Needle-based refractive index measurement using low-coherence interferometry

We present a novel needle-based device for the measurement of refractive index and scattering using low-coherence interferometry. Coupled to the sample arm of an optical coherence tomography system, the device detects the scattering response of, and optical path length through, a sample residing in a fixed-width channel. We report use of the device to make near-infrared measurements of tissues and materials with known optical properties. The device could be used to exploit the refractive index variations of tissue for medical and biological diagnostics accessible by needle insertion.     

Spatially resolved Fourier holographic light scattering angular spectroscopy

We show for what is the first time to our knowledge that digital Fourier holography can be used to record spatially resolved angular light scattering spectra from microscopically structured samples. This is achieved in one or a few digital image captures over large millimeter-scale fields of view. Such spectra are a sensitive measure of microscopic morphology, with wide applications in biological and medical imaging. We demonstrate good agreement between results of experiment and Mie theory for the angular scattering spectra of microspheres in water extracted from local regions within reconstructed 2 x 1 millimeter image sets.     

Correlation of static speckle with sample properties in optical coherence tomography

We present theoretical calculations, based on a random phasor sum model, which show that the optical coherence tomography speckle contrast ratio is dependent on the local density of scattering particles in a sample, provided that the effective number of scatterers in the probed volume is less than about five. We confirm these theoretical predictions experimentally, using suspensions of microspheres in water. The observed contrast ratios vary in value from the Rayleigh limit of 0.52 to in excess of 2, suggesting that the contrast ratio could be useful in optical coherence tomography, particularly when imaging in ultrahigh-resolution regimes.     

Substituted derivatives of [Fe2(CO)9] and [Ru2(CO)9] and their susceptibility to electrophilic attack: X-ray crystal structure of [Fe2(μ-Br)(CO)4{μ-(C6H5O)2PN(C2H5)P(OC6H5)2}2]PF6

Bis- and, in particular, tetra-substituted ditertiary phosphine and diphosphazane derivatives of [Fe₂(CO)₉] and [Ru₂(CO)₉], readily synthesised by reaction of the appropriate bidentate ligand with [Fe₂(CO)₉] and [Ru₃(CO)₁₂], respectively, are very susceptible to electrophilic attack by reagents such as halogens and protons; the solid state structure of one of the products [Fe₂(μ-Br)(CO)₄ {μ-(PhO)₂PN(Et)P(OPh)₂}₂]PF₆ has been determined by X-ray crystallography.     

Stepwise BAN estimators for exponential families with multivariate normal applications

Consistent, asymptotically efficient and asymptotically normal stepwise estimators are given for a subclass of the uniparametric and multiparametric exponential families. The estimators are derived by using the Robbins-Monro stochastic approximation procedure with certain families of random variables arising from the normalized log-likelihood. Considered in detail are three multivariate normal examples where the maximum likelihood estimators are not tractable.     

The geometry of certain fixed marginal probability distributions

The geometry of the set of p × q probability mass function matrices with fixed marginals is discussed. The positively quadrant dependent and negatively quadrant dependent subsets are also considered. Explicit graphical representations of these sets are given in the 2 × 2 and 2 × 3 cases.     

Transannular aldol condensations within macrocyclic lactones: A novel approach to 8-membered carbocyclic rings.

A novel method has been developed for the construction of 8-membered carbocyclic rings, involving as the key step a chemoselective transannular aldol condensation within an 11-membered ketolactone ring.     

Diameter-selective solubilization of single-walled carbon nanotubes by reversible cyclic peptides

We have utilized reversible cyclic peptides (RCPs)-peptides containing alternating l- and d-amino acids with N- and C-termini derivatized with thiol-containing groups allowing reversible peptide cyclization-to solubilize and noncovalently functionalize carbon single-walled nanotubes (SWNTs) in aqueous solution. Solubilization occurs through wrapping of RCPs around the circumference of a SWNT, followed by the formation of head-to-tail covalent bonds, yielding closed rings on the nanotubes. By controlling the length of the RCPs, we have demonstrated limited diameter-selective solubilization of the SWNTs as revealed by UV/vis/NIR and Raman spectroscopies, as well as atomic force microscopy.     

Synthesis of fluorinated derivatives of glutethimide and aminoglutethimide

Aminoglutethimide (1), used in the treatment of hormone dependent breast cancer, interacts with enzyme complexes desmolase and aromatase. Its action is not specific and its metabolism gives rise to toxic and non-inhibitory metabolites. The work described here explores the impact of fluorine substitution within the glutethimide (2) framework, on the enzyme inhibitory properties of aminoglutethimide. Four new fluorinated derivatives (5), (6), (8) and (9) have been prepared, in which fluorine substituents have been introduced into the phenyl ring and the ethyl side chain. 4-Fluoroglutethimide (5) and 3-trifluoroglutethimide (6) were synthesised from the corresponding fluorophenylacetonitriles (10) and (14) via sequential monoethylation, Michael addition to methyl propenoate and cyclisation. An alternative strategy, devised for the synthesis of (8), involved the monoarylation of ethyl cyanoacetate, and gave rise to the intermediate (29). Incorporation of fluorine was carried out by SF₄ fluorination of the cyanoketoester (33), which was subsequently converted to the difluoroaminoglutethimide (8). For the synthesis of trifluoromethyl glutethimide (9), the trifluoromethyl group was introduced by alkylation of phenylcyanoacetate (16) with 2-iodo-1,1,1,-trifluoroethane. Preliminary enzyme inhibition results have been obtained for compounds (5), (6) and (8).     

Some nitro derivatives of 1,4-benzodioxino[2,3-b]pyridine. Crystal and molecular structure of 2,7,8-trinitro-1,4-benzodioxino[2,3-b]pyridine

The electrophilic nitration of 1,4-benzodioxino[2,3-b]pyridine 1 with nitric acid in sulfuric acid has been studied. Some of the products of nitration including 7 - and 8 -nitro derivatives 2a and 2b , respectively, 7,9-, 7,8- and 6,8-dinitro derivatives 3a , 3b and 3c , respectively, and 2,7,8-trinitro derivative 4 have been isolated and characterized. The structure of isomers have been assigned for derivatives 3b and 4 while tentative structures have been proposed for the other products. The cyclopentadienyliron complex of 1 gives the same reaction products under similar conditions while for some other milder nitrating reagents no reaction was observed. 2,7,8-Trinitro-1,4-benzodioxino[2,3-b]pyridine 4 crystallizes in the monoclinic system, space group P2₁/c; the dihedral angle between the planes of outer rings was found to be 174.65(8) degrees. The planes of the nitro groups have been found to be rotated with respect to the appropriate pyri-dine and benzene ring planes by 11.13(11) degrees for the 2-nitro group and 47.56(9) and 29.80(9) degrees for the 7-nitro and 8-nitro groups, respectively.