Complexation of copper ions with histidine-containing tripeptides immobilized on solid surfaces

Short oligopeptides that complex with metal ions with high affinity and high specificity are of interest to the design of chemical sensors. In this study, we compare the complexation properties of two copper-selective tripeptides, Gly-Gly-His and His-Gly-Gly, either in aqueous solutions or immobilized on solid surfaces. Our results show that the copper complex formed by Gly-Gly-His is more stable than the complex formed by His-Gly-Gly in aqueous solutions, because the position of histidine (His) in the Gly-Gly-His permits the formation of a tetragonal copper complex with a high stability. However, when the tripeptides are immobilized on aldehyde-decorated silicon wafer surfaces under a reaction condition that gives rise to near maximum surface densities of tripeptides, both immobilized Gly-Gly-His and His-Gly-Gly experience strong steric hindrance on the over-crowded surfaces. The surface crowding effect causes less complexation with copper ions than that in aqueous solutions. To ensure a proper surface density on the surface for complexation with copper ions, a so-called two-dimensional (2D) metal-ion imprinting technique is employed to avoid the surface crowdedness. By immobilizing Gly-Gly-His in the presence of copper ions, we create a tripeptide-functionalized surface that exhibits high complexation capability for copper ions. We attribute the higher copper complexation capability to the proper intermolecular distances obtained from the ion-imprinting procedure that gives the copper-tripeptide complex a preferential tetragonal geometry. Our results show that the amounts of copper complexed to a copper-imprinted surface functionalized with Gly-Gly-His are 62% higher than those of a nonimprinted surface.     

Crosslinked chitosan nanofiber mats fabricated by one-step electrospinning and ion-imprinting methods for metal ions adsorption

The Pb(Ⅱ)ion-imprinting electrospun crosslinked chitosan nanofiber mats were fabricated by one-step electrospinning and ion-imprinting methods and their application as adsorbents for metal ions was also investigated.The resulting chitosan nanofiber mats were characterized by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and thermal gravimetric analysis(TGA).The Pb(Ⅱ)ion-imprinting electrospun crosslinked chitosan nanofiber mats were used as adsorbents for the removal of Pb(Ⅱ)ions from aqueous or acid solutions.The effects of p H values,contact time,content of crosslinker(glutaraldehyde)on Pb(Ⅱ)ions adsorption were studied.The results indicated that the Pb(Ⅱ)ion-imprinting electrospun crosslinked chitosan nanofiber mats had the highest adsorption capacity of 110.0 mg/g at p H 7.The kinetic study demonstrated that the adsorption of Pb(Ⅱ)ions followed the pseudo-second-order model.The equilibrium isotherm data showed that the Langmuir model was the most suitable for predicting the adsorption isotherm of the studied system.The Pb(Ⅱ)ion-imprinting electrospun crosslinked chitosan nanofiber mats had good adsorption selectivity,which illustrates the equilibrium adsorption capacity in the order of Pb(Ⅱ)Cu(Ⅱ)Zn(Ⅱ)Cd(Ⅱ)Ni(Ⅱ).The Pb(Ⅱ)ion-imprinting electrospun crosslinked chitosan nanofiber mats were stable and had good reuse ability.     

Influence of Imidazole and Hydrocyanic Acid Derivatives on the ‘Possible Prebiotic’ polyphosphate induced peptide synthesis in aqueous solution

Glycine in aqueous solutions of trimetaphosphate or linear polyphosphate at pH adjusted to 8.1-9.0, is condensed at room temperature to diglycine and very small amounts of triglycine. The addition of imidazole increases the yield of triglycine by a factor of almost 10; supplementary addition of magnesium ion does not increase this effect. On the contrary to what has been observed at pH 11.5-12.0, the addition of sodium cyanide or cyanamide at pH 8.1-9.0 diminishes strongly the yield of triglycine and to a lesser degree that of diglycine. The prebiotic significance of the condensation of amino acids in aqueous solutions of polyphosphates in the presence of imidazole is discussed.     

Polymerization of methyl methacrylate initiated by oligoglycine,water, cupric ion,and carbon tetrachloride

The polymerization of methyl methacrylate (MMA) was carried out in the presence of oligoglycines (glycine, its dimer, trimer, tetramer, etc.), water, cupric ions, and carbon tetrachloride. It was found that poly-MMA is formed in the water layer and that the system using triglycine gives the maximum polymer yield. On the effect of pH of water layer, the rate of polymerization is faster in the alkalic condition (pH 8–10) than in normal condition (pH 3.8), while in the acidic media (pH 2–3), the rate is not accelerated. From the results of kinetic studies, the polymerization rate is dependent on the 0.5 power of the amount of diglycine or cupric ion, and it is independent of the amount of MMA. The polymerization mechanism was discussed.     

Separation of amino acids, peptides and corresponding Amadori compounds on a silica column at elevated temperature

Maillard reaction of glucose with amino acids and peptides has become a very important experimental model in the food flavor and pharmaceutical industries for better understanding the mechanism of food flavor generation and drug stability. Because of the amino acid and sugar functional groups present in their structures, most of the reaction components formed during the initial stages of Maillard reaction as well as the substrates are relatively polar. These compounds are poorly retained on a conventional reversed phase column. While polar stationary phases like HILIC column do provide better retention for these polar components, method selectivity could still be a challenge due to the structural similarity between these analytes. In this report, parameters such as pH, mobile phase composition and temperature were investigated using different brands of bare silica columns in order to separate glycine (G), diglycine (DG), triglycine (TG), and the corresponding Amadori compounds of glucose-glycine (GG), glucose-diglycine (GDG) and glucose-triglycine (GTG). An excellent separation for glycine, glycine peptides and their Amadori compounds was obtained on a bare silica column at an elevated temperature.     

Influencing the selectivity of zeolite Y for triglycine adsorption

In prior work we studied the adsorption of triglycine on zeolite Y under reference conditions. This study aims to solve the question of which adsorbent properties and process conditions influence the adsorption triglycine from an aqueous solution by zeolite Y. Relevant zeolite parameters to study are: the amount of acidic sites (Si/Al(2) ratio), counter ion, micropore structure. Process conditions that may influence triglycine adsorption are pH, other components such as sugars, amino acids and salts, and temperature. Adsorption of triglycine on zeolite HY is dominated by ionic interaction. The capacity and selectivity of zeolite HY for triglycine can be changed by choosing different Si/Al(2) ratios or changing the counter ion. The presence of cations and basic anions in solutions reduces triglycine adsorption. Fructose and glycine have no significant influence on triglycine adsorption. Temperature only has a slight influence. The pore structure of zeolite Y is not a critical factor for triglycine adsorption, provided pores are accessible to triglycine and in the micropore range (<2 nm). While this allows other zeolites than zeolite Y to be applied, the presence of the supercage structure of zeolite Y is beneficial to obtain better adsorption of triglycine in its neutral form.     

Rapid radiochemical separation in neutron activation analysis : Part 1. The use of C18-bonded silica gel and selective complexation for determinations of manganese,copper and zinc in biological materials

A rapid radiochemical separation method based on the removal of metal ions by columns of C₁₈-bonded silica gel after selective complexation by 8-quinolinol, ammonium pyrolidinedithiocarbamate or cupferron is described for the determination of manganese, copper and zinc in neutron-activated biological materials. The removal of the metal ions, either by adsorption or by a combination of filtration and adsorption on columns of C₁₈-bonded silica gel, was investigated to optimise the separation procedure. Analysis of several National Bureau of Standards and International Atomic Energy Agency biological reference materials demonstrated the effectiveness of this technique. The method is simple and reliable and readily adaptable in all radiochemical laboratories. Furthermore, columns of C₁₈-bonded silica gel have been successfully recycled a number of times without deterioration.     

Preparation, Properties and Mechanism of Inhomogeneous Calcium Alginate Ion Cross-linking Gel Microspheres

Inhomogeneous calcium alginate ion cross-linking gel microspheres,a novel ion absorbent,were prepared by dropping a sodium alginate solution to a calcium chloride solutioin via an electronic droplet generator.Calcium alginate microspheres have uniform particle sizes.a smooth surface and a microporous structure.The electrode probe reveals the inhomogeneous distribution of calcium ions with the highest concentration on the surface,and the lowest concentration in the cores of the spheres.As a novel ion adsorbent,calcium alginate gel microspheres have a lower limiting adsorption mass concentration,a higher enrichment capacity and a higher adsorption capacity for Pb^2 than usual ion exchange resins.The highest percentage of the adsorption is 99.79%.The limiting adsorption mass concentration is 0.0426mg/L.The adsorption capacity for Pb^2 is 644mg/g,Calcium alginate gel microspheres have a much faster ion exchange velocity than D418 chelating resin and D113 polyacrylate resin.The moving boundary model was employed to interpret the ion exchange kinetics process,which indicates that the ion exchange process is controlled by intraparticle diffusion of adsorbable ions.So the formation of inhomogeneous gel microspheres reduces the diffusion distance of adsorbable ions within the spheres and enhances the ion exchange velocity.Alginate has a higher selectivity for pb^2 than for Ca^2 and the selectivity coefficient KCa^Pb is 316. As an ion cross-linking gel,calcium alginate inhomogeneous microspheres can effectively adsorb heavy metal Pb^2 at a higher selectivity and a higher adsorption velocity.It is a novel and good ion adsorbent.     

表面印迹法制备钴(Ⅱ)离子印迹硅胶及性能

采用表面印迹技术, 以Co(Ⅱ)离子作为印迹离子, 二乙烯三胺基丙基三甲氧基硅烷为功能分子, 硅胶为支撑物, 环氧氯丙烷为交联剂, 在硅胶表面制备Co(Ⅱ)离子印迹硅胶材料, 利用红外光谱仪、扫描电镜和热重分析仪等进行了表征, 采用平衡吸附法研究了印迹硅胶材料的吸附性能和选择识别能力. 结果表明, 印迹硅胶材料和非印迹硅胶材料的最大吸附量分别为35.2和6.5 mg/g; 印迹硅胶材料对Co(Ⅱ)离子的吸附行为符合Langmuir模型; 20 min即可达到吸附平衡; 当pH=3.9~7.8时, 印迹硅胶材料保持了较好的吸附容量; 印迹硅胶材料对Co(Ⅱ)离子具有较强的选择性识别能力; 重复使用时性能稳定.     

Removal of cadmium(II) and lead(II) ions from model aqueous solutions using sol–gel-derived inorganic oxide adsorbent

A study was conducted concerning the preparation and application of a novel synthetic oxide adsorbent of MgO-SiO₂ type. The material was prepared via a sol–gel route, utilizing magnesium ethoxide and tetraethoxysilane as precursors of magnesium oxide and silica respectively, and ammonia as a catalyst. The powder was comprehensively analyzed with regard to chemical composition (EDS method), crystalline structure, morphology, characteristic functional groups, electrokinetic stability and porous structure parameters (BET and BJH models). The synthesized oxide adsorbent is amorphous, with irregularly shaped particles, a relatively large surface area of 612 m²/g, and negative surface charge over almost the whole pH range. Comprehensive adsorption studies were performed to investigate the adsorption of Cd(II) and Pb(II) ions on the MgO–SiO₂ oxide adsorbent, including evaluation of adsorption kinetics and isotherms, the effect of pH, contact time and mass of adsorbent. It was shown that irrespective of the conditions of the adsorption process, the synthesized MgO–SiO₂ adsorbent exhibits slightly better affinity to lead(II) than to cadmium(II) ions (sorption capacity of 102.02 mg(Pb²⁺)/g and 94.05 mg(Cd²⁺)/g). The optimal time for removal of the analyzed metal ions was 60 min, although adsorption reached equilibrium within 10 min for Pb(II) and within 15 min for Cd(II) ions, which was found to fit well with a type 1 pseudo-second-order kinetic model. Additionally, adsorption efficiency was affected by the pH of the reaction system—better results were obtained for pH ≥7 irrespective of the type of metal ion.     

以铜离子为模板的褐藻酸凝胶对铜离子的选择性富集研究

以铜离子为模板，制备了褐藻酸凝胶（Cu-alginate)，通过吸附实验及过柱渗滤实验，试验了该吸附剂对铜离子的选择性吸附性能，并且采用该吸附剂富集了自来水中微量的Cu^2 ，结合原子吸收法测定了水样中Cu^2 的含量。结果表明：该吸附剂对Cu^2 有较高的选择性吸附性能，显著优于一些化学合成铜离子模板缩聚物及非铜模板褐藻酸凝胶（如Ca-alginate),非重金属离子（如K^ 、Na^ 、Ca^2 ）及某些重金属离子（如Ni^2 、Cd^2 ）等对Cu^2 的吸附均不产生明显干扰。用该吸附剂富集水中的微量铜离子，回收率可达97.7%。     

Separation and preconcentration of metal ions and their estimation in vitamin, steel and milk samples using o-vanillin-immobilized silica gel

o-Vanillin-immobilized silica gel has been used for the adsorption and estimation of copper, cobalt, iron and zinc by both batch and column techniques. Metal ions were quantitatively retained on the column packed with immobilized silica gel in the pH range 4.0-6.0 for Cu, 5.0-6.0 for Co, 4.5-6.0 for Fe and 6.0-8.0 for Zn. The distribution coefficient D determined for each metal was as follows (ml g(-1)): Fe, 5.4x10(2); Cu, 4.9x10(2); Zn, 4.4x10(2); Co, 3.8x10(2). Methods have been developed to estimate zinc, copper and cobalt in milk, steel and vitamin samples, respectively.     

Additional purification of alkali or alkaline earth salts by using silica gel modified with pyrocatechol violet as a sorbent

Sorption of 14 metal ions on silica gel impregnated with a mixture of Aliquat 336 and Pyrocatechol Violet was investigated. It was found that alkali metals and calcium are not retained on the sorbent, magnesium is retained from solutions of pH > 6, contrary to other metal ions. The sorbent was used for purification of some salts from trace amounts of heavy metals and magnesium. Some metals ion mixtures have also been separated by using column extraction chromatography stepwise elution with perchloric acid solutions.     

Highly sensitive spectrofluorimetric determination of cysteine by Cu2+-morin complex

p-Toluenesulfonylamide was immobilized on silica gel and on nm-sized silicium dioxide (SiO₂). Their adsorption efficiency toward metal ions was investigated by the batch equilibrium technique. Although silica gel and nm-SiO₂ have the same composition (silicon and oxygen), the difference in their sizes and surface structures results in distinct chemical activity and selectivity. At pH 4, the adsorption capacity of modified silica gel adsorbent was found to be 4.9, 5.0, 33.2, and 12.6 mg g⁻¹ for Cr(III), Cu(II), Pb(II) and Zn(II), respectively. However, the adsorption capacity of nm-SiO₂ adsorbent toward Cr(III) was 26.7 mg g⁻¹ under ultrasonic dispersing. The potential application of p-toluenesulfonylamide-modified silica gel for simultaneous preconcentration of trace chromium, copper, lead and zinc from two standard reference materials and two food samples was performed with satisfactory results. Correspondence: Xijun Chang, Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R. China     

Sol–gel derived ion imprinted thiocyanato-functionalized silica gel as selective adsorbent of cadmium(II)

A Cd(II)-imprinted thiocyanato-functionalized silica gel adsorbent with high adsorption capacity was prepared by surface imprinting technique combined with sol–gel process for the selective adsorption of Cd(II) ion in aqueous solution, and was characterized by Fourier-transform infrared spectroscopy, nitrogen gas sorption and thermogravimetric analysis. The influences of different conditions (such as the pH of solutions, the contact time and the initial concentrations of Cd(II) ions) on the adsorption capacity of Cd(II) were investigated. The optimum pH of adsorption was in the range of 4–8.5. The adsorption equilibrium could be reached in 20 min. The relatively selectivity coefficients of the imprinted silica were higher than those of the non-imprinted adsorbents. Ho’s pseudo-second-order model well described the kinetics of the adsorption reaction. The adsorption process of metals followed Redlich–Peterson isotherm model, and the experimental value of maximum adsorption capacity for Cd(II) was 72.8 mg·g^?1. The positive value of ΔH ^o suggested endothermic nature of Cd(II) adsorption on the imprinted silica adsorbent. Increase in entropy of adsorption reaction was shown by the positive value of ΔS ^o and the negative value of ΔG ^o indicating that the adsorption was spontaneous in nature.     

Hydrophobic Effects of o-Phenanthroline and 2,2′-Bipyridine on Adsorption of Metal(II) Ions onto Silica Gel Surface

The effects of o-phenanthroline and 2,2′-bipyridine on the adsorption of metal(II) (Fe, Co, Ni and Cu) ions onto silica gel surface have been studied. The adsorption is expressed in terms of the measured concentrations of both metal and ligand at equilibrium. Each adsorption of the four metal ions is increased with the presence of the ligands. In addition, adsorption increases slowly with pH at low pH values and then increases rapidly up to near the pK_a value of silica gel (≈6.5). The adsorption of each metal ion at low pH is increased with increased ligand concentration. However, at high pH the adsorptions of Fe(II) and Cu(II) are decreased with increased ligand concentration whereas the adsorptions of Co(II) and Ni(II) are always increased. At low pH values the ligand to metal ratio adsorbed on the silica gel surface is ca. 3:1 while at high pH values it is 1:1, 2:1, and 3:1, corresponding to the initial ligand to metal ion concentration ratio. The addition of ethanol to the phenanthroline-SiO₂ solution results in a decrease in the adsorption of phenanthroline. The effect of ethanol is also observed in the Fe(II)-phenanthroline-SiO₂ system. The behavior of the adsorption is interpreted qualitatively by hydrophobic expulsion, the formation of surface complexes, and electrostatic interaction. It is concluded that hydrophobic expulsion plays an important role in the adsorption of metal ions in the presence of hydrophobic ligands on silica gel surface.     

Chemically functionalized silica gel with alizarin violet and its application for selective solid-phase extraction of lead from environmental samples

A new material for solid-phase extraction of Pb(II) was prepared using chemically functionalized silica gel with alizarin violet. This material is stable in 6molL(-1) of HCl, 6molL(-1) of H(2)SO(4), common organic solvents and pH 1.0-9.0 aqueous solutions. The influences of analytical parameters including pH of the aqueous solution, amount of the functionalized silica gel, stirring time and flow rates of sample solutions on the quantitative recoveries of Pb(II) were investigated. At the optimum conditions, Pb(II) can be adsorbed with almost 100.0% retention, the adsorption equilibration for Pb(II) was achieved within 15min, and the adsorption capacity of the sorbent for Pb(II) is 3.45mgg(-1) of dry functionalized silica gel. For Pb(II) solution of 10ngmL(-1), the pre-concentration factor is as high as 500, and the recovery is higher than 92%. The new solid-phase extractant has been used for the pre-concentration of low level of Pb(II) in water and soil samples with high recoveries. The standard reference water sample (GSBZ 50009-88(2)) was introduced for accuracy and precision of analytical data.     

Silica-based optical chemosensors for detection and removal of metal ions

Because some metal ions are highly toxic even at trace level, a constant demand of developing methods for monitoring and removing these metal ions is extremely urgent. Silica-based optical chemosensors are supposed as good alternatives to classical instrumental methods for detecting and adsorbing metal ions, due to their effect and lower price. Silica nanoparticles, silica gel and mesoporous silica are used as supporting platforms to fabricate optical chemosensors. They have certain properties containing high porosity and expectant adsorption capacity. Chromogenic-type and fluorogenic-type optical probes, such as azobenzene, naphthalimide and rhodamine, are grafted to the surface of silica-based materials by sol–gel reaction, the limit of detection, response time and selective properties of optical sensors are improved sequentially. In this paper, the articles of silica-based optical chemosensors are retrospected since 2008, describing silica-based optical sensors used for sensing metal ions. The sensing mechanism, optical phenomenon, detection limit, adsorption capacity and application are also reviewed.     

氨基酸和肽从水到多羟基化合物溶液的迁移焓研究

采用RD-496Ⅱ型精密微量热量计分别测定了甘氨酸、L-丙氨酸、L-丝氨酸、L-苏氨酸、甘氨酰甘氨酸和甘氨酰甘氨酰甘氨酸在纯水以及不同浓度甘露醇、山梨醇和肌醇水溶液中的溶解焓, 计算了这些氨基酸和肽从水到3种多元醇溶液中的迁移焓. 实验发现, 氨基酸和肽从水到多元醇溶液中的迁移焓均为负值, 且随多元醇浓度的增加而减小. 根据共球交盖模型分析了水溶液中氨基酸和肽分子与多元醇分子间的相互作用.     

Adsorption of calcium and magnesium ions on surfaces

The adsorption of calcium and magnesium ions at trace levels in solution on borosilicate glass and polypropylene is described. The rate and extent of adsorption increases with increasing pH and the process is not completely reversible. The apparent energies of activation for the adsorption of calcium and magnesium ions on borosilicate glass are 17.5 and 10.5 kJ mol^?1, respectively. The corresponding half-lives are 568 and 127 h. For polypropylene the half-lives increase to 5775 and 537 h, respectively.