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A possibility was assessed to modify physico-chemical properties of ferronematic mixtures by introducing additional mesogenic and non-mesogenic components. The mixture, consisting of RM734 and DIO at the 70:30 weight ratio of the components, was doped with standard nematic 5CB and its chiral isomer CB15. This allowed a substantial lowering of the ferronematic temperature range, as well as induction of helical twisting in both nematic (N) and ferronematic (NF) phases. The effects of 5CB and CB15 on the NF to N phase transition were nearly identical, but the isotropic transition temperature decreased more strongly upon addition of CB15. Optical transmission vs. temperature measurements showed lower transmittance in the NF phase, probably due to scattering on the domain boundaries. In the vicinity of the NF - N transition, a noticeable range of anomalously low transmission was noted both on heating and cooling, suggesting a complex character of molecular reorientation features. In the chiral NF (N*F) system, helical twisting was recorded using Grandjean-Cano wedge, with the helical pitch decreasing upon cooling in both N* and N*F phases. In the cooling mode, transient undulations emerged in the N*F phase. The complex picture of the ferronematic transition is supported by POM images taken at different temperatures., Comment: 21 pages, 10 figures

Background: Model lipid membranes are widely used nowadays to elucidate membranotropic action (MA) of pharmaceuticals as well as for development of liposomal drugs. Meanwhile, membrane lipid composition could substantially affect a drug-membrane interaction. Objectives: Comparision of MA of certain pharmaceuticals on model membranes with various lipid compositions. Materials and methods: By means of differential scanning calorimetry (DSC) lauric acid, fenspiride and kaolin were studied with respect of their effects on phase transitions of model membranes based on hydrated phospholipids. Along with “standard” membrane based on L-α-dipalmitoyl­phos­pha­ti­dyl­choline (DPPC), a membrane containing cerebrosides (DPPC-C) was used, as well as one composed of DPPC, L-α-dipalmitoyl­phospha­tidylethanolamine and cholesterol (DPPC-DPPE-Chol). According to literature, DPPC and DPPC-C membranes are characterized by lipid phase homogeneity, as distinct from membrane DPPC-DPPE-Chol, where two different lipid phases coexist both below and above phase transition region. Results: It was shown that fenspiride manifested similar MA on membranes of all three types. MA of lauric acid in DPPC and DPPC-C membranes were qualitatively similar, whereas, in DPPC-DPPE-Chol membrane, different effects were observed. As to kaolin, distinctions in its MA were observed even between DPPC and DPPC-C membranes, namely, elevation of phase transition temperatures in DPPC-C membrane and a tendency to their reduction in DPPC one. In DPPC-DPPE-Chol membrane, kaolin markedly lowered phase transition temperatures coupled with opposite changes in cooperativity. Conclusions: By the examples of separated substances it was shown that strong disordering MA may be practically independent on lipid composition of membrane. Lipid rearrangement and cooperativity changes in membrane can be induced not only by incorporation of guest substances in the bulk, but also by their adsorption on membrane surface.The obtained results could be useful in adjustment of model membrane composition for MA studies of different pharmaceuticals.

Optical transmission and selective reflection data are reported for suspensions of single-walled carbon nanotubes (CNTs) in photoactive nematic material ZhK-440 with a mesogenic chiral dopant M5. At small concentrations of CNTs (C ≈ 0.01–0.05%), the preferential localisation of CNTs at oily sticks (cholesteric topological defects) and suppression of the network of oily streaks by CNTs were observed. At the same time, the optical density D was shown to be essentially non-linear and a minimum at certain concentration of CNTs, C ≈ 0.05–0.08%, was observed. This anomalous behaviour was explained by the presence of the structural transition from the loose (ramified) aggregates with highly anisotropic shape (oriented along the anchoring direction on rubbed polyvinyl alcohol) to the compact aggregates with denser packing. The location of this minimum, as well as the selective reflection maximum (helical pitch), was sensitive to partially reversible UV-induced trans–cis–trans isomerisation effects. The UV-controlled helical pitch variation was shown to be only slightly affected by introduction of CNTs.

In order to study the effects caused by silver nitrate (AgNO3) on model lipid membranes, we studied multibilayer membranes based on L-α-dipalmitoylphosphatidylcholine (DPPC) and AgNO3 aqueous soluitions in a wide concentration range (up to 30 wt%) by means of differential scanning calorimetry. It has been shown that the presence of AgNO3 leads both to an increase in the main phase transition temperature (T(m)) and appearance of an additional phase transition peak (T(m)), suggesting increasing of both density and heterogeneity of the lipid membrane. The effect of nitrate ions (NO ) was shown to be of the opposite nature (bilayer fluidizing), so the integral densifying effect of AgNO3 can be referred solely to the action of silver ions (Ag(+)). With increasing AgNO3 concentration, the tendency was observed to opposite changes in T(m) and T'(m) peaks intensity, thereby at about 26. wt% of AgNO3 the initial peak (T(m)) disappeared. In the range of Ag+ therapeutic concentrations (up to 2 wt%) no significant changes in the DPPC membrane were revealed. This can be one of the reasons of the absence of a damaging effect of silver drugs on a host organism with simultaneous pronounced bactericidal effect.

We have studied the action of some membranotropic agents (MTAs) on the parameters of mono- and multilayers of dipalmitoylphosphatidylcholine (DPPC). The MTAs used included an antimicrobial drug, decamethoxinum, the model amphiphilic agent stearoyl-L-alpha-alanine, and cholesterol as a reference substance. Using differential scanning calorimetry and the Langmuir monolayer technique, we measured the temperature and enthalpy of the main phase transition of DPPC, the mean molecular area, the collapse pressure and the free energy of the mixed monolayers of DPPC and MTA. A good correlation has been obtained between the structure of the MTA used and changes in the parameters of both mono- and multilayers. Thus, for cholesterol, its well-known condensing effect in the L alpha phase correlates with its behavior in the mixed monolayers. The disturbing action of decamethoxinum (depression of the phase transition in DPPC multilayers and relatively high free energy of mixing in monolayers) is presumably connected with interaction of its charged ammonium moieties with polar phospholipid heads. At the same time, stearoyl-L-alpha- alpha-alanine condensed the lipid layers and increased the melting point of DPPC, owing to its interaction with both polar and non-polar lipid moieties. One can conclude that the three MTAs used can really be considered as representative examples of three different types of behavior in mono- and multilayers.

The polymorphism and conformational properties of 4-cyano-4- n -alkoxybiphenyl crystals were studied using infrared spectroscopy (experimental and theoretical analysis of normal modes), X-ray diffraction and differential scanning calorimetry. Several different solid crystalline forms were found the appearance of which depended on the thermal history of the samples. Spectral characteristics and structural peculiarities of these forms were established.

Near-IR spectroscopy studies of gel formation mechanism are reported for gelatin-water systems. Relative absorbance in 1.4-μm and 1.9-μm bands was shown to be sensitive to the helix to coil phase transition in the pre-melting region. The formation mechanism of a metastable “coil” phase is in agreement with DSC and TGA data obtained in parallel experiments on the 10% gelatin gel.

The polymorphism and conformational properties of 4-cyano-4- n -alkoxybiphenyl crystals were studied using infrared spectroscopy (experimental and theoretical analysis of normal modes), X-ray diffraction and differential scanning calorimetry. Several different solid crystalline forms were found the appearance of which depended on the thermal history of the samples. Spectral characteristics and structural peculiarities of these forms were established.

To look into the nature of intermolecular forces responsible for the induced smectic mesophase formation, model binary systems were studied comprising components of different chemical classes. Three distinct types of systems could be singled out, with translational order enhancement presumably due to (a) steric factors, (b) dipole-dipole in eractions, and (c) change-transfer complex formation.

Mechanisms of interaction between the antimicrobial drugs decamethoxinum and aethonium, which are based on bisquaternary ammonium compounds, and a phospholipid component of biological membranes, dipalmitoylphosphatidylcholine, were studied by means of liquid secondary ion mass spectrometry (LSIMS) and differential scanning calorimetry (DSC). Supramolecular complexes of the drugs with this phospholipid were recorded under secondary ion mass spectrometric conditions. The dependence of the structures of these complexes on structural parameters of the dications of the bisquaternary ammonium compounds was demonstrated. Tandem mass spectrometric investigations of the metastable decay of doubly charged ions of decamethoxinum and aethonium complexes with dipalmitoylphosphatidylcholine allowed estimation of structural parameters of these complexes in the gas phase. Interactions of decamethoxinum and aethonium with model membrane assemblies built from hydrated dipalmitoylphosphatidylcholine were studied using DSC. It was shown that while both drugs can interact with model membranes, the mechanisms of such interactions for decamethoxinum and aethonium differ. The correlation between the nature of these interactions and structural and electronic parameters of the dications of the two bisquaternary agents is discussed. Interpretation of combined mass spectrometric and calorimetric experimental data led to proposals that the molecular mechanisms of antimicrobial action of bisquaternary ammonium compounds are related to their effect on the membrane phospholipid components of microbial cells.

Induced cholesteric systems with reentrant mesomorphism were observed by doping reentrant nematic mixtures with optically active tygogenyn and l-menthol derivatives. Helix unwinding was observed on approaching T Ch -S A in both cholesteric phases. Influence of the dopant concentration upon the stability of the intermediate smectic phase and helical pitch is discussed Des systemes cholesteriques presentant un mesomorphisme rentrant ont ete obtenus en dopant un melange possedant une phase nematique rentrante avec des substances optiquement actives comme des derives de la tygogenyne et du l-menthol. Le deroulement de l'helice cholesterique a ete observe a l'approche de la transition T Ch -S A dans les phases cholesteriques haute et basse temperature. L'influence de la concentration du dopant sur la stabilite de la phase smectique intermediaire et sur la valeur du pas cholesterique est discutee

Phase transition temperatures, densities, rotational viscosities and their activation energies are determined for 4-cyano derivatives of biphenyl (4-cyano-4'-pentylbiphenyl and 4-cyano-4'-heptylbiphenyl) and phenylcyclohexane (trans-4-heptyl-(4'-cyanophenyl)-cyclohexane and trans-4-pentyl-(4'-cyanophenyl)- cyclohexane) mixed with azoxy compounds (4-butyl-4'-methoxyazoxybenzene and 4-butyl-4'-heptanoyloxy-azoxybenzene). Macroscopic properties of the mixtures comprising 4-cyano-4'-alkyl-biphenyls (CB) as the polar compounds are found to differ significantly from those comprising trans-4-alkyl-(4'-cyanophenyl) cyclohexanes (PCH). The results obtained are discussed in terms of specific intermolecular interactions and associate formation.

Viscous properties of induced cholesteric systems with different steroidal and nonsteroidal opically active dopants were investigated in flat capillaries. In all the systems studied, when helical pitch values were sufficiently low we observed a pronounced non-Newtonian behaviour interpreted in the terms of “permeation” model. With high pitches and high shear rates, however, properties were much more nematic-like. Comparisons are made with data obtained for mesogenic cholesterol esters and tube capillaries.

Recent studies of cholesteric systems are briefly reviewed, with special attention paid to the relationship between the molecular structure of the optically active molecules and the helical twisting features. Microscopic models are presented which provide an account of specific intermolecular interactions, conformational equilibria, etc. Mechanisms of dopant-induced helix distortions are discussed based on N.M.R. studies. The use of cholesteric systems as solvents for selective reflection spectroscopy is considered.

It is shown that on the introduction of small quantities (≤ 10%) of optically active dopants (mesogenic as well as nonmesogenic) into a smectogenic nematic matrix a typical picture of pretransitional phenomena is obtained, with P → ∞ near translational phase transition point.