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Isosbestic Points (isosbestic + point)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

ChemInform Abstract: Energy Isosbestic Points in Third-Row Transition Metal Alloys

CHEMINFORM, Issue 3 2002
Eugeny Todorov
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Spectral, kinetic, and redox properties of basic fuchsin in homogeneous aqueous and sodium dodecyl sulfate micellar media

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2003
N. Ramanathan
Effect of anionic surfactant on the optical absorption spectra and redox reaction of basic fuchsin, a cationic dye, has been studied. Increase in the absorbance of the dye band at 546 nm with sodium dodecyl sulfate (SDS) is assigned to the incorporation of the dye in the surfactant micelles with critical micellar concentration (CMC) of 7.3 × 10,3 mol dm,3. At low surfactant concentration (<5 × 10,3 mol dm,3) decrease in the absorbance of the dye band at 546 nm is attributed to the formation of a dye,surfactant complex (1:1). The environment, in terms of dielectric constant, experienced by basic fuchsin inside the surfactant micelles has been estimated. The association constant (KA) for the formation of dye,SDS complex and the binding constant (KB) for the micellization of dye are determined. Stopped-flow studies, in the premicellar region, indicated simultaneous depletion of dye absorption and formation of new band at 490 nm with a distinct isosbestic point at 520 nm and the rate constant for this region increased with increasing SDS concentration. The reaction of hydrated electron with the dye and the decay of the semireduced dye are observed to be slowed down in the presence of SDS. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 629,636, 2003 [source]

Structural, Spectroscopic, and Proton-Coupled Electron-transfer Behavior of Pyrazolyl-3,5-bis(benzimidazole)-Bridged Homo- and Heterochiral RuIIRuII, OsIIOsII, and OsIIRuII 2,2,-Bipyridine Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2010
Sujoy Baitalik
Abstract The homo- and heterobimetallic complexes [(bpy)2MII(H2pzbzim)M,II(bpy)2](ClO4)3·nH2O (1, 3, 5) and their corresponding deprotonated complexes [(bpy)2MII(pzbzim)M,II(bpy)2](ClO4)·nH2O (2, 4, 6) [where MII, M,II = Ru (1, 2) = Os (3, 4); MII = Os and M,II = Ru (3, 5); bpy = 2,2,-bipyridine; H3pzbzim = pyrazole-3,5-bis(benzimidazole)] were synthesized, separated to their heterochiral (a, ,,/,,) and homochiral (b, ,,/,,) diastereoisomers, and characterized by elemental analyses, ESI-MS, and 1H NMR spectroscopy. The X-ray structures of 1a, 3a, and 5a show the involvement of two pyridine rings of two bpy ligands in strong intramolecular nonbonded ,,, interaction. The occurrence of a C,H···, interaction between an aromatic C,H and the ,-cloud of a pyridine ring leads to strong electronic shielding of this proton (1H NMR). In all cases, the two diastereoisomers show practically no differences in their absorption spectra, redox potentials, and pK values. The large shifts in the E1/2 values to less positive potentials and substantial redshifts in the MLCT bands that occur on deprotonation of 1, 3, and 5 are energetically correlated. From the profiles of E1/2(1), (2) vs. pH over the pH range 1,12, the equilibrium constants and standard redox potentials for all the complex species in the metal oxidation states II·II, II·III, and III·III and the bridged ligand in the protonation states H2pzbzim,, Hpzbzim2,, and pzbzim3, have been evaluated. Using these values the bond dissociation free energies for the benzimidazole N,H bonds have been estimated. Spectroelectrochemical studies have been carried out for 1a, 3a, and 5a in the range 400,1100 nm. With stepwise oxidation of the metal centers replacement of MLCT bands by LMCT bands occur gradually with the observation of sharp isosbestic points. In the case of 1a, a band observed at ,max = 910 nm for the RuIIRuIII species has been ascribed to intervalence charge transfer (IVCT) transition. [source]

Coordination of nickel and copper dithiolate to 2,2,-bipyridine-based ,-conjugated polymers

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2004
Shin-ichiro Kato
Abstract ,-Conjugated polymers (Poly1,Poly3) containing a 2,2,-bipyridine (bpy) unit were subjected to coordination to nickel and copper dithiolate for the purpose of manipulating the photophysical properties. The absorption maximum peak of Poly1 [maximum wavelength (,max) = 446 nm] redshifted by 36 nm upon the coordination of bpy to NiCl2, which produced Poly1,NiCl2. A further bathochromic shift was observed in the spectrum of Poly1,mntNi [mntNi = (maleonitrile dithiolate)nickel; ,max = 499 nm] bearing the dithiolate ligand, which stemmed from the extension of the conjugated system over the nickel dithiolate moiety through the bpy unit. An increase in the [Ni]/[bpy] ratio in Poly1,mntNi rendered the original maximum peak at 446 nm smaller and the lower energy charge-transfer peak at 499 nm larger; the isosbestic points remained at 380 and 475 nm. The green fluorescence (,max = 504 nm) emitted from Poly1 markedly diminished upon the coordination of nickel dithiolate because of the effective energy transfer. The absorption maximum peak of Poly1,mntNi in chloroform at 499 nm blueshifted to 471 nm when the volume ratio of the chloroform/N,N -dimethylformamide solvent reached 10:90. The coordination of nickel dithiolate to Poly2 and Poly3 also brought about redshifts of the absorption maximum peaks of as much as 55 and 61 nm, respectively. The absorption maximum peak of Poly1,(phenyldithiolate)nickel(pdtNi) (,max = 474 nm) redshifted by 28 nm in comparison with that of Poly1, whereas the magnitude of the shift of Poly1,bis(thiophenoxide)nickel(btpNi) bearing two thiophenoxide ligands was 20 nm. Poly1,mntCu with a tetrahedral copper center was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2631,2639, 2004 [source]