bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Types of Potentially Antimalarial Agents: Epidioxy‐substituted norditerpene and norsesterpenes from the marine sponge Diacarnus levii
Authors: D'Ambrosio Michele , Guerriero Antonio , Deharo Eric , Debitus Cécile , Munoz Victoria , Pietra Francesco 
Published: December 2004

AbstractNatural free carboxylic acids from the hadromerid sponge Diacarnus levii (Kelly‐Borges and Vacelet) were esterified to yield the new cyclic norditerpene peroxides ent‐muqubilin benzyl ester (= (αR,3S,6R)‐α,6‐dimethyl‐6‐[(E)‐4‐methyl‐6‐(2,6,6‐trimethyl‐cyclohex‐1‐en‐1‐yl)hex‐3‐enyl]‐1,2‐dioxan‐3‐acetic acid benzyl ester; 6, diacarnoate B methyl ester(= (αS,3R,6R)‐α,6‐dimethyl‐6‐{2‐(4aS,8aS)‐3,4,4a,5,6,7,8,8a‐octahydro‐3‐oxo‐2,5,5,8a‐tetramethylnaphthalen‐1‐yl)ethyl}‐1,2‐dioxan‐3‐acetic acid methyl ester; 9), and deoxydiacarnoate B benzyl ester (= (αS,3R,6R)‐α,6‐dimethyl‐6‐{2‐[(4aS,8aS)‐3,4,4a,5,6,7,8,8a‐octahydro‐2,5,5,8a‐tetramethyl‐1‐naphthalenyl]ethyl}‐1,2‐dioxan‐3‐acetic acid benzyl ester; 10), which were isolated following extensive chromatography. The relative configuration of the peroxide/α‐methylacetate moiety of 6, 9, and 10, was directly determined from their NMR spectra. The absolute configurations of the peroxide/α‐methylacetate moiety was deduced from comparative 1H‐NMR data of the (S)‐ and (R)‐phenylglycine methyl ester derivatives 7 and 8 as well as 11/13 and 12/14, all obtained from a mixture of the precursors of 3, 6, and 10. The absolute configuration at the carbobicyclic moiety of enone 9 and of 10, is identical, as established by chemical interconversion, 9 and 10 belong to the normal labdane series according to empirical CD rules, applied either directly to 9 or to the parent (+)‐sclareolide‐derived enone 20. In contrast, molar rotation additivity rules suggest the ent‐labdane configuration for 9 and 10. The epidioxides 1–3, 6, and 10 proved active in vitro against the malaria parasite Plasmodium falciparum; especially the previously isolated methyl 3‐epinuapapuanoate (2) was active against a chloroquine‐resistant strain, and this with a good security index.
Minor Coumarins from Calophyllum teysmannii var. inophylloide and Synthesis of Cytotoxic Calanone Derivatives
Authors: Cao Shu‐Geng , Wu Xiao‐Hua , Sim Keng‐Yeow , Tan Benny H. K. , Vittal Jagadese J. , Pereira Joan T. , Goh Swee‐Hock 
Published: December 2004

AbstractA Chemotaxonomic survey for biologically active compounds from Malaysian Calophyllum species led to the findings of the four new benzoylcoumarins 1a, 2, 3, and 4a (including the unusual prenylated 6‐benzoylcoumann 1a), two uncommon coumarins 5 and 6a with a pyran‐4‐one moiety fused at C(6) and C(7), and compounds 7a, 9, and 10, all isolated from the bark of C. teysmannii var. inophylloide. Their structures were determined by spectroscopic analysis and chemical transformations. X‐Ray crystal‐structure determination of 2 provided information on the conformational preferences of substituents in this class of coumarins. The syntheses of the cytotoxic calanone (7a) and of some related coumarins are described.
Nucleosides. Part LXIII. Acetals as new 2′‐O‐protecting functions for the synthesis of oligoribonucleotides: Synthesis of uridine building blocks and evaluation of their relative acid stability
Authors: Matysiak Stefan , Fitznar Hans‐Peter , Schnell Ralf , Pfleiderer Wolfgang 
Published: December 2004

AbstractA broad variety of new acyclic vinyl ethers (see6–41) have been synthesizedviathe vinyl‐interchange reaction of ethyl vinyl ether at room temperature using mercury(II) trifluoroacetate as a highly efficient catalyst. The appropriate vinyl ethers were reacted under acidic conditions with 3′,5′‐O‐silyl‐protected uridine42to the corresponding 2′‐O‐(1‐alkoxyethyl) derivatives43–83which gave, on desilylation of F−ions, in high yields the uridine‐2′‐O‐acetal derivatives84–124. The relative stabilities of the newly synthesized compounds under acidic and basic conditions were determined using TLC and HPLC techniques. Protected protecting groups offer the best properties for oligoribonucleotide syntheses. Interestingly, the very acid‐stable acetals of the β‐substituted ethyl‐type118–121and123can be cleaved by a β‐elimination process providing a series of base‐labile acetals of potential synthetic value.
Bonding mechanism evidence in a ceramic–nonprecious alloy system
Authors: Anusavice K. J. , Ringle R. D. , Fairhurst C. W. 
Published: December 2004

AbstractBonding between porcelain and dental ceramic alloys is thought to be dependent upon the establishment of a continous electron structure across the ceramicmetal interface (Pask, Proc. Procelain Enamel Inst., 33, 1, 1971). Such a structure most likely results from the compatibility of metal ions at the metal surface saturated in an oxide form with the complex oxide structure of the ceramic matrix. Reaction zone compounds are expected to play a prominent role in the strength of the ceramic–metal bonds but thus far none have been detected or identified.The present study was centered on the determination of possible adherence zone compounds in four composite ceramic–metal couples examined by x‐ray energy analysis. Elemental analysis of four couples revealed the presence of a predominant AlCr interaction resulting from the formation of an AlCrO compound or mixed oxide complex. The Cr ions were supplied by the Cr2O3 oxide layer at the metal surface and the Al was provided by the initial bonding‐agent coating.
Degradation rates of oral resorbable implants (polylactates and polyglycolates): Rate modification with changes in PLA/PGA copolymer ratios
Authors: Miller Robert A. , Brady John M. , Cutright Duane E. 
Published: December 2004

AbstractThis study determined the difference in rate of degradation between pure polymers of lactic acid (PLA), glycolic acid (PGA), and various ratios of copolymers of these two substances. Fast‐cured and slow‐cured polyglycolide was compared with copolymers of glycolide/lactide intermixed in ratios of 75:25, 50:50, and 25:75, as well as pure polylactide. A total of 420 rats were implanted with carbon‐14 and tritium‐labeled polymers in bone and soft tissue. At intervals of 1, 2, 3, 5, 7, 9, and 11 months, groups of five animals with the implants in bone and five with the implants in the abdominal wall were sacrificed. The implant area as well as tissue from the liver, spleen, kidney, lung and some muscle tissue was analyzed for radioactivity along with the urine and feces collected throughout the experiment. Half‐lives of the different polymers and copolymers were calculated from the radioactivity present in the implant area for each time interval. Half‐life of the polymers and copolymers decreased from 5 months for 100% PGA to 1 week with 50:50 PGA:PLA copolymer and rapidly increased to 6.1 months for 100% PLA. Fast‐cured PGA had a half‐life in tissue of 0.85 months. No difference in rate of degradation was seen in soft tissue or bone. No significant radioactivity was detected in urine, feces, or tissue samples. From this study, it is concluded that control of degradation rate of the implant could best be attained by varying the composition of PLA and PGA between 75% and 100% PLA along with a corresponding 25% to 0% PGA. This would provide a half‐life range of the implant of from 2 weeks to 6 months.
The appearances of wear on polyethylene—a comparison of in vivo and in vitro wear surfaces
Authors: Rostoker W. , Chao E. Y. S. , Galante J. O. 
Published: December 2004

AbstractAn examination has been made of the wear surfaces of 21 ultra‐high‐molecular‐weight polyethylene components of hip and knee joint prostheses removed from patients. Both light optics and scanning electron microscope systems of examination have been used. The appearances are compared with specimens subjected to two different in vitro wear tests. Surface appearances related to the wear experience have been classified into seven modes. At least four of these are evidences of what may be four different wear mechanisms. Entrapment of bone‐cement particles between articulating surfaces is fundamentally extraneous but is seen to generate the most severe wear. In the absence of bone‐cement particles, in vivo, wear seems to be mild. Wear in vitro produces similar surface modes but with different relative emphasis.
Evaluation of sunlight stability of polyurethane elastomers for maxillofacial use. I
Authors: Chu C. C. , Fischer T. E. 
Published: December 2004

AbstractThe evaluation of the efficiency of polymer additives with special emphasis on uv absorbers and antioxidants in polyurethane elastomers has been completed. Aliphatic polyurethanes were chosen for this study because their properties closely relate to the requirements of maxillofacial prosthesis. The polyurethane elastomers were either synthesized by ourselves or formulated according to the manufacturer's recommendation. Eleven different types of uv absorbers, coupled with one antioxidant, were incorporated into the polyurethane systems. The Atlas twin‐lamp carbon arc Weatherometer was used as the source of uv. The samples were periodically withdrawn for examination of yellowing and tackiness. It was found that, although the incorporation of uv stabilizers enhanced the uv resistance of polyurethanes, the problem of tackiness resulting from uv aging was not solved satiafactorily. The phenomenon of yellowing, however, was significantly improved, mainly due to the aliphatic structure of polyurethanes. The most promising uv absorbers are Tinuvin 770 and the combination of Tinuvin 328, ZnO, and an antioxidant. Their effectiveness in other polyurethane systems is not known and further research is underway to explore this field. Hopefully, these findings will greatly assist the successful application of polyurethane elastomers in maxillofacial prosthesis.
Hydraulic permeability of hollow‐fiber membranes
Authors: Stevenson James F. , Parry John S. , Gupta Krishna M. 
Published: December 2004

AbstractTwo experimental methods have been developed to characterize the pressure‐driven flow of a liquid through the walls of single hollow‐fiber membranes. In one method, the permeation rate is measured directly by following the air–water interface in a pressurized pipet connected to a hollow fiber which is sealed at one end. With the second method, the permeation rate is determined by tracking the descent of an air bubble inside a pressurized hollow fiber sealed at one end. Results obtained by the two experimental methods are in good agreement. Darcy's law is used to analyze the experimental data because the Darcy permeability constant, k, is an intrinsic property of the material. The membrane dimensions and the Darcy permeability constant for reconstituted collagen hollow fibers are shown to be quite sensitive to hydrogen ion concentration and ionic strength. A conceptual link between the Darcy permeability constant and the membrane microstructure is obtained by combining the aligned‐rod structural model for reconstituted collagen proposed by Kramer with a hydrodynamic calculation due to Happel and electrical double‐layer theory. On the average, the predictions of this model for volume fraction solids and microstructure dimensions are in reasonable agreement with experimental observations.
Endothelial cell culture on Dacron fabrics of different configurations
Authors: Eskin S. G. , Trevino L. , Chimoskey J. E. 
Published: December 2004

AbstractThe growth of tissue‐cultured aortic endothelial cells from the calf using 12 different configurations of Dacron polyester (U.S. Catheter and Instrument Co.) as substrates was studied. Scanning electron microscopy showed maximum cell coverage on tightly knit configurations, whereas loose knits and velours did not support cell growth.
Histological evaluation of porous titanium cardiac pacemaker electrode tips
Authors: Hirshorn M. S. , Holley L. K. , Money D. K. , Spector M. , Young F. A. , Hales J. R. S. 
Published: December 2004

AbstractAn investigation of the tissue reaction to five porous titanium alloy pacemaker electrode tips inserted in sheep hearts was made. Attachment of the electrode tips to the endocardial wall was facilitated by fibrous tissue ingrowth into the porous material. Vascularized fibrocollagenous tissue was found within the pores of the tips. One tip was found to be infected. The presence of occasional multinucleated foreign‐body giant cells within the porosity was related to the particulate features of the porous tip. The electrode tips had a reduced sensing impedance compared with conventional solid platinum tips. The present findings are consistent with previous observations relating to porous cobalt‐chromium alloy and porous platinum‐iridium alloy tips and suggest that porous titanium alloy may be a suitable pacemaker electrode tip material.
The interface of permucosal dense apatite ceramic implants in humans
Authors: Denissen H. W. , Veldhuis A. A. H. , Jansen H. W. B. , van den Hooff A. 
Published: December 2004

AbstractDense apatite ceramic implants inserted into fresh extraction sockets of teeth and submerged under full lower dentures may develop permucosal dehiscences because of vertical alveolar ridge resorption. In a 5‐year clinical follow‐up study, 16 out of 81 of such implants showed this dehiscence, offering the opportunity to study histologically the reaction of the mucosal tissue and the alveolar bone to dense apatite ceramic implants in humans. The histologic findings indicate that there is no bonding between mucosa and the permucosal part of the dense apatite ceramic implant under full lower dentures in humans. On the other hand, a very intimate bonding exists between alveolar bone and the dense apatite ceramic material.
Cell responses to biomaterials II: Endothelial cell adhesion and growth on perfluorosulfonic acid
Authors: McAuslan B. R. , Johnson G. , Hannan G. N. , Norris W. D. , Exner T. 
Published: December 2004

AbstractWe report here the use of perfluorosulfonic acid (Nafion) as a substratum for the growth of bovine aortal endothelial cells. This support which can be generated in a number of forms is at least as efficient in maintaining the growth of endothelial and other cell types as tissue culture grade polystyrene (TCP) and represents and advance in this regard over polytetrafluoroethylene (Teflon). The mechanism underlying the different cell attachment capacities of these three polymers is not readily related to their different protein binding patterns. While Nafion adsorbs more total protein from serum than Teflon or TCP, it adsorbs relatively less of the major cell adhesive proteins, vitronectin and fibronectin, than does Teflon. Both Nafion and Teflon had comparable but low thrombogenic potential by in vitro tests. Teflon or expanded Teflon (Gore‐tex) coated with a thin film of Nafion assumes the cell supportive characteristics of Nafion and hence the modification of these surfaces by the induction of a stable bond between Teflon (in various forms) and Nafion may provide a composite vascular graft material which has all the desirable qualities of both materials.
The effect of phase differences on the time‐dependent variation of the zeta potential of hydroxyapatite
Authors: Ducheyne P. , Kim C. S. , Pollack S. R. 
Published: December 2004

AbstractThe osteoconductive nature of calcium phosphate ceramics (CPC) follows from several proven effects, such as a direct bone attachment and enhanced bone tissue formation. Mechanisms leading to these phenomena are still largely undiscovered. Specifically, little is known about the CPC surface and cell‐driven reactions. These atomic and molecular level events are involved in tissue attachment and enhanced tissue formation. It is hypothesized that the zeta potential of these ceramics is directly related to the surface reactivity governing osteoconductivity. As a first step in our analysis, the zeta potential of stoichiometric and Ca‐deficient hydroxyapatite was determined as a function of immersion time. It is concluded that, under the conditions of the experiment, the observations support the hypothesis in a dual way. First, the absolute values of the zeta potential which were measured are related to electrokinetic potentials known to cause substantial effect on the cellular activities and bone tissue formation when applied exogenously. Second, the magnitude and duration of the changes in zeta potential are related to an ion exchange between the hydrated layer around the ceramic and the ceramic surface, and a net precipitation of new material. If these findings could be confirmed in other solutions, i.e., solutions with a substantially equivalent composition as the fluids in developing bone tissue, a basis would be provided to explain the bridging of the ceramic surface with the surrounding developing tissue.
Differences in ceramic–bone interface between surface‐active ceramics and resorbable ceramics: A study by scanning and transmission electron microscopy
Authors: Neo M. , Kotani S. , Fujita Y. , Nakamura T. , Yamamuro T. , Bando Y. , Ohtsuki C. , Kokubo T. 
Published: December 2004

AbstractThe interface between bioactive ceramics and bone was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The materials were apatite‐wollastonite‐containing glass ceramic (A‐W · GC) as a representative surface‐active ceramic, and calcite and p‐tricalcium phosphate (p‐TCP) as resorbable ceramics. Particles of these materials, ranging between about 100 pm and 300 pm in diameter, were implanted into rat tibiae, and specimens were prepared for observation at 8 weeks after implantation. Both SEM and TEM demonstrated that A‐W · GC was bonded t o bone through a thin Ca‐P‐rich layer consisting of fine apatite crystals apparently different from those of bone in shape, size, and orientation. Collagen fibers of the bone reached the surface of this layer, and chemical bonding between A‐W · GC and the bone was speculated. Calcite and p‐ TCP, on the other hand, made direct contact with the bone, and no apatite layer was present at the interface. The surfaces of the implants became rough due to degradation, and bone grew into the finest surface irregularities. However, we were unable to demonstrate any continuity of crystals between the resorbable implants and bone by high‐resolution TEM. Ac‐ cordingly, the bonding strength was considered to be mainly attributable to mechanical interlocking.
Effect of surface processing on the attachment, orientation, and proliferation of human gingival fibroblasts on titanium
Authors: Köunönen M. , Hormia M. , Kivilahti J. , Hautaniemi J. , Thesleff I. 
Published: December 2004

AbstractThe adhesion, orientation, and proliferation of human gingival fibroblasts was studied on electropolished (elpTi), etched etchTi, and sandblasted (sblTi) titanium surfaces. The texture, chemical state, and composition of the titanium surfaces were analyzed using a surface tracing instrument and electron spectroscopy for chemical analysis. Considerable differences were evident in the surface texture and chemical composition of the differently treated titanium plates. Electropolishing produced the smoothest and cleanest surface. Human gingival fibroblasts attached, spread, and proliferated on all titanium surfaces. However, cells on elpTi exhibited an extremely flat morphology and seemed to form cellular bridges with adjacent cells, whereas the etchTi and sblTi surfaces harbored both round and flat cells with many long processes. Cells on elpTi appeared to grow in thick layers with no specific orientation, whereas on etchTi surfaces they were migrating along the parallel, irregular minor grooves caused by mechanical polishing, and on sblTi surfaces they seemed to grow in clusters. Stress‐fiber type actin bundles and vinculin‐containing focal adhesions were present in cells spreading on elpTi and etchTi surfaces but not in cells spreading on sblTi surfaces. Cell shape, orientation, and proliferation appear to depend on the texture of the titanium surface and probably also on the properties of the oxide layer and adjacent bulk material. Our findings suggest that smooth or finely grooved titanium surfaces could be optimal in implants adjacent to soft tissues as they support the attachment and growth of human gingival fibroblasts. © 1992 John Wiley & Sons, Inc.
Toxic effect of ethylene‐oxide‐sterilized freeze‐dried bone allograft on human gingival fibroblasts
Authors: Kudryk Val L. , Scheidt Michael J. , McQuade Michael J. , Sutherland Donald E. , Vandyke Thomas E. , Hollinger Jeffery O. 
Published: December 2004

AbstractFreeze‐dried bone allograft (FDBA) which either had or had not been sterilized by exposure to ethylene oxide (EtO) prior to lyophilization was obtained from two commercial sources. EtO‐sterilized FDBA was reexposed to EtO as a positive control. Gas chromatograph assays revealed that three out of four commercially obtained EtO sterilized FDBA had no detectable EtO, with one sample having 0.21 parts per million (PPM). Surprisingly, 0.24 PPM was detected in one sample which had not been sterilized with EtO gas. This was presumed due to contamination from a gas‐sterilized rubber stopper. In the cell toxicity study, FDBA and human gingival fibroblasts (HGF) were added simultaneously, incubated for 72 h, and fixed and stained. Samples of FDBA sterilized with EtO which were free of EtO did not alter HGF growth. However, the positive control FDBA which contained 0.72 PPM EtO had a deleterious effect on HGF. FDBA with EtO residuals caused morphologic change in HGF. © 1992 John Wiley & Sons, Inc.
Alteration of hydroxylapatite coatings exposed to chemicals used in histological fixation
Authors: Kieswetter K. , Bauer T. W. , Brown S. A. , Van Lente F. , Merritt K. 
Published: December 2004

AbstractHistological evaluation of retrieved devices allows for assessment of the biological response to the implants. Interaction between the biomaterial and the fluids used in the processing may alter the appearance or composition of the device. This may result in artifacts due to processing which are misinterpreted as being caused by the biological response. Alteration by the fluids used in fixation may be particularly important with materials that have a propensity to interact with aqueous environments, as in the case of calcium phosphate ceramics. Therefore, we examined the effects of various standard histological fixation techniques on hydroxylapatite coated metal implants. Of the techniques examined, fixation with ethanol appeared to affect the surface morphology the least, whereas fixation in unbuffered formalin appeared to affect the bulk composition of these samples the least. Fixation in buffered formalin resulted in marked changes in both surface morphology and bulk composition. © 1994 John Wiley & Sons, Inc.
Poloxamer 407 as a bacterial abhesive for hydrogel contact lenses
Authors: Portolés Marta , Refojo Miguel F. , Leong Fee‐Lai 
Published: December 2004

AbstractBacterial adherence and colonization of biomedical prosthetic implants is one of the main causes for implant withdrawal. The abhesive (anti‐adhesive) effect of poloxamer 407 on several Gram‐positive and Gramnegative strains and the site of action of its effect have been investigated. Poloxamer 407 significantly inhibited 92–99% of Pseudomonas aeruginosa adherence to hydrophilic contact lenses (P <.05). This adherence inhibition was concentration‐dependent. A reduction of about 50–60% was obtained for Staphylococcus strains, and 50–70% for Gram‐negative strains other than Pseudomonas. The poloxamer seems to act on the bacteria surface, but not on the contact lens surface. Poloxamer 407 could potentially prevent implant‐related infections and keratitis associated with contact lens wear, by inhibiting bacterial adherence onto the implant or contact lens surface. © 1994 John Wiley & Sons, Inc.