Reduction of thrombogenicity of PVC-based sodium selective membrane electrodes using heparin-modified chitosan

Heparin-modified chitosan (H-chitosan) membrane was utilized to enhance biocompatibility of sodium selective membrane electrode based on the highly thrombogenic polyvinyl chloride (PVC). Sodium ion sensing film was prepared using PVC, sodium ionophore-X, potassium tetrakis(chlorophenyl)-borate, and o-nitrophenyloctylether. The PVC-based sensing film was sandwiched to chitosan or H-chitosan to prevent platelet adhesion on the surface of PVC. Potentiometric response characteristics of PVC-chitosan and PVC-H-chitosan membrane electrodes were found to be comparable to that of a control PVC based sodium-selective electrode. This indicates that chitosan and H-chitosan layers do not alter the response behaviour of the PVC-based sensing film. Biocompatibility of H-chitosan was confirmed by in vitro platelet adhesion study. The platelet adhesion investigations indicated that H-chitosan film is less thrombogenic compared to PVC, which could result in enhancement of biocompatibility of sodium selective membrane electrodes based on PVC, while maintaining the overall electrochemical performance of the PVC-based sensing film.

Amodiaquine polymeric membrane electrode

The construction and electrochemical response characteristics of two types of poly(vinyl chloride) (PVC) membrane sensors for the determination of amodiaquine hydrochloride (ADQ.2HCl) are described. The sensing membrane comprised an ion-pair formed between the cationic drug and sodium tetraphenyl borate (NaTPB) or potassium tetrakis(4-chlorophenyl) borate (KTCPB) in a plasticized PVC matrix. Eight PVC membrane ion-selective electrodes were fabricated and studied. Several plasticizers were studied namely, dioctyl phthalate (DOP), 2-nitrophenyl octyl ether (NPOE), dioctyl phenylphosphonate (DOPP) and bis(2-ethylhexyl)adipate (EHA). The sensors display a fast, stable and near-Nernstian response over a relative wide ADQ concentration range (3.2 x 10(-6) to 2.0 x 10(-2) M), with slopes comprised between 28.5 and 31.4 mV dec(-1) in a pH range comprised between pH 3.7 and 5.5. The assay of amodiaquine hydrochloride in pharmaceutical dosage forms using one of the proposed sensors gave average recoveries of 104.3 and 99.9 with R.S.D. of 0.3 and 0.6% for tablets (Malaritab) and a reconstituted powder containing ADQ.2HCl, respectively. The sensor was also used for dissolution profile studies of two drug formulations. The sensor proved to have a good selectivity for ADQ.2HCl over some inorganic and organic compounds, however, berberine chloride interfered significantly. The results were validated by comparison with a spectrophotometric assay according to the USP pharmacopoeia.

Organic cation transport by Malpighian tubules ofDrosophila melanogaster: application of two novel electrophysiological methods

Transport of the prototypical organic cation tetraethylammonium (TEA) by the Malpighian tubules, ureters and gut of Drosophila melanogasterwas studied using two novel electrophysiological techniques. Both techniques exploited the high selectivity of the cation exchanger potassium tetra-p-chlorophenylborate for tetraalkylammonium compounds relative to inorganic cations such as K+. In the first technique, TEA fluxes were measured using a non-invasive self-referencing TEA-selective microelectrode positioned in the unstirred layer near the surface of each tissue. TEA fluxes from bath to lumen as large as 6 pmol cm–2s–1 were measured across the lower (reabsorptive) segment of the Malpighian tubule and the ureter bathed in saline containing 0.1 mmol l–1 TEA. Corresponding bath-to-lumen fluxes across the secretory main segment of the Malpighian tubule and the posterior midgut were∼1 pmol cm–2 s–1. TEA transport by the lower Malpighian tubule was enhanced by hyperpolarization of the basolateral membrane potential and was inhibited by cimetidine, quinidine, vinblastine and verapamil. In the second technique, TEA concentration was measured using a TEA-selective microelectrode positioned in droplets of fluid secreted by Malpighian tubules set up in saline droplets under oil in a Ramsay assay. Results from the Ramsay assay confirmed the dominant role of the lower Malpighian tubule in net transepithelial secretion of TEA and inhibition of TEA transport by cimetidine. Kinetic parameters (Jmax and Kt) were determined using both approaches.

A novel potentiometric approach for detection of beta-adrenergics and beta-adrenolytics in high-performance liquid chromatography

Potentiometric approach enabling sensitive and reliable detection for a series of 20 autonomic beta-adrenergic ligands with the use of poly(vinyl chloride) (PVC) based liquid membrane electrode coatings in the normal-bore cation exchange HPLC and narrow-bore reversed phase HPLC system is presented. It was found that in both kinds of HPLC modes with a contemporary hybrid polymer-silica packings an application of electrodes containing a tetrakis(p-chlorophenyl)borate (TCPB) gives limits of detection below to 8.0x10(-7) mol l(-1) (injected concentrations). In case of highly hydrophobic beta-adrenergic drugs the use of binary aqueous mobile phases with high concentrations of acetonitrile (up to 25% v/v) shifting an observable detection limits (DL) down to 2.0x10(-8) mol l(-1), especially for electrodes with addition of trioctylated alpha-cyclodextrin. The characteristics of developed potentiometric detectors was established by proposed a quantitative structure-potentiometric response relationships (QSPRRs) for a series of diversified beta-adrenergic compounds and for a set of the PVC based electrodes using TCPB alone as well as in combination with trioctylated alpha-cyclodextrin, dibenzo-18-crown-6, or calix[6]arene hexaethylester as the neutral macrocycle ionophore. A highly significant QSPRRs equations were obtained leading to reasonable prediction of the DL of specified electrodes in terms of the computationally derived set of molecular descriptors of beta-adrenergics and beta-blocking agents and similar amino alcohol type xenobiotics.

Fentanyl-selective polymeric membrane electrode

A poly (vinyl chloride) membrane electrode with dibutyl phthalate as plasticizer based on a fentanyl-tetrakis(4-chlorophenyl)borate ion-pair complex for the determination of fentanyl citrate in injections is described. A linear response over the range 1 x 10(-5) mol.dm-3 to 1 x 10(-2) mol.dm-3 drug with a slope of 59.3 +/- 0.6 mV/decade was established. The optimum pH range was 1 to 6. The lower detection limit was 8 x 10(-6) mol.dm-3 fentanyl citrate (2.7 micrograms cm-3 fentanyl). There were negligible interferences from a number of inorganic cations, structural analogues, and some common drug additives used in injections. The electrode proposed has been successfully applied to determine fentanyl citrate in injections. The results correlated well with those obtained by the United States Pharmacopoeia standard procedure.

A chronoamperometric method to estimate changes in the membrane composition of ion-selective membranes

A new chronoamperometric method is used to estimate changes in the membrane composition of mobile-site, ionophore-based membranes. The characteristic features of the chronoamperometric curves (initial current, slope, break time) of valinomycin-based, potassium-selective membranes loaded with potassium tetrakis(4-chlorophenyl)borate are correlated with the mobile-site and free ionophore concentration in the membrane. limiting cases for strong and negligible ion pair formation are distinguished. Replicate measurements indicate a relative standard deviation in the calculated values less than 10%. The practical applicability of the method was tested with membranes incorporated into conventional ion-selective electrode bodies or cast onto microfabricated planar sensor structures.

Aldol reaction of enol esters catalyzed by cationic species paired with tetrakis(pentafluorophenyl)borate

The crossed aldol reaction of enol esters, which are weak carbon nucleophiles, with aldehydes was effectively carried out under mild conditions by using a catalytic amount of several cationic species paired with tetrakis(pentafluorophenyl)borate.

In vivo antileishmanial action of Ir-(COD)-pentamidine tetraphenylborate on Leishmania donovani and Leishmania major mouse models

Ir-(COD)-pentamidine tetraphenylborate which has previously been studied on promastigote forms of Leishmania, was investigated for its antileishmanial properties compared with pentamidine used as reference compound. In vitro, the iridium complex had the same IC50 value on intracellular forms of Leishmania as pentamidine (15 microM). In vivo, the compound could not be injected intravenously due to the DMSO excipient so that the treatments were performed intraperitoneally or subcutaneously. On the L. donovani LV9/Balb/C mouse model, the iridium complex was not toxic after intraperitoneal treatment at 232 mg/kg/day x 5 or 147 mumoles/kg/day x 5, whereas all the mice died within five days when treated at the same dose with pentamidine isethionate. However, only 23% of parasite suppression was observed with the iridium complex. On a L. major MON 74/Balb/C mouse model, susceptible to intravenously administered pentamidine at 6.7 mumoles/kg/day x 5 (54% of parasite suppression), the iridium complex exhibited 32% of parasite suppression after a treatment at 76 mumoles/kg/day x 5 administered subcutaneously. This slight activity is of interest since pentamidine isethionate is not active under these conditions. Transmission electron microscopy of amastigotes from infected and treated mice show aggregation of ribosomal material, distension of the nuclear membrane and kDNA depolymerization. The mechanism of action therefore involves several targets: membranes, ribosomes and kDNA. According to our results, the Iridium complex is a suitable candidate to be encapsulated in drug carriers such as liposomes or nanoparticles.

Uptake into leishmania donovani promastigotes and antileishmanial action of an organometallic complex derived from pentamidine

Iridium (Ir)-(COD)-pentamidine tetraphenylborate (CAS 225-75-4) was selected from a primary screening to be evaluated in vitro on three Leishmania (L.) strains comparatively to pentamidine used as reference compound. The IC50 values obtained from in vitro evaluation on promastigotes of L. major CRE 26, L. donovani DD8 and L. donovani LV9 were 3.9, 23.5, and 3.3 mumol/l for Ir-(COD)-pentamidine tetraphenylborate and 1.6, 7.7, and 3.9 mumol/l for pentamidine isethionate, respectively. Cytotoxicity on mouse peritoneal macrophages led to determine a chemotherapeutic index of 1.7 for Ir-(COD)-pentamidine tetraphenylborate and 4 for pentamidine. Considering L. donovani DD8, the uptake of iridium complex by the promastigotes was shown to be saturable with a Km value of 17.4 mumol/l and Vmax of 1.3 nmol/mg protein/2 h. After 2 and 4 h incubation of treated promastigotes in drug free medium the absence of Ir-complex efflux is in favour of intracellular drug binding. As a matter of fact iridium complex was shown to bind ribosomal subunits in vitro, with no effect on macromolecular biosynthesis.

Structure of tBuCO-Gly-Gly psi [CH2-N+H2]NHEt.BPh4-

N-(tert-Butylcarbonylglycylaminoethyl)-N-(ethyl)ammonium tetraphenylborate, C11H24N3O+2.C24H20B-, Mr = 549.57, triclinic, P-1, a = 11.567 (2), b = 11.922 (2), c = 14.484 (3) A, alpha = 70.99 (2), beta = 74.83 (2), gamma = 59.33 (1) degrees, V = 1613.1 A3, Z = 2, D chi = 1.13 g cm-3, lambda(Cu K alpha) = 1.5418 A, mu = 4.69 cm-1, mu Rmax much less than 1, F(000) = 592, T = 293 K, R = 0.058 for 3491 observed reflections. This pseudopeptide is folded by a short N(+)-H ... O = C hydrogen bond (N3 ... O1 = 2.81 A) which closes a ten-membered ring. This results in a beta-turn structure that can be classified as type II on the basis of the conformational angles for the N-terminal glycine. The conformational angles phi 1, psi 1, phi 2 and psi 2 are -53.4 (6), 139.7 (4), 91.5 (5) and -62.6 (6) degrees respectively.

Structure of hexakis(N-methylimidazole-N')iron(II) tetraphenylborate dichloromethane solvate

[Fe(C4H6N2)6][B(C6H5)4]2.CH2Cl2, Mr = 1271.88, monoclinic, P2(1)/c, a = 20.5320 (6), b = 15.113 (3), c = 23.611 (7) A, beta = 109.01 (3) degrees, V = 6926.9 (1) A3, Z = 4, Dx = 1.23 g cm-3, mu(Mo K alpha) = 0.70966 A, graphite monochromator, mu = 3.37 cm-1, F(000) = 2680, T = 298 K, R = 0.057 for 2310 unique observed reflections. The asymmetric unit consists of a single [Fe(C4H6N2)6]2+ cation, two distinct BPh-4 anions, and one CH2Cl2. The Fe atom is octahedrally coordinated by six N-methylimidazole ligands. The six Fe-N bond distances per cation range from 2.174 (11) to 2.228 (10) A, the average being 2.207 (12) A. This average distance is within the range previously observed for high-spin ferrous complexes. The ring planes of N-methylimidazole ligands that lie trans to each other have interplane angles of 17.56, 18.48 and 157.56 degrees. These ring planes lie approximately either parallel or perpendicular to equatorial Fe-N bonds.

Structural requirement for the rapid movement of charged molecules across membranes. Experiments with tetraphenylborate analogues

Charge-pulse experiments were performed in the presence of structural analogues of tetraphenylborate (TPB) on membranes made of dioleoyl phosphatidylethanolamine and dioleoyl phosphatidylcholine. The analysis of the experimental results using a previously proposed model allowed the calculation of the partition coefficient, beta, and of the translocation rate constant, kappa i. The temperature dependence of the partition coefficients was used to calculate the thermodynamics of the adsorption of the lipophilic ions to the membranes. The analysis of the translocation rate constants obtained at different temperatures yielded detailed information on the free energy of the TPB-analogues within artificial lipid bilayer membranes, and on the activation energy of the translocation rate constants. The adsorption of the different TPB-analogues to the membranes was only slightly affected by their structure, whereas a dramatic influence of the structure on the free energy of the lipophilic ions within the membranes was observed. The free energy of the ions in the membranes decreased from triphenylcyanoborate (TPCB) to tetrakis(3-trifluoromethylphenyl)borate (TTFPB) by more than 31 kJ/mol (7.4 kcal/mol). This could be concluded from the observed increase in the translocation rate constant by almost six orders of magnitude. The change of the free energy in the membrane was used for the estimation of an effective radius of the TPB-analogues with respect to TPB.

A liquid ion-exchanger alternative to KCl for filling intracellular reference microelectrodes

We have developed a filling solution for silanised microelectrodes consisting of potassium tetrakis (p-chlorophenyl) borate in octanol. Microelectrodes filled with this reference liquid ion-exchanger (RLIE) have equal selectivities to Na and K, and give the same membrane potential as do KCl-filled microelectrodes. The RLIE microelectrodes are more stable, less damaging to the cell membrane and do not leak Cl- ions. Their high resistance, however, makes them unsuitable for recording rapid potential changes or for passing current.