bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermotropic polyesters with non‐linear links
Authors: Griffin Brian P. , Cox Michael K. 
Published: July 2010

AbstractThe use of different linking units to promote liquid crystal behaviour in rigid rod like polyarylates is reviewed. By systematically varying the proportion of non linear, meta, ortho, or bent bisphenol units in one particular series based on chloro‐ 1,4 phenylene: 4,4′ oxydibenzoate/terephthalate, complete series of compositions, extending from liquid crystal through to isotropic behaviour, have been prepared, characterised and compared. Using this data, parallels between thermotropic and lyotropic behaviour are illustrated and used to postulate physical models for the structure of liquid crystalline melts and solids.
X‐Ray and Infrared Investigation of the Supramolecular Structure of PVC
Authors: Biais RéGine , Geny Chuong , Mordini Claude , Carrega Marc 
Published: July 2010

AbstractTwo types of crystalline morphology seem to be present in commercial PVC powder, both related to syndiotactic sequences in Natta orthorhombic cell: (1) ribbon‐like crystats formed during the second stage of the mass‐process and in suspension or by annealing PVC samples above Tg. (2) high melting fringed‐micelles are the main crystalline feature of emulsion type powder and of low‐conversion mass PVC.A second less ordered phase, which does not fit the Natta cell is found also in emulsion powder and in highly strained samples (like fibres).Ribbon‐like crystals and fringed‐micelles influence the i.r. absorption at 604 and 638 cm−1 respectively. 685cm−1 might be related to the low‐order phase, the X‐ray spacing of which is 3.8‐‐4.0 Å along the chain.
Synthesis of Poly(p‐Benzenesulphonamide) Part I. Preparation of Sulphanilic Acid Derivatives for Use as Intermediates
Authors: Contreras Jordi , Jones J. Idris 
Published: July 2010

AbstractIn view of the unique properties of poly (p‐benzamide), particularly as a fibre, the synthesis of the structurally related poly (p‐benzenesulphonamide) has been investigated. This first paper describes the preparation of two groups of possible precursors of the polymer starting with sulphanilic acid. The first group includes N‐sulphinylaniline‐4‐sulphochloride, aniline‐4‐sulphochloride hydrochloride and aniline‐4‐sulphochloride. The key to the synthesis of these intermediates is the conversion of sulphanilic acid to N‐sulphinylaniline‐4‐sulphochloride by reaction with thionyl chloride in the presence of a catalytic amount of dimethyl formamide. For the synthesis of poly (N‐methyl‐benzenesulphonamide), N‐methylsulphanilic acid has been converted into N‐methylaniline‐4‐sulphochloride hydrochloride by treatment with thionyl chloride.Some N‐acetylated sulphanilic acid derivatives, CH3CONH‐C6H4‐SO2X, where XOH, OEt, OC6H5 and Cl, and N‐acetyl‐1‐naphthylamine‐4‐sulphochloride have also been prepared for evaluation as monomers in the synthesis of polysulphonamides by melt polymerisation.
Magnesium complexes incorporated by sulfonate phenoxide ligands as efficient catalysts for ring‐opening polymerization of ε‐caprolactone and trimethylene carbonate
Authors: Chen Po‐Sheng , Liu Yi‐Chang , Lin Chia‐Her , Ko Bao‐Tsan 
Published: July 2010

AbstractTwo novel sulfonate phenol ligands—3,3′‐di‐tert‐butyl‐2′‐hydroxy‐5,5′,6,6′‐tetramethyl‐biphenyl‐2‐yl 4‐X‐benzenesulfonate (XCF3, LCF3‐H, and XOCH3, LOMe‐H)—were prepared through the sulfonylation of 3,3′‐di‐tert‐butyl‐5,5′,6,6′‐tetramethylbiphenyl‐2,2′‐diol with the corresponding 4‐substituted benzenesulfonyl chloride (1 equiv.) in the presence of excess triethylamine. Magnesium (Mg) complexes supported by sulfonate phenoxide ligands were synthesized and characterized structurally. The reaction of MgnBu2 with L‐H (2 equiv.) produces the four‐coordinated monomeric complexes (LCF3)2Mg (1) and (LOMe)2Mg (2). Complexes 1 and 2 are efficient catalysts for the ring‐opening polymerization of ε‐caprolactone (ε‐CL) and trimethylene carbonate (TMC) in the presence of 9‐anthracenemethanol; complex 1 catalyzes the polymerization of ε‐CL and TMC in a controlled manner, yielding polymers with the expected molecular weights and narrow polydispersity indices (PDIs). In ε‐CL polymerization, the activity of complex 1 is greater than that of complex 2, likely because of the greater Lewis acidity of Mg2+ metal caused by the electron‐withdrawing substitute trifluoromethyl (CF3) at the 4‐position of the benzenesulfonate group. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3564–3572, 2010
Steric effects and competitive intra‐ and intermolecular host‐guest complexation between beta‐cyclodextrin and adamantyl substituted poly(acrylate)s in water: A 1H NMR, rheological and preparative study
Authors: Guo Xuhong , Wang Jie , Li Li , Pham Duc‐Truc , Clements Philip , Lincoln Stephen F. , May Bruce L. , Chen Qingchuan , Zheng Li , Prud'homme Robert K. 
Published: July 2010

AbstractA 1H NMR and rheological study of host‐guest complexation interactions between three β‐cyclodextrin and three adamantyl substituted poly(acrylate)s, and also between them and adamantan‐1‐carboxylate and native β‐cyclodextrin, respectively, is reported. A close correllation between molecular level interactions and macroscopic characteristics of polymer networks in aqueous solution exists. It is found that intra‐ and intermolecular host‐guest complexation between the host β‐cyclodextrin and guest adamantyl substituents and the length of the aliphatic tether between them and the poly(acrylate) backbone have important roles. Dominantly, steric effects and competitive intra‐ and intermolecular host‐guest complexation are found to control poly(acrylate) isomeric interstrand linkage in polymer network formation. The preparations of five new 3% randomly substituted poly(acrylate)s are reported. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1818–1825, 2010
Thermodynamic characterization of poly(2,2,3,3,3‐pentafluoropropyl methacrylate)
Authors: Papadopoulou Stella K. , Karapanagiotis Ioannis , Zuburtikudis Ioannis , Panayiotou Costas 
Published: July 2010

AbstractThe thermodynamic characterization of a fluorinated methacrylic homopolymer was conducted by means of inverse gas chromatography (IGC), at infinite dilution. The homopolymer under study, poly(2,2,3,3,3‐pentafluoropropyl methacrylate) (PPFPMA), was synthesized via a free radical polymerization reaction and was characterized by the employment of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and size exclusion chromatography (SEC) techniques. The specific retention volume of 15 solvents, used as probes, was used for the assessment of the Flory–Huggins interaction parameter, the weight fraction activity coefficient, the molar heat, energy and entropy of sorption, the partial heat of mixing of the probes, as well as the solubility parameter of the polymer. The results demonstrate that PPFPMA is insoluble in most organic solvents even at increased temperatures, with the exception of solvents like 2‐Butanone. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1826–1833, 2010
Meconium exposure dependent cell death and apoptosis in human alveolar epithelial cells
Authors: Jeng Mei‐Jy , Soong Wen‐Jue , Lee Yu‐Sheng , Tsao Pei‐Chen , Yang Chia‐Feng , Chiu Shih‐Yun , Tang Ren‐Bin 
Published: July 2010

AbstractAlveolar epithelial cells of neonates are directly exposed to aspirated meconium during meconium aspiration syndrome (MAS). This study was designed to investigate the influence of quantity and time of meconium exposure on the cell viability and caspase activity in type II human alveolar epithelial cells. Human alveolar epithelial cells were incubated with human meconium suspension at different concentrations and for different times. Cell viability and DNA fragmentation were investigated together with caspases activity and the amount of Bcl‐2 protein present. We found that cell viability was significantly lower in cells exposed to a higher concentration of meconium. This was also true for cells exposed to meconium for longer. Significantly higher DNA fragmentation, an approximately two‐ to fivefold increase, was observed in cells that had been exposed to higher (5% and 10%) concentration of meconium compared to those treated with lower (0.1% and 1%) concentrations (P < 0.05). The activity of most apoptotic initiators (caspase 2, 8, 9, 10) and effectors (caspase 3, 6) were found to be significantly higher in cells subject to greater meconium exposure compared to cells with no or minor meconium exposure. The level of Bcl‐2 was also found to be significantly decreased in meconium‐exposed cells (P < 0.05). In conclusion, human meconium would seem to induce direct cell death as well as caspase‐dependent apoptosis in alveolar epithelial cells; the amount and period of exposure to meconium are crucial factors in this process. Thus, removing aspirated meconium should alleviate lung cell damage in neonates and improve the outcome with MAS. Pediatr. Pulmonol. 2010; 45:816–823. © 2010 Wiley‐Liss, Inc.
Solution structure of the cysteine‐rich domain in Fn14, a member of the tumor necrosis factor receptor superfamily
Authors: He Fahu , Dang Weirong , Saito Kohei , Watanabe Satoru , Kobayashi Naohiro , Güntert Peter , Kigawa Takanori , Tanaka Akiko , Muto Yutaka , Yokoyama Shigeyuki 
Published: July 2010

AbstractFn14 is the smallest member of the tumor necrosis factor (TNF) receptor superfamily, and specifically binds to its ligand, TWEAK (TNF‐like weak inducer of apoptosis), which is a member of the TNF superfamily. The receptor‐ligand recognition between Fn14 and TWEAK induces a variety of cellular processes for tissue remodeling and is also involved in the pathogenesis of some human diseases, such as cancer, chronic autoimmune diseases, and acute ischaemic stroke. The extracellular ligand‐binding region of Fn14 is composed of 53 amino acid residues and forms a single, cysteine‐rich domain (CRD). In this study, we determined the solution structure of the Fn14 CRD (Glu28‐Ala70) by heteronuclear NMR, with a 13C‐/15N‐labeled sample. The tertiary structure of the CRD comprises a β‐sheet with two strands, followed by a 310 helix and a C‐terminal α‐helix, and is stabilized by three disulfide bonds connecting Cys36‐Cys49, Cys52‐Cys67, and Cys55‐Cys64. Comparison of the disulfide bond connectivities and the tertiary structures with those of other CRDs revealed that the Fn14 CRD is similar to the fourth CRD of TNF receptor 1 (A1‐C2 module type), but not to the CRD of B‐cell maturation antigen and the second CRD of transmembrane activator and CAML (calcium modulator and cyclophilin ligand) interactor (A1‐D2 module type). This is the first structural report about the A1‐C2 type CRD that could bind to the known target.
Involvement of a carboxylated lysine in UV damage endonuclease
Authors: Meulenbroek Elisabeth M. , Paspaleva Keti , Thomassen Ellen A. J. , Abrahams Jan Pieter , Goosen Nora , Pannu Navraj S. 
Published: July 2010

AbstractUV damage endonuclease is a DNA repair enzyme that can both recognize damage such as UV lesions and introduce a nick directly 5′ to them. Recently, the crystal structure of the enzyme from Thermus thermophilus was solved. In the electron density map of this structure, unexplained density near the active site was observed at the tip of Lys229. Based on this finding, it was proposed that Lys229 is post‐translationally modified. In this article, we give evidence that this modification is a carboxyl group. By combining activity assays and X‐ray crystallography on several point mutants, we show that the carboxyl group assists in metal binding required for catalysis by donating negative charge to the metal‐coordinating residue His231. Moreover, functional and structural analysis of the K229R mutant reveals that if His231 shifts away, an increased activity results on both damaged and undamaged DNA. Taken together, the results show that T. thermophilus ultraviolet damage endonuclease is carboxylated and the modified lysine is required for proper catalysis and preventing increased incision of undamaged DNA.
Carboxylic acid‐modified polyethylene: A novel support for the covalent immobilization of polypeptides for C‐terminal sequencing
Authors: Shenoy Narmada R. , Bailey Jerome M. , Shively John E. 
Published: July 2010

AbstractWe have developed a method for the covalent immobilization of peptides, for the purpose of C‐terminal sequencing, to a novel solid support, carboxylic acid‐modified polyethylene (PE‐COOH) film. The peptides are attached by coupling the N‐terminal amino group to the activated carboxyl groups of the film. Reagents for carboxyl group activation, including 1,3‐dicyclohexylcarbodiimide (DCC), 1,1′‐carbonyldiimidazole (CDI), 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide hydrochloride (EDC), benzotriazol‐1‐yl‐oxy‐tris(dimethylamino)phosphonium hexafluorophosphate (BOP), and 1,3‐diisopropylcarbodiimide (DICD) were compared. The best yields were obtained with DCC for a variety of tested peptides and averaged approximately 50%. The covalent attachment at pH 6.7 of peptides was shown to occur predominantly through the α‐amino group for the peptide, SIGSLAK, which after attachment to the PE‐COOH support permitted the C‐terminal lysine residue to be sequenced in good yield, indicating that the ‐amino group of lysine is not covalently attached. This support offers a number of advantages over other solid supports, such as silica and polyvinylidene difluoride, for C‐terminal sequencing including (1) stability to base and the high temperatures (65 °C) employed for C‐terminal sequencing, (2) wettability with both aqueous and organic solvents, (3) a high capacity (1.6 nmol/mm2) for covalent coupling of polypeptides, and (4) easy divisibility into 1 × 5‐mm pieces for use in our continuous flow reactor (CFR), which is also used for automated N‐terminal sequencing (Shively, J.E., Miller, P., & Ronk, M., 1987, Anal. Biochem. 163, 517–529). Automated C‐terminal sequencing on these supports is described in the companion paper (Bailey, J.M., Shenoy, N.R., Ronk, M., & Shively, J.E., 1992, Protein Sci. 1, 68–80).
Primary structure of a protein isolated from reef shark (Carcharhinus springeri) cartilage that is similar to the mammalian C‐type lectin homolog, tetranectin
Authors: Neame Peter J. , Young Carmen N. , Treep James T. 
Published: July 2010

AbstractDuring the course of characterization of low molecular weight proteins in cartilage, we have isolated a protein from reef shark (Carcharhinus springeri) cartilage that bears a striking resemblance to the tetranectin monomer originally described by Clemmensen et al. (1986, Eur. J. Biochem. 156, 327–333). The protein was isolated by extraction of neural arch cartilage with 4 M guanidine hydrochloride, dialysis of the extract to bring the guanidine to 0.4 M (reassociating proteoglycan aggregates), followed by cesium chloride density gradient removal of the proteoglycans. The amino acid sequence had 166 amino acids and a calculated molecular weight of 18,430. The shark protein was 45% identical to human tetranectin, indicating that it was in the family of mammalian C‐type lectins and that it was likely to be a shark analog of human tetranectin. The function of tetranectin is unknown; it was originally isolated by virtue of its affinity for the kringle‐4 domain of plasminogen. Sequence comparison of human tetranectin and the shark‐derived protein gives clues to potentially important regions of the molecule.
Environment‐specific amino acid substitution tables: Tertiary templates and prediction of protein folds
Authors: Overington John , Donnelly Dan , Johnson Mark S. , Šali Andrej , Blundell Tom L. 
Published: July 2010

AbstractThe local environment of an amino acid in a folded protein determines the acceptability of mutations at that position. In order to characterize and quantify these structural constraints, we have made a comparative analysis of families of homologous proteins. Residues in each structure are classified according to amino acid type, secondary structure, accessibility of the side chain, and existence of hydrogen bonds from the side chain. Analysis of the pattern of observed substitutions as a function of local environment shows that there are distinct patterns, especially for buried polar residues. The substitution data tables are available on diskette with Protein Science. Given the fold of a protein, one is able to predict sequences compatible with the fold (profiles or templates) and potentially to discriminate between a correctly folded and misfolded protein. Conversely, analysis of residue variation across a family of aligned sequences in terms of substitution profiles can allow prediction of secondary structure or tertiary environment.
pH dependence of the reverse reaction catalyzed by phosphofructokinase I from Escherichia coli: Implications for the role of Asp 127
Authors: Auzat Isabelle , Garel Jean‐Renaud 
Published: July 2010

AbstractThe kinetics of the reverse reaction catalyzed by Escherichia coli phosphofructokinase, i.e., the synthesis of ATP and fructose‐6‐phosphate from ADP and fructose‐1,6‐bisphosphate, have been studied at different pH values, from pH 6 to pH 9.2. Hyperbolic saturations of the enzyme are observed for both substrates. The affinity for fructose‐1,6‐bisphosphate decreases with pH following the ionization of a group with a pK of 6.6, whereas the catalytic rate constant and perhaps the affinity for ADP are controlled by the ionization of a group with a pK of 6. Several arguments show that the pK of 6.6 is probably that of the carboxyl group of Asp 127, whereas the pK of 6 is tentatively attributed to the carboxyl group of Asp 103.The pK of 6.6 is assigned to the carboxyl group of Asp 127 in the free enzyme, and a simple model suggests that the same group would have an abnormally high pK, above 9.6, in the complex between phosphofructokinase and fructose‐1,6‐bisphosphate. It is proposed that the large pK shift of more than 3 pH units upon binding of fructose‐1,6‐bisphosphate is due to an electrostatic repulsion that could exist between the 1‐phosphate group and the carboxyl group of Asp 127, which are close to each other in the crystal structure of phosphofructokinase (Shirakihara, Y.&Evans, P.R., 1988, J. Mol. Biol. 204, 973–994). The same interpretation would also explain the much higher affinity of the enzyme for fructose‐1,6‐bisphosphate when Asp 127 is protonated. Because of its pK above 9.6, Asp 127 would be protonated in the complex between phosphofructokinase and fructose‐1,6‐bisphosphate, and could act as a proton donor, in agreement with its catalytic role as a proton acceptor in the forward reaction (Hellinga, H.W.&Evans, P.R., 1987, Nature 327, 437–439).
Substrate polarization by residues in Δ5‐3‐ketosteroid isomerase probed by site‐directed mutagenesis and UV resonance Raman spectroscopy
Authors: Austin Janina C. , Spiro Thomas G. , Kuliopulos Athan , Mildvan Albert S. 
Published: July 2010

AbstractΔ5‐3‐Ketosteroid isomerase (KSI: EC 5.3.3.1) of Pseudomonas testosteroni catalyzes the isomerization of Δ5‐3‐ketosteroids to Δ4‐3‐ketosteroids by the stereospecific transfer of the steroid 4β‐proton to the 6β‐position, using Tyr‐14 as a general acid and Asp‐38 as a base. Ultraviolet resonance Raman (UVRR) spectra have been obtained for the catalytically active double mutant Y55F + Y88F, which retains Tyr‐14 as the only tyrosine residue (referred to as the Y140 mutant), and the Y14F mutant, which has 50,000‐fold lower activity. The UVRR results establish that binding of the product analog and competitive inhibitors 19‐nortestosterone or 4‐fluoro‐19‐nortestosterone to the Y140 mutant does not result in the formation of deprotonated Tyr‐14. The UVRR spectra of the steroid inhibitors show large decreases in the vinyl and carbonyl stretching frequencies on binding to the Y140 enzyme but not on binding to the Y14F enzyme. These changes cannot be mimicked by protonation of the steroids. For 19‐nortestosterone, the vinyl and carbonyl stretching frequencies shift down (with respect to the values in aqueous solution) by 18 and 27 cm−1, respectively, on binding to Y140 KSI. It is proposed that the changes in the steroid resonance Raman spectrum arise from polarization of the enone moiety via the close proximity of the charged Asp‐38 side chain to the vinyl group and the directional hydrogen bond between Tyr‐14 and the 3‐carbonyl oxygen of the steroid enone. The 230‐nm‐excited UVRR spectra do not, however, show changes that are characteristic of strong hydrogen bonding from the tyrosine hydrogen. It is proposed that this hydrogen bonding is compensated by a second hydrogen bond to the Tyr‐14 oxygen from another protein residue.UVRR spectra of the Y140 enzyme obtained using 200 nm excitation show enhancement of the amide II and S Raman bands. The secondary structure of KSI was estimated from the amide II and S intensities and was found to be low in α‐helical structure. The δ‐helix content was estimated to be in the range of 0–25% (i.e., 10 ± 15%).
Yeast ferrochelatase: Expression in a baculovirus system and purification of the expression protein
Authors: Eldridge Marlies G. , Dailey Harry A. 
Published: July 2010

AbstractThe terminal step of the heme biosynthetic pathway is catalyzed by the enzyme ferrochelatase (EC 4.99.1.1). In eukaryotes this enzyme is bound to the inner mitochondrial membrane with its active site facing the matrix side of the membrane. Previously this laboratory has characterized this enzyme via kinetic and protein chemical modification techniques, and with the recent cloning of the enzyme from yeast, mouse, and human sources it now becomes possible to approach structure‐function questions by using site‐directed mutagenesis. Of primary significance to this is the development of an efficient expression vector. This is of particular significance for ferrochelatase, as it is a low‐abundance protein whose DNA coding sequence has a very low codon bias. In the current work we describe the production of yeast ferrochelatase in a baculovirus system. This system is shown to be an excellent one in which to produce large quantities of active ferrochelatase. The expressed enzyme is membrane associated and is not released into the growth medium either during or after virus development and cell lysis. The expressed protein can be purified in a procedure that requires only 1 day and makes use of a Pharmacia Hi Trap blue affinity column. The measured Km's for the substrates mesoporphyrin and iron are the same as those reported previously for the yeast enzyme. To our knowledge this is the first example of a mitochondrial membrane protein that has been expressed in a baculovirus system.
Purified chaperonin 60 (groEL) interacts with the nonnative states of a multitude of Escherichia coli proteins
Authors: Viitanen Paul V. , Gatenby Anthony A. , Lorimer George H. 
Published: July 2010

AbstractIn vitro experiments employing the soluble proteins from Escherichia coli reveal that about half of them, in their unfolded or partially folded states, but not in their native states, can form stable binary complexes with chaperonin 60 (groEL). These complexes can be isolated by gel filtration chromatography and are efficiently discharged upon the addition of Mg · ATP. Binary complex formation is substantially reduced if chaperonin 60 is presaturated with Rubisco‐I, the folding intermediate of Rubisco, but not with native Rubisco. Binary complex formation is also reduced if the transient species that interact with chaperonin 60 are permitted to progress to more stable states. This implies that the structural elements or motifs that are recognized by chaperonin 60 and that are responsible for binary complex formation are only present or accessible in the unfolded states of proteins or in certain intermediates along their respective folding pathways. Given the high‐affinity binding that we have observed in the present study and the normal cellular abundance of chaperonin 60, we suspect that the folding of most proteins in E. coli does not occur in free solution spontaneously, but instead takes place while they are associated with molecular chaperones.