Structure of a diruthenium(II,III) complex with benzamidato bridging ligands

The compound Ru₂Cl(C₆H₅CONH)₄ has now been obtained in crystalline form and the crystal and molecular structure determined by X-ray met     

Multivariate analysis of time-resolved mass spectral data

Multvariate analysis of time-resolved pyrolysis/mass spectrometric data is described. The approach is based on the variance diagram (VARDIA), a recently developed technique that quantifies the clustering of variables in two-dimensional factor analysis (sub)-spaces in a rotational scanning procedure. A maximum in the VARDIA plot indicates a correlated behavior of the mass variables, indicating a common origin. This common origin is generally caused by a change in the concentration of a chemical component. With this information the “factor spectrum” and the scores of the component can be retrieved. For time-resolved serial data, consideration of the clustering behavior of the variables as a function of time is more appropriate than a rotational scanning procedure. Adaptation of the VARDIA for serial data, such as time-resolved data, is described. This approach has the advantage that all the factors can be used. It will be shown that the resolution of the obtained curve than the total ion current curve as a function of time. Examples will be given for time-resolved data of coal, rubber and wood samples.     

Metal-assisted red light-induced DNA cleavage by ternary L-methionine copper(II) complexes of planar heterocyclic bases

Ternary copper(II) complexes [Cu(l-met)B(Solv)](ClO4) (1-4), where B is a N,N-donor heterocyclic base like 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 3) and dipyrido[3,2-a:2'],3'-c]phenazene (dppz, 4), are prepared and their DNA binding and photo-induced DNA cleavage activity studied (L-Hmet =L-methionine). Complex 2, structurally characterized by X-ray crystallography, shows a square pyramidal (4 + 1) coordination geometry in which the N,O-donor L-methionine and N,N-donor heterocyclic base bind at the basal plane and a solvent molecule is coordinated at the axial site. The complexes display a d-d band at approximately 600 nm in DMF and exhibit a cyclic voltammetric response due to the Cu(II)/Cu(I) couple near -0.1 V in DMF-Tris-HCl buffer. The complexes display significant binding propensity to the calf thymus DNA in the order: 4(dppz) > 3(dpq) > 2(phen> 1(bpy). Control cleavage experiments using pUC19 supercoiled DNA and distamycin suggest major groove binding for the dppz and minor groove binding for the other complexes. Complexes 2-4 show efficient DNA cleavage activity on UV (365 nm) or red light (632.8 nm) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The DNA cleavage activity of the dpq complex is found to be significantly more than its dppz and phen analogues.     

Synthesis,characterization and cyclic voltammetric studies of monopicolinate complexes of ruthenium(II)

Summary Two stable monopicolinate complexes of ruthenium(II), [Ru(bipy)₂(pic)]ClO₄ and [Ru(pap)₂(pic)]ClO₄ [bipy = 2,2-bipyridine, pic = picolinate anion, pap = 2-(phenylazo)-pyridine], were prepared and characterized. The complexes are diamagnetic and behave as 1:1 electrolytes in MeCN solution. In the i.r. spectra, they show characteristic vibrations of bipy or pap, pic and ClO _inf4 ^p– . In MeCN solution, both complexes display three intense absorption bands in the visible region, which have been assigned to metal-to-ligand charge-transfer transitions. Each complex shows a reversible ruthenium(II)-ruthenium(III) oxidation in MeCN, the formal potential (E _inf298 ^p0 ) being 0.75 V versus a saturated calomel reference electrode (SCE) for [Ru-(bipy)₂(pic)]⁺ and 1.44 V versus SCE for [Ru(pap)₂(pic)]⁺. Multiple reductions of the coordinated bipy and pap ligands have also been observed.Author to whom all correspondence should be directed.     

Steric protection of a photosensitizer in a N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine-copper(II) bowl that enhances red light-induced DNA cleavage activity

Ternary copper(II) complexes [Cu(py2phe)B](ClO4)2 (1-3), where py2phe is a tripodal ligand N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine and B is a heterocyclic base (viz., 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 2), or dipyrido[3,2-a:2',3'-c]phenazine (dppz, 3)), are prepared and their DNA-binding and photoinduced DNA-cleavage activities are studied. Complex 1 has been structurally characterized by single crystal X-ray crystallography. The molecular structure shows an axially elongated square-pyramidal (4 + 1) coordination geometry in which the phen ligand binds at the basal plane. The tripodal ligand py2phe displays an axial-equatorial binding mode with the amine nitrogen bonded at the axial site. A chemically significant CH-pi interaction involving the CH moiety of the phenyl group of the tripodal ligand and the aromatic ring of phen is observed. The complexes display good binding propensity to calf thymus DNA giving a relative order of 3 (dppz) > 2 (dpq) > 1 (phen). The DNA binding constants (K(b)) for 1-3, determined from absorption spectral studies, are 6.2 x 10(3), 1.0 x 10(4), and 5.7 x 10(4) M(-1), respectively. The complexes show chemical nuclease activity in the presence of 3-mercaptopropionic acid as a reducing agent forming hydroxyl radicals as the cleavage active species. The photoinduced DNA-cleavage activity of the complexes has been studied using UV radiation of 365 nm and red light of 632.8 and 694 nm. The phen complex in absence of any photosensitizing moiety does not show any DNA cleavage upon photoirradiation. The dpq and dppz ligands with their photoactive quinoxaline and phenazine moieties display significant photoinduced DNA-cleavage activity. The dppz complex is more active than its dpq analogue because of the better steric protection of the DNA-bound photosensitizing dppz ligand from the solvent molecules. Control experiments reveal the formation of singlet oxygen in the light-induced DNA-cleavage reactions. The observed efficient photoinduced DNA-cleavage activity of 2 and 3 is akin to the "light switch" effect known for the tris-chelates of ruthenium(II).     

Polymerization of N-vinylcarbazole by chlorides and oxychlorides of some group V elements. II. Kinetics and mechanism of the polymerization initiated by arsenic trichloride

The polymerization of N-vinylcarbazole (NVC) initiated by AsCl₃ in benzene and nitrobenzene solvents was studied at 33°C. R_p is proportional to the first power of the initiator concentration. R_p varies in a first-order manner with NVC concentration up to a certain optimum concentration of the latter, after which it falls and ultimately levels off. The rate and the molecular weight are depressed by the addition of various amines, preformed poly-NVC, and water. HCl does not have any cocatalytic effect on the system. Rate and the molecular weight are increased in nitrobenzene. The degree of polymerization stays independent of the initiator and NVC concentration and also of increasing conversion. These results suggest a conventional cationic mechanism, and overrule the possibility of a cation radical initiation. A suitable kinetic scheme has been proposed in conformity with the findings.