An Efficient GaMD Multi-Level Enhanced Sampling Strategy for Polarizable Force Fields Simulations of Large Biological Systems

We introduce a novel multi-level enhanced sampling strategy grounded on Gaussian accelerated Molecular Dynamics (GaMD). First, we propose a GaMD multi-GPUs -accelerated implementation within Tinker-HP. For the specific use with the flexible AMOEBA polarizable force field (PFF), we introduce the new "dual–water" GaMD mode. By adding harmonic boosts to the water stretching and bonding terms, it accelerates the solvent-solute interactions while enabling speedups with fast multiple–timestep integrators. To further reduce time-to-solution, we couple GaMD to Umbrella Sampling (US). The GaMD—US/dual–water approach is tested on the 1D Potential of Mean Force (PMF) of the CD2–CD58 system (168000 atoms) allowing the AMOEBA PMF to converge within 1 kcal/mol of the experimental value. Finally, Adaptive Sampling (AS) is added enabling AS–GaMD capabilities but also the introduction of the new Adaptive Sampling–US–GaMD (ASUS–GaMD) scheme. The highly parallel ASUS–GaMD setup decreases time to convergence by respectively 10 and 20 compared to GaMD–US and US.

Atomistic Assessment of Solute-Solute Interactions during Grain Boundary Segregation

Grain boundary solute segregation is becoming increasingly common as a means of stabilizing nanocrystalline alloys. Thermodynamic models for grain boundary segregation have recently revealed the need for spectral information, i.e., the full distribution of environments available at the grain boundary during segregation, in order to capture the essential physics of the problem for complex systems like nanocrystalline materials. However, there has been only one proposed method of extending spectral segregation models beyond the dilute limit, and it is based on simple, fitted parameters that are not atomistically informed. In this work, we present a physically motived atomistic method to measure the full distribution of solute-solute interaction energies at the grain boundaries in a polycrystalline environment. We then cast the results into a simple thermodynamic model, analyze the Al(Mg) system as a case study, and demonstrate strong agreement with physically rigorous hybrid Monte Carlo/molecular statics simulations. This approach provides a means of rapidly measuring key interactions for non-dilute grain boundary segregation for any system with an interatomic potential.

A Spectrum of Preferential Flow Alters Solute Mobility in the Critical Zone

Preferential flow reduces water residence times and allows rapid transport of pollutants such as organic contaminants. Conventional understanding of solute transport implies that preferential flow reduces the influence of soil matrix-solute interactions; however, this assumption lacks robust validation in the field. To better understand how physicochemical properties affect solute transport across a range of preferential flow conditions, we applied deuterium-labeled rainfall to field plots containing manure spiked with eight common antibiotics with a range of affinity for the soil. We then quantified preferential flow and solute transport using 48 soil pore water samplers spread along a hillslope. Based on >700 measurements, our data showed that solute transport to lysimeters was similar – regardless of antibiotic affinity for soil – when preferential flow represented less than 15% of the total water flow. When preferential flow exceeded 15%, however, concentrations were higher for compounds with relatively low affinity for soil. These results suggest that bypassing water flow can select for compounds that are more easily released from the soil matrix, thus providing fundamental insight into how flow heterogeneity affects pollutant mobility in soils. Moreover, because these data do not fully align with existing solute transport theory, they may be useful for building improved process-based transport models.

Using Volumetric Method the Study of Molecular Interactions of NSAID (DP) in Water and Water + 1M Urea at Different Temperatures

Understanding possible interactions of drugs and the factors that command such interactions could be helpful to control their disadvantageous effects upon human health. In this study, volumetric properties for the solution of diclofenac potassium (DP), a non-steroidal anti-inflammatory drug (NSAID), were investigated for the first time to look into its molecular interactions at four different temperatures varying from 298.15 K to 313.15 K at 5 K intervals in water as well as aqueous hydrotropic agent urea (1M) solutions. Experimental density data obtained using a pycnometer have been taken to estimate apparent molar properties, i.e., limiting apparent molar volume (〖V_ɸ〗^0), apparent molar volume (V_ɸ), limiting apparent molar expansibility (〖E_ɸ〗^0) and apparent molar expansibility (E_ɸ). The results obtained were discussed in terms of solute-solvent and solute-solute interactions in the studied systems. The obtained results from volumetric data were explored in terms of the existence of solute-solvent interactions in aqueous systems of drug solutions.

Aminophosphonates in Nanofiltration and Reverse Osmosis Permeates

Aminophosphonates such as aminotris(methylenephosphonic acid) (ATMP) are common constituents of antiscalants. In nanofiltration (NF) and reverse osmosis (RO) processes, ATMP prevents inorganic scaling leading to more stable membrane performance. So far, little attention has been paid to the possible permeation of aminophosphonates through NF and RO membranes. We have investigated the permeability of these membrane types for ATMP and its potential metabolites iminodi(methylenephosphonic acid) (IDMP) and amino(methylenephosphonic acid) (AMPA) with two different NF membranes (TS40 and TS80) and one RO membrane (ACM2) and three different water compositions (ultra-pure water, synthetic tap water and local tap water). We found traces of phosphonates in all investigated permeates. The highest phosphonate rejection occurred with local tap water for all three membranes investigated. Filtration experiments with a technical antiscalant formulation containing ATMP indicated similar trends of phosphonate permeability through all three membranes. We assume that the separation mechanisms of the membranes are the results of a very complex relationship between physico-chemical properties such as Donnan exclusion, feed pH, feed ionic strength and feed concentration, as well as solute–solute interactions.

The role of dislocation-solute interactions on the creep behaviour of binary Mg–RE alloys

The effect of dislocation-RE atoms interactions on the creep behaviour has been studied via creep testing and HAADF-STEM analysis of two extruded alloys; Mg–0.5Ce and Mg–2Gd (wt%). Almost no Ce atoms are detected in the Mg matrix due to the low solid solubility and faster diffusion rate in as-extruded condition. However, Gd solute segregations are observed along dislocations and hexagonal dislocation patterns. Such segregations can not only pin the dislocation motion and enhance the creep strengthening via dislocation patterns, but also lead to dynamic precipitation. Thus, combing with the stress exponent values, the transition of creep mechanism between Mg–0.5Ce alloys and Mg–2Gd alloys has been found and dislocation-Gd atoms interactions are determined to be the main factor for superior creep resistance of Mg–2Gd alloys.

Concentration and Temperature Dependence of the Thermodynamic Properties of Novel Biologically Active 3-Substituted Schiff Base of 4-Piperidyl N-(4-chlorophenyl)maleimide

In present work, the concentration and temperature dependence of the thermodynamic properties of 3-substituted Schiff base of 4-piperidyl N-(4-chlorophenyl)maleimide compound in 80% DMSO was estimated. Concentration (0.002-0.01 M) and temperature (298-313 K) dependent densitometric and viscometric measurement were employed to evaluate limiting molar volume (φv 0), semi-empirical parameter (Sv), Falkenhagen (A) and Jones-Dole (B) viscosity coefficient. The obtained results suggest the presence of weaker solute-solvent interactions and stronger solute-solute interactions. It was observed that these interactions strongly depend on the temperature of the system. Furthermore, the Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) of the system were also evaluated. The negative values of ΔG and ΔH and positive values of ΔS indicating reaction was spontaneous and exothermic in nature.