Tetrabutylammonium Salts Research Articles

Synthesis of Cu (II) and Zn (II) Complexes of a Quinoline Based Flexible Amide Receptor as Fluorescent Probe for Dihydrogen Phosphate and Hydrogen Sulphate and Their Antibacterial Activity.

A novel 8-hydroxy quinoline-derived amide receptor, in conjunction with its Cu (II) and Zn (II) complexes, has been strategically developed to function as remarkably efficient fluorescent receptors with a distinct capability for anion sensing. The comprehensive characterization of the synthesized compounds were achieved through UV-Vis, IR, NMR, and HRMS spectroscopic techniques. Among the Cu (II) and Zn (II) complexes, the latter exhibits superior selectivity for anions, specifically dihydrogen phosphate and hydrogen sulfate, as their tetrabutylammonium salts in a 9:1 acetonitrile-water (v/v) mixture. The Cu (II) complex demonstrates enhanced anion binding compared to the amide ligand, albeit with reduced selectivity. Furthermore, the affinity was evaluated using the Benesi-Hildebrand plot. The binding constants and Limit of Detection (LOD) for both complexes were precisely quantified. The Job plot illustrates a clear 1:1 binding interaction between the metal complexes and the guest anions. Significantly, both metal-complex receptors display a broad spectrum of antibacterial activity, against both gram-positive and gram-negative bacteria. It is worth highlighting that the Zn (II) complexed receptor outperforms the Cu (II) complexed receptor, as evidenced by its considerably lower Minimum Inhibitory Concentration (MIC) value against both bacterial strains.

Electrochemistry of tri-N-methylpyridyl porphyrins

Trisubstituted porphyrin derivatives [(TriMPyP)M][Formula: see text]([Formula: see text])3 [Formula: see text][Formula: see text] containing three [Formula: see text]-methyl-4-pyridyl ([Formula: see text][Formula: see text] groups were synthesized and characterized electrochemically and spectroscopically in DMSO containing 0.1 M tetrabutylammonium salts. The effect of specific counter-anions, type of metal ion and number of meso-[Formula: see text][Formula: see text] groups on the redox behavior and spectroscopic properties of the neutral and reduced species are examined before and after controlled potential reduction in a thin-layer cell. Each tri-cationic derivative initially undergoes a global two-electron reduction to give a two-banded absorption spectrum with a broad near-IR band ranging from 750–807 nm depending on the type of metal ion. The position of the near-IR band for the doubly reduced porphyrin was also found to correlate with the number of meso-[Formula: see text][Formula: see text] groups on the macrocycle which varied from 1 to 4 while the first reduction potential remained essentially unchanged upon going from macrocycles with two to three to four meso-[Formula: see text][Formula: see text] groups.

What the anion tells us about the structure of tetrabutylammonium salt/phenol-based deep eutectic solvents? A combined infrared spectroscopic and DFT study

In this study, a series of new Deep Eutectic Solvents (DESs) composed of phenol as the HBD (Hydrogen Bond Donor) and tetrabutyl ammonium (TBA) salts with different molecular anions as HBA (Hydrogen Bond Acceptor) were prepared and investigated using ATR-IR spectroscopy and DFT calculations in order to understand the solvation mechanism at work in these DESs. In particular, the OH stretching mode of phenol is significantly shifted to lower frequencies in the DESs in comparison with that reported for pure phenol. Similarly, characteristic vibrational modes of the anions in the investigated DESs display significant shifts in frequency in comparison with that measured for the pure TBA salt. As a representative example, the frequency shifts observed for the azide anion as a function of the HBA:HBD molar ratio were fully interpreted by the DFT calculations putting in evidence strong hydrogen bonding interactions that occurs between the anion and the phenol molecules. Interestingly, a minimum of the calculated free energy interaction of −25.9 kcal/mol was found at a 1:3 HBA:HBD molar ratio that is consistent with thermodynamic results reported for the Choline-chloride/Phenol DES for which the lowest freezing temperature was reported at this ratio.

Novel synthesis and evaluation of anion-π interactions in one-walled meso-cyanophenyl substituted calix[4]pyrrole (C4P): Experimental and computational insights

A novel one-walled meso-cyanophenyl functionalized calix[4]pyrrole (4) was synthesized from cyanophenyl appended dipyrromethane (3) through conventional strategy and also by utilizing deep eutectic solvent of N,N'-dimethyl urea (DMU) & L-(+)-tartaric acid (TA) in a ratio of 7:3. The structural confirmation of 4 was done through 1H-NMR, 13C-NMR, FT-IR, and HRMS spectral data. Anion binding studies of the receptor 4 with several anions (halides, trigonal oxoanions, tetragonal oxoanions, etc.) used as tetrabutylammonium (TBA) salts, were successfully investigated by virtue of UV–Vis spectroscopy and time dependent density functional theory (TD-DFT). Notably, the UV–Vis absorbance titrations performed in CH3CN solvent, revealed significantly higher anion binding of receptor 4 with F¯, Cl¯, Br¯, and SCN¯ in comparison to the simple C4P. This can be ascribed to the fact that the cyanophenyl moiety is π-acidic in nature which participates in anion complexation through weak anion-π interactions (observed through 1H-NMR spectroscopy) and hence modulates anion binding through cooperative effect of preliminary NH-hydrogen bonding due to C4P scaffold and anion-π contacts due to cyanophenyl moiety.

Synthesis, Spectral, Redox, and Sensing Studies of β-Dicyanovinyl-Appended Corroles and Their Metal Complexes.

A new family of β-dicyanovinyl (DCV)-appended corroles represented as MTPC(MN) (where M = 3H, Cu, Ag, and Co(PPh3) and MN = malononitrile and TPC = 5,10,15-triphenylcorrole) were synthesized starting from the free base mono β-formyl corrole, H3TPC(CHO), and characterized along with their respective MTPC(CHO) and MTPC complexes as to their spectroscopic and electrochemical properties in nonaqueous media. Comparisons between the two series of corroles demonstrate a pronounced substituent effect of the β-DCV group on the physicochemical properties making the MTPC(MN) derivatives substantially easier to reduce and more difficult to oxidize than the formyl or unsubstituted corroles. In addition, the colorimetric and spectral detection of 11 different anions (X) in the form of tetrabutylammonium salts (TBAX, X = PF6-, OAc-, H2PO4-, CN-, HSO4-, NO3-, ClO4-, F-, Cl-, Br-, and I-) were also investigated in nonaqueous media. Of the investigated anions, only CN- was found to induce changes in the UV-vis and 1H NMR spectra of the β-DCV metallocorroles. This data revealed that CuTPC(MN) and AgTPC(MN) act as chemodosimeters for selective cyanide ion detection via a nucleophilic attack at the vinylic carbon of the DCV substituent, while (PPh3)CoTPC(MN) acts as a chemosensor for cyanide ion sensing via axial coordination to the cobalt metal center. A low-limit detection of cyanide ions was observed at 1.69 ppm for CuTPC(MN) and 1.17 ppm for AgTPC(MN) in toluene.

Investigation on Asphaltene Dispersion Activity of Tetrabutylammonium Carboxylate Ionic Liquids

Asphaltene destabilization is still known as one of the main problems of the petroleum industry and imposes many costs on this industry during crude oil production, transportation, and refining. The most important solution to control this problem is using chemical compounds to disperse asphaltene aggregates. Ionic liquids, as an emerging industrial solvent and catalyst, have been used for this purpose in the last two decades. In this work, three ionic liquids having a tetrabutylammonium cation and oleate, stearate, and cinnamate anions were synthesized and used as asphaltene dispersants. The efficiency of the synthesized ionic liquids on the stability of asphaltene aggregates was investigated using cluster size, polydispersity index, zeta potential, and ultraviolet spectroscopy data. It was found that tetrabutylammonium cinnamate and tetrabutylammonium oleate (dispersion indices of 82.5 and 60.2, respectively) have a much higher efficiency than tetrabutylammonium stearate (dispersion index of 20.6). The results of cluster size, polydispersity index, and zeta potential analysis were confirmed by ultraviolet spectroscopy and optical microscopy data. For instance, the mean radius of asphaltene clusters was 2179.8 nm, reduced to 253, 680, and 1402 nm after adding tetrabutylammonium salt of cinnamate, oleate, and stearate, respectively. The same trend was observed in the results of the polydispersity index (0.417, 0.470, and 0.624) and zeta potential analysis (31.4, 1.81, and −0.56). The cinnamate, oleate, and stearate anions have four, one, and no carbon–carbon π bonds, respectively. It seems that the presence of π bonds that can form π–π interactions with π bonds of the asphaltene molecules is an essential factor in asphaltene stabilization by these ionic liquids. In addition, the results showed that the higher the net negative charge of the anion, the greater the ability of the anion to stabilize asphaltene aggregates. This stabilization, which was mainly done through electrostatic interactions between polar groups of asphaltene and the carboxylate anions, was confirmed by zeta potential data.

Bioactive Phenolate Salts: Thymol Salts.

Phenolate salts of bioactive agents have been reported only scarcely. This is the first report on the formation and characterization of thymol phenolate salts as representatives of phenol-containing bioactive molecules. Thymol has been used in medicine and agriculture for decades owing to its excellent therapeutic properties. However, in light of its poor aqueous solubility, thermal instability, and especially its high chemical volatility, the utility of thymol is hampered. The present work focuses on tuning the physicochemical properties of thymol by modifying its chemical structure through salt formation. In this context, a series of metal (Na, K, Li, Cu, and Zn) and ammonium (tetrabutylammonium and choline) salts of thymol were synthesized and characterized using IR, NMR, CHN elemental analysis, and DSC analyses. The molecular formulae of thymol salts were determined based on CHN analysis and thymol quantification studies from UV-Vis spectrometric analysis. In most cases, the thymol phenolate was prepared as a 1 : 1 molar ratio with metal/ammonium ion. Only the Cu salt of thymol was isolated at a ratio of two phenolate units per copper ion. Most of the synthesized thymol salts were found to have increased thermal stability relative to thymol. The physicochemical properties such as solubility, thermal stability, and evaporation rate of thymol salts were thoroughly studied in comparison with thymol. The in vitro release studies of Cu from the copper salt of thymol is pH-dependent: rapid release of copper was observed in the lower pH release medium (100 % release at pH 1 for 12 days) and the rates of release were slower at higher pH values (5 % release at pH 2, and <1 % release at pH 4, 6, 8, and 10) over a period of about three weeks.

Facile Attachment of Halides and Pseudohalides to Dodecaborate(2-) via Pd-catalyzed Cross-Coupling

Cross-coupling reactions with [B12H11I]2- as one partner have been used successfully for Kumada and Buchwald Hartwig couplings with Pd catalysis. Here, we found that the iodide could be substituted easily, and unexpectedly, with other halides such as Br and Cl, and with pseudohalides such as cyanide, azide, and isocyanate. We found that for Cl, Br, N3, and NCO, tetrabutylammonium salts-or sodium salts-were successful halide sources, whereas for cyanide, CuCN was the only halide source that allowed a successful exchange. The azide could be reacted further in a click reaction with triazoles. While no substitution with fluoride occurred, tetrabutylammonium fluoride in the presence of water led to [B12H11OH]2-. Yields were high to very high, and reaction times were short when using a microwave oven as a heating source.

Role of Multiple Vanadium Centers on Redox Buffering and Rates of Polyvanadomolybdate-Cu(II)-Catalyzed Aerobic Oxidations.

A recent report established that the tetrabutylammonium (TBA) salt of hexavanadopolymolybdate TBA4H5[PMo6V6O40] (PV6Mo6) serves as the redox buffer with Cu(II) as a co-catalyst for aerobic deodorization of thiols in acetonitrile. Here, we document the profound impact of vanadium atom number (x = 0-4 and 6) in TBA salts of PVxMo12-xO40(3+x)- (PVMo) on this multicomponent catalytic system. The PVMo cyclic voltammetric peaks from 0 to -2000 mV vs Fc/Fc+ under catalytic conditions (acetonitrile, ambient T) are assigned and clarify that the redox buffering capability of the PVMo/Cu catalytic system derives from the number of steps, the number of electrons transferred each step, and the potential ranges of each step. All PVMo are reduced by varying numbers of electrons, from 1 to 6, in different reaction conditions. Significantly, PVMo with x ≤ 3 not only has much lower activity than when x > 3 (for example, the turnover frequencies (TOF) of PV3Mo9 and PV4Mo8 are 8.9 and 48 s-1, respectively) but also, unlike the latter, cannot maintain steady reduction states when the Mo atoms in these polyoxometalate (POMs) are also reduced. Stopped-flow kinetics measurements reveal that Mo atoms in Keggin PVMo exhibit much slower electron transfer rates than V atoms. There are two kinetic arguments: (a) In acetonitrile, the first formal potential of PMo12 is more positive than that of PVMo11 (-236 and -405 mV vs Fc/Fc+); however, the initial reduction rates are 1.06 × 10-4 s-1 and 0.036 s-1 for PMo12 and PVMo11, respectively. (b) In aqueous sulfate buffer (pH = 2), a two-step kinetics is observed for PVMo11 and PV2Mo10, where the first and second steps are assigned to reduction of the V and Mo centers, respectively. Since fast and reversible electron transfers are key for the redox buffering behavior, the slower electron transfer kinetics of Mo preclude these centers functioning in redox buffering that maintains the solution potential. We conclude that PVMo with more vanadium atoms allows the POM to undergo more and faster redox changes, which enables the POM to function as a redox buffer dictating far higher catalytic activity.

Selective CO2 Fixation to Styrene Oxide by Ta-Substitution of Lindqvist-Type [(Ta,Nb)6O19]8− Clusters

Metal oxide clusters composed of group 5 metal ions, such as Nb and Ta, exhibit catalytic activities for CO2 fixation to styrene oxide (SO) due to the highly negative natural bonding charge of the terminal O atoms that could work as CO2 activation sites. In this study, tetrabutylammonium (TBA) salts of [TaxNb6−xO19]8− (TBA-TaxNb6−x, x = 0–6) were prepared and Ta-substitution effect on the catalytic properties of TBA-TaxNb6−x for CO2 fixation to SO was investigated. We found that TBA-Ta1Nb5 shows the highest styrene carbonate (SC) selectivity (95%) among TBA-TaxNb6−x, although the SO conversion monotonously increases with the incremental Ta substitution amount. The CO2 fixation to SO under various conditions and in situ X-ray absorption fine structure measurements reveal that CO2 is activated on both terminal O sites coordinated to the Ta (terminal OTa) and Nb (terminal ONb) sites, whereas the activation of SO proceeds on the terminal OTa and/or bridge O sites that are connected to Ta. Density functional theory (DFT) calculations reveal that the terminal OTa of TBA-Ta1Nb5 preferentially adsorbs CO2 compared with other ONb base sites. We conclude that the selective CO2 activation at terminal OTa of TBA-Ta1Nb5 without SO activation is a crucial factor for high SC selectivity in the CO2 fixation to SO.

Synthesis of Disubstituted Carboxonium Derivatives of Closo-Decaborate Anion [2,6-B10H8O2CC6H5]-: Theoretical and Experimental Study.

A comprehensive study focused on the preparation of disubstituted carboxonium derivatives of closo-decaborate anion [2,6-B10H8O2CC6H5]- was carried out. The proposed synthesis of the target product was based on the interaction between the anion [B10H11]- and benzoic acid C6H5COOH. It was shown that the formation of this product proceeds stepwise through the formation of a mono-substituted product [B10H9OC(OH)C6H5]-. In addition, an alternative one-step approach for obtaining the target derivative is postulated. The structure of tetrabutylammonium salts of carboxonium derivative ((C4H9)4N)[2,6-B10H8O2CC6H5] was established with the help of X-ray structure analysis. The reaction pathway for the formation of [2,6-B10H8O2CC6H5]- was investigated with the help of density functional theory (DFT) calculations. This process has an electrophile induced nucleophilic substitution (EINS) mechanism, and intermediate anionic species play a key role. Such intermediates have a structure in which one boron atom coordinates two hydrogen atoms. The regioselectivity for the process of formation for the 2,6-isomer was also proved by theoretical calculations. Generally, in the experimental part, the simple and available approach for producing disubstituted carboxonium derivative was introduced, and the mechanism of this process was investigated with the help of theoretical calculations. The proposed approach can be applicable for the preparation of a wide range of disubstituted derivatives of closo-borate anions.

Experimental and computational anion binding studies of meso-substituted one-walled phthalimide-based Calix[4]pyrrole

Anion binding studies of meso‑substituted one-walled phthalimide-based calix[4]pyrrole (m-PC4P, 6) were investigated through UV–vis spectroscopy in acetonitrile and corroborated by time-dependent density functional theory (TD-DFT) calculations using 6–311G(d) basis set. Notably, to our expectation, the m-PC4P (6) displayed higher anion binding affinities in comparison to the parent C4P system, probably due to the additional weak CH-anion interactions besides four NH-hydrogen bonds of the C4P framework (supported by 1H NMR evidence). Herein, we have observed the usual trend with halide anions (used as their tetrabutylammonium salts), i.e. with increase in size of the halides from fluoride to iodide, the anion binding affinity decreases. Moreover, with the nitrate anion, appreciable better binding was observed in the case of m-PC4P (6) as compared to the simple C4P (1).

Catalytic System for Aerobic Oxidation That Simultaneously Functions as Its Own Redox Buffer.

The control of the solution electrochemical potential as well as pH impacts products in redox reactions, but the former gets far less attention. Redox buffers facilitate the maintenance of potentials and have been noted in diverse cases, but they have not been a component of catalytic systems. We report a catalytic system that contains its own built-in redox buffer. Two highly synergistic components (a) the tetrabutylammonium salt of hexavanadopolymolybdate TBA4H5[PMo6V6O40] (PV6Mo6) and (b) Cu(ClO4)2 in acetonitrile catalyze the aerobic oxidative deodorization of thiols by conversion to the corresponding nonodorous disulfides at 23 °C (each catalyst alone is far less active). For example, the reaction of 2-mercaptoethanol with ambient air gives a turnover number (TON) = 3 × 102 in less than one hour with a turnover frequency (TOF) of 6 × 10-2 s-1 with respect to PV6Mo6. Multiple electrochemical, spectroscopic, and other methods establish that (1) PV6Mo6, a multistep and multielectron redox buffering catalyst, controls the speciation and the ratio of Cu(II)/Cu(I) complexes and thus keeps the solution potential in different narrow ranges by involving multiple POM redox couples and simultaneously functions as an oxidation catalyst that receives electrons from the substrate; (2) Cu catalyzes two processes simultaneously, oxidation of the RSH by PV6Mo6 and reoxidation of reduced PV6Mo6 by O2; and (3) the analogous polytungstate-based system, TBA4H5[PW6V6O40] (PV6W6), has nearly identical cyclic voltammograms (CV) as PV6Mo6 but has almost no catalytic activity: it does not exhibit self-redox buffering.

Polyoxometalates immobilized on MIL-100 (Fe) as an emerging platform for eliminating breast cancer tumor cells

Polyoxometalates (POMs) have shown promising antitumor activities attributed to their virtue of incomparable structural versatility and interesting redox properties. However, the clinical application of POM drugs is limited by their poor stability and low anticancer specificity. To overcome these shortcomings, a multifunctional platform based on POMs (the tetrabutylammonium salts of [PW12O40]3−, [V10O28H3]3− and [Mo6O19]2−) and MIL-100 (Fe) was successfully developed for combined chemical and chemodynamic therapy, ultimately inducing cancer cell apoptosis. The prepared POMs@MIL-100 (Fe) composites showed great efficiency in killing MCF-7 and 4T1 cells while with a low toxicity to normal MCF-10A and C2C12 cells.

Disentangle a Complex MALDI TOF Mass Spectrum of Polyethylene Glycols into Three Separate Spectra via Selective Formation of Protonated Ions and Sodium or Potassium Adducts.

In MALDI TOF MS analysis, complicated mass spectra can usually be recorded for polymers with high affinities to protons and alkali metal ions. For these polymers, protonated ions and sodium and potassium adducts can often be formed concomitantly. By distributing these ions into three separate spectra of protonated ions, sodium adducts, and potassium adducts, significantly simplified spectra can be acquired. Mass spectra consisting of only sodium or potassium adducts can often be obtained by simply adding sodium salt and potassium salt, respectively. We report here a method to selectively generate protonated ions. A polyethylene glycol (PEG) sample with amino end groups was selected as the model polymer and α-cyano-4-hydroxycinnamic acid (CHCA) as the matrix. Octadecylamine (ODA) or a mixture of a tetrabutylammonium (TBA) salt and an ammonium salt was used as the co-matrix to inhibit the release of sodium and potassium ions and their related adducts into the MALDI gas phase plume. By depositing the polymer sample on top of a preloaded layer of CHCA with a co-matrix, the generation of Na+ and K+ adducts is suppressed, while [ODA + H]+ and NH4+ released from the preloaded matrix layer can serve as protonation reagents to protonate the polymer molecules via proton transfer reactions. It is clearly demonstrated that disentangling a complex mass spectrum filled densely with various series of ions into three separate spectra, with each one consisting of only one type of ions, allows unambiguous identification of mass peaks and greatly helps the interpretation of MS results.

Calix[4]pyrrole-Based Molecular Capsule: Dihydrogen Phosphate-Promoted 1:2 Fluoride Anion Complexation.

A molecular capsule (1) consisting of two calix[4]pyrroles connected via ethylene diamide linkers has been prepared as an anion receptor. 1H NMR spectroscopic studies carried out in CD2Cl2 revealed that receptor 1 recognizes a variety of anions with different binding modes and stoichiometries. For instance, receptor 1 binds fluoride and acetate with 1:2 receptor/anion stoichiometry and other test anions with 1:1 stoichiometry in solution when their respective tetrabutylammonium (TBA+) salts were used. In contrast, with tetraethylammnium (TEA+) salts, receptor 1 forms 1:2 complexes with chloride and bromide in addition to fluoride, overcoming expected Columbic repulsions between the anions co-bound in close proximity. Receptor 1 is also able to bind oxoanions, such as oxalate (C2O42-), dihydrogen phosphate (H2PO4-), sulfate (SO42-), and hydrogen pyrophosphate (HP2O73-), in the form of 1:1 complexes as the result of presumed cooperation between the two calix[4]pyrrole subunits. The selectivity of receptor 1 for fluoride versus dihydrogen phosphate varies depending on their relative concentrations. For instance, in the presence of less than 1.0 equiv of an equimolar mixture of fluoride and dihydrogen phosphate, receptor 1 shows high selectivity for dihydrogen phosphate. In contrast, in the presence of ≥2.0 anion equiv, receptor 1 binds fluoride preferentially, forming a 1:2 complex. Moreover, when treated with F-, the preformed 1:1 H2PO4- complex of receptor 1 is converted to the corresponding 1:2 receptor/fluoride complex with the release of the prebound dihydrogen phosphate anion. As inferred from gas-phase computations, this seemingly counterintuitive behavior is rationalized in terms of the precomplexed dihydrogen phosphate serving to reduce the reorganization energy required to bind two fluoride anions. The presence of a water molecule in addition to the bound fluoride anions may also favor the formation of the 1:2 F- complex. The present study provides a new approach for fine-tuning the binding selectivity of polytopic anion receptors.

Probing Electrolyte Influence on CO2 Reduction in Aprotic Solvents

Selective CO2 capture and electrochemical conversion are important tools in the fight against climate change. Industrially, CO2 is captured using a variety of aprotic solvents due to their high CO2 solubility. However, most research efforts on electrochemical CO2 conversion use aqueous media and are plagued by competing hydrogen evolution reaction (HER) from water breakdown. Fortunately, aprotic solvents can circumvent HER, making it important to develop strategies that enable integrated CO2 capture and conversion. However, the influence of ion solvation and solvent selection within nonaqueous electrolytes for efficient and selective CO2 reduction is unclear. In this work, we show that the bulk solvation behavior within the nonaqueous electrolyte can control the CO2 reduction reaction and product distribution occurring at the catalyst–electrolyte interface. We study different tetrabutylammonium (TBA) salts in two electrolyte systems with glyme ethers (e.g., 1,2 dimethoxyethane or DME) and dimethyl sulfoxide (DMSO) as a low and high dielectric constant medium, respectively. Using spectroscopic tools, we quantify the fraction of ion pairs that forms within the electrolyte. Also, we show how ion pair formation is prevalent in DME and is dependent on the anion type. More importantly, we show that as ion pair formation decreases within the electrolyte, CO2 current densities increase, and a higher CO Faradaic efficiency is observed at low overpotentials. Meanwhile, in an electrolyte medium where the ion pair fraction does not change with the anion type (such as in DMSO), a smaller influence of solvation is observed on CO2 current densities and product distribution. By directly coupling bulk solvation to interfacial reactions and product distribution, we showcase the importance and utility of controlling the reaction microenvironment in tuning the electrocatalytic reaction pathways. Insights gained from this work will enable novel electrolyte designs for efficient and selective CO2 conversion to desired fuels and chemicals.

Tritopic Bis-Urea Receptors for Anion and Ion-Pair Recognition.

This work reports on the synthesis and characterization of three tritopic receptors and their binding properties toward various anions, as their tetrabutylammonium salts, and three alkali metal–acetate salts by UV–vis, fluorescence, 1H, 7Li, 23Na, and 39K NMR in MeCN/dimethyl sulfoxide (DMSO) 9:1 (v/v). Molecular recognition studies showed that the receptors have good affinity for oxyanions. Furthermore, these compounds are capable of ion-pair recognition of the alkali metal–acetate salts studied through a cooperative mechanism. Additionally, molecular modeling at the density functional theory (DFT) level of some lithium and sodium acetate complexes illustrates the ion-pair binding capacity of receptors. The anion is recognized through strong hydrogen bonds of the NH– groups from the two urea sites, while the cation interacts with the oxygen atoms of the polyether spacer. This work demonstrates that these compounds are good receptors for anions and ion pairs.

Tetrabutyl Ammonium Salts of Keggin-Type Vanadium-Substituted Phosphomolybdates and Phosphotungstates for Selective Aerobic Catalytic Oxidation of Benzyl Alcohol

A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of the addenda atom nature, the catalytic activity increased with the number of V in the Keggin anion structure. For both series of catalysts, TBA salts of polyoxometalates with the highest V-substitution degree (TBA5PMo10V2O40 and TBA5PW10V2O40) showed higher activity. The maximum benzyl alcohol conversions obtained were 93% and 97% using (TBA)5PMo10V2O40 and (TBA)5PW10V2O40 as catalysts, respectively. In all the cases, the selectivity toward benzaldehyde was higher than 99%.

Red-Emitting Polymerizable Guanidinium Dyes as Fluorescent Probes in Molecularly Imprinted Polymers for Glyphosate Detection

The development of methodologies to sense glyphosate has gained momentum due to its toxicological and ecotoxicological effects. In this work, a red-emitting and polymerizable guanidinium benzoxadiazole probe was developed for the fluorescence detection of glyphosate. The interaction of the fluorescent probe and the tetrabutylammonium salt of glyphosate was studied via UV/vis absorption and fluorescence spectroscopy in chloroform and acetonitrile. The selective recognition of glyphosate was achieved by preparing molecularly imprinted polymers, able to discriminate against other common herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (dicamba), as thin layers on submicron silica particles. The limits of detection of 4.8 µM and 0.6 µM were obtained for the sensing of glyphosate in chloroform and acetonitrile, respectively. The reported system shows promise for future application in the sensing of glyphosate through further optimization of the dye and the implementation of a biphasic assay with water/organic solvent mixtures for sensing in aqueous environmental samples.