bluuebunny/crossref_metadata_2025 huggingface dataset:
The glutaraldehyde‐stabilized porcine aortic valve xenograft. I. Tensile viscoelastic properties of the fresh leaflet material
Authors: Lee J. Michael , Courtman David W. , Boughner Derek R.
Published: December 2004

The tensile viscoelastic properties of radial and circumferential strips of fresh porcine aortic valve leaflets have been examined and compared with the fiber architecture of the leaflets as seen in the scannng electron microscope. The leaflet material showed nonlinear viscoelasticity, largely independent of strain rate, and dependent on the degree of preconditioning by cyclic loading. Preconditioning to a stable stress‐strain response could only be accomplished on 1‐cm‐long strips above a minimum width of 4 mm (circumferential) and 6 mm (radial). Preconditioning yielded a more elastic and extensible material with reduced hysteresis. The leaflets were markedly anisotropic. Circumferential strips were up to 8 times stronger and stiffer than radial strips, and displayed greater stress relaxation and less creep. The circumferential mechanical properties were due to well‐aligned circumferential collagen bundles reinforcing the composite structure, while radial properties were due to a more random collagenous support throughout the leaflet. Despite the presence of a septal shelf on the right coronary leaflet, no mechanical differences could be discerned between leaflets.
On the true wear rate of ultrahigh molecular weight polyethylene in the total knee prosthesis
Authors: Rose Robert M. , Ries Michael D. , Paul Igor L. , Crugnola Aldo M. , Ellis Edward
Published: December 2004

The objective of this investigation was to assess the magnitude of the true wear of the polyethylene components of several total knee replacements. Five different prostheses were tested by total joint simulation for the equivalent of 1 month of use. The true wear rates of the tibial components were measured by quantitative recovery of the polyethylene debris. After testing, the tibial components were examined in the scanning electron microscope, and the molecular weight distributions were analyzed. The wear rates were found to range from 0.3 to 1.8 mg per month. The soluble fraction molecular weights ranged from 179,000 to 393,000 with 53–78% soluble. The wear rates, significantly larger than those observed for total hip prostheses, are dominated by the high contact stresses in these prostheses. The wear results in dimensional changes, which are of the same order of magnitude as those due to creep. The debris had two components: fine fibrous particles, found in all cases, and coarse granules, found when the wear rate is relatively high. Evidence for fatigue cracking was found at the surfaces of the tibial component with the highest wear rate. This behavior is consistent with other investigations of the material itself and indicates that continuous deterioration of the polyethylene should be expected in this class of prosthesis.
The effect of humoral components on the cellular response to textured and nontextured PTFE
Authors: Korman N. J. , Sudilovsky O. , Gibbons D. F.
Published: December 2004

The investigation was undertaken to determine the role that humoral components play in the biological response to ion beam textured and smooth PTFE. It was found that exudates obtained from smooth PTFE implants contained factors capable of promoting the attachment and growth of cells in vitro. Exudates obtained from textured PTFE contained significantly more growth promoting activity at 2 days after implantation and significantly more attachment promoting activity at 2 and 7 days after implantation than corresponding exudates obtained from smooth PTFE. The underlying reasons for the temporal nature of these results are not known, but cellular mechanisms were proposed to explain the observed differences. In order to examine protein adsorption to implants in vivo, a technique was developed utilizing the Selye air pocket and electrocautery to minimize cell adhesion to the implants. The results demonstrated the dynamic quality of protein adsorption to surfaces and indicated that the nature of protein exchange at the material surface differed between textured and smooth PTFE for the first 30 min post‐implantation. Both albumin and fibrinogen were identified on textured and smooth surfaces, but fibronectin was not identified on any of the surfaces.
Heparin immobilization onto segmented polyurethaneurea surfaces—effect of hydrophilic spacers
Authors: Park Ki Dong , Okano Teruo , Nojiri Chisato , Kim Sung Wan
Published: December 2004

Heparin was immobilized onto segmented polyurethane‐urea surfaces (Biomer) using hydrophilic poly(ethylene oxide) spacers of different chain lengths. The use of the hydrophilic spacer, poly(ethylene oxide), reduces protein adsorption and subsequent platelet adhesion on the surface. In addition, the bioactivity of the immobilized heparin is enhanced by the incorporation of these spacers. Immobilized heparin bioactivity is shown to be a function of PEO spacer length. Use of hydrophilic PEO spacers demonstrates that immobilized heparin's bioactivity is consistently higher than that of the C6 alkyl spacer, but heparin‐immobilized surfaces demonstrate no chain length effect on platelet adhesion, even though they show less platelet adhesion compared to Biomer controls. In the case of PEO‐grafted surfaces, platelet adhesion is decreased compared to Biomer controls, and C6 alkyl spacer‐grafted surfaces, and exhibits a minimum at PEO 1000. In ex vivo A–A shunt experiments under low flow and low shear conditions, all heparinized surfaces exhibit significant prolongation of occlusion times compared to Biomer controls, indicating an ability of immobilized heparin to inhibit thrombosis in whole blood.
In vitro synergistic, antagonistic, and duration of exposure effects of metal cations on eukaryotic cells
Authors: Wataha J. C. , Hanks C. T. , Craig R. G.
Published: December 2004

Effects of duration of exposure of single metal cations (Ag+1, Cd+2, Cu+2, Ga+3, Ni+2, and Zn+2) on 3H‐thymidine (3H‐Tdr) incorporation and 3‐[4,5‐dimethylthiazol‐2yl‐]‐2,5‐diphenyl tetrazolium bromide‐formazan (MTT‐f) production in cultured murine fibroblasts (Balb/c 3T3) were investigated, and the synergistic and antagonistic effects of two metal cations applied simultaneously to the fibroblasts were assessed. The effects of duration of exposure were quantified using TC50 values (concentration of an element required to cause 50% toxicity compared with controls) measured after 24, 48, or 72 h. Using MTT‐f production, Cd+2, Cu+2, Ga+3, and Ni+2 showed significantly lower TC50 values with increasing time of exposure, whereas the TC50 values for Ag+1 and Zn+2 remained constant. The TC50 values using 3H‐Tdr incorporation exhibited a similar pattern with time of exposure, but the effects were less pronounced. The TC50 values for 3H‐Tdr and MTT‐f tended to equalize at 72 h. All combinations of cations tested (Ag‐Cu, Ag‐Zn, Ag‐Ni, Cu‐Zn, Cu‐Ni, Cu‐Ni, Ga‐Ni, and Cu‐Cd) exhibited synergistic and antagonistic effects were not necessarily mutually exclusive in the same system. © 1992 John Wiley & Sons, Inc.
Tissue compatibility of collagen‐silicone composites in a rat subcutaneous model
Authors: Wallace Donald G. , Rosenblatt Joel , Ksander G. A.
Published: December 2004

Collagen‐silicone composites were fabricated and tested for biocompatibility by subcutaneous implantation in rats. The silicone component consisted of addition cure or condensation cure sheets. The collagen component was either (a) a sponge layer 2 mm thick, (b) a thin film 12‐20 μm thick, or (c) residual collagen bonded to or incorporated in the silicone rubber. Collagen sponges were mechanically bonded to silicone sheets, and collagen thin films and residual collagen were physically and chemically attached to epoxyderivatized silicone sheets. Analysis of implanted samples showed that reduced capsule formation occurred around collagen spongesilicone, compared to control silicone sheets. Only where the underlying silicone sheet, or interpenetrating silicone, was exposed to the tissue, did limited capsule formation occur. In contrast, thin capsule developed completely around silicone coated with a thin collagen film and around silicone bonded to residual collagen. Sponge‐silicone composites and control silicone sheets were free of acute and chronic inflammation, except for occasional foreign body giant cells in sponge adjacent to silicone. Silicone coated with micron‐thick collagen films exhibited some inflammation, but residual collagen‐silicone did not. This study suggests that, to prevent capsule formation, a collagen coat must be of minimum thickness and surface coverage sufficient to prevent any contact between silicone and tissue. © 1992 John Wiley & Sons, Inc.
Hydroxyapatite coatings on Ti produced by hot isostatic pressing
Authors: Herø Håkon , Wie Henrik , Jørgensen Randi B. , Ruyter I. Eystein
Published: December 2004

Plasma spraying is a technique currently used in the production of HA‐coated titanium implants. These coatings have been shown to be porous; they dissolve and have a weak bond to the substrate. The long‐term interface strength has been questioned in particular. The aim of the present work was to produce HA coatings without the shortcomings of those produced by plasma spraying. Hot isostatic pressing (HIP) at 850°C and 1000 bar with no holding time was applied for this purpose. Initially, the HA powder was mixed with water and air sprayed on the Ti substrate. The Ti specimens were then cold‐pressed, enclosed by a protective Pt foil, and encapsulated in an evacuated glass ampulla. Subsequent to HIP, the glass and the Pt foil were removed. These coatings were denser than those produced by plasma spraying. The bonding was measured to be > 62 MPa, which is considered to be satisfactory. The structure of the coating was checked by X‐ray diffraction and IR spectroscopy, and was found to correspond to that of HA. Some cracks were observed in the coating running predominantly vertical to the surface. Whether these are acceptable has to be verified by in vivo experiments. © 1994 John Wiley & Sons, Inc.
Factor XII fragment and kallikrein generation in plasma during incubation with biomaterials
Authors: van der Kamp K. W. H. J. , van Oeveren W.
Published: December 2004

Blood biocompatibility of medical devices is in many ways dependent on surface characteristics and biochemical blood material interactions. In this study, the contact system, in which the activation of factor XII and plasma kallikrein is included, is highlighted. This article describes a simple chromogenic assay to determine the Hageman Factor fragment (HFf, or factor XIIf) and kallikrein activity in vitro. The assay is based on conversion of Z‐Lys‐Phe‐Arg‐pNA. 2HCl to which human factor XIIf and kallikrein appeared to have a high affinity. To discriminate between the serine proteases factor XIIf and kallikrein to cleave this substrate, aprotinin was added to one of two complementary samples. In this in vitro study, standardized disks from glass, high‐density polyethylene (HDPE), polytetrafluoro ethylene (PTFE), and polydimethyl siloxane (PDMS) were studied for their capacity to generate factor XIIf and kallikrein in plasma. Kaolin was used as positive control. On glass disks the highest and on HDPE the lowest generation of factor XIIf and kallikrein were found, both with a ratio of 1 : 1. On PDMS and on PTFE disks protease activities were intermediate, but with a factor XIIf and kallikrein activity ratio of 1 : 2 and 1 : 4, respectively. Apparently because of the hydrophobic surface character of PDMS and PTFE, these surfaces absorb or fail to produce the factor XIIf. This assay appeared to be discriminative even for materials that are considered mild activators of the contact system and can therefore be used as a standard method to qualify biomaterials. NOTE: Factor XIIf(mol wt. 28,000) is designated in the literature as HFf, β‐factor XIIa, or factor XIILMW and factor XIIa (mol wt. 80,000) as HFa, factor XIIaHMW, or α‐factor XIIa. To avoid the unfashionable use of β‐factor XIIa or α‐factor XIIa, we chose in this study the use of factor XIIf and factor XIIa, according to the article by R. A. Pixley et al., Blood, 66, 198–300 (1985). © 1994 John Wiley & Sons, Inc.
Inhibition of platelet spreading from plasma onto glass by an adsorbed layer of a novel fluorescent‐labeled poly(ethylene oxide)/poly(butylene oxide) block copolymer: Characteristics of the exclusion zone probed by means of polystyrene beads and macromolecules
Authors: Gingell D. , Owens N.
Published: December 2004

We have investigated the anti‐adhesive properties of a newly synthesized fluorescent triblock copolymer containing poly(ethylene oxide). This adsorbs from aqueous solution onto glass that has been rendered hydrophobic. When the polymer‐treated surface was exposed to human platelet‐rich plasma (PRP) or whole blood at 37°C, platelet adhesion and spreading were prevented. Avid adhesion and rapid platelet spreading occurred along tracks scraped in the adsorbed polymer coating, as seen by video‐enhanced interference reflection microscopy. Leukocytes from whole blood are eventually able to adhere to the polymer‐treated surface and were seen to remove labeled polymer from their vicinity and accumulate it at the cell body. Interferometry using polystyrene spheres showed that they do not adhere to polymer‐coated glass and are unable to approach closer than 70–95 nm. On scraped tracks, beads make molecular contacts with the glass. Because the fully extended solvated (EO)400 arms may extend up to 100 nm from the glass, this suggests that the polymer forms a monolayer with the hydrophilic arms projecting into the water, whereas the hydrophobic (BO)55 segment binds the molecule to the hydrophobic surface. Another tribloc copolymer with shorter hydrophilic arms allows particles to approach more closely. © 1994 John Wiley & Sons, Inc.
Long‐term in vivo and in vivo aging of a zirconia ceramic used in orthopaedy
Authors: Cales B. , Stefani Y. , Lilley E.
Published: December 2004

A detailed study of a commercial zirconia (Y‐TZP) aged at 37°C held in Ringer's solution or transplanted in animals or humans is reported. No degradation in strength was found for MOR bars or for hip joint heads subjected to stresses caused by pressing titanium alloy trunnions into the head tapers with loads up to 30 kN. Polished specimens also showed no increase in the monoclinic phase percentage upon aging for 1 year. Small specimens transplanted in animals experience no change in the micro‐indentation KIC toughness value, suggesting no degradation. Zirconia heads recovered after 2 years of human implantation showed no loss of strength. The difference between the excellent performances of this ceramic presented here and other studies can be accounted by the microstructural design and quality of the zirconia. © 1994 John Wiley & Sons, Inc.
An ab initio study of the influence of substituents and intramolecular hydrogen bonding on the carbonyl bond length and stretching force constant. I. Monosubstituted carbonyl compounds
Authors: Bock Charles W. , Trachtman Mendel , George Philip
Published: December 2004

The CO bond length and fCO,CO, the corresponding harmonic stretching force constant, are calculated ab initio using the 4‐31G basis set (augmented by polarization functions on the sulfur and chlorine) with full geometry optimization for the monosubstituted carbonyl compounds RCHO, where R = H, CHO, CHCH2, CO2H, CHCHOH, OH, OC(O)OH, OOH, SH, Li, F, Cl, and NH2. Straight‐line relationships are found in plots of ln[fCO,CO] vs. ln[rCO] for the series of compounds in which carbon atoms and oxygen atoms are bonded directly to the carbonyl carbon, in accordance with the empirical expression f = C′/rn. The slopes and intercepts give n = 7.62 and 6.47, C′ = 62.6 and 48.6, for the lines with carbon and oxygen as the atom bonded directly to the carbonyl carbon, respectively. The point for formaldehyde lies very close to the C line, whereas the points for SH, Li, F, Cl, and NH2 lie closer to the O line.
Cavity boundary effects within the onsager theory for dielectrics
Authors: Ehrenson S.
Published: December 2004

Means by which the Onsager theory of dielectrics may be modified in a general way to include important structurally nonspecific electrical effects exercised at or near the cavity boundary are developed and discussed. In essence they rely upon extraction of limiting numerical solutions of the Laplace equation potentials for multiple shells approximating regions of smoothly varying permittivity surrounding the dipole‐containing cavity. The results of several such modifications, which usefully retain the original reaction and cavity field forms, are applied to evaluate the dielectric constants of polar solvents acting as support media for mean‐space‐charge attenuation of intracavity electrical interactions, and in correlation of isolated molecule and condensed phase properties of formally nonassociated solvents. For the most part such predictions and correlations are found to be improved by a wide variety of physically reasonable continuity functions. Where they are not, more rational patterns of deviations consistent with possible modes of intramolecular charge transfer and weak intermolecular association in formally nonassociated liquids are detected. Some limited comparisons with particle‐ and structure‐dependent theories, e.g., the mean spherical model and discrete lattice formulations, also suggest that the present permittivity modifications can effectively simulate important short‐range nonspecific liquid ordering effects. Various factors relating to possible adaption of the limit procedures developed to other inhomogeneous dielectric medium calculations are also briefly outlined.
The electrical nature of CH bonds and its relationship to infrared intensities
Authors: Wiberg Kenneth B. , Wendoloski John J.
Published: December 2004

The charge distributions along the CH bonds of methane, ethylene, and acetylene have been obtained by numerical integration of 6‐31G** wavefunctions. Several criteria for assigning electron populations to carbon and hydrogen lead to negative charge on H for methane and ethylene and a positive charge on H for acetylene. These results are contrasted with the charges derived from the μ obtained from infrared intensity measurements. The difference between the results from infrared intensities and from the electron density calculations has been shown to result from incomplete orbital following in the molecular deformation and the creation of a “bent‐bond” moment. Its magnitude has been estimated.
A systematic preparation of new contracted Gaussian‐type orbital sets. V. From Na through Ca
Authors: Sakai Yoshiko , Tatewaki Hiroshi , Huzinaga Sigeru
Published: December 2004

Minimal compact contracted Gaussian basis sets are constructed for the atoms from Na to Ca. They give satisfactory valence shell orbital energies, although they are minimal‐type basis sets. Split‐type basis sets are also derived from the minimal Gaussian basis sets in order to enhance the flexibility of the basis sets for molecular calculations.
A systematic preparation of new contracted Gaussian‐type orbital sets. VI. Ab initio calculation on molecules containing Na through Cl
Authors: Sakai Yoshiko , Tatewaki Hiroshi , Huzinaga Sigeru
Published: December 2004

Compact contracted Gaussian basis sets introduced in the preceding article are tested for ab initio molecular calculations on molecules containing third‐row atoms (Na through Cl). It is found that the effect of splitting valence orbitals is essential for these molecules and addition of polarization functions to split basis sets can yield computed geometries, spectroscopic constants, and atomization energies in close agreement with the result of near Hartree–Fock calculations.
Li+F− in aqueous solution
Authors: David Carl W. , David Elaine Eisler
Published: December 2004

The energy hypersurface for the system Li(H2O)–F(H2O) is investigated using the polarization model. A possible mechanism for the production of HF in this solution droplet is observed.
A theoretical approach to substituent effects. A comparison of the isoelectronic BH, CH3, and NH groups and their interaction with substituents in disubstituted benzenes
Authors: Kemister Gary , Pross Addy , Radom Leo , Taft Robert W.
Published: December 2004

Ab initio molecular orbital theory with the STO‐3G basis set is used to examine both charge and energy interactions in a series of meta‐ and para‐substituted phenylborate anions and toluenes. Comparison of the results is made with data for substituted anilinium cations. It is concluded that whereas NH is a powerful σ acceptor, with essentially no π interaction, BH is primarily a π donor, and, to a slight extent only, a π donor. CH3 is indicated to be both a weak σ and π donor. Energies of interaction of BH and NH with a series of substituents are an order of magnitude larger than corresponding values for CH3. Interaction energies for BH are of opposite sign to those for NH. The results may be understood qualitatively using perturbation molecular orbital (PMO) theory.
A systematic preparation of new contracted Gaussian‐type orbital sets. VIII. MINI‐1 and MIDI‐1 sets for Ga through Cd
Authors: Sakai Yoshiko , Tatewaki Hiroshi , Huzinaga Sigeru
Published: December 2004

Minimal contracted Gaussian basis sets are presented for Ga through Cd. Characteristically these Gaussian‐based minimal sets give far better d orbital energies than those by minimal STO basis sets. These new basis sets were tested on Br2 for which a new benchmark calculation was also performed. The test result is satisfactory in that these basis sets produce good general agreement with the near Hartree–Fock calculation with respect to the molecular spectroscopic constants.
Pitfalls in the use of the torsion angle driving method for the calculation of conformational interconversions
Authors: Burkert Ulrich , Allinger Norman L.
Published: December 2004

Several deficiencies and potential sources of error in the torsion angle driving method, the approach employed most frequently for the simulation of conformational interconversions, have been studied. A general explanation of the observed effects is given in terms of the energy surface and of the effects brought about by “side valleys.” Several examples of molecular mechanics calculations of conformational interconversions, among them the cyclohexane ring inversion, illustrate the problems.
Calculation of macromolecular force constants
Authors: Putnam B. F. , Van Zandt L. L.
Published: December 2004

Force constant refinement may be carried under a system of constraints imposed on well characterized modes as the refinement proceeds. Resulting stability permits the accurate calculation of many independent macromolecular force constants. A useful formalism for this technique is developed. Prediction of initially poorly characterized modes can emerge from this stability. A brief discussion of currently used refinement schemes has been included. We show that the standard least‐squares procedure is a special case of our present more general method, the former being useful when the molecule is not too large.
Structures of some fluorinated benzenes determined by ab initio computation
Authors: Boggs James E. , Pang Frank , Pulay Péter
Published: December 2004

The structures of fluorobenzene, 1,3‐difluorobenzene, 1,3,5‐trifluorobenzene, 1,2,3‐trifluorobenzene, pentafluorobenzene, and hexafluorobenzene have been determined by the ab initio gradient method with a 4‐21 basis set. Approximate corrections have been developed to yield re and r0 structures so that comparison can be made with the available experimental information. The CF bond distance decreases in a uniform manner with increasing fluorination of the ring, either on adjacent or on meta sites. The ring structure also shows systematic deformation, with a decrease of about 0.01 Å in the CC bond length adjacent to the point of substitution and an increase of about 2.5˚ in the ring angle at the substitution site in those cases where the requirement of ring closure permits.
Mechanisms of conformational chirality inversion in bicyclo[4.2.1]nonan‐9‐one and bicyclo[4.2.2]decane as studied in two‐parametric torsional energy surfaces
Authors: Ōsawa Eiji
Published: December 2004

With the purpose of deciphering conformational inversion processes of typical mobile bicyclic molecules, torsional energy surfaces near the enantiomers of bicyclo[4.2.1]nonan‐9‐one (1) and bicyclo‐[4.2.2]decane (2) were prepared using molecular mechanics with an improved two‐bond drive technique. Inversion of 1 takes place most favorably via a Cs transition state with the tetramethylene chain over the ethano bridge [1B, ΔH± 6.1 (calculated) vs. 6.8 (observed) kcal/mol]. An alternative pathway involving a Cs local energy minimum (1C), in which the tetramethylene chain is bent over the carbonyl, has a barrier 2.4 kcal higher than 1B. The global energy minimum conformation of 2 has boat–chair cyclooctane and twist–boat cyclohexane rings (BCTB), and enantiomerizes into its mirror image (BCTB') via three intermediates: TCTB, CB, and TCTB'. The highest point in the proposed pathway, a saddlepoint CB, is calculated to lie 8.0 kcal/mol above BCTB (observed ΔH± 7.8 kcal/mol). The advantage of the two‐parametric over the one‐parametric torsional energy surface is discussed.
MNDO Calculations of silicon‐containing molecules
Authors: Verwoerd W. S.
Published: December 2004

A comparison is made of MNDO and MINDO/3 calculations for saturated silicon‐containing molecules, and with experimental values, for heats of formation, molecular geometries, charge distributions, and ionization potentials. Except for bond angles, it is found that with the published parameter values the MINDO/3 program gives more reliable results than MNDO. For unsaturated molecules, a comparison of bond lengths and stabilities of Si multiple bonds as given by the two programs and ab initio methods is made, and large discrepancies between predicted structures are pointed out. Some reasons for the dicrepancies are discussed.
Quasi‐one‐dimensional systems and localized defects: Some results of the Green's matrix formalism
Authors: Seel M. , Del Re G. , Ladik J.
Published: December 2004

The application of the self‐consistent field (SCF) local‐impurity formalism to quasi‐one‐dimensional systems is discussed. We describe a general procedure for an accurate numerical determination of the Green's function matrix elements of the unperturbed system. An application to a local impurity in a model chain with two orbitals per unit cell is reported. The changes in the charge‐bond‐order matrix and in local and total density of states due to the impurity are discussed with special emphasis on the changes at the critical points (van Hove singularities) at the band edges. The Green's matrix approach is used to reexamine long‐range Friedel oscillations caused by an impurity in a strictly one‐dimensional metal. The extent of the long‐range tail of the perturbed charge density is in an inverse relation to the localization length of the impurity state: the stronger the perturbation the more localized is the bound state and the more extended are the oscillations in the charge distribution. The results for the model chain with two orbitals per unit cell indicate that the impurity‐induced change in charge distribution may be locally screened by redistribution of the population of the on‐site orbitals, therefore damping possible oscillations and leading to a faster decay than in strictly one‐dimensional systems.
Thermodynamical properties and structural data of radicals calculated by MNDO–UHF
Authors: Bischof P. , Friedrich G.
Published: December 2004

The MNDO–UHF method has been applied to a large number of organic and inorganic radical species. The obtained results demonstrate that thermodynamical data as well as their equilibrium structures are in reasonable agreement with experimental findings.
The structure and acid–base properties of methyl and silyl amines and phosphines: An ab‐initio SCF study
Authors: Glidewell Chistopher , Thomson Colin
Published: December 2004

The structures of the methyl and silyl amines and phosphines and their ions have been calculated using ab‐initio SCF theory and the 3‐21G basis set. The computed structures give excellent agreement with the available experiment data without the inclusion of d functions, with the exception of (SiH3)2N– and the isoelectronic molecules (SiH3)2O and (SiH3)2C2− where d functions are essential. The observed trends in computed basicities and acidities are reproduced by the calculations.
The 6‐31G++ basis set: An economical basis set for correlated wavefunctions
Authors: Nobes Ross H. , Rodwell William R. , Radom Leo
Published: December 2004

The 6‐31G++ basis set is described. This basis set is very similar to the existing 6‐31G** set but is somewhat smaller through the use of five (rather than six) second‐order Gaussians (d functions) and has polarization function exponents optimized for correlated rather than Hartree–Fock wavefunctions. The performance of 6‐31G++ is compared with that of the 6‐31G** and 6‐31G** basis sets through calculation of the geometries and atomization energies for the set of molecules LiH, FH, H2O, NH3, CH4, N2, CO, HCN, and HCCH.
Computational study on the interaction of water with 2‐ and 3‐hydroxypyridine and the corresponding pyridones
Authors: La Manna Gianfranco , Venuti Eduardo
Published: December 2004

SCF–MO–LCAO ab‐initio computations were carried out for the four tautomers 2‐pyridone, 2‐hydroxypyridine, 3‐pyridone, and 3‐hydroxypyridine interacting with a water molecule placed at different positions and orientations around each of them. The computed interaction energies were fitted by an analytical potential consisting of a 6–12 Lennard‐Jones term plus a Coulombic one. The root‐mean‐square deviation of the fit is 2.5 kJ/mol. We report isoenergy contour maps for some important cross sections and obtain a qualitative trend of the solvation entropy, in agreement with available experimental data. The obtained potentials were used for Monte Carlo simulation of four clusters consisting of a tautomer molecule as solute and 50 water molecules, at 300 K. The problem of the transferability of fitting constants is also examined.
Comparison of RHF, NDDO, and MOM molecular one‐electron expectation values calculated using weighted and unweighted STO–NG (ω) basis functions
Authors: Zeiss G. D. , Whitehead M. A.
Published: December 2004

The effect of basis functions on molecular one‐electron property expectation values calculated by approximate methods is examined using weighted and unweighted least‐squares Gaussian‐type orbital function expansions of Slater‐type orbital functions.
Ab initio studies of a proposed mechanism for N‐Nitrosamine formation
Authors: Herzig L. , Sapse A. M. , Snyder G.
Published: December 2004

The geometry of a proposed intermediate (α‐dialkylamino nitrite ester) of N‐nitrosamine synthesis from nitrites is studied by ab initio SCF methods. The energy of a zwitterion is calculated and found to be high.
A fast algorithm for calculation of the distance matrix of a molecule
Authors: Bersohn Malcom
Published: December 2004

A rapid method is described for calculating the number of bonds on the shortest path between each two pairs of atoms of a molecule.
Ground states of molecules. 53.MNDO calculations for molecules containing chlorine
Authors: Dewar Michael J. S. , Rzepa Henry S.
Published: December 2004

MNDO calculations of heats of formation, dipole moments, ionization potentials, and structures are reported for a wide range of compounds containing chlorine in its characteristic valence state (ClI) and one or more of the elements H, B, Be, C, N, O, and F. The calculated errors in the heats of formation and the dipole moments are not significantly greater than those previously reported for compounds containing no chlorine. First vertical ionization potentials were on average 0.95 eV too high. The ordering of higher cationic states was found to be correct, even for species such as Cl2O, Cl2, and HOCl, where ab initio–Koopmans' theorem calculations predict the incorrect ordering. The calculated energies and geometries of compounds such as CIF3 are qualitatively incorrect, probably because of the lack of 3d atomic orbitals in the orbital basis set.
Gaussian basis sets for the fourth‐row main group elements, In–Xe
Authors: Strömberg Ann , Gropen Odd , Wahlgren Ulf
Published: December 2004

Gaussian basis sets, consisting of 15 s‐type, 11 p‐type, and 6 d‐type functions, for the fourth‐row main group elements, In‐Xe, are presented. In order to compare these basis sets with larger ones, calculations have been performed in I2 and TeO2.
Molecular orbital theory of the hydrogen bond. XXX. Water‐cytosine complexes
Authors: Del Bene Janet E.
Published: December 2004

Ab initio SCF and SCF‐CI calculations with the STO‐3G basis set have been performed to investigate the structures and energies of water–cytosine complexes and the intermolecular water–cytosine surface in the cytosine molecular plane. Although there are six nominal hydrogen‐bonding sites in this plane, only three dimers are distinguishable in the ground state. The most stable has an energy of −10.7 kcal/mol, and is found in the N1H and O2 region. An asymmetric cyclic structure in which the water molecule bridges adjacent N1H and O2 sites is the preferred form of this dimer. The dimer in the region between O2 and N4H′ of the amino group is slightly less stable at −10.4 kcal/mol, and also has an asymmetric cyclic structure as the preferred structure, with the water molecule bridging amino N4H′ and N3 hydrogen‐bonding sites. The third dimer has the amino group as the proton donor to water through the hydrogen cis to C5, and a stabilization energy of −7.0 kcal/mol. The water‐cytosine surface is characterized by deeper minima and higher barriers than the water‐thymine surface and by a decreased mobility of the water molecule between adjacent hydrogen‐bonding sites. Absorption of energy by the C2O group leads to the first n → π* excited state in which interactions of water with O2 are broken. The water‐cytosine dimers remain bound in this state, but may change structurally. In the second n → π* state interactions between water and N3 are no longer stabilizing. As a result, the dimer in the O2 and N4H′ region collapses to either a dimer with water the proton donor to O2, or one with N4H′ the proton donor to water. The other two dimers remain bound. All excited dimers are destabilized on vertical excitation relative to the ground state.
Computer‐assisted pseudorotation analysis of five‐membered rings by means of proton spin–spin coupling constants: Program PSEUROT
Authors: De Leeuw Frank A. A. M. , Altona Cornelis
Published: December 2004

A computer method for the calculation of the pseudorotational parameters in five‐membered rings from vicinal proton spin–spin coupling constants is described. Some typical problems met in practice are discussed. Applications of the program in the conformational analysis of some substituted cyclopentanes are presented.
Determination and characterization of a transition structure for water–formaldehyde addition
Authors: Spangler Dale , Williams Ian Henderson , Maggiora Gerald M.
Published: December 2004

Quantum mechanical calculations of the geometric, energetic, electronic, and vibrational features of a transition structure for gas‐phase water–formaldehyde addition (FW1‡) are described, and a new transition‐structure search algorithm is presented. Basis‐set‐dependent effects are assessed by comparisons of computed properties obtained from self‐consistent field (SCF) molecular orbital (MO) calculations with STO‐3G, 4‐31G, and 6‐31G** basis sets in the absence of electron correlation. The results obtained suggest that STO‐3G‐level calculations may be sufficiently reliable for the prediction of the transition structure of FW1‡ and for the transition structures of related carbonyl addition reactions. Moreover, the calculated activation energy for formation of FW1‡ from water and formaldehyde (−44 kcal mol−1) is very similar in all three basis sets. However, the energy of formaldehyde hydration predicted by STO‐3G (˜ −45 kcal mol−1) is about three times larger than that predicted by the other two basis sets, with the activation energy for dihydroxymethane dehydration also being too large in STO‐3G. Calculated force constants in all three basis sets are generally too large, leading to vibrational frequencies that are also too large. However, uniformly scaled force constants (in internal coordinates) give much better agreement with experimental frequencies, scaled 4‐31G force constants being slightly superior to scaled STO‐3G force constants.
Counting of resonance structures for large benzenoid polynuclear hydrocarbons
Authors: Brown R. L.
Published: December 2004

A method is presented for counting the number of resonance structures for large benzenoid polynuclear hydrocarbons. Structure counts for even systems are made and compared with those of the odd systems resulting from the removal of one of the π centers from various points in the even structure. A computer program for performing the calculations is also given.
Ab initio evaluation of absorption and emission transitions for molecular solutes, including separate consideration of orientational and inductive solvent effects
Authors: Bonaccorsi R. , Cimiraglia R. , Tomasi J.
Published: December 2004

An ab initio computation procedure to obtain electronic transition wave numbers in solution is presented and discussed. The continuum description of the bulk solvent is adopted, and solute–solvent interaction is reduced to a closed‐form interaction operator added to the solute Hamiltonian. The resulting Schrödinger equations are solved variationally. No limitations are imposed on the shape of the solvent cavity or on the level of accuracy of the ab initio procedure.
Extended basis CNDO calculations of linear and nonlinear electric susceptibilities of some molecular dianions and carbonions using coupled Hartree–Fock perturbation theory
Authors: Waite J. , Papadopoulos M. G.
Published: December 2004

The results of calculating the average polarizabilities, first and second hyperpolarizabilities and molar Kerr constants of C5H, C6H, 2‐C10H, 2‐C14H, C8H and C8H are reported. The main elements of our computational scheme are McWeeny's coupled Hartree–Fock perturbation theory and an extended basis CNDO wave function. It is shown that the studied anions have nonlinearities within the same order of magnitude as their respective uncharged parent molecules. The Kerr constants of these anions are analyzed and the contribution of the various terms is appraised.
Operator technique for obtaining the recursion formulas of characteristic and matching polynomials as applied to polyhex graphs
Authors: Hosoya Haruo , Ohkami Noriko
Published: December 2004

A simple and efficient method, called an operator technique, for obtaining the recurrence relation of a given counting polynomial, e.g., characteristic PG(x) or matching MG(x) polynomial, for periodic networks is proposed. By using this technique the recurrence relations of the PG(x) and MG(x) polynomials for the linear zigzag‐type and kinked polyacene graphs were obtained. For the lower members of these series of graphs, the coefficients of PG(x) and MG(x) polynomials are tabulated.
Ab initio studies on polymers. VI. Torsional potential in regular polyethylene chains
Authors: Karpfen Alfred , Beyer Anton
Published: December 2004

Ab initio crystal orbital calculations have been performed on regular polyethylene chains applying basis sets of minimal and double‐zeta quality. Relative stabilities of periodic all‐trans, all‐gauche, and alternating trans–gauche conformers have been evaluated, including extensive geometry optimization. Potential curves for a simultaneous rotation around CC single bonds from the all‐trans to the all‐gauche conformation have been computed applying the rigid‐rotor approximation, the flexible‐rotor approximation, and an additional reoptimization of CC distances. A rigid‐rotor potential curve from the all‐trans to the alternating trans‐gauche conformation has been computed as well. Results obtained are compared with ab initio calculations on butane and pentane and with semiempirical and empirical force‐field studies on polyethylene.
MNDO study of catenated sulfur: The molecules and ions S3 to S8
Authors: Baird N. Colin
Published: December 2004

Semiempirical molecular orbital calculations by the MNDO method are reported for sulfur rings and chains S3 through S8, for the corresponding dications, S through S, and for S. The MNDO method seems quite successful in predicting the geometries of neutral catenated sulfur molecules, even the unusual bond‐length alternation and extent of coplanarity in cyclo‐S7. In contrast to hydrocarbon rings, for which its prediction of strain is erratic, MNDO is consistent in its calculated strain energies in small cyclosulfur rings; unfortunately all the strain energies are overestimated by 70%. As a consequence of this error, the method must be considered unreliable in its predictions of structures for the dications S, since many of these ions could potentially exist as strained bicyclic systems. In addition, MNDO appears to have difficulty handling long, partial SS σ bonds, as are found to occur in S. It may be for this reason that MNDO predicts, apparently incorrectly, that the open‐chain isomers of S are more stable than are any of the cyclic forms, at least for S to S. With respect to neutral Sn molecules, however, the MNDO predictions appear more reliable than ab initio molecular orbital (MO) calculations using small basis sets without polarization functions and without configuration interaction (CI). However, MNDO apparently underestimates by about a factor of two the strength of the three‐electron π bonds present in the terminal links of sulfur diradical chains.
On computationally adjusting the Hill equation of adsorption
Authors: Cortés Joaquin , Puschmann Heinrich , Valencia Eliana
Published: December 2004

We discuss the implementation and computational efficiency of one approach to adjusting the Hill equation of adsorption to a set of empirical data, pointing out some aspects that seem to be valid in the general case. The approach consists basically of minimizing squares of deviations of the adsorbed amounts, which are numerically computed in terms of the empirical pressures and the parameters. Hill's equation is dealt with as a prototype of nonlinear equations seldom used by chemists because none of their variables can be set free.
Molecular mechanics assessment of the configurational statistics of polyoxyethylene
Authors: Baldwin D. Theodore , Mattice Wayne L. , Gandour Richard D.
Published: December 2004

Previous investigators have shown that statistical mechanical averages for configuration‐dependent physical properties of long unperturbed polyoxyethylene chains are sensitive to the gauche–trans energy difference for rotation about CC bonds. Agreement between theory and experiment could be obtained only by significant adjustment of this energy away from values predicted by semiempirical conformational energy computations. The present work examines the success of MM2 in evaluating conformational properties of long unperturbed polyoxyethylene chains. Calculations are performed which identify the rotational isomers, and their energies, for the indicated bonds in CH3OCH2CH2OCH2CH2OCH2CH2OCH3. These energies are used to assign statistical weights utilized in the configuration partition function for a rotational isomeric state chain with symmetric threefold interdependent rotations. The customary generator matrix scheme is employed to evaluate the mean‐square unperturbed end‐to‐end distance, mean‐square unperturbed dipole moment, and their temperature coefficients. Contrary to computational schemes employed previously, MM2 is found to provide an estimate of the gauche–trans energy difference for rotation about CC which is in harmony with the known dimensions and dipole moments of the unperturbed polymer. MM2 also provides good estimates for most of the other parameters required in the rotational isomeric state treatment. A notable exception is provided by the gauche–trans energy difference for rotation about the CO bond. This energy difference is overestimated by MM2.
A quantum mechanical study of the equilibrium between 1,4‐ and 1,6‐dialkylcyclooctatetraenes
Authors: Tosi Camillo
Published: December 2004

The equilibrium between three pairs of 1,4‐ and 1,6‐dialkylcyclooctatetraenes was investigated with the two quantum mechanical algorithms, IBMOL and PCILO. PCILO computations reproduce the trend of stability within each pair of isomers obtained earlier by Allinger with molecular mechanics calculations, while IBMOL computations do not. These results not only can be explained in the light of, but also are a confirmation of Allinger's conclusions that the conformational stability is governed by the magnitude of the van der Waals' attraction between the two alkyl groups: The dispersion energy, which is essentially an electron correlation effect, is not accounted for by a method like IBMOL that, albeit ab initio, is based on the Hartree–Fock independent particle model, while it is fairly well reproduced by a method like PCILO that, albeit semiempirical, is based on a configuration interaction approach. Simulation of the full configuration interaction (CI) correction through a suitable dispersion term brings IBMOL results to a good agreement with the molecular mechanics ones.
Ground states of molecules. 67.MNDO Calculations for compounds containing iodine
Authors: Dewar Michael J. S. , Healy Eamonn F. , Stewart James J. P.
Published: December 2004

MNDO has been parametrized for iodine. Since d atomic orbitals (AOS) are not included, the calculations are restricted to II. Heats of formation, molecular geometries, ionization energies, and dipole moments are reproduced with useful accuracy.
Calculation of energies of excited states using MNDO
Authors: Dewar Michael J. S. , Fox Marye Anne , Campbell Kay A. , Chen Chia‐Chung , Friedheim James E. , Holloway Mary K. , Kim Shi Choon , Liescheski Phillip B. , Pakiari Ali M. , Tien Tze‐Pei , Zoebisch Eve G.
Published: December 2004

The energies of the lowest singlet (S1) and triplet (T1) states of 28 molecules have been calculated by the “half‐electron” (MNDO‐HE) and spin‐unrestricted (UMNDO) versions of MNDO. While most of the calculated values are too negative, because of overestimation of the correlation energy in MNDO‐HE and UMNDO, the errors are systematic and depend in an understandable way on the nature of the molecular orbitals (MOS) involved. When appropriate corrections are applied, the calculated energies agree with experiment almost as well as they do for ground states. This justifies the use of MNDO‐HE or UMNDO for studies of excited state processes.