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PubMed1990

Proton flow along lipid bilayer surfaces: effect of halothane on the lateral surface conductance and membrane hydration.

Impedance dispersion in liposomes measures the lateral charge transfer of lipid membrane surfaces. Depending on the choice of frequency between 1 kHz and 100 GHz, relaxation of the counterions at the interface, orientation of the head group, and relaxation of the bound and free water are revealed. This study measured the impedance dispersion in dipalmitoylphosphatidylcholine (DPPC) liposomes at 10 kHz. The surface conductance and capacitance showed breaks at pre- and main transition temperatures. Below the pre-transition temperature, the activation energy of the ion movement was 18.1 kJ.mol-1, which corresponded to that of the spin-lattice relaxation time of water (18.0 kJ.mol-1). At temperatures between pre- and main transition it increased to 51.3 kJ.mol-1, and agreed with 46.2-58.0 kJ.mol-1 of the activation energy of the dielectric relaxation of ice. Because the present system was salt-free, the ions were H3O+ and OH-, hence, their behavior represents that of water. The above results show that below the pre-transition temperature, the conductance is regulated by the mobility of free ions, or the number of free water molecules near the interface. On the other hand when the temperature exceeded pre-transition, melting of the surface-bound water crystals became the rate-limiting step for the proton flow. Halothane did not show any effect on the ion movement when the temperature was below pre-transition. When the temperature exceeded pre-transition, 0.35 mM halothane (equilibrium concentration) decreased the activation energy of the ion movement to 29.3 kJ.mol-1. This decrease indicates that halothane enhanced the release of the surface-bound water molecules at pre-transition. The surface-disordering effect of halothane was also shown by depression of the pre-transition temperature and decrease of the association energy among head groups from 9.7 kJ.mol-1 of the control to 5.2 kJ.mol-1 at 0.35 mM.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2001

Dynamics of a spin-1 Ising system in the neighborhood of equilibrium states.

The dynamics of a spin-1 Ising system containing biquadratic interactions near equilibrium states is formulated by the method of thermodynamics of irreversible processes. From the expression for the entropy production, generalized forces and fluxes are determined. The kinetic equations are obtained by introducing kinetic coefficients that satisfy the Onsager relation. By solving these equations a set of relaxation times is calculated and examined for temperatures near the phase transition temperatures, with the result that one of the relaxation times approaches infinity near the second-order phase transition temperature on either side, whereas it is sharply cusped at the first-order phase transition temperature. On the other hand, the other relaxation time has a cusp at the second-order phase transition temperature but displays a different behavior at the first-order phase transition, just a jump discontinuity. The behavior of both relaxation times is also investigated at the tricritical point. Moreover, the phase transition behaviors of the relaxation times are also obtained analytically via the critical exponents. Results are compared with conventional kinetic theory in the random-phase or generalized molecular-field approximation and a very good overall agreement is found.

Journal Article↗

PubMed1996

Low density lipoprotein particle size and core cholesteryl ester physical state affect the proton NMR magnetic environment of fatty acid methylene and methyl nuclei.

Recent studies using proton NMR to quantify plasma lipoprotein concentrations have shown that lipoprotein particle size affects the chemical shift of methyl and methylene resonances. The purpose of this study was to investigate the interrelationship of low density lipoprotein (LDL) size and cholesteryl ester (CE) physical state on the chemical shift of methyl and methylene protons. LDL were isolated from the plasma of nonhuman primates fed diets containing lard or fish oil to result in a wide range of LDL particle sizes and CE core transition temperatures for NMR analysis. The proportion of nuclei in the fluid state in LDL at different temperatures, measured as proton NMR peak intensity, paralleled the melting profile of LDL CE determined by differential scanning calorimetry. At 37 degrees C the linewidths of several resolvable fatty acyl resonances, but not the choline methyl resonance, were significantly less in the fish oil LDL, indicating a less restrictive environment along the fatty acyl chain. The (CH2)n and t-CH3 resonances demonstrated an upfield shift (i.e., smaller chemical shift) with increasing temperature for both diet groups, but the peaks for fish oil LDL were always upfield from those of the lard LDL regardless of temperature. No change in the chemical shift of the choline CH3 resonance was observed as a function of dietary fat or temperature. Above the transition temperature for LDL CE there was a significant positive correlation between LDL size and the chemical shift of the (CH2)n and t-CH3 resonances. This relationship was not statistically significant for the same LDL below the Ce transition temperature. We conclude that LDL CE must be fully melted to obtain accurate results for LDL particle size distribution as well as mass quantification using portion NMR spectroscopy.

Animals↗

PubMed1998

A long-lifetime Ru(II) metal-ligand complex as a membrane probe.

A luminescent metal-ligand complex, [Ru(bpy)2(dppz)]2+, (where dppz is dipyrido[3,2-a:2',3'-c] phenazine), was used as a photoluminescence probe for investigating submicrosecond lipid dynamics in a dipalmitoyl-L-alpha-phosphotidylglycerol (DPPG) model bilayer system. The luminescence of [Ru(bpy)2(dppz)]2+ in buffer is completely quenched but becomes luminescent when intercalated into DPPG vesicles. The experimental results show that the emission intensity of [Ru(bpy)2(dppz)]2+ intercalated into DPPG vesicles increases dramatically as temperature is increased towards the lipid phase transition temperature. This effect is abolished in bilayers containing a high concentration (> 30 mol%) of cholesterol, suggesting this probe is sensitive to the membrane composition. Frequency-domain emission intensity decays, measured as a function of increasing temperature towards the lipid phase transition temperature (2 to 57 degrees C), display two major lifetime components. The short lifetime disappears at temperatures well above the phase transition temperature. A comparison of oxygen quenching with iodide quenching suggests the heterogeneity of probe location at temperatures well below the lipid phase transition temperature and the homogeneity of probe location at temperature well above the lipid phase transition temperature. [Ru(bpy)2(dppz)]2+ displays polarized emission, enabling the study of membrane dynamics. The long decay time displayed by this probe allows measurement of the overall rotational correlation time of lipid vesicles on the microsecond time-scale. Because of the long lifetime, polarized emission, and background free nature of the photoluminescence measurements, [Ru(bpy)2(dppz)]2+ has numerous applications in the biophysical studies of membranes.

Anisotropy↗

PubMed1976

Interactions between anesthetics and lipid mixtures. Normal alcohols.

The effects of normal alcohols up to 1-dodecanol on phase transitions in phosphatidylcholines and phosphatidylethanolamines have been studied using chlorophyll a as fluorescent probe. With the phosphatidylcholines, alcohols up to octanol cause a lowering of the transition temperature, and a broadening of the transition, whereas for dipalmitoylphosphatidylethanolamine, only a lowering of the transition is observed. The lowering of the phase transition temperature in dipalmitoylphosphatidylcholine by butanol and hexanol is close to that expected for ideal behavior, but the behavior of the longer chain alcohols becomes less ideal. The effects of these alcohols on mixtures of lipids have been studied, and they illustrate the care necessary if these plots of temperatures of onset and completion of gel phase formation are to be called "phase diagrams". The effect of 1 -octanol on mixtures of lipids is to increase the proportion of lipid present in the lipid-crystalline state. In contrast, 1-decanol causes an increase in the phase transition temperature for dimyristoylphosphatidylcholine, although it lowers the transition temperature for dipalmitoylphosphatidylcholine, and 1 -dodecanol raises the transition temperature for both of these phosphatidylcholines, although it lowers that for dipalmitoylphosphatidylethanolamine. Dodecanol appears to behave in these lipid bilayer membranes as a lipid with a phase transition temperature of ca. 55 degrees C. Anesthesia is discussed as a phenomenon of liquidus extension: alcohols up to 1 -octanol increase the proportion of lipid in the liquidus state and result in anesthesia, whereas the longer alcohols do not, and result in catalepsy.

Anesthetics↗

PubMedDate not supplied

Solubility and diffusion of nitrogen in maltodextrin/protein tablets.

The gas transport properties of compacted tablets consisting of an amorphous mixture of maltodextrin and sodium caseinate were studied by dissolving nitrogen gas in the tablets and then determining the gas release over time as a function of temperature and water activity. Gas was dissolved in the tablet matrix by heating the tablets under pressure, generally to temperatures above the glass transition temperature of the matrix, holding them at these conditions for a specified time and then rapidly cooling them while maintaining the external pressure. The solubility of nitrogen was found to be largely determined by the free volume of the matrix, which in turn can be influenced to some degree by thermal and pressure treatments during gas loading. At the levels of free volume studied, the dissolved nitrogen is densely packed in the free volume, the packing density being virtually independent of the externally applied pressure. Release of gas from the tablets at temperatures below the glass transition temperature is generally well described by Fickian diffusion. The effective diffusion coefficient of gas release is strongly dependent on the microstructure and porosity of the tablet matrix, and an approximate model describing the relationship between tablet structure and rate of gas release is formulated. The model is in semiquantitative agreement with the rates of gas diffusion obtained for tablets and dense granules. Owing to the structural heterogeneity and variability of the tablets and the history-dependent properties of the tablet matrix, the effective diffusion coefficients of gas release from the tablets showed a relatively large spread. The temperature dependence of diffusional release follows an Arrhenius relation below the glass transition temperature. This allows the prediction of the nitrogen retention in the tablets as function of time, temperature and pressure.

Diffusion↗

PubMed1977

Interaction of glucagon with dimyristoyl glycerophosphocholine.

Glucagon can form amphipathic helices and can interact with dimyristoyl glycerophosphocholine at temperatures below the phase transition leading to a shift in the fluorescence emission maximum of tryptophan from 350 to 338 nm and a 3-fold enhancement of fluorescence intensity as well as a change in the polarization of fluorescence. The circular dichroism properties of the lipid-associated glucagon indicates that it has an increased content of alpha-helix. The phase transition temperature of the lipid as monitored by pyrene excimer fluorescence is not altered by interaction with glucagon although at higher glucagon/lipid ratios a decrease in excimer formation is noted at low temperature. Above the phase transition temperature, the addition of lipid has no effect on the fluorescence emission or circular dichroism of glucagon. Thus this hormone can interact with dimyristoyl glycerophosphocholine and this interaction is stronger below the phase transition temperature than above it.

Amino Acid Sequence↗

PubMed1995

X-ray diffraction and calorimetric study of N-lignoceryl sphingomyelin membranes.

Differential scanning calorimetry and x-ray diffraction have been used to investigate hydrated multibilayers of N-lignoceryl sphingomyelin (C24:0-SM) in the hydration range 0-75 wt % H2O. Anhydrous C24:0-SM exhibits a single endothermic transition at 81.3 degrees C (delta H = 3.6 kcal/mol). At low hydration (12.1 wt % H2O), three different endothermic transitions are observed: low-temperature transition (T1) at 39.4 degrees C (transition enthalpy (delta H1) = 2.8 kcal/mol), intermediate-temperature transition (T2) at 45.5 degrees C, and high-temperature transition (T3) at 51.3 degrees C (combined transition enthalpy (delta H2 + 3) = 5.03 kcal/mol). On increasing hydration, all three transition temperatures of C24:0-SM decrease slightly to reach limiting values of 36.7 degrees C (T1), 44.4 degrees C (T2), and 48.4 degrees C (T3) at approximately 20 wt % H2O. At 22 degrees C (below T1), x-ray diffraction of C24:0-SM at different hydration levels shows two wide-angle reflections, a sharp one at 1/4.2 A-1 and a more diffuse one at 1/4.0 A-1 together with lamellar reflections corresponding to bilayer periodicities increasing from d = 65.4 A to a limiting value of 71.1 A. Electron density profiles show a constant bilayer thickness dp-p approximately 50 A. In contrast, at 40 degrees C (between T1 and T2) a single sharp wide-angle reflection at approximately 1/4.2 A-1 is observed. The lamellar reflections correspond to a larger bilayer periodicity (increasing from d = 69.3-80.2 A) and there is some increase in dp-p (52-56 A) with hydration. These structural parameters,together with calculated lipid thickness and molecular area considerations, suggest that the low temperature endotherm(T1) of hydrated C24:0-SM corresponds to a transition from a tilted, gel state (Gel I) with partially interdigitated chains to an untilted, or less tilted, gel state (Gel 11). At 600C (above T3), the usual liquid-crystalline La bilayer structure (d = 59.5-66.3A; dp p -46 A) is present at all hydrations. Comparison with the behavior of C18:0-SM indicates that the in equivalence of length of the sphingosine (C18) and lignoceryl (C24) chains results in a more complex gel phase polymorphism for the sphingosine (C18) and lignoceryl (C24) chains results in a more complex gel phase polymorphism for C24:0-SM.

Animals↗

PubMedDate not supplied

The effect of different lipid components on the in vitro stability and release kinetics of liposome formulations.

Liposomes are colloidal carriers that form when certain (phospho)lipid molecules are hydrated in an aqueous media with some energy input. The ideal liposome formulation with optimum stability will improve drug delivery by decreasing the required dose and increasing the efficacy of the entrapped drug at the target organ or tissue. The most important parameter of interest in this article was to compare the efficacy of three different liposomes formulated with DSPC, DMPC, and DPPC, all saturated neutral phospholipids with different acyl chain lengths and transition temperatures. DMPC has a phase transition temperature (Tc) below 37 degrees C, whereas the other two phospholipids possess Tcs above the physiological temperature. These lipids were then added to a cholesterol concentration of 21% to optimize the stability of the vesicles. The liposomes were prepared by a sonication and incubated in phosphate buffered saline (PBS) at 4 degrees C and 37 degrees C. The encapsulation efficiency, initial size, and drug retention of the vesicles were tested over a 48-hr period employing radiolabeled inulin as a model drug. The phase transition temperature of liposomes, which depends on the Tc of the constituent lipids, was an important factor in liposome stability. Of all the liposomes tested, the greatest encapsulation efficiency was found for the DSPC liposomes (2.95%) that also had the greatest drug retention over 48 hr at both 4 degrees C (87.1 +/- 6.8%) and 37 degrees C (85.2 +/- 10.1%), none of these values being significantly different from time zero. The lowest drug retention was found for DMPC liposomes for which a significant difference in drug retention was seen after only 15 min at both 4 degrees C (47.3 +/- 6.9%) and 37 degrees C (53.8 +/- 4.3%). The DPPC liposomes showed a significant difference in drug retention after 3 hr at 4 degrees C (62.1 +/- 8.2%) and after 24 hr at 37 degrees C (60.8 +/- 8.9%). Following the initial drop at certain time intervals a plateau was reached for all of the liposome formulations after which no significant difference in drug retention was observed. In conclusion, liposomes with higher transition temperatures appear to be more stable in PBS either at 4 degrees C or 37 degrees C, indicating that the increase in acyl chain length (and therefore transition temperature) is directly proportional to stability.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2005

Influence of annealing temperature on the strength of dental glass ceramic materials.

OBJECTIVES: Dental glass ceramic components are always loaded by residual stresses because of the manufacturing process. For a reliable mechanical characterization, residual stress-free specimens are needed. Residual stresses can be removed by an annealing process. The hypothesis of this work was, that the annealing temperature must be individually chosen to reliably remove possible residual stresses without changing the characteristics of the glass ceramic material. METHODS: Knoop-indented specimens made of the glass ceramic materials Duceram Opaker (Degudent, Hanau, Germany, formerly Ducera, Rosbach, FRG), Empress 1 (Ivoclar Vivadent, Schaan, Liechtenstein), In-Ceram Alumina (Vita Zahnfabrik, Bad Säckingen, Germany), Optec OPC (Jeneric Pentron, Wellingford, USA), and Vita Omega Opaker (Vita Zahnfabrik, Bad Säckingen, Germany) were annealed at various temperatures below and above the respective glass transition temperature. The Weibull strength parameters and the lengths of the indentations before and after annealing were determined. RESULTS: A strength increase caused by relaxation of residual stresses was found after annealing at elevated temperatures. A local maximum of increased strength was determined after annealing at a temperature of 100K below the glass transition temperature. After annealing at temperatures above the glass transition temperature, microplasticity was observed. SIGNIFICANCE: It is recommended to anneal glass ceramic components that are intended to be mechanically characterized at a temperature 100K below the respective glass transition temperature before testing to determine 'true' mechanical values that are not influenced by possible residual stresses.

Aluminum Silicates↗

PubMed1991

Structural changes in plasma membranes prepared from irradiated Chinese hamster V79 cells as revealed by Raman spectroscopy.

The effect of gamma irradiation on the integrity of plasma membranes isolated from Chinese hamster V79 cells was investigated by Raman spectroscopy. Plasma membranes of control V79 cells show transitions between (-) 10 and 5 degrees C (low-temperature transition), 10 and 22 degrees C (middle-temperature transition), and 32 and 40 degrees C (high-temperature transition). Irradiation (5 Gy) alters these transitions markedly. First, the low-temperature transition shifts to higher temperature (onset and completion temperatures 4 and 14 degrees C). Second, the middle-temperature transition shifts up to the range of about 20-32 degrees C, but the width remains unchanged. Third, the higher temperature transition broadens markedly and shifts to the range of about 15-40 degrees C. Protein secondary structure as determined by least-squares analysis of the amide I bands shows 36% total helix, 55% total beta-strand, and 9% turn plus undefined for control plasma membrane proteins. Plasma membrane proteins of irradiated V79 cells show an increase in total helix (40 and 45% at 5 and 10 Gy, respectively) and a decrease in the total beta-strand (48 and 44% at 5 and 10 Gy, respectively) structures. The qualitative analysis of the Raman features of plasma membranes and model compounds in the 1600 cm-1 region, assigned to tyrosine groups, revealed that irradiation alters the microenvironment of these groups. We conclude that the radiation dose used in the survival range of Chinese hamster V79 cells can cause damage to plasma membrane proteins without detectable lipid peroxidation, and that the altered proteins react differently with lipids, yielding a shift in the thermal transition properties.

Animals↗

PubMed1988

Acid-induced fusion of liposomes: studies with 2,3-seco-5 alpha-cholestan-2,3-dioic acid.

The effect of 2,3-seco-5 alpha-cholestan-2,3-dioic acid on the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine is markedly dependent on pH. Above pH 6.56, the 2,3-seco-5 alpha-cholestan-2,3-dioic acid raises the temperature of this transition, i.e., it stabilizes the bilayer phase. At pH 6.56 there is little effect of this sterol derivative on the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine. However, below pH 6.56, the 2,3-seco-5 alpha-cholestan-2,3-dioic acid markedly lowers the temperature of this transition. The promotion of hexagonal phase formation increases both with increasing mol fraction of this sterol derivative and with lower pH, particularly in the range between pH 6.56 and pH 5.0. Below about pH 6, 2,3-seco-5 alpha-cholestan-2,3-dioic acid also induces vesicle fusion as measured both by lipid mixing as well as by mixing of aqueous contents. For these assays vesicles made of phosphatidylethanolamine (made from egg phosphatidylcholine) and extruded through 0.2 micron pore membranes were used. At higher concentrations or at lower pH the 2,3-seco-5 alpha-cholestan-2,3-dioic acid induces some leakage of the contents of these vesicles. Nevertheless, with vesicles containing only 2 weight% sterol derivative, it was possible to demonstrate substantial mixing of aqueous contents of the vesicles over the pH range 3.5 to 5.5. Several of the properties of 2,3-seco-5 alpha-cholestan-2,3-dioic acid indicate that this compound may be useful in sensitizing vesicles to acid-induced fusion for the purpose of endocytic drug delivery.

Cholestanes↗

PubMed2002

Binding and release of drugs into and from thermosensitive poly(N-vinyl caprolactam) nanoparticles.

Three model drug substances, the beta-blocking agents nadolol and propranolol and a choline-esterase inhibitor tacrine, were used in order to determine how different drug molecules affect the behavior of thermally responsive polymer nanoparticles composed of poly(N-vinylcaprolactam) (PVCL). Pure PVCL particles in water exist in a swollen state at room temperature, but the size of the particles decreases discontinuously when the temperature is raised above the volume phase transition temperature. At temperatures above this transition temperature, water is expelled out from the nanoscopic hydrogel particles. Light scattering studies revealed that the more hydrophobic drug substances, propranolol and tacrine, considerably swell the PVCL-microgel. The more hydrophilic drug, nadolol, decreased the transition temperature of PVCL particles, whereas the transition temperature values of pure PVCL particles and that of the added propranolol and tacrine were quite similar. Attenuated drug release results showed that the beta-blocking agents were tightly bound to the microgel, and this was more evident at higher temperatures. On the contrary, the release of tacrine across the cellulose membrane was increased when PVCL particles were present. Thus, both physical and chemical properties of the drugs clearly affected their binding to PVCL particles and the release of drugs was affected by the temperature.

Adrenergic beta-Antagonists↗

PubMed1992

Effect of oligomers of ethylene glycol on thermotropic phase transition of dipalmitoylphosphatidylcholine multilamellar vesicles.

The effect of oligomers of ethylene glycol (EG) on thermotropic phase transitions of dipalmitoylglycerophosphatidylcholine multilamellar vesicles (DPPC-MLV) were investigated. Diethylene glycol (di-EG) had a biphasic effect on transition temperature, reducing pre-transition temperature (Tp) at low concentrations but increasing main transition temperature (Tm) and extinguishing pre-transition at high concentration. Results of the X-ray diffraction method and the excimer method indicated that di-EG induced interdigitated gel phase (L beta 1 phase) in the DPPC membranes at high concentration. Phase diagram of temperature-di-EG concentration for DPPC-MLV was determined by use of X-ray diffraction and differential scanning calorimetry, which was similar to that of temperature-EG concentration. The minimum concentration of di-EG where L beta 1 phase was induced was 42%(w/v), which was larger than that of EG (30%(w/v)). On the other hand, in the presence of triethylene glycol (tri-EG), Tm and Tp increased with an increased in tri-EG concentration, as well as poly(ethylene glycol). These differences, between the effects of di-EG and those of tri-EG, might be due to the differences of their sizes.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2003

Temperature-dependent transitions between normal and inverse equilibrium isotope effects for coordination and oxidative addition of C-H and H-H bonds to a transition metal center.

The temperature dependence of the equilibrium isotope effects (EIEs) for coordination and oxidative addition of C-H and H-H bonds to the tungstenocene species {[H2Si(C5H4)2]W} has been determined with the aid of DFT (B3LYP) calculations. The EIE for coordination of CH4 and CD4 does not exhibit typical van't Hoff type behavior in which there is a monotonic variation of EIE with temperature; rather, the temperature dependence of the EIE exhibits a maximum, with inverse values (<1) at low temperature and normal values (>1) at high temperatures. The temperature dependence of the EIE for oxidative addition of CH4 and CD4 differs significantly from that for coordination, with the EIE being normal at all temperatures and approaching infinity at 0 K. In contrast to oxidative addition of methane which is normal at all temperatures, the EIE for oxidative addition of H2 and D2 exhibits a transition from inverse to normal upon raising the temperature. The existence of inverse EIEs in these systems at low temperatures is a result of the zero point energy changes for the products upon isotopic substitution being greater than those for the reactants (H2 or CH4).

Journal Article↗

PubMed2003

Comparative study of bone cements prepared with either HA or alpha-TCP and functionalized methacrylates.

The properties of bone cements prepared with both hydroxyapatite (HA) and alpha-tricalcium phosphate (alpha-TCP) and methacrylates containing acidic or basic groups are the main interest of this article. The presence of methacrylic acid or diethyl amino ethyl methacrylate as comonomers in the bone cement and both ceramic types as filler were found not to affect the amount of residual monomer, which was generally less than 4.5 wt%. In contrast, setting times, maximum temperature, and glass transition temperature were found to be composition dependent. For samples with acidic comonomer, a faster setting time, a higher maximum temperature, and higher glass transition temperatures were observed compared to those with the basic comonomer. The presence of the fillers slightly increased the setting time but did not affect the other parameters. The mechanical properties of the filled bone cements depended mainly on composition and type of testing. Both HA or alpha-TCP filled systems fulfilled the minimum compressive strength required for bone cement application, although a significantly lower value was observed for the alkaline comonomer systems. The minimum bending strength was not satisfied by any of these formulations. The tensile and shear strength of these composites ranged from 20 to 37.9 and from 18 to 27 MPa, respectively. In all cases it was higher for bone cements containing methacrylic acid. The results of this study suggest that the properties of dry unfilled bone cements prepared with MAA are comparable to CMW 3 in mechanical terms but inferior in their setting properties.

Bone Cements↗

PubMed1998

Temperature change of the lamellar structure of DPPC/disaccharide/water systems with low water content.

Temperature change in l-alpha-dipalmitoyl phosphatidylcholine (DPPC)/disaccharide systems with low water content (less than 8 wt. %) was investigated using X-ray diffraction within a range of two transition temperatures. X-ray diffraction above the higher transition temperature showed a broad symmetric peak, indicating the Lalpha phase. Below the higher transition temperature, two overlapping diffraction peaks were observed. After peak separation, temperature change in these systems was analyzed using peak parameters of the two peaks. Peak parameters of the lower angle peak changed continuously up to and above the higher transition temperature, suggesting the systems to be in a liquid crystal phase below the higher transition temperature. Fourier-transform infrared (FT-IR) spectra of the DPPC/trehalose system with 5.5 wt.% water showed the wave number of asymmetric stretching of phosphate groups to change at the lower transition temperature and that of symmetric stretching of CH2 groups, to change between the lower and higher transition temperatures. Thus, below the lower transition temperature, the system is shown to be in a gel phase. Conformational change in phosphate groups occurred at the lower transition temperature. Within the lower and higher transition temperatures, two phases were found to coexist and transition from the gel phase to Lalpha phase to occur continuously. Above the higher transition temperature, the system is in the Lalpha phase.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2004

Shear modulus and thermal properties of gutta percha for root canal filling.

The purpose of this investigation was to investigate the rheological properties of four commercially available gutta perchas for root canal filling. The relaxation modulus [Gr(0): instantaneous shear modulus] and specific volume of their materials were examined. In addition, the quantity of heat was also studied by differential scanning calorimeter. In a lower temperature range than the first-order transition temperature (melting point), the Gr(0) values of each material were almost identical. A marked decrease of Gr(0) was observed at the melting point, and the range of the first-order transition temperature at heating was from 42.0 to 60.0 degrees C. At higher temperatures than the first-order transition temperature of each material, a considerable difference in Gr(0) values was observed. The transition temperatures obtained by the results of the Gr(0), specific volume and quantity of heat agreed with one another. A marked specific volume change was observed at the first-order transition temperature. The technique using melted gutta percha may not be favourable compared with the conventional lateral condensation technique because melted gutta percha undergoes a large amount of shrinkage during setting.

Gutta-Percha↗