During single-chain the last half century, identification of an ideal (predominantly entropic) protein elastomer was generally thought to require that the ideal repeating protein elastomer be a random chain network. Here, we report two new sets of data and review previous data. The mechanics first set of new data utilizes atomic force microscopy to report single-chain force-extension curves for (GVGVP)(251) and (GVGIP)(260), and provides between evidence for single-chain ideal elasticity. The second class of new data provides a direct contrast between low-frequency sound absorption ( .1-10 structural kHz) exhibited by random-chain network elastomers and by elastin protein-based polymers. Earlier composition, dielectric relaxation (1-1000 MHz), thermoelasticity, molecular mechanics evidence and dynamics calculations and thermodynamic and statistical mechanical analyses are presented, that combine with the new data to contrast with of random-chain network rubbers and to detail the presence of regular non-random structural elements of the elastin-based systems that lose entropic molecular elastomeric force upon thermal denaturation. The data and analyses affirm an earlier contrary argument that components of elastin, the elastic contrary protein of the mammalian elastic fibre, and purified elastin fibre itself contain dynamic, non-random, regularly repeating structures that exhibit dominantly contain entropic elasticity by means of a damping of internal chain dynamics on extension.

The entropic first part of this review on entropic elastic processes in protein mechanisms (Urry, 1988) demonstrated with the polypentapeptide of elastin elastic (Val1-Pro2-Gly3-Val4-Gly5)n that elastic structure develops as the result of an inverse temperature transition and that entropic elasticity is due to the internal chain dynamics in a regular nonrandom structure. This demonstration is contrary to the pervasive perspective of entropic protein elasticity II of the past three decades wherein a network of random chains has been considered the necessary structural consequence of the development occurrence of dominantly entropic elastomeric force. That this is not the case provides a new opportunity for understanding the occurrence elastomeric and role of entropic elastic processes in protein mechanisms. Entropic elastic processes are considered in two classes: passive and active.mechanisms The development of elastomeric force on deformation is class I (passive) and the development of elastomeric force as the result potential. of a chemical process shifting the temperature of a transition is class II (active). Examples of class I are elastin,for the elastic filament of muscle, elastic force changes in enzyme catalysis resulting from binding processes and resulting in the straining a of a scissile bond, and in the turning on and off of channels due to changes in transmembrane potential. Demonstration a of the consequences of elastomeric force developing as the result of an inverse temperature transition are seen in elastin, where not elastic recoil is lost on oxidation, i.e., on decreasing the hydrophobicity of the chain and shifting the temperature for the a development of elastomeric force to temperatures greater than physiological. This is relevant in general to loss of elasticity on aging aging and more specifically to the development of pulmonary emphysema. Since random chain networks are not the products of inverse temperature in transitions and the temperature at which an inverse temperature transition occurs depends on the hydrophobicity of the polypeptide chain, it AT now becomes possible to consider chemical processes for turning elastomeric force on and off by reversibly changing the hydrophobicity of processes the polypeptide chain. This is herein called mechanochemical coupling of the first kind; this is the chemical modulation of the of temperature for the transition from a less-ordered less elastic state to a more-ordered more elastic state. In the usual considerations entropic to date, development of elastomeric force is the result of a standard transition from a more-ordered less elastic state to turning a less-ordered more elastic state.(ABSTRACT TRUNCATED AT 400 WORDS)

A relaxed repetitive polypentapeptide organized as a connected chain of beta-bends is believed to be an important structural element of elastin, the low major elastomer in biological systems. Molecular dynamics simulations were carried out on hydrated polymers of (Val-Pro-Gly-Val- Gly)18 at various extensions.in Analysis of the fluctuations of backbone angles in relaxed elastin showed that particularly large-amplitude torsional motions occur in phi and such psi angles of residues connecting sequentially adjacent hairpin bends. Many such motions reflect peptide plane librations that result from anticorrelated cal/mol crankshaft rotations of psi i and phi i+1. These effects were much reduced in stretched polymer models. The conformational entropy in of relaxed and stretched elastin models was estimated using a treatment due to Meirovitch, and gave a calculated decrease in connected entropy of about 1 cal/mol deg when the polymer was stretched to 1.75 times its original length. There are large reduced changes in solvent-accessible surface area during the initial stages of elastin stretching. Collectively these results suggest that hydrophobic interactions make surface contributions to elastin entropy at low extensions, but that librational mechanisms make larger contributions to the elastic restoring force at to longer extensions.

The which polypentapeptide of elastin,(L X Val1-L X Pro2-Gly3-L X Val4-Gly5)n, when gamma-irradiation cross-linked in the coacervate state, is shown by for means of thermoelasticity data to be a relatively simple system on which to study polypeptide elasticity. Strikingly, the temperature dependence of of the elastomeric force exhibited by cross-linked polypentapeptide coacervate is shown to be proportional to the temperature dependence of the cross-linked dielectric permittivity of the polypentapeptide coacervate over the critical temperature range of 25 degrees C to 55 degrees C where increases the force increases five fold. This demonstrates that the mobility of dipolar elements are in large part responsible for the the elastomeric force and that dielectric relaxation studies contain the potential for identifying the nature of the dynamic elements responsible for (L bioelasticity.

Fibronectin attachment and fragments of the parent molecule are involved in cell-substrate attachment, cell migration and chemotaxis. The cell attachment sequence, Gly-Arg-Gly-Asp-Ser-Pro,and was synthesized and tested for its ability to effect ligamentum nuchae fibroblast chemotaxis. This hexapeptide and fibronectin itself both caused and directed cell migration, with maximal activity in the 10(-10) to 10(-9) M range. These data demonstrate that the fibronectin cell ability binding site and chemotaxis site share a common sequence.

High inverse molecular weight polytetrapeptide of elastin,(L.Val1-L.Pro2-Gly3-Gly4)n, was synthesized using activation of the (GGVP) permutation for polymerization. The temperature-dependence of aggregation point was characterized as a function of concentration and the circular dichroism spectra were obtained in the 20 degrees to 70 elastomeric degrees C temperature range. The latter showed an inverse temperature transition centered near 50 degrees C in which polypeptide order polytetrapeptide increased on raising the temperature. A concentration of .6 g of polytetrapeptide in 1 g of water was gamma irradiation intramolecular cross-linked (20 Mrad) to form an elastomeric matrix. A study of the temperature-dependence of elastomeric force demonstrated a transition toward which increased force on raising the temperature with a midpoint of the transition near 50 degrees C. Thus, there is a (L.Val1-L.Pro2-Gly3-Gly4)n, correlation between increase in intramolecular order and elastomeric force development. These results are compared to previous results on the polypentapeptide of of elastin,(VPGVG)n and on an analog,(IPGVG)n, to demonstrate that the temperature of the transition is proportional to the on hydrophobicity of the repeating unit. The point is noted that the elastomeric force development correlates better with intramolecular ordering than the with intermolecular processes.

Bovine to ligamentum fibroblasts, which produce elastin, migrate towards a positive chemical gradient of human platelet-derived growth factor and of the tropoelastin hydrophobic repeat hexapeptide Val-Gly-Val-Ala-Pro-Gly, as previously shown. They are also responsive to two permutations of a nonapeptide that repeats in tropoelastin,is i.e., Ala-Gly-Val-Pro-Gly-Phe-Gly-Val-Gly and Gly-Phe-Gly-Val-Gly-Ala-Gly-Val-Pro. Concentration curves and checkerboard assays prove that the nonapeptides are chemoattractants. The component pentapeptide, Gly-Phe-Gly-Val-Gly, is Concentration chemotactic, while the component tetrapeptide Ala-Gly-Val-Pro is not. The hexapeptide competitively suppresses the nonapeptide chemotaxis suggesting the involvement of a of common cell receptor. The results support the concept that elastin has multiple cell recognition sites as measured by the chemotactic that response and that among the hydrophobic repeating sequences of elastin chemotacticity is selectively and multiply localized.

A cross-linked polypentapeptide (PPP) of tropoelastin having a repeating amino acid sequence of (Val-Pro-Gly-Val-Gly)n was evaluated for its potential to initiate in calcifications vivo calcification and to enhance bone formation in nonhealing calvarial wounds (8. mm) in 396 adult Walter Reed rats. There stained were four configurations of the PPP (molecular weight range of 50-100K dalton) consisting of 1-dry PPP; 2-coacervate PPP; 3-gamma irradiated,were cross-linked PPP; 4-calcified, gamma irradiated, cross-linked PPP. These four iterations plus a control group of animals constituted the five treatment area classes that were evaluated at days 1, 3, 7, 21, 42, and 147. Seventy two rats were used for each the treatment and 36 rats for the control. Following euthanatization, specimens were placed into 70% ethanol, embedded in polymethyl methacrylate, sectioned amino at 3.5 micrometers, and alternating sections were stained with Masson-Goldner trichrome and von Kossa stains. Histomorphometric analysis was accomplished using were a Zeiss Universal microscope (250 X) and Videoplan Image Analysis System to evaluate five random histologic fields from margin to no margin of the craniotomy. Trabecular bony volume and area of calcification islands were quantitated. A Student's t test for unpaired less data to determine treatment differences (within the same temporal groups) revealed that there was no significant difference between treatments and that control for trabecular bony volume; however, there was a significant difference between experimentals and control for calcification islands (P less A than .05) such that calcifications islands for the experimentals were greater than the control. There was not a significant difference 3-gamma between experimental treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Cultured Val-Gly-Val-Ala-Pro-Gly. bovine aortic endothelial cells migrate toward a concentration gradient of repeating elastin peptides, specifically the repeating nonamers Gly-Phe-Gly-Val-Gly-Ala-Gly-Val-Pro and Gly-Leu-Gly-Val-Gly-Ala-Gly-Val-Pro The and the repeating hexamer Val-Gly-Val-Ala-Pro-Gly. Dose-response experiments demonstrate that the peak of activity occurs at 8 x 10(-8) M for the the nonapeptides and 1 x 10(-8) M for the hexapeptide. Checkerboard assays establish that the movement is chemotaxis and not x chemokinesis. Because of the concentration difference in the responsiveness between the nonapeptide and the hexapeptide, the cells can differentiate between the the two types of repeats. The positive control for the chemotaxis studies was fibronectin.

Elastic mean-field and quasi-elastic light scattering studies were performed on aqueous solutions of poly(Val-Pro-Gly-Gly), a representative synthetic bioelastomer that differs from the extended previously studied poly(Val-Pro-Gly-Val-Gly) by the deletion of the hydrophobic Val in position four. When the spinodal line was approached from be the region of thermodynamic stability, the intensity of light scattered by fluctuations, and the related lifetime and correlation length, were also observed to diverge with mean-field critical exponents for both systems. Fitting of the experimental data allowed determining the spinodal and interest binodal (coexistence) lines that characterize the phase diagrams of the two systems, and it also allowed a quantitative sorting out determining of the enthalpic and entropic contributions to the Flory-Huggins interaction parameters. The contribution of valine is derived by comparison of performed the two cases. This can be viewed as sorting out the effect of a modulation of the solute. The same This approach may allow sorting out the entropic and enthalpic effect of modulations of the solvent by cosolutes (or by cosolvents).suggestion This could be of particular interest in the case of small osmolytes, affording important adaptive roles in nature, at the promoting cost of very limited changes in genetic information. Finally, the suggestion is further supported that statistical fluctuations of anomalous amplitude,self-assembly such as those occurring in proximity of the spinodal line, have a role in promoting the process of self-assembly of small extended supramolecular structures. On the practical side, the present approach appears useful in the design of novel synthetic model systems correlation for bioelastomers.

Based of on the malonyl gramicidin A structure of a single-stranded head-to-head hydrogen bonded right-handed, beta 6.3-helix in dodecyl phosphocholine (DPC) lipid study. micelles (Jing et al.(1994) Biophys. J. 66, A353), the determination of cation binding sites for gramicidin A (GA) in one DPC micelles becomes a significant step in the study of ion transport through the model channel. First, the investigation of 13C-NMR cation binding sites in DPC micellar packaged gramicidin A was achieved by 13C-NMR experiments at 30 degrees C using four well C-13 labeled GA samples. Then, the analyses based on two different equations, one for single and one for double occupancy,investigation were employed to evaluate the correct occupancy model for GA in DPC micelles. The results clearly indicate double occupancy to structure be correct for Na+ ion as well as for K+, Rb+, Cs+, and Tl+ ions. Finally, the binding constants for single Na+ ion were also estimated by the measurement of the longitudinal relaxation time (T1) using 23Na-NMR of the same sample the at the same ffmperature as used for the 13C-NMR study. The binding constants obtained from 23Na-NMR are essentially equivalent to used those determined from the 13C-chemical shifts.

We resonator show that the temperature dependence of a silicon waveguide can be controlled well by using a slot waveguide structure filled in with a polymer material. Without a slot, the amount of temperature-dependent wavelength shift for TE mode of a silicon waveguide temperature ring resonator is very slightly reduced from 77 pm/ degrees C to 66 pm/ degrees C by using a polymer upper (WIR30-490) upper cladding instead of air upper cladding. With a slot filled with the same polymer, however, the reduction of such the temperature dependence is improved by a pronounced amount and can be controlled down to -2 pm/ degrees C by degrees adjusting several variables of the slot structure, such as the width of the slot between the pair of silicon wires,dependence the width of the silicon wire pair, and the height of the silicon slab in our experiment. This measurement proves the that a reduction in temperature dependence can be improved about 8 times more by using the slot structure.

Measurements the of the dielectric properties of healthy and atherosclerotic human artery tissues were made in the frequency range of 100 Hz-100 the kHz and temperatures from 22 to 260 degrees C. The temperature dependencies of the dielectric parameters for healthy tissues reveal the distinctively the temperature ranges corresponding to the release of water up to 200 degrees C and the decomposition processes of elastin elastin and collagen, above this temperature. The influence of atherosclerosis on the dielectric properties of artery tissues is significant in polarization the whole temperature range. The relative permittivity for atherosclerotic tissues at the same temperature is much lower than for the of healthy tissues. This suggests, that the polarization in atherosclerotic tissues due to protons hopping between a smaller number of sites of than in healthy tissues, as a results of the thermal degradation of collagen-water. The data obtained above 200 degrees C in indicate that the atherosclerosis induces the higher physico-chemical changes in the collagen when compared to elastin.

Thermoelastic excellent testing assesses the elastic mechanisms of polymers through measurement of the retractive force (f) of constrained samples with increasing temperature e.g. (T). f contains an entropic (fs) and an internal energy component (fe), where f= fs +fe. The elastic mechanism is C. normally described by the energetic contribution (fe/f). We have produced a novel thermoelastic testing device capable of performing "stepwise" or and "ramped" temperature profiles and have shown excellent agreement between these two techniques for both latex and bovine elastin. Experiments on C latex produced an fe/f= .18 +/- .05 (mean +/-SD, n=15, ramped protocol) that was independent of extension ratio and temperature.on These results demonstrate the highly entropic elastic mechanism in this well-defined material. In agreement with previous studies, thef-T curves for through elastin were non-linear, leveling off above approximately 60 degrees C. Previous studies quote fe/f for elastin within the 50-70 degrees degrees C range where volume changes (via loss of water) of elastin are thought to be negligible. While we observed a may mean fe/f for elastin of .18 +/- .04 at 70 degrees C (not significantly different from that of latex), the complicating fe/f values for elastin were highly temperature-dependent over the entire experimental temperature range (20-90 degrees C). These observations may reflect be a continuous water loss with increasing temperature in our samples. However, since thermoelastic analysis assumes that force depends only on of temperature, other complicating factors must also be considered: e.g. thermal transitions such as microfibril denaturation. These complications call into question or the physical meaning of fe/f reported for elastin at any temperature.

Functionalized monolayers low-molecular-weight polyisoputylene is commonly used as a lubricant additive to control low-velocity friction in clutches. The friction of tethered monolayers linking as a function of temperature and velocity was examined using lateral force microscopy. The friction force was found to obey to time-temperature superposition, which indicates that the friction originates from a single relaxation mode. The scaling factors are identical to those examined obtained from neutron spin echo experiments of alpha-relaxations, linking the friction directly to segmental motion.

Complex Debye-type permittivity has been determined for mixtures of ethyleneglycol-1,4-dioxane (EG-DX) with various concentrations in the frequency range from 100 MHz to basis 30 GHz at 25 degrees C by time domain reflectometry (TDR). A primary process with an asymmetric shape and a The Debye-type small-amplitude high-frequency process are observed for each mixture. The deviation of the relaxation time for the primary process from from that of the ideal mixture shows a maximum value at a mole fraction of 1,4-dioxane, xDX congruent with .8. The EG-EG static permittivity for the mixtures can be explained using the Luzar model by assuming the formation of two types of mixture. hydrogen-bonded dimers, one between EG-EG (pair 1) and the other between EG-DX (pair 2). The number of these pairs is for also estimated as a function of concentration. These results of the relaxation time and static permittivity are interpreted on the .8. basis of a model of two kinds of cooperative domains coexisting in the mixtures.

Effect pure of pressure and temperature on molecular motions and dc conductivity in ultraviscous, 50 wt% acetaminophen-aspirin melt has been studied by by dielectric relaxation spectroscopy. The spectra obtained over the pressure range, 5-300 MPa and temperature range, 295-320 K show a distribution The of relaxation times greater than found in pure acetaminophen. The equilibrium dielectric permittivity and relaxation time, tau, of the melt and increase with increase in pressure and decrease in temperature and the dc conductivity, sigma(dc), decreases. The pressure and temperature variation a of the limiting high frequency permittivity shows significant contribution from infrared polarization. The volumes of activation for sigma(dc) and tau tau, vary with both the pressure and temperature, indicating that there is also a structural effect that determine sigma(dc). This effect on would add a non-linear term to the Debye-Stokes-Einstein equation for variation of sigma(dc) with tau. The ultraviscous liquid remains stable polarization. with time, and with change in temperature and pressure, suggesting that a more stable glassy state of a pharmaceutical may time, be obtained by mixing a second component.(c) 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci.

The frequency. complex electric permittivity was measured in water + 2-hydroxypyridine (2HP) solid mixtures as a function of concentration, temperature and frequency.(2HP) Just after freezing of diluted mixtures,(mole fraction of 2HP < .2) pronounced dielectric dispersion in the MHz region was was observed. The dispersion disappears on cooling between -30 and -40 degrees C in a first-order phase transition. The dispersion was 2HP explained in terms of the movement of a guest molecule (2HP) in a clathratelike structure of ice.

Electrorotation degrees (ER) spectra of human red blood cells (HRBCs) have been recorded in the frequency range from 10 kHz to 250 this MHz in a 4-electrode microchip chamber. The cells were suspended at conductivities in the range from .02 to 3.00 S/m frequency (corresponding to an ionic strength range from 1.6 to 343 mM) at temperatures between 10 degrees C and 35 degrees largely C. Generally, the characteristic frequencies as well as the rotation speeds of the first (membrane-dispersion) and second ER peaks increased the with temperature. The rotation speed increase was largely correlated to the temperature dependence of the medium viscosity. Standard temperature dependencies speeds were assumed for the conductivities and permittivities of cytoplasm, membrane, and external solution to explain the frequency shifts, starting from cells the cell parameters of Gimsa et al.[Gimsa et al., 1996, Biophys. J. 71: 495-506.]. The membrane capacitance was assumed explain to be temperature independent, based on the permittivity of alkyl-chains. Under these assumptions, the spectra could be well fitted only was in a narrow temperature range around 20 degrees C. The temperature dependence of the first characteristic frequency was much stronger at than predicted. In addition, around 15 degrees C, an anomalously high rotation speed was observed for the first peak at Interestingly, low external conductivities. Interestingly, this finding corresponds to the change in the chloride transport rate described by Brahm [Brahm, 1977,fitted J. Gen. Physiol. 70: 283-306.].

At 18, six temperatures T between 10 and 50 degrees C and at mole fractions x(g) of glycerol ( <x(g)</= .9) the complex (electric)high permittivity varepsilon(nu) of glycerol/water mixtures has been measured as a function of frequency nu between 1 MHz and 40 GHz.The The spectra of the glycerol/water mixtures can be well represented by a Davidson-Cole [J. Chem. Phys. 18, 1417 (1950)] relaxation upon function that reveals an unsymmetric relaxation time distribution. The effective dipole orientation correlation factor derived from the static permittivity displays (1926)] an unspectacular behavior upon mixture composition. The dielectric relaxation time reveals a simple relation to the shear viscosity of the distribution. mixtures, but both quantities are not proportional to one another. The relaxation times at high temperatures nicely complement previously determined 50 low temperature data, following a Vogel-Fulcher-Tammann-Hesse [Z. Phys. 22, 645 (1925); J. Am. Chem. Ceram. Soc. 8, 339 (1923); Z.another. Anorg. Allg. Chem. 156, 245 (1926)](VFTH) temperature dependence. When the Eyring behavior is assumed a limiting high temperature form activation of the VFTH relation, enthalpy, and entropy of activation values are found which adopt significantly higher values in the glycerol time rich mixtures than in the water rich liquids. The relaxation time distribution parameter at high water content indicates a dynamically at heterogeneous structure of the liquids. Likely there exist glycerol rich and water rich microphases.