Photosensitizer in a molecular bowl and its effect on the DNA-binding and -cleavage activity of 3d-metal scorpionates

Ternary 3d -metal complexes [M(Tp (Ph))(B)](ClO 4) ( 1- 8), where M is Co(II), Ni(II), Cu(II) and Zn(II), Tp (Ph) is anionic tris(3-phenylpyrazolyl)borate, and B is N,N-donor heterocyclic base, namely, 1,10-phenanthroline (phen, 1- 4) and dipyrido[3,2- d:2',3'- f]quinoxaline (dpq, 5- 8), were prepared from a reaction of the perchlorate salt of the metal with KTp (Ph) and B in CH 2Cl 2. The complexes were characterized by various physicochemical methods. 4- 6 and 8 were structurally characterized by single-crystal X-ray crystallography. The crystal structures of the complexes show the presence of discrete cationic complexes having a square-pyramidal (4 + 1) coordination geometry in which two nitrogen atoms of the phenanthroline base (B) and two nitrogen atoms of the Tp (Ph) ligand occupy the basal plane and one nitrogen of the Tp (Ph) ligand binds at the axial site. The phenyl groups of the Tp (Ph) form a bowl-shaped structure that essentially encloses the {M(phen/dpq)} moiety. DNA-binding studies were carried out using various spectral techniques and from viscosity measurements. The complexes show moderate binding propensity to calf thymus DNA at the minor groove, giving binding constant values ( K b) of approximately 10 (4) M (-1). The complexes exhibit poor DNA-cleavage activity in the dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide (H 2O 2). The photoinduced DNA-cleavage activity of the complexes was investigated using UV-A radiation of 365 nm and visible light of two different wavelengths with a tunable multicolor Ar-Kr mixed gas ion laser source. The dpq complexes show efficient photoinduced DNA-cleavage activity via a metal-assisted photoexcitation process involving the formation of singlet oxygen as the cleavage active species in a type-II pathway. The paramagnetic d (7)-Co(II)-dpq and d (9)-Cu(II)-dpq complexes exhibit efficient DNA-cleavage activity in visible light. The paramagnetic d (8)-Ni(II)-dpq complex displays only minor DNA-cleavage activity in visible light. Diamagnetic d (10)-Zn(II)-dpq complex shows only UV-A light-induced DNA cleavage but no apparent DNA-cleavage activity in visible light. Steric protection of the photoactive quinoxaline moiety of the dpq ligand inside the hydrophobic {M(Tp (Ph))} molecular bowl has a positive effect on the photoinduced DNA-cleavage activity.     

Synthesis and characterization of {Ni(NO)}10 and {Co(NO)2}10 complexes supported by thiolate ligands

Nitric oxide is an important molecule in biology and modulates a variety of physiological and pathophysiological processes. Some of its regulatory functions are exerted through interactions with redox-active elements, including iron, nickel, cobalt, and sulfur. Metalloenzymes containing [ nFe- nS] ( n = 2 or 4) clusters can be activated or inactivated by reaction with NO, affording dinitrosyl iron complexes. Studies of the NO chemistry of small-molecule iron thiolate complexes have provided insight into these biological processes and suggested probable intermediates. To explore this chemistry from a different perspective, we prepared nickel and cobalt thiolate complexes and investigated their reactions with NO and related compounds. We report here the first examples of anionic complexes containing {Ni(NO)} (10) and {Co(NO) 2} (10) units, the reactivity of which suggests possible intermediates in the interconversion of iron thiolate nitrosyl compounds. Our results demonstrate new chemistry involving NO and simple complexes of nickel and cobalt supported by thiolates, which have been known for more than 30 years. The use of mass balance methodology was key to their discovery. Among the novel complexes reported are (Et 4N) 2[Ni(NO)(SPh) 3] ( 2), from (Et 4N) 2[Ni(SPh) 4] ( 1) and NO, (Et 4N) 2[Ni 2(NO) 2(mu-SPh) 2(SPh) 2] ( 3), from 1 and NO (+) or 2 and Me 3O (+), (Et 4N)[Co(NO) 2(SPh) 2] ( 5), from (Et 4N) 2[Co(SPh) 4] ( 4) and NO, and [Co 3(NO) 6(mu-SPh) 3] ( 6), from 5 and Me 3O (+). In the syntheses of 2 and 5, NO could be replaced by the convenient solid Ph 3CSNO.     

Chiral ionic liquid-catalyzed Biginelli reaction: stereoselective synthesis of polyfunctionalized perhydropyrimidines

A chiral ionic liquid-catalyzed, efficient and unprecedented version of the Biginelli reaction using new variants of its active methylene component, viz. 2-phenyl-1,3-oxazol-5-one/2-methyl-2-phenyl-1,3-oxathiolan-5-one, with aromatic aldehydes and urea/thiourea enantio- and diastereoselectively, yields 5-amino-/mercaptoperhydropyrimidines. This three-component domino cyclocondensation reaction is effected via ring transformation of an isolable intermediate in a one-pot procedure.     

Ionic liquid [Hmim]HSO4-promoted one-pot oxidative conjugate addition of sulfur-centred nucleophiles to Baylis-Hillman adducts

The first example of the one-pot oxidative conjugate addition of sulfur-centred nucleophiles to Baylis-Hillman adducts is reported. The reaction involves oxidation of Baylis-Hillman adducts with NaNO₃ in the Brønsted acidic ionic liquid [Hmim]HSO₄ to give [E]-α-cyanocinnamaldehydes followed by conjugate hydrothiocyanation/hydrosulfenylation with NH₄SCN/PhSH to afford the corresponding β-thiocyanato (or β-phenylsulfenyl)-α-cyanohydrocinnamaldehydes diastereoselectively in 76-89% yields in a one-pot procedure. After isolation of the product, the ionic liquid [Hmim]HSO₄ could be easily recycled for further use.     

Thiourea to bicyclic scaffolds: highly regio- and stereoselective routes to dithiazolopyrimidines

Microwave-activated solvent-free Michael addition of 3-imino-1,4,2-dithiazoles to 4-arylidene-5(4H)-oxazolones furnished isolable adducts regio- and diastereoselectively, which underwent ring transformation to yield the target dithiazolopyrimidines. Alternatively, the similar conjugate addition of methanesulfinylmethylisothioureas to 4-arylidene-5(4H)-oxazolones diastereoselectively afforded Michael adducts, which underwent ring transformation followed by heterocyclization via deoxygenative demethylation with thionyl chloride to yield the same products dithiazolopyrimidines regio- and diastereoselectively.     

Ternary iron(II) complex with an emissive imidazopyridine arm from Schiff base cyclizations and its oxidative DNA cleavage activity

The ternary iron(II) complex [Fe(L')(L")](PF6)3(1) as a synthetic model for the bleomycins, where L' and L" are formed from metal-mediated cyclizations of N,N'-(2-hydroxypropane-1,3-diyl)bis(pyridine-2-aldimine)(L), is synthesized and structurally characterized by X-ray crystallography. In the six-coordinate iron(ii) complex, ligands L' and L" show tetradentate and bidentate chelating modes of bonding. Ligand L' is formed from an intramolecular attack of the alcoholic OH group of L to one imine moiety leading to the formation of a stereochemically constrained five-membered ring. Ligand L" which is formed from an intermolecular reaction involving one imine moiety of L and pyridine-2-carbaldehyde has an emissive cationic imidazopyridine pendant arm. The complex binds to double-stranded DNA in the minor groove giving a Kapp value of 4.1 x 10(5) M(-1) and displays oxidative cleavage of supercoiled DNA in the presence of H2O2 following a hydroxyl radical pathway. The complex also shows photo-induced DNA cleavage activity on UV light exposure involving formation of singlet oxygen as the reactive species.     

Bromodimethylsulfonium bromide (BDMS): a useful reagent for conversion of aldoximes and primary amides to nitriles

An operationally simple and high yielding procedure has been developed for the preparation of nitriles from aldoximes and primary amides using bromodimethylsulfonium bromide (BDMS) as a novel and efficient reagent in the absence of any added base or catalyst. The optimal protocol is applicable to access a wide range of cyano compounds including aromatic, heterocyclic, and aliphatic species. The conversion of aldoximes to nitriles takes place at room temperature in acetonitrile, whereas acetonitrile at reflux temperature is required for rapid conversion in the case of primary amides.     

Population model with diffusion and supplementary forest resource in a two-patch habitat

A mathematical model is proposed to study the role of supplementary self-renewable resource on species population in a two-patch habitat. It is assumed that the density of forest resource biomass is governed by the logistic equation in both the regions but with the different intrinsic growth rate but the same carrying capacity in the entire habitat. It is further assumed that the densities of species population is also governed by the generalized logistic equations in both the regions but with different growth rates and carrying capacities. It is shown that the steady state solutions are positive, monotonic and continuous under both reservoir and no-flux boundary conditions. The linear and non-linear asymptotic stability conditions of non-uniform steady state are compared with the case of the model with and without diffusion in a homogeneous habitat.     

Population Genetic Structure and Marker Trait Associations Using Morphological,Phytochemical and Molecular Parameters in <Emphasis Type="Italic">Habenaria edgeworthii</Emphasis>—a Threatened Medicinal Orchid of West Himalaya,India

Habenaria edgeworthii Hook. f. ex Collett is an important terrestrial orchid used in different Ayurvedic formulations. In the present study, variations among morphological, phytochemical and molecular markers were assessed. A significant difference was observed among populations using morphological traits. Inter-simple sequence repeat (ISSR) data revealed lower genetic diversity at population level (He = 0.207) as compared to species level (He = 0.334). Analysis of molecular variance (AMOVA) indicates 74 % variation among populations and 26 % within population. Tuber extracts showed significantly (p < 0.05) higher total phenolics and flavonoids among the populations. Antioxidant activity determined by 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) assays exhibited considerable antioxidant potential. Furthermore, the associations between molecular and morphological and phytochemical attributes were studied using multiple regression analysis (MRA). Several ISSR fragments were associated with some morphological and phytochemical traits. These ISSR fragments can be useful for breeding programme of the species when no other genetic information, such as linkage maps and quantitative trait loci, is available.