Indirect detection of the 183W and 57Fe nuclei using 119Sn‐relayed 1H,X correlation spectroscopy

Recently reported triple‐resonance Y‐relayed ¹H,X correlation experiments have been utilized to characterize ¹⁸³W and ⁵⁷Fe chemical shifts using ¹¹⁹Sn as the Y‐relaying nucleus instead of the previously used ³¹P. Application of an adaptation of Gudat's original INEPT/HMQC sequence results in a significant enhancement of the signal‐to‐noise (S/N) ratio for two‐dimensional ¹¹⁹Sn‐relayed ¹H,¹⁸³W and ¹H, ⁵⁷Fe correlation spectra with efficient detection of the transition metal nucleus in tungsten and iron complexes lacking an observable direct scalar coupling between the transition metal and any hydrogen nuclei. Strengths and shortcomings of the novel sequence and the original sequences reported by Gudat are discussed in the context of ¹¹⁹Sn‐relayed proton detection of very low frequency transition metal nuclei. Copyright © 2010 John Wiley & Sons, Ltd.     

Photoluminescent energy transfer from poly(phenyleneethynylene)s to near‐infrared emitting fluorophores

Photoluminescent energy transfer was investigated in conjugated polymer‐fluorophore blended thin films. A pentiptycene‐containing poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission and the enhancement of the fluorophore emission. Near‐infrared emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near‐infrared region on a completely dark background, offer substantial possibilities for designing highly sensitive turn‐on sensors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3382–3391, 2010     

A novel approach to modelling counter-current chromatography

Literature lists a number of counter-current chromatography (CCC) models that can predict the retention time and to a certain extent the peak width of a solute eluting from a CCC column. The approach described in this paper distinguishes itself from previous reports by relating all model parameters directly to column dimensions and experimental settings. Most importantly, this model can predict a chromatogram from scratch without resorting to traditional calibration using empirical values. The model validation with experimental results obtained across a range of CCC instruments demonstrated that the solute retention time, peak width, and peak resolution could be predicted within reasonable accuracy. Additionally, the effect of several process parameters, such as mobile phase flow rate, rotational speed of the column or β-value, showed that the model is robust and applicable to a wide range of CCC instruments. Overall, this model proved to be a useful tool for parameter estimation and, most significantly, separation optimisation.     

Sensitivity to point-spread function parameters in medical ultrasound image deconvolution

Clinical ultrasound images are often perceived as difficult to interpret due to image blurring and speckle inherent in the ultrasound imaging. But the image quality can be improved by deconvolution using an estimate of the point-spread function. However, it is difficult to obtain a sufficiently accurate estimate of the point-spread function in vivo because of the unknown properties of the soft tissue in clinical applications. Local variations in the speed of sound and attenuation change the pulse and beam shape. These in turn affect the point-spread function. The purpose and novelty of this paper is therefore to explore the sensitivity of a state-of-the-art deconvolution algorithm to uncertainty in the point-spread function. The point-spread function in our restoration algorithm is made shift invariant in the lateral dimension but shift dependent in the axial direction, and is modelled to match a 128-element 1D linear array often found in clinical use. We present simulated and in vitro sensitivity analyses of two-dimensional deconvolution while varying six parameters on which the point-spread function depends. Uncertainty in the ultrasound machine is analysed by varying the axial depths of lateral and elevational foci alongside height and width of transducer elements. Sensitivity to tissue influence is investigated by varying the speed of sound and frequency-dependent attenuation of the electro-mechanical impulse response. The results are analysed both quantitatively and in terms of the perceived image quality. First, the assessment of deconvolution using the logarithmic image amplitude is found to be a better indicator of the perceived improvement in the restoration. Secondly, the two most critical parameters for two-dimensional deconvolution are discovered to be the lateral focus and the speed of sound, because the success of deconvolution is perceived primarily in terms of deblurring. We also observed similar patterns for the simulation and in vitro experiment. Finally, we show that it is possible to restore in vivo ultrasound images using an assumed point-spread function and hence conclude that an exact point-spread function is not necessary for enhancing ultrasound image quality by deconvolution.     

(+)‐Gibberellin C: hydrogen‐bonding pattern of the monohydrate of a non‐racemic pentacyclic diterpenoid

In the monohydrate of the title compound, (+)‐2β,4aα‐di­hydroxy‐1,7‐di­methyl‐8‐oxo‐4bβ,7α‐gibbane‐1α,10β‐di­carb­ox­yl­ic acid‐1,4a‐lactone, C₁₉H₂₄O₆·H₂O, intermolecular hydrogen bonding progresses helically along b from carboxyl to ketone [O?O = 2.694 (5) Å]. The carboxyl and lactone carbonyl groups in translationally related mol­ecules within a helix both accept hydrogen bonds from the same water of hydration. The oxy­gen of this water in turn accepts a hydrogen bond from the hydroxyl group of a third screw‐related mol­ecule in an adjacent counterdirectionally oriented helix, yielding a complex three‐dimensional hydrogen‐bonding array. Intermolecular O?H—C close contacts were found to the carboxyl and lactone carbonyls, the hydroxyl, and the water.     

High‐performance liquid chromatography/mass spectrometric and proton nuclear magnetic resonance spectroscopic studies of the transacylation and hydrolysis of the acyl glucuronides of a series of phenylacetic acids in buffer and human plasma

The use of high‐performance liquid chromatography/mass spectrometry (HPLC/MS) and proton nuclear magnetic resonance (¹H NMR) spectroscopy for the kinetic analysis of acyl glucuronide (AG) isomerisation and hydrolysis of the 1‐β‐O‐acyl glucuronides (1‐β‐O‐AG) of phenylacetic acid, (R)‐ and (S)‐α‐methylphenylacetic acid and α,α‐dimethylphenylacetic acid is described and compared. Each AG was incubated in both aqueous buffer, at pH 7.4, and control human plasma at 37°C. Aliquots of these incubations, taken throughout the reaction time‐course, were analysed by HPLC/MS and ¹H NMR spectroscopy. In buffer, transacylation reactions predominated, with relatively little hydrolysis to the free aglycone observed. In human plasma incubations the calculated rates of reaction were much faster than for buffer and, in contrast to the observations in buffer, hydrolysis to the free aglycone was a significant contributor to the overall reaction. A diagnostic analytical methodology based on differential mass spectrometric fragmentation of 1‐β‐O‐AGs compared to the 2‐, 3‐ and 4‐positional isomers, which enables selective determination of the former, was confirmed and applied. These findings show that HPLC/MS offers a viable alternative to the more commonly used NMR spectroscopic approach for the determination of the transacylation and hydrolysis reactions of these AGs, with the major advantage of having the capability to do so in a complex biological matrix such as plasma. Copyright © 2010 John Wiley & Sons, Ltd.     

An efficient one-pot multicomponent approach to 5-amino-7-aryl-8-nitrothiazolo[3,2-a]pyridines

A series of thiazolo[3,2-a]pyridines have been prepared using a multicomponent reaction between aromatic aldehydes, 2-nitromethylenethiazolidine and nitriles containing an active methylene group (malononitrile, ethyl 2-cyanoacetate and 2-phenylsulfonylacetonitrile) in the presence of Et₃N under mild conditions with high yields. One of the compounds shows promising anticancer activity across a range of cancer cell lines.     

Doubly diastereoselective conjugate addition of enantiopure lithium amides to enantiopure N-enoyl oxazolidin-2-ones: a mechanistic probe

The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure N-enoyl oxazolidin-2-ones has been used as a mechanistic probe to determine that the reactive conformation is the anti-s-cis form. The β-amino carbonyl products resulting from these conjugate addition reactions are useful templates for further elaboration into an α,β,α-pseudotripeptide.     

Sol–gel nanocoating on commercial TiO<Subscript>2</Subscript> nanopowder using ultrasound

The surface of commercial titania particles was coated by a layer of silica by a two-step process which involved a power ultrasound initiated sol–gel reaction. In the first step of this solution process, aminosilane, i.e. organosilane with amino functional group, was used to modify the surface of pristine nanoparticles. Subsequent silica nanocoating was initiated and sustained under power ultrasound agitation in a mixture of surface modified particles and epoxysilane. As a result, a homogenous coverage of silica on the nanoparticles’ surface, with thickness controllable from one to several nanometers, was obtained. Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and particle surface zeta potential measurements were employed to follow steps in the process and to confirm the reaction mechanism.