 2-furoic acid. However, the difference might be caused by the two substances 5-hydroxymethylfurfural and 2,5-furandimethanol. The present study found no difference in the amount of leached furfuryl alcohol between leachates from furfurylated softwood and furfurylated hardwood species. Earlier studies have indicated differences in grafting of furfuryl alcohol to lignin. However, nothing was found in the present study that could support this. The leachates of furfurylated wood still need to be investigated further to identify the chemical differences between wood furfurylated with furfuryl alcohol monomers and furfuryl alcohol prepolymers.
Branched arabino-oligosaccharides isolated from sugar beet arabinan
Westphal, Y. ; Kuhnel, S. ; Waard, P. de; Hinz, S.W.A. ; Schols, H.A. ; Voragen, A.G.J. ; Gruppen, H. - \ 2010
Carbohydrate Research : an international journal 345 (2010)9. - ISSN 0008-6215 - p. 1180 - 1189.
cell-walls - structural characterization - feruloyl oligosaccharides - polysaccharides - acid - nmr - pectins - pulp
Sugar beet arabinan consists of an a-(1,5)-linked backbone of l-arabinosyl residues, which can be either single or double substituted with a-(1,2)- and/or a-(1,3)-linked l-arabinosyl residues. Neutral branched arabino-oligosaccharides were isolated from sugar beet arabinan by enzymatic degradation with mixtures of pure and well-defined arabinohydrolases from Chrysosporium lucknowense followed by fractionation based on size and analysis by MALDI-TOF MS and HPAEC. Using NMR analysis, two main series of branched arabino-oligosaccharides have been identified, both having an a-(1,5)-linked backbone of l-arabinosyl residues. One series carries single substituted a-(1,3)-linked l-arabinosyl residues at the backbone, whereas the other series consists of a double substituted a-(1,2,3,5)-linked arabinan structure within the molecule. The structures of eight such branched arabino-oligosaccharides were established.
Non-native hydrophobic interactions detected in unfolded apoflavodoxin by paramagnetic relaxation enhancement
Nabuurs, S.M. ; Kort, B.J. de; Westphal, A.H. ; Mierlo, C.P.M. van - \ 2010
European Biophysics Journal 39 (2010)4. - ISSN 0175-7571 - p. 689 - 698.
beta parallel protein - azotobacter-vinelandii apoflavodoxin - denatured state - folding mechanism - hydrogen-exchange - molten globule - flavodoxin-ii - native-like - pathway - nmr
Transient structures in unfolded proteins are important in elucidating the molecular details of initiation of protein folding. Recently, native and non-native secondary structure have been discovered in unfolded A. vinelandii flavodoxin. These structured elements transiently interact and subsequently form the ordered core of an off-pathway folding intermediate, which is extensively formed during folding of this a–ß parallel protein. Here, site-directed spin-labelling and paramagnetic relaxation enhancement are used to investigate long-range interactions in unfolded apoflavodoxin. For this purpose, glutamine-48, which resides in a non-native a-helix of unfolded apoflavodoxin, is replaced by cysteine. This replacement enables covalent attachment of nitroxide spin-labels MTSL and CMTSL. Substitution of Gln-48 by Cys-48 destabilises native apoflavodoxin and reduces flexibility of the ordered regions in unfolded apoflavodoxin in 3.4 M GuHCl, because of increased hydrophobic interactions in the unfolded protein. Here, we report that in the study of the conformational and dynamic properties of unfolded proteins interpretation of spin-label data can be complicated. The covalently attached spin-label to Cys-48 (or Cys-69 of wild-type apoflavodoxin) perturbs the unfolded protein, because hydrophobic interactions occur between the label and hydrophobic patches of unfolded apoflavodoxin. Concomitant hydrophobic free energy changes of the unfolded protein (and possibly of the off-pathway intermediate) reduce the stability of native spin-labelled protein against unfolding. In addition, attachment of MTSL or CMTSL to Cys-48 induces the presence of distinct states in unfolded apoflavodoxin. Despite these difficulties, the spin-label data obtained here show that non-native contacts exist between transiently ordered structured elements in unfolded apoflavodoxin