Trifluoromethyl)phenyl]borate Research Articles

Quantification of Pharmaceutical Bitterness Using a Membrane Electrode Based on a Hydrophobic Tetrakis [3,5-Bis (trifluoromethyl) phenyl] Borate

Technologies for quantifying bitterness are essential for classifying medicines. As previously reported, taste sensors with lipid polymer membranes can respond to bitter hydrochloride substances in pharmaceuticals. However, the acid hydrolysis reaction between the lipid phosphoric acid di-n-decyl ester (PADE) and the plasticizer tributyl o-acetylcitrate (TDAB) led to a deterioration in sensor responses during storage. Given the cost of transportation and preservation for commercialization, membrane components that maintain physical and chemical stability during long-term storage are needed. Here we present a membrane electrode based on hydrophobic tetrakis [3,5-bis (trifluoromethyl) phenyl] borate (TFPB) and a plasticizer 2-nitrophenyl octyl ether (NPOE) for the quantification of pharmaceutical bitterness; they maintain a stable response before and after accelerated deterioration, as well as high selectivity and sensitivity. It is a first attempt to use a completely dissociative substance to replace non-completely dissociative lipids. Our work offsets the long-term stability issue of a bitterness sensor with a negatively charged hydrophobic membrane. Meanwhile, we provide the opportunity to select surface charge modifiers for a membrane surface using ester plasticizers containing oppositely charged impurities.

Cyclic Octamer Peptoids: Simplified Isosters of Bioactive Fungal Cyclodepsipeptides.

Cyclic peptoids have recently emerged as an important class of bioactive scaffolds with unique conformational properties and excellent metabolic stabilities. In this paper, we describe the design and synthesis of novel cyclic octamer peptoids as simplified isosters of mycotoxin depsipeptides bassianolide, verticilide A1, PF1022A and PF1022B. We also examine their complexing abilities in the presence of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) salt and explore their general insecticidal activity. Finally, we discuss the possible relationship between structural features of free and Na+-complexed cyclic octamer peptoids and bioactivities in light of conformational isomerism, a crucial factor affecting cyclic peptoids’ biomimetic potentials.

Using Alkali Metal Ions To Template the Synthesis of Interlocked Molecules.

In 1987, Pedersen, Cram, and Lehn were awarded the Nobel Prize in Chemistry to honor their achievements in, among other things, the selective recognition of alkali metal ions by synthetic hosts. Almost three decades later, the 2016 Nobel Prize went to Stoddart, Sauvage, and Feringa for the development of artificial molecular machines, in which interlocked molecules play a significant role. Surprisingly, although many rotaxane- and catenane-based molecular machines have been constructed using various templating approaches, alkali metal ions, which are good templates for crown ether synthesis, have only rarely been applied as templates for the assembly of these interlocked molecules. This paucity of examples is probably due to the less well defined coordination numbers and geometries in the complexation of alkali metal ions to common oxygen-containing ligands, resulting in much weaker metal-ligand interactions and less predictable structures for their complexes compared with those formed between transition metal ions and common pyridine-containing ligands. Nevertheless, the ease of removing alkali metal ions from interlocked compounds and their much lower toxicity compared with that of transition metal ions are attractive features that have inspired their use as templates in the synthesis of interlocked molecules. About a decade ago, we began investigating the feasibility of using alkali metal ions to template the formation of catenanes and rotaxanes, with the hope of developing facile, broadly applicable, green, and efficient methods for their construction. We noticed that the interactions between oxygen-containing ligands and alkali metal ions can be strengthened by minimizing the effects of competing interactions from solvent molecules and counteranions. Thus, to increase the solubility of the metal ion salts in less polar solvents (e.g., CH2Cl2, CHCl3) and minimize ion pairing, we chose tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), a weakly coordinating anion, as the counteranion for the alkali metal ions applied as templates. Our strategy has been based on the association of simple and general recognition units: (i) the orthogonal arrangement of two oligo(ethylene glycol) chains around an alkali metal ion and (ii) the encircling of a single urea/amide unit by an oligo(ethylene glycol)-containing macrocycle in the presence of a templating alkali metal ion. The former recognition system has allowed the facile construction of many interesting interlocked structures, including cyclic [2]catenane trimers and tetramers; the latter has provided several rotaxanes, including some incorporating monomers of practically important (macro)molecules (e.g., peptides, polymers) and some that behave as switches with unique functions (e.g., catalysis, gelation). The components in these recognition systems possess high flexibility in terms of their structures and the choice of suitable alkali metal ion templates. This Account tells the story of the concept behind this alkali metal ion-templating approach as well as its elaboration, scope, and recent advances. We hope to convince the reader that alkali metal ions are powerful templates for assembling interlocked structures and compounds and also to demonstrate the range of possibilities that they provide for future endeavors.

Threading of a double-calix[6]arene system with dialkylammonium axles

The threading of a double-calix[6]arene system (4) with dialkylammonium axles (2 and 3) has been investigated in the presence of the ‘superweak’ tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) anion. NMR and ESI(+)-mass spectrometry analyses showed that singly and doubly threaded pseudorotaxanes can be stepwise formed under appropriate conditions. The directional threading of an alkylbenzylammonium axle with double-calix[6]arene 4 occurs with an endo-alkyl preference in accordance with the ‘endo-alkyl rule’. DFT calculations confirmed this preference and evidenced that the pseudo[3]rotaxane complexes are characterised by an anti-conformation around the bonds, which led to a spatial divergence of the two calix-cavities.

Counter anion dependent swelling behaviour of poly(octadecyl acrylate)-based lipophilic polyelectrolyte gels as superabsorbent polymers for organic solvents

Molecular design of superabsorbent materials for organic solvents has attracted much attention due to their superior applications for the removal of hazardous leakages or spillages of volatile organic compounds (VOCs) and waste oils. One approach for preparing such soft matter is loosely crosslinked lipophilic polyelectrolytes. Here, we demonstrate the counter anion effect for superabsorbency for various organic solvents in a series of poly(octadecyl acrylate)-based lipophilic polyelectrolyte gels bearing tetraalkylammonium with relatively hydrophobic counter-anions: dodecyl sulfate (DS), tetrakis(3,5-bis(trifluoromethyl)phenyl) borate (TFPB) and (μ-(1H-imidazolato κ-N1:κ-N3) hexakis(pentafluorophenyl borate) (IM). The benefit of high-swelling abilities due to dissociation of ionpairs was observed in less- and non-polar media (3 < e < 13), when TFPB and IM were selected as counter anions. These results indicate that molecular design of superabsorbent materials requires that the ionic groups have sufficient bulkiness and lipophilicity for ionic dissociation in nonpolar solvents.

Toward the design of superabsorbent materials for non-polar organic solvents and oils: ionic content dependent swelling behaviour of cross-linked poly(octadecyl acrylate)-based lipophilic polyelectrolytes

Oil spills and other industrial chemical leaks to natural environments can cause long-term impact on ecosystems, and the use of polymer-based absorbent materials for such media is a promising technique for cleaning up contaminated sites. Here, we prepared a set of poly(octadecyl acrylate)-based lipophilic polyelectrolyte gels bearing tetraalkylammonium tetrakis(3,5-bis(trifluoromethyl)phenyl) borate (TFPB) with different contents of the ionic groups from 1.0 mol% (EG18(1%)) to 10 mol% (EG18(10%)), and investigated their swelling behaviours in organic solvents and oils. The swelling degrees of the polymer gels in non- or less-polar media (3 < ε < 14) increased both with increasing the contents of TFPB salt on the polymer chain and increasing the dielectric constants of the solvents. The swelling degrees of EG18(10%) in dichloromethane and 1,2-dichloroethane showed over 300 times as much as its dry weight. In nonpolar media (ε < 3) such as toluene and hexane, however, EG18(10%) collapsed and showed low swelling degrees owing to their low dielectric constants. But, the addition of ethanol (ε = 24.6) to them increased the solvent polarities as mixtures, resulting in the high swelling degrees over 100 times by polyelectrolyte effects. The lipophilic polyelectrolyte gels could find applications as protective barriers for volatile organic compounds (VOCs) spilled in the environment and as absorbents for waste oil.

Potentiometric Response Characteristics of Membrane-BasedCs+-Selective Electrodes Containing Ionophore-Functionalized Polymeric Microspheres

Cs+-selective solvent polymeric membrane-based ion-selective electrodes (ISEs) were developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-(3,5-bis(trifluoromethyl)phenyl) borate (TFPB) as the ion exchanger. A systematic study examining the effects of the membrane plasticizers bis(2-ethylhexyl) sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), and 2-fluorophenyl nitrophenyl ether (FPNPE) on the potentiometric response and selectivity of the corresponding electrodes was performed. Under certain conditions, P-EG-based ion-selective electrodes (ISEs) containing TFPB and plasticized with NPOE exhibited a super-Nernstian response between1×10−3and1×10−4 M Cs+, a response characteristic not observed in analogous membranes plasticized with either DOS or FPNPE. Additionally, the performance of P-EG-based ISEs was compared to electrodes based on two mobile ionophores, a neutral lipophilic ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) and a charged metallacarborane ionophore, sodium bis(dicarbollyl)cobaltate(III) (CC). In general, P-EG-based electrodes plasticized with FPNPE yielded the best performance, with a linear range from 10-1–10-5 M Cs+, a conventional lower detection limit of8.1×10−6 M Cs+, and a response slope of 57.7 mV/decade. The pH response of P-EG ISEs containing TFPB was evaluated for membranes plasticized with either NPOE or FPNPE. In both cases, the electrodes remained stable throughout the pH range 3–12, with only slight proton interference observed below pH 3.

Endo-Cavity Complexation and Through-the-Annulus Threading of Large Calixarenes Induced by Very Loose Alkylammonium Ion Pairs

A general mode to obtain endo-complexation and through-the-annulus threading of scarcely efficient macrocyclic hosts was obtained by exploiting the inducing effect of the weakly coordinating tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) anion that gives free "naked" cations. This method works very well with simple, conformationally mobile calix[6-7]arene ethers, which give conformationally blocked endo-calix or [2]pseudorotaxane complexes.

Synthesis and Characterization of a Novel, Colored Lipophilic Additive for Spectral Imaging the Transport in Ionophore Based Ion‐Selective Membranes

AbstractThe synthesis and application of a novel colored lipophilic additive (2,4,6‐trinitro‐3‐pentadecylphenol (TNPDP)) as optical tracer for imaging membrane transport is presented. It was found that TNPDP (estimated pKa=5.53) does not dissociate completely in the studied membranes, even in the presence of the highly basic ETH 5294 chromoionophore (pKa=12.0). In voltage polarization experiments the TNPDP compounded, ETH 5294 based membranes behaved similarly to fixed site membranes, i.e., the external field did not induce concentration polarization in TNPDP and the protonated chromoionophore. To interpret this peculiar behavior, original methods have been implemented to i) compare the diffusion properties and determine the diffusion coefficients of multiple species in ion‐selective membranes by hyperspectral imaging, and ii) determine the ion pair formation constant of the ETH 5294 with the novel colored lipophilic anion and a commonly used tetraphenylborate derivative by impedance spectroscopy. Using the “merged membrane” method individual diffusion coefficients of (2.39±0.07)×10−8 cm2/s (N=5), and (2.34±0.02)×10−8 cm2/s (N=2) were determined for the unprotonated form of ETH 5294 and for the undissociated form of TNPDP, respectively. Once in combination with a counter anion, the diffusion coefficient of the protonated ETH 5294 depended on the properties of the lipophilic anion in the membrane. The apparent diffusion coefficient of the protonated ETH 5294 were much smaller when paired with TNPDP ((1.8±0.8)×10−9 cm2/s, N=9) than with tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (TFPB) ((1.19±0.42)×10−8 cm2/s, N=5). In agreement, the ion pair formation constants of the ETH 5294 with TNPDP (3.14×104 M−1) were almost three orders of magnitude higher than with TFPB (83 M−1).

Microcavity Based Solid‐Contact Ion‐Selective Microelectrodes

AbstractA novel design and fabrication procedure is proposed for the preparation of robust ionophore based ion‐selective microelectrodes. The essential component of the new design is a microcavity that is formed after recessing a voltammetric inlaid disk type gold microelectrode by chemical etching of the gold microwire. The microcavity of ca. 50 pL volume and 25 μm diameter accommodates the inherently conducting polymeric inner contact and the ion‐selective liquid membrane, which are thereby mechanically protected from the sample environment. As inner contacts poly(3,4‐ethylenedioxythiophene) (PEDOT) films doped with poly(4‐styrenesulfonate) (PSS) and tetrakis[3,5‐bis‐(trifluoromethyl)phenyl]borate (TFPB) electropolymerized from aqueous and organic solvents, respectively, were used. Potassium‐ and calcium‐selective microelectrodes fabricated according to the new procedure exhibited potentiometric characteristics similar to the conventional electrodes. The formation of an aqueous layer below the ion‐selective membrane could be avoided by using the proposed electrode construction.

Facilitating Access to the Most Easily Ionized Molecule: an Improved Synthesis of the Key Intermediate, W2(hpp)4Cl2, and Related Compounds

A far superior synthesis is reported for W(2)(hpp)(4)Cl(2), a key intermediate in the synthesis of the most easily ionized closed-shell molecule W(2)(hpp)(4) (hpp = the anion of the bicyclic guanidine compound 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). At 200 degrees C, the one-pot reaction of the air-stable and commercially available compounds W(CO)(6) and Hhpp in o-dichlorobenzene produces W(2)(hpp)(4)Cl(2) in multigram quantities with isolated yields of over 90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)(2)(CO)(4) or W(2)(mu-CO)(2)(mu-hpp)(2)(eta(2)-hpp)(2), which are isolable in good purity depending upon the specific conditions employed. These compounds provide insight into the reaction pathway to W(2)(hpp)(4)Cl(2) and W(2)(hpp)(4). Two additional derivatives, W(2)(hpp)(4)X(2) where X is PF(6)(-) or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesized and structurally characterized. A comparison of the electrode potentials of W(2)(mu-CO)(2)(mu-hpp)(2)(eta(2)-hpp)(2) and the di-p-anisylformamidinate analogue shows that oxidation of the hpp compound is significantly displaced (1.12 V) and shows that the bicyclic guanidinate ligand is considerably better than the formamidinate anion at stabilizing high oxidation states. A differential pulse voltammogram of W(2)(hpp)(4)(TFPB)(2) in THF shows two reduction processes with an E(1/2) of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W(2)(hpp)(4)(2+) units in W(2)(hpp)(4)X(2) compounds show that the metal-metal bonding orbitals are destabilized by the axial ligands, which accounts for significant variations in the W-W distances. The low-energy gas-phase ionizations of W(2)(hpp)(4) are also reported and discussed.

Cs +-selective membrane electrodes based on ethylene glycol-functionalized polymeric microspheres

A new strategy for improving the robustness of membrane-based ion-selective electrodes (ISEs) is introduced based on the incorporation of microsphere-immobilized ionophores into plasticized polymer membranes. As a model system, a Cs +-selective electrode was developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) as the ion exchanger. Electrodes were evaluated with respect to Cs + in terms of sensitivity, selectivity, and dynamic response. ISEs containing P-EG and TFPB that were plasticized with 2-nitrophenyl octyl ether (NPOE) yielded a linear range from 10 −1 to 10 −5 M Cs +, a slope of 55.4 mV/decade, and a lower detection limit (log a Cs) of −5.3. In addition, these membranes also demonstrated superior selectivity over Li +, Na +, and alkaline earth metal ion interferents when compared to analogous membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) or membranes containing a lipophilic, mobile ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) as ionophore.

Ion-pairing ability, chemical stability, and selectivity behavior of halogenated dodecacarborane cation exchangers in neutral carrier-based ion-selective electrodes.

Recently, it has been discovered that carba-closo-dodecaborates can be used as cation exchangers in neutral carrier-based ion-selective chemical sensors. Because of their inherent chemical stability and versatile functionalization chemistries, they offer many advantages that may potentially be exploited for ion analyses that require nontraditional sample conditions, including strongly acidic media. In this work, trimethylammonium salts of undecachlorinated (UCC), undecabrominated (UBC), hexabrominated (HBC), and undecaiodinated (UIC) carborane anions were prepared and evaluated for their potential use in solvent polymeric membrane-based sensors. Computational methods including Natural population analysis and electrostatic mapping were used to predict the ion-exchanging ability of each lipophilic anion. In addition, the sandwich membrane technique was used to evaluate the ion-pairing ability of each carborane anion in situ (i.e., within bis(2-ethylhexyl) sebacate (DOS)- and 2-nitrophenyl octyl ether (o-NPOE)-plasticized ISE membranes). The results of the computational and potentiometric studies found that binding affinity of the anions followed the generalized trend HBC > UCC > UBC > UIC. PVC-DOS bulk optode thin films containing the chromoionophore ETH 5315 and a respective anion were used to determine the chemical stability/lipophilicity of the carboranes and tetrakis[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) in acidic media (0.2 M HOAc) under flowing conditions. The studies found that in terms of stability/lipophilicity UIC > UBC > TFPB approximately UCC >> HBC. Electrodes containing a Pb(2+)-selective ionophore, tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide)(lead IV), were used to evaluate the functionality of each cation exchanger. An evaluation of response characteristics such as slope and selectivity found that UIC and UBC were quite comparable to the behavior of TFPB. Interestingly, both UIC and UBC showed a marked selectivity improvement over cadmium, with log K(pot)(pb),(Cd) values of -7.19 and -7.29, respectively, with TFPB giving a value of -5.89. Demonstrating excellent stability and suitable electrostatic properties, the carboranes, UIC in particular, are a very promising alternative to the tetraphenylborates and should find widespread application in the field of chemical sensors.

Weakly coordinating bulky anions designed by efficient use of polyfluoro-substitution

The molecular design and applications of weakly coordinating tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (TFPB) and tetrakis(pentafluorophenyl)borate (FTPB) are reviewed.

Formation and Structure of Protonated Tetrasilatetrahedrane-monooxide, (tert-Bu3Si)4Si4OH+

Abstract The reaction of tetrakis(tri-tert-butylsilyl)tetrasilatetrahedrane (1) with trityl tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) gave protonated tetrasilatetrahedrane-monooxide, (tert-Bu3Si)4Si4OH+ (2+), whose structure was determined by X-ray crystallography.

η3-, η4- and η6-Co-ordination complexes of the weakly co-ordinating anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate

Single-crystal X-ray diffraction has established η3-, η4- and η6-co-ordination of the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) in the complexes Ag(TFPB)(2,2′-bipy) (2,2′-bipy = 2,2′-bipyridine), Ag(TFPB)(1,2-C6H4I2) and Rh(TFPB)(cod) (cod = cycloocta-1,5-diene) respectively.

Synthesis, Lipophilicity, and Stability of Tetrakis (pentafluorophenyl) borate (FTPB) Anion under Highly Acidic Conditions in Comparison with Those of Tetrakis (3,5-bis (trifluoromethyl) phenyl) borate (TFPB) Anion

An improved synthetic method for tetramethylammonium FTPB by a metal-halogen exchange reaction of pentafluorophenyl bromide with magnesium in the presence of a catalytic amount of butyl bromide and by a subsequent reaction with boron trifluoride diethyl ether was developed. The lipophilicity of tetramethylammonium FTPB in a range of hydrophobic organic solvents and its stability under highly acidic conditions were investigated in comparison with those of tetramethylammonium TFPB.

Mechanism of Azo Coupling Reactions: Part XXXVI. The Relationship between the Structure and the Catalytic Activity of Anionic Phase-Transfer Catalysts in Azo Coupling Reactions

Abstract A series of 15 sodium arenesulfonates containing alkyl, hydroxyl or methoxyl groups was investigated for the phase-transfer catalysis of the azo coupling reaction of the 4-methoxybenzenediazonium ion (1) with 1,3,5-trimethoxybenzene (2) in a dichloromethane/water two-phase system, in which the yields, initial reaction rates and influence of the decomposition of the diazonium ion 1 were measured. The influence of counter anions on the partition coefficient (α) for the diazonium ion 1 in a dichloromethane/water system, and the effects of the solvent polarity and structure of counter anions on the reaction rates of the azo coupling of the diazonium ion 1 with N,N-dimethylaniline (4) and 1,3,5-trimethoxybenzene (2) in organic solvents and in dichloromethane/water system, were investigated. The symmetrical structure of the tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) anion was proved to be an essential factor regarding the remarkably high α for the diazonium ion 1 ion-paired with TFPB. The looseness and tightness of ion pairs of highly desolvated diazonium ion 1 in a nonpolar organic media is one of the most significant factors concerning the reactivity of the diazonium ion 1 in a rate-limiting azo coupling with 4. In a reaction of the diazonium ion 1 with 2 in a dichloromethane/water system, however, the amount of saturated water and/or additives in the dichloromethane phase, which serves as a base for the rate-limiting deprotonation, becomes the most influential factor for an effective azo coupling reaction under phase-transfer catalysis conditions.

ＴＦＰＢイオンを用いたアニオン型相間移動触媒反応

Tetrakis [3, 5-bis (trifluoromethyl) phenyl] borate (TFPB), a highly lipophilic fluoroaromatic borate ion which is remarkably stable under acid and oxidative conditions, was designed as an anionic phase-transfer catalyst, whose function is to transfer cationic species such as diazonium and oxonium ions in reactive form of ion pair from an aqueous (or solid) phase into a nonpolar organic phase and to promote catalytically the electrophilic reactions in two-phase systems. Some effecive examples of anionic phase-transfer catalysis (PTC) with TFPB were demonstrated in the diazo coupling, the Friedel-Crafts alkylation, the nitrosation (in situ diazo coupling), the acid-mediated hydrolysis of esters, and the redox reactions with methylviologen in liquid membrane system. Kinetic investigations of these PTC reactions clearly indicated that the enhanced reactivities of the cationic species and the specificities of the electrophilic reactions were due to the dehydration of such cationic species ion-paired with TFPB in nonpolar organic phase.

Anion-catalyzed Phase-transfer Catalysis. II. Effects of Anionic Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate Catalyst in Phase-transfer-catalyzed Sulfonium Ylide Formation

Abstract Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) ion as an anionic phase-transfer catalyst promoted the formation of oxirane from various carbonyl substrates and trimethylsulfonium chloride in a two-phase mixture of dichloromethane and concentrated aqueous sodium hydroxide.