Basab Chattopadhyay

A New Half-Condensed Schiff Base Compound: Highly Selective and Sensitive pH-Responsive Fluorescent Sensor

A new probe, 3-[(3-benzyloxypyridin-2-ylimino)methyl]-2-hydroxy-5-methylbenzaldehyde (1-H) behaves as a highly selective fluorescent pH sensor in a Britton-Robinson buffer at 25 °C. The pH titrations show a 250-fold increase in fluorescence intensity within the pH range of 4.2 to 8.3 with a pK(a) value of 6.63 which is valuable for studying many of the biological organelles.

A highly selective fluorescent chemosensor for zinc ion and imaging application in living cells.

A new 2,6-bis(5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazolin-6-yl)-4-methylphenol (1) serves as a highly selective and sensitive fluorescent probe for Zn(2+) in a HEPES buffer (50 mM, DMSO:water = 1:9 (v/v), pH = 7.2) at 25 °C. The increase in fluorescence in the presence of Zn(2+) is accounted for by the formation of dinuclear Zn(2+) complex [Zn(2)(C(35)H(25)N(6)O)(OH)(NO(3))(2)(H(2)O)] (2), characterized by X-ray crystallography. The fluorescence quantum yield of the chemosensor 1 is only 0.019, and it increases more than 12-fold (0.237) in the presence of 2 equiv of the zinc ion. Interestingly, the introduction of other metal ions causes the fluorescence intensity to be either unchanged or weakened. By incubation of cultured living cells (A375 and HT-29) with the chemosensor 1, intracellular Zn(2+) concentrations could be monitored through selective fluorescence chemosensing.

Unraveling unprecedented charge carrier mobility through structure property relationship of four isomers of didodecyl[1]benzothieno[3,2-b][1]benzothiophene

The structural and electronic properties of four isomers of didodecyl[1]-benzothieno[3,2-b][1]benzothiophene (C12-BTBT) have been investigated. Results show the strong impact of the molecular packing on charge carrier transport and electronic polarization properties. Field-induced time-resolved microwave conductivity measurements unravel an unprecedented high average interfacial mobility of 170 cm(2) V(-1) s(-1) for the 2,7-isomer, holding great promise for the field of organic electronics.

Synthesis of Selenoxo Peptides and Oligoselenoxo Peptides Employing LiAlHSeH

Synthesis of selenoxo peptides by the treatment of N(α)-protected peptide esters with a combination of PCl(5) and LiAlHSeH is delineated. The method is simple, high-yielding, and free from racemization. Thus obtained selenoxo peptides are used as units for N-terminal chain extension through N(α)-deprotection/coupling to yield peptide-selenoxo peptide hybrids. Multiple selenation is demonstrated by conversion of two peptide bonds of tripeptides into selenoxo peptide bonds. Amino acid derived arylamides are also converted into aryl selenoamides. C(6)H(5)-CSeNH-Val-OMe 8f is obtained as single crystal, and its structure was determined through X-ray diffraction study.

Synthesis and characterization of isomerically pure anti- and syn-anthradiindole derivatives

Synthesis, isolation, and characterization of isomerically pure syn- and anti-anthradiindole (ADI) derivatives are described. The anti- and syn-ADI structures are demonstrated by (13)C NMR spectroscopy and by single-crystal X-ray diffraction. The spectroscopic and electrochemical properties as well as the stability of these newly synthesized π-conjugated systems are evaluated and supported by quantum-chemical calculations.

Structural study of three o-hydroxyacetophenone derivatives using X-ray powder diffraction: interplay of weak intermolecular interactions

A family of three o-hydroxyacetophenone derivatives, 2-hydroxy-5-methoxy-4-methylacetophenone (1), 5-methoxy-4-methyl-2-(phenylmethoxy)acetophenone (2) and 2-O-(α-methyl carboethoxy)-5-methoxy-4-methyl-acetophenone (3) were synthesized and their crystal structures were solved using laboratory X-ray powder diffraction data along with a detailed analysis of the Hirshfeld surfaces and 2D-fingerprint plots, facilitating a comparison of intermolecular interactions. The DFT optimized molecular geometries in 1 and 3 agree closely with those obtained from the crystallographic studies. In 2, however, the relative orientation of the two planar phenyl rings as established by the X-ray analysis and quantum mechanical calculations differs by 34.9°. The crystal packing in the compounds is stabilized by an interplay of weak hydrogen bonds, such as C–H⋯O, C–H⋯π and π⋯π interactions, forming supramolecular assemblies. The intermolecular C–H⋯O hydrogen bonds in 1–3 generate C11(6) chains and Rmn(X) rings, which are further connected through C–H⋯π hydrogen bonds and π⋯π interactions to produce parallel molecular sheets built by fused R22(24) rings in 1, a three-dimensional architecture with C22(16)[R22(6)][R22(14)] synthons in 2, and a two-dimensional columnar framework in 3.

Substrate-induced phases: transition from a liquid-crystalline to a plastic crystalline phase via nucleation initiated by the substrate

The presence of substrate-induced phases in thin films is an intriguing phenomenon with the physical and chemical factors responsible for their formation are not yet clearly understood. In this article, we present the structure and morphological changes associated with a substrate-induced phase in a discotic liquid crystal. The thin films of the discotic molecule are characterised by a combination of various X-ray diffraction methods to investigate the structural properties. Atomic force microscopy and polarised optical microscopy are used to determine the thin film morphologies. This is the first experimental proof of the presence of a substrate-induced phase in discotic liquid crystal, although they are known in thin films of molecular crystals. Moreover, we sought to decipher how the substrate-induced phase behaves with the evolution of time, temperature and changes at the interfaces. This work gives a unique example where the two-dimensional liquid-crystalline phase converts to a three-dimensional crystal plastic phase because of nucleation caused by the solid substrate over a time scale of a month or longer.

Design, Synthesis, Chemical Stability, Packing, Cyclic Voltammetry, Ionisation Potential, and Charge Transport of [1]Benzothieno[3,2-b][1]benzothiophene Derivatives

Five new molecular semiconductors that differ from dioctylbenzothienobenzothiophene, by the introduction of ether or thioether side chains, have been synthesized and obtained in good yields. Their availability in sufficient quantities has allowed investigation of their electrochemical behaviour in solution and their electronic properties in solid state. Both ether and thioether compounds oxidise rather easily in solution, but nevertheless, they exhibit rather high ionisation potentials. This is a consequence of their crystal structure. Dioctylthioetherbenzothienobenzothiophene is rather sensitive to oxidation and degrades easily in close to ambient conditions. Dioctyletherbenzothienobenzothiophene is more stable. Its charge carrier mobility remains however rather moderate, on the order of 0.5 cm2 V−1 s−1, whereas that of dioctylbenzothienobenzothiophene reached 4 cm2 V−1 s−1, in the same conditions. The difference is explained by intrinsic factors as shown by a theoretical modelling.

Structural study of four benzyloxybenzoic acids and benzyloxyanilines using X-ray powder diffraction: interplay of strong and weak intermolecular interactions

Crystal structures of two benzyloxybenzoic acids (1 and 2) and two benzyloxyanilines (3 and 4) have been solved from laboratory X-ray powder diffraction data using the direct space methodology. The refinements of structures 1, 2, 3 and 4 have been carried out following the Rietveld method. The nature of intermolecular interactions in 1–4 has been analyzed through the Hirshfeld surfaces and 2D fingerprint plots. The COOH functional group generates a cyclic R22(8) synthon via intermolecular O–H⋯O hydrogen bonds in 1 and 2. An interplay of O–H⋯O and C–H⋯O hydrogen bonds, and C–H⋯π interactions in 1 and 2 facilitates the formation of three-dimensional supramolecular frameworks in 1 and a one-dimensional step-like architecture in 2. While the combination of N–H⋯π and C–H⋯π interactions link the molecules in 3 into parallel columns along the [100] direction, no such molecular assembly has been observed in 4. Hirshfeld surface analyses of 1–4 as well as a few related benzyloxybenzoic acid and benzyloxyaniline derivatives retrieved from the Cambridge structural database (CSD) indicate that about 90% of Hirshfeld surface areas in this class of compounds are due to H⋯H, C⋯H and O⋯H contacts.

Molecular Dynamics Study and Electronic Structure Evolution of a DNA Duplex d(CCCGATCGGG)2

The molecular dynamics simulations and electronic structure evolution of a A-DNA decamer, d(CCCGATCGGG)(2), in the presence and absence of [Co(NH(3))(6)](3+) ions have been investigated. In both cases, the results of 2.5 ns MD simulation indicate a A-DNA→B-DNA transition. Ab initio DFT calculations were performed on a series of conformations representing the A→B transitions to reveal the dynamical behavior of the electronic structure of the decamer. The results suggest that the conformational parameters as well as the surrounding environment have no direct correlation with the electronic structures. Instead, the thermal fluctuations play an important role in the electronic structure of the present DNA system.