Thermotropic phase behavior of long-chain alkylammonium-alkylcarbamates

A series of alkylammonium-alkylcarbamates with different chain length including transdermal permeation enhancer Transkarbam 12 have been prepared and characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), temperature-dependent Fourier transform infrared spectroscopy (FTIR) and temperature-dependent X-ray powder diffraction. Four transitions have been observed including solid-solid transition (I), melting (II), decomposition of the carbamate salt (III) and boiling of the released amine (IV). The first transition was connected with rearrangement of the hydrocarbon chain packing and unusual shift of symmetric CH₂ stretching vibration in the IR spectra to lower wavenumbers indicated increase of conformational order. The second transition represented melting of the molecule and the third one was attributed to the decomposition of the carbamate salt into two amine molecules and carbon dioxide as evidenced by combination of DSC and TGA curves.     

Thermotropic and lyotropic phase behaviour of monoalkyl glycosides

We have studied the thermotropic and lyotropic phase behaviour of seven monoalkyl glycosides using polarizing microscopy, differential scanning calorimetry and X-ray diffraction. The phase behaviour of these non-ionic surfactants is compared with that of two previously studied monoalkyl glycosides \[1]. We have found that small modifications in chemical structure can lead to large changes in the phase behaviour. The results reveal the effect of changes in alkyl glycoside chemical structure on the phase behaviour, in particular, on the melting point, the clearing point, the solubility in water, and the extent of the lamellar and curved phases. Seven out of the nine surfactants were found to exhibit thermotropic mesomorphism. Furthermore, in the presence of water, three formed lamellar (L ), type I cubic (Q ) and type I hexagonal (H ) phases, two formed lamellar and cubic phases, and two I I formed only lamellar phases. The cubic phase in each case was indexed, either from powderlike or monodomain samples, as spacegroup I a3 d . The lowest order low angle X-ray spacings were found to lie on single, continuous lines with varying water content across the L , Q and H phases, implying epitaxial relationships between these phases at the phase boundaries. I a a I     

Thermotropic phase behaviour of mixed liposomes of archaeal diether and conventional diester lipids

During preformulation studies of pharmaceutical solid dosage forms, thermal analysis techniques are very useful to detect physical or chemical incompatibilities between the drug and adjuvants of interest that might interfere with efficacy and safety of the final drug product. Differential scanning calorimetry (DSC) and thermogravimetry (TG) are useful tools for this purpose. The aim of this study was to investigate the thermoanalytical behavior of olanzapine (OLZ) when mixed with several excipients commonly used in solid dosage forms such as microcrystalline cellulose, croscarmellose, dicalcium phosphate dihydrate (DCPD), lactose, magnesium stearate, and povidone. Following DSC and TG analyses, powder X-ray diffraction tests were carried out. Thermoanalytical methods showed evidence of interaction between OLZ and magnesium stearate, lactose, and povidone. These results can be useful during the selection of excipients for pharmaceutical formulation development.     

Thermotropic phase behaviour and miscibility properties of phosphatidylcholines containing branched fatty acid chains

Phosphatidylcholines with branched fatty acid chains were investigated by differential scanning calorimetry, X-ray diffraction, and ESR-spectroscopy. Depending on both the length of the branches in 2-position of the acyl chains and the position of the methyl branches in the acyl chains, the main-transition temperatures and enthalpies pass through a minimum. The systematic change of the phase transition parameters is connected with a modified structural polymorphism.In the gel phase the miscibility properties depend on the phase structures of the components. For one system a phase diagram with a critical point has been found.

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Zusammenfassung Phosphatidylcholine mit verzweigtkettigen Fettsäureresten wurden mittels DSC, Röntgenbeugung und ESR-Spektroskopie untersucht. In Abhängigkeit sowohl von der Länge der Seitenkette in 2-Stellung der Acylkette als auch von der Stellung einer Methylverzweigung in der Acylkette gehen die Temperaturen und Enthalpien der Hauptumwandlung durch ein Minimum. Die systematische änderung der Umwandlungsparameter ist mit einem modifizierten Strukturpolymorphismus verknüpft.In der Gelphase hängen die Mischbarkeitseigenschaften von der Phasenstruktur der Komponenten ab. Für ein System wurde ein Phasendiagramm mit einem kritischen Punkt gefunden.

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Thermotropic phase behaviour of sodium oleate as studied by FT-Raman spectroscopy and X-ray diffraction

The thermotropic behaviour of sodium oleate (NaOl) has been studied in the temperature range 10–125°C by using Fourier transform-Raman spectroscopy, X-ray diffraction and differential scanning calorimetry (DSC). The temperature dependence of conformationally sensitive bands in the CH₂ stretching (2800–2900 cm⁻¹), C–C stretching (1050–1150 cm⁻¹) and CH₃ rocking region (830–900 cm⁻¹) has been used to characterize the order/disorder behaviour of alkyl chains. It is found that in phase I, NaOl exhibits the crystalline ordered lamellar structure with a repeat period of 4.51 nm. The first broad peak in the DSC trace is due to superposition of two transitions (phase I to phase II and phase II to phase III), therefore, it is not possible to determine the lamellar structure of phase II. This broad transition from phase I to phase III is associated with the melting of methyl-sided chains and increase in gauche conformers in carboxylate-sided chains. Finally, NaOl undergoes a transition from crystalline to a liquid crystalline phase IV, which is associated with the melting of the carboxylate-sided chain.     

Thermotropic behaviour of dipalmitoylphosphatidylcholine liposomes containing retinoids

Differential scanning calorimetry has been used to investigate the thermotropic behaviour of DPPC liposomes in the presence of different amounts of retinoids in a study of the sites concerned in the mutual lipid-retinoid interaction. The perturbing effect of retinal and retinol on DPPC liposome gel-liquid crystal phase transition has been related to the difference in the polar end group of retinoid. The hydrophilic polar group prevalence over the apolar tail has been evidentiated. Membrane fluidity increases by increasing the retinoid amount. These liposomes displayed a phase separation at high retinal or retinol concentrations.     

Thermotropic and lyotropic phase properties of glycolipid diastereomers: role of headgroup and interfacial interactions in determining phase behaviour

Recent advances in the area of glycobiology have been paralleled by progress in our understanding of the physical properties of glycoglycerolipids (GGLs). These advances have been accelerated by interest in the new found roles of these simple glycolipids in nature, by advances in synthetic procedures, and by an interest in the technological application of a group of amphiphiles with unique physical and chemical properties. Here, we consider the phase properties of some GGL/water systems containing either a single hexopyranoside or pentopyranoside headgroup. Recent calorimetric and X-ray diffraction measurements of some GGL diastereomers suggest that both headgroup and interfacial hydration play a major role in determining both lyotropism and mesomorphic phase properties as the chemical structure of the lipid headgroup, interface and hydrocarbon chains are systematically altered. For GGLs of a given chain length, interactions between the headgroup/interface and water determine whether or not a highly ordered, lamellar crystalline phase is formed, the number of such phases and their rate of formation and, in some cases, the nature of the molecular packing of those phases. In the liquid crystalline phases, the hydrocarbon chains determine the area per molecule in the lamellar liquid crystalline phase, but it is the cross-sectional area of the hydrated headgroup and the penetration of water into the interface which determines the nature of the non-lamellar phases, probably through small changes in interfacial geometry as the lateral stresses in the headgroup region increase.     

Thermotropic liquid-crystalline behaviour from mixtures of non-mesogenic molecules

A class of non-mesogenic molecules, which as mixtures exhibit monotropic nematic phases, is described.     

Thermotropic liquid-crystalline behaviour from mixtures of non-mesogenic molecules

Abstract

A class of non-mesogenic molecules, which as mixtures exhibit monotropic nematic phases, is described.     

Thermotropic liquid crystal behaviour of gemini imidazolium-based ionic amphiphiles

Thermotropic ionic liquid crystals (LCs) are useful for a number of applications such as anisotropic ion transport and as organised reaction media/solvents because of their ordered fluid properties and intrinsic charge units. A large number of different ionic LC architectures are known, but only a handful of examples of gemini (i.e. paired or dimeric) ionic LCs have been prepared and studied. In this work, a series of 20 new symmetric, imidazolium-based, gemini cationic LCs containing two bridged imidazolium cations and two pendant alkyl chains was synthesised, and the thermotropic LC behaviours were characterised. The imidazolium unit provides a highly tunable and modular platform for the design and synthesis of gemini cationic LCs which offers excellent structure control. As expected, the thermotropic LC properties of these new amphilphilic, gemini ionic LCs were found to be strongly influenced by the length of the spacer between the imidazolium units, the length of the pendant alkyl tails, and the nature of the anion. Smectic A (SmA) thermotropic LC phases were observed in more than half of the gemini imidazolium LC systems studied.     

Thermotropic liquid crystal behaviour of alkaline-earth-metal dihexadecyl phosphate salts

Alkaline-earth-metal dihexadecyl phosphate salts were synthesized, and their thermal stability was evaluated by thermogravimetry. Their thermotropic liquid crystal behaviour was investigated by differential scanning calorimetry, polarizing optical microscopy, dilatometry, and X-ray diffraction. On heating, the calcium, strontium, and barium salts exhibit columnar liquid crystal phases, whereas the less ionic beryllium and magnesium salts melt directly into isotropic liquids.     

Thermotropic liquid crystalline behaviour of piperazinium and homopiperazinium alkylsulphates

A series of 1,4-piperazinium di- n -alkyl sulphates was synthesized and compared with an analogous series of 1,5-homopiperazinium di- n -alkyl sulphates. Their thermotropic liquid crystalline behaviour was studied by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. For the piperazinium salts, two ordered smectic phases were established, in which the lateral packing of the molecules within the layers is rectangular or tetragonal. Both phases are characterized by an alternate periodic packing of the positive and negative ionic groups in the polar sublayer, while the lipophilic sublayers of the alkyl chains are in a disordered conformation. Substitution of the piperazinium by the less symmetrical homopiperazinium group disfavours organization within the smectic layer and as a result smectic A phases were obtained.     

Thermotropic liquid crystal behaviour of alkaline-earth-metal dihexadecyl phosphate salts

Alkaline-earth-metal dihexadecyl phosphate salts were synthesized, and their thermal stability was evaluated by thermogravimetry. Their thermotropic liquid crystal behaviour was investigated by differential scanning calorimetry, polarizing optical microscopy, dilatometry, and X-ray diffraction. On heating, the calcium, strontium, and barium salts exhibit columnar liquid crystal phases, whereas the less ionic beryllium and magnesium salts melt directly into isotropic liquids.     

Thermotropic liquid crystalline behaviour of piperazinium and homopiperazinium alkylsulphates

A series of 1,4-piperazinium di-n-alkyl sulphates was synthesized and compared with an analogous series of 1,5-homopiperazinium di-n-alkyl sulphates. Their thermotropic liquid crystalline behaviour was studied by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. For the piperazinium salts, two ordered smectic phases were established, in which the lateral packing of the molecules within the layers is rectangular or tetragonal. Both phases are characterized by an alternate periodic packing of the positive and negative ionic groups in the polar sublayer, while the lipophilic sublayers of the alkyl chains are in a disordered conformation. Substitution of the piperazinium by the less symmetrical homopiperazinium group disfavours organization within the smectic layer and as a result smectic A phases were obtained.     

Thermal behaviour of mixed long-chain alkylammonium tetrachlorozincates

Mixed crystals of composition (n-C_mH_2m+1NH₃)_2xm(n-C_nH_2n+1 · NH₃)_2?2xm ZnCl₄ (m= 12; n=14, 16, 18) are formed upon annealing mechanical mixtures of layer compounds (n-C_nH_2n+1NH₃)₂ZnCl₄, through solid state diffusion of the n-alkylammonium cations. From a common high temperature monophasic modification, in which the polymethylenic chains are conformationally molten, different modifications are obtained on cooling [depending on the (n ? m) value] in which chain crystallinity is developed. The structure of such modifications is speculated on the grounds of DSC and preliminary X-ray diffractometric and IR data, and compared with that of similar previously characterized systems.     

Thermotropic phase transition in soluble nanoscale lipid bilayers

The role of lipid domain size and protein-lipid interfaces in the thermotropic phase transition of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) bilayers in Nanodiscs was studied using small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and generalized polarization (GP) of the lipophilic probe Laurdan. Nanodiscs are water-soluble, monodisperse, self-assembled lipid bilayers encompassed by a helical membrane scaffold protein (MSP). MSPs of different lengths were used to define the diameter of the Nanodisc lipid bilayer from 76 to 108 A and the number of DPPC molecules from 164 to 335 per discoidal structure. In Nanodiscs of all sizes, the phase transitions were broader and shifted to higher temperatures relative to those observed in vesicle preparations. The size dependences of the transition enthalpies and structural parameters of Nanodiscs reveal the presence of a boundary lipid layer in contact with the scaffold protein encircling the perimeter of the disc. The thickness of this annular layer was estimated to be approximately 15 A, or two lipid molecules. SAXS was used to measure the lateral thermal expansion of Nanodiscs, and a steep decrease of bilayer thickness during the main lipid phase transition was observed. These results provide the basis for the quantitative understanding of cooperative phase transitions in membrane bilayers in confined geometries at the nanoscale.     

Thermotropic and lyotropic liquid crystalline behaviour of 4-alkoxyphenyl beta-D-glucopyranosides

The liquid crystalline properties of a series of 4-alkoxyphenyl beta -D-glucopyranosides (methoxy to decyloxy and dodecyloxy) were studied using polarized light microscopy and differential scanning calorimetry. The compounds with the shortest alkoxy substituents are not liquid crystalline. The butoxy derivative displays a monotropic smectic A phase and the higher homologues display enantiotropic smectic A phases. The lyotropic behaviour was studied as a function of concentration and temperature. Hexagonal, cubic and lamellar phases were observed for compounds with alkoxy chains longer than butoxy. The nonyloxy derivative forms long ribbons in dilute solution as revealed by electron microscopy.     

Thermotropic behaviour,self-assembly and photophysical properties of a series of squaraines

A series of squaraine dyes, based on 2,4-bis[4-(N,N-di-n-alkylamino)-2-hydroxyphenyl] squaraine including ethyl, propyl, butyl, pentyl, hexyl and heptyl derivatives, were synthesised by condensation of the corresponding 4-(N,N-di-n-alkylamino)-2-hydroxyphenol with squaric acid. The thermal behaviour of the series was recorded using both thermogravimetic analysis and differential scanning calorimetry while their crystalline structures were elucidated via single-crystal X-ray diffraction. The length of the alkyl chain proved to have a significant effect on both the thermotropic behaviour and the crystalline structure of the squaraine series. Two derivatives, butyl and heptyl, revealed the presence of liquid crystalline mesophases, smectic and nematic, respectively, which were confirmed and characterised via polarised light microscopy and X-ray diffraction. Several of the derivatives formed H- and/or J-aggregates upon thin film formation via spin coating before and after the thermal annealing treatment as indicated by UV–vis spectroscopy. The molecular and crystal structure, aggregation and thermal behaviour provide insight into the supramolecular assembly of this important class of materials. Photophysical measurements revealed large molar absorptivity, reasonably high fluorescence quantum yields and significant fluorescence anisotropy by making these derivatives suitable candidates for a number of electro-optic and photonics applications.     

Synthesis and thermal behaviour of new benzo-1,2-thiazine long-chain aryl-piperazine derivatives

A series of potential biologically active 2-[3-(4-phenyl-1-piperazinyl)propyl]-3-(4-substituted-benzoyl)-4-hydroxy-2H-1,2-benzothiazine 1,1-dioxides was synthesized in a straightforward manner by condensation of respective 3-substituted-4-hydroxy-1,2-benzothiazine 1,1-dioxides with 1-(1-chloropropyl)-4-phenylpiperazine. The structures of all of the newly formed compounds were identified by elemental analysis, FTIR and ¹H NMR. The synthesized compounds were subjected to preliminary evaluation using differential scanning calorimetry (DSC) to determine the existence of multiple crystal forms. The DSC scans for all compounds show more than one endothermic effect, which might suggest dynamic proton transfer between two or three possible tautomeric forms: O-keto/O-enol, O-enol/O-keto and O-keto/O-keto/CH₂ in crystals 2-[3-(4-phenyl-1-piperazinyl)propyl]-3-(4-substituted-benzoyl)-4-hydroxy-2H-1,2-benzothiazine 1,1-dioxides.     

Thermotropic lanthanidomesogens

Due to their high and variable coordination numbers leading to poorly predictable three-dimensional coordination spheres, the trivalent lanthanide metal ions are challenging molecular objects for introduction into thermotropic liquid crystals. Conversely, their predictive electronic, optical and magnetic metal-centred properties make them particularly attractive for being incorporated into switchable macroscopic materials responding to external electric and magnetic stimuli. We briefly describe here some of the important concepts and strategies leading to the recent successful preparation of luminescent thermotropic lanthanide-containing mesophases, for which the generic term lanthanidomesogens is proposed.