Ranjan Das

The dynamic equilibrium between “Free water & Bound water” in an extracellular matrix is found to be responsible for structural integrity maintaining functional flexibility (viscoelastic adaptability) in a mimic hydrogel.

Nerve gases are the most lethal chemical agents for their toxicity, persistence, accessibility, and their recent use as a chemical warfare agent. While nerve gas agents are well known to be poisonous when inhaled, the toxicity of the agents in public water is equally harmful for their high-water solubility; however, they are less noticed in the contemporary literature considering their non-toxic hydrolysis products. Thus, contamination of public water by nerve gas can be a direct act of terrorism. Here, we have developed two strategies, namely detection of nerve gas simulator in public water with the limit of detection in the range of ppb (parts per billion) using a novel spectroscopic nano-sensor and collection of water samples which essentially retard the hydrolysis of nerve gases in the sample, assuring the concentration of the gases almost similar during the detection at a later date. We have shown that the second strategy (nanoformulation) can be effective by encapsulating the pollutant water into a suitable micelle, which prevents nerve-gas concentration loss through hydrolysis. We have developed an optical spectroscopy-based prototype for detecting nerve gas agents in public water and we have prepared a nano-formulation using a nontoxic surfactant cetyltrimethylammonium bromide (CTAB).

Charge separation is at the heart of solar energy applications, and efficient materials require fast photoinduced electron transfer (ET) and slow charge recombination (CR). Using time-dependent self-consistent charge density functional tight-binding theory combined with nonadiabatic (NA) molecular dynamics, we report a detailed analysis of ET and CR in hybrids composed of photoactive covalent organic polyhedra (COP) and encapsulated fullerenes. The ET occurs on a subpicosecond time scale and accelerates with increasing fullerene diameter, C₆₀ to C₇₀ to C₈₄. As the fullerene size increases, the π-electron system available for interaction with the COP grows, the fullerene-COP separation decreases, and the number of fullerene states available to accept the photoexcited electron increases, accelerating the ET. In comparison, the CR occurs on a nanosecond time scale and correlates with the length of the fullerene shortest axis because the relevant fullerene state is polarized in that direction. The largest and least symmetrical C₈₄ exhibits the fastest ET and the slowest CR, making COP@C₈₄ the most promising hybrid. Both high-frequency bond stretching and bending vibrations and low-frequency breathing modes are involved in the ET and CR processes, with more modes present in the C₈₄ system due its lower symmetry. The 10-20 fs vibrationally induced coherence loss in the electronic subsystem contributes to long lifetimes of the charge-separated states. The comprehensive investigation of the structure-property relationship of the charge carrier dynamics in the COP@fullerene hybrids provides a detailed atomistic understanding of interfacial ET processes and generates guidelines for rational design of high-performance materials for solar energy and related applications.

A biomimetic cell-based carrier system based on monocyte membranes and liposomes has been designed to create a hybrid "Monocyte-LP" which inherits the surface antigens of the monocytes along with the drug encapsulation property of the liposome. Fo''rster resonance energy transfer (FRET) and polarization gated anisotropy measurements show the stiffness of the vesicles obtained from monocyte membranes (Mons), phosphatidylcholine membranes (LP), and Monocyte-LP to follow an increasing order of Mons > Monocyte-LP > LP. The dynamics of interface bound water molecules plays a key role in the elasticity of the vesicles, which in turn imparts higher delivery efficacy to the hybrid Monocyte-LP for a model anticancer drug doxorubicin than the other two vesicles, indicating a critical balance between flexibility and rigidity for an efficient cellular uptake. The present work provides insight on the influence of elasticity of delivery vehicles for enhanced drug delivery.

Liposomes of a cationic lipid dioctadecyldimethylammonium bromide (DODAB) are efficient nanocarriers of nucleic acids. Incorporation of a neutral lipid monoolein (MO) in excess (x_MO>0.5) changes the lamellar organization of DODAB liposomes into non‐lamellar inverted structures of DODAB/MO liposomes facilitating nucleic acid delivery to cells. Photoexcitation of 8‐hydroxypyrene‐1,3,6‐trisulfonic acid (HPTS), a photoacid, initiates an excited state proton transfer (ESPT) reaction in its protonated form (ROH*) generating the deprotonated anionic form (RO⁻*). The fluorescence intensity ratio (I_ROH*/I_RO−*) of these two forms is governed by the ESPT dynamics, and increases with increasing MO content (x_MO) in the cationic liposomes of DODAB. Transition from lamellar organization of DODAB liposomes into non‐lamellar inverted structures of DODAB/MO liposomes, due to incorporation of MO (x_MO~0.7), is manifested by a significant increase of ESPT time (τ_PT) and the time constant of wobbling motion (τ_W) of HPTS. Thus, the lamellar organizations of DODAB or DODAB‐rich (x_MO 0.2) liposomes and the non‐lamellar organizations of MO‐rich (x_MO~0.7) liposomes are recognized by significantly different excited state dynamics of the photoacid.

Following the seminal discovery of Richard Feynman, several micromachines have been made that are capable of several applications, such as solar energy harvesting, remediation of environmental pollution, etc. Here we have synthesized a nanohybrid combining TiO₂ nanoparticle and light harvesting robust organic molecule RK1 (2-cyano-3-(4-(7-(5-(4-(diphenylamino)phenyl)-4-octylthiophen-2-yl)benzo[c][1,2,5] thiadiazol-4-yl)phenyl) acrylic acid) as a model micromachine having solar light harvesting ability potential for application in photocatalysis, preparation of solar active devices, etc. Detailed structural characterization, including High Resolution Transmission Electronic Microscopy (HRTEM) and Fourier-transform infrared spectroscopy (FTIR), has been performed on the nanohybrid. We have studied the excited-state ultrafast dynamics of the efficient push-pull dye RK1 in solution, on mesoporous semiconductor nanoparticles, and in insulator nanoparticles by streak camera (resolution of the order of 500 fs). The dynamics of such photosensitizers in polar solvents have been reported, and it has been observed that completely different dynamics occur when they are attached to the surface of the semiconductor/insulator nanosurface. A femtosecond-resolved fast electron transfer has been reported when photosensitizer RK1 has been attached to the surface of the semiconductor nanoparticle, which in turn plays a crucial role in the development of an efficient light harvesting material. The generation of reactive oxygen species as a result of femtosecond-resolved photoinduced electron injection in the aqueous medium is also investigated in order to explore the possibility of redox-active micromachines, which are found to be crucial for efficient and enhanced photocatalysis.

Enzyme function can be altered via modification of its amino acid residues, side chains and large-scale domain modifications. Herein, we have addressed the role of residue modification in catalytic activity and molecular recognition of an enzyme alpha-chymotrypsin (CHT) in presence of a covalent cross-linker formalin. Enzyme assay reveals reduced catalytic activity upon increased formalin concentration. Polarization gated anisotropy studies of a fluorophore 8-Anilino-1-naphthalenesulfonic acid (ANS) in CHT show a dip rise pattern in presence of formalin which is consistent with the generation of multiple ANS binding sites in the enzyme owing to modifications of its local amino acid residues. Molecular docking study on amino acid residue modifications in CHT also indicate towards the formation of multiple ANS binding site. The docking model also predicted no change in binding behavior for the substrate Ala-Ala-Phe-7-amido-4-methylcoumarin (AMC) at the active site upon formalin induced amino acid cross-linking.