Atmospheric fate of methacrolein. 1. Peroxy radical isomerization following addition of OH and O2

Peroxy radicals formed by addition of OH and O(2) to the olefinic carbon atoms in methacrolein react with NO to form methacrolein hydroxy nitrate and hydroxyacetone. We observe that the ratio of these two compounds, however, unexpectedly decreases as the lifetime of the peroxy radical increases. We propose that this results from an isomerization involving the 1,4-H-shift of the aldehydic hydrogen atom to the peroxy group. The inferred rate (0.5 ± 0.3 s(-1) at T = 296 K) is consistent with estimates obtained from the potential energy surface determined by high level quantum calculations. The product, a hydroxy hydroperoxy carbonyl radical, decomposes rapidly, producing hydroxyacetone and re-forming OH. Simulations using a global chemical transport model suggest that most of the methacrolein hydroxy peroxy radicals formed in the atmosphere undergo isomerization and decomposition.     

Atmospheric fate of methacrolein. 2. Formation of lactone and implications for organic aerosol production

We investigate the oxidation of methacryloylperoxy nitrate (MPAN) and methacrylicperoxy acid (MPAA) by the hydroxyl radical (OH) theoretically, using both density functional theory [B3LYP] and explicitly correlated coupled cluster theory [CCSD(T)-F12]. These two compounds are produced following the abstraction of a hydrogen atom from methacrolein (MACR) by the OH radical. We use a RRKM master equation analysis to estimate that the oxidation of MPAN leads to formation of hydroxymethyl-methyl-α-lactone (HMML) in high yield. HMML production follows a low potential energy path from both MPAN and MPAA following addition of OH (via elimination of the NO(3) and OH from MPAN and MPAA, respectively). We suggest that the subsequent heterogeneous phase chemistry of HMML may be the route to formation of 2-methylglyceric acid, a common component of organic aerosol produced in the oxidation of methacrolein. Oxidation of acrolein, a photo-oxidation product from 1,3-butadiene, is found to follow a similar route generating hydroxymethyl-α-lactone (HML).     

A practical electromediated ipso-hydroxylation of aryl and alkyl boronic acids under an air atmosphere

An efficient electromediated aerobic ipso-hydroxylation reaction of aryl and alkyl boronic acids has been developed. Furthermore, mechanistic insight into the role of superoxide anions in this reaction has also been provided based on electrochemical studies and experimental results.     

Covalent attachment of antagonists to the α7 nicotinic acetylcholine receptor: synthesis and reactivity of substituted maleimides

The 3-methylmaleimide congeners of the natural product methyllycaconitine (MLA) and an analogue covalently attach to functional cysteine mutants of the α7 nicotinic acetylcholine receptor (nAChR).     

CuII Coordination Chemistry of Patellamide Derivatives: Possible Biological Functions of Cyclic Pseudopeptides

Two synthetic derivatives of the naturally occurring cyclic pseudooctapeptides patellamide A–F and ascidiacyclamide, that is, H₄pat², H₄pat³, as well as their Cu^II complexes are described. These cyclic peptide derivatives differ from the naturally occurring macrocycles by the variation of the incorporated heterocyclic donor groups and the configuration of the amino acids connecting the heterocycles. The exchange of the oxazoline and thiazole groups by dimethylimidazoles or methyloxazoles leads to more rigid macrocycles, and the changes in the configuration of the side chains leads to significant differences in the folding of the cyclic peptides. These variations allow a detailed study of the various possible structural changes on the chemistry of the Cu^II complexes formed. The coordination of Cu^II with these macrocyclic species was monitored by high‐resolution electrospray mass spectrometry (ESI‐MS), spectrophotometric (UV/Vis) and circular dichroic (CD) titrations, and electron paramagnetic resonance (EPR) spectroscopy. Density functional theory (DFT) calculations and molecular mechanics (MM) simulations have been used to model the structures of the Cu^II complexes and provide a detailed understanding of their geometric preferences and conformational flexibility. This is related to the Cu^II coordination chemistry and the reactivity of the dinuclear Cu^II complexes towards CO₂ fixation. The variation observed between the natural and various synthetic peptide systems enables conclusions about structure–reactivity correlations, and our results also provide information on why nature might have chosen oxazolines and thiazoles as incorporated heterocycles.     

Effect of Residual Water and Microwave Heating on the Half‐Life of the Reagents and Reactive Intermediates in Peptide Synthesis

Precise microwave heating has changed the way many small molecules are being synthesized and, currently, the field of solid‐phase peptide synthesis is undergoing dramatic changes owing to the use of microwave heating. To fully reap the benefits of precise microwave heating for the formation of amide bonds in peptide synthesis, it is important to understand the kinetics of formation and break‐down of activated esters and their N‐acylation of the nascent peptide chain at elevated temperatures. Herein, we present systematic studies of, first, the rate of formation of activated esters by NMR spectroscopy and, second, their N‐acylation during peptide synthesis. A study of the amount of residual water in the solvents revealed a significant effect on electrophilic reagents and intermediates. This observation was expanded into a general study of microwave heating in peptide synthesis.     

Optimal Control and the Fibonacci Sequence

We bridge mathematical number theory with optimal control and show that a generalised Fibonacci sequence enters the control function of finite-horizon dynamic optimisation problems with one state and one control variable. In particular, we show that the recursive expression describing the first-order approximation of the control function can be written in terms of a generalised Fibonacci sequence when restricting the final state to equal the steady-state of the system. Further, by deriving the solution to this sequence, we are able to write the first-order approximation of optimal control explicitly. Our procedure is illustrated in an example often referred to as the Brock–Mirman economic growth model.