Probing the Interior of Self-Assembled Caffeine Dimer at Various Temperatures |
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Authors: | Soma Banerjee Pramod Kumar Verma Rajib Kumar Mitra Gautam Basu Samir Kumar Pal |
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Institution: | (1) Unit for Nano Science & Technology, Department of Chemical, Biological & Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata, 700 098, India;(2) Department of Biophysics, BOSE INSTITUTE, P 1/12, C. I. T. Road, Scheme – VIIM, Kolkata, 700054, West Bengal, India;(3) Arthur Amos Noyes Laboratory of Chemical Physics California Institute of Technology (CALTECH), 1200 East California Boulevard, Pasadena, CA 91125, USA; |
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Abstract: | The self-assembly of non-toxic well-consumed small caffeine molecules into well-defined structures has important implications
for future medical applications seeking to target the transport of small drugs in human body. Particularly, the solvation
of the microenvironments of the self assembly ultimately dictates the interaction with the drug molecules and their therapeutic
efficacy. We present femtosecond-resolved studies of the dynamics of aqueous solvation within self-assembled dimeric structure
of caffeine molecules. We have placed small hydrophobic probes 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran
(DCM), coumarin 500 (C500) into the caffeine dimer to enable spectroscopic examinations of the interior. While molecular modeling
and NMR studies of the probes in the caffeine dimers reveal a well-defined location (stacked in between two caffeine molecules),
dynamical light scattering (DLS), Fourier transform infrared (FTIR) spectroscopy, densimetric and sonometric experiments explore
the structural evolution of the dimer upon complexation with the probes. We have extended our studies in various temperatures
in order to explore structural evolution of the self assembled structure and consequently the dynamics of solvation in the
interior of the dimer. Picoseconds/femtosecond resolved dynamics and the polarization gated spectroscopic studies unravel
the hydration and energetics associated with activated viscous flow of the confined probes. Our studies indicate that the
interior of the caffeine dimer is well-solvated; however, the dynamics of solvation is retarted significantly compared to
that in bulk water, clearly revealing the dimers maintain some ordered water molecules. We have also explored the consequence
of the retarded dynamics of solvation on the photo-induced electron transfer (ET) reaction of a model probe, 2-(p-toluidino)
naphthalene-6-sulfonate (TNS) encapsulated in the dimer. |
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