Highly Selective Dissociation of a Peptide Bond Following Excitation of Core Electrons.

The controlled breaking of a specific chemical bond with photons in complex molecules remains a major challenge in chemistry. In principle, using the K-edge absorption of a particular atomic element, one might excite selectively a specific atomic entity in a molecule. We report here highly selective dissociation of the peptide bonds in N-methylformamide and N-methylacetamide on tuning the X-ray wavelength to the K-edge absorption of the atoms connected to (or near) the peptide bond.

Core excitation, specific dissociation, and the effect of the size of aromatic molecules connected to oxygen: phenyl ether and 1,3-diphenoxybenzene.

Near-edge X-ray absorption fine structure (NEXAFS) spectra of phenyl ether at the carbon K-edge and 1,3-diphenoxybenzene at both the carbon and oxygen K-edges were measured in the total ion yield mode using X-rays from a synchrotron and a reflectron time-of-flight mass spectrometer. Time-dependent density functional theory was adopted to calculate the carbon and oxygen K-edge NEXAFS spectra of phenol, phenyl ether, and 1,3-diphenoxybenzene. The assignments and a comparison of the experimental and calculated spectra are presented.

Near-edge X-ray absorption fine structure spectra and site-selective dissociation of phenol.

A time-of-flight mass spectrometer with orthogonal acceleration and soft X-rays from synchrotron radiation were utilized to measure near-edge X-ray absorption fine structure (NEXAFS) spectra of carbon and oxygen in phenol and the corresponding ionic fragments following core excitation. The photon energies were in the range of 284-298 eV for the carbon K-edge and 529.5-554.

N-Doped, porous TiO2 with rutile phase and visible light sensitive photocatalytic activity.

Nitrogen-doped, porous rutile has been prepared by hydrothermal reaction of TiN in nitric acid, with the nitrogen atoms present in the interstitial sites and in the form of adsorbed nitrate ions. The N-rutile powder exhibits outstanding photocatalytic activity toward degradation of adsorbed methylene blue under visible light irradiation.

1,2-Dibromoethane on Cu(100): bonding structure and transformation to C2H4.

Temperature-programmed reaction/desorption, mass spectrometry, reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and density functional theory calculations have been employed to explore the reaction and bonding structure of 1,2-C(2)H(4)Br(2) on Cu(100). Both the trans and gauche conformers are found to dissociate by breaking the C-Br bonds on clean Cu(100) at 115 K, forming C(2)H(4) and Br atoms. Theoretical investigations for the possible paths of 1,2-C(2)H(4)Br(2) → C(2)H(4) + 2Br on Cu(100) suggest that the barriers of the trans and gauche molecules are in the ranges of 0-4.

Reaction pathways of 2-iodoacetic acid on Cu(100): coverage-dependent competition between C-I bond scission and COOH deprotonation and identification of surface intermediates.

The chemistry of 2-iodoacetic acid on Cu(100) has been studied by a combination of reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reaction/desorption (TPR/D), and theoretical calculations based on density functional theory for the optimized intermediate structures. In the thermal decomposition of ICH(2)COOH on Cu(100) with a coverage less than a half monolayer, three surface intermediates, CH(2)COO, CH(3)COO, and CCOH, are generated and characterized spectroscopically. Based on their different thermal stabilities, the reaction pathways of ICH(2)COOH on Cu(100) at temperatures higher than 230 K are established to be ICH(2)COOH --> CH(2)COO + H + I, CH(2)COO + H --> CH(3)COO, and CH(3)COO --> CCOH.

Photochemistry catalyzed by copolymer-templated mesoporous SiO2: Decomposition of methanol and formic acid.

Photochemical reactions of methanol and formic acid on L64 copolymer-templated mesoporous SiO2 have been investigated by Fourier transform infrared spectroscopy. Although SiO2 has been generally recognized to be photochemically inert, the reaction pathways HCOOH(a), HCOO(a)/SiO2 --> CO(2(g)) and CH3OH(a), CH3O(a)/SiO2 --> CH2O(a) --> HCOO(a) --> CO(2(g)) are demonstrated. The photons used in this study are unable to promote the SiO2 valance band electrons to the conduction band.

FTIR study of adsorption and surface reactions of N(CH3)3 on TiO2.

Fourier transform infrared spectroscopy has been employed to investigate the N(CH3)3 adsorption, thermal stability, and photochemical reactions on powdered TiO2. N(CH3)3 molecules are adsorbed on TiO2 without dissociation at 35 degrees C and are completely desorbed from the surface at 300 degrees C in a vacuum. The CH3 rocking frequencies of N(CH3)3 on TiO2 are affected via the interaction between N(CH3)3 and TiO2 surface OH groups.

Crotonaldehyde formation from decomposition of ICH2CH2OH on powdered TiO2.

Adsorption and reactions of 2-iodoethanol on TiO(2) have been studied by Fourier transform infrared spectroscopy. ICH(2)CH(2)OH possesses two reactive centers of C-I and C-OH. It is found that its decomposition leads to the formation of crotonaldehyde on TiO(2).