Correlation between catalytic activity and surface ligands of monolayer protected gold nanoparticles

Gold nanoparticles (GNPs) are known to be a very good catalyst. Also, the anchoring of GNPs with stabilizing ligands is essential for surface modification, tuning of size and shapes, and to prevent from aggregation in suspension. But the effect of ligand on the catalytic property of ligand-capped GNP is yet to be explored in detail. In this paper, we perform an in-depth study of effect of ligands on the catalytic activity of monolayer protected GNPs. For this study, a series of different ligand functionalized GNPs in suspension as well as functionalized GNPs' thin film on glass substrate are prepared and used as catalysts in two model reactions, viz. borohydride reduction of 4-nitrophenol and redox reaction between potassium ferricyanide and sodium thiosulfate. The functionalization of GNPs with any ligand reduces its virgin catalytic activity, no matter whether the GNPs are suspended or supported as thin film. An increase in alkyl chain length of alkanethiols and alkylamines ligands and their graft density to the surface of GNP reduces its catalytic activity. Interestingly, the capping of GNPs with 11-mercaptoundecanoic acid and 11-mercaptoundecanol ligands completely destroys its catalytic activity. The effect of anchoring group of ligand molecules on the catalytic activity of ligand-protected GNPs is also discussed.     

Photophysical processes involved within the anisole-thioindoxyl dyad system

The photophysical properties and the nature of the photoinduced electron transfer (PET) reactions within a synthesized anisole (A)-thioindoxyl (T) dyad system (24MBTO) have been studied by electrochemical, steady-state, and time-resolved spectroscopic techniques. Computations on the dyad were performed both in gas phase as well as solvent environment by TD-DFT method with B3LYP density function. The geometry optimization calculation of 24MBTO was done by 6-311G(d,p) basis function set implemented in the Gaussian package. The theoretical values of singlet vertical excitation energies were found to correlate well with the experimentally observed ones. The electrochemical measurements indicate the possibility of occurrence of PET reactions within 24MBTO between the linked redox centers A and T. Both steady-state and time-resolved spectroscopic measurements on the novel synthesized 24MBTO dyad demonstrate the formations of the two types of isomeric species: Z- and E- forms, resulted from the charge separation reactions. From the detailed studies it reveals that the present thioaurone may behave as a versatile photoswitchable system. It has been hinted that the loss process (charge recombination) within 24MBTO could possibly be prevented by incorporating it within the hydrophobic cavity of beta-cyclodextrin (betaCD).     

Reactions of potassium bis(phosphinimino)methanide with group 11 compounds

Transmetalation of the potassium methanide complex, K{CH(PPh2NSiMe3)2}, with [(Ph3P)2CuI] afforded the corresponding copper complex [{CH(PPh2NSiMe3)2}CuPPh3] (1), whereas the reaction of K{CH(PPh2NSiMe3)2} with [Ph3PAuCl] resulted in the dinuclear gold complex [(Ph3PAu)2{C(PPh2NSiMe3)2}] (2). The solid-state structure of 1 shows the formation of a six-membered metallacycle (N1-P1-C1-P2-N2-Cu) that has a twist boat conformation. In contrast, compound 2 is an alpha,alpha-diaurated species, in which the two gold atoms are coordinated in a linear fashion onto the ligand backbone. Photoluminescence measurements show that the latter compound has a strong violet emission.     

Phase transfer of gold nanoparticles from aqueous to organic solution containing resorcinarene

Citrate-capped gold nanoparticles (NPs) in aqueous solution were transferred directly into the organic solution mesitylene containing C-undecylcalix[4]-resorcinarene (C11-resorcinarene). C11-resorcinarene, which has long hydrophobic tails and phenolic hydroxyl groups, acted as both a phase-transfer and a capping agent. The C11-resorcinarene-capped gold particles could be isolated and dispersed in different organic solvents. Optical absorption spectra corresponding to surface plasmon resonance provided a broad band centered at 534 nm for C11-resorcinarene-capped gold NPs in mesitylene. High-resolution transmission electron micrograph images revealed that the average particle diameter of C11-resorcinarene-capped gold NPs is approximately 12 nm.     

Zero-field spin splitting in a two-dimensional electron gas with the spin-orbit interaction revisited

We consider a two-dimensional electron gas (2DEG) with the Rashba spin-orbit interaction (SOI) in the presence of a perpendicular magnetic field. We derive analytical expressions of the density of states (DOS) of a 2DEG with the Rashba SOI in the presence of a magnetic field by using the Green's function technique. The DOS allows us to obtain the analytical expressions of the magnetoconductivities for spin-up and spin-down electrons. The conductivities for spin-up and spin-down electrons oscillate with different frequencies and give rise to the beating patterns in the amplitude of the Shubnikov-de Haas (SdH) oscillations. We find a simple equation which determines the zero-field spin splitting energy if the magnetic field corresponding to any beat node is known from the experiment. Our analytical results reproduce well the experimentally observed non-periodic beating patterns, number of oscillations between two successive nodes and the measured zero-field spin splitting energy.     

Zitterbewegung of electrons in quantum wells and dots in the presence of an in-plane magnetic field

We study the effect of an in-plane magnetic field on the zitterbewegung (ZB) of electrons in a semiconductor quantum well (QW) and in a quantum dot (QD) with the Rashba and Dresselhaus spin-orbit interactions (SOIs). We obtain a general expression of the time-evolution of the position vector and current of the electron in a semiconductor QW. The amplitude of the oscillatory motion is directly related to the Berry connection in momentum space. We find that in presence of the magnetic field the ZB in a QW does not vanish when the strengths of the Rashba and Dresselhaus SOIs are equal. The in-plane magnetic field helps to sustain the ZB in QWs even at a low value of k(0)d (where d is the width of the Gaussian wavepacket and k(0) is the initial wavevector). The trembling motion of an electron in a semiconductor QW with high Landé g-factor (e.g. InSb) is sustained over a long time, even at a low value of k(0)d. Further, we study the ZB of an electron in QDs within the two sub-band model numerically. The trembling motion persists in time even when the magnetic field is absent as well as when the strengths of the SOI are equal. The ZB in QDs is due to the superposition of oscillatory motions corresponding to all possible differences of the energy eigenvalues of the system. This is an another example of multi-frequency ZB phenomenon.     

Application of a Multilayer Perceptron Artificial Neural Network for the Prediction and Optimization of the Andrographolide Content in Andrographis paniculata

Andrographolide, the principal secondary metabolite of Andrographis paniculata, displays a wide spectrum of medicinal activities. The content of andrographolide varies significantly in the species collected from different geographical regions. Therefore, this study aims at investigating the role of different abiotic factors and selecting suitable sites for the cultivation of A. paniculata with high andrographolide content using a multilayer perceptron artificial neural network (MLP-ANN) approach. A total of 150 accessions of A. paniculata collected from different regions of Odisha and West Bengal in eastern India showed a variation in andrographolide content in the range of 0.28–5.45% on a dry weight basis. The MLP-ANN was trained using climatic factors and soil nutrients as the input layer and the andrographolide content as the output layer. The best topological ANN architecture, consisting of 14 input neurons, 12 hidden neurons, and 1 output neuron, could predict the andrographolide content with 90% accuracy. The developed ANN model showed good predictive performance with a correlation coefficient (R²) of 0.9716 and a root-mean-square error (RMSE) of 0.18. The global sensitivity analysis revealed nitrogen followed by phosphorus and potassium as the predominant input variables influencing the andrographolide content. The andrographolide content could be increased from 3.38% to 4.90% by optimizing these sensitive factors. The result showed that the ANN approach is reliable for the prediction of suitable sites for the optimum andrographolide yield in A. paniculata.     

Thermal transition behavior in the miscible polyester/acrylic polymer pair poly(ϵ‐caprolactone) and poly(phenyl methacrylate)

Two carbonyl containing polymers, poly(ε‐caprolactone) (PCL) and poly(phenyl methacrylate) (PPhMA), were found to form a miscible blend in the full range of composition as evidenced using results of differential scanning calorimetry (DSC), optical microscopy, and infrared spectroscopy studies. No lower critical solution temperature (LCST) was found, indicating phase stability within the wide temperature range investigated.