Bridging Hydrogen Bonds Research Articles

Effect of LiF as Sintering Agent on the Densification and Phase Formation in Al2O3-4 Wt Pct Nb2O5 Ceramic Compound

Different amounts of LiF were added to an Al2O3-4 pct Nb2O5 basic ceramic, as sintering agent. Improved new ceramics were obtained with LiF concentrations varying from 0.25 to 1.50 wt pct and three sintering temperatures of 1573 K, 1623 K, and 1673 K (1300 °C, 1350 °C, and 1400 °C). The addition of 0.5 wt pct LiF yielded the highest densification, 94 pct of the theoretical density, in association with a sintering temperature of 1673 K (1400 °C). Based on X-ray diffraction (XRD), this improvement was due not only to the presence of transformed phases, more precisely Nb3O7F, but also to the absence of LiAl5O8. The preferential interaction of LiF with Nb2O5, instead of Al2O3, contributed to increase the alumina sintering ability by liquid phase formation. Scanning electron microscopy (SEM) results revealed well-connected grains and isolated pores, whereas the chemical composition analysis by energy dispersive energy (EDX) indicated a preferential interaction of fluorine with niobium, in agreement with the results of XRD. It was also observed from thermal analysis that the polyethylene glycol binder burnout temperature increased for all LiF concentrations. This may be related to the formation of hydrogen bridge bonds.

Conformational Heterogeneity and the Role of the C(2)-H Donor in Mono- and Dihydrated Clusters of Benzoxazole.

The significance of the heteroatom in influencing the acidity and binding affinity of the C(2)-H donor in five-membered heterocyclic rings is explored. The water clusters of benzoxazole (BOX) are studied in a supersonic jet by IR-UV double resonance spectroscopy and compared with those of benzimidazole (BIM) and its N-methyl derivative (MBIM). Two conformers are identified for the monohydrated cluster, both of which are O-H···N bound and differ in their orientation with respect to the intermolecular hydrogen bond. IR spectroscopy of the doubly hydrated cluster shows the presence of an intensity enhanced C(2)-H (carbon atom between the heteroatoms in the five-membered ring) stretching mode in addition to two red-shifted bound OH stretches, indicating that the water molecules form a hydrogen-bonded bridge encompassing the N acceptor and the weakly activated C(2)-H bond in oxazole. Comparison of the topological parameters of electron density, natural bond orbital analyses, and computed binding energies of the analogous hydrated structures of BOX, BIM, and MBIM indicates that the C(2)-H bond in the former is a more potent H-bond donor.

Adsorption Behavior and Mechanism of SCA-1 on a Calcite Surface: A Molecular Dynamics Study.

The crystallization mechanism for natural mineral, especially the role of biological molecules in biomineralization, is still under debate. Protein adsorption on material surfaces plays a key role in biomineralization. In this article, molecular dynamics (MD) simulations were performed to systematically investigate the adsorption behavior of struthio camelus eggshell protein struthiocalcin-1 (SCA-1) on the calcite (104) surface with several different starting orientations in an explicit water environment. For each binding configuration, detailed adsorption behaviors and a mechanism were presented with the analysis of interaction energy, binding residues, hydrogen bonding, and structures (such as DSSP, dipole moment, and the electrostatic potential calculation). The results indicate that the positively charged and polar residues are the dominant residues for protein adsorption on the calcite (104) surface, and the strong electrostatic interaction drives the binding of model protein to the surface. The hydrogen bond bridge was found to play an important role in surface interactions as well. These results also demonstrate that SCA-1 is relatively rigid in spite of strong adsorption with few structural changes in α-helix and β-sheet contents. The results of the orientation calculation suggest that the dipole moment of the protein tends to remain parallel to calcite in most stable cases, which was confirmed by electrostatic potential isosurfaces analysis.

Hydrogen-bridge Si(μ-H)3CeH and inserted H3SiCeH molecules: Matrix infrared spectra and DFT calculations for reaction products of silane with Ce atoms

Reactions of laser-ablated cerium atoms with silane were investigated by matrix isolation infrared spectroscopy and theoretical calculations. The reaction products, Si(μ-H)3CeH, H3SiCeH, H2Si(μ-H)CeH and HSi(μ-H)2CeH were identified on the basis of the SiD4 isotopic substitutions and DFT frequency calculations. In the solid argon or krypton matrix, the inserted H3SiCeH molecule was observed as initial product on deposition, which rearranged to hydrogen bridge species Si(μ-H)3CeH on follow-up annealing through H2Si(μ-H)CeH and HSi(μ-H)2CeH species. The SiHCe hydrogen bridge was investigated by NBO and ELF analysis. Calculation suggested that in Si(μ-H)3CeH molecule Ce atom donated one electron to Si atom, resulting in electron-rich SiH3 subunit, which was confirmed by ESP and AIM analysis. The increased basicity of SiH bond facilitates the formation of hydrogen bridge bond between Si and Ce. For comparison only insertion H3CCeH structure was obtained from the reaction of Ce atoms with CH4.

Variation of Nanostructures, Molecular Interactions, and Anisotropic Elastic Moduli of Lignocellulosic Cell Walls with Moisture

A combination of experimental, theoretical and numerical studies is used to investigate the variation of elastic moduli of lignocellulosic (bamboo) fiber cell walls with moisture content (MC). Our Nanoindentation results show that the longitudinal elastic modulus initially increased to a maximum value at about 3% MC and then decreased linearly with increasing MC. In contrast, the transverse moduli decrease linearly with MC. We showed that amorphous materials in cell walls have key roles in the variation of elastic modulus with increasing MC. Elastic modulus of lignin, calculated by molecular dynamics simulations, increases initially with increasing MC, and then decreases. In contrast, elastic modulus of hemicellulose decreases constantly with MC. Below 10% MC, water molecules tend to break hydrogen bonds between polymer chains and form new hydrogen bond bridges between the polymer chains, while above 10% MC, water molecules aggregate together and create nano-droplets inside the materials. During the process of bridging, the fractional free volume of lignin decreases. The free volume reduction along with formation of hydrogen bond bridges causes a growth in elastic modulus of lignin at low MC. The constant increase of hemicellulose free volume, however, causes the aggregation of voids in the system and diminution of elastic properties.

Double and Triple Si-H-M Bridge Bonds: Matrix Infrared Spectra and Theoretical Calculations for Reaction Products of Silane with Ti, Zr, and Hf Atoms.

Infrared spectra of matrix isolated dibridged Si(μ-H)2MH2 and tribridged Si(μ-H)3MH molecules (M = Zr and Hf) were observed following the laser-ablated metal atom reactions with SiH4 during condensation in excess argon and neon, but only the latter species was observed with titanium. Assignments of the major vibrational modes, which included terminal MH, MH2 and hydrogen bridge Si-H-M stretching modes, were confirmed by the appropriate SiD4 isotopic shifts and density functional vibrational frequency calculations (B3LYP and BPW91). The Si-H-M hydrogen bridge bond is calculated as weak covalent interaction and compared with the C-H···M agostic interaction in terms of electron localization function (ELF) analysis and noncovalent interaction index (NCI) calculations. Furthermore, the different products of Ti, Zr, and Hf reactions with SiH4 are discussed in detail.

Dinuclear Complexes Formed by Hydrogen Bonds: Synthesis, Structure and Magnetic and Electrochemical Properties.

The synthesis is reported of a series of homo- and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis(1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between coordinated alcohols and coordinated alkoxides. Homonuclear divalent MII MII , mixed-valent MII MIII and heteronuclear MII M'III species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O⋅⋅⋅O distances for the hydrogen bonds. Magnetic measurements show the hydrogen-bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves, which are attributed to rapid intramolecular proton transfer facilitated by the hydrogen-bonded structure.

Unusual 4-arsonoanilinium cationic species in the hydrochloride salt of (4-aminophenyl)arsonic acid and formed in the reaction of the acid with copper(II) sulfate, copper(II) chloride and cadmium chloride.

Structures having the unusual protonated 4-arsonoanilinium species, namely in the hydrochloride salt, C6H9AsNO3+·Cl-, (I), and the complex salts formed from the reaction of (4-aminophenyl)arsonic acid (p-arsanilic acid) with copper(II) sulfate, i.e. hexaaquacopper(II) bis(4-arsonoanilinium) disulfate dihydrate, (C6H9AsNO3)2[Cu(H2O)6](SO4)2·2H2O, (II), with copper(II) chloride, i.e. poly[bis(4-arsonoanilinium) [tetra-μ-chlorido-cuprate(II)]], {(C6H9AsNO3)2[CuCl4]}n, (III), and with cadmium chloride, i.e. poly[bis(4-arsonoanilinium) [tetra-μ-chlorido-cadmate(II)]], {(C6H9AsNO3)2[CdCl4]}n, (IV), have been determined. In (II), the two 4-arsonoanilinium cations are accompanied by [Cu(H2O)6]2+ cations with sulfate anions. In the isotypic complex salts (III) and (IV), they act as counter-cations to the {[CuCl4]2-}n or {[CdCl4]2-}n anionic polymer sheets, respectively. In (II), the [Cu(H2O)6]2+ ion sits on a crystallographic centre of symmetry and displays a slightly distorted octahedral coordination geometry. The asymmetric unit for (II) contains, in addition to half the [Cu(H2O)6]2+ ion, one 4-arsonoanilinium cation, a sulfate dianion and a solvent water molecule. Extensive O-H...O and N-H...O hydrogen bonds link all the species, giving an overall three-dimensional structure. In (III), four of the chloride ligands are related by inversion [Cu-Cl = 2.2826 (8) and 2.2990 (9) Å], with the other two sites of the tetragonally distorted octahedral CuCl6 unit occupied by symmetry-generated Cl-atom donors [Cu-Cl = 2.9833 (9) Å], forming a two-dimensional coordination polymer network substructure lying parallel to (001). In the crystal, the polymer layers are linked across [001] by a number of bridging hydrogen bonds involving N-H...Cl interactions from head-to-head-linked As-O-H...O 4-arsonoanilinium cations. A three-dimensional network structure is formed. CdII compound (IV) is isotypic with CuII complex (III), but with the central CdCl6 complex repeat unit having a more regular M-Cl bond-length range [2.5232 (12)-2.6931 (10) Å] compared to that in (III). This series of compounds represents the first reported crystal structures having the protonated 4-arsonoanilinium species.

Computational Exploration of the Water Concentration Dependence of the Proton Transport in the Porous UiO–66(Zr)–(CO2H)2 Metal–Organic Framework

The UiO–66(Zr)–(CO2H)2 metal–organic framework (MOF) has been recently revealed as a promising proton conducting material under humidification. Here, aMS-EVB3 molecular dynamics simulations are performed to reveal at the molecular level the structure, thermodynamics, and dynamics of the hydrated proton in three-dimensional (3D)-cages MOF as a function of the water loading. It is found that the most stable proton solvation structure corresponds to a H7O3+ cation and that a transition between this complex and a Zundel cation likely governs the proton transport in this MOF occurring via a Grotthuss-type mechanism. It is further shown that the formation of a H2O hydrogen-bonded bridge that connects the cages occurs only at high water concentration and this creates a path allowing the excess proton to jump from one cage to another. This leads to a faster self-diffusivity of proton at high water concentration, thereby supporting the increase of the proton conductivity with the water loading as experimentally ev...

Silane activation by laser-ablated Be atoms: Formation of HBeSiH3 and HBe(μ-H)3Si molecules

Laser-ablated beryllium atoms have been reacted with silane molecules during condensation in excess neon and argon at 4K. Absorptions due to HBeSiH3 and HBe(μ-H)3Si were observed and identified on the basis of isotopic IR spectroscopy, deuterium substitution with SiD4, and quantum chemical frequency calculations. The observed results show excited Be atom (1P1:2s12p1) can insert into SiH bond spontaneously and the insertion product rearranges to HBe(μ-H)3Si upon photolysis. The electron localization function (ELF) analysis suggests that 3c-2e hydrogen bridge bond (BeHSi) was formed by the donation of electrons for SiH σ bond to the empty p orbital of Be atom for HBe(μ-H)3Si molecule, which shows much difference from CH bond complexes.

Quantum Mechanical Enhancement of Rate Constants and Kinetic Isotope Effects for Water-Mediated Proton Transfer in a Model Biological System.

Biological systems have been shown to shuttle excess protons long distances by taking advantage of tightly organized hydrogen-bonded water bridges in hydrophobic protein cavities, and similar effects have been observed in carbon nanotubes. In this theoretical study we investigate how quantum effects of proton motion impact the rate constants for charge transfer in a model system consisting of a donor and acceptor molecule separated by a single-molecule water bridge. We calculate quantum and classical rate constants for the transfer of an excess proton over two possible paths, one with an H3O+ intermediate, and one with an OH- intermediate. Quantum effects are included through ring polymer molecular dynamics (RPMD) calculations. We observe a 4-fold enhancement of reaction rate constants due to proton tunneling at temperatures between 280 and 320 K, as shown by transmission coefficient calculations. Deuteration of the donor and acceptor proton are shown to decrease the reaction rate constant by a factor of 50, and this is another indicator that tunneling plays an important role in this proton transfer mechanism.

Spin-Polarization-Induced Preedge Transitions in the Sulfur K-Edge XAS Spectra of Open-Shell Transition-Metal Sulfates: Spectroscopic Validation of σ-Bond Electron Transfer.

Sulfur K-edge X-ray absorption spectroscopy (XAS) spectra of the monodentate sulfate complexes [MII(itao)(SO4)(H2O)0,1] (M = Co, Ni, Cu) and [Cu(Me6tren)(SO4)] exhibit well-defined preedge transitions at 2479.4, 2479.9, 2478.4, and 2477.7 eV, respectively, despite having no direct metal-sulfur bond, while the XAS preedge of [Zn(itao)(SO4)] is featureless. The sulfur K-edge XAS of [Cu(itao)(SO4)] but not of [Cu(Me6tren)(SO4)] uniquely exhibits a weak transition at 2472.1 eV, an extraordinary 8.7 eV below the first inflection of the rising K-edge. Preedge transitions also appear in the sulfur K-edge XAS of crystalline [MII(SO4)(H2O)] (M = Fe, Co, Ni, and Cu, but not Zn) and in sulfates of higher-valent early transition metals. Ground-state density functional theory (DFT) and time-dependent DFT (TDDFT) calculations show that charge transfer from coordinated sulfate to paramagnetic late transition metals produces spin polarization that differentially mixes the spin-up (α) and spin-down (β) spin orbitals of the sulfate ligand, inducing negative spin density at the sulfate sulfur. Ground-state DFT calculations show that sulfur 3p character then mixes into metal 4s and 4p valence orbitals and various combinations of ligand antibonding orbitals, producing measurable sulfur XAS transitions. TDDFT calculations confirm the presence of XAS preedge features 0.5-2 eV below the rising sulfur K-edge energy. The 2472.1 eV feature arises when orbitals at lower energy than the frontier occupied orbitals with S 3p character mix with the copper(II) electron hole. Transmission of spin polarization and thus of radical character through several bonds between the sulfur and electron hole provides a new mechanism for the counterintuitive appearance of preedge transitions in the XAS spectra of transition-metal oxoanion ligands in the absence of any direct metal-absorber bond. The 2472.1 eV transition is evidence for further radicalization from copper(II), which extends across a hydrogen-bond bridge between sulfate and the itao ligand and involves orbitals at energies below the frontier set. This electronic structure feature provides a direct spectroscopic confirmation of the through-bond electron-transfer mechanism of redox-active metalloproteins.

A TDDFT study on the excited-state double proton transfer reaction of 8-hydroxyquinoline along a hydrogen-bonded bridge

The mechanism of excited-state multiple proton transfer reaction is demonstrated to be controlled by a hydrogen-bonded bridge.

Synthesis of dispersed PrBaCo0.9Cu0.1O5+δ cathode nanopowders with layered perovskite structure for intermediate temperature solid oxide fuel cells

PrBaCo1.9Cu0.1O5+δ (PBCCO) nanopowders were synthesized by an EDTA-citrate complexing process using water and ethanol as solvents, and their structures and electrochemical properties were characterized. PBCCO precursor gels were highly oxidized at 450°C, using either water (PBCCO-W) or ethanol (PBCCO-E) as the solvent. PBCCO powders calcined at 450°C had a second phase, while those calcined at 850°C for 4h were obtained as single phase PBCCO with a layered perovskite structure in the P4mm space group. PBCCO-E primary particles were approximately 5–10nm in size and were well-dispersed compared with those of the PBCCO-W powder. We hypothesized that the enhanced dispersibility of the PBCCO-E powder was caused by a decrease in bridging hydrogen bonds on the chelate surface, which prevents chelate agglomeration in sol state. It causes the larger specific surface area of PBCCO-E powders and thus a lower polarization resistance (Rp) than that of PBCCO-W powders at the measured temperature. The Rp value of PBCCO-E powder was 0.041Ωcm2 at 750°C, which is about 1.5times lower than that of PBCCO-W at the same temperature.

Proton-Coupled Electron Transfer in a Hydrogen-Bonded Charge-Transfer Complex.

A proton-coupled electron transfer (PCET) reaction in a hydrogen-bonded charge-transfer (CT) complex of 4-([2,2'-bipyridin]-4-yl)phenol (bpy-phenol) with a F- ion has been investigated by ultrafast time-resolved transient absorption spectroscopy. The phenolic receptor molecule, bpy-phenol, binds to the F- ion through a hydrogen bond and senses the F- ion via the Stokes-shifted CT band. Upon photoexcitation, CT from the phenol residue to the bpy residue promotes proton transfer from the phenol radical cation (ArOH•+) to the fluoride ion at ultrafast time scales of <150 fs (instrument response function limited) and 3 ps, separately. The fast and slow proton-transfer times are linked to two different types of hydrogen-bonding networks between the phenol residue and fluoride ion. Crystalline water in the fluoride salt hydrates mediates the proton-transfer reaction. This work demonstrates the participation of a hydrogen-bonded water bridge within a PCET reaction in a water-restricted environment.

Meaning and consequence of the coexistence of competitive hydrogen bond/salt forms on the dissociation orientation of non-covalent complexes.

Non-covalent complexes (NCC) between hexose monophosphates (HexP) and arginine (R) were analyzed using ESI MS and MS/MS in negative mode under different (hard, HC and soft, SC) desolvation conditions. High resolution mass spectrometry (HRMS) revealed the presence of different ionic species, namely, homo- and heteromultimers of R and HexP. Deprotonated heterodimers and corresponding sodiated species were enhanced under HC likely due to a decrease in available charge number associated with the reduction of H+/Na+ exchange. The quantum calculations showed that the formation of covalent systems is very little exothermic, therefore, such systems are disfavored. Desolvation dependent CID spectra of deprotonated [(HexP+R)‒H]- complexes demonstrated that they can exist within the hydrogen bond (HB) and salt bridge (SB) forms, yielding either NCC separation or covalent bond cleavages, respectively. Although HB forms are the main species, they cannot survive under HC; therefore, the minor SB forms became detectable. Energy-resolved mass spectrometry (ERMS) experiments revealed diagnostic fragment ions from both SB and HB forms, providing evidence that these isomeric forms are inconvertible. SB formation should result from the ionic interactions of highly acidic group of HexP with strongly basic guanidine group of arginine and thus requires an arginine zwitterion (ZW) form. This was confirmed by quantum calculations. Ion-ion interactions are significantly affected by the presence of sodium cation as demonstrated by the fragmentation patterns of sodiated complex species. Regarding CID data, only SB between protonated amino group of R and deprotonated phosphate group of HexP could be suggested, but the primary amine is not enough basic then, the SB must be fleeting. Nevertheless, the observation of the covalent bond cleavages suggests the presence of structures with a free negative charge able to induce fragmentations. Indeed, according to quantum calculations, solvated salt (SS) systems involving Na+/COO- salt solvated by neutral phosphate and negative charge on sugar ring are preferentially formed.

Spectroscopic and Computational Study of Acetic Acid and Its Cyclic Dimer in the Near-Infrared Region.

Anharmonic vibrational analysis of near-infrared (NIR) spectra of acetic acid was carried out by anharmonic quantum chemical calculation in a wide concentration range of its CCl4 solution. By predicting vibrational spectra of acetic acid for the first time over a wide NIR region, it was possible to elucidate the influence of the formation of acetic acid cyclic dimer on its NIR spectrum. Quantum chemical simulations were based on coupled cluster and density functional theory quantum methods. Additionally, Møller-Plesset perturbation theory was employed for the additional calculation of hydrogen bonding stabilization energies. An anharmonic vibrational analysis was performed with the use of generalized second-order vibrational perturbation theory (GVPT2). A hybrid approach was assumed, in which monomeric species was treated by CCSD(T)/aug-cc-pVDZ (harmonic approximation) and B3LYP/SNSD (anharmonic approximation) methods. For the cyclic dimer, B3LYP and B2PLYP single and double hybrid functionals, paired with an SNSD basis set, were employed. DFT calculations were augmented with additional empirical dispersion correction. It was found that quantum chemically calculated vibrational modes in the NIR region are in a good agreement with experimental data. The results of anharmonic vibrational analysis were supported by a harmonic shift analysis, for elucidating the very strong anharmonic coupling observed between stretching modes of hydrogen bonded bridge in the cyclic dimer. However, the calculated wavenumbers for combination modes of double hydrogen bonded bridge in the cyclic dimer, which are very sensitive to the formation of hydrogen bonding, were found to be underestimated by quantum chemical methods. Therefore, by band fitting, the wavenumbers and shape parameters for these bands were found, and the modeled spectra were adjusted accordingly. A high accuracy of simulated spectra was achieved, and a detailed analysis of the experimental NIR spectra of acetic acid was possible, with successful identification of numerous experimental bands, including those which originate from concentration effects. It was also found that the main spectral features observed in the NIR spectra of carboxylic acid upon the formation of hydrogen bond should be accounted for combination modes of the stretching and bending vibrations of double hydrogen-bonded bridge in the cyclic dimers of acetic acid.

The staple role of hydrogen and halogen bonds in crystalline (E)-8-((2,3-diiodo-4-(quinolin-8-ylthio)but-2-en-1-yl)thio)quinolin-1-ium triiodide

The crystal structure of (E)-8-((2,3-diiodo-4-(quinolin-8-ylthio)but-2-en-1-yl)thio)quinolin-1-ium triiodide, determined at 100 K in the space group C2/c, contains the bridge hydrogen bond [N···H···N]+ linking two neighboring quinolinium fragments; the distance N···N is 2.6927(15) A. The experimental difference Fourier maps at 293 and 100 K lead to a conclusion about the dynamic nature of the H atom disorder. Calculated vibrational modes obtained for the same compound in the space groups C2/c and Cc are in agreement with the experimental Raman spectrum in the low-frequency region; together, they are consistent with a previous supposition about the dynamic nature of the H atom disorder. We have found that the cation–anion interactions are realized through the charge-assisted iodine–iodine halogen bond.

Contextual Role of a Salt Bridge in the Phage P22 Coat Protein I-Domain

The I-domain is a genetic insertion in the phage P22 coat protein that chaperones its folding and stability. Of 11 acidic residues in the I-domain, seven participate in stabilizing electrostatic interactions with basic residues across elements of secondary structure, fastening the β-barrel fold. A hydrogen-bonded salt bridge between Asp-302 and His-305 is particularly interesting as Asp-302 is the site of a temperature-sensitive-folding mutation. The pKa of His-305 is raised to 9.0, indicating the salt bridge stabilizes the I-domain by ∼4 kcal/mol. Consistently, urea denaturation experiments indicate the stability of the WT I-domain decreases by 4 kcal/mol between neutral and basic pH. The mutants D302A and H305A remove the pH dependence of stability. The D302A substitution destabilizes the I-domain by 4 kcal/mol, whereas H305A had smaller effects, on the order of 1-2 kcal/mol. The destabilizing effects of D302A are perpetuated in the full-length coat protein as shown by a higher sensitivity to protease digestion, decreased procapsid assembly rates, and impaired phage production in vivo By contrast, the mutants have only minor effects on capsid expansion or stability in vitro The effects of the Asp-302-His-305 salt bridge are thus complex and context-dependent. Substitutions that abolish the salt bridge destabilize coat protein monomers and impair capsid self-assembly, but once capsids are formed the effects of the substitutions are overcome by new quaternary interactions between subunits.

A description of hydrogen bonds in the chromium(III)-crosslinked collagen: insight from the molecular dynamics simulation

The paper investigated the conformation and stability of the chromium(III)-crosslinked collagen fibers under different moisture contents by the molecular dynamics method, focusing on making a qualitative and quantitative analysis for the H-bonds. The water-mediated hydrogen bonding and direct hydrogen bonding interaction between neighboring bundles are the main driving force of the assembly of collagen fibrils. The right amount of moisture can well trig the conformation of collagen fibrils, during which water acts as a crosslinking role through the bridging hydrogen bonds. The Gly, Glu, Arg, Asp, and Lys play major roles in the formation of the direct hydrogen bonds, in which the amino acid with a long side chain, such as Arg and Glu, is particularly likely to form intrachain hydrogen bonds. The competition and disturbance of the water molecules lead to the great loss of the direct H-bonds. Anyway, a certain amount of intrachain hydrogen bonds is able to block the active sites in collagen and keep these sites away from the other molecules.