Oxygen-Independent Decarbonylation of Aldehydes by Cyanobacterial Aldehyde Decarbonylase: A New Reaction of Diiron Enzymes
作者:Debasis Das、Bekir E. Eser、Jaehong Han、Aaron Sciore、E. Neil G. Marsh
DOI:10.1002/anie.201101552
日期:2011.7.25
Just add water: Structurally, cyanobacterialaldehydedecarbonylases are members of the non‐heme diiron oxygenase family of enzymes. However, the enzyme catalyzes the hydrolysis of aliphatic aldehydes to alkanes and formate (see scheme), in an oxygen‐independent reaction. This unusual and chemically difficult reaction most likely involves free radical intermediates.
A study of the structure and dynamics of dimethyloctadecylsilyl-modified silica using wide-line 2H NMR techniques
作者:Robert C. Zeigler、Gary E. Maciel
DOI:10.1021/ja00017a001
日期:1991.8
The structure and dynamics of dimethyloctadecylsilyl-modified silica gel (C18-silica) were studied by using solid-state H-2 NMR techniques. In order to reproduce with a theoretical model the H-2 line shapes that were observed for the C18-silica samples, it was necessary to assume that a variety of environments are present on the C18-silica surface and that this heterogeneity results in different details of the motion of silane groups that are bonded to different regions of the C18-silica surface. H-2 spectra that were taken on the C18-silica samples at temperatures below room temperature appear to be superpositions of two line shapes, indicating that some silane groups move with a simple two-site jump motion, along with others that move with a more complex distribution of motions. At -50-degrees-C, the addition of wetting liquids can affect the H-2 line shape; different liquids can have dramatically different effects on the observed H-2 line shapes. Simple surface structures for Cl8-silica are proposed that are consistent with the NMR data observed in this study.
Structure and Dynamics in Alkanethiolate Monolayers Self-Assembled on Gold Nanoparticles: A DSC, FT-IR, and Deuterium NMR Study
作者:Antonella Badia、Louis Cuccia、Linette Demers、Fred Morin、R. Bruce Lennox
DOI:10.1021/ja963571t
日期:1997.3.1
Gold nanoparticles, cn. 30 Angstrom in diameter, have been derivatized with specifically deuterated (position 1 and positions 10 to 13) and perdeuterated (positions 2 to 18) octadecanethiols (C18SH). The phase behavior of the octadecanethiolate monolayers chemisorbed onto the colloidal Sold surface was characterized by differential scanning calorimetry(DSC). The DSC thermograms show that the C18SH-derivatized Au nanoparticles undergo distinct phase transitions which can be associated with the reversible disordering of the alkyl chains. Despite the highly curved geometry of these Au particles, there is a remarkable degree of conformational order in the alkanethiolate chains and the thermotropic behavior of the thiol-modified gold nanoparticles is very similar to that of conventional, planar self-assembled monolayers. Both the peak maximum temperature and the enthalpy associated with the DSC transition strongly parallel those of the gel-to-liquid crystalline transition of n-diacylphosphatidylcholine lipid bilayer membranes of equivalent chain length. Restricted chain mobility due to covalent bonding of the sulfur head group to the gold surface does not affect the cooperativity of the transition in terms of the transition temperature and enthalpy. Local chain ordering and dynamics in the deuterated C18S/Au nanoparticles have been probed using variable-temperature solid-state deuterium NMR spectroscopy and transmission FT-IR spectroscopy. The temperature dependence of the symmetric CD2 stretching frequency has confirmed that the DSC-detected phase transition involves a thermally-induced change from a predominantly all-trans conformation to a chain disordered state. A comparison of the thermal behavior of d(35)-C18S/Au and 10,10, II, II, IZ, 12, 13, 13-d(8)-C18S/Au shows that disordering originates in the chain terminus region and propagates toward the middle of the chain as the temperature increases, Studies of I,1-d(2)-C18S/Au show that the disorder does not extend to the tethered sulfur head group. Deuterium NMR spectroscopy specifically establishes that chain melting arises from an increased frequency of gauche bonds in the alkanethiolate chains. The H-2 NMR line shapes further indicate that the tethered alkanethiolate chains are undergoing rapid trans-gauche bond isomerization and axial chain rotation.
The nominal butyl ester ion in the mass spectra of long-chainn-alkyl esters: A postscript
作者:Seymour Meyerson、Eugene S. Kuhn、Imre Puskas、Ellis K. Fields、Leonard C. Leitch、Thomas A. Sullivan
DOI:10.1002/oms.1210180305
日期:1983.3
Abstractn‐Octadecyl benzoate, taken as a model for long‐chain n‐alkyl carboxylates generally, loses C14H28 under electron impact to yield a product with the same elemental composition as the butyl benzoate molecular ion. This product retains quantitatively one hydrogen from C‐6, and seems to be formed as an oxygen‐protonated 4‐benzoyloxybutyl radical. It reacts further to lose H2O, in which deuterium labeling demostrates that the second hydrogen atom comes predominantly from C‐4. The intermediate reorganization, for which the driving force is presumably furnished by the instability associated with a primary radical, is pictured in terms of cyclization via bonding between the C‐4 radical site and the benzoyl carbon concerted with hydrogen migration via a 4‐membered quasicyclic transition state.