bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of cold plastic deformation on critical pitting potential of AISI 316 L and 304 L steels in an artificial physiological solution simulating the aggressiveness of the human body
Authors: Cigada A. , Mazza B. , Pedeferri P. , Sinigaglia D.
Published: December 2004

The effect of cold working on critical pitting potential of AISI 316 L and 304 L steels in a buffered physiological solution has been studied. In particular, the importance of deformation degree, orientation of the specimen surface to the deformation direction, and cold working temperature in lowering the critical pitting potential is shown.
Wear of dental amalgam
Authors: Roberts J. C. , Powers J. M. , Craig R. G.
Published: December 2004

The wear of dental amalgam was studied by single‐ and double‐pass sliding and by a silicon carbide abrasion test. A dispersed amalgam showed significantly better resistance to two‐body abrasion than the spherical amalgams tested. The wear of amalgam was determined by resistance to penetration and by a ductile mode of surface failure over the load range studied. Differences in the wear of amalgam and restorative resins and composites are discussed.
An in vitro and in vivo analysis of anodized tantalum capacitive electrodes: Corrosion response, physiology, and histology
Authors: Johnson P. F. , Bernstein J. J. , Hunter G. , Dawson W. W. , Hench L. L.
Published: December 2004

Oxidation–reduction reactions which can destroy high current‐density metalstimulating electrodes are avoided when using capacitive electrodes. The results of in vitro and in vivo testing of anodized, high surface area, sintered tantalum electrodes are presented. The corrosion response of the electrodes is excellent; there is no evidence of dissolution of the electrode. A deposit forms on the surface of the electrodes, but has little effect on the voltage response to constant current stimulation. The physiological and histopathological results indicate the capacitive tantalum electrode to be the safest yet tested.
Evaluation of hip arthroprostheses by means of body environment simulators
Authors: Cappozzo Aurelio , Cini Leopoldo , Pizzoferrato Arturo , Trentani Claudio , Cortesi Sergio Sandrolini
Published: December 2004

Laboratory tests carried out by means of body environment simulators have proved to be very important for the evaluation of endoprostheses potentially useful for implantation. The present paper examines the problems connected with the design of such a simulator. The results obtained with an initial, very primitive simulator concerning the outlines of the phenomena of wear, corrosion, and friction and some wear properties of commercially available hip endoprostheses are presented. From these results, the motivation that led to the design of a more advanced simulator is presented. This latter simulator is also described.
Temperature control of a bone cement by addition of a crystalline monomer
Authors: Lee H. B. , Turner D. T.
Published: December 2004

The peak temperature reached during the polymerization of a bone cement was reduced by addition of solid N‐vinylcarbazole to the powder component. It was also necessary to saturate the liquid component with N‐vinylcarbazole to prevent dissolution from the modified powder component on mixing. It is believed that this technique is generally applicable and opens up the possibility of achieving temperature control of bone cements with choice from a range of crystalline monomers.
Immobilization of urea cycle enzymes. I. Characterization of immobilized carbamoylphosphate synthetase and ornithine carbamoyltransferase
Authors: Miura Yoshiharu , Miyamoto Kazuhisa , Raze J. M. , Urabe Hideaki
Published: December 2004

Carbamoylphosphate synthetase (EC 2.7.2.5) and ornithine carbamoyl‐transferase (EC 2.1.3.3) extracted from frog liver were successfully immobilized on CNBr‐activated Sepharose 4B. The immobilized preparation had a better stability towards heat. The apparent Michaelis constant values for N‐acetyl‐glutamate, ammonia, and ATP were not significantly changed by immobilization.
Immobilization of urea cycle enzymes. II. Characterization of immobilized argininosuccinate synthetase
Authors: Miura Yoshiharu , Miyamoto Kazuhisa , Urabe Hideaki , Nagata Chikako , Hane Yumiko
Published: December 2004

Argininosuccinate synthetase (EC 6.3.4.5) was immobilized on CNBr‐activated Sepharose 4B. Properties of the immobilized enzyme are described and compared with those of the native enzyme. The immobilized enzyme was much more stable than the native enzyme at 37°C. It was further stabilized in the presence of the assay reagents. The optimum pH of the immobilized enzyme shifted towards alkalinity (approximately 0.5 unit). The apparent Michaelis constants measured for the immobilized enzyme were not greatly different from those measured for the native enzyme.

Urea formation from citrulline was confirmed in a continuous column reactor by the coimmobilized argininosuccinate synthetase, argininosuccinate lyase (EC 4.3.2.1), and arginase (EC 3.5.3.1).
Force production and decay rate in Alastik modules
Authors: Varner Robert E. , Buck Douglas L.
Published: December 2004

The production and decay of forces produced by Alastik modules was studied under conditions simulating clinical usage over a time period of 2 hr to 4 weeks. Force decay was moderate and all Kx modules tested produced approximately 1 lb of force at the end of the 4‐week test period. Therefore, from a clinical standpoint, modules need not be changed more frequently than once every 4 weeks.
The effect of antibiotic additions on the mechanical properties of acrylic cement
Authors: Nelson Russell C. , Hoffman Richard O. , Burton Thomas A.
Published: December 2004

Early work on hip prosthesis showed that the metal component would loosen in bone even when screws were used. This practice resulted in the death and resorption of the bone; thus cement was used in orthopedic surgery for firm implantation of prostheses. In recent years antibiotics have been added to the cement as a prophylaxis against infection.

This research investigates the effects of antibiotics on the diametral tensile and compression strength of the cement. Samples made with 2 g of antibiotic per surgical packet of bone cement containing the antibiotics gentamicin, keflin, and a combination of the two were tested. These samples were aged at ambient temperature for periods of 1 day and 1, 2, 8, 13, and over 30 weeks.

A statistical analysis using a two‐way analysis of variance with interaction was conducted. It was concluded that the compression strength was affected by the antibiotic, and not by the aging period, but that there is an antibiotic‐aging period interaction. The tensile strength is not affected by either the antibiotic or the aging period, and there is an antibiotic‐aging period interaction. Current work being conducted will analyze additional factors and interactions.
Adhesive bonding of various materials to hard tooth tissues. X. Initial rates of adsorption of nickel or copper ions on hydroxyapatite surface
Authors: Misra D. N. , Bowen R. L.
Published: December 2004

Initial rates of ion‐exchange adsorption of nickelous or cupric ions with calcium ions on the surface of synthetic hydroxyapatite were studied in aqueous nitrate solutions. A kinetic interpretation has been proposed. The determination of the initial rates is important for a systematic investigation of adhesion of certain properly designe substances that may mediate a chemical bonding between dental resins and “moralanted” calcified tissues.
Interactions of bovine thrombin and plasma albumin with low‐energy surfaces
Authors: Waugh David F. , Lippe Jo Ann , Freund Yvonne R.
Published: December 2004

Surface configurations are vessels fabricated from tubing and plate, films deposited on the surface of vessels, and beads confined in vessels. The average association constant between thrombin and sites on commercial poly(methyl methacrylate) surface (Lucite) is near 4 × 108 liters/mole at 22°C, pH 7.0, and ionic strength 0.15. Depending on Lucite composition, average adsorption U, in molecules/cm2 of apparent solution‐surface interface, ranges from 0.7 to 8.8 × 1011. Analysis based on the assumptions that solution dimensions are preserved, adsorption is random, and surface rearrangement is negligible indicates a paucity of surface sites. Plasma albumin competes with thrombin for surface sites. Attempts to detect, by thrombin adsorption, the presence of free sites at 4.5 × 10−9 M albumin or the displacement of bound albumin indicate an albumin‐site association contrast greater than 1.6 × 109. Cross‐linked poly(methyl acrylate) bead surface has U less than 5 × 1010. In contrast to acrylic resins are silicone gum, polypropylene, and polyisobutylene, for which U ranges from 15 to 20 × 1011. Analysis as above indicates that sites are of frequent occurrence. Material composition suggests that thrombin can interact with nonpolar groups. Further characteristics of low‐energy surfaces are that progressive surface denaturation is small and there is a large variance between nominally equivalent configurations.
Defects in failed stems of hip prostheses
Authors: Rostoker W. , Chao E. Y. S. , Galante J. O.
Published: December 2004

A study has been made of the fractures and associated material from 34 prostheses broken in service. All the fractures appear to be of the fatigue type. Search by me‐tallographic analysis for cracklike generating defects in material near the fracture reveals such conditions as abnormally coarse crystals, large nonmetallic inclusions, large inclusion population, undissolved master alloy particles, abnormal carbide segregation, interdendritic segregation, shrinkage, and gas porosity. Recommendations are made for the choice of metallic alloys for femoral stem application.
Adsorption of plasma proteins on hydrophobic surfaces. III. Serum, plasma, and blood
Authors: Bagnall R. D.
Published: December 2004

Liquid–air and liquid–liquid interfaces were used as models for the liquid‐solid system of plasma proteins and hydrophobic surfaces in the study of adsorption of serum, plasma, and blood onto these surfaces. The interfacial tension is determined for three phases: air, methylene iodide, and isooctane. Curves of interfacial tension versus time for the various systems are given from which a triple‐intersection point, where the protein solution is in equilibrium with each surface, is found. It is shown that albumin, γ‐globulin, and a mixed solution of these at in vivo concentrations behave in characteristic and constant manners at the three interfaces of air, methylene iodide, and isooctane. A range of synthetic surfaces which have constant behavior at equilibrium is deduced and it is concluded that any soft tissue response differences between such surfaces could not be the result of albumin or γ‐globulin.
Interaction of fibroblasts and polymer surfaces: relationship between surface free energy and fibroblast spreading
Authors: van der Valk P. , van Pelt A. W. J. , Busscher H. J. , de Jong H. P. , Wildevuur Ch. R. H. , Arends J.
Published: December 2004

Cell spreading and cell division rates of a transformed line of mouse lung fibroblasts were studied on various polymer surfaces in the presence of serum proteins. The bare polymer surfaces, as well as the protein‐coated surfaces, were characterized by their polar (γ) and dispersion (γ) surface free energies. Cell spreading appeared to be dependent on the polar surface free energy. Cell spreading is low when the γ of the bare surface is lower than 5 erg cm−2; marked spreading occurs when γ is higher than 15 erg cm−2. A similar relationship was found between cell spreading and polarity of the protein‐coated surfaces, although less pronounced than for the bare surfaces. Cell spreading appeared independent of the dispersion surface free energy. Cell division rate was the same on all surfaces tested.
The development of modified denture base materials
Authors: Abou‐Tabl Z. M. , Tidy D. C. , Combe E. C. , Grant A. A.
Published: December 2004

This work has been undertaken in an attempt to develop improved materials for the construction of dentures. In particular, a material was sought that would combine radiopacity with high impact resistance. Eight particulate radiopaque glasses were prepared and incorporated into poly(methyl methacrylate) denture base material, and the properties of the resultant composites were measured. Experiments were also carried out with glass fiber fillers, which were found to increase impact strength. It was shown that the incorporation of both a particulate radiopaque glass and glass fiber, 20% of each, yielded composites with improved properties.
Crosslinked agarose encapsulated sorbents resistant to steam sterilization. Preparation and mechanical properties
Authors: de Koning Henk W. M. , Chamuleau Rob A. F. M. , Bantjes Adriaan
Published: December 2004

The application of agarose in hemoperfusion is hampered by the lack of a suitable sterilization method. A technique has been developed for the crosslinking of agarose encapsulated sorbents by the reaction with 1,3‐dichloro‐2‐propanol (DCP) under strong alkaline conditions. A twofold molar excess of DCP with respect to agarose and an equimolar amount of sodium hydroxide at a concentration of 0.3 mol/L with a reaction time of 1–4 h at 50°C are found to be the optimal conditions. The compressive strength of crosslinked beads is increased by a factor of 4. Agarose capsules are found to degrade by the influence of γ radiation, but are resistant to steam sterilization at 134°C during at least 30 min when crosslinked.
Compressive strength of implanted porous replamineform hydroxyapatite
Authors: Piecuch Joseph F. , Goldberg A. Jon , Shastry Chakrakody V. , Chrzanowski Robert B.
Published: December 2004

Porous replamineform hydroxyapatite is a nontoxic, nonallergenic synthetic ceramic currently under investigation as an implant for restoration of atrophic edentulous ridges. Previous studies have demonstrated its capacity to permit the ingrowth of bone into its pores. Evaluation of the material was carried out to determine its eventual compressive strength following implantation. Bony penetration results in a significant increase in strength, judged to be sufficient for support of dentures.
Influence of blood flow and the effect of protamine on the thromboresistant properties of a covalently bonded heparin surface
Authors: Arnander C. , Olsson P. , Larm O.
Published: December 2004

Polyethylene tubings, 2‐mm inner diameter and the length of 1 m, untreated or furnished with a covalently bonded heparin surface layer, were inserted as arterio‐venous shunts bilaterally in dogs. By compressing the middle part, the initial blood flow was adjusted to 10 or 40 mL/min. The thrombogenecity of the tubings was assessed by the patency of the shunts and by assaying the generation of fibrinopeptide A (FPA) in arterial blood and in blood after its passage through the shunts. In untreated shunts clotting rapidly occurred preceded by high FPA generation in blood passing through the shunts. The blood flow in heparinized shunts remained unchanged throughout the test period. At the low flow rate a certain degree of FPA generation in the shunts occurred. At the high flow rate no changes in FPA levels occurred. The function of the heparin surface is thus flow rate dependent. Systemtic heparinization and subsequent neutralization with protamine or administration of protamine alone did not interfere with the function of the heparin surface.
The effect of glass–ceramic bone implant materials on the in vitro formation of hydroxyapatite
Authors: Blumenthal N. C. , Posner A. S. , Cosma V. , Gross U.
Published: December 2004

The extracts of four glass‐ceramic bone implant materials were investigated for dissolved material, for effects on in vitro formation of hydroxyapatite, and for surface morphology of glass–ceramic particles in scanning electron microscopy. In vitro leaching released substances that affected in vitro formation of hydroxyapatite, i.e., initiation time and growth of crystals. Leaching also changed the surface morphology of the materials. The ability of the materials to bond to bone did not correlate with the inhibition of hydroxyapatite formation by the released substances. Surface morphology and other factors at present not yet known are probably involved in controlling the bonding to bone of these ceramics.
In situ polymerization of a microencapsulating medium round living cells
Authors: Dupuy B. , Gin H. , Baquey C. , Ducassou D.
Published: December 2004

A new process for microencapsulating living cells is described. Pancreatic islet cells in solution in agarose were extruded from a syringe into a paraffin‐oil‐containing medium. A rigid interface around each bead was produced when the agarose gelled. A polymerizable mixture of monomers containing 30% of acrylamide and 1.5% of bisacrylamide was then added to these beads. Polymerization was initiated by a photochemical process using riboflavin as a photosensitizer, which enabled use of oxygenated solutions. As other polymerizations initiated by an oxido‐reduction reaction, this method did not require heating, and could thus be carried out at ambient temperature. The oil phase near the agarose beads effectively prevented any rise in temperature, and also led to formation of an acrylamide concentration gradient in the aqueous phase, which reduced the potential cytotoxicity of the reaction. Radioimmunoassay of insulin liberated from encapsulated islets of Langerhans demonstrated a good viability of the cells.
Enzymatic activity toward poly(L‐lactic acid) implants
Authors: Schakenraad J. M. , Hardonk M. J. , Feijen J. , Molenaar I. , Nieuwenhuis P.
Published: December 2004

Tissue reactions toward biodegradable poly(L‐lactic acid) implants were monitored by studying the activity pattern of seven enzymes as a function of time: alkaline phosphatase, acid phosphatase, α‐naphthyl acetyl esterase, β‐glucuronidase, ATP‐ase, NADH‐reductase, and lactate dehydrogenase. Cell types were identified by their specific enzyme patterns, their morphology and location. Special attention was paid to the enzyme patterns of macrophages, fibroblasts and polymorphonuclear granulocytes (PMNs), being involved in foreign body reactions or inflammatory responses. One day after implantation, an influx of neutrophilic and eosinophilic granulocytes was observed, coinciding with activity of alkaline phosphatase (PMN's) and β‐glucuronidase (eosinophils). From day 3 on, macrophages containing ATP‐ase, acid phosphatase and esterase could be observed. From day 7 on, lactate dehydrogenase, the enzyme normally involved in the conversion of lactic acid, and its coenzyme NADH‐reductase were observed in macrophages and fibroblasts. These two enzymes demonstrated more activity than expected on basis of wound‐healing reactions upon implantation of a nonbiodegradable, inert biomaterial (as, e.g., Teflon). It is concluded that the biodegradable poly (L‐lactic acid) used in these implantation studies is tissue compatible, and evokes a foreign body reaction with minor macrophage and giant cell activity, as observed during this 3‐week implantation period. Most enzyme patterns were simply due to a wound‐healing reaction. The slightly increased levels of LDH and NADH suggest the release of lactic acid from the implant, and thus confirms the biodegradable nature of this polymer.
Effect of vacuum mixing on the mechanical properties of antibiotic‐impregnated polymethylmethacrylate bone cement2
Authors: Askew Michael J. , Kufel Mark F. , Fleissner Paul R. , Gradisar Ivan A. , Salstrom Sara‐Jane , Tan James S.
Published: December 2004

Polymethylmethacrylate bone cement, containing either no added antibiotic, 0.5 g of Vancomycin, 1.0 g of Vancomycin, or 1.0 g of Tobramycin, was mixed either in air or a vacuum chamber. Following storage in a water bath at 37°C for 48 h, the specimens were tested in four‐point bending. The porosity of the specimens was assessed radiographically, and their antibacterial activity was monitored for 21 days. The bending strength of the vacuum mixed specimens containing no antibiotic was 40% greater than that of similar air‐mixed specimens. However, there were no significant differences in the bending strength of either the air‐or vacuum‐mixed specimens when any of the antibiotic dosages were added. The bending modulus of the vacuum‐mixed specimens, containing no antibiotic, was significantly greater than the moduli of all the other specimen groups which did not differ from each other. Vacuum mixing reduced the apparent porosity of the specimens fivefold, and while the addition of antibiotic did not effect porosity of the air‐mixed specimens, that of the vacuum‐mixed specimens was doubled. Although initial rapid decreases were seen, leaching of antibiotic from the cement and antibacterial activity continued through the 21‐day monitoring period.
Biological response to chopped‐carbon‐fiber‐reinforced peek
Authors: Jockisch K. A. , Brown S. A. , Bauer T. W. , Merritt K.
Published: December 2004

Polymer composites are being recognized as important implant materials for fracture fixation plates. The use of a composite material is dependent upon the mechanical properties of the material and its biocompatibility. The primary objective of this project was to evaluate 30% chopped‐carbon‐fiber‐reinforced poly(etherether‐ ketone) (CFRPEEK) as a potential material for use as a fracture fixation plate. A two‐ phase study was conducted. The first phase analyzed the short‐term biocom‐patibility of CFRPEEK through rabbit muscle implant testing. CFRPEEK exhibited a nonspecific foreign body tissue reaction similar to the response observed with ultra‐high‐molecular‐weight polyethylene (UHMWPE). In the second phase, four‐hole CFRPEEK plates were implanted as internal fixation devices for transverse midshaft femoral osteotomies in beagles. The plates were effective in promoting fracture healing. A nonspecific foreign body reaction was observed to the plates and to particulate debris.
Acute nephrotoxicity as an adverse effect after intraperitoneal injection of massive amounts of bioactive ceramic powders in mice and rats
Authors: Kawanabe Keiichi , Yamamuro Takao , Kotani Seiya , Nakamura Takashi
Published: December 2004

Silicon elution from bioactive ceramic powders was measured using an in uitro solubility test, in which the powders were soaked in phosphate buffer solution. Silicon elution was highest in Bioglass (BG), followed by Ceravital (KGS), apatite‐ wollastonite‐containing glass ceramics (A‐W·GC), and hydroxyapatite (HA), respectively. Silicon elutions on this in uitro solubility test were correlated with the rates of rapid death in mice following intraperitoneal injection of each of these bioactive ceramic powders. Histopathological examination of the mice revealed nephropathy, which was considered to be the cause of death. The nephropathy was characterized by epithelial degeneration in the renal tubules and increased silicon content throughout the entire kidney, findings suggesting silicon nephropathy. It is considered that, because a large quantity of silicon eluted from the powder was absorbed from the peritoneum, concentration in the glomerular filtrate and urine increased until silicon polymerization occurred, after which the silicon polymer became deposited in the renal tubules. A single injection of furosemide prevented the acute nephrotoxicity of bioactive ceramic powder.
Platelet adherence and detachment with adsorbed fibrinogen: A flow study with a series of hydroxyethyl methacrylate‐ethyl methacrylate copolymers using video microscopy
Authors: Feuerstein Irwin A. , Glenn McClung W. , Horbett Thomas A.
Published: December 2004

The adhesion and detachment of platelets were studied on glass coatings of a series of copolymers of hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA) with preadsorbed fibrinogen. Observations of the interactions of acridine‐orange‐labeled washed platelets with these surfaces from a flowing (500 s−1 wall shear rate) suspension in Tyrode's solution containing albumin and red cells were made with epifluorescent video microscopy (EVM). In some cases preadsorbed materials were incubated for 24 h, during which little or no loss of protein occurred. Protein surface concentration, by itself, was a poor indicator of expected cell adhesion and morphology. Surface chemistry was a second important factor which must be considered. A third observation is that for the 100% EMA copolymer, 24 h of incubation led to a large reduction in platelet adhesion when compared to the 100% EMA material without incubation. For the 0% and 100% EMA polymers, the percentage of contacting platelets which adhere and detach is greater for the 24‐h incubation cases than for those not incubated. These results led to the conclusion that our most hydrophilic surface favors adhesion with detachment, transient cell contact, over long‐term adhesion, as does incubation of adsorbed protein. A brief discussion is presented of a possible connection between this behavior and platelet consumption in viuo for hydrogels.
Investigation of an organic delivery system for demineralized bone matrix in a delayed‐healing cranial defect model
Authors: Damien Christopher J. , Parsons J. Russell , Prewett Annamarie B. , Rietveld Derk C. , Zimmerman Mark C.
Published: December 2004

The osteogenic potential of demineralized bone matrix (DBM) has been demonstrated in multiple animal models and clinical applications. A particulate form of DBM is generally used to fill defects because it is easily packed into a defect site without operative planning or shaping. One potential disadvantage in the use of a particulate is the migration of particles from the defect site. To stem this, glycerol was added to DBM to improve handling properties. A study was undertaken to compare two forms of DBM with glycerol, with DBM particulate and autograft in a bony defect site. The model chosen consisted of bilateral 8‐mm trephine defects created in the parietal skull of 40 rabbits. Animals were sacrificed at 2 and 8 weeks. Results demonstrated both cartilage and bone induction with the three forms of DBM, with 75–90% of the linear width of the defect filled with new bone by 2 weeks. This was similar to the autograft (86%) and significantly greater than the unfilled defects (26%) at 2 weeks. The addition of glycerol to the DBM did not affect the inductive capacity, and produced a response similar to that of DBM particulate alone or autogenous bone. © 1994 John Wiley & Sons, Inc.
Diffusive and convective solute transport through hemodialysis membranes: A hydrodynamic analysis
Authors: Langsdorf Leah J. , Zydney Andrew L.
Published: December 2004

Recent clinical studies have shown that the overall effectiveness of hemodialysis is determined by both the convective and diffusive transport of a wide range of different molecular weight solutes. In this study, transport data were obtained for vitamin B12 and for polydisperse dextrans with a wide range of molecular weights using flat sheet Cuprophan and AN69 polyacrylonitrile membranes. The flux dependence of the actual sieving coefficient was described using classical membrane transport theory, allowing accurate measurements of both the diffusive and convective contributions to the overall solute transport through the porous structure of these dialysis membranes. Asymptotic membrane sieving coefficients and hindered diffusivities were in good agreement with a hydrodynamic model that accounts for the membrane pore size distribution through an expression for the solute partition coefficient in a random porous medium. This model provides an accurate quantitative description of both solute diffusion and convection through hemodialysis membranes, which is critical for the effective design and operation of hemodialyzers. © 1994 John Wiley & Sons, Inc.
Stabilization of pericardial tissue by dye‐mediated photooxidation
Authors: Moore Mark A. , Bohachevsky Irina K. , Cheung David T. , Boyan Barbara D. , Chen Wen‐Min , Bickers Rhonda R. , McIlroy Brian K.
Published: December 2004

Bovine pericardial tissue was stabilized through a dyemediated photooxidation reaction. Shrink temperature analysis of the stabilized tissue indicated a material with similar properties to untreated pericardial tissue and unlike identical tissue treated with glutaraldehyde. Photooxidized tissue was resistant to extraction when compared with untreated tissue or control tissue treated in the absence of light or dye. Photooxidized tissue was also resistant to enzymatic digestion by pepsin and to chemical digestion by cyanogen bromide (CNBr). In contrast, untreated or control treated tissues were readily digested by these reagents. Reduction of photooxidized tissue with β‐mercaptoethanol prior to CNBr digestion partially restored susceptibility of the tissue to CNBr digestion, indicating the photooxidation of methionine residues. Soluble collagen derived from bovine pericardium was used as a model compound for the photooxidation reaction. Polyacrylamide gel electrophoresis analysis indicated the photooxidative conversion of collagen into higher molecular weight aggregates consistent with intermolecular crosslink formation. Photooxidized tissue was stable to in vivo degradation when compared with control tissue. Results presented here indicate a crosslinked pericardial tissue produced by dye‐mediated photooxidation possessing properties of chemical stability, enzymatic stability, in vivo stability, and biomechanical integrity suitable for use as a biomaterial. © 1994 John Wiley & Sons, Inc.
Fibroblast response to microtextured silicone surfaces: Texture orientation into or out of the surface
Authors: Green Andrew M. , Jansen John A. , van der Waerden J. P. C. M. , Von Recum Andreas F.
Published: December 2004

Previous studies suggested that surface topographic configurations of 1–3 μm influence cellular behavior and tissue response. They did not address which specific aspect of the configurations elicits the cellular response. We therefore investigated the effect of the orientation of several surface configurations. Seven different textures on polydimethyl siloxane (silicone; Dow Corning Silastic®) specimens were used to test the question of whether orientation into (down) or out of the surface (up) affected cellular response to a material. The textures were smooth and photoetched configurations of 2 μm up, 2 μm down, 5 μm up, 5 μm down, 10 μm up, and 10 μm down. The response of cultured fibroblasts on these surfaces was compared with that of a standard tissue culture material, polyethylene terephalate (ThermanoxTM). The cell density was measured over a 12‐day period with the use of a colorimetric assay. The uptake of methylene blue was measured daily and compared as an absorbance in a destaining agent. Cells on the 2 and 5 μm up arrays showed increased rates of proliferation and cell density as compared with their down counterparts. This would indicate that textures of 2 and 5 μm have a significant influence on cell growth, and that the surface with hills has a greater effect than the surface with wells. In contrast, the 10 μm up and 10 μm down arrays did not prove to be statistically different from smooth ones. This indicates that the orientation effect is related to the configuration size and that this configuration size is not viewed differently from smooth silicone by the cells. The presented data are in agreement with results of this laboratory and others that fibroblasts recognize the dimensions of surface configurations and react accordingly. Specifically, they appear to react to the uppermost surface area presented to them, but conclusive data can only be obtained from a study of the focal adhesions. © 1994 John Wiley & Sons, Inc.
CN Stretching frequencies in amide systems
Authors: Randhawa H. S. , Kapoor J. L.
Published: December 2004

The CN stretching frequencies in amides have been predicted satisfactorily by the CNDO/2 method. The large variation in ΔE is explained on the basis of extent of resonance in amides.
Studies in hydrogen bonding: Association in methanol using an empirical potential
Authors: Brink George , Glasser Leslie
Published: December 2004

The empirical potential, EPEN, has been used to establish the structures of isolated hydrogen‐bonded clusters in methanol. The most stable configuration of the dimer is found to have a trans near‐linear form, whereas the most stable forms of the trimer and tetramer are cyclic. Charge interactions in the tetramer make it the most stable, in terms of energy per hydrogen bond, of these three species. These results are in conformity with various types of experiment. Other species of dimer, trimer, and tetramer, corresponding to local energy minima, have also been identified.
Calculation of partition coefficients by the charge density method
Authors: Klopman Gilles , Iroff Linda D.
Published: December 2004

A new method is presented for the calculation of partition coefficients of solutes in water lipid systems. Log P values are calculated based on the charge densities of the atoms as determined by quantum mechanical methods. In this article, the results have been obtained from charge densities calculated by two methods: MINDO/3 and Hückel‐type calculation based primarily on topology. Results are favorably compared with those obtained by fragment analysis.
Studies in hydrogen bonding: Association in ammonia using an empirical potential
Authors: Brink George , Glasser Leslie
Published: December 2004

The empirical potential EPEN/2 has been used to establish the structures of isolated hydrogen‐bonding ammonia clusters. The most stable forms of the dimer have a linear or near‐linear structure. The trimer has a closed structure with zero dipole moment. Two stable tetramer forms were found: one with a closed structure and zero dipole moment in agreement with experimental findings, and one with a pyramidal structure with nonzero dipole moment which may be an artifact of the EPEN/2 potential. The relation of the dimer structures to the limited available experimental information is discussed.
Bicyclo[1.1.0]butadiene (trialene): An experimentally viable molecule?
Authors: Andrade Juan G. , Chandrasekhar Jayaraman , Schleyer Paul Von Ragué
Published: December 2004

Molecular orbital calculations on the C4H2 potential energy surface indicate singlet trialene (1) not only to be thermodynamically unstable, but also to have negligible barriers to interconversion to diacetylene.
Minimal basis study of inner‐shell ionization potentials for molecules containing sulfur: S,S‐Diphenyl‐N‐p‐Tolylsulfonyl‐Sulfilimine
Authors: Theodorakopoulos G. , Kucsman Á. , Kapovits I. , Náray‐Szabó G. , Csizmadia I. G.
Published: December 2004

Ab initio calculations with a minimal (STO‐3G) basis set on a number of sulfur‐containing molecules are used to show that Koopmans' theorem and minimal basis calculations may be a simple but adequate way of obtaining inner‐shell ionization potentials and chemical shifts of large molecules. The x‐ray photoelectron spectrum of (C6H5)2SNSO2C6H4CH3 is discussed with reference to an ab initio SCF minimal basis calculation on the model molecule H2SNSO2H.
Determination of electrical double‐layer parameters for the adsorption of neutral molecules at the electrode–solution interface
Authors: Batana A. , Filho R. C. Rocha , Avaca L. A. , González E. R.
Published: December 2004

The study of the structure of the electrode–solution interface usually involves the measurement of the differential capacity–potential characteristics of the system. In order to obtain the double‐layer parameters from these data, integration and differentiation procedures are required and, for this purpose, the use of computational methods is of great value. Two computer programs have been written for the treatment of data for the adsorption of neutral molecules on electrodes. The programs use the charge density and the electrode potential as the electrical variable, respectively, and, in both cases, the differentiation procedures have been optimized by the use of an adequate numerical function. The advantages of doing a simultaneous analysis on both electrical variables are pointed out.
Three electron bonds. I. The H2SSH radical cation
Authors: Clark Timothy
Published: December 2004

Ab initio molecular orbital calculations are reported for H2S, its radical cation, and the H2SSH radical cation. At the MP2/4‐31G level the SS three‐electron bond is 2.85 Å long, and has a dissociation energy of 31.2 kcal mole−1. The performance of MNDO semiempirical molecular orbital theory is compared with the ab initio results.
Recent computational developments with the self‐consistent electron pairs method and application to the stability of glycine conformers
Authors: Dykstra Clifford E. , Chiles Richard A. , Garrett Michael D.
Published: December 2004

Significant improvements in calculational efficiency and capability with the self‐consistent electron pairs (SCEP) method has resulted from several new computational developments. A new procedure for constructing the important internal Coulomb and exchange operators has substantially reduced the preiteration time. A general scheme for utilizing molecular symmetry has been used to advantage in reducing the number of pair functions and external operators that must be found explicitly at each iteration. A projection operator tool has been implemented and found to be quite effective at minimizing the number of iterations required at some point on a potential energy surface when an SCEP wavefunction exists for some nearby point. These and other improvements in the program construction have yielded sizable reductions in time for some representative test cases, including water and a potential energy curve for formaldehyde. The new SCEP program also performs low‐order perturbation theory treatments and coupled electron pair approximation (CEPA) calculations using the same operator approach. The usefulness of the approach is demonstrated by very large scale calculations on the stability of the two interstellar glycine conformers. These calculations involve the variational treatment of 82,205 symmetry‐adapted singly and doubly substituted configurations involving 225 internal electron pairs.
A reassessment of some restricted Hartree–Fock limit molecular energies and an investigation of the applicability of Ermler and Kern's procedure for their estimation
Authors: George Philip , Trachtman Mendel , Bock Charles W.
Published: December 2004

New estimates of Hartree–Fock limit energies (ERHF) for selected AH and AHn hydrides, diatomic and linear polyatomic molecules have been made utilizing ESCF values recently reported in the literature for HF, N2, CO, NH3, and CH4 which are very close to the respective limits. These new values have been used to investigate the applicability of Ermler and Kern's procedure for estimating ERHF: i.e., a factor f is first evaluated from data for reference molecules, where f = ERHF/ESCF, which is then used with ESCF values for other molecules to obtain their ERHF values. f has been evaluated for three groups of reference moleculesHF, H2O, NH3, CH4, N2, and CO; CH4, C2H2, C2H4, and C2H6; and C2H2, HCN, and N2utilizing ESCF data in the literature for many Gaussian‐type orbital (GTO) basis sets together with some new values calculated at the (9,5,1) to (13,8,2) levels. Trends in the variation of f within each group of reference molecules from one basis set to another, and the trends in f from one group of reference molecules to another, are discussed in detail. To minimize the influence of these effects in an ERHF estimate it is recommended that the f value should be derived from reference molecules which possess a similar combination of structural features, i.e., bonded hydrogen, single, double, or triple bonds, and the number of lone‐pair electrons. Further calculations show that an f value based on data for closed‐shell molecules is not applicable to open‐shell species.
On computation of the topological resonance energy
Authors: Mohar B. , Trinajstić N.
Published: December 2004

The topological resonance energy (TRE) model was introduced independently by the Zagreb Group (in 1975) and by Aihara (in 1976). Several practical obstacles arise in the computation of TRE. Ways to surmount them are pointed out. Descriptions of algorithms, optimizations, and the efficient computer program are presented. Possible numerical instability is discussed.
Ab initio studies of structural features not easily amenable to experiment. 17. The molecular structures of some strained cyclic hydrocarbons and estimates of their strain energies
Authors: Van Alsenoy C. , Scarsdale J. N. , Schäfer Lothar
Published: December 2004

The molecular structures of tricyclohexane, norbornane, quadricyclane, and cubane were completely refined by standard ab initio force relaxation on the 4‐21G level. The results can be used as a basis to interpret some contradictory experimental reports found in the literature and to establish some hitherto unobserved structural trends involving the CC and CH bond distances of the cases studied. Group Delta;E values for C(H)3(C), C(H)2(C)2, and C(H)(C)3 (Benson's notation) derived from the total energies of the completely relaxed 4‐21G geometries of a number of unstrained hydrocarbons are also listed. The values are used to estimate the strain energies of the systems studied and of the optimized 4‐21G geometries of cyclopropane, cyclobutane, cyclohexane, and bicyclo (2.1.0)pentane. Cooperative effects in the strain energies are discussed.
An Ab initio study on the conformations of protonated, neutral, and deprotonated amidine
Authors: Zielinski Theresa Julia , Peterson Michael R. , Csizmadia Imre G. , Rein Robert
Published: December 2004

Ab initio SCF molecular orbital calculations have been performed to ascertain the conformational preferences of protonated, neutral, and deprotonated amidine [HC(NH)NH2], using the 3‐21G split valence basis set. The states of eight stable species, eight transition states, and four higher‐order saddle points have been determined by complete geometry optimization utilizing analytic energy gradient techniques. Protonation at the amidine NH is preferred over the –NH2 site by 37.1 kcal/mol. Neutral amidine has rotational barriers of 9.6 and 11.7 kcal/mol for the HNCN cis and trans isomers, respectively, while all the stable HC(NH2)2+ and HC(NH)2− species possess torsional barriers larger than 23 kcal/mol. There is, however, essentially free C—N single‐bond rotation in HC(NH)NH3+, the calculated barriers being 0.7 and 1.8 kcal/mol for the cis and trans HNCN isomers, respectively.
Computer generation of nuclear spin species and nuclear spin statistical weights
Authors: Balasubramanian K.
Published: December 2004

This article develops computer programs for computer generation of nuclear spin species and nuclear spin statistical weights of rovibronic levels. The programs developed here generate nuclear spin species and statistical weights from the group structures known as generalized character cycle indices (GCCIs) which are computed easily from the character table of the PI group of the molecule under consideration. Procedures are illustrated with examples.
The conformation of malformin A
Authors: Hall David , Lyons Paul John , Pavitt Nicola , Trezise John A.
Published: December 2004

The conformation of the cyclic pentapeptide malformin A has been deduced by systematically generating possible models for the molecule, and minimizing the conformation energy of each. Only one of the low‐energy solutions is fully consistent with the reported CD and NMR spectra, and this is the proposed model. The disulfide ring linking adjacent cystine residues is highly strained, as has been predicted from the SS vibration frequency. The conformation of the backbone, but not that of the disulfide ring, is similar to a model previously proposed.
Graph theoretical classification and coding of chemical reactions with a linear mechanism
Authors: Bonchev D. , Kamenski D. , Temkin O. N.
Published: December 2004

Linear mechanisms of catalytic and noncatalytic chemical reactions which are theoretically feasible have been classified and coded using a detailed procedure for the unique numbering of cycles, edges, and vertices in the kinetic graphs. The following classification criteria are used in a hierarchical order: number of cycles and vertices, mutual connectivity of the cycles, manner of linking any pair of cycles, number of elements linking two cycles, mutual position of two cycles joined to a third one, orientation of edges, and presence of pendant vertices. All the types and classes of mechanisms are presented for reactions having up to five and four routes, respectively.
A quantum mechanical test of diophantine methods
Authors: Burdick S. A.
Published: December 2004

A blend of Haselgrove's method and the biased selection method for evaluating multidimensional integrals was tested. The results were mixed. The error estimate varied from being proportional to 1/N when N was less than ca. 60,000 to being proportional to 1/√N when N was greater than 60,000. Also, for N greater than 60,000, the error estimate was one‐half the error estimate given by biased selection alone. These numbers should be compared with the 10,000 points used to find an optimum set of Haselgrove's parameters. It is reasonable to expect that if 100,000 points were used in the optimization of Haselgrove's parameters that the above results would be found with 60,000 replaced by 600,000.
Spherically symmetric axial Gaussian lobe 3d and 4f orbitals
Authors: Shillady Donald D. , Talley David B.
Published: December 2004

The axial Gaussian lobe orbital (AGLO) representations of 3d and 4f orbitals proposed by LeRouzo and Silvi have been angularly optimized to ensure spherical symmetry of filled 3d and 4f shells. The functions have been tested on the hydrogen atom in the presence of high quality s and p basis sets and found to provide excellent minimal Gaussian representations of polarization functions. Exact orbital degeneracy is not obtained within each shell, however. Tabulated values are given to allow arbitrary scaling of the 3d and 4f lobe mimic orbitals.
Koopmans' defects in metal group VIII carbonyls—a many‐body approach
Authors: Böhm Michael C. , Gleiter Rolf
Published: December 2004

The ionization potentials of iron pentacarbonyl (1), ethylene–iron tetracarbonyl (2), cobalt tetracarbonylhydride (3), and nickel tetracarbonyl (4) have been calculated using a Green's function perturbation method based on the INDO approximation. It is shown that the deviations from Koopmans' theorem are largest in the Co complex, while the smallest reorganization energies of strongly localized MOs with predominant metal 3d character are found in the Fe carbonyls 1 and 2. The calculated Koopmans' defects are analyzed by an investigation of the relaxation terms of the self‐energy part and are compared with previous INDO results for Cr, Mn, and Fe tricarbonyl derivatives. Additionally, orbital energies, bond indices, and net charges for the ground states of 1–4 are calculated and compared with experimental data.
MINDO/3 Calculation of carbocation heats of formation
Authors: Harris J. Milton , Shafer Steven G. , Worley S. D.
Published: December 2004

Heats of formation calculated by MINDO/3 are reported for 42 carbocations for which experimental heats of formation have been published. Errors associated with these calculations can be large, with an overall range of ±13 kcal/mol. Correction of systematic errors in the MINDO/3 calculations by means of hydrocarbon models and isodesmic relationships results in a reduction in the range of errors to ±8 kcal/mol. Comparison with experimental heats of reaction of hydride transfer equilibria minimizes experimental errors and gives an average absolute error of 2 kcal/mol with a range of ±3 kcal/mol.