bluuebunny/crossref_metadata_2025 huggingface dataset:
Semi‐interpenetrating polymer networks based on polyurethane and polymethacrylate functional prepolymers: Morphology and mechanical properties in dependence of the concentration of functional groups
Authors: Anžlovar Alojz , Žigon Majda
Published: August 2002

Grafted semi‐interpenetrating polymer networks (IPNs) were prepared from polyurethane (PU) prepolymers with polyester soft segments and hard segments containing carboxylic functional groups as well as polymethacrylate (PM) prepolymers with tertiary amine functional groups. The dependence of morphological and mechanical properties on the concentration of functional groups was studied. The enhanced miscibility of PU and PM prepolymers was observed at concentrations of functional groups of 0.25 mmol/g of polymer and above. Despite the improved miscibility, the PM prepolymers showed a tendency toward phase separation. Because the observed glass‐transition temperature shifts of PU prepolymers indicated substantial miscibility, we ascribed this phenomenon to the presence of methyl methacrylate rich sequences in the PM prepolymer. The observed changes in mechanical properties by increasing the content of functional groups were typical for ionomers. Young's modulus increased as a result of physical interactions between functional groups. A significant drop in tensile strength was observed in IPN samples with phase‐separated PU and PM prepolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 115–123, 2002
Novel etching phenomena in poly(3‐hydroxy butyrate) and poly(oxymethylene) spherulites
Authors: Shahin M. M. , Olley R. H.
Published: August 2002

Poly‐3‐hydroxy butyrate has been etched and studied under scanning and transmission electron microscopes. It displays three of the following unusual features: (1) spherulites develop in a loose spiral rather than radial structure, which appears to reflect the chiral nature of the polymer; (2) in the banded spherulitic structure, lamellae oriented flat‐on to the surface are etched more deeply in relation to edge‐on lamellae; and (3) material crystallized at high temperature is less resistant to etching than that crystallized at low temperature, whereas the most rapid rate of etching appears to be where growth occurred at an intermediate temperature where the growth rate was at its maximum. The second and third phenomena are contrary to what is found in polymers such as polyethylene and polyethylene terephthalate and are attributed to excess free volume in the material located between the main lamellar bundles. Polyoxymethylene also displays the same unusual relationship of etching rate with crystallization temperature. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 124–133, 2002
Angular dependence in the transmittance from self‐organized striped pattern of refractive indices in photopolymer
Authors: Uematsu Takafumi , Maenosono Shinya , Watanabe Akira , Yamaguchi Yukio
Published: August 2002

We report on a self‐organized striped pattern of refractive indices in a photopolymer and the resulting angular dependence in the transmittance as a result of the microstructure. The photopolymer plates were obtained by photoreaction of a monomer mixture placed in a space between two glass plates. The monomer mixture was prepared by mixing bifunctional methacrylate monomer, cyanoethylmethacrylate, and 2,4,6‐trimethylbenzoyldiphenylphosphine oxide as photoinitiator. After the photoreaction by uniform irradiation of UV light, the self‐organized striped pattern was observed in the crosslinked photopolymer plate by optical microscopy. Electron probe microanalysis of the cross section of the polymer plate confirms that a compositional inhomogeneity in the medium is quite small. The result suggests that the optically observed striped pattern is not due to the compositional and/or density modulation through the diffusion of monomers. We attribute the striped pattern to the crosslink density modulation and the resulting refractive‐index modulation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 216–225, 2002
Microphase separation in poly(acrylonitrile–butadiene–styrene) (ABS) studied with paramagnetic spin probes. II. Simulation of electron spin resonance spectra
Authors: Varghese Biji , Schlick Shulamith
Published: August 2002

We recently presented electron spin resonance spectra of poly(acrylonitrile–butadiene–styrene) (ABS) doped with 10‐doxylnonadecane (10DND) and 5‐doxyldecane (5DD) as spin probes. The spectra were measured in three types of ABS that differed in their butadiene contents and methods of preparation. Results for the ABS polymers were evaluated by comparison with similar studies on the homopolymers polybutadiene (PB) and polystyrene (PS) and the copolymers poly(styrene‐co‐acrylonitrile) (SAN) and poly(styrene‐co‐butadiene) (SB). Only one spectral component was detected for 10DND in PB, PS, SAN, and SB. In contrast, two spectral components differing in their dynamic properties were detected in the ABS samples and were assigned to spin probes located in butadiene‐rich domains (the fast component) and SAN‐rich domains (the slow component). The presence of two spectral components was taken as an indication of microphase separation. In this study, we present details on the dynamics and microphase separation by simulating spectra of 10DND in ABS, PB, PS, and SAN. The simulations are based on a dynamic model defined by the components of the rotational diffusion tensor and the diffusion tilt angle between the symmetry axis of the rotational diffusion tensor and the direction of the nitrogen 2pz atomic orbital. The jump diffusion model led to good agreement with experimental spectra. In this model, the spin probe has a fixed orientation for a given time and then jumps instantaneously to a new orientation. The temperature variation of the rotational correlation time in PB and PS consisted of two dynamic regimes, with different activation energies. The transition temperature at which the change in dynamics occurs (Ttr) is 380 K for PS and 205 K for PB, essentially the same as the corresponding glass‐transition temperatures measured by differential scanning calorimetry. We suggest that Ttr is a better indicator of the glass transition than the temperature at which the total spectral width is 50 G, especially for large probes. The simulation program allowed the determination of the relative intensities of the fast and slow spectral components as a function of temperature; this information was used to clarify the redistribution of the probe above the glass transition of the SAN‐rich component in ABS systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 424–433, 2002; DOI 10.1002/polb.10110
Diffusion measurements with fourier transform infrared attenuated total reflectance spectroscopy: Water diffusion in polypropylene*
Authors: Yi Xiaohua , Pellegrino John
Published: August 2002

The diffusion of pure liquid water into a commercial polypropylene (PP) film at 278–348 K was studied with Fourier transform infrared attenuated total reflectance spectroscopy. Abnormal diffusion behavior was indicated by a significant deviation between the experimental data and a Fickian diffusion model with the conventional saturated boundary condition applied at the water/PP interface. This deviation was observed at all the temperatures studied. With a modified boundary condition that took into account a mass‐transfer resistance at the water/PP interface, the Fickian model was able to represent the experimental data satisfactorily. The average water diffusion coefficient varied between 1.41 and 7.64 × 10−9 cm2/s, with an activation energy of diffusion of about 19.3 kJ/mol. The interfacial mass‐transfer resistance was represented by an exponential model with an empirical relaxation parameter. The relaxation parameter β increased as the temperature increased and reached an apparent plateau. The infrared spectrum indicated a positive chemical shift of 18 cm−1 for the less strongly hydrogen‐bonded component of the broad hydroxyl stretching band with respect to pure liquid water, indicating that hydrogen‐bonding interactions were weakened or broken when water molecules diffused into the PP matrix. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 980–991, 2002
Interaction mechanism of a novel polymer electrolyte composed of poly(acrylonitrile), lithium triflate, and mineral clay
Authors: Chen Hsien‐Wei , Chang Feng‐Chih
Published: August 2002

The addition of optimum cetyl pyridium chloride (CPC)–modified montmorillonite (CM) increases the ionic conductivity of poly(acrylonitrile)‐based electrolytes by roughly two orders of magnitude. Specific interactions between the silicate layer, the nitrile group, and the lithium cation were investigated by FTIR, solid‐state NMR, dielectric analyzer, and alternating current impedance. IR and NMR spectra confirm that the negative charges in the silicate layers alter the ionic charge environment of the PAN‐based electrolyte composites, which have the same function as the polar group in PAN. The optimum CM content to achieve the maximum ionic conductivity is 6 phr. However, untreated montmorillonite leads to insignificant polymer intercalation, the negative charges in the silicate layers fail to appreciably disturb the attractive force of the lithium salt, and the resulting conductivity improvement is also less than that of the CM additives. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2407–2419, 2001
Simulation of two‐dimensional streptavidin crystallization
Authors: Zhdanov V.P. , Höök F. , Kasemo B.
Published: August 2002

We present lattice Monte Carlo simulations of the growth of streptavidin islands at a biotinylated lipid layer. The model employed takes into account attractive anisotropic lateral interactions between streptavidin tetramers. With a minimal set of interactions, we reproduce the formation of rectangular islands experimentally observed at pH ≥ 9.0. Specifically, we analyze two scenarios of the island growth. First, if streptavidin is rapidly adsorbed at t = 0 (stepwise coverage change without ongoing adsorption), the average linear island size is found to grow according to the Lifshitz–Slyozov law, R ∝ t1/3. Second, if the island growth occurs in parallel with streptavidin adsorption limited by diffusion in the solution, the Lifshitz–Slyozov law is also applicable, but only at the late stage, when the streptavidin coverage is appreciable. Proteins 2001;43:489–498. © 2001 Wiley‐Liss, Inc.
Metabolism of diafenthiuron by microsomal oxidation: procide activation and inactivation as mechanisms contributing to selectivity
Authors: Kayser Hartmut , Eilinger Philipp
Published: August 2002

The 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

The 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

The 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

Hypoglycaemic 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

The 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

This 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

Orbital 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

New 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

6‐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

In 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

In 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

Quantum 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

Old 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

Reactions 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

Oscillator 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

We 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
The early glycation products of the Maillard reaction: mass spectrometric characterization of novel imidazolidinones derived from an opioid pentapeptide and glucose
Authors: Roščić Maja , Versluis Cornelis , Kleinnijenhuis Anne J. , Horvat Štefica , Heck Albert J. R.
Published: August 2002

Glucose‐substituted imidazolidinones related to the endogenous opioid peptide leucine‐enkephalin have been investigated using fast atom bombardment tandem mass spectrometry (FAB‐MS/MS) and electrospray ionization tandem mass spectrometry (ESI‐MS/MS). In addition to Amadori compounds, the studied imidazolidinones represent a novel type of the early glycation products formed in the Maillard reaction. To obtain insight into the fragmentation behavior of these carbohydrate‐peptide adducts, we also studied synthetic precursors of the glucose‐substituted imidazolidinones as well as the corresponding isopropylidene derivatives. The collision‐induced dissociation (CID) spectra of [M + H]+ ions of all these imidazolidinones have been compared. Detailed analysis showed that fragmentation of each compound generates two ions at m/z 566 and m/z 598 which are characteristic and undoubtedly confirm the imidazolidinone‐type structure. These two significant ions were identified as the M + 10 and M + 42 modifications of the N‐terminus of the parent opioid pentapeptide effected by the carbohydrate moiety. Furthermore, the ion at m/z 178 is identified as the M + 42 modification of the immonium ion of the N‐terminal amino acid (tyrosine) also effected by the carbohydrate moiety. They can be used as diagnostic ions for imidazolidinone‐type compounds in studying the Maillard reaction. Thus, we have demonstrated the utility of FAB‐MS/MS and ESI‐MS/MS in the structural determination and identification of such novel peptide‐carbohydrate adducts, useful in understanding the details of the mechanism of non‐enzymatic glycation in vivo. Copyright © 2001 John Wiley & Sons, Ltd.
Fragmentation mechanism of novel compounds: 3,3‐dichloro‐1‐[2‐(2,2‐dichloro‐1‐oxoethylthio)phenyl]‐4‐(4‐methoxyphenyl)‐4‐(1‐phenylvinyl)‐2‐azetidinone and its derivatives
Authors: He Meiyu , Yuan Jinfang , He Zhenpei Yu Xiaoran , Wang Hongzhong , Zhou Xin , Jin Sheng
Published: August 2002

Electron impact mass spectra of five new compounds are reported. Under electron impact conditions all five compounds yielded abundant fragment ions and lower abundances of molecular ions. Apart from the expected i‐and α‐cleavages, three additional unusual fragmentation processes were observed. The proposed fragmentation mechanisms were supported by D‐labeling experiments, accurate mass measurements, and mass‐analyzed ion kinetic energy spectrometry. Copyright © 2001 John Wiley & Sons, Ltd.
5‐Ethyl‐2‐mercaptothiazole as matrix for matrix‐assisted laser desorption/ionization of a broad spectrum of analytes in positive and negative ion mode
Authors: Raju N. Prasada , Mirza Shama P. , Vairamani M. , Ramulu A. Raghu , Pardhasaradhi M.
Published: August 2002

A preliminary investigation of the use of 5‐ethyl‐2‐mercaptothiazole as matrix in matrix‐assisted laser desorption/ionization (MALDI) of a broad spectrum of analytes is reported. The analytes studied are substance P, insulin, β‐cyclodextrin, triacylglycerols of coconut oil and polypropylene glycol 2000 (PPG 2000). In the positive ion mass spectra of the matrix/analyte combinations, the formation of [M + H]+ and [M + cation]+ species were observed and compared with those obtained by using well‐established matrices such as α‐cyano‐4‐hydroxycinnamic acid, genticic acid, sinapinic acid and dithranol. In addition, the usefulness of this new matrix for MALDI in negative ion mode is also described using substance P and β‐cyclodextrin as examples. Copyright © 2001 John Wiley & Sons, Ltd.
Direct detection of polyaromatic hydrocarbons, estrogenic compounds and pesticides in water using desorption chemical ionisation membrane inlet mass spectrometry
Authors: Aggerholm Tenna , Lauritsen Frants R.
Published: August 2002

This paper describes the use of desorption chemical ionisation membrane inlet mass spectrometry (DCI‐MIMS) for the detection of a broad range of common contaminants in water. In addition, we discuss the advantages/disadvantages of two different types of chemical ionisation reagent gases, i‐butene (a Broensted acid reagent) and argon (a charge exchange reagent). We found that polyaromatic hydrocarbons was detectable at ppt levels, the estrogenic compounds diethyl phthalate and octylphenol at high ppt levels, steroid hormones at ppb levels, hydrophobic pesticides at low ppb levels, whereas hydrophilic pesticides and bisphenol A were not detectable at all. With the exception of the polyaromatic hydrocarbons and pentachlorophenol, none of the reported compounds have to our knowledge been detected previously by other MIMS systems. In most cases the Broensted acid reagent gave characteristic ions at high mass/charge ratio, whereas the charge exchange reagent gave less characteristic ions at low m/z ratio. However, the sensitivity was generally not as good with the Broensted acid reagent as with the charge exchange reagent, since the Broensted acid reagent, i‐butene, gave a large chemical background. Copyright © 2001 John Wiley & Sons, Ltd.
Electrospray ionization mass spectrometric investigation of ammonium ion complexes with anomeric 2,3‐O‐isopropylidene‐1α‐ and ‐1β‐D‐ribofuranosyl azides: anomeric and kinetic isotope effects in ammonium affinities
Authors: Kralj Bogdan , Kocjan Darko , Kobe Joz̆e
Published: August 2002

[Methanol + ammonium acetate] solutions of anomeric 2,3‐O‐isopropylidene‐1α‐ and 1β‐ribofuranosyl azides were investigated by electrospray ionization mass spectrometry (ESI‐MS). The compounds included d6‐labeled and/or unlabeled isopropylidene groups that enable the identification of peaks characteristic of the ammonium‐attached monomeric (MNH4+), ammonium‐bound homodimeric ([M]2NH4+) and heterodimeric ([MNH4M1]+) complex ions in ESI mass spectra of solutions of a pair of compounds. The intensities of the product ion peaks obtained by the collisionally activated ammonium‐bound dimeric ions are related to the secondary isotope effect kα/kαd6 = 0.88 and kβ/kβd6 = 1.25 or to isotope plus anomeric effects kα/kβd6 = 1.43 and kβ/kαd6 = 0.59 in the ammonium affinities of these compounds. The calculations of solely anomeric effects in the ammonium affinities of α and β anomeric compounds obtained from the data presented previously give two series of values: kα/kβ = (kα/kαd6)(kαd6/kβ) = 1.49 and kαd6/kβd6 = (kαd6/kβ)(kβ/kβd6) = 2.12 or kα/kβ = (kα/kβd6)(kβd6/kβ) = 1.14 and kαd6/kβd6 = (kαd6/kα)(kα/kβd6) = 1.63. The disparities of these results indicate the different structures of hydrogen bonding in ammonium‐bound dimeric complexes which decompose to monomeric ions with different rate constants. Comparison of experimental results obtained by the qualitative approach of the kinetic method and ammonium affinities of these compounds calculated by the semi‐empirical molecular orbital method (AM1) show that the [MNH4M1]+ dimeric complex ions dissociate to the most stable MNH4+ and M1NH4+ monomeric ions. The obtained relative order of ammonium affinities of these compounds is: αd6 > α > β > βd6. Copyright © 2001 John Wiley & Sons, Ltd.
Negative ion clusters in self‐condensation of GeH4
Authors: Antoniotti Paola , Operti Lorenza , Rabezzana Roberto , Vaglio Gian Angelo , Guarini Alessandro
Published: August 2002

Formation of negative ion clusters from GeH4 has been studied as a function of germane pressure, in the 25–450 mTorr range, by chemical ionisation mass spectrometry. At the lowest pressures, only the GeHn− (n = 0–3) ion family is formed, whilst at increasing pressures GemHn− (m = 1–9) ion clusters of increasing size are observed in the mass spectra. A variable contribution of the ions with different hydrogen content is observed as a function of the pressure of germane in all the GemHn− (m = 1–9) clusters. Increasing pressures induce a general increase of ion species with a low content of hydrogen atoms. In fact, at 450 mTorr, 38% of the ion current is due to the bare Gem− (m = 2–5) clusters and 83% to the sum of abundances of the GemHn− ions without hydrogen (n = 0) and with a number of hydrogen atoms not higher than the number of germanium atoms (n = 0–m). This trend suggests that a contribution of negative clusters to the deposition of the amorphous solid a‐Ge:H from gaseous systems containing GeH4, activated by radiolytic methods, can enhance the formation of solids with a low hydrogen content, which show better photoelectrical properties. Copyright © 2001 John Wiley & Sons, Ltd.
Capillary electrophoresis/electrospray ion trap mass spectrometry for the analysis of negatively charged derivatized and underivatized glycans
Authors: Gennaro Lynn A. , Delaney Jeannine , Vouros Paul , Harvey David J. , Domon Bruno
Published: August 2002

The increasing interest in the development of glycoproteins for therapeutic purposes has created a greater demand for methods to characterize the sugar moieties bound to them. Traditionally, released carbohydrates are derivatized using such methods as permethylation or fluorescent tagging prior to analysis by high performance liquid chromatography (HPLC), capillary electrophoresis (CE), or direct infusion mass spectrometry. However, little research has been performed using CE with on‐line mass spectrometry (MS) detection. The CE separation of neutral oligosaccharides requires the covalent attachment of a charged species for electrophoretic migration. Among charged labels which have shown promise in assisting CE and HPLC separation is the fluorophore 8‐aminonaphthalene‐1,3,6‐trisulfonic acid (ANTS). This report describes the qualitative profiling of charged ANTS‐derivatized and underivatized complex glycans by CE with on‐line electrospray ion trap mass spectrometry. Several neutral standard glycans including a maltooligosaccharide ladder were derivatized with ANTS and subjected to CE/UV and CE/MS using low pH buffers consisting of citric and 6‐aminocaproic acid salts. The ANTS‐derivatized species were detected as negative ions, and multiple stage MS analysis provided valuable structural information. Fragment ions were easily identified, showing promise for the identification of unknowns. N‐Linked glycans released from bovine fetuin were used to demonstrate the applicability of ANTS derivatization followed by CE/MS for the analysis of negatively charged glycans. Analyses were performed on both underivatized and ANTS‐derivatized species, and sialylated glycans were separated and detected in both forms. The ability of the ion trap mass spectrometer to perform multiple stage analysis was exploited, with MS5 information obtained on selected glycans. This technique presents a complementary method to existing methodologies for the profiling of glycan mixtures. Copyright © 2002 John Wiley & Sons, Ltd.
Determination of drug binding sites to proteins by electrospray ionisation mass spectrometry: the interaction of cisplatin with transferrin
Authors: Allardyce Claire S. , Dyson Paul J. , Coffey Jonathan , Johnson Neil
Published: August 2002

Cisplatin, cis‐[PtCl2(NH3)2], is known to bind to human serum transferrin, but the binding site remains a matter of some debate. Electrospray ionisation mass spectrometry has been used to characterise the interaction of cisplatin with transferrin. The studies indicate that cisplatin initially docks with, and subsequently bonds covalently to, the hydroxyl functional group of threonine 457, with the loss of HCl affording a transferrin‐O‐PtCl(NH3)2 adduct. Copyright © 2002 John Wiley & Sons, Ltd.
Electron capture dissociation of polypeptides using a 3 Tesla Fourier transform ion cyclotron resonance mass spectrometer
Authors: Polfer Nicolas C. , Haselmann Kim F. , Zubarev Roman A. , Langridge‐Smith Pat R. R.
Published: August 2002

Electron capture dissociation (ECD) of polypeptides has been demonstrated using a commercially available 3 Tesla Fourier transform ion cyclotron resonance (FTICR) instrument. A conventional rhenium filament, designed for high‐energy electron impact ionisation, was used to effect ECD of substance P, bee venom melittin and bovine insulin, oxidised B chain. A retarding field analysis of the effective electron kinetic energy distribution entering the ICR cell suggests that one of the most important parameters governing ECD for this particular instrument is the need to employ low trapping plate voltages. This is shown to maximise the abundance of low‐energy electrons. The demonstration of ECD at this relatively low magnetic field strength could offer the prospect of more routine ECD analysis for the wider research community, given the reduced cost of such magnets and (at least theoretically) the greater ease of electron/ion cloud overlap at lower field. Copyright © 2002 John Wiley & Sons, Ltd.
Automatic Detection of Lung Cancers in Chest CT Images by the Variable N‐Quoit Filter
Authors: Miwa Tomoko , Kako Jun‐ichi , Yamamoto Shinji , Matsumoto Mitsuomi , Tateno Yukio , Iinuma Takeshi , Matsumoto Toru
Published: August 2002

The authors have developed the quoit filter, which is a kind of mathematical morphological filter, for automatic extraction of candidate pathological areas of lung cancer. The method has problems, however, in processing speed or extraction accuracy. To overcome these problems, this paper proposes variable quoit filtering, in which the filter size is adjusted flexibly according to the pathological shadow, and distance transformation with gray‐level weight is applied as preprocessing before the main filtering procedure. First, the performance of the method is analyzed using a model, and the effectiveness of the proposed method is shown. Then, trial applications to images of 82 actual cases (including 21 cancer areas) show that all of the cancer areas were correctly extracted. Compared to the conventional algorithm, the processing time is reduced to less than 1/20. © 2001 Scripta Technica, Syst Comp Jpn, 33(1): 53–63, 2002
Characterization of the Ziegler‐Natta olefin polymerization system: surface science studies on model catalysts
Authors: Kim Seong Han , Somorjai Gabor A.
Published: August 2002

Modern surface science techniques have been applied to the heterogeneous Ziegler‐Natta catalysis system, polymerizing α‐olefins to produce polyolefins, and revealed the correlation between the catalyst surface structure and polymer properties. Two types of thin films—TiClx/MgCl2 and TiCly/Au—were fabricated on an inert gold substrate, using chemical vapor deposition methods, to mimic the high‐yield catalysts of MgCl2‐supported TiCl4 and TiCl3‐based catalysts, respectively. Once activated with triethylaluminum (AlEt3) vapor, both catalysts were active for polymerization of ethylene and propylene in the absence of excess AlEt3. The model catalyst films were as active as the high‐surface‐area industrial catalysts. Both catalysts were terminated with chlorine at the surface but had different surface structures. The TiClx/MgCl2 film had a distribution of two structures: the dominant sites had the (001) basal plane of these halide crystallites and the minority sites had a non‐basal plane structure. The surface of the TiCly/Au film assumed only the non‐basal plane structure. These structural differences resulted in different tacticity of the polypropylene produced with these catalysts. The TiClx/MgCl2 catalyst produced both atactic and isotactic polypropylene, whereas the TiCly catalyst without the MgCl2 support produced exclusively isotactic polypropylene. The titanium oxidation states did not appear to be an important factor in determining the tacticity of the polypropylene. Copyright © 2001 John Wiley & Sons, Ltd.