Palladium on carbon–bromobenzene mediated esterification and transesterification

A series of carboxylic acids were converted into their corresponding esters using the Pd/C catalyzed hydrogenation conditions in the presence of catalytic bromobenzene in alcohols and the method could also be applicable for the transesterification of esters. Good to excellent yields were obtained for different aliphatic or aromatic starting materials. The success of this esterification relies on the in situ generation of hydrobromic acid (HBr) from bromobenzene which provides a mild and acidic reaction environment. The palladium catalyst exhibits a remarkable activity and is reusable for up-to three consecutive cycles.     

Elucidating the therapeutic activity of selective curcumin analogues: DFT-based reactivity analysis

Structural Chemistry - Density functional theory (DFT) has been employed to study the structure, stability and reactivity of curcumin and some of its important analogues by computing HOMO-LUMO...     

Molecular and Biochemical Characteristics of Recombinant β-Propeller Phytase from Bacillus licheniformis Strain PB-13 with Potential Application in Aquafeed

Phytic acid is the major storage form of organic phosphorus in nature- and plant-based animal feed. It forms insoluble complexes with nutritionally important metals and proteins that are unavailable for monogastric or agastric animals. Phytases initiate the stepwise hydrolysis of phytic acid and release inorganic orthophosphate. In the present investigation, the phytase gene from a phytase producing Bacillus licheniformis strain PB-13 was successfully expressed in Escherichia coli BL21. Recombinant phytase ‘rPhyPB13’ was found to be catalytically active, with an activity of 0.97 U/mL and specific activity of 0.77 U/mg. The rPhyPB13 was purified to 14.10-fold using affinity chromatography. Similar to other β-propeller phytases, purified rPhyPB13 exhibited maximal activity at pH 6.0–6.5 and 60 °C in the presence of 1 mM Ca²⁺ and was highly active over a wider pH range (pH 4.0–8.0) and high temperature (80 °C). It has shown maximum activity towards Na-phytate as substrate. The observed K _m , V _max and k _cat of purified rPhyPB13 were 1.064 mM, 1.32 μmol/min/mg and 27.46 s^?1, respectively. PhyPB13 was resistant to trypsin inactivation, activated in presence of Ca²⁺ and inhibited in presence of EDTA. Crude rPhyPB13 has good digestion efficiency for commercial feed and soybean meal. These results indicate that PhyPB13 is a β-propeller phytase that has application potential in aquaculture feed.     

Phosphine-Catalyzed [4+1] Cycloadditions of Allenes with Methyl Ketimines,Enamines, and a Primary Amine

Unprecedented phosphine-catalyzed [4+1] cycloadditions of allenyl imides have been discovered using various N-based substrates including methyl ketimines, enamines, and a primary amine. These transformations provide a one-pot access to cyclopentenoyl enamines and imines, or (chiral) γ-lactams through two geminal C−C bond or two C−N bond formations, respectively. Several P-based key intermediates including a 1,4-(bis)electrophilic α,β-unsaturated ketenyl phosphonium species have been detected by ³¹P NMR and HRMS analyses, which shed light on the postulated catalytic cycle. The synthetic utility of this new chemistry has been demonstrated through a gram-scaling up of the catalytic reaction as well as regioselective hydrogenation and double condensation to form cyclopentanoyl enamines and fused pyrazole building blocks, respectively.     

Stimuli‐Responsive Naphthalene Diimide as Invisible Ink: A Rewritable Fluorescent Platform for Anti‐Counterfeiting

Herein, we report an approach to combat counterfeiting and storage of valuable information based on the solid‐state fluorescence switching behavior of isoniazid functionalized naphthalene diimide (ISO_NDI) in response to an external stimuli (i. e., HCl vapor). The unique feature of ISO_NDI is further utilized to develop an invisible ink (ISO_NDI‐PVA) with commercial polymer polyvinyl alcohol (PVA). A solid‐state fluorescence recovery was observed while loading with HCl vapors. This exclusive property of the material could be applied directly as a security ink for confidential data storage purpose. Based on above strategy, we successfully realized the rewritable application by using ISO_NDI‐PVA ink and confirm its practical efficacy on various substrates by creating different patterns. The solid‐state fluorescence switching behavior of ISO_NDI‐PVA ink exhibited reversible on/off signal for multiple cycles under the influence of HCl/NH₃ vapors. Mechanistic investigation supports a clear participation of intermolecular charge transfer (ICT) phenomenon in the solid‐state fluorescence switching property. The ease of fabricating the ink with invisible to visible characteristics in response to HCl vapors provides new opportunities for exploring the application of ISO_NDI‐PVA as invisible ink for targeted security applications.     

Production of Raw Starch-Saccharifying Thermostable and Neutral Glucoamylase by the Thermophilic Mold <Emphasis Type="Italic">Thermomucor indicae-seudaticae</Emphasis> in Submerged Fermentation

Among physical and nutritional parameters optimized by “one variable at a time” approach, four cultural variables (sucrose, MgSO₄ ^.7H₂O, inoculum size, and incubation period) significantly affected glucoamylase production. These variables were, therefore, selected for optimization using response surface methodology. The p-values of the coefficients for linear effect of sucrose and inoculum size were less than 0.0001, suggesting them to be the key experimental variables in glucoamylase production. The enzyme production (34 U/ml) attained under optimized conditions (sucrose, 2%; MgSO₄ ^.7H₂O, 0.13%; yeast extract, 0.1%; inoculum size, 5 × 10⁶ spores per 50 ml production medium; incubation time, 48 h; temperature, 40°C; and pH 7.0) was comparable with the value predicted by polynomial model (34.2 U/ml). An over all 3.1-fold higher enzyme titers were attained due to response surface optimization. The experimental model was validated by carrying out glucoamylase production in shake flasks of increasing capacity (0.25–2.0 l) and 22-l laboratory bioreactors (stirred tank and airlift), where the enzyme production was sustainable. Furthermore, the fermentation time was reduced from 48 h in shake flasks to 32 h in bioreactors.     

Glyoxylic acid in the reaction of isatoic anhydride with amines: a rapid synthesis of 3-(un)substituted quinazolin-4(3H)-ones leading to rutaecarpine and evodiamine

A dual reactant/catalyst role of glyoxylic acid in the reaction of isatoic anhydride with various amines afforded a novel, robust and rapid synthesis of 3-(un)substituted quinazolin-4(3H)-ones. This metal catalyst-free reaction proceeds via an unusual and unexpected cleavage of C–C bond. A shorter and common route to two alkaloids, that is, rutaecarpine and evodiamine is also accomplished.     

超导纳米线单光子探测器件的制备

超导纳米线单光子探测器件(SNSPD)是超导单光子探测系统的核心器件。文中介绍了成功制备的基于5nm厚的NbN超导超薄薄膜的SNSPD器件。器件核心结构为150nm宽的纳米曲折线结构,纳米线条占空比为75%,面积为20μm×20μm。超导纳米线是利用电子束曝光(EBL)技术和反应离子刻蚀(RIE)等工艺技术制备的。所制备的SNSPD样品,在温度3.5K下的临界电流约12.9μA;在1310nm波长光波辐照,12.5μA的偏置电流下,探测效率约0.016%。     

Obtaining functional form for chaotic time series evolution using genetic algorithm

A genetic algorithm (GA) based strategy is presented for deducing an exact or near-exact functional form from a time series. The GA formalism proposed here utilizes (i) the "postfix" representation with a view to reduce the procedural complexities and (ii) the "elitist mating" scheme to produce fitter offspring strings. The GA procedure is exemplified by considering chaotic time series of the well-known logistic, Henon and universal maps. The GA correctly recovers the underlying functional forms for the respective time series. Measurements from a number of finite-dimensional physical, biological, and other systems often give rise to complex time series and the presented methodology should prove useful in obtaining functional forms describing accurately the evolution of the time series. (c) 1999 American Institute of Physics.