Ruma Basu

Heat-induced structural changes in merocyanine dyes: X-ray and thermal studies

Abstract Certain merocyanine dyes undergo heat-induced isomerisation, which is responsible for their thermovoltage generation properties. Using these dyes, our studies reveal the correlation between their thermal properties and their crystalline structure. Differential thermal analysis of hexadecyl, decyl and pentyl dyes showed reversible phase transitions at their respective characteristic temperatures (Tc) owing to thermal isomerisation of the dyes. X-Ray diffraction patterns indicated heat-induced changes in the crystal structure of the dyes. This was also supported by the results obtained from polarising microscopy studies and thermogravimetric analysis. Further heating of these dyes caused a permanent deformation in the crystal structure, which ultimately led to total disintegration as recorded in the thermogravimetric studies.

Lipid perturbation by corticosteroids: an anisotropic study

Abstract Corticosteroids are the group of steroid hormones which influence the intermediary metabolism. Normal membrane fluidity, necessary for normal functioning of cells, is affected by different drugs. It has been reported previously by us and by other workers that the nature of membrane perturbation by drugs is closely related to their biochemical actions. In this paper we have studied the nature of liquid perturbation by some corticosteroids (hydrocortisone, prednisolone, betamethasone and dexamethasone) in the liposomal membrane of dipalmitoyl phosphatidyl choline using fluorescence polarisation of 1,6-diphenyl-1,3,5-hexatriene. Our result shows that all the corticosteroids fluidise or disorder the liposomal membrane only before phase transition. The two stereoisomers, betamethasone and dexamethasone, have the same effect on the fluidity throughout the experimental temperature range. An explanation for the observed results has been sought in terms of interaction between the lipid and drug molecules at the molecular level.

Lipid perturbation of liposomal membrane of dipalmitoyl phosphatidylcholine by chloroquine sulphate — a fluorescence anisotropic study

Abstract Chloroquine sulphate (CQS) is a water-soluble anti-malarial drug having blood schizontocidal activity against Plasmodium falciparum, P. ovale, P. vivax and P. malarine . It has been reported that the lipid-soluble chloroquine base, which has similar anti-malarial and other biochemical effects, rigidifies (orders) the liposomal membrane in vivo. Here, in order to examine the lipid perturbation mechanism of CQS, we have studied the effect of incorporation of this drug into the liposomal membrane of dipalmitoyl phosphatidylcholine as measured by the fluorescence polarization of the membrane-embedded probe, 1,6-diphenyl-1,3,5-hexatriene. Our results show that the drug CQS also rigidifies the liposomal membrane even though the mechanism of the drug metabolism in vivo plays an important role. Probably the anti-malarial and other biochemical effects of CQS are exercised through this membrane rigidification.

Lipid-disordering effect of aspirin on the liposomal membrane of dipalmitoyl phosphatidyl choline — A fluorescence anisotropy study

Abstract Aspirin (Asp), acetyl salicyclic acid, is a drug widely used as an analgesis, an antipyretic and, in particular, as an inhibitor of platelet aggregation. Recently, a lipid perturbation mechanism for drug action has been given much priority as it is critically important for the rearrangements of membrane surface proteins, receptors, etc. In the present paper we have reported the lipid-ordering effect of Asp in the liposomal membrane of dipalmitoyl phosphatidyl choline from a fluorescence anisotropy study of a membrane-embedded fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene. The result of our study indicates that the drug Asp disorders the liposomal membrane. This probably arises because of the structure (flat ring) of Asp, and the fact that its lipophilicity is greater than its hydrophilicity (solution spectrum); it also accounts for the analgesic as well as inhibitory effects of Asp on platelet aggregation.

Photoinduced proton transport mechanism in merocyanine-dye-probed planar lipid membranes.

Planar lipid membranes were used to study photovoltage generation after the incorporation of various merocyanine dyes. These dyes undergo photochemical isomerization on illumination and can act as a photon-driven facilitated proton transport system under suitable conditions. This system has the advantage of preventing back recombination of the photodissociated charges, thus improving its storage capacity. A sufficiently high photovoltage, with a long storage time and good reproducibility, was obtained with these dyes. The spectral studies indicate the formation of a 1:1 complex between dye and lipid molecules. Our results show that the strength and stability of complex formation increase with the hydrophobicity of the dye which, in turn, increase the magnitude and storage of the photovoltage generated in the system.

Heat-induced voltage generation in hexadecyl merocyanine dye-probed planar lipid membranes

Abstract A hexadecyl merocyanine dye was used as a heat driven proton gate, by incorporating it in a planar lipid membrane which is a good model for biological membranes. Being hydrophobic in nature, it prevents charge recombination, and transmembrane voltages of high magnitude (∼310 mV) were obtained upon heating. The process was reversible and the whole cycle took about 20 h, suggesting that the system could be used as a heat driven storage cell. Comparison of the X-ray diffraction patterns of the thin films of the dye at 30°C showed a heat-induced conformational change in the crystalline structure of the dye. From differential thermal analysis three reversible phase transitions were observed, at 39·2°C, 53·7°C and 62·1°C, and the associated enthalpy changes were calculated. The results indicate that the heat-induced conformational change of the dye molecule is responsible for the observed thermovoltage generation.

Nonlinear conduction in bilayer lipid membranes – effect of temperature

We present here our investigation on the effect of temperature on the reversible nonlinearity as manifested in the DC I–V characteristic of bilayer lipid membrane (BLM). Vc and Ic, the values of voltage and current at the onset of nonlinearity, have been found to be functions of temperature, and the nonlinearity has been found to decrease with increase in temperature. By proper scaling of voltage and current by Vc and Ic, respectively, the I–V curves taken at different temperatures collapse into one single curve, showing the universality in their nature. A log–log plot of Ic vs. σ0 (linear conductance) is a straight line where Ic scales with σ0 as Ic∼σ01.56. A possible mode of charge conduction in BLM, which is a disordered composite system of lipid and water molecules, has been proposed on the basis of these experimental results.

Photoinduced changes in structure and function of hexadecyl merocyanine dyes incorporated into lipid membranes

Abstract In the purple membrane of Halobacterium halobium, bacteriorhodopsin (BR) acts as a proton pump leading to a transmembrane potential difference. A biomimetic system can be formed using merocyanine derivative dye which, when incorporated into a bilayer lipid membrane, creates a potential difference across the membrane. In this system, the dye molecules in combination with the lipid molecules act as a proton transport pump due to a light-induced conformational change of the dye. In this paper, we report the photovoltaic properties and crystal structure of hexadecyl merocyanine dye, together with the change in peak intensity in the X-ray diffraction pattern of the dye and dye-lipid system after illumination. We show that, at room temperature (σ300 K), merocyanine dyes exhibit a crystalline form with a long-chain, fibre-like structure (diameter, 2.89 nm). However, on interaction with light, the crystalline form of the dye changes but the diameter remains the same.

Characterization and haemocompatibility of Aurum metallicum for its potential therapeutic application

Background: The objective of the study was to characterize homoeopathic nanomedicine Aurum metallicum and evaluate its biocompatibility, to explore its possible application as injectables. Metal-based homoeopathic medicine, Aurum metallicum, was chosen as a model drug and the haemocompatibility of the drug at three different potencies 6C, 30C, and 200C were studied to find the justification of the drug as an injectable candidate for clinical application. Methods: The model drug Aurum metallicum at the three potencies was characterized by dynamic light scattering (DLS), zeta potential, field emission scanning electron microscopy (FESEM), and energy dispersive X-ray analysis. Hemocompatibility of the homoeopathic medicine was performed by haemolysis assay. Red blood cell obtained from fresh human blood by centrifugation was incubated with Aurum metallicum. Haemoglobin release was measured using UV-vis spectrophotometer at 540 nm. Results: The DLS and FESEM studies show a decrease of particle size with increasing potency. The zeta potential values show a fairly constant value measured at an interval of 10 days. The haemolysis percentage for 6C, 30C, and 200C was 9.73%, 8.16%, and 0.73%, respectively. Conclusion: The nanomedicine Aurum metallicum was nontoxic at all doses of 6C, 30C, and 200C. The haemolytic percentage also shows that 200C is nonhemolytic, showing haemolysis <2% as per the American Society for Testing and Materials guidelines. The undertaking of larger controlled and in-depth qualitative studies is warranted.

Effect of n-decane on lecithin phase transition temperatures: a microscopic study

Lipid, a major membrane-constituent molecule, being amphiphilic in nature, can adopt different aggregated structures in the presence of different agents. Using polarized light microscopy, we report here our study on how the incorporation of n-decane in the dipalmitoyl lecithin–water system can produce a change from lamellar to non-lamellar phase and affect the different phase transition temperatures as well.