A comparative study on DNA and protein binding properties of thymol and thymoquinone.

Two phytochemicals, thymol and thymoquinone obtained from thymes (Thymus vulgaris L., Lamiaceae etc.) and Nagila Sativa seed, respectively. Both the phytochemicals show several biochemical activities like anticancer, antimicrobial etc. In this paper, we studied the affinities of thymol and thymoquinone towards calf thymus DNA (CT-DNA) and protein (bovine serum albumin). Spectroscopic and molecular modelling studies revealed that both compounds have a high affinity toward both the receptors; DNA and protein. Both phytochemicals binds to the minor grooves of DNA and suitable pockets of protein. Several free energy function and hydrogen bonding play significant role during the binding phenomenon.Communicated by Ramaswamy H. Sarma.

A comparison on the biochemical activities of Fluorescein disodium, Rose Bengal and Rhodamine 101 in the light of DNA binding, antimicrobial and cytotoxic study.

Biochemical activities of Fluorescein, Rose Bengal and Rhodamine 101 were studied by DNA binding, antibacterial and cytotoxic studies. DNA binding studies were done using spectroscopic, thermodynamic and molecular modeling techniques. Antibacterial activities were investigated against a gram-negative bacteria Escherichia coli and a gram-positive bacteria Staphylococcus aureus. Cytotoxic activities were studied against Wi-38 cell line. We observed these dyes bound to minor groove of DNA and structural diversity of dyes affect the phenomenon. No significant antibacterial and cytotoxic activities of these dyes were found in our observations.

Influence of chain length of alcohols on Stokes' shift dynamics in catanionic vesicles.

In this paper, we explore the effects of the chain length of simple monohydroxy alcohol (C(n)OH, 2 ≤ n ≤ 8) and benzyl alcohol (C(6)H(5)CH(2)OH) upon the fluorescence dynamics of a dipolar solute probe, coumarin 153 (C153), in vesicles formed in aqueous solutions of two oppositely charged (cationic and anionic) surfactants in the presence of 0.05 mol kg(-1) alcohol. The catanionic vesicles are composed of 70 mol % sodium dodecyl sulfate (SDS) and 30 mol % cetyltrimethylammonium bromide (CTAB). The presence of alcohols of different chain length improves the stability of the catanionic vesicles. Dynamic light scattering (DLS) experiments suggest a gentle increase in the hydrodynamic diameter of the catanionic vesicle with alcohol chain length up to n=4 and then an abrupt increase for the rest of the alcohols considered. The polarity and dynamics of the catanionic vesicles, probed by the steady-state and time-resolved fluorescence spectroscopy, indicate a signature of confined water. Quantities measured from fluorescence experiments of these vesicles also show a mild variation for alcohols of chain length n ≤ 4, followed by a sudden variation for alcohols with n > 4. Interestingly, pentanol and benzyl alcohol in catanionic vesicles showed roughly similar effects due to their equivalent chain length. All of these data are remarkably correlated with the recently observed depression of the solubility temperature of catanionics with alcohol chain length (Langmuir2009, 25, 12516-12521).

Heterogeneity in binary mixtures of (water + tertiary butanol): temperature dependence across mixture composition.

The temperature dependence of solution heterogeneity in binary mixtures of water and tertiary butanol (TBA) and its effects on a chemical reaction have been investigated by using steady-state and time-resolved spectroscopic experiments within the temperature range of 278 ≤ T/K ≤ 373. Eleven different mole fractions of TBA, covering extremely low TBA mole fractions to pure TBA, have been considered. An organic chromophore that undergoes a photoexcited intramolecular charge-transfer reaction is employed to reveal the signature of the solution heterogeneity. Upon increasing the solution temperature, the absorption spectrum of the dissolved chromophore exhibits a red shift at very low TBA concentrations but shifts toward higher energy (blue shift) at higher alcohol concentrations. This is a reflection of temperature-assisted aggregation of TBA molecules in very dilute aqueous solutions. The magnitude of the temperature-induced red shift is the largest at around 0.04 mol fraction of TBA, and a larger variation of the spectral line width across the temperature suggests enhanced solution heterogeneity. Reaction time constants measured at various mixture compositions are found to follow an Arrhenius-type temperature dependence. The average activation energy, when plotted as a function of mixture composition, steeply rises with TBA concentration in the limit of the very low TBA mole fraction and then suddenly levels off to a plateau upon further addition of TBA. The alcohol concentration-dependent activation energy abruptly changes its slope at a TBA mole fraction ∼0.1, at which a transition from the three-dimensional water-type network to the zigzag alcohol chain structure is known to occur. The plateau value of the activation energy is ∼6k(B)T and agrees well with the earlier estimate for the same chromophore from the pure solvent data at room temperature. The observed increase in the spectral red shift with temperature at low TBA mole fractions is in general agreement with the existing experimental results which support the view that temperature assists the aggregation of TBA molecules in dilute aqueous solutions of TBA. However, unlike in the small-angle neutron scattering study [ Bowron, D. T.; Finney, J. L. J. Phys. Chem. B 2007, 111, 9838], which finds clustering of TBA molecules reaching a maximum at ∼353 K, the present data do not indicate any such temperature maximum within the temperature range of 278 ≤ T/K ≤ 373.

Fluorescence spectroscopic studies of (acetamide + sodium/potassium thiocyanates) molten mixtures: composition and temperature dependence.

Steady state and time-resolved fluorescence spectroscopic techniques have been used to explore the Stokes' shift dynamics and rotational relaxation of a dipolar solute probe in molten mixtures of acetamide (CH(3)CONH(2)) with sodium and potassium thiocyanates (Na /KSCN) at T approximately 318 K and several other higher temperatures. The dipolar solute probe employed for this study is coumarin 153 (C153). Six different fractions (f) of KSCN of the following ternary mixture composition, 0.75 CH(3)CONH(2) + 0.25[(1 - f)NaSCN + fKSCN], have been considered. The estimated experimental dynamic Stokes' shift for these systems ranges between 1800 and 2200 cm(-1) (+/-250 cm(-1)), which is similar to what has been observed with the same solute probe in several imidazolium cation based room temperature ionic liquids (RTIL) and in pure amide solvents. Interestingly, this range of estimated Stokes' shift, even though not corresponding to the megavalue of static dielectric constant reported in the literature for a binary mixture of molten CH(3)CONH(2) and NaSCN, exhibits a nonmonotonic KSCN concentration dependence. The magnitudes of the dynamic Stokes' shift detected in the present experiments are significantly less than the estimated ones, as nearly 40-60% of the total shift is missed due to the limited time resolution employed (full-width at half-maximum of the instrument response function approximately 70 ps). The solvation response function, constructed from the detected shifts in these systems, exhibits triexponential decay with the fastest time constant (tau(1)) in the 10-20 ps range, which might be much shorter if measured with a better time resolution. The second time constant (tau(2)) lies in the 70-100 ps range, and the third one (tau(3)) ranges between 300 and 800 ps. Both these time constants (tau(2) and tau(3)) show alkali metal ion concentration dependence and exhibit viscosity decoupling at higher viscosity in the NaSCN-enriched region. Time dependent rotational anisotropy has been found to be biexponential at all mixture compositions studied. Both the average solvation () and rotation () times of C153 in these mixtures exhibit fractional power law dependence on medium viscosity ( is proportional to eta(p), x being solvation or rotation). For solvation, p is found to be 0.46, which is very different from that obtained for common polar and nonpolar solvents, and RTILs (p approximately = 1). For rotation, p approximately = 0.65, which is again different from the value (p approximately = 1) obtained for common polar solvents and RTILs but very similar to that (p approximately = 0.6) found for nonpolar solvents. In addition, experimentally measured average rotation times in these mixtures are found to exhibit slip behavior in the low eta/T region, which gradually transforms to subslip as eta/T increases. Calculations using a recently developed semimolecular theory predict a total dynamic Stokes' shift for C153 (dipolar solute) in these molten mixtures near approximately 1600 cm(-1) where the solute-solvent (dipole-dipole) and the ion-solute (ion-dipole) interactions contribute respectively approximately 80% and approximately 20% to the calculated total shift. Like in experiments, the theoretically predicted solvation response function in the overdamped limit at each mixture composition has been found to be triexponential. The calculations in the underdamped limit, however, suggest a biphasic decay where a composition independent subpicosecond component and a much slower component with the time constant spreading over 150-850 ps contribute equally to constitute the total decay. The calculated average solvation times in this limit are found to be in better agreement with experimental results than the predictions from the overdamped limit.

Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: temperature dependence.

Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO(4)) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267-343 K. The temperature dependent spectral peak shifts and reaction driving force (-DeltaG(r)) in electrolyte solutions of these solvents can be explained qualitatively in terms of interaction between the reactant molecule and ion-atmosphere. Time resolved studies indicate that the decay kinetics of P4C is biexponential, regardless of solvents, LiClO(4) concentrations, and temperatures considered. Except at higher electrolyte concentrations in EA, reaction rates in solutions follow the Arrhenius-type temperature dependence where the estimated activation energy exhibits substantial electrolyte concentration dependence. The average of the experimentally measured activation energies in these three neat solvents is found to be in very good agreement with the predicted value based on data in room temperature solvents. While the rate constant in EA shows a electrolyte concentration induced parabolic dependence on reaction driving force (-DeltaG(r)), the former in ethanol and ACN increases only linearly with the increase in driving force (-DeltaG(r)). The data presented here also indicate that the step-wise increase in solvent reorganization energy via sequential addition of electrolyte induces the ICT reaction in weakly polar solvents to crossover from the Marcus inverted region to the normal region.