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PubMed2005

Comparison of the supramolecular structures of two glyco lipids with chiral and nonchiral methyl-branched alkyl chains from natural sources.

Two alkyl glycosides with the same type of disaccharide headgroups (melibiose) and different methyl-branched alkyl chains, short chiral [(2R,4R,6R,8R)-2,4,6,8-tetramethyldecyl, extracted from an animal source] and long nonchiral (3,7,11,15-tetramethylhexadecyl, from a plant source), were synthesized. The supramolecular aggregate structure formed in dilute solutions was investigated by small-angle neutron scattering and surface tension measurements. The lyotropic phase diagram was studied by differential scanning calorimetry and water penetration scans. The thermotropic phase behavior was investigated by polarizing microscopy. The compounds showed unusual phase behavior: (i) The liquid-crystalline polymorphism is reduced to only form smectic A phases in the pure state; the formation of lyotropic phases such as hexagonal or lamellar phases was not observed. (ii) The compound with the longer nonchiral alkyl chain is more soluble in water than the one with the shorter chiral chain, most likely because of the different flexibilities of the chains. (iii) For the long-chain compound, the formation of micelles is observed, whereas the short-chain compound forms large disklike/bilayer aggregates. The method of methylation of the chain controls the self-assembly and can explain different biological functions for either plants (variable temperature) or animals (constant temperature).

Animals↗
PubMed2006

Thermotropic phase behavior of cationic gemini surfactants and their equicharge mixtures with sodium dodecyl sulfate.

The lyotropic phase behavior for the neat cationic gemini surfactants alkanediyl-alpha,omega-bis(alkyldimethylammonium bromide), designated here as m-s-m, has been investigated previously in several works, but the thermotropic behavior has not been well characterized. Only for 15-s-15 and 14-s-12 have thermotropic liquid crystals (Lc) been reported. In this work, for the first time and in contrast to previous reports, we observe thermotropic Lc formation for m-2-m geminis with m = 12, 14, 16, and 18, by means of polarizing microscopy and differential scanning calorimetry (DSC). Furthermore, we investigate mixtures of m-2-m and SDS, m-2-m Br2.2SDS, which exhibit crystal-to-crystal phase transitions at lower temperature and, at high temperature, smectic Lc phases. The transition temperatures and enthalpies for Lc phases, obtained by DSC, present clear trends upon increase of the chain lengths. Combining Langmuir film experiments, possible lamellar arrangements for the different phases are tentatively discussed.

Journal Article↗
PubMed2004

Phase behavior of 1-alkylpyridinium octane-1-sulfonates. effect of the 1-alkylpyridinium counterion size.

The temperature-versus-composition phase diagrams of eight different 1-alkylpyridinium octane-1-sulfonates (APOSs) in water were studied by 1H NMR, 2H NMR, pulsed gradient spin-echo NMR, small-angle X-ray diffraction, differential scanning calorimetry, surface tension and conductivity measurements, and polarizing microscopy. The number of carbons (n(c)) in the hydrocarbon chain of the pyridinium counterions was varied from n(c) = 1 to n(c) = 8 to study how the phase behavior of the APOS/2H2O systems was affected by a change in the chain length of the counterion. The sodium octane-1-sulfonate (NaOS)/water system was used as a reference. This system formed an isotropic micellar solution (L1) phase and a normal hexagonal (H(I)) phase. All APOSs were readily soluble in water and formed L1 phases. The surface tension above the critical micelle concentration for n(c) between 1 and 3 was higher than that for NaOS, and it decreased steadily for the different APOSs with increasing chain length. The area per molecule at the air/solution interfaces was rather constant at 68 A2 for n(c) between 1 and 7. For 1-octylpyridinium octane-1-sulfonate (OPOS), it was about 5 A2 smaller, which was just outside the estimated error. However, the smallest area was obtained for NaOS. At higher surfactant concentrations, liquid crystalline phases formed. Both cubic and H(I) phases were found for n(c) = 1 and 2, while for n(c) between 3 and 5 only an H(I) phase was observed. H(I) and lamellar liquid crystalline (Lalpha) phases formed for n(c) = 6 and 7. The only liquid crystalline phase found in the OPOS system was a Lalpha phase. The NaOS H(I) phase was the only liquid crystalline phase that showed a linear relation between the 2H2O NMR quadrupolar splitting (deltaW) and Xsurf/X(W), where Xsurf and X(W) are the mole fractions of surfactant and water. The OPOS lamellae were found to be much thinner than expected, indicating a defect lamellar structure. This was further supported by the behavior of the quadrupolar splitting ofdeuterated OPOS. The anomalous behaviors of the 2H2O NMR quadrupolar splitting observed in the Lalpha phases of 1-heptylpyridinium octane-1-sulfonate and OPOS were interpreted in terms of changes in the population of the water molecules residing in different sites combined with a continuous rearrangement of the lamellae surface with the possible development of holes. The appearances of the phase diagrams were discussed in terms of surfactant molecular geometry and the packing of the amphiphiles in the aggregates formed.

Journal Article↗
PubMed2004

Phase behavior of the lecithin/water/isooctane and lecithin/water/decane systems.

The isothermal pseudo-ternary-phase diagram was determined at 25 degrees C for systems composed oflecithin, water, and, as oil, either isooctane or decane. This was accomplished by a combination of polarizing microscopy, small-angle X-ray scattering, and NMR techniques. The lecithin-rich region of the phase diagram is dominated by a lamellar liquid-crystalline phase (Lalpha). For lecithin contents less than 60% and low hydration (mole ratio water/lecithin = W0 < 5.5), the system forms a viscous gel of branched cylindrical reverse micelles. With increase in the water content, the system phase separates into two phases, which is either gel in equilibrium with essentially pure isooctane (for lecithin < 25%) or a gel in equilibrium with Lalpha (for lecithin > 25%). These two-phase regions are very thin with respect to water dilution. For 8 < W0 < 54 very stable water-in-oil emulsions form. It is only after ripening for more than 1 year that the large region occupied by the emulsion reveals a complex pattern of stable phases. Moving along water dilution lines, one finds (i) the coexistence of gel, isooctane and Lalpha, (ii) equilibrium between reverse micelles and spherulites, and, finally, (iii) disconnected reverse micelles that fail to solubilize water for W0 > 54. This results in a Winsor II phase equilibrium at low lecithin content, while for lecithin > 20% the neat water is in equilibrium with a reverse hexagonal phase and an isotropic liquid-crystalline phase. The use of the decane as oil does not change the main features of the phase behavior.

Alkanes↗
PubMed2005

Solvent/gelator interactions and supramolecular structure of gel fibers in cyclic bis-urea/primary alcohol organogels.

An organogel system consisting of trans-(1S,2S)-bis(ureidododecyl)cyclohexane (SS-BUC) and a series of primary alcohols was explored with optical polarizing microscopy (OPM), electron microscopy, circular dichroism (CD), wide-angle X-ray scattering (WAXS), and synchrotron small-angle X-ray scattering (SAXS). OPM, SAXS, and especially WAXS showed that the gel fiber of SS-BUC/methanol gels essentially consists of SS-BUC crystal itself. SAXS showed that the SS-BUC crystal in the gel takes a lamella with a domain spacing of 5.2 nm. When we left the gel at room temperature, the spacing decreased to 3.1 nm after several months. This distance change may correspond to the structural transition from a double-layer structure to an intercalated-layer structure, which was proposed by Feringa et al. (Chem.-Eur. J. 1999, 5, 937-950) as a possible arrangement of the molecular packing. When the gels in ethanol, propanol, butanol, or octanol were examined, they never showed crystalline peaks in WAXS and SAXS, indicating the amorphous nature of the gels. With increasing the alkyl chain length from ethanol to octanol, dramatic changes were observed in the CD spectrum in the 200-500-nm range. Because these CD changes are correlated to the absorbance of urea, those can be considered as the evidence that the solvents strongly relate to the spatial arrangement between the adjacent urea groups. For the amorphous gels, the cross-sectional correlation function [gammaCu] was directly obtained by the inverse Hankel transform of the SAXS data. The value of gammaCu for the gels is decreased with increasing u (distance between the two scattering bodies, see eq 5). Furthermore, it more rapidly decreases than that of the rigid cylinder model. This feature can be explained by the speculation that many solvent molecules permeate into the SS-BUC fiber. There was a clear difference between ethanol and the other gels, indicating that the solvents with a longer alkyl chain give the more permeated and diffused fiber. This permeated fiber (i.e., wet fiber) can rationalize the dramatic CD change, by presuming that the permeated solvent molecules alter the molecular stacking form.

Alcohols↗
PubMed2005

Orientations of nematic liquid crystals on surfaces presenting controlled densities of peptides: amplification of protein-peptide binding events.

We report a study of the orientations of nematic liquid crystals (LCs) in contact with peptide-modified, oligoethylene glycol-containing, self-assembled monolayers (SAMs). The SAMs were formed on gold films that were prepared by physical vapor deposition at an oblique angle of incidence. Two peptides were investigated: the optimized substrate for the Src protein kinase (IYGEFKKKC) and the synthetic equivalent of that peptide after kinase modification (IpYGEFKKKC). Polarization modulation-infrared reflectance absorbance spectroscopy (PM-IRRAS) was used to characterize the relative areal densities and orientations of these peptides at the interface. We conclude that the presence/absence of a phosphate group can influence the maximum packing density of immobilized peptide. We evaluated the orientations of the nematic liquid crystal 5CB in contact with these peptide-modified surfaces by using polarized microscopy. The time required for the nematic phase of 5CB to exhibit long-range orientational ordering (uniform alignment) was found to increase with increasing areal densities of immobilized peptide. We also found that the specific binding event between anti-phosphotyrosine IgG and the surface-immobilized phosphopeptide leads to an increase in the time required for the liquid crystal to achieve uniform anchoring (exceeding the experimentally accessible time scales). These results, when combined, suggest that the areal density and size of biomolecules at an interface can influence the time required for liquid crystals in contact with nanostructured surfaces to exhibit long-range orientational order. Finally, we illustrate the potential utility of this system by demonstrating that liquid crystals can be used to amplify and report protein binding events occurring on a spatially resolved peptide array.

Amino Acid Sequence↗
PubMed2007

Liquid crystalline phases and their dispersions in aqueous mixtures of glycerol monooleate and glyceryl monooleyl ether.

The aqueous phase behavior of mixtures of 1-glycerol monooleate (GMO) and its ether analogue, 1-glyceryl monooleyl ether (GME) has been investigated by a combination of polarized microscopy, X-ray diffraction, and NMR techniques. Three phase diagrams of the ternary GMO/GME/water system have been constructed at 25, 40, and 55 degrees C. The results demonstrate that the increasing amount of GME favors the formation of the reversed phases, evidenced by the transformation of the lamellar and bicontinuous cubic liquid crystalline phases of the binary GMO/water system into reversed micellar or reversed hexagonal phases. For a particular liquid crystalline phase, increasing the GME content has no effect on the structural characteristics and hydration properties, thus suggesting ideal mixing with GMO. Investigations of dispersed nanoparticle samples using shear and a polymeric stabilizer, Pluronic F127, show the possibility of forming two different kinds of bicontinuous cubic phase nanoparticles by simply changing the GMO/GME ratio. Also NMR self-diffusion measurements confirm that the block copolymer, Pluronic F127, used to facilitate dispersion formation, is associated with nanoparticles and provides steric stabilization.

Chemistry, Physical↗
PubMed1996

Solubility behavior, phase transition, and structure-based nucleation inhibition of etanidazole in aqueous solutions.

PURPOSE: The solubility behavior, phase transition and inhibition of the nucleation process of etanidazole were characterized. METHODS: Solubility measurements as a function of time permitted characterization of the solubility behavior and phase transition. The precipitate from saturated solutions was isolated and characterized by differential scanning calorimetry, polarized light microscopy, x-ray powder diffraction and coulometric analysis. The physical stability of metastable systems was examined in the presence of various structure-based nucleation inhibitors. RESULTS: Etanidazole is soluble in water with an equilibrium solubility of 68.1 mg/mL, pH 6.5 with changes in pH having virtually no effect on the solubility. Etanidazole reaches concentrations in excess of 150 mg/mL within one hour. Etanidazole solutions prepared at 150 mg/ mL contained crystals after rotating for 24 hours. The crystals were isolated and characterized as etanidazole monohydrate. the solubility of etanidazole monohydrate in water increased with time reaching an equilibrium solubility of 68 mg/mL after 24 hours. Therefore, the solubility studies were actually determining the solubility of the more stable monohydrate from of etanidazole. Etanidazole solutions at concentrations of 50, 100 and 150 mg/mL were stabilized to varying degrees with structure-based nucleation inhibitors (imidazole, ethanolamine or diethanolamine). CONCLUSIONS: Anhydrous etanidazole undergoes a transition in aqueous solutions to the more stable monohydrate when the solubility of the monohydrate is exceeded. The physical stability of etanidazole solutions at 4 degrees C is improved following autoclaving. The addition of structure-based nucleation inhibitors effectively stabilized the metastable systems.

Calorimetry, Differential Scanning↗
PubMed1994

An improved microscope stage for direct observation of freezing and freeze drying.

A microscope stage for observation of freezing and freeze drying is described. The stage uses thermoelectric (Peltier) heaters configured in two stages, with circulating fluid as a heat sink on the high temperature side. Lowest attainable sample temperature is about -47 degrees C. Principal advantages of this system are closed-loop control of stage temperature, rapid response to changes in temperature set point, and improved documentation of experiments by use of a video recorder system with a character generator which allows display of sample identity and temperature. Accuracy of measuring the sample temperature in the field of view was validated by comparing observed values of eutectic melting with published values for a series of solutes with eutectic temperatures in the range from -2 degrees C to -32 degrees C. Good agreement was obtained throughout this range.

Freeze Drying↗
PubMed1994

Structural rheology of a model ointment.

A model ointment consisting of white petrolatum, mineral oil and microcrystalline wax was studied using rheology, microscopy and thermal techniques. Rheograms studied over a temperature range of 25-40 degrees C indicated that the overall rheogram shape changed little as the temperature increased. However, two inflections gradually disappeared as the temperature increased. Thermal optical analysis showed that the temperature range over which these inflection disappeared correlated with the melting transition of the components forming the secondary structure. Another series of rheograms obtained from ointments with different combinations of the raw materials showed the rheology of the ointment is primarily controlled by the white petrolatum and mineral oil and that the microcrystalline wax acts to build-up the structure by incorporating itself into the existing white petrolatum structure. Thermal optical analysis of comelts of the raw materials proved that the ointment network structure is essentially a recombination of the naturally occurring components in differing ratios. The knowledge obtained from these studies is applied to a discussion of the thermal and mechanical stresses encountered in the filling operation.

Drug Packaging↗
PubMed2002

Organization and distribution of intramuscular connective tissue in normal and immobilized skeletal muscles. An immunohistochemical, polarization and scanning electron microscopic study.

Collagen fiber network is a major contributor to the coherence and tensile strength of normal skeletal muscle. Despite the well-recognized importance of the intramuscular connective tissue to the normal integrity and function of the skeletal muscle, the specific architecture including the location and three-dimensional orientation of the intramuscular connective tissue within the muscle tissue is poorly described. The structure of the intramuscular connective tissue was studied by immunohistochemistry, polarization microscopy (the crimp length and angle of the collagen fibers) and scanning electron microscope (SEM) in rat skeletal muscles (gastrocnemius, soleus and tibialis anterior) in normal situation and after 3 weeks of disuse (immobilization). Three separate networks of collagen fibers were distinguished by SEM in the normal endomysium; fibers running longitudinally on the surface of the muscle fibers (the main collagen orientation), fibers running perpendicularly to the long axis of the muscle fibers and having contacts with adjacent muscle fibers, and fibers attached to the intramuscular nerves and arteries. Similarly, the SEM analysis also disclosed three distinct collagen fiber networks running in different directions in the perimysium, but, contrary to the endomysium, the main fiber orientation could not be established. Immobilization resulted in a marked increase in the endo- and perimysial connective tissue, the majority of the increased endomysial collagen being deposited directly on the sarcolemma of the muscle cells. Immobilization also resulted in substantial increase in the number of perpendicularly oriented collagen fibers with contacts to two adjacent muscle fibers in the endomysium. Further, immobilization clearly disturbed the normal structure of the endomysium making it impossible to distinguish the various networks of fibers from each other. In the perimysium, immobilization-induced changes were similar, the number of longitudinally oriented collagen fibers was increased, the connective tissue was very dense, the number of irregularly oriented collagen fibers was markedly increased, and consequently, the different networks of collagen fibers could not be distinguished from each other. Of the three studied intact muscles, the crimp angle of the collagen fibers was lowest in the soleus and highest in the gastrocnemius muscle, and the crimp angle decreased over 10% in all muscles after the immobilization-period. Altogether, the above described quantitative and qualitative changes in the intramuscular connective tissue are likely to contribute to the deteriorated function and biomechanical properties of the immobilized skeletal muscle.

Animals↗
PubMed2004

Stability and solubility of celecoxib-PVP amorphous dispersions: a molecular perspective.

PURPOSE: The purpose of the current study is to evaluate the solubility advantage offered by celecoxib (CEL) amorphous systems and to characterize and correlate the physical and thermodynamic properties of CEL and its amorphous molecular dispersions containing poly(vinylpyrrolidone) (PVP). METHODS: The measurement of crystalline content, glass transition temperatures, and enthalpy relaxation was performed using differential scanning calorimetry. Solubility and dissolutions studies were conducted at 37 degrees C to elucidate release mechanisms. Further, the amorphous systems were characterized by polarized light microscopy and X-ray powder diffraction studies. RESULTS: The PVP content has a prominent effect on the stability and solubility profiles of amorphous systems. A dispersion of 20% w/w PVP with CEL resulted in a maxima in terms of solubility enhancement and lowering of relaxation enthalpy. The release of drug from amorphous molecular dispersions was found to be drug-dependent and independent of the carrier. CONCLUSIONS: The solubility enhancement and enthalpy relaxation studies with respect to PVP concentration helped in a better prediction of role of carrier and optimization of concentration in the use of solid dispersions or amorphous systems. The drug release mechanism is drug-controlled rather than carrier-controlled.

Algorithms↗
PubMed2004

Supercooled smectic nanoparticles: a potential novel carrier system for poorly water soluble drugs.

PURPOSE: The possibility of preparing nanoparticles in the supercooled thermotropic liquid crystalline state from cholesterol esters with saturated acyl chains as well as the incorporation of model drugs into the dispersions was investigated using cholesteryl myristate (CM) as a model cholesterol ester. METHODS: Nanoparticles were prepared by high-pressure melt homogenization or solvent evaporation using phospholipids, phospholipid/ bile salt, or polyvinyl alcohol as emulsifiers. The physicochemical state and phase behavior of the particles was characterized by particle size measurements (photon correlation spectroscopy, laser diffraction with polarization intensity differential scattering), differential scanning calorimetry, X-ray diffraction, and electron and polarizing light microscopy. The viscosity of the isotropic and liquid crystalline phases of CM in the bulk was investigated in dependence on temperature and shear rate by rotational viscometry. RESULTS: CM nanoparticies can be obtained in the smectic phase and retained in this state for at least 12 months when stored at 230C in optimized systems. The recrystallization tendency of CM in the dispersions strongly depends on the stabilizer system and the particle size. Stable drug-loaded smectic nanoparticles were obtained after incorporation of 10% (related to CM) ibuprofen, miconazole, etomidate, and 1% progesterone. CONCLUSIONS: Due to their liquid crystalline state, colloidal smectic nanoparticles offer interesting possibilities as carrier system for lipophilic drugs. CM nanoparticles are suitable model systems for studying the crystallization behavior and investigating the influence of various parameters for the development of smectic nanoparticles resistant against recrystallization upon storage.

Calorimetry, Differential Scanning↗
PubMed2002

Bovine-HA spongiosa blocks and immediate implant placement in sinus augmentation procedures. Histopathological and histomorphometric observations on different histological stainings in 10 consecutive patients.

Bovine mineral spongiosa block (B-SB) was used as a bone substitute in sinus augmentation procedures in 10 consecutive patients. Implants were placed during the same session. The purpose of this study was to histopathologically examine the healing of the grafted site around the implants at 12 months. Radiographic follow-up showed apparent bone apposition in the augmented area around the implants. Clinically, all 36 implants were stable and integrated with the surrounding tissue. Histopathologically, new bone formation was evident in all specimen hard tissue cores. Hydroxyapatite particles were present in direct contact with the remodeled osseous tissue. Mallory trichrome staining showed different stages of mineralization and maturation of the newly formed bone around the grafted mineral particles. Morphometric evaluation of Picrosirius red stained slides under polarized light microscopy was performed at the peripheral/external and deep section slides of all specimens. The average bone area fraction was 34.2%, with a 1 : 5.4 mean lamellar/woven bone ratio at the peripheral side and 53.0%, with 1 : 2.5 mean ratio at the deep side. The differences of both parameters between the two sites were statistically significant. B-SB proved to be a suitable grafting material with simultaneously placed implants in sinus floor augmentation procedures.

Adult↗
PubMed1980

Optical properties of single elastin fibres indicate random protein conformation.

In describing the properties of fibrous proteins it has been common practice to attribute the macroscopic mechanical properties to the organization at the molecular level. Hence, the high tensile stiffness of collagen and silk has been viewed as an inevitable consequence of their crystalline structure. For elastin, however, there has been considerable controversy and confusion in assigning a conformation to this rubber-like protein. The mechanical and thermodynamic properties of elastin are consistent with the kinetic theory of rubber elasticity, and this theory is based on an isotropic network of kinetically free, random-coil molecules. In contrast, numerous electron microscope studies of negatively stained elastins obtained by autoclave and alkali purification, as well as coacervates of the various soluble elastins, reveal a highly ordered (anisotropic) structure, consisting of 3- to 5-nm filaments that apparently run parallel to the long axis of elastin fibres. These filaments have been accepted as evidence for an anisotropic molecular structure in elastin that is dramatically different from the random network of the kinetic theory. We have now used polarized light microscopy to distinguish these two types of structure. We find that both purified and unpurified, water-swollen, single elastin fibres are optically isotropic, in agreement with the predictions of the kinetic theory of rubber elasticity.

Animals↗
PubMed1989

The highly concentrated liquid-crystalline phase of DNA is columnar hexagonal.

The DNA molecule is extremely compacted in bacteria, in cell nuclei, sperm heads and virus capsids. These interactions between DNA molecules are important to our understanding of chromatin condensation. DNA forms multiple liquid-crystalline phases whose nature depends on the polymer concentration, and it has been suggested that the highly concentrated phase of 50-nm DNA molecules is two-dimensionally ordered and smectic-like. We rule out this smectic hypothesis and demonstrate by polarizing microscopy, electron microscopy and X-ray diffraction that this phase is characterized by a columnar longitudinal order and a hexagonal lateral order, with intermolecular distances ranging from 2.8 to 4.0 nm depending on the DNA concentration.

Crystallization↗
PubMed1970

Migration of asbestos fibres from subcutaneous injection sites in mice.

Crocidolite asbestos fibres, suspended in physiological saline, were injected subcutaneously into one or both flanks of 95 CBA/Lac female mice; 75 control mice received injections of saline only. Most animals were killed at chosen intervals of between 2 and 42 days after injection but some were left for longer periods of up to 623 days. At autopsy, many lymphoid and non-lymphoid structures were removed and examined for the presence of asbestos by the following techniques: haematoxylin and eosin staining followed by conventional and polarized light microscopy; Perl's stain; microincineration followed by phase-contrast microscopy; maceration with KOH followed by phase-contrast microscopy; and electron microscopy.A combination of haematoxylin and eosin staining and microincineration was found to be the most convenient and reliable method for demonstrating asbestos fibres in the tissues. Electron microscopy was essential for detecting very small fibres and for locating them to specific intracellular structures.The morphological findings indicate that some migration of asbestos fibres away from the initial site of injection takes place. Dissemination is usually along lymphatic pathways and fibres tend to accumulate in the lymphoid tissues, particularly in the regional (axillary) lymph nodes; smaller amounts were found in inguinal, mediastinal and lumbar nodes. The fibres were usually intracellular, lying inside the phagosomes of macrophages, but larger fibres weresometimes encountered lying free. Small numbers of fibres were seen in the spleen and also in non-lymphoid organs such as the liver, kidneys and brain-suggesting that some asbestos may enter the blood stream. There was no evidence of massive or selective spread to subserosal tissues in the thorax or abdomen, though trapping of asbestos fibres was observed in pleural "milky spots" in long-term survivors. The possible role of milky spots in the development of pleural plaques and mesotheliomata is discussed.

Animals↗