Principles Of Physical Chemistry Research Articles

Developing physical-chemical principles to manufacture effective heating systems when using mica

The organization of effective heating systems in non-industrial, industrial and livestock buildings is an urgent problem. The developing of heating is especially relevant for utilizing in agricultural industry. Energy prices are steadily rising, and as a result, the efficient utilization of energy resources is of great significance for this industry. One of the most prospective lines of development in this area can be the trend to utilize resistive heaters where mica is used as a basic material. The research aim. Developing physical-chemical principles to manufacture effective heating systems when using mica for the construction industry. The possibility of employing composite materials to produce an economically sound, reliable, electro-permissible and stable heater is considered. Finding physical and chemical laws of interaction of mica with the binder element in the technology of micaceous composites. Research methods. The methods of thermodynamic quantum chemical calculations, as well as kinetic studies that involve a number of advanced techniques of physical and chemical studies (x-ray phase analysis, thermal analysis, and IR spectroscopy). Electro physical and mechanical characteristics of composites and starting materials were determined by the standardized methods to comply with the All Union State Standard. Research results. The foundations of effective heating systems when utilizing micalex have been worked out by means of scientific generalizations and experimental studies. The developed technology of electric heating elements (mica ceramic electric heating) is employed in various fields of construction industry.

The transition model of RTK activation: A quantitative framework for understanding RTK signaling and RTK modulator activity

Here, we discuss the transition model of receptor tyrosine kinase (RTK) activation, which is derived from biophysical investigations of RTK interactions and signaling. The model postulates that (1) RTKs can interact laterally to form dimers even in the absence of ligand, (2) different unliganded RTK dimers have different stabilities, (3) ligand binding stabilizes the RTK dimers, and (4) ligand binding causes structural changes in the RTK dimer. The model is grounded in the principles of physical chemistry and provides a framework to understand RTK activity and to make predictions in quantitative terms. It can guide basic research aimed at uncovering the mechanism of RTK activation and, in the long run, can empower the search for modulators of RTK function.

Seeking to uncover biology's chemical roots

Despite the considerable advances in molecular biology over the past several decades, the nature of the physical-chemical process by which inanimate matter become transformed into simplest life remains elusive. In this review, we describe recent advances in a relatively new area of chemistry, systems chemistry, which attempts to uncover the physical-chemical principles underlying that remarkable transformation. A significant development has been the discovery that within the space of chemical potentiality there exists a largely unexplored kinetic domain which could be termed dynamic kinetic chemistry. Our analysis suggests that all biological systems and associated sub-systems belong to this distinct domain, thereby facilitating the placement of biological systems within a coherent physical/chemical framework. That discovery offers new insights into the origin of life process, as well as opening the door toward the preparation of active materials able to self-heal, adapt to environmental changes, even communicate, mimicking what transpires routinely in the biological world. The road to simplest proto-life appears to be opening up.

Cobalt-catalyzed nitrile hydrogenation: Insights into the reaction mechanism and product selectivity from DFT analysis

When primary amines are the desired product of nitrile hydrogenation, the use of cobalt catalysts are commonly recommended. Nitrile hydrogenation using heterogeneous catalysis is an important commercial process for the production of primary, secondary, and tertiary amines. In recent years, modern experimental methods have investigated the detailed mechanism underlying the surface reactions of nitrile hydrogenation. These experimental studies provide new insights, but also raise additional questions. To help resolve these inconsistencies, modern theoretical techniques have been applied by way of periodic plane-wave Density Functional Theory (DFT) calculations to study acetonitrile adsorption and hydrogenation to primary (monoethylamine), secondary (diethylamine), and tertiary amines (triethylamine) over flat Co surfaces, specifically the Co(0001) surface facet. The presented theoretical analysis applies fundamental physical chemistry and reaction engineering principles to better understand surface reaction mechanisms in the kinetically-controlled regime at low surface coverages. Reaction pathways for acetonitrile hydrogenation and the most probable routes for secondary and tertiary amine formations are discussed. The presented first-principles analysis is in line with experimental observations of gas-phase acetonitrile hydrogenation on flat Co surfaces. Key mechanistic findings are discussed in the context of larger alkane nitrile hydrogenation processes, which are ordinarily performed in the liquid phase.

Biogeochemical Equation of State for the Sea-Air Interface

We have recently argued that marine interfacial surface tension must have a distinctive biogeography because it is mediated by fresh surfactant macromolecules released locally through the food web. Here we begin the process of quantification for associated climate flux implications. A low dimensionality (planar) equation of state is invoked at the global scale as our main analysis tool. For the reader’s convenience, fundamental surfactant physical chemistry principles are reviewed first, as they pertain to tangential forces that may alter oceanic eddy, ripple, and bubble fields. A model Prandtl (neutral) wind stress regime is defined for demonstration purposes. It is given the usual dependence on roughness, but then in turn on the tension reduction quantity known as surface pressure. This captures the main net influences of biology and detrital organics on global microlayer physics. Based on well-established surrogate species, tangent pressures are related to distributed ecodynamics as reflected by the current marine systems science knowledge base. Reductions to momentum and related heat-vapor exchange plus gas and salt transfer are estimated and placed on a coarse biogeographic grid. High primary production situations appear to strongly control all types of transfer, whether seasonally or regionally. Classic chemical oceanographic data on boundary state composition and behaviors are well reproduced, and there is a high degree of consistency with conventional micrometeorological wisdom. But although our initial best guesses are quite revealing, coordinated laboratory and field experiments will be required to confirm the broad hypotheses even partially. We note that if the concepts have large scale validity, they are super-Gaian. Biological control over key planetary climate-transfer modes may be accomplished through just a single rapidly renewed organic monolayer.

2D materials: molecular design and engineering perspectives

Guest Editors Deep Jariwala and Mark Hersam introduce this themed collection showcasing the latest research leveraging principles of surface, physical, and covalent chemistry to modify the properties of 2D materials and guide the understanding of charge and energy transfer across mixed-dimensional heterointerfaces to enable enhanced performance or distinct functionality in emerging applications.

First-principles analysis of acetonitrile reaction pathways to primary, secondary, and tertiary amines on Pd(111)

Nitrile hydrogenation using heterogeneous catalysis is an important commercial process for the production of primary, secondary, and tertiary amines. In recent years, modern experimental methods have investigated the detailed mechanism underlying the surface reactions of nitrile hydrogenation. These experimental studies provide new insights, but also raise additional questions. To help resolve these inconsistencies, modern theoretical techniques have been applied by way of periodic plane-wave Density Functional Theory (DFT) calculations to study acetonitrile adsorption and hydrogenation to primary (monoethylamine), secondary (diethylamine), and tertiary amines (triethylamine) over flat Pd surfaces. The presented theoretical analysis applies fundamental physical chemistry and reaction engineering principles to better understand surface reaction mechanisms in the kinetically-controlled regime at low surface coverages. Reaction pathways for acetonitrile hydrogenation and the most probable routes for secondary and tertiary amine formations are discussed. The presented first-principles analysis is in line with experimental observations of gas-phase acetonitrile hydrogenation on flat Pd surfaces. Key mechanistic findings are discussed in the context of larger alkane nitrile hydrogenation processes, which are ordinarily performed in the liquid phase.

Size Exclusion Chromatography: A Teaching Aid for Physical Chemistry

All analytical techniques are governed by the principles of physical chemistry, and chromatography is certainly no exception. By examining the underlying concepts of size exclusion chromatography (SEC), students can gain greater appreciation of and insight into the science and utility of thermodynamics, as well as solution properties of macromolecules. In this paper we will show how the separation mechanism that governs SEC, an unusual form of chromatography, can be explained using the tenets of thermodynamics. This paper gives educators access to an HPLC technique usually not included in undergraduate chemistry curriculum.

The Physical Chemistry for the Self-assembly of Peptide Hydrogels

Peptide hydrogels have been widely used for diverse biomedical applications. However, our current understanding of the physical principles underlying the self-assembly process is still limited. In this review, we summarize our current understanding on the physical chemistry principles from the basic interactions that drive the self-assembly process to the energy landscapes that dictate the thermodynamics and kinetics of the process. We discuss the effect of different factors that affect the kinetics of the self-assembly of peptide fibrils and how this is related to the macroscopic gelation process. We provide our understanding on the molecular origin of the complex and rugged energy landscape for the self-assembly of peptide hydrogels. The hierarchical self-assembled structures and the diverse self-assembling mechanism make it difficult and challenging to rationally design the physical and chemical properties of peptide hydrogels at the molecular level. We also give our personal perspective to the potential future directions in this field.

Methods for Removing of Phosphates from Wastewater

The paper offers update information on wastewater removal from phosphates. The writers describe the most commonly used efficient methods to remove phosphates from wastewater based on principles of biology, chemistry, physical chemistry and biological chemistry. The paper presents the results of research on phosphate-removing wastewater treatment methods using iron-bearing reinforced charge material.

Allosteric HIV-1 integrase inhibitors promote aberrant protein multimerization by directly mediating inter-subunit interactions: Structural and thermodynamic modeling studies.

Allosteric HIV-1 integrase (IN) inhibitors (ALLINIs) bind at the dimer interface of the IN catalytic core domain (CCD), and potently inhibit HIV-1 by promoting aberrant, higher-order IN multimerization. Little is known about the structural organization of the inhibitor-induced IN multimers and important questions regarding how ALLINIs promote aberrant IN multimerization remain to be answered. On the basis of physical chemistry principles and from our analysis of experimental information, we propose that inhibitor-induced multimerization is mediated by ALLINIs directly promoting inter-subunit interactions between the CCD dimer and a C-terminal domain (CTD) of another IN dimer. Guided by this hypothesis, we have built atomic models of inter-subunit interfaces in IN multimers by incorporating information from hydrogen-deuterium exchange (HDX) measurements to drive protein-protein docking. We have also developed a novel free energy simulation method to estimate the effects of ALLINI binding on the association of the CCD and CTD. Using this structural and thermodynamic modeling approach, we show that multimer inter-subunit interface models can account for several experimental observations about ALLINI-induced multimerization, including large differences in the potencies of various ALLINIs, the mechanisms of resistance mutations, and the crucial role of solvent exposed R-groups in the high potency of certain ALLINIs. Our study predicts that CTD residues Tyr226, Trp235 and Lys266 are involved in the aberrant multimer interfaces. The key finding of the study is that it suggests the possibility of ALLINIs facilitating inter-subunit interactions between an external CTD and the CCD-CCD dimer interface.

Organic Nanoparticles in Foods: Fabrication, Characterization, and Utilization.

In the context of food systems, organic nanoparticles (ONPs) are fabricated from proteins, carbohydrates, lipids, and other organic compounds to a characteristic dimension, such as a radius smaller than 100 nm. ONPs can be fabricated with bottom-up and top-down approaches, or a combination of both, on the basis of the physicochemical properties of the source materials and the fundamental principles of physical chemistry, colloidal and polymer sciences, and materials science and engineering. ONPs are characterized for dimension, morphology, surface properties, internal structures, and biological properties to understand structure-function correlations and to explore their applications. These potential applications include modifying physical properties, improving sensory attributes and food quality, protecting labile compounds, and delivering encapsulated bioactive compounds for improved bioactivity and bioavailability. Because ONPs can have digestion and absorption properties different from conventional materials, the eventual applications of ONPs require in vitro and in vivo studies to guide the development of safe food products that utilize the unique functionalities of ONPs.

Fluoride technology of obtaining REM magnetic alloys and master alloys

Rare earth permanent magnets (REPM) based on neodymium-Fe-boron system are the most promising, since they have the highest magnetic and satisfactory mechanical characteristics. The paper covers physical-chemical principles and shows the results of experimental studies of the process of obtaining REM alloys and master alloys using fundamentally new fluoride technology based on ladle calciothermal REM fluorides and Fe reduction.

Understanding and Engineering Thermostability in DNA Ligase from Thermococcus sp. 1519.

The physical chemical principles underlying enzymatic thermostability are keys to understand the way evolution has shaped proteins to adapt to a broad range of temperatures. Understanding the molecular determinants at the basis of protein thermostability is also an important factor for engineering more thermoresistant enzymes to be used in the industrial setting, such as, for instance, DNA ligases, which are important for DNA replication and repair and have been long used in molecular biology and biotechnology. Here, we first address the origin of thermostability in the thermophilic DNA ligase from archaeon Thermococcus sp. 1519 and identify thermosensitive regions using molecular modeling and simulations. In addition, we predict mutations that can enhance thermostability of the enzyme through bioinformatics analyses. We show that thermosensitive regions of this enzyme are stabilized at higher temperatures by optimization of charged groups on the surface, and we predict that thermostability can be further increased by further optimization of the network among these charged groups. Engineering this DNA ligase by introducing selected mutations (i.e., A287K, G304D, S364I, and A387K) eventually produced a significant and additive increase in the half-life of the enzyme when compared to that of the wild type.

Has Stewart approach improved our ability to diagnose acid-base disorders in critically ill patients?

The Stewart approach-the application of basic physical-chemical principles of aqueous solutions to blood-is an appealing method for analyzing acid-base disorders. These principles mainly dictate that pH is determined by three independent variables, which change primarily and independently of one other. In blood plasma in vivo these variables are: (1) the PCO2; (2) the strong ion difference (SID)-the difference between the sums of all the strong (i.e., fully dissociated, chemically nonreacting) cations and all the strong anions; and (3) the nonvolatile weak acids (Atot). Accordingly, the pH and the bicarbonate levels (dependent variables) are only altered when one or more of the independent variables change. Moreover, the source of H(+) is the dissociation of water to maintain electroneutrality when the independent variables are modified. The basic principles of the Stewart approach in blood, however, have been challenged in different ways. First, the presumed independent variables are actually interdependent as occurs in situations such as: (1) the Hamburger effect (a chloride shift when CO2 is added to venous blood from the tissues); (2) the loss of Donnan equilibrium (a chloride shift from the interstitium to the intravascular compartment to balance the decrease of Atot secondary to capillary leak; and (3) the compensatory response to a primary disturbance in either independent variable. Second, the concept of water dissociation in response to changes in SID is controversial and lacks experimental evidence. In addition, the Stewart approach is not better than the conventional method for understanding acid-base disorders such as hyperchloremic metabolic acidosis secondary to a chloride-rich-fluid load. Finally, several attempts were performed to demonstrate the clinical superiority of the Stewart approach. These studies, however, have severe methodological drawbacks. In contrast, the largest study on this issue indicated the interchangeability of the Stewart and conventional methods. Although the introduction of the Stewart approach was a new insight into acid-base physiology, the method has not significantly improved our ability to understand, diagnose, and treat acid-base alterations in critically ill patients.

Practical approach to physical-chemical acid-base management. Stewart at the bedside.

The late Peter Stewart developed an approach to the analysis of acid-base disturbances in biological systems based on basic physical-chemical principles. His key argument was that the traditional carbon dioxide/bicarbonate analysis with just the use of the Henderson-Hasselbalch equation does not account for the important role in the regulation of H(+) concentration played by strong ions, weak acids and water itself. Acceptance of his analysis has been limited because it requires a complicated set of calculations to account for all the variables and it does not provide simple clinical guidance. However, the analysis can be made more pragmatic by using a series of simple equations to quantify the major processes in acid-base disturbances. These include the traditional PCO2 component and the addition of four metabolic processes, which we classify as "water-effects," "chloride-effects," "albumin effects," and "others." Six values are required for the analysis: [Na(+)], [Cl(-)], pH, Pco2, albumin concentration, and base excess. The advantage of this approach is that it gives a better understanding of the mechanisms behind acid-base abnormalities and more readily leads to clinical actions that can prevent or correct the abnormalities. We have developed a simple free mobile app that can be used to input the necessary values to use this approach at the bedside (Physical/Chemical Acid Base Calculator).

Physics-based enzyme design: predicting binding affinity and catalytic activity.

Computational enzyme design is an emerging field that has yielded promising success stories, but where numerous challenges remain. Accurate methods to rapidly evaluate possible enzyme design variants could provide significant value when combined with experimental efforts by reducing the number of variants needed to be synthesized and speeding the time to reach the desired endpoint of the design. To that end, extending our computational methods to model the fundamental physical-chemical principles that regulate activity in a protocol that is automated and accessible to a broad population of enzyme design researchers is essential. Here, we apply a physics-based implicit solvent MM-GBSA scoring approach to enzyme design and benchmark the computational predictions against experimentally determined activities. Specifically, we evaluate the ability of MM-GBSA to predict changes in affinity for a steroid binder protein, catalytic turnover for a Kemp eliminase, and catalytic activity for α-Gliadin peptidase variants. Using the enzyme design framework developed here, we accurately rank the most experimentally active enzyme variants, suggesting that this approach could provide enrichment of active variants in real-world enzyme design applications.

Future Fire Probability Modeling with Climate Change Data and Physical Chemistry

Climate has a primary influence on the occurrence and rate of combustion in ecosystems with carbon-based fuels such as forests and grasslands. Society will be confronted with the effects of climate change on fire in future forests. There are, however, few quantitative appraisals of how climate will affect wildland fire in the United States. We demonstrated a method for estimating changes in fire probability based on future climate simulations of temperature and precipitation. The probability of a fire occurring in a particular climate was extracted from the Physical Chemistry Fire Frequency Model (PC2FM) and represented the rate of change in fire due to climate. Climate output data from two global climate models (GCMs) were applied to the PC2FM to estimate changes in fire probability. We calculated change in fire frequency and probabilities from the difference between current and future climates and mapped climate-forced percentage change in fire probability under each GCM for the nation at a 1.2 km 2 scale. Future fire probability estimates increased in cooler northern and high elevation regions but decreased slightly in some hotter and drier regions of the southwestern United States. Our approach’s greatest strength may be reliance on only climate data and the simple principles of physical chemistry; many other nonclimatic factors that affect fire are often difficult to predict in the distant future.

Engineering of nano-crystalline drug suspensions: Employing a physico-chemistry based stabilizer selection methodology or approach

This paper describes a systematic approach to select optimum stabilizer for the preparation of nano-crystalline suspensions of an active pharmaceutical ingredient (API). The stabilizer can be either a dispersant or a combination of dispersant and wetting agent. The proposed screening method is a quick and efficient way to investigate a large number of stabilizers based on the principles of physical-chemistry and employs a stepwise approach. The methodology has been divided in two main parts; the first part being focused on the qualitative screening with the objective of selecting the best candidate(s) for further investigation, the second part has been focused on quantitative screening with the objective to optimize the ratio and amount of wetting and dispersing agents, based on wettability, surface charges measurement, adsorption evaluation, process-ability evaluation and storage stability.The results showed clearly that SDS/PVP 40/60% (w/w) (sodium dodecyl sulfate/poly(vinyl pyrrolidone)) at a total concentration of 1.2% was the optimum stabilizer composition, at which the resulting nanosuspensions were stable for more than 50 days at room temperature.

Reflections on my career as a marine physical chemist, and tales of the deep.

This is a personal review of how one can apply the principles of physical chemistry to study the ocean and other natural waters. Physical chemistry is the study of chemical thermodynamics, kinetics, and molecular structure. My long-term interest in the chemistry of seawater is an extension of my early work on water and the interactions that occur in aqueous electrolyte solutions, which I began as part of my PhD research on the thermodynamics of organic acids in water. Over the years, I have attempted to apply the tools of physical chemistry to elucidate the structures of seawater, brines, lakes, and rivers. I have developed and continue to work on ionic interaction models that can be applied to all natural waters. Here, I reflect on how my students, postdocs, research assistants, and scientific colleagues have influenced my life, my career, and the field of marine physical chemistry. My hope was and is to use these tools to understand the molecular structures of natural waters.