Experimental detection of one case of benzene epoxidation by a peroxy radical and computational prediction of another

Reaction of the beta-styryl radical with O2 in benzene results in a low yield of benzene oxide, which is shown by isotopic labeling to arise from the solvent. Ab initio and DFT calculations elucidate the mechanism of this reaction, and identify the properties of other radicals that should be more effective promoters of the reaction. The CN radical is found to be one candidate.     

Fluorescence polarization immunoassays for pesticides

Fluorescence polarization immunoassay methods for the detection of pesticides and their metabolites or degradation products are reviewed. Advantages and limitations for application to pesticide detection in environmental and food samples are discussed. The influence of the structure of fluorescent-labeled tracers and the affinity and specificity of antibodies on analytical performance is examined. The methods are simple, readily automated, and rapid (total time for assay of a water sample is about 1 min) with sensitivity of 1 - 10 ng/ml pesticide in 0.01 - 0.1 ml sample.     

A novel diacetylenic bilirubin

An etiobilirubin‐IIβ analog with the central C(10) CH₂ group replaced by a diacetylene unit ( 1 ) was synthesized by base‐catalyzed condensation of bis‐[3‐methyl‐4‐ethyl‐5‐formylpyrrol‐2‐yl]‐diacetylene ( 3 ) with 3‐methyl‐4‐ethyl‐5‐p‐toluenesulfonyl‐2‐pyrrolinone ( 10 ). Diacetylenic rubin 1 is a dark red solid, giving orange solutions with uv‐visible absorption maxima near 460 nm.     

Evidence for the direct isomerization of a platinocyclobutane to an olefin complex

Dichloro-2,3,3-trimethyl-1-platinocyclobutane,

, prepared by the metathetical reaction of Zeise's dimer and 1,1,2-trimethylcyclopropane, reacts with pyridine in chloroform to produce a platinum complex of 2,3-dimethyl-1-butene

. Reaction of I with pyridine at low temperatures (ca. ?40° C) leads to a pyridine addition compound (III) in which the platinocyclobutane ring remains intact. The thermal isomerization of III, which may be conveniently studied using NMR, produces a mixture of II and the free olefin.     

Lanczos cluster expansion for non-extensive systems

A cluster expansion of the Lanczos recursion for non-extensive systems is developed based on the plaquette expansion for extensive systems, in which an auxiliary scaling parameter, Ω, plays the role of volume and introduces extensivity into the problem. Connected Hamiltonian moments of the non-extensive system are computed and introduced into the plaquette expansion in the usual way with Ω. The extensive energy is calculated for increasing orders of the expansion in 1/Ω and the ground state and mass gap of the finite few body problem recovered in the limit Ω → ∞. This new non-perturbative method is applied to the case of N bosons interacting harmonically in one dimension and the ground state energy and mass gap in the vacuum sector are calculated exactly.     

Structural refinements of praseodymium and neodymium orthophosphate

The crystal structures of PrPO₄ and NdPO₄ have been determined by single crystal X-ray diffraction techniques. The structures are isostructural with CePO₄ and LaPO₄, and are monoclinic in space group $\text{P2}{}_1\text{n}$. The cell constants are a = 6.741(3), b = 6.961(4), c = 6.416(3) Å, and β = 103.63(3)° for PrPO₄ and a = 6.722(1), b = 6.933(1), c = 6.390(2) Å, and β = 103.72(2)° for NdPO₄. The least-squares structural refinements of PrPO₄ and NdPO₄ yielded R values of 0.034 and 0.038 based on 810 and 947 unique reflections, respectively. The lanthanide metal atoms are coordinated with nine oxygens and are linked together by very slightly distorted tetrahedral phosphate groups. The nine oxygen atoms ligating the lanthanide atoms form a polyhedron that is best described as a pentagonal interpenetrating tetrahedron.     

A modular nanoparticle-based system for reagentless small molecule biosensing

Metalloprotein tethered CdSe nanoparticles have been generated to provide selective and reagentless maltose biosensing. As opposed to cell or protein detection by semiconducting nanoparticle bioconjugates, a modular method for small-molecule detection using semiconducting nanoparticle bioconjugates has been difficult. Here we report a method for reagentless protein-based semiconducting nanoparticle biosensors. This method uses Ru(II) complex-CdSe nanoparticle interactions and the maltose-induced conformation changes of maltose binding protein to alter the CdSe nanoparticle fluorescence emission intensity. In this proof-of-principle system, the maltose-induced protein conformation changes alter the Ru(II) complex-CdSe nanoparticle interaction, which increases the CdSe emission intensity. Altered CdSe emission intensity effects are best described as electron transfer from the Ru(II) complex to the CdSe excited state forming the nonfluorescent CdSe anion. Four surface-cysteine, Ru(II) complex-attached maltose-binding proteins have been studied for maltose dependent alteration of CdSe emission intensities. With 3.0-3.5 nm diameter CdSe nanoparticles, all ruthenated maltose-binding proteins display similar maltose-dependent increases (1.4-fold) in CdSe emission intensity and maltose binding affinities (KA = 3 x 106 M-1). For these four systems, the only difference was the sample-to-sample variation in maltose-dependent responses. Thus, very few surface cysteine mutations need to be examined to find a successful biosensor, as opposed to analogous systems using organic fluorophores. This strategy generates a unimolecular, or reagentless, semiconducting nanoparticle biosensor for maltose, which could be applied to other proteins with ligand-dependent conformation changes.     

Extensions and generalizations of a theorem of Widder and of the theory of symmetric local semigroups

The theory of symmetric local semigroups due to A. Klein and L. Landau (J. Funct. Anal.44 (1981), 121–136) is generalized to semigroups indexed by subsets of $\text{R}$ⁿ for n > 1. The result implies a similar result of A. E. Nussbaum (J. Funct. Anal.48 (1982), 213–223). It is further generalized to semigroups that are symmetric local in some directions and unitary in others. The results are used to give a simple proof of A. Devinatz's (Duke Math. J.22 (1955), 185–192) and N. I. Akhiezer's (“the Classical Moment Problem and Some Related Questions,” Hafner, New York, 1965) generalization of a theorem of Widder concerning the representation of functions as Laplace integrals. This result is extended to the representation as a Laplace integral of a function taking values in $\text{B}$($\text{R}$), the set of bounded linear operators on a Hilbert space $\text{R}$. Also, a theorem is proved encompassing both the result of Devinatz and Akhiezer, and Bochner's theorem on the representation of positive definite functions as Fourier integrals.     

Finding pathways between distant local minima

We report a new algorithm for constructing pathways between local minima that involve a large number of intervening transition states on the potential energy surface. A significant improvement in efficiency has been achieved by changing the strategy for choosing successive pairs of local minima that serve as endpoints for the next search. We employ Dijkstra's algorithm [E. W. Dijkstra, Numer. Math. 1, 269 (1959)] to identify the "shortest" path corresponding to missing connections within an evolving database of local minima and the transition states that connect them. The metric employed to determine the shortest missing connection is a function of the minimized Euclidean distance. We present applications to the formation of buckminsterfullerene and to the folding of various biomolecules: the B1 domain of protein G, tryptophan zippers, and the villin headpiece subdomain. The corresponding pathways contain up to 163 transition states and will be used in future discrete path sampling calculations.     

Synthesis of 2-carboxy-4-methylazetidine. A novel isomeric analog of dl-proline

L-Azetidine-2-carboxylic acid is a naturally occurring azetidine currently used in the synthesis of abnormally high molecular weight polypeptides. The synthesis of 2-carboxy-4-methylazetidine is now reported which is a novel isomeric analog of dl -proline. Reaction of α,β-dibromo carbonyl ester with three molar equivalents of benzylamine yields 1-benzyl-2-carbomethoxy-4-methyl-azetidine. Hydrolysis of the latter compound with barium hydroxide yields 1-benzyl-2-carboxyl-4-methylazetidine which, if subjected to catalytic hydrogenation., yields the title compound in practical yield. The cis configuration is tentatively assigned to the title compound on the basis of previously published arguments.