Ultrafast Spectroscopic Study on Caffeine Mediated Dissociation of Mutagenic Ethidium from Synthetic DNA and Various Cell Nuclei

A Mutagen Acts as a Potent Reducing Agent of Glycated Hemoglobin: a Combined Ultrafast Electron Transfer and Computational Studies

Glycated hemoglobin (GHb) found in mammals undergoes irreversible damage when exposed to external redox agents, which is much more vulnerable than its normal counterpart hemoglobin (Hb). Besides the oxygen regulation throughout the body, Hb plays a vital role in balancing immunological health and the redox cycle. Photoinduced ultra-fast electron transfer phenomena actively participate in regulation of various kind of homeostasis involved in such biomacromolecules. In the present study we have shown that a well-known mutagen Ethidium Bromide (EtBr) reduces GHb in femtosecond time scale (efficiently) upon photoexcitation after efficient recognition in the biomolecule. We have performed similar experiment by colocalizing EtBr and Iron (Fe(III)) on the micellar surface as Hb mimic in order to study the excited state EtBr dynamics to rationalize the time scale obtained from EtBr in GHb and Hb. While other experimental techniques including Dynamic Light Scattering (DLS), Zeta potential, absorbance and emission spectroscopy have been employed for the confirmation of structural perturbation of GHb compared to Hb, a detailed computational studies involving molecular docking and density functional theory (DFT) have been employed for the explanation of the experimental observations.

Polyethylene glycols affect electron transfer rate in phenosafranin-DNA complex

Long distance electron transfer (ET) between small ligands and DNA is a much studied phenomenon and is principally believed to occur through electron (or hole) hopping. Several studies have been carried out in aqueous environments while in real biological milieu the DNA molecules experience a more dense and heterogeneous environment containing otherwise indifferent molecular crowders. It is therefore expected that the ET could get modified in the presence of crowding agent and to investigate that we have made elaborate studies on steady state and time-resolved (picosecond (ps) and femtosecond (fs)-resolved) emission properties of a phenosafranine (PSF) intercalated to calf thymus (CT) DNA in the presence of ethylene glycol (EG) and polyethylene glycols (PEG) of different chain lengths (PEG 200, 400 and 1000). The emission of PSF gets considerably quenched when intercalated to DNA; the quenching is released when PEGs are added into it. The structural integrity of the CT DNA has been established using circular dichroism spectroscopy. CD measurements have evidenced only marginal changes in the DNA structure upon the addition of PEGs. ps-Resolved fluorescence measurements show significant decrease in the contribution of the DNA induced quenched time-constant of PSF upon the addition of PEGs, however, fs-resolved measurements show less noticeable changes in the time constants. Our study shows that the electron hopping rate through the guanine base in DNA core remains unaffected whereas the 'through space' electron transfer process does get affected in the presence of molecular crowders.

Solubility of Caffeine in Supercritical CO2: A Molecular Dynamics Simulation Study

The extraction of caffeine from green tea leaves and cocoa beans is a common industrial process for the production of decaffeinated beverages and pharmaceuticals. The choice of the solvent critically determines the yield of this extraction process. Being an environmentally benign and recyclable solvent, supercritical carbon dioxide (scCO₂) has emerged as the most desirable green solvent for caffeine extraction. The present study investigates the solvation properties of caffeine in scCO₂ at two different temperatures (318 and 350 K) using molecular dynamics simulations. Unlike in water, the caffeine molecules in scCO₂ do not aggregate to form clusters due to relatively stronger caffeine-CO₂ interactions. A well-structured scCO₂ solvent shell envelops each caffeine molecule as a result of strong electron-donor-acceptor (EDA) and hydrogen-bonding interactions between these two species. Upon heating, although marginal site-specific changes in the distribution of nearest CO₂ around caffeine are observed, the overall distribution is retained. At a higher temperature, the caffeine-CO₂ hydrogen-bonding interactions are weakened, while their EDA interactions become relatively stronger. The results underscore the importance of the interplay of these interactions in determining stable solvent structures and solubility of caffeine in scCO₂.

The theory of interceptor-protector action of DNA binding drugs

The review discusses the theory of interceptor-protector action (the IPA theory) as the new self-consistent biophysical theory establishing a quantitative interrelation between parameters measured in independent physico-chemical experiment and in vitro biological experiment for the class of DNA binding drugs. The elements of the theory provide complete algorithm of analysis, which may potentially be applied to any system of DNA targeting aromatic drugs. Such analytical schemes, apart from extension of current scientific knowledge, are important in the context of rational drug design for managing drug's response by changing the physico-chemical parameters of molecular complexation.

Prediction of self-assembly of adenosine analogues in solution: a computational approach validated by isothermal titration calorimetry

The recent discovery of the role of adenosine-analogues as neuroprotectants and cognitive enhancers has sparked interest in these molecules as new therapeutic drugs. Understanding the behavior of these molecules in solution and predicting their ability to self-assemble will accelerate new discoveries. We propose a computational approach based on density functional theory, a polarizable continuum solvation description of the aqueous environment, and an efficient search procedure to probe the potential energy surface, to determine the structure and thermodynamic stability of molecular clusters of adenosine analogues in solution, using caffeine as a model. The method was validated as a tool for the prediction of the impact of small structural variations on self-assembly using paraxanthine. The computational results were supported by isothermal titration calorimetry experiments. The thermodynamic parameters enabled the quantification of the actual percentage of dimer present in solution as a function of concentration. The data suggest that both caffeine and paraxanthine are present at concentrations comparable to the ones found in biological samples.

First Evidence of the Liposome-Mediated Deintercalation of Anticancer Drug Doxorubicin from the Drug-DNA Complex: A Spectroscopic Approach

Biocompatible liposomes were used for the first time to study the deintercalation process of a prominent anticancer drug, doxorubicin (DOX), from doxorubicin-intercalated DNA (DOX-DNA complex) under controlled experimental conditions. The study revealed that anionic liposomes (DMPG liposomes) appeared to be the most effective to bring in the highest percentage of drug release while cationic liposomes (DOTAP liposomes) scored the lowest percentage of release. The drug release was primarily attributed to the electrostatic interaction between liposomes and drug molecules. Apart from this interaction, changes in the hydrophobicity of the medium upon addition of liposomes to the DNA-drug solution accompanied by lipoplex formation between DNA and liposomes were also attributed to the observed deintercalation. The CD and the time-resolved rotational relaxation studies confirmed that lipoplex formation took place between liposomes and DNA owing to electrostatic interaction. The confocal study revealed that in the postrelease period, DOX binds with liposomes. The reason behind the binding is electrostatic interaction as well as the unique bilayer structure of liposomes which helps it to act as a "hydrophobic sink" for DOX. The study overall highlighted a novel strategy for deintercalation of drug using biocompatible liposomes, as the release of the drug can be controlled over a period of time by varying the concentration and composition of the liposomes.

Role of caffeine in DNA recognition of a potential food-carcinogen benzo[a]pyrene and UVA induced DNA damage

Electron transfer (ET) reactions are important for their implications in both oxidative and reductive DNA damages. The current contribution investigates the efficacy of caffeine, a xanthine alkaloid in preventing UVA radiation induced ET from a carcinogen, benzo[a]pyrene (BP) to DNA by forming stable caffeine-BP complexes. While steady-state emission and absorption results emphasize the role of caffeine in hosting BP in aqueous medium, the molecular modeling studies propose the energetically favorable structure of caffeine-BP complex. The picosecond-resolved emission spectroscopic studies precisely explore the caffeine-mediated inhibition of ET from BP to DNA under UVA radiation. The potential therapeutic activity of caffeine in preventing DNA damage has been ensured by agarose gel electrophoresis. Furthermore, time-gated fluorescence microscopy has been used to monitor caffeine-mediated exclusion of BP from various cell lines including squamous epithelial cells, WI-38 (fibroblast), MCF-7 (breast cancer) and HeLa (cervical cancer) cells. Our in vitro and ex vivo experimental results provide imperative evidences about the role of caffeine in modified biomolecular recognition of a model carcinogen BP by DNA resulting dissociation of the carcinogen from various cell lines, implicating its potential medicinal applications in the prevention of other toxic organic molecule induced cellular damages.