Effects of gamma-aminobutyric acid, progesterone and ionophore A23187 on acrosome reaction of tree shrew sperm in vitro: examination of acrosome reaction with an improved fluorescence microscopy

A number of acrosome reaction (AR) initiators have been found to be effective in inducing AR of human, laboratory and domestic animal sperm. Using an improved simple fluorescence microscopy, effects of gamma-aminobutyric acid (GABA), progesterone and ionophore A23187 on sperm AR of tree shrew, a useful animal model in biomedical research, have been investigated. Spontaneous AR in 4.92-7.53% of viable sperm was observed. Complete AR in 10.31-18.25% of viable tree shrew sperm was obviously induced by 5 mu M and 10 mu M calcium ionophore A23187, 1 mM GABA, and 5 mu M progesterone, and there were no significant differences between their abilities to initiate complete AR. No significant differences of AR percentages between 1- and 2-h treatments with A23187, progesterone and/or GABA were observed. These results suggested that the responses of tree shrew sperm to these AR initiators are similar to that of human and other mammalian sperm. (C) 1997 Elsevier Science B.V.

Mercury selective electrochemical sensor based on a double armed crown ether as ionophore

PVC based membranes of a double armed crown ether, N, N'-dibenzyl, 1,4,10,13-tetraoxa-7, 16-diaza cyclooctadecane (I) as ionophore with sodium tetra phenyl borate (NaTPB) as anion excluder and with many plasticizing solvent mediators have been prepared and used for Hg(II) ion determination. The membrane with DBBP (dibutyl butyl phosphonate ) as plasticizer with various ingredients in the ratio PVC: I: NaTPB: DBBP (150: 12: 2: 100) shows the best results in terms of working concentration range (3.1x10-5-1.0x10-tM) with a Nernstian slope (29.0′0.5 mV/decade of activity). The electrode works in the pH range 2.1-4.5. The response time of the sensor is 15s and it can be used for about 4 months in aqueous as well as in non-aqueous medium. It has good stability and reproducibility. The potentiometric selectivity coefficient values for mono-, di-, and trivalent cations are tabulated. The sensor is highly selective for Hg2+ in the presence of normal interferents like cadmium, silver, sodium and iron.

ALKALI AND ALKALINE-EARTH METAL-ION TRANSFER ACROSS THE LIQUID-LIQUID INTERFACE FACILITATED BY IONOPHORE ETH157

The H+, Li+, Na+, K+, Mg2+, Ca2+ and Ba2+ ion transfer across the water/nitrobenzene (NB) and water/1,2-dichloroethane (DCE) interfaces, facilitated by the ionophore ETH157, has been investigated by cyclic voltammetry (CV). The mechanism of the transfer process has been discussed, and the diffusion coefficients and the stability constants of the complexes formed in the nitrobenzene phase have been determined.

Ionophore Based Bismuth Film Electrode for Lead

A Nafion/ionophore, 4-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) composite coated and bismuth film modified glassy carbon electrode. (GC/NA-IONO/BiFE) was described to determine trace lead sensitively and selectively. The characteristics of such modified GC/NA-IONO/BiFE were studied by scanning electron microscopy and cyclic voltammetry. The influence of various experimental parameters upon the stripping lead signal at the GC/NA-IONO/BiFE was explored. Under the optimized conditions, the differential pulse voltammetric stripping response is highly linear over the 0.1-8.0 nM lead range examined (180s preconcentration at -1.2V), with a detection limit of 0.044nM and good precision (RSD=5.4% at 0.5nM). Also applicability to seawater samples was demonstrated at such modified electrode. The high selectivity of ionophore coupled with the excellent electrochemical characteristics of bismuth endow the GC/NA-IONO/BiFE a promising and robust tool for monitoring of trace lead rapidly and precisely.

新型纳米材料及离子载体化学修饰电极的制备及其在痕量重金属检测中的应用

随着工农业生产的迅速发展，重金属污染问题越来越严重。由于重金属能 够在土壤、水体等环境中不断积累，并且通过食物链而进入人体内蓄积，因此对 人类健康构成潜在的危害。当人体内重金属含量过量时，会导致各种疾病的发生。 所以对痕量重金属污染物进行监测和分析，在食品安全、临床诊断和环境监测等 方面具有重要的现实意义。因此，研究快速、准确、灵敏、方便的检测重金属的 新方法十分必要。 近年来，化学修饰电极由于能够赋予电极新的、特定的功能，在提高电化 学选择性和灵敏度方面有着独特的优越性，因而成为电分析化学领域研究的热 点，并且被广泛应用于重金属元素的测定。但是，由于电极材料的限制，灵敏度 虽然有所改进，却始终很难达到一个新的高度。要提高化学修饰电极对重金属检 测的灵敏度，必须加入一些辅助的方法。 最近，纳米材料在很多分析方法中得到广泛应用，这些材料表现出很多它 们在常规尺度时所没有的独特的性质，如量子尺寸效应、表面效应、小尺寸效应、 量子隧道效应以及介电限域效应等。因此，作为一种新型的电极材料在电化学检 测和分析方面受到人们的日益关注。由于纳米材料本身具有大的比表面积和高的 表面自由能，这种纳米材料修饰电极的灵敏度得到大幅度提高。 离子载体是一类具有一个特定空腔的大环分子，能够从溶液中实现对某一 特定离子的萃取使之进入到有机相中。离子载体是电位型传感器敏感膜中的核心 成分，尽管它具有很高的选择性，但是除了电位分析外，在其它方面的用途却很 少被关注，可能是由于其本身的非导电性能所致。本论文采用纳米材料所特有的 对重金属离子强大的吸附性能和离子载体优良的选择性，制备了纳米材料及离子 载体修饰玻碳电极并用来对实际水样中痕量的重金属进行检测。主要内容包括以 下几个方面： 1.制备新型碳纳米管/铋膜复合修饰电极，研究了重金属钴在电极上的电化 学性能。结果表明，这种新型复合修饰电极的灵敏度得到显著提高，能实现最低 检测限为8´10-11 M的钴的吸附富集溶出。 2.利用羟基磷灰石的强吸附能力和碳纳米管的优异电化学性能，制备了新型 新型纳米材料及离子载体化学修饰电极的制备及其在痕量重金属污染物检测中的应用 II 的碳纳米管-纳米羟基磷灰石的双纳米复合材料，并将其用于金属镉的富集溶出。 结果表明，双纳米复合材料具有比单一材料更优异的性能，更有助于金属镉的富 集溶出。采用碳纳米管-纳米羟基磷灰石的双纳米复合材料修饰电极，能实现最 低检测限为4´10-9 M的镉的富集溶出，灵敏度得到明显提高。 3. 将导电性好、抗氧干扰能力强的铋膜与对重金属具有良好选择性的离子 载体相结合，制备了基于铋膜/离子载体的新型修饰电极，研究了金属铅在其表 面的富集溶出。结果表明，这种新型修饰电极的灵敏度和选择性都大为提高，具 有更高的溶出峰电流和更好的抗干扰能力，可以实现最低检测限为4.4´10-11 M 的铅的富集溶出。 4. 利用羟基磷灰石的强吸附能力和其三维多孔结构、离子载体对重金属离 子优异的选择性以及Nafion 膜良好的离子交换作用和化学稳定性，制备了基于 纳米材料和离子载体的新型化学修饰电极。这种方法不仅有助于提高对金属铅的 选择性和灵敏度，而且大大提高了富集效率。采用该新型化学修饰电极，能够实 现最低检测限为1´10-9 M的铅的富集溶出。

Novel Potentiometric Membrane Sensor for the Determination of Trace Amounts of Chromium(III) Ions

A plasticized Cr3+ ion sensor by incorporating 2,3,8,9-tetraphenyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene (TTCT) ionophore exhibits a good potentiometric response for Cr3+ over a wide concentration range (1.0×10-6-1.0×10-1 M) with a slope of 19.5 mV per decade. The sensor response is stable for at least three months. Good selectivity for Cr3+ in comparison with alkali, alkaline earth, transition and heavy metal ions, and minimal interference are caused by Li+, Na+, K+, Co2+, Hg2+, Ca2+, Pb2+ and Zn2+ ions, which are known to interfere with other chromium membrane sensors. The TTCT-based electrode shows a fast response time (15 s), and can be used in aqueous solutions of pH 3 - 5.5. The proposed sensor was used for the potentiometric titration of Cr3+ with EDTA and for a direct potentiometric determination of Cr3+ content in environmental samples.

Facilitated ion transfer across the micro-liquid /liquid interface supported at the tip of a silanized micropipette

Glass micropipettes with silanized inner walls can be filled with an organic solvent for voltammetric measurements in an aqueous solution. This arrangement was employed to investigate systematically the mechanism of facilitated potassium ion transfer by an ionophore dibenzo-18-crown-6 (DB18C6) across a micro-water/1.2-dichloroethane(W/DCE) interface supported at the tip of a silanized micropipette. Our experimental results verify that this facilitated ion transfer across the liquid/liquid interface did occur by an interfacial complexation-dissociation process (TIC-TID mechanism). The ratio of the diffusion coefficient of DB18C6 to that of its complexed ion in the DCE phase was calculated to be 1.74 +/- 0.07.

Alkali metal ions transfer across a water/1,2-dichloroethane interface facilitated by a novel monoaza-B15C5 derivative

In this paper, a novel monoaza-B15C5 derivative, N-(2-tosylamino)-isopentyl-monoaza-15-crown-5 (L), is used as an ionophore to facilitate alkali metal cations transfer across a water/1,2-dichloroethane (W/DCE) interface. Well-defined voltammetric behaviors are observed at the polarized W/DCE interfaces supported at micro- and nano-pipets except Cs+. The diffusion coefficient of this ionophore in the DCE phase is calculated to be equal to (3.3+/-0.2) x 10(-6) cm(2) s(-1). The experimental results indicate that a 1:1 (metal: ionophore) complex is formed at the interface with a TIC/TID mechanism. The selectivity of this ionophore towards alkali ions follows the sequence Na+ > Li+ > K+ > Rb+ > Cs+. The logarithm of the association constants (log beta(1)(0)) of the LiL+, NaL+, KL+ and RbL+ complexes in the DCE phase are calculated to be 10.6, 11.6, 9.0 and 7.1, respectively. The kinetic parameters are determined by steady-state voltammograms using nanopipets. The standard rate constants (k(0)) for Li+, Na+, K+ and Rb+ transfers facilitated by L are 0.54+/-0.05, 0.63+/-0.09, 0.51+/-0.04 and 0.46+/-0.06 cm s(-1), respectively. The pH values of aqueous solution have little effect on the electrochemical behaviors of these facilitated processes. The results predicate that this new type of ionophore might be useful to fabricate electrochemical sensor of sodium ion.

Study of facilitated potassium ion transfer across a water vertical bar 1,2-dichloroethane interface using different phase volume ratio systems

A study of potassium ion transfer across a water \ 1,2-dichloroethane (W \ DCE) interface facilitated by dibenzo-18-crown-6 (DB18C6) with various phase volume ratio systems is presented. The key point was that a droplet of aqueous solution containing a redox couple, Fe(CN)(6)(3-)/Fe(CN)(6)(4-), with equal molar ratio, was first attached to a platinum electrode surface, and the resulting droplet electrode was then immersed into the organic solution containing a hydrophobic electrolyte to construct a platinum electrode/aqueous phase/organic phase system. The interfacial potential of the W \ DCE within the series could be externally controlled because the specific compositions in the aqueous droplet make the Pt electrode function like a reference electrode as long as the concentration ratio of Fe(CN)(6)(3-)/Fe(CN)(6)(4-) remains constant. In this way, a conventional three-electrode potentiostat can be used to study the ion transfer process at a liquid \ liquid (L \ L) interface facilitated by an ionophore with variable phase volume ratio (r = V-o/V-w). The effect of r on ion transfer and facilitated ion transfer was studied in detail experimentally. We also demonstrated that as low as 5 x 10(-8) M DB18C6 could be determined using this method due to the effect of the high phase volume ratio.

Investigation of ion transfer across the micro-water/nitrobenzene interface facilitated by a fullerene derivative

A functionalized fullerene derivative containing a monoaza-18-crown-6 moiety was investigated by facilitated ion (such as Li+, Na+, K+, NH4+, Mg2+, and Ca2+) transfer across the micro-water/nitrobenzene interface supported at the tip of a micropipet. The current responses were detected by cyclic voltammetry and Osteryoung square wave voltammetry, which demonstrated that the facilitated ion transfer does occur by an interfacial complexation-dissociation process. The diffusion coefficient of this compound in nitrobenzene was approximately (5.90 +/- 0.04) x 10(-7) cm(2) s(-1), which is 1 order of magnitude less than other common ionophores due to the large size of the molecule. The selectivity of this molecule toward the metal ions followed the sequence Na+ > Li+ > K+ > NH4+ > Ca2+ similar to Mg2+. In addition, this compound was also easy to form film at the water/nitrobenzene interface to inhibit the simple ion transfer of tetramethylammonium ion. However, the adsorption of this ionophore has less influence on the facilitated metal ion transfer.

Voltammetric study of the sodium ion transfer across micro-water/1,2-dichloroethane interface facilitated by terminal-vinyl liquid crystal crown ether

Sodium ion transfer across micro-water/1,2-dichloroethane (DCE) interface facilitated by a novel ionophore, terminal-vinyl liquid crystal crown ether (LCCE) was studied by cyclic voltammetry. LCCEs have potential applications because of their physicochemical properties and the utilization of crown ethers as selective ionophoric units in other functionalized compounds are interesting. Host-guest-type behavior for such compounds in the liquid-crystalline state is studied. The experimental results suggest that the transfer of the sodium ion facilitated by LCCE was controlled by diffusion of LCCE from bulk solution of DCE to the interface. The diffusion coefficient of LCCE in DCE was calculated to be equal to (3.62 +/- 0.20) x 10(-6) cm(2)/s. Steady-state voltammograms are due to sodium ion transfer facilitated by the formation of 1: 1 metal (M)-LCCE complex at the interface and the mechanism tends to be transfer by interfacial complexation or dissociation (TIC or TID). The stability constant of the complex formed was determined to be log beta(o) = 5.5 in DCE phase. The influence of parameters such as concentration of sodium ion and concentration of LCCE on the sodium ion transfer was investigated.

Sodium ion transfer across micro water/1,2-DCE interface facilitated by liquid crystal crown ether

The sodium ion transfer across the micro-water/1,2-dichloroethane interface facilitated by a novel ionophore, liquid crystal crown ether was studied systematically. The sodium ion transfer facilitated by LCCE is controlled by diffusion studied by cyclic voltammetry. The diffusion coefficient of LCCE in 1,2-dichloroethane was calculated to be equal to (2.61 +/- 0.12) X 10(-6) cm(2)/s and the stability constant of the complex between Na+ and LCCE was determined as lg beta (o) = 5.7 in 1,2-dichloroethane.

THE TRANSFER OF METAL-IONS ACROSS THE WATER-NITROBENZENE INTERFACE FACILITATED BY NEUTRAL CARRIER ETH-129

The transfer of H+, Li+, Na+, Zn2+, Mg2+ and Cu2+ facilitated by ionophore ETH 129 (N, N, N', N'-tetracyolohexyl-3-oxapentanediamide) across water/nitrobenzene interface has been studied by the cyclic voltammetry. The mechanism of the transfer process has been discussed. The diffusion coefficients and the stability constants of the complexes formed in the nitrobenzene phase have been determined.

INVOLVEMENT OF CA(2+) SIGNALING PATHWAY DURING OOCYTE MATURATION OF THE NORTHERN QUAHOG MERCENARIA MERCENARIA

In many molluses, it has been found that Ca2+ signaling pathway is involved in the resumption of meiotic maturation in oocytes. To better understand the possible role of Ca2+ signaling pathway in regulating meiotic maturation in oocytes of the northern quahog Mercenaria mercenaria, free extracellular Ca2+, A23187 (calcium ionophore), verapamil (calcium channel blocker), and trifluoperazin (calmodulin antagonist) were used to incubate oocytes or serotonin-induced oocytes by pharmacological methods. Results show that extracellular Ca2+ (50 similar to 200 mM) and A23187 (1 similar to 10 mu M) can stimulate the meiotic maturation. In addition, verapamil (1 similar to 100 mu M) and trifluoperazin (10 similar to 1,000 mu M) could inhibit serotonin-induced oocyte maturation. Therefore, Ca2+ is essential for the reinitiation of meiotic maturation in oocytes of the northern quahog. Moreover, an increase i [Ca2+]i can promote meiotic maturation.