bluuebunny/crossref_metadata_2025_split huggingface dataset:
Second Virial Coefficients for Solutions of Polystyrene Mixtures Obtained With Low‐Angle Laser Light Scattering
Authors: Welzen Theo L. 
Published: July 2010

AbstractLow‐angle laser light scattering measurements were performed on practically binary mixtures of standard polystyrenes dissolved in toluene. Second virial coefficients A2 were obtained as a function of the composition of the mixed polymer. No solid evidence was found for the existence of maxima in A2 vs composition. Existing theories predict a maximum. The possible existence of minima such as reported by Suzuki5 could not be confirmed with the present system.
UV‐induced refractive index modulation of photoreactive polymers bearing N‐acylcarbazole groups
Authors: Griesser T. , Wolfberger A. , Edler M. , Belzik M. , Jakopic G. , Trimmel G. , Kern W. 
Published: July 2010

AbstractIn this study, we report on the synthesis and characterization of photoreactive polymers bearing N‐acetylcarbazole and N‐formylcarbazole groups, respectively. These polymers were easily accessible by polymer analogous acylation of commercially available poly‐(2‐vinylcarbazole). While poly(1‐(2‐vinyl‐9H‐carbazol‐9‐yl)ethanone) (poly‐1) undergoes a partial photochemical Fries rearrangement, poly(2‐vinyl‐9H‐carbazole‐9‐carbaldehyde) (poly‐2) decarbonylates smoothly when exposed to UV irradiation. The difference in reactivity between the two acylated polymers is because of the lower stability of the formyl radical, which is formed in the first stage of this photoreaction. Ellipsometric measurements of thin films showed that the photo‐Fries rearrangement in poly‐1 causes a change in refractive index by Δn = +0.01 at 650 nm. UV illumination of poly‐2 results in a change of the refractive index by Δn = +0.03 at 650 nm, which can be explained by the high yield of the photodecarbonylation of the N‐formylcarbazole groups. Refractive index patterns can be easily realized using lithographic techniques as demonstrated by optical microscopy using a phase contrast set‐up for visualization. Patterned films of poly‐1 and poly‐2 with feature sizes of about 5 μm were obtained with a mask aligner. Photoreactive polymers bearing N‐acylcarbazole groups are of potential interest for optical applications such as waveguides, optical switches, and data storage devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010
Dendronized copolymers functionalized with crown ethers and their reversible modification through host–guest interaction
Authors: Xiong Xingquan , Chen Yongming , Feng Shu , Wang Wei 
Published: July 2010

AbstractCrown ether‐functionalized dendronized copolymers with an alternating structure were synthesized by free radical copolymerization of styrene derivatives pendent with Percec‐type polyether dendron of two generations and maleimide pendent with dibenzo[24]crown‐8 (24C8). Novel dendronized copolymers bearing tremendous host molecular cavities have been characterized by 1H NMR, 13C NMR spectroscopy, static light scattering (SLS), and differential scanning calorimetry (DSC) analysis as well as atomic force microscopy (AFM) techniques. Host–guest interactions between 24C8 units dispersed along the dendronized copolymers and organic ammonium salts of pyrene, anthracene, and phenol have been explored. These molecular recognition processes can be monitored by 1H NMR spectroscopy and fluorescence excitation spectroscopy. These results showed that the supramolecular polymer systems are acid–base controllable, demonstrating that dendronized copolymers may be modified reversibly via host–guest interaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010
Sulfonated polybenzimidazoles: Proton conduction and acid–base crosslinking
Authors: Thomas Owen D. , Peckham Timothy J. , Thanganathan Uma , Yang Yunsong , Holdcroft Steven 
Published: July 2010

AbstractA series of soluble, benzimidazole‐based polymers containing sulfonic acid groups (SuPBI) has been synthesized. SuPBI membranes resist extensive swelling in water but are poor proton conductors. When blended with high ion exchange capacity (IEC) sulfonated poly(ether ether ketone) (SPEEK), a polymer that has high proton conductivity but poor mechanical integrity, ionic crosslinks form reducing the extent of swelling. The effect of sulfonation of PBI on crosslinking in these blends was gauged through comparison with nonsulfonated analogs. Sulfonic acid groups present in SuPBI compensate for acid groups involved in crosslinking, thereby increasing IEC and proton conductivity of the membrane. When water uptake and proton conductivity were compared to the IEC of blends containing either sulfonated or nonsulfonated PBI, no noticeable distinction between PBI types could be made. Comparisons were also made between these blends and pure SPEEK membranes of similar IEC. Blend membranes exhibit slightly lower maximum proton conductivity than pure SPEEK membranes (60 vs. 75 mS cm−1) but had significantly enhanced dimensional stability upon immersion in water, especially at elevated temperature (80 °C). Elevated temperature measurements in humid environments show increased proton conductivity of the SuPBI membranes when compared with SPEEK‐only membranes of similar IEC (c.f. 55 for the blend vs. 42 mS cm−1 for SPEEK at 80 °C, 90% relative humidity). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3640–3650, 2010
Sequential conversion of orthogonally functionalized diblock copolymers based on pentafluorophenyl esters
Authors: Nilles Katja , Theato Patrick 
Published: July 2010

AbstractStatistic and block copolymers exhibiting activated ester side groups were synthesized by reversible addition‐fragmentation chain transfer polymerization in the presence of cumyl dithiobenzoate, benzyl dithiobenzoate, and 4‐cyano‐4‐((thiobenzoyl)sulfanyl)pentanoic acid as chain transfer agents. Pentafluorophenyl methacrylate and pentafluorophenyl 4‐vinylbenzoate were used to enable a sequential functionalization of the obtained copolymers by conversion of the activated esters with different amines. 1H NMR spectroscopy, 19F NMR spectroscopy, and FTIR spectroscopy showed the successful step‐by‐step conversion of the different activated esters by aniline followed by aliphatic amines, thereby realizing a sequential functionalization of block copolymers with just one specific reactive group. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3683–3692, 2010
A description of heterosexual couples' sexual adjustment to androgen deprivation therapy for prostate cancer
Authors: Walker Lauren M. , Robinson John W. 
Published: July 2010

AbstractObjective: It is estimated that 600 000 men are currently living in North America with castrate levels of testosterone as a result of androgen deprivation therapy for prostate cancer. The goal of this study was to explore how patients and their partners adjust to changes associated with androgen deprivation therapy (ADT).Methods: Eighteen couples were interviewed regarding their adjustment to ADT side effects.Results: Three distinct patterns of adjustment were observed. One group of couples had assumed sex to be impossible after commencing ADT, and quickly accepted the loss of sex in exchange for a life extending treatment (four couples). Another group was found to be struggling to either maintain satisfying sex or adapt to the loss of their sexual relationship (five couples). The third group had struggled, but found that they were satisfied with their sexual outcome (nine couples). A subset of these couples successfully adjusted to changes in the man's sexual function and found satisfying ways to be sexually active (five couples).Conclusions: The finding that some couples are able to enjoy satisfying sex, despite castrate levels of testosterone, raised questions about how patients are prepared to undergo ADT and how they are managed. It is possible that both the couples who gave up on sex because they believed that satisfying sex was impossible, and the couples who continued to struggle to adjust, may have faired better if they had known how other couples are able to maintain satisfying sex while the man is androgen‐deprived. Copyright © 2010 John Wiley & Sons, Ltd.
Solution structure of the FCS zinc finger domain of the human polycomb group protein L(3)mbt‐like 2
Authors: Lechtenberg Bernhard C. , Allen Mark D. , Rutherford Trevor J. , Freund Stefan M. V. , Bycroft Mark 
Published: July 2010

AbstractPolycomb group proteins are epigenetic regulators that maintain patterns of gene expression over multiple rounds of cell division. Many of these proteins, including polyhomeotic and the MBT repeat containing proteins SCM and dSfmbt, contain an atypical C2C2 zinc finger with a characteristic phenylalanine–cysteine–serine sequence motif. The reoccurrence of this so‐called FCS zinc finger in a variety of polycomb group proteins suggests that it has an important regulatory function. We have determined the solution structure of the FCS zinc finger of the human dSfmbt homologue L(3)mbt‐like 2 (L3MBTL2). The structure consists of a β‐hairpin followed by an α‐helix. The zinc ligands are situated in the β‐hairpin and at the N‐terminus of the α‐helix an arrangement typical of the treble clef class of zinc fingers. The structure is consistent with the proposal that FCS zinc fingers bind to regulatory RNAs.
The importance of surface loops for stabilizing an eightfold βα barrel protein
Authors: Urfer Roman , Kirschner Kasper 
Published: July 2010

AbstractAn important step in understanding how a protein folds is to determine those regions of the sequence that are critical to both its stability and its folding pathway. We chose phosphoribosyl anthranilate isomerase from Escherichia coli, which is a monomeric representative of the (βα)8 barrel family of proteins, to construct a variant that carries an internal tandem duplication of the fifth βα module. This (βα)9 variant was enzymically active and therefore must have a wild‐type (βα)8 core. It had a choice a priori to fold to three different folding frames, which are distinguished by carrying the duplicated segment as an insert into one out of three different loops. Steady‐state kinetic constants, the fluorescence properties of a crucial tryptophan residue, and limited proteolysis showed that the stable (βα)9 variant carries the insertion between β‐strand 5 and α‐helix 5. This preference can be explained by the important role of loops between α helices and β strands in stabilizing the structure of the enzyme.
Spontaneous degradation of polypeptides at aspartyl and asparaginyl residues: Effects of the solvent dielectric
Authors: Brennan Todd V. , Clarke Steven 
Published: July 2010

AbstractWe have investigated the spontaneous degradation of aspartate and asparagine residues via succinimide intermediates in model peptides in organic co‐solvents. We find that the rate of deamidation at asparagine residues is markedly reduced in solvents of low dielectric strength. Theoretical considerations suggest that this decrease in rate is due to the destabilization of the deprotonated peptide bond nitrogen anion that is the postulated attacking species in succinimide formation. This result suggests that asparagine residues in regions with low dielectric constants, such as the interior of a protein or in a membrane bilayer, are protected from this type of degradation reaction. On the other hand, we found little or no effect on the rate of succinimide‐mediated isomerization of aspartate residues when subjected to the same changes in dielectric constant. In this case, the destabilization of the attacking peptide bond nitrogen anion may be balanced by increased protonation of the aspartyl side chain carboxyl group, a reaction that results in a superior leaving group. Consequently, any protein structure or conformation that would increase the protonation of an aspartate side chain carboxyl group can be expected to render that residue more labile. These results may help explain why particular aspartate residues have been found to degrade in proteins at rates comparable to those of asparagine residues, even though aspartyl‐containing peptides degrade more slowly than corresponding asparaginyl‐containing peptides in aqueous solutions.
Frequency analysis of infrared absorption and vibrational circular dichroism of proteins in D2O solution
Authors: Pancoska Petr , Wang Lijiang , Keiderling Timothy A. 
Published: July 2010

AbstractThe IR absorption frequencies as derived from second derivatives of the Fourier transform IR spectra of the amide I' bands of globular proteins in D2O are compared to those obtained from band fitting of the vibrational circular dichroism (VCD) spectra. The two sets of frequencies are in very good agreement, yielding consistent ranges where amide I' VCD and IR features occur. Use of VCD to complement the IR allows one to add sign information to the frequency information so that features occurring in the overlapping frequency ranges that might arise from different secondary structures can be better discriminated. From this comparison, it is clear that correlation just of the frequency of a given IR transition to secondary structure can lead to a nonunique solution. Different sign patterns were identified for correlated groups of globular proteins in restricted frequency ranges that have been previously assigned to defined secondary structural elements. Hence, different secondary structural elements must contribute band components to a given frequency range.
Bacterial expression and photoaffinity labeling of a pheromone binding protein
Authors: Prestwich Glenn D. 
Published: July 2010

AbstractThe first high‐level production of a binding‐active odorant binding protein is described. The expression cassette polymerase chain reaction was used to generate a DNA fragment encoding the pheromone binding protein (PBP) of the male moth Antheraea polyphemus. Transformation of Escherichia coli cells with a vector containing this construct generated clones which, when induced with isopropyl β‐d‐thiogalactopyranoside, produced the 14‐kDa PBP in both the soluble fraction and in inclusion bodies. Purification of the soluble recombinant PBP by preparative isoelectric focusing and gel filtration gave >95% homogeneous protein, which was immunoreactive with an anti‐PBP antiserum and exhibited specific, pheromone‐displaceable covalent modification by the photoaffinity label [3H]6E, 11Z‐hexadecadienyl diazoacetate. Recombinant PBP was indistinguishable from the insect‐derived PBP, as determined by both native and denaturing gel electrophoresis, immunoreactivity, and photoaffinity labeling properties. Moreover, the insoluble inclusion body protein could be solubilized, refolded, and purified by the same procedures to give a recombinant PBP indistinguishable from the soluble PBP. Proton NMR spectra of the soluble and refolded protein provide further evidence that they possess the same folded structure.
Mapping the surface properties of macromolecules
Authors: Chapman Michael S. 
Published: July 2010

AbstractMethods are presented for the rapid computation of schematic projections of the surfaces of macromolecules, similar to the “roadmaps” used to illustrate the surfaces of viruses (Rossmann, M.G. & Palmenberg, A.C., 1988, Virology 164, 373–382). Several types of projections are described, extending the application of “roadmaps” to the external surfaces of all macromolecules and their interior binding pockets and pores. The surface projections, showing the positions of residues, can be colored, shaded, contoured, and annotated to show physical, sequence, or functional properties such as surface topology, hydrophobicity, or sequence conservation, for example. The automated procedures are useful for surveys of the surface features of proteins sharing similar functional properties.
Prediction of the three‐dimensional structures of the biotinylated domain from yeast pyruvate carboxylase and of the lipoylated H‐protein from the pea leaf glycine cleavage system: A new automated method for the prediction of protein tertiary structure
Authors: Brocklehurst Simon M. , Perham Richard N. 
Published: July 2010

AbstractA new, automated, knowledge‐based method for the construction of three‐dimensional models of proteins is described. Geometric restraints on target structures are calculated from a consideration of homologous template structures and the wider knowledge base of unrelated protein structures. Three‐dimensional structures are calculated from initial partly folded states by high‐temperature molecular dynamics simulations followed by slow cooling of the system (simulated annealing) using nonphysical potentials. Three‐dimensional models for the biotinylated domain from the pyruvate carboxylase of yeast and the lipoylated H‐protein from the glycine cleavage system of pea leaf were constructed, based on the known structures of two lipoylated domains of 2‐oxo acid dehydrogenase multienzyme complexes. Despite their weak sequence similarity, the three proteins are predicted to have similar three‐dimensional structures, representative of a new protein module. Implications for the mechanisms of posttranslational modification of these proteins and their catalytic function are discussed.
Modeling the structure of pyrococcus furiosus rubredoxin by homology to other X‐ray structures
Authors: Wampler John E. , Bradley Elizabeth A. , Adams MICHAEL W.W. , Stewart David E. 
Published: July 2010

AbstractThe three‐dimensional structure of rubredoxin from the hyperthermophilic archaebacterium, Pyrococcus furiosus, has been modeled from the X‐ray crystal structures of three homologous proteins from Clostridium pasteurianum, Desulfovibrio gigas, and Desulfovibrio vulgaris. All three homology models are similar. When comparing the positions of all heavy atoms and essential hydrogen atoms to the recently solved crystal structure (Day, M.W., et al., 1992, Protein Sci. 1, 1494–1507) of the same protein, the homology models differ from the X‐ray structure by 2.09 Å root mean square (RMS). The X‐ray and the zinc‐substituted NMR structures (Blake, P.R., et al., 1992b, Protein Sci. 1, 1508–1521) show a similar level of difference (2.05 Å RMS). On average, the homology models are closer to the X‐ray structure than to the NMR structures (2.09 vs. 2.42 Å RMS).
Investigation of the backbone dynamics of the igg‐binding domain of streptococcal protein g by heteronuclear two‐dimensional 1H‐15N nuclear magnetic resonance spectroscopy
Authors: Barchi Joseph J. , Grasberger Bruce , Gronenborn Angela M. , Clore G. Marius 
Published: July 2010

AbstractThe backbone dynamics of the immunoglobulin‐binding domain (Bl) of streptococcal protein G, uniformly labeled with 15N, have been investigated by two‐dimensional inverse detected heteronuclear 1H‐15N NMR spectroscopy at 500 and 600 MHz. 15N T1, T2, and nuclear Overhauser enhancement data were obtained for all 55 backbone NH vectors of the B1 domain at both field strengths. The overall correlation time obtained from an analysis of the T1/T2 ratios was 3.3 ns at 26 °C. Overall, the B1 domain is a relatively rigid protein, consistent with the fact that over 95% of the residues participate in secondary structure, comprising a four‐stranded sheet arranged in a ‐1, +3x, ‐1 topology, on top of which lies a single helix. Residues in the turns and loops connecting the elements of secondary structure tend to exhibit a higher degree of mobility on the picosecond time scale, as manifested by lower values of the overall order parameter. A number of residues at the ends of the secondary structure elements display two distinct internal motions that are faster than the overall rotational correlation time: one is fast (<20 ps) and lies in the extreme narrowing limit, whereas the other is one to two orders of magnitude slower (1‐3 ns) and lies outside the extreme narrowing limit. the slower motion can be explained by large‐amplitude (20‐40°) jumps in the n‐h vectors between states with well‐defined orientations that are stabilized by hydrogen bonds. in addition, residues in the helix and in the outer β‐strands (particularly β‐strand 2) display a small degree of chemical exchange line broadening, possibly due to a minor rotational motion of the helix relative to the sheet that curls around it.
Structural analysis and localization of the carbohydrate moieties of a soluble human interferonγreceptor produced in baculovirus‐infected insect cells
Authors: Manneberg Michael , Friedlein Arno , Kurth Holger , Lahm Hans‐Werner , Fountoulakis Michael 
Published: July 2010

AbstractA soluble form of the human interferon γ receptor that is required for the identification of interferonγantagonists was expressed in baculovirus‐infected insect cells. The protein carried N‐linked carbohydrate and showed a heterogeneity on denaturing polyacrylamide gels. We investigated the utilization of the potential sites for N‐linked glycosylation and the structure of the carbohydrate moieties of this soluble receptor. Amino acid sequence analysis and ion spray mass spectrometry revealed that of the five potential sites for N‐linked glycosylation, Asn” and Asn69 were always utilized, whereas Asn62 and Asn162 were utilized in approximately one‐third of the protein population. Asn223 was never found to be glycosylated. The soluble receptor was treated with N‐glycosidase F and the oligosaccharides released were analyzed by matrix‐assisted laser desorption mass spectrometry, which showed that the protein carried six types of short carbohydrate chains. The predominant species was a hexasaccharide of molecular mass 1,039, containing a fucose subunit linked to the proximal N‐acetylglucosamine residue.
“Frozen” dynamic dimer model for transmembrane signaling in bacterial chemotaxis receptors
Authors: Kim Sung‐Hou 
Published: July 2010

AbstractThe crystal structures of the ligand binding domain of a bacterial aspartate receptor suggest a simple mechanism for transmembrane signaling by the dimer of the receptor. On ligand binding, one domain rotates with respect to the other, and this rotational motion is proposed to be transmitted through the membrane to the cytoplasmic domains of the receptor.