Completing extended metric spaces: An alternative approach

This paper proves the completion of extended metric spaces using the concept of $\epsilon$-approach nearness spaces, in terms of clusters that are a generalization of Cauchy sequences.     

Endoperoxide synthesis by photocatalytic aerobic [2 + 2 + 2] cycloadditions

Structurally novel endoperoxides can be sythesized by the photocatalytic cyclotrimerization of bis(styrene) substrates with molecular oxygen. The optimal catalyst for this process is Ru(bpz)(3)(2+), which is a markedly more efficient catalyst for these photooxygention reactions than conventional organic photosensitizers. The 1,2-dioxolane products are amenable to synthetic manipulation and can be easily processed to 1,4-diols and γ-hydroxyketones. An initial screen of the biological activity of these compounds reveals promising inhibition of cancer cell growth.     

New perspectives for microbial glycolipid fractionation and purification processes

Microbial glycolipids produced from renewable sources are of considerable interest in light of their promising biological activities and surfactant characteristics when compared to petroleum derived surfactants. Intense research efforts are currently being made to reduce their production costs and optimize recovery as selected mixtures through downstream processes. Due to the high complexity of natural glycolipid mixtures, efficient purification techniques are also required to examine the biological mechanisms of individual species towards human systems for their application in health-related areas. This review deals with recent advances in the development of glycolipid extraction, fractionation and purification methods, with a particular focus on solid support-free liquid-liquid separation techniques including centrifugal partition chromatography (CPC) and counter-current chromatography (CCC). These techniques offer promising perspectives for the preparative or large-scale separation of glycolipids from complex crude extracts, mainly because of their flexibility in solvent system selection and applicability to a diversity of structures of any polarity.     

Synthesis of fractal light pulses by quasi-direct space-to-time pulse shaping

We demonstrated a simple diffractive method to map the self-similar structure shown in squared radial coordinate of any set of circularly symmetric fractal plates into self-similar light pulses in the corresponding temporal domain. The space-to-time mapping of the plates was carried out by means of a kinoform diffractive lens under femtosecond illumination. The spatio-temporal characteristics of the fractal pulses obtained in this way were measured by means of a spectral interferometry technique assisted by a fiber optics coupler (STARFISH). Our proposal allows synthesizing suited sequences of focused fractal femtosecond pulses potentially useful for several current applications, such as femtosecond material processing, atomic, and molecular control of chemical processes or generation of nonlinear effects.     

Orbital interactions in Fe(II)/Co(III) heterobimetallocenes: single versus double bridge

Ferrocenyl cobaltocenium hexafluorophosphate (1) and ferrocenylene cobaltocenylenium hexafluorophosphate (2) are investigated by a range of spectroscopic methods. Both compounds are diamagnetic, in contrast to an earlier report indicating a temperature-dependent paramagnetism of 2. Electronic absorption spectra of 1 and 2 are presented and fully assigned up to 50 000 cm(-1) on the basis of electronic structure (DFT) calculations and spectral comparisons with ferrocene and cobaltocenium. The lowest-energy bands, I, of both 1 and 2 correspond to metal-to-metal CT (MMCT) transitions; further intermetallocene charge-transfer bands are identified at higher energy (bands III and V). On the basis of the spectroscopic properties, a trans geometry and a twisted structure are derived for 1 and 2, respectively, in solution. Analysis of the I bands gives orbital mixing coefficients, alpha, electronic-coupling matrix elements, V(AB), and reorganization energies, lambda. Importantly, alpha and V(AB) are larger for 1 than for 2 (0.07 and 1200 cm(-1) vs 0.04 and approximately 600 cm(-1), respectively), apparently in contrast to the presence of one bridge in 1 and two bridges in 2. This result is explained in terms of the respective electronic and geometric structures. Reorganization energies are determined to be 7600 cm(-1) for 1 and 4600 cm(-1) for 2, in qualitative agreement with the analogous Fe(II)-Fe(III) compounds. The general implications of these findings with respect to the spectroscopic and electron-transfer properties of bimetallocenes are discussed.     

Unexpected photoisomerization of a pincer-type amido ligand leads to facial coordination at Pt(IV)

The divalent complex (BQA)PtMe undergoes oxidative addition with MeI to afford the octahedral complex cis-(mer-BQA)PtMe2I {(BQA)- = bis(8-quinolinyl)amide}. When this molecule is irradiated with visible light, it isomerizes to (fac-BQA)PtMe2I, where the BQA ligand adopts an unexpected facial coordination mode. The amide nitrogen in this molecule is sp3 hybridized and can be easily quarternized with HBF4, resulting in [H(fac-BQA)PtMe2I][BF4], with only minor perturbation to the coordination sphere.     

Catalytic reduction and intramolecular cyclization of haloalkynes in the presence of nickel(I) salen electrogenerated at carbon cathodes in dimethylformamide

[reaction: see text] Pentylidenecyclopentane can be conveniently prepared in up to 86% yield via the catalytic reduction of 1-iodo- or 1-bromo-5-decyne by [[2,2'-[1,2-ethanediylbis(nitrilomethylidyne)]bis[phenolato]]-N,N',O,O']nickelate(I) electrogenerated at a carbon cathode in dimethylformamide containing tetramethylammonium tetrafluoroborate. This electrosynthesis can be accomplished at potentials for which the haloalkynes are electroinactive, and it can be completed within 30 min at room temperature. Attempts to synthesize pentylidenecyclobutane and pentylidenecyclohexane from 1-halo-4-nonynes and 11-halo-5-undecynes, respectively, under similar conditions afford the carbocycles in very low yields (2% and 6%, respectively). Other products derived from the various haloalkynes are dimers, alkynes, and 1-alkenynes. Dimers (alkadiynes) arising from 1-halo-4-nonynes and 11-halo-5-undecynes are formed in yields ranging from 80% to 89%, whereas icosa-5,15-diyne (the dimer obtained from a 1-halo-5-decyne) is found in significantly lower yield (相似文献   

Synthesis and characterization of azobenzene-confined porphyrins

A versatile synthetic method has been developed to incorporate photochromic azobenzene moieties into tetraphenylporphyrin frameworks in an orthogonal fashion, positioning the phenylazo substituents above and below the plane of the macrocycle. Surprisingly, photoisomerization is completely suppressed in the resulting azobenzene-confined porphyrins.     

Further evidence of an inverted region in proton transfer within the benzophenone/substituted aniline contact radical ion pairs; importance of vibrational reorganization energy

The dynamics of proton transfer within the triplet contact radical ion pair of a variety of substituted benzophenones with N,N-diethylaniline, N,N-dimethyl-p-toluinide, and N,N-diallylaniline are examined in solvents of varying polarity. The correlation of the rate constants with driving force reveal both a normal region and an inverted region providing support for the nonadiabatic nature of proton transfer within these systems. The reorganization of both the solvent and the molecular framework are central in governing the overall reaction dynamics.     

Hydration dependent studies of highly aligned multilayer lipid membranes by neutron scattering

We investigated molecular motions on a picosecond timescale of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) model membranes as a function of hydration by using elastic and quasielastic neutron scattering. Two different hydrations corresponding to approximately nine and twelve water molecules per lipid were studied, the latter being the fully hydrated state. In our study, we focused on head group motions by using chain deuterated lipids. Information on in-plane and out-of-plane motions could be extracted by using solid supported DMPC multilayers. Our studies confirm and complete former investigations by Ko?nig et al. [J. Phys. II (France) 2, 1589 (1992)] and Rheinsta?dter et al. [Phys. Rev. Lett. 101, 248106 (2008)] who described the dynamics of lipid membranes, but did not explore the influence of hydration on the head group dynamics as presented here. From the elastic data, a clear shift of the main phase transition from the P(β) ripple phase to the L(α) liquid phase was observed. Decreasing water content moves the transition temperature to higher temperatures. The quasielastic data permit a closer investigation of the different types of head group motion of the two samples. Two different models are needed to fit the elastic incoherent structure factor and corresponding radii were calculated. The presented data show the strong influence hydration has on the head group mobility of DMPC.