Synthesis and water solubility of adamantyl-OEG-fullerene hybrids

[reaction: see text] A series of new adamantyl-oligoethyleneglycol-fullerene hybrids was prepared via Bingel-Hirsch functionalization of the C60 fullerene with various adamantyl-oligoethyleneglycol malonates. As NMDA-targeted antioxidants, these compounds may have the potential to be developed as therapeutic agents for the treatment of neurological disorders.     

A tunable narrowband optical filter via phase conjugation by nondegenerate four-wave mixing in a doppler-broadened resonant medium

The formulation of phase conjugation via nondegenerate four-wave mixing in a Doppler-broadened resonant medium is generalized to include nondegenerate pump frequencies. This process is shown capable of yielding a tunable optical band-pass filter whose central frequency can be tuned over the entire Doppler profile with only a small degradation of the filter efficiency while still maintaining a bandwidth limited by the homogeneous linewidth.     

An Infinite Number of Effectively Infinite Clusters in Critical Percolation

An infinite number of effectively infinite clusters are predicted at the percolation threshold, if effectively infinite means that a cluster's mass increases with a positive power of the lattice size L. All these cluster masses increase as L _D with the fractal dimension D = d – /v, while the mass of the rth largest cluster for fixed L decreases as 1/r , with = D/d in d dimensions. These predictions are confirmed by computer simulations for the square lattice, where D = 91/48 and = 91/96.     

Substituent effect and multisite protonation in the fragmentation of alkyl benzoates

The dissociation of protonated alkyl benzoates (para H, CN, OMe and NO(2)) into protonated benzoic acids and alkyl cations was studied in the gas phase. It was found that the product ratio depends on the substituent at the para position of the phenyl ring. The substituent effect is probably the result of the formation of an ion-neutral complex intermediate that decomposes to an ion and a neutral, according to the relative proton affinities of the two moieties. The experimental results and theoretical calculations indicate that the favored protonation site in these compounds is the ester's carbonyl and that proton transfer from the phenyl ring to the ester group is very likely to occur under chemical ionization conditions. It is most probable that the carbonyl protonated form is a common intermediate in the fragmentation process, regardless of the protonation site.     

Optimal control of locusts in subsistence farming areas

Locust swarms hit subsistence-staple-crop-growing households at random and are not privately controllable. An aerial-spraying optimal control model that supports the said households’ livelihood at least expected cost is therefore developed. The qualitative properties of the model are analysed under economically plausible but mild assumptions. The steady state comparative statics reveal that the locust swarm size and the probability of a household’s crop being destroyed by a swarm decrease with the number of households, yield per household, and the staple crop’s replacement price, and increase with the marginal cost of spraying and the planner’s discount rate. A local comparative dynamics analysis is also conducted, as it provides the necessary economic intuition behind other ostensibly anomalous steady-state comparative statics results.     

Towards a fully conjugated, double-stranded cycle: a mass spectrometric and theoretical study.

The two compounds, 1 and 5, are investigated by means of collision-induced dissociation experiments by using ion cyclotron resonance mass spectrometry and other mass spectrometric techniques as to their ability to act as precursors for the fully unsaturated double-stranded target compound 2. These experiments are complemented by flask-type pyrolyses of 5, the products of which are analyzed by mass spectrometry. For 1, no conditions were found under which the expected molecular ion of 2 at m/z 932 appeared, however, for its derivative 5 this was possible. This interesting finding is not in contradiction with the chemical structure of the long sought for compound 2 but calculations suggest that this compound may have isomerized into one where the conjugation is interrupted by hydrogen shift from the solubilizing alkyl chains into the cycle's perimeter. The key driving force for such an isomerization would be the considerable relief of strain energy.     

A model reaction assesses contribution of h-tunneling and coupled motions to enzyme catalysis

To assess the contribution of physical features to enzyme catalysis, the enzymatic reaction has to be compared to a relevant uncatalyzed reaction. While such comparisons have been conducted for some hydrolytic and radical reactions, it is most challenging for biological hydride transfer and redox reactions in general. Here, the same experimental tools used to study the H-tunneling and coupled motions for enzymatic hydride transfer between two carbons were used in the study of an uncatalyzed model reaction. The enzymatic oxidations of benzyl alcohol and its substituted analogues mediated by alcohol dehydrogenases were compared to the oxidations by 9-phenylxanthylium cation (PhXn(+)). The PhXn(+)serves as an NAD(+) model, while the solvent, acetonitrile, models the protein environment. Experimental comparisons included linear free energy relations with Hammett reaction constant (ρ) of zero versus -2.7; temperature-independent versus temperature-dependent primary KIEs; deflated secondary KIEs with deuteride transfer (i.e., primary-secondary coupled motion) versus no coupling between secondary KIEs and H- or D-transfer; and large versus small secondary KIEs for the enzymatic versus uncatalyzed alcohol oxidation. Some of the differences may come from differences in the order of microscopic steps between the catalyzed versus uncatalyzed reactions. However, several of these comparative experiments indicate that in contrast to the uncatalyzed reaction the transition state of the enzymatic reaction is better reorganized for H-tunneling and its H-donor is better rehybridized prior to the C-H→C transfer. These findings suggest an important role for these physical features in enzyme catalysis.     

The effect of active-site isoleucine to alanine mutation on the DHFR catalyzed hydride-transfer

Comparison of the nature of hydride transfer in wild-type and active site mutant (I14A) of dihydrofolate reductase suggests that the size of this side chain at position 14 modulates H-tunneling.