Bound Solvent Molecules Research Articles

Jumping Exothermic Effect in Polymer Gels

The specific reaction of polymer gels to the effect of an alternating temperature field is explored that is manifested in an exothermic effect, the position of which on the temperature scale depends on the thermal prehistory of the gel. It is found that the described exothermic effect is observed in polymer gels of any nature, and for its manifestation it is necessary to have a spatial network structure in which both free and bound solvent molecules are present.

Solid polymer electrolytes with hydrates for structural supercapacitors

Structural supercapacitors that simultaneously carry mechanical loads and store electrical energy show great promise to increase the functionality and efficiency of countless mobile systems. Current iterations of all structural supercapacitors use bi-continuous electrolytes with two phases that provide mechanical and electrochemical functions separately. Here we demonstrate a single-phase hydrate-based solid polymer electrolyte with improved multifunctionality. The new structural electrolyte composed of polyethylene terephthalate (PET) and lithium perchlorate trihydrate (LiClO4·3H2O) is created through mix-melting of PET and LiClO4 followed by controlled hydration of the salt. The bound water molecules in the hydrates significantly improve the ionic conductivity while retaining the high mechanical stiffness of the electrolyte, which reduces the trade-off between the two functions as in previous reports. The electrolyte with the optimal composition achieves a flexural modulus of 2.1 GPa with an ionic conductivity of 1.05 μS/cm. Moreover, the single-phase electrolyte exhibits a much better electrochemical interface with electrodes compared to other structural electrolytes. The interfacial capacitance measured with our electrolyte is the same order of magnitude as that tested with a liquid electrolyte. The creation of this electrolyte allows for the development of more efficient structural supercapacitors. The strategy of introducing bound solvent molecules to improve the ionic conductivity without sacrificing the mechanical properties of solid polymer electrolytes can also be used to develop better electrolytes for all-solid-state batteries.

Probing the thermal stability of μ-oxo triruthenium clusters

This work presents for the first time a systematic investigation on the thermal decomposition and thermal stability of ten representative triruthenium clusters of general formula [Ru3(μ3-O)(μ-Ac)6(L)2L′]n (Ac = CH3COO− and L = N-heterocycles or H2O; L′ = py, Ac, H2O, CO or NO; n = 1+ or 0). Despite the variation of the N-heterocyclic L ligands, the pyridyl, nitrosyl and carbonyl species are quite similar in terms of their thermal decomposition path. The loosely bound solvent molecules are lost first, followed by the loss of the N-heterocyclic ligands, with the final collapse of the metallic core upon acetates oxidation in the range from 270 to 300 °C. Their thermal stability depends on the nature of the L and L′ ligands, varying up to 60°depending on the presence of NO, CO or N-heterocyclic ligands.

Evaluation of an Efficient 3D-RISM-SCF Implementation as a Tool for Computational Spectroscopy in Solution.

The 3D-RISM-SCF solvent-model implementation of Gusarov et al. [ J. Phys. Chem. A 2006, 110, 6083-6090] in the Amsterdam density functional program has been improved and extended. In particular, an accurate yet efficient representation of the solute electrostatic potential is provided. The Coulomb-potential fitting of many DFT codes can be used advantageously in this context. The extra effort compared to a point-charge representation is small for a given SCF cycle and compensated by faster SCF convergence. This allows applications to large solutes, as demonstrated by evaluation of the solvatochromism of Reichardt's dye. In general, TDDFT applications to excitation energies in solution stand out and are highlighted. Applications to the 17O NMR chemical shifts of N-methylformamide in different solvents also demonstrate the distinct advantages of 3D-RISM over continuum solvents. Limitations are observed in this case for water solvent, where the solvent shielding is overestimated. This shortcoming applies also to the 17O gas-to-liquid shift of water, where we used localized molecular orbital analyses for a deeper understanding. For such cases of extremely strong solute-solvent interactions, couplings between solute and solvent orbitals induced by the magnetic perturbation are relevant. These clearly require a quantum-mechanical treatment of the most closely bound solvent molecules. Except for such extreme cases, 3D-RISM-SCF is very well suited to treat solvent effects on NMR parameters. More serious limitations pertain to the treatment of vibrational spectra, where the absence of the coupling between solute and solvent vibrational modes limits the accuracy of applications of 3D-RISM-SCF. The reported extended, efficient, and numerically accurate 3D-RISM-SCF implementation should provide a useful tool to study chemical and spectroscopic properties of molecules of appreciable size in a realistic solvent environment.

EXAFS Study on the Coordination Chemistry of the Solvated Copper(II) Ion in a Series of Oxygen Donor Solvents.

The structures of the solvated copper(II) ion in water and nine organic oxygen donor solvents with similar electron-pair donor ability, but with different space-demanding properties at coordination, have been studied by EXAFS. N,N′-Dimethylpropyleneurea and N,N,N′,N′-tetramethylurea are sufficiently space demanding at coordination to make the axial positions not accessible, resulting in square-planar copper(II) solvate complexes with an intense green color. The mean Cu–O bond distances in these two solvate complexes are 1.939(3) and 1.935(3) Å, respectively. The best fits of the remaining solvates, which are light blue in different hues, are obtained with a Jahn–Teller distorted-octahedral model consisting of four strongly bound solvent molecules in the equatorial positions at 1.96(2) Å and two in the axial positions but with different Cu–Oax bond distances: ca. 2.15 and 2.32 Å. This is in agreement with observations in solid-state structures of compounds containing hexaaquacopper(II) complexes crystallizing in noncentrosymmetric space groups and all reported crystal structures containing a [Cu(H2O)5(O-ligand)] complex with Jahn–Teller distortion. Such a structure is in agreement with previous EPR and EXAFS studies proving the hydrated copper(II) ion to be a noncentrosymmetric complex in aqueous solution. The refinements of the EXAFS data of the solids [Cu(H2O)6](ClO4)2, [Cu(H2O)6](BrO3)2, [Cu(H2O)6]SiF6, Cu(NO3)2·2.5H2O, and CuSO4·5H2O gave Cu–O bond distances significantly different from those reported in the crystallographic studies but similar to the configuration and bond distances in the hydrated copper(II) ion in aqueous solution. This may depend on whether the orientation of the axial positions is random in one or three dimensions, giving a mean structure of the solid with symmetry higher than that of the individual complexes. This study presents the very first experimental data from the new X-ray absorption spectroscopy beamline Balder at the MAX IV synchrotron radiation facility in Lund, Sweden, as well as the utilized properties of the beamline.

2.7 Å cryo-EM structure of vitrified M. musculus H-chain apoferritin from a compact 200 keV cryo-microscope.

Here we present the structure of mouse H-chain apoferritin at 2.7 Å (FSC = 0.143) solved by single particle cryogenic electron microscopy (cryo-EM) using a 200 kV device, the Thermo Fisher Glacios®. This is a compact, two-lens illumination system with a constant power objective lens, without any energy filters or aberration correctors, often thought of as a “screening cryo-microscope”. Coulomb potential maps reveal clear densities for main chain carbonyl oxygens, residue side chains (including alternative conformations) and bound solvent molecules. We used a quasi-crystallographic reciprocal space approach to fit model coordinates to the experimental cryo-EM map. We argue that the advantages offered by (a) the high electronic and mechanical stability of the microscope, (b) the high emission stability and low beam energy spread of the high brightness Field Emission Gun (X-FEG), (c) direct electron detection technology and (d) particle-based Contrast Transfer Function (CTF) refinement have contributed to achieving high resolution. Overall, we show that basic electron optical settings for automated cryo-electron microscopy imaging can be used to determine structures approaching atomic resolution.

UV-Denaturation Assay to Assess Protein Photostability and Ligand-Binding Interactions Using the High Photon Flux of Diamond B23 Beamline for SRCD.

Light irradiation with high photon flux in the vacuum and far-UV region is known to denature the conformation of biopolymers. Measures are in place at Diamond Light Source B23 beamline for Synchrotron Radiation Circular Dichroism (SRCD) to control and make this effect negligible. However, UV denaturation of proteins can also be exploited as a novel method for assessing biopolymer photostability as well as ligand-binding interactions. Usually, host–ligand binding interactions can be assessed monitoring CD changes of the host biopolymer upon ligand addition. The novel method of identifying ligand binding monitoring the change of relative rate of UV denaturation using SRCD is especially important when there are very little or insignificant secondary structure changes of the host protein upon ligand binding. The temperature study, another method used to determine molecular interactions, can often be inconclusive when the thermal effect associated with the displacement of the bound solvent molecules by the ligand is also small, making the determination of the binding interaction inconclusive. Herein we present a review on the UV-denaturation assay as a novel method to determine the relative photostability of protein formulations as well as the screening of ligand-binding interactions using the high photon flux Diamond B23 beamline for SRCD.

A (T–P) phase diagram for the adsorption/desorption of carbon dioxide and hydrogen in a Cu(II)-MOF

Solvothermal synthesis of a highly porous metal–organic framework (PMOF) of Cu(II) had been achieved with a bent tetracarboxylate linker, L4− incorporating an –NH2 group in the middle. The design of the linker afforded paddle-wheel secondary building unit (SBU) with metal bound solvent molecules. Upon activation by heating, the overall integrity of the structure remained intact with the result of a PMOF embellished with unsaturated metal centers (UMCs) and free –NH2 groups. This activated PMOF showed adsorption of 6.6% by weight of H2 gas at 77 K and 62 bar and very high 60% by weight of CO2 gas at 298 K and 32 bar. The adsorption/desorption properties of this MOF has been probed theoretically to obtain additional insights into physisorption of these strategically important gases. The binding energy values reveal the willingness of the CO2 and H2 gas molecules to get absorbed in Cu(II)-MOF. Temperature–pressure (T–P) phase diagrams have been generated for both of the gas absorption processes at ωB97x-D/TZVP level of theory. Temperature and pressure regions have been identified where Gibbs free energy is negative that is the absorption process is spontaneous. The ab initio molecular dynamics study reveals that the gas saturated Cu(II)-MOFs are stable. Thus this Cu(II)-MOF can be used as an effective gas storage material.

Aerobic Oxidation of Alcohols Catalysed by Cu(I)/NMI/TEMPO System and Its Mechanistic Insights

Homogeneous Cu(I)/NMI/TEMPO catalyst system (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) has been investigated for its catalysis on the aerobic oxidation of 1-octanol and other alcohols into aldehydes under room temperature. The catalytic species was found to be a Cu(I) centre coordinated by two NMI molecules and other two weakly bound solvent molecules, [Cu(NMI)2(Sol)2]+ (Sol = solvent). When CuI was used, this species could be [Cu(NMI)I(Sol)2]. Not like being speculated previously, NMI in this system acts solely as a ligand and its role coordinated to the copper centre enhanced the electron density on the metal centre which promoted the O2 binding in the catalysis. The labile solvent binding to the Cu(I) centre is essential to ensure both oxygen and substrate binding. The catalyst system is suitable for the oxidation of various alcohols using a simple reaction setup and workup. In particular, the system possesses strong oxidizing capability in quantitative conversion of benzylic alcohols regardless of the substituents on the phenyl ring and allylic alcohols into aldehydes. A plausible mechanism was also proposed for the catalysis. The aerobic oxidation of primary alcohols at room temperature to corresponding aldehydes was achieved by the catalyst composed by Cu(I) and methyl imidazole (NMI) mediated by TEMPO in acetonitrile. The catalytic species is proposed to be such a Cu(I) complex that two of its four coordinating sites are occupied by a strong ligand(s) and the rest two are weakly bound by solvent molecules.

One-step Access to Resorcinsalens-Solvent-Dependent Synthesis, Tautomerism, Self-sorting and Supramolecular Architectures of Chiral Polyimine Analogues of Resorcinarene.

Substituted 2,4- and 4,6-dihydroxyisophthalaldehydes were condensed with optically pure and racemic trans-1,2-diaminocyclohexane to form resorcinarene-like polyimine macrocycles (resorcinsalens), the structure and stoichiometry of which were controlled by the choice of the reaction medium. Particularly, the cyclocondensation reactions were driven by the solubility, tautomerization, or by social self-sorting. The resorcinsalens crystallized as inclusion compounds, in which the guest molecules were situated either in channels or in voids. In the highly hydrated crystals of one of the [2+2] macrocycles and chloroform-solvated crystals of a [4+4] product the channels were interconnected, as in zeolites, enabling possible migration of loosely bound solvent molecules in three dimensions. The association mode depended on the structural modification of the host molecule and the type of included solvent molecule(s).

Isomeric Broadening of C60+ Electronic Excitation in Helium Droplets: Experiments Meet Theory.

Helium is considered an almost ideal tagging atom for cold messenger spectroscopy experiments. Although helium is bound very weakly to the ionic molecule of interest, helium tags can lead to shifts and broadenings that we recorded near 963.5 nm in the electronic excitation spectrum of C60+ solvated with up to 100 helium atoms. Dedicated quantum calculations indicate that the inhomogeneous broadening is due to different binding energies of helium to the pentagonal and hexagonal faces of C60+, their dependence on the electronic state, and the numerous isomeric structures that become available for intermediate coverage. Similar isomeric effects can be expected for optical spectra of most larger molecules surrounded by nonabsorbing weakly bound solvent molecules, a situation encountered in many messenger-tagging spectroscopy experiments.

On the structure of monohalomercury(II) complexes in dimethylsulfoxide, pyridine and N,N-dimetylthioformamide solution

The structures of the monohalomercury(II) complexes, [HgX]+, in dimethylsulfoxide (dmso), pyridine and N,N-dimethylthioformamide (dmtf) solution have been studied by means of EXAFS. All complexes in the Hg2+-X− systems, X = Cl, Br and I, in dmso and pyridine have the unique property with wide range of predominance of all individual complexes. This means that all complexes can be individually characterized in solution. The previously reported complex formation thermodynamics in dmso and pyridine predicted a substantial desolvation at the formation of the first complex. This study shows that the dmso and pyridine solvated [HgX]+ complexes have one solvent molecule strongly bound “trans” to the halide ion and another two weakly bound solvent molecules in the remaining positions of linearly distorted tetrahedra. This shows that a substantial desolvation of the hexasolvated mercury(II) ions takes place at the formation of the [HgX]+ complexes. The strongly bound dmso molecule binds through its oxygen atom to mercury(II) in the [HgCl]+ and [HgBr]+ complexes, while in the [HgI]+ complex through its sulfur atom. The Hg–X bonds are slightly shorter in the [HgX]+ complexes than in corresponding [HgX2] complexes, and the short Hg–O and Hg–N bond distances are ca. 0.35 and 0.25 Å shorter than in the octahedral hexakis(dmso)- and -(pyridine)mercury(II) solvates, respectively. In dmtf solution, the dmtf solvated mercury(II) ion is four-coordinate in tetrahedral fashion. The structures of the dmtf solvated [HgX]+ complexes show the same basic tetrahedral configuration as the mercury(II) solvate. This shows that a simple substitution reaction takes place at the formation of the [HgX]+ complexes in dmtf.

In Situ Measurement of Surface Functional Groups on Silica Nanoparticles Using Solvent Relaxation Nuclear Magnetic Resonance

In situ analysis and study on the surface of nanoparticles (NPs) is a key to obtain their important physicochemical properties for the subsequent applications. Of them, most works focus on the qualitative characterization whereas quantitative analysis and measurement on the NPs under their storage and usage conditions is still a challenge. In order to cope with this challenge, solvation relaxation-based nuclear magnetic resonance (NMR) technology has been applied to measure the wet specific surface area and, therefore, determine the number of the bound water molecules on the surface of silica NPs in solution and the hydrophilic groups of various types grafted on the surface of the NPs. By changing the surface functional group on silica particles, the fine distinction for the solvent-particle interaction with different surface group can be quantitatively differentiated by measuring the number of water molecules absorbed on the surface. The results show that the number of the surface hydroxyl, amine, and carboxyl group per nm2 is 4.0, 3.7, and 2.3, respectively, for the silica particles with a diameter of 203 nm. The method reported here is the first attempt to determine in situ the number of bound solvent molecules and any solvophilic groups grafted on nanoparticles.

Cobalt(II) chloride adducts with acetonitrile, propan-2-ol and tetrahydrofuran: considerations on nuclearity, reactivity and synthetic applications.

High-spin cobalt(II) complexes are considered useful building blocks for the synthesis of single-molecule magnets (SMM) because of their intrinsic magnetic anisotropy. In this work, three new cobalt(II) chloride adducts with labile ligands have been synthesized from anhydrous CoCl2, to be subsequently employed as starting materials for heterobimetallic compounds. The products were characterized by elemental, spectroscopic (EPR and FT-IR) and single-crystal X-ray diffraction analyses. trans-Tetrakis(acetonitrile-κN)bis(tetrahydrofuran-κO)cobalt(II) bis[(acetonitrile-κN)trichloridocobaltate(II)], [Co(C2H3N)4(C4H8O)2][CoCl3(C2H3N)]2, (1), comprises mononuclear ions and contains both acetonitrile and tetrahydrofuran (thf) ligands, The coordination polymer catena-poly[[tetrakis(propan-2-ol-κO)cobalt(II)]-μ-chlorido-[dichloridocobalt(II)]-μ-chlorido], [Co2Cl4(C3H8O)4], (2'), was prepared by direct reaction between anhydrous CoCl2 and propan-2-ol in an attempt to rationalize the formation of the CoCl2-alcohol adduct (2), probably CoCl2(HOiPr)m. The binuclear complex di-μ-chlorido-1:2κ4Cl:Cl-dichlorido-2κ2Cl-tetrakis(tetrahydrofuran-1κO)dicobalt(II), [Co2Cl4(C4H8O)4], (3), was obtained from (2) after recrystallization from tetrahydrofuran. All three products present cobalt(II) centres in both octahedral and tetrahedral environments, the former usually less distorted than the latter, regardless of the nature of the neutral ligand. Product (2') is stabilized by an intramolecular hydrogen-bond network that appears to favour a trans arrangement of the chloride ligands in the octahedral moiety; this differs from the cis disposition found in (3). The expected easy displacement of the bound solvent molecules from the metal coordination sphere makes the three compounds good candidates for suitable starting materials in a number of synthetic applications.

Luminescence Solvato- and Vapochromism of Alkynyl-Phosphine Copper Clusters.

The reaction of [Cu(NCMe)4][PF6] with aromatic acetylenes HC2R and triphosphine 1,1,1-tris(diphenylphosphino)methane in the presence of NEt3 results in the formation of hexanuclear Cu(I) clusters with the general formula [Cu6(C2R)4{(PPh2)3CH}2][PF6]2 (R = 4-X-C6H4 (1-5) and C5H4N (6); X = NMe2 (1), OMe (2), H (3), Ph (4), CF3 (5)). The structural motif of the complexes studied consists of a Cu6 metal core supported by two phosphine ligands and stabilized by σ- and π-coordination of the alkynyl fragments (together with coordination of pyridine nitrogen atoms in cluster 6). The solid state structures of complexes 2-6 were determined by single crystal XRD analysis. The structures of the complexes in solution were elucidated by (1)H, (31)P, (1)H-(1)H COSY NMR spectroscopy, and ESI mass spectrometry. Clusters 1-6 exhibit moderately strong phosphorescence in the solid state with quantum yields up to 17%. Complexes 1-5 were found to form solvates (acetone, acetonitrile) in the solid state. The coordination of loosely bound solvent molecules strongly affects emission characteristics and leads to solvato- and vapochromic behavior of the clusters. Thus, solvent-free and acetonitrile solvated forms of 3 demonstrate contrasting emission in orange (615 nm) and blue (475 nm) regions, respectively. The computational studies show that alkynyl-centered IL transitions mixed with those of MLCT between the Cu6 metal core and the ligand environment play a dominant role in the formation of excited states and can be considerably modulated by weakly coordinating solvent molecules leading to luminescence vapochromism.

A novel tripodal CMPO ligand: Affinity for f-elements, computational investigations and luminescence properties

The synthesis and characterization of a new ligand bearing three carbamoylmethylphosphine oxide (CMPO) groups linked with a tris(2-aminoethyl)amine (TREN) capping scaffold is reported. Lanthanide and actinide complexes with this tripodal, hexadentate ligand have been prepared and characterized in solution and in the solid state. Further, we have investigated the general f-element binding and coordination geometries of these complexes using computational methods. This ligand demonstrates low extraction ability within the series of f-elements studied as rationalized by the computational data and protonation behavior presented. Modest extraction selectivity was observed, however, for Tb3+. Sensitization of Eu3+ and Tb3+ in solutions of methanol is also achieved by the ligand and the resultant photophysical properties are discussed. Luminescence lifetime data for the Eu3+ complex have been used to determine a value of approximately 1.5 bound solvent molecules in solution, providing further insight into the f-element coordination chemistry of this new CMPO-based ligand.

Solvation and cavity occupation in biomolecules

BackgroundSolvation density locations are important for protein dynamics and structure. Knowledge of the preferred hydration sites at biomolecular interfaces and those in the interior of cavities can enhance understanding of structure and function. While advanced X-ray diffraction methods can provide accurate atomic structures for proteins, that technique is challenged when it comes to providing accurate hydration structures, especially for interfacial and cavity bound solvent molecules. MethodsAdvances in integral equation theories which include more accurate methods for calculating the long-ranged Coulomb interaction contributions to the three-dimensional distribution functions make it possible to calculate angle dependent average solvent structure, accurately, around and inside irregular molecular conformations. The proximal radial distribution method provides another approximate method to determine average solvent structures for biomolecular systems based on a proximal or near neighbor solvent distribution that can be constructed from previously collected solvent distributions. These two approximate methods, along with all-atom molecular dynamics simulations are used to determine the solvent density inside the myoglobin heme cavity. Discussion and resultsMyoglobin is a good test system for these methods because the cavities are many and one is large, tens of Å3, but is shown to have only four hydration sites. These sites are not near neighbors which implies that the large cavity must have more than one way in and out. ConclusionsOur results show that main solvation sites are well reproduced by all three methods. The techniques also produce a clearly identifiable solvent pathway into the interior of the protein. General significanceThe agreement between molecular dynamics and less computationally demanding approximate methods is encouraging.This article is part of a Special Issue entitled Recent developments of molecular dynamics.

Solvation structure and dynamics of Li+ ion in liquid water, methanol and ethanol: A comparison study

Car–Parrinello molecular dynamics was performed on Li+ in water, methanol and ethanol. Structural and dynamical properties of Li+ were studied and compared with experimental data. Excellent agreement was obtained with the experimental data for the structure of the first solvation shell. The results show the Li+ has a more stable tetrahedral coordination in water and methanol than that in ethanol. The diffusion of water in its first solvation shell was rather slow. Compared to water and methanol, the ethanol in the first solvation shell diffuses slower. The decay of orientational profiles of the solvent molecules in the solvation shell shows slower relaxation for first and second rank correlations compared to bulk water and methanol. The decay of orientational correlations for solvation shell molecules shows faster relaxation compared to that of bulk ethanol. Spectral of bound solvent molecules are compared to those of the bulk. Reasonable agreement is obtained with experiments.

Elucidating the roles of enthalpy, entropy, and donor atom in the chelate effect for binding different bidentate ligands on the same metal center

We present a thermodynamic study of the chelate effect for a series of P–P, N–N, and P–N bidentate ligands binding to PdCl2(MeCN)2 in acetonitrile (MeCN), using isothermal titration calorimetry (ITC) to measure the solution-phase binding thermodynamics. The chelate effect is considered to be an entropic effect, that is, the enthalpic contributions attributed to binding for comparable monodentate and bidentate ligands are nearly identical, meaning that changes in ΔG are due to favorable changes in ΔS upon displacement of bound solvent molecules. However, our results demonstrate that enhanced enthalpic contributions (i.e. large and exothermic) control the stability of the chelated complexes and generally are accompanied by large entropic penalties. We discuss the contribution of solvent reorganization and its role in enthalpy–entropy compensation for the binding equilibria studied.

Monosaccharide and disaccharide isomerization over Lewis acid sites in hydrophobic and hydrophilic molecular sieves

Lewis acid sites isolated within low-defect, hydrophobic molecular sieves (Sn-Beta-F, Ti-Beta-F) catalyze monosaccharide (glucose–fructose) and disaccharide (lactose–lactulose) aldose–ketose isomerization reactions in liquid water at initial turnover rates (per total metal atom; 373K) that are, respectively, ∼10–30 and ∼103–104 factors higher than sites isolated within highly defective, hydrophilic molecular sieves (Ti-Beta-OH) or amorphous co-precipitated oxides (TiO2–SiO2). Glucose-H2/glucose-D2 kinetic isotope effects of ∼2 (at 373K) for intramolecular C2–C1 hydride shift isomerization to fructose indicate that glucose transport to active sites within Ti-Beta-F or Ti-Beta-OH does not limit turnover rates in liquid water or methanol, in spite of dramatic differences in the volumetric occupation of hydrophobic and hydrophilic void spaces by physisorbed solvent molecules. Glucose isomerization turnover rates (per total Ti; 373K) in liquid water are first-order in aqueous glucose concentration (at least up to 1.5% (w/w)). The mechanistic interpretation of measured first-order isomerization rate constants indicates that they reflect free energies of kinetically relevant isomerization transition states relative to two bound solvent molecules, which adsorb competitively with sugars at Lewis acid sites and are the most abundant surface intermediates during steady-state catalysis. The lower isomerization rate constants on Ti centers in highly defective environments, in part, reflect stronger coordination of solvent molecules to Ti centers via additional hydrogen bonding interactions with proximal surface hydroxyl groups. The direct measurement of glucose isomerization rate constants in the liquid phase provides a rigorous and quantitative description of the catalytic differences prevalent among Lewis acidic silica-based solids with hydrophobic or hydrophilic properties, and their interpretation using a mechanism-based rate equation provides further clarity into the inhibition of catalytic turnovers at Lewis acid sites by solvent coordination.