The primary event that initiates vision is the photoinduced isomerization of retinal in the visual pigment rhodopsin (Rh). Here, we use a scaled quantum mechanics/molecular mechanics potential that reproduces the isomerization path determined with multiconfigurational perturbation theory to follow the excited-state evolution of bovine Rh. The analysis of a 140-fs trajectory provides a descripti...

Isomerization of the glucose content of high fructose corn syrup (HFCS) into fructose needs to be strictly controlled in order to obtain a balanced product for sweetness and solubility, creating a non-trival problem. This work presents an approach to modelling of a real industrial isomerization reactor by artificial neural networks (ANN) pre-processed with principal component analysis (PCA). Th...

The dissociation of the hydroxymethyl radical, CH(2)OH, and its isotopolog, CD(2)OH, following the excitation of high OH stretch overtones is studied by quasi-classical molecular dynamics calculations using a global potential energy surface (PES) fitted to ab initio calculations. The PES includes CH(2)OH and CH(3)O minima, dissociation products, and all relevant barriers. Its analysis shows tha...

We demonstrate the application of molecular rotational spectroscopy to measure the conformation isomerization rate of vibrationally excited pent-1-en-4-yne (pentenyne). The rotational spectra of single quantum states of pentenyne are acquired by using a combination of IR-Fourier transform microwave double-resonance spectroscopy and high-resolution, single-photon IR spectroscopy. The quantum sta...

Urinary excretion of the type I collagen C-telopeptide (CTx) has been shown to be a sensitive index of the rate of bone resorption. The human type I collagen sequence A(1209)HDGGR(1214) of CTx can undergo racemization of the aspartic acid residue Asp(1211) and isomerization of the bond between this residue and Gly(1212). These spontaneous non-enzymic chemical reactions takes place in vivo in bo...

Proline is a unique amino acid owing to the relatively small energy difference between the cis and trans conformations of its peptide bond. The X-Pro imide bond readily undergoes cis-trans isomerization in the context of short peptides as well as some proteins. However, the direct detection of cis-trans proline isomerization in folded proteins is technically challenging. NMR spectroscopy is wel...

Analysis of the chromophore p-coumaric acid, extracted from the ground state and the long-lived blue-shifted photocycle intermediate of photoactive yellow protein, shows that the chromophore is reversibly converted from the trans to the cis configuration, while progressing through the photocycle. The detection of the trans and ¢is isomers was carried out by high performance capillary zone elect...

The isomerization reactions of HOOX --> HOXO --> HXO2 (X = Cl, Br, I) have been studied by using the density functional theory. The breakage and formation of the chemical bonds of the titled reactions have been discussed by the topological analysis method of electronic density. The calculated results show that there is a transitional structure of a three-membered ring on each of the isomerizati...

In a previous article we introduced a reaction coordinate based on the unstable normal mode at the saddle point of the potential energy surface. We here calculate the free-energy distribution along this coordinate for the isomerization of calix@4#arene in vacuo and in chloroform using umbrella sampling, with one umbrella covering the entire range of the reaction coordinate. An excellent first g...

Promoted sulfated zirconia samples were prepared by the incipient wetness technique to produce isomerization catalysts which were active for the conversion of n-butane to isobutane at 338K (up to 10% conversion of 1% n-butane, 1atm., 0.25 h(-1) WHSV). The local structure of Fe and Mn in promoted sulfated zirconia was investigated using fluorescence yield XAS. Spectra were taken of calcined samp...