Hydrogen bond

About: Hydrogen bond is a research topic. Over the lifetime, 57701 publications have been published within this topic receiving 1306326 citations.

The energetics of hydrogen bonds in model systems : Implications for enzymatic catalysis

Abstract: Low-barrier or short, strong hydrogen bonds have been proposed to contribute 10 to 20 kilocalories per mole to transition-state stabilization in enzymatic catalysis The proposal invokes a large increase in hydrogen bond energy when the pKa values of the donor and acceptor (where Ka is the acid constant) become matched in the transition state (delta pKa=0) This hypothesis was tested by investigating the energetics of hydrogen bonds as a function of delta pKa for homologous series of compounds under nonaqueous conditions that are conducive to the formation of low-barrier hydrogen bonds In all cases, there was a linear correlation between the increase in hydrogen-bond energy and the decrease in delta pKa, as expected from simple electrostatic effects However, no additional energetic contribution to the hydrogen bond was observed at delta pKa=0 These results and those of other model studies suggest alternative mechanisms by which hydrogen bonds can contribute to enzymatic catalysis, in accord with conventional electrostatic considerations

Confinement or the nature of the interface? Dynamics of nanoscopic water.

Abstract: The dynamics of water confined in two different types of reverse micelles are studied using ultrafast infrared pump-probe spectroscopy of the hydroxyl OD stretch of HOD in H2O. Reverse micelles of the surfactant Aerosol-OT (ionic head group) in isooctane and the surfactant Igepal CO 520 (nonionic head group) in 50/50 wt % cyclohexane/hexane are prepared to have the same diameter water nanopools. Measurements of the IR spectra and vibrational lifetimes show that the identity of the surfactant head groups affects the local environment experienced by the water molecules inside the reverse micelles. The orientational dynamics (time-dependent anisotropy), which is a measure of the hydrogen bond network rearrangement, are very similar for the confined water in the two types of reverse micelles. The results demonstrate that confinement by an interface to form a nanoscopic water pool is a primary factor governing the dynamics of nanoscopic water rather than the presence of charged groups at the interface.

Tunable Inhibition and Denaturation of α-Chymotrypsin with Amino Acid-Functionalized Gold Nanoparticles

Abstract: Water-soluble gold nanoparticles bearing diverse l-amino acid terminals have been fabricated to probe the effect of receptor surface on protein surface binding. The interaction of these nanoparticles with α-chymotrypsin (ChT) was investigated by activity assay, gel electrophoresis, zeta-potential, circular dichroism, and fluorescence spectroscopy. The results show that both electrostatic and hydrophobic interactions between the hydrophobic patches of receptors and the protein contribute to the stability of the complex. The microscopic binding constants for these receptor−protein systems are 106−107 M-1, with the capacity of the nanoparticle receptors to bind proteins determined by both their surface area and their surface charge density. Furthermore, it is found that the hydrophilic side chains destabilize the ChT structure through either competitive hydrogen bonding or breakage of salt bridges, whereas denaturation was much slower with hydrophobic amino acid side chains. Significantly, correlation betwee...

Molecular differences in the formation and structure of fine-stranded and particulate beta-lactoglobulin gels.

Abstract: In order to reveal at a molecular level differences between fine-stranded and particulate gels, we present an Fourier transform infrared spectroscopic study of the thermal behavior of beta-lactoglobulin (beta-lg) in salt-free D(2)O solutions and low ionic strength at different pDs. Differences are found in the denaturation mechanism, in the unfolded state of the protein, in the aggregate formation, and in the strength of the intermolecular interactions. For fine-stranded gels (pD 2.8 and 7.8), heating induces the dissociation of the dimers into monomers. The protein undergoes extensive structural modifications before aggregation begins. Aggregation is characterized by the appearance of a new band attributed to intermolecular beta-sheets which is located in the 1613-1619 cm(-1) range. For particulate gels (pD 4.4 and 5.4), the protein structure is almost preserved up to 75-80 degrees C with no splitting of the dimers. The band characteristic of aggregation originates from the component initially located at 1623 cm(-1), suggesting that at the beginning of aggregation, globular beta-lg in the dimeric form associate to constitute oligomers with higher molecular mass. Aggregation may result in the association of globular slightly denatured dimers, leading to the formation of spherical particles rather than linear strands. The aggregation band is always located in the 1620-1623 cm(-1) range for particulate gels showing that hydrogen bonds are weaker for these aggregates than for fine-stranded ones. This has been related to a more extensive protein unfolding for fine-stranded gels that allows a closer alignment of the polypeptide chains, and then to the formation of much stronger hydrogen bonds. Small differences are also found in protein organization and in intermolecular hydrogen bond strength vs pD within the same type of gel. Protein conformation and protein-protein interactions in the gel state may be responsible of the specific macroscopic properties of each gel network. A coarse representation of the different modes of gelation is described.