Synthetic analogue approach for the functional domains of copper(II) bleomycins and its DNA cleavage activity

The dicopper(II) complex [Cu2(R'SSR)2(SO4)2] (1), where R'SSR is a Schiff base, has been prepared from the reaction of CuSO4.5H2O with the Schiff base N,N'-1,1'-dithiobis(ethylenesalicylaldimine)(H2RSSR) and structurally characterized by X-ray crystallography. The crystal structure of 1 shows two {Cu(R'SSR)}2+ units linked by two sulfate ligands each showing a eta3,mu2-binding mode. The Cu...Cu distance is 4.562(2)A with each copper having a square pyramidal (4 + 1) CuNO4 coordination geometry. The monoanionic Schiff base R'SSR has a pendant cationic amine -SCH2CH2NH3+ group which is presumably formed from the hydrolysis of one imine bond of H2RSSR. Complex 1 models the N- and C-terminus domains of bleomycins. The metal centers in 1 are essentially magnetically non-interacting giving a -2J value of 3 cm(-1) with the singlet as the ground state. Using complex 1 as a precursor, ternary copper(II) complexes [Cu(R'SSR)B(SO4)] (2-4)- are prepared, characterized and their DNA binding and cleavage properties studied (B: kanamycin A, 2; 2,2'-bipyridine, 3; 1,10-phenanthroline, 4). IR spectral data suggest a square pyramidal (4 + 1) geometry for the one-electron paramagnetic ternary complexes with the sulfate bound to copper. The complexes are non-conducting in DMF but show conductivity in aqueous medium due to dissociation of the sulfate ligand. They bind to calf thymus DNA in the minor groove giving the relative order: 4 > 2 > 1 approximately 3 (Kapp= 5.4 x 10(5) M(-1) for 4). The precursor complex 1 does not show any apparent chemical nuclease activity when treated with supercoiled (SC) DNA in the presence of 3-mercaptopropionic acid (MPA). The kanamycin A and phen adducts as such or generated under in situ reaction conditions using 1 nd the ligand display efficient chemical nuclease activity in the presence of MPA, while the bpy species shows poor cleavage activity. The ternary kanamycin A complex presents the first synthetic model for three functional domains of bleomycins.     

Synthetic studies towards complex diterpenoids—VII : Stereoselective synthesis and conformational analysis of all four possible racemates of 1,2,3,4,4a,9a-hexadydro-1-methylfluorene-1-carboxylic acids

Synthesis of the unsaturated acid 3 through H₂SO_4? catalysed cyclodehydration of the keto-ester 1 and its conversion to lactone 4 are described. The PPA induced cyclization of the keto-acid 9, on the other hand resulted in a stereoisomeric mixture of the octahydroanthracene derivatives 10a and 10b. The four possible racemates of the hydrofluorene derivatives 5, 6, 7, and 8 have been synthesized by chemical and catalytic reduction of 3 and 4. Li-liquid ammonia induced reductive cleavage of the lactone 4 proceeds with 65% retention and 35% inversion of configuration at the benzylic C-4a asymmetric centre to afford the trans and cis acids 5 and 8 respectively, while catalytic hydrogenolysis of 4 proceeds with inversion to give the cis acid 8. Li-liquid ammonia reduction of 3 gives trans acid 6 and cis7 in 23% and 53% yields respectively, whereas catalytic hydrogenation of 3 affords 81% of cis acid 8 and 13% of cis acid 7. Some conformational properties of the methyl esters 17, 18, 19, and 20 have been deduced from chemical and NMR spectral data.     

Competitive fluorescence polarization assays for the detection of phosphoinositide kinase and phosphatase activity

We describe the development and implementation of competitive fluorescence polarization (FP) based assays for determining activity of phosphoinositide 3-kinase (PI 3-K) and the type-II SH2-domain-containing inositol 5-phosphatase (SHIP2). These assays are based on the interaction of specific phosphoinositide binding proteins with fluorophore-labeled phosphoinositide and inositol phosphate tracers. Enzyme reaction products are detected by their ability to compete with the fluorescent tracers for protein binding, leading to an increase in the amount of free tracer and a decrease in polarization (mP) values. A variety of fluorophore-labeled tracers were evaluated, and assay sensitivity and specificity for products of PI 3-K and SHIP2 activity was determined. Assay performance was evaluated using recombinant PI 3-Kalpha and SHIP2 with diC(8)-PI(4,5)P(2) and diC(8)-PI(3,4,5)P(3) as respective substrates. IC(50) values for previously characterized PI 3-K inhibitors were within expected ranges. These assays are homogeneous, sensitive, and rapid, and suitable for HTS applications, and will facilitate screening for novel inhibitors of phosphoinositide kinases and phosphatases in drug development.     

Ferrocene-conjugated copper(II) dipyridophenazine complex as a multifunctional model nuclease showing DNA cleavage in red light

The copper(II) complex [Cu(L)(dppz)](ClO₄)₂ (1) having a tripodal ligand ferrocenylmethylbis(2-pyridylmethylamine) (L) with a pendant ferrocenyl unit and a planar NN-donor dipyrido-[3,2-a:2′,3′-c]-phenazine (dppz) base is prepared and its DNA binding and cleavage properties studied. The complex is redox active showing cyclic voltammetric responses at 0.52 and –0.01 V vs. SCE due to Fe(III)/Fe(II) and Cu(II)/Cu(I) couples, respectively. The complex that binds to the major groove of DNA shows dual chemical nuclease activity involving both the metal centres. The complex displays efficient photo-induced DNA cleavage activity in visible laser light of 458 and 568 nm wavelengths forming cleavage active hydroxyl radicals. Significant DNA cleavage is also observed in red light of 647 nm within the photodynamic therapy (PDT) window.     

Generating inherent structures of liquids: comparison of local minimization algorithms

Properties of minima obtained by two different local minimization algorithms, the conjugate gradient and the limited-memory Broyden-Fletcher-Goldfarb-Shanno, are compared for a liquid whose particles interact via a modified Lennard-Jones pair interaction. The average properties of inherent structures obtained by the two minimization procedures are shown to agree within statistical error, though for a given starting configuration the two algorithms may not quench to identical minima.     

Spectrophotometric determination of zinc at trace level in environmental samples

Summary Zinc is selectively extracted with N-hydroxy-N,N-diphenylbenzamidine and spectrophotometrically determined with 4-(2-pyridylazo)resorcinol. The molar absorptivity is 9.4×10⁴l·mol^–1 cm^–1. Relative standard deviation is ±1.5%.     

Relationship between crystalline order and melting mechanisms of solids

The mechanism for homogeneous nucleation of the liquid phase in Lennard-Jones solids is studied by combining the Landau free energy approach with some of the methodology developed to characterise transition path ensembles. The second-order bond orientational order parameter, Q ₆ which indexes the overall degree of crystalline order, is shown to provide a dynamically significant collective coordinate describing the melting process. Trajectories generated from configurations sampled in the vicinity of the maximum in the Landau free energy curve, F(Q ₆), are shown to have equal likelihood of teminating in either the solid or liquid-like free energy minima. It is also demonstrated that Q ₆ is necessary but not sufficient as a dynamical coordinate to describe melting and it is necessary to explore possiblities for additional coordinates which are critical for initiating melting. Our sudy suggests that the additional coordinates for describing the melting process would be some type of localised defect, much smaller in spatial extent than the size of the critical nucleus predicted by classical nucleation theory.      

Photon transport in thin disordered slabs

We examine using Monte Carlo simulations, photon transport in optically ‘thin’ slabs whose thickness L is only a few times the transport mean free path l*, with particles of different scattering anisotropies. The confined geometry causes an auto-selection of only photons with looping paths to remain within the slab. The results of the Monte Carlo simulations are borne out by our analytical treatment that incorporates directional persistence by the use of the Ornstein-Uhlenbeck process, which interpolates between the short time ballistic and long time diffusive regimes.     

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

Obliquely propagating altra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic field and dustmagnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role.