bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metabolism of diafenthiuron by microsomal oxidation: procide activation and inactivation as mechanisms contributing to selectivity
Authors: Kayser Hartmut , Eilinger Philipp 
Published: August 2002

AbstractThe thiourea insecticide/acaricide diafenthiuron represents a biologically inactive propesticide that requires transformation into the active carbodiimide derivative. The carbodiimide inhibits mitochondrial respiration by selective and covalent binding to the proteolipid (8 kDa) of Fo‐ATPase in the inner membrane and to porin (30 kDa) in the outer membrane. The thiourea can be activated by light as well as by cytochrome P450 in the insect. To get insight into the enzymatic mechanisms of activation, model in vitro studies were performed using [14C]diafenthiuron and microsomes from various vertebrate livers and from locust Malpighian tubules. Though there was a common set of metabolites, their quantities varied significantly with the species and assay conditions. As a typical product, p‐hydroxydiafenthiuron was identified in assays with rat and mouse microsomes. The sulfomonoxide predominated in hen and fish assays, whereas pig and bovine microsomes almost exclusively produced the carbodiimide. The sulfoxide was shown to be a precursor of the carbodiimide. Formation of all metabolites was dependent on the presence of NADPH and active microsomes. The effects of inhibitors and the requirement for NAPDH suggested a role of cytochrome P450‐dependent monooxygenase(s) in the formation of both the hydroxylated product and the carbodiimide. FAD‐dependent monooxygenases (FMOs) may also be involved in a step following sulfoxidation. These in vitro studies revealed potential mechanisms contributing to biological selectivity of the effects of a pesticide that acts in a non‐selective mode at a conserved mitochondrial site.© 2001 Society of Chemical Industry
Rate of bentazone transformation in four layers of a humic sandy soil profile with fluctuating water table
Authors: Leistra Minze , Smelt Johan H , Matser Arriënne M , Bogte Jaap J , van der Pas Leo J T 
Published: August 2002

AbstractThe rate of transformation of a pesticide as a function of the depth in the soil is needed as an input into computations on the risk of residues leaching to groundwater. The herbicide bentazone was incubated at 15 °C in soil materials derived from four layers at depths of up to 2.5 m in a humic sandy soil profile with a fluctuating water table (0.8 to 1.4 m), while simulating the redox conditions existing in the field. Gamma‐irradiation experiments indicated that bentazone is mainly transformed by microbial activity in the soil. The rate constant for transformation was highest in the humic sandy top layer; it decreased with depth in the sandy vadose subsoil. However, material from the top of the phreatic aquifer had a higher rate constant than that from the layers just above. The presence of fossil organic material in the fluviatile water‐saturated sediment probably stimulated microbial activity and bentazone transformation. The changes in the transformation rate constant with depth showed the same trend as those in some soil factors, viz organic carbon content, water‐extractable phosphorus and microbial density as measured by fluorescence counts. However, the (low) concentration of dissolved organic carbon (DOC) in the top of the aquifer did not fit the trend. The rate constant for bentazone transformation in the layers was higher at lower initial contents of the herbicide.© 2001 Society of Chemical Industry
The relaxation of isolated rabbit corpus cavernosum by the herbal medicine Catuama® and its constituents
Authors: Antunes E. , Gordo W. M. , de Oliveira J. F. , Teixeira C. E. , Hyslop S. , De Nucci G. 
Published: August 2002

AbstractThe effects of the Brazilian herbal medicine Catuama® and each of its plant constituents (Paullinia cupana, Trichilia catigua, Zingiber officinalis and Ptychopetalum olacoides) were investigated on rabbit corpus cavernosum (RbCC) using a bioassay cascade. Catuama® caused short‐lived and dose‐dependent relaxations (11% ± 7%, 26% ± 5% and 82% ± 9%, at doses of 1, 3 and 10 mg, respectively). Neither the nitric oxide synthesis inhibitor Nω‐nitro‐L‐arginine methyl ester (L‐NAME; 10 μM) nor the soluble guanylate cyclase inhibitor ODQ (10 μM) significantly affected the Catuama®‐induced relaxations. Similarly, the selective ATP‐dependent K+ channel (KATP) blocker glibenclamide (10 μM), the muscarinic receptor antagonist atropine (1 μM) and the voltage‐dependent Na+ channel blocker tetrodotoxin (1 μM) all failed to affect significantly the Catuama®‐induced relaxations. These results indicate that the relaxations induced by Catuama® involve neither nitric oxide release nor KATP channel activation. The extracts of P. cupana, Z. officinalis and P. olacoides caused short‐lived and dose‐dependent RbCC relaxations, whereas T. catigua evoked long‐lasting relaxations which were occasionally preceded by a brief contractile effect. The extract of P. cupana was the most active in relaxing RbCC strips. The relaxations induced by all extracts were not significantly affected by L‐NAME (10 μM). The infusion of ODQ (10 μM) had no significant effect on the P. cupana‐ and Z. officinalis‐induced relaxations but reduced by >50% (p < 0.05) those evoked by P. olacoides and T. catigua. Incubations of RbCC with Catuama® (10 mg/mL for 0.25 to 5 min) caused increases of cAMP levels (143% increase at 5 min of incubation). Incubations of RbCC with P. cupana extract (1 mg/mL) increased the cAMP levels by 200% whereas higher doses (10 and 100 mg/mL) caused smaller increases in the nucleotide levels (150% and 89%, respectively). The extracts of Z. officinalis and P. olacoides (same doses) caused smaller increases of the cAMP levels compared with the P. cupana extract, whereas T. catigua (1–100 mg) did not increase the levels of this nucleotide above the basal values. Our results show that of the four extracts assayed, P. cupana was the most effective, indicating that it is the main extract responsible for the relaxing effect of Catuama® on rabbit cavernosal tissue. Copyright © 2001 John Wiley & Sons, Ltd.
Triterpenes from Agarista Mexicana as potential antidiabetic agents
Authors: Perez G. R. M. , Vargas S. R. 
Published: August 2002

AbstractHypoglycaemic activity‐guided fractionation together with chemical analysis led to the isolation of 12‐ursene and a novel triterpene 23,24 dimethyl‐24‐ethyl‐stigmast‐25‐ene from the chloroform extract of the dried stem of A. mexicana. Identification was based on spectroscopic methods. The isolated triterpenes were tested for hypoglycaemic activity in normal and alloxman‐diabetic CD1 mice 25–30 g at a dose of 50 mg/kg body weight. The blood glucose levels were determined before and 1.5, 3, 4.5 and 24 h after intraperitoneal drug administration. The results showed that the triterpenes produced a significant hypoglycaemic effect in normal as well as in diabetic mice. Comparison was made between the action of the triterpenes and a known hypoglycaemic drug, tolbutamide (50 mg/kg). The 12‐ursene was found to be slow and less effective than tolbutamide, and the 23,24 dimethyl‐24‐ethyl‐stigmast‐25‐ene was shown to be more effective than tolbutamide. Copyright © 2002 John Wiley & Sons, Ltd.
Packaging materials for fermented milk: effects of material crystallinity and polarity on food quality
Authors: Jansson S. E. A. , Edsman C. J. , Gedde U. W. , Hedenqvist M. S. 
Published: August 2002

AbstractThe ability of a packaging material to protect the food product and extend its shelf‐life depends on several material properties. In this work the effects of material crystallinity and polarity on the quality of fermented milk were studied. The fermented milk is a high‐quality Swedish product, similar to yoghurt. The quality of the food product was determined as a function of storage time by containing the liquid in pouches of different materials. The material crystallinity was varied by using very low‐density polyethylene, high‐density polyethylene and aluminium laminate as packaging materials. Aluminium was used on account of its ‘100%’ gas‐tightness. The polarity was varied by comparing an aliphatic polyketone with polyethylene of similar crystallinity. The carbon dioxide (CO2) and oxygen (O2) contents in the headspace of the pouches were determined. The food quality was determined by measuring whey syneresis, viscosity and the content of desired Bifidobacteria, as well as of undesired yeast and mould. A trained taste panel determined the degree of acidity and of the sparkling taste. It was found that the content of CO2 increased and that of O2 decreased in the pouches with increasing degree of crystallinity and increasing polarity. The sparkling taste of fermented milk was a clear function of the headspace CO2 content. The data presented here could thus be used to ‘design’ a package for a desired sparkling taste of the fermented milk by selecting a certain material crystallinity. Whey syneresis, viscosity and content of Bifidobacteria were found to be independent of pouch material. While the degree of whey syneresis and the viscosity increased with increasing storage time, the content of Bifidobacteria slowly decreased. The content of yeast and mould in the liquid was below the existing limit values for foodstuffs. The degrees of acidity and sparkling taste were highest for the liquids contained in aluminium and polyketone pouches, although the differences in acidulous taste between the various pouch materials were small. Copyright © 2001 John Wiley & Sons, Ltd.
Reducing search time for optimal geometry of small molecular clusters
Authors: Steen Kay J. , Smith Lars Erik 
Published: August 2002

AbstractThis work has developed and tested an optimal geometry search algorithm. The results shows that response modeling of the energy hypersurface reduce the number of single‐point calculations needed to find the optimal geometry. In large systems it seems to reduce the number of necessary points by 50% or more. The method is based on an updating partial least‐squares regression (PLSR) algorithm for choosing a set of candidate configurations by minimizing the predicted response. Since the PLSR modeling time is short, compared to the quantum chemical calculations, the search time is reduced by approximately the same percentage as the reduction in number of single‐point calculations needed. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002
Orbital functional theory of linear response and excitation
Authors: Nesbet R. K. 
Published: August 2002

AbstractOrbital functional theory (OFT) is based on a rule that determines a single‐determinant reference state Φ for any exact N‐electron eigenstate Ψ. An OFT model postulates an explicit correlation energy functional Ec of occupied orbital functions {ϕi} and occupation numbers {ni}. The orbital Euler–Lagrange equations are analogous to Kohn–Sham equations, but do not in general contain local potential functions. Time‐dependent Hartree–Fock theory is generalized in OFT to a formally exact linear response theory that includes electronic correlation. In the exchange‐only limit, the theory reduces to the random‐phase approximation of many‐body theory. The formalism determines excitation energies. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Pure representability problem and new models of the electronic Fock space
Authors: Panin A. I. 
Published: August 2002

AbstractNew models of the Fock space sector corresponding to some fixed number of electrons are introduced. These models originate from the representability theory and their practical implementation may lead to essential reduction of dimensions of intermediate CI spaces. A certain zero‐order theory is proposed that gives wavefunctions approximately equivalent to ones obtained by accounting for all excitations from the Hartree–Fock reference state up to the qth order. Simple numerical examples are given to illustrate our approach. © 2001 Wiley Periodicals, Inc. Int J Quantum Chem, 2001
Quantum mechanical investigation of the electronic structure and spectral properties of 6,8‐dimethylisoxanthopterin
Authors: Seibert Eleanore , Ross J. B. Alexander , Osman Roman 
Published: August 2002

Abstract6‐Methylisoxanthopterin (6‐MI) is a fluorescent guanine analog that is suitable for studying deoxyribonucleic acid (DNA) structure and dynamics. To aid in the interpretation of spectroscopic data, we have carried out an ab initio quantum mechanical investigation of the electronic structure of 6‐MI. The geometries of the ground state and the nonplanar emitting state were optimized at the second‐order Møller–Plesset (MP2) level. Using complete active space multiconfigurational self‐consistent field (CASSCF) theory and time‐dependent density functional theory (TDDFT), we have characterized the low‐lying excitation and emission transitions. The lowest energy transition is a ππ* transition. We also observe a nearby nπ* state, which is not accessible spectroscopically. The calculated energies of the ππ* absorption and emission are in good agreement with experimental results. A large increase in the molecular dipole moment for 6‐MI in the excited state compared to the ground state yields the prediction that 6‐MI absorbance and emission spectra should be very sensitive to the polarity of the solvent. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 28–33, 2002
Metastability of protein native folds with respect to global variations in primary sequence
Authors: Arteca Gustavo A. , Veluri Kalyani 
Published: August 2002

AbstractIn the absence of water, a range of rapid large‐scale conformational rearrangements is accessible in principle to a protein. Despite this, experiments and computer simulations suggest that native states need not be totally unstable once a protein is dehydrated. Here, we explore further the possibility that native folds act as conformational attractors in vacuo, despite variations on their primary structure. To this end, we carry molecular dynamics simulations on “protein chimeras,” where a protein sequence is threaded onto the backbone corresponding to the native state of a different protein with the same chain length. The simulations mimic the conditions of unrestricted rotation and translation found in gas‐phase or in vacuo experiments. We find that the chimeras show a range of motions commensurable to that of the original native state. In no case do we observe a complete change in folding features during early relaxation; in most cases, the original fold is actually metastable. The results suggest that the initial dynamical behavior of a protein may be dictated by the large‐scale backbone folding features, and not by details of the primary structure. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 220–225, 2002
Assessment of the bioactive conformation of the vasoactive intestinal peptide by computational methods
Authors: Filizola Marta , Perez Juan J. 
Published: August 2002

AbstractIn the present work, we report the results of a computational study aimed at assessing the structural features of the bioactive conformation of the vasoactive intestinal peptide (VIP). Based on previous structure–activity studies the present work reports the results of a comparative analysis of the conformational profiles of the segments 1–11 of the native peptide, two VIP antagonists and two inactive analogs. All these analogs exhibit the same sequence as VIP at C‐terminus and only differ in some of the amino acids of the N‐terminus. Analogs selected for the present study include VIP(7–28) fused to neurotensin (6–11) (Met‐hydrid) and [Ac‐Tyr1, D‐Phe2]‐VIP (both antagonists) and [Ala3]‐VIP and [Ala6]‐VIP (two inactive analogs). The conformational space of the five peptides was thoroughly explored using simulated annealing in an iterative fashion as sampling technique. The bioactive conformation was selected from pairwise cross‐comparisons between each of the unique low energy conformations found for VIP(1–11) and each of the different analogs, within a 3 kcal/mol threshold in regard of the respective lowest energy conformation characterized. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002
Enzyme catalysis: Transition structures and quantum dynamical aspects: Modeling rubisco's oxygenation and carboxylation mechanisms
Authors: Tapia O. , Fidder Henk , Safont Vicent S. , Oliva Mónica , Andrés Juan 
Published: August 2002

AbstractQuantum dynamics is introduced with the help of molecular states (MS) for systems decomposable into n electrons and N nuclei. These states, when projected onto the electronic and nuclear configuration spaces, r and R, respectively, are represented as products of electronic and nuclear wave functions of the type Φk(r;αk°)χkj(R;αk°). The 3N coordinates αk° are the positions of positive charges in real space that are equivalent to the nuclear charges. The stationary geometry is derived from quantum chemical analytical gradient optimization procedures. The set {Φk(r;αk°)χkj(R;αk°)} is assumed to contain all cluster partitioning including corresponding asymptotic states. These MSs provide a basis to represent a quantum state as a particular linear superposition. Quantum states are (row) vectors in a dual space whose components are the complex coefficients in the linear superposition of MSs. A reactive system is represented in the direct product space of the MS and surrounding medium: ∣MS〉⊗∣E〉. The surrounding basis states {∣E〉} may be other molecular state systems (protein, solvent) or electromagnetic fields. A chemical reaction is represented as a time evolution of vectors in the dual space driven by the interaction with an energy source or sink system. A theory of catalysis is constructed on this new basis for which the protein–substrate interaction operator drives the quantum change of state. The chemical reaction catalyzed by rubisco is examined and used to introduce the theoretical scheme. The mechanism of carboxylation and oxygenation expressed as sets of transition structures is discussed from this new quantum mechanical perspective. For a protein in thermal equilibrium with a thermal bath at absolute temperature T, in so far as time evolution in the reactant system is concerned, the protein may be replaced by a blackbody radiation field. In real situations, both the protein–substrate and electromagnetic field–substrate interactions provide mechanisms to favor particular time evolutions of the quantum system. A mapping to a unit hypersphere with the axis represented by (orthogonalized) MSs permits a simple “visualization” of all bound quantum states related to the system as points on the surface of the hypersphere. Time evolution of complex systems can be systematized in this new way. © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002
Computational studies of electron‐transfer processes in old yellow enzyme
Authors: Chateauneuf Ginger M. , Brown Richard E. , Brown Bette Jo 
Published: August 2002

AbstractOld Yellow Enzyme (OYE) is a flavoenzyme that was first isolated from brewer's bottom yeast. Homologues have been identified in other strains of yeast, bacteria, and plants. In plants, the OYE homologue functions enzymatically in the synthesis of plant hormones, but the biological function of OYE in yeast is still unknown. Flavin mononucleotide (FMN) is the cofactor that is noncovalently bound in the enzyme. OYE binds several phenolic ligands that serve as models for reactive biological substrates. These complexes have broad long‐wavelength absorption bands, which have been ascribed to charge‐transfer interactions, with the phenolate anion acting as the electron donor and the FMN as the acceptor [Abramovitz, A. S.; Massey, V. J Bio Chem 1976, 251, 5327–5336]. The computational characterization of these electronic transitions in the active site will help in understanding the biological processes in the enzyme. It was found that at several levels of computational methods, and through computationally mutating relevant amino acids, a charge‐transfer process is occurring. This result agrees with previous experimental work and is consistent with all ultraviolet–visible spectrophotometric data. The preliminary results for the computational studies of these electron‐transfer processes will be presented. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
C28 (D2): Fullerene growth mechanism
Authors: Rama K. Mishra  , Lin Ying‐Ting , Lee Shyi‐Long 
Published: August 2002

AbstractReactions among the mono‐ to polycyclic carbon clusters have been analyzed using semiempirical AM1 and HF/6‐31G* methods. The C28 (D2) fullerene cage has been considered. Various precursors are chosen with the appropriate carbon belts. It is observed that the reactions between the precursors and the belts are essentially endoergic in nature, whereas the reactions between the stable intermediates and the final belts are exoergic. Further, the second step of the process is really akin to an annealing mechanism. Also, it has been observed that, in the annealing process, a cascade type of bond‐forming mechanism is in operation. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001
Spectral properties of neutral selenium and tellurium. A relativistic treatment
Authors: Lavín C. , Velasco A. M. , Martín I. 
Published: August 2002

AbstractOscillator strengths for fine‐structure transitions in the complex atomic systems, neutral selenium, and tellurium, are reported. The calculations were carried out using the relativistic quantum defect orbital method. The resulting oscillator strengths are analyzed in terms of other theoretical and experimental data. In addition, to estimate the correctness of our oscillator strengths for these species, we have also analyzed the regularities complied by the calculated f‐values. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001
Molecular treatment of charge transfer cross sections in N5+collisions with H2
Authors: Errea L. F. , Macías A. , Méndez L. , Rabadán I. , Riera A. , Sanz P. 
Published: August 2002

AbstractWe present cross sections for electron capture in N5++H2collisions in the energy range 100 eV/amu≤E≤6 keV/amu. We employ a model potential aproximation to treat the interaction of the active electron with the cores, and a recently proposed method, which applies the independent particle model to evaluate the Hamiltonian matrix elements. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001