A mild, expedient, one-pot trifluoromethanesulfonic anhydride mediated synthesis of N-arylimidates

The direct transformation of various secondary amides into N-arylimidates via mild electrophilic amide activation with trifluoromethanesulfonic anhydride (Tf₂O) in the presence of 2-chloropyridine (2-ClPyr) is described. Low-temperature amide activation followed by C-O bond formation with 2-naphthol provides the desired N-arylimidates in short overall reaction times. In contrast, reaction with oxindole proceeds via formation of a C-C bond to give 1-(1H-indol-2-yl)naphthalene-2-ol.     

Sample stacking microemulsion electrokinetic capillary chromatography induced by reverse migrating pseudostationary phase for the quantification of phenobarbital and its p-hydroxyphenobarbital metabolite in rat urine

For the first time, a capillary electrophoretic (CE) method with sample stacking induced by a reverse migrating pseudostationary phase (SRMP) technique has been developed and validated for sensitive determination of phenobarbital (PB) and its p-hydroxyphenobarbital (PHPB) metabolite in rat urine samples. Separation and determination were optimized on a fused-silica capillary with a total length of 50 cm (effective length 40 cm) and 75 μm ID. The microemulsion background electrolyte consisted of 0.8% (v/v) ethyl acetate, 6.6% (v/v) butan-2-ol, 1.0% (v/v) acetonitrile, 2.0% (w/v) sodium n-dodecyl sulfate (SDS), and 89.6% (v/v) of 7.5 mM ammonium formate at pH 8. When this preconcentration technique was used, the sample stacking and the separation processes took place successively with changing the voltage with an intermediate polarity switching step. For practical application, a solid-phase extraction (SPE), C(18) sorbent with n-hexane/ethyl acetate (1?:?1%, v/v) as the elution solvent was used for sample purification and concentration. The SPE method gave good extraction yields for all the analytes, with absolute recovery values of 96.9% and 99.1% for PB and PHPB, respectively. The regression equations for PB and PHPB showed excellent linearity over a concentration range of 55-1386 ng mL(-1) for PB and PHPB (r = 0.998). The developed microemulsion electrokinetic capillary chromatography (MEEKC) method for separation of the studied compounds with SRMP as the electrophoretic preconcentration technique allowed detection limits in urine samples at 16.8 ng mL(-1) for PB and PHPB which are 15-fold lower than the reported CE method in the literature. The precision results, expressed by the intra-day and inter-day relative standard deviation (RSD) values range from 3.6 to 7.1% (repeatability) and from 3.2 to 7.2% (intermediate precision) for PB and PHPB, respectively, which were in line with Food and Drug Administration (FDA) criteria.     

Protein splicing in cis and in trans

Intein-mediated protein splicing is a self-catalytic process in which the intervening intein sequence is removed from a precursor protein and the flanking extein segments are ligated with a native peptide bond. Splice junction proximal residues and internal residues within the intein direct these reactions. The identity of these residues varies in each intein, as groups of related residues populate conserved motifs. Although the basics of the four-step protein splicing pathway are known, mechanistic details are still unknown. Structural and kinetic analyses are beginning to shed some light. Several structures were reported for precursor proteins with mutations in catalytic residues, which stabilize the precursors for crystallographic study. Progress is being made despite limitations inherent in using mutated precursors. However, no uniform mechanism has emerged. Kinetic parameters were determined using conditional trans-splicing (splicing of split precursor fragments after intein reassembly). Several groups concluded that the rate of the initial acyl rearrangement step is rapid and Asn cyclization (step 3) is slow, suggesting that this latter step is rate limiting. Understanding the protein splicing pathway has allowed scientists to harness inteins for numerous applications.     

Cardioprotective Effect of Tangeretin by Inhibiting PTEN/AKT/mTOR Axis in Experimental Sepsis-Induced Myocardial Dysfunction

Sepsis aggregates undesirable immune response causing depression of ventricular myocardium and diastolic dysfunction. This present study examined the effect of a plant-derived flavone tangeretin (TG) on autophagy and reduction in myocardial dysfunction. The sepsis was induced by cecum ligation and puncture (CLP) in male Sprague–Dawley rats. Abnormal changes were seen in the heart after the sepsis induction. These abnormalities were analyzed based on the cardiac markers, namely Cardiac myosin light chain-1 (cMLC1) and Cardiac troponin I (cTnl), echocardiography, and plasma parameters, like Lactate dehydrogenase (LDH) and Creatinine kinase (CK). Microanatomy of the heart was studied using hematoxylin and eosin stained histopathological samples of cardiac tissue. Western blot technique was used to detect the nature and extent of protein with the amount of a specific RNA (gene expression) in the cardiac homogenate. Oxidative damage was analyzed using redox marker, reduced glutathione. This study successfully showed that TG attenuated sepsis-induced myocardial dysfunction by inhibiting myocardial autophagy via silencing the Phosphatase and tensin homolog (PTEN) expression and acting on the AKT/mTOR pathway. The present findings supported that TG is a novel cardioprotective therapeutic target for sepsis induced myocardial dysfunction.     

Analyticity and nonexistence of classical steady Hele‐Shaw fingers

This paper concerns analyticity of a classical steadily translating finger in a Hele‐Shaw cell and nonexistence of solutions when relative finger width λ is smaller than ½. It is proved that any classical solution to the finger problem, if it exists for sufficiently small but nonzero surface tension and is close to some Saffman‐Taylor zero‐surface‐tension solution and satisfies some algebraic decay conditions at ∞, must belong to the analytic function space A ₀, as defined in Section 1, and chosen in a previous study [34] of existence of finger solutions. Further, it is proved that for any fixed λ ∈ (0, ½), there can be no classical steady finger solution when surface tension is sufficiently small, in disagreement with a previous conclusion based on numerical simulation. © 2002 Wiley Periodicals, Inc.     

Elimination of photorefractive grating writing instabilities in iron-doped lithium niobate

Two types of instabilities, one slow (seconds) and one fast (nanoseconds), are observed while writing volume gratings in bulk crystals of iron-doped lithium niobate using contra-directional two-beam coupling along the c axis. A method to eliminate the fast instability was achieved by coating the z surfaces of the crystal with either dielectric (anti-reflection) or transparent conductive coatings. For the second case, electrically shorting the crystal eliminated the slow instability.     

DC conduction processes and electrical parameters of the organic semiconducting zinc phthalocyanine, ZnPc, thin films

Electronic conduction in thermally evaporated thin films of organic semiconductor zinc phthalocyanine (ZnPc) has been investigated in a broad temperature range using gold Ohmic contacts. Electronic conduction by charge carrier hopping was dominated at low temperatures and for all applied voltages. At higher temperatures and at voltages just below 2 V conduction was found to obey Ohm's law, while at higher voltages space-charge-limited conduction (SCLC) was the dominated mechanism, which was controlled by hole-trapping states distributed exponentially within the band gap.In freshly prepared samples adsorbed oxygen was responsible for lower hole mobility and higher charge carrier concentrations. Prolonged heating of ZnPc films at 425 K resulted in lower defect state density, and thus reduced trap concentration and higher charge carrier mobility.     

Studies with enaminones: Synthesis and chemical reactivity of 2‐(4‐dimethylamino‐2‐oxobut‐3‐enyl)‐isoindole‐1,3‐dione and of 4‐(4‐dimethylamino‐2‐oxobut‐3‐enyloxy)‐2H‐phthalazin‐1‐one

The title compounds were synthesized via condensing acetonylphthalimide and 4‐acetonyloxyphthalazine‐1‐one with dimethylformamide dimethylacetal (DMFDMA). The reaction of these enaminones with electrophiles and nucleophiles is reported as a route to polyfunctional heteroaromatics.     

Turn‐On Ratiometric Fluorescent Probe for Selective Discrimination of Cr3+ from Fe3+ in Aqueous Media for Living Cell Imaging

Pyrene‐based turn‐on ratiometric fluorescent probe 1 demonstrates high sensitivity and exceptional selectivity toward Cr³⁺ in the presence of other metals, including Fe³⁺ in aqueous media. Interaction of Cr³⁺ with probe 1 brings pyrene moieties close enough to have better aligned π–π stacking, thus enhancing the excimer peak many fold. On the other hand, the interaction of Fe³⁺ with probe 1 brings forth a negligible difference in stacking, resulting in an insignificant change in fluorescence intensity. Exceptional selectivity of probe 1 with Cr³⁺ over Fe³⁺ and other metals has been confirmed by theoretical studies in addition to experimental results. Imaging of HeLa cells observed by confocal fluorescence microscopy reveals that probe 1 can be used to monitor Cr³⁺ in live cells to map its subcellular distribution.     

A non-standard finite difference scheme for convection in a porous cavity

In this paper, a non-standard finite difference scheme is proposed for solving a steady finite Rayleigh number convection in a porous cavity with an inclined magnetic field and non-uniform internal heating. Numerical results are compared with the classical finite difference scheme.