Diphenylmethane transformations over boron trifluoride modified alumina and silica-alumina

Transformations of diphenylmethane were investigated in a flow system in the presence of alumina and silica-alumina modified with boron trifluoride at atmospheric pressure and elevated temperatures. Hydrogen transfer reaction was observed on addition of tetralin to the substrate stream. This revised version was published online in August 2006 with corrections to the Cover Date.     

9,11-DIcis-12-FLUORORHODOPSIN. CHROMOPHORE PROPERTIES FROM 19F-NMR STUDIES

From a 19F-NMR study of 9,11-dicis-12-fluororhodopsin and its photobleached product, we concluded that the initially formed chromophore retained its configuration and the photoproduct corresponded to the two-bond isomerized all-trans. Upon standing, it slowly isomerized to the 9-cis isomer. The method represents a direct, non-destructive procedure for determining configuration purity of the pigment formed. Its unique fluorine opsin shift value is consistent with the expected different orientation of the fluoro-substituent in a dicis pigment.     

Quantification of lithium at ppm level in geological samples using nuclear reaction analysis

Journal of Radioanalytical and Nuclear Chemistry - Proton-induced reaction (p,α) is one type of nuclear reaction analysis (NRA) suitable especially for light element quantification....     

A two‐step reaction scheme leading to singlet carbene species that can be detected under matrix conditions for the reaction of Zr(3F) with either CH3F or CH3CN

The results obtained from CASSCF‐MRMP2 calculations are used to rationalize the singlet complexes detected under matrix‐isolation conditions for the reactions of laser‐ablated Zr(³F) atoms with the CH₃F and CH₃CN molecules, without invoking intersystem crossings between electronic states with different multiplicities. The reaction Zr(³F) + CH₃F evolves to the radical products ZrF· + ·CH₃. This radical asymptote is degenerate to that emerging from the singlet channel of the reactants Zr(¹D) + CH₃F because they both exhibit the same electronic configuration in the metal fragment. Hence, the caged radicals obtained under cryogenic‐matrix conditions can recombine through triplet and singlet paths. The recombination of the radical species along the low‐multiplicity channel produces the inserted structures H₃C? Zr? F and H₂C?ZrHF experimentally detected. For the Zr(³F) + CH₃CN reaction, a similar two‐step reaction scheme involving the radical fragments ZrNC· + ·CH₃ explains the presence of the singlet complexes H₃C? Zr? NC and H₂C?Zr(H)NC revealed in the IR‐matrix spectra upon UV irradiation. © 2014 Wiley Periodicals, Inc.     

Poly(4-vinylpyridine) catalyzed hydrolysis of methyl bromide to methanol and dimethyl ether

The hydrolysis of methyl bromide with neutral water is performed in the presence and absence of various amines in a batch reactor at different temperatures (50–125 °C). Screening of poly(4-vinylpyridine) as a potential reusable solid amine catalyst showed maximum efficiency. This significant enhancement in efficiency is due to the capture of HBr by solid PVP and remains phase-separated driving the reaction forward. The major advantage of this process is that the polymer can be easily regenerated and reused without loss of activity making it a very effective catalyst for the conversion of methyl halides to methanol and dimethyl ether.     

A simple and efficient approach to the synthesis of β-N-methylamino-l-alanine (BMAA)

A novel, efficient, and straightforward synthesis of β-N-methylamino-l-alanine (BMAA) in two steps starting from l-N,N-dibenzylserine benzyl ester is described. This method, in the light of other syntheses of BMAA, provides benefits such as mild reaction conditions, a simple work-up procedure, good yields, and the retention of the serine stereochemistry.     

ANALYZING THE RED-SHIFT CHARACTERISTICS OF AZULENIC,NAPHTHYL, OTHER RING-FUSED AND RETINYL PIGMENT ANALOGS OF BACTERIORHODOPSIN*

Prompted by the near infrared-absorbing properties of some of the azulenic bacteriorhodopsin (bR) analogs, we have analyzed their absorption characteristics along with 11 new related ring-fused analogs and the corresponding Schiff bases (SB) and protonated Schiff bases (PSB). The following three factors are believed to contribute to the total red shift of each of the pigment analogs (α_RS): perturbation of the basic chromophore (SB shift, ΔSB), protonation of the SB (PSB shift, PSBS) and protein perturbation (the opsin shift, OS). For each factor, effects of structural modifications were examined. For the red-shifted pigments, percent OS has been suggested as an alternate way of measuring protein perturbation. Computer-simulated chromophores provided evidence against any explanation involving altered shapes of the binding pocket as a major cause for absorption differences. Implications of the current bR results on preparation of further red-shifted bR and possible application to visual pigment analogs are discussed.     

Simultaneous stochastic effects of a thermal reservoir and an electromagnetic field on the optical susceptibility of a two-level system

In this paper we derive analytical expressions for the optical susceptibility of a two-level system immersed in a thermal bath and interacting with an external electromagnetic field, where both of them are considered as noise sources. The dynamics of the system is described by a set of optical stochastic Bloch equations. The noise sources are modeled as Ornstein-Uhlenbeck processes. The optical stochastic Bloch equations are perturbatively solved up to second order in the external field. We found that each noise affects the dynamics in a different manner. Thus, at first order, the bath modifies the transverse relaxation time, whereas the effect of a random field can only be appreciated if the expansion is calculated up to second order, where correlations begin to be important.     

Progress in natural polymer engineered biomaterials for transdermal drug delivery systems

The route of a specific drug carrier system is always a significant platform of development that combines the principles of biomedical technology, nanotechnology, and pharmaceutical drug design. Transdermal (TD) drug delivery involves the release of the drug via the stratum corneum of the tissue membrane into the sustained release by diffusion across the epidermal layer. This method (often known as topical drug delivery) has increased noteworthy research enthusiasm in the course of recent decades due to its relatively simpler and non-invasive administration. Over the past few decades, considerable advancement was achieved in TD delivery and a number of drugs are now successfully reported. In this review, we focus on the progress regarding applications of important biopolymers described for the TD drug release applications and related aspects. Three mostly reported plant and animal-derived polymers (such as natural rubber, chitosan, and cellulose for the development of TD carrier system) were extensively analyzed. The general principle of TD drug delivery, advantages, and limitations of the works reported were also discussed.     

Oxygenation of aromatic substrates over Pd(II) catalysts bearing bis(pyrazol-1-yl)alkanes ligands

Summary Liquid phase oxygenation of 1-tetralin, ethylbenzene, cyclohexane and toluene is describe using four catalyst precursors such as: (CH₂)n(PzR)PdCl₂ (n=1,2; R=H, Me) at T=100°C, P_air= 5.4 atm, substrate/catalyst ratio=100 for 3 h,. It was observed that the type of alkyl bridge between the pyrazolyl ligands has an effect on the catalytic activity.