Stereospecific interactions between dinuclear complex cations involving square-planar [Pt(II)(μ-S)2(bpy)] (bpy = 2,2′-bipyridine) frameworks derived from optically active octahedral Co(III) units with d- or l-penicillaminates

The reaction of the octahedral mononuclear complex, trans(N)-[Co(l-pen-N,O,S)₂]⁻ (pen = penicillaminate), with [PtCl₂(bpy)] (bpy = 2,2′-bipyridine) stereoselectively gave an optically active S-bridged dinuclear complex, [Pt(bpy){Co(l-pen)₂}]Cl · 3H₂O (2Cl · 3H₂O), whose structure is enantiomeric to the previously reported [Pt(bpy){Co(d-pen)₂}]Cl · 3H₂O (1Cl · 3H₂O). The mixture of equimolar amounts of 1Cl · 3H₂O and 2Cl · 3H₂O in H₂O crystallizes as [Pt(bpy){Co(d-pen)₂}]_0.5[Pt(bpy){Co(l-pen)₂}]_0.5Cl · 7H₂O (3Cl · 7H₂O), in which the enantiomeric complex cations 1 and 2 are included in the ratio of 1:1. The crystal structures of 2Cl · 3H₂O and 3Cl · 7H₂O were determined by X-ray crystallography, and compared with that of 1Cl · 3H₂O. The structural feature for 2 is essentially consistent with that for 1, except for the absolute configurations around the octahedral Co(III) center. The optically active complex cation 2 exists as a monomer, accompanied by no intermolecular interactions in the π-electronic systems of bpy moieties. In the crystals of 3Cl · 7H₂O, on the other hand, the enantiomeric complex cations, [Pt(bpy){Co(d-pen)₂}]⁺ and [Pt(bpy){Co(l-pen)₂}]⁺, are arranged alternately while overlapping the bpy planes along a axis, and the π electronic system of the bpy framework in [Pt(bpy){Co(d-pen)₂}]⁺ interacts with those in [Pt(bpy){Co(l-pen)₂}]⁺. Differences between the crystal structures of 2Cl · 3H₂O and3Cl · 7H₂O significantly reflect their diffuse reflectance spectra. In aqueous solution, each cation in both 2Cl · 3H₂O and 3Cl · 7H₂O is comparatively put on a free environment without such intermolecular interactions.     

New cationic palladium(II) compounds with several bidentate nitrogen-donor ligands: Synthesis, spectroscopic analyses and X-ray crystal structure

A series of PdN₄core complexes has been synthesised. Reaction of [PdCl₂(CH₃CN)₂] with N-alkylaminopyrazole (NN′) ligands, 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[2-(ⁱpropylamino)ethyl]-3,5-dimethylpyrazole (deai), and 1-[2-(^tbutylamino)ethyl]-3,5-dimethylpyrazole (deat) in the presence of AgBF₄ led to [Pd(NN′)₂](BF₄)₂. These palladium(II) compounds were characterised by elemental analyses, conductivity measurements, IR, ¹H and ¹³C{¹H} NMR spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed. The X-ray analyses of one representative complex, [Pd(deat)₂](BF₄)₂, is reported. The crystal structure consists of discrete centrosymmetric cations involving a coordinated Pd(N_pz)₂(N_amino)₂core with planar geometry and anions.     

Ruthenium(II) mixed-ligand complexes containing 2-(6-methyl-3-chromonyl)imidazo[4,5-f][1,10]-phenanthroline: Synthesis, DNA-binding and photocleavage studies

Two novel Ru(II) complexes [Ru(bpy)₂(MCMIP)]²⁺ (1) and [Ru(phen)₂(MCMIP)]²⁺ (2) (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline; MCMIP = 2-(6-methyl-3-chromonyl)imidazo[4,5-f][1,10]-phenanthroline) have been synthesized and characterized by elemental analysis, mass spectra and ¹H NMR. The DNA-binding properties of the complexes were investigated by absorption, emission, melting temperature and viscosity measurements. Experimental results indicate that the two complexes can intercalate into DNA base pairs. Upon irradiation at 365 nm, two Ru(II) complexes were found to promote the cleavage of plasmid pBR 322 DNA from supercoiled form I to nicked form II, and the mechanisms for DNA cleavage by the complexes were also investigated.     

Two new end-to-end single dicyanamide bridged Cu(II) complexes with Schiff base ligands: Structural, electrochemical and magnetic properties

The synthesis, crystal structures and magnetic properties of two different copper(II) complexes of formula [Cu(L¹)(dca)]_n · nClO₄ (1) and [Cu(L²)]₂(dca)(ClO₄) (2) [L¹ = N,N-dimethylethylene-N′-(pyridine-2-carbaldiiminato), HL² = N,N-dimethylethylene-N′-salicylaldiiminato, dca = dicyanamide anion] are described. Spectroscopic and electrochemical properties have also been discussed. A one-dimensional chain structure with single, symmetrical, μ_1,5-dca bridges is found in compound 1. The copper atom in 1 has a square pyramidal geometry. A tridentate Schiff base ligand, having NNN donor sites, and one nitrogen atom from dca occupy the basal plane. N(18) of a neighbouring unit occupies the apical site. The Schiff base used in compound 2 is a tridentate anion with NNO donor sites, which changes the structure in a dinuclear unit of copper atoms bridged by single end-to-end dicyanamide ion. The environment around copper in 2 is square planar. Magnetic susceptibility measurements for 1 and 2 reveal the occurrence of weak antiferromagnetic interaction through the dca ligand.     

A new tyrosinase model with 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene: Binuclear copper(I) and phenoxo/hydroxo-bridged dicopper(II) complexes

The ligand 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene (baib) reacts with [Cu(MeCN)₄][ClO₄] to form a binuclear copper(I) complex . Crystal structure analysis reveals that the distorted tetrahedral coordination of each copper(I) center is satisfied by one bidentate arm of each ligand. The complex undergoes ready aromatic ring hydroxylation at position 2 of the phenyl ring when reacted with molecular oxygen in MeCN/MeOH/CH₂Cl₂, producing a four-coordinate μ-phenoxo- and μ-hydroxo-bridged dicopper(II) complex, [Cu₂(baib-O)(OH)(OClO₃)₂] · 1.5H₂O (2) (baib-OH: 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol). This reaction mimics the reactivity of the copper monooxygenase tyrosinase. A trend is observed for the extent of aromatic ring hydroxylation (25 °C): MeCN > MeOH > CH₂Cl₂. Cyclic voltammetric experiment of 1 in MeCN reveals an appreciably high redox potential (anodic peak potential, E_pa = 0.69 V versus SCE) for the redox process. Complex 2 has been characterized by single-crystal X-ray crystallography. Variable temperature (60-300 K) magnetic susceptibility measurements on 2 establish that the copper(II) centers in 2 are antiferromagnetically coupled (2J = −280 cm⁻¹).     

Genetic transformation of peanut (Arachis hypogaea L.) using cotyledonary node as explant and a promoterlessgus::nptII fusion gene based vector

We have generated putative promoter tagged transgenic lines inArachis hypogaea cv JL-24 using cotyledonary node (CN) as an explant and a promoterless gus::nptII bifunctional fusion gene mediated byAgrobacterium transformation. MS medium fortified with 6-benzylaminopurine (BAP) at 4 mg/l in combination with 0.1 mg/l α-napthaleneacetic acid (NAA) was the most effective out of the various BAP and NAA combinations tested in multiple shoot bud formation. Parameters enhancing genetic transformation viz. seedling age,Agrobacterium genetic background and co-cultivation periods were studied by using the binary vector p35SGUSINT. Genetic transformation with CN explants from 6-day-old seedlings co-cultivated withAgrobacterium GV2260 strain for 3 days resulted in high kanamycin resistant shoot induction percentage (45%); approximately 31% transformation frequency was achieved with p35S GUSINT in Β-glucuronidase (GUS) assays. Among thein vivo GUS fusions studied with promoterless gus::nptII construct, GUS-positive sectors occupied 38% of the total transient GUS percentage. We have generated over 141 putative T₀ plants by using the promoterless construct and transferred them to the field. Among these, 82 plants survived well in the green house and 5 plants corresponding to 3.54% showed stable integration of the fusion gene as evidenced by GUS, polymerase chain reaction (PCR) and Southern blot analyses. Twenty-four plants were positive for GUS showing either tissue-specific expression or blue spots in at least one plant part. The progeny of 15 T₀ plants indicated Mendelian inheritance pattern of segregation for single-copy integration. The tissue-specific GUS expression patterns were more or less similar in both T₀ and corresponding T₁ progeny plants. We present the differential patterns of GUS expression identified in the putative promoter-tagged transgenic lines in the present communication.     

Structure and dynamics of the N-terminal loop of PsbQ from photosystem II of Spinacia oleracea

Infrared and Raman spectroscopy were applied to identify restraints for the structure determination of the 20 amino acid loop between two beta-sheets of the N-terminal region of the PsbQ protein of the oxygen evolving complex of photosystem II from Spinacia oleracea by restraint-based homology modeling. One of the initial models has shown a stable fold of the loop in a 20 ns molecular dynamics simulation that is in accordance with spectroscopic data. Cleavage of the first 12 amino acids leads to a permanent drift in the root means square deviation of the protein backbone and induces major structural changes.     

Caldesmon restricts the movement of both C- and N-termini of tropomyosin on F-actin in ghost fibers during the actomyosin ATPase cycle

New data on the movements of tropomyosin singly labeled at alpha- or beta-chain during the ATP hydrolysis cycle in reconstituted ghost fibers have been obtained by using the polarized fluorescence technique which allowed us following the azimuthal movements of tropomyosin on actin filaments. Pronounced structural changes in tropomyosin evoked by myosin heads suggested the "rolling" of the tropomyosin molecule on F-actin surface during the ATP hydrolysis cycle. The movements of actin-bound tropomyosin correlated to the strength of S1 to actin binding. Weak binding of myosin to actin led to an increase in the affinity of the tropomyosin N-terminus to actin with simultaneous decrease in the affinity of the C-terminus. On the contrary, strong binding of myosin to actin resulted in the opposite changes of the affinity to actin of both ends of the tropomyosin molecule. Caldesmon inhibited the "rolling" of tropomyosin on the surface of the thin filament during the ATP hydrolysis cycle, drastically decreased the affinity of the whole tropomyosin molecule to actin, and "freezed" tropomyosin in the position characteristic of the weak binding of myosin to actin.     

Highly functionalized glyco-conjugated hexahydroazepindiones from saccharide imides via the Norrish type II reaction

Starting from readily available protected 6-tosylates of D-glucose and D-mannose in both their pyranoside and furanoside forms as well as 6-tosylates of alpha-D-galactopyranose, the corresponding primary succinimido derivatives were obtained in good yield by nucleophilic displacement with potassium succinimide. These imido sugars were photochemically transformed into hexahydroazepindione derivatives such as by means of a Norrish type II reaction. As expected, the intramolecular alkylation proceeded via an 1,6 H-abstraction leading to a stabilized diradical. The regiochemistry of the photoreaction was controlled by configurational, conformational and electronic features and was sometimes influenced by the protecting groups. Using this route, a facile approach to a novel class of highly functionalized sugar derived heterocycles was developed.