Weak Acid Groups Research Articles

Highly Efficient Copper(II) Ion Sorbents Obtained by Calcium Carbonate Mineralization on Functionalized Cross‐Linked Copolymers

A new type of Cu(II) ion sorbents is presented. These are obtained by CaCO3 mineralization from supersaturated solutions on gel-like cross-linked polymeric beads as insoluble templates. A divinylbenzene-ethylacrylate-acrylonitrile cross-linked copolymer functionalized with weakly acidic, basic, or amphoteric functional groups has been used, as well as different initial inorganic concentrations and addition procedures for CaCO3 crystal growth. The morphology of the new composites was investigated by SEM and compared to that of the unmodified beads, and the polymorph content was established by X-ray diffraction. The beads, before and after CaCO3 mineralization, were tested as sorbents for Cu(II) ions. The newly formed patterns on the bead surface after Cu(II) sorption were observed by SEM, and the elemental distribution on the composites and the chemical structure of crystals after interaction with Cu(II) were investigated by EDAX elemental mapping and by FTIR-ATR spectroscopy, respectively. The sorption capacity increased significantly after CaCO3 crystals growth on the weak anionic bead surface (up to 1041.5 mg Cu(II) /g sample) compared to that of unmodified beads (491.5 mg Cu(II) /g sample).

Effect of pH and ionic strength on the electrical charge and particle size distribution of starch nanocrystal suspensions

The current study investigates the amount of charged groups induced by sulfuric acid hydrolysis on the surface of starch nanocrystals. Conductometric titration revealed the existence of both weak and strong acidic groups. Strong acidic groups (sulfate ester groups) were present at low amounts (13.2 mmol kg−1) and their concentration increased with increasing duration of hydrolysis. The amounts of weak acidic groups (carboxylic acid) were greater (32–38 mmol kg−1) and the duration of hydrolysis appeared to have no effect. Negative zeta potential values were measured in the studied pH ranges (2.3 and 10). Zeta potential decreased for pH values fewer than 4, remained constant between 4 and 8, then decreased for higher values. Absolute zeta potential values were low (−6 to −29 mV) which could explain the poor suspension stability and the great tendency for particles to aggregate and settle in an aqueous medium. The increase in the pH of the suspension resulted in a lower aggregation as the mean apparent size of the particles decreased in this case. The increase in ionic strength had a similar effect, although the mechanisms involved were hypothesised to be quite different.

Study on Enhancing the Slurry Performance of Coal–Water Slurry Prepared with Low-Rank Coal

Although coal–water slurry (CWS) with low-rank Shenhua coal has poor slurry performance, it is a good power coal with many advantages including low ash content and ease of incineration. This article establishes differences between the slurry performance of CWS prepared with low-rank Shenhua coal and medium-rank Shandong coal. Moreover, we examined the effects of coal powder gradation, water pre-adsorption, formulation of modified sodium lignosulfonate (SL-M) with other dispersants and stabilizer, and a combined preparation of coal samples on the apparent viscosity of CWS. Results showed that the existence of weak acid groups, strong water adsorption ability, and high-density mineral substances were the major factors that affected the slurry performance of low-rank Shenhua coal. Furthermore, when the average coal particle size was 26.19 µm, the apparent viscosity of CWS was lowest according to bimodal distribution. When low-rank coal was treated first with water pre-adsorption, the slurry performance of CWS was greatly improved and the apparent viscosity was only 1200 mPa · s when the solid concentration was 63%, showing an increase of 3%. Finally, when low-rank Shenhua coal was combined with medium-rank Shandong coal, apparent viscosity was enhanced.

Surface grafted chitosan gels. Part I. Molecular insight into the formation of chitosan and poly(acrylic acid) multilayers.

Composite polyelectrolyte multilayers of chitosan and low molecular weight poly(acrylic acid) (PAA) have been assembled by sequential adsorption as a first step toward building a surface anchored chitosan gel. Silane chemistry was used to graft the first chitosan layer to prevent film detachment and decomposition. The assembly process is characterized by nonlinear growth behavior, with different adsorption kinetics for chitosan and PAA. In situ analysis of the multilayer by means of surface sensitive total internal reflection Raman (TIRR) spectroscopy, combined with target factor analysis of the spectra, provided information regarding composition, including water content, and ionization state of weak acidic and basic groups present in the thin composite film. Low molecular weight PAA, mainly in its protonated form, diffuses into and out of the composite film during adsorption and rinsing steps. The higher molecular weight chitosan shows a similar behavior, although to a much lower extent. Our data demonstrate that the charged monomeric units of chitosan are mainly compensated by carboxylate ions from PAA. Furthermore, the morphology and mechanical properties of the multilayers were investigated in situ using atomic force microscopy operating in PeakForce tapping mode. The multilayer consists of islands that grow in lateral dimension and height during the build-up process, leading to close to exponentially increasing roughness with deposition number. Both diffusion in and out of at least one of the two components (PAA) and the island-like morphology contribute to the nonlinear growth of chitosan/PAA multilayers.

English

In order to reveal the formation mechanism of hydrochemical characteristics in Tongchuan City, we collected and detected 39 samples of underground water. Correlation analytical method, hydrochemical method and ion ratio coefficient method were employed to investigate the hydrochemical characteristics, influencing factors and principles of changing. Results demonstrate that the main factors, controlling the shallow water salinization, are the SO42-, NO3-, Cl- and K+. The contents of SO42-, NO3- and Cl- are greatly different and other indexes are relatively stable. The values of γNa/γCl demonstrate that the Na+ is released from the soil aquifer in the runoff process. There is an exchange between the Ca2+ in water and Na+ in soil, which leads to γNa＞γCl. As the exchange time in deep water is longer than that of shallow water, the exchange and adsorption of ions are more sufficient. The value of γNa/(γNa+γCl) demonstrates that with increasing of ground water depth, the level of cation exchange enhances, which leads to the dominant cation turning to Ca2+ from Na+. The value of γHCO3+γSO4/γCa+γMg demonstrates the shallow water is mainly from atmospheric rainfall and the influence of cation exchange is more obvious on deep water. The types of shallow water in Tongchuan City are mainly HCO3·SO4-Ca. Its classification is relatively complex. Whereas, the deep water is mainly HCO3-Na and the category of underground water is simple. As for shallow water, the content of alkaline earth metal is larger than that of alkali metal. For the deep water, the content of weak acid group is larger than that of strong acid group. In the region of upper reaches, the features of both shallow and deep waters are mainly weak acid and alkaline earth metal. The chemical composition mainly consists of carbonate leaching. With the flowing of underground water, the shallow water turns to be strong acid and alkaline earth metal and the deep water turns to be weak acid and alkali metal.   Key words: Tongchuan City, underground water, hydrochemical characteristics, ion ratio coefficient method.

Determination of ion exchange constants for pairs of metal ions to lignocellulosic materials by column chromatography

Abstract A method based on column chromatography has been developed for determination of ion exchange (IE) constants for pairs of metal ions for different types of wood, pulp, and bark samples. Bark was found to have higher selectivity than wood and pulp for the metal ions studied. Of the 14 different metal ions studied, the toxic transition metal ions Pb, Cu, and Cd were most strongly bound to all the materials used in this work. The validity of the column method was tested by means of different mixtures of metal ions as the loading solution. The IE constants obtained by the column method showed a good agreement with those obtained by the batch method reported earlier by our group. The IE constants were also determined for synthetic cation exchanger (CE) based on weak and strong acid groups. The IE constants of most pairs of metal ions are highest for the weakly acidic CE followed by bark, wood, pulp, and strongly acidic CE.

Comparative experimental investigation on the actuation mechanisms of ionic polymer–metal composites with different backbones and water contents

Water-based ionic polymer–metal composites (IPMCs) exhibit complex deformation properties, especially when the water content changes. To explore the general actuation mechanisms, both Nafion and Flemion membranes are used as the polymer backbones. IPMC deformation includes three stages: fast anode deformation, relaxation deformation, and slow anode deformation, which is mainly dependent on the water content and the backbone. When the water content decreases from 21 to 14 wt. %, Nafion–IPMC exhibits a large negative relaxation deformation, zero deformation, a positive relaxation deformation, and a positive steady deformation without relaxation in sequence. Despite the slow anode deformation, Flemion–IPMC also shows a slight relaxation deformation, which disappears when the water content is less than 13 wt. %. The different water states are investigated at different water contents using nuclear magnetic resonance spectroscopy. The free water, which decreases rapidly at the beginning through evaporation, is proven to be critical for relaxation deformation. For the backbone, indirect evidence from the steady current response is correlated with the slow anode deformation of Flemion-IPMC. The latter is explained by the secondary dissociation of the weak acid group –COOH. Finally, we thoroughly explain not only the three deformations by swelling but also their evolvement with decreasing water content. A fitting model is also presented based on a multi-diffusion equation to reveal the deformation processes more clearly, the results from which are in good agreement with the experimental results.

Adsorption of the Prototype Anionic Anthraquinone, Acid Blue 25, on a Modified Banana Peel: Comparison with Equilibrium and Kinetic Ligand–Receptor Biochemical Data

The adsorptive behavior of dye Acid Blue 25 (AB25) on the banana peel is studied with two objectives in view. First, from an environmental point of view, AB25 is considered a model of the anionic dyes, and the banana peel is a quite abundant agricultural waste which can be reused as adsorbent. Second, and on account of the recent research on possible applications of 1-aminoanthraquinone derivatives in pharmacological research, physicochemical studies on the interaction of AB25 anionic prototype and related dyes with different kinds of biomass surfaces can be useful in the basic modeling studies on the antagonist-P2 receptor interactions carried out by different researchers with 1-aminoanthraquinone dyes. A careful analysis of the acid–base properties of the biomass provides the number of weak acid groups, that was found to be 0.288(7) mmol g–1 for modified banana peel in 0.1 M KNO3. An uptake capacity value of 0.215(13) mmol g–1 is obtained when data from batch experiments are fitted to sorption isotherms. Specific surface is calculated and compared with other biosurfaces. Kinetics of the process allows calculating an intraparticle diffusion coefficient, Di, of 0.331(1) × 10–13 m2 s–1. Desorption and column experiments demonstrate the feasibility for an application for AB25 recovery in remediation. Finally, a comparison with thermodynamic and kinetic data from receptor–ligand studies is also carried out.

Born energy, acid-base equilibrium, structure and interactions of end-grafted weak polyelectrolyte layers

This work addresses the effect of the Born self-energy contribution in the modeling of the structural and thermodynamical properties of weak polyelectrolytes confined to planar and curved surfaces. The theoretical framework is based on a theory that explicitly includes the conformations, size, shape, and charge distribution of all molecular species and considers the acid-base equilibrium of the weak polyelectrolyte. Namely, the degree of charge in the polymers is not imposed but it is a local varying property that results from the minimization of the total free energy. Inclusion of the dielectric properties of the polyelectrolyte is important as the environment of a polymer layer is very different from that in the adjacent aqueous solution. The main effect of the Born energy contribution on the molecular organization of an end-grafted weak polyacid layer is uncharging the weak acid (or basic) groups and consequently decreasing the concentration of mobile ions within the layer. The magnitude of the effect increases with polymer density and, in the case of the average degree of charge, it is qualitatively equivalent to a small shift in the equilibrium constant for the acid-base equilibrium of the weak polyelectrolyte monomers. The degree of charge is established by the competition between electrostatic interactions, the polymer conformational entropy, the excluded volume interactions, the translational entropy of the counterions and the acid-base chemical equilibrium. Consideration of the Born energy introduces an additional energetic penalty to the presence of charged groups in the polyelectrolyte layer, whose effect is mitigated by down-regulating the amount of charge, i.e., by shifting the local-acid base equilibrium towards its uncharged state. Shifting of the local acid-base equilibrium and its effect on the properties of the polyelectrolyte layer, without considering the Born energy, have been theoretically predicted previously. Account of the Born energy leads to systematic, but in general small, corrections to earlier theoretical predictions describing the behavior of weak polyelectrolyte layers. However, polyelectrolyte uncharging results in a decrease in the concentration of counterions and inclusion of the Born Energy can result in a substantial decrease of the counterion concentration. The effect of considering the Born energy contribution is explored for end-grafted weak polyelectrolyte layers by calculating experimental observables which are known to depend on the presence of charges within the polyelectrolyte layer: inclusion of the Born energy contribution leads to a decrease in the capacitance of polyelectrolyte-modified electrodes, a decrease of conductivity of polyelectrolyte-modified nanopores and an increase in the repulsion exerted by a planar polyelectrolyte layer confined by an opposing wall.

Synthesis, characterization and acid catalysis of solid acid from peanut shell

A strong Brønsted solid acid was synthesized by sulfonation of the partially carbonized agricultural biowaste peanut shell. The acidity of the Brønsted solid acid was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectra (FT-IR) and solid-state nuclear magnetic resonance (NMR) spectroscopy. The characterization results show that sulfonation on the peanut shell carbon produces a carbon based solid acid containing three functional Brønsted acid sites: weak acidic OH groups, strong acidic COOH and SO3H groups. The acid strength of the solid acid is stronger than that of HZSM-5(Si/Al=75), but still weaker than that of 100% H2SO4. The catalytic reaction tests indicate that this solid acid catalyst exhibits high activity and excellent recyclability for biodiesel production.

Pd nanoparticles prepared by grafting of Pd complexes on phenol-functionalized carbon supports for liquid phase catalytic applications

An activated carbon was functionalized by oxidation with HNO3 or H2O2 to increase the number of acidic groups on its surface. A sample of HNO3-oxidized carbon was treated thermally to remove unstable functions. Detailed characterization by a combination of techniques revealed that this stabilization procedure allowed selecting weaker acid sites of phenolic type. H2O2 functionalization gave also mainly surface phenols but in lower amounts. Palladium grafting was carried out in water at room temperature by ligand exchange between a carboxylate complex and the surface oxygenated groups. Activation was carried out thermally and the samples grafted on the most oxidized supports proved more difficult to reduce. The catalytic activity of the obtained Pd/C catalysts was evaluated in the reduction of 2-methyl-2-nitropropane (MNP) into t-butylamine (TBA). The most active materials were those prepared on H2O2-modified carbon and on the stabilized support. In the latter case, the superior activity was explained by the robustness of the grafting anchors which could not decompose during thermal activation together with the active role of weak acidic groups in the catalytic reaction itself.

Preparation of highly developed mesoporous activated carbon by H4P2O7 activation and its adsorption behavior for oxytetracycline

Preparation of highly developed mesoporous activated carbons from renewable source Arundo donax Linn was performed using H4P2O7 as activator. The influences of chemical impregnation ratio (mass of H4P2O7:A. donax Linn), activation temperature and soaking time on the properties (yield, BET surface area, pore volume and surface functional group) of activated carbon were investigated. The optimal activated carbon (ALAC) was characterized by scanning electron micrograph (SEM), N2 adsorption/desorption isotherms, X-ray photoelectron spectrometry (XPS) and oxytetracycline (OTC) adsorption experiments. Results showed that the pore development was significant at temperatures >400°C, and reached a maximum BET surface area (1463m2/g) at 600°C and maximum total pore volume (1.24cm3/g) at 500°C. At a low impregnation ratio of 0.4, BET surface area and pore volume could reach as high as 1150.69m2/g and 0.59m3/g. Both BET surface area and pore volume initial increase followed by a decrease after reaching a maximum, with the maximal surface area was obtained at an impregnation ratio of 0.75 and maximal pore volume at 1.0. BET surface area and mesopore volume reached maximum after 10h of soaking. Acidic surface groups followed the order of: strong acidic groups>weak acidic groups>intermediate acidic groups. Low activation temperature was favorable to the formation of acidic surface functional groups. With the increase of soaking time, the acidic surface functional initial increase was followed by a gradual decrease and finally tended to level off.

Modification of submicron barium titanate particles via sol-gel synthesis of interface layers of SiO2 for fabrication of polymer-inorganic composites with improved dielectric properties

Modification of the surface of submicron BaTiO3 particles by SiO2 layer using sol-gel method has led to significant (>50%) increase in the dielectric permittivity and decrease in the dielectric losses of the composites prepared via introduction of BaTiO3 into a matrix of poly(vinyl alcohol) cyanoethyl ester. The effect has been due to the formation of basic hydroxy groups (Bronsted centers) at the filler surface; these groups can interact with weakly acidic hydroxyl groups of poly(vinyl alcohol) cyanoethyl ester, thus improving the compatibility of the polymer matrix and the filler.

The Mechanism of Heavy Metal Biosorption on Green Marine Macroalga Enteromorpha linza

The biosorption mechanism of divalent Ni(II), Cd(II), and Pb(II) ions onto calcium treated Entemorpha linza was investigated as a function of pH, contact time, biomass dose, and temperature. The experimental data were evaluated by Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. The uptake capacity of the tested metal ions was markedly influenced by pH in the range of 2–3.5 and maximum rates were observed at pH 5–5.5. The kinetics of the metal ions adsorption were rather rapid, with 90% of adsorption occurring within 10 min. In addition to batch sorption tests, the functional groups on the cell wall matrix of the biomass were revealed by potentiometric titration data and Fourier transform infrared analysis. The relative contribution of the chemical groups involved in metal biosorption such as carboxyl, amino, sulfonate was evaluated to characterize their binding mechanisms using these instrumental techniques. The density of strong and weak acidic functional groups in the biomass was found to be 0.25 and 0.95 mmol g−1 biomass, respectively. In conclusion, the present work showed that the marine algae E. linza could be used as a potentially cost‐effective biosorbent for the treatment of complex wastewater containing heavy metals.

Synthesis and properties of amphoteric copolymer of 5-vinyltetrazole and vinylbenzyl phosphonic acid

Amphoteric polymers have been studied for various applications such as separation of low molecular weight organic molecules from inorganic salt mixtures, selective ion transport, drug delivery through membranes of biological interest, separation of ionic drugs and proteins, and separation of alcohol and water. Typical amphoteric polymers consist of weak base and weak acid groups. In present study, the copolymerization of 5-vinyltetrazole (VT) and diisopropyl-p-vinylbenzyl phosphate (DIPVBP) via free radical polymerization is studied. The reactivity ratio of VT and DIPVBP, which is calculated from Kelen-Tudos plot, is 0.251 and 0.345, respectively. The amphoteric copolymer of VT and diisopropyl-p-vinylbenzyl phosphonic acid (poly(VT-co-VBPA)) is obtained from hydrolysis of the copolymer of VT and DIPVBP (poly(VT-co-DIPVBP)). Poly(VT-co-VBPA) is thermally stable under 190 °C. The anhydrous proton conductivity of amphoteric poly(VT-co-VBPA) can reach 1.54 × 10-4 S cm−1 at 170 °C with an activation energy of 114.7 kJ mol−1. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3486–3493

Synthesis and structure–activity relationships of carboxylic acid derivatives of pyridoxal as P2X receptor antagonists

Carboxylic acid derivatives of pyridoxal were developed as potent P2X1 and P2X3 receptor antagonists with modifications of a lead compound, pyridoxal-5′-phosphate-6-azophenyl-2′,5′-disulfonate (5b, iso-PPADS). The designing strategies included the modifications of aldehyde, phosphate or sulfonate groups of 5b, which may be interacted with lysine residues of the receptor binding pocket, to weak anionic carboxylic acid groups. The corresponding carboxylic acid analogs of pyridoxal-5′-phosphate (1), 13 and 14, showed parallel antagonistic potencies. Also, most of 6-azophenyl derivatives (24–28) of compound 13 or 14 showed potent antagonistic activities similar to that of 5b at human P2X3 receptors with 100 nM range of IC50 values in two-electrode voltage clamp (TEVC) assay system on the Xenopus oocyte. The results indicated that aldehyde and phosphoric or sulfonic acids in 5b could be changed to a carboxylic acid without affecting antagonistic potency at mouse P2X1 and human P2X3 receptors.

Efficient Tertiary Amine/Weak Acid Bifunctional Mesoporous Silica Catalysts for Michael Addition Reactions

AbstractWe describe the development and application of efficient bifunctional acid–base mesoporous silica catalysts, denoted hereafter as Ext‐SBA‐15‐NMe2, comprising tertiary amine and silanol (weak acid) groups for the Michael addition reaction. The catalysts were synthesized by grafting tertiary amine containing organosilane into the mesoporous channel pores of SBA‐15 mesoporous silica in polar protic solvent (isopropyl alcohol) or nonpolar solvent (toluene). The resulting materials, Ext‐SBA‐15‐NMe2‐IPA or Ext‐SBA‐15‐NMe2‐Tol, respectively, were used as catalysts for the Michael addition reactions between trans‐β‐nitrostyrene(s) and active methylene compounds, such as malononitrile, acetylacetone, and diethylmalonate, at different temperatures. A variable‐temperature NMR‐array technique was used to monitor the reactant conversion and the reaction progress. Among the active methylene compounds tested with trans‐β‐nitrostyrene, malononitrile gave the highest conversion of 90 % in 0.3 h at 0 °C if catalyzed by the catalyst Ext‐SBA‐15‐NMe2‐IPA, the silanol groups of which were not passivated by trimethysilyl (SiMe3) groups. Compared with Ext‐SBA‐15‐NMe2‐Tol, the Ext‐SBA‐15‐NMe2‐IPA material (whose the amine groups were grafted in polar‐protic solvents), in particular, demonstrated an effective cooperative bifunctional catalysis because of its optimized proportions of tertiary amine groups and a significant number of surface silanol groups that were judiciously left behind on the material with this optimized synthetic strategy. The catalytic activity of this material was found to be significantly higher than that of the corresponding material that was grafted in toluene and that contained less optimized proportions of these two catalytic groups (i.e., amine and silanol groups). The bifunctional catalysts also showed good recyclability upon washing with acetone, which offered an effective way of regenerating the catalyst free from any undesired product/substrate bound on the surface of the catalysts.

New solution-processable small molecules as hole-transporting layer in efficient polymer solar cells

Small molecules TPDA, TPDB, and TPDH, comprising the same backbone TPD (N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine) and different carboxyl side chains were designed and synthesized as hole-transporting materials in polymer solar cells. These small molecules demonstrated improved solubility in polar solvents due to the introduction of the weakly acidic carboxyl groups. The lengths of the side chains can also influence the film forming ability. Compared to conventional PEDOT:PSS, these small molecules showed higher transmittance in the visible range as revealed by UV-vis measurements. Desirable energy-level alignment for efficient hole-transporting and electron-blocking ability was indicated by their absorption and UPS spectra. Without applying any post-treatment to these buffer layers, comparable and improved device performances were achieved compared with PEDOT:PSS buffered control devices. A high power conversion efficiency of 6.51% was realized by a TPDB buffered device employing a low band gap polymer PBDTTPD as the active material, which showed ∼15% efficiency enhancement over the control devices. Equally important, better device stability was demonstrated by using TPDB as the new hole-transporting layer.

Comparative study of sulfite pretreatments for robust enzymatic saccharification of corn cob residue

BackgroundCorn cob residue (CCR) is a kind of waste lignocellulosic material with enormous potential for bioethanol production. The moderated sulphite processes were used to enhance the hydrophily of the material by sulfonation and hydrolysis. The composition, FT-IR spectra, and conductometric titrations of the pretreated materials were measured to characterize variations of the CCR in different sulfite pretreated environments. And the objective of this study is to compare the saccharification rate and yield of the samples caused by these variations.ResultsIt was found that the lignin in the CCR (43.2%) had reduced to 37.8%, 38.0%, 35.9%, and 35.5% after the sulfite pretreatment in neutral, acidic, alkaline, and ethanol environments, respectively. The sulfite pretreatments enhanced the glucose yield of the CCR. Moreover, the ethanol sulfite sample had the highest glucose yield (81.2%, based on the cellulose in the treated sample) among the saccharification samples, which was over 10% higher than that of the raw material (70.6%). More sulfonic groups and weak acid groups were produced during the sulfite pretreatments. Meanwhile, the ethanol sulfite treated sample had the highest sulfonic group (0.103 mmol/g) and weak acid groups (1.85 mmol/g) in all sulfite treated samples. In FT-IR spectra, the variation of bands at 1168 and 1190 cm-1 confirmed lignin sulfonation during sulfite pretreatment. The disappearance of the band at 1458 cm-1 implied the methoxyl on lignin had been removed during the sulfite pretreatments.ConclusionsIt can be concluded that the lignin in the CCR can be degraded and sulfonated during the sulfite pretreatments. The pretreatments improve the hydrophility of the samples because of the increase in sulfonic group and weak acid groups, which enhances the glucose yield of the material. The ethanol sulfite pretreatment is the best method for lignin removal and with the highest glucose yield.

Mitochondrial accumulation of a lipophilic cation conjugated to an ionisable group depends on membrane potential, pH gradient and pK a: implications for the design of mitochondrial probes and therapies

Mitochondria play key roles in a broad range of biomedical situations, consequently there is a need to direct bioactive compounds to mitochondria as both therapies and probes. A successful approach has been to target compounds to mitochondria by conjugation to lipophilic cations, such as triphenylphosphonium (TPP), which utilize the large mitochondrial membrane potential (Δψ(m), negative inside) to drive accumulation. This has proven effective both in vitro and in vivo for a range of bioactive compounds and probes. However so far only neutral appendages have been targeted to mitochondria in this way. Many bioactive functional moieties that we would like to send to mitochondria contain ionisable groups with pK (a) in the range that creates an assortment of charged species under physiological conditions. To see if such ionisable compounds can also be taken up by mitochondria, we determined the general requirements for the accumulation within mitochondria of a TPP cation conjugated to a carboxylic acid or an amine. Both were taken up by energised mitochondria in response to the protonmotive force. A lipophilic TPP cation attached to a carboxylic acid was accumulated to a greater extent than a simple TPP cation due to the interaction of the weakly acidic group with the pH gradient (ΔpH). In contrast, a lipophilic TPP cation attached to an amine was accumulated less than the simple cation due to exclusion of the weakly basic group by the ΔpH. From these data we derived a simple equation that describes the uptake of lipophilic cations containing ionisable groups as a function of Δψ(m), ΔpH and pK(a). These findings may facilitate the rational design of additional mitochondrial targeted probes and therapies.