Differentiation of diasteromeric α-sulfanyl-β-amino acid derivatives by electrospray ionization tandem mass spectrometry

A set of diastereomeric α-sulfanyl-β-amino acid derivatives, which are important building blocks for pharmaceuticals with potent biological activity, are studied by electrospray ionization tandem mass spectrometry. The collision induced dissociation (CID) spectra of [M+H](+), [M+NH(4)](+), [M+Na](+) and [M+Li](+) of the diastereomers were studied, among them the CID of [M+Na](+) and [M+Li](+) showed consistent differences in the relative abundance of characteristic ions that enabled distinction of the anti isomers from syn isomers. The decomposition pathways for the diagnostic ions were arrived at based on high-resolution mass spectrometry data, multiple mass spectrometry data, deuterium labeling experiments and the mass shift in accordance with the substituents located at different places. Loss of (R(1)-C(6)H(4)-CH=NH) and (Cat-NH-SO(2)R(2)) from [M+Cat](+), where Cat=Na and Li, and the product ions as a results of McLafferty rearrangement involving either >S=O or >C=O group were found to be diagnostic. The McLafferty rearrangement product ions involving >S=O group were more abundant in syn isomers while those involving >C=O group were more abundant in anti isomer. The selectivity observed in the decomposition of [M+Li](+) ions was found to be similar to that of [M+Na](+) ions, but in few cases the differences are marginal in the decomposition [M+Li](+) ions.     

Asymmetric Michael addition of malonates to enones catalyzed by nanocrystalline MgO

Highly enantioselective Michael addition of malonates to cyclic and acyclic enones has been achieved by using nanocrystalline magnesium oxide at −20 °C.     

Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

Is potential coordination of alkali metal ions to stereodefined polyoxygenated cyclohexanes an adequate driving force for fostering the adoption of axial conformers?

Inositol orthoesters have been developed as precursors to stereodefined hexakis polyoxygenated cyclohexanes. The objective of the study was to determine if all-trans systems could be coaxed by alkali metal ions into adopting the all-axial coordinative features. This high level coordination cannot be matched by epimers whose only option is to experience monocomplexation. Only very low levels of coordination were exhibited in solution by the ligands in question. Electrospray ionization mass spectrometry was also used to evaluate the metal complexation properties of the inositol ligands based on competition experiments involving each ligand and one or more metals.     

The first total synthesis of a bioactive metabolite, a spirobenzofuran isolated from the fungi Acremonium sp. HKI 0230

The first total synthesis of a bioactive metabolite, isolated from the fungi Acremonium sp. HKI 0230, containing a cyclopentaspirobenzofuran carbon framework, employing an Ireland ester Claisen rearrangement and RCM reaction based strategy has been accomplished.     

Ambient temperature ATRP of benzyl methacrylate as a tool for the synthesis of block copolymers with styrene

The rapid atom transfer radical polymerization (ATRP) of benzyl methacrylate (BnMA) at ambient temperature was used to synthesize block copolymers with styrene as the second monomer. Various block copolymers such as AB diblock, BAB symmetric and asymmetric triblock, and ABABA pentablock copolymers were synthesized in which the polymerization of one of the blocks namely BnMA was performed at ambient temperature. It is demonstrated that the block copolymerization can be performed in a controlled manner, regardless of the sequence of monomer addition via halogen exchange technique. Using this reaction condition, the composition (ratio) of one block (here BnMA) can be varied from 1 to 100. It is further demonstrated that in the multiblock copolymer syntheses involving styrene and benzyl methacrylate, it is better to start from the PS macroinitiator compared with PBnMA macroinitiator. The polymers synthesized are relatively narrow dispersed (<1.5). It is identified that the ATRP of BnMA is limited to certain molecular weights of the PS macroinitiator. Additionally, a preliminary report about the synthesis of the block copolymer of BnMA‐methyl methacrylate (MMA), both at ambient temperature, is demonstrated. Subsequent deprotection of the benzyl group using Pd/C? H₂ results in methacrylic acid (MAA)–methyl methacrylate (MAA–MMA) amphiphilic block copolymer. GPC, IR, and NMR are used to characterize the synthesized polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2848–2861, 2006     

Polybenzimidazoles. VI. Polybenzimidazoles containing aryl sulfone linkages

Four new polybenzimidazoles with aryl sulfone linkages between the recurring units have been prepared in order to study their thermal stability and solubility properties. The polymers prepared were high molecular weight materials with good thermal stability.     

Lattice dynamics and thermodynamic functions of a CaF2 slab with (110) free surfaces

We present results of lattice dynamical calculations for a eleven layer CaF₂ slab with (110) free surfaces. From a comparison with earlier results for NaCl and CsCI structured slabs, we find that new surface modes appear both in the optical and acoustical range of frequencies. The additional modes occur due to the presence of the Raman active band. Results pertaining to the contribution of the surface vibrational modes to the thermodynamic properties are presented.