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PubMed2002

Characterization of ciclosporin A loaded poly (D,L lactide-co-glycolide) microspheres using modulated temperature differential scanning calorimetry.

The aim of this study was to investigate the physical structure of poly (D,L lactide-co-glycolide) (PLGA) microspheres loaded with ciclosporin A in terms of the amorphous properties of the individual components and the phase separation characteristics of the binary systems. Microspheres were prepared using a standard oil-in-water emulsion technique. The thermal properties of the PLGA, ciclosporin A and loaded spheres were investigated using modulated temperature differential scanning calorimetry (MTDSC) using a TA Instruments MTDSC 2920, with scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and high-performance liquid chromatography used as supportive techniques. MTDSC indicated a glass transition for ciclosporin A in the reversing heat flow signal at 107 degrees C, supported by temperature cycling studies, while XRD showed clear evidence for diffraction peaks, thereby indicating that the material as received is semi-crystalline. The unloaded PLGA spheres showed a glass transition (Tg) at 43 degrees C, with no reduction in Tg being observed on loading the peptide up to 50%, w/w. Similarly, no evidence for diffraction peaks were seen for the drug-loaded systems, although the glass transition corresponding to the peptide was observed for the loaded microspheres, suggesting that the drug is present as a separate amorphous phase. Similarly, SEM studies showed the appearance of distinct "islands" on the surface of the spheres that are suggested to correspond to the drug phase, with the size of the islands increasing with drug loading. Evidence is therefore presented that ciclosporin A may exist in a range of solid states, with the degree of crystallinity being altered by processing. In addition, there appears to be little or no miscibility between the drug and PLGA using the manufacturing protocol employed here. These findings may have implications for the choice of manufacturing protocol, the release of peptide drugs from PLGA microspheres and the chemical and physical stability of such drugs.

Biocompatible Materials↗

PubMed2002

Reverse-phase HPLC separation of D-amygdalin and neoamygdalin and optimum conditions for inhibition of racemization of amygdalin.

In boiling aqueous solution, D-amygdalin usually begins to convert into neoamygdalin in 3 min and more than 30% of the initial D-amygdalin is found as neoamygdalin after 30 min. In this report, we establish methods for simple HPLC analysis and the inhibition of D-amygdalin conversion. D-Amygdalin and its conversion product, neoamygdalin, were clearly separated on reverse-phase column chromatography by an optimized eluent of 10 mM sodium phosphate buffer (pH 3.8) containing 6% acetonitrile. Linearity for analyzing D-amygdalin and neoamygdalin was observed in the range from 0.05 to 0.5 mM. The detection limits for D-amygdalin and neoamygdalin were ca. 5 microM per injected amount. We found that D-amygdalin conversion was completely inhibited by adding 0.05% citric acid to the aqueous solution before boiling. To prevent the loss of pharmaceutical potency of Tonin, we applied this method to measure the conversion rate of D-amygdalin. We confirmed that D-amygdalin conversion in Tonin is effectively inhibited by acidic boiling solution with 0.1% citric acid.

Amygdalin↗

PubMed1996

[Interaction of sugar with phospholipid bilayer--study on the stabilization of liposomes].

Sugars have the capacity to stabilize structure and function of lipid bilayer. In the presence of sugars, liposomes could remain in their intact biological structure and retain as much as 100% of their original contents after drying-rehydration circle. In this review we present molecular mechanism of preserving effect of sugars on lipid bilayer: preventing membrane fusion, affecting the main transition temperature, preventing lateral phase separation and phase transition of L alpha to H(I). This paper also describes the prospect of the application of these studies.

Carbohydrates↗

PubMed2005

pH-Induced structural transitions during complexation and coacervation of beta-lactoglobulin and acacia gum.

pH-Induced structural changes during complex coacervation between beta-lactoglobulin (BLG) and Acacia gum (AG) in aqueous solutions were determined by coupling slow in situ acidification of BLG/AG mixed dispersions and different experimental methods. The combined signal evolution of dynamic light scattering at 90 degrees scattering angle (I(90)), electrophoretic mobility, turbidimetry (tau), circular dichroism, and phase contrast microscopy allowed the distinction of critical structural transitions and the definition of their corresponding pH. The formation of soluble BLG/AG complexes was initiated at pH(sc) (4.90), since I(90) and tau significantly increased from the baseline. In parallel or just following complexation, a conformational change of BLG was detected at pH(pct) (4.8). An increase in positive charge density of BLG induced complex aggregation at pH(ca) (4.7). More efficient charge neutralization of aggregated complexes, especially through the lowering of the number of AG negative charges, promoted initiation of phase separation at pH(psi) (4.4). Mixed dispersions became unstable and phase separation occurred at pH(ps) (4.2). The phase separation of mixed dispersions was suggested by the maximum value of scattered light, by an important acceleration of the dispersion turbidity, by a strong increase of hydrodynamic radii, and by the first appearance of light fluctuations as observed by phase contrast microscopy. At the microscopic level, the first coacervates were observed at pH(coa) (4.0), near the pH of the maximum of turbidity. It was also noticed that, from the onset of interactions between biopolymers, the pH decrease led to (i) a gradual homogenization of particle size in the mixed dispersion as suggested by the decrease of dispersion polydispersity and (ii) conformational transitions of the protein (a loss of alpha-helix structure at pH(pct) and a gain in protein secondary structure near pH(coa), probably involving beta-sheet components).

Acacia↗

PubMed2001

Role of stress in thin film alloy thermodynamics: competition between alloying and dislocation formation.

Using scanning tunneling microscopy (STM) and first-principles local-spin-density-approximation calculations to study submonolayer films of Co (1-c)Ag (c)/Ru(0001) alloys, we have discovered a novel phase-separation mechanism. When the Ag concentration c exceeds 0.4, the surface phase separates between a dislocated, pure Ag phase and a pseudomorphically strained Co(0.6)Ag (0.4) surface alloy. We attribute the phase separation to the competition between two stress relief mechanisms: surface alloying and dislocation formation. The agreement between STM measurements and our calculated phase diagram supports this interpretation.

Journal Article↗

PubMed2006

Clouding and phase behavior of nonionic surfactants in hydrophobically modified hydroxyethyl cellulose solutions.

Clouding phenomena and phase behaviors of two nonionic surfactants, Triton X-114 and Triton X-100, in the presence of either hydroxyethyl cellulose (HEC) or its hydrophobically modified counterpart (HMHEC) were experimentally studied. Compared with HEC, HMHEC was found to have a stronger effect on lowering the cloud point temperature of a nonionic surfactant at low concentrations. The difference in clouding behavior can be attributed to different kinds of molecular interactions. Depletion flocculation is the underlying mechanism in the case of HEC, while the chain-bridging effect is responsible for the large decrease of cloud point for HMHEC. Composition analyses for the formed macroscopic phases were carried out to provide support for associative phase separation for the case of HMHEC, in contrast to segregative phase separation for HEC. An interesting three-phase-separation phenomenon was reported in some HMHEC/Triton X-100 mixtures at high surfactant concentrations.

Journal Article↗

PubMed1997

Phenotypic characterization of Lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice: physical-chemistry of gallbladder bile.

Lith genes control susceptibility to cholesterol gallstone formation in inbred strains of mice on a lithogenic diet containing high fat, high cholesterol and 0.5% cholic acid. Our study defines the physical-chemical phenotypes of C57L, AKR, and (C57L x AKR) F1 mouse gallbladder biles during 56 days on the lithogenic diet. We found enhanced cholesterol supersaturation, accumulation of mucin gel, and larger gallbladders in all C57L and F1 mice, as well as more frequent gallstone formation in male C57L and F1 mice (80%) compared to females (40%) or AKR mice (15%). In male C57L and F1 mice, mucin gel accumulated at 3 days, followed by cholesterol supersaturation and phase separation of liquid crystals, solid monohydrate crystals, and, in 43% of mice, anhydrous cholesterol crystals; whereas, in females, phase separations were delayed 2 to 9 days, and anhydrous crystals did not form. In AKR mice, cholesterol supersaturation and phase separations were infrequent and delayed, and gender did not influence the phenotype. Taurocholate invariably replaced endogenous bile salts, especially tauro-beta-muricholate, with crystallization sequences matching taurocholate-containing model bile systems. We conclude: i) Lith genes determine biliary cholesterol supersaturation, mucin gel accumulation, gallbladder size, phase-separation, and prevalence of cholesterol gallstones. ii) Identical phenotypes in C57L and F1 mice indicate susceptibility to cholesterol gallstones is genetically dominant, favoring males 2:1. iii) Mucin gel accumulation, crystallization, and stone formation are rare in AKR mice. This definition of the physical chemistry of lithogenesis should aid in further elucidation of the Lith genes and the proteins they encode.

Animals↗

PubMed2006

Partial filling micellar electrokinetic chromatography analysis of androgens and testosterone derivatives using two sequential pseudostationary phases.

Separation of anabolic and androgenic steroids by micellar electrokinetic chromatography (MEKC) has been little studied. Simultaneous separation of the endogenous alpha-epimers testosterone and epitestosterone has not been achieved with any electroseparation technique. Here, a partial filling micellar electrokinetic chromatographic (PF-MEKC) method is described for the analysis of three endogenous steroid hormones (androstenedione, testosterone, epitestosterone) and two synthetic anabolic steroids (fluoxymesterone, methyltestosterone). The resolution efficiency of single-isomer sulphated gamma-cyclodextrins and the surfactants sodium dodecyl sulphate and sodium taurocholate was exploited. The method is based on the sequential introduction of short plugs of two different pseudostationary phases into the capillary. The separation was completed in less than 10 min. The method can be used in quantitative analysis. Linear correlation was obtained between concentration and peak area of 0.996 or better. The repeatability (RSD) of the compound peak areas ranged from 3.6% (methyltestosterone) to 6.2% (androstenedione). Limits of detection were between 73 microg/L (testosterone) and 160 microg/L (fluoxymesterone). As a demonstration of the method, androstenedione, testosterone and epitestosterone were determined in a spiked urine sample.

Androgens↗

PubMed1995

Mechanism of liposome destabilization by polycationic amino acids.

Polycationic amino acids induce the leakage and fusion of liposomes containing anionic lipids. We have investigated the nature and extent of the changes in membrane physical properties caused by these polypeptides which could result in the observed membrane destabilization. We found that in the range of pH 5 to pH 7 both poly-L-histidine and poly-L-lysine were ineffective in shifting the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine, either in the presence of absence of 1-palmitoyl-2-oleoylphosphatidylserine. We also studied the gel to liquid crystalline phase transition properties of 1:1 mixtures of phosphatidylserine and phosphatidylethanolamine, both in dimyristoyl forms as well as the 1-palmitoyl-2-oleoyl forms, as a function of pH and in the presence and absence of polycationic amino acids. We observed that these two lipids were largely miscible at all pH values and in the presence and absence of the polypeptides. However, there was some increased tendency for phase separation at higher pH and in the absence of polypeptide. Thus neither changes in curvature strain nor lateral phase separation induced by the polycationic amino acids could account for their marked ability to induce leakage and fusion. Phosphatidylethanolamine labelled with pyrene on one of the acyl chains gives rise to fluorescent emission from both monomer and excimer forms. The ratio of emission intensity from these two forms is indicative of lateral phase separation and the degree of lateral mobility of this probe. In equimolar mixtures of the 1-palmitoyl-2-oleoyl forms of phosphatidylserine and phosphatidylethanolamine in the liquid crystalline phase at 30 degrees C we find little effect of pH on the ratio of excimer to monomer emission intensity. However poly-L-lysine markedly lowers the fraction of excimer emission from these liposomes through the pH range from 5 to 7. Poly-L-histidine lowers the excimer to monomer emission ratio at pH 5 but not at pH 7. This is opposite to what one would expect for lateral phase separation and is interpreted at being the consequence of the polypeptide lowering the rate of lateral diffusion of the lipids. This effect of poly-L-histidine is observed over a range of temperatures from 0 to 40 degrees C in both gel and liquid crystalline phases. There is no evidence from the behaviour of the pyrene fluorescent probe for lipid interdigitation.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetry, Differential Scanning↗

PubMedDate not supplied

Complexation of DNA with poly(methacryl oxyethyl trimethylammonium chloride) and Its poly(oxyethylene) grafted analogue.

Intermolecular complexes of genomic polydisperse DNA with synthetic polycations have been studied. Two cationic polymers have been used, a homopolymer poly(methacryl oxyethyl trimethylammonium chloride) (PMOTAC) and its analogue grafted with poly(oxyethylene). The amount of poly(oxyethylene) grafts in the copolymer was 15 mol % and Mw of the graft was 200 g/mol. Salmon DNA (sodium salt) was used. The average molecular weight (Mw) of DNA was 10.4 x 10(6) g/mol. Conductivity, pH, and dynamic light scattering studies were used to characterize the complexes. The size and shape of the polyelectrolyte complex particles have been studied as a function of the cation-to-anion ratio in aqueous solutions of varying ionic strengths. The polyelectrolyte complexes have extremely narrow size distributions taking into account the polydispersity of the polyelectrolytes studied. The poly(oxyethylene) grafts on PMOTAC promote the formation of small colloidally stabile complex particles. Addition of salt shifts the macroscopic phase separation toward lower polycation content; that is, complexes partly phase separate with the mixing ratios far from 1:1. Further addition of salt to the turbid, partly phase separated solution results in the dissociation of complexes and the polycation and DNA dissolve as individual chains.

Ammonium Chloride↗

PubMed2000

Wetting-driven structure formation of a binary mixture in the presence of a mobile particle pinning potential

We investigate the pattern formation on the solid substrate of phase-separating films containing mobile wetting particles with a preferential attraction for one component of the mixtures. The presence of mobile particles under the surface-particle interaction modulation breaks the isotropy of the bulk phase-separating process, leading to the formation of orientational structure due to the interplay between phase separation and wetting particle ordering under a modulated pinning potential at the late stage. Simulations suggest that the phase-separation morphology can be changed through the adjustment of the wettable-phase-particle interaction and the surface-particle interaction. It provides some important insights into this "wetting-directed spinodal decomposition."

Journal Article↗

PubMed2003

Multi-dimensional liquid phase based separations in proteomics.

This review covers recent developments towards the implementation of multi-dimensional (MuD) liquid phase based systems for proteome investigations. Although two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) has been used as a standard approach in proteomics, its drawbacks including the limited dynamic range and molecular mass range, together with lack of on-line integration with biological mass spectrometery (Bio-MS) have limited its widespread use and applications in proteomics. In the meantime, various liquid-phase based multi-dimensional separation techniques have been explored. Especially, with the emergence of the combination of nanoflow capillary high-performance liquid chromatography (cHPLC) and Bio-MS, attention is again refocused on utilizing multi-dimensional liquid-phase based separation of proteins. Some remarkable applications of on-line analysis of intact proteins and on-column digested proteins, and the emergence of approaches such as multiple HPLC-electrospray ionization tandem MS and capillary array electrophoresis-matrix assisted laser desorption ionization MS, have stimulated thinking towards developing a automated multi-dimensional system (MuDSy) that integrates liquid phase based separation, digestion and identification of proteins in complex biological mixtures.

Chromatography, Liquid↗

PubMed2000

The distribution of alpha-tocopherol in mixed aqueous dispersions of phosphatidylcholine and phosphatidylethanolamine.

The effect of alpha-tocopherol on the structure and phase behaviour of mixed aqueous dispersions of phosphatidylcholine and phosphatidylethanolamine has been examined by synchrotron X-ray diffraction. Equimolar mixtures of dioleoylphosphatidylethanolamine:dioleoylphosphatidylcholine and dimyristoylphosphatidylcholine:dioleoylphosphatidylethanolamine did not show evidence of phase separation of an inverted hexagonal structure typical of alpha-tocopherol and phosphatidylethanolamine from lamellar phase. Mixed dispersions of dioleoyl derivatives of phosphatidylethanolamine:phosphatidylcholine (3:1) form a typical miscible gel phase at low temperatures but which phase separates into lamellar liquid-crystal and inverted hexagonal phases at temperatures greater than 65 degrees C. The presence of 1, 2 or 5 mol% alpha-tocopherol caused a decrease in the temperature at which the inverted hexagonal phase appears. Phase separation of non-lamellar phase from lamellar gel phase can be detected in the presence of 7.5 and 10 mol% alpha-tocopherol, indicating a limited capacity of the phosphatidylcholine to incorporate alpha-tocopherol into the lamellar domain. A partial phase diagram of the ternary mixture has been constructed from the X-ray scattering data. It was concluded that there is no preferential interaction of alpha-tocopherol with phosphatidylethanolamine in mixed aqueous dispersions containing phosphatidylcholines.

Lipid Bilayers↗

PubMed1989

Interaction of sphingomyelins and phosphatidylcholines with fluorescent dehydroergosterol.

The fluorescent sterol dehydroergosterol was used as a cholesterol analogue in conjunction with multifrequency phase and modulation (1-250 MHz) fluorometry to examine whether sterols (1) interact preferentially with fluid- or solid-phase phospholipids and (2) interact preferentially with sphingomyelin in phase-separated or phase-miscible cosonicated phospholipid membranes. Cosonicated small unilamellar vesicles (SUV) were produced by mixing lipids in organic solvents, drying the mixture, adding buffer, sonicating, and separating SUV. Phospholipids of synthetic as well as biological origin were utilized. In phase-separated, cosonicated SUV of dimyristoylphosphatidylcholine/distearoylphosphatidylcholine (DMPC/DSPC, 1:1 molar ratio), the fluorescent sterol (0.5 mol %) interacted preferentially with the fluid-phase lipid (partition coefficient, Kf/s = 2.6-3.4) according to four criteria. First, dehydroergosterol detected only the phase transition of DMPC, the phospholipid with the lower phase transition temperature. Second, the dehydroergosterol fluorescence polarization, limiting anisotropy, order parameter, and rotational relaxation time in the cosonicated vesicle were similar to those of dehydroergosterol in SUV composed only of DMPC. Third, the number of dehydroergosterol fluorescence lifetime components as well as the distribution in the cosonicated SUV was similar to that of dehydroergosterol in SUV composed of DMPC. Fourth, dehydroergosterol concentration-dependent self-quenching was detected in DSPC SUV at much lower dehydroergosterol concentration than in DMPC SUV. Preference of dehydroergosterol for fluid-phase lipids was also observed by monitoring dehydroergosterol exchange between individually sonicated DMPC SUV and DSPC SUV after the two types of vesicles were mixed in equal proportions. In these SUV mixtures, the dehydroergosterol also partitioned into the more fluid SUV, 99:1.(ABSTRACT TRUNCATED AT 250 WORDS)

Ergosterol↗

PubMed1997

Isolation of alpha and beta brain tubulin subunits after alkaline treatment of the protein.

We demonstrate here that brain purified tubulin can be dissociated into alpha and beta subunits at pH > 10 and that the subunits can be separated by using the Triton X-114 phase separation system. After phase partition at pH > 10, alpha tubulin but not beta tubulin behaves as a hydrophobic compound appearing in the detergent rich phase. After three extractions of the alkaline aqueous phase with Triton X-114, about 90% of the alpha tubulin was recovered in the detergent rich phase. The hydrophobic behavior observed for alpha tubulin after its dissociation at pH 11.5 was not due to an irreversible change of the protein, because when the detergent rich phase containing alpha tubulin was diluted with a buffer solution at pH 7.3 and the solution allowed to partition again, alpha-tubulin is recovered in the aqueous phase. The detergent in the aqueous phase of the alpha and beta tubulin preparations can be removed up to 90% by 12 h dialysis. The alpha and beta subunits of tubulin from kidney and liver behave, in this phase separation system, like those of brain tubulin.

Animals↗

PubMed2005

Inhibition of a solid phase reaction among excipients that accelerates drug release from a solid dispersion with aging.

Hydrophobic drug substances can be formulated as a solid dispersion or solution using macromolecular matrices with high glass transition temperatures to attain satisfactory dissolution. However, very few marketed products have previously relied on solid dispersion technology due to physical and chemical instability problems, and processing difficulties. In the present study, a modified release product of a therapeutic drug for hypertension, Barnidipine hydrochloride, was developed. The drug product consisted of solid dispersion based on a matrix of carboxymethylethylcellulose (CMEC), which was produced using the spray-coating method. An enteric coat layer was sprayed on the surface of the solid dispersion to control drug release. Interestingly, the release rate accelerated as the drug product aged, while there were no indications of deceleration of the release rate which was due to crystallization of the drug substance. To prevent changes in the dissolution kinetics during storage periods, a variety of processing conditions were tried. It was found that not only use of non-aqueous solvents but also a reduction in coating temperatures consistently resulted in stable solid dispersions. The molecular bases of dissolution of the drug substance from those matrices were investigated. The molecular weight of CMEC was found to be a dominant factor that determined dissolution kinetics, which followed zero-order release, suggesting an involvement of an osmotic pumping mechanism. While dissolution was faster using a higher molecular weight CMEC, the molecular weight of CMEC in the drug product slowly increased with aging (solid phase reaction) depending on the processing conditions, causing the time-induced elevation of dissolution. While no crystalline components were found in the solid dispersion, the amorphous structure maintained a degree of non-equilibrium by nature. Plasticization by water in the coating solution relaxed the amorphous system and facilitated phase separation of the drug substance and CMEC upon production. The solid phase reaction advanced differentially in the solid dispersion depending on the degree of phase separation set initially. The use of non-aqueous solvents and/or a decrease in the coating temperatures inhibited the occurrence of phase separation upon production, thereby preventing the formation of CMEC-rich phases where the solid phase reaction occurred during storage.

Carboxymethylcellulose Sodium↗

PubMed1999

Lipid-induced organization of a primary amphipathic peptide: a coupled AFM-monolayer study.

To better understand the nature of the mechanism involved in the membrane uptake of a vector peptide, the interactions between dioleoylphosphatidylcholine and a primary amphipathic peptide containing a signal peptide associated with a nuclear localization sequence have been studied by isotherms analysis of mixed monolayers spread at the air-water interface. The peptide and the lipid interact through strong hydrophobic interactions with expansion of the mean molecular area that resulted from a lipid-induced modification of the organization of the peptide at the interface. In addition, a phase separation occurs for peptide molar fraction ranging from about 0.08 to 0.4 Atomic force microscopy observations made on transferred monolayers confirm the existence of phase separation and further reveal that mixed lipid-peptide particles are formed, the size and shape of which depend on the peptide molar fraction. At low peptide contents, round-shaped particles are observed and an increase of the peptide amount, simultaneously to the lipidic phase separation, induces morphological changes from bowls to filamentous particles. Fourier transform infrared spectra (FTIR) obtained on transferred monolayers indicate that the peptide adopts a beta-like structure for high peptide molar fractions. Such an approach involving complementary methods allows us to conclude that the lipid and the peptide have a nonideal miscibility and form mixed particles which phase separate.

Lipids↗

PubMed2001

Synthesis and evaluation of polymer-based zwitterionic stationary phases for separation of ionic species.

Three different zwitterionic functional stationary phases for chromatography were synthesized on the basis of 2-hydroxyethyl methacrylate (HEMA) polymeric particles. Two synthesis routes, producing materials designated S300-ECH-DMA-PS or S300-TC-DMA-PS, involved activation of the hydroxyl groups of the HEMA material with epichlorohydrin or thionyl chloride, respectively, followed by dimethylamination and quaternizing 3-sulfopropylation with 1,3-propane sultone. The third route was accomplished by attaching methacrylate moieties to the HEMA through a reaction with methacrylic anhydride, followed by graft photopolymerization of the zwitterionic monomer 3-[N,N-dimethyl-N-(methacryloyloxyethyl)ammonium] propanesulfonate, initiated by benzoin methyl ether under 365-nm light. According to elemental analyses, both the S300-ECH-DMA-PS and S300-TC-DMA-PS materials appeared to have overall charge stoichometries close to unity, whereas the grafted material, S300-MAA-SPE, seemed to carry an excess of anion exchange sites in addition to the zwitterionic groups. Yet all three zwitterionic stationary phases were capable of separating inorganic anions and cations simultaneously and independently using aqueous solutions of perchloric acid or perchlorate salts as eluent, albeit with markedly different selectivities. On the S300-TC-DMA-PS and S300-MAA-SPE materials, the retention times increased for cations and decreased for anions with increasing eluent concentration, whereas with the S300-ECH-DMA-PS material, the retention times of both anions and cations decreased with increasing eluent concentration. These results demonstrate the importance of choosing appropriate synthesis conditions in order to prepare covalently bonded zwitterionic separation materials with an acceptable charge balance.

Journal Article↗