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PubMed1985

Hydration of noncharged lipid bilayer membranes. Theory and experiments with phosphatidylethanolamines.

Calorimetric measurements have been made on the thermodynamics of the chain-melting phase transition of saturated diacylphosphatidylethanolamines, with chains containing 12-20 carbons, as a function of water content. The transition temperature, Tt, and the transition enthalpy, and entropy all decrease with an increase in water content; however, the effect on Tt lessens with an increase in chainlength. These results are compared with a theoretical description of lipid hydration in terms of the interlamellar water polarization (i.e., modified water structure) in the interbilayer region. The measured free energy, enthalpy and entropy of the transition and the transition temperature have an approximate hyperbolic tangent dependence on water content, infinity tanh (dw/2 xi), where dw is the interlamellar water-layer thickness and xi approximately equal to 0.25 nm is the water-order correlation length, in agreement with the theory. Auxiliary x-ray diffraction experiments yield results on the repulsive hydration forces between lipid lamellae consistent with the theory, and allow an estimate of the water orienting potential of the interface. The molecular origin of this potential is discussed in electrostatic terms, and the values of its associated molecular parameters are found to yield the right size of hydrational thermodynamic quantities. The theory thus provides an integrated, clear, and simple approach to the hydration properties of lipid membranes.

Biophysical Phenomena↗

PubMed1989

Thermotropic phase behavior of phosphatidylcholines with omega-tertiary-butyl fatty acyl chains.

The thermotropic phase behavior of a homologous series of phosphatidylcholines containing acyl chains with omega-tertiary butyl groups was studied by differential scanning calorimetry, Fourier transform infrared spectroscopy, and 31P-nuclear magnetic resonance spectroscopy (31P-NMR). Upon heating, aqueous dispersions of these lipids exhibit single transitions which have been identified as direct conversions from Lc-like gel phases to the liquid-crystalline state by both infrared and 31P-NMR spectroscopy. The calorimetric data indicate that the thermodynamic properties of the observed transition are strongly dependent upon whether the acyl chains contain an odd- or an even-number of carbon atoms. This property is manifest by a pronounced odd/even alternation in the transition temperatures and transition enthalpies of this homologous series of lipids, attributable to the fact that the odd-numbered compounds form gel phases that are more stable than those of their even-numbered counterparts. The spectroscopic data also suggest that unlike other lipids which exhibit the so-called odd/even effect, major odd/even discontinuities in the packing of the polymethylene chains are probably not the dominant factors responsible for the odd/even discontinuities exhibited by these lipids, because only subtle differences in the appropriate spectroscopic parameters were detected. Instead, the odd/even alternation in the physical properties of these lipids may be attributable to significant differences in the organization of the carbonyl ester interfacial regions of the lipid bilayer and to differences in the intermolecular interactions between the terminal t-butyl groups of the odd- and even-numbered homologues. Our results also suggest that the presence of the bulky t-butyl groups in the center of the lipid bilayer reduces the conformational disorder of the liquid-crystalline polymethylene chains, and promotes the formation of Lc-like gel phases. However, these Lc-like gel phases are considerably less ordered than those formed by saturated, straight-chain lipids.

Calorimetry, Differential Scanning↗

PubMed1987

Indications of the existence of ferroelectric units in excitable-membrane channels.

Previous work in excitability has focused primarily on the mathematical description of the phenomena, while mechanisms postulated to explain these were simple mechanical interpretations of the terms of this description. The problem considered here is that of the physical mechanism underlying excitation. The experimental facts to be explained must be not only the electrical behavior of the membrane, but also its electromechanical, electro-optic and thermoelectric behavior. Previous work on the physically grounded electrodiffusion theory foundered not because of the incorrectness of the electrodiffusion approach, but because the assumed description of the dielectric properties of the membrane was too simple. Extension of the dielectric equation of state to a nonlinear polynomial form converts the classical electrodiffusion system of equations into a nonlinear polynomial form converts the classical electrodiffusion system of equations into a ferroelectric electrodiffusion system. The consideration of ferroelectric behavior in excitable channels makes possible straight-forward physical explanation of the phenomena of membrane swelling during action potential, currents induced by temperature changes, transition temperatures, current-voltage hysteresis, nonlinear electrical behavior, voltage-dependent birefringence and rectangular pulses from single channels. The hypothesis is therefore proposed that excitable channels contain ferroelectric transmembrane units. These may be crystals or liquid crystals.

Animals↗

PubMed1997

Cell dynamics of folding in two-dimensional model proteins.

BACKGROUND: Functionally useful proteins are sequences of amino acids that fold rapidly under appropriate conditions into their native states. It is believed that rapid folders are sequences for which the folding dynamics entail the exploration of restricted conformations-the phase space can be thought of as a folding funnel. While there are many experimentally accessible predictions pertaining to the existence of such funnels and a coherent picture of the kinetics of folding has begun to emerge, there have been relatively few simple studies in the controlled setting of well-characterized lattice models. RESULTS: We design rapidly folding sequences by assigning the strongest couplings to the contacts present in a target native state in a two-dimensional model of heteropolymers. Such sequences have large folding transition temperatures and low glass transition temperatures. The dependence of median folding times on temperature is investigated. The pathways to folding and their dependence on the temperature are illustrated via a study of the cell dynamics-a mapping of the dynamics into motion within the space of the maximally compact cells. CONCLUSIONS: Folding funnels can be defined operationally in a coarse-grained sense by mapping the states of the system into maximally compact conformations and then by identifying significant connectivities between them.

Models, Chemical↗

PubMed2006

Chiral ionic liquid that functions as both solvent and chiral selector for the determination of enantiomeric compositions of pharmaceutical products.

We have successfully synthesized both enantiomers of a novel chiral ionic liquid, (R)- and (S)-[(3-chloro-2-hydroxypropyl) trimethylammonium][bis((trifluoromethyl)sulfonyl)amide] ((R)- and (S)-[CHTA]+[Tf2N]-) in optically pure form by a simple ion exchange reaction from corresponding chloride salts that are commercially available. In addition to the ease of preparation, this chiral IL has relatively high thermal stability (up to 300 degrees C), is liquid at room temperature (glass transition temperature of -58.4 degrees C), and exhibits strong enantiomeric recognition. The high solubility power and strong enantiomeric recognition ability make it possible to use this chiral IL to solubilize an analyte and to induce diastereomeric interactions for the determination of enantiomeric purity. In fact, we have successfully developed a novel method based on the near-infrared technique with this chiral IL serving both as solvent and as a chiral selector for the determination of enantiomeric purity. Enantiomeric compositions of a variety of pharmaceutical products and amino acids with different shape, size, and functional groups can be sensitively (milligram concentration) and accurately (enantiomeric excess as low as 0.6%) determined by use of this method.

Chlorpromazine↗

PubMed1984

Effect of surface composition on triolein hydrolysis in phospholipid vesicles and microemulsions by a purified acid lipase.

Sonicated dispersions of egg yolk phosphatidylcholine and triolein as vesicles and microemulsions have been used as substrates for the assay of a purified acid lipase. Previous studies have also shown that triolein localized in the surface phase of emulsions is the preferred substrate. In this study, we examined enzyme activity following several surface modifications using both vesicles and microemulsions. When the acidic phospholipids phosphatidylserine and phosphatidic acid were incorporated into both vesicles and microemulsions at up to 10 mol % of the total phospholipid, a dose-dependent reduction in the apparent Km was observed. Using the vesicles as substrate, a dose-dependent decrease in Vmax was also observed. Agarose gel electrophoresis was used to verify suspected changes in net particle charge. Analogous inclusion of phosphatidylethanolamine, sphingomyelin, or cholesterol did not affect kinetic parameters. Addition of oleic acid to sonication mixtures produced vesicles with a decreased apparent Km and Vmax, but triolein hydrolysis in microemulsions was not significantly altered. Triolein-containing vesicles prepared by using dimyristoyl- or dipalmitoylphosphatidylcholine were hydrolyzed maximally at the gel liquid-crystalline transition temperatures of the appropriate phospholipid. Differential scanning calorimetry was used to verify the temperatures of transition in these vesicles. The results indicate that acid lipase activity is influenced by the charge or physical state of the surface phase of model substrates and suggest that degradation of core components of naturally occurring substrates such as lipoprotein may be influenced by chemical changes on the surface of these particles.

Animals↗

PubMed1977

Orientation and dynamics of phospholipid head groups in bilayers and membranes determined from 31P nuclear magnetic resonance chemical shielding tensors.

31P nuclear magnetic resonance (NMR) powder spectra have been used to determine the principal values of the chemical shielding tensors of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidic acid. The shielding tensors in all cases were clearly nonaxial. The principal values for the monoester phosphatidic acid shielding tensor are -40, -4, and 48 ppm relative to 85% H3PO4. By contrast the diesters have values of -87, -25, and 119 ppm for phosphatidylcholine, -81, -20, and 105 ppm for phosphatidylethanolamine, and -80, -20, and 112 ppm for phosphatidylserine. This difference reflects the sensitivity of the 31P shielding tensor to chemical environment. Anisotropic motion of the molecules in lamellar dispersions of phospholipids caused an incomplete averaging of the shielding tensors resulting in partially narrowed spectra. Spectra of various phospholipid dispersions were recorded as a function of temperature and transitions observed at the gel-liquid crystalline phase transition temperatures. Using a reasonable set of initial conditions, it was shown that a simple model of molecular motion could successfully predict the observed spectra and their temperature dependences. The model includes rotations about the P-O(glycerol) bond and the molecular z axis and a wobble of the molecule about the bilayer normal. As the temperature increases, the wobble amplitude increases and the spectra narrow. A preliminary 31 P NMR spectrum of chick embryo fibroblasts is included. The similarities between this spectrum and those of the lamellar dispersions indicate that some of the predominant features are due to the phospholipid resonances.

Animals↗

PubMedDate not supplied

Thermosensitive lanthanide complexes of hyaluronan.

Addition of trivalent lanthanide salts to solutions of hyaluronan (HA), a naturally occurring anionic polysaccharide, resulted in an unexpected reverse-temperature phase transition (RTPT); i.e., the complexes were soluble when cooled but precipitated when warmed. A unique lower critical solution transition temperature (LCST) was observed for each lanthanide in the order (increasing LCST) Eu(3+) < Nd(3+)< Ce(3+) < Gd(3+) < La(3+) < Tb(3+) < Dy(3+) < Yb(3+) < Lu(3+) for high molecular weight HA. Moreover, the LCST values increased as the molecular weight of the HA decreased from 1730 to 190 kDa. The precipitation-dissolution behavior was fully reversible in a cyclical fashion; a lag in redissolution was observed as the temperature was lowered, and longer incubation times at each temperature minimized this lag. The RTPT behavior could be ablated by titration with 8 kDa HA to produce complexes soluble at ambient temperature. This is the first description of RTPT behavior in a biologically important glycosaminoglycan.

Chemical Precipitation↗

PubMed2005

A docking analysis of the statistical physics of protein-protein recognition.

We describe protein-protein recognition within the frame of the random energy model of statistical physics. We simulate, by docking the component proteins, the process of association of two proteins that form a complex. We obtain the energy spectrum of a set of protein-protein complexes of known three-dimensional structure by performing docking in random orientations and scoring the models thus generated. We use a coarse protein representation where each amino acid residue is replaced by its Voronoï cell, and derive a scoring function by applying the evolutionary learning program ROGER to a set of parameters measured on that representation. Taking the scores of the docking models to be interaction energies, we obtain energy spectra for the complexes and fit them to a Gaussian distribution, from which we derive physical parameters such as a glass transition temperature and a specificity transition temperature.

Biophysics↗

PubMed1976

Thiols of myosin. IV. "Abnormal" reactivity of S1 thiol and the conformational changes around S2 thiol.

The flexibility of the tertiary structure around the active site of myosin ATPase [EC 3.6.1.3] was studied using the reactivity of two specific thiol groups, S1 and S2, as a structural probe. The following four maleimide derivatives were used as thiol-directed reagents: N-ethylmaleimide (NEM), N-(4-methoxy-2-benzimidazolyl methyl) maleimide (MBM), N-(p-(2-benzimidazolyl)phenyl)maleimide (BIPM) and N-(4-dimethyl-amino-3,5-dinitrophenyl)maleimide (DDPM). 1. All the maleimide derivatives used activated the Ca2+-ATPase activity and inhibited the EDTA-ATPase activity, like NEM, indicating that they modified S1. The rate of modification of S1 by NEM and BIPM increased with increasing pH, while that by DDPM decreased. BIPM simultaneously modified S1 and S2. 2. S1 showed much higher reactivity toward the maleimides, except for BIPM, than did N-acetylcysteine (N-Ac-Cys) a low molecular-weight model compound. The extremely small pKa value of S1, 6.28, accounted for this high reactivity. In addition, the ATP-induced increase in its reactivity inducated that S1 was in a buried state. Kinetic analysis showed that the teritiary structure around S1 at alkaline pH differed from that at acidic pH. 3. The apparent rate constant of S2-modification with NEM was approximately one seven-hundredth and one four-hundredth of those of S1 and N-Ac-Cys, respectively. Fluorimetric studies using BIPM revealed that S2 in the buried state was exposed upon adding ATP; this was compensated by the burying of some other thiol group(s) (Sp). Non-linearity of the Arrhenius plots of the reaction rate of S2 suggested that the S2 region of myosin had different conformations at high and low temperatures, the transition temperature being 10--15degrees. This non-linearity completely disappeared in the presence of Mg2+-ATP. On the other hand, Arrhenius plots for the thiols reactive to BIPM did not show non-linearity in the presence or absence of ATP.

Acetylcysteine↗

PubMed1997

Stress and asymmetry during arrested development of the Australian sheep blowfly.

The dieldrin and diazinon resistance systems of the Australian sheep blowfly (Lucilia cuprina) have been used previously to relate stress, departures from bilateral symmetry, developmental stability and relative fitness. These systems are now used to consider stress and asymmetry in a developmental context. Larval to adult development is shown to be significantly impaired after arrested development at 8 degrees C, however the asymmetry score of adults of a given genotype is similar after arrested or continuous development. Selection against dieldrin-resistant and unmodified diazinon-resistant genotypes occurs during arrested development because greater proportions of these genotypes pupae at 8 degrees C than do susceptible or modified diazinon-resistant genotypes. Pre-pupae of all genotypes complete development equally successfully when transferred from 8 degrees C to 27 degrees C. Adults fail to emerge when pupae formed at 8 degrees C undergo this temperature transition. Temperature-shift experiments show the asymmetry score is determined between pre-pupal and pupal stages of the life cycle. This stage occurs at 27 degrees C in arrested and continuously developing cultures providing an explanation for the independence of stress, selective mortality during developmental arrest and asymmetry score. The results emphasize the need for genetic, environmental and developmental data before an asymmetry phenotype can be directly related to developmental stability and relative fitness.

Animals↗

PubMed2001

Superconductivity near itinerant ferromagnetic quantum criticality.

Superconductivity mediated by spin fluctuations in weak and nearly ferromagnetic metals is studied close to the zero-temperature magnetic transition. We solve analytically the Eliashberg equations for p-wave pairing and obtain the quasiparticle self-energy and the superconducting transition temperature T(c) as a function of the distance to the quantum critical point (QCP). We show that the reduction of quasiparticle coherence and lifetime due to scattering by quasistatic spin fluctuations is the dominant pair-breaking process, which leads to a rapid suppression of T(c) to a nonzero value near the QCP. We point out the differences and similarities of the problem to that of paramagnetic impurities in superconductors.

Journal Article↗

PubMed2003

Energy landscape theory, funnels, specificity, and optimal criterion of biomolecular binding.

We study the nature of biomolecular binding. We found that in general there exists several thermodynamic phases: a native binding phase, a non-native phase, and a glass or local trapping phase. The quantitative optimal criterion for the binding specificity is found to be the maximization of the ratio of the binding transition temperature versus the trapping transition temperature, or equivalently the ratio of the energy gap of binding between the native state and the average non-native states versus the dispersion or variance of the non-native states. This leads to a funneled binding energy landscape.

Drug Design↗

PubMed2006

Intermediate-temperature superfluidity in an atomic fermi gas with population imbalance.

We derive the underlying finite temperature theory which describes Fermi gas superfluidity with population imbalance in a homogeneous system. We compute the pair formation temperature, superfluid transition temperature Tc, and superfluid density in a manner consistent with the standard ground state equations and, thereby, present a complete phase diagram. Finite temperature stabilizes superfluidity, as manifested by two solutions for Tc or by low T instabilities. At unitarity, the polarized state is an "intermediate-temperature superfluid."

Journal Article↗

PubMed1992

Effect of thermal placement techniques on some physical properties of gutta-percha.

Some clinical techniques for the placement of gutta-percha root fillings involve the application of heat. This study was undertaken to assess the effects of intracanal heating techniques on the following properties of gutta-percha: coefficient of thermal expansion, softening temperature, phase transition temperature and organic content. Samples from each of four products were prepared by three different methods. The materials were studied by thermomechanical analysis, simultaneous thermogravimetry and differential thermal analysis, and by measurement of weight loss on ashing. It was shown that the techniques of gutta-percha placement involving heating in the root canal caused reversible physical changes in the materials without any apparent change in chemical composition. The average coefficient of thermal expansion was 137 x 10(-6)/degrees C, the softening temperature was 55.5 degrees C, there were two characteristic phase changes, and the organic content was 25%.

Differential Thermal Analysis↗

PubMed2006

Chitosan-soyprotein interaction as determined by thermal unfolding experiments.

Chitosan interaction with soybean beta-conglycinin beta(3) was investigated by thermal unfolding experiments using CD spectroscopy. The negative ellipticity of the protein was enhanced with rising solution temperature. The transition temperature of thermal unfolding of the protein (T(m)) was 63.4 degrees C at pH 3.0 (0.15 M KCl). When chitosan was added to the protein solution, the T(m) value was elevated by 7.7 degrees C, whereas the T(m) elevation upon addition of chitosan hexamer (GlcN)(6) was 2.2 degrees C. These carbohydrates appear to interact with the protein stabilizing the protein structure, and the interaction ability could be evaluated from the T(m) elevation. Similar experiments were conducted at various pHs from 2.0 to 3.5, and the T(m) elevation was found to be enhanced in the higher pH region. We conclude that chitosan interacts with beta-conglycinin through electrostatic interactions between the positive charges of the chitosan polysaccharide and the negative charges of the protein surface.

Antigens, Plant↗

PubMedDate not supplied

Two intermediate states I and J trapped at low temperature in the photocycles of two BLUF domain proteins of cyanobacteria Synechocystis sp. PCC6803 and Thermosynechococcus elongatus BP-1.

We identified the two intermediate states, I and J, that are common in the photocycles of the cyanobacterial BLUF (sensor of Blue Light Using Flavin) domain proteins of Slr1694 of Synechocystis sp. PCC6803 and Tll0078 of Thermosynechococcus elongatus BP-1 by analyzing the absorption spectra at 5 K. Illumination at 5 K accumulated intermediate forms (designated as I5 and I9), which showed 5 and 9 nm redshifts of the absorption bands of flavin in the Tll0078 and Slr1694 proteins, respectively. I5 (I9) was converted into the next intermediate, which have 11 nm (14 nm) red-shifted absorption bands J11 (J14) after dark annealing at 230 K (240 K). Further dark annealing at 280 K (270 K) of J11 (J14) produced the signal-transmitting final form F490 (F495), with a small increase in the absorption at around 490 nm (495 nm). The results indicate that the BLUF proteins of Tll0078 and Slr1694 exhibit the common photocycle of D471 (D467) --> I5 (I9) --> J11 (J14) --> F490 (F495) at low temperature. The transition temperatures for these intermediate forms differ for two proteins. The amount of I5 (I9) accumulated at 5 K was small and increased at a higher temperature, suggesting heterogeneity of the protein structure that determines the reaction pathway.

Amino Acid Sequence↗

PubMed1988

The effect of gangliosides on the lamellar phase behaviour of phosphatidylethanolamines.

The thermotropic properties of aqueous phosphatidylethanolamine dispersions vary with hydration. Measured by EPR-spectroscopy freshly hydrated dimyristoylphosphatidylethanolamine dispersions exhibit a gel to liquid-crystalline phase transition at Tml = 48 degrees C. Dehydration could be induced by prolonged incubation of a hydrated sample at 4 degrees C. The phase transition temperature of the dehydrated phase was determined to be Tmh = 54 degrees C. From the measured phase transition curves we followed the dehydration with time and found a cooperative nucleation process. A 50% dehydration was reached after 5 days. This dehydration process could be prevented by gangliosides: 1.5 mol% of GT1b, 4 mol% of GM1 or 7 mol% of GD1a or GM3 but also 7 mol% of phosphatidic acid were able to stabilize the hydrated phase completely. The effect of gangliosides GM1, GM3, GD1a, GT1b and of the negatively charged phosphatidic acid on the phase behaviour of dimyristoylphosphatidylethanolamine (DMPE) dispersions were investigated. The phase transition temperature of freshly hydrated DMPE samples was successively decreased from 48 to 43 degrees C with increasing amounts of GD1a up to 10 mol% whereby the phase transition was significantly broadened. Gangliosides GM1, GM3 and GT1b as well as phosphatidic acid had minor effects. Dispersions of pure DMPE prepared below the transition temperature Tml form the dehydrated phase again with a melting temperature of Tmh = 54 degrees C. In the presence of 10 mol% GD1a or GT1b this value is reduced to Tml, the phase transition temperature of the hydrated phase. The reduction induced by GM3 is less pronounced. With GM1 or phosphatidic acid the samples remain partially dehydrated and the phase transition curves become biphasic up to 7 mol% ganglioside or phosphatidic acid.

Chemical Phenomena↗