http://192.168.1.40:8080/xmlui/handle/123456789/1103 2026-05-31T15:23:32Z 2026-05-31T15:23:32Z Das, Pradip Sinha, R.K., Basu, S. http://192.168.1.40:8080/xmlui/handle/123456789/2457 2013-04-03T06:18:47Z 2006-03-28T00:00:00Z

Ultraviolet-visible-near infrared and mid-Fourier transform infrared spectroscopic studies of intermolecular interaction in cholesteryl oleyl carbonate in mesophases Das, Pradip; Sinha, R.K.,; Basu, S. Ultraviolet-visible-near infrared (UV-Vis-NIR) and Fourier transform infrared (FTIR) spectroscopic studies are presented of molecular association between like molecules of cholesteryl oleyl carbonate, each containing suitable pi-donor (steroid ring C = C) and pi-acceptor (C-O single bonds united with a C = O bond to give a carbonate group) moieties. Frequency shifts and intensity enhancements of donor and acceptor oscillators appear to be governed by reduced mass, vibronic coupling constants, and a few other parameters such as relative change in force constants, etc. Donor-acceptor complex formation is characterized not only by the appearance of new bands in the mid-FTIR spectrum but also by the emergence of a new, intense electronic band centered at similar to 3700 cm(-1), the so-called charge-transfer band, in the UV-Vis-NIR spectrum. This band is strong in the smectic-A and solid phases, but progressively diminishes when temperature is raised to realize the upper end of the cholesteric phase and eventually the isotropic phase. Also, a new, small electronic band at similar to 360 nm, only seen in the entire thermal range of the cholesteric phase, is attributed to the Lifshitz-van der Waals interaction between pretransitional smectic-A domains existing in the cholesteric phase. It is argued that mesophases may owe their thermodynamic stability to both Lifshitz-van der Waals and vibronic coupling (or electron-phonon coupling in extended systems such as smectics and solids) interactions. DOI: 10.1063/1.2180782

2006-03-28T00:00:00Z Das, Pradip Basu, S. K. Sinha, Randhir Kumar Das, U. http://192.168.1.40:8080/xmlui/handle/123456789/2456 2013-04-03T05:28:27Z 2005-07-20T00:00:00Z

Dipole-induced chiral smectic-C phase in a eutectic mixture of cholesterol esters Das, Pradip; Basu, S. K.; Sinha, Randhir Kumar; Das, U. Both cholesteryl oleate (CO) and cholesteryl oleyl carbonate (COC) are thermotropic mesogens with a general cooling phase sequence: isotropic cholesteric -> smectic crystal. They are almost identical with respect to molecular structure and the central location of molecular dipole. However, the orientation of the latter is axial for CO and transverse for COC. A eutectic mixture of these components shows a phase sequence like the above but involving an induced smectic-C* phase. We explain this discovery on the basis of computer simulation results involving rigid core-dipole-flexible tail model of a mesogen and argue in favor of a ferroelectric liquid crystal model of the induced phase. DOI: 10.1016/j.cplett.2005.05.111

2005-07-20T00:00:00Z Das, Pradip Sinha, Randhir Kumar Basu, Sandip Kumar http://192.168.1.40:8080/xmlui/handle/123456789/2276 2013-03-19T05:31:30Z 2006-03-28T00:00:00Z

Ultraviolet-visible-near infrared and mid-Fourier transform infrared spectroscopic studies of intermolecular interaction in cholesteryl oleyl carbonate in mesophases Das, Pradip; Sinha, Randhir Kumar; Basu, Sandip Kumar Ultraviolet-visible-near infrared (UV-Vis-NIR) and Fourier transform infrared (FTIR) spectroscopic studies are presented of molecular association between like molecules of cholesteryl oleyl carbonate, each containing suitable pi-donor (steroid ring C = C) and pi-acceptor (C-O single bonds united with a C = O bond to give a carbonate group) moieties. Frequency shifts and intensity enhancements of donor and acceptor oscillators appear to be governed by reduced mass, vibronic coupling constants, and a few other parameters such as relative change in force constants, etc. Donor-acceptor complex formation is characterized not only by the appearance of new bands in the mid-FTIR spectrum but also by the emergence of a new, intense electronic band centered at similar to 3700 cm(-1), the so-called charge-transfer band, in the UV-Vis-NIR spectrum. This band is strong in the smectic-A and solid phases, but progressively diminishes when temperature is raised to realize the upper end of the cholesteric phase and eventually the isotropic phase. Also, a new, small electronic band at similar to 360 nm, only seen in the entire thermal range of the cholesteric phase, is attributed to the Lifshitz-van der Waals interaction between pretransitional smectic-A domains existing in the cholesteric phase. It is argued that mesophases may owe their thermodynamic stability to both Lifshitz-van der Waals and vibronic coupling (or electron-phonon coupling in extended systems such as smectics and solids) interactions. DOI: 10.1063/1.2180782

2006-03-28T00:00:00Z Chakrabarti, N. Das, Pradip http://192.168.1.40:8080/xmlui/handle/123456789/2079 2018-11-27T11:49:21Z 2007-01-01T00:00:00Z

Isotropic to nematic phase transition in F-actin Chakrabarti, N.; Das, Pradip Like a few other rod-like and semi-rigid polyelectrolytes, filamentous actin (F-actin) shows, respectively, an isotropic to nematic (I-N) phase transition and an aggregation to a hexagonal liquid crystal followed by paracrystals at low and moderately high salt concentrations. Its polyion characteristics, e.g., large bare diameter, imposing chain length, high molecular weight per unit chain contour length and large electronic charge spacing along the chain contour, make it stand out among the members of the family of rigid and semi-rigid lyotropic mesogens. The first-order I-N phase separation has been explored, at the level of the second virial approximation, for a rod-like model of the actin filament in a solution containing simple electrolytes such as KCl and MgCl 2. The calculation of concentrations in the coexisting isotropic and anisotropic (nematic) phases, and of the order parameter in the anisotropic phase has been attempted by following the approach of Stroobants et al. which takes account the repulsive but not the attractive interactions. A criterion for the stability of the isotropic phase, according to Odijk, considers the second and the third virial coefficients, and has been employed to describe the I-N phase diagram depicting filament length versus actin concentration. The nature of the I-N phase transition, which has both first-order and higher-order (continuous) parts, has been discussed.

2007-01-01T00:00:00Z