Kartierung des Hydratwassers um Alkoholketten mittels THz‐Kalorimetrie

Abstract

¾nderungen im Wasserstoffbrückennetzwerk von in Wasser gelçsten Alkoholketten wurden mithilfe der THz-Spektroskopie gemessen. Die THz-Spektren wurden zerlegt und die einzelnen Komponenten normalem Wasser,t etraedrisch angeordnetem Hydratwasser und ungeordneterem Hydratwasser zugeordnet. Das tetraedrischa ngeordnete Wasser erzeugt eine Bande bei 195 cm À1 und ist am hydrophoben Teil des Alkohols lokalisiert. Die zweite Komponente zeigt eine Bande bei 165 cm À1 und wird dem Hydratwasser in der ersten Solvatationsschale zugeordnet. Die vermessenen, temperaturabhängigen ¾nderungen im THz-Spektrum von gelçsten Alkoholketten kçnnen direkt mit ¾nderungen von Wärmekapazität, Entropie und freier Energie korreliert werden. Dabei ist überraschenderweise nichtd as tetraedrisch angeordnete Wasser,s ondern hauptsächlich das ungeordnete Hydratwasser fürdie temperaturabhängigen ¾nderungen von DC p und DGv erantwortlich. Der fürd en gelçsten Stoff spe-zifischeU nterschied in der freien Energie ist auf die Bildung von Kavitäten zurückzuführen und skaliert linear mit der Kettenlänge der Alkohole.

Spectroscopic Fingerprints of Cavity Formation and Solute Insertion as a Measure of Hydration Entropic Loss and Enthalpic Gain

“…drug discovery. [30] In the present work, we seek for a pathway to experimentally access both hydrophilic and hydrophobic contributions via THz-calorimentry [31] (i.e. via correlating THz vibrational fingerprints with entropy and enthalpy) and evaluate their synergy in dictating hydration free energies within a simple thermodynamic model.…”

“…[31,34] The THz spectrum of the solute and its hydration shell is obtained by subtracting the volumescaled absorption spectrum of bulk water from the absorption spectrum of a solution containing the solute of interest. [27,31] Hydration-shell vibrational spectroscopies provide valuable information on the intermolecular interactions involving the solute and its hydration water molecules. [31,[35][36][37] In our previous studies we focused on the HB intermolecular stretching region (100-300 cm À 1 ), i.e.…”

“…Building on our previous work, [27,31] we aim for a direct experimental characterization of the hydrophilic and hydrophobic contributions described by each of the two steps of Figure 1 and their interplay to determine the hydration free energy of molecules composed of both polar and apolar groups. Our study focuses on aqueous alcohol solutions as model systems, but the developed methodology can be generalized to more complex molecules and bio-interfaces, where the balance and distribution of polar and apolar groups are crucial parameters in determining hydration free energies and biological function.…”

“…[16,18,26] We have previously introduced THz absorption spectroscopy to characterize the water HB-network formed around hydrated solutes. [31,34] The THz spectrum of the solute and its hydration shell is obtained by subtracting the volumescaled absorption spectrum of bulk water from the absorption spectrum of a solution containing the solute of interest. [27,31] Hydration-shell vibrational spectroscopies provide valuable information on the intermolecular interactions involving the solute and its hydration water molecules.…”

“…[27,31] Hydration-shell vibrational spectroscopies provide valuable information on the intermolecular interactions involving the solute and its hydration water molecules. [31,[35][36][37] In our previous studies we focused on the HB intermolecular stretching region (100-300 cm À 1 ), i.e. the low frequency region showing the collective vibrations of the water HBnetwork, and we were able to identify two characteristic bands of the HB-network in the alcohol hydration layer.…”