6 research outputs found
gas phase vibrational spectroscopy of V3O6-8+
We present gas phase vibrational spectra of the trinuclear vanadium oxide
cations V3O6+·He1â4, V3O7+·Ar0,1, and V3O8+·Ar0,2 between 350 and 1200 cmâ1.
Cluster structures are assigned based on a comparison of the experimental and
simulated IR spectra. The latter are derived from B3LYP/TZVP calculations on
energetically low-lying isomers identified in a rigorous search of the
respective configurational space, using higher level calculations when
necessary. V3O7+ has a cage-like structure of C3v symmetry. Removal or
addition of an O-atom results in a substantial increase in the number of
energetically low-lying structural isomers. V3O8+ also exhibits the cage
motif, but with an O2 unit replacing one of the vanadyl oxygen atoms. A chain
isomer is found to be most stable for V3O6+. The binding of the rare gas atoms
to V3O6â8+ clusters is found to be strong, up to 55 kJ/mol for Ar, and
markedly isomer-dependent, resulting in two interesting effects. First, for
V3O7+·Ar and V3O8+·Ar an energetic reordering of the isomers compared to the
bare ion is observed, making the ring motif the most stable one. Second,
different isomers bind different number of rare gas atoms. We demonstrate how
both effects can be exploited to isolate and assign the contributions from
multiple isomers to the vibrational spectrum. The present results exemplify
the structural variability of vanadium oxide clusters, in particular, the
sensitivity of their structure on small perturbations in their environment
Carbohydrate-aromatic interactions: a computational and IR spectroscopic investigation of the complex, methyl alpha-L-fucopyranoside·toluene, isolated in the gas phase
a b s t r a c t A carbohydrate-aromatic complex, methyl a-L-fucopyranoside Ă toluene, which provides a model for probing the physical basis of carbohydrate-protein 'stacking' interactions, has been created in a molecular beam and probed through IR ion dip spectroscopy in the CH and OH regions. The results are interpreted in the light of DFT calculations using the MO5-2X functional. They indicate the creation of stacked structures with the aromatic molecule bonded either to the upper or to the lower face of the pyranoside ring, through CH 3,4 -p (upper) or CH 1 -p (lower) interactions leading to binding energies 618 kJ mol Ă1
Identification of preferred carbohydrate binding modes in xenoreactive antibodies by combining conformational filters and binding site maps
Carbohydrates are notoriously flexible molecules. However, they have an important role in many biochemical processes as specific ligands. Understanding how carbohydrates are recognized by other biological macromolecules (usually proteins) is therefore of considerable scientific value. Interfering with carbohydrate-protein interactions is a potentially useful strategy in combating a range of disease states, as well as being of critical importance in facilitating allo- and xenotransplantation. We have devised an in silico protocol for analyzing carbohydrate-protein interactions. In this study, we have applied the protocol to determine the structures of aGal-terminating carbohydrate antigens in complex with a panel of xenoreactive antibodies. The most important feature of the binding modes is the fixed conformation of the GalĂ(1,4)Glc/GlcNAc linkage across all of the binding modes. The preferred conformation of the terminal Gala(1,3)Gal linkage varies depending on the antibody binding site topography, although it is possible that some of the antibodies studied recognize more than one Gala(1,3)Gal conformation. The binding modes obtained indicate that each antibody uses distinct mechanisms in recognizing the target antigens. © The Author 2010. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: [email protected]
Molecular bases of cyclodextrin adapter interactions with engineered protein nanopores
Engineered protein pores have several potential applications in biotechnology: as sensor elements in stochastic detection and ultrarapid DNA sequencing, as nanoreactors to observe single-molecule chemistry, and in the construction of nano- and micro-devices. One important class of pores contains molecular adapters, which provide internal binding sites for small molecules. Mutants of the α-hemolysin (αHL) pore that bind the adapter ÎČ-cyclodextrin (ÎČCD) âŒ104 times more tightly than the wild type have been obtained. We now use single-channel electrical recording, protein engineering including unnatural amino acid mutagenesis, and high-resolution x-ray crystallography to provide definitive structural information on these engineered protein nanopores in unparalleled detail