Supercontraction in Nephila spider dragline silk - Relaxation into equilibrium state

Time-resolved Fourier transform infrared (FTIR) spectroscopy is combined with dynamic mechanical measurements in order to unravel the interplay between the amorphous chains and nanocrystals in spider silk under conditions of selective swelling. The sample remains humid after supercontraction, identifying in this way the role of the softened amorphous phase. For the first time, the amount of pre-stress in the fibers can be determined by direct comparison between microscopic and macroscopic stress during humidity increase. Nanocrystal stress decreases by ∼120 MPa, even though the external stress increases at the same time. The current findings suggest that water and its interplay with pre-stress determine the relative contribution of crystals and amorphous matrix to the mechanical properties. Increased water content and release of pre-stress deteriorate the macroscopic mechanical properties, as the system becomes viscoelastic and loses its stiffness.     

The color of dragline silk produced in captivity by the spider Nephila clavipes

Fifty-six N. clavipes spiders from the same region of Florida were kept in captivity under the same conditions and fed a similar diet of crickets. Their major ampulate glands were forcibly silked. Dates, silking times, and the colors of the dragline silk produced were recorded. The colors ranged from all white through various combinations of white and yellow upon different silkings to all yellow. If a spider had been producing white silk for at least 4 h, the color being produced could suddenly change to yellow 38% of the time. These observations indicate that factors beyond diet and environment influence the color of silk produced in captivity by forcible silking. They also indicate that the spiders store both pigmented and unpigmented silks and that some aspect of forcible silking precludes the spiders' choosing the color. The yellow and white silks exhibit similar exterior surface morphologies as well as similar tensile properties.     

Nanostructural physical and chemical information derived from the unit cell scattering amplitudes of a spider dragline silk

Characterizing the nanostructures of spider major ampullate (dragline) silks is an important step in understanding the origin of their high mean strength and toughness, and for producing polymeric analogs that mimic these properties. Here we present transmission electron microscopy (TEM) diffraction patterns and an accompanying structure factor analysis for the dragline silk of Latrodectus hesperus (black widow spider). The chemical and physical composition of crystalline regions in this silk fiber was studied by manipulating the positions and size of amino acid side groups in a theoretical model, and comparing the expected unit cell scattering amplitudes with experimental electron diffraction patterns. The results suggest that—in addition to the smaller amino acid side groups such as alanine, glycine and serine—some of the bulkier amino acid side groups such as tyrosine and leucine are included in the crystalline fraction of the major ampullate silk. The structure factor analysis also demonstrates a marked sensitivity of the respective diffraction spot intensities to a slight change in both side group position and side group bulkiness. These observations point to a unique function for TEM in characterizing silk and other polymers.     

Molecular order in spider major ampullate silk (dragline): Effects of spinning rate and post‐spin drawing

Optical birefringence measurements are used to characterize how the molecular order of spider (Nephila clavipes) major ampullate silk is affected by linear spinning rate, by the extent of post‐spin drawing, and by post‐spin drawing rate. Results are interpreted qualitatively in terms of a simple microstructural model, in which birefringence depends on both the overall degree of molecular orientation and the extent to which crystalline regions are present. In contrast to the behavior of conventional, synthetic polymers, birefringence is found to be an unreliable predictor of tensile stiffness: microstructural changes that lead to increased birefringence may leave stiffness unchanged or, in some cases, lower than before. It is unlikely that economic processing of silk‐like polymers into fiber that exhibits biomimetic tensile properties can be achieved with spinning followed by drawing, or with a single spinning step. Instead, spinning followed by thermochemical treatment under load may be needed to obtain the critical combination of molecular orientation and crystallinity in commercially satisfactory time scales. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 895–903, 1999     

Exploring the backbone dynamics of native spider silk proteins in Black Widow silk glands with solution-state NMR spectroscopy

Spider dragline silk is an outstanding biopolymer with a strength that exceeds steel by weight and a toughness greater than high-performance fibers like Kevlar. For this reason, understanding how a spider converts the gel-like, aqueous protein spinning dope within the major ampullate (MA) gland into a super fiber is of great importance for developing future biomaterials based on spider silk. In this work, the initial state of the silk proteins within Black Widow MA glands was probed with solution-state NMR spectroscopy. ¹⁵N relaxation parameters, T₁, T₂ and ¹⁵N-{¹H} steady-state NOE were measured for twelve backbone environments at two spectrometer frequencies, 500 and 800 MHz. The NMR relaxation parameters extracted for all twelve environments are consistent with MA silk protein backbone dynamics on the fast sub-nanosecond timescale. Therefore, it is concluded that the repetitive core of spider MA proteins are in an unfolded, highly flexible state in the MA gland.     

The critical role of water in spider silk and its consequence for protein mechanics

Due to its remarkable mechanical and biological properties, there is considerable interest in understanding, and replicating, spider silk's stress-processing mechanisms and structure-function relationships. Here, we investigate the role of water in the nanoscale mechanics of the different regions in the spider silk fibre, and their relative contributions to stress processing. We propose that the inner core region, rich in spidroin II, retains water due to its inherent disorder, thereby providing a mechanism to dissipate energy as it breaks a sacrificial amide-water bond and gains order under strain, forming a stronger amide-amide bond. The spidroin I-rich outer core is more ordered under ambient conditions and is inherently stiffer and stronger, yet does not on its own provide high toughness. The markedly different interactions of the two proteins with water, and their distribution across the fibre, produce a stiffness differential and provide a balance between stiffness, strength and toughness under ambient conditions. Under wet conditions, this balance is destroyed as the stiff outer core material reverts to the behaviour of the inner core.     

Model for the impedance analysis in a three electrode solid state electrochemical cell

A T-network model for the determination of the electrode impedances in a three electrode solid state electrochemical cell is postulated and discussed. The model is applied to a Li solid battery where the electrolyte is the polymer (PEO)₈LiCF₃SO₃ and the positive electrode is the insertion electrode V₆O_{13 + x}. The Li metal reference electrode is found to have an impedance considerably greater than that of the working (V₆O₁₃ + x) or the counter electrode (Li). The significance of these impedances is discussed in relation to the geometry and construction of solid electrolyte cells, and to their suitability for potentiostatic measurements.     

Study of phase separation in blends of silk fibroin and sodium alginate in solution and in solid state

Silk fibroin (SF) and sodium alginate (SA) are natural polymers with many applications as biomaterials. It is possible to make blends with them in order to improve their properties. Those blends are partially miscible; therefore, understanding the mechanism and phase equilibrium of this system is important to better understand the interaction between these natural polymers. This work analyzed the mechanism of phase separation of SF and SA blends with different composition in solution and in the solid state (as membranes) using small angle light scattering with a He-Ne laser. Polymer interaction and conformation were investigated by Fourier-Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR-ATR) and X-Ray Diffraction (XRD), and membrane morphology was analyzed by Scanning Electron Microscopy (SEM). SEM images showed interpenetrated globules in the matrix. Light scattering profile for blends in solution and in the solid state showed a peak of intensity suggesting that phase separation occurs by spinodal decomposition.     

Use of covariance analysis for the prediction of structural domain boundaries from multiple protein sequence alignments

Current methods for identification of domains within proteinsequences require either structural information or the identificationof homologous domain sequences in different sequence contexts.Knowledge of structural domain boundaries is important for foldrecognition experiments and structural determination by X-raycrystallography or nuclear magnetic resonance spectroscopy usingthe divide-and-conquer approach. Here, a new and conceptuallysimple method for the identification of structural domain boundariesin multiple protein sequence alignments is presented. Analysisof covariance at positions within the alignment is first usedto predict 3D contacts. By the nature of the domain as an independentfolding unit, inter-domain predicted contacts are fewer thanintra-domain predicted contacts. By analysing all possible domainboundaries and constructing a smoothed profile of predictedcontact density (PCD), true structural domain boundaries arepredicted as local profile minima associated with low PCD. Atraining data set is constructed from 52 non-homologous two-domainprotein sequences of known 3D structure and used to determineoptimal parameters for the profile analysis. The alignmentsin the training data set contained 48 ± 17 (mean ±SD) sequences and lengths of 257 ± 121 residues. Of the47 alignments yielding predictions, 35% of true domain boundariesare predicted to within 15 amino acids by the local profileminimum with the lowest profile value. Including predictionsfrom the second- and third-lowest local minima increases thecorrect domain boundary coverage to 60%, whereas the lowestfive local minima cover 79% of correct domain boundaries. Throughfurther profile analysis, criteria are presented which reliablyidentify subsets of more accurate predictions. Retrospectiveanalysis of CASP3 targets shows predictions of sufficient accuracyto enable dramatically improved fold recognition results. Finally,a prediction is made for geminivirus AL1 protein which is infull agreement with biochemical data, yielding a plausible,novel threading result.     

固相法合成乙酰丙酮镧

以无机镧盐、固体碱、乙酰丙酮(Hacac)为原料,在室温下无溶剂固相研磨合成乙酰丙酮镧。考察了碱的种类,乙酰丙酮的量,NaOH的量,以及研磨时间对产率的影响。采用红外、热重及X射线衍射对目标产物进行了表征,结果与标准谱图基本一致。实验结果表明LaCl3.6H2O 10mmol,Hacac 40mmol,NaOH 30mmol,室温下研磨1 h所得乙酰丙酮镧的产率达97.48%,高出经典液相法8.48个百分点。     

Modeling of solid state polymer properties at the stage of synthesis: Fractal analysis

The genetic relationship between the polymer structures in solution and the condensed state are discovered within the framework of fractal analysis. It allows us to predict and model the properties of polymers already at the stage of synthesis, using the representation of a cluster model of the amorphous polymer state. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1137–1140, 2002     

Critical chain length for the formation of the α-helix in the solid state: synthesis and conformation of sequential oligopeptides and polypeptide having l-leucyl-l-leucylglycine sequence

Synthesis and conformation in the solid state of a novel series of sequential oligopeptides and polypeptides having the sequence of l-leucyl-l-leucylglycine have been studied to demonstrate critical chain length for the formation of the α-helix of the peptide. The far infra-red spectra and X-ray powder diffraction patterns suggest that the dodeca and lower peptides take the β-structure and the pentadeca and higher peptides form the α-helix in the solid state. This result leads to the conclusion that the formation of the α-helix of this peptide system begins at the pentadecapeptide. This is consistent with the result of our earlier study on the sequential oligopeptide Nps-(l-Ala-l-Leu-Gly)_n-OEt.     

Phase separation of phosphonated polystyrenes in the solid state

Polymer Bulletin - The goal of this is to point out, using the Electron Spectroscopy for Chemical Analysis (ESCA) method, that the repartition of phosphorus atoms of phosphonated telechelic...     

Nonlinear dynamics of a gas–solid fluidized bed by the state space analysis

The S-statistic based on the comparison of two reconstructed attractors in the phase space was utilized to study whether two dependent time series (namely, evaluation and reference time series) were originated from the same mechanism or not. Evaluation time series were measured during the bed operation in a gas–solid bubbling fluidized bed and reference time series were generated according to phase randomized surrogate data series from the evaluation series. The results indicated that nonlinearity can be observed where the energy contribution of the macro-structures is more than that of the finer structures. It was found that a minimum in the energy of the finer structures with an increase in velocity corresponds to the transition between macro-structures and finer structures of the bubbling fluidization system. This conclusion can eventually help choose proper control systems and evaluation methods of signals in fluidized beds.     

Sequences annotated by structure: a tool to facilitate the use of structural information in sequence analysis

With the aim of bridging the gap between protein sequence and structural analyses, we have developed a tool to aid the identification of new protein sequences by recognizing distant homologues using structural information. The tool generates sequence annotated by structure (SAS) files, applying structural information derived from structural analyses to a given protein sequence. A World Wide Web interface allows a given sequence to be submitted either for structural annotation or, where its structure is unknown, for search and alignment against sequences of known structure. In both cases, SAS will colour residues in the sequence of known structure according to a selection of properties, including secondary structure, interatomic contacts and active site information. SAS can also be used to inspect properties of a single structure.      

Radiation-induced copolymerization of maleimides and acenaphthylene in the solid state

The γ-ray-induced polymerizations in the binary systems of maleimide-acenaphthylene and N-methylmaleimide-acenaphthylene have been studied. The phase diagrams of the two systems show that an eutectic was formed in each system. It has been proven by the solvent extraction and the turbidimetric titration of obtained polymer that copolymer was formed in the eutectic of each system together with homopolymers. The fraction of total homopolymers in the maleimide-acenaphthylene system was nearly the smallest in the monomer mixture of the eutectic composition. The composition of the copolymer, which was isolated by the extractions, was almost independent of the monomer composition. In order to elucidate these results, it was postulated that the copolymerization occurred at grain boundaries between the two components in the eutectic.     

Dielectric properties of some long-chain esters in the solid state

The dielectric properties of a series of long-chain alkyl esters were investigated over a wide temperature range (+25C to −35C) and frequency range (0.05kc to 100kc). The series included esters of all combinations of tetradecanol, hexadecanol, and octadecanol alcohols with tetradecanoic, hexadecanoic, and octadecanoic acids. The thermodynamic parameters were calculated and related to chain length, position of ester group in the chain, and crystal structure. Presented at the AOCS Meeting, Houston, April 1965. E. Utiliz. Res. Dev. Div., ARS, USDA.     

In-source and post-irradiation polymerization of acenaphthylene in the solid state

Radiation-induced solid state polymerization of acenaphthylene was studied by using ⁶⁰Co γ-rays. The extent of polymerization at room temperature reached 68% when acenaphthylene was irradiated with a dose of 2–5 MGy. Prolonged exposure to the radiation decreased the molecular weight of the polymers. The post-polymerization of acenaphthylene was found to occur at relatively high temperatures close to the melting point of acenaphthylene. Absence of an effective termination step allows the enhancement of post-polymerization at higher temperatures after a limiting conversion is accomplished.     

Compilation of mechanical properties for the structural analysis of solid oxide fuel cell stacks. Constitutive materials of anode-supported cells

The mechanical failure of one cell is sufficient to lead to the end of service of a solid oxide fuel cell (SOFC) stack. Therefore, there is growing interest in gaining knowledge on the mechanical properties of the cell materials for stress analysis.This study compiles available data from the literature on the mechanical properties of the most common materials used in intermediate-temperature anode-supported cells: nickel and yttria-stabilized zirconia (Ni–YSZ) anodes, YSZ electrolytes, yttria (YDC) or gadolinia-doped ceria (GDC) compatibility layers and lanthanum strontium manganite (LSM) or lanthanum strontium cobalt ferrite (LSCF) cathodes. The properties for the simulation of stresses, i.e. coefficient of thermal expansion (CTE), Young's modulus, Poisson's ratio, creep behaviour and strength are reported, with an emphasis on temperature and porosity dependence and the evolution upon aging or cycling when available. Measurements of our Ni(O)–YSZ anode material includes the CTE (oxidised and reduced state), Young's modulus and strength at room temperature (oxidised and reduced) and 1073 K (oxidised).