Synthesis of multidentate functional monomer for ion imprinting

In this work, N,N,N‐tri(2‐carboxyethyl)‐3‐(2‐aminoethylamino)propyl‐trimethoxysilane was prepared as a multidentate functional monomer. The 3D model of the monomer coordinating with Cu²⁺ indicated that the monomer is able to provide five ligating atoms like ethylenediaminetetraacetic acid‐Cu²⁺ to complex with Cu²⁺. When Cu²⁺ was used as a template ion, the synthesis conditions of Cu²⁺‐imprinted polymers were optimized upon orthogonal design. It is interesting to find that Cu²⁺‐imprinted polymer offers a selectivity coefficient of 192.2 when the molar ratio of Cu²⁺ to monomer was exactly 1:1. That means there is no excess ligating atom in the ion‐imprinted polymer and therefore, the nonspecific adsorption could be avoided. Benefiting from the excellent selectivity of Cu²⁺‐imprinted polymer, even if the concentration of Zn²⁺ was 25 times that of Cu²⁺, Cu²⁺‐imprinted polymer still affords a high selectivity coefficient. Finally, the optimal synthesis conditions for Cu²⁺‐imprinted polymer, except the pH, were adopted to prepare Ni²⁺‐imprinted polymer, and Ni²⁺‐imprinted polymer also offered satisfying selectivity to Ni²⁺. That implies this multidentate monomer is adaptable in ion imprinting and, the optimal synthesis conditions of Cu²⁺‐imprinted polymer except pH are likely suitable for the imprinting of other ions besides Cu²⁺.     

Novel Potentiometric Sensor Based on Molecular Imprinted Polyacrylamide for the Determination of Shikimic Acid in Herbal Medicine

ABSTRACT

A novel potentiometric sensor based on a molecular imprinted polymer was developed for the determination of shikimic acid in herbal medicine. The imprinted polymer was synthesized via bulk polymerization of the functional monomer in the presence of trimethylolpropane triacrylate as the cross-linker with 2,2′-azo-bisisobutyronitrile as the initiator and shikimic acid as the template. The sensing membrane was constructed by the inclusion of imprinted polymer in the polyvinyl chloride matrix. The effect of the identity of the imprinted polymer on the potentiometric response was observed. The optimal imprinted polyacrylamide was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The performance of the imprinted membrane based sensor, including the effects of pH, response time and selectivity coefficient, was investigated. The imprinted sensor exhibited a fast near-Nernstian response in the concentration range of 1?×?10^?5 to 1?×?10^?1?mol/L with a detection limit of 9?×?10^?6?mol/L. The analytical performance of the sensor supported the direct determination of shikimic acid in herbs, and the obtained results were validated by ultraviolet-visible absorption spectrophotometry. Advantages of the potentiometric sensor include enhanced sensitivity, high selectivity, long-term stability and low-cost fabrication, suggesting the device offers promise for the analysis of Chinese herbal medicine.     

Kinetics and Mechanism of the Demetallation of Macrocyclic Nickel(II) Complexes by Cyanide

The kinetics and the mechanism of the cyanide‐induced demetallation of a series of Ni²⁺ complexes with macrocyclic ligands of different ring size (12‐ to 14‐membered; see 1 – 4 ) and steric constraints was studied. Although the rates differ by almost five orders of magnitude when compared to each other under fixed experimental conditions (pH 10.5, [CN^?]=10^?2 M ), all reactions proceed through the relatively rapid formation of cyano adducts [Ni(CN)_nL] (n=1, 2), which then react with additional CN^? or HCN to give the final products. Of paramount importance for the reaction rate is the geometry and configuration of the cyano adducts [Ni(CN)_nL] (n=1,2). cis‐Dicyano derivatives with a folded macrocycle react faster than trans‐compounds. In the case of (1,4,8,11‐tetraazacyclotetradecane)nickel(2+) ([Ni ( 4 )]²⁺), which gives a trans‐ dicyano adduct, the base‐catalyzed N‐inversion necessary to obtain the cis‐dicyano derivative becomes rate determining at high CN^? concentrations.     

Reversible Synthesis of Sub‐10 nm Spherical and Icosahedral Gold Nanoparticles from a Covalent Au(CN)2− Precursor and Recycling of Cyanide to form Ferric Ferrocyanide for Cell Staining

A solution approach based on Au(CN)₂^? chemistry is reported for the formation of nanoparticles. The covalent character of the Au(CN)₂^? precursor was exploited in the formation of sub‐10 nm nanospheres (≈2.4 nm) and highly monodisperse icosahedral Au nanoparticles (≈8 nm) at room temperature in a one‐pot aqueous synthesis. The respective spherical and icosahedral Au morphologies can be controlled by either the absence or presence of the polymer polyvinylpyrrolidone (PVP). Using Au(CN)₂^? as a metal ion source, our findings suggest that the addition of citrate ions is necessary to enhance the particle formation rate as well as to generate a more homogeneous colloidal dispersion. Because of the presence of oxygen and the operation of a CN^? etching process associated with Au(CN)₂^? complex formation, an interesting reversible formation–dissolution process was observed, which allowed us to repeatedly prepare spherical and icosahedral Au nanoparticles. Time‐dependent TEM images and UV/Vis spectra were carefully acquired to study the reversibility of this formation–dissolution process. In view of the accompanying generation of toxic cyanide anions, we have developed a protocol to recycle cyanide in the presence of citrate ions through ferric ferrocyanide formation. After completion of particle formation, the residual solutions containing citrate ions and cyanide ions were processed to stain iron oxide nanoparticles endocytosized in cells. Additionally, the as‐prepared 8 nm Au icosahedra could be isolated and grown to larger 57 nm‐sized icosahedra using the seed‐mediated growth approach.     

Preparation of “dummy” l‐phenylalanine molecularly imprinted microspheres by using ionic liquid as a template and functional monomer

In this study, dummy imprinting technology was employed for the preparation of l‐ phenylalanine‐imprinted microspheres. Ionic liquids were utilized as both a “dummy” template and functional monomer, and 4‐vinylpyridine and ethylene glycol dimethacrylate were used as the assistant monomer and cross‐linker, respectively, for preparing a surface‐imprinted polymer on poly(divinylbenzene) microspheres. By the results obtained by theoretical investigation, the interaction between the template and monomer complex was improved as compared with that between the template and the traditional l‐ phenylalanine‐imprinted polymer. The batch experiments indicated that the imprinting factor reached 2.5. Scatchard analysis demonstrated that the obtained “dummy” molecularly imprinted microspheres exhibited an affinity of 77.4 M·10^?4, significantly higher that of a traditional polymer directly prepared by l‐ phenylalanine, which is in agreement with theoretical results. Competitive adsorption experiments also showed that the molecularly imprinted polymer with the dummy template effectively isolated l‐ phenylalanine from l‐ histidine and l‐ tryptophan with separation factors of 5.68 and 2.68, respectively. All these results demonstrated that the polymerizable ionic liquid as the dummy template could enhance the affinity and selectivity of molecularly imprinted polymer, thereby promoting the development of imprinting technology for biomolecules.     

A molecularly imprinted polymer receptor for the enantiomeric recognition of amino acid hydantoins mimicking cooperative hydrogen bonds between nucleotide bases

Using acrylamide as hydrogen bonding functional monomer and (5R)-5-benzylhydantoin as template, a molecularly imprinted polymer was prepared in a polar solvent, which exhibited good enantiomeric recognition properties. The binding characteristics and selectivity of the polymer were evaluated by batch methods. Scatchard analysis showed that two classes of binding sites were produced in the polymer matrix and their dissociation constants were calculated to be 3.5 × 10-5mol/L and 4.3 ×10-4 mol/L, respectively, by utilizing the model of multiple independent classes of binding sites. These results were more reasonable than those obtained by Scatchard analysis , which was in agreement with the prediction of the binding characteristics of the polymer by exploring the effect of acrylamide on UV spectra of (5R)-5-benzylhydantoin. The substrate- and enantio-selectivity of the polymer was investigated. Finally, the study of effect of water on the chiral separation factor of the polymer further proved that the hy     

A Post‐Synthetically Modified MOF for Selective and Sensitive Aqueous‐Phase Detection of Highly Toxic Cyanide Ions

Selective and sensitive detection of toxic cyanide (CN^?) by a post‐synthetically altered metal–organic framework (MOF) has been achieved. A post‐synthetic modification was employed in the MOF to incorporate the specific recognition site with the CN^? ion over all other anions, such as Cl^?, Br^?, and SCN^?. The aqueous‐phase sensing and very low detection limit, the essential prerequisites for an effective sensory material, have been fulfilled by the MOF. Moreover, the present detection level meets the standard set by the World Health Organization (WHO) for the permissible limit of cyanide concentration in drinking water. The utilization of MOF‐based materials as the fluorometric probes for selective and sensitive detection of CN^? ions has not been explored till now.     

A Novel Macrocyclic Nickel(II) and Ferricyanide 1D Zigzag Chain: Synthesis,Crystal Structure,and Magnetic Properties

A novel cyan‐bridged macrocyclic nickel complex [{NiL¹}{Fe(bipy)(CN)₄}]2·5H₂O 1 (L¹ = 3,10‐dimethyl‐1,3,6,8,10,12‐hexaazacyclotetradecane, bipy = 2,2‐bipyridine) was synthesized and structurally characterized. The complex exhibits one‐dimensional zigzag chain structures. Each ferrous(II) ion connects two nickel(II) ions using two trans CN^? groups, and the remaining CN^? groups are terminal. Magnetic measurement shows weak ferromagnetic interaction between the nearest Ni(II) ions through the diamagnetic Fe(II) ion.     

Design of EGDMA‐Crosslinked Theophylline Imprinted Polymer with High Specificity and Selectivity

An attempt has been made to design theophylline selective polymers with maximum selectivity and specificity, and to relate the rebinding capacity of the polymers with the degree of crosslinking, as well as with the template‐monomer ratio. The theophylline imprinted and non‐imprinted polymers based on methacrylic acid as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking agent (35–80 mol%) were prepared. The developed imprinted polymers were characterized by FT‐IR, ¹H and ¹³C‐NMR spectra. Equilibrium binding of theophylline by the imprinted and non‐imprinted polymers were investigated and optimized the conditions. Imprinted polymers showed specific binding of the template theophylline. Selectivity of the imprinted polymers was investigated towards caffeine and nicotine. Imprinted polymers showed specific and selective binding of theophylline, which varied with the degree of EGDMA crosslinking. Equilibrium rebinding experiments proved that imprinted polymer with moderate (70%) crosslinking with 1∶2 template‐functional monomer ratio is ideal with maximum specificity and selectivity.     

Electrochemical Sensor for Sensitive Determination of Ga(III) Ion Based on β‐Cyclodextrin Incorporated Multi‐walled Carbon Nanotubes and Imprinted Sol‐gel Composite Film

A novel sensor for detection of trace gallium ion [Ga(III)] was created by stepwise modification of a gold electrode with β‐cyclodextrin (β‐CD)/multi‐walled carbon nanotubes (MWCNTs) and an ion imprinted polymer (IIP). The sensor surface morphology was characterized by scanning electron microscopy. The electrochemical performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The sensor displayed excellent selectivity towards the target Ga(III) ion. Meanwhile, the introduced MWCNTs displayed noticeable catalytic activity, and β‐CD demonstrated significant enrichment capacity. A linear calibration curve was obtained covering the concentration range from 5.0×10^?8 to 1.0×10^?4 mol·L^?1, with a detection limit of 7.6×10^?9 mol·L^?1. The proposed sensor was successfully applied to detect Ga(III) in real urine samples.     

Molecularly Imprinted Polymer Monolithic Column Separation of Isomers and Analogues of Vanillin by Capillary Electrochromatography

A vanillin imprinted capillary monolithic column was synthesized by in situ polymerization reaction using ethylene-glycol dimethacrylate as cross-linking monomer and methacrylic acid as functional monomer. Under the optimum conditions of capillary electrochromatography, this molecularly imprinted polymer （MIP）-based column showed high selectivity and could recognize not only template molecule vanillin but also positional isomer o-vanillin from their structural analogues.     

A Reversible Dual Mode Chemodosimeter for the Detection of Cyanide Ions in Natural Sources

Herein, we report the synthesis of two indolium probes 1 and 2 based on anthracene and pyrene derivatives and their interactions with various anions. Of these probes, the pyrene conjugate 2 acts as a dual colorimetric and fluorescent chemodosimeter for the selective and sensitive detection of cyanide ions. The detection limit of probe 2 for CN^? ions was found to be 10 ppb (30 nM ). The nature of interaction has been thoroughly studied through various techniques such as ¹H NMR and IR spectroscopy, HRMS, and isothermal calorimetric (ITC) studies. These studies confirm that probe 2 forms a 1,2‐adduct in the presence of CN^? ions. Kinetic studies using probe 2 showed the completion of the reaction within 15 s with a rate constant of k′=0.522±0.063 s^?1_. This probe can be coated on a solid surface (dipstick) and a polymer matrix for the on‐site analysis and quantification of endogenous cyanide ions in natural sources such as Indian almonds.     

Aluminum(III) Porphyrins as Ionophores for Fluoride Selective Polymeric Membrane Electrodes

Aluminum(III) porphyrins are examined as potential fluoride selective ionophores in polymeric membrane type ion‐selective electrodes. Membranes formulated with Al(III) tetraphenyl (TPP) or octaethyl (OEP) porphyrins are shown to exhibit enhanced potentiometric selectivity for fluoride over more lipophilic anions, including perchlorate and thiocyanate. However, such membrane electrodes display undesirable super‐Nernstian behavior, with concomitant slow response and recovery times. By employing a sterically hindered Al(III) picket fence porphyrin (PFP) complex as the membrane active species, fully reversible and Nernstian response toward fluoride is achieved. This finding suggests that the super‐Nernstian behavior observed with the nonpicket fence metalloporphyrins is due to the formation of aggregate porphyrin species (likely dimers) within the membrane phase. The steric hindrance of the PFP ligand structure eliminates such chemistry, thus leading to theoretical response slopes toward fluoride. Addition of lipophilic anionic sites into the organic membranes enhances response and selectivity, indicating that the Al(III) porphyrin ionophores function as charged carrier type ionophores. Optimized membranes formulated with Al(III)‐PFP in an o‐nitrophenyloctyl ether plasticized PVC film exhibit fast response to fluoride down to 40 μM, with very high selectivity over SCN^?, ClO₄^?, Cl^?, Br^? and NO₃^? (k^pot<10^?3 for all anions tested). With further refinements in the membrane chemistry, it is anticipated that Al(III) porphyrin‐based membrane electrodes can exhibit potentiometric fluoride response and selectivity that approaches that of the classical solid‐state LaF₃ crystal‐based fluoride sensor.     

One‐pot synthesis of surface‐functionalized molecularly imprinted polymer microspheres by iniferter‐induced “living” radical precipitation polymerization

This article describes for the first time the development of a new polymerization technique by introducing iniferter‐induced “living” radical polymerization mechanism into precipitation polymerization and its application in the molecular imprinting field. The resulting iniferter‐induced “living” radical precipitation polymerization (ILRPP) has proven to be an effective approach for generating not only narrow disperse poly(ethylene glycol dimethacrylate) microspheres but also molecularly imprinted polymer (MIP) microspheres with obvious molecular imprinting effects towards the template (a herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D)), rather fast template rebinding kinetics, and appreciable selectivity over structurally related compounds. The binding association constant K_a and apparent maximum number N_max for the high‐affinity sites of the 2,4‐D imprinted polymer were determined by Scatchard analysis and found to be 1.18 × 10⁴ M^?1 and 4.37 μmol/g, respectively. In addition, the general applicability of ILRPP in molecular imprinting was also confirmed by the successful preparation of MIP microspheres with another template (2‐chloromandelic acid). In particular, the living nature of ILRPP makes it highly useful for the facile one‐pot synthesis of functional polymer/MIP microspheres with surface‐bound iniferter groups, which allows their direct controlled surface modification via surface‐initiated iniferter polymerization and is thus of great potential in preparing advanced polymer/MIP materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3217–3228, 2010     

Salts of HCN‐Cyanide Aggregates: [CN(HCN)2]− and [CN(HCN)3]−

Although pure hydrogen cyanide can spontaneously polymerize or even explode, when initiated by small amounts of bases (e.g. CN^?), the reaction of liquid HCN with [WCC]CN (WCC=weakly coordinating cation=Ph₄P, Ph₃PNPPh₃=PNP) was investigated. Depending on the cation, it was possible to extract salts containing the formal dihydrogen tricyanide [CN(HCN)₂]^? and trihydrogen tetracyanide ions [CN(HCN)₃]^? from liquid HCN when a fast crystallization was carried out at low temperatures. X‐ray structure elucidation revealed hydrogen‐bridged linear [CN(HCN)₂]^? and Y‐shaped [CN(HCN)₃]^? molecular ions in the crystal. Both anions can be considered members of highly labile cyanide‐HCN solvates of the type [CN(HCN)_n]^? (n=1, 2, 3 …) as well as formal polypseudohalide ions.     

Adsorption of carbaryl using molecularly imprinted microspheres prepared by precipitation polymerization

To obtain the desired specific adsorbents for carbaryl to enrichment, separation, and analysis of trace pesticide residues in environmental water, molecularly imprinted polymer (MIP) microspheres were prepared by precipitation polymerization using carbaryl, methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA), azobisisobutyronitrile (AIBN), and acetonitrile as template, functional monomer, cross‐linker, initiator, and porogen, respectively. Molecular modeling software was used to compute rational interaction between the template molecule and function monomer. The adsorption properties of carbaryl in acetonitrile for imprinted microspheres were evaluated by equilibrium rebinding experiments. Scatchard plot analysis revealed that there was one class of binding sites populated in the imprinted polymer microspheres with dissociation constants of 3.3 × 10^?2 mol/l and an apparent maximum number of 1.95 µmol/g. The specificity of the imprinted microspheres was investigated by binding analysis using carbaryl and structurally related carbamate pesticides. The results indicated that the obtained imprinted microspheres showed a good selectivity for carbaryl. Copyright © 2007 John Wiley & Sons, Ltd.     

Voltammetric Sensing of Mercury and Copper Cations at Poly(EDTA‐like) Film Modified Electrode

Complexing polymer‐coated electrodes have been synthesized by oxidative electropolymerization of ethylenediamine tetra‐N‐(3‐pyrrole‐1‐yl)propylacetamide (monomer L ). The presence of four polymerizable pyrrole fragments on the same EDTA skeleton was thought to confer enhanced rigidity and controlled dimensionality to the resulting complexing materials, which were used for the electrochemical detection of Hg(II), Cu(II), Pb(II) and Cd(II) ions by means of the chemical preconcentration‐anodic stripping technique. The polyamide electrode material showed particularly a significant selectivity towards mercury ions, even in the presence of a large excess of other metal cations. Moreover, the use of imprinted polymer‐coated electrodes prepared by electropolymerization of L in the presence of metal cations turned out to significantly improve the detection limits, down to 5×10^?10 mol L^?1 for Hg(II) and Cu(II) species.     

Dramatic Influence of an Anionic Donor on the Oxygen‐Atom Transfer Reactivity of a MnV–Oxo Complex

Addition of an anionic donor to an Mn^V(O) porphyrinoid complex causes a dramatic increase in 2‐electron oxygen‐atom‐transfer (OAT) chemistry. The 6‐coordinate [Mn^V(O)(TBP₈Cz)(CN)]^? was generated from addition of Bu₄N⁺CN^? to the 5‐coordinate Mn^V(O) precursor. The cyanide‐ligated complex was characterized for the first time by Mn K‐edge X‐ray absorption spectroscopy (XAS) and gives Mn?O=1.53 Å, Mn?CN=2.21 Å. In combination with computational studies these distances were shown to correlate with a singlet ground state. Reaction of the CN^? complex with thioethers results in OAT to give the corresponding sulfoxide and a 2e^?‐reduced Mn^III(CN)^? complex. Kinetic measurements reveal a dramatic rate enhancement for OAT of approximately 24 000‐fold versus the same reaction for the parent 5‐coordinate complex. An Eyring analysis gives ΔH^≠=14 kcal mol^?1, ΔS^≠=?10 cal mol^?1 K^?1. Computational studies fully support the structures, spin states, and relative reactivity of the 5‐ and 6‐coordinate Mn^V(O) complexes.     

Design and Development of Imprinted Polymer Inclusion Membrane‐Based Field Monitoring Device for Trace Determination of Phorate (O,O‐Diethyl S‐Ethyl Thiomethyl Phophorodithioate) in Natural Waters

A biomimetic potentiometric field monitoring device was developed for the trace determination of phorate (O,O‐diethyl S‐ethyl thiomethyl phophorodithioate) in natural waters. The sensing element was fabricated by the inclusion of phorate imprinted polymer materials in the polyvinyl chloride (PVC) matrix. The sensor surface can be reused without conditioning unlike most other conventional sensors. Operational parameters such as amount and nature of plasticizers sensing material, pH and response time were optimized. The response characteristics of the non‐imprinted (NIPIM) and imprinted polymer inclusion membrane (IPIM) sensors for phorate were compared under optimum conditions. The IPIM sensor responds linearly to phorate in the concentration in the ranges 1×10^?9 to 1×10^?6 M and 1×10^?6 to 1×10^?5 M of different slopes with a detection limit of 1×10^?9 M. The selectivity was tested with various common organophosphorous (OP) pesticides and herbicides. In addition to superior sensitivity and selectivity of IPIM over NIPIM‐based sensor, IPIM‐based phorate sensor was found to be stable for 3 months and can be used for more than 40 times without any loss in sensitivity. The applicability for analyzing ground, river and tap‐water samples was successfully demonstrated via recovery studies.     

基于石墨烯修饰的铜离子印迹电化学传感器研制与应用

以铜离子为模板离子,多巴胺为功能单体,采用电聚合法在石墨烯修饰碳电极表面成功制备对铜离子有高选择性和高灵敏性的印迹电化学传感器。采用差分脉冲伏安法和循环伏安法对该印迹传感器的电化学行为进行详细研究。优化检测条件,该印迹电化学传感器的响应电流与铜离子浓度的负对数在5×10_-6~5×10_-11 mol/L的浓度范围内呈良好的线性关系,最低检测限为1.0 × 10_-11mol/L。该印迹电化学传感器成功用于实际水样中的微量铜离子分析。