Interlayer Hydrogen Bonds Research Articles

Biofunctionalization of Si(111)7×7 by "renewable" L-cysteine transitional layer.

Surface functionalization of an inorganic surface with bio-organic molecules is often aimed at creating a "permanent" bio-organic surface with receptor functional groups. We show here that L-cysteine can be used to transform a highly reactive Si(111)7×7 surface to not just a permanent bio-organic surface but also a semipermanent (or renewable) and a temporary bio-organic surfaces by manipulating the exposure. In the early growth stage, the strong bonding between the first cysteine adlayer and the Si substrate through Si-N or Si-S linkages in unidentate or bidentate arrangement provides permanent biofunctionalization by this interfacial layer. This interfacial layer can be used to build a transitional layer (second adlayer) mediated by interlayer vertical hydrogen bonding between an amino group and a carboxylic acid group. Further exposure of cysteine eventually leads to a zwitterionic multilayer film involving electrostatic interactions between cation (-NH3(+)) and anion moieties (-COO(-)). The interlayer hydrogen bonding therefore provides temporary trapping of bio-organic molecules as the second transitional layer that is stable up to 175 °C. This transitional layer can be easily removed by annealing above this temperature and then regenerated with the same molecular layer or a different one by "renewing" the interlayer hydrogen bonds. We also illustrate coverage-dependent adsorption structures of cysteine, from bidentate to unidentate attachments and to self-assembled multimers, involving formation of intralayer horizontal N···H-O hydrogen bonds, by combining our X-ray photoemission data with the local density-of-state images obtained by scanning tunnelling microscopy.

Sub-zeolite of FER topology derived from an interlayer modification of PLS-3 lamellar precursor

A simple HCl–EtOH solution treatment has been conducted to modify the structure of Al-PLS-3, a kind of FER lamellar precursor with various Si/Al ratios (60–∞). With prolonging the treatment time from 15min to 24h at 443K, the precursors underwent a variety of structural changes, including removal of occluded organic species, loss of layer stacking order and restoration of an ordered structure by interlayer pillaring. The post structural modification gave rise to a sub-zeolite of FER topology within a short time of 40min, which possessed disordered stacking of FER sheets, named as ECNU-8. The physicochemical properties of ECNU-8 were characterized by means of various techniques and in comparison to those of conventional FER topology. Still composed of a collection of FER sheets but without an ordered stacking manner along (100) direction, the structure of ECNU-8 was constructed by a reorientation of interlayer hydrogen bond moieties caused by partial removal of interlayer organic structure directing agent. The ECNU-8 materials with different Al contents possessed external surface areas enlarged by 23.1–36.8% in comparison to corresponding three-dimensional FER zeolites. Containing the FER laminates and tetrahedral Al in framework, but mitigating the spatial restrictions in particular for the bulk molecule reactions, ECNU-8 proved to be a promising solid acid catalyst for processing larger substrates.

Post-synthesis and catalytic performance of FER type sub-zeolite Ti-ECNU-8

Abstract A titanosilicate Ti-ECNU-8 with a FER type sub-zeolite structure was developed by pots-synthesis and applied to the epoxdiation of alkenes with hydrogen peroxide. A controlled acid treatment on the pure silica layered precursor PLS-3 of FER topology gave rise to a sub-zeolite ECNU-8. Composed of a collection of FER sheets without an ordered stacking manner along layer related [1 0 0] direction, the structure of ECNU-8 was constructed by a reorientation of interlayer hydrogen bond moieties caused by partial removal of interlayer organic structure directing agent. ECNU-8 possessed an external surface area enlarged by ca. 30% in comparison to corresponding three-dimensional FER zeolite. Through a solid–gas reaction with TiCl4 vapor, tetrahedral Ti active sites were introduced into the framework. The resultant Ti-ECNU-8 retained the structural properties of ECNU-8, and exhibited an excellent catalytic performance for the epoxidation of cycloalkenes owing to the accessible Ti sites located in open reaction space.

The two-dimensional coordination polymer poly[diaqua(μ2-1H-imidazo[4,5-f][1,10]phenanthroline)-μ4-sulfato-μ3-sulfato-dicadmium(II)

In the title coordination polymer, [Cd2(SO4)2(C13H8N4)(H2O)2]n, there are two crystallographically independent Cd(II) centres with different coordination geometries. The first Cd(II) centre is hexacoordinated by four O atoms of four sulfate ligands, one water O atom and one N atom of a 1H-imidazo[4,5-f][1,10]phenanthroline (IP) ligand, giving a distorted octahedral coordination environment. The second Cd(II) centre is heptacoordinated by four O atoms of three sulfate ligands, one water O atom and two N atoms of one chelating IP ligand, resulting in a distorted monocapped anti-trigonal prismatic geometry. The symmetry-independent Cd(II) ions are bridged in an alternating fashion by sulfate ligands, forming one-dimensional ladder-like chains which are connected through the IP ligands to form two-dimensional layers. These two-dimensional layers are linked by interlayer hydrogen bonds, leading to the formation of a three-dimensional supramolecular network.

A Novel Aqua Ligand Assisted Water Octamer Confinement in the Hydrophilic Channels of a Zn(II) Supramolecular Architecture

A new two-dimensional polymeric [Zn2(4-pzpt)(btc)(H2O)2·3H2O] (1) (4-Hpzpt = 3-(pyridin-4-yl)-5-(pyrazin-2-yl)-1H-1,2,4-triazole, H3btc = 1,2,3-benzenetricarboxylate), has been synthesized and structurally characterized and features a 3D supramolecular framework with 1D hydrophilic channels formed by the interlayer hydrogen bonds. An unprecedented aqua ligand assisted octameric water cluster consisting of a quasiplanar cyclic hexameric core and two dangling water molecules is captured in 1. The thermal stability and solid state fluorescent property of 1 are discussed.

An insight on the weakening of the interlayer bonds in a Cameroonian kaolinite through DMSO intercalation

In this study, intercalation of dimethylsulphoxide (DMSO) in a Cameroonian kaolinite is used to achieve weakening of the interlayer hydrogen bonds, in the perspective of dispersion or even exfoliation of the clay within polymer composite materials. Displacement of intercalated DMSO by ethyl acetate and ammonium acetate is studied in order to simulate the interactions with the polymer matrix. The exfoliation of the kaolinite is well evidenced by X-ray diffraction and SEM observations. The disruption of the interlayer bonds is shown by the displacement of the FT-IR vibration modes of both Al–OH and Si–O functions, and by the decrease of the dehydroxylation temperature recorded by Controlled Rate Thermal Analysis. Complete displacement of DMSO by ethyl acetate is achieved and the crystalline structure is deeply disordered as a result of interlayer bonds weakening. The displacement of DMSO by ammonium acetate leads to a ternary composite of DMSO/ammonium acetate with respective intercalation ratio of 62.4% and 57.7%.

Synthesis, crystal structures and properties of three glutarato and adipato bridged manganese(II) coordination polymers under ambient conditions

Three Mn(II) polymers Mn(H2O)4(C5H6O4) 1, [Mn(H2O)2(C5H6O4)]·H2O 2 and Mn(H2O)(C6H8O4) 3 were synthesized (H2(C5H6O4) = glutaric acid, H2(C6H8O4) = adipic acid) under mild ambient conditions. The [Mn(H2O)2]2+ units in 2 are interlinked by the glutarate anions with a η4μ3 bridging mode to form 2D (4·82) topological networks, which are stacked via interlayer hydrogen bonds into a 3D (43·65·82)(47·63) topological net. Compound 3 crystallizes in the acentric space group P21 and exhibits significant ferroelectricity (remnant polarization Pr = 0.371 nC cm−2, coercive field Ec = 0.028 kV cm−1, saturation of the spontaneous polarization Ps = 0.972 nC cm−2). The adjacent MnO6 octahedrons in 3 are one atom-shared to generate the Mn2O11 bi-octahedron, leading into 1D metal oxide chains. The resulting chains are interconnected by the η5μ5 adipate anions to form new 2D (48·62) networks, which are held together via strong interlayer hydrogen bonds into 3D α-Po topological supra-molecular architecture. The temperature-dependent magnetic susceptibility data of 1–3 shows overall anti-ferromagnetic interactions between the metal ions bridged by the carboxylate groups.

Lanthanide coordination compounds with 1H-benzimidazole-2-carboxylic acid: syntheses, structures and spectroscopic properties

A flexible multidentate ligand, 1H-benzimidazole-2-carboxylic acid, was synthesized to construct a series of lanthanide coordination polymers [Ln(HBIC)3]n (Ln = Eu (1), Tb (2), Gd (3), Pr (4), Nd (5); H2BIC = 1H-benzimidazole-2-carboxylic acid) under hydrothermal conditions. All the compounds were fully characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, thermal analysis and various spectroscopic techniques. Structural analyses reveal that they are isostructural and feature a 2D wave-like layer structure with distorted grids, in which the adjacent Ln3+ centers are bridged by the HBIC− ligands with two kinds of new coordination modes and the adjacent HBIC− ligands are tightly bound by two types of distinct intra-layer hydrogen bonds. The adjacent 2D layers are further interconnected by strong inter-layer hydrogen bond ring motifs R22(10) to generate a 3D supramolecular architecture. Optical studies indicate that the compounds 1, 2, 4 and 5 exhibit characteristic luminescence emission bands of the corresponding lanthanide ions in the visible or near-infrared regions at room temperature. In particular, compound 2 displays bright green luminescence in the solid state with a satisfactory 5D4 lifetime of 1.2 ms and a high overall quantum yield of 31%, due to an ideal energy gap between the lowest triplet state energy level of H2BIC ligand and the 5D4 state energy level of Tb3+. The energy transfer mechanisms in compounds 1 and 2 were also described and discussed.

Syntheses and characterizations of two-dimensional lanthanide coordination polymers based on anthraquinone-1,4,5,8-tetracarboxylic acid

A series of isostructural two-dimensional lanthanide complexes with the formula [Ln(Haqtc)(H 2 O) 4 ·xH 2 O] n (Ln = Nd, 1 ; Sm, 2 ; Eu, 3 ; Tb, 4 ; Dy, 5 ; Er, 6 .) were synthesized by treating H 4 aqtc (H 4 aqtc = anthraquinone-1,4,5,8-tetracarboxylic acid) with lanthanide(III) salts under hydrothermal conditions. 3-D structures are formed by inter-layer hydrogen bonds. Magnetic susceptibility measurements of complexes 4 and 5 in temperature range 2–300 K were performed, which showed dominant weak ferromagnetic interactions in 4 and slow magnetization relaxation in 5 . Six isostructural lanthanide complexes, based on anthraquinone-1,4,5,8-tetracarboxylic acid (H 4 aqtc), showed layer-like structures and 3-D frameworks formed by interlayer hydrogen bonds. The magnetic properties of complexes 4 and 5 were investigated. ► Six isostructural lanthanide complexes were synthesized and characterized. ► 3-D structures are formed by inter-layer hydrogen bonds. ► Magnetic properties results showed slow magnetization relaxation in complex 5.

Two Zinc(II) Coordination Polymers Based on the Ligand 1, 4‐Bis[(2‐methyl‐imidazol‐1‐yl)methyl]benzene: Syntheses, Crystal Structures and Properties

AbstractTwo coordination polymers (CPs), {[Zn2(BMB)(5‐AIPA)2]·2H2O}n(1) and [Zn(BMB)(5‐NIPA)]n(2) {BMB = 1, 4‐bis[(2‐methyl‐imidazol‐1‐yl)methyl]benzene, 5‐AIPA = 5‐aminoisophthalic acid, 5‐NIPA = 5‐nitroisophthalic acid}, were synthesized under hydrothermal conditions. Compound 1 displays a 2D double‐layer structure, which is packed into a 3D supramolecule by interlayer hydrogen bonds and π–π stacking interactions. Compound 2 displays a threefold interpenetrating 3D network, which is composed of left‐handed helical chains and two types of meso‐helical chains along different directions.

Atomic-scale friction in graphene oxide: An interfacial interaction perspective from first-principles calculations

Atomic-scale friction in graphene oxide is investigated using density functional theory calculation including a long-range dispersion correction (DFT-D). The sliding behaviors between two graphene oxide layers with different functional groups or oxidation levels are quantitatively studied based on the constructed potential energy surfaces. Sliding paths with minimum energy corrugations and the corresponding static lateral forces and shear strengths for different systems are derived, suggesting moderately higher friction in graphene oxide compared with graphene. The effects of load on friction in different graphene oxide models are also investigated. Moreover, the largest lateral force existing in the graphene oxide system with both epoxide and hydroxyl groups is dominated by the interlayer hydrogen bond interaction, the instability of which also simultaneously leads to dissipation and hence gives rise to the friction. An in-depth understanding of the relationship between atomic-scale friction and interfacial interactions reveals that certain levels of friction can be achieved by controllable structural and chemical modifications to the sliding surfaces, which sheds light on friction control and design of new lubricant materials.

Theoretical investigation of layered zeolite frameworks: Interaction between IPC-1P layers derived from zeolite UTL

Interaction between layers of layered zeolite framework IPC-1P was investigated computationally. The inter-layer interaction is controlled by inter-layer hydrogen bonds formed between silanols on adjacent layers. Due to a relatively large concentration of surface silanols in IPC-1P the inter-layer hydrogen bonds account for about 80% of inter-layer interactions. Large number of possible arrangements of neighboring layers exist; the stability of individual arrangements depends primarily on the number of inter-layer hydrogen bonds and their strength. The most stable structure is formed when silanol groups are all parallel with the ac plane and forming a hydrogen-bonded analogue of 10R channel along b direction. Several different arrangements were found with similar interaction energies (within 2.5kJmol−1 per surface silanol). The reliability of computational methods was also investigated. The non-local vdW-DF2 exchange-correlation functional was found to give very accurate description of inter-layer interactions.

Examining the frictional forces between mixed hydrophobic – hydrophilic alkylsilane monolayers

Monolayers presenting methyl-terminated (hydrophobic) and hydroxyl-terminated (hydrophilic) surfaces on silica have been studied by molecular dynamics simulation and the effects of hydrogen bonding, chain length, and chain mixing on the frictional properties determined. The hydroxyl-terminated monolayers were found to show large adhesion zones as a result of strong interfacial interlayer hydrogen bonds; the interfacial sliding forces observed in the hydroxyl-terminated monolayers being one order of magnitude higher than the interfacial forces for the hydrophobic surfaces at the characteristic point of zero-load. Mixed hydroxyl- and methyl-terminated monolayers of equal length were found to exhibit intermediate shear stress values between those observed for pure monolayers, with the magnitude of the shear stress depending on the surface content of the hydroxyl-terminated chains. For mixed monolayers of unequal chain lengths, at high loads a maximum in the magnitude of the shear stress as a function of the length of the methyl-terminated chain was observed due to the creation of a buffer zone between the hydroxyl-terminated chains that produces strong hydrogen-bonding interactions. The effect of a constant normal load or constant separation simulation ensemble on the results has also been studied and in general found to have minimal influence on the observed behavior, although some differences are observed for the shear stress at intermediate normal loads due to the formation of stronger hydrogen bond networks at constant load compared to constant separation.

Mechanism of dehydroxylation temperature decrease and high temperature phase transition of coal-bearing strata kaolinite intercalated by potassium acetate

The thermal decomposition and dehydroxylation process of coal-bearing strata kaolinite–potassium acetate intercalation complex (CSKK) has been studied using X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analysis, mass spectrometric analysis and infrared emission spectroscopy. The XRD results showed that the potassium acetate (KAc) have been successfully intercalated into coal-bearing strata kaolinite with an obvious basal distance increase of the first basal peak, and the positive correlation was found between the concentration of intercalation regent KAc and the degree of intercalation. As the temperature of the system is raised, the formation of KHCO3, KCO3 and KAlSiO4, which is derived from the thermal decomposition or phase transition of CSKK, is observed in sequence. The IR results showed that new bands appeared, the position and intensities shift can also be found when the concentration of intercalation agent is raised. The thermal analysis and mass spectrometric analysis results revealed that CSKK is stable below 300°C, and the thermal decomposition products (H2O and CO2) were further proved by the mass spectrometric analysis. A comparison of thermal analysis results of original coal-bearing strata kaolinite and its intercalation complex gives new discovery that not only a new mass loss peak is observed at 285°C, but also the temperature of dehydroxylation and dehydration of coal bearing strata kaolinite is decreased about 100°C. This is explained on the basis of the interlayer space of the kaolinite increased obviously after being intercalated by KAc, which led to the interlayer hydrogen bonds weakened, enables the dehydroxylation from kaolinite surface more easily. Furthermore, the possible structural model for CSKK has been proposed, with further analysis required in order to prove the most possible structures.

The cosolvent-dependent assembly of a family of three blue fluorescent lead(ii)-coordination polymers with 5-amino-2,4,6-tribromoisophthalic acid

By modulating the synthetic strategy based on changing the cosolvent in the synthesis, the aqueous medium assembly of lead(II) with H2ATBIP in the presence of different cosolvents, N,N-dimethylacetamide (DMA), methanol (CH3OH) or N,N-dimethylformamide (DMF), leads to a family of three lead(II) coordination polymers: [Pb(ATBIP)(H2O)2]·2H2O (1), [Pb(ATBIP)(H2O)(CH3OH)]·H2O (2) and [Pb(ATBIP)(H2O)(DMF)]·H2O (3) [H2ATBIP = 5-amino-2,4,6-tribromoisophthalic acid]. Complex 1 exhibits an interesting double chain structure with [Pb2(OH2)2] as the secondary building unit (SBU), which further assembles into a 3D supramolecular framework through the C–Br⋯Br halogen bonds and hydrogen bonds. Furthermore, the discrete water octamer (H2O)8 is found. The cosolvents, DMF and CH3OH, which simultaneously act as the coordinated small molecules, have significant influences on the formation of different crystalline architectures. Complex 2 features a 2D network constructed by the 21 helical carboxylate-bridged Pb(II) chains [Pb2(COO)2]n (SBUs) linked by the ligand ATBIP2−. The intralayer C–Br⋯Br halogen bond is found and a 3D supramolecular framework is formed by the interlayer hydrogen bonds. Complex 3 crystallizes in the chiral space group P41212 and possesses a 2D (4,4)-homochiral layer built from the centrosymmetrical SBU [Pb2(COO)2] bridged by the ligand ATBIP2−. The interlayer hydrogen bonds further extend the chiral layers in 3 into a 3D supramolecular homochiral framework. The coordination modes of the ligand ATBIP2− are greatly dependent on the cosolvents. Complex 3 loses crystallinity in the air and forms the material [Pb(ATBIP)(DMF)] (3A). Thermal stability and solid state fluorescent properties of 1, 2 and 3A have been studied. The second harmonic generation (SHG) property of 3A is also studied.

Theoretical study of structural, mechanical and spectroscopic properties of boehmite (γ-AlOOH)

The structural, mechanical and spectroscopic properties of boehmite (AlOOH polymorph)were investigated by means of first-principle density functional theory (DFT) andsemiempirical density functional based tight binding (DFTB) methods. Apart from amarginal underestimation of interlayer hydrogen bond distances the DFT method wellreproduces the experimental equilibrium low-pressure structure. For the DFTB methodsimilar good agreement was obtained for lattice parameters, however bond lengths andangles showed a larger deviation from experiment in comparison to DFT results. Theexperimental spectrum of the OH stretching region was interpreted by means of thecalculated frequencies within the frame of the harmonic approximation and by calculatingthe power spectra of the hydroxyl groups obtained from molecular dynamicssimulations. Using the latter approach, the strong coupling between the individualOH modes was demonstrated. Isostatic structural compression of the boehmitestructure was performed in order to obtain the bulk modulus and the dependenceof the vibrational spectrum on the pressure. The DFT method gives a value of97 GPa in the athermal limit. Comparison with available bulk moduli for otherAlOOH polymorphs reveals that boehmite shows the highest compression, forwhich mainly a strong shortening mechanism of interlayer hydrogen bonds isresponsible. The DFT method also described correctly the dependence of the OHstretch frequencies upon compression resulting in a strong red shift. Althoughgood performance is observed for the low-pressure region, the DFTB methodis not found to be suitable for high-pressure studies in cases such as boehmite.

Structure and property variations of lead iodide–organic coordination polymers tuned by substituted groups on phenanthroline

Three lead iodide–organic coordination polymers with different substituents on 1,10-phenanthroline, [(5-S-phen)PbI2]n (S = –NO2(1), –Cl(2) and –NH2(3)) have been synthesized in polar organic solvent under nearly the same conditions. 1 and 2 are structurally similar to each other, and exhibit 3-D networks based on inter-layer hydrogen bond interactions. 3 also gives 3-D arrangement viahydrogen bonds among 1-D chains. To our interest, we found that the ligand's electronic nature is the dominant factor in the dimension extending behavior; EWGs (electron-withdrawing group) on the phenanthroline ring will lead to larger electron mobility in a coordinated skeleton, but EDGs (electron-donating group) will give a smaller charge carrier mobility. Consequently, from EWGs to EDGs, an enlarged band gap can be observed. Their luminescences were also discussed.

New butane-1,2,3,4-tetracarboxylato bridged cobalt(II) complexes

Four butane-1,2,3,4-tetracarboxylato bridged supramolecular complexes [Co2(H2O)5(BTC)]·2H2O 1, [Co2(H2O)5(BTC)]·2H2O 2, [Co2(H2O)6(bpy)2(BTC)]·4H2O 3 and [Co2(H2O)2(bpy)2(BTC)] 4, (H4BTC=butane-1,2,3,4-tetracarboxylic acid, 2,2-bpy=2,2-bipydine) are synthesized and characterized by single-crystal X-ray diffraction. IR spectroscopy, TG-DTA analyses, elemental analyses, powder X-ray diffraction and magnetic measurements for 3 and 4 are carried out. The dinuclear Co unit in 2 is bridged by BTC4− anions into 2D layers, which are assembled via interlayer hydrogen bonds into a 3D (44·62)(45·65)2(46·68·8) topological supramolecular architecture. In 3, the [Co2(H2O)6(bpy)2(BTC)] molecules are aggregated to 2D layers via π–π stacking interactions, the resulting layers are engaged in hydrogen bonding leading to a novel 3D supramolecular architecture with the schläfli symbol of (102.12)2(4.102)2(42.102.122). The Co atoms in 4 are linked by BTC4− anions into a 1D chain, then the hydrogen bonding and π–π stacking interactions result in formation of a 3D novel (43.62.8)2(46.66.83)(63)2 topological networks. The variable temperature magnetic characterizations on 3 and 4 suggest weak antiferromagnetic or ferromagnetic coupling exchange via π···π stacking interactions (J=–0.03cm−1 for 3, J=0.11cm−1 for 4).

Hydrogen bonds and local symmetry in the crystal structure of gibbsite

First-principles quantum mechanical calculations of NMR chemical shifts and quadrupolar parameters have been carried out to assign the (27)Al MAS NMR resonances in gibbsite. The (27)Al NMR spectrum shows two signals for octahedral aluminum revealing two aluminum sites coordinated by six hydroxyl groups each, although the crystallographic positions of the two Al sites show little difference. The presence of two distinguished (27)Al NMR resonances characterized by rather similar chemical shifts but quadrupolar coupling constants differing by roughly a factor of two is explained by different character of the hydrogen bonds, in which the hydroxyls forming the corresponding octahedron around each aluminum site, are involved. The Al-I site characterized by a C(Q) = 4.6 MHz is surrounded by OH-groups participating in four intralayer and two interlayer hydrogen bonds, while the Al-II site with the smaller quadrupolar constant (2.2 MHz) is coordinated by hydroxides, of which two point toward the intralayer cavities and four OH-bonds are aligned toward the interlayer gallery. In high-resolution solid-state (1)H CRAMPS (combination of rotation and multiple-pulse spectroscopy) four signals with an intensity ratio of 1:2:2:1 are resolved which allow to distinguish six nonequivalent hydrogen sites reported in the gibbsite crystal structure and to ascribe them to two types of structural OH groups associated with intralayer and interlayer hydrogen bonds. This study can be applied to characterize the gibbsite-like layer-intergallery interactions associated with hydrogen bonding in the more complex systems, such as synthetic aluminum layered double hydroxides.

Hydrogen Bond Networks in Graphene Oxide Composite Paper: Structure and Mechanical Properties

A multilayered composite structure formed by a random stacking of graphene oxide (GO) platelets is an attractive candidate for novel applications in nanoelectromechanical systems and paper-like composites. We employ molecular dynamics simulations with reactive force fields to elucidate the structural and mechanical properties of GO paper-like materials. We find that the large-scale properties of these composites are controlled by hydrogen bond networks that involve functional groups on individual GO platelets and water molecules within the interlayer cavities. Water content controls both the extent and collective strength of these interlayer hydrogen bond networks, thereby affecting the interlayer spacing and elastic moduli of the composite. Additionally, the chemical composition of the individual GO platelets also plays a critical role in establishing the mechanical properties of the composite--a higher density of functional groups leads to increased hydrogen bonding and a corresponding increase in stiffness. Our studies suggest the possibility of tuning the properties of GO composites by altering the density of functional groups on individual platelets, the water content, and possibly the functional groups participating in hydrogen bonding with interlayer water molecules.