Electrochemical Studies of Thiol Self‐Assembled Monolayers at a Heated Gold‐Wire Microelectrode

Mercaptoundecanoic acid (MUA) and glutathione (GSH) self‐assembled monolayers were prepared on gold‐ wire microelectrode. Cyclic voltammetry was used to investigate the influence of temperature on electrochemical behaviors of Fe(CN)₆^3?/4? and Ru(NH₃)₆^3+/2+ at these SAMs modified electrodes in aqueous solution. It is found that temperature shows great influence on electron transfer (ET) and mass transport (MT) for the two SAMs modified electrodes and the influence of temperature depends on the charge properties of the redox couples and terminal groups of SAMs and the structure of the monolayer on gold surface. The temperature can greatly increase MT rate of Fe(CN)₆^3?/4? at both MUA and GSH modified electrodes. However, the increased MT rate doesn't have any effect on the CV's for Fe(CN)₆^3?/4? /MUA system. For Ru(NH₃)₆^3+/2+ , temperature can greatly improve the electrochemical reaction in both MUA and GSH modified electrodes, which is ascribed to temperature‐induced diffusion and convection and the electrostatic interaction between Ru(NH₃)₆^3+/2+ and negatively charged carboxyl groups on the electrode surface.     

Luminescent Study on Nd3+ Complexes Containing Carboxylate‐Dithiolene and Alkoxide‐Dithiolene Ligands

Reaction of ligand L H₂ (4,5‐bis[carboxymethylthio]‐1,3‐dithiol‐2‐thione) with neodymium silyl‐amide (Nd[N(TMS)₂]₃; TMS= ‐SiMe₃), in a ratio 2:1, yields a neodymium‐dithiolene‐carboxylato complex ( 1 ) (Nd( L H) L ). Similarly, reaction of 2 equivalents of L′ H₂ (4,5‐bis[2′‐hydroxyethyl)thio]‐1,3‐dithiol‐2‐thione) and one equivalent of neodymium silyl‐amide (Nd[N(TMS)₂]₃) allowed the isolation of complex 2 , with a ligand:metal ratio of 3:2. ATR‐IR spectrum of 1 displays a broad band characteristic of an OH group showing that one carboxylate group remains protonated. Emission spectrum of complex 1 under excitation in the visible region (at 360 nm i.e. on the ligand) displayed typical emission bands of the Nd³⁺, showing that energy transfer from the ligand to the lanthanide was achieved (i.e. “antenna effect”). No significant quenching from the remaining –OH group was detected. In the case of complex 2 , the main emission bands characteristic of the Nd³⁺ ion have been observed, by excitation at 495 nm.     

A Water‐Stable Uranyl Organic Framework as a Highly Selective and Sensitive Bifunctional Luminescent Probe for Fe3+ and Tetracycline Hydrochloride

A new coordination polymer (H₂bpy)_0.5?[(UO₂)_1.5(ipa)₂(H₂O)] ( 1 ) (H₂ipa=isophthalic acid, bpy=4,4′‐bipyridine) was synthesized by hydrothermal condition. It was characterized by IR spectroscopy, elemental analysis, TG‐DTA analysis, and powder X‐ray diffraction. Analysis of single‐crystal X‐ray diffraction results showed that the title compound exhibited a double chain bridged by the different uranyl ions and ipa^2? ligands. Through the hydrogen bond interactions and π???π stacking interactions, the double chains were assembled into the three‐dimensional supramolecular framework. Furthermore, the compound can be used as a promising bifunctional luminescence sensor for detecting and identifying Fe³⁺ and tetracycline hydrochloride antibiotic molecules with high selectivity and sensitivity in aqueous solutions. Moreover, the luminescent sensing mechanisms for different analytes were proposed. Moreover, the electronic properties of title compound were explored by density functional theory (DFT) calculations. The sensor system has been successfully applied for the detection of Fe³⁺ and tetracycline hydrochloride with high recovery percentages and low relative standard deviation in real river water samples.     

Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene: A Redox‐Active Ligand with a Pronounced Selectivity for Divalent Metal Ions

Octamethyl‐1, 1′‐di(2‐pyridyl)ferrocene ( 1 ) acts as molecular electrochemical sensor for magnesium, calcium, zinc, and cadmium ions in acetonitrile solution. The new redox peak, anodically shifted by ca. 0.40 V, which appears in the cyclic voltammogram of 1 in the presence of even small amounts (10 mol %) of these ions, is unaffected by an excess of alkali metal ions. Metal complexation is accompanied by a batho‐ and hyper‐chromic shift of the band in the visible region of the UV‐Vis spectrum of 1 . A detailed study of the behaviour of 1 towards zinc chloride in acetonitrile solution has revealed that 1 is able to accommodate a maximum of two zinc ions. Oxidation of zinc‐coordinated 1 leads to partial decomplexation. The N‐methyl and N‐benzyl species 1 Me⁺, 1 Me₂²⁺, 1 Bzl⁺ and 1 Bzl₂²⁺ have been synthesized and the former two structurally investigated by X‐ray diffraction. Alkylation causes an anodic shift of the redox potential of the ferrocene nucleus, which is linearly dependent on the number of alkyl groups introduced. Octamethyl‐1, 1′‐di(2‐thiophenyl)ferrocene ( 2 ) has also been synthesized and structurally characterized by X‐ray diffraction. Cyclic voltammetry has revealed that, in contrast to 1 , 2 does not respond to the divalent metal ions studied.     

Studies of Adsorption Kinetics and Defects of Self‐Assembled Thiol Monolayers on Gold by Capacitance Plane Plot

The capacitive property of an electrode/electrolyte interface can be described by complex capacitance. The capacitance plane plots (CPPs) of ideal polarized and kinetic controlled electrodes are derived based on the concept of complex capacitance. By using CPPs, the capacitance of electrode/electrolyte interface can be conveniently determined. In this work, CPPs obtained in ac impedance experiments are employed for the first time in studying the kinetics of adsorption process of the thiol monolayer. The coverage of octadecanethiol (ODT) monolayer on gold is examined as a function of adsorption time. The adsorption process of ODT molecules on gold exhibits two distinct phases: an initial rapid step followed by a slow one. The simple Langmuir model best explains our experimental data in the initial adsorption stage. CPPs and cyclic voltammetry (CV) indicate that, in the initial adsorption step, the ODT monolayer contains defects whose number decreases with the increasing of adsorption time.     

Synthesis,Crystal Structure,and Electrochemical Behaviour of an Azido μ‐bridged Ni2+ Complex

A homo‐dinuclear Ni^II complex was prepared from 2, 6‐bis(3, 5‐dimethylpyrazolyl)pyridine (Me₄‐bpp) and azide ions in nonaqueous media. It was characterized by single crystal X‐ray structural analysis, IR spectroscopy, and elemental analysis. In addition, the electrochemical properties of the compound were determined with cyclic voltammetry in DMF. The title compound crystallizes in the P2₁/n monoclinic space group, with unit cell parameters a = 8.978(1), b = 12.459(1), c = 17.764(1) Å, ß =100.603(3)°, V = 1953.0(3) ų, Z = 2. The Ni²⁺ ion has a distorted octahedral environment involving three nitrogen atoms of the Me₄‐bpp ligand, two nitrogen atoms from the bridged azide group, and one nitrogen atom from the terminal azide group. The Ni···Ni distance is 3.273(5) Å.     

Electrochemistry of Levo‐Thyroxin on Edge‐Plane Pyrolytic Graphite Electrode: Application to Sensitive Analytical Determinations

The electrochemical response of sodium levo‐thyroxin (T₄) at the surface of an edge plane pyrolytic graphite (EPPG) electrode is investigated using cyclic voltammetric technique in the presence of 0.1 M HCl as supporting electrolyte. T₄ underwent totally irreversible oxidation at this system and a well‐defined peak at 821 mV was obtained. Compared to the signals obtained in the optimized conditions at bare glassy carbon and carbon paste electrodes, the oxidation current of T₄ at an EPPG electrode was greatly enhanced. The electrochemical process of T₄ was explored and the experimental conditions were optimized. The oxidation peak current represented a linear dependence on T₄ concentration from 0.01 to 10 µM. The detection limit of 3 nM (S/N=3) was obtained for 250 s accumulation at 0.3 V. Determination of T₄ in a synthetic serum sample demonstrated that this sensor has good selectivity and high sensitivity.     

Synthesis,Crystal Structures,and Luminescent Properties of Two Complexes based on 5‐tert‐Butylisophthalic Acid and 1, 2‐Bis(4‐pyridyl) Ethane

Abstract. Two coordination polymers, namely, [Zn(bpe)_0.5(Htbip)(tbip)_0.5] · H₂O ( 1 ) and [Cd(bpe)_0.5(tbip)] ( 2 ) [H₂tbip = 5‐tert‐butylisophthalic acid and bpe = 1, 2‐ bis(4‐pyridyl) ethane] were synthesized through hydrothermal reactions. Single‐crystal X‐ray diffraction analysis reveals that complex 1 presents a three‐dimensional (3D) six‐connected uninodal structure with the type of topology of svi‐x/I4/mcm → Ibam, whereas complex 2 holds a 2D 4⁴‐sql layer structure. Moreover, the photoluminescent properties of the complexes at room temperature were investigated.     

pH‐Directed Synthesis of Two Luminescent Zinc(II) Coordination Compounds based on 5‐Aminotetrazole‐1‐propanoic Acid

Two Zn^II‐tetrazole‐carboxylate coordination compounds are reported, mononuclear [Zn(atzpa)₂(H₂O)₄] · 2H₂O ( 1 ) and one‐dimensional [Zn(atzpa)₂(H₂O)₂]_n ( 2 ), derived from 5‐aminotetrazole‐1‐propanoic acid (Hatzpa). The structures of both compounds are determined by the pH value of the reaction system. The luminescence properties of Hatzpa and the compounds were investigated at room temperature in the solid state. Furthermore, differential scanning calorimetry (DSC) and thermogravimetric‐differential thermogravimetric (TG‐DTG) analyses were applied to evaluate the thermal decomposition behavior of such compounds. The relevant thermodynamic parameters (ΔH, ΔS, and ΔG) of the decompostion process of compound 1 were calculated, as well.     

Ferrocenyl‐Functionalised Molybdenum Imido Complexes: An Approach to Redox‐Tunable Olefin Polymerisation Catalysts

[(FcdippN)₂MoCl₂(DME)] ( 1 ) was used as starting material for the synthesis of the novel ferrocenyl‐functionalised complexes [(FcdippN)₂Mo(CH₂CMe₂Ph)₂] ( 2 ), [(FcdippN)₂Mo(OTf)₂(DME)] ( 3 ), and [(FcdippN)Mo(CHCMe₂Ph)(O^tBu)₂] ( 4 ) (Fcdipp = 4‐ferrocenyl‐2,6‐diisopropylphenyl). The crystal structure of 2 was determined. Electrochemical investigations by cyclic voltammetry suggest a communication of the ferrocenyl unit and the molybdenum centre in these compounds. The monoalkylation of [(DippN)₂MoCl₂(DME)] ( 5 ) to [(DippN)₂Mo(CH₂CMe₂Ph)Cl] ( 6 ) (Dipp = 2,6‐diisopropylphenyl) was achieved.     

Gold Nanoparticles Functionalized by a Dextran‐Based pH‐ and Temperature‐Sensitive Polymer

A dextran‐based dual‐sensitive polymer is employed to endow gold nanoparticles with stability and pH‐ and temperature‐sensitivity. The dual‐sensitive polymer is prepared by RAFT polymerization of N‐isopropylacrylamide from trithiocarbonate groups linked to dextran and succinoylation of dextran after polymerization. The functionalized nanoparticles show excellent stability under various conditions and can be stored in powder‐form. UV and DLS measurements confirm that the temperature‐induced optical changes and aggregation behaviors of the particles are strongly dependent on pH.

     

Carbon‐Supported Pt Particles as a Catalyst for Electrooxidation of Methanol and Cyclic Voltammetry Studies Under Acidic Conditions

Electrooxidation of methanol on glassy carbon (GC) electrode modified by optimum carbon supported Pt electrocatalyst (Pt‐C/GC) in acid media is investigated. The catalyst is prepared by ultrasonicating Pt/C powders in aqueous media. The activity of prepared Pt‐C/GC electrode is studied in potential range of 0–1000 mV (versus SCE) by cyclic voltammetry. The results showed that the Pt/C dispersed layer at the surface of glassy carbon electrode, behaves as an electrocatalyst for the oxidation of methanol in acid medium by optimum loading of Pt (0.2 mg cm^?2). The electrochemical properties of prepared electrode are studied under various conditions. However the effect of various parameters in the catalytic enhancement of Pt/C, such as platinum loading, sulfuric acid concentration, different scan rates, different final potentials, and medium temperature are considered and examined.     

Synthesis and Luminescent Properties of Two Zinc(II) Coordination Polymers Constructed by 4‐(Pyridin‐4‐ylmethoxy)benzolic Acid Ligand

Two coordination polymers, namely [Zn(L)Cl] ( 1 ) and [Zn(L)₂] ( 2 ) [L = 4‐(pyridin‐4‐ylmethoxy)benzolic acid] were synthesized under hydrothermal conditions and characterized by single‐crystal X‐ray diffraction analyses, powder X‐ray diffraction, and thermogravimetric analysis. Compounds 1 and 2 have a two‐dimensional square‐shaped structure (the dimensions are 15.43 × 15.43 Å for 1 and 12.064 × 15.017 Å for 2 ) with (4⁴ · 6²) topology. Moreover, compounds 1 and 2 exhibit a 3D supramolecular structure made up by strong π–π interactions from the adjacent layers. Furthermore, compounds 1 and 2 show good fluorescence properties in the solid state at room temperature.     

Nucleophilic Addition of Thiaproline to Electrochemically Derived o‐Quinone,Application to the Sensitive Voltammetric Detection of Thiaproline

The mechanism of electrochemical behavior of catechol in the presence of thiaproline is investigated by cyclic voltammetry, controlled‐potential coulometry and spectrophotometric tracing of the reaction coordinate. The results indicate that thiaproline participate in with an ECEC mechanism in a nucleophilic (Michael) addition to o‐quinone. Effect of pH of buffer solution on reaction pathway is studied and showed that addition of thiaproline to the o‐quinone is performed only in solutions with pHs higher than 5. These results indicate that the addition of thiaproline is occurred first from amine functional group. In the second step, the addition of carboxylate group of thiaproline to C‐5 of catechol results the final product with a lactone ring in its structure. Observation of two isosbestic point in absorption spectrum during the progress of the electrolysis together with the FT‐IR results for final product can be presented as evidence for two step addition of thiaproline to catechol. Final product, due to the electron donor property of thiaproline, more easily oxidized respect to the former catechol and as a result, a new redox couple is obtained for this compound in lower potentials. The easier anodic oxidation of addition product (relative to catechol) caused to an increase in anodic current for catechol, which is proportional to the thiaproline concentration. The differential pulse voltammetry (DPV) is applied as a sensitive voltammetric method for the detection of thiaproline. A linear range from 5×10^?8 to 5×10^?6 M with a detection limit of 1×10^?8 M is resulted for thiaproline. With respect to the reversibility of the electrochemical reactions in the mechanism, and also more facile oxidation of the addition products, the square‐wave voltammetry is presented as a method with considerably more sensitivity for the detection of sub‐micromolar amounts of thiaproline. The advantageous properties of the voltammetric method for thiaproline detection lie in its excellent catalytic activity, sensitivity and simplicity.     

Luminescence Regulation of Silver‐Thiolate Clusters Protected by 1,2‐Dithiolate‐o‐carborane

Engineering the surface of the metal clusters with the core structure maintained and tuning their luminescence in a wide range is still a challenge in the nanomaterial research. We modified six mono‐pyridyl ligands with different electronic effects (conjugation effect or induction effect) on a superatomic silver cluster [Ag₁₄(C₂B₁₀H₁₀S₂)₆(CH₃CN)₈] (denoted as Ag₁₄) through in situ site‐specific surface engineering, and obtained the corresponding clusters [Ag₁₄(C₂B₁₀H₁₀S₂)₆(CH₃CN)₆(L₁/L₂)₂] (denoted as NC‐1, 2, L₁/L₂ = 4‐acetylpyridine/ 4‐carboxypyridine) and [Ag₁₄(C₂B₁₀H₁₀S₂)₆(L₃/L₄/L₅/L₆)₈] (denoted as NC‐3, 4, 5, 6, L₃/L₄/L₅/L₆ = 4‐phenylpyridine/4‐(1‐naphthyl)pyridine/9‐(4‐pyridine)anthracene/9‐(4‐pyridine)pyrene). Through the modification of the Ag₁₄ cluster, a wide‐range luminescence from blue to red was realized. This work might provide a practical guide for improving the emission performance of metal clusters via surface engineering.     

A New Zinc(II) Coordination Polymer with a Threefold‐Interpenetrating Diamondoid Net: Synthesis,Crystal Structure and Luminescent Property

The three‐dimensional (3D) coordination polymer, [Zn(dpa)(bib)]_n ( 1 ) [H₂dap = diaphonic acid and bib = 1,4‐bis(imidazol‐1‐yl)benzene], was prepared by hydrothermal synthesis and characterized by single‐crystal X‐ray diffraction, FT‐IR spectroscopy, XRPD, and elemental analysis. Crystal structure determination revealed that complex 1 shows a threefold diamond topological net. Furthermore, the solid‐state luminescent property of [Zn(dpa)(bib)]_n was investigated.     

Polyethyleneimine Solubilized Luminescent Au(I)‐Thiolate Complexes for Highly Sensitive and Selective Cyanide Anion Sensing

Cyanide (CN^?) is a highly toxic anion to human beings, exploring efficient probes for sensitive and selective detection of it is very important. In this study, we explore a simple one‐pot reaction to synthesize polyethyleneimine (PEI) solubilized Au(I)‐MUA (11‐mercaptoundecanoic acid) complexes under mild condition. The as prepared Au(I)‐MUA complexes exhibit strong red photoluminescence (PL) and can act as sensitive and selective CN^? optical sensor in aqueous media based on the chemical reaction between CN^? and gold atom that quench the fluorescence, and the limit of detection is 10 nM, which is ～270 times lower than the maximum contamination level (2.7 μM) in drinking water permitted by WHO. Additionally, real water sample from a local lake is tested with these optical sensors, and the PL variation caused by 0.1 μ CN^? can be observed.     

Synthesis,Crystal Structure,Theoretical Study,and Luminescence Spectroscopy of A W/Cu/S Cluster with 1, 10‐Phenanthroline

The reaction of [NH₄]₂WOS₃ with Cu(CH₃CN)₄ClO₄ and 1, 10‐phenanthroline(phen) in CH₂Cl₂ afforded the butterfly‐shaped cluster {[WOS₃Cu₂(phen)₂] · CH₂Cl₂} ( 1 ), which was characterized by elemental analysis, single‐crystal X‐ray diffraction as well as IR and fluorescence spectroscopy. The complex crystallizes in the triclinic system with space group P$\bar{1}$ [a = 8.3976(17) Å, b = 9.6771(19) Å, c = 18.460(4) Å, α = 89.94(3)°, β = 80.33(3)°, γ = 70.38(3)°, V = 1390.5(5) ų, and Z = 2]. Single crystal X‐ray diffraction analysis reveals that complex 1 displays pairwise π–π stacking. Density functional theory and time‐dependent density functional theory calculations at the B3LYP/LanL2DZf+6‐31G* level were performed on complex 1 to rationalize its experimental absorption spectra. Fluorescence spectroscopy reveals that complex 1 exhibits luminescence in EtOH solution at room temperature.     

Stimuli‐Responsive Shape Switching of Polymer Colloids by Temperature‐Sensitive Absorption of Solvent

The dynamic manipulation of colloidal particle shape offers a novel design mechanism for the creation of advanced responsive materials. To this end, we introduce a versatile new strategy for shape control of anisotropic polymeric colloidal particles. The concept utilizes temperature‐sensitive absorption of a suitable solvent from a binary mixture. Specifically, increasing the temperature in the vicinity of the demixing transition of a binary mixture causes more solvent to be absorbed into the polymeric colloidal particle, which, in turn, lowers the glass transition temperature of the polymer inside the particle, with a concomitant decrease in viscosity. The balance between the internal viscosity and surface tension of the particle is thus disrupted, and the anisotropic shape of the particle shifts to become more spherical. Subsequent rapid temperature quenching can halt the process, leaving the particle with an intermediate anisotropy. The resultant shape anisotropy control provides new routes for studies of the phase transitions of anisotropic colloids and enables the fabrication of unique particles for materials applications.