Liquid crystalline paracyclophane derivatives

Various paracyclophane derivatives incorporating 4,4'-biphenyl, 2,5-diphenyl-1,3,4-thiadiazole, phenyl benzoate and 2,6-disubstituted naphthyl rigid cores were synthesized and their mesomorphic behaviour was studied using polarizing microscopy, DSC and X-ray diffraction. Most of these macrocyclic compounds possess liquid crystalline properties with unexpectedly high clearing temperatures compared to those of conventional calamitic mesogens. In this way, the coupling of two appropriate rigid units using flexible chains to form a macrocycle constitutes a new and powerful approach towards mesophase induction and stabilization. The types of mesophase formed by these macrocycles do not depend only on the nature of the bridging chains, but also strongly on the structure of the rigid aromatic system. The smectic A phase and the E phase are formed by polyetherbiphenylophanes. Poly-ethercyclophanes incorporating the 2,5-diphenylthiadiazole rigid core form nematic and smectic C phases. The nematic phase is the only mesophase when the rigid core is the phenyl benzoate unit. No mesomorphic properties could be detected for macrocycles which featured either the benzyl phenyl ether moiety or the 2,6-disubstituted naphthalene unit in their constitution.     

Controlled enzymatic synthesis of natural-linkage, defined-length polyubiquitin chains using lysines with removable protecting groups

E2 enzymes catalyze the ATP-dependent polymerization of polyubiquitin chains which function as molecular signals in the regulation of numerous cellular processes. Here we present a method that uses genetically encoded unnatural amino acids to halt and re-start ubiquitin polymerization providing access to natural-linkage, precision-length ubiquitin chains that can be used for biochemical, structural, and dynamics studies.     

Fourier-transform infrared spectroscopy discriminates a spectral signature of endometriosis independent of inter-individual variation

Endometriosis is the growth of endometrial tissue outside of the uterine cavity. Its aetiology remains obscure, and it is difficult to diagnose ranging from asymptomatic to debilitating disease. Mid-infrared (IR) spectroscopy has become recognised as a potential clinical diagnostic tool. Biomolecules absorb mid-IR (4000 cm(-1) to 400 cm(-1)) and from this, a biochemical-cell fingerprint in the form of an absorbance spectrum can be derived. We set out to determine if IR spectroscopy could be used to identify underlying biochemical differences between endometrial tissues growing outside of the uterus (ectopic) from endometrial tissue of the uterus (eutopic). For comparative purposes, endometrial tissues from endometriosis-free women were also obtained (benign eutopic). Attenuated total reflection Fourier-transform IR (ATR-FTIR) spectroscopy or transmission FTIR microspectroscopy was employed for spectral acquisition. Principal component analysis (PCA)-linear discriminant analysis (LDA) was used for chemometric analysis. A clear segregation was exhibited between the three categories independent of inter-individual confounding differences. Importantly, there was a marked difference between eutopic endometrial tissue from patients with or without endometriosis. This indicates that IR spectroscopy coupled with multivariate analysis (e.g., PCA-LDA) may provide a non-invasive diagnostic tool for endometriosis. By analysing the underlying biochemistry of these endometrial tissues, this approach may facilitate a better understanding of this pathology.     

One‐Pot Decarboxylative Acylation of N‐, O‐, S‐Nucleophiles and Peptides with 2,2‐Disubstituted Malonic Acids

Monocarbonyl activation of 2,2‐disubstituted malonic acids with benzotriazole leads to decarboxylation of one of the carboxy groups and formation of a C?H bond. Intermediate carbonyl benzotriazoles then readily acylate nucleophilic reagents and peptides resulting in libraries of conjugates and peptidomimetics.     

Gallium trichloride-catalyzed conjugate addition of indole and pyrrole to α,β-unsaturated ketones in aqueous media

Michael addition of indole and pyrrole to a variety ofα,β-unsaturated ketones was efficiently promoted by a catalytic amount of GaCl_3 in aqueous media to afford the corresponding products in good to excellent yields.     

Stability of Parallel Fluid Loaded Plates: A Nonlocal Approach

We consider the motion of a collection of fluid loaded elastic plates, situated horizontally in an infinitely long channel. We use a new, unified approach to boundary value problems, introduced by A.S. Fokas in the late 1990s, and show the problem is equivalent to a system of one‐parameter integral equations. We give a detailed study of the linear problem, providing explicit solutions and well‐posedness results in terms of standard Sobolev spaces. We show that the associated Cauchy problem is completely determined by a matrix, which depends solely on the mean separation of the plates and the horizontal velocity of each of the driving fluids. This matrix corresponds to the infinitesimal generator of the C₀ ‐semigroup for the evolution equations in Fourier space. By analyzing the properties of this matrix, we classify necessary and sufficient conditions for which the problem is asymptotically stable.     

Automated solid-phase extraction method for the determination of piperaquine in plasma by peak compression liquid chromatography

A validated bioanalytical method for the determination of piperaquine (PQ) in plasma by solid-phase extraction (SPE) and liquid chromatography (LC) using peak compression is presented. Protein is precipitated from plasma with acetonitrile-1% aqueous acetic acid (85:15, v/v). An internal standard (IS) is added to the samples before they are loaded onto a strong cation exchanger (Isolute PRS) SPE column. PQ and the IS are analyzed by LC on a Zorbax SB-CN column (250 x 4.0 mm) with the mobile phase acetonitrile-phosphate buffer [I = 0.1, pH 2.5 (12:88, v/v)] and UV detection at 345 nm. Trichloroacetic acid (TCA) is added to the samples prior to injection into the chromatography system. PQ elutes in a gradient of TCA, which enables peak compression of PQ and significantly higher peak efficiency as a result. The intraassay precision for plasma is determined to be 5.4% at 3.00 microM and 5.8% at 0.050 microM. The interassay precision for plasma is 1.3% at 3.00 microM and 10.0% at 0.050 microM. The lower limit of quantitation and the limit of detection are 0.025 and 0.005 microM, respectively.