bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mutagenic potential of root canal sealers: Evaluation through Ames testing
Authors: Stea Susanna , Savarino L. , Ciapetti G. , Cenni E. , Stea Stefano , Trotta F. , Morozzi G. , Pizzoferrato A. 
Published: December 2004

AbstractThe mutagenic potential of 12 commercially available dental cements and of two ‘pure substances’ (zinc oxide and eugenol) used in root canal filling were examined. The cements were prepared according to the manufacturers' indications and set for defined times. Ames tests were performed in their extracts by using Salmonella typhimurium strains TA 98 and TA 100. The results showed that most cements present strong bactericidal activity that disappears or decreases remarkably in time. One of the tested cements showed mutagenicity with both Salmonella strains. Two cements yielded doubtful results. The remaining cements and the two ‘pure substances’ showed no mutagenic potential. The authors conclude that it is convenient to examine endodontic cements with the Ames test and to eliminate those that present mutagenicity in time. © 1994 John Wiley & Sons, Inc.
Mechanisms of biomaterial‐induced superoxide release by neutrophils
Authors: Kaplan S. S. , Basford R. E. , Jeong M. H. , Simmons R. L. 
Published: December 2004

AbstractBiomaterial‐centered infection is an important cause of the failure of prosthetic implants and organs. Because neutrophils mediate host defense against infection, the effect of biomaterials on neutrophil superoxide release and the mechanism of that effect were investigated using three materials commonly employed in surgical practice. The graft materials were expanded polytetrafluorethylene (PTFE), polyurethane and woven dacron. Polystyrene, a commonly used laboratory support vessel, was also studied. Both polystyrene and polyurethane were activating, but serum inhibitable, whereas PTFE was nonactivating, and woven dacron was not activating unless serum was present. The signaling mechanisms used by these materials demonstrated time and material dependency. Pertussis toxin inhibition of G proteindependent activation had little or no effect on biomaterial induced activation, whereas FMLP‐induced activation of the same biomaterial‐associated cells was inhibited. Protein kinase C inhibition with staurosporine greatly inhibited polystyrene‐induced activation, but had only a partial effect with polyurethane and even less effect with the activation associated with serum‐treated woven dacron. These studies demonstrated that biomaterial contact‐induced neutrophil activation differed from that described for cells in suspension, and showed that activation mechanisms on one material cannot be extrapolated to mechanisms on other materials. © 1994 John Wiley & Sons, Inc.
Activation of human neutrophils by Arg‐Gly‐Asp‐Ser immobilized on microspheres
Authors: Kasuya Yuji , Fujimoto Keiji , Miyamoto Masaki , Kawaguchi Haruma 
Published: December 2004

AbstractThe adhesive interaction of cells with extracellular matrix components is essential for a variety of cellular functions, and is frequently mediated by a tetra peptide, Arg‐Gly‐Asp‐Ser (RGDS), located within fibronectin and other proteins. In this study, the RGDS‐mediated activation of polymorphonuclear leukocytes accompanied by phagocytosis was investigated using monodisperse polymeric microspheres carrying RGDS. The parent and Arg‐Gly‐Glu‐Ser (RGES)‐carrying microspheres, which have no adhesion activity, were employed as controls. The ingestion of microspheres into PMN was not enhanced by immobilizing RGDS. However, PMNs exhibited unique oxygen consumption and enhanced liberation of reactive oxygen when RGDS‐carrying microspheres were phagocytosed. These PMN responses disappeared with the addition of soluble RGDS. Furthermore, cytochalasin D, which inhibits actin polymerization, showed a marked inhibitory effect on oxygen consumption in the RGDS‐carrying microsphere system, as compared with those in other systems. These findings show that RGDS‐carrying microspheres induced the biospecific activation of PMNs by the signal transduction via RGDS‐integrin binding without alteration in the degree of phagocytosis. © 1994 John Wiley & Sons, Inc.
Interactions of plasminogen and fibrinogen with model silica glass surfaces: Adsorption from plasma and enzymatic activity studies
Authors: Woodhouse K. A. , Weitz J. I. , Brash J. L. 
Published: December 2004

AbstractThe adsorption of fibrinogen and plasminogen from plasma to silica glass, sulfonated silica glass, and lysinederivatized silica glass has been investigated. The data indicate that the sulfonated material has a high affinity for both fibrinogen and plasminogen, but that the ratio of plasminogen to fibrinogen is greater on the lysinederivatized surface. The adsorption data also suggest plasminogen as a possible contributor to the fibrinogen Vroman effect, whereby initially adsorbed fibrinogen is displaced from the surface. The plasmin activity of plasminogen adsorbed to the lysine‐derivatized silica glass and its sulfonated precursor was assessed by both a chromogenic substrate assay and a radioimmunoassay for the plasmin cleavage product of fibrinogen, the Bβ 1–42 peptide. The data indicate that (1) the adsorbed plasminogen is not inherently plasmin‐like; (2) the enzymatic activity associated with the bound plasminogen is significantly enhanced on both surfaces in the presence of activator; and (3) in the presence of activator, the plasmin activity per mole of bound plasminogen on the lysinized material is approximately a factor of two greater than on the sulfonated material based on the chromogenic substrate assay, and a factor of four greater based on the Bβ 1–42 radioimmunoassay. The lysinized material thus exhibits several properties that are different from its sulfonated precursor. It adsorbs more plasminogen relative to fibrinogen after the Vroman peak, and this adsorbed plasminogen appears to be in a conformation that is more readily activated to plasmin. Once activated, the surface bound plasmin shows enhanced ability to cleave either a low molecular weight chromogenic substrate or a macromolecular substrate. These properties appear to be directly related to lysine residues on the surface and may be the result of specific conformational changes occurring when plasminogen engages its lysine binding sites. © 1994 John Wiley & Sons, Inc.
Internalization of poly(D,L‐1actic acid) nanoparticles by isolated human leukocytes and analysis of plasma proteins adsorbed onto the particles
Authors: Leroux Jean‐Christophe , Gravel Patricia , Balant Luc , Volet Bernard , Anner Beatrice M. , Allémann Eric , Doelker Eric , Gurny Robert 
Published: December 2004

AbstractThe objective of this work was to investigate the interactions of poly(D,L‐lactic acid) nanoparticles prepared by a recently developed salting‐out process, with lymphocytes and monocytes isolated from healthy human donors. Nanoparticles were labeled with a hydrophobic fluorescent dye and incubated with lymphocytes and monocytes, and their uptake was followed by flow cytometry in the presence and absence of plasma. Plasma protein adsorption increased nanoparticle uptake by monocytes, whereas a decrease of cellular binding of the nanoparticles to lymphocytes was noted. The cellular uptake for both cell types consisted in a passive adsorption and in an energy requiring process, because the cells became 2–3 times more fluorescent when the incubation temperature was increased from 4 to 37°C. When nanoparticles were coated with polyethylene glycol 20,000, uptake by monocytes decreased by 43 and 78% in phosphatebuffered saline and plasma, respectively; a similar decrease in nanoparticle uptake was observed for lymphocytes. Two‐dimensional gel electrophoresis was performed to identify the plasma opsonins adsorbed onto the nanoparticle surface. Protein mappings for uncoated and polyethylene glycol‐coated nanoparticles differed for two spot series. These spots, not yet clearly identified, may represent specific apolipoproteins involved in the metabolism of human lipoproteins, indicating the possible involvement of specific receptors in the uptake of the nanoparticles. © 1994 John Wiley & Sons, Inc.
Adsorption of a novel fluorescent derivative of a poly(ethylene oxide)/poly(butylene oxide) block copolymer on octadecyl glass studied by total internal reflection fluorescence and interferometry
Authors: Gingell D. , Owens N. , Hodge P. , Nicholas C. V. , O'dell R. 
Published: December 2004

AbstractWe have used total internal reflection fluorescence (TIRF) to measure the adsorption kinetics of a newly synthesized fluorescent derivative of a triblock copolymer comprising two poly(ethylene oxide) arms connected by a poly(butylene oxide) segment. The composition is (EO)400 (BO)55 (EO)400, in which EO represents ethylene oxide, BO represents butylene oxide, and one or both of the terminal OH groups of the two (EO)400 arms are labeled with tetramethylrhodamine. The poly(butylene oxide) segment binds to hydrophobic octadecyl glass, used as a substratum. The TIRF signal is shown to be derived almost entirely from surface‐adsobed polymer. This facilitates calculation of adsorption isotherms from 0.1–0.005% bulk polymer solution by means of diffusion kinetics. Information about the effective thickness of the adsorbed polymer, determined by optical interference microscopy, corresponds with what is known about the conformation of similar molecules at interfaces and indicates monolayer adsorption on the glass. © 1994 John Wiley & Sons, Inc.
Mineral apposition rates of human cancellous bone at the interface of porous coated implants
Authors: Bloebaum Roy D. , Bachus Kent N. , Momberger Nate G. , Hofmann Aaron A. 
Published: December 2004

AbstractHuman cancellous bone ingrowth studies were conducted on 19 consenting bilateral total knee arthroplasty (TKA) patients. Titanium porous coated cylinders were implanted into the medial femoral condyle of the contralateral knee during the first of two TKAs. Retrieval was performed at the time of the second TKA (6–131 weeks later), and fluorochrome analysis was conducted. Mean mineral apposition rates (MAR) at the interface measured 1.0 μm/day, whereas 4 mm away, the peripheral bone had a mean MAR of 0.8 μm/day. This represented a 25% acceleration in the interface bone remodeling rate when compared with the periphery (P< .05). This study showed the bone advanced appositionally at the interface at a rate of ≈ 1 μm/day. Analysis showed that when bone was over 50 μm from the porous coating, bone ingrowth did not occur. These results emphasize the need for surgical precision and careful postoperative management to achieve bone ingrowth. © 1994 John Wiley & Sons, Inc.
In vivo tensile testing of fluorapatite and hydroxylapatite plasma‐sprayed coatings
Authors: Kangasniemi I. M. O. , Verheyen C. C. P. M. , van der Velde E. A. , De Groot K. 
Published: December 2004

AbstractA tensile test has been developed to test bioactive coating materials. Hydroxylapatite (HA) and fluorapatite (FA) coatings with various roughnesses were tested using sandblasted titanium (Ti) as a control material. Twelve goats received 7 implants each for 6 (2 goats), 12 (5), and 24 (4) week implantation periods. After 12 weeks the mean tensile strength values were highest for polished hydroxylapatite (HAP) followed by HA > FAP (polished fluorapatite) > FA > Ti, and hydroxylapatite type coatings were found to exhibit significantly higher values than fluorapatite type coatings or titanium implants. After 24 weeks no statistically significant differences could be found between any of the implant types. The order of the mean strength values was now HAP > HA > FA > FAP > Ti. Fracture always occurred between the coating and titanium if bone contact had been established. In conclusion, it is suggested that results from different types of test methods cannot be used to compare different types of bioactive coatings. © 1994 John Wiley & Sons, Inc.
Ion‐selective membranes with low plasticizer content: Electroanalytical characterization and biocompatibility studies
Authors: Lindner E. , Cosofret V. V. , Ufer S. , Buck R. P. , Kao W. J. , Neuman M. R. , Anderson J. M. 
Published: December 2004

AbstractHigh molecular weight poly(vinyl chloride) and aliphatic polyurethane (Tecoflex)‐based ion selective membranes, with normal and reduced amounts of plasticizer, as well as without plasticizer, were tested with respect to their analytical properties, their biocompatibility, and cellular responses. The analytical properties of the membranes did not change significantly within a wide range of polymer to plasticizer rations. However, the membranes with reduced plasticizer content had better adhesive properties, less anion interference, extended life time, and better biocompatibility. Using the cage implant system, the results showed that an increase of plasticizer weight percent in Tecoflex membranes correlated positively with the increase in host inflammatory response up to 14 days of implantation. The results also demonstrated that both PVC and Tecoflex‐based ion‐selective membranes with the most common membrane composition (1:2 polymer to plasticizer ratio) exhibited a similar acute inflammatory response, but the PVC‐based membrane elicited a reduced chronic inflammatory response when compared with the Tecoflex‐based membrane. © 1994 John Wiley & Sons, Inc.
Conformational preferences of 34 valence electron A2X4 molecules: An ab initio Study of B2F4, B2Cl4, N2O4, and C2O
Authors: Clark Timothy , Von Ragué Schleyer Paul 
Published: December 2004

AbstractAb initio molecular orbital structures and energies of B2F4, B2Cl4, N2O4, and C2O have been calculated for both perpendicular D2d and planar D2h rotamers. The experimental trend toward greater preference for the D2d forms in going from B2F4 to B2Cl4 is reproduced. N2O4 favors the planar conformation, although the rotation barrier is overestimated at the theoretical levels used. The oxalate dianion is calculated to be more stable in the D2d conformation; the experimental planar arrangement in the solid may be due to crystal packing forces. The preferences for one conformation over another are small; analysis indicates that different effects may predominate in each case: π stabilization for B2F4, hyperconjugation for B2Cl4, lone‐pair interactions for N2O4, and electrostatic repulsions for C2O.
Simple calculation of electrostatic isopotential maps from bond fragments
Authors: Náaray‐Szabó G. , Grofcsik A. , Kósa K. , Kubinyi M. , Martin A. 
Published: December 2004

AbstractA simple and very rapid method for the calculation of electrostatic isopotential maps is proposed. The potential is composed of transferable bond fragments. According to chemical evidence, σ‐, lone‐pair, and π‐bond contributions are considered. The computational work is proportional to the first power of the number of bond orbitals; therefore very large systems, such as enzymes or DNA, can be handled also. Transferability of bond orbital characteristics such as polarity, s character, and orientation is discussed. Though the absolute value of the potential is overestimated, trends obtained with STO‐3G calculations are reflected correctly.
On the applicability of the MINDO/3 method in studies of molecular structures in the vapor phase. Geometries, conformational energies, and vibrational amplitudes of alkenes and chloroalkanes
Authors: Van Hemelrijk D. , Versichel W. , Van Alsenoy C. , Geise H. J. 
Published: December 2004

AbstractThe geometries and force fields of the different conformers of five alkenes and five chloroalkanes (17 conformers in total) were calculated in the MINDO/3 approximation and compared with the corresponding experimental values. The direct use of geometrical or vibrational parameters derived from MINDO/3 either as starting values or as a source of constraints in the analysis of gas‐phase electron diffraction data presents great risks. After a scaling procedure in which the calculated values are fitted to the experimental ones for a small number of compounds, scale factors can be obtained which, with due caution, are transferable to other molecules in the same class. Scaled MINDO/3 produces geometries and force fields that fit to experiment considerably better than their unscaled counterparts. However, scaled MINDO/3 does not produce better results than molecular mechanics. Calculated energy differences between rotamers are generally too high.
Electron density redistribution in the stabilization of a molecular stacking complex: The nature and correction of basis set superposition errors
Authors: Osman Roman , Topiol Sid , Weinstein Harel 
Published: December 2004

AbstractThe effect of the basis set superposition error (BSSE) on the calculated electronic structure of a molecular stacking complex is analyzed with the counterpoise correction method. The complex between para‐hydroxyaniline (PHA) and formamidinium cation (FAM) is calculated ab initio with the STO‐3G and Whitman–Hornback minimal bases, and with two split valence basis sets: 4‐31G and STO‐3G(D). When the counterpoise correction is applied, the charge redistribution in the PHA/FAM complex calculated with all four basis sets suggests that the complex is electrostatic in nature and that the main polarization is from the PHA toward FAM. The FAM cation is polarized away from the intermolecular region, thus causing further increase in the electrostatic interaction. This picture is not evident with the STO‐3G related bases if the counterpoise correction is not applied. Thus, the BSSE in the charge redistribution is shown to be particularly large in the STO‐3G basis and in the diffuse, split valence, STO‐3G(D). Both these basis sets suffer from an inappropriate description of the core region. Where there is an improved description of the electron density in the core region, as in the calculations with the energy‐optimized Whitman–Hornback basis and with the 4‐31G basis, the counterpoise correction has only a very small effect on the charge redistribution. After the counterpoise correction is applied, the two minimal basis sets yield nearly identical charge redistribution results, as do the two split valence bases. It is therefore suggested that basis sets used in the calculation of molecular complexes might be classifiable according to criteria such as the degree of contraction and the quality of the description of angular polarization. This would help in the comparative evaluation of results obtained with different bases since minimal basis sets (or split valence bases) would become directly identifiable as groups yielding qualitatively similar results.
Geometry and energy of tetra‐tert‐butylethylene
Authors: Favini G. , Simonetta M. , Todeschini R. 
Published: December 2004

AbstractThe geometry and energy of tetra‐tert‐butylethylene have been determined by the molecular mechanics method. A twisting of the double bond by 45.5° was found. The ground state of the molecule should be a singlet. The calculated strain energy is higher than those of tri‐tert‐butylmethane and tetra‐iso‐propylethylene, but the possibility of synthesis of the compound is not excluded.
AMBER: Assisted model building with energy refinement. A general program for modeling molecules and their interactions
Authors: Weiner Paul K. , Kollman Peter A. 
Published: December 2004

AbstractWe describe a computer program we have been developing to build models of molecules and calculate their interactions using empirical energy approaches. The program is sufficiently flexible and general to allow modeling of small molecules, as well as polymers. As an illustration, we present applications of the program to study the conformation of actinomycin D. In particular, we study the rotational isomerism about the D‐Val‐, L‐Pro, and L‐Pro‐Sar amide bonds as well as comparing the energy and structure of the Sobell model and the x‐ray structure of actinomycin D.
Representation of the molecular electrostatic potential by a net atomic charge model
Authors: Cox S. R. , Williams D. E. 
Published: December 2004

AbstractElectrostatic potentials and Mulliken net atomic charges were calculated from STO‐3G, 6‐31G, and 6‐31G** SCF‐MO wavefunctions for hydrogen fluoride, water, ammonia, methane, acetylene, ethylene, carbon dioxide, formaldehyde, methanol, formamide, formic acid, acetonitrile, diborane, and carbonate ion. In each case optimized net atomic charges (potential‐derived charges) were also obtained by fitting the electrostatic potentials calculated directly from the wavefunctions in a shell enveloping the molecules outside of their van der Waals surfaces. The electrostatic potentials calculated from the potential‐derived charge distributions were then compared with the defined quantum mechanical electrostatic potentials and with the electrostatic potentials of the Mulliken charge distributions.
Molecular mechanics of organic halides. V. Conformational equilibria in solution
Authors: Meyer A. Y. 
Published: December 2004

AbstractWith a view of using data on solutions and liquids for parameter fitting in molecular mechanical force fields, Abraham's theory of solvation is incorporated in the force field procedure. Geometries and bond moments are estimated internally, partial account being taken of bond–bond induction, and used to calculate the intramolecular electrostatic energy, dipole moment, and the dipole and quadrupole terms in the solvation energy. Three dielectric constants are used, one for the solute in the vapor, one for the solution, and one for the intramolecular space through which dipole–dipole interactions take place. Examples are given, including such where computation differs with measurement, to illustrate the performance of the scheme.
Monte Carlo simulation for inhomogeneous chemical kinetics: Application to the Belousov–Zhabotinskii reaction
Authors: Zaera F. , Rusinek Isak 
Published: December 2004

AbstractA Monte Carlo algorithm, capable of simulating numerically the time and space dependence of chemical concentrations in a reacting system, is presented. This method is used to study the phenomenon of trigger waves in the Oregonator model of the Belousov–Zhabotinskii reaction, including the diffusion of species X and Y in one dimension. The results show that a small disturbance in a homogeneous mixture can grow into a chemical (trigger) wave propagating in space at constant velocity. The dependence of this velocity on several factors is studied, namely, initial concentrations, the diffusion of Y, and the stoichiometry of the autocatalytic step of the model. A comparison of the Monte Carlo results with a previous simulation also is discussed.
Ab initio studies of structural features not easily amenable to experiment. 18. Conformational analysis and molecular structure of glycine methyl ester
Authors: Schäfer Lother , Van Alsenoy C. , Scarsdale J. N. , Klimkowski V. J. , Ewbank J. D. 
Published: December 2004

AbstractThe structures of four conformations of the methyl ester of glycine were determined by standard single‐determinant molecular orbital (MO) calculations using Pulay's force method and the 4‐21G basis set. The most stable conformation of this compound has a symmetry plane which contains all the heavy atoms; it is stabilized by hydrogen bonds between the NH2 group and the carbonyl oxygen; it corresponds to the most stable, stretched form of free glycine. The structural parameters in the different conformations can vary significantly (bond distance by more than 0.02 Å and bond angles by up to 15°). The structural changes which are caused in glycine by esterification are discussed and some of them are interpreted in terms of hyperconjugative π‐electron delocalization.