An infra-red spectroscopic study of molecular orientation and conformational changes in poly(ethylene terephthalate)

Polarized infra-red (i.r.) spectroscopy has been used to study the changes in molecular orientation and conformation which occur on drawing poly(ethylene terephthalate) sheets. The i.r. data provided orientation functions 〈P₂(θ)〉_ir where θ is the angle between the molecular chain axis and the draw direction for these uniaxially oriented sheets. Excellent agreement was obtained between the i.r. orientation functions for absorption bands associated with benzene ring mode vibrations, and orientation functions obtained from optical birefringence. Infra-red orientation functions for absorption bands associated with the trans and gauche conformations of the glycol residue, were then combined with i.r. estimates of the trans/gauche concentrations to examine the changes occurring in drawing. For drawing at 80°C up to a draw ratio of about 3·5, there was good agreement with expectations based on the deformation of a rubberlike network.     

Ligand-induced conformational changes in wild-type and mutant yeast pyruvate kinase

A mutant form of pyruvate kinase in which serine 384 has beenmutated to proline has been engineered in the yeast Saccharomycescerevisiae. Residue 384 is located in a helix in a subunit interfaceof the tetrameric enzyme, and the mutation was anticipated toalter the conformation of the helix and hence destabilize theinterface. Previous results indicate that the mutant favoursthe T quarternary conformation over the R conformation, andthis is confirmed by the results presented here. Addition ofphosphoenol-pyruvate (PEP), ADP and fructose-1,6-bisphosphate(Fru 1,6-P₂) singly to the wild-type and mutant enzymes resultsin a significant quenching of tryptophan fluorescence (12–44%),and for Fru-1,6-P₂, a red shift of 15 nm in the emission maximum.Fluorescence titration experiments showed that PEP, ADP andFru-1,6-P₂ induce conformations which have similar ligand-bindingproperties in the wild-type and mutant enzymes. However, theFru-1,6-P₂ induced conformation is demonstrably different fromthose induced by either ADP or PEP. The enzymes differ in theirsusceptibility to trypsin digestion and N-ethylmaleimide inhibition.The thermal stability of the enzyme is unaltered by the mutantion.Far-UV CD spectra show that both enzymes adopt a similar overallsencondary structure in solution. Taken together, the resultssuggest that the Ser384-Pro mutaion causes the enzyme to adopta diffenrent tertiary and/or quaternary structure from the wild-typeenzyme and affects the type and extent of the conformationalchanges induced in the enzyme upon ligand binding. A simplifiedminimal reaction mechanism is proposed in which the R and Tstates differ in both affinity and K_cat. Thus, in terms of themodels of cooperativity and allsoteric interaction, pyruvatekinase is both a K and a V system.     

Structure of operating domains of loop reactors

A loop reactor (LR), composed as an N-unit loop with step-wise shifted inlet and outlet ports, is one of suggested technological solutions for low-concentration volatile organic compounds (VOC) combustion. Such a scheme ensures a sufficiently high temperature with autothermal behavior and nearly uniform catalytic utilization. The main drawback of the LR is a very narrow window of switching velocities that sustain a stable “frozen” solution that exists if the switching and the pulse velocity are synchronized. In the present work we show the existence of many “finger”-like domains of complex frequency-locked solutions that allow to significantly extend the operation domain, rendering the LR scheme more attractive for practical implementation. A brief comparison with the other heat recuperation technologies (reverse flow and circular loop reactors) is presented. © 2008 American Institute of Chemical Engineers AIChE J, 2008     

Folding and conformational studies on SCR1-3 domains of human complement receptor 1

Short consensus repeats SCR3 and SCR1-3 are soluble recombinantproteins, consisting of the third and first three N-terminaldomains of complement receptor 1, respectively, which retainsome anti-complement activity. The conformational stabilitiesand folding/unfolding of SCR3 and SCR1-3 have been studied usingcircular dichroism and equilibrium and pre-equilibrium fluorescencespectroscopy. Denaturation by guanidinium hydrochloride (GdnHCl)is rapid and completely reversible. Reduction of disulphidebridges in the folded proteins by ß-mercaptoethanolleads to an increase in fluorescence intensity. The fluorescenceintensity of the folded proteins is {small tilde}7.5% of thatof the respective unfolded proteins. The data can be approximatedto a two-state transition between native and denatured formsof the proteins. SCR3 has a conformational stability in waterof 12–13 kJ/mol whereas that of SCR1-3 is 19.5–19.9kJ/mol depending upon the technique utilized. The heat capacitychange associated with the unfolding of SCR1-3 was obtainedby a series of GdnHCl unfolding experiments over a range oftemperatures and was found to be 6.6 kJ/K.mol or 33.8 J/K.mol_residue.The refolding process of SCR3 was found to be simple, describedby a single exponential equation, whereas that of SCR1-3 wasfound to be complex and could be fitted to a double exponentialequation indicating the presence of folding intermediates.     

Influence of laboratory ware related changes in conformational and mechanical properties of collagen

Enzyme‐treated acid‐solubilized bovine collagen (ESBC Type I) prepared in laboratory‐grade glass and polypropylene ware under identical conditions have shown different conformational and mechanical properties. Circular dichroism (CD) studies on ESBC have shown higher triple‐helical contents in polypropylene laboratory‐grade ware compared to laboratory ware of glass. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetric (DSC) studies have supported the conformational changes performed on both preparations. Both preparations, in membrane form, were evaluated for their mechanical properties—viz., shrinkage temperature (St), dissolution temperature (Dt), and tensile strength (Ts). The collagen membrane of ESBC prepared in polypropylene showed significantly higher values compared to glass ones. No difference was seen in shrinkage temperature data of the two membranes. Reduced viscosity of ESBC was also measured for both preparations, and it had a significantly higher value in polypropylene ware compared to ESBC prepared in glassware. We postulate that the presence of silicate ions (SiO₃^?2) in glassware has a role in all these changes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2186–2192, 2003     

水溶性醇类对溶菌酶空间结构和折叠过程的影响

利用多角度激光光散射仪和圆二色谱仪研究小分子水溶性一元醇和多元醇对溶菌酶分子的稳定性以及对变性溶菌酶的空间构象和折叠复性的影响.发现在一元醇和二元醇溶液中溶菌酶分子的稳定性均随着醇浓度的增大而提高,而变性酶分子在醇溶液中形成过多的α螺旋和β折叠等二级结构不利于酶的折叠复性;只有较低浓度的多元醇和甲醇有辅助变性溶菌酶复性的作用,其中10％甲醇、20％甘油和30％乙二醇有利于促进酶的复性.     

Fusion peptides and transmembrane domains of fusion proteins are characterized by different but specific structural properties

Membrane fusion is essential for many biological processes. Though there have been many structure and fusion studies of cellular and viral fusion proteins in the last years, their functional mechanism remains elusive. In particular, the structural modes of operation of the transmembrane domains and viral fusion peptides of fusion proteins during membrane fusion have not been elucidated, although work on de novo designed fusogenic peptides suggested that conformational flexibility was necessary. In addition, the use of different and incompatible measurement criteria has made a comparative overview difficult. Here, we report a systematic structural analysis of viral fusion peptides from different fusion protein classes and transmembrane domains of viral and cellular fusion proteins by using circular dichroism spectroscopy. The data that were obtained demonstrate that class I viral fusion peptides show a structural flexibility between helix and irregular secondary structures, whereas fusion peptides of class II viral fusion proteins are characterized by a stable random coil and turn structure. Thus, conformational flexibility does not seem to be a universal criterion for the fusion activity of a fusion peptide. On the contrary, the transmembrane domains of fusion proteins are distinguished by a structural flexibility between helix and sheet structure that is similar to de novo designed unnatural peptides with high fusion activities (M. W. Hofmann et al. PNAS 2004, 101, 14 776-14 781). Thus, the conformational behavior of the fusogenic unnatural peptides most closely resembles that of fusion protein transmembrane domains, and allows them to be used to gain a deeper understanding of the membrane fusion process.     

Infrared spectroscopy study on crystalline and conformational changes in solution-cast syndiotactic polystyrene

Fourier transform infrared (FT-IR) analysis was used to investigate the conformation and the effects on crystals in syndiotactic polystyrene (sPS) subjected to different solvent and/or thermal treatments. It was found that the original helical conformation in sPS cast from a solution of 1,1,2,2-tetrachloroethane could transform to an all-traps planar conformation as the sPS was heated to temperatures above 200 °C. The spectra of sPS showed that the helical conformation chain varied with different casting solvents and the band positions and relative intensities also differed slightly owing to different interactions between the solvent molecule and the δ-type sPS crystalline phase. The solution-casting temperature also had a significant effect on the crystal forms in sPS. Lower temperatures (casting below ∼100 °C) produced helical crystals while the higher temperatures (casting above 120 °C) yielded all-trans crystals. In addition, spectra evidence of different crystals (α-and β-crystals in all-trans conformation) in sPS are discussed and identified in this study.     

Structure characterization of alginate and conformational behaviors of various alkali-metal alginates in solution

Summary The M/G ratio, i. e., number-ratio of D-mannuronate (M) to L-gluronate (G), and diad (MM, GG, MG, etc.) and triad (MMM, MMG, MGM, etc.) frequencies were determined with 100 MHz ¹³C-NMR spectra for two alginate samples, M-rich and G-rich samples. The M/G ratios obtained were in accord with those determined from chemical analysis on hydrolyzed products fairly well. Molecular chain dimensions in solution were investigated by viscosity method for five alkali-metal alginates carrying Li, Na, K, Rb and Cs, and the results were discussed based on ion radius and electronegativity of alkali-metals. Finally, ion-exchange characteristics of these alginates by Ca⁺⁺ ion were interpreted with M/G ratio and electronegativity.     

Synthesis of well-aligned millimeter-sized tetragon-shaped graphene domains by tuning the copper substrate orientation

We present a simple processing method for synthesizing well-aligned millimeter-sized tetragon-shaped graphene domains on a polycrystalline copper substrate via low-pressure chemical vapor deposition. The tetragonal shape is achieved simply by wet loading the copper substrate with processing conditions previously used for the growth of millimeter-sized hexagon-shaped graphene domains. Electron backscatter diffraction (EBSD) shows that the wet loaded copper substrate is uniformly textured with a surface plane between Cu (1 0 0) and Cu (1 1 0). The in-plane rotation of the crystalline orientation across the Cu grains is very small. However, the EBSD showed that the surface orientation of the dry loaded substrate is close to the (1 1 1) crystal plane. The different surface orientation of the wet and dry loaded samples is attributed to the different surface oxygen concentration, which changes the relative stability of the (0 0 1), (1 1 0), and (1 1 1) plane during copper sublimation and recrystallization. These results provide an approach to tune the surface crystal orientation and thus the shape and orientation of the graphene domains.     

沥青质加氢过程中的结构组成变化

综述了原油沥青质在加氢处理中结构组成变化的研究现状。现有的研究主要针对沥青质加氢过程中H/C原子比随加氢条件变化如何变化,S,N,V,Ni脱除状况,以及加氢处理中沥青质相对分子质量及分子结构的变化,沥青质晶体结构参数的变化。结果表明:加氢处理后沥青质C,H质量分数降低,H/C原子比且随加氢条件变化苛刻而降低。沥青质的S较易脱除,由于N,V,Ni位于沥青质芳环系中,所以难以脱除,且随着反应条件的苛刻,其质量分数增加。反应中沥青质烷基侧链变短、侧链数变少,芳环数减少,芳核缩合度增加,芳香度增加,沥青质平均相对分子质量降低,总环数增加。加氢转化后沥青质芳香层层数M减少,芳香层层间距dm和芳香层堆积高度Lc降低。通过这几方面的研究结果分析,对解决加氢处理中沥青质引起的催化剂生焦及轻质油收率低等不利影响具有重要的理论指导意义。     

Structure of rigid domains and viscoelastic properties of ion-containing polyurethane semicarbazides

By using small-angle X-ray scattering, thermo-mechanical analysis, stress relaxations under constant deformation, etc. the effect of different quaternizing agents on the structure formation in cation-active segmented polyurethanes was investigated. The results obtained have been used for developing a model of a rigid domain, according to which the domain is a complex particle consisting of hard block microassociates. The hard block microassociates result from dipole-dipole, dipole-ion, and ion-ion interactions. The optimum viscoelastic and thermomechanical characteristics of polyurethane ionomers of the given chemical structure are realized when a part of tertiary nitrogen atoms remains unquaternized.     

The conformational changes,crystal structure and melting behavior of poly(ethylene/ trimethylene terephthalate) copolyesters

The conformational changes, crystal structure and melting behavior of poly(ethylene/trimethylene terephthalate) (ET) copolyesters were investigated using in situ Fourier transform infrared (FTIR) spectroscopy, wide‐angle X‐ray diffraction (WAXD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) under isothermal crystallization conditions. The results show that the minimum melting temperature was observed in ET53, in which the relative amount of ethylene glycol (EG) to 1,3‐propanediol (PDO) was 52.68/47.32 and the PDO‐dimethyl terephthalate (DMT)‐PDO segments in the molecular chain dominated the crystal formation. The minimum crystallinity of ET copolyesters was found in ET66, in which the relative amount of EG/PDO was 65.91/34.09 and the EG‐DMT‐EG segments in the molecular chain dominated the crystal formation. A rapid and continuous conformational transition in ET copolyesters was observed using in situ FTIR in the first 10 min under isothermal crystallization conditions. The continuously adjusting conformation in the molecules reflects the crystallization of ET copolyesters. Based on the DSC and the X‐ray analyses of the crystallization behavior in the ET copolyesters, crystalline conformation transitions of molecules in ET copolyesters take place rapidly and early. Copyright © 2012 Society of Chemical Industry     

Using FlAsH to probe conformational changes in a large HEAT repeat protein

We have investigated the use of FlAsH, a small fluorogenic molecule that binds to tetracysteine motifs, to probe folding of the 15-HEAT repeat protein PR65A. PR65A is one of a special class of modular non-globular proteins known as tandem repeat proteins, which are composed of small structural motifs that stack to form elongated, one-dimensional architectures. We were able to introduce linear and bipartite tetracysteine motifs at several sites along the α-helical HEAT array of PR65A without disrupting the structure or stability. When the linear tetracysteine motif CCPGCC was used, FlAsH fluorescence reported globally on the folding of the protein. When the tetracysteine motif was displayed in bipartite mode through the engineering of pairs of cysteines on adjacent HEAT repeats, FlAsH fluorescence became a reporter of local conformation and of oligomerisation. Thus, by designing FlAsH-binding sites at different locations along the repeat array one can interrogate specific properties of PR65A, paving the way for structure-function analysis of this protein both in vitro and in the cell.     

Structure,molecular orientation,and resultant mechanical properties in core/ sheath poly(lactic acid)/polypropylene composites

We study the coaxial spinning of poly(lactic acid) (PLA) with polypropylene (PP) in a core/sheath configuration. PP_core/PLA_sheath and PLA_core/PP_sheath fibers maintain the high breaking strength that PP and PLA exhibit individually, showing marked improvement in strength over previous reports of PP/PLA blend fibers. Crystalline morphologies are greatly affected by the location within the fiber (i.e., core, sheath, or spun individually), and hence, co-spinning provides a route to tailor the morphology and fiber diameter beyond that available with single component fibers. A new approach to estimate molecular orientation of core sheath fibers based on the tensile response of the fiber is developed, and indicates that co-spinning PP with PLA results in a synergistic effect with increases in the molecular orientation above that which is possible with spinning either PP or PLA individually.     

Deformation-induced conformational changes in stretched samples of amorphous poly(ethylene terephthalate)

The combination of Fourier transform Raman spectroscopy and thermal analysis has been proved to be adequate for the study of the quantitative structural changes which take place in amorphous poly(ethylene terephthalate) on stretching. The two-phase conformational model previously proposed for annealed samples was applied to uniaxially stretched samples. The samples were deformed at different temperatures and speeds. Different conformer contents were found in the stretched sample depending on the stretching conditions. In general, deformation induces a conformational transition of gauche to trans. This behavior was lost at a narrow range of temperatures above the glass transition and at the lowest speeds, where the stretching seemed not to induce conformational changes. This different behavior has been associated to the high mobility of the polymer chains under these conditions, which imposes a different process of deformation marked by a high degree of chain slipping. This kind of deformation is present all along the sample and with the absence of necking in the uniaxial drawing process. © 1996 John Wiley & Sons, Inc.     

Influence of orientation and ferroelectric domains on the photochemical reactivity of La2Ti2O7

The effects of crystal orientation and ferroelectric domain structure on the photochemical reactivity of La₂Ti₂O₇ have been measured. Electron backscattered diffraction was used to determine the orientations of the surfaces of crystals in a ceramic specimen, piezo-force microscopy was used to determine the domain structure, and the photocathodic reduction of silver from an aqueous silver nitrate solution was used to evaluate the photochemical reactivity. The reactivity is greatest on (001) surfaces (this is the orientation of the layers in this (110)_p layered perovskite structure) while surfaces perpendicular to this orientation have the least reactivity. Complex domain structures were observed within the grains, but they appeared to have no effect on the photocathodic reduction of silver, in contrast to previous observations on other ferroelectrics. La₂Ti₂O₇ is an example of a ferroelectric oxide in which the crystal orientation has a greater influence on the photochemical reactivity than polarization from the internal domain structure.     

Synthesis,structures, and conformational analysis of dibenzodioxadisilocins

Novel dibenzodioxadisilocins were prepared using a dehalogenative coupling reaction between (2,6-dichlorophenoxy)t-butyldimethylsilane and dimethyldichlorosilane with magnesium via an intramolecular 1,3-anionic rearrangement of the silyl group. Their structures were unequivocally confirmed by X-ray crystallography. For a comparison with the X-ray data, molecular orbital calculations on the conformations of the organosilicon macrocyclics were also carried out.     

国内外烧碱市场变化及走向

回顾了2007年国内外烧碱市场的特点,特别是中国、美国和日本的市场变化情况,预测了今后的发展趋势。