Ternary Complexes in Solution: Mixed Ligand Pb(II) Complexes with 2,2′-Bipyridyl or 1,10-Phenanthroline and Some Bivalent Mercapto Acid Amides

Abstract

The stability constants of ternary Pb(II) complexes containing 2,2′-bipyridyl (Bipy) or 1,10-phenanthroline (phen) as the first ligand and N-phenyl-2-mercapto acid amide, N-(p-chloro)phenyl-2-mercapto acid amide, N-(p-tolyl)-2-mercapto acid amide, N-(p-anisyl)-2-mercapto acid amide, or N-phenyl-2-mercapto-propionamide as the second ligand were determined in 70% v/v dioxane-water medium at 30 ± 1°C and constant ionic strength (0.1 M NaClO₄) in a nitrogen atmosphere. The results give evidence that all these complexes have the same structure and therefore the binding sites of the ligands have to be the imino nitrogen and sulfur of the sulfhydryl group. The stability difference between the ternary and the binary complexes are in good agreement with this interpretation. It is of interest to note that these ternary complexes are significantly more stable than expected from statistical reasons, i.e., the difference; Δ log K_M = log K^MA _MAL - log K^M _ML is positive (except for PMP) (where A = Bipy or phen and L is the second ligand). In addition, the enhanced stability of the ternary complexes is suggested on the basis of the π-accepting qualities of the hetero aromatic N-base. The effect of the chelate ring size is discussed.     

Surface chemistry of lipid raft and amyloid Aβ (1-40) Langmuir monolayer

Lipid rafts being rich in cholesterol and sphingolipids are considered to provide ordered lipid environment in the neuronal membranes, where it is hypothesized that the cleavage of amyloid precursor protein (APP) to Aβ (1-40) and Aβ (1-42) takes place. It is highly likely that the interaction of lipid raft components like cholesterol, sphingomylein or GM1 leads to nucleation of Aβ and results in aggregation or accumulation of amyloid plaques. One has investigated surface pressure-area isotherms of the lipid raft and Aβ (1-40) Langmuir monolayer. The compression-decompression cycles and the stability of the lipid raft Langmuir monolayer are crucial parameters for the investigation of interaction of Aβ (1-40) with the lipid raft Langmuir monolayer. It was revealed that GM1 provides instability to the lipid raft Langmuir monolayer. Adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing neutral (POPC) or negatively charged phospholipid (DPPG) was examined. The adsorption isotherms revealed that the concentration of cholesterol was important for adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing POPC whereas for the lipid raft Langmuir monolayer containing DPPG:cholesterol or GM1 did not play any role. In situ UV-vis absorption spectroscopy supported the interpretation of results for the adsorption isotherms.     

Electronic structure studies of Mg0.95Mn0.05Fe2−2xTi2xO4 (0x0.8)

The electronic structure of Mg_0.95Mn_0.05Fe_2−2xTi_2xO₄ (0x0.8) compound is investigated using near edge X-ray absorption fine structure, (NEXAFS) spectroscopy measurements, carried out at O K, Fe and Ti L_3,2-edges at room temperature. The O K-edge spectra indicate that the Fe 3d orbitals have been considerably modified and a new spectral feature start dominating in the pre-edge region at higher Ti doping. The Fe 2p NEXAFS spectra exhibit a mixed valent Fe²⁺/Fe³⁺ states apart from the conversion of Fe³⁺ to Fe²⁺ with the substitution of Ti ions. The Ti L_3,2-edge spectra indicate that Ti ions remain unchanged at 4+ state. These variations in the host electronic structure due to Ti substitution are consistent with the dielectric and transport properties of the material.     

Photoluminescence of two thienylpyrrole polymers

Photoluminescence of two thienylpyrrole polymers, one containing three thiophene and one pyrrole rings in the repeat, and the other having four thiophene and one pyrrole rings in the repeat, were studied. The photoluminescence peaks were observed to shift with the change of the excitation frequencies. The shift in the peak position had a nearly linear dependence on the shift in the excitation frequency. This result showed that using different excitation frequencies optical gaps corresponding to different conjugation lengths were accessed, and, thus, the corresponding photoluminescence peaks were observed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 461–464, 1999     

Raman spectroscopic investigation of frozen and deparaffinized tissue sections of pediatric tumors: neuroblastoma and ganglioneuroma

Raman spectroscopy is a nondestructive technique that can provide information at the molecular level about the biochemicals in tissues. We have investigated the cellular regions in neuroblastoma and ganglioneuroma using Raman spectroscopy and compared their spectral characteristics with those of the corresponding normal adrenal gland. Thin sections from both the frozen and the corresponding formalin‐fixed paraffin‐processed (FFPP) tissues were studied in conjunction with the pathological examination of the tissues. Investigation of the spectral data shows that the normal adrenal gland tissues have higher levels of carotenoids, lipids, and cholesterol compared with the neuroblastoma and ganglioneuroma frozen tissues. However, in comparison with the frozen tissues, the FFPP tissues show a significant alteration of several biochemicals, including the complete removal of carotenoids, lipids, and cholesterol in the adrenal tissues. A quantitative analysis using chemometric methods of principal component analysis and discriminant function analysis of the Raman spectral data obtained from the frozen tissues show a clear‐cut classification among pathological groups with high sensitivity and specificity. We have validated the classification results of the FFPP tissues against a training set data obtained from the archived FFPP tissues of nine other patients. The validation process correctly identified and grouped the data with the training set of normal adrenal gland (>97% of the time) and neuroblastoma (100% of the time) tissues, whereas the validation was not so strong for ganglioneuroma. This study shows that Raman spectroscopy combined with chemometric methods can be successfully used to distinguish neuroblastoma and ganglioneuroma at cellular level in frozen tissue sections. This study also shows that formalin fixation and paraffinization/deparaffinization of tissues can alter their biochemical composition. Copyright © 2012 John Wiley & Sons, Ltd.     

Cobalt-Catalyzed, 2-Aminopyridine-N-Oxide-Directed C(sp2)−H Bond Functionalization with Maleimides: Facile Access to Isoindolone Spirosuccinimides

A cobalt-catalyzed, N,O-bidentate directing group-assisted C−H bond functionalization of benzamides with maleimides was developed for the facile access to isoindolone spirosuccinimides in good to excellent yields. This C−H bond activation and spirocyclization employing pyridine N-oxide as directing group provided very good substrate scope and tolerated various functional groups. Furthermore, the mechanistic investigation revealed that the C−H bond activation is the rate-determining step of this reaction.     

Lewis Acid Catalysed Chemoselective Amination of Alcohols Using Heterocyclic Thiones: An Avenue to Thiotetrazole Derivatives

Herein,a protocol for the chemoselective formation of C−N bond using Cu(OTf)₂ as catalyst has been described using heterocyclic thiones. The reaction occurs preferentially at the nitrogen centre over the sulphur atom leading to C−N bond formation. Water being the only by-product, the reaction is environmentally friendly. The reaction proceeds without any additive, ligand or inert atmosphere and shows good tolerance towards variety of alcohols and thiotetrazole derivatives. Our developed protocol could be scaled up to gram scale efficiently, which highlights the efficacy of this method and might offer potential application in synthetic industry.