Journal of Thermodynamics & Catalysis
Open Access

Reaction on Protein Stability by Water Thermodynamics

John Tang^{* *}Correspondence: John Tang, Department of Thermodynamics, The University of Manchester, Oxford Road, Manchester, United Kingdom, Email:

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Description

Water is one of the most fascinating academic topics, especially because of its importance in biology. It has one of the most basic molecular structures, but it is distinguished by intriguing and complex thermodynamic features, particularly in the liquid form, that are still poorly understood. As a result, when compared to other liquids, water exhibits a variety of peculiar characteristics, the most well-known of which is the maximum density at 277 K. We now know that this complexity is attributable to its polymorphism, an original hypothesis that has been scientifically proven. Liquid water, like its amorphous phase, is polymorphic; in particular, it is owing to two liquids of differing densities: HDL and LDL, or high- and low-density liquids. A networking structure gives rise to the LDL structure. Because of the noncovalent attractive hydrogen bond interaction, the process has a tetrahedral symmetry (HB). Relevant factors include the fact that HDL and LDL coexist in a broad portion of the water phase diagram, and that they can move from one to the other by a first order transition when pressure or temperature is changed: the liquid-liquid transition hypothesis (LLT). The thermodynamic response functions (compressibility, specific heats, expansivity, and entropy) of the system, as well as its variables, represent polymorphism, determining the system's entire attributes and fluctuations. This holds true for both bulk water and its solutions, implying that the HB, as represented in local molecule structure and configuration, determines the chemical-physical properties of water and water systems.

Thermodynamic Anomalies of Liquid Water

Density anomaly

The density anomaly is one of the oldest known water phenomena. Water expands when cooled below 277 K at ambient pressure, unlike other simple liquids that expand when heated. Ice floats on water because of this anomaly, and fish can survive in warm seas beneath a covering of ice at temperatures much below 0 degrees Celsius. As the pressure is increased, the temperature of maximum density, TM D, drops until it disappears the above 200 MPa. The density of anomaly is found in the (T, P) plane, just below the locus of TM D. Computer simulations of various water models find the TM D in the same way that experiments do. Recent investigations on water contained in nanopores have revealed that the supercooled liquid exhibits a phase transition below 210 K.

Dynamics and thermodynamics of water

kB is the Boltzmann constant, while S is the entropy. Since any thermal fluctuation should reduce as temperature decreases, one would anticipate CP to behave similarly. In the case of water, however, it rises dramatically as the temperature falls below around 330 K. At 228 K, CP appears to diverge as a power-law.

Diffusion anomaly

When simple liquids are pressurised, their dynamics slow down. Instead, as the pressure is increased, the dynamics of water become faster, reaching a maximum at a constant temperature. The density anomaly in the (T,P) plane is included in the dynamic anomaly's region. The experimental results are recovered using computer simulations of several water models. They show that when P decreases, the diffusion constant D lowers until it reaches a minimum value at a negative pressure below which normal behaviour returns. The breakdown of hydrogen bonds is responsible for the unusual rise in diffusion when pressurised. As the pressure rises, more hydrogen bonds are disrupted, allowing water molecules to disperse freely from their neighbours and thereby increasing diffusion.

Non-arrhenius to arrhenius dynamic crossover at low temperatures

Liquids with Arrhenius(or activated) behaviour have relaxation times that are an exponential function of 1/T, whereas those with non-Arrhenius behaviour have relaxation times that are a different function of 1/T. If the viscosity is used to characterise the dynamics instead of the relaxation time of some specific degree of freedom, then the variation of viscosity as an exponential function of 1/T is called "strong" behaviour, while a different function of 1/T is called "fragile" behaviour.