74 research outputs found
Good vibrations: probing biomolecular structure and interactions through spectroscopy in the gas phase
Infrared Photodissociation Spectroscopy of C2n+1N− Anions with n = 1 – 5
The gas phase vibrational spectroscopy of cryogenically cooled C2n + 1N−
anions with n = 1 − 5 is investigated in the spectral range of the C≡C and C≡N
stretching modes (1850–2400 cm–1) by way of infrared photodissociation (IRPD)
spectroscopy of messenger-tagged C2n+1N–· mD2 complexes. The IRPD spectra are
assigned based on a comparison to previously reported anharmonic and harmonic
CCSD(T) vibrational frequencies and intensities. Experimentally determined and
predicted anharmonic vibrational transition energies lie within ± 21 cm–1. For
the harmonic CCSD(T)/vqz+ vibrational frequencies a scaling factor of 0.9808
is determined, resulting in comparable absolute deviations. The influence of
the D2-messenger molecules on the structure and the IRPD spectrum is found to
be small. Compared to the results of previous IR matrix isolation studies
additional, in particular weaker, IR-active transitions are identified
gas phase vibrational spectroscopy of V3O6-8+
We present gas phase vibrational spectra of the trinuclear vanadium oxide
cations V3O6+·He1–4, V3O7+·Ar0,1, and V3O8+·Ar0,2 between 350 and 1200 cm−1.
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 V3O6–8+ 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 Á 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 À1
Exploiting the CH-π interactions in supramolecular hydrogels of aromatic carbohydrate amphiphiles
A novel class of supramolecular hydrogels derived from amino sugars is reported, where the self-assembly of aromatic carbohydrate amphiphiles is driven by CH-π interactions, rather than π–π stacking and H-bonding associated with gelators based on aromatic peptide amphiphiles. Spectroscopic data is provided as evidence for this mode of self-assembly and in silico studies revealed that a combination of CH-π and T-stacking of the fluorenyl groups contribute to the formation of the aggregated structures
Thermochemistry of Microhydration of Sodiated and Potassiated Monosaccharides
The thermochemical properties ΔHon , ΔSon, and ΔGon for the hydration of sodiated and potassiated monosaccharides (Ara = arabinose, Xyl = xylose, Rib = ribose, Glc = glucose, and Gal = galactose) have been experimentally studied in the gas phase at 10 mbar by equilibria measurements using an electrospray high-pressure mass spectrometer equipped with a pulsed ion beam reaction chamber. The hydration enthalpies for sodiated complexes were found to be between −46.4 and −57.7 kJ/mol for the first, and −42.7 and −52.3 kJ/mol for the second water molecule. For potassiated complexes, the water binding enthalpies were similar for all studied systems and varied between −48.5 and −52.7 kJ/mol. The thermochemical values for each system correspond to a mixture of the α and β anomeric forms of monosaccharide structures involved in their cationized complexes
Carbohydrate-aromatic interactions: A computational and IR spectroscopic investigation of the complex, methyl alpha-L-fucopyranoside center dot toluene, isolated in the gas phase
Conformational change and selectivity in explicitly hydrated carbohydrates
The combination of vibrational spectroscopy, conducted in a supersonic jet expansion, with computation through molecular mechanics, density functional theory (DFT) and ab initio calculation, has provided a new approach to the conformational and structural assignment of carbohydrates and their molecular complexes. This article reviews the new insights it has provided on the regioselectivity and conformational choice in singly and multiply hydrated monosaccharides. It reveals a systematic pattern of conformational preference and binding site selectivity, driven by the provision of optimal, co-operative hydrogen-bonded networks in the hydrated sugars. Water binding is invariably 'focused' around the hydroxymethyl group (when present); the bound water molecules (on multiply hydrated mannose) are located exclusively on its hydrophilic face while the hydrophobic face remains 'dry'; and there is a correlation between the locale of the preferred binding sites and those involved in protein-carbohydrate molecular recognition. © 2009 Elsevier Ltd. All rights reserved
Conformational change and selectivity in explicitly hydrated carbohydrates
The combination of vibrational spectroscopy, conducted in a supersonic jet expansion, with computation through molecular mechanics, density functional theory (DFT) and ab initio calculation, has provided a new approach to the conformational and structural assignment of carbohydrates and their molecular complexes. This article reviews the new insights it has provided on the regioselectivity and conformational choice in singly and multiply hydrated monosaccharides. It reveals a systematic pattern of conformational preference and binding site selectivity, driven by the provision of optimal, co-operative hydrogen-bonded networks in the hydrated sugars. Water binding is invariably 'focused' around the hydroxymethyl group (when present); the bound water molecules (on multiply hydrated mannose) are located exclusively on its hydrophilic face while the hydrophobic face remains 'dry'; and there is a correlation between the locale of the preferred binding sites and those involved in protein-carbohydrate molecular recognition. © 2009 Elsevier Ltd. All rights reserved
Carbohydrate-Aromatic Interactions: Vibrational Spectroscopy and Structural Assignment of Isolated Monosaccharide Complexes with p-Hydroxy Toluene and N-Acetyl L-Tyrosine Methylamide
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