K. Usha Deniz

Interaction of Aspirin with DPPC in the Lyotropic, DPPC-Aspirin-H2O/D2O Membrane

Abstract In recent years, the analgesic, aspirin, has been found to be a platelet aggregation inhibitor. Its interaction with membranes at a molecular level is not yet understood. In this paper, we describe DSC and proton NMR work, carried out to study aspirin-DPPC interaction in the lyotropic, DPPC-water model membrane. Our results show that (1) the aromatic group of aspirin interacts significantly with the glycerol moiety of DPPC and (2) aspirin decreases the chain melting transition point, thus enhancing the permeability of the membrane.

Structure of the Short Range Ordered Nematic Phases of nBABA (n = 1 to 9

Abstract X-ray diffraction measurements have been carried out on the nematic phase of nBABA (n = 1 to 9). Our results show that this nematic phase is a fibre type one having in addition to the orientational long range order, two types of short range orders, (SROs): (i) one dimensional correlations of the molecular dimers along the nematic director (ň) and (ii) Sc type SRO. The strength of 1-d correlation increases with increasing n for 1 6. The n-dependence of the length of the correlated units shows that the chains are disordered for large n The Sc type order which is length (ξ2) is found to be asymmetric with ξ2∥(∥[ncirc]) > ξ2⊥ (⊥[ncirc]). This asymmetry decreases with increasing n The formation of the observed structures in the SROs has been qualitatively explained taking into account various types of intermolecular interactions.

Thermal and Structural Studies of the Different Phases of HxBPA

Abstract We have investigated the temperatures as well as the heats of transition involving the various crystalline and liquid-crystalline phases of HxBPA (4-n-hexyloxybenzilidene-4′-n-propyl-aniline) using a differential scanning calorimeter. From our observations we have arrived at the scheme of transitions given below.

X-ray and Raman investigations of two smectic phases of HxBPA

Abstract The temperature dependence of certain lattice parameters of HxBPA (4-n-hexyloxybenzylidene-4′-n-propylaniline) has been determined from 250 K to 300 K, in the smectic phases, S m and S H , by X-ray diffraction. There is a marked difference in the Raman spectra for the two phases in the frequency range, 200 to 1100 cm -1 . In the light of our observations, it seems that the S m → S H transition is due to the onset of disorder in the hydrocarbon chains.

Nuclear magnetic resonance and thermal studies of drug doped dipalmitoyl phosphatidyl choline-H2O systems

The influence of the sulfone drugs, diamino diphenyl sulfone and diamino monophenyl sulfone on the phase transitions and dynamics of dipalmitoyl phosphatidyl choline-H2O/D2O vesicles have been investigated using differential scanning calorimetry and nuclear magnetic resonance. Our results show that diamino diphenyl sulfone interacts quite strongly with the headgroups of dipalmitoyl phosphatidyl choline whereas the diamino monophenyl sulfone-dipalmitoyl phosphatidyl choline interaction is quite weak. This is attributed to the difference in the structure and hydrophobic character of the two drugs.

Structure of the Nematic Phase of Pbaba

Abstract X-ray diffraction investigations of the nematic phase (191°C - 276°C) of p-n-propyloxybenzylidene-p-amino benzoic acid have shown that this phase is a skewed cybotactic nematic phase. The diffraction patterns, obtained with aligned samples, reveal an additional surprising structural feature, - the presence of one dimensional molecular correlation in a direction parallel to the nematic director. At 192°C, it is found that the molecular unit, thus correlated, is about 37 A in length (dimer length) and the correlation range extends up to about seven such units. This l-d correlation persists up to the N-I transition.

Investigation of Structure and Dynamics in the Fibre-Type Nematic Phase of nBABA

Abstract Neutron diffraction measurements have been carried out with chain deuterated (D-) and non-deuterated (H-) compounds, p-n-AlkoxyBenzylidene-p-Amino Benzoic Acids (nBABA, n = 1, 3, 4 and 7) in the fibre-type nematic (N F) phase. For n = 3 and 4, our results indicate the presence of strings of one dimensional (1-d) correlated molecules parallel to ň, the nematic director. The number of strings as well as the correlation length, ξ1 ⊥, perpendicular to ň, decrease rapidly with increasing temperature. However, ξ1 ‖, the correlation length parallel to ň, remains almost constant for T PN ≤ T < T PN + 30°C (T PN = crystal to nematic transition temperature), but decreases for larger T. Neutron quasi-elastic scattering experiments carried out with 4BABA (both D- and H-) in the NF phase have shown that, (a) the rotational diffusion times, τ r 1 and τ f 1, for the rigid and flexible parts of the molecule, are not very different, and are ∼10−11s for T ≈ TPN , and (b) these motions are not influenced greatly by...

DSC and X-ray diffraction studies of HxBPA☆

Abstract A detailed DSC study has been done for the substance HxBPA in the temperature range 170 to 380 K and the scheme of transitions in this compound has been deduced. From X-ray work, values for the smectic layer thickness and inplane intermolecular distance have been found in two of the liquid crystalline phases, P 2 and S H .

Positional short-range order in the nematic phase of n BABAs

Abstract The positional short-range order, SRO ⊥ , perpendicular to the nematic director n has been studied in the fibre-type nematics, n BABAs, by neutron diffraction. SRO ⊥ is found to be dependent on other types of nematic short-range order but not on the orientational long-range order.

Temperature dependence of the lattice parameters in the S1G and S2G phases of HxBPA

Abstract The temperature dependence of the monoclinic lattice constants in the two smectic phases, S 1 G and S 2 G , of HxBPA, has been obtained from X-ray diffraction data, in the temperature range 300 K T b (unique axis) is consistent with the chain ordering in the S 2 G phase indicated by Raman and NMR measurements.