A beta-lactone route to chiral gamma-substituted alpha-amino acids: application to the concise synthesis of (S)-alpha-azidobutyro lactone and a natural amino acid

[reaction: see text] Beta-lactones are useful synthetic intermediates allowing access to a number of functional arrays. In this report, enantiomerically pure 4-trichloromethyl-2-oxetanone is shown to be a versatile amino acid synthon leading to a variety of gamma-substituted alpha-amino acid precursors. The utility of this methodology was demonstrated by the concise synthesis of a protected homoserine equivalent, alpha-azidobutyro lactone, and a naturally occurring alpha-amino acid from the seeds of Blighia unijugata.     

Volterra Convolution Operators with Values in Rearrangement Invariant Spaces

The Volterra convolution operator Vf(x) = ^x₀(x–y)f(y)dy,where (·) is a non-negative non-decreasing integrablekernel on [0, 1], is considered. Under certain conditions onthe kernel , the maximal Banach function space on [0, 1] onwhich the Volterra operator is a continuous linear operatorwith values in a given rearrangement invariant function spaceon [0, 1] is identified in terms of interpolation spaces. Thecompactness of the operator on this space is studied.     

Design and development of a fiber-optic immunosensor utilizing near-infrared fluorophores

The design and application of a fluorescent fiber-optic immunosensor (FFOI) are reported. The FFOI is utilized for the detection of antibody/antigen binding within the near-infrared (NIR) spectral region. The technique is developed through the combined use of fiber-optic, semiconductor laser-excitation, fluorescence detection, NIR dye, and immunochemical techniques. The antibody is immobilized on the FFOI and utilized as a recognition component for trace amounts of specific antigen. The FFOI is constructed to utilize an antibody sandwich technique. The assay involves the immobilization of the capture antibody on the sensing tip of the FFOI followed by the exposure of the immobilized sensing tip to the antigen. The antigen-coated FFOI is then introduced to a second antibody previously labeled with the NIR dye. Typical measurements are performed in about 15 min. A semiconductor laser provides the excitation (780 nm) of the immune complex. The resulting emission is detected by a silicon photodiode detector (820 nm). The intensity of the resulting fluorescence is directly proportional to the concentration of the antigen. The sensitivity of the analysis reaches 10 ng/ml and the response time is 10–15 min.     

Affine-Invariant Distances, Envelopes and Symmetry Sets

Affine invariant symmetry sets of planar curves are introduced and studied in this paper. Two different approaches are investigated. The first one is based on affine invariant distances, and defines the symmetry set as the closure of the locus of points on (at least) two affine normals and affine-equidistant from the corresponding points on the curve. The second approach is based on affine bitangent conics. In this case the symmetry set is defined as the closure of the locus of centers of conics with (at least) 3-point contact with the curve at two or more distinct points on the curve. This is equivalent to conic and curve having, at those points, the same affine tangent, or the same Euclidean tangent and curvature. Although the two analogous definitions for the classical Euclidean symmetry set are equivalent, this is not the case for the affine group. We present a number of properties of both affine symmetry sets, showing their similarities with and differences from the Euclidean case. We conclude the paper with a discussion of possible extensions to higher dimensions and other transformation groups, as well as to invariant Voronoi diagrams.     

Optimal threat strategies of bimatrix games

A bi-matrix threat game is defined as a triple (A,B,S) whereA andB arem×n payoff matrices, andS is a closed convex subset of the plane, with (a _ij,B _ij) εS for eachi,j. Given (threat) mixed strategiesx andy,Nash's model suggests that the eventual outcome will be that point (u, v) εS which maximizes the product (u ?xAy ^t) (v ?xBy ^t) subject tou ≥xAy ^t,v ≥xBy ^t. Optimality of the threat strategies is then defined in the obvious way. A constructive proof of existence of optimal threat strategies is given; in particular, it is shown that they are optimal strategies for the matrix gameA-kB, wherek is to be determined. In this paper,k is approximated by aNewton-Raphson technique. Two examples are solved in detail.     

Spectral- and frequency-encoded fluorescence imaging

A method for obtaining fluorescence images with a high number of resolvable points by using spectral and frequency encoding is presented. Broadband excitation light is encoded with a wavelength-dependent frequency modulation and dispersed onto the sample with a grating to simultaneously illuminate an entire image line. The Fourier transform of the frequency-encoded fluorescence emission provides one line of the image. Mechanical scanning along a direction orthogonal to the wavelength-encoded axis allows creation of the two-dimensional fluorescent image. This method is applicable for developing submillimeter diameter endoscopes. The principles of the technique are validated by imaging indocyanine green fluorescence in microfluidic channels.     

Single and double metallic layer-containing ruthenium dendrimers. Synthesis and catalytic properties

The reaction of a series of phosphanyl-terminated carbosilane dendrimers displaying only one phosphorus ligand per arm with [RuCl(2)(p-cymene)](2) resulted in the grafting of RuCl(p-cymene) moieties on the periphery of the dendrimer. In these species, the chloride ligand is easily displaced by the organic bases pyridine, 4-cyanopyridine and 4,4[prime or minute]-bipyridine to afford new cationic metallodendrimers. NMR studies have confirmed the chirality of the ruthenium centre. The species containing 4,4[prime or minute]-bipyridine reacts through the uncoordinated pyridyl nitrogen with a new equivalent of [RuCl(2)(p-cymene)](2) or [RhCl(CO)(2)](2) to lead to homo- or hetero-bimetallic layer-containing dendrimeric systems. The ruthenodendrimers were tested as catalysts in the transfer hydrogenation of cyclohexanone by propan-2-ol and their activity compared with that of some analogous mononuclear ruthenium(ii) complexes.     

Alpha,omega-bis(thioacetyl)oligophenylenevinylene chromophores from thioanisol precursors

The selective cleavage of arylmethyl thioethers provides a convenient protocol for the synthesis of all-E isomers of alpha, omega-bis(thioacetyl)oligophenyenevinylene molecules (OPVs). The S-methyl group is tolerant of Wittig-type and Heck-type reactions for forming OPV structures and can be converted to the S-acetyl group by treatment with sodium thiomethoxide and acetyl chloride. The thermal conditions of the deprotection/reprotection step concurrently isomerize the conjugated chromophore to the all-E isomer, regardless of the stereochemistry of the starting olefins. This approach is demonstrated for a variety of linear and [2.2]paracyclophane containing OPVs, which have been characterized by electrochemical and spectroscopic techniques. Additionally, these S-acetyl-terminated OPVs self-assemble on gold surfaces. Monolayers containing these molecules were characterized by water contact angle measurements, ellipsometry, and X-ray photoelectron spectroscopy.     

In vivo human retinal imaging by ultrahigh-speed spectral domain optical coherence tomography

An ultrahigh-speed spectral domain optical coherence tomography (SD-OCT) system is presented that achieves acquisition rates of 29,300 depth profiles/s. The sensitivity of SD-OCT and time domain OCT (TD-OCT) are experimentally compared, demonstrating a 21.7-dB improvement of SD-OCT over TD-OCT. In vivo images of the human retina are presented, demonstrating the ability to acquire high-quality structural images with an axial resolution of 6 microm at ultrahigh speed and with an ocular exposure level of less than 600 microW.