Organic-inorganic Interactions Research Articles

Interaction of saccharides and sugar alcohols with well cement

This paper reports on experimental investigations into the reactions of various saccharides and sugar alcohols in well (Portland) cement slurries at 90°C. At elevated temperatures the important element in saccharide chemistry is the overriding of a low activation energy barrier for the purpose of ring opening/cleavage and the formation of anionic molecules in cement slurries. The resulting experiments show a joint three-step reaction sequence for saccharides and sugar alcohols, accompanied by one set acceleration and two retardations of the cement hydration. The step-wise setting courses are explained by the spontaneous anion formation of polyhydroxy compounds owing to the Lobry de Bruyn–Alberda van Ekenstein rearrangement (keto-enol tautomerism) and charge neutralisation, as well as by well-known traditional organic–inorganic interactions. Furthermore the paper underlines the high relevance of temperature adjustment and cement aging on the course of setting of well cements.

Organic-inorganic interactions of single crystalline organolead halide perovskites studied by Raman spectroscopy.

Organolead halide perovskites exhibit superior photoelectric properties, which have given rise to the perovskite-based solar cells whose power conversion efficiency has rapidly reached above 20% in the past few years. However, perovskite-based solar cells have also encountered problems such as current-voltage hysteresis and degradation under practical working conditions. Yet investigations into the intrinsic chemical nature of the perovskite material and its role on the performance of the solar cells are relatively rare. In this work, Raman spectroscopy is employed together with CASTEP calculations to investigate the organic-inorganic interactions in CH3NH3PbI3 and CH3NH3PbBr3-xClx perovskite single crystals with comparison to those having ammonic acid as the cations. For Raman measurements of CH3NH3PbI3, a low energy line of 1030 nm is used to avoid excitation of strong photoluminescence of CH3NH3PbI3. Raman spectra covering a wide range of wavenumbers are obtained, and the restricted rotation modes of CH3-NH3(+) embedded in CH3NH3PbBr3 (325 cm(-1)) are overwhelmingly stronger over the other vibrational bands of the cations. However, the band intensity diminishes dramatically in CH3NH3PbBr3-xClx and most of the bands shift towards high frequency, indicating the interaction with the halides. The details of such an interaction are further revealed by inspecting the band shift of the restricted rotation mode as well as the C-N, NH3(+) and CH3 stretching of the CH3NH3(+) as a function of Cl composition and length of the cationic ammonic acids. The results show that the CH3NH3(+) interacts with the PbX3(-) octahedral framework via the NH3(+) end through N(+)-HX hydrogen bonding whose strength can be tuned by the composition of halides but is insensitive to the size of the organic cations. Moreover, an increase of the Cl content strengthens the hydrogen bonding and thus blueshifts the C-N stretching bands. This is due to the fact that Cl is more electronegative than Br and an increase of the Cl content decreases the lattice constant of the perovskite. The findings of the present work are valuable in understanding the role of cations and halides in the performance of MAPbX3-based perovskite solar cells.

Authigenic albite formation due to water–rock interactions — Case study: Magnus oilfield (UK, Northern North Sea)

It is the aim of this contribution to test whether organic–inorganic interactions could induce the formation of authigenic albite. This concept and related results are being compared with modelling scenarios which are purely based on inorganic geochemical reactions. In order to unravel the pathway of authigenic albite formation, this paper presents results of a multidisciplinary study from imaging, geochemistry, mineralogy, and hydrogeochemical modelling. The Jurassic reservoir sandstones of the Magnus oilfield (UK, North Sea) were chosen as a test site.Albite occurs with 4–18wt.% in the Magnus sandstones and its contents vary with depth. However, albite contents increase with increasing K-feldspar contents and decreasing grain size. It occurs in three forms: (1) as lamellae in perthite, (2) as overgrowth on/in corroded feldspar, and, (3) as cloudy replacing albite patches in K-feldspar. The albite overgrowth has the highest chemical purity (100% albite) whilst albite lamellae and replacing albite patches are slightly less pure (containing 1–4% anorthite). Albite appears non-altered, and has a euhedral morphology and dull cathodoluminescence. It commonly co-occurs with corroded K-feldspar grains.The precipitation of diagenetic albite in the Magnus sandstones is attributed to deep burial 80Ma ago and may have continued until today at temperatures between 90–120°C. The results of hydrogeochemical modelling offer two possible pathways for the authigenic albite formation: (1) Dissolution of unstable minerals (such as kaolinite and chalcedony) coupled to reduction of ferric iron minerals by products generated during oil generation, migration and degradation; (2) Dissolution of non-end member feldspar, such as K-feldspar with 10% albite, coupled to illite formation can account for trace amounts of albite due to an elevated Na+/K+ activity ratio in the pore water.

Immobilization of Proteins in Biopolymer-Silica Hybrid Materials: Functional Properties and Applications

Biohybrid materials combine the natural diversity of biomolecules with the flexibility of the inorganic sol-gel process. Association of biopolymers with silica is particularly useful for the preparation of three-dimensional hosts for protein immobilization with tailored physical and chemical stability. They are easily tunable in terms of composition, structure and shape, including silicified hydrogels, core-shell particles, and thin films. Such a versatility also allows for the fine tuning of the bio-mineral interface so as to insure the integrity of the encapsulated species, and even improve their biological activity. Biohybrid materials are currently widely explored as drug delivery systems, in biocatalysis as well as to develop new biorecognition devices. They also raise more fundamental questions related to organic-inorganic interactions, both from a chemical and biological perspective.

From shale oil to biogenic shale gas: retracing organic-inorganic interactions in the Alum Shale (Furongian-Lower Ordovician) in southern Sweden

Methane-rich gas occurs in the total organic carbon–rich Alum Shale (Furongian to Lower Ordovician) in southern Sweden. The lower part of the thermally immature Alum Shale was impregnated by bitumen locally generated by heating from magmatic intrusions from the Carboniferous to the Permian. Organic geochemical data indicate that the migrated bitumen is slightly degraded. In the upper Alum Shale, where methane is the main hydrocarbon in thermovaporization experiments, centimeter-size calcite crystals occur that contain fluid inclusions filled with oil, gas, or water. The Alum Shale is thus considered a mixed shale oil–biogenic shale gas play. The presented working hypothesis to explain the biogenic methane occurrence considers that water-soluble bitumen components of the Alum Shale were converted to methane. A hydrogeochemical modeling approach allows the quantitative retracing of inorganic reactions triggered by oil degradation. The modeling results reproduce the present-day gas and mineralogical composition. The conceptual model applied to explain the methane occurrence in the Alum Shale in southern Sweden resembles the formation of biogenic methane in the Antrim Shale (Michigan Basin, United States). In both models, melting water after the Pleistocene glaciation and modern meteoric water may have diluted the contents of total dissolved solids (TDS) in basinal brines. Such pore waters with low TDS contents create a subsurface aqueous environment favorable for microbes that have the potential to form biogenic methane. Today, biogenic methane production rates, with shale as the substrate using different hydrocarbon-degrading microbial enrichment cultures in incubation experiments, range from 10 to 620 nmol per gram and per day.

Synthesis and Structural Characterization of [(Pb6I22)(DMF)2(DPB)5] Directed by 1,1′-dipentyl-4,4′-bipyridinium Cation

In this study, one novel hexanuclear black crystals, namely [(Pb6I22)(DMF)2(DPB)5] were obtained from the solution-phase reaction of PbI2 in the present of excess KI directed by viologen-based linear templates in MeOH/DMF (DPB= 1,1′-dipentyl-4,4′-bipyridinium). Single-crystal X-ray diffraction analysis showed that this supramolecular compound crystallized in the monoclinic system with the space group P2(1)/c. Electrostatic interactions between the organic dications and inorganic moieties and hydrogen-bond interactions between structural unit are present and contribute to the crystal packing. IR spectroscopy was performed to further characterize title compound.

Effect of the Materials Properties of Hydroxyapatite Nanoparticles on Fibronectin Deposition and Conformation.

Hydroxyapatite (HAP, Ca10(PO4)6(OH)2) nanoparticles with controlled materials properties have been synthesized through a two-step hydrothermal aging method to investigate fibronectin (Fn) adsorption. Two distinct populations of HAP nanoparticles have been generated: HAP1 particles had smaller size, plate-like shape, lower crystallinity, and more negative ζ potential than HAP2 particles. We then developed two-dimensional platforms containing HAP and Fn and analyzed both the amount and the conformation of Fn via Förster resonance energy transfer (FRET) at various HAP concentrations. Our FRET analysis reveals that larger amounts of more compact Fn molecules were adsorbed onto HAP1 than onto HAP2 particles. Additionally, our data show that the amount of compact Fn adsorbed increased with increasing HAP concentration due to the formation of nanoparticle agglomerates. We propose that both the surface chemistry of single nanoparticles and the size and morphology of HAP agglomerates play significant roles in the interaction of Fn with HAP. Collectively, our findings suggest that the HAP-induced conformational changes of Fn, a critical mechanotransducer protein involved in the communication of cells with their environment, will ultimately affect downstream cellular behaviors. These results have important implications for our understanding of organic–inorganic interactions in physiological and pathological biomineralization processes such as HAP-related inflammation.

Organic-inorganic interactions in the system ofpyrrole-hematite-water at elevated temperaturesand pressures

Abstract The distribution and abundance of pyrrolic compoundsin sediments and crude oils are most likely influencedby inorganic sedimentary components. In thispaper, thermal simulation experiments on the systempyrrole-hematite-water were carried out at elevated temperaturesand pressures in order to investigate the effectof organic-inorganic interactions on the preservationof pyrrolic compounds. Compositions of the reactionproducts were analyzed with GC-MS and GC-FIDmethods. In the closed system pyrrole-hematite-water, thenitrogen-oxygen exchange obviously occurred at temperaturesabove 350ºC in accordance with the thermochemicalcalculation. Large amounts of furan and ammonia weregenerated after simulation experiments, indicating thatthe conversion of pyrrole into furan was the dominant reaction.Thermochemical exchange effect between organicnitrogen and inorganic oxygen was obviously facilitatedby elevated temperatures and found to be catalyzed byhematite, but inhibited by the increasing volume of water.Thermodynamically water spontaneously reacts with pyrroleabove 300ºC. The reaction of pyrrole-hematite-wateris an exothermic process in which the reaction heat positivelycorrelates with temperature. The heat released wasestimated as 9.0 KJ/(mol) pyrrole - 15.0 KJ/(mol) pyrrole intypical oil reservoirs (100ºC–150ºC) and 15.0–23.0 KJ/(mol)pyrrole in typical gas reservoirs (150ºC–200ºC). The calculatedactivation energy of the nitrogen-oxygen atom exchangeis about 129.59 kJ/mol. According to the experimentalresults, a small amount of water may effectivelyinitiate the nitrogen-oxygen exchange. The study wouldimprove our evaluating of the preservation and fate ofpyrrolic compounds in deeply buried geologic settings andfurther understanding of thermochemical processes behindthe degradation of petroleum.

Hybrid inorganic-organic materials with an optoelectronically active aromatic cation: (C7H7)2SnI6 and C7H7PbI3.

Inorganic materials with organic constituents-hybrid materials-have shown incredible promise as chemically tunable functional materials with interesting optical and electronic properties. Here, the preparation and structure are reported of two hybrid materials containing the optoelectronically active tropylium ion within tin- and lead-iodide inorganic frameworks with distinct topologies. The crystal structures of tropylium tin iodide, (C7H7)2SnI6, and tropylium lead iodide, C7H7PbI3, were solved using high-resolution synchrotron powder X-ray diffraction informed by X-ray pair distribution function data and high-resolution time-of-flight neutron diffraction. Tropylium tin iodide contains isolated tin(IV)-iodide octahedra and crystallizes as a deep black solid, while tropylium lead iodide presents one-dimensional chains of face-sharing lead(II)-iodide octahedra and crystallizes as a bright red-orange powder. Experimental diffuse reflectance spectra are in good agreement with density functional calculations of the electronic structure. Calculations of the band decomposed charge densities suggest that the deep black color of tropylium tin iodide is attributed to iodide ligand to tin metal charge transfer, while the bright red-orange color of tropylium lead iodide arises from charge transfer between iodine and tropylium states. Understanding the origins of the observed optoelectronic properties of these two compounds, with respect to their distinct topologies and organic-inorganic interactions, provides insight into the design of tropylium-containing compounds for potential optical and electronic applications.

Long- and Short-Range Constraints for the Structure Determination of Layered Silicates with Stacking Disorder

Layered silicates have important applications as host materials, supports for catalysis, and zeolite precursors. However, their local structures are often challenging to establish due to disorder of the sheet assemblies. We present a new protocol that combines long- and short-range structural constraints from diffraction and solid-state NMR techniques, respectively, to determine the molecular structure of layered silicates in the presence of various extents of stacking disorder. Solid-state 29Si NMR data are largely insensitive to the incomplete extent of three-dimensional (3D) crystallinity that limits the interpretation of diffraction data alone to the identification of possible unit cells and space groups. State-of-the-art NMR crystallography techniques consequently provide a simplified view of materials from which candidate framework structures can be built and evaluated based on local structural constraints, including interatomic distances, Si site numbers and multiplicities, and Si–O–Si connectivities, and refined using density functional theory. This protocol was applied to a new layered silicate material named CLS-1, of composition [Si5O11H][C9N2H15]·1.9(H2O), synthesized by using a fluoride-based protocol and cationic alkylaminopyridinium as a structure-directing agent (SDA). Despite the intrinsic complexity and partial ordering of the intersheet arrangements and organic–inorganic interactions, this led to the identification of a single space group that is compatible with both NMR and diffraction data, from which the silicate framework structure could be established,. The remarkable similarities between the layered framework structures of CLS-1, HUS-2 (Tsunoji et al. J. Mater. Chem. 2012, 22, 13682), and another layered silicate material with a radically different morphology and extent of stacking order and interlayer dynamics, established by using a similar approach (Brouwer et al. J. Am. Chem. Soc. 2013, 135, 5641), point to the remarkable robustness of this previously unknown silicate framework type.

Organics Exposure in Orbit (OREOcube): A next-generation space exposure platform.

The OREOcube (ORganics Exposure in Orbit cube) experiment on the International Space Station (ISS) will investigate the effects of solar and cosmic radiation on organic thin films supported on inorganic substrates. Probing the kinetics of structural changes and photomodulated organic-inorganic interactions with real-time in situ UV-visible spectroscopy, this experiment will investigate the role played by solid mineral surfaces in the (photo)chemical evolution, transport, and distribution of organics in our solar system and beyond. In preparation for the OREOcube ISS experiment, we report here laboratory measurements of the photostability of thin films of the 9,10-anthraquinone derivative anthrarufin (51 nm thick) layered upon ultrathin films of iron oxides magnetite and hematite (4 nm thick), as well as supported directly on fused silica. During irradiation with UV and visible light simulating the photon flux and spectral distribution on the surface of Mars, anthrarufin/iron oxide bilayer thin films were exposed to CO2 (800 Pa), the main constituent (and pressure) of the martian atmosphere. The time-dependent photodegradation of anthrarufin thin films revealed the inhibition of degradation by both types of underlying iron oxides relative to anthrarufin on bare fused silica. Interactions between the organic and inorganic thin films, apparent in spectral shifts of the anthrarufin bands, are consistent with presumed free-electron quenching of semiquinone anion radicals by the iron oxide layers, effectively protecting the organic compound from photodegradation. Combining such in situ real-time kinetic measurements of thin films in future space exposure experiments on the ISS with postflight sample return and analysis will provide time-course studies complemented by in-depth chemical analysis. This will facilitate the characterization and modeling of the chemistry of organic species associated with mineral surfaces in astrobiological contexts.

Kinetics of N–S Atom Exchange in the Pyrrole–H2S System

Factors affecting the abundance and the distribution of pyrrolic N compounds in sediments and crude oils have been traditionally attributed to palaeoenvironment of deposition, thermal maturity and source characteristics, as well as to migration effects. In this paper, experiments simulating reactions between pyrrole and hydrogen sulfide (H2S) were conducted using a Hastelloy alloy tube confined system to investigate the effect of organic–inorganic interactions on the alteration of pyrrolic N compounds in real subsurface reservoirs. Experimental results showed that thermochemical N–S atom exchange evidently occurred at 400 °C in the pyrrole–H2S system, with thiophene and ammonium hydrosulfide as the main products. Kinetic analysis of experimental data according to the integral composite method showed that the conversion of pyrrole into thiophene is best described by the second-order reaction model. The calculated apparent activation energy was about 39.010 kJ/mol and the frequency factor A was estimated equal to 5.935 × 10−4 s−1. This study indicates that pyrrolic N compounds may be susceptible to hydrogen sulfide under the conditions of real subsurface reservoirs, which is of great relevance to the stability of reservoir pyrrolic N compounds.

Crystallization and preliminary X-ray analysis of the C-type lectin domain of the spicule matrix protein SM50 fromStrongylocentrotus purpuratus

Sea urchin spicules have a calcitic mesocrystalline architecture that is closely associated with a matrix of proteins and amorphous minerals. The mechanism underlying spicule formation involves complex processes encompassing spatio-temporally regulated organic-inorganic interactions. C-type lectin domains are present in several spicule matrix proteins in Strongylocentrotus purpuratus, implying their role in spiculogenesis. In this study, the C-type lectin domain of SM50 was overexpressed, purified and crystallized using a vapour-diffusion method. The crystal diffracted to a resolution of 2.85 Å and belonged to space group P212121, with unit-cell parameters a = 100.6, b = 115.4, c = 130.6 Å, α = β = γ = 90°. Assuming 50% solvent content, six chains are expected to be present in the asymmetric unit.

Intergrowth and Interfacial Structure of Biomimetic Fluorapatite–Gelatin Nanocomposite: A Solid-State NMR Study

The model system fluorapatite-gelatin allows mimicking the formation conditions on a lower level of complexity compared to natural dental and bone tissues. Here, we report on solid-state NMR investigations to examine the structure of fluorapatite-gelatin nanocomposites on a molecular level with particular focus on organic-inorganic interactions. Using (31)P, (19)F, and (1)H MAS NMR and heteronuclear correlations, we found the nanocomposite to consist of crystalline apatite-like regions (fluorapatite and hydroxyfluorapatite) in close contact with a more dissolved (amorphous) layer containing first motifs of the apatite crystal structure as well as the organic component. A scheme of the intergrowth region in the fluorapatite-gelatin nanocomposite, where mineral domains interact with organic matrix, is presented.

Hydration layer structures on calcite facets and their roles in selective adsorptions of biomolecules: A molecular dynamics study

The selective adsorptions of biomolecules onto crystal faces are the key issues in the studies of biomineralization. Frequently, the adsorption processes are understood by using the direct binding model between organic compounds and inorganic crystals during the molecular dynamic studies. However, water molecules near crystals always exhibit intense ordering and preferential orientation to form structured hydration layer. By using the adsorption of poly acrylic acid oligomer, acrylic acid (AA) dimer, onto calcite as an example, we demonstrate that the induced hydration layers contribute significant effects on the organic-inorganic interactions. In particular, on calcite (104) plane, two carboxyl groups of AA dimer both interact with the crystal but the molecule has to compete with water due to the well-structured hydration layer. On (110) plane, although only one carboxyl group of AA dimer interacts with this surface, the water layer is relatively loose so that the molecule can easily replace water. With a consideration of the hydration layer, our free energy analysis indicates that AA dimer has a stronger interaction with (110) face than with (104) face, which is consistent with the experimental observations. The study follows that the attachment of organic additive onto inorganic crystal facet is greatly mediated by near-surface hydration layers, and therefore, the critical role of structured water layers must be taken into account in the understanding of biomineralization interfaces.

Controls on CO2 fate and behavior in the Gullfaks oil field (Norway): How hydrogeochemical modeling can help decipher organic-inorganic interactions

Oil degradation in the Gullfaks field led to hydrogeochemical processes that caused high CO2 partial pressure and a massive release of sodium into the formation water. Hydrogeochemical modeling of the inorganic equilibrium reactions of water-rock-gas interactions allows us to quantitatively analyze the pathways and consequences of these complex interconnected reactions. This approach considers interactions among mineral assemblages (anorthite, albite, K-feldspar, quartz, kaolinite, goethite, calcite, dolomite, siderite, dawsonite, and nahcolite), various aqueous solutions, and a multicomponent fixed-pressure gas phase (CO2, CH4, and H2) at 4496-psi (31-mPa) reservoir pressure. The modeling concept is based on the anoxic degradation of crude oil (irreversible conversion of n-alkanes to CO2, CH4, H2, and acetic acid) at oil-water contacts. These water-soluble degradation products are the driving forces for inorganic reactions among mineral assemblages, components dissolved in the formation water, and a coexisting gas at equilibrium conditions. The modeling results quantitatively reproduce the proven alteration of mineral assemblages in the reservoir triggered by oil degradation, showing (1) nearly complete dissolution of plagioclase; (2) stability of K-feldspar; (3) massive precipitation of kaolinite and, to a lesser degree, of Ca-Mg-Fe carbonate; and (4) observed uncommonly high CO2 partial pressure (61 psi [0.42 mPa] at maximum). The evolving composition of coexisting formation water is strongly influenced by the uptake of carbonate carbon from oil degradation and sodium released from dissolving albitic plagioclase. This causes supersaturation with regard to thermodynamically stable dawsonite. The modeling results also indicate that nahcolite may form as a CO2-sequestering sodium carbonate instead of dawsonite, likely controlling CO2 partial pressure.

Self-Assembly Mechanism of Folate-Templated Mesoporous Silica

A method to form ordered mesoporous silica based on the use of folate supramolecular templates has been developed. Evidence based on in situ small-angle X-ray scattering (SAXS), electron microscopy, infrared spectroscopy, and in situ conductivity measurements are used to investigate the organic-inorganic interactions and synthesis mechanism. The behavior of folate molecules in solution differs distinctively from that of surfactants commonly used for the preparation of ordered mesoporous silica phases, notably with the absence of a critical micellar concentration. In situ SAXS studies reveal fluctuations in X-ray scattering intensities consistent with the condensation of the silica precursor surrounding the folate template and the growth of the silica mesostructure in the initial stages. High-angle X-ray diffraction shows that the folate template is well-ordered within the pores even after a few minutes of synthesis. Direct structural data for the self-assembly of folates into chiral tetramers within the pores of mesoporous silica provide evidence for the in register stacking of folate tetramers, resulting in a chiral surface of rotated tetramers, with a rotation angle of 30°. Additionally, the self-assembled folates within pores were capable of adsorbing a considerable amount of CO2 gas through the cavity space of the tetramers. The study demonstrates the validity of using a naturally occurring template to produce relevant and functional mesoporous materials.

Glyoxal secondary organic aerosol chemistry: effects of dilute nitrate and ammonium and support for organic radical–radical oligomer formation

Environmental context Atmospheric waters (clouds, fogs and wet aerosols) are media in which gases can be converted into particulate matter. This work explores aqueous transformations of glyoxal, a water-soluble gas with anthropogenic and biogenic sources. Results provide new evidence in support of previously proposed chemical mechanisms. These mechanisms are beginning to be incorporated into transport models that link emissions to air pollution concentrations and behaviour. Abstract Glyoxal (GLY) is ubiquitous in the atmosphere and an important aqueous secondary organic aerosol (SOA) precursor. At dilute (cloud-relevant) organic concentrations, OH• radical oxidation of GLY has been shown to produce oxalate. GLY has also been used as a surrogate species to gain insight into radical and non-radical reactions in wet aerosols, where organic and inorganic concentrations are very high (in the molar region). The work herein demonstrates, for the first time, that tartarate forms from GLY+OH•. Tartarate is a key product in a previously proposed organic radical–radical reaction mechanism for oligomer formation from GLY oxidation. Previously published model predictions that include this GLY oxidation pathway suggest that oligomers are major products of OH• radical oxidation at the high organic concentrations found in wet aerosols. The tartarate measurements herein provide support for this proposed oligomer formation mechanism. This paper also demonstrates, for the first time, that dilute (cloud or fog-relevant) concentrations of inorganic nitrogen (i.e. ammonium and nitrate) have little effect on the GLY+OH• chemistry leading to oxalate formation in clouds. This, and results from previous experiments conducted with acidic sulfate, increase confidence that the currently understood dilute GLY+OH• chemistry can be used to predict GLY SOA formation in clouds and fogs. It should be recognised that organic–inorganic interactions can play an important role in droplet evaporation chemistry and in wet aerosols. The chemistry leading to SOA formation in these environments is complex and remains poorly understood.

Preparation and Characterization of AgA Zeolite/Polysulfone Membranes

In present study, a few polysulfone composite membranes with the introduction of silver ion-exchange treated zeolite were prepared and evaluated by several characterization methods. Regularly-ordered zeolite particles were generally finely dispersed in the continuous PSF phase with appreciated organic-inorganic interfacial interactions as reflected by SEM and FTIR results. Gas permeation test shows that after incorporating zeolite the polysulfone membrane exhibits significantly decreased gas permeability for H2, N2, and CO2 whereas they show increased permselectivity for CO2/N2, H2/CO2 and H2/N2 gas pairs as compared to neat polysulfone membrane.

Scanning the Potential Energy Surface for Synthesis of Dendrimer-Wrapped Gold Clusters: Design Rules for True Single-Molecule Nanostructures

The formation of true single-molecule complexes between organic ligands and nanoparticles is challenging and requires careful design of molecules with size, shape, and chemical properties tailored for the specific nanoparticle. Here we use computer simulations to describe the atomic-scale structure, dynamics, and energetics of ligand-mediated synthesis and interlinking of 1 nm gold clusters. The models help explain recent experimental results and provide insight into how multidentate thioether dendrimers can be employed for synthesis of true single-ligand-nanoparticle complexes and also nanoparticle-molecule-nanoparticle "dumbbell" nanostructures. Electronic structure calculations reveal the individually weak thioether-gold bonds (325 ± 36 meV), which act collectively through the multivalent (multisite) anchoring to stabilize the ligand-nanoparticle complex (∼7 eV total binding energy) and offset the conformational and solvation penalties involved in this "wrapping" process. Molecular dynamics simulations show that the dendrimer is sufficiently flexible to tolerate the strained conformations and desolvation penalties involved in fully wrapping the particle, quantifying the subtle balance between covalent anchoring and noncovalent wrapping in the assembly of ligand-nanoparticle complexes. The computed preference for binding of a single dendrimer to the cluster reveals the prohibitively high dendrimer desolvation barrier (1.5 ± 0.5 eV) to form the alternative double-dendrimer structure. Finally, the models show formation of an additional electron transfer channel between nitrogen and gold for ligands with a central pyridine unit, which gives a stiff binding orientation and explains the recently measured larger interparticle distances for particles synthesized and interlinked using linear ligands with a central pyridine rather than a benzene moiety. The findings stress the importance of organic-inorganic interactions, the control of which is central to the rational engineering and eventual large-scale production of functional building blocks for nano(bio)electronics.