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At least 919 records · Page 51Linked to original sources
PubMed1993

Polymerizable phospholipids with lipoic acid as head group: synthesis and phase properties.

Lipoic acid-substituted phospholipids were synthesized from phosphatidyl cholines by exchanging the choline residue with a glycol group using phospholipase D, forming phosphatidylglycols, and coupling of lipoic acid (1,2-dithiolane-3-pentanoic acid) to the residual glycol hydroxyl group by esterification. The thermotropic properties of aqueous dispersions of the phosphatidylglycols and the phosphatidylglycolipoates with different chain lengths were studied by differential scanning calorimetry (DSC) and differential scanning densitometry (DSD). The exchange of choline with glycol increases the phase transition temperature Tm for the gel to liquid-crystalline phase transition by approximately 5 degrees, independent of the chain length. Consecutive esterification of the glycol residue with lipoic acid causes a decrease of the transition temperature Tm by approximately 22 degrees compared with the phosphatidylglycols. Polymerization of vesicles prepared from phosphatidylglycolipoates was induced by the addition of dithiothreitol and followed by DSC and DSD. Polymerization has only slight influence on the transition behavior, indicating that the polymer chain in the head group is effectively decoupled from the hydrocarbon region. Polymerized vesicles show increased stability towards aggregation and fusion.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1977

Lateral phase separations and structural integrity of the inner membrane of rat-liver mitochondria. Effect of compression. Implications in the centrifugation of these organelles.

When maintained in the vicinity of the lower transition temperature of their membrane lipids, rat-liver mitochondria undergo lysis as shown by the release of malate dehydrogenase, (an enzyme located within the mitochondrial matrix), in the surrounding medium. Structural changes take place in the membranes of mitochondria subjected to increasing pressure at 0 degrees C, when the pressure reaches 750 kg/cm2. Freeze-fracture electron microscopy shows the appearance of smooth areas devoid of particles in fracture faces of mitochondrial membranes, together with zones, where aggregated particles can be seen. Concurrently, a suppression of the malate dehydrogenase structure-linked latency is observed. These structural changes can be prevented by increasing the temperature at which compression is performed. The freeze-etching observations suggest that lateral phase separations occur in mitochondrial membranes subjected to high pressure. This can be explained by supposing that pressure promotes the gel-phase appearance in a lipid system and raises the transition temperature since the transition liquid crystal lead to gel is accompanied by a decrease in volume. The deterioration of mitochondria subjected to high pressure is interpreted as a result of the lateral phase separation induced by compression in the membranes. These results are discussed with respect to our interpretation of the damaging effects that hydrostatic pressure, generated by centrifugation, exerts on rat-liver mitochondria.

Animals↗
PubMed1999

Mechanistic studies of molecular transdermal transport due to skin electroporation.

The application of electrical high voltage pulses has been shown to greatly enhance the transdermal transport of water-soluble compounds. The resistance of the skins most important barrier, the stratum corneum, drops within less than 1 µs by orders of magnitude. This effect is attributed to electroporation, a nonthermic phenomena known to occur in phospholipid double layers. The striking difference between the stratum corneum lipid layers and the usually investigated phospholipid systems is the phase transition temperature. While lipid layers used for electroporation experiments are in liquid crystal phase above the phase transition temperature, the stratum corneum lipids (phase transition at approximately 70 degrees C) form a rigid quasi-crystalline membrane at room temperature.After the electrical stimulus a recovery of the passive flux was found making high voltage pulsing a suitable tool for controlling transdermal drug delivery. By ordinary light microscopy no dramatic changes in skin structure were found supporting the thesis of electroporation. However the microstructure shows clearly persistent structural changes. Recently the involvement of Joule heating due to the electric stimulus was shown as an important factor for skin permeabilization and molecular transport.

Journal Article↗
PubMed2003

Photoinduced magnetization in a two-dimensional cobalt octacyanotungstate.

A new type of cyano-bridged Co-W bimetallic assembly, CsI[{CoII(3-cyanopyridine)2}{WV(CN)8}].H2O was synthesized. This compound exhibited a temperature-induced phase transition and a photoinduced magnetization. Irradiating with light induced a spontaneous magnetization with a magnetic phase transition temperature at 30 K. This photoinduced magnetization is due to the phase transition from CoIII(LS; S = 0)-WIV(S = 0) to CoII(HS; S = 3/2)-WV(S = 1/2) phases by the irradiation.

Journal Article↗
PubMed1985

On the correlation between HII phase and the contact-induced destabilization of phosphatidylethanolamine-containing membranes.

The abundance of phosphatidylethanolamine (PtdEtn) in biological membranes and the capacity of this lipid to sustain nonbilayer structures have been promoted as evidence for a role of PtdEtn in biological fusion processes. To date there has been no direct evidence of a connection between the kinetics of bilayer destabilization and the polymorphism accessible to PtdEtn. We have developed a model system to examine this point directly using the proton-induced destabilization of PtdEtn/cholesterylhemisuccinate unilamellar liposomes. We find that the initial rate of bilayer mixing rapidly increases with temperature and reaches a maximal level just below the HII-phase transition temperature. The leakage from these liposomes rapidly increases, both in rate and extent, within the HII-phase transition temperature range. Of an even greater significance is that at no temperature is there any mixing of aqueous contents within the liposomes. Thus, these lipids can begin to undergo the lamellar- to HII-phase transition at the stage of two apposed liposomes. However, the nonbilayer structures formed do not cause fusion--i.e., the concomitant mixing of aqueous contents.

Calorimetry↗
PubMed1976

Theory of lipid monolayer and bilayer phase transitions: effect of headgroup interactions.

Headgroup and soft core interactions are added to a lipid monolayer-bilayer model and the surface pressure-area phase diagrams are calculated. The results show that quite small headgroup interactions can have biologically significant effects on the transition temperature and the phase diagram. In particular, the difference in transition temperatures of lecithins and phosphatidyl ethanolamines is easy to reproduce in the model. The phosphatidic acid systems seem to require weak transient hydrogen bonding which is also conjectured to play a role in most of the lipid systems. By a simple surface free energy argument it is shown that monolayers under a surface pressure of 50 dynes/cm should behave as bilayers, in agreement with experiment. Although the headgroup interactions are biologically very significant, in fundamental studies of the main phase transition in lipids they are secondary in importance to the hydrocarbon chain interactions (including the excluded volume interaction, the rotational isomerism, and the attractive van der Waals interaction).

Chemical Phenomena↗
PubMed2006

Low-energy excitations and the fast process of polystyrene thin supported films studied by inelastic and quasielastic neutron scattering.

We studied the low-energy excitations in the meV region as well as the picosecond fast process in polystyrene thin supported films using inelastic and quasielastic neutron scattering in a temperature range from 11 to 430 K , covering the bulk glass transition temperature Tg. It was found that the mean square displacement u2 decreased with the film thickness below and above the glass transition temperature Tg, suggesting that the hardening occurs with decreasing the film thickness. Corresponding to the decrease in u2, it was also found that the density of phonon states G(omega) decreased with film thickness. This decrease occurs mainly in the Debye mode while the contribution of the boson peak mode also decreases with the film thickness without changing the boson peak energy. As for the fast process, which appeared above at about 150 K as a quasielastic scattering, the fraction A(fast)(Q) decreased with the film thickness in a similar manner with the boson peak without changing the relaxation rate, suggesting a common origin for the boson peak and the fast process. These observations showing the hardening were well explained by assuming a hard dense layer at the interface, where the numbers of the boson peak mode as well as the fast process are less than the bulk state.

Journal Article↗
PubMed1996

Detection of Bordetella pertussis by rapid-cycle PCR and colorimetric microwell hybridization.

The use of rapid-cycle PCR combined with colorimetric microwell hybridization for detecting Bordetella pertussis was investigated. Rapid cycling was performed with an air thermocycler (model 1605; Idaho Technology, Idaho Falls, Idaho). Although the instrument was originally designed to be used with capillary tubes, an adapter that allows this instrument to be used with PCR tubes has recently been introduced. Because of the low heat capacity of air, the thermocycler has rapid transition rates between temperatures. The combination of a rapid temperature transition rate, small sample volume (10 microliters), and overshooting or undershooting of the temperature set points allowed the cycles to be reduced to 5 s for denaturation and 10 s for extension and annealing. Thus, the amplification could be completed in a total of approximately 35 min. Amplified DNA was detected with biotin-labeled primers and by hybridization to a capture probe immobilized in microwell plates. When simulated clinical specimens consisting of pooled nasopharyngeal washes with known numbers of B. pertussis organisms were examined by this procedure, as little as one organism per 5 microliters of sample could be detected. Six nasopharyngeal aspirates or washes from culture-positive patients were positive by PCR, as were two of seven specimens obtained from patients that were negative by culture and direct fluorescent-antibody assay. The two patients who were PCR positive but culture and direct fluorescent-antibody assay negative had clinical disease compatible with pertussis. This method appears to be a sensitive, convenient means of detecting B. pertussis in clinical specimens. The total time required for specimen processing, amplification, and detection is about 2.5 h.

Bacteriological Techniques↗
PubMed2006

Membrane lipid composition and the interaction of pardaxin: the role of cholesterol.

Modulation by pardaxin of the phase transitions of dimyristoyl phosphatidylcholine, 1-stearoyl-2-oleoyl phosphatidylcholine or 1-stearoyl-2-oleoyl phosphatidylglycerol in the presence or absence of cholesterol was studied by differential scanning calorimetry. The transition enthalpy of each of the phospholipids was lowered by pardaxin and there was a small decrease in the transition temperature. Addition of cholesterol and pardaxin to dimyristoyl phosphatidylcholine resulted in a very marked lowering of the transition temperature. Although the peptide broadens the transition of the pure phospholipids, it sharpens the transition of mixtures of the phospholipids with cholesterol. This and the observation that pardaxin also causes the formation of crystallites of anhydrous cholesterol, suggest that the peptide promotes redistribution of cholesterol in the membrane.

Calorimetry, Differential Scanning↗
PubMed2004

Estimation of the fragility index of indomethacin by DSC using the heating and cooling rate dependency of the glass transition.

In this study we have investigated the features of the glass transition relaxation of indomethacin using Differential Scanning Calorimetry (DSC). The purpose of this work is to provide an estimation of the activation energy at the glass transition temperature, as well as of the fragility index, of amorphous indomethacin from DSC data. To do so, the glass transition temperature region of amorphous indomethacin was characterized in both cooling and heating regimes. The activation energy for structural relaxation (directly related to glass fragility) was estimated from the heating and cooling rate dependence of the location of the DSC profile of the glass transition. The obtained results were similar in the heating and in the cooling modes. The results on the fragility index of indomethacin obtained in the present study, m = 60 in the cooling mode and m = 56 in the heating mode, are compared with other values previously published in the literature.

Calorimetry, Differential Scanning↗
PubMed2006

Use of phospholipid transfer protein as a probe to study the lipid dynamics and alkaline phosphatase activity in the brush border membrane of human term placenta.

Incubation of placental brush border membrane (BBM) along with sonicated vesicles of exogenous lipids (egg yolk PC) in the presence of phospholipid-transfer protein (PL-TP) showed a decrease in the alkaline phosphatase activity due to the change in the membrane micro-environment, such as fluidity. Effect of substrate concentration was tested by Lineweaver-Burk plot, which showed decreased V(max) and K(M). The effect of temperature was probed by the Arrhenius plot, which showed no change in transition temperature, but a decline in the energy of activation both below and above the transition temperature. The protein-catalyzed transfer of phospholipid from the donor unilamellar vesicles resulted in a substantial increase in the BBM phospholipid and a net decrease in cholesterol/phospholipid molar ratio. The change in membrane fluidity was assessed by translational as well as rotational diffusion of membrane extrinsic fluorescent probes, pyrene and diphenyl-hexatriene. An increased lateral mobility was recorded by the increased pyrene excimer formation. A decrease in fluorescent polarization of diphenyl-hexatriene was observed, which led to the decrease in fluorescence anisotropy and order parameter, and therefore, an increase in membrane fluidity (rotational diffusion). Mean anisotropy parameter was also decreased in the presence of PL-TP. Thus, the placental BBM alkaline phosphatase activity showed a distinct lipid dependence which may have important physiological consequences.

Alkaline Phosphatase↗
PubMedDate not supplied

Solid-state characterization of falicaine hydrochloride and isomorphic dyclonine hydrochloride. Part IV. Crystal polymorphism of local anaesthetic drugs.

Two homologous local anaesthetic drugs, falicaine (propipocaine) hydrochloride (1-(4-propoxyphenyl)-3-(1-piperidinyl)-1-propanone hydrochloride, PPCHC) and dyclonine hydrochloride (1-(4-butoxyphenyl)-3-(1-piperidinyl)-1-propanone hydrochloride, DCNHC) were characterized by thermal analysis (hot-stage-microscopy, differential scanning calorimetry, thermogravimetry), vibrational spectroscopic methods (FTIR-, FT-Raman-spectroscopy), powder X-ray diffractometry, solid-state-/solution-NMR and water-vapor sorption analysis. The formation and thermodynamic stability of the two different solid phases of both the compounds is described and presented in a flow chart and energy/temperature-diagram, respectively. Of the two substances investigated, mod. II degrees is the thermodynamically stable form at room temperature. This form is present in commercial products of PPCHC as well as of DCNHC, and it endothermally transforms to the less stable form mod. I, at about 10K prior to the melting points. The stable mod. II degrees crystallizes from all tested solvents. Mod. I crystallizes from the super cooled melt. According to the heat of transition rule, mod. I is the thermodynamically less stable form below the transition temperature (enantiotropism). The transition temperatures as well as the melting points of the stable forms could be experimentally determined. The sorption isotherms show a distinct higher hygroscopicity for the less stable mod. I of PPCHC and DCNHC. Solid-state NMR spectra were used to obtain both structural- and molecular-level mobility information.

Anesthetics, Local↗
PubMed1988

Domain structure, stability, and interactions of human complement C1s-: characterization of a derivative lacking most of the B chain.

A better understanding of the structure and function of C1 requires knowledge of the regions (domains) of the subcomponents that are responsible for Ca2+-dependent assembly. Toward this end, C1-s was digested with trypsin in the presence of Ca2+, a treatment that rapidly degraded the B chain, leaving a 56-kDa fragment comprised of a complete A chain disulfide linked to a small (less than 4-kDa) residual piece of the B chain. The purified fragment, referred to as C1-s-A, was shown by fast exclusion chromatography to be similar to C1-s in its ability to (1) reversibly dimerize in the presence of Ca2+, (2) substitute for C1-s in the formation of C1-r2-s2 tetramers, and (3) associate with C1-r and C1q to form macromolecular C1. Although C1-s-A was itself catalytically and hemolytically inactive, it competitively inhibited the expression of the hemolytic activity of C1-s in a reconstitution assay. When heated in the absence of Ca2+, C1-s exhibited a low-temperature transition (LTT) near 31 degrees C and a high-temperature transition (HTT) near 51 degrees C, similar to those previously observed in the homologous protein C1-r [Busby, T. F., & Ingham, K. C. (1987) Biochemistry 26, 5564-5571]. The midpoint of the LTT was shifted to 58 degrees C in 5 mM Ca2+ whereas the HTT was unaffected by Ca2+. C1-s-A exhibited only a LTT whose midpoint and Ca2+ dependence were similar to those of the LTT in C1-s. The HTT, which was accompanied by a loss of esterolytic activity, was reproduced in a plasmin-derived fragment representing the catalytic domain. These results provide strong support for the structural and functional independence of the catalytic and interaction domains of C1-s and strengthen current models regarding the role of these domains in various interactions. They also provide direct proof for the occurrence of Ca2+ binding sites on the A chain and demonstrate that all or most of the sites on C1-s that are responsible for its interaction with C1-r and C1q are located on the A chain.

Amino Acid Sequence↗
PubMed1986

A comparative study of the biologic and immunologic response to medical devices derived from dermal collagen.

We examined collagen materials for soft tissue augmentation [Zyderm Collagen Implant (ZCI), glutaraldehyde cross-linked (GAX) collagen, and Koken Atelocollagen (Atelocollagen)]; hemostatic collagens [Gelfoam Gelatin Powder (Gelfoam), Avitene Microfibrillar Collagen Hemostat (Avitene), and Collastat Collagen Hemostat (Collastat)]; and reconstituted, intact fibrillar collagen from bovine skin in a subcutaneous guinea pig model. After 11, 25, and 39 days in situ, explants from animals injected with GAX collagen demonstrated greater wet-weight persistence than all other materials. Conversely, at all time points, the explants of Atelocollagen were the least persistent. Following 25 days in vivo, explants were examined using differential scanning calorimetry; ZCI and Atelocollagen displayed thermal transition temperatures of 58 degrees C. Avitene and Gelfoam explants displayed transition points of 30 degrees C and 32 degrees C, indicating denatured or cleaved collagen. By contrast, GAX collagen explants had a high (68 degrees C) transition temperature, reflecting its cross-linking. With respect to immunogenicity, day 39 sera from ZCI treated animals showed significantly lower titers in the ELISA to their respective implant collagen than all other groups examined, while antibody activity in the GAX collagen, Gelfoam, Atelocollagen, and intact collagen groups were not significantly different. Collastat elicited antibodies with a greater affinity than observed in these previous groups. Sera from Avitene treated animals demonstrated the highest antibody levels and were the only sera which reacted with bovine serum albumin. Thus, Avitene was the most immunogenic of the collagen materials examined, while GAX collagen demonstrated the greatest persistence and minimal immunogenicity, and ZCI was the least immunogenic.

Animals↗
PubMed1996

Effects of cholesterol on the lamellar and the inverted hexagonal phases of dielaidoylphosphatidylethanolamine.

Effects of cholesterol on the lamellar and the inverted hexagonal (HII ) phases of dielaidoylphosphatidylethanolamine (DEPE) were studied by means of not only differential scanning calorimetry (DSC) but also simultaneous X-ray diffraction and DSC (XDDSC). XDDSC shows that structural changes are related to thermotropic events of the mixtures. Addition of cholesterol to DEPE induces to broaden the transition from the lamellar gel (L beta) to lamellar liquid-crystalline (L alpha) phase. In fact, in the broad transition region, a coexistence of two lamellar X-ray diffraction peaks of the L beta and L alpha phases take place. In samples containing above 30 mol% cholesterol, no peak at the L beta-L alpha phase transition was observed in the DSC thermogram. On the other hand, cholesterol causes biphasic effects on the L alpha-HII phase transition: At low cholesterol concentrations below 20 mol%, the incorporation of cholesterol reduces the transition temperature and at high cholesterol concentrations about 30 mol%, the transition temperature increases by addition of cholesterol. Based upon the results of X-ray diffraction, the thermal expansion coefficients of lattice spacings, i.e., the temperature dependence of lattice spacings, were calculated in each phase. Addition of cholesterol reduces the thermal expansion coefficients of the lamellar phases and, in contrast, increases that of the HII phase. From the above results it is suggested that cholesterol in cell membranes works in keeping the bilayer membrane nature notwithstanding the change of external conditions.

Calorimetry, Differential Scanning↗
PubMed1994

Side-chain structure and dynamics at the lipid-protein interface: Val1 of the gramicidin A channel.

High resolution dynamics and structural information has been resolved from 2H solid-state NMR spectra of the Val-1 side-chain of the gramicidin channel in a lipid bilayer. Both powder pattern lineshapes and spectra from uniformly aligned samples of gramicidin in lipid bilayers have been analyzed to achieve a fully consistant interpretation of the data. Torsional motions about the C alpha C beta axis (chi 1) are shown to be three-state jumps in which the occupancy of the states is given by the ratio, 75:15:10 for the chi 1 angles of 184 degrees:304 degrees:64 degrees. The dominant conformer is also the most common conformation observed for valines in well defined protein structures. The distribution of conformational substates that represents the chi 1 dynamics appears to be largely independent of the lipid phase transition and the hydration of the sample. However, there is evidence that the residence time between jumps is dependent on the lipid phase transition. Although this time is shown to be approximately 1 microseconds below the phase transition temperature, it is in the fast exchange limit above the transition temperature.

Amino Acid Sequence↗
PubMed2006

Plasticization of a protein-based film by glycerol: a spectroscopic, mechanical, and thermal study.

Kafirin, the seed storage protein of the cereal sorghum, is highly homologous with the maize storage protein zein. The effects of plasticisation of a kafirin film by glycerol in the absence of water were examined by a combination of spectroscopic (NMR and infrared), rheological, and calorimetric methods. The results suggest that at low glycerol levels the glycerol is absorbed onto and possibly into the protein. Increasing the level of glycerol increases the motion of the protein and changes the protein conformation. There are corresponding changes of the mechanical properties of protein films. At 40% (w/w) of glycerol, two glass transition temperatures were observed, one of which corresponded to the glass transition temperature of pure glycerol. This result indicates that at this level of plasticizer there are sufficient glycerol/glycerol interactions occurring to allow a separate glass formation process for glycerol.

Calorimetry↗
PubMed2003

Ferroelectric emission studies for electron emission lithography applications.

Ferroelectric switching emission, dielectric switching emission, and pyroelectric emission were studied by patterning images on electron resist for electron emission lithography applications. It was observed that the pyroelectric emission is most acceptable for a high throughput 1:1 electron projection lithography application. A 1:1 electron projection lithography was demonstrated by patterning images with line widths of 30 microm and using pyroelectric emission. A degradation of the pyroelectric emission property of the material was observed during repeated heating cycles below the phase-transition temperature of the ferroelectric material. Annealing excursions above the phase transition temperature prevented the degradation of the pyroelectric emitter.

Journal Article↗