Molecular Sheets Research Articles

Enhanced Cross-Flow Ultrafiltration of Apple Juice Using Electric Field

Electric field-enhanced cross-flow ultrafiltration of enzyme-treated apple juice is studied in a rectangular cell using a 30 kDa molecular weight cut-off flat sheet polyethersulfone membrane under turbulent flow conditions for various operating conditions. Application of direct current (DC) electric field has resulted in a significant augmentation of permeate flux. Using classical film theory, a steady-state gel polarization model incorporating the effect of electric field and pressure-dependent mass transfer coefficient is proposed for the prediction of permeate flux. From the steady-state model, gel layer concentration, effective diffusivity and effective viscosity of gel-forming solute in apple juice are estimated. A gel layer model based on resistance-in-series theory is proposed and numerically solved to quantify the transient flux decline and development of gel layer thickness over the membrane surface. The model predictions are successfully compared with the experimental results. Practical Applications To the best of our knowledge, quantification of ultrafiltration performance of apple juice in the presence of electric field is attempted for the first time and its modeling for prediction of steady-state flux as well as unsteady-state flux profile has not been reported so far. The present study aims to investigate the potentiality of an electric field-assisted ultrafiltration in the clarification of apple juice for the first time, as an alternative to conventional processing methods. The effects of various operating parameters such as electric field, transmembrane pressure, feed flow rate on the permeate flux and fouling resistance are investigated.

Nanoindentation measurements of Teflon‐AF nanosheets

ABSTRACTWe report the formation of cohesive, mechanically robust thin films of Teflon‐AF formed via self‐assembly of nanoparticles at both air/water and oil/water interfaces of micro‐emulsion droplets. We also present results of morphological and mechanical investigations of thin films formed at these oil/water interfaces. Scanning electron microscope and low angle X‐ray diffraction characterization of drop cast thin films from the micro‐emulsions showed the presence of stacks of nanosheets with an average thickness of 6 nm. Atomic force microscopy (AFM) characterization put the thickness at a much lower value of around 2 nm implying that these sheets are comprised of molecular sheets of Teflon‐AF. AFM characterization also indicated that these sheets are stretched molecular films comprising inter‐diffused molecular chains, arranged in a regular fashion. Nanoindentation studies of these films unambiguously demonstrated the “tablet sliding” mechanism, similar to nacre, for dissipating applied stress. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41360.

Non-nuclear electron transport channels in hollow molecules

Electron transport in inorganic semiconductors and metals occurs through delocalized bands formed by overlapping electron orbitals. Strong correlation of electronic wave functions with the ionic cores couples the electron and lattice motions, leading to efficient interaction and scattering that degrades coherent charge transport. By contrast, unoccupied electronic states at energies near the vacuum level with diffuse molecular orbitals may form nearly-free-electron bands with density maxima in non-nuclear interstitial voids, which are subject to weaker electron-phonon interaction. The position of such bands typically above the frontier orbitals, however, renders them unstable with respect to electronic interband relaxation and therefore unsuitable for charge transport. Through electronic-structure calculations, we engineer stable, non-nuclear, nearly-free-electron conduction channels in low-dimensional molecular materials by tailoring their electrostatic and polarization potentials. We propose quantum structures of graphane-derived Janus molecular sheets with spatially isolated conducting and insulating regions that potentially exhibit emergent electronic properties, as a paradigm for molecular-scale non-nuclear charge conductors; we also describe tuning of their electronic properties by application of external fields and calculate their electron--acoustic-phonon interaction.

Crystal Structures and Fluorescence Spectroscopic Properties of Cyano-Substituted Diphenylhexatrienes

The crystal structures and spectroscopic properties of (E,E,E)-1,6-di(x-cyanophenyl)-1,3,5-hexatrienes (2: x = 2, 3: x = 3, 4: x = 4) have been investigated. The single crystal X-ray structure analysis reveals that the molecules are linked via sp2-CH···N≡C hydrogen bonds in each crystal. The existence of the sp2-CH···N≡C hydrogen bonds in crystals 2–4 is spectroscopically evidenced by the fact that the IR peaks due to C≡N stretching vibration shift to lower wavenumbers in the solid state relative to those in solution. The molecules of 3 are hydrogen bonded to form orthogonally oriented ribbons, whereas those of 2 and 4 are organized into molecular sheets. The distance and displacements between the nearest stacking molecules are larger in 3 than those in 2 and 4. For each triene, the absorption and fluorescence spectra in the solid state shift to longer wavelengths than those in solution. The magnitude of the red shift is similar for 2–4 in the absorption spectra, but larger for 2 and 4 than for 3 in the fluorescence spectra. We conclude that the origin of the solid-state fluorescence is monomeric for 3 and excimeric for 2 and 4. The relationship between crystal structure and fluorescence properties is discussed.

Super-fast oil uptake using porous ultra-high molecular weight polyethylene sheets

This paper presents the oil uptake of porous sorbent polymer sheets consisting of ultra-high molecular weightpolyethylene. A comprehensive set of experiments are performed showing the saturation contact time, retentionvalue, mechanical properties, oil pick-up ratio, pick-up density, and dynamic dripping profile. Kinetic modeling ofthe oil sorption is also provided. The experimental results show a good correlation with the pseudo-second ordermodel. The sheets exhibit high oil uptake speeds, requiring less than 2min in contact with the oil to reachsaturation. The sheets fulfill the criteria of high uptake kinetics, high so rption capacity, and high mechanical strengthsimultaneously.Thosecharacteristicsenabletheiruseinpracticalspill response.Copyright©2014JohnWileyS uptake capacity; dripping; polymer

Structure prediction of N-heteroacenes as potential organic semiconductors

Organic electronics offer exciting new alternatives to traditional inorganic devices based on advantages such as lower cost, ease of manufacture and flexibility. Small molecule semiconductors such as pentacene and rubrene are the focus of intense research due to performance approaching that of inorganic semiconductors. Charge transfer in polyaromatic hydrocarbons (PAHs) relies on the degree of π-conjugation and overlap of the π-systems of neighbouring molecules in the solid state. Small changes in the intermolecular interactions can lead to important changes in crystal packing and electronic properties. Thus, functionalization of PAHs is often used to improve their packing in the solid state. The addition of electronegative atoms into the ring system of pentacene has been proposed for improving stability while retaining attractive properties. [1] N-heteroacenes result from the substitution of nitrogen into the arene ring structure. The resulting potential for weak hydrogen bonding could direct coplanar molecular arrangements, sheet formation and favourable π-overlap for charge transport. Theoretical studies [2] have been carried out showing promising properties at the molecular level. As of yet no analysis of the solid state of these molecules has been performed to investigate how this substitution affects the packing and electronic properties. Here, we present the results of crystal structure prediction studies and calculation of charge transport properties aimed at understanding the influence of nitrogen substitution on the crystal packing of N-heteropentacenes and their performance as semiconducting materials.

Supramolecular architectures of 4-hydroxytetraphenylporphyrin with aza-donors

Molecular adducts of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (1) with aza-donors like 4,4'-bipyridine (a), 1,2-bis(4-pyridyl)ethane (b), trans-1,2-bis(4-pyridyl)ethylene (c), 4,4'-trimethylene-dipyridine (d), phenazine (e), 1,10-phenanthroline (f), 1,7-phenanthroline (g) and 4,7-phenanthroline (h) have been prepared. All the molecular complexes are crystallized along with the solvent of crystallization, except in the complex with the aza-donor b. Detailed structural analysis of the obtained complexes has been carried out by single crystal X-ray diffraction. The three dimensional structures of the molecular adducts are facilitated by directional hydrogen bonding features of hydroxyl groups with aza donors as well as solvent molecules, leading to the formation of different types of supramolecular architectures like sheets, tapes, host-guest assembly etc. For example, in the complex of 1 and aza donor a, which crystallizes as a hydrate, the porphyrin molecules interact with water and 4,4'-bipyridine through O-H...O and O-H...N hydrogen bonds, which leads to the formation of molecular sheets in two dimensional arrangement. An important noteworthy observation is that the molecular complexes are crystalline even after removal of the solvents by heating, as characterized by thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD). Further, all the complexes are found to be fluorescence sensitive, perhaps due to the porphyrin molecules.

Theoretical study of the structural stability of molecular chain sheet models of cellulose crystal allomorphs.

The structural stabilities of the molecular chain sheets constituting the crystal structures of the cellulose allomorphs Iα, Iβ, II, and IIII were investigated by density functional theory (DFT) optimization of the isolated chain sheet models with finite dimensions. The DFT-optimized chain sheet models of the two native cellulose crystals developed a right-handed twist with a similar amount of twisting. The DFT-optimized cellulose II (010) and (020) models twisted in opposite directions with right- and left-handed chirality, respectively. The cellulose IIII (1-10) model retained the initial flat structure after the DFT-optimization. The structural features of the DFT-optimized chain sheet models were reflected in the structures of the parent crystal models observed in solvated molecular dynamics (MD) simulations. The minor conformations of the hydroxymethyl groups proposed in the real crystal structures were detected in the MD crystal models and the DFT-optimized (010) model of cellulose II. The crystal chain packing and crystal conversions are interpreted in terms of principal chain sheet stacking.

All-carbon vertical van der Waals heterostructures: non-destructive functionalization of graphene for electronic applications.

Non-destructive chemical functionalization of graphene for applications in electronic devices (e.g., sensors or transducers) is achieved via assembly of carbon nanomembrane (CNM)/single-layer graphene (SLG) van der Waals heterostructures. The CNMs are 1 nm-thick, dielectric molecular sheets terminated with functional amino groups. The structure and performance of heterostructured field-effect transistors (FETs) are characterized by photoelectron/Raman spectroscopy and by electric transport measurements in vacuum, ambient conditions and water.

Ultrathin Sheets of Metal or Metal Sulfide from Molecularly Thin Sheets of Metal Thiolates in Solution

Materials that exist as single molecule thick two-dimensional sheets are in great demand because they hold promise as precursors for synthesis of layered functional materials. We demonstrate that metal thiolates, that exist as lamellar assemblies in the neat state, can be disassembled into individual molecular sheets simply by dilution in apolar organic solvents and that these can form ultrathin metallic layers on substrates upon heat treatment. We establish the pathway to the disassembly of metal thiolates in solution using a combination of techniques, including X-ray diffraction, light scattering, FTIR, and TEM. Our results indicate that the lamellar structure of Pd-thiolates is preserved in toluene up to a concentration of 300% w/v and the average intersheet distance is unchanged. Interestingly, the dynamics of the Pd-thiolate sheets remain correlated even on diluting them up to 30% w/v, though the disorder within the lamellar stacks increases with a decrease in their coherence length. Finally, at dilutions less than about 5% w/v, individual sheets of these structures can be accessed that are isolated and directly observed using TEM. Heat treatment of the ultrathin films of metal thiolates deposited on appropriate substrates resulted in the formation of metal or metal sulfides with retention of sheetlike morphologies.

4,5-Dicyano-3,6-diethylbenzo-1,2-diselenete, a highly stable 1,2-diselenete: its preparation, structural characterization, calculated molecular orbitals, and complexation with tetrakis(triphenylphosphine)palladium.

The first isolable benzo-1,2-diselenete, 4,5-dicyano-3,6-diethylbenzo-1,2-diselenete (4), was prepared by the reaction of 4,5-(o-xylylenediseleno)-3,6-diethylphthalonitrile (3) with aluminum chloride in toluene. X-ray crystallographic analysis demonstrated that 4 contains a trapezoidal diselenide ring rather than a benzo-1,2-diselenone structure. In crystal form, 4 undergoes self-assembly and generates structures based on layered molecular sheets since the unit cell contains only one molecule. While the cyclic voltammogram of 4 exhibited only one irreversible peak (Ep = 1.59 V) during oxidation and two quasireversible couples during reduction, three peaks were observed in the differential pulse voltammogram of the reduction couples (E1/2 = -1.19, -0.75, and -0.69 V). Although a THF solution of 4 in the presence of sodium metal was EPR silent, various signals were readily observed in its (1)H, (13)C, and (77)Se NMR spectra. Molecular orbital calculations for 4 demonstrated that the HOMO orbital is primarily localized at the two selenium atoms and four of the benzene carbon atoms while the LUMO orbital is situated solely on the diselenete ring. It appears that the HOMO and LUMO orbitals of 4 receive significant stabilization from the nitrile groups compared to the level of stabilization in the unsubstituted benzo-1,2-diselenete (BDS). The reaction of 4 with tetrakis(triphenylphosphine)palladium in benzene was found to produce a dinuclear palladium complex (8), and the structure of this complex was determined by X-ray crystallographic analysis. The central four membered ring of 8 consists of the Pd1, Se2, Pd2, and Se3 atoms and is not planar but rather adopts a folded arrangement.

Redetermination of 2-methyl-4-nitro-pyridine N-oxide.

An improved crystal structure of the title compound, C6H6N2O3, is reported. The structure, previously solved [Li et al. (1987 ▶). Jiegou Huaxue (Chin. J. Struct. Chem.), 6, 20–24] in the ortho­rhom­bic space group Pca21 and refined to R = 0.067, has been solved in the ortho­rhom­bic space group Pbcm with data of enhanced quality, giving an improved structure (R = 0.0485). The mol­ecule adopts a planar conformation with all atoms lying on a mirror plane. The crystal structure is composed of mol­ecular sheets extending parallel to the ab plane and connected via C—H⋯O contacts involving ring H atoms and O atoms of the N-oxide and nitro groups, while van der Waals forces consolidate the stacking of the layers.

Influence of dyestuffs on the crystallinity of a bacterial cellulose and a regenerated cellulose

The crystal structures of bacterial cellulose (BC) obtained by cultivation of an Enterobacter species CJF 002 stock under the presence of direct, acid, and basic dyestuffs were examined. Optical microscopic observation showed that direct and basic dyestuffs stained BC samples but acid dyestuff did not. This suggests that direct and basic dyestuffs are contained within the resulting BC samples. Analysis of wide angle x-ray diffraction (WAXD) data indicates that direct dyestuffs inhibited crystallization of BC at dyestuff concentration in culture media ( Cdye) of more than 0.05 wt% with lower angle shift of the diffraction peak for the (200) plane of BC, but almost no influence on BC crystallization in the case of basic dyestuff was observed. In addition, we investigated the crystallinity of regenerated cellulose (RC) from a cuprammonium solution and the reaction of RC with the dyestuffs. The dyestuffs had almost no impact on the crystallinity of RC even in cases where the samples showed staining. It was found that the apparent crystallite size of (110) and (020) in the RC samples with dyestuffs were slightly lower than that in the RC blank sample, while the apparent crystallite size of ([Formula: see text]) in the RC samples with dyestuffs retain the values at the same level as the RC blank sample. These results suggest that the cellulose molecular sheets held together by van der Waals interactions were the basic structure formed from RC and they probably retain their structure in the cuprammonium solution at relatively high concentrations of cellulose.

Nonnuclear Nearly Free Electron Conduction Channels Induced by Doping Charge in Nanotube–Molecular Sheet Composites

Nearly free electron (NFE) states with density maxima in nonnuclear (NN) voids may have remarkable electron transport properties ranging from suppressed electron-phonon interaction to Wigner crystallization. Such NFE states, however, usually exist near the vacuum level, which makes them unsuitable for transport. Through first principles calculations on nanocomposites consisting of carbon nanotube (CNT) arrays sandwiched between boron nitride (BN) sheets, we describe a stratagem for stabilizing the NN-NFE states to below the Fermi level. By doping the CNTs with negative charge, we establish Coulomb barriers at CNTs walls that, together with the insulating BN sheets, define the transverse potentials of one-dimensional (1D) transport channels, which support the NN-NFE states.

Enhanced photocatalytic hydrogen evolution from water by niobate single molecular sheets and ensembles.

We report single molecular sheets of niobate prepared by a simple bottom-up approach using hydrothermal synthesis of niobium ethoxide with the aid of triethanolamine as a structural modifier: the high kinetic stability of these molecular entities against self-assembly allows them to mix well with other colloids and facilitates their extensive electronic interactions and thus photocatalytic hydrogen evolution activity from water is much enhanced over composite of single niobate sheets with graphene and MoS2 due to efficient electron transfer and charge separation.

(E)-N′-(2-Chlorobenzylidene)-1-methyl-4-nitro-1H-pyrrole-2-carbohydrazide

In the title compound, C13H11ClN4O3, the phenyl and pyrrolyl ring are linked by an ac­yl–hydrazone (R 2C=N—N—CO—R) group, forming a slightly bent mol­ecule: the dihedral angle subtended by the the phenyl and pyrrolyl rings is 8.46 (12)°. In the crystal, the three-dimensional supra­molecular structure is assembled by N—H⋯O hydrogen bonding. Mol­ecular sheets are formed parallel to (101) in a herringbone arrangement by weak van der Waals inter­actions; weak π–π [centroid–centroid phen­yl–phenyl and pyrrol­yl–pyrrolyl distances of 3.7816 (3) and 3.8946 (2) Å, respectively] inter­actions occur between neighbouring sheets.

5-Bromobenzene-1,3-dicarbonitrile

The asymmetric unit of the title compound, C8H3BrN2, consists of two mol­ecules. The crystal structure features undulating mol­ecular sheets with the mol­ecules linked by C—H⋯N hydrogen bonds with one N atom acting as a bifurcated acceptor. N⋯Br inter­actions also occur [N⋯Br = 2.991 (3) and 3.099 (3) Å]. Inter­layer association is accomplished by offset face-to-face arene inter­actions [centroid–centroid distance = 3.768 (4) Å].

Investigating the structure of biomass-derived non-graphitizing mesoporous carbons by electron energy loss spectroscopy in the transmission electron microscope and X-ray photoelectron spectroscopy

We have investigated the microstructure and bonding of two biomass-based porous carbon chromatographic stationary phase materials (alginic acid-derived Starbon® and calcium alginate-derived mesoporous carbon spheres (AMCS)) and a commercial porous graphitic carbon (PGC), using high resolution transmission electron microscopy, electron energy loss spectroscopy (EELS), N2 porosimetry and X-ray photoelectron spectroscopy (XPS). The planar carbon sp2-content of all three material types is similar to that of traditional non-graphitizing carbon although, both biomass-based carbon types contain a greater percentage of fullerene character (i.e. curved graphene sheets) than a non-graphitizing carbon pyrolyzed at the same temperature. This is thought to arise during the pyrolytic breakdown of hexauronic acid residues into C5 intermediates. Energy dispersive X-ray and XPS analysis reveals a homogeneous distribution of calcium in the AMCS and a calcium catalysis mechanism is discussed. That both Starbon® and AMCS, with high-fullerene character, show chromatographic properties similar to those of a commercial PGC material with extended graphitic stacks, suggests that, for separations at the molecular level, curved fullerene-like and planar graphitic sheets are equivalent in PGC chromatography. In addition, variation in the number of graphitic layers suggests that stack depth has minimal effect on the retention mechanism in PGC chromatography.

Room-Temperature Ceramic Nanocoating Using Nanosheet Deposition Technique

We present a novel procedure for ceramic nanocoating using oxide nanosheet as a building block. A variety of oxide nanosheets (such as Ti1−δO2, MnO2 and perovsites) were synthesized by delaminating appropriate layered precursors into their molecular single sheets. These nanosheets are exceptionally rich in both structural diversity and electronic properties, with potential applications including conductors, semiconductors, insulators, and ferromagnets. Another attractive aspect is that nanosheets can be organized into various nanoarchitectures by applying solution-based synthetic techniques involving electrostatic layer-by-layer assembly and Langmuir-Blodgett deposition. It is even possible to tailor superlattice assemblies, incorporating into the nanosheet galleries with a wide range of materials such as organic molecules, polymers, and inorganic/metal nanoparticles. Sophisticated functionalities or paper-like devices can be designed through the selection of nanosheets and combining materials, and precise control over their arrangement at the molecular scale.

Structural changes in the molecular sheets along (hk0) planes derived from cellulose Iβ by molecular dynamics simulations

We studied the stability of molecular sheets with four cellotetraoses in an aqueous environment by molecular dynamics simulation to identify the molecular details of first structure as one of the possibilities in the course of crystallization of cellulose I. After simulation, the molecular sheets formed by van der Waals forces along the (110) and (110) crystal plane did not change their structures in an aqueous environment, whereas the other ones formed by hydrogen bonds along the (100) and (200) crystal plane changed into a van der Waals associated molecular sheet, similar to the former. These simulated molecular sheets formed by van der Waals forces were structurally stable in water because of their hydrophilic exterior and hydrophobic interior. Therefore, if the molecular sheet structures are formed in the real system, the sheets formed by van der Waals forces are probably the initial structure of crystallization. A close analysis indicated that these sheets could be classified into two groups in terms of the hydrogen bonding networks, camber angle, and main and side chain conformations. One group was the molecular sheets corresponding to the (110) after simulation. This sheet is probably rigid because intramolecular hydrogen bonds of the chains in the sheet are highly developed. The other group was the molecular sheets corresponding to (200), (100), and (110) crystal plane: the chains in these sheets seemed to be rather flexible due to their moderately developed intramolecular hydrogen bonds.