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PubMed2002

Development of novel topical tranexamic acid liposome formulations.

The aims of this study were to develop novel liposome formulations for tranexamic acid (TA) from various lipid compositions [neutral (hydrogenated soya phosphatidylcholine and cholesterol), positive (stearylamine) or negative (dicetyl phosphate) charged lipid], and to investigate the effects of concentrations of TA (5 and 10% in DI water) and charges on the physicochemical properties of liposomes. Liposomes were prepared by chloroform film method with sonication. The physical (appearance, pH, size, morphology) and chemical (drug encapsulation efficiency, transition temperature, enthalpy of transition) properties of liposomes were characterized. The TA contents were determined spectrophotometrically at 415 nm, following derivatization with 2,4,6-trinitrobenzosulfonic acid. The charged liposomes demonstrated better physical stability than the neutral liposomes. The percentages of TA entrapped in all liposome formulations varied between 13.2 and 15.6%, and were independent of TA concentrations and charges of liposomes. Charges affected the physical stability, pH and size of liposomes. The particle sizes of negative blank and positive liposomes (with and without the entrapped drug) were approximately 10 times larger than the negative liposome with the entrapped TA. The multilamellar 7:2:1 molar ratio of hydrogenated soy phosphatidylcholine/cholesterol/dicetyl phosphate entrapped with 10% TA liposome (10%TA,-) was selected for further release study, due to its high physical stability, small particle size and relatively high drug encapsulation efficiency.

Administration, Topical↗

PubMed2000

1-Naphthol as an excited state proton transfer fluorescent probe for erythrocyte membranes.

The microenvironmental dependence of excited state prototropism of 1-naphthol and the corresponding changes in its fluorescence emission is utilized to monitor the acyl chain melting phase transition behavior of liposome membrane made from human erythrocyte lipids. A sharp increase in the ratio of neutral/anionic form fluorescence intensity is noticed at the phase transition temperature (19 degrees C). This provides a convenient method for obtaining phase transition temperature in lipid membranes. The membrane modifying effect of cholesterol on the erythrocyte liposome is successfully sensed by 1-naphthol fluorescence.

Cholesterol↗

PubMed2001

Probes of hydrogen tunneling with horse liver alcohol dehydrogenase at subzero temperatures.

The temperature dependence of steady-state kinetics has been studied with horse liver alcohol dehydrogenase (HLADH) using protonated and deuterated benzyl alcohol as substrates in methanol/water mixtures between +3 and -50 degrees C. Additionally, the competitive isotope effects, k(H)/k(T) and k(D)/k(T), were measured. The studies indicate increasing kinetic complexity for wild-type HLADH at subzero temperatures. Consistent with earlier findings at 25 degrees C [Bahnson et al. (1993) Biochemistry 31, 5503], the F93W mutant shows much less kinetic complexity than the wild-type enzyme between 3 and -35 degrees C. An analysis of noncompetitive deuterium isotope effects and competitive tritium isotope effects leads to the conclusion that the reaction of F93W involves substantial hydrogen tunneling down to -35 degrees C. The effect of methanol on kinetic properties for the F93W mutant was analyzed, showing a dependence of competitive KIEs on the NAD(+) concentration. This indicates a more random bi--bi kinetic mechanism, in comparison to an ordered bi-bi kinetic mechanism in water. Although MeOH also affects the magnitude of the reaction rates and, to some extent, the observed KIEs, the ratio of ln k(H)/k(T) to ln k(D)/k(T) for primary isotope effects has not changed in methanol, and we conclude little or no change in kinetic complexity. Importantly, the degree of tunneling, as shown from the relationship between the secondary k(H)/k(T) and k(D)/k(T) values, is the same in water and MeOH/water mixtures, implicating similar trajectories for H transfer in both solvents. In a recent study of a thermophilic alcohol dehydrogenase [Kohen et al. (1999) Nature 399, 496], it was shown that decreases in temperatures below a transition temperature lead to decreased tunneling. This arises because of a change in protein dynamics below a break point in enzyme activity [Kohen et al. (2000) J. Am. Chem. Soc. 122, 10738-10739]. For the mesophilic HLADH described herein, an opposite trend is observed in which tunneling increases at subzero temperatures. These differences are attributed to inherent differences in tunneling probabilities between 0 and 100 degrees C vs subzero temperatures, as opposed to fundamental differences in protein structure for enzymes from mesophilic vs thermophilic sources. We propose that future investigations of the relationship between protein flexibility and hydrogen tunneling are best approached using enzymes from thermophilic sources.

Acetonitriles↗

PubMed1989

1H NMR study of the solution properties of the polypeptide neurotoxin I from the sea anemone Stichodactyla helianthus.

The solution properties of the polypeptide neurotoxin I from the sea anemone Stichodactyla helianthus (Sh I) have been investigated by high-resolution 1H nuclear magnetic resonance (NMR) spectroscopy at 300 MHz. The pH dependence of the spectra has been examined over the range 1.1-12.2 at 27 degrees C. Individual pKa values have been obtained for the alpha-ammonium group of Ala-1 (8.6) and the side chains of Glu-8 (3.7), Tyr-36 (10.9), and Tyr-37 (10.8). For the remaining seven carboxyl groups in the molecule (from five Asp, Glu-31, and the C-terminus), four pKa values, viz., 2.8, 3.5, 4.1 and 6.4, can be clearly identified. The five Lys residues titrate in the range 10.5-11, but individual pKa values could not be obtained because of peak overlap. Conformational changes associated with the protonation of carboxylates occur below pH 4, while in the alkaline pH range major unfolding occurs above pH 10. The molecule also unfolds at elevated temperatures, having a transition temperature of ca. 55 degrees C at pH 5.25. Exchange of the backbone amide protons has been monitored at various values of pH and temperature in the ranges pH 4-5 and 12-27 degrees C. Up to 18 slowly exchanging amides are observed, consistent with the existence of a core of hydrogen-bonded secondary structure, most probably beta-sheet.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1981

Dynamic properties of the lipid-water interface of model membranes as revealed by lifetime-resolved fluorescence emission spectra.

We examined the dynamic properties of the lipid-water interface region of model membranes, on the nanosecond time scale, by using the fluorescent probe 2-p-toluidinylnaphthalene-6-sulfonic acid (TNS). In particular, we examined the steady-state emission spectra of TNS as its average lifetime was decreased by oxygen quenching. Under these quenching conditions the centers of gravity (Vcg) of the emission spectra shift ot shorter wavelengths. The lifetime dependence of these shifts reveals the time dependence of membrane relaxation around the excited-state dipole moment of TNS. The lipids investigated include dioleoyl-, dimyristoyl-, and dipalmitoyl-L-alpha-phosphatidylcholines, bilayers containing cholesterol, and an ether analogue of dipalmitoyl-L-alpha-phosphatidylcholine. For these lipids, the spectral relaxation times and the temperature dependence of the relaxations are similar in magnitude. Most relaxation times fall in the range of 0.6-6 ns, and except for the ether analogue, the inactivation energies for spectral relaxation are 10 plus or minus 2 kcal/mol. The average energy loss during spectral relaxation was 1000 cm(-1). However, for the saturated phosphatidylcholines at temperatures below their transition temperatures, smaller relaxation losses were observed (approximately 600 cm(-1)). We attribute these smaller losses to ordering of the polar head groups around the ground-state dipole moment of TNS. Overall, these results indicate that the dynamic properties of the lipid-water interface region are similar among the phosphatidylcholines and depend only slightly on the chemical composition and phase state of the acyl side chains.

Fluorescent Dyes↗

PubMed1980

Thermotropic behavior of dipalmitoylphosphatidylcholine vesicles reconstituted with the glycoprotein of vesicular stomatitis virus.

The vesicular stomatitis virus glycoprotein reconstituted into dipalmitoylphosphatidylcholine (DPPC) vesicles exerts a profound effect upon the DPPC gel to liquid-crystalline phase transition. The glycoprotein was reconstituted into DPPC vesicles by octyl glucoside dialysis. The gel to liquid-crystalline phase transition of these vesicles was monitored by differential scanning calorimetry. Vesicles formed in the absence of glycoprotein (600--2100-A diameter) underwent the phase transition at 41.0 degrees C and had an associated enthalpy change of 8.0 +/- 1.6 kcal/mol. Increasing the mole ratio of glycoprotein to DPPC in the vesicles to 0.15 mol % reduced both the transition temperature and the transition enthalpy change. The enthalpy change as a function of the mole percent glycoprotein could be fit to a straight line by a least-squares procedure. Extrapolation of the results to the glycoprotein concentration where the enthalpy change was zero indicated one glycoprotein molecule bound 270 +/- 150 molecules of DPPC.

Calorimetry, Differential Scanning↗

PubMed2000

Reaction rate modeling in cryoconcentrated solutions: alkaline phosphatase catalyzed DNPP hydrolysis.

The hydrolysis of disodium p-nitrophenyl phosphate catalyzed by alkaline phosphatase was chosen as a model to study the kinetics of changes in frozen food products. The initial reaction rate was determined in concentrated sucrose solutions down to -24 degrees C, and the enzymatic characteristics K(M) and V(max) were calculated. The experimental data were compared to the kinetics predicted by assuming that the reaction was viscosity dependent. Indeed, an analysis of the enzymatic reaction demonstrated that both the diffusion of the substrate and the flexibility of the enzyme segments were controlled by the high viscosity of the media. When the temperature was too low for the viscosity to be measured simply, the Williams-Landel-Ferry equation was used to predict the viscosity, taking, as reference temperature, the glass transition temperature (T(g)) corresponding to the concentration of the freeze-concentrated phase at the test temperature. Predicted values of the reaction rate were very close to the experimental ones in the studied temperature range.

Alkaline Phosphatase↗

PubMed2004

Pseudo real-time method for monitoring of the limiting anisotropy in membranes.

Data acquisition and analysis of the time-resolved fluorescence anisotropy is typically a time consuming process preventing usage of this experimental method for monitoring of time-dependent phenomena. We describe a method for pseudo real-time monitoring of the limiting fluorescence anisotropy r(infinity) allowing to track changes of the membrane order occurring on the time scale of minutes. Principle and performance of the method is demonstrated in the time domain with the time-correlated single photon counting detection. DMPC liposomes stained with 1,6-diphenyl-1,3,5-hexatriene (DPH) have been used to test influence of the diffusion membrane potential on the membrane order during the temperature-induced phase transition in DMPC membranes. It has been found that the transmembrane field of the order of -70 mV increases the phase transition temperature by about 1.5 degrees C-2 degrees C. It is proposed that the full advantage of the method can be utilized with a gated detection, which besides a faster data acquisition brings additional advantage of excitation light suppression. The method can be also used for imaging.

Dimyristoylphosphatidylcholine↗

PubMed1978

The interaction of purified acetylcholinesterase from pig brain with liposomes.

The binding of pig brain acetylcholinesterase to artificial phospholipid membranes was investigated at different temperatures. Calculation of the thermodynamic parameters revealed a small negative enthalpy change, but a large negative change in the free energy and a large positive change in the entropy on binding. The large entropy change might be interpreted as being responsible for forming the enzyme-membrane complex and was indicative of hydrophobic interactions between lipid and protein. This conclusion would also favour the hypothesis that the enzyme was an integral protein. Further support for this theory was provided by the study of acetylcholinesterase binding to liposomes containing the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine. Lowering the temperature below the transition temperature or incorporating cholesterol into the liposomes decreased enzyme binding. Both factors could be interpreted as decreasing the fluidity of the hydrocarbon side chains of the phospholipids, causing an increase in bilayer thickness due to closer packing of side chains. This membrane condensation would certainly not favour the binding of integral protein molecules.

Acetylcholinesterase↗

PubMed2006

Pressure effects on the alpha and alpha' relaxations in polymethylphenylsiloxane.

In some polymers, in addition to the usual structural alpha relaxation, a slower alpha' relaxation is observed with a non-Arrhenius temperature dependence. In order to understand better the molecular origin of this alpha' relaxation in poly(methylphenylsiloxane) (PMPS) we have studied, for the first time, the pressure dependence of its relaxation time, together with the usual temperature dependence, by means of dynamic light scattering (DLS). For the same material the alpha relaxation was also studied by means of DLS and dielectric spectroscopy (DS) in broad temperature and pressure ranges. We find that the temperature dependence of both alpha and alpha' relaxation times, at all pressures studied, can be described by a double Vogel-Fulcher-Tammann (VFT) law. The pressure dependence of the characteristic temperatures Tg (glass transition temperature) and T0 (Vogel temperature) as well as the activation volumes for both alpha and alpha' processes are very similar, indicating, that both relaxation processes originate from similar local molecular dynamics. Additionally, for both alpha and alpha' relaxations the combined temperature and pressure dependences of the relaxation times can be described using a parameter Gamma=rhon/T with the same value of the exponent n.

Computer Simulation↗

PubMed1995

Phase transition behavior and molecular structures of monounsaturated phosphatidylcholines. Calorimetric studies and molecular mechanics simulations.

High resolution differential scanning calorimetric studies were performed to investigate the thermotropic phase behavior of 26 molecular species of sn-1 saturated/sn-2 monounsaturated phosphatidylcholines. In parallel with calorimetric studies, the energy-minimized structures and steric energies of the diglyceride moieties of these monoenoic lipids were determined using a molecular mechanics approach. The combined calorimetric and computational studies led to the following results and conclusions. (i) When a single cis-carbon-carbon double bond (delta) is incorporated into a saturated diacylphosphatidylcholine molecule at any position within the central segment of the long sn-2 acyl chain, the resulting monoenoic lipid molecules will, in excess water, exhibit reduced phase transition temperature (Tm) and transition enthalpy (delta H) as they undergo the gel to liquid-crystalline phase transition. The Tm and delta H-lowering effects of the delta bond can be attributed to a decrease in the chain length of the sn-2 acyl chain, a change in the chain length difference between the sn-1 and sn-2 acyl chains, and a local perturbation of the chain-chain van der Waals interaction in the vicinity of the delta bond. (ii) For a series of positional isomers of 1-stearoyl-2-cis-octadecenoylphosphatidylcholine, C(18):C(18:1 delta n)PC, with a delta bond at different positions along the sn-2 acyl chain, the Tm value depends critically on the position of the delta bond. Specifically, the Tm value is minimal as the delta bond is located at the geometric center of the linear segment of the sn-2 acyl chain, and the Tm value is progressively increased as the delta bond migrates toward either end of the sn-2 acyl chain. (iii) The various monoenoic phosphatidylcholines under study can be divided into two groups. The Tm values of most lipids in each group can be correlated in an identical manner with their structural parameters, yielding a common Tm-structure relationship.

Calorimetry, Differential Scanning↗

PubMed1983

Outer and inner membrane preparations of extreme thermophile and their physico-chemical properties.

Outer and inner (cytoplasmic) membranes were partially purified from the gram negative extremely thermophilic bacteria, Thermus thermophilus HB-8 by sucrose density gradient centrifugation. In spite of our efforts to separate them, the inner membrane fraction contained some outer membrane components as determined by enzyme assay and electrophoresis. When studied by 5DS spin labeling, the outer membranes showed a larger 2T11 value (lower fluidity) than the inner membranes, although the fatty acid compositions were similar. The inner membranes of the cells cultured at higher temperature showed a larger 2T11 value than the cells cultured at lower temperature. A similar phenomenon was observed with the TEMPO parameter of liposomal membranes. The upper break point (Th) of the inner membranes observed by spin labeling was slightly lower than the culture temperature of the cells, and the lower break point (T1) corresponded well to the lowest temperature limit of growth. The calorimetric heating curve of the inner membranes had a broader temperature range of transition than that of the liposomal membranes. The transition temperature observed by calorimetry seems to reflect the melting properties of the membrane lipids, while fatty acid spin probe probably reports the local environment of the membrane, which is more directly related to its biological function.

Adaptation, Physiological↗

PubMed2004

Phase-transition phenomena of 0.8 microm superfluid 3He slab.

We have investigated the transition phenomena of superfluid 3He in thin 0.8 microm slabs with a cw-NMR method. We found that, just below the phase-transition temperature, only the A phase appeared at any pressure. At lower temperatures, the phase transition to the B phase occurred between 0.3 and 2.74 MPa. We obtained a universal critical thickness delta as a function of pressure. When the reduced slab thickness, d/xi(T), is smaller than delta, only the A phase becomes stable.

Journal Article↗

PubMed1986

Effect of thermal history on the glassy state of indapamide.

The effects of thermal history, e.g. cooling rate, annealing, etc., on the thermal behaviour of indapamide glass were determined by differential scanning calorimetry (DSC). The glass was prepared by heating indapamide crystals (m.p. 162 degrees C) to 180 degrees C, and then cooling the melt to room temperature. The glass transition temperature (Tg) of the material was 98 degrees C. An endotherm, due to thermal relaxation of the glass, was observed in the DSC thermogram when indapamide glass was prepared by slow cooling or was annealed isothermally at a temperature below Tg. Such enthalpy relaxation may be observed during ageing of pharmaceutical glasses and might influence their physico-chemical properties.

Calorimetry, Differential Scanning↗

PubMed2004

In-plane spectral weight shift of charge carriers in YBa2Cu3O6.9.

The temperature-dependent redistribution of the spectral weight of the CuO2 plane-derived conduction band of the YBa2Cu3O6.9 high-temperature superconductor (superconducting transition temperature = 92.7 kelvin) was studied with wide-band (0.01- to 5.6-electron volt) spectroscopic ellipsometry. A superconductivity-induced transfer of the spectral weight involving a high-energy scale in excess of 1 electron volt was observed. Correspondingly, the charge carrier spectral weight was shown to decrease in the superconducting state. The ellipsometric data also provide detailed information about the evolution of the optical self-energy in the normal and superconducting states.

Journal Article↗

PubMed1975

Separation of phenylalanine transport events by using selective inhibitors, and identification of a specific uncoupler activity in Yersinia pestis.

Phenylalanine transport in Yersinia pestis TJW was differentially inhibited by sulfhydryl blocking reagents, uncoupling agents, and respiratory inhibitors. Kinetic studies with potassium cyanide and sodium azide showed that these compounds have no immediate effect on the initial rate of phenylalanine transport, but have an immediate and severe inhibitory effect on the rate of oxygen uptake. Identical studies with p-chloromercuribenzoate (pCMB) and 2,4-dinitrophenol (DNP) showed that these compounds have an instantaneous and total inhibitory effect on phenylalanine transport. DNP stimulated oxygen uptake, and pCMB caused only a sluggish inhibiton of oxygen uptake. pCMB acted as a competitive inhibitor of phenylalanine transport, whereas DNP inhibitied noncompetitively. Arrenius plots of the initial rate of phenylalanine transport in pCMB- and DNP-treated cells showed that DNP alters the transition temperature of the phenylalanine transport system from 17 C for control cells to 12 C. DNP did not inhibit transport when cells were treated at temperatures of 2 to 10 C. PCMB did not alter the normal transition temperature and inhibited phenylalanine transport over a 2 to 30 C temperature range. Efflux induced by both pCMB and DNP were blocked by placing cells at low temperatures (2 to 20 C). Inhibition of adenosine 5'-triphosphate synthesis by DNP did not show any temperature sensitivity as did phenylalanine transport. These data indicate that: (i) respiration is not obligatory for active transport of phenylalanine in Y. pestis TJW; and (ii) pCMB inhibits transport activity by reacting with the sulfhydryl group(s) at the carrier binding site. The data show that the uncoupler, DNP, selectively alters a temperature-dependent property of phenylalanine transport, that is not related to uncoupling activity of DNP , and probably involves membrane lipid alterations.

Adenosine Triphosphate↗

PubMed2004

Degradation of poly-L-lactide. Part 2: increased temperature accelerated degradation.

Poly-L-lactide (PLLA) is one of the most significant members of a group of polymers regarded as bioresorbable. The degradation of PLLA proceeds through hydrolysis of the ester linkages in the polymer's backbone; however, the time for the complete resorption of orthopaedic devices manufactured from PLLA is known to be in excess of five years in a normal physiological environment. To evaluate the degradation of PLLA in an accelerated time period, PLLA pellets were processed by compression moulding into tensile test specimens, prior to being sterilized by ethylene oxide gas (EtO) and degraded in a phosphate-buffered solution (PBS) at both 50 degrees C and 70 degrees C. On retrieval, at predetermined time intervals, procedures were used to evaluate the material's molecular weight, crystallinity, mechanical strength, and thermal properties. The results from this study suggest that at both 50 degrees C and 70 degrees C, degradation proceeds by a very similar mechanism to that observed at 37 degrees C in vitro and in vivo. The degradation models developed also confirmed the dependence of mass loss, melting temperature, and glass transition temperature (Tg) on the polymer's molecular weight throughout degradation. Although increased temperature appears to be a suitable method for accelerating the degradation of PLLA, relative to its physiological degradation rate, concerns still remain over the validity of testing above the polymer's Tg and the significance of autocatalysis at increased temperatures.

Absorbable Implants↗

PubMedDate not supplied

Localization of an entrapped item within unilamellar vesicle compartments: use of ultrasound disruption as a procedure to separate aqueous phase and lipidic lamellae.

A procedure has been carried out previously to separate the aqueous phase and the lipidic lamellae from multilamellar liposomes (Bakouche and Gerlier, Analyt. Biochem., 1983, 130, 379). This procedure consisted in multiple short bursts of sonication at a temperature below the transition temperature (Tm) of the lowest melting component followed by an ultracentrifugation. The aqueous phase and the lipidic lamellae were recovered in the supernatant and in the pellet respectively. This procedure was adapted for unilamellar vesicles by modifying the second step of the procedure. A suspension of unilamellar liposomes containing 5,6-carboxyfluorescein (5,6-CF) as a probe for the aqueous phase was disrupted by sonication at low temperature. After gel filtration on to a Sephadex G100 column, the phospholipid bilayers were readily separated from the aqueous probe 5,6-CF. Such a procedure should allow the localization of any item within the unilamellar liposome compartments.

Chromatography, Gel↗