The sensitive and reliable detection of Hg2+ and CN− as harsh environmental contaminants are of great importance. In view of this, a novel ‘on–off–on’ fluorescent probe based on nitrogen-rich silicon quantum dots (NR-SiQDs) has been designed for sensitive detection of Hg2+ and CN− ions in aqueous medium. NR-SiQDs were synthesized using a facile, one-step, and environment friendly procedure in the presence of 3-aminopropyl trimethoxysilane (APTMS) and ascorbic acid (AA) as precursors, with l -asparagine as a nitrogen source for surface modification. The NR-SiQDs exhibited strong fluorescence emission at 450 nm with 42.34% quantum yield, satisfactory salt tolerance, and superior photostability and pH stability. The fluorescence emission was effectively quenched using Hg2+ (turn-off) due to the formation of a nonfluorescent stable NR-SiQDs/Hg2+ complex, whereas after the addition of cyanide ions (CN−), Hg2+ ions could be leached from the surface of the NR-SiQDs and the fluorescence emission intensity of the quenched NR-SiQDs fully recovered (turn-on) due to the formation of highly stable [Hg(CN)4]2− species. After optimizing the response conditions, the obtained limits of detection were found to be 53 nM and 0.46 μM for Hg2+ and CN−, respectively. Finally, the NR-SiQD-based fluorescence probe was utilized to detect Hg2+ and CN− ions in water samples and satisfactory results were obtained, suggesting its potential application for environmental monitoring. 相似文献
Chloride anation of trans-Pt(CN)4ClOH2− has been studied with and without Pt(CN)42− present at 25.0°C by use of stopped-flow and conventional spectrophotometry and a 1.00 M perchlorate medium. The rate law in the absence of Pt(CN)42− is Rate=(p1 + p2 [H+] ) [Cl−]2 [complex]/(1 + q [Cl−]) with p1=(3.0 ± 0.1) × 10−5 M−2s−1, p2=(3.6 ± 0.1) × 10−5 M−3 s−1 and q=(0.62 ± 0.02) M−1. It is compatible with a chloride assistance via an intermediate of the type Cl-Cl-Pt(CN)4···OH22−, in which the reactivity of the aqua ligand is enhanced due to a partial reduction of the platinum. This mechanism of halide assistance is in principle the same as the modified reductive elimination oxidative addition (REOA) mechanism proposed by Poë, in which the intermediate is not split into free halogen, platinum(II) and water, and in which electron transfer not necessarily involves complete reduction to platinum(II). To avoid confusion with complete reductive eliminations, reactions without split of the intermediates are here termed halide-assisted reactions. The pH-dependence indicates acid catalysis via a protonated intermediate ClClPt(CN)4···OH3−.The Pt(CN)42−accelerated path has the rate law Rate= [Cl-] [Pt(CN)42−] [complex] where k=(39.9±0.5) M−2 s−1 and Ka=(4.0±0.2)10−2 M is the protolysis constant of trans-Pt(CN)4ClOH2−.Reaction between PtCl5OH2− and chloride is accelerated by Pt(CN)42− and gives PtCl62− as the reaction product. The rate law is Rate=k [Cl−] [Pt(CN)42−] [PtCl5OH2−] with k=(5.6 ± 0.2)10−3 M−2 s−1 at 35.0°C and for a 1.50 M perchlorate acid medium. The reaction takes place without central ion exchange. Alternative mechanisms with two consecutive central ion exchanges can be excluded. The role of Pt(CN)42− in this reaction is very similar to that of the assisting halide in the halide assisted anations. [p ]Reaction between trans-Pt(CN)4ClOH2− and PtCl42− gives Pt(CN)42− and PtCl5OH2− as products and has the rate law Rate=k[PtCl42−] [trans-Pt(CN)4ClOH2−] with k=(3.32 ± 0.02) M−1 s−1 at 25 °C for a 1.00 M perchloric acid medium. The formation of an aqua complex as the primary reaction product and the rate independent of [Cl−] shows that formation of a bridged intermediate of the type Pt(II)Cl4ClPt(IV)(CN)4OH23− is formed in the initial reaction step, not five-coordinated PtCl53−. 相似文献
Energy-transfer rate-constants from photo-excited [Ru(N–N)3]2+ (N–N = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (4dmb), 5,5′-dimethyl-2,2′-bipyridine (5dmb)) to [Cr(O–O)3]3− (O–O2− = ox2− ((COO−)2), mal2− (CH2(COO−)2)) and [Cr(CN)6]3− in encounter complexes were evaluated in aqueous solutions containing alkali metal ion. The rate constant depends on the molecular size of the ruthenium(II) complex: 1.8 × 108 s−1 for [Ru(bpy)3]2+ (molecular radius, r = 5.8 Å), 1.4 × 108 s−1 for [Ru(5dmb)3]2+ (r = 6.1 Å) and 0.96 × 108 s−1 for [Ru(4dmb)3]2+ (r = 6.7 Å) in the system of [Ru(N–N)3]2+–[Cr(ox)3]3− in aqueous solution. However, the rate constant is much more sensitive to the chromate(III) complex than to ruthenium(II) complex; 1.8 × 108 s−1 and 0.43 × 108 s−1 for [Cr(ox)3]3− (r = 4.0 Å) and [Cr(mal)3]3− (r = 4.2 Å) in the [Ru(bpy)3]2+–[Cr(O–O)3]3− systems, respectively. We conclude that the congeniality between the donor’s and acceptor’s ligands in encounter complex plays an important role in energy transfer in aqueous solution. 相似文献
The stoichiometry and kinetics of the reaction between [Cu(dien)(OH)]+ and [Fe(CN)6]3− in aqueous alkaline medium are described. The rate equation − (d[Fe(III)]/dt = {k1[OH−]2[[Cu(dien)(OH)]+] + k2[OH−] × [[Cu(dien)(OH)]+]2}([Fe(III)]/[Fe(II)]) (Fe(III) = [Fe(CN)6]3−; Fe(II) = [Fe(CN)6]4−, the 4:4:1 OH−/Fe(III)/[Cu(dien)(OH)]+ stoichiometric ratio and the nature of the ultimate products identified in the reaction solution suggest the fast formation of a doubly deprotonated Cu(III)-diamido complex which slowly undergoes an internal redox process where the ligand is oxidised to the Schiff base H2NCH2CH2NCHCHNH.The [[Cu(dien)(OH)]+]2 term in the rate equation is explained with the formation of a transient μ-hydroxo mixed-valence Cu dimer. A two-electron internal reduction of the Cu(III) complex yielding a Cu(I) intermediate is suggested to account for the presence of monovalent copper in a precipitate which forms at relatively high reactant concentrations and in the absence of dioxygen. 相似文献
The glow curve of chloroplasts excited by continuous light of high intensity (500 W · m−2) at pH 7.5 during cooling from +2 to −80°C consisted of seven bands appearing at about −30°C (TL−30), −15°C (TL−10), +10°C (TL+10), +30°C (TL+30), +50°C (TL+50), +65°C (TL+65) and +85°C (TL+80), in which TL stands for thermoluminescence. In the pH range from 5.5 to 9.0 the peak positions of the TL−30, TL−10, TL+50, TL+65 and TL+80 bands were independent of pH. On the other hand the peak positions of the TL+10 and TL+30 bands were gradually shifted from +25 to −5°C and from +20 to +40°C, respectively, as the pH was decreased from 9.0 to 5.5. The same pH-induced shift (from +25 to −5°C) was observed for the TL+10 band when electron transport was inhibited by DCMU. In dinoseb-treated chloroplasts the peak position of the main thermoluminescence band also exhibited pH dependency, and shifted from +20 to −20°C upon lowering the pH from 9.0 to 5.5. After the water-splitting system had been inactivated by Tris or NH2OH treatment no pH-induced shifts were observed in the peak positions of the thermoluminescence bands of DCMU and dinoseb-treated chloroplasts. The results suggest that the effect of pH on the thermoluminescence of untreated and inhibitor-treated chloroplasts is associated with protonation/deprotonation reactions occurring at the donor and acceptor sides of Photosystem II during the S1 → S2 transition of the water-splitting system. 相似文献
Potassium channels play essential roles in the regulation of male fertility. However, potassium channels mediating K+ currents in human sperm (IKSper) remain controversial. Besides SLO3, the SLO1 potassium channel is a potential candidate for human sperm KSper. This study intends to elucidate the function of SLO1 potassium channel during human sperm capacitation. Human sperm were treated with iberiotoxin (IbTX, a SLO1 specific inhibitor) and clofilium (SLO3 inhibitor) separately or simultaneously during in vitro capacitation. A computer-assisted sperm analyzer was used to assess sperm motility. The sperm acrosome reaction (AR) was analyzed using fluorescein isothiocyanate-conjugated Pisum sativum agglutinin staining. Sperm protein tyrosine phosphorylation was studied using western blotting. Intracellular Ca2+, K+, Cl−, and pH were analyzed using ion fluorescence probes. Independent inhibition with IbTX or clofilium decreased the sperm hyperactivation, AR, and protein tyrosine phosphorylation, and was accompanied by an increase in [K+]i, [Cl−]i, and pHi, but a decrease in [Ca2+]i. Simultaneously inhibition with IbTX and clofilium lower sperm hyperactivation and AR more than independent inhibition. The increase in [K+]i, [Cl−]i, and pHi, and the decrease in [Ca2+]i were more pronounced. This study suggested that the SLO1 potassium channel may have synergic roles with SLO3 during human sperm capacitation. 相似文献
Equilibrium data of aqueous two-phase systems composed of polyethylene glycol (4000 g mol−1 or 6000 g mol−1) and Li2SO4, (NH4)2SO4 or Na2SO4 at pH 6.5 and 25 °C were obtained. The efficiency of these in the partition of amylases derived from Aspergillus niger was determined. The experimental data of binodal curves and tie lines were used to estimate the group interaction parameters using the UNIFAC model. Additionally, the influence of phases on the activity of the enzymes was investigated. The results indicate that the polymer molar mass did not influence the biphasic region size. However, the cations under study presented differences in induction to phase formation. It was verified that the systems formed with the Na+ presented a larger biphasic region. The increase in the molar mass of the polymer caused the increase in the exclusion volume from 3970.732 g mol−1 to 5700.873 g mol−1. The transfer Gibbs free energy of enzymes presented values between −1296.30 kJ mol−1 and −2867.70 kJ mol−1, that is, the process was spontaneous for all systems studied. The systems formed by (NH4)2SO4 and PEG 4000 g mol−1 presented the best Ke result (3.421) and theoretical recovery of 80.35 %. 相似文献
Binding of [3H]aflatoxin B1 to rat plasma was investigated in vivo and vn vitro. Column chromatographic and polyacrylamide gel electrophoretic analysis clearly demonstrated that aflatoxin B1 bound primarily plasma albumin. Very little binding activity was shown by other plasma proteins. Spectrofluorimetric studies were undertaken to gain some insight into the nature of the aflatoxin-albumin interaction. Quenching of the lone tryptophan fluorescence intensity upon aflatoxin binding was due, at least in part, to a ligand-induced conformational change in the albumin molecule. Aflatoxin B1 binds an apolar site with an association constant of 30 mM−1 at pH 7.4 and 20°C. Neither charcoal treatment of rat albumin nor the presence of 0.15 M NaCl had many significant effect on the interaction. The association constant was pH-dependent, increasing about 1.7-fold as the pH increased from 6.1 to 8.4. This pH dependence is ascribed to a pH-induced conformational change in the albumin molecule. Thermodynamic studies indicated that the aflatoxin-albumin interaction was exothermic (ΔH = −29.3 kJ·mol−), with a ΔS value of −13.8 J·mol−1·K−1. 相似文献
The present study examines the kinetics and mechanism of the system [FePDTA(OH)]2− + 5CN− ⇌ [Fe(CN)5OH]3− + PDTA4− at pH= 11.0±0.02, I= 0.25 M and temperature = 25 ± 0.1 °C. The reaction has been studied spectrophotometrically at 395 nm (λmax of [Fe(CN)5OH]3−). The data show that the reaction has three distinguishable stages; the first stage is formation of [Fe(CN)5OH]3−, the second is conversion of [Fe(CN)5OH)]3− to [Fe(CN)6]3− and last is reduction of [Fe(CN)6]3− to [Fe(CN)6]3− by the released ligand, viz., PDTA. The first reaction shows variable order dependence on cyanide concentration, one at high cyanide concentration and two at low cyanide concentration. The second reaction exhibits first order dependence on the concentration of [Fe(CN)5OH]3− as well as cyanide. The reverse reaction between [Fe(CN)5OH]3− and PDTA is first order in [Fe(CN)5OH]3− and PDTA, and inverse first order in cyanide. On the basis of forward and reverse rate studies, a five-step mechanism has been proposed for the first reaction. 相似文献
The enthalpies of the hexokinase-catalyzed phosphorylation or glucose, mannose, and fructose by ATP to the respective hexose 6-phosphates have been measured calorimetrically in TRIS/TRIS HCl buffer at 25.0, 28.5, and 32.0°C. The effects on the measured enthalpy of the glucose/hexokinase reaction due to variation of pH (over the range 6.7 to 9.0) and ionic strength (over the range 0.02 to 0.25) have been examined. Correction for enthalpy of buffer protonation leads to δHo and δCpo values for the processes: eq-D-hexose + ATP4− = eq-D-hexose 6-phosphate2− + ADP3−+ H+. Results are δHo = −23.8 ± 0.7 kJ · mol−1 and δCpo = −156 ± 280 J·mol−1·K−1 for glucose. δHo = −21.9 ± 0.7 kJ·mol−1 and δCpo = 10 ± 140 J·mol−1·K−1 for mannose, and δHo = −15.0 ± 0.9 kJ·mol−1 and δCpo = −41 ± 160 J·mol−1·K−1 for fructose. Combination of these measured enthalpies with Gibbs energy data for hydrolysis of ATP4− and that for the hexose 6-phosphates lead to δSo values for the above hexokinase-catalyzed reactions. 相似文献
A novel ruthenium(II) complex of dipyridophenazine (DPPZ) with the ancillary ligand imidazole[4,5-f] [1,10]phenanthroline (IP), [Ru(IP)2(DPPZ)] (PF6)2, has been synthesized and characterized by elemental analysis, 1D and 2D 1H NMR, fast-atom bombardment mass spectra (FABMS), electronic spectroscopy and cyclic voltammetry. The DNA-binding properties of the complex were studied by spectroscopic methods. The intrinsic binding constant, K =2.1 × 107M−1, of the complex to calf thymus DNA has been determined by absorption titration in 5 mmol dm−3 Tris-HCl, 50 mmol dm−3 NaCl buffer (pH 7.0). The excited state lifetimes and luminescence quenching with [Fe(CN)6]4− as the quencher in the presence of DNA were also tested and mono-exponentiality was observed for the emission decay curves. Viscosity measurements together with the optical titrations unambiguously proved that the complex bound with DNA intercalatively and that the binding affinity to DNA was several times larger than that of the parent complex [Ru(bpy)2(DPPZ)]2+. 相似文献
In this study, 5,10,15,20-(4-sulphonatophenyl)porphyrin (TPPS4) was selected as a fluorescent probe due to its excellent characteristics including high quantum yield, good water solubility, and exceptional biocompatibility. With an excitation wavelength set at 515 nm, the optimal fluorescence emission wavelength for TPPS4 was measured at 642 nm. At this moment, the fluorescence signal of TPPS4 pink solution was in the ‘ON’ state. The fluorescence intensity of TPPS4 was quenched when ascorbic acid (AA) was introduced, which was due to the electron transfer quenching effect between AA and TPPS4. The colour of the corresponding solution changed from pink to green, and the fluorescence signal was in the ‘OFF’ state. When HPO42− was further introduced into the TPPS4–AA system, the quenched fluorescence intensity of TPPS4 was recovered due to the unique interaction between HPO42− and AA. At this time, the colour of the corresponding solution changed from green to red, and the fluorescence signal was in the ‘ON’ state. Therefore, an ‘ON–OFF–ON’ signal-switchable fluorescent probe was constructed based on TPPS4 to detect HPO42−. The results showed that the linear range of HPO42− was 4.0 × 10−9 to 1.7 × 10−6 M, and the detection limit was 1.3 × 10−9 M (S/N = 3). The sensing system exhibited high accuracy and sensitivity, and it could be used successfully to detect HPO42− in real samples. 相似文献
Previously discussed topological models of metal cluster bonding are now extended to the treatment of anionic rhodium carbonyl clusters having structures consisting of fused polyhedra. Examples of such rhodium carbonyl clusters built from fused octahedra include the ‘biphenyl analogue’ [Rh12(CO)30]−2, the ‘face-sharing naphthalene analogue’ [Rh9- (CO)19]3−, and the ‘perinaphthene analogue’, [Rh11- (CO)23]3−. More complicated anionic rhodium carbonyl clusters treated in this paper include the [Rh13(CO)24H5−q]q− anions (q = 2, 3, 4) having an Rh13 centered cuboctahedron, the [Rh14(CO)25- H4−q]q− (q = 3,4) and [Rh14(CO)26]2− anions based on a centered pentacapped cube, the [Rh15- (CO)30]3− anion having an Rh15 centered 14-vertex deltahedron, the [Rh15(CO)27]3− anion having a tricapped centered 11-vertex polyhedron, the [Rh17- (CO)30]3− anion having a tetracapped centered cuboctahedron, and the [Rh22(CO)37]4− anion having a hexacapped centered cuboctahedron fused to an octahedron so that the octahedron and the cuboctahedron share a triangular face. Analyses of the bonding topologies in [Rh9(CO)19]3−, [Rh17- (CO)30]3−, and [Rh22(CO)37]4− indicate that a polyhedral network containing several fused globally delocalized polyhedral chambers will not necessarily have a multicenter core bond in the center of each such polyhedral chamber. This observation is of potential importance in extending topological models of metal cluster bonding to bulk metals. 相似文献
qazTin-119 and phosphorus-31 NMR spectra have been recorded for a series of adducts of RSnX3 (R Me, Ph; X Cl, Br) with halide, tributylphosphine (P) and tributylphosphine oxide (L). The adducts were either 1:1 five coordinate or 1:2 six coordinate complexes. The tin-ll9 NMR spectra of mixtures of corresponding chloro and bromo complexes reveal, in most cases, all possible mixed halide species but much additional structural information is obtained from these spectra which could not be extracted from the spectra of individual compounds themselves. Thus in some cases, in the five coordinate species the Berry pseudorotation between isomers within a particular stoichiometry could be slowed on the NMR timescale which allowed a determination of the molecular structure. An equimolar mixture of [PhSnCl5]2− and [PhSnBr5]2− shows eleven of the twelve geometries possible for [PhSnClxBr5−x]2−. In the six coordinate series [RSnX4P]− the tin-119 NMR spectra of the mixtures of [RSnCl4P]− and [RSnBr4P]− allow the geometry to be determined as trans. Application of the pairwise additivity model for calculation of the tin-119 chemical shift positions for the mixed halide systems are discussed. 相似文献
The oscillations of the ZV and A thermoluminescence bands were investigated in spinach chloroplasts which had been dark-adapted for various time periods and subjected to a series of flashes at +2°C before continuous illumination at various low temperatures. When excited with continuous light below −65°C, the ZV band exhibited period-4 oscillation, with maxima on preflashes 0, 4 and 8. Above −65°C, the oscillation pattern depended greatly on the dark-adaptation period of the chloroplasts. In preilluminated samples (15 s light followed by 3 min dark), when the QB pool is half oxidized, the oscillation of the thermoluminescence intensity measured at −50°C was similar to that observed below −65°C. However, after the thorough dark-adaptation of the chloroplasts (6 h), when the major fraction of the QB pool is assumed to be oxidized, a binary oscillation appeared in the oscillation pattern, with maxima at odd flash numbers. Below −65°C, period-2 oscillation of the ZV band could not be induced by the dark-adaptation of the chloroplasts, suggesting an inhibition of electron exchange between QA and QB. Upon excitation of the chloroplasts with continuous light at −30°C, the A band oscillated with a periodicity of 4 with maxima at preflash numbers 2 and 6. At pH 7.5, the period-4 oscillation was converted into a period-2 oscillation by thorough dark-adaptation of the chloroplasts (24 h). Model calculations of the oscillatory patterns suggest that the period-4 oscillations of the ZV and A bands are determined by the concentrations [S0] + [S1] and [S2] + [S3], respectively, which are present after the preflashes prior to the low-temperature continuous illumination. The period-2 oscillations in the amplitudes of the ZV and A bands reflect the changes occurring in the redox state of the QB pool in a sequence of flashes. The possible relationship between the characteristics of the ZV and A bands and the temperature-dependence of the S state transitions was investigated. Comparison of the amplitudal changes of the B (S2Q−B and S3Q−B recombination) and Q (S2Q−A recombination) thermoluminescence bands as a function of the excitation temperature suggests that the S2 → S3 and S3 → S4 transitions are blocked at about −65 and −40°C, respectively. It is also concluded that the thermoluminescence intensity emitted by the reaction center is about twice as high in the S3 state as in the S2 state. 相似文献
The effects of single (unilateral) eyestalk ablation on the growth and reproduction of male and female Penaeus canaliculatus (Olivier) were compared with those of unablated (control) individuals. Prawns ≤ 10 mm in carapace length ablated in the premoult stage suffered high mortality. Prawns recognized as immature when ablated always moulted irrespective of their moulting stage; ovaries in females did not become vitellogenic nor did spermatogenesis occur in males. Mature females ablated in the premoult stage underwent moulting while those in the postmoult stage developed mature ovaries. Mature males in the postmoult or intermoult stages took longer to moult than those that were in the premoult stage when ablated. The Von Bertalannfy equations describing growth in P. canaliculatus were as follows: Lt = 25.6 [1−e−0.0756(t−to)]for ablated males; Lt = 25.3 [1−e−0.059(t−to)] for unablated males; Lt= 37.2 [1−e−0.048(t−to)] forablated females; Lt = 33.4 [1−e−0.044(t−to)] for unablated females. Differences in the growth rates were a result of both the moulting frequency and the increment in size at moult. However, the relative contribution of these two factors to growth varied with sex as well as with size. In both sexes, ablated individuals became sexually mature earlier; females spawned earlier. Although moulting frequency and the total number of spawns were greater for ablated females, the mean number of eggs produced (per spawn as well as total) by unablated females was higher and the mean hatching success was better. 相似文献