Water-soluble cyclodiphosphazanes: synthesis, gold(I) metal complexes and their in vitro antitumor studies

The newly synthesized water-soluble cyclodiphosphazane ligands and their gold(I) complexes inhibit HeLa cell proliferation by activating p53 protein and inducing apoptosis.     

Enhanced fluorescence of epicocconone in surfactant assemblies as a consequence of depth-dependent microviscosity

The extents of fluorescence enhancement of epicocconone are found to be different in the micelles of the surfactants sodium dodecyl sulfate (SDS) and Triton X100 (TX 100). A decrease in fluorescence, observed in the cationic cetyltrimethylammonium bromide (CTAB) micelles, is rationalized by the formation of anions of the fluorophore at the Stern layer. To understand the difference in the effects of SDS and TX 100, the nature of the excited-state process in the fluorophore has been investigated by fluorescence spectroscopy, supported by complementary quantum chemical calculations. The excited-state dynamics of epicocconone is found to depend on polarity and viscosity of the medium, with a more pronounced dependence on viscosity. An inspection of the molecular orbitals involved in the electronic absorption of the molecule reveals the possibility of photoisomerization, which conforms to the observed solvent dependence of the fluorescence spectral properties. An apparent mismatch between trends observed in steady-state spectra and those in temporal decays indicates a significant contribution of an ultrafast component, which cannot be detected in the time resolution of our instrument. The viscosity dependence of the fluorescence quantum yields provides an explanation for the difference in the extents of fluorescence enhancement in the two micelles, in the light of location of the fluorophore at different depths of the micelle. The enhancement of fluorescence, with an unchanged fluorescence maximum, opens up the possibility that the fluorophore could be a useful dual emitting marker for fluorescence microscopy of heterogeneous systems, as the fluorescence of protein-bound epicocconone has been previously reported to be significantly red-shifted.     

A new example of a steroid-amino acid hybrid: construction of constrained nine membered D-ring steroids

A new archetype of steroid-amino acid hybrids containing a nine membered D-ring with hetero atoms has been synthesized for the first time from estrone and amino acids by using Yamaguchi coupling reactions.     

Atmospheric pressure laser ionization (APLI) coupled with Fourier transform ion cyclotron resonance mass spectrometry applied to petroleum samples analysis: comparison with electrospray ionization and atmospheric pressure photoionization methods

The analysis of crude oil samples remains a tough challenge due to the complexity of the matrix and the broad range of physical and chemical properties of the various individual compounds present. In this work, atmospheric pressure laser ionization (APLI) is utilized as a complementary tool to other ionization techniques for crude oil analysis. Mass spectra obtained with electrospray ionization (ESI) and atmospheric pressure photoionization (APPI) are compared. APLI is primarily sensitive towards non‐polar aromatic hydrocarbons, which are generally present in high amounts especially in heavy crude oil samples. The ionization mechanisms of APLI vs. APPI are further investigated. The results indicate the advantages of APLI over established methods like ESI and APPI. The application of APLI in combination with Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) is thus demonstrated to be a powerful tool for the analysis of aromatic species in complex crude oil fractions. Copyright © 2011 John Wiley & Sons, Ltd.     

Biophysical,spectroscopic vis-à-vis biochemical investigation on DNA–metalloprotein interaction: a model study involving cobalt(II)-glutathione complex

Abstract  The interaction of cobalt(II)-glutathione (CoGSH) with deoxyribonucleic acid (DNA) has been studied by UV–vis, fluorescence, circular dichroism (CD), thin-film infrared (IR), and viscometric techniques. From the UV-spectroscopic method, binding constant (K _b) was determined and was found to be 2.3 × 10⁶ M⁻¹. In fluorimetric analysis, the quenching of fluorescence intensity of DNA bound to ethidium bromide (EB) was investigated. The Stern–Volmer quenching constant (K _sv) was also estimated from this study and was found to be 2.8 × 10⁶ M⁻¹at 37 °C. The solution CD spectra of DNA and DNA–CoGSH indicate that in each case, DNA exists in the ‘B’ conformation and suggested an intercalative binding mode. Thin-film IR data also reveal that DNA attains the ‘B’ family of conformations after interaction with CoGSH complex. The increase in DNA viscosity in the presence of CoGSH complexes is attributed to the lengthening of DNA helix due to intercalation. Graphical Abstract  The spectrophotometric, CD, thin film IR, viscometric and fluorimetric studies on the interaction of CoGSH with DNA indicated an intercalative binding mode with the retention of ‘B’ conformation of DNA.      

A “classical” trajectory driven nuclear dynamics by a parallelized quantum‐classical approach to a realistic model Hamiltonian of benzene radical cation

We explore the workability of a parallelized algorithm of time‐dependent discrete variable representation (TDDVR) methodology formulated by involving “classical” trajectories on each DOF of a multi‐mode multi‐state Hamiltonian to reproduce the population dynamics, photoabsorption spectra and nuclear dynamics of the benzene radical cation. To perform such dynamics, we have used a realistic model Hamiltonian consists of five lowest electronic states (X²E_1g, B²E_2g, C²A_2u, D²E_1u, and E²B_2u) which are interconnected through several conical intersections with nine vibrational modes. The calculated nuclear dynamics and photoabsorption spectra with the advent of our parallelized TDDVR approach show excellent agreement with the results obtained by multiconfiguration time‐dependent Hartree method and experimental findings, respectively. The major focus of this article is to demonstrate how the “classical” trajectories for the different modes and the “classical” energy functional for those modes on each surface can enlight the time‐dependent feature of nuclear density and its' nodal structure. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Multichromophoric dye-sensitized solar cells based on supramolecular zinc-porphyrinperylene-imide dyads

Multichromophoric dye-sensitized solar cells (DSCs) based on self-assembled zinc-porphyrinperyleneimide dyads on TiO(2) films display more efficient light-to-electrical energy conversion than DSCs based on individual dyes. Higher efficiency of multichromophoric dyes can be attributed to co-sensitization as well as vectorial electron transfer that lead to better electron-hole separation in the device.     

A state-to-state dynamical study of the Br + H(2) reaction: comparison of quantum and classical trajectory results

We present a detailed theoretical investigation of the dynamics corresponding to the strongly endothermic Br + H(2) (v = 0-1, j = 0) → H + HBr reaction in the 0.85 to 1.9 eV total energy range. State-averaged and state-to-state results obtained through time-independent wave packet (TIWP) and time-independent quantum mechanical (TIQM) calculations and quasiclassical trajectories (QCT) are compared and analyzed. The agreement in the results obtained with both quantum mechanical results is very good overall. However, although QCT calculations reproduce the general features, their agreement with the QM results is sometimes only qualitative. The analysis of the mechanism based on state-averaged results turns out to be deceptive and conveys an oversimplified picture of the reaction consistent with a direct-rebound mechanism. Consideration of state-to-state processes, in contrast, unveils the existence of multiple mechanisms that give rise to a succession of maxima in the differential cross section (DCS). Such mechanisms correlate with different sets of partial waves and display similar collision times when analyzed through the time-dependent DCS.     

Inter- and intramolecular Mitsunobu reaction and metal complexation study: synthesis of S-amino acids derived chiral 1,2,3,4-tetrahydroquinoxaline, benzo-annulated [9]-N3 peraza, [12]-N4 peraza-macrocycles

Substituted 1,2,3,4-tetrahydroquinoxaline, benzo-annulated unsymmetrical chiral [9]-N(3) peraza, and [12]-N(4) peraza-macrocycles have been synthesized employing an inter- and intramolecular Mitsunobu reaction from an amino acid derived common synthetic intermediate 3. The metal complexation study of these macrocycles has been investigated by UV-visible spectroscopic technique with binding constant (K(b)) value 1.84 × 10(3) dm(3) mol(-1) using the Benesi-Hildebrand equation and a Gibbs free energy (ΔG) -19.4 kJ mol(-1) at 35 °C for 14d with Co(2+). The binding properties of the metal were dependent on the structure of polyaza-macrocycles that were confirmed by the DFT optimized structure of two macrocycles. A detailed investigaton of UV-visible spectra of macrocycles and their complete interpretation with the help of TD-DFT along with the frontier molecular orbital calculations are presented.