bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of γ‐irradiation on collagen molecules, isolated α‐chains, and crosslinked native fibers
Authors: Cheung David T. , Perelman Natalya , Tong Deborah , Nimni Marcel E. 
Published: December 2004

AbstractThis study shows how collagen molecules are readily damaged by γ‐radiation at dosages commonly used for sterilizing biomedical products. At 1 Mrad, while the reported effectiveness of the radiation at such a low dosage to completely sterilize a material is questionable, less damage was caused to the collagen peptide backbone. Above such dosage, however, significant damage was clearly demonstrated with collagen alone and collagen in a chemically crosslinked tissue matrix. The enzyme digestion study showed that the material exposed to a very high dosage of radiation resisted degradation by pronase. However, molecular weight analysis showed a significant number of peptide bonds being cleaved by the radiation which could cause considerable changes in the long‐term characteristics of the material. Therefore, tissues exposed to high dosages of γ‐radiation should be tested for long term functional changees. We want to caution against the usag of the enzyme degradation assay as a universal test for all bioprosthetic derived from biological tissues.
Mechanism and strength of bonding between two bioactive ceramics in vivo
Authors: Fujita Yoshitsugu , Yamamuro Takao , Nakamura Takashi , Kitsugi Toshiaki , Kotani Seiya , Ohtsuki Chikara , Kokubo Tadashi 
Published: December 2004

AbstractA study was conducted to examine the mechanism and strength of bonding between two bioactive ceramic plates in vivo. Rectangular plates (15 mm × 10 mm × 2 mm) of Bioglass®, apatitewollastonite‐containing glass ceramic (designated A‐W · GC), and two types of hydroxyapatite sintered a t 900° and 1200° (designated HA900 and HA1200) were prepared. Two plates of the same materials tied together with silk thread were implanted subcutaneously into rats. The force required to detach the mutually bonded bioactive ceramic plates was measured 4, 8,12, and 24 weeks after implantation. The interface between the two bonded plates was examined by SEMEPMA and thin‐film x‐ray diffraction analysis. At 24 weeks after implantation, 1991 the mutual bonding of Bioglassm and A‐W · GC was stronger than that of the two HA types. SEM‐EPMA and thin‐film x‐ray diffraction analysis of the bonded area of Bioglassm and A‐W · GC plates showed bonding zones with a patiteinthe margins, and a bonding zone with calcite in the center. The greater strength of bonding of Bioglassm and A‐W · GC plates compared with the two types of HA plate 24 weeks after implantation is explained by the wider bonding zone provided by the calcite layer formed in the center of the plates, which is considered to have been perfused with P04‐poor body fluids resulting from PO4 consumption for apatite formation in the margins. © 1992 John Wiley & Sons, Inc.
Polypropylene small‐diameter vascular grafts
Authors: Greisler Howard P. , Tattersall Charles W. , Henderson Scott C. , Cabusao Emma A. , Garfield Jacqueline D. , Kim Dae Un 
Published: December 2004

AbstractPolypropylene's physical properties (e.g., high tensile strength) and relatively inert behavior suggest that fabrication into an arterial substitute may result in an efficacious prosthesis. Grafts were woven from polypropylene yarn into conduits 4 mm I.D. × 50 mm in length. Control grafts were Dacron and ePTFE. Baseline platelet aggregometry on all dogs was performed with 10−5M ADP. Aspirin and dipyridamole were given for three days preoperatively and maintained for 2 weeks after surgery. Fifty‐four grafts were placed into the aortoiliac position, two different graft materials per dog. The grafts were explanted at intervals of 2 weeks through 16 months; photographed for thrombusfree surface area determinations; and preserved for light, scanning, and transmission electron microscopy. Late (4–16 month) patency was 81% (13/16) for polypropylene, 69% (9/13) for Dacron, and 20% (1/5) for ePTFE. These data include one year patencies of 11/12 (92%) for polypropylene and 7/10 (70%) for Dacron. Late patency for polypropylene grafts was better than for PTFE (p < 0.05). Platelet aggregation status did not predict graft patency. Light microscopy of 2‐week polypropylene explants showed inner capsules composed of myofibroblasts and macrophages, with patchy areas of endothelial cells lining the lumen. By 1 month, a confluent endothelialized surface was seen in all polypropylene explants. Progressive thickening of inner capsules with myofibroblasts and collagen continued through 4 months, reaching a mean thickness of 142 ± 50 μm compared to 150 ± 30 μm for Dacron. These findings suggest potential clinical efficacy for polypropylene as an arterial substitute. © 1992 John Wiley & Sons, Inc.
Porous polyurethane vascular prostheses with variable compliances
Authors: Liu Shu Qin , Kodama Makoto 
Published: December 2004

AbstractA new technique for the preparation of porous vascular prostheses was investigated. Polyurethane solution (5 to 15 wt%) was injected into a mold. After freezing at low temperature (0°C–196°C), solvents were dissolved out with water at 0°C to form porous tubes. The average pore size (several microns to 70 μm), pore occupation (10% to 51%), and compliance (3% to 35%) were easily changed by changing polyurethane concentration, freezing temperature, and freezing methods. Compliances could be decreased gradually by heat treatment. This technique can give a proper pore size (30‐60 μm) for tissue ingrowth, and a suitable compliance for matching with arteries and veins. This method might give a desired compliant graft for artificial implantation with the presently valid medical polymers. © 1992 John Wiley & Sons, Inc.
Biocompatibility and tissue regenerating capacity of crosslinked dermal sheep collagen
Authors: van Wachem P. B. , van Luyn M. J. A. , Damink L. H. H. Olde , Dijkstra P. J. , Feijen J. , Nieuwenhuis P. 
Published: December 2004

AbstractThe biocompatibility and tissue regenerating capacity of four crosslinked dermal sheep collagens (DSC) was studied. In vitro, the four DSC versions were found to be noncytotoxic or very low in cytoxicity. After subcutaneous implantation in rats, hexamethylenediisocyanatecrcrosslinked DSC (HDSC) seldom induced an increased infiltration of neutrophils or macrophages, as compared with normal wound healing; whereas new formation of collagen was observed. DSC crosslinked with glutaraldehyde (GDSC) followed by reaction with NaBH4 shortly after implantation showed an increased infiltration of neutrophils with a deviant morphology. Furthermore, a high incidence of calcification was observed, which may explain the minor ingrowth of giant cells and fibroblasts, and the poor formation of new rat collagen. Acyl azide‐crosslinked DSC (AaDSC) first induced an increased infiltration of macrophages, and then of giant cells, both with high lipid formation. AaDSC degraded at least twice as slowly as HDSC and GDSC, finally leaving a matrix of newly formed rat collagen. Samples crosslinked with 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride and N‐hydroxysuccinimide (ENDSC) induced the same mild cellular reaction as HDSC; whereas, similar to AaDSC, the degradation rate was slow and an optimal rat collagen matrix was formed. Of the crosslinked DSC samples, ENDSC seems most promising for tissue regeneration. © 1994 John Wiley & Sons, Inc.
Mathematical modeling of water permeability of surgical fabrics for vascular use
Authors: Chu C. C. , Rawlinson Jeremy 
Published: December 2004

AbstractThe purpose of this study was to derive new mathematic formulae that could be used reliably to predict water permeability of surgical fabrics before they are made and tested for water permeability. Such a theoretical prediction of water permeability, Qprd, of surgical fabrics is needed for not only timely characterization but also for assisting in more efficient future design and development of better surgical fabrics. Two mathematic formulae, Qw and Qk, were derived from the Buckingham Pi Theorem, in which relevant fiber and fabric parameters were placed into dimensionless π groups and computed for 25 commercial and experimental vascular fabrics. Linear regression analysis of the relationship between these π groups with water permeability on the woven and knitted grafts yielded coefficients for the corresponding π groups that were required for constructing appropriate mathematic formulae to predict water permeability of vascular fabrics. When proper sources of the experimentally determined water permeability, Qexp, were chosen for comparison, we found that 86% of woven fabrics (6 of 7) and 77% of knitted fabrics (14 of 18) had their Qprd within 10% of their Qexp. This high percentage of close matching (within 10%) between Qprd and Qexp should be considered satisfactory because the experimental error for obtaining Qexp is generally higher than 10%. The difference between Qprd and Qexp ranged from as small as 0.27% to as high as 74.2%, depending on the type of fabrics and source of Qexp. It appeared that the formulae worked well with fabrics of simpler structure such as those experimental woven vascular fabrics that showed 100% close match between Qprd and Qexp. Nonlinear relationship among the parameters and additional new parameters are required to fine‐tune for existing mathematic formulae to improve their accuracy of predicting water permeability for more complex fabric structures such as knitted fabrics. A computer program had been written that uses these theoretical formulae for predicting water permeability of vascular fabrics. Users could simply input five major fabric and fiber parameters of a surgical fabric and the computer would calculate its water permeability instantaneously. © 1994 John Wiley & Sons, Inc.
AM‐1 molecular orbital calculations of silica–alanine–nitrogen interaction
Authors: West Jon K. , Hench Larry L. 
Published: December 2004

AbstractChemical binding of proteins with bioactive surfaces is modeled using a semi‐empirical molecular orbital theory (AM‐1). The model calculates the optimized molecular structures of an amino acid (L‐alanine) interacting with a cyclotetrasiloxane silica cluster (a four‐membered hydrated silica ring). The calculated heats of formation for various orientations of alanine show +5 kcal/mol difference for binding via the −NH2 group following a condensation reaction with a pentacoordinate Si intermediate. Hydrogen bonding of the alanine via the COOH group occurs with +13 to +15 kcal/mole differences in heats of formation and imposes a highly specific geometric orientation on the amino acid. Association of a diatomic N2 molecule with the silica cluster before interaction with alanine inhibits formation of an intermolecular bond, as is observed experimentally in studies of silicaalanine epitaxy. © 1994 John Wiley & Sons, Inc.
Molecular potential, cation binding, and hydration properties of the carboxylate anion. Ab initio studies with an extended polarized basis set
Authors: Berthod H. , Pullman A. 
Published: December 2004

AbstractThe carboxylat anion, involved in the structure of numerous compounds of biological interest, participates in a number of intermolecular interactions involving water, cations, and other cellular constituents. A set of ab initio SCF computations have been carried out with an extended polarized basis set on HCOO–, its molecular electrostatic potential, and its interaction with Li+, Na+, K+, and H2O. The results are compared with those of a minimal good quality basis set. An evaluation of the basis set superposition error is made in the two basis as well as that of the contribution of the dispersion energy to the hydration. The analogies and differences in the nucleophilic character of the formate and the phosphate groups are discussed.
Ab initioMO calculations for the oxides, oxyacids, and oxyanions of S(IV) and S(VI)
Authors: Baird N. Colin , Taylor Kathleen F. 
Published: December 2004

AbstractAb initio molecular orbital (MO) calculations for two series of sulfur–oxygen compounds are reported: the S(IV) system of SO2, H2SO3, HSO, and SO, and the S(VI) system of SO3, H2SO4, HSO, and SO. Geometries about the sulfur atoms were optimized using the STO‐3G* basis set; energies at these geometries were computed by the STO−3G and 44‐31G basis sets both with and without five Gaussian d orbitals on S. The sulfur–oxygen bond lengths and the angles about the central atoms agree fairly well with experiment. The stabilization energy associated with the addition of the d orbitals was found to be a constant amount per bond (ca. 54 and 28 kcal mole−1 in the minimal and extended bases, respectively) in hypervalent compounds. The isomer HSO was predicted to be more stable than SO2(OH)−, but the reverse was true for HSO2(OH) compared to SO(OH)2. The deprotonation energies for the acids and the hydration energies for the oxides also were computed and discussed with reference to experimental data.
A computerized structure–activity correlation program for relating bacterial mutagenesis activity to chemical structure
Authors: Tinker John F. 
Published: December 2004

AbstractThe program employs a substructure recognition process based on the procedure of Hodes et al. Structural information is accepted from connection tables (Chemical Abstracts Registry II or III) or MCC‐TSS ciphers. Typically in this program the basic substructure unit (ganglion) is an atom triplet. Data for correlation are provided by over 1000 results from mutagenesis tests run in the Ames Salmonella typhimurium test, obtained from the literature. Activity may be calibrated in two to eight levels. Statistical weights for ganglia are calculated from the program of Hodes et al. The results of the program reveal the dependence of biological data on chemical structure, the self‐consistency of the data, and the level of activity to be expected of an unknown structure, with an estimate of confidence. The value of the program was shown with 34 unknowns simultaneously tested for activity in the Ames test and submitted to structure–activity analysis. Of these 74% were correctly predicted for the level of activity, and 88% to within one level of activity. It is expected that experience with the program in a trial application setting will enable us to restrict the number of activity calibrations to two. This will allow a simple selection of an inactive or active prediction to be made.
Ab initio study of 4‐monosubstituted pyrimidines in ground and excited n → π* states
Authors: Del Bene Janet E. 
Published: December 2004

AbstractAb initio SCF and SCF‐CI calculations have been performed to investigate substituent effects on ground‐ and excited‐state properties of 4‐R‐pyrimidines, and to compare these with substituent effects in 2‐ and 4‐R‐pyridines, with R including the π donating and σ withdrawing groups CH3, NH2, OH, F, and C2H3 and the σ and π electron‐withdrawing groups CHO and CN. Substitution leads to significant changes in the internal angles of the pyrimidine ring, which are independent of the nature of the substituent. The geometry of the pyrimidine ring is more sensitive to substitution in the 4 position than the pyridine ring geometry is to substitution in either the 2 or the 4 position. The isodesmic reaction energies for substituent transfer from the 4 position of pyrimidine to the 2 or 4 position of pyridine indicate that all R groups except CN have a relative stabilizing effect in pyrimidine. The presence of a π donating group leads to an increase in the n→π* transition energy of 4‐R‐pyrimidines, while the π withdrawing group CN leads to a decrease in the transition energy relative to pyrimidine. Orbital energy differences and virtual excitation energies tend to correlate with n→π* transition energies of 4‐R‐pyrimidines with saturated R groups, but such correlations are masked by π conjugation, n orbital interaction, and configurational mixing when the unsaturated groups C2H3, CHO, and CN are present. The electronic effects of a π donating group are stronger when the group is bonded to pyrimidine than to pyridine, but those of a π withdrawing group are weaker when the group is bonded to pyrimidine.
A systematic preparation of new contracted Gaussian‐ type orbital sets. VII. MINI‐3, MINI‐4, MIDI‐3, and MIDI‐4 sets for transition metal atoms
Authors: Tatewaki Hiroshi , Sakai Yoshiko , Huzinaga Sigeru 
Published: December 2004

AbstractTwo minimal contracted Gaussian‐type orbital (CGTO) sets are developed for the transition metal atoms. The expansion terms for the first set, MINI‐3, are 4, 3, 3, and 3 for s‐type CGTOs and others are all three. The abbreviation would be (4333/33/3) where the slash divides symmetry. The expansion terms for the other set, MINI‐4, is (4333/43/4). The split‐type basis sets, MIDI‐3 and MIDI‐4, are derived directly from MINI‐3 and MINI‐4, MINI‐3 and MIDI‐3 provide the outer‐shell orbital energies which are far better than those by single‐zeta (SZ) STOs. MINI‐4 and MIDI‐4 provide the outer‐shell orbital energies which are almost as good as those by double‐zeta (DZ) STOs. The total energies given by the present sets are better than those of SZ except for MINI‐3 for Sc and Ti: the energies by MINI‐4 and MIDI‐4 are only 0.8–1.7 a.u. higher than DZ. The basis sets were tested on the Cu2 molecule, where a large basis set was also used.
Force field and self‐consistent field calculations on a trans coplanar disulfide: Bis(2‐pyrimidyl)disulfide
Authors: Boyd Donald B. , Lipkowitz Kenny B. 
Published: December 2004

AbstractTwo diaryl disulfides, bis(2‐pyrimidyl)disulfide and diphenyldisulfide, have been characterized by molecular mechanics and molecular orbital calculations. When complexed with Cu(I), the pyrimidyl disulfide is known to have a unique 180° CSSC dihedral angle and to be coplanar. Our analysis of the conformational energies of the rotamers suggests that copper–ring interactions are primarily responsible for altering the molecular and electronic structure of the disulfide such that the trans barrier to rotation about the SS bond is effectively overcome. In contrast, the phenyl and uncomplexed pyrimidyl disulfides prefer the usual CSSC torsional angle near 85° and have trans barriers greater than 7 kcal/mol. The barrier to rotation about SC bonds (2–3 kcal/mol) is low and consistent with ab initio calculations and experiments on other molecules. The force field calculations were done using MMP1. A serious problem was encountered in the use of the MMP1 computer program on molecules with N‐type atoms that contribute only one electron to the π‐electron system. A solution is to modify the variable electronegativity self‐consistent field (VESCF) part of the MMP1 calculation to use another set of parameters in the program that pertain to a type of nitrogen with one π electron. CNDO/2 was used for most of the MO calculations, although INDO and extended Hückel were also used.
Semiempirical spin–orbit coupling calculations. I. Theory and method. Benzophenone as a test case
Authors: Pasternak R. , Wagnière G. 
Published: December 2004

AbstractThe molecular spin–orbit coupling operator is brought into a simplified form through a convenient choice of origin for the orbital angular momentum operator. The eigenvalue problem of the Hamiltonian that includes the spin–orbit (SOC) operator as a perturbation is solved by means of a linear variational procedure in the basis of the spin‐pure molecular eigenstates. Test calculations on benzophenone are presented and the results are compared to experiment. We discuss the minimal size of the spin‐pure variational basis needed to achieve stable results as well as the amount of single‐excitation configurational mixing needed to describe the spin‐pure molecular eigenstates.
An ab initio study of the guanidinium fragments in tetrodotoxin and saxitoxin
Authors: Sapse A. M. , Santoro A. 
Published: December 2004

AbstractSCF Hartree–Fock calculations are used to predict properties of the guanidinium fragment present in tetrodotoxin and saxitoxin, toxins known to block the sodium channels of the nerve cell membrane. The results, in terms of net atomic charges and geometries, are compared to similar calculation results obtained for the Na+–H2O complex.
On efficient integration techniques for oscillatory integrals in periodic system calculations
Authors: Schneider W. J. , Ladik J. J. 
Published: December 2004

AbstractQuantum chemical calculations of polymers and solids, especially on an ab initio level, represent a large computational task and therefore necessitate efficient computing methods. This is particularly true for the oscillatory integrals appearing in such calculations. For these integrals efficient integration methods based both on the Chebyshev series and the spline representation of the nonoscillatory part of the integrand are considered; they are found far superior compared with more standard integration rules. In two‐ and three‐dimensional systems, directions with maximum oscillatory behavior can be selected along which these new efficient integration techniques can be used advantageously. The ideas are illustrated by Hückel crystal orbital (HCO) bond orders for the polyacetylene chain and the graphite layer. In the latter example, also, a method for the integration of oscillatory integrands with a singularity is given.
Space modification: An alternative approach to chemistry problems involving geometry
Authors: Silver G. L. 
Published: December 2004

AbstractThe sequential simplex optimization algorithm has been translated into non‐Euclidean space. A study of the algorithm in this space suggests that the path of convergence of the simplex depends on the properties of the space so that different convergence paths can be obtained even with the same starting points. The path of convergence approaches the path observed in Euclidean space as the metric constant of the hyperbolic space increases.
An ab initioCI calculation of the triplet–triplet absorption spectrum of naphthalene
Authors: Ha Tae‐Kyu , Wild Urs P. 
Published: December 2004

AbstractThe triplet–triplet absorption spectrum of naphthalene (3B1g ← 3B2u; 3Ag ← 3B2u) was calculated using an ab initio method with a STO‐3G basis set and moderately large configuration interaction. Eight bands were found in the region 18,000–45,000 cm−1 and compared with those of the experimental spectrum. The strongest band observed at about 44,000 cm−1 was assigned to a 3Ag ← 3B2u tansition. The excited triplet and singlet ground‐state electronic charge distributions are compared.
Theory of lone pairs. IV. Molecular ion hole states of ten‐electron hydrides. Molecular ionization potentials and proton affinities by direct SCF calculations
Authors: Kozmutza C. , Kapuy E. , Robb M. A. , Daudel R. , Csizmadia I. G. 
Published: December 2004

AbstractClosed‐shell SCF calculations on the ground states and direct SCF calculations on the ionized doublet states were carried out for a series of ten‐electron hydrides. The correlation of ionization potentials with the degree of protonation and the nuclear charge has been studied for hole states derived from excitation out of both the core and valence molecular orbitals. Calculated proton affinities of the ground states and hole states derived from a given symmetry orbital show a similar trend to that of the ionization potentials.
Iterative calculation of eigenvalues and eigenvectors of large, real matrix systems with overlap
Authors: Gallup G. A. 
Published: December 2004

AbstractAn improved method for obtaining a few eigenvalues and eigenvectors of the symmetric matrix system is presented:

where S ≠ I. The method allows us to handle larger systems more easily than any other known to the author. It requires the inversion of S, and N3 step, but thereafter each eigenvector and eigenvalue is obtained in a length of time proportional to N2. The relation of this method to the MOR and MMOR methods developed recently for handling the case, S = I, is discussed.