Effect of Nucleotides on Thermal Transitions of Myosin

The internal dynamics and the thermal stability of myosin in rabbit psoas muscle fibres in different intermediate states of the ATP hydrolysis cycle were studied by differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) spectroscopy. Three overlapping endotherms were detected in rigor, in strongly binding and weakly binding state of myosin to actin. The transition at 58.4°C can be assigned to the nucleotide-binding domain. The transition at highest temperature represents the unfolding of the actin and the contributions arising from the actin-myosin interaction. The transition of 54°C reflects the interaction between the subunits of myosin. Nucleotide binding induced shifts of the melting temperatures and produced variations in the calorimetric enthalpy changes. The changes of the EPR parameters indicated local rearrangements of the internal structure in myosin heads. This revised version was published online in August 2006 with corrections to the Cover Date.     

Broadened glass transition in a liquid-crystalline polymer studied by thermally stimulated currents,AC dielectric,dynamic mechanical,and DSC methods

Thermally stimulated currents (TSC), a. c. dielectric, dynamic mechanical (DMTA), and differential scanning calorimetry (DSC) methods were used to study the glass transition in a thermotropic liquid-crystalline copolyester. All the techniques were consistent in the determination of the main glass transition temperature. Using the high sensitivity of the TSC thermal sampling method, it was shown that cooperative glass transition-like relax-ations occur down to 100°C below the main glass transition. DSC was sensitive only to a broadening of the glass transition to about ca. 30°C, so it was concluded that the thermal sampling method is sensing a very small fraction of cooperatively relaxing species which cannot be detected by DSC. Ac dielectric measurements and DMTA also indicated that the glass transition was broad, but difficulties with overlapping transitions prevented quantitative determination of the breadth of the glass transition. The results suggest that the broad glass transition, in this mostly amorphous LCP, is due to chemical heterogeneity of the copolyester chain. Other evidence indicates that the broadening is not due to the oriented nature of the glassy state. Some discussion is presented concerning how the heterogeneous nature of the LCP glass leads to compensation of the Arrhenius curves obtained by the thermal sampling method. © 1993 John Wiley & Sons, Inc.     

角度重叠模型的应用 Ⅰ.计算过渡金属配合物电子光谱的微机程序

按照角度重叠模型,用FORTRAN语言编写了计算过渡金属配合物电子光谱的微机程序。     

Vanadate (Vi) and ADP induced domain motions in myosin head by DSC and EPR

Thermal stability and internal dynamics of myosin head in psoas muscle fibres of rabbit in the intermediate state AM.ADP.P_i - mimicked by AM.ADP.V_i - of the ATP hydrolysis cycle was studied by differential scanning calorimetry and spin label electron paramagnetic resonance spectroscopy. Three overlapping endotherms were detected in rigor, in strongly binding ADP and weakly binding AM.ADP.V_i state of myosin to actin. The transition at 54.0°C can be assigned to the 50 k actin-binding domain. The transition at highest temperature (67.3°C) represents the unfolding of actin and the contributions arising from the nucleotide-myosin head interaction. The transition at 58.4°C reflects the melting of the large rod part of myosin. Nucleotide binding (ADP, ATP plus orthovanadate) induced shifts of the melting temperatures and produced changes in the calorimetric enthalpies. The changes of the EPR parameters indicated local rearrangements of the internal structure in myosin heads in agreement with DSC findings. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal transitions in PHEA hydrogels by thermomechanical analysis. A comparison with DSC data

The thermal transitions observed in hydrogels are frequently explained by invoking the existence of different kinds of water such as ‘bound’ and ‘free’ water. However these interpretations are intuitive and do not consider neither the thermodynamics of phase equilibrium nor kinetic aspects. Alternatively, the complicated experimental DSC thermograms have been simply explained in a thermodynamic framework with the help of a transitions diagram where the temperature of the transitions is plotted versus water concentration in the gel. In this work we further support the interpretation of the DSC thermograms on the basis of this diagram by comparing those thermograms with TMA results. The volume changes in the cooling and heating scans can be correlated with the enthalpy changes in the material and can be explained with the transition diagram.     

Thermodynamics of activated phase transitions of 8CB: DSC and MC calorimetry

The present paper reports the heating rate effect on the phase transitions of a pure liquid crystal octylcyanobiphenyl (8CB) with use of Differential Scanning Calorimetry (DSC) and Modulation Calorimetry (MC) techniques. The DSC runs were taken at various temperature ramp rates from 20 to 0.5 K/min for heating and cooling scans. Well-defined endothermic/exothermic peaks were found at the melting/crystallization, smectic-A to nematic (SmA-N), and nematic to isotropic (N-I) transitions on heating/cooling scans, respectively. All transitions shift in temperature significantly with different ramp rates. The temperature shift of C(p) peaks between heating and cooling scans indicates the order of the transitions. In addition, all transitions follow an Arrhenius behavior. The activation energy of a transition increases as the total energy involved in the transition decreases. The respective enthalpy and entropy change of each transition provides information on the Gibbs free energy. The significance of the results is discussed in terms of the order of transitions. A comparative analysis of MC and DSC techniques highlights the significance of the two techniques. MC is a practicable tool for observing the phase dynamics whereas DSC is a good tool for studying the rate kinematics of the transitions.     

Calorimetric study of blends of poly(butylene terephthalate) and a liquid crystalline polyester

The thermal properties of solution-prepared blends of poly(butylene terephthalate) (PBT) and liquid crystalline poly(biphenyl-4,4′-ylene sebacate) (PB8) have been studied by differential scanning calorimetry (DSC). The smectic-to-isotropic (s → i) transition of the mesomorphic component is observed at temperatures slightly increasing with the PB8 content, in the 270–280°C range; on cooling, the mesophase formation (i → s transition) takes place at temperatures that decrease markedly with decreasing PB8 content. The temperatures of the crystal-to-smectic and smectic-to-crystal transitions of PB8 are almost invariant with blend composition. The melting and crystallization temperatures of the PBT phase decrease on increasing the content of the liquid crystalline component. These results, together with those of isothermal calorimetry of both the crystallization of the PBT component and the mesophase formation of the PB8 component of the blends, indicate that the two polymers are not immiscible in the isotropic state. In this latter state, however, the two polyesters undergo transesterification, which can be followed through changes in the DSC scans. The effect of the thermal history on the properties of the blends has been studied with particular attention. Both the dynamic and the isothermal calorimetric measurements provide evidence of an increase of the degree of crystallinity of PBT on addition of the liquid crystalline component up to about 35–50% by weight.     

Differential Scanning Calorimetry and Hydrodynamic Study of Bacterial Viruses. About possible heat effects in hermetically closed calorimetric vessels with free volume above the liquid

The phase transitions occurring in aqueous solutions of macromolecules and their complex structures (like order-disorder transitions in proteins or nucleic acids solutions) are usually accompanied by small changes in their specific partial volumes. If the quantity of these substances in the closed calorimetric vessels is relatively large (few mg) and if the phase transition is accompanied by a high change of specific partial volume (like in solution of bacteriophages),it is possible to detect some imaginary heat effects in the DSC calorimeters which have closed (sealed) vessels with free volume above the liquid. This revised version was published online in July 2006 with corrections to the Cover Date.     

Retrieval of spectral and dynamic properties from two-dimensional infrared pump-probe experiments

We have developed a fitting algorithm able to extract spectral and dynamic properties of a three level oscillator from a two-dimensional infrared spectrum (2D-IR) detected in time resolved nonlinear experiments. Such properties go from the frequencies of the ground-to-first and first-to-second vibrational transitions (and hence anharmonicity) to the frequency-fluctuation correlation function. This last is represented through a general expression that allows one to approach the various strategies of modeling proposed in the literature. The model is based on the Kubo picture of stochastic fluctuations of the transition frequency as a result of perturbations by a fluctuating surrounding. To account for the line-shape broadening due to pump pulse spectral width in double-resonance measurements, we supply the fitting algorithm with the option to perform the convolution of the spectral signal with a Lorentzian function in the pump-frequency dimension. The algorithm is tested here on 2D-IR pump-probe spectra of a Gly-Ala dipeptide recorded at various pump-probe delay times. Speedup benchmarks have been performed on a small Beowulf cluster. The program is written in FORTRAN language for both serial and parallel architectures and is available free of charge to the interested reader.     

DSC study on the motor protein myosin in fibre system

We have examined by DSC the complexes of myosin with actin in fibre system in the absence of nucleotides and the intermediate state of ATP hydrolysis by mimicking stable complex with myosin and ADP and beryllium fluoride in muscle fibres. Comparing the DSC results with other structural analogues of phosphate P_i leads the conclusion that the AM.ADP.BeF_x complex favours the AM.ADP.P_i complex in fibre system. The deconvolution of DSC scans resulted in four transitions, the first three transition temperatures were almost independent of the intermediate state of the muscle, the last transition temperature was shifted to higher temperature, depending on the actual intermediate states of ATP hydrolysis. In AM.ADP.V_i state the transition temperature at the second and third transitions (actin binding domain and myosin rod) varied only slightly, whereas the last one (the fourth transition) shifted markedly to higher temperature depending on the ternary complex, e.g. in case of ADP plus BeF_x it was 77.7 °C, the highest value in weakly binding state of myosin to actin. The sum of calorimetric enthalpies of the first and last curves was practically constant, but their fractions depended on the state of the muscle. In strongly binding state of myosin to actin (rigor, ADP state) the fraction of the first transition was much larger, than the last one, whereas in weakly binding state of myosin to actin, the fraction of the first transition decreased at the expense of the last one. It supports also the view that these transitions are parts of the same portion of the myosin molecule.     

Calorimetric study of activated kinetics of the nematic and smectic phase transitions in an aligned nano-colloidal liquid crystal+aerosil gel

This study explores the calorimetric analysis of an aligned nano-colloidal aerosil dispersed octyl-cyanobiphenyl gel. This system was prepared by solvent dispersion method (SDM). Heating scans were performed at different heating rates from 20 to 1 K min⁻¹ using DSC. Aligned samples follow Arrhenius behavior and showed a temperature shift in SmA-N and N-I transitions towards lower temperature. These samples show a decreased activated kinetics and an interesting relationship with their enthalpy. This behavior can be explained in terms of surface and molecular interaction between aerosil nano-particles and 8CB molecules and produced strain in the system.     

DSC examination of alloys

The formation and thermal dissolution of dispersed particles was studied in aluminium alloys. It was found that only high heating rates (80°C min⁻¹) could provide DSC curves characteristic of the phase structure of the samples. The kinetic evaluation of the DSC curves was carried out by least squares curve fitting. In this way reasonable kinetic parameters and reliable peak resolution could be obtained for the overlapping peaks.     

Effect of tetracaine on model and erythrocyte membranes by DSC and EPR

Summary DSC and EPR experiments were performed on human erythrocyte membranes and DPPC vesicles in order to study the effect of the anaesthetic drug tetracaine on structure and dynamics of the lipid region. Experiments using spin label technique showed that tetracaine induced fluidity changes of the lipid region in the environment of the fatty acid probe molecules incorporated into the membranes in the vicinity of the lipid-water interface. Similarly to EPR observations, DSC measurements reported decrease of the main melting and the pretransition temperature in comparison to control DPPC vesicles, which is the sign of destabilisation of the structure in the head group region of the lipids. Similar effect was observed in the case of erythrocytes where the protein conformation was also controlled in the presence of drug. A separated membrane melting with well distinguished membrane protein phase transition was found that was affected significantly by tetracaine. These results suggest that tetracaine is able to modify not only the internal dynamics of erythrocyte membranes and produce destabilisation of the lipid structure, but the protein system as well. These might lead to further damage of the biological functions.     

Investigation of poly[oligo(ethylene glycol)diacrylates] as potential stationary phases in GC

Poly[oligo(ethylene glycol)diacrylate]s were investigated as potential candidates for application as stationary phases in capillary gas chromatography. Depending on the molar mass of the monomer, up to three different phase transitions were observed in calorimetric scans of the polymers. Two transitions have been identified as the glass transition and melting of crystallites while the nature of the third effect remains unknown. The new stationary phases demonstrate a good separating ability and selectivity in the viscous‐elastic state, i.e. at temperatures above the glass transition and melting points. The new polymeric stationary phases possess selectivity similar to conventional PEG columns but provide better thermal stability than conventional PEG stationary phases.     

Confinement and orientational study at liquid crystal phase transitions

Abstract

We have studied the heat capacity of the thermotropic liquid crystal, octylcyanobiphenyl (8CB), confined to the nearly cylindrical, 0·2 μm diameter pores of Anopore membranes. Orientation of the nematic director within the pores can be controlled with surface treatment. It is known from NMR measurements that the nematic director is aligned parallel to the pore axis in the untreated membrane. A perpendicular alignment is obtained when the pore surface is treated with lecithin. The second order smectic A to nematic (S_A–N) and the weakly first order nematic to isotropic (N–I) phase transitions of 8CB were studied in these pores, for both director orientations, using an AC calorimetry technique. Effects on heat capacity amplitudes, transition temperature shifts, rounding and broadening of these phase transitions will be presented and contrasted with bulk measurements.     

The calorimetric calibration of differential scanning calorimetry cells

In this paper it is shown that in many cases enthalpy determinations can be carried out with a precision <1%. The influences of various sample and instrumental properties are described. The enthalpies of 24 compounds with 30 phase changes (polymorphic transitions or melting points) were redetermined. Twelve of the compounds with 15 transitions in the temperature range 0?670°C are selected and recommended for calorimetric DSC calibration. The linearization of the calibration curve as stated by the manufacturer of the instrument employed was fully confirmed.     

Differential scanning calorimetry (DSC) of semicrystalline polymers

Differential scanning calorimetry (DSC) is an effective analytical tool to characterize the physical properties of a polymer. DSC enables determination of melting, crystallization, and mesomorphic transition temperatures, and the corresponding enthalpy and entropy changes, and characterization of glass transition and other effects that show either changes in heat capacity or a latent heat. Calorimetry takes a special place among other methods. In addition to its simplicity and universality, the energy characteristics (heat capacity C _P and its integral over temperature T—enthalpy H), measured via calorimetry, have a clear physical meaning even though sometimes interpretation may be difficult. With introduction of differential scanning calorimeters (DSC) in the early 1960s calorimetry became a standard tool in polymer science. The advantage of DSC compared with other calorimetric techniques lies in the broad dynamic range regarding heating and cooling rates, including isothermal and temperature-modulated operation. Today 12 orders of magnitude in scanning rate can be covered by combining different types of DSCs. Rates as low as 1 μK s⁻¹ are possible and at the other extreme heating and cooling at 1 MK s⁻¹ and higher is possible. The broad dynamic range is especially of interest for semicrystalline polymers because they are commonly far from equilibrium and phase transitions are strongly time (rate) dependent. Nevertheless, there are still several unsolved problems regarding calorimetry of polymers. I try to address a few of these, for example determination of baseline heat capacity, which is related to the problem of crystallinity determination by DSC, or the occurrence of multiple melting peaks. Possible solutions by using advanced calorimetric techniques, for example fast scanning and high frequency AC (temperature-modulated) calorimetry are discussed.     

Deconvolution of composite metastable peaks: A new method for the determination of metastable transitions occurring in the first field free region

The masses of daughter ions resulting from metastable transitions in the first field free region of a “reversed geometry” mass spectrometer can be accurately determined through a mass analysed ion kinetic energy scan at the apparent mass at which these daughter ions travel through the magnetic sector. A combination of these mass analysed ion kinetic scans with scanning the magnetic flux allows the resolution of overlapping metastable diffuse peaks.     

Dynamics of p-terphenyl crystals at the phase transition temperature: a zero-field EPR study of the photoexcited triplet state of pentacene in p-terphenyl crystals

Pulsed zero-field electron paramagnetic resonance free induction decay (ZF EPR FID) techniques are employed to study the phase transition of p-terphenyl crystals (Tc = 193 K) by measuring selectively populated photoexcited triplet ZF transitions of dilute pentacene molecules in p-terphenyl single crystals. The sensitivity of ZF spectroscopy to small shifts in local magnetic fields enables the studies of guest-host configuration changes over a wide temperature range. Here we report the observation of guest pentacene (-h(14) and -d(14)) triplet ZF EPR FID spectra that disappear abruptly at Tc and of spectral broadening and shift below Tc. We interpret these spectral changes as evidence for guest couplings to host phenyl rings. Further, these data allow assignments of spectroscopic sites to crystallographic sites that occur in the phase transition.     

Two phase transitions of poly(N-isopropylacrylamide) brushes bound to gold nanoparticles

The thermally induced phase transition of the poly(N-isopropylacrylamide) (PNIPAM) brush covalently bound to the surface of the gold nanoparticles was studied using high-sensitivity microcalorimetry. Two types of PNIPAM monolayer protected clusters (MPCs) of gold nanoparticles were employed, denoted as the cumyl- and the cpa-PNIPAM MPCs, bearing either a phenylpropyl end group or a carboxyl end group on each PNIPAM chain, respectively. The PNIPAM chains of both MPCs exhibit two separate transition endotherms; i.e., the first transition with a sharp and narrow endothermic peak occurs at lower temperature, while the second one with a broader peak occurs at higher temperature. With increase of the MPC concentration, the transition temperature corresponding to the first peak only slightly changes but the second transition temperature strongly shifts to lower temperature. The calorimetric enthalpy change in the first transition is much smaller than that in the second transition. The ratio of the calorimetric enthalpy change to the van't Hoff enthalpy change indicates that in the first transition PNIPAM segments show much higher cooperativity than in the second one. The investigation of pH dependence of two-phase transitions further indicates the PNIPAM brush reveals two separate transitions even with a change in interchain/interparticle association. The observations are tentatively rationalized by assuming that the PNIPAM brush can be subdivided into two zones, the inner zone and the outer zone. In the inner zone, the PNIPAM segments are close to the gold surface, densely packed, less hydrated, and undergo the first transition. In the outer zone, on the other hand, the PNIPAM segments are looser and more hydrated, adopt a restricted random coil conformation, and show a phase transition, which is dependent on both concentration of MPC and the chemical nature of the end groups of the PNIPAM chains. Aggregation of the particles, which may also affect the phase transition, is briefly discussed.