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PubMed1991

Phosphorylation and dephosphorylation modulation of an inverse temperature transition.

Poly[15(IPGVG),(RGYSLG)], where RGYSLG is a protein kinase site, was synthesized. On raising the temperature of a 5 mg/ml solution, this polypeptide undergoes an inverse temperature transition at 18 degrees C in which it folds into a contracted state by optimizing intramolecular hydrophobic interactions. Averaging the data of five experiments, phosphorylation by means of a 3':5' cyclic AMP dependent protein kinase to the extent of one phosphate in 360 residues raises the temperature of the folding transition to 32 degrees C. The shift is completely reversed on dephosphorylation by alkaline phosphatase. Phosphorylation is hereby shown to be the most potent chemical perturbation known for shifting the temperature of an inverse temperature transition, which has been shown to be an efficient mechanism for achieving chemomechanical transduction (mechanochemical coupling).

Alkaline Phosphatase↗
PubMed2007

Spin correlations in the electron-doped high-transition-temperature superconductor Nd2-xCexCuO4+/-delta.

High-transition-temperature (high-T(c)) superconductivity develops near antiferromagnetic phases, and it is possible that magnetic excitations contribute to the superconducting pairing mechanism. To assess the role of antiferromagnetism, it is essential to understand the doping and temperature dependence of the two-dimensional antiferromagnetic spin correlations. The phase diagram is asymmetric with respect to electron and hole doping, and for the comparatively less-studied electron-doped materials, the antiferromagnetic phase extends much further with doping and appears to overlap with the superconducting phase. The archetypal electron-doped compound Nd2-xCexCuO4+/-delta (NCCO) shows bulk superconductivity above x approximately 0.13 (refs 3, 4), while evidence for antiferromagnetic order has been found up to x approximately 0.17 (refs 2, 5, 6). Here we report inelastic magnetic neutron-scattering measurements that point to the distinct possibility that genuine long-range antiferromagnetism and superconductivity do not coexist. The data reveal a magnetic quantum critical point where superconductivity first appears, consistent with an exotic quantum phase transition between the two phases. We also demonstrate that the pseudogap phenomenon in the electron-doped materials, which is associated with pronounced charge anomalies, arises from a build-up of spin correlations, in agreement with recent theoretical proposals.

Journal Article↗
PubMed1999

An evaluation of the transition temperature range of super-elastic orthodontic NiTi springs using differential scanning calorimetry.

Differential scanning calorimetry (DSC) was used to determine the transition temperature ranges (TTR) of four types of super-elastic orthodontic nickel-titanium coil springs (Sentalloy). A knowledge of the TTR provides information on the temperature at which a NiTi wire or spring can assume superelastic properties and when this quality disappears. The spring types in this study can be distinguished from each other by their characteristic TTR during cooling and heating. For each tested spring type a characteristic TTR during heating (austenite transformation) and cooling (martensite transformation) was evaluated. The hysteresis of the transition temperature, found between cooling and heating, was 3.4-5.2 K. Depending on the spring type the austenite transformation started (As) at 9.7-17.1 degrees C and finished (Af) at 29.2-37 degrees C. The martensite transformation starting temperature (Ms) was evaluated at 32.6-25.4 degrees C, while Mf (martensite transformation finishing temperature) was 12.7-6.5 degrees C. The results show that the springs become super-elastic when the temperature increases and As is reached. They undergo a loss of super-elastic properties and a rapid decrease in force delivery when they are cooled to Mf. For the tested springs, Mf and As were found to be below room temperature. Thus, at room temperature and some degrees lower, all the tested springs exert super-elastic properties. For orthodontic treatment this means the maintenance of super-elastic behaviour, even when mouth temperature decreases to about room temperature as can occur, for example, during meals.

Body Temperature↗
PubMed1980

Asymmetric antagonistic effects of an inhalation anesthetic and high pressure on the phase transition temperature of dipalmitoyl phosphatidic acid bilayers.

The phase transition temperature (Tt) of dipalmitoyl phosphatidic acid multilamellar liposomes is depressed 10 degrees C by the inhalation anesthetic methoxyflurane at a concentration of 100 mmol/mol lipid. Application of 100 atm of helium pressure to pure phosphatidic acid liposomes increased Tt only 1.5 degrees C. However, application of 100 atm helium pressure to dipalmitoyl phosphatidic acid lipsomes containing 100 mmol methoxyflurane/mol lipid almost completely antagonized the effect of the anesthetic. A non-linear pressure effect is observed. In a previous study, a concentration of 60 mmol methoxyflurane/mol dipalmitoyl phosphatidylcholine depressed Tt only 1.5 degrees C, exhibiting a linear pressure effect. The completely different behavior in the charged membrane is best explained by extrusion of the anesthetic from the lipid phase.

Atmospheric Pressure↗
PubMed2005

Determination of phase transition temperatures of lipids by light scattering.

Various techniques have been proposed to specify the phase transition temperatures of surfactant molecules. The work reported herein deals with a new general method of T(c) determination based on the optical properties' modifications of aqueous surfactant solutions when the phase transitions occur in the phospholipid membrane. The shape alteration of supramolecular systems induced by the phase transition was correlated with the refraction and absorption coefficients of their aqueous dispersion. The mean count rate (average number of photons detected per second) measured with a Zetasizer Nano-S model ZEN1600 Dynamic Light Scattering Instrument, is representative of an emerging macroscopic phenomenon, but not directly size dependent and has been adapted to our expectations. Changes in the measured scattering intensity reflect changes in the optical properties of the material during temperature variations. Thus, this method allowed to specify the phase transition temperature of many natural or synthetic surfactants independently of their polar head or hydrophobic part.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1994

Modulating the phase transition temperature and thermosensitivity in N-isopropylacrylamide copolymer gels.

Temperature-responsive copolymer (or ternary copolymer) gels of N-isopropylacrylamide (IPAAm) were synthesized with hydrophobic alkyl methacrylate (RMA), hydrophilic acrylamide (AAm), N,N'-dimethylacrylamide (DMAAm), and N-acryloylpyrrolidine (APy) as comonomers. The effects of these comonomers on the phase transition temperature (LCST) and the thermosensitivity have been discussed. The LCST of poly(IPAAm) gel in phosphate buffered saline (PBS) was lowered by the introduction of hydrophobic RMA, and the change in equilibrium swelling ratio with temperature change became smaller with an increase in RMA content. However, a stable skin layer to achieve complete 'on-off' regulation of drug release was formed at a higher temperature by RMA due to hydrophobic interaction of alkyl chains. The LCST of poly(IPAAm-co-AAm) gel increased with an increase in AAm content. However, the thermosensitivity of the gel became smaller. It was suggested that hydrophilic AAm prevented the formation of a dense skin layer at a higher temperature. It was difficult to obtain a complete 'off' state due to an insufficiently dense skin layer in order to stop the drug release. The LCST was raised and great thermosensitivity was possible by the introduction of DMAAm or APy. Poly(IPAAm-co-DMAAm) enabled 'on-off' drug release in response to smaller temperature changes around the body temperature. The molecular design to control transition temperature and thermosensitivity of gel was established.

Acrylamides↗
PubMed2002

The glass transition temperature of mixtures of trehalose and hydroxyethyl starch.

Although mixtures of HES and sugars are used to preserve cells during freezing or drying, little is known about the glass transition of HES, or how mixtures of HES and sugars vitrify. These difficulties may be due to the polydispersity between HES samples or differences in preparation techniques, as well as problems in measuring the glass transition temperature (T(g)) using differential scanning calorimetry (DSC). In this report, we examine the T(g) of mixtures of HES and trehalose sugar with <1% moisture content using DSC measurements. By extrapolating these measurements to pure HES using the Gordon-Taylor and Fox equations, we were able to estimate the T(g) of our HES sample at 44 degrees C. These results were additionally confirmed by using mixtures of glucose-HES which yielded a similar extrapolated T(g) value. Our approach to estimating the glass transition temperature of HES may be useful in other cases where glass transitions are not easily identified.

Calorimetry, Differential Scanning↗
PubMed1997

Effect of glass transition temperature on the stability of lyophilized formulations containing a chimeric therapeutic monoclonal antibody.

PURPOSE: The purpose of this study is to highlight the importance of knowing the glass transition temperature, Tg, of a lyophilized amorphous solid composed primarily of a sugar and a protein in the interpretation of accelerated stability data. METHODS: Glass transition temperatures were measured using DSC and dielectric relaxation spectroscopy. Aggregation of protein in the solid state was monitored using size-exclusion chromatography. RESULTS: Sucrose formulation (Tg approximately 59 degrees C) when stored at 60 degrees C was found to undergo significant aggregation, while the trehalose formulation (Tg approximately 80 degrees C) was stable at 60 degrees C. The instability observed with sucrose formulation at 60 degrees C can be attributed to its Tg (approximately 59 degrees C) being close to the testing temperature. Increase in the protein/sugar ratio was found to increase the Tgs of the formulations containing sucrose or trehalose, but to different degrees. CONCLUSIONS: Since the formulations exist in glassy state during their shelf-life, accelerated stability data generated in the glassy state (40 degrees C) is perhaps a better predictor of the relative stability of formulations than the data generated at a higher temperature (60 degrees C) where one formulation is in the glassy state while the other is near or above its Tg.

Antibodies, Monoclonal↗
PubMed2004

Relationship between the unbinding and main transition temperatures of phospholipid bilayers under pressure.

Using neutron diffraction and a specially constructed high pressure cell suitable for aligned multibilayer systems, we have studied, as a function of pressure, the much observed anomalous swelling regime in dimyristoyl- and dilauroyl-phosphatidylcholine bilayers, DMPC and DLPC, respectively. We have also reanalyzed data from a number of previously published experiments and have arrived at the following conclusions. (a). The power law behavior describing anomalous swelling is preserved in all PC bilayers up to a hydrostatic pressure of 240 MPa. (b). As a function of increasing pressure there is a concomitant decrease in the anomalous swelling of DMPC bilayers. (c). For PC lipids with hydrocarbon chains >or=13 carbons the theoretical unbinding transition temperature T small star, filled is coupled to the main gel-to-liquid crystalline transition temperature T(M). (d). DLPC is intrinsically different from the other lipids studied in that its T small star, filled is not coupled to T(M). (e). For DLPC bilayers we predict a hydrostatic pressure (>290 MPa) where unbinding may occur.

Binding Sites↗
PubMed1985

Carbon-13 NMR relaxation studies demonstrate an inverse temperature transition in the elastin polypentapeptide.

Carbon-13 NMR longitudinal relaxation time and line-width studies are reported on the coacervate concentration (about 60% water by weight) of singly carbonyl carbon enriched polypentapeptides of elastin: specifically, (L-Val1-L-[1-13C]Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-Gly3-L-Val4-[1-13C]Gly5)n. On raising the temperature from 10 to 25 degrees C and from 40 to 70 degrees C, carbonyl mobility increases, but over the temperature interval from 25 to 40 degrees C, the mobility decreases. The results characterize an inverse temperature transition in the most fundamental sense of temperature being a measure of molecular motion. This transition in the state of the polypentapeptide indicates an increase in order of polypeptide on raising the temperature from 25 degrees C to physiological temperature. This fundamental NMR characterization corresponds with the results of numerous other physical methods, e.g., circular dichroism, dielectric relaxation, and electron microscopy, that correspondingly indicate an increase in order of the polypentapeptide both intramolecularly and intermolecularly for the same temperature increase from 25 to 40 degrees C. Significantly with respect to elastomeric function, thermoelasticity studies on gamma-irradiation cross-linked polypentapeptide coacervate show a dramatic increase in elastomeric force over the same interval that is here characterized by NMR as an inverse temperature transition. The temperature dependence of mobility above 40 degrees C indicates an activation energy of the order of 1.2 kcal/mol, which is the magnitude of barrier expected for elasticity.

Amino Acid Sequence↗
PubMed1988

The relationship between the bilayer to hexagonal phase transition temperature in membranes and protein kinase C activity.

A number of substances affect the activity of protein kinase C. Among uncharged and zwitterionic compounds, those which activate protein kinase C also lower the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine while substances which inhibit protein kinase C raise this transition temperature. Using this criteria, we have identified 3 beta-chloro-5-cholestene, 5 beta-cholan-24-ol and eicosane as new protein kinase C activators and have shown that Z-Ser-Leu-NH2, Z-Gly-Leu-NH2, Z-Tyr-Leu-NH2, cyclosporin A and cholestan-3 beta, 5 alpha, 6 beta-triol are protein kinase C inhibitors.

Cholesterol↗
PubMed1984

Warming-induced hyperpolarization of cardiac muscle cells and snail neurones: interpretation based on temperature transition of cooperatively linked surface anionic sites between K+ and Na+ adsorbing states.

The resting potential of a variety of living cells exhibits pronounced hyperpolarization when the cooled cells are brought to a higher temperature. It was shown that this phenomenon can be quantitatively described by the surface adsorption theory of the cell electrical potential in terms of a cooperative temperature transition of the protein-ion-water system at the cell surface. As such, the basic mechanism resembles the temperature transition demonstrated for the bulk phase K+-Na+ distribution in these and similar cells. The paper also discusses the resting potentials of frog muscles and squid axons which do not exhibit hyperpolarization on warming.

Animals↗
PubMed1998

Chain-melting transition temperatures of phospholipids with acylated or alkylated headgroups (N-acyl phosphatidylethanolamines and O-alkyl phosphatidic acids), or with alpha-branched chains.

The biphasic dependence of the chain-melting transition temperature on chainlength, nN, of the headgroup-attached chain of N-acyl phosphatidylethanolamines and of O-alkyl phosphatidic acids is interpreted in terms of a different linear dependence of the transition enthalpy and entropy on nN for long and short chains, respectively. A consistent expression of the form [equation: see text], where DeltanN is the critical chainlength at which the packing mode of the headgroup-attached chains changes, is found to apply systematically to the transition temperatures for both sets of lipids, over the range nN=2-18. This thermodynamic analysis demonstrates that the headgroup-attached chain is located in an environment that differs for long and short chains. Similar considerations apply also to phosphatidylcholines with alpha-branched glycerol-attached chains.

Entropy↗
PubMed1991

The ability of cationic amphiphilic compounds to depress the transition temperature of dipalmitoylphosphatidic acid liposomes depends on the spatial arrangement of the lipophilic moiety.

The hypothesis was tested with the help of model compounds that the ability of cationic amphiphilic drugs to depress the phase-transition temperature Tt of dipalmitoylphosphatidic acid (DPPA) liposomes depends on the spatial arrangement of the lipophilic moiety. The main structure of the compounds with identical cationic side chain was 1-dimethylamino-3-phenylpropane (compound I). A further phenyl ring was introduced either at C3 of the propane chain (compound II) to broaden the lipophilic moiety, or in para-position of the phenyl ring (compound III) to elongate it. As shown by differential scanning calorimetry, the reduction of Tt (control 64 degrees) amounted for compound I to 29 degrees, for compound II to 28 degrees and for compound III to 53 degrees. In order to assess the binding affinity of the compounds to DPPA, their inhibitory effect on 45Ca(2+)-binding to DPPA films was measured. The IC50 values were 2100 microM for compound I, 40 microM for compound II, and 9 microM for compound III. Thus, binding affinity corresponded with the hydrophobicity of the compounds. In contrast, the depressing effect on the transition temperature was only augmented by the additional phenyl ring when substituted in the elongating position.

Calcium↗
PubMedDate not supplied

Prediction of the formulation dependence of the glass transition temperatures of amine-epoxy copolymers using a QSPR based on the AM1 method.

A designer Quantitative Structure-Property Relationship, based upon molecular properties calculated using the AM1 semiempirical quantum mechanical method, was developed to predict the glass transition temperature of amine-cured epoxy resins based on the diglycidyl ether of bisphenol A. The QSPR (R2 = 0.9977) was generated using the regression analysis program, COmprehensive DEscriptors for Structural and Statistical Analysis. By applying an ad hoc treatment based on the elementary probability theory to the quantitative structure-property relationship analysis a method was developed for computing bulk polymer glass transition temperatures for stoichiometric and nonstoichiometric monomeric formulations. A model polymer was synthesized and found to validate our model predictions.

Journal Article↗
PubMed1998

Proton NMR Study of Rouse Dynamics and Ideal Glass Transition Temperature of Poly(ethylene oxide) LiCF3SO3 Complexes.

A range of low-molecular-weight linear poly(ethylene oxide) chains with LiCF3SO3 have been examined via the transverse proton NMR relaxation. From the measured relaxation functions it is shown that the chains obey Rouse dynamics. This analysis gives the molecular weight of a Rouse statistical subunit and the fundamental Rouse relaxation time. It was found that varying the temperature and salt concentration had no effect on the size of a Rouse statistical segment and therefore none on the conformation of the chains. The temperature dependence of the fundamental Rouse relaxation time was found to be well modeled by the Vogel-Tamman-Fulcher equation. The NMR-measured correlation times were then successfully used to predict the glass transition temperature as measured by DSC. The main conclusion of this paper is that under the addition of salt the ideal glass transition temperature T0 is found to remain constant or indeed to slightly decrease.

Journal Article↗
PubMed2006

Temperature scanning FTIR analysis of hydrogen bonding states of various saccharides in amorphous matrixes below and above their glass transition temperatures.

Temperature scanning Fourier transform infrared, TS-FTIR, spectroscopy of various amorphous sugar matrixes was conducted to investigate the relationship between the glass transition temperature, T(g), of an amorphous sugar matrix and the nature of the hydrogen bonds in the matrix. An amorphous sugar matrix was prepared by air-drying an aqueous solution of sugar, and the degree of formation of hydrogen bonds in the matrix was evaluated at different temperatures using the peak positions of the IR band corresponding to the O-H stretching vibration at around 3400 cm(-1). The T(g) value increased with increasing peak position of the O-H stretching vibration at T(g) and were correlated reasonably well with the magnitude of the peak shift by the temperature increase (from 25 degrees C) to the T(g) value. This demonstrates that the amorphous sugar matrix, in which the segments are fixed by fewer hydrogen bonds, has a higher thermal resistance. The glycosidic linkage largely contributes to the restriction of the segments, pyranose ring, rather than a hydrogen bond. As the degree of polymerization of pyranose rings increases, the degree of hydrogen bond formation needed to hold the matrix in a fixed position decreases. However, the magnitude of the restriction of pyranose rings by a glycosidic linkage changes depending on the type: the restrictions imposed by alpha-1,1 and -1,6 glycosidic linkages are the tightest and most flexible of all of the types of glycosidic linkages, respectively.

Hydrogen Bonding↗
PubMed1989

The effect of n-alcohols on vesicular permeability induced at the lipid phase transition temperature: a 1H-NMR study.

The effect of a series of n-alcohols on the permeability of small, unilamellar dipalmitoyl phosphatidylcholine (DPPC), dimyristoyl phosphatidylcholine (DMPC) and distearoyl phosphatidylcholine (DSPC) vesicles at the gel-to-liquid crystal phase transition temperature was investigated. It was found that the permeability took the form of the transient lysis of a fraction of the population of vesicles. The effect on this lysis of the n-alcohols was seen to be very chain-length dependent, with a minimum at n = 8 (octan-1-ol) for DPPC vesicles. A similar minimum was observed in the presence of 0.1 mM Triton X-100, but the detergent could then interact with certain of the alcohols to produce permanent channels. The results are discussed in terms of the semi-empirical model of Brasseur et al. (1985) Biochim. Biophys. Acta 814, 227-236, for the interaction of the n-alcohols with a DPPC membrane. The effect of various n-alcohols on the outer and inner monolayers of DPPC vesicles was also studied and the results related to their fluidising effect, allowing channels to open at the phase transition temperature.

Alcohols↗