Molecular Engineering of Metal Alkoxides for Solution Phase Synthesis of High-Tech Metal Oxide Nanomaterials

The ‘bottom-up’ synthesis of inorganic nanomaterials with precision at the atomic/molecular level offers many opportunities for the design and improvement of the nanomaterials for various applications. Molecular engineering during soft chemical processing for the synthesis of functional nanomaterials enables the desired chemical and physical properties of the precursors, such as solubility or volatility, clean decomposition, control of stoichiometry for multimetallic species to name a few, and leads to easy control of uniform particle size distribution, stoichiometry…. This Minireview illustrates some important aspects of the molecular engineering in light of some recent developments from the molecular synthesis of nanomaterials involving non-silicon metal alkoxide systems for high-tech applications.     

Organo-sulfonic acid catalyzed degradation kinetics and thermodynamic studies of nylon-6 by hydrothermal method

Nylon-6 as an engineering polymer and its starting monomer are both costly. Chemical reutilization offers some economic and environmental benefits. Depolymerization of nylon-6 was carried out by the conventional technique of hydrothermal method using various organo-sulfonic acids such as Methane sulfonic acid (MSA), para-toluene sulfonic acid (p-TSA), benzene sulfonic acid (BSA), and tetra-butyl ammonium bromide (TBAB) as a phase transfer catalyst. Various parameters such as temperature, time, normality of acids, and phase transfer catalyst concentration were varied to optimize its parameters, and characterization techniques such as amine value titrations and Fourier transform infrared spectroscopy were used for quantitative measurements. Solid-state ¹³C NMR was done for structure confirmation. A chemical kinetics interpretation shows degradation mechanism follows first-order kinetics under various catalysts. MSA has the highest reaction rate of 8.49 × 10^?2 h^?1 at 90°C; it decreases to 7.72 × 10^?2 h^?1 at 100°C. At the same time, aromatic Sulfonic acids such as p-TSA and BSA have a higher reaction rate of 8.995 × 10^?2 h^?1 and 5.582 × 10^?2 h^?1, respectively. The activation energy was lowered as the acidity of organo-sulfonic acids increased as benzene sulfonic acid has the lowest E_a. Followed by p-TSA, and MSA has the highest E_a. Free energy shows a similar kind of value. A simple theoretical model was used to calculate the activation energy. Thermodynamic parameters such as heat of enthalpy and entropy of reaction were evaluated using the Eryig–Polanyi equation. The combined catalytic effect of organo-sulfonic acids and phase-transfer catalyst provides a better environment-friendly method for depolymerizing nylon-6.     

An anhydrous precursor approach to BaYF5-based upconverting nanocrystals

With an objective to have easy access to high quality BaYF₅ matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentration around these nanocrystals (NCs) to enhance their UC efficiency without requiring the usual core-shell structure. The precursors and the BaYF₅ NCs co-doped with Yb³⁺/Tm³⁺ ions were thoroughly characterized. The NCs were studied for upconversion properties and preliminary results are presented here. On the basis of these results, a mechanism for the energy transfer in Yb–Tm system is proposed.     

Active participation of membrane lipids in inhibition of multidrug transporter P-glycoprotein

P-glycoprotein (Pgp) is a major efflux pump in humans, overexpressed in a variety of cancers and associated with the development of multi-drug resistance. Allosteric modulation by various ligands (e.g., transport substrates, inhibitors, and ATP) has been biochemically shown to directly influence structural dynamics, and thereby, the function of Pgp. However, the molecular details of such effects, particularly with respect to the role and involvement of the surrounding lipids, are not well established. Here, we employ all-atom molecular dynamics (MD) simulations to study the conformational landscape of Pgp in the presence of a high-affinity, third-generation inhibitor, tariquidar, in comparison to the nucleotide-free (APO) and the ATP-bound states, in order to characterize the mechanical effects of the inhibitor that might be of relevance to its blocking mechanism of Pgp. Simulations in a multi-component lipid bilayer show a dynamic equilibrium between open(er) and more closed inward-facing (IF) conformations in the APO state, with binding of ATP shifting the equilibrium towards conformations more prone to ATP hydrolysis and subsequent events in the transport cycle. In the presence of the inhibitor bound to the drug-binding pocket within the transmembrane domain (TMD), Pgp samples more open IF conformations, and the nucleotide binding domains (NBDs) become highly dynamic. Interestingly, and reproduced in multiple independent simulations, the inhibitor is observed to facilitate recruitment of lipid molecules into the Pgp lumen through the two proposed drug-entry portals, where the lipid head groups from the cytoplasmic leaflet penetrate into and, in some cases, translocate inside the TMD, while the lipid tails remain extended into the bulk lipid environment. These “wedge” lipids likely enhance the inhibitor-induced conformational restriction of the TMD leading to the differential modulation of coupling pathways observed with the NBDs downstream. We suggest a novel inhibitory mechanism for tariquidar, and potentially for related third-generation Pgp inhibitors, where lipids are seen to enhance the inhibitory role in the catalytic cycle of membrane transporters.

Lipid invasion of P-glycoprotein, enhanced by binding of an inhibitor.     

Representation of cyclotomic fields and their subfields

Let $\mathbb{K}$ be a finite extension of a characteristic zero field $\mathbb{F}$ . We say that a pair of n × n matrices (A,B) over $\mathbb{F}$ represents $\mathbb{K}$ if $\mathbb{K} \cong {{\mathbb{F}\left[ A \right]} \mathord{\left/ {\vphantom {{\mathbb{F}\left[ A \right]} {\left\langle B \right\rangle }}} \right. \kern-0em} {\left\langle B \right\rangle }}$ , where $\mathbb{F}\left[ A \right]$ denotes the subalgebra of $\mathbb{M}_n \left( \mathbb{F} \right)$ containing A and 〈B〉 is an ideal in $\mathbb{F}\left[ A \right]$ , generated by B. In particular, A is said to represent the field $\mathbb{K}$ if there exists an irreducible polynomial $q\left( x \right) \in \mathbb{F}\left[ x \right]$ which divides the minimal polynomial of A and $\mathbb{K} \cong {{\mathbb{F}\left[ A \right]} \mathord{\left/ {\vphantom {{\mathbb{F}\left[ A \right]} {\left\langle {q\left( A \right)} \right\rangle }}} \right. \kern-0em} {\left\langle {q\left( A \right)} \right\rangle }}$ . In this paper, we identify the smallest order circulant matrix representation for any subfield of a cyclotomic field. Furthermore, if p is a prime and $\mathbb{K}$ is a subfield of the p-th cyclotomic field, then we obtain a zero-one circulant matrix A of size p × p such that (A, J) represents $\mathbb{K}$ , where J is the matrix with all entries 1. In case, the integer n has at most two distinct prime factors, we find the smallest order 0, 1-companion matrix that represents the n-th cyclotomic field. We also find bounds on the size of such companion matrices when n has more than two prime factors.     

Effects of heavy-ion irradiation on the electrical properties of rf-sputtered HfO2 thin films for advanced CMOS devices

HfO₂-based metal-oxide semiconductor (MOS) capacitors were irradiated with high-energy ion beam to study the irradiation effects in these films. HfO₂ thin films deposited by radio frequency (rf)-sputtering were irradiated with 80 MeV O⁶⁺ ions. The samples were irradiated and characterized at room temperature. Devices were characterized via 1 MHz capacitance–voltage (C?V) measurements using the midgap method. The irradiation induced dispersion in accumulation and depletion regions with increasing fluence is observed. After irradiation, the midgap voltage shift (Δ V _mg) of?0.61 to?1.92 V, flat band voltage shift (Δ V _fb) of?0.48 to?2.88 V and threshold voltage shift (Δ V _th) of?0.966 to?1.96 V were observed. The change in interface trap charge and oxide trap charge densities after 80 MeV O⁶⁺ ions irradiation with fluences were determined from the midgap to flat band stretch out of C?V curves. The results are reported and explained in terms of changes in microstructure and dielectric properties of the HfO₂ thin films after irradiation.     

Equation of state of Al for compressed and expanded states from first-principles calculations

Results of theoretical calculations of equation of state and critical temperature of Al are presented using a three-term EOS model. In this model cold (0 K) term is calculated from first-principles method near normal conditions. Cold curve is extrapolated to ultrahigh pressures using Thomas– Fermi–Dirac model and to expanded states using a soft sphere function. Electron thermal term is calculated using Thomas–Fermi statistical model. Ion-thermal term is calculated using the modified Cowan model. In expanded state, the adjustable parameters of the modified Cowan model are tuned using quantum molecular dynamics (QMD) results. In compressed state, P−ρ$P-\rho$ and U_s−U_p$U_{\mathrm{s}}-U_{\mathrm{p}}$ Hugoniots derived using our results show good agreement with the reported experimental results. In expanded state, the estimated critical temperature shows good agreement with the reported results and pressure versus internal energy along isochores show reasonably good agreement with the reported experimental results.     

A general method for palladium-catalyzed reactions of primary sulfonamides with aryl nonaflates

A general method for Pd-catalyzed sulfonamidation of aryl nonafluorobutanesulfonates (aryl nonaflates) is described. A biaryl phosphine ligand, t-BuXPhos, formed the most active catalyst, and K(3)PO(4) in tert-amyl alcohol was found to be the optimal base-solvent combination for the reaction. The reaction conditions were tolerant of various functional groups such as cyano, nitro, ester, aldehyde, ketone, chloride, carbamate, and phenol. Heterocyclic aryl nonaflates were found to be suitable coupling partners. High yields of the coupled products were obtained from the reactions between inherently disfavored substrates such as electron-rich nonaflates and electron-poor sulfonamides. Kinetic data suggest reductive elimination to be the rate-limiting step for the reaction. The only limitation of this methodology that we have identified is the inability of 2,6-disubstituted aryl nonaflates to efficiently participate in the reaction.