Simulation of the electronic and vibrational structure of hydrogenated amorphous silicon using cluster models

A set of simple models of hydrogenated amorphous silicon (a-Si:H) consisting of hypothetical silane molecules with diamond or similar lattices was studied by the semiempirical AM1 method. Densities of states and infrared spectra were calculated for the silane molecules and similar molecules with dangling bonds disorder, and with boron or phosphorus substitution to simulate doping. Some examples are presented, and a comparison is made with experimental properties of a-Si:H. It is proposed to use these models in a study of the Staebler–Wronski photodegradation of a-Si:H and other aspects of amorphous silicon technology. © John Wiley & Sons, Inc.     

End-to-end single cyanato and thiocyanato bridged Cu(II) polymers with a new tridentate Schiff base ligand: crystal structure and magnetic properties

A new tridentate Schiff base ligand HL (L = C14H19N2O), derived from the condensation of benzoylacetone and 2-dimethylaminoethylamine in a 1:1 ratio, reacts with copper(ii) acetate and cyanate, thiocyanate or azide, to give rise to several end-to-end polymeric complexes of formulae [CuL(mu(1,3)-NCO)]n 1, [CuL(mu(1,3)-NCS)]n 2 and the complex 3 has two crystallographically independent units of formula [CuL(N3)] in the asymmetric unit cell. Complex 3 exists in dimeric form rather than as a polymeric chain. Compound 1 is the first report of a singly end-to-end cyanate bridged polymeric chain of Cu(II) with a Schiff base as a co-ligand. There are many examples of double NCS bridged polymeric chains, but fewer singly bridged ones such as compound 2. We have characterized these complexes by analytical, spectroscopic, structural and variable temperature magnetic susceptibility measurements. The coordination geometry around the Cu(II) centers is distorted square pyramidal for 1 and 2 and square planar for complex 3. The magnetic susceptibility data show slight antiferromagnetic coupling for the polymers having J values -0.19 and -0.57 cm(-1) for complexes 1 and 2 respectively. The low values of J are consistent with the equatorial-axial disposition of the bridges in the polymers.     

Evaluating and clustering retrosynthesis pathways with learned strategy

With recent advances in the computer-aided synthesis planning (CASP) powered by data science and machine learning, modern CASP programs can rapidly identify thousands of potential pathways for a given target molecule. However, the lack of a holistic pathway evaluation mechanism makes it challenging to systematically prioritize strategic pathways except for using some simple heuristics. Herein, we introduce a data-driven approach to evaluate the relative strategic levels of retrosynthesis pathways using a dynamic tree-structured long short-term memory (tree-LSTM) model. We first curated a retrosynthesis pathway database, containing 238k patent-extracted pathways along with ∼55 M artificial pathways generated from an open-source CASP program, ASKCOS. The tree-LSTM model was trained to differentiate patent-extracted and artificial pathways with the same target molecule in order to learn the strategic relationship among single-step reactions within the patent-extracted pathways. The model achieved a top-1 ranking accuracy of 79.1% to recognize patent-extracted pathways. In addition, the trained tree-LSTM model learned to encode pathway-level information into a representative latent vector, which can facilitate clustering similar pathways to help illustrate strategically diverse pathways generated from CASP programs.

Tree-structured long short-term memory neural model learns to understand the retrosynthesis design strategies from patent-extracted retrosynthetic pathway data.     

Thermostability of <Emphasis Type="Italic">Cromobacterium viscosum</Emphasis> lipase in AOT/isooctane reverse micelle

The thermostability of Cromobacterium viscosum lip ase (EC 3.1.1.3) entrapped in AOT (sodium bis-[2-ethylhexyl] sulfosuccinate) reverse micelles was in creased by the addition of short-chain polyethylene glycol (PEG 400). Two different approaches were considered: (1) the determination of half-life time and (2) the mechanistic analysis of deactivation kinetics. The half-life of lipase entrapped in AOT/isooctane reverse micelles with PEG 400 at 60°C was 28h, ninefold higher than that in reverse micelles without PEG 400. The lip ase entrapped in both reverse micellar systems followed a series-type deactivation mechanism involving two first-order steps. The deactivation constant for the first step at 60°C in PEG containing reverse micelles was 0.055 h¹¹, 11-fold lower than that in reverse micelles without PEG, whereas it remained almost constant for the second step. The inactivation energy of the lip ase entrapped in reverse micelles with and without PEG 400 was 88.12 and 21.97 kJ/mol, respectively.     

Improvement in enzyme activity and stability by addition of low molecular weight polyethylene glycol to sodium bis(2-ethyl-L-hexyl)sulfosuccinate/isooctane reverse micellar system

The activity and stability of Chromobacterium viscosum lipase (glycerolester hydrolase, EC 3.1.1.3)-catalyzed olive oil hydrolysis in sodium bis (2-ethyl-1-hexyl)sulfosuccinate (AOT)/isooctane reverse micelles is increased appreciably when low molecular weight polyethylene glycol (PEG 400) is added to the reverse micelles. To understand the effect of PEG 400 on the phase behavior of the reverse micellar system, the phase diagram of AOT/PEG 400/water/isooctane system was studied. The influences of relevant parameters on the catalytic activity in AOT/PEG 400 reverse micelles were investigated and compared with the results in the simple AOT reverse micelles. In the presence of PEG 400, the linear decreasing trend of the lipase activity with AOT concentration, which is observed in the simple AOT reverse micelles, disappeared. Enzyme entrapped in AOT/PEG reverse micelles was very stable, retaining>75% of its initial activity after 60 d, whereas the half-life in simple AOT reverse micelles was 38 d. The kinetics parameter maximum velocity (V _max)exhibiting the temperature dependence and the activation energy obtained by Arrhenius plot was suppressed significantly by the addition of PEG 400.     

A systematic investigation on flavonoids,catechin, β-sitosterol and lignin glycosides from Saraca asoca (ashoka) having anti-cancer & antioxidant properties with no side effect

Saraca asoca is an IUCN red-listed tree species that extensively famous in the Ayurvedic medicine field. Saraca asoca (Roxb.) de Wilde belongs to the family Fabaceae, has been used to treat various gynecological disorders, bacterial infections, worm infestations, haemmorhagic dysentery, uterine pain, skin diseases, cancer, circulatory, cardiovascular disorders, and many others. All parts of the Saraca asoca have medicinal values. Numerous antioxidant compounds like flavonoids, catechin, beta-sitosterol, lignin glycosides are present in the bark, leaf, and flower of Saraca asoca plant, which help to stabilize free radicals molecules that are associated with the development of cancer conditions. Currently in the cancer research study field new and more effective modes of natural therapies are recently being analyzed. Traditional medicines have been used for their preventative role against various diseases in the human population. Plant based therapy for cancer prevention is becoming more demanding due to its various unique properties such as natural chemical composition, less expensiveness, naturally available., easily orally administrable, significant chemo-protective activities, nontoxic to normal cells in the body, less side effects compared to other synthetic chemotherapeutic drugs. The chemotherapeutic drugs will be harmful to both cancer and normal cells. Additionally, some common side effects or health consequences like vomiting, nausea, bleeding, hair fall, alopecia, hyperuricemia, thrombocytopenia, bone marrow depression, mucositis are very common after chemotherapeutic drug treatment in cancer. This review paper summarizes the evidences which agree with the fact that flavonoids and other phenolic compounds in Saraca asoca plant possess significant antioxidant activity and an efficient chemopreventive characteristic against different types of cancer. This paper reviews the anticancer activities of Saraca asoca bark and flower and discusses the potential preventive roles of phenolic and flavonoids compounds, present in bark and flower of Saraca asoca in the cancer treatment process.     

New coupled Liouville system: Prolongation structure,soliton solution,and complete integrability

We suggest a new coupled Liouville equation which is exactly solvable. We obtain the Lax pair through a prolongation analysis and also obtain the exact one-soliton-like solution by a direct procedure. We confirm our result through a Painlevé analysis of the similarity reduced systems.     

Simulated annealing‐based optimal control over tunneling process through SDWP and Eckart barrier: A momentum basis representation

For a reaction to proceed via tunneling mechanism, it is essential that the reactants will cross the potential barrier (E_P), where its initial energy (E₀) is below the potential barrier E_P. Tunneling probability τ is defined as the probability of having momentum higher than k_m, where . In the momentum basis representation, τ can be directly calculated by integrating from the limit k_m to infinity, where is the wave function in the momentum space. Instead of the continuous basis, if we chose momentum grid space, τ can be expressed as . Our target here is to increase this τ by applying a polychromatic field, so that the reaction rate can be enhanced. By applying Simulated Annealing technique we have designed some polychromatic electric fields, spatially symmetric and asymmetric type, which enhances the tunneling rate in symmetric double well system and Eckart barrier confined in an infinite well.