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Biomedical subjects

H R Schulten

Publications and source records attributed to H R Schulten.

At least 19 recordsLinked to original sources
PubMed2001

Humic complexes of diethyl phthalate: molecular modelling of the sorption process.

The sorption mechanisms and complex formation between humic acid (HA) and a successively increasing number of diethyl phthalate (DEP) molecules have been studied theoretically using molecular mechanics, the number (n) of DEP molecules being varied from 1 to 30. The energy components of the single HA x nDEP complexes have been used as explanatory variables in a principal component analysis for exploring the presence of similarities/dissimilarities in the energetic properties of the individual xenobiotic complexes. The sorption can be explained in terms of a two-step mechanism. Absorption takes place as long as the host humic acid structure offers (a) enough internal docking space and (b) favorable interactions (energy release) with the guest molecule. This takes place for up to 7 DEP molecules. Further increase in the number to 30 DEP molecules will, due to the lack of free available internal voids, lead to surface controlled adsorption. The two-step sorption process apparently results in (a) a linear increase in energy gain by DEP bonds, and similarly (b) a constant incremental rise in molecular properties of the complexes such as volume and surface area. Three outstanding observations emerge: (1) Structural features at the atomic level (nanochemistry), such as partial atomic charges and high aromaticity of the humic acid, are observed to be dominating the intermolecular interactions in the complexes at the specific sorption sites. (2) Torsional relief and favorable changes in bonding energy also prevail for the growing complex. The latter indicates both the structural flexibility of the HA host and the stabilizing effect of DEP on the complex, by filling of the voids within the HA molecule. (3) The intermolecular forces are described mainly by hydrogen bonds (electrostatic energy) and interactions between dipole-dipole, such as carboxylic functions and uncharged moieties such as aromatic rings (van der Waals energy).

Absorption↗
PubMed2001

Interaction of imidazolinone herbicides with soil humic acids. Experimental results and molecular modeling.

Adsorption and desorption isotherms of the herbicides imazapyr, imazethapyr and imazaquin on a soil humic acid have been performed at pH 2.8 and 4.0 (below and above the pKa of the herbicides). At both pH, adsorption increased according to the lipophilic character of the molecules (imazapyr < imazethapyr << imazaquin). The extent of adsorption was higher at pH 2.8 than at pH 4.0 because of the partial ionization of the carboxylic groups of both herbicides and humic acids at increasing pH. Desorption of imazapyr and imazethapyr was nearly complete at pH 4 and higher than 60% at pH 2.8 while desorption of imazaquin was 45 and 8% at pH 4 and 2.8, respectively. No differences between adsorption isotherms at 10 degrees C and 25 degrees C were observed a pH 4.0 indicating that adsorption involved very weak bonds while at pH 2.8, adsorption was higher at 10 degrees C than at 25 degrees C indicating an exothermic process. The isosteric enthalpy of adsorption of each herbicide was low (about -1 kJoule mole(-1)) suggesting that low energetic bonds were involved. Adsorption on different humic acids has indicated that for each herbicide, the extent of adsorption expressed as Kd was correlated with the amount of carboxylic and aromatic groups of humic acids suggesting that hydrogen bonding and/or charge-transfer complexes formation could take place. Molecular modeling and geometry optimization of humic acid and soil organic matter (SOM) herbicide complexes were also performed. The results obtained with this theoretical approach gave a consistent chemical interpretation of the experimental results. To the best of our knowledge this is the first report to contribute to a better understanding of site-specific bonding of herbicides in SOM complexes by nanochemical modeling and distinct energy descriptors.

Adsorption↗
PubMed1996

Differentiation of resin-modified paints by pyrolysis-gas chromatography/mass spectrometry and principal component analysis.

The combination of pyrolysis (Py) with gas chromatography/mass spectrometry (GC/MS) is already well established for polymer analysis. A first approach is reported using this method for detailed quality monitoring of a complex technical polymer system. Six similar solvent-based paints (one standard and five modifications) have been used for evaluation. The major pyrolysis products were identified and qualitative and quantitative modifications were detected and specified. Principal component analysis (PCA) was applied for visualization of differences and similarities.

Journal Article↗
PubMed1988

Fast profiling of food by analytical pyrolysis.

The analytical application of direct pyrolysis (Py) field ionization (FI)-mass spectrometry (MS) und Curie-point pyrolysis gas chromatography-mass spectrometry (Py-GC/FIMS) to various whole foodstuffs is described for the first time. The former technique yields highly differentiated information from the sample in typically 15 min, namely the molecular weight distribution of released volatiles and pyrolysis products in a single spectrum which, owing to the good reproducibility and high significance of the resulting data, has previously been shown to be suitable for the application of chemometric methods. Such mass spectral peaks are further characterized and assigned by high resolution mass measurement and/or by electron ionization after Curie-point pyrolysis and gas chromatographic separation of the components. In this first report, typical results are presented for ground roasted coffee, rosehip tea, wheatmeal biscuit, chocolate drink powder and milk chocolate. The FI mass spectrum obtained from the latter sample is compared with those obtained using the complementary soft ionization techniques of chemical ionization (CI) and direct chemical ionization (DCI).

Animals↗
PubMed1986

Identification of nucleic acid adducts from trans-4-acetylaminostilbene.

It has been proposed that trans-4-acetylaminostilbene (AAS) is an initiator for tumor formation in rat liver and that the metabolically formed hydroxamic acid ester ultimately reacts with nucleic acids in vivo. We have now studied the generation of a major adduct in vitro. trans-4-N-Acetoxy-N-acetylaminostilbene (N-acetoxy-AAS) was reacted with guanosine at pH 7.5 and reaction products were separated by chromatography on Sephadex LH-20 and RP18 HPLC. The major adduct isolated consists of four isomers which have been tentatively identified by mass- and 1H-NMR spectroscopy as (S,S)- and (R,R)-guanosine-N2,beta-N3,alpha-N-acetylaminobibenzyl and the respective regio isomers guanosine-N2,alpha-N3,beta-N-acetylaminobibenzyl. These adducts are formed in a ratio of 9:9:1:1. Under acidic conditions (pH 2) the ribose moiety is removed and two regio isomeric base adducts are formed in the ratio 9:1. Results to be published indicate that the adducts are also formed in vivo in rat liver RNA and DNA.

Animals↗
PubMed1986

Factors responsible for the formation of different N-alkylated porphyrins in rat liver microsomal systems exposed to norethindrone. The role of 3 alpha-hydroxysteroid dehydrogenase.

Incubation of rat liver microsomes with norethindrone and a NADPH-generating system leads to the formation of one N-alkylated porphyrin (green pigment, GP1). Administration of this steroid to male rats in vivo results in the formation of three more-polar green pigments (GP2, 3 and 4). A cytosolic protein (green-pigment converting protein) has been purified from rat liver that, when added to liver microsomal mixtures containing norethindrone (0.03 mM) and a NADPH-generating system, results in the formation of all four green pigments (GP1, 2, 3 and 4). Field-desorption mass spectrometry of the purified green pigments gave protonated molecules, [M + H]+, at m/z 905 for GP1, m/z 909 for GP2, m/z 925 for GP3 and 4. The Mr of the purified cytosolic protein on SDS/polyacrylamide-gel electrophoresis or gel filtration was 37000. Polyacrylamide-gel isoelectric focusing gave a pI value of 5.9. Antibodies raised in rabbits against this protein, after preincubation with rat liver cytosol, subsequently prevented the formation of the more-polar norethindrone-induced green pigments (GP2, 3 and 4). The purified protein in the presence of either NADH or NADPH catalysed the reduction of delta 4-ring-reduced norethindrone, 5 alpha-oestran-17 alpha-ethynyl-17 beta-ol-3-one and, with the appropriate cofactor, the oxidation and reduction of steroids lacking the ethynyl function, e.g. androsterone or dihydrotestosterone. Indomethacin inhibited the reduction of dihydrotestosterone by this protein with an I50 (concn. causing 50% inhibition) value of 4.9 microM. From its physical and enzymic properties it is concluded that green-pigment converting protein is the same as 3 alpha-hydroxysteroid dehydrogenase (EC 1.1.1.50).

3-Hydroxysteroid Dehydrogenases↗
PubMed1984

Lithium, sodium, potassium and rubidium cation concentrations during the development of certain organs of unborn rabbits.

The distribution of lithium, sodium, potassium and rubidium in rabbit fetuses was determined during the last two weeks of gestation. Samples of eye, brain, lung, heart, liver and kidney were investigated. Co-actions between the ion pairs Li+/Na+ and K+/Rb+ could be discerned. The essential properties of lithium and rubidium for the fetal development of rabbits were examined by investigating the supply of the fetal organs with these elements. Correlations between organ differentiation processes and metal concentrations were established and compared with the results obtained for the fetal development of other vertebrates.

Animals↗
PubMed1983

Determination of rubidium in human serum.

Field desorption mass spectrometry (FD-MS) combined with stable isotope dilution has been used to determine rubidium concentrations from human serum. Samples obtained from 110 healthy volunteers (50 males, 60 females) were examined. The rubidium concentrations found varied from 0.96 to 3.56 mumoles/l, the average value being 1.96 mumoles/l. The precision of the measurements within a batch was 0.8%. The time for 1 analysis, including sample preparation is about 30 min, the total sample consumption is 100-200 mul. The corresponding potassium concentrations were also determined from all these serum samples; a weak trend towards higher potassium levels with increasing rubidium concentration is found.

Female↗
PubMed1983

Time-dependent excretion of lithium, sodium, potassium, rubidium, magnesium and strontium in the urine of a multiple sclerosis patient.

Field desorption mass spectrometry and stable isotope dilution have been used for direct trace analysis of metals in urine. Samples were collected over 24 h at 2 h intervals from a hospitalized multiple sclerosis patient. Quantitative determinations of Li+, Rb+, Mg2+ and Sr2+ from individual samples have been made and correlated with the amounts of urine excreted as well as with the time of day. The concentrations of Na+ and K+ were determined by flame photometry. The quantities of metals excreted in urine during the course of 24 h were 0.0129 mg for lithium, 4700 mg for sodium, 2100 mg for potassium, 1.4 mg for rubidium, 78.8 mg for magnesium and 0.2356 mg for strontium. The maximal absolute quantities excreted of all metals determined correspond with the largest volume of urine. The highest amounts of potassium, rubidium and strontium were found in urine during the daytime (8.00-20.00), whilst magnesium was excreted increasingly during the night hours (20.00-8.00). The excretion of lithium and sodium is fairly even over the entire 24 h period. It is noteworthy that similarities in the excretion profile and the concentration course are observed between Li+ and Na+ on one hand and between K+ and Rb+ on the other. Moreover, the lower concentration of Rb+ ions in urine of multiple sclerosis patients, in comparison to healthy individuals and clinical controls as reported previously, was confirmed.

Adult↗
PubMed1983

Cyclophosphamide levels in serum and spinal fluid of multiple sclerosis patients treated with immunosuppression.

The cyclophosphamide content of urine, serum and spinal fluid of immuno-suppressed multiple sclerosis patients was determined using a newly developed off-line combination of high pressure liquid chromatography and field desorption mass spectrometry. Although urinary excretion of the drug varied considerably between patients, the levels in serum and spinal fluid were in the same range, a relationship that may facilitate control of the dosage.

Adult↗
PubMed1983

Concentrations of electrolytes and trace metals in amniotic fluid and body tissues of rabbits during the last two weeks of gestation.

Uterus and placenta of the mother animals, amniotic fluid as well as skin, ossified bone tissue and skeletal muscle of the fetuses were examined. The natural concentrations of Li+, Na+, K+, Rb+, Mg2+, Sr2+, Ba2+-ions were determined in the third and fourth weeks of gestation. The concentrations of trace metals down to 10(-9) g metal/g tissue could be determined, with a standard deviation of less than +/- 10%, by field desorption mass spectrometry. Correlations between lithium concentrations and bone growth were discerned. Differentiation-processes of the fetal skin were indirectly verified by the marked decrease of all metal ions with the progress of gestation. Concentration changes of metals in uterus tissue during gestation correspond to the changes in maternal serum at the same stage.

Amniotic Fluid↗
PubMed1983

Thallium determinations in fetal tissues and maternal brain and kidney.

The transfer of T1+ cations through the placental barrier of pregnant mice and rats was studied by comparing the thallium concentrations in the maternal brain and kidney and those in fetal tissue at times of 10 min to 50 h after dosage of the animals with 10 mg/kg body wt. T1(2)SO4. The quantitative determinations were performed with field desorption mass spectrometry after dilution of the homogenised tissue samples with enriched stable isotopes of thallium. The total sample quantity required for one complete assay is 1-3 micrograms, the analysis time for one determination about 30 min.

Animals↗
PubMed1982

Off-line combination of liquid chromatography and field desorption mass spectrometry: principles and environmental, medical and pharmaceutical applications.

Field desorption mass spectrometry (FD-MS), which is applicable to analyses of compounds of low volatility and thermal instability, is used as a sensitive, specific and fast detection method for high-performance liquid chromatography (HPLC). Owing to its simplicity and efficiency, off-line combination is the preferred technique for the analysis of substances in chromatographic effuents. The principles of identification, purity control and quantification are presented. Characteristic examples of mental, medical and pharmaceutical areas are given. Qualitative and quantitative results for drugs and endogenous compounds, e.g., tranquillizers, immunosuppressive and antitumour agents and free amino acids, in human body fluids, biocides, e.g., phenylureas, carbamates, organophosphorus and organometallic compounds, in river water, and natural and synthetic products, e.g., saponins, chlorophyll and deoxyribonucleotides, are presented.

Barbiturates↗
PubMed1982

Determination of lithium and rubidium in physiological fluids and tissues of rabbits during the reproductive phase.

1. The natural concentrations of lithium and rubidium were determined during the reproductive phase of rabbits by field desorption mass spectrometry. 2. Samples of serum, milk, amniotic fluid and placenta tissue were analysed. 3. The concentration changes in serum during the reproductive phase were between 2.61 and 5.02 micrograms/l for lithium and between 107.78 and 136.28 micrograms/l for rubidium. 4. Correlations between the concentration in maternal serum and bone growth of the fetus as well as the formation of milk were found. 5. Concentrations of 9.30 micrograms/l lithium and 1780.00 micrograms/l rubidium in the milk lead to the assumption that these trace metals are essential for the metabolism of the young rabbit.

Amniotic Fluid↗
PubMed1981

Isolation, identification and determination of cyclophosphamide and two of its metabolites in urine of a multiple sclerosis patient by high pressure liquid chromatography and field desorption mass spectrometry.

The off-line combination of high pressure liquid chromatography and field desorption mass spectrometry has been used for the simultaneous isolation, identification and determination of cyclophosphamide and two of its metabolites, 4-ketocyclophosphamide and carboxyphosphamide in urine from a patient suffering from multiple sclerosis. Cyclophosphamide and its metabolites were separated using reverse phase liquid chromatography. Field desorption mass spectrometry was employed for identification and quantification. The technique applied needs no derivatization for analysis. The limits of detection by field desorption mass spectrometry for 1, 2 and 3 are factor of about 4 X 10(3)-10(5) lower than those of a common variable ultraviolet detector. Quantitative determination was carried out using the method of stable isotope dilution with deuterated analogues of 1, 2 and 3. In a pilot study, the ratio of 1:2:3 was determined to 1:0.02:0.6. One ml of urine is sufficient for simultaneous analysis of the three compounds. The typical analysis time, including separation by liquid chromatography and field desorption measurement, is about 30 minutes.

Chromatography, High Pressure Liquid↗
PubMed1980

Determination of cyclophosphamide in urine, serum and cerebrospinal fluid of multiple sclerosis patients by field desorption mass spectrometry.

The levels of cyclophosphamide in samples of urine, serum and cerebrospinal fluid of multiple sclerosis patients, who had received the drug orally (4 x 100 mg/day) have been determined by field desorption mass spectrometry using the principle of stable isotope dilution. After thorough preparation of the samples, concentrations of cyclophosphamide of 10 to 60 micrograms/ml in urine and 200 to 400 ng/ml in serum and cerebrospinal fluid have been determined from 0.6-3 ml samples. The first quantitative data for cyclophosphamide in cerebrospinal fluid of multiple sclerosis patients could be established without the use of radioactive material. The relatively high level of the parent drug found in the fluid at the end of a 3-weeks treatment may shed some light on the mechanism of action of this drug in the treatment of the disease.

Cyclophosphamide↗