Biomedical subjects

N Hertkorn

Publications and source records attributed to N Hertkorn.

10 recordsLinked to original sources

PubMed2004

A potentiometric and 113Cd NMR study of cadmium complexation by natural organic matter at two different magnetic field strengths.

The binding of cadmium to Suwannee River natural organic matter (NOM) has been investigated across a broad range of Cd/C ratios (0.00056-0.0056) and pH values (3.5-11) by (113)Cd NMR spectroscopy at two magnetic field strengths (B(0) = 9.4 and 11.7 T). Caused by the very peculiar and highly complex nature of the Cd-NOM exchanging system, these (113)Cd NMR spectra are characterized by a pH- and concentration-dependent superposition of slow, intermediate, and fast chemical exchange. The complex interplay of solution chemistry and chemical exchange requires a thorough mapping of this Cd-NOM chemically exchanging system through NMR acquisition at two magnetic field strengths and a systematic variation of Cd/C ratios and pH values. The interpretation of (113)Cd NMR spectra is greatly facilitated and constrained by simultaneous measurements of pH and pCd, which allows a model-independent calculation of organically bound Cd(2+) under all experimental conditions. Within the range of chemical conditions applied in this study, (113)Cd NMR spectrometric evidence is consistent with coordination of cadmium by oxygen, nitrogen, and sulfur ligands in NOM. Under all experimental conditions, cadmium is primarily coordinated to oxygen; however, several lines of evidence point to the participation of nitrogen ligands, even in acidic solutions where nitrogen ligands are primarily bound to protons. Under alkaline conditions, up to one-third of cadmium may be coordinated to nitrogen, and a small, but unquantifiable, percentage of cadmium is coordinated to sulfur ligands, as evidenced by far-low-field (113)Cd NMR resonances.

Journal Article↗

PubMed2002

Utilization and transformation of aquatic humic substances by autochthonous microorganisms.

Aquatic humic substances (HS) from a bog lake water, a riverwater, and a groundwater were isolated after enrichment on XAD 8 columns and added to a Czapek-Dox nutrient broth which was used either in full strength or without glucose and/or NaNO3. The individual flasks were inoculated with natural microbial populations of corresponding water samples or with a Pseudomonas fluorescens strain isolated from groundwater. The presence of HS resulted in an increase of bacterial numbers in nearly all cultures incubated for 3 weeks at 25 degrees C on a shaker. HS reisolated from cultures without glucose or NaNO3 showed no or only minor quantitative differences as compared to those from sterile controls. In full strength nutrient broth up to 27% of HS were utilized. Data obtained by spectroscopic methods (UV/vis/FTIR) and elemental analysis indicated a decrease in particle size and a loss in aromaticity and aliphatic carbon in HS reisolated from the microbial cultures. Simultaneously an increase in the N content of HS was observed, which probably originated from some constituents of microbial biomass such as proteins and amino sugars. The NMR data also documented that significant transformations of HS occurred in the individual microbial cultures. After incubation, increased amounts of aromatic acids were detected in some liquid media and residual HS by GC/MS or capillary electrophoresis. 1H NMR spectroscopy was less effective in indicating structural differences in the HS than 13C NMR but revealed considerable detail of the microbial degradation of riverine HS, when limited sample was available. The newly developed NMR increment analysis provided substantial detail of aromatic structures in a microbially altered HS. The microbial degradation of HS strongly depended on the composition of the HS, the species selection of the microorganisms, and to a lesser extent on the culture conditions. For any series of identical inoculum and HS, full broth media initiated the most extensive alteration of HS.

Biological Availability↗

PubMed2001

Regioselective synthesis of a branched isomer of nonylphenol, 4-(3',6'-dimethyl-3'-heptyl)phenol, and determination of its important environmental properties.

A method for the synthesis of a pure nonylphenol isomer, 4-(3',6'-dimethyl-3-heptyl)phenol, by Friedel-Crafts reaction between anisole and 3-bromo-3,6-dimethylheptane that gives a 47.3% overall yield is reported. The reactions were followed by GC-MS, and the chemical structures are in agreement with the NMR and IR spectra. The log K(ow) value for this compound, its water solubility, vapor pressure, and Henry's Law constant were also determined. These physicochemical properties were required for prediction of the compound's behavior in aquatic ecosystems.

Journal Article↗

PubMed2001

Quantitative and qualitative precision improvements by effective mobility-scale data transformation in capillary electrophoresis analysis.

By transforming the time-based x-axis of electropherograms in capillary zone electrophoresis (CZE) into the corresponding effective mobility-scale, we propose a simple and robust data representation for a better qualitative and quantitative capillary electrophoresis (CE) analysis. The time scale of the raw electrophoretic data (detection signal versus time) is transformed into an effective electrophoretic mobility scale (mu eff-scale) with account of the electroosmotic flow (EOF) peak or of an internal standard of known effective mobility. With the new scaling (detection signals versus effective mobility), the obtained electropherograms are more representative of the velocity-based electrophoretic separation and the comparison of complete electropherograms is directly possible. This is of importance when tracking peaks in real samples where alteration in EOF stability can occur or when comparing electrophoretic runs from different experimental setups (independence in column length and voltage). Beside the qualitative possibilities, a quantitative improvement is achieved in the mu eff-scale with significant better peak area reproducibility and equal to more precision in quantitative analysis than with the primary time-scale integration.

2,4,5-Trichlorophenoxyacetic Acid↗

PubMed2001

Chemical studies of proanthocyanidins and hydrolyzable tannins.

We investigated a number of natural polyphenols representing flavan-3-ols, gallotannins, and ellagitannins with regard to their antioxidant potential. For this purpose we used pulse radiolysis to determine scavenging rate constants with hydroxyl radicals and decay rates of the respective aroxyl radicals and EPR spectroscopy to identify the radicals after in situ oxidation. Using NMR spectroscopy, we could confirm phenolic coupling reactions of epigallocatechin gallate and pentagalloyl glucose after radical-induced oxidation.

Anthocyanins↗

PubMed2000

Flavonoid 6-hydroxylase from soybean (Glycine max L.), a novel plant P-450 monooxygenase.

Cytochrome P-450-dependent hydroxylases are typical enzymes for the modification of basic flavonoid skeletons. We show in this study that CYP71D9 cDNA, previously isolated from elicitor-induced soybean (Glycine max L.) cells, codes for a protein with a novel hydroxylase activity. When heterologously expressed in yeast, this protein bound various flavonoids with high affinity (1.6 to 52 microm) and showed typical type I absorption spectra. These flavonoids were hydroxylated at position 6 of both resorcinol- and phloroglucinol-based A-rings. Flavonoid 6-hydroxylase (CYP71D9) catalyzed the conversion of flavanones more efficiently than flavones. Isoflavones were hardly hydroxylated. As soybean produces isoflavonoid constituents possessing 6,7-dihydroxy substitution patterns on ring A, the biosynthetic relationship of flavonoid 6-hydroxylase to isoflavonoid biosynthesis was investigated. Recombinant 2-hydroxyisoflavanone synthase (CYP93C1v2) efficiently used 6,7,4'-trihydroxyflavanone as substrate. For its structural identification, the chemically labile reaction product was converted to 6,7,4'-trihydroxyisoflavone by acid treatment. The structures of the final reaction products for both enzymes were confirmed by NMR and mass spectrometry. Our results strongly support the conclusion that, in soybean, the 6-hydroxylation of the A-ring occurs before the 1,2-aryl migration of the flavonoid B-ring during isoflavanone formation. This is the first identification of a flavonoid 6-hydroxylase cDNA from any plant species.

Base Sequence↗

PubMed1999

Tumor promoting diterpenes from Euphorbia leuconeura L.

Diterpene esters of the phorbol and ingenol types are known to be highly active tumor promoting agents that typically occur in members of the Euphorbiaceae. In the present work, Euphorbia leuconeura, a rare indoor plant, is analyzed for its tumor promoting potential. Latex as well as total leaf extracts exhibited Epstein-Barr-virus (EBV) inducing activity comparable to 12-O-tetradecanoyl-phorbol-13-O-acetate, a well known tumor promoter. The activity of individual fractions correlated with their ingenol ester content. Three ingenol esters with EBV inducing activity could be isolated and identified. They belong to the milliamine type of diterpene esters that contain aromatic peptidyl groups. Two of them (milliamines L and M) are already known from E. milii. The third compound is identified as an isomer of milliamine F with a novel 3,20-diester arrangement. The data show a close relationship between E. leuconeura and the more popular indoor plant E. milii whose latex is also used as a powerful molluscicide.

Carcinogens↗

PubMed1998

Partial purification of a GTP-insensitive (1-->3)-beta-glucan synthase from Phytophthora sojae.

A (1 --> 3)-beta-glucan synthase activity was identified in cell membrane preparations from the oomycete Phytophthora sojae, a soybean pathogen. The activity could be solubilized using the zwitterionic detergent CHAPS at relatively low concentrations (3 mg/ml). High salt concentrations were not effective in removing the activity from the membranes. Detergent solubilization of the enzyme resulted in a six-fold increase of calculated Vmax values (2.5 vs. 0.4 nkat/mg protein) but only minor alteration of the Km (10.6 vs. 10.7 mM). Analysis of the reaction product of the solubilized enzyme by enzymatic degradation and by 2D NMR spectroscopy confirmed its identity as a linear high molecular weight (1 --> 3)-beta-glucan. Glucan synthase activity in both membrane and solubilized preparations was not activated by GTP or divalent cations as reported for other fungal or plant glucan synthases, The activity was inhibited, as expected, in a competitive manner by UDP with a Ki of 2.9 mM. Partial purification of the enzyme was achieved by anion exchange chromatography followed by product entrapment. This procedure resulted in the selective enrichment of a protein band with apparent Mr 108,000 in SDS-PAGE which was not visible in any of the steps preceding product entrapment. The glucan pellets from product entrapment contained up to 3% of the initial enzyme activity present in the fraction used for the procedure.

Chromatography, Ion Exchange↗

PubMed1998

A new intermediate in the mineralization of 3,4-dichloroaniline by the white rot fungus Phanerochaete chrysosporium.

Phanerochaete chrysosporium ATCC 34541 has been reported to be unable to mineralize 3,4-dichloroaniline (DCA). However, high mineralization is now shown to occur when a fermentation temperature of 37 degrees and gassing with oxygen are used. Mineralization did not correlate with lignin peroxidase activity. The latter was high under C limitation and low under N limitation, whereas the reverse was true for mineralization. The kinetics of DCA metabolism was studied in low-N and low-C and C- and N-rich culture media by metabolite analysis and 14CO2 determination. In all cases, DCA disappeared within 2 days, and a novel highly polar conjugate termed DCAX accumulated in the growth medium. This metabolite was a dead-end product under C and N enrichment. In oxygenated low-C medium and in much higher yield in oxygenated low-N medium, DCAX was converted to DCA-succinimide and then mineralized. DCAX was purified by high-performance liquid chromatography and identified as N-(3,4-dichlorophenyl)-alpha-ketoglutaryl-delta-amide by high-performance liquid chromatography and mass spectroscopy, gas chromatography and mass spectroscopy, and nuclear magnetic resonance spectroscopy. The formation of conjugate intermediates is proposed to facilitate mineralization because the sensitive amino group of DCA needs protection so that ring cleavage rather than oligomerization can occur.

Aniline Compounds↗

PubMedDate not supplied

Comparative analysis of partial structures of a peat humic and fulvic acid using one- and two-dimensional nuclear magnetic resonance spectroscopy.

Nuclear magnetic resonance (NMR) resonance integrals obtained from one-dimensional NMR spectra provide semiquantitative contents of humic constituents with limited resolution in structural detail. When supplemented by connectivity information available from homo- and heteronuclear two-dimensional NMR spectra a more reliable assignment of humic substructures becomes available. This is demonstrated with a comparative one- and two-dimensional NMR analysis of a fulvic and a humic acid obtained from Eriophorum peat. An example of a detailed analysis of the proton chemical shift region normally attributed to carbohydrates shows substantial contributions from amino acids, amino and desoxy sugars, and highly oxidized aliphatic chains of intermediate length. The very good resolution of structural detail by a combined analysis of all NMR spectra shows that the effect of the fractionation procedure on the composition and chemical structure of humic materials is very significant. The comparison of the partial structures comprising humic acid (HA) and fulvic acid (FA) of the peat humic materials studied indicates that FA is diagenetically downstream of HA, favoring the biopolymer degradation (BD) model of humification.

Benzopyrans↗