Addition Of Hexamethylphosphoramide Research Articles

Surface Overpotential as a Key Metric for the Discharge-Charge Reversibility of Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) are receiving increasing attention for power-grid energy storage systems. Nevertheless, warranting long-term reversible operation is not trivial owing to uncontrolled interfacial phenomena related to zinc dendritic growth and parasitic reactions. Herein, the addition of hexamethylphosphoramide (HMPA) to the electrolyte revealed the surface overpotential (|ηs|) to be a key metric of the reversibility. HMPA adsorbs onto active sites on the zinc metal surface, raising the surface overpotential toward lowering the nucleation energy barrier and decreasing the critical size (rcrit) of nuclei. We also correlated the observed interface-to-bulk properties by the Wagner (Wa) dimensionless number. The controlled interface enables a Zn|V6O13 full cell to retain 75.97% capacity for 2000 cycles, with a capacity loss of only 1.5% after 72 h resting. Our study not only delivers AZIBs with unparalleled cycling and storage performance but also proposes surface overpotential as a key descriptor regarding the sustainability of AZIB cycling and storage.

Samarium Diiodide Acting on Acetone-Modeling Single Electron Transfer Energetics in Solution.

Samarium diiodide is a versatile single electron transfer (SET) agent with various applications in organic chemistry. Lewis structures regularly insinuate the existence of a ketyl radical when samarium diiodide binds a carbonyl group. The study presented here investigates this electron transfer by the means of computational chemistry. All electron CASPT2 calculations with the inclusion of scalar relativistic effects predict an endotherm electron transfer from samarium diiodide to acetone. Energies calculated with the PBE0-D3(BJ) functional and a small core pseudopotential are in good agreement with CASPT2. The calculations confirm the experimentally measured increase of the samarium diiodide reduction potential through the addition of hexamethylphosphoramide also known as HMPA.

Using Hmpa As an Additive in Sodium Supercapacitor Electrolyte to Increase Thermal Stability

The development of hybrid electric vehicles (HEV) and portable electronic devices has caused greater demand for high energy and power density devices typically in the form of batteries, but supercapacitors are being integrated into these devices. Supercapacitors boast high power densities (104 W/kg), long cycle lives (>100,000), and simplicity in fabrication. One issue that arises in the practical use of supercapacitors in HEVs is the instability of the electrolyte at elevated temperatures (above 60° C) in the working environment. A number of these sytems use electrolyte systems are unstable at elevated temperaturesr have high vapor pressures that can lead to dangerous conditions for devices. Another concern of supercapacitors is their narrow voltage window that directly affects the overall power density. One novel electrolyte has been discovered that contains sodium hexafluorophosphate (NaPF6) in dimethoxyethane (DME) that boasts a 4V voltage window. The issue arises when this electrolyte is placed at elevated temperatures. PF6 -based salts are well known for quick and irreversible thermal degradation that leads to device failure. This degradation is due to an equilibrium that forms between PF6 - and PF5 - that occurs at elevated temperatures. PF5 - is unstable and will begin to decompose and react with the solvent, impurities, or the electrolyte itself which leads to an autocatalytic degradation reaction. In lithium ion batteries, this issue can be alleviated by the addition of hexamethylphosphoramide (HMPA). HMPA acts as a complexing agent with PF5 -, the thermal decomposition product of NaPF6. This complexing inhibits further decomposition of PF6 - which ultimately increases the thermal stability of the electrolyte. Our work investigates the limitations and advantages of using HMPA as an additive in NAPF6 in DME. A combination of electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR) provides enough evidence to prove that NaPF6 in DME does not degrade at elevated temperatures.

Regioselectivity of Addition of Organolithium Reagents to Enones: The Role of HMPA.

Regioselectivity of Addition of Organolithium Reagents to Enones: The Role of HMPA.

Semisynthetic fluorohydrolases prepared by chemical modification of ribonuclease

A process for conformational modification of protein, which we have previously reported, was investigated as a means of generating fluorohydrolase activity in bovine ribonuclease (RNase). The resulting modified RNase had catalytic activity that depended upon the chosen modifier. Bovine pancreatic ribonuclease, modified by addition of hexamethylphosphoramide (HMPA) at pH 3, was derivatized with diimidates of chain lengths from C 1 to C 8. The derivative with the highest activity was obtained when RNase was crosslinked with dimethyl pimelimidate (C 5). This derivative, which was active over a pH range of 6.5 to 8.0 with an optimum pH of 7.4, hydrolyzed phenylmethylsulfonylfluoride (PMSF) and the potent acetylcholinesterase inhibitor, diisopropyl phosphorofluoridate (DFP). The mean fluorohydrolase activity for four preparations using dimethyl pimelimidate was 0.8 ± 0.2 U mg -1. Gel filtration on G-75 Sephadex and SDS-polyacrylamide gel electrophoresis showed components having a molecular weight of 13,000 and 27,000, with activity restricted to the 27,000 molecular weight fraction. After gel filtration, the specific activity was 9.1 ± 2.4 U mg -1, resulting in a molecular activity of 125 min -1. The mechanism of this unique transformation of RNase into a fluorohydrolase is not known, nor has the location of the active site been determined.

Synthesis and molecular structure of a mononuclear barium aryloxide-ethanolamine complex, Ba(2,6-tert-Bu2C6H3O)2(HOCH2CH2NMe2)4.cntdot.2C7H8, exhibiting extensive hydrogen bonding

The reaction of barium metal granules in tetrahydrofuran with 2,6-di-tert-butylphenol, utilizing gaseous ammonia as a catalyst, followed by addition of hexamethylphosphoramide, yields a monomeric barium species. The corresponding reaction of barium metal granules, 2-(dimethylamino) ethanol, and 2,6-di-tert-butylphenol in toluene yields an identical compound. The species has been characterized by IR, 1 H NMR and 13 C NMR spectroscopy and single-crystal X-ray studies