Hydrogen-bonded Structure Research Articles

The effect of tritiated water on the alkaline phosphatase inactivation after ultrasound and gamma-rays irradiation

Comparative analysis of the alkaline phosphatase post-inactivation dynamics in natural and tritiated water (H2O and HTO, respectively) after ultrasonic or γ-irradiations was performed. It has been established that in HTO, unlike in H2O, the enzyme retains its activity up to 15 days. It is hypothesised that different hydrogen bond structure of tritiated water results in a lower effect of ultrasound or gamma-irradiation reactive species onto enzyme globules.

Green and designable deep eutectic solvents for extraction separation of oxygenated compounds in Fischer-Tropsch oil products: Hydrogen bond descriptors and structure–activity study

In this work, choline fluoride, choline chloride, and 2-fluoroethyl-trimethylammonium bromide containing –F, –Cl, and –Br structures were used as hydrogen bond receptors. Acetamide, urea, trifluoroacetamide, xylitol, ethylene glycol, malonic acid and lactic acid containing –HN2, –COOH, –OH, and –F structures were used as hydrogen bond donors. We constructed functional deep eutectic solvents rich in hydrogen bond donors and acceptors while providing alcohol hydrogen bond attraction sites and aldehyde and ketone hydrogen bond attraction sites. The efficient separation and enrichment of trace alcohols, aldehydes, and ketones in Fischer-Tropsch (F-T) oil products were achieved through hydrogen bond interaction. The mechanism of selective extraction of different types of oxygenated compounds by functionalized deep eutectic solvents was revealed, and the linear relationship among structure, hydrogen bond descriptor, and extraction performance was clarified through quantum chemistry calculations. Further, liquid–liquid extraction was used to extract and separate the oxygenated compounds from high-temperature F-T oil products using the synthesized functional deep eutectic solvent. The experimental results showed that propanol, butyraldehyde, and methylethylketone could be extracted simultaneously and efficiently, and the solvent effects were consistent with the results of quantum chemistry calculation. The excellent extraction and separation effects were due to the large number of hydrogen bonds and oxyphilic atomic forces of deep eutectic solvents. The modern solvent was reasonably designed, which is significant for extracting different oxygenated compounds from high-temperature F-T oil products.

Exploring the change of hydrogen bond evolution in NMP-H2O solution through 2D Raman-COS spectra analysis

The transitions of Hydrogen Bond (HB) structure with in the cluster structures of NMP-H2O solutions was conducted by combining Density Functional Theory (DFT) calculations and Two-dimensional Correlation Raman Spectroscopy (2D Raman-COS). When VNMP < 20 %, NMP molecule is incorporated into the tetrahedral structure of water through an "insertion" mechanism, by displacing some H2O molecules and establishing HB. This interaction strengthens the tetrahedral arrangement in water, causing the free OH bond length to be compressed. When VNMP > 20 %, large amounts of NMP molecules were self-assembled through dipole-dipole alignment, and the NMP·2H2O, NMP·H2O, and 2NMP·H2O clusters gradually substitute the tetrahedral structure of water, leading to the disruption of the HB network in water. Furthermore, it was observed that the pulsed laser beam accelerated the transition point of the HB structure in the NMP-H2O solution. This research provides references for the application of NMP in the fields of aqueous batteries from the view of HB with electrolyte.

Solution NMR assignments and structure for the dimeric kinesin neck domain.

Kinesin is a motor protein, comprised of two heavy and two light chains that transports cargo along the cytoskeletal microtubule filament network. The heavy chain has a neck domain connecting the ATPase motor head responsible for walking along microtubules, with the stalk and subsequent tail domains that bind cargo. The neck domain consists of a coiled coli homodimer with about five heptad repeats, preceded by a linker region that joins to the ATPase head. Here we report 1H, 15N, and 13C NMR assignments and a solution structure for the kinesin neck domain from rat isoform Kif5c. The calculation of the NMR structure of the homodimer was facilitated by unambiguously assigning sidechain NOEs between heptad a and d positions to interchain contacts, since these positions are too far apart to give sidechain contacts in the monomers. The dimeric coiled coil NMR structure is similar to the previously described X-ray structure, whereas the linker region is disordered in solution but contains a short segment with β-strand propensity- the β-linker. Only the coiled coil is protected from solvent exchange, with ∆G values for hydrogen exchange on the order of 4-6kcal/mol. The high stability of the hydrogen-bonded α-helical structure makes it unlikely that unzippering of the coiled coil is involved in kinesin walking. Rather, the linker region serves as a flexible hinge between the kinesin head and neck.

Crystal structure and photocatalytic activity of luminescent 3D-Supramolecular metal organic framework of dysprosium

A 3D supramolecular metal organic framework of dysprosium has been fabricated through a facile hydrothermal procedure with the ligand, 2,6-naphthalene disulphonic acid and the co-ligand, 4,4′-bipyridine. The MOF has been characterized as [C60H81DyN8O30S4] by routine analytical procedures. SXRD studies of the MOF show the existence of a hydrogen-bonded 3D supramolecular structure with high porosity. It crystallizes in monoclinic space group P21/n with unit cell parameters, a = 16.5424(6) Å, b = 37.0052(14) Å, c = 24.4361(9) Å, β = 100.7410°, α = γ = 90°. The Dy-MOF has eight coordinated water molecules around the metal centre and exhibits square anti-prismatic geometry. The band gap is 3.11 eV. The degradation experiments under visible light confirmed that Dy-MOF can act as a photocatalyst. Addition of hydrogen peroxide remarkably increases the degradation efficiency of the MOF through an advanced oxidation process. The newly synthesized MOF produced sharp emission peaks characteristic of dysprosium ion.

Exploring the dynamic changes in hydrogen bond structure of water and heavy water under external perturbation of DMF

The Raman spectra of DMF-water/heavy water binary solutions at different volume ratios are measured to investigate the hydrogen bond structure between N, N-dimethylformamide (DMF) and water/heavy water. It was observed that when VDMF below 40 %, DMF reinforces the hydrogen bond among water molecules through the substitution of a small amount of water molecules within the tetrahedral structure. However, a similar enhancement phenomenon is not observed in heavy water. When VDMF is less than 60 %, the hydrogen bonds among DMF and heavy water molecules affect the symmetry of OD covalent bond. Furthermore, as VDMF exceeds 40 %/60 %, the tetrahedral structures of water and heavy water are gradually replaced by DMF·3H2O/3D2O, DMF·2H2O/2D2O, and DMF·H2O/D2O clusters. The transition point of hydrogen bond structure in DMF- aqueous solution moved to VDMF = 15 % under the influence of under the influence of dynamic high pressure caused by pulsed laser beam. This study provides valuable insights into the microstructure of water/heavy water clusters.

The Molecular Ocean

We report on progress in observing the hydrogen-bonded structure of water and sea water by deep-ocean Raman spectroscopy. In the normal ocean, the abundance of single H2O species is less than 20%. The principal form is the tetrahedral pentamer, and the (H2O)[Formula: see text] nH2O equilibrium plays a dominant role in controlling physicochemical processes and the speed of sound. The enthalpy of the H-bond in water is 2.624 kcal/mol, and in sea water 2.258 kcal/mol due to the quantity of non-HB water in the solvation shell of sea salt ions. The activation energy of viscous flow is 4.28 kcal/mol at one atmosphere pressure, consistent with the need to break hydrogen bonds and overcome the van der Waals intermolecular forces. The activation energy decreases exponentially with depth/pressure and is 10% less at 4,000 m depth. We suggest this is due to the pressure-induced shift in the water equilibrium to favor the less compressible quasi-planar pentamer, tetramer, and so on forms. We address the long-standing conclusion that microbial swimming by means of rotating flagella is only 1%–2% efficient. This neglects the need for microbes to overcome the activation energy of viscous flow; [Formula: see text]95% of the mechanical energy produced by the flagella must be used to break H-bonds and overcome intermolecular forces.

Molecular analysis of hydrogen-bond structures in polymer electrolyte membrane in polymer electrolyte fuel cells below freezing temperatures

The PEFC has been attracted to achieve carbon neutralization with using of cars and so on. Unclearness of the internal state of the polymer electrolyte membrane (PEM) below freezing temperature is one of the biggest problems toward expansion of operating temperature. Our final objective is to reveal the internal state of PEM and transport mechanism in such environment. We performed the reactive force field molecular dynamics to analyze the internal structure of PEM because under such environment chemical reaction is the key transport mechanisms. A radial distribution function (RDF) was performed to analyze the structure in PEM. Our RDF was in good agreement with other simulation results. We found the increase of water molecules in the overlapped solvation area with the decrease in temperature. The water molecules hardly move in the overlapped area, indicating that proton diffusivity decreases.

UV-curing polyurethane pressure-sensitive adhesive with high shear strength and good adhesion properties inspired by spider silk

It is a challenge to develop polyurethane pressure-sensitive adhesive (PU-PSA) simultaneously with good cohesion and adhesion properties. Inspired by the structure of multiple hydrogen bonds in spider silk, we introduced Acylsemicarbazide (ASCZ) moiety that can form multiple hydrogen bonds in the polymer network into PU-PSA. The characteristic absorption peaks of ester groups at 1600–1780 cm−1 were analyzed in FTIR testing, and the results showed that ASCZ formed multiple hydrogen bonds in PU-PSA, and the hydrogen bond content increased with the increase of ASCZ content. In particular, PUA-AD20% with 24.3 % hydrogen bond content showed higher shear strength (0.51 MPa) and debonding energy (3.3 KJ m−2). Rheological tests showed that PU-PSA storage modulus and loss modulus increased with increasing frequency, which was highly frequency dependent. Therefore, as dynamic and reversible sacrificial bonds, hydrogen bonds can dissipate energy efficiently and resist external forces. In addition, the ASCZ component also provided PU-PSA with the polar groups required for adhesion. Therefore, PUA-AD20% had excellent adhesion properties. Compared to PUA, PUA-AD20% tack and peel strength increased by 36.1 % and 146.8 %, with values of 4.9 N and 11.6 N, respectively. In summary, this work offered a simple and versatile approach to designing PU-PSA with outstanding overall performance.

Tailoring the interfacial interaction of collagen fiber/waterborne polyurethane composite via plant polyphenol for mechanically robust and breathable wearable substrate

Collagen fiber-waterborne polyurethane composites possess great potential applications in flexible wearable devices owing to their excellent biocompatibility, flexibility, and biodegradability. However, the weak interfacial interactions which result in poor mechanical strength and breathability, have significantly hindered their practical application. Herein, high-performance collagen fiber-based wearable substrates prepares by constructing a hydrogen-bonded cross-linked network structure using bayberry tannin, a natural plant polyphenol, as a coupling bridge to bind collagen fibers and waterborne polyurethane (WPU). The dynamic rupture and reformation of sacrificial hydrogen bonds on the molecular scale effectively dissipate energy under mechanical stress, endowing these composites with remarkable toughness and ultrahigh water vapor permeability (WVP). The resultant composite’s tensile strength and WVP are 100% and 60 times higher than WPU, respectively. Additionally, this cost-effective strategy enables easy large-scale composite production. This method guides the development of high-performance, multifunctional collagen fiber-based wearable composites while advancing the tannery solid waste circular economy.

Hydrogen-bonding and vibrational coupling of water in a hydrophobic hydration shell: Significance of alkyl chain configuration and charge on the hydrophobe

The interaction between a molecular hydrophobe and water is crucial for their mutual structure and reactivity. Here, we have investigated the hydrogen-bonding (H-bonding) structure and intermolecular vibrational coupling i.e., the collective nature of water, in the hydration shell (HS) of charged and uncharged molecular hydrophobes, using polarization-resolved Raman difference spectroscopy with simultaneous curve fitting (Raman-DS-SCF) and isotopic dilution spectroscopy. Raman-DS-SCF provides the vibrational spectrum of water pertaining to the HS of the hydrophobes. The HS-spectra reveal that the positive charge on the hydrophobe (e.g., deuterated tetramethylammonium cation, d-TMA+) as well as the branching of the alkyl chain (n-butyl alcohol (BA) vs. tert-butyl alcohol (TBA)) reinforces the intermolecular vibrational coupling of water in the HS. The water-water H-bonding in the HS of d-TMA+ and d-TBA are similar to each other, but stronger than that of the bulk water. Apart from the strongly H-bonded water, the hydrophobic hydration shells exhibit weakly interacting dangling OH (ν¯max≈3670) which is intramolecularly coupled with the H-bonded OH of the same water molecule. The prevalence of the dangling-OH decreases with chain-branching and net positive charge on the hydrophobe: BA > d-TBA > d-TMA+. Altogether, the collective nature of water and its propensity for dangling-OH in a hydrophobic hydration shell strongly depend on the net charge and alkyl chain configuration of the hydrophobe.

An Azomethine-H-Based Fluorogenic Sensor for Formic Acid.

Formic acid (FA) is an important C1-containing feedstock that serves as a masked source of dihydrogen gas (H2). To encourage the adoption of cleaner (noncarbonaceous) energy sources, FA detection and sensing is thus of considerable interest. Here, we examine the use of a commercially available dye, azomethine-H (Az-H), for FA sensing. Solution studies confirm that FA quenches both the absorbance and the luminescence properties of Az-H. FA was additionally found to attenuate a known Az-H (E)-to-(Z) conformational change, suggesting an Az-H/FA interaction, possibly through hydrogen bonding; this phenomenon was probed using 1H NMR spectroscopy. Moving toward a solid-state sensor, the Az-H probe was incorporated into a gelatin-based matrix. On exposure to FA, the luminescence of this system was found to increase in a FA-dependent manner, attributed to the formation of stable hydrogen-bonded structures, facilitating a (Z)-to-(E) isomerization via imine protonation, allowing for production of the more luminescent (E)-isomer. This fluorogenic signal was used as a FA sensor with an estimated detection limit of ca. 0.4 ppb FA vapor. This work constitutes an important step toward a highly sensitive FA sensor in both the solution and solid state, opening new space for the detection of organic acids in differing chemical environments.

Turning gas hydrate nucleation with oxygen-containing groups on size-selected graphene oxide flakes

Gas hydrate is a promising alternative for gas capture and storage due to its high gas storage capacity achieved with only structured water molecules. Nucleation is the critical controlling step in gas hydrate formation. Adding an alien solid surface is an effective approach to regulate gas hydrate nucleation. However, how the solid surface compositions control the gas hydrate nucleation remains unclear. Benefiting from the fact that the surface compositions of graphene oxide (GO) can be finely tuned, we report the effect of functional groups of size-selected GO flakes on methane hydrate nucleation. The carbonyl and carboxyl of GO flakes showed a more prominent promotion for methane hydrate nucleation than the hydroxyl of GO flakes. Surface energy, zeta potential, Raman spectra, and molecular dynamics simulation analysis were used to reveal the regulation mechanism of the functional groups of size-selected GO flakes on methane hydrate nucleation. The GO flakes with abundant carbonyl and carboxyl exhibited higher charge density than those enriched in hydroxyl. The negatively charged GO flakes can induce water molecules to form an ordered hydrogen-bonded arrangement via charge-dipole interactions. Therefore, the water molecules surrounding the carboxyl and carbonyl showed a more ordered hydrogen-bonded structure than those around the hydroxyl of GO flakes. The ordered water arrangement, similar to methane hydrate cages, significantly accelerated methane hydrate nucleation. Our study shows how the surface chemistry of solids control gas hydrate nucleation and sheds light on the design of effective heterogeneous nucleators for gas hydrate.

Synthesis, X-ray Structure, Hirshfeld Surface Analysis and Antimicrobial Assessment of Tetranuclear s-Triazine Hydrazine Schiff Base Ligand

The unexpected tetranuclear [Cu4(DPPT)2Cl6] complex was obtained by self-assembly of CuCl2.2H2O and (E)-2,4-di(piperidin-1-yl)-6-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)-1,3,5-triazine, (HDPPT) in ethanol. In this tetranuclear [Cu4(DPPT)2Cl6] complex, the organic ligand acts as mononegative chelate bridging two crystallographically independent Cu(II) sites. The DPPT− anion acts as a bidentate ligand with respect to Cu(1), while it is a tridentate for Cu(2). The Cu(1)N2Cl3 and Cu(2)N3Cl spheres have square pyramidal and square planar coordination geometries with some distortion, respectively. Two of the chloride ions coordinating the Cu(1) are bridging between two crystallographically related Cu(1) sites connecting two [Cu2(DPPT)Cl3] units together, leading to the tetranuclear formula [Cu4(DPPT)2Cl6]. The packing of the [Cu4(DPPT)2Cl6] complex is dominated by C-H…Cl contacts, leading to one-dimensional hydrogen-bond polymeric structure. According to Hirshfeld surface analysis of molecular packing, the non-covalent interactions H…H, Cl…H, Cl…C, C…H, and N…H are the most significant. Their percentages are 52.8, 19.0, 3.2, 7.7, and 9.7%, respectively. Antimicrobial assessment showed good antifungal activity of the Cu(II) complex against A. fumigatus and C. albicans compared to Ketoconazole as positive control. Moreover, the [Cu4(DPPT)2Cl6] complex has higher activity against Gram-positive bacteria than Gentamycin as positive control. The opposite was observed when testing the tetranuclear [Cu4(DPPT)2Cl6] complex against the Gram-negative bacteria.

Unified view of the hydrogen-bond structure of water in the hydration shell of metal ions (Li+, Mg2+, La3+, Dy3+) as observed in the entire 100–3800 cm−1 regions

Hydrogen-bond (H-bond) structure of water in the hydration shell of an anion is fairly well understood, but the corresponding knowledge for cation hydration shell is sparse, mainly because of the overwhelming effect of anion on water that easily masks the subtle effect of cation. Moreover, most of the hydration shell investigations are confined to the OH stretch band of water. Using Raman difference spectroscopy with simultaneous curve fitting (Raman-DS-SCF), we have retrieved the spectrum of water pertaining to the hydration shell of different metal ions (Li+, Mg2+, La3+, Dy3+) in the entire spectral region of 100–3800 cm−1, encompassing the intermolecular H-bond stretch (HOH---OH2; 200 cm−1), librational (300–1000 cm−1), HOH bend (1640 cm−1), bend-librational combination (2120 cm−1) and intramolecular O–H stretch (3000–3700 cm−1) of water. The hydration shell spectra and their polarization dependence (Polarized Raman) are compared for different metal ions and with the hydration shell of Cl− anion and also the high temperature water component (80 °C; extracted by Raman-DS-SCF). These results reveal that the hydration shells of high charge density metal ions have “enhanced” as well as “reduced” H-bond structure. The intermolecular H-bonds become stiffer and the librational freedom of the water gets restricted in the hydration shell. The bend-librational combination band blue-shifts to a large extent and appears toward the tail of the OH stretch, which is expected to facilitate the ultrafast energy dissipation of higher vibrational modes of water.

Ultralow Coefficient of Thermal Expansion and a High Colorless Transparent Polyimide Film Realized Through a Reinforced Hydrogen-Bond Network by In Situ Polymerization of Aromatic Polyamide in Colorless Polyimide.

Colorless polyimides (CPIs) are a key substrate material for flexible organic light-emitting diode (OLED) displays and have attracted worldwide attention. Here, in this paper, the dispersion and interfacial interaction of aromatic polyamide (PA) in CPI (synthesized from 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFMB)) were significantly improved by in situ polymerization, and colorless transparent macromolecular polyimide composites (CPI-PAx) were successfully prepared by PA and CPI. By adjusting the ratio of PA to CPI, a high-performance engineering plastic with excellent film-forming properties was obtained. Molecular simulations confirmed the uniform distribution of PA in CPI and its interaction in polymers. In CPI-PAx, the CPI was locked by the PA chain, and numerous molecular chains were mutually entangled to form a hydrogen-bond network structure. Due to the strong interaction between the chains imparted by the hydrogen bonds of the PA, they do not slide under external forces and heating. In addition, the additive PA has excellent dimensional stability, thermal, and mechanical properties, and CPI has outstanding optical properties, so the synthesized CPI-PAx combines the comprehensive properties of PA and CPI. The CPI-PAx has excellent thermal and mechanical properties, with a thermal decomposition temperature of 499 °C, a glass transition temperature of 385 °C, a coefficient of thermal expansion of 0.8 ppm K-1, a tensile strength of 50.9 MPa, and an elastic modulus of 3.9 GPa. Particularly, CPI-PAx has a 90% transmittance in the visible region. These data prove that the strategy of combining PA and CPI by in situ polymerization is an effective method to circumvent the bottleneck of CPI in the current flexible window application, and this design strategy is universal.

Chemical features and machine learning assisted predictions of protein-ligand short hydrogen bonds

There are continuous efforts to elucidate the structure and biological functions of short hydrogen bonds (SHBs), whose donor and acceptor heteroatoms reside more than 0.3 Å closer than the sum of their van der Waals radii. In this work, we evaluate 1070 atomic-resolution protein structures and characterize the common chemical features of SHBs formed between the side chains of amino acids and small molecule ligands. We then develop a machine learning assisted prediction of protein-ligand SHBs (MAPSHB-Ligand) model and reveal that the types of amino acids and ligand functional groups as well as the sequence of neighboring residues are essential factors that determine the class of protein-ligand hydrogen bonds. The MAPSHB-Ligand model and its implementation on our web server enable the effective identification of protein-ligand SHBs in proteins, which will facilitate the design of biomolecules and ligands that exploit these close contacts for enhanced functions.

Effect of static electric fields on liquid water, its structure, dynamics, and hydrogen bond asymmetry: A molecular dynamics simulation study of TIP4P/2005 water model.

We study the effect of static electric fields of 0.1, 0.4, and 1.0 V/nm on the hydrogen bond structure and dynamics of TIP4P/2005 water at 1bar and at temperatures between 300 and 200K using molecular dynamics simulations. At all these temperatures, simulating liquid water with electric fields of 0.1 and 0.4 V/nm has no additional effect on its structural and dynamical changes, which otherwise already take place due to cooling. However, the introduction of 1.0 V/nm field enhances the slowing down of liquid water dynamics, crystallizes it to cubic ice at 240 and 220K, and amorphizes it at 200K. At 240 and 220K, crystallization occurs within 5 and 50ns, respectively. An electric field of 1 V/nm increases the relaxation times in addition to what cooling does. We note that when liquid water's metastability limit is reached, crystallization is averted and amorphization takes place. Both equilibrium (liquid-solid) and non-equilibrium (liquid-amorphous) transformations are observed at 1 V/nm. Moreover, with an increase in the electric field, H-bonds become stronger. However, the donor-acceptor asymmetry (the difference between the strengths of two donor/acceptor bonds) remains even when crystallization or amorphization takes place. At low temperatures, increasing electric fields on liquid water increases both its crystallization and amorphization tendencies.

Atomic insights into the heterogeneity and the interface interactions of nanoconfined aqueous electrolyte solution

The structure and properties of nanoconfined electrolyte (nano electrolyte) solutions are important subjects in biochemistry, electrochemistry, separation science, etc. In the present work, neutron scattering and data driven reverse Monte Carlo were employed to quantitatively reveal the microstructure of aqueous CaCl2 solution in mesoporous silica MCM-41 at the atomic level. The electrolyte solution distributes in-homogeneously in the pores of mesoporous silica along the radial direction, which can be divided into the core, the transition, and the interface regions. The hydrogen bond structure of water in nano electrolytes is strengthened in the core region, analogous to that of nano water confined in nanochannels, and the ion association was enhanced in the transition region. The structure of the solution in the interface region was analogous to the bulk electrolyte solution under high pressure because of the confinement and interface effects. When the package ratio of nano electrolyte solution is insufficient, small amount of solution quasi-monolayer adsorb on the internal surface of mesoporous silica, the majority solution preferentially forms clusters with different sizes to adhere to the wetted interface. The anomalous hydrogen-bonding structure and ion association found in the present work improve our understanding of nanoconfined electrolyte solutions.

Vibrational Coupling and Hydrogen-Bond Structure of Water in the Extended Hydration Shell of Metal Ions.

Intra- and intermolecular vibrational coupling (VC) and hydrogen bonding (H-bonding) of water are sparsely understood in the hydration shell (HS) of a metal ion, though the corresponding knowledge for an anion is quite extensive. This is primarily due to the overwhelming effect of anions on water, which masks the subtle perturbing influence of most of the cations. Using Raman difference spectroscopy with simultaneous curve fitting (Raman-DS-SCF) in combination with isotopic dilution and polarized Raman spectroscopy, we have elucidated the VC and H-bonding of water in the HS of bi- and trivalent metal ions─Mg2+, Ca2+, La3+, Gd3+, Dy3+. Polarized Raman measurement of the HS water with VC "turned on" and "turned off" (using isotopically diluted water, HOD) reveals that water retains the intra- and intermolecular vibrational coupling in the HS of high-charge-density metal ions, which is in stark contrast to that of an anion. Hydration shell spectroscopy in HOD unambiguously shows that the average H-bonding of water becomes stronger in the HS than that of bulk water. The first HS water strongly donates two H-bonds to the second HS water (ν̅max ≈ 3200 cm-1) but weakly accepts a H-bond from the second HS water (ν̅max ≈ 3590 cm-1), which makes the HS water heterogeneous in terms of its H-bond structure. The weakly interacting OH (ν̅max 3585 cm-1 in HOD) red-shifts by ∼ 15 cm-1 while the VC is "turned on" (ν̅max ≈ 3600 cm-1 in H2O), revealing the intramolecular coupling of water in the HS of metal ions.