Water Activity

Abstract

Microorganisms require water for their metabolic activities. Only a fraction of water in foodstuffs, the so-called free water, is available for this purpose. The amounts of free water previously estimated by two different methods (Frosch et al. (2010), Frosch et al. (2011), and Low (1969)) are compared for aqueous solutions of four electrolytes, NaCl, NH4Cl, Na2SO4, (NH4)2SO4: (i) vapour pressure measurements of the solutions relative to that of pure water (water activities) and (ii) low-wavenumber Raman spectra in the R(ν)-representation. For each electrolyte deviations were found between results from the two methods. All water molecules in the illuminated volume contribute to the Raman data. The vapor pressure measurements refer to water molecules at the water/atmosphere interface where surface tension is important. Differences in surface tension for the four electrolytes qualitatively explain deviations between the amounts of “free water” observed by the two methods.

RETRACTED ARTICLE: New insights into the microscopic interactions associated with the physical mechanism of action of highly diluted biologics

“…At all of the distances probed we find a weak mode ~ 175 cm −1 . The ~ 175 cm −1 mode has been previously identified as a low frequency translational mode of pure liquid water in a number of THz 18 , 36 , 37 and Raman 38 experimental measurements. There is no dispersion (propagation) in the translational mode as a function of distance indicating that it is an optical-like mode in the water hydration shell.…”

Modeling of protein hydration dynamics is supported by THz spectroscopy of highly diluted solutions

“…At all of the distances probed we find a weak mode ∼175 cm −1 . The ∼175 cm −1 mode has been previously identified as a low frequency translational mode of pure liquid water in a number of THz ( Conti Nibali and Havenith, 2014 ; Penkov et al, 2015 ; Grechko et al, 2018 ) and Raman ( Nielsen et al, 2012 ) experimental measurements. There is no dispersion (propagation) in the translational mode as a function of distance indicating that it is an optical-like mode in the water hydration shell.…”

Isochores and Heat Capacity of Liquid Water in Terms of the Ion–Molecular Model

“…For many years, it presented an insoluble problem for the molecular interpretation [ 44 ]. Many arguments have been proposed in favor of different models, mainly focused around that, we quote, the 180 cm −1 peak is related to hindered longitudinal translations of water molecules in the HB network with a distinct collective character [ 45 ], that it arises from the molecular translation modes [ 46 ], that it is due to the stretching vibrations of nearly linear hydrogen bonds, or due to cage vibrations or more exotic hydrogen bond network relaxations [ 23 ], that it is due to the presence of water with a tetrahedral hydrogen bond conformation [ 47 ], that it is due to a coupling between the translational degrees of freedom of the water molecule and the electronic cloud [ 48 ].…”