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Abstract  

The crystalline phase of dimyristoylphosphatidylethanolamine (DMPE)-water system was obtained by annealing the gel phase at around −5°C for periods up to 30 days. It was investigated by differential scanning calorimetry and negative-stain electron microscopy, particularly focusing on the behavior of water molecules. The crystalline phase showed a two-dimensional ribbonlike structure composed of regularly-stacked lamellae with an interlamellar spacing narrower than that of the gel phase. The conversion of the gel to crystalline phases on annealing was accompanied by a change in the bonding model of water molecules from a loosely-bound interlamellar water to a more loosely-bound water outside the lamellae. Ice-melting curves were deconvoluted using a computer program and different structures of water were estimated from enthalpy changes of each deconvoluted component. In accordance with a micrograph, only the loosely-bound water of one molecule of H2O per lipid was shown to be located between lamellae of the crystalline phase.

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Abstract  

The effect of free radicals obtained in hydroxyl and cerium(IV)-nitrilotriacetic acid free radical generating systems on contractile proteins (actin, myosin and their complexes in glycerinated muscle fibres) was studied using differential scanning calorimetry and spin trapping electron paramagnetic resonance technique. The analysis of spectra showed that selective attack of thiol groups – Cys-257 and Cys-374 residues of actin, and among others Cys-707 residue of myosin – and random attack of sidechains of the main proteins of muscle tissue produced structural and functional changes, which affected the ATP hydrolysis cycle and very likely the dynamics of actin. The melting curves obtained on protein systems support the view that global conformational changes accompany the local damage of free radicals.

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Abstract  

Hydration properties of lipid bilayer systems are compared for symmetric chain sphingomyelin (N-palmitoylsphingomyelin) and asymmetric chain sphingomyelin (N-lignoceroylsphingomyelin). These sphingomyelins were semisynthesized by a deacylation- reacylation process with a natural sphingomyelin used as a starting material. The number of differently bound water molecules was estimated by a deconvolution analysis of the ice-melting curves obtained by a differential scanning calorimetry (DSC) and was used to construct a water distribution diagram for these water molecules. Similarly to a natural sphingomyelin used for comparison, the asymmetric chain sphingomyelin was found to form small size vesicles having an internal cavity and incorporate 15 water molecules per molecule of lipid into its cavity, in contrast with 5 H2O/lipid for freezable interlamellar water observed for large size multilamellar vesicles formed by the symmetric chain sphingomyelin.

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Abstract  

The thermal denaturation of β-lactoglobulin in the presence of urea and alkylurea solutions were measured. In the presence of a high concentration of urea this protein shows not only heat but also cold denaturation. For studying the effect of temperature two methods were used, differential scanning calorimetry (DSC) and UV-spectroscopy. DSC provides direct model-independent determination of the transition enthalpy in comparison with UV-spectroscopy, which gives only apparent or van't Hoff enthalpy of transition. The UV-melting curves were analyzed on the basis of a two-state approximation. The apparent standard enthalpies of thermal denaturation, ΔH app. o , were compared with calorimetric ones.

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The intermolecular interactions of molecules within the bilayer are responsible for the lipid organisation, e.g. domain formation, and the interaction and stabilisation of proteins within the lipid matrix. The mixing behaviour of lipids, which reflects the intrinsic molecular interactions, can be deduced from the shape of the phase diagram (temperature vs. mole fraction diagram), which is constructed from the analysis of heat capacity curves obtained by DSC. However, there are no objective procedures to determine the temperatures corresponding to the border lines of the coexistence region, i.e. the liquidus and solidus curves of the phase diagram. The main challenge to overcome is to develop an objective method for the correct determination of the onset and offset temperatures of the melting curve for every single transition curve in a standardized manner. The presented paper describes a procedure for the simulation of heat capacity curves. In a second step, based on the results from the heat capacity curve simulation, a phase diagram is calculated using a non-ideal, non-symmetric mixing model. The non-ideality parameters obtained from the calculation describe the intermolecular interaction of both components in a single phase region. Using this procedure, examples of the mixing behaviour of various binary phospholipid systems are analysed and it is shown how the mixing behaviour is influenced by external factors like e.g. the pH or ionic strength.

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Congruent melting of binary compounds with non-negligible vapour pressure

I. Theoretical aspects of the congruent melting of a hydrate

Journal of Thermal Analysis and Calorimetry
Authors: J. Rouland, A. Thorén, J. Fournival, and R. Céolin

Abstract  

A theoretical temperature-specific volume-molar fraction (T-v-x) phase diagram of the binary systemA-H2O presenting a hydrateH with congruent melting is studied. The phase diagram is divided into two subsystems by the one-component phase diagram of the hydrateH. The eutectic invariant planes which occur in both subsystems are described. The relationships between the invariants are given. Isochoric and isoplethal theoretical sections are given. The one-component phase diagram of the hydrateH is described. It is pointed out that the triple line solid-liquid-vapour which relates the congruent melting is not necessarily perpendicular to the molar fraction axis. The means that the three phases, solid, liquid and vapour, have not necessarily the same composition. TheT-v-x representation gives an explanation to the deviation between the maximum of the melting curve and the stoichiometric composition of the hydrate which is often observed in theT-x binary diagramA-H2O.

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Journal of Thermal Analysis and Calorimetry
Authors: P. P. Fedorov, Yu. G. Sizganov, B. P. Sobolev, and M. Shvanner

A phase diagram of the system CaF2-GdF3 was studied by thermal and X-ray analysis. Two wide domains of solid solutions based on CaF2 and a high-temperature modification of α-GdF3 (LaF3-structural type) are present in this system. Two maxima were found on the melting curves of the Ca1−xGdxF2+x and α-(Gd1−yCayF3−y solid solutions, at 1428 ± 10‡ (5 mole % GdF3) and 1282 ± 5‡ (85 mole % GdF3), respectively. The coordinates of the eutectic are 60 mole % GdF3 and 1233 ± 5‡.

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melting curve. We have to remark here that polymorphic composition can be evaluated from melting curves only if the samples were not cooled below T R ∗ (step 3), because βα-recrystallization occurs below T R ∗ . This process disturbs the melting profile

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Acta Veterinaria Hungarica
Authors: Fumina Sasaoka, Jin Suzuki, Toh-Ichi Hirata, Toshihiro Ichijo, Kazuhisa Furuhama, Ryô Harasawa, and Hiroshi Satoh

. , Sato , S. and Harasawa , R. ( 2010 ): Differential detection of hemotropic Mycoplasma species in cattle by melting curve analysis of PCR products . J. Vet. Med. Sci. 72 , 77 – 79 (Erratum, J. Vet. Med. Sci. 72 , 1704

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. and Bartram, C. R. 2000: Rapid and reliable detection of Nras mutations in acute lymphoblastic leukemia by melting curve analysis using LightCycler technology. Leukemia 14 , 312-315. Rapid and reliable detection of Nras

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