341 research outputs found
Reductive CâC Coupling from α,ÎČâUnsaturated Nitriles by Intercepting Keteniminates
We present an atomâeconomic strategy to catalytically generate and intercept nitrile anion equivalents using hydrogen transfer catalysis. Addition of α,ÎČâunsaturated nitriles to a pincerâbased RuâH complex affords structurally characterized ÎșâNâcoordinated keteniminates by selective 1,4âhydride transfer. When generated inâ
situ under catalytic hydrogenation conditions, electrophilic addition to the keteniminate was achieved using anhydrides to provide αâcyanoacetates in high yields. This work represents a new application of hydrogen transfer catalysis using α,ÎČâunsaturated nitriles for reductive CâC coupling reactions.An atomâeconomic strategy to catalytically generate and intercept nitrile anion equivalents by hydrogen transfer catalysis has been developed. Addition of α,ÎČâunsaturated nitriles to a pincerâbased RuâH complex affords keteniminates by selective 1,4âhydride transfer, which were employed in a net hydrogenative acylation reaction.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149503/1/anie201904530.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149503/2/anie201904530-sup-0001-misc_information.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149503/3/anie201904530_am.pd
Gas phase reactions of trimethyl borate with phosphates and their non-covalent complexes
Manipulating the fragmentation patterns of phosphopeptides via gas-phase boron derivatization: Determining phosphorylation sites in peptides with multiple serines
Sources of artefacts in the electrospray ionization mass spectra of saturated diacylglycerophosphocholines: From condensed phase hydrolysis reactions through to gas phase intercluster reactions
Fetal Window of Vulnerability to Airborne Polycyclic Aromatic Hydrocarbons on Proportional Intrauterine Growth Restriction
Background: Although the entire duration of fetal development is generally considered a highly susceptible period, it is of public health interest to determine a narrower window of heightened vulnerability to polycyclic aromatic hydrocarbons (PAHs) in humans. We posited that exposure to PAHs during the first trimester impairs fetal growth more severely than a similar level of exposure during the subsequent trimesters. Methods: In a group of healthy, non-smoking pregnant women with no known risks of adverse birth outcomes, personal exposure to eight airborne PAHs was monitored once during the second trimester for the entire cohort (n = 344), and once each trimester within a subset (n = 77). Both air monitoring and self-reported PAH exposure data were used in order to statistically estimate PAH exposure during the entire gestational period for each individual newborn. Results: One natural-log unit increase in prenatal exposure to the eight summed PAHs during the first trimester was associated with the largest decrement in the Fetal Growth Ratio (FGR) (23%, 95 % Confidence Interval (CI), 25 to20%), birthweight (2105 g, 95 % CI, 2188 to 222 g), and birth length (20.78 cm, 95 % CI, 21.30 to 20.26 cm), compared to the unit effects of PAHs during the subsequent trimesters, after accounting for confounders. Furthermore, a unit exposure during the first trimester was associated with the largest elevation in Cephalization Index (head to weight ratio) (3 mm/g, 95 % CI, 1 to 5 mm/g). PAH exposure was not associated with evidence of asymmetric growth restriction in this cohort
Isomeric recognition by ion/molecule reactions: The ionized phenol-cyclohexadienone case
Hydrogen Bonding Constrains Free Radical Reaction Dynamics at Serine and Threonine Residues in Peptides
Free radical-initiated peptide sequencing (FRIPS) mass spectrometry derives advantage from the introduction of highly selective low-energy dissociation pathways in target peptides. An acetyl radical, formed at the peptide N-terminus via collisional activation and subsequent dissociation of a covalently attached radical precursor, abstracts a hydrogen atom from diverse sites on the peptide, yielding sequence information through backbone cleavage as well as side-chain loss. Unique free-radical-initiated dissociation pathways observed at serine and threonine residues lead to cleavage of the neighboring N-terminal C_αâC or NâC_α bond rather than the typical CαâC bond cleavage observed with other amino acids. These reactions were investigated by FRIPS of model peptides of the form AARAAAXAA, where X is the amino acid of interest. In combination with density functional theory (DFT) calculations, the experiments indicate the strong influence of hydrogen bonding at serine or threonine on the observed free radical chemistry. Hydrogen bonding of the side-chain hydroxyl group with a backbone carbonyl oxygen aligns the singly occupied Ï orbital on the ÎČ-carbon and the NâC_α bond, leading to low-barrier ÎČ-cleavage of the NâC_α bond. Interaction with the N-terminal carbonyl favors a hydrogen-atom transfer process to yield stable c and zâą ions, whereas C-terminal interaction leads to effective cleavage of the C_αâC bond through rapid loss of isocyanic acid. Dissociation of the C_αâC bond may also occur via water loss followed by ÎČ-cleavage from a nitrogen-centered radical. These competitive dissociation pathways from a single residue illustrate the sensitivity of gas-phase free radical chemistry to subtle factors such as hydrogen bonding that affect the potential energy surface for these low-barrier processes
An ion/molecule reaction for the identification of analytes with two basic functional groups
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