Photocytotoxic and anaerobic DNA cleavage activity of binuclear 3,3′-dithiodipropionic acid cobalt(II) complexes having phenanthroline bases

Dicobalt(II) complexes [{(B)Co^II}₂(μ-dtdp)₂] (1–3) of 3,3′-dithiodipropionic acid (dtdp) and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3), have been prepared, characterized and their photo-induced anaerobic DNA cleavage activity studied. The elemental analysis and mass spectral data suggest binuclear formulation of the complexes. The redox inactive complexes have magnetically non-interacting dicobalt(II) core showing magnetic moment of ∼3.9 μ_B per cobalt(II) center. The complexes show good binding propensity to calf thymus DNA giving K_b values within 4.3 × 10⁵–4.0 × 10⁶ M⁻¹. Thermal melting and viscosity data predict DNA groove binding and/or partial intercalative nature of the complexes. The complexes show significant anaerobic DNA cleavage activity in green light under argon atmosphere possibly involving radical species generated from the disulfide moiety in a type-I pathway. The DNA cleavage reaction under aerobic medium in green light is found to involve hydroxyl radical species. The dppz complex 3 exhibits significant photocytotoxicity in HeLa cervical cancer cells with an IC₅₀ value of 2.3 μM in UV-A light of 365 nm, while it is essentially non-toxic in dark giving an IC₅₀ value of >200 μM. A significant reduction of the dark toxicity of the organic dppz base (IC₅₀ = 8.3 μM in dark) is observed on binding to the cobalt(II) center while essentially retaining its photocytotoxicity in UV-A light (IC₅₀ = 0.4 μM).     

Influence of Catalyst on the Formation of 5(10)-Ene Ketals From Estra-4-en-3-ones

The effect of catalyst on formation of isomeric ketals from 19-nortestosterone and 19-nor-ethisterone is reported. Regioselectivity has been achieved with metal hydrides as catalyst, reported for the first time, to give 5(10)-ene ketals.

     

The effects of thermal treatment of ZnO–ZnCr<Subscript>2</Subscript>O<Subscript>4</Subscript> catalyst on the particle size and product selectivity in dehydrocyclization of crude glycerol and ethylenediamine

The ZnO–ZnCr₂O₄ (Zn–Cr–O) sample obtained by decomposition of Zn-Cr hydrotalcite precursor was subjected to the thermal treatment at different temperatures and the physico-chemical properties of the Zn–Cr–O system were compared with its catalytic behavior in dehydrocyclization of crude glycerol and ethylenediamine (EDA). Upon high temperature treatment of Zn–Cr–O the Cr⁶⁺ ions underwent autoreduction to form stable Cr³⁺ species and the particle size of both ZnO and ZnCr₂O₄ increased dramatically. Thermal effect did not influence the intermolecular cyclisation of EDA to form pyrazine. By contrast, an inversely proportional dependence was found between the rate of formation of 2-methylpyrazine and the particle size of Zn–Cr–O whereas the rate of 2-pyrazinylmethanol was directly proportional to the particle size.     

Preparation,Characterization, and Electrochemical Performance of the Hematite/Oxidized Multi-Walled Carbon Nanotubes Nanocomposite

In this research work, a hematite (α-Fe₂O₃) nanoparticle was prepared and then mixed with oxidized multi-walled carbon nanotubes (O-MWCNT) to form a stable suspension of an α-Fe₂O₃/O-MWCNTs nanocomposite. Different characterization techniques were used to explore the chemical and physical properties of the α-Fe₂O₃/O-MWCNTs nanocomposite, including XRD, FT-IR, UV-Vis, and SEM. The results revealed the successful formation of the α-Fe₂O₃ nanoparticles, and the oxidation of the MWCNT, as well as the formation of stable α-Fe₂O₃/O-MWCNTs nanocomposite. The electrochemical behaviour of the α-Fe₂O₃/O-MWCNTs nanocomposite was investigated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV), and the results revealed that modification of α-Fe₂O₃ nanoparticles with O-MWCNTs greatly enhanced electrochemical performance and capacitive behaviour, as well as cycling stability.     

Annulation of aromatic imines via directed C-H bond activation

A directed C-H bond activation approach to the synthesis of indans, tetralins, dihydrofurans, dihydroindoles, and other polycyclic aromatic compounds is presented. Cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using (PPh3)3RhCl (Wilkinson's catalyst). The cyclization of a range of aromatic ketimines and aldimines provides bi- and tricyclic ring systems with good regioselectivity. Different ring sizes and substitution patterns can be accessed through the coupling of monosubstituted, 1,1- or 1,2-disubstituted, and trisubstituted alkenes bearing both electron-rich and electron-deficient functionality.     

Highly efficient and enantioselective cyclization of aromatic imines via directed C-H bond activation

The first highly enantioselective catalytic reaction involving aromatic C-H bond activation is communicated. Enantioselective cyclization of aromatic ketimines containing alkenyl groups tethered at the meta position of an imine directing group has been achieved using 5 mol % [RhCl(coe)2]2 and 15 mol % of an (S)-binol-derived phosphoramidite ligand. Selectivities of up to 96% ee and up to quantitative yields were obtained. Moreover, the identified catalyst system enables the intramolecular alkylation reaction to be performed at temperatures 75 degrees C lower than our previously reported achiral system. The reaction can even be performed at room temperature for one of the optimal substrates.     

Fluorescence of cis-1-amino-2-(3-indolyl)cyclohexane-1-carboxylic acid: a single tryptophan chi(1) rotamer model

A constrained derivative, cis-1-amino-2-(3-indolyl)cyclohexane-1-carboxylic acid, cis-W3, was designed to test the rotamer model of tryptophan photophysics. The conformational constraint enforces a single chi(1) conformation, analogous to the chi(1) = 60 degrees rotamer of tryptophan. The side-chain torsion angles in the X-ray structure of cis-W3 were chi(1) = 58.5 degrees and chi(2) = -88.7 degrees. Molecular mechanics calculations suggested two chi(2) rotamers for cis-W3 in solution, -100 degrees and 80 degrees, analogous to the chi(2) = +/-90 degrees rotamers of tryptophan. The fluorescence decay of the cis-W3 zwitterion was biexponential with lifetimes of 3.1 and 0.3 ns at 25 degrees C. The relative amplitudes of the lifetime components match the chi(2) rotamer populations predicted by molecular mechanics. The longer lifetime represents the major chi(2) = -100 degrees rotamer. The shorter lifetime represents the minor chi(2) = 80 degrees rotamer having the ammonium group closer to C4 of the indole ring (labeled C5 in the cis-W3 X-ray structure). Intramolecular excited-state proton transfer occurs at indole C4 in the tryptophan zwitterion (Saito, I.; Sugiyama, H.; Yamamoto, A.; Muramatsu, S.; Matsuura,T. J. Am. Chem. Soc. 1984, 106, 4286-4287). Photochemical isotope exchange experiments showed that H-D exchange occurs exclusively at C5 in the cis-W3 zwitterion, consistent with the presence of the chi(2) = 80 degrees rotamer in solution. The rates of two nonradiative processes, excited-state proton and electron transfer, were measured for individual chi(2) rotamers. The excited-state proton-transfer rate was determined from H-D exchange and fluorescence lifetime data. The excited-state electron-transfer rate was determined from the temperature dependence of the fluorescence lifetime. The major quenching process in the -100 degrees rotamer is electron transfer from the excited indole to carboxylate. Electron transfer also occurs in the 80 degrees rotamer, but the major quenching process is intramolecular proton transfer. Both quenching processes are suppressed by deprotonation of the amino group. The results for cis-W3 provide compelling evidence that the complex fluorescence decay of the tryptophan zwitterion originates in ground-state heterogeneity with the different lifetimes primarily reflecting different intramolecular excited-state proton- and electron-transfer rates in various rotamers.     

Detection of membrane biointeractions based on fluorescence superquenching

Assays for biointeractions of molecules with supported lipid bilayers using fluorescence superquenching are described. A conjugated cationic polymer was adsorbed on to silica microspheres, which were then coated with an anionic lipid bilayer. The lipid bilayer attenuated superquenching by acting as a barrier between the conjugated polymer and its quencher. Biointeractions of the lipid bilayer with a membrane lytic peptide, melittin, were detected and quantitated by superquenching of the conjugated polyelectrolyte in flow cytometric and microfluidic bioassays. A higher sensitivity for detecting melittin lysis of the lipid bilayer at lower concentrations and shorter times for melittin action was found using flow cytometry in this study in comparison to other existing methods. This study combined the sensitivity of superquenching and flow cytometry to detect biointeractions with a lipid bilayer, which serves as a platform for developing functional assays for sensor applications, lipid enzymology, and investigations of molecular interactions. In addition, this study demonstrated proof-of-concept for using superquenching detected as a result of lipid bilayer disruption in a microfluidic format.     

A Critical Review of Chemical Vapor-Deposited (CVD) Diamond for Electronic Applications

The objective of this article is to describe the present understanding of the growth, processing, and properties of diamond for electronic applications.     

Continuous Procrustes Distance Between Two Surfaces

The Procrustes distance is used to quantify the similarity or dissimilarity of (three‐dimensional) shapes and extensively used in biological morphometrics. Typically each (normalized) shape is represented by N landmark points, chosen to be homologous, as far as possible, and the Procrustes distance is then computed as $\inf_{R}\sum_{j=1}^N \|Rx_j-x'_j\|^2$ , where the minimization is over all euclidean transformations, and the correspondences $x_j \leftrightarrow x'_j$ are picked in an optimal way. The discrete Procrustes distance has the drawback that each shape is represented by only a finite number of points, which may not capture all the geometric aspects of interest; a need has been expressed for alternatives that are still easy to compute. We propose in this paper the concept of continuous Procrustes distance and prove that it provides a true metric for two‐dimensional surfaces embedded in three dimensions. We also propose an efficient algorithm to calculate approximations to this new distance. © 2012 Wiley Periodicals, Inc.