A robust nanocontainer based on a pure organic free radical

A new pure organic paramagnetic porous molecular material, which combines hydrophilic windows with large hydrophobic nanocontainers, is shown to be stable even in absence of solvent guest molecules.     

On speciality of bernstein jordan algebras *

The problem of speciality for Bernstein Jordan algebras is considered. Two examples of exceptional Bernstein Jordan algebras with special nucleus are constructed. The examples correspond to two different types of exceptional Jordan algebras: the first one is i-exceptional, and the second one is i-special.     

Chiral crystalline hosts derived from lactic acid.* X-ray crystal structures of optically resolved and racemic host compound 1,1-diphenyl-1,2-propanediol and a 2:1 complex between optically resolved host and 3-picoline

Abstract

The X-ray crystal structures of racemic (1) and S-1,1-diphenyl-1,2-propanediol (2), and of a 2:1 inclusion complex (3) of 2 with 3-picoline are reported. Three different binding schemes characterize the packing of these structures. Only one of the two hydroxy groups (that which is not related to the asymmetric carbon) is involved in O-H…O hydrogen bonds responsible for the formation of dimers and chains in 1 and 2, leaving the other OH group for stabilization of dimers through OH…phenyl interactions in 1 or free of interactions in 2. In the crystal structure of the chiral complex 3, the hydroxy groups link the two independent host molecules, A and B, the 3-picoline guest to the B host molecule, and a remaining one forms H-bonded chains along the c axis.     

Synthesis of polyhydroxycyclohexanes and relatives from (-)-quinic acid

An efficient and versatile strategy for the synthesis of polyhydroxycyclohexanes and related compounds 3-6 is reported. The successful synthesis of these analogues has been achieved from a common intermediate, quinic acid derived lactone 2, rapidly accessible from cheap and commercially available (-)-quinic acid (1) as a chiral template. A practical route involving stereocontrolled epoxide formation and hydrolysis has been developed for the synthesis of 2,3-trans analogues 3 and 4. The preparation of the 2,3-cis analogues 5 and 6 has been realized by diasteroselective oxidation of a 5,6-double bond.     

Solvent tuning from normal to inverted marcus region of intramolecular electron transfer in ferrocene-based organic radicals

The solvent dependence of spectroscopic data of two neutral paramagnetic donor-acceptor dyads, based on a polychlorinated triphenylmethyl radical acceptor unit linked through a vinylene pi-bridge to a ferrocene (compound 1) or a nonamethylferrocene donor (compound 2) unit, is described. Both compounds exhibit broad absorptions in the near-IR region, with band maxima appearing around 1000 and 1500 nm for 1 and 2, respectively. These bands correspond to the excitation of a neutral DA ground state to the charge-separated D+A- state, indicative of an intramolecular electron-transfer process. Compounds 1 and 2 show two reversible one-electron redox processes associated with the oxidation of the ferrocene and the reduction of the polychlorotriphenylmethyl radical subunits. The solvent dependence of the redox potentials was also investigated, allowing the determination of the redox asymmetries DeltaG degrees of both dyads. The latter values, along with the experimental Eopt spectroscopic data, allow us to estimate, using the total energy balance Eopt = lambda + DeltaG degrees , the reorganization energy values, lambda, and their solvent polarity dependence. Since DeltaG degrees and lambda are of the same order of magnitude but exhibit opposite trends in their solvent polarity dependence, a unique shift from the normal to the inverted Marcus region with the change in solvent polarity is found. The kinetics of the charge recombination step of the excited charge-separated D+A- state was studied by picosecond transient absorption spectroscopy, which allows us to observe and monitor for the first time the charge-separated D+A- state, thereby confirming unambiguously the photoinduced electron-transfer phenomena.     

The conformational rigidity of butane-1,2-diacetals as a powerful synthetic tool

Butane-1,2-diacetals are selective protecting groups for trans-diequatorial-1,2-diols and have been widely used in carbohydrate chemistry. The scope of diacetal protection has been extended more recently to include other important hydroxylated chiral templates containing trans-1,2-diols, such as quinic and shikimic acids, the protection of which as diacetals leads to a strong conformational rigidity that induces excellent diastereoselectivity control. In addition, the chiral information stored in the diacetal backbone has also been exploited in the synthesis of important building blocks, such as glycerate, glycolate and tartrate diacetal derivatives. In this critical review, the synthetic power of the conformational rigidity and the chirality stored in the diacetal backbone is described. This phenomenon will be illustrated with recent examples of applications in the synthesis of natural products or biologically interesting compounds (80 references).     

Imprinted nanoporous organosilicas for selective adsorption of nitroenergetic targets

Periodic mesoporous organosilicas incorporating diethylbenzene bridges in their pore walls were applied for the adsorption of nitroenegetic targets from aqueous solution. The materials were synthesized by co-condensing 1,4-bis(trimethoxysilylethyl)benzene (DEB) with 1,2-bis(trimethoxysilyl)ethane to improve structural characteristics. Molecular imprinting of the pore surfaces was employed through the use of a novel target-like surfactant to further enhance selectivity for targets of interest (tri- and dinitrotoluenes) over targets of similar structure ( p-cresol and p-nitrophenol). The headgroup of the commonly used alkylene oxide surfactant Brij76 was modified by esterification with 3,5-dinitrobenzoyl chloride. This provided a target analogue which was readily miscible with the Brij76 surfactant micelles used to direct material mesopore structures. The impact of variations in precursor ratios and amounts of imprint molecule was evaluated. The use of 12.5% of the modified Brij surfactant with a co-condensate employing 30% DEB was found to provide the best compromise between total capacity and selectivity for nitroenergetic targets.