Protein hydration water: Focus on low density and high density local structures upon cooling

Deciphering Density Fluctuations in the Hydration Water of Brownian Nanoparticles via Upconversion Thermometry

“…Furthermore, we hypothesize that the decrease in the T c of the aqueous nanofluids derived from Figure c compared to pure water stems from a decrease in the high- to low-density liquid water fluctuations as a consequence of the prevalence of a higher concentration of HDL patches relative to LDL regions in the volume of nanofluid moving cooperatively with UCNPs. Notably, this hypothesis corroborates previous findings, both in silico and in experiments, about the hydration water of the lysozyme protein. This hydration water (defined as the water molecules encompassing the protein within a 0.6 nm shell) exhibits local distortions when compared to bulk water.…”

“…Notably, this hypothesis corroborates previous findings, both in silico and in experiments, about the hydration water of the lysozyme protein. This hydration water (defined as the water molecules encompassing the protein within a 0.6 nm shell) exhibits local distortions when compared to bulk water. For instance, its density is much higher than that of the bulk and the dielectric constant of interfacial water in the double layer is much lower than that of bulk water .…”

“…This hypothesis agrees with simulations conducted by Gallo's group, indicating a slower decrease in the rate of LDL domains at the biomolecule interface with an increase in temperature. 71 Moreover, for a constant |ζ| value, nanofluids with smaller UCNPs exhibit a higher T c , consistent with the findings depicted in Figure 2c. It is noteworthy that the same conclusion can be drawn exclusively from upconversion thermometry and by combining upconversion thermometry with ζ potential measurements.…”

“…Therefore, there is a strong demand for experimental techniques for microscopically deciphering H-bond structures in liquid water as well as in aqueous solutions of electrolytes, suspensions of biomolecules, and inorganic materials. These systems have garnered more attention due to their potential to unveil the intricate relationship among charged interfaces, high- to low-density liquid fluctuations, and their role in the formation of large-scale H-bond supramolecular structures, as suggested by molecular dynamics simulations of the hydration shell of the lysozyme protein . Supramolecular structures of orientationally ordered water as large as 1 μm have been reported in light scattering measurements of aqueous solutions of low-molar mass compounds − and in wide-field second harmonic (SH) microscopy of divalent cations interacting with water and negatively charged free-standing lipid bilayers, , although not explicitly connected to HDL and LDL domains.…”

“…For instance, its density is much higher than that of the bulk and the dielectric constant of interfacial water in the double layer is much lower than that of bulk water . These distortions induce a different ordering of water molecules at the interface, characterized by a higher concentration of HDL domains than LDL domains, compared to bulk water. , Like the impact of the lysozyme protein in liquid water, the presence of UCNPs also influences the local structure of water within the aqueous nanofluids. Consequently, nanofluids with larger UCNPs (lower S / V ratios) contain a relatively higher proportion of HDL domains in the hydration shell of the nanoparticles, leading to lower T c values (Figure c).…”