Synthesis and UV absorption properties of 5-sulfosalicylate-intercalated Zn-Al layered double hydroxides

5-sulfosalicylic acid (SSA) anions have been intercalated into layered double hydroxides (LDHs) by an anion-exchange reaction using ZnAl-NO₃-LDHs as a precursor. The samples were characterized by XRD, FT-IR, TG-DTA/MS and UV-visible spectroscopy. The results show that the NO₃⁻ anions in the precursor have been completely replaced by SSA anions to give ZnAl-SSA-LDHs having a high degree of crystallinity. Detailed studies reveal the existence of a supramolecular structure in ZnAl-SSA-LDHs involving electrostatic attraction between opposite charges, hydrogen bonding and other weak chemical bonding interactions between host layers and SSA anions. The thermal stability of ZnAl-SSA-LDHs is considerably enhanced compared with that of a mixture of ZnAl-NO₃-LDHs and SSA. After addition of 2.0 wt% ZnAl-SSA-LDHs to polypropylene (PP), the resistance of the polymer to UV degradation is significantly improved.     

Supramolecular polymer/metal salt complexes containing quadruple hydrogen bonding units

A supramolecular material containing quadruple hydrogen bonding sites was prepared by reacting the amines of methyl isocytosine and the epoxy groups of poly (ethylene glycol diglycidyl ether). This supramolecular polymer was complexed with metal salt, that is potassium iodide, to produce polymer electrolytes, and their physical properties, specific interactions, and conductivity behavior were investigated. The ionic conductivity of polymer electrolytes continuously increased with increasing salt concentration up to 0.4 of salt weight fraction, presenting usually high solubility limit of salt in the supramolecular polymer. Wide angle X‐ray scattering data also presented that the metal salt was completely dissolved in the supramolecular polymer up to 0.4 of salt weight fraction. Upon the introduction of metal salt, the mechanical properties of the supramolecular polymer were significantly enhanced by around 10 times and the glass transition temperature of the polymer increased by about 50 °C, as revealed by complex melt viscosities and differential scanning calorimetry. These unusual behaviors of salt solubility and mechanical properties for supramolecular polymer/metal salt complexes were attributed to the strong, additional metal ion coordination to hydrogen bonding sites as well as ether oxygens of polymer matrix, as supported by FTIR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3181–3188, 2007     

Quadruple hydrogen bonding containing supramolecular thermoplastic elastomers: Mechanical and morphological correlations

We report the design of bioinspired, reversible supramolecular thermoplastic elastomers (TPEs) functionalized with ureido‐cytosine (UCyt) complementary quadruple hydrogen bonding (QHB) sites. The polymer contained a soft poly(n‐butyl acrylate) central block that imparted flexibility and two external, hard nucleobase‐containing blocks that contributed to structural integrity. In addition, the hard block with pendant QHB motifs served as efficient physical crosslinks to further enhance the thermomechanical performance, where the polymer service window extended up to 30 °C higher compared to the controls that bear dimeric hydrogen bonding units. The resulting UCyt copolymers also exhibited improved surface and bulk morphology, which self‐assembled into well‐ordered lamellar microstructures. Moreover, the polymer displayed an unexpected moisture‐resistant property with less than 1 wt % equilibrium moisture uptake even at 95% relatively humidity, which presumably correlated with its well‐ordered and densely‐packed morphology facilitated by strong hydrogen bonding. Variable temperature Fourier‐transform infrared spectroscopy experiments further confirmed the thermoreversibility of hydrogen bonding, indicating melt‐processablility and recyclability of the polymer. These physical properties verified quadruple bonding dominated behavior, and structure–property–morphology relationships suggest key design parameters for future TPEs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 13–23     

Chiral supramolecular metal-organic architectures from dinuclear copper complexes

Two new chiral dinuclear Cu(II) complexes [Cu₂(μ-Cl)₂(HL¹)₂] · C₂H₅OH (1) and [Cu₂(μ-Cl)₂(HL²)₂] · CH₃OH (2), have been synthesized and structurally characterized, where the chiral ligands H₂L¹ and H₂L² are derived from the chiral amino alcohols (S)-(−)-2-amino-3-phenyl-1-propanol and (S)-(+)-2-phenylglycinol. Single-crystal X-ray crystallographic analyses revealed that in these complexes, the dominant hydrogen bonding property of metal bound chloride anion directs the self assembly of complex molecules through C–H···Cl hydrogen bonding interactions leading to the formation of intriguing hydrogen bonded metallo-supramolecular architectures in their respective crystal lattices. The supramolecular systems described here belong to the rare class of metal-organic architectures that are formed as a result of metal directed hydrogen bonding interactions among chiral complex molecules. Complexes 1 and 2 are further characterized by IR, ESR, UV–Vis and CD spectroscopy.     

A pseudo‐quadruple hydrogen‐bonding motif consisting of six N—H⋯O hydrogen bonds in trimethoprim formate

The title compound, trimethoprim (TMP) formate [systematic name: 2,4‐di­amino‐5‐(3,4,5‐tri­methoxy­benzyl)­pyrimidin‐1‐ium formate], C₁₄H₁₉N₄O₃⁺·CHO₂^?, reveals a pseudo‐quadruple hydrogen‐bonding motif consisting of six N—H?O hydrogen bonds involving two unpaired TMP cations and two formate anions which are symmetrically disposed. The hydrogen‐bonding motif is strikingly comparable with that observed in other TMP salts where the amino­pyrimidine moieties of the TMP cations are centrosymmetrically paired. These conserved hydrogen‐bonding motifs may serve as robust synthons in crystal engineering and design. The characteristic pseudo‐quadruple hydrogen‐bonding motif and other intermolecular hydrogen bonds operating in the crystal form a two‐dimensional supramolecular sheet structure.     

Determination of benzimidazolic fungicides in fruits and vegetables by supramolecular solvent-based microextraction/liquid chromatography/fluorescence detection

A supramolecular solvent consisting of vesicles, made up of equimolecular amounts of decanoic acid (DeA) and tetrabutylammonium decanoate (Bu₄NDe), dispersed in a continuous aqueous phase, is proposed for the extraction of benzimidazolic fungicides (BFs) from fruits and vegetables. Carbendazim (CB), thiabendazole (TB) and fuberidazole (FB) were extracted in a single step and no clean-up or concentration of extracts was needed. The high extraction efficiency obtained for BFs was a result of the different types of interactions provided by the supramolecular solvent (e.g. hydrophobic and hydrogen bonds) and the high number of solubilisation sites it contains. Besides simple and efficient, the proposed extraction approach was rapid, low-cost, environment friendly and it was implemented using conventional lab equipments. The target analytes were determined in the supramolecular extract by LC/fluorescence detection. They were separated in a Kromasil C₁₈ (5 μm, 150 mm × 4.6 mm) column using isocratic elution [mobile phase: 60:40 (v/v) 50 mM phosphate buffer (pH 4)/methanol] and quantified at 286/320 nm (CB) and 300/350 nm (TB and FB) excitation/emission wavelengths, respectively. Quantitation limits provided by the supramolecular solvent-based microextraction (SUSME)/LC/fluorescence detection proposed method for the determination of CB, TB and FB in fruits and vegetables were 14.0, 1.3 and 0.03 μg kg⁻¹, respectively, values far below the current maximum residue levels (MRLs) established by the European Union, i.e. 100-2000 μg kg⁻¹ for CB, 50-5000 μg kg⁻¹ for TB and 50 μg kg⁻¹ for FB. The precision of the method, expressed as relative standard deviation, for inter-day measurements (n = 13) was 3.3% for CB (50 μg kg⁻¹), 3.5% for TB (10 μg kg⁻¹) and 2.8% for FB (0.5 μg kg⁻¹) and recoveries for fruits (oranges, tangerines, lemons, limes, grapefruits, apples, pears and bananas) and vegetables (potatoes and lettuces) fortified at the μg kg⁻¹ level were in the interval 93-102%.     

A thallium(I) tetranuclear cubic cage unit in an interpenetrated supramolecular polymer: A new precursor for the preparation of Tl2O3 nanostructures

A new thallium(I) supramolecular polymer, [Tl₄(μ₃-4-BN)₄]_n (1) [9-HBN = 4-hydroxy benzonitrile], with a disordered cubic cage structural unit has been synthesized and characterized. The single-crystal X-ray data of compound 1 shows one type of Tl^I ion in the tetranuclear cubic cage structure with a coordination number of three. In addition to two intra cage thallophilic interactions in 1, each thallium(I) atom has a weak Tl?N secondary interaction with the nitrile group of the 4-BN⁻ ligand. Finally the Tl-ions attain the O₃Tl?NTl₂ coordination sphere with a stereo-chemically ‘active’ electron lone pair on the metal. The self assembly between the benzonitrile groups of one cubic cage structure with an adjacent one with a Tl?N short contact, by π-π stacking and weak hydrogen bonding interactions, results in the formation of a new interpenetrating thallium(I) supramolecular polymer. The thermal stability of 1 was studied by thermo gravimetric (TG) and differential thermal analyses (DTA). Nanostructures of thallium(III) oxide were prepared from a calcination process of compound 1 fine powder at 743 K. These nanostructures were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).     

Effect of pendant arm position and length on the structure and properties of nickel aromatic dicarboxylate coordination polymers incorporating a kinked organodiimine

Hydrothermal synthesis has afforded three nickel coordination polymers incorporating both aromatic dicarboxylates and the kinked and hydrogen bonding capable organodiimine 4,4′-dipyridylamine (dpa). These were characterized by single-crystal X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis. [Ni(1,2-phda)(dpa)(H₂O)]_n (1,2-phda = 1,2-phenylenediacetate, 1) displays (4,4) rhomboid grid-like 2D layers that aggregate into 3D through O–H?O hydrogen bonding. Shortening one of the pendant arms of the dicarboxylate ligand resulted in a shift to (6,3) herringbone style 2D coordination layer motifs in {[Ni(hmph)(dpa)] · 1.33H₂O}_n (hmph = homophthalate, 2), which stack in an AA′B pattern. [Ni(1,3-phda)(dpa)(μ-H₂O)_0.5]_n (1,3-phda = 1,3-phenylenediacetate, 3) manifests a canted primitive cubic type coordination polymer lattice constructed from dinuclear {Ni₂(μ-H₂O)} kernels linked into 3D through tethering 1,3-phda and dpa ligands. Analysis of the variable temperature magnetic susceptibility of 3 indicated the presence of antiferromagnetic superexchange within its dinuclear units (g = 2.290(2), J = −4.21(2) cm⁻¹).     

Carboxylic acid to thioamide hydrogen bonding

The lactam groups of dipyrrinones avidly engage in amide-amide hydrogen bonding to form dimeric association complexes in non-polar solvents (in CHCl₃, K_D ∼25,000 M⁻¹ at 22 °C). The corresponding thioamides (dipyrrinthiones), prepared from dipyrrinones by reaction with Lawesson's reagent, also form intermolecularly hydrogen-bonded dimers in non-polar solvents, albeit with much weaker association constants (in CHCl₃, K_D ∼200 M⁻¹ at 22 °C). When a carboxylic acid group is tethered to C(9) of the dipyrrinone, as in the hexanoic acid of [6]-semirubin, tight intramolecular hydrogen bonding between the carboxylic acid group and the lactam moiety (intramolecular K_assoc ?25,000) is found in CHCl₃ with no evidence of dimers. In contrast, the analogous dipyrrinthione, [6]-thiosemirubin, eschews intramolecular hydrogen bonds, as determined using NMR spectroscopy and vapor pressure osmometry, preferring to form intermolecularly hydrogen-bonded dimers of the thioamide-thioamide type.     

Enhanced gelation property due to intra-molecular hydrogen bonding in a new series of bis(amino acid)-functionalized pyridine-2,6-dicarboxamide organogelators

A series of pyridine-2,6-dicarboxamide derivatives containing two α-amino acid pendant groups was prepared and characterized. Three of the synthesized compounds obtained from this series, all having aromatic amino acid side chains, were found to be excellent organogelators toward aromatic solvents (mgc∼10-20 mg/mL), alcoholic solvents (mgc∼4-15 mg/mL), and CCl₄ (mgc∼4-10 mg/mL). It was found that the intra-molecular hydrogen bonds between the pyridine dicarboxamide N-Hs and the pyridine N atom were the key structural elements for gel formation. This series of compounds represented one of the rare examples where both inter- and intra-molecular hydrogen bonds were needed for effective gel formation. FTIR, ¹H NMR, and CD spectroscopy revealed that both hydrogen bonding and π-π aromatic stacking were the driving forces for gelation.     

FTIR study on molecular structure of poly(N-isopropylacrylamide) in mixed solvent of methanol and water

The intrachain and interchain hydrogen bonding of poly(N-isopropylacrylamide) (PNIPA) and intermolecular hydrogen bonding between PNIPA chains and the solvent molecules in the mixed solvent of methanol and water have been quantitatively investigated by using Fourier transform infrared (FTIR) spectroscopy at 25 °C. In this spectroscopic system with curve fitting program, we found that in the C-H stretching region, both the N-isopropyl group and the backbone underwent conformational change upon the solvent composition. An analysis of the amide I band suggested that the amide groups of PNIPA were mainly involved in intermolecular hydrogen bonding with water molecules, and the polymer chains were flexible and disordered in the mixed solvent when the methanol volume fraction (χ_v) was lower than 15%. While χ_v was in the range of 15-65%, about 30% of these intermolecular hydrogen bonding between the polymer and water were replaced by intrachain and interchain hydrogen bonding, consequently, PNIPA shrinked as aggregates. If χ_v was above 65%, the interchain hydrogen bonding became predominant due to the solubility characteristics of amphiphilic methanol, and the PNIPA system was homogeneous solution again. We believe that the reentrant transition is related to the weaker interaction between PNIPA molecules and methanol-water complexes, (H₂O)_m(CH₃OH)_n (m/n = 5/1, 5/2, 5/3, 5/4, 5/5) as compared to that between PNIPA and free water or free methanol.     

A second crystal form of [Ni(2,2′-bipyridine)(H2O)3(NO3)](NO3) featuring a different molecular orientation

The molecular structure of a second form of [Ni(2,2′-bipyridine)(H₂O)₃(NO₃)](NO₃) is reported. The previous report is for a blue monoclinic polymorph. The second form is orthorhombic and crystallises as green blocks with unit cell parameters a = 9.1201(12) Å, b = 14.444(2) Å, c = 21.805(4) Å, V = 2872.4(8) Å³, Z = 8. The complex was characterised by elemental analysis, infrared spectroscopy, UV-Vis spectroscopy, and thermogravimetry. The bipyridine acts as a bidentate ligand to Ni²⁺ and the octahedral coordination is completed by three water molecules and one monodentate nitrate ion. A second nitrate forms hydrogen bonds to the bound water molecules. The difference between the two forms in terms of the molecular geometry is described in relation to other similar compounds. The key difference between the two forms is the orientation of the two nitrate anions, and hence the hydrogen bonding present.     

Conformation and coordination of β-diketonates in mixed-ligand copper(II) chelates of 1,2-diamines. Theoretical approach and experimental verification. Crystal structure of [bis(N,N′-dimethyl-1,2-diaminoethane) bis(3-cyano-2,4-pentanedionate)copper(II)]dihydrate

The reaction of the bis(2,4-pentanedionato)copper(II), Cu(acac)₂, and its substituted derivatives (Cu(NC-acac)₂, Cu(O₂N-acac)₂, and Cu(tfac)₂), with 1,2-diaminoethane (en), 1,2-diaminopropane (pn) and certain N-substituted derivatives of 1,2-diaminoethane, enR, is reported. The reaction products were found to depend on the reaction conditions, the extent of N-substitution of the diamine and the nature of the β-diketonate anion, β⁻. The [Cu(enR)β₂] addition compounds are not always sufficiently stable and in most instances the tetragonal species [Cu(enR)₂β₂] prevail as the final product. The 1,2-diamine molecules in [Cu(enR)₂β₂] form chelate rings attaining the gauche conformation while the β-diketonato anions essentially confer electrical neutrality. Density functional theory (DFT) calculations suggest that the active sites of the β-diketonato anion and its conformation depend on their ability to create hydrogen bonds and on the substituents in 3-position. The Fukui indices of chemical reactivity favor the carbonyl oxygens as binding sites of most anions while in the case of the 3-cyano-2,4-pentanedionato anion, NC-acac⁻, bonding through the cyano nitrogen is envisaged with the S(E, Z) conformer having the lowest energy. These findings are in accord with experimental data and further proof is given by single crystal X-ray diffraction analysis of the structure of [Cu(MeenMe)₂(NC-acac)₂] · 2H₂O (MeenMe denoting N,N′-dimethyl-1,2-diaminoethane). In this compound the NC-acac⁻ attains the S(E, Z) conformation and interacts with the square-planar entity [Cu(MeenMe)₂]²⁺ through the cyano nitrogen, while intermolecular hydrogen bonding involving the water molecules leads to supramolecular structure.     

Synthesis of dinitrosyl iron complexes (DNICs) with intramolecular hydrogen bonding

HSCH₂CONHCH₃ and HSCH₂CON(CH₃)₂ containing a peptide bond are prepared for the synthesis of DNICs with/without intra-molecular hydrogen bonding, respectively. The IR ν(NO) bands of [(NO)₂Fe(SCH₂CONHCH₃)₂]⁻ (2) appears at 1751, 1700 cm⁻¹. In complex 2, the presence of intramolecular [NH?S] hydrogen bonding was verified by the observation of IR spectroscopy with N−H stretching frequency 3334 cm⁻¹ (CDCl₃) and subsequently confirmed by single-crystal X-ray diffraction showing N−S distance of 2.94 Å. Complex 2 displays the rhombic EPR spectrum with g₁ = 2.039, g₂ = 2.031 and g₃ = 2.013 at in frozen H₂O. Complexes 2 and 3 rapidly release NO when exposed to light. The time needed for photolysis reactions of 2 is two times faster than that of 3 in less polar solvent. Representative time courses for the photolability of 2 and 3 in THF display the NO-off ability: 2 > 3.     

Halogen Bonding Directed Supramolecular Quadruple and Double Helices from Hydrogen‐Bonded Arylamide Foldamers

Halogen bonding has been used to glue together hydrogen‐bonded short arylamide foldamers to achieve new supramolecular double and quadruple helices in the solid state. Three compounds, which bear a pyridine at one end and either a CF₂I or fluorinated iodobenzene group at the other end, engage in head‐to‐tail N???I halogen bonds to form one‐component supramolecular P and M helices, which stack to afford supramolecular double‐stranded helices. One of the double helices can dimerize to form a G‐quadruplex‐like supramolecular quadruple helix. Another symmetric compound, which bears a pyridine at each end, binds to ICF₂CF₂I through N???I halogen bonds to form two‐component supramolecular P and M helices, with one turn consisting of four (2+2) molecules. Half of the pyridine‐bearing molecules in two P helices and two M helices stack alternatingly to form another supramolecular quadruple helix. Another half of the pyridine‐bearing molecules in such quadruple helices stack alternatingly with counterparts from neighboring quadruple helices, leading to unique quadruple helical arrays in two‐dimensional space.     

Supramolecular solvent-based hollow fiber liquid phase microextraction of benzodiazepines

A new, efficient, and environmental friendly hollow fiber liquid phase microextraction (HF-LPME) method based on supramolecular solvents was developed for extraction of five benzodiazepine drugs. The supramolecular solvent was produced from coacervation of decanoic acid aqueous vesicles in the presence of tetrabutylammonium (Bu₄N⁺). In this work, benzodiazepines were extracted from aqueous samples into a supramolecular solvent impregnated in the wall pores and also filled inside the porous polypropylene hollow fiber membrane. The driving forces for the extraction were hydrophobic, hydrogen bonding, and π-cation interactions between the analytes and the vesicular aggregates. High-performance liquid chromatography with photodiode array detection (HPLC-DAD) was applied for separation and determination of the drugs. Several parameters affecting the extraction efficiency including pH, hollow fiber length, ionic strength, stirring rate, and extraction time were investigated and optimized. Under the optimal conditions, the preconcentration factors were obtained in the range of 112–198. Linearity of the method was determined to be in the range of 1.0–200.0 μg L⁻¹ for diazepam and 2.0–200.0 μg L⁻¹ for other analytes with coefficient of determination (R²) ranging from 0.9954 to 0.9993. The limits of detection for the target benzodiazepines were in the range of 0.5–0.7 μg L⁻¹. The method was successfully applied for extraction and determination of the drugs in water, fruit juice, plasma and urine samples and relative recoveries of the compounds studied were in the range of 90.0–98.8%.     

Orthogonal chain length control in calix[5]arene-based AB-type supramolecular polymers

New AB-type supramolecular polymers have been prepared by acid-promoted self-assembly of an aminododecyloxy-calix[5]arene monomer precursor. The number-average degree of polymerization has been found to be dependent on the concentration of the salt monomer and on the nature of the counterion (i.e., chloride, picrate or hexafluorophosphate).Chain-length regulation experiments have been carried out, employing orthogonal chain stoppers capable of selectively interacting with a given moiety of the AB-type monomer/polymer. Competitive calix[5]arene ‘caps’ and n-butylammonium ion ‘plugs’ have been used to control the extent of self-assembly of the polymer, in turn interacting with the ammoniumdodecyloxy or with the cavity end-groups of the supramolecular calixarene assembly. These experiments, conveniently carried out at a 10 mM concentration, can be easily followed by ¹H NMR spectroscopy.     

Polymeric assembling through reciprocal metal-η-arene π-interactions: Synthesis and X-ray characterization of [Hg(RPhNNNPhR′)2Py]2 (R = NO2, R′ = F), an asymmetric bis diaryl-substituted triazenide-pyridinyl complex of Hg(II)

Hg(SCN)₂ reacts with 3-(2-fluorophenyl)-1-(4-nitrophenyl)triazene in tetrahydrofuran in the presence of triethylamine to give orange crystals of [Hg^II(RPhNNNPhR′)₂Py]₂ (R = NO₂, R′ = F), a new polymeric triazenide-pyridinyl complex of Hg(II) with reciprocal metal-η²-arene π-interactions. The crystal structure belongs to the triclinic space group , and the lattice of [Hg^II(RPhNNNPhR′)₂Py]₂ can be viewed as a supramolecular unidimensional assembling of tectonic [Hg^II(RPhNNNPhR′)₂Py] units linked through intermolecular metal-arene π interactions and non-classical C-H?O hydrogen bonding.     

Synthesis and application of a T-2 toxin imprinted polymer

The synthesis of a T-2 toxin imprinted polymer and its application in food analysis are reported for the first time. A molecularly imprinted polymer (MIP) for the selective recognition of T-2 toxin (T-2) was synthesized by bulk polymerization. Methacrylamide and ethyleneglycol dimethacrylate were applied as functional monomer and cross-linker, respectively. Molecularly imprinted solid-phase extraction (MISPE) procedures were optimized for further application in the analysis of T-2. Scatchard plot analysis revealed that two classes of imprinted binding sites were formed in the imprinted polymer. The dissociation constant (K_D) of the higher affinity binding sites was 7.0 μmol/l, while the K_D of the lower affinity binding sites was 54.7 μmol/l. The performance of the MIP throughout the clean-up of spiked maize, barley and oat sample extracts was compared with the results obtained when using non-imprinted polymer, OASIS HLB^® and immunoaffinity columns (IAC). Depending on the food matrix and the spiked concentration, recoveries after MISPE and non-imprinted solid-phase extraction varied respectively from 60% to 73% and from 21% to 57%. Recoveries obtained after clean-up using OASIS HLB^® and IAC were in the range of 74–104% and 60–85%, respectively. Although highest recoveries were obtained with OASIS HLB^® sorbents, the designed MIP and the IAC were superior regarding selectivity, cross-reactivity, matrix effect, limits of detection (LOD) and limits of quantification (LOQ). Depending on the matrix, LOD after MISPE ranged from 0.4 μg/kg to 0.6 μg/kg and LOQ from 1.4 μg/kg to 1.9 μg/kg. LOD and LOQ after OASIS HLB^® clean-up varied from 0.9 μg/kg to 3.5 μg/kg and from 3.1 μg/kg to 11.7 μg/kg, respectively. The LOD and LOQ values obtained with IAC were in the range of 0.3–2.3 μg/kg and 1.0–7.7 μg/kg, respectively. Analysis of 39 naturally contaminated samples (maize, barley and oat) by liquid chromatography tandem mass spectrometry revealed that the MIP could be an excellent alternative for clean-up of contaminated food samples.     

The effect of the counter anion on the transport of thiourea in a PVC-based polymer inclusion membrane using Capriquat as carrier

This paper describes the effect of four counter anions (CH₃COO⁻, Cl⁻, NO₃⁻, ClO₄⁻) of the trioctylmethylammonium (TOMA) cation on the rate of solvent extraction of thiourea and its transport across poly(vinyl chloride) (PVC)-based polymer inclusion membranes (PIMs). The membranes also contained 2-nitrophenyl octyl ether (NPOE) as the plasticizer while chloroform was used as diluent in the solvent extraction studies. It is demonstrated that the counter anion affects substantially the rate of membrane transport and the degree of extraction follows the order: CH₃COO⁻ > Cl⁻ > NO₃⁻ ? ClO₄⁻. The transport rate is negligible for the perchlorate anion. This order is consistent with thiourea interacting with the counter anion through hydrogen bonding to form a heteroconjugate anion.