19F-detected dual-optimized inverted 1JCC 1,n-ADEQUATE

Modification of the recently reported ¹⁹F-detected 1,1-ADEQUATE experiment that incorporates dual-optimization to selectively invert a wide range of ¹J_CC correlations in a 1,n-ADEQUATE experiment is reported. Parameters for the dual-optimization segment of the pulse sequence were modified to accommodate the increased size of ¹J_CC homonuclear coupling constants of poly- and perfluorinated molecules relative to protonated molecules to allow broadband inversion of the ¹J_CC correlations. The observation and utility of isotope shifts are reported for the first time for 1,1- and 1,n-ADEQUATE correlations.     

Rapid,Acid‐Mediated Deprotection of Silyl Ethers Using Microwave Heating

Microwave heating of triethylsilyl (TES)‐ and tert‐butyldimethylsilyl (TBS)‐protected 1° and 2° alcohols in a mixture of equal parts acetic acid, tetrahydrofuran (THF), and water allows deprotection in as little as 5 min. tert‐butyldiphenylsilyl (TBDPS)‐ and triisopropylsilyl (TIPS)‐protected alcohols and silyl‐protected phenols are stable in these conditions. Thus, selective deprotection of TES‐ and TBS‐protected alcohols in the presence of TIPS or TBDPS ethers is possible. Similarly, alkyl silyl ethers can be deprotected in the presence of aryl silyl ethers.     

Development of a Solid-Phase Extraction Procedure for the Simultaneous Determination of Polyphenols, Organic Acids and Sugars in Wine

A solid-phase extraction (SPE) procedure that fractionates wine samples into 2 sub-samples containing sugars and organic acids (sub-sample 1) and low molecular weight polyphenols (sub-sample 2), respectively, together with rugged LC procedures for their analyses are described. Wine is adjusted to pH 2.5 and loaded on a styrene-divinylbenzene (SDB) cartridge. The organic acids and sugars are eluted with 20 mM sulphuric acid and the monomeric polyphenols with ethyl acetate. Glucose and fructose are analysed by normal phase LC with evaporative light scattering detection and the organic acids by ion exclusion chromatography with UV detection at 210 nm. Analysis of the phenolic fraction is performed by reversed phase LC with diode array detection. Recoveries and repeatabilitys for 27 standard compounds (2 sugars, 7 organic acids and 18 polyphenols) are presented. The method represents an improvement in terms of productivity and robustness compared to currently used procedures.     

Disentangling proton connectivity networks in highly overlapped 1H-NMR spectra of polynuclear aromatics using 1D-HOHAHA

One-dimensional ( 1D ) variants of two-dimensional ( 2D ) nmr techniques can frequently provide the required information in a much shorter period of time than the 2D experiment from which they were derived. Application of the 1D homonuclear Hartmann-Hahn (1D-HOHAHA) experiment to establish proton-proton connectivity networks in highly overlapped four-spin systems in the proton nmr spectra of polynuclear aromatics is described. Selective subspectra are contrasted to the data obtained in a COSY experiment on the same molecule, benzo[f][l]benzothieno [2,3 -c]quinoline. Results from the 1D-HOHAHA technique are especially useful when component resonances from several spin systems are heavily overlapped. Relayed 1D-HOHAHA provides the means of exploiting small, long range coupling pathways of polynuclear aromatics.     

RPE65 and the Accumulation of Retinyl Esters in Mouse Retinal Pigment Epithelium

The RPE65 protein of the retinal pigment epithelium (RPE) enables the conversion of retinyl esters to the visual pigment chromophore 11‐cis retinal. Fresh 11‐cis retinal is generated from retinyl esters following photoisomerization of the visual pigment chromophore to all‐trans during light detection. Large amounts of esters accumulate in Rpe65^?/? mice, indicating their continuous formation when 11‐cis retinal generation is blocked. We hypothesized that absence of light, by limiting the conversion of esters to 11‐cis retinal, would also result in the build‐up of retinyl esters in the RPE of wild‐type mice. We used HPLC to quantify ester levels in organic extracts of the RPE from wild‐type and Rpe65^?/? mice. Retinyl ester levels in Sv/129 wild‐type mice that were dark adapted for various intervals over a 4‐week period were similar to those in mice raised in cyclic light. In C57BL/6 mice however, which contain less Rpe65 protein, dark adaptation was accompanied by an increase in ester levels compared to cyclic light controls. Retinyl ester levels were much higher in Rpe65^?/? mice compared to wild type and kept increasing with age. The results suggest that the RPE65 role in retinyl ester homeostasis extends beyond enabling the formation of 11‐cis retinal.     

Nonlinear evolution of secondary instabilities in boundary-layer transition

Methods of nonlinear stability theory are applied to analyze the evolution of disturbances in the three-dimensional stage immediately preceding the breakdown of a laminar boundary layer. A perturbation scheme is used to solve the nonlinear equations and to develop a dynamical model for the interaction of primary and secondary instabilities. The first step solves for the two-dimensional primary wave in the absence of secondary disturbances. Once this finite-amplitude wave is calculated, it is decomposed into a basic-flow component and an interaction component. The basic-flow component acts as a parametric excitation for the three-dimensional secondary wave, while the interaction component captures the resonance between the secondary and primary waves. Results are presented in two principal forms: amplitude growth curves and velocity profiles. Our results agree with experimental data and the few available results of transition simulations and, moreover, reveal the origin of the observed phenomena. The method described establishes the basis for physical transition criteria in a given disturbance environment.This work has been supported by the Air Force Office of Scientific Research under Contract F46920-87-K-0005 and Grant AFOSR-88-0186 (TH) and by an ONT Postdoctoral Fellowship (JDC).     

Elastic curves on the sphere

This paper deals with the derivation of equations suitable for the computation of elastic curves on the sphere. To this end, equations for the main invariants of spherical elastic curves are given. A new method for solving geometrically constraint differential equations is used to compute the curves for given initial values. A classification of the fundamental forms of the curves is presented.     

A software-driven,single-pump liquid chromatographic system for column-switching applications

A general-purpose, software-driven high-performance liquid chromatographic (HPLC) instrument is described for multidimensional chromatographic experiments. The system consists of a laboratory microcomputer, a commercial solvent delivery system, a flexible, computer-controlled valving system and a conventional, mixed-wavelength, ultraviolet (u.v.) detector. Reconfiguration of the instrument for a variety of multidimensional experiments involves only a change in software and the column/valve connections. Several single-valve and two-valve configurations, including those for back-flushing, auto-injection, heartcutting, sample cleanup and selectivity programming are illustrated along with chromatograms obtained on various complex mixtures.