Pradip Kr. Bhattacharyya

Substituent and Solvent Effects on the Absorption Spectra of Cation-π Complexes of Benzene and Borazine: A Theoretical Study.

Time-dependent density functional theory (TDDFT) has been used to predict the absorption spectra of cation-π complexes of benzene and borazine. Both polarized continuum model (PCM) and discrete solvation model (DSM) and a combined effect of PCM and DSM on the absorption spectra have been elucidated. With decrease in size of the cation, the π → π* transitions of benzene and borazine are found to undergo blue and red shift, respectively. A number of different substituents (both electron-withdrawing and electron-donating) and a range of solvents (nonpolar to polar) have been considered to understand the effect of substituent and solvents on the absorption spectra of the cation-π complexes of benzene and borazine. Red shift in the absorption spectra of benzene cation-π complexes are observed with both electron-donating groups (EDGs) and electron-withdrawing groups (EWGs). The same trend has not been observed in the case of substituted borazine cation-π complexes. The wavelength of the electronic transitions corresponding to cation-π complexes correlates well with the Hammet constants (σp and σm). This correlation indicates that the shifting of spectral lines of the cation-π complexes on substitution is due to both resonance and inductive effect. On incorporation of solvent phases, significant red or blue shifting in the absorption spectra of the complexes has been observed. Kamlet-Taft multiparametric equation has been used to explain the effect of solvent on the absorption spectra of complexes. Polarity and polarizability are observed to play an important role in the solvatochromism of the cation-π complexes.

B-Hb⋯π interactions in benzene–borazine sandwich and multidecker complexes: a DFT study

The stabilization energy of benzene–borazine sandwich and multidecker complexes bridged via B2H6 have been estimated using density functional theory. The gas and solvent phase calculations showed that the stabilization energy increases with the size of the complexes; in contrast, trifling reduction in the average stabilization energy is observed with increasing size of the complexes. The values of reactivity parameters, namely the energy of the HOMO, global hardness and chemical potential, suggest that the benzene complexes are more stable as compared to the borazine complexes. The complexes with as many as six aromatic rings containing B-Hb⋯π interactions are studied and are predicted to be stable (in terms of stabilization energy). The effect of solvents on the stability of the complexes is not so pronounced.

Understanding reactivity, aromaticity and absorption spectra of carbon cluster mimic to graphene: a DFT study

Effect of doping B and/or N on the reactivity, aromaticity and absorption spectra of graphene and functionalized (–OH and –COOH) carbon cluster mimicking graphene is studied using DFT, DFRT and TD-DFT. As expected, doping B and/or N resulted in substantial changes in the reactivity (both local and global) and aromaticity of the considered graphene and functionalized graphene. The absorption spectra of graphene and functionalized graphene are obtained in the UV-visible-IR region and significant blue and red shift is observed depending on the nature of the dopants. The reactivity of graphene and functionalized graphene changes significantly in the solvent phase. However, no significant difference between the gas phase and solvent phase absorption spectra is observed.

Condensation Product of Phenylalanine and Salicylaldehyde: Fluorescent Sensor for Zn(2.).

The condensation product of phenylalanine and salicylaldehyde (L) was synthesised and characterised which was found to be selective fluorescent “off-on” sensor for Zn2+ ion with the detection limit 10−5 M. The sensor is free of interferences from metal ions - Na+, K+, Al3+, Mn2+, Co2+, Ni2+, Cu2+, Pb2+, Cd2+ and Hg2+. The Fluorescence and the UV/visible spectral data reveals a 1:1 interaction between the sensor and Zn2+ ion with binding constant 108. The DFT and TDDFT calculations confirm the structures of the sensor and the sensor-Zn2+ complex.

B–Hb⋯π interaction in borane–graphene complexes: coronene as a case study

B–Hb⋯π interactions in the complexes formed between boranes (diborane-6, tetraborane-10 and pentaborane-9) and a model graphene (coronene) system are studied in the light of density functional theory. Stabilization energies are calculated and the complexes are predicted to be stable in both gas and solvent phases. Thermochemical analysis also predicts the feasibility of such complexes. The presence of dopants such as N/B/BN on the coronene moiety significantly affects the stabilization energy of the complexes depending upon the number of dopants. The HOMO energy of the complexes successfully predicts their stability. The presence of a solvent phase does not impart any substantial effect on the stability of the complex formed. The absorption spectra of the free coronene units (undoped/doped) and their respective complexes are found to be similar.

Unique cation–cyclohexane interactions in tri- and hexa-fluorocyclohexane multidecker complexes in the gas phase: a DFT study

The formation of stable sandwich and multidecker complexes through electrostatic interaction in tri- and hexa-fluorocyclohexane has been analyzed in the light of density functional theory. Both tri- and hexa-fluorocyclohexane are observed to form multidecker complexes and their corresponding interaction energies are quite remarkable. The covalent bond lengths in both the tri- and hexa-fluorocyclohexane molecules do not get affected upon complexation. The complexation is observed to be dependent on individual bond moment rather than the overall dipole moment of tri- or hexa-fluorocyclohexane. The gas phase BSSE corrected interaction energy increases with the size of the complexes (upto n = 3; where n is the number of cyclohexane unit); however, higher multidecker complexes with n = 4 possess smaller interaction energy. Variation of functional or basis set has minimal impact on the interaction energy calculations. Reactivity parameters viz. energy of HOMO, global hardness and electrophilicity are analyzed. Results reveal that the complexes formed possess substantial chemical stability.

A New Fluorescent "Off-On" Sensor for Al(3+) Derived from L-alanine and Salicylaldehyde.

The condensation product of L-alanine and salicylaldehyde was synthesised and characterised which was found to be selective fluorescent “on” sensor for Al3+ ion with the detection limit 10−6 M. The sensor is free of interferences from metal ions - Na+, K+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Pb2+, Cd2+, Hg2+ and Fe3+. The Fluorescence and the UV/visible spectral data reveals a 1:1 interaction between the sensor and Al3+ ion with binding constant 104.5. The DFT and TDDFT calculations confirm the structures of the sensor and the sensor-Al3+ complex.

Variation of reactivity of aziridinium ion during alkylation

Reactivity/stability of the tricyclic aziridinium ion intermediate of the mustine drug molecule varies with the ∠NCC bond angle of the tricyclic ring during alkylation of guanine. A sharp variation in reactivity of the aziridinium ion intermediate is observed along the intrinsic reaction coordinate. Further, shifting of the lowest unoccupied molecular orbital towards the carbon centre that interacts with guanine is also observed. Thermochemical analysis shows that the alkylation reaction is exothermic and presence of polar solvent effect activation energy.

Effect of external electric field on Cyclodextrin-Alcohol adducts: A DFT study

AbstractEffect of external electric fields on the interaction energy between cyclodextrin and alcohol was analyzed in the light of density functional theory (DFT) and density functional reactivity theory (DFRT). Stability of the cyclodextrin-alcohol adducts was measured in terms of DFT based reactivity descriptor, global hardness, electrophilicity, and energy of the HOMO. Stability of adducts was observed to be sensitive towards the strength as well as direction of the applied external electric field. In addition, reactivity pattern follows the maximum hardness and minimum electrophilicity principles. Graphical AbstractCyclodextrin-alcohol adducts show remarkable response towards the strength and direction of the applied electric field.

Reactivity of chitosan derivatives and their interaction with guanine: A computational study

AbstractThe present study delves into the reactivity of a few chitosan derivatives (CSDs) and their interaction with guanine in vacuum and in different phases. Increase in the polarity of the solvent lowers reactivity of the chosen derivatives (evaluated by using reactivity descriptors). Interaction between the CSDs and guanine (measured by interaction energy) weakens in solvent media and CSD-guanine interaction is weaker than the interaction between guanine and unmodified chitosan (CS). Chemical stability of CSD-guanine adducts remains similar to that of CS-guanine adduct in both polar and non-polar media. Moreover, CSD-guanine adducts exhibit comparable thermodynamic stability (quantified by free energy of solvation, ΔGsol) to that of unmodified CS-guanine adduct in non-polar solvent but in polar medium they are immensely destabilized in comparison to CS-guanine adduct. Observed theoretical results are expected to provide guidance for future relevant experimental research on gene delivery by CS derivatives. Graphical AbstractFunctional modification of chitosan alters it’s reactivity and strength of interaction in chitosan-nucleobase adducts.