bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Vitro effect of metal ions on cellular metabolism and the correlation between these effects and the uptake of the ions
Authors: Wataha J. C. , Hanks C. T. , Craig R. G. 
Published: December 2004

AbstractThe effects of Ag+1, Au+3, Cd+2, Cu+2, Ga+3, In+3, Ni+2, Pd+2, and Zn+2 on DNA synthesis, protein synthesis, succinic dehydrogenase activity, and total cellular protein of mammalian fibroblasts were measured for exposures less than 12 h. The rates at which these cellular functions responded to metal ion exposure were compared and related to the uptake rate of the ions into the cells. These rates of response were significantly different: DNA synthesis decreased the fastest, followed by protein synthesis, succinic dehydrogenase activity, and total protein. This order of response was similar for most metal ions. At 4 h, the rate of uptake of the metal ions correlated most closely with depression of succinic dehydrogenase activity, whereas at 8 h, the uptake correlated most closely with depression of protein synthesis. The similar response of cells to all metal ions may imply that these ions act on cells by similar mechanisms. The rates of uptake of Ag+1, Cu+2, and Zn+2 were sufficiently fast that in vivo exposures of tissues to these metals for periods less than 12 h would be capable of disrupting cellular metabolism. © 1994 John Wiley & Sons, Inc.
Granule secretion markers on fluid‐phase platelets in whole blood perfused through capillary tubing
Authors: Rhodes N. P. , Zuzel M. , Williams D. F. , Derrick M. R. 
Published: December 2004

AbstractThe effect of material composition and shear rate on fluid‐phase platelet activation was investigated using a capillary perfusion model. Citrated whole blood was perfused along the lumens of tubes constructed from silicone, PVC, Pellethane, W124 (an experimental polyetherurethane), and glass. Platelet activation was determined by measuring the increase in α‐granule membrane protein P‐selectin (GMP‐140, CD62) and the lysosomal granule membrane protein GP‐53 (CD63) on fluid‐phase platelets by flow cytometry. All tubes caused an increase over the negative control in the number of P‐selectin and GP‐53 molecules detectable on the surface of these platelets. The activation response of platelets to changes in shear rate was also investigated. It was found that lysosomal release paralleled α‐granule release in glass, but not in Pellethane, over a range of wall shear rates (100–1,000 s−1). © 1994 John Wiley & Sons, Inc.
Creep of a poly(etherurethane urea) in an oxidative environment
Authors: Wu Y. K. , Lodoen G. A. , Anderson J. M. , Baer E. , Hiltner A. 
Published: December 2004

AbstractThe creep behavior of a PEUU without added stabilizers was examined in H2O2/CoCl2, an environment that simulates the biodegradation of this polymer. Creep in the control environments, air, water, and H2O2, was logarithmic with time as is characteristic of primary or viscoelastic creep. At short times, creep in H2O2/CoCl2 followed the same time dependency as creep in H2O2; however, at longer times an acceleration in the creep rate was observed. Creep in H2O2/CoCl2 was satisfactorily described by addition of a linear time term to the creep equation with an induction time, ti. The induction time was extended by stress‐induced crystallization of the soft segments, but was reduced by an increase in H2O2 concentration. Oxidative degradation of the PEUU soft segments was detected by infrared and GPC analysis at times less than ti. This led to the speculation that an initial “precursor” layer was created at the surface by chain cleavage. Microcracking in a subsequent stage was postulated to be responsible for the observed effect on the creep behavior. © 1994 John Wiley & Sons, Inc.
A light and laser scanning microscopy study of bone/hydroxyapatite‐coated titanium implants interface: Histochemical evidence of unmineralized material in humans
Authors: Piattelli Adriano , Trisi Paolo 
Published: December 2004

AbstractThe authors describe a light and laser scanning microscopy study of hydroxyapatite‐coated titanium implants retrieved from humans. A histochemical technique, using von Kossa and basic fuchsin, allowed clear differentiation between mineralized bone and unmineralized bone matrix. The bone‐hydroxyapatite (HA) interface presented variable features: in some areas the mineralized bone was directly apposed to the HA surface, while in others an unmineralized red‐stained material, probably osteoid, was interposed. Laser scanning microscopy confirmed these findings showing a thin layer of fluorescent material at the interface. © 1994 John Wiley & Sons, Inc.
Evaluation of carcinogenicity and chronic toxicity associated with orthopedic implants in mice
Authors: Takamura Kazuyuki , Hayashi Kazuo , Ishinishi Noburu , Yamada Teruki , Sugioka Yoichi 
Published: December 2004

AbstractThe carcinogenicity and chronic toxicity of 316L stainless steel, nickel, Ti‐6Al‐4V, hydroxyapatite (HA)‐coated Ti‐6Al‐4V, aluminum oxide containing yttrium oxide were evaluated by implanting solid rods of each material in the thigh muscle of C57BL/6N mice for 24 months. Nickel alloy showed high carcinogenic and toxic potencies, whereas other materials showed no evidence of them. Tumors retaining nickel alloys were malignant fibrous histiocytoma or fibrosarcoma. In some cases, lymphomata that seemed to develop spontaneously were found around the implants because lymphocytes were known to accumulate in chronic inflammatory lesions, and this phenomenon also might be applied to lymphoma. © 1994 John Wiley & Sons, Inc.
The origins of barriers to orbital symmetry/topology‐allowed pericyclic reactions: Conjugate addition of methylene to s‐cis‐1,3‐butadiene
Authors: Bauld Nathan L. , Wirth David 
Published: December 2004

AbstractThe barriers on the MINDO/3 reaction paths for π and σ approaches to concerted cycloaddition of methylene to s‐cis‐1,3‐butadiene are analyzed by a new energy decomposition scheme and compared to the results of published extended Hückel calculations. The relatively small (6 kcal) preference for the σ approach is essentially based on next‐nearest‐neighbor (1,3) resonance interactions, which are stabilizing in the σ but destabilizing in the π approach. Both routes are characterized by large distortion energies (mainly disrotation at the diene termini in the case of the π approach) and nonbonded repulsions. The excessive magnitude of both of these effects ultimately derives from the weak pericyclic binding which prevails at initial diene geometries, especially the pericyclic topology involving the methylene LUMO. Although previous work has emphasized the contribution of closed‐shell repulsions to the barrier, no such effect is explicitly included in MINDO. The closed‐shell repulsions to which the extended Hückel barrier has been solely attributed are shown to involve next‐nearest‐neighbor (antiaromatic) resonance interactions.
Ab initio calculation of spin–orbit interaction in polyatomic molecules using Gaussian‐type wavefunctions
Authors: Breulet Jacques 
Published: December 2004

AbstractA set of programs has been developed to calculate molecular spin–orbit interaction with Gaussian‐type wavefunctions in connection with the popular GAUSSIAN 76 program. The spin–orbit contributions to the fine structure of O2 (X3∑g−), NH (X3∑−), and CH2 (X3B1) are evaluated with the standard STO‐3G and 6‐31G basis sets; for NH the influence of bond functions added to the latter basis set is also investigated. The results are compared to values previously obtained with other types of basis sets.
Molecular orbital theory of the hydrogen bond. 27. Substituent effects in water: 4‐R‐pyrimidine complexes
Authors: Bene Janet E. Del 
Published: December 2004

AbstractAb initio SCF calculations with the STO‐3G basis set have been performed to investigate substituent effects on the structures and stabilization energies of water:4‐R‐pyrimidine complexes, with R including CH3, NH2, OH, F, C2H3, CHO, and CN. Except for the cyclic water:4‐aminopyrimidine complex hydrogen bonded at N3, these complexes have open structures stabilized by a nearly linear hydrogen bond formed through a nitrogen lone pair of electrons. When hydrogen bonding occurs at N3, the complexes may have planar or perpendicular conformations depending on the substituent, but when hydrogen bonding occurs at N1, the perpendicular is generally slightly preferred, and there is essentially free rotation of the 4‐R‐pyrimidine. Primary substituent effects alter the electronic environment at the nitrogens, and tend to make N3 a poorer site for hydrogen bonding than N1, primarily because of a stronger π electron‐withdrawing effect at N3. However, the relative stabilities of complexes hydrogen bonded at N1 and N3 are also influenced by secondary substituent effects, which may be significant in stabilizing complexes bonded at N3. Substitutent effects on the structures and stabilization energies of the water:4‐R‐pyrimidine complexes are similar to substitutent effects in water:2‐R‐pyridine and water:4‐R‐pyrimidine complexes are similar to substitutent effects in water:2‐R‐pyridine and water:4‐R‐pyridine complexes. Configuration interaction calculations indicate that although absorption of energy by the pyrimidine ring destabilizes the water:4‐R‐pyrimidine complexes, these may still remain bound in the excited n → π* state. This is in contrast to the fate of open water:2‐R‐pyridine and water:4‐R‐pyridine complexes, which dissociate in this state.
Conformational energy calculation on the neurotensin c‐terminal pentapeptide Arg–Pro–Tyr–Ile–Leu OH
Authors: Cotrait Michel , Ptak Marius 
Published: December 2004

AbstractThe conformational behavior of the C‐terminal neurotensin pentapeptide, Arg–Pro–Tyr–Ile–Leu OH [NT(9–13)], was investigated using empirical energy calculations. A special aim was to display the specific contribution of each residue to induce conformations able to interact with biological receptors. Restrictions were then introduced in intramolecular interactions involving the Arg side chain and the terminal COOH group. The stablest conformations include in the order of decreasing stability: a distorted helical form for the C‐terminal tetrapeptide, a (Pro2–Tyr3) β turn I, an α helix, an extended form, and a (Tyr2–Ile3) β turn III, which are energetically rather close (ΔE < 3 kcal/mol). The NT(9–13) peptide appears then as a rather flexible molcule with a noteworthy ability of adaptation to a substrate. Extended forms would be in agreement with a zipper model of interactions with receptors, whereas folded forms involving helices and β, γ turns would support a lock and key model. The specific contribution of side chains, specially those of Tyr and Arg residues as well as the key position of the Pro residue emerge clearly from this study.
Studies in hydrogen bonding: Association within mixed dimers of water, methanol, ammonia, and methylamine using the empirical potential EPEN
Authors: Brink George , Glasser Leslie 
Published: December 2004

AbstractAn empirical potential EPEN has been used to find the stable geometries and approximate hydrogenbond energies of the mixed dimers formed between molecules of water, methanol, ammonia, and methylamine. These results are compared with results in the literature obtained using ab initio methods.
Thermochemical data from ab initio calculations. I. Estimation of SCF energies for augmented basis sets and Hartree–Fock limit energies
Authors: Cremer Dieter 
Published: December 2004

AbstractA procedure is outlined which allows an estimation of molecular energies both for a finite basis set including polarization functions and for the Hartree–Fock limit. It is shown that the orbital error of a given minimal basis is covered to a certain relatively constant percentage by an augmented basis set calculation. Thus an improvement factor Qav can be determined by analyzing the corresponding results of small molecules where reasonable estimates of HF limit energies can be taken from the literature. For a combination of Pople's STO‐3G and 6‐31G* basis sets Qav turns out to be 0.955.
Fast semiempirical calculations
Authors: Stewart J. J. P. , Császár P. , Pulay P. 
Published: December 2004

AbstractMost quantum chemists regard semiempirical methods as ephemeral and computationally cost efficient. For this reason, an article dealing with computational efficiency of semiempirical methods is probably very unfashionable. However, experience at a big computer installation, shared by ab‐initio and semiempirical quantum chemists shows that the second group actually consumes more computer time than the first. Obviously, the greater size of the molecules in semiempirical calculations outweighs the inherent efficiency of these methods. The present article describes a simple method for accelerating SCF‐type semiempirical methods.
Stabilization of methyl anions by first‐row substituents. The superiority of diffuse function‐augmented basis sets for anion calculations
Authors: Spitznagel Günther W. , Clark Timothy , Chandrasekhar Jayaraman , Schleyer Paul Von Ragué 
Published: December 2004

AbstractThe entire set of methyl anions, XCH2−, substituted by first‐row substituents, Li, BeH, BH2, CH3, NH2, OH, and F, was examined at various ab initio levels. Diffuse orbital‐augmented basis sets, such as 4−31+G and 6−31+G*, are needed to describe the energies of these anions adequately. Estimates of proton affinities are further improved by second‐order Møller–Plesset (MP2) electron correlation corrections, but relative energies are less affected. The methyl group in the ethyl anion is destabilizing, the amino substituent is borderline, but all other groups are stabilizing. Very large π effects are exhibited by BH2 and BeH groups; inductive stabilization by the electronegative F and OH groups is less effective. Lithium also is stabilizing, but the best singlet geometry of CH2Li− is not planar. A planar CH2Li− triplet with a π1 configuration may be lower in energy.
Principles for a direct SCF approach to LICAO–MOab‐initio calculations
Authors: Almlöf J. , Faegri K. , Korsell K. 
Published: December 2004

AbstractThe principles and structure of an LCAO‐MO ab‐initio computer program which recalculates all two‐electron integrals needed in each SCF iteration are formulated and discussed. This approach—termed “direct SCF”—is found to be particularly efficient for calculations on very large systems, and also for calcuations on small and medium‐sized molecules with modern minicomputers. The time requirements for a number of sample calculations are listed, and the distribution of two‐electron integrals according to magnitude is investigated for model systems.
An ab initio study of the relative stabilities of the isomers of CH2N2 and SiH2N2
Authors: Thomson Colin , Glidewell Christopher 
Published: December 2004

AbstractAb initio SCF calculations of the equilibrium geometries have been carried out on nine possible isomers of MH2N2, where M = C or Si, and compared with the results of MNDO calculations. The results for the carbon compounds are in good agreement with available experimental data, but in the case of the silicon compounds, the molecules are predicted to be unstable with respect to decomposition to SiH2 and N2. The inclusion of electron correlation at the MP3 level does not alter the order of the relative stabilities, although the importance of the correlation contribution varies substantially between the different isomers.
Ab initio studies on calicene
Authors: Hess B. A. , Schaad L. J. , Ewig C. S. , Čársky P. 
Published: December 2004

AbstractOptimum geometries of planar and 90°‐twisted C2v calicene are calculated with single‐configuration STO‐3G and 3‐21‐G wavefunctions. The barrier to ring–ring rotation is computed. Bond alternation is pronounced in the planar form and decreases in the twisted form, while dipolar character increases on twisting.
Computation of electron repulsion integrals using the rys quadrature method
Authors: Rys J. , Dupuis M. , King H. F. 
Published: December 2004

AbstractFollowing an earlier proposal to evaluate electron repulsion integrals over Gaussian basis functions by a numerical quadrature based on a set of orthogonal polynomials (Rys polynomials),

a computational procedure is outlined for efficient evaluation of the two‐dimensional integrals Ix, Iy, and Iz. Compact recurrence formulas for the integrals make the method particularly fitted to handle high‐angular‐momentum basis functions. The technique has been implemented in the HONDO molecular orbital program.
Molecular symmetry. IV. The coupled perturbed Hartree–Fock method
Authors: Takada Toshikazu , Dupuis Michel , King Harry F. 
Published: December 2004

AbstractSymmetry methods employed in the ab initio polyatomic program HONDO are extended to the coupled perturbed Hartree–Fock (CPHF) formalism, a key step in the analytical computation of energy first derivatives for configuration interaction (CI) wavefunctions, and energy second derivatives for Hartree–Fock (HF) wavefunctions. One possible computational strategy is to construct Fock‐like matrices for each nuclear coordinate in which the one‐ and two‐electron integrals of the usual Fock matrix are replaced by the integral first derivatives. “Skeleton” matrices are constructed from the unique blocks of electron‐repulsion integral derivatives. The correct matrices are generated by applying a symmetrization operator. The analysis is valid for many wavefunctions, including closed‐ or open‐shell spin‐restricted and spin‐unrestricted HF wavefunctions. To illustrate the method, we compare the computer time required for setting up the coupled perturbed HF equations for eclipsed ethane using D3h symmetry point group and various subgroups of D3h. Computational times are roughly inversely proportional to the order of the point group.
Proton and lithium cation affinities calculated with floating orbital geometry optimization (FOGO)
Authors: Huber Hanspeter , Latajka Zdzisław 
Published: December 2004

AbstractThe FOGO method is used to calculate proton affinities and lithium cation affinities. The molecules of primary interest in this study are the methyl‐substituted amines. In addition, the lithium cation affinity of HF, H2O, CH3OH, H2CO, and HCN are calculated for comparison. Geometries of all species are fully optimized with a double‐zeta (DZ) basis set, including polarization on hydrogen and the first‐row elements by floating orbitals. Comparison with experimental values demonstrates that structural data and proton affinities resulting from this type of ab initio calculation are of chemical accuracy. The lithium cation affinities are also reasonably well reproduced, but the small experimental differences are not within the accuracy, which can be expected from this type of calculation.
A technique for determining the symmetry properties of molecular graphs
Authors: Davis Michael I. , Ellzey M. Lawrence 
Published: December 2004

AbstractA procedure has been devised to determine the automorphism partition and the automorphism group for nondirected graphs. The general approach is to reveal the permutational symmetry by means of its systematic destruction. Symmetry decomposition pathways are created by numerically weighting specific series of vertices. Each pathway leads to a discrete ordered vector. Each pair of pathways that match reveals an element of the automorphism group. Results are presented for two molecular graphs. Further potential applications of this approach to problems of isomorphism, canonical labeling, and structural indexing are discussed.
Molecular mechanics studies of enthalpies of formation and strain energies of azoxyalkanes
Authors: Byström Katarina 
Published: December 2004

AbstractA force field has been developed, on the basis of available experimental and partial retention of diatomic differential overlap (PRDDO) data, to permit molecular mechanics calculations on azoxyalkanes. The calculated structures and enthalpies of formation are in fair agreement with experimental results. The calculated enthalpies of formation and strain energies are compared with the corresponding quantities for analogous azoalkanes.
Nonrelativistic and quasirelativistic model potential calculations on AgH and Ag2
Authors: Klobukowski M. 
Published: December 2004

AbstractThe major relativistic effects are included into the model potential (MP) method of Bonifacic and Huzinaga. The effects are incorporated on the level of Cowan and Griffin's relativistic Hartree–Fock (RHF) method. The model potential parameters are determined using the results of nonrelativistic Hartree–Fock (NHF) and RHF calculations. A new scheme of selection of the basis functions for use in atomic and molecular MP calculations is proposed. To obtain agreement with the Hartree–Fock calculations on AgH and Ag2, the 4p shell has to be included explicitly in the MP calculations. The explicit treatment of the 4p electrons and the resulting reduction of the core size are necessary in order to overcome difficulties with approximate representation of the large 4p–4d core‐valence interactions on the MP level.
A method for the calculation of normal‐mode vibrational frequencies using symmetry coordinates. Application to the calculation of secondary deuterium isotope effects on carbocations
Authors: Hout Robert F. , Levi Beverly A. , Hehre Warren J. 
Published: December 2004

AbstractA method is introduced for the calculation of normal‐mode vibrational frequencies of polyatomic molecules based on numerical differencing of analytical gradients in symmetry coordinates. This procedure requires a number of gradient evaluations equal to the largest number of symmetry coordinates belonging to any single irreducible representation of the molecular point group (plus a single gradient evaluation at the equilibrium configuration), which is fewer than the 3N‐6 (N atoms) gradient evaluations needed for schemes based on Cartesian or internal coordinates. While the proposed method will not generally be as efficient as procedures which involve the direct calculation of energy second derivatives analytically (as are now available for single‐determinant wavefunctions) it appears to be equally accurate, and it should be the method of choice for frequency calculations involving multideterminant wavefunctions for which analytical second‐derivative algorithms have yet to be developed. The method is illustrated by the calculation of equilibrium secondary deuterium‐isotope effects on a number of reactions involving simple carbocations.
Ground states of molecules. 64.MNDO Calculations for compounds containing bromine
Authors: Dewar Michael J. S. , Healy Eamonn 
Published: December 2004

AbstractMNDO has been parametrized for bromine. Since d atomic orbitals (AOS) are not included, the calculations are restricted to BrI. Heats of formation, molecular geometries, ionization energies, and dioole moments are reproduced with useful accuracy.
Orbital relaxation in the Rydberg series of the lithium atom. An excited state SCF calculation
Authors: Chang Tse‐Chiang 
Published: December 2004

AbstractSelf‐consistent‐field (SCF) calculations for a series of Rydberg states (1s2ns)2S of the Li atom are performed using the generalized Brillouin theorem (GBT) method. The calculated energy is a proper upper bound to the excited state energy. The SCF term values of the Rydberg states are almost the same as those of the frozen‐core approximation ones. The orbital behavior shows that the core is slightly expanded by the penetration of the Rydberg orbitals, and the higher Rydberg orbitals can be very well represented by the modified hydrogen‐like orbitals.
Remarks on the molecular mechanical calculations of functionalized hydrocarbons
Authors: Meyer A. Y. 
Published: December 2004

AbstractMolecular mechanical calculations for hetero‐substituted hydrocarbons present certain difficulties that are not encountered in dealing with hydrocarbons. Ways are proposed to overcome such difficulties, sometimes by two‐step or iterative computation. The following topics are considered: fitting the force field by using data from studies in solution; ways to estimate atomic charges or, alternatively, bond moments; ways to account for field effects upon atomic charges and bond moments.