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The Cell Membrane in the Steady State
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The mechanisms underlying channel selectivity are rather complicated. Because water molecules are polar, ions in aqueous solutions are hydrated, that is, they have associated with them a number of water molecules, referred to as the hydration number, which increases the effective size of the ion. Na+ have an atomic radius of 0.95 Å whereas K+ have an atomic radius of 1.33 Å. Since both Na+ and K+ have the same charge, Na+ have a larger surface charge density, so they attract more water molecules by a weak electrostatic force, and consequently have a larger hydration number than K+. The hydrated Na+ is therefore larger than the hydrated K+ and is of lower mobility in solution. The hydration number for K+ is 3–4, whereas that for Na+ is 4–5.
Kosmotropic Chromatography of Proteins
Published in Nelu Grinberg, Peter W. Carr, Advances in Chromatography Volume 57, 2020
Carlos Calleja-Amador, J. F. Ogilvie, Rigoberto Blanco
There are two main drawbacks to the hydration theory. First, the theory implies that the predicted number of water molecules surrounding the ion (the hydration number) is a fixed number. This number is independent of the nature of the non-electrolyte that is being salted out, which contradicts experimental findings [50]. Second, these theories do not explain the dependence of the salting constant k from Equation (3.1) on the size of the non-electrolyte [51]. An additional observation is that hydration theories do not provide an explanation for salting in [27].
Novel methodology for the calculation of the enthalpy of enclathration of methane hydrates using molecular dynamics simulations
Published in Molecular Physics, 2020
Ioannis N. Tsimpanogiannis, Vasileios K. Michalis, Ioannis G. Economou
Consider the dissociation of solid (s) methane hydrate to liquid (l) water and gaseous (g) methane, described by the following reaction which is valid for temperatures higher than 273.15 K, while for temperatures lower than 273.15 K water is in the form of ice (i): where nw, is the hydration number (i.e. the number of water molecules per hydrate guest molecule). The hydration number for sI hydrates is defined as: , where the number 46 indicates the number of water molecules per unit cell of the sI hydrate crystal, and are the cage occupancies of the small (S) and large (L) cages respectively. Two small and six large cages make up the unit cell of the sI hydrate structure [1]. The presence of a variable (with respect to pressure and temperature) hydration number in Equation (1) is a result of the fact that clathrate hydrates are not stoichiometric compounds. In particular, the case when , denotes that all eight cages of the sI structure are occupied by a single guest molecule (i.e. stoichiometric case), while , denotes partial cage occupancy (i.e. non-stoichiometric case; namely, some cages are empty) [1].
Insight into intermolecular interactions and hydration properties of biologically active amino acids in aqueous solutions of cefepime: volumetric, compressibility and viscometric studies
Published in Journal of Dispersion Science and Technology, 2021
Suvarcha Chauhan, Neetika Kumari, Lalita Pathania
The degree of hydration of a solute in water can be expressed in terms of hydration number. The method of determination of hydration number as proposed by Millero[42] using the equation: where Ve0 and Vb0 are partial molar volumes of electrostricted and bulk water respectively. is -3.3 × 10−6 m3.mol−1 at 298.15 K.