Tetrapropylammonium Cations Research Articles

Molecular dynamics simulation of TCDD adsorption on organo-montmorillonite

In this work, molecular dynamics simulation was applied to investigate the adsorption of Tetrachlorodibenzo-p-Dioxin (TCDD) on tetramethylammonium (TMA) and tetrapropylammonium (TPA) modified montmorillonite, with the aim of providing novel information for understanding the adsorptive characteristics of organo-montmorillonite toward organic contaminants. The simulation results showed that on both outer surface and interlayer space of TPA modified montmorillonite (TPA-mont), TCDD was adsorbed between the TPA cations with the molecular edge facing siloxane surface. Similar result was observed for the adsorption on the outer surface of TMA modified montmorillonite (TMA-mont). These results indicated that TCDD had stronger interaction with organic cation than with siloxane surface. While in the interlayer space of TMA-mont, TCDD showed a coplanar orientation with the siloxane surfaces, which could be ascribed to the limited gallery height within TMA-mont interlayer. Comparing with TMA-mont, TPA-mont had larger adsorption energy toward TCDD but smaller interlayer space to accommodate TCDD. Our results indicated that molecular dynamics simulation can be a powerful tool in characterizing the adsorptive characteristics of organoclays and provided additional proof that for the organo-montmorillonite synthesized with small organic cations, the available interlayer space rather than the attractive force plays the dominant role for their adsorption capacity toward HOCs.

Two inclusion compounds of guanylthiourea and 1,3,5-thiadiazole-5-amido-2-carbamate

In the crystal structure of [(n-C4H9)4N]+·[NH2(C2N2S)NHCOO−]·NH2CSNC(NH2)2 (1), guanylthiourea molecules and 1,3,5-thiadiazole-5-amido-2-carbamate ions are joined together by intermolecular N–H…O, N–H…N, and weak N–H…S hydrogen bonds to generate stacked host layers corresponding to the (110) family of planes, between which the tetra-n-butylammonium guest cations are orderly arranged in a sandwich-like manner. In the crystal structure of [(n-C3H7)4N]+·[NH2(C2N2S)NHCOO−]·NH2CSNC(NH2)2·H2O (2), the tetrapropyl ammonium cations are stacked within channels each composed of hydrogen bonded ribbons of guanylthiourea molecules, 1,3,5-thiadiazole-5-amido-2-carbamate ions and water molecules.

ε-Keggin-based coordination networks: Synthesis, structure and application toward green synthesis of polyoxometalate@graphene hybrids

Four coordination networks based on the {ε-PMo(V)(8)Mo(VI)(4)O(40)(OH)(4)Zn(4)} Keggin unit (εZn) have been synthesized under hydrothermal conditions. (TBA)(3){PMo(V)(8)Mo(VI)(4)O(36)(OH)(4)Zn(4)}[C(6)H(4)(COO)(2)](2) (ε(isop)(2)) is a 2D material with monomeric εZn units connected via 1,3 benzenedicarboxylate (isop) linkers and tetrabutylammonium (TBA) counter-cations lying between the planes. In (TPA)(3){PMo(V)(8)Mo(VI)(4)O(37)(OH)(3)Zn(4)}[C(6)H(3)(COO)(3)] (TPA[ε(trim)](∞)), 1D inorganic chains formed by the connection of εZn POMs, via Zn-O bonds, are linked via 1,3,5 benzenetricarboxylate (trim) ligands into a 2D compound with tetrapropylammonium (TPA) cations as counter-cations. (TBA){PMo(V)(8)Mo(VI)(4)O(40)Zn(4)}(C(7)H(4)N(2))(2)(C(7)H(5)N(2))(2)·12H(2)O (ε(bim)(4)) is a molecular material with monomeric εZn POMs bound to terminal benzimidazole (bim) ligands. Finally, (TBA)(C(10)H(10)N(4))(2)(HPO(3)){PMo(V)(8)Mo(VI)(4)O(40)Zn(4)}(2)(C(10)H(9)N(4))(3)(C(10)H(8)N(4)) (ε(2)(pazo)(4)) is a 1D compound with dimeric (εZn)(2) POMs connected by HPO(3)(2-) ions and terminal para-azobipyridine (pazo) ligands. In this compound an unusual bond cleavage of the central N[double bond, length as m-dash]N bond of the pazo ligand is observed. We report also a green chemistry-type one-step synthesis method carried out in water at room temperature using ε(2)(pazo)(4) and ε(isop)(2) as reducing agent of graphite oxide (GO) to obtain graphene (G). The POM@G hybrids were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, powder X-ray diffraction, energy dispersive X-ray analysis, infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and cyclic voltammetry.

Two‐Step Electrochemically Directed Synthesis of Pr4N(TCNQ)n(n=1, 2): Preparation, Structure, and Properties of a Magnetically Isolated Dimer and a Quasi‐One‐Dimensional Chain

Solid-state electrochemistry of a tetracyanoquinodimethane (TCNQ)-modified electrode in contact with a tetrapropylammonium cation (Pr(4)N(+)) electrolyte showed two electron-transfer steps to give Pr(4)N(TCNQ)(2) (1) and Pr(4)N(TCNQ) (2) rather than the traditional one-electron step to directly give Pr(4)N(TCNQ). Two thermodynamically stable Pr(4)N(+)-TCNQ stoichiometries, 1 and 2, were synthesized and characterized. The degree of charge transfer (ρ) calculated from the crystal structure is -0.5 for the TCNQ moieties in 1 and -1.0 for those in 2. Raman spectra for Pr(4)N(TCNQ)(2) show only one resonance for the extracyclic C=C stretching at 1423 cm(-1), which lies approximately midway between that of TCNQ at 1454 cm(-1) and TCNQ(-) at 1380 cm(-1). Both the magnetic susceptibility and EPR spectra are temperature-dependent, with a magnetic moment close to that for one unpaired electron per (TCNQ)(2) unit in 1, whereas 2 is almost diamagnetic. Pressed discs of both complexes show conductivity (1-2×10(-5) S cm(-1)) in the semiconductor range. For 1, the position of zero current for the steady-state voltammograms implies 50% of TCNQ(-) and 50% TCNQ(0) is present in solution, thereby supporting a dissociation of (TCNQ)(2)(-) in solution, but is indicative of only TCNQ(-) being present for 2.

In Situ PFG NMR of Silicalite-1 Synthesis Mixtures

The interactions between tetrapropylammonium cations and the silica nanoparticles present in silicalite-1 precursor solutions were characterized at 70 °C using in situ pulsed field gradient (PFG) NMR experiments. In situ PFG NMR results show that the organocation diffusion coefficients at 70 °C are larger than those at 25 °C. Although the adsorption isotherms calculated from the diffusion data present similar trends at both temperatures, the adsorption isotherms at 70 °C could not be accurately described using a Lineweaver–Burk analysis. Therefore, the Freundlich equation was used to fit the adsorption data and Gibbs free energies between 6 and 15 kJ/mol were obtained. Time evolution studies show that organocation diffusion coefficients increased with the time, reached a maximum at about 6 days, and trended to a plateau towards the end of the synthesis. This maximum in the diffusion coefficient of the organocation coincides in time with the exothermic–endothermic transition that is known to occur near the...

Hierarchically Porous ZSM-5 Synthesized by Nonionic- and Cationic-Templating Routes and Their Catalytic Activity in Liquid-Phase Esterification

Hierarchically porous MFI zeolites (ZSM-5) have been synthesized by hydrothermal treatment in the presence of trialkoxysilylated-derivatives of nonionic poly(oxyethylene) alkyl ether or alkyl quaternary ammonium cation as mesopore-generating agent, along with tetrapropylammonium cation as zeolite structure-directing agent. Powder X-ray diffraction revealed that zeolites have been crystallized, and scanning electron microscopy showed rugged surface morphology that was quite different from conventional ZSM-5. The mesoporosity was confirmed by nitrogen adsorption-desorption measurement showing type IV isotherms with narrow distribution of mesopore diameters. The catalytic activity of these mesoporous ZSM-5 was tested in liquid-phase esterification of benzyl alcohol with hexanoic acid. The conversion of benzyl alcohol on mesoporous ZSM-5 prepared via cationic-templating route was almost 100%, being much higher than on mesoporous ZSM-5 prepared with silylated nonionic surfactant as well as on conventional ZSM-5 with no mesopores. The presence of Bronsted acid sites, together with the mesopores, was responsible for this catalytic conversion, as confirmed by pyridine adsorption monitored by in situ infrared and 27 Al magic angle spinning nuclear

Pulsed Field Gradient NMR Investigations of Alkyltripropylammonium−Silica Mixtures

Pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy has been used to study the organocation−silica interactions in silica−alkyltripropylammonium solutions. Mixtures containing silica and methyltripropylammonium, ethyltripropylammonium, and tetrapropylammonium cations have been investigated to determine how the organocation structure and hydrophobicity affect organocation−silica interactions. PFG NMR results show that, in the presence of silica, the diffusion coefficients of the tetraalkylammonium organocations decreased compared with those of the cations in water alone. This decrease is attributed to a reduction in the cation mobility as the cations interact with the silica nanoparticles. The diffusion coefficients as a function of the organocation concentration were measured to determine the fraction of organocations bound to the silica through a model that considers the cation in either a free or a bound state. The resulting adsorption isotherms were fit with the Langmuir model, from which the free energy of binding was determined to be between 10 and 13 kJ/mol. This value appeared insensitive to the organocation identity and the silica content of the mixture, although the most hydrophilic cation had the highest binding energy. The results show that the organocation−silica interactions play an important role in zeolite formation and can help to develop a more general approach to making high-silica zeolites from optically transparent mixtures containing silica nanoparticles.

Synthesis of silicalite-1 using a disiloxane-based structure-directing agent

A cationic organosiloxane compound where two tetrapropylammonium (TPA) cations are bridged by a tetramethyldisiloxane unit (MSi-TPA) has been used as a structure-directing agent (SDA) for the synthesis of a pure silica MFI-type zeolite, silicalite-1, with a unique microstructure and particle morphology. The hydrothermal treatment of the mixture of tetraethoxysilane as a silica source, MSi-TPAOH, and water yields solid products that are identified as silicalite-1 by X-ray diffraction and solid-state 29Si MAS NMR. Solid-state 29Si and 13C CP/MAS NMR and elemental analyses confirm that MSi-TPA is covalently incorporated in the MFI framework via cleavage of the disiloxane linkage. Compared with conventional silicalite-1 prepared with TPA cations, the amount of defect sites is higher, which can be attributed to the attachment of the organosilyl groups to the framework by Si–O–Si bonds. Scanning electron microscopic (SEM) observation shows spherical particle morphology that is quite different from the typical coffin-shaped crystals obtained with TPA. Importantly, MFI is not formed when triethoxysilyl- and diethoxysilyl-TPAs, instead of MSi-TPA, are used as SDAs under similar conditions, suggesting that the possible number of Si–O–Si linkages formed by SDAs greatly affects the crystallization process of MFI zeolite.

ChemInform Abstract: Novel Large‐Pore Aluminophosphate Molecular Sieve STA‐15 Prepared Using the Tetrapropylammonium Cation as a Structure Directing Agent.

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The Influence of short-chain tetraalkylammonium cations on the recrystallization of magadiite into zeolites

A study on magadiite recrystallization is undertaken to relate the influence of short-chain tetraalkylammonium (TAA +) cations to the zeolite obtained. Using different types of short-chain TAA + cations under various reactant conditions, OFF, MOR and MFI zeolites are obtained respectively. The infrared spectroscopy (IR), N 2 adsorption analysis, thermogravimetry and differential thermal analysis (TG/DTA) of MOR zeolite in the presence or absence of tetraethylammonium (TEA +) cations are carried out for comparison purpose; these results elucidate that TEA + cations exist in the micropore of MOR zeolite. The roles of TAA + cations in the recrystallization of magadiite into zeolites are systematically investigated. It is possible that OFF zeolite could be prepared easily when a small quantity of tetramethylammonium (TMA +) cations are used and TEA + cations interact strongly with MOR zeolite framework. The influence of tetrapropylammonium (TPA +) cations and tetrabutylammonium (TBA +) cations is structure directing on the magadiite recrystallization.

PFG NMR Investigations of Tetraalkylammonium−Silica Mixtures

The results from PFG NMR studies of several tetraalkylammonium−silica mixtures are reported. pH data of these mixtures correlate well with previously reported literature. 1H NMR shows line broadening and shifting of resonances for hydrogen atoms on the periphery of the TAA cations as the silica content is increased. Transverse relaxation measurements show a strong correlation with the pH data in that T2 decreases strongly until the silica critical aggregation concentration (cac) is reached at which point the T2 plateaus. These results point to organocation−silica interactions, which were quantified by using pulsed-field gradient NMR. The self-diffusion coefficient of a series of TAA cations in the presence of silica were measured, and a systematic decrease of the diffusion coefficient is observed as the cation/silica ratio decreases. Subsequent analysis gives confidence that the diffusion behavior of the TAA cations can be described as a two-state system, where cations are either free in solution or bound to the silica nanoparticles in the mixture. On the basis of this binding isotherms can be constructed and binding energies can be determined. These values are in the range of −10 to −14 kJ/mol, with tetramethylammonium on the high end and tetrapropylammonium cations on the low end. One conclusion drawn from this work is that the more hydrophilic TMA cations associate more strongly with the silica nanoparticles than TPA. The investigation shows that PFG NMR is a powerful tool for investigating these clear mixtures, and the results are discussed in the context of zeolite nucleation and growth.

Studies on formation of hollow silicalite-1 microcapsules

In the present work, the detailed formation process of hollow silicalite-1 microcapsules (HSMs) was investigated in the hydrothermal system of silicalite-1 pre-seeded mesoporous silica spheres (MSSs). The effects of the starting gel composition together with the hydrothermal synthesis conditions such as alkalinity, tetra-propylammonium cation (TPA +) content, and temperature on the features of microcapsules are comprehensively discussed, and a related mechanism is presented. It is found that the matching of core dissolution rate ( R cd) and silicalite-1 shell inter-growth rate ( R si) is crucial for the formation of perfect HSMs. The proper addition of tetraethoxy-orthosilane (TEOS) as supplemental silica source could accelerate R si whereas excess TEOS will dramatically suppress the consumption of siliceous species from the MSS cores owing to the higher activity of siliceous species in TEOS for the zeolite crystallization. The excellent HSMs with dense inter-grown shell structure as well as perfect hollow center can be fabricated by controlling the relative rates of the dissolution of silica template core and the formation of zeolitic shell.

Evolution of Surface Morphology with Introduction of Stacking Faults in Zeolites

This paper sets out to try to determine some of the nanoscopic details of template action in zeolites. The problem has been addressed by monitoring the effects of competitive templating using, in particular, atomic force microscopy and high-resolution scanning electron microscopy. Using these techniques, it is possible to determine the subtle crystal growth changes that occur as a result of altering the concentration of these competitive templating agents. This work concerns the two important intergrowth systems MFI-MEL and FAU-EMT. It was found that some organic templating agents provide much greater structure-directing specificity. So much so in the case of the MFI-MEL system that a 2 mol% doping with the highly specific tetrapropylammonium cation drastically changes the fundamental growth processes. Furthermore, the effect of template crowding is shown to reduce specificity. This work shows how extensive frustrated intergrowth structures can still be accommodated within a nominal zeolite single crystal.

Self-assembly of a novel functional molecule: 1,2,4,5-tetra( p-hydroxyphenyl)benzene

A new rigid tetraaryl-substituted benzene, 1,2,4,5-tetra( p-hydroxyphenyl)benzene (C 30H 22O 4, TetHPB), has been synthesized. Its crystalline hydrate C 30H 22O 4·2H 2O ( 1) and the inclusion compound of its anions with the tetrapropylammonium cations, [(C 30H 21O 4) 2H] −·( n-C 3H 7) 4N + ( 2), have been prepared and characterized by single crystal X-ray diffraction. The results of the structural study show that the four peripheric para hydroxyl benzene rings of the TetHPB molecules twist around the aryl–aryl bonds and adopt an X-shaped configuration thus avoiding steric congestion. In the crystal structure of 1 hydrogen-bonded TetHPB chains are connected to a 3D architecture by hydrogen bonds mediated through the solvent water molecules and by C–H… π interactions. In compound 2, the TetHPB anions construct an anionic arrangement based on O–H…O hydrogen bonds. The resulting host contains cavities which accommodate the tetrapropylammonium cations, thus forming a channel-like inclusion compound. These results demonstrate that TetHPB molecules allow to construct hydrogen-bonded networks with cavities; co-crystallized water molecules may cooperate in the formation of these extended structures.

Novel Large-Pore Aluminophosphate Molecular Sieve STA-15 Prepared Using the Tetrapropylammonium Cation As a Structure Directing Agent

The novel aluminophosphate STA-15 (St Andrews microporous solid-15) is prepared by hydrothermal synthesis in the presence of tetrapropylammonium hydroxide (TPAOH), which acts as a structure directing agent. The crystallization is accelerated by the addition of low concentrations of tetraphenylphosphonium or other bulky organic cations, and the purity is improved by the addition of silica to the gel, but these additives are not included in the final crystalline product. The structure of STA-15 was solved by a combination of synchrotron X-ray powder diffraction and modeling. The as-prepared form of STA-15 (Iba2, a = 14.7953(1) A, b = 27.3634(3) A, c = 8.34464(6) A at 100 K) has unit cell composition Al32P32O128(OH)1.8TPA1.8·3H2O. It has a system of one dimensional channels, limited by strongly elliptical 12-membered rings (12 tetrahedral cations and 12 oxygen atoms, 8.7 × 5.7 A ) in which the TPA+ cations reside. The charge-balancing hydroxide ions are coordinated to framework Al, as shown by 27Al and 31P M...

Specificity of Ion−Protein Interactions: Complementary and Competitive Effects of Tetrapropylammonium, Guanidinium, Sulfate, and Chloride Ions

The interactions of ions with a model peptide (a single melittin alpha-helix) in solutions of tetrapropylammonium sulfate or guanidinium chloride were examined by molecular dynamics simulations. The tetrapropylammonium cation shares the geometrical property of essentially flat faces with the previously examined guanidinium cation, and it was found that that this geometry leads to a strong preference for tetrapropylammonium to interact in a similar stacking-type fashion with flat nonpolar groups such as the indole side chain of tryptophan. In contrast to guanidinium, however, tetrapropylammonium does not exhibit strong ion pairing or clustering with sulfate counterions in the solution. Sulfate was found to interact almost exclusively and strongly with the cationic groups of the peptide, such that, already in a 0.1 m solution of tetrapropylammonium sulfate, the 6+ charge of the peptide is effectively locally neutralized. In combination with previous simulations, neutron scattering studies, and experiments on the conformational stability of model peptides, the present results suggest that the Hofmeister series can be explained in higher detail by splitting ions according to the effect they have on hydrogen bonding, salt bridges, and hydrophobic interactions in the protein and how these effects are altered by the counterion.

Transport properties of Nafion membranes modified with tetrapropylammonium ions for direct methanol fuel cell application

This work presents a study of transport properties (proton conductivity, methanol permeability, and water uptake) and acid-base properties of commercial Nafion-112, -115, and -117 membranes modified with tetrapropylammonium (TPA) cations. In the interaction between TPA hydroxide and protons of sulfonate groups in the Nafion matrix, some of the protons are shown to be bound to sulfonate groups and do not participate in transport processes. These findings are confirmed by IR spectroscopy, acid-base titration, and data on proton conductivity of the modified membranes. Proton conductivity of the modified membranes is shown to be effectively described by a percolation model with parameters that agree with published data for commercial Nafion membranes. Based on these results, a model is proposed for the interaction of TPA cations with the sulfonate groups in Nafion membranes. According to this model, TPA cations form hydrophobic clusters in hydrophilic regions of the polymer matrix, thus preventing some of the protonated sulfonate groups from participating in transport processes.

From ill-resolved atomic to ZSM-5 type of ordering in mesoporous lamellar aluminosilica nanoparticles

Mesoporous lamellar aluminosilicate–surfactant nanoparticles as small as 50 nm can be hydrothermally synthesized at 140 °C using a mixture of cationic and anionic surfactants as a templating agent and tetrapropylammonium cations (TPA+), known to be the structure directing agent of the MFI type of zeolite. The nanophases exhibit some ill-resolved atomic ordering after 1 to 3 d of crystallization. A definitive ZSM-5 ordering occurs for longer crystallization times, concomitant with a progressive contraction of the lamellar array. In most cases, calcination at 550 °C leads to a collapse of the lamellar structure, while the zeolitic ordering is preserved. For short crystallization times, the lamellar structure with its atomic ordering is maintained when the aluminium source is the nitrate salt, instead of Al(OH)3 or Boehmite. Then, after 3 d of crystallization, highly porous systems are produced with a surface area of ∼650 m2 g−1 and pore volume of ∼1.1 cm3 g−1. For longer crystallization time, the collapse of the lamellar phase under calcination does not affect the well-defined ZSM-5-like atomic ordering and leads to non-faceted nanoparticles of ca. 200 nm size with rugged shapes. These conclusion are supported by cross investigations using X-ray diffraction patterns, infrared spectra, scanning electron microscopy and high-resolution transmission electron microscopy with selected area electron diffraction. The ordering of the inorganic sheet of the aluminosilicate–surfactant mesophase is likely favoured by the high diffusion rate of TPA+ in the nanosized particles.

Influence of tetralkylammonium cations on the formation of silicoaluminophosphates CAL-2

SAPO molecular sieves were synthesized under hydrothermal conditions from gels containing AlPO-kanemite, silica and a series of four tetralkylammonium (TAA +) salts. The influence of each of the tetralkylammonium cations on the molecular sieve syntheses was studied at constant SiO 2/Al 2O 3 and TAA +/SiO 2 molar ratios of 1.0. The obtained materials were characterized by typical physico-chemical techniques for solid materials such as powder X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), thermal analysis (thermogravimetry), elemental analysis (CHN), scanning electron microscopy (SEM) and multinuclear 13C- and 29Si-solid state nuclear magnetic resonance. A theoretical evaluation of the n-butylammonium conformers, energy of interconversion and molecular sizes, was useful to understand the behavior of each system containing different SDA’s. Thus different structures were obtained depending on the TAA + cation used: in the case of tetramethylammonium the sodalite structure was prepared, tetraethylammonium and tetrapropylammonium cations on the other hand, directed the formation of chabazite structures and for the tetrabutylammonium cation the layered structure of the reactant was not changed. The presence of silicon islands is clear and is an important part of this work. 29Si-solid state nuclear magnetic resonance, elemental analysis of C, H and N and energy dispersive spectroscopy (EDS) techniques were all applied to characterize this aspect.

Multiple functions of ionic liquids in the synthesis of three-dimensional low-connectivity homochiral and achiral frameworks.

Multiple functions of ionic liquids in the synthesis of three-dimensional low-connectivity homochiral and achiral frameworks.