Electrochemical investigation of Pb2+ binding and transport through a polymerized crystalline colloidal array hydrogel containing benzo-18-crown-6

The transport of Pb2+ through a sensory gel, a polymerized crystalline colloidal array hydrogel with immobilized benzo-18-crown-6, is important for understanding and optimizing the sensor. Square wave voltammetry at a Hg/Au electrode reveals many parameters. The partition coefficient for Pb2+ into a control gel (no crown ether), K(p), is 1.00 +/- 0.018 (errors reported are SEM). The porosity, epsilon, of the gel is 0.90 +/- 0.01. Log K(c) for complexation in the gel is 2.75 +/- 0.014. Log K(c) in aqueous solution for Pb2+ with the ligand 4-acryloylamidobenzo-18-crown-6 is 3.01 +/- 0.010 with dissociation rate k(d) = (8.34 +/- 0.45) x 10(2) s(-1) and association rate k(f) = (8.79 +/- 0.025) x 10(7) M(-1) s(-1). The partition coefficient of the ligand 4-acryloylamidobenzo-18-crown-6 into the control gel, K(p,L) is 2.07 +/- 0.15. The diffusion coefficient of Pb2+ in the control gel is 6.72 x 10(-6) +/- 0.12 cm(2)/s. For the sensor gel, but not control gel, diffusion coefficients are location dependent. The range of diffusion coefficients for Pb2+ in the probed locations was found to be (6.11-12.60) x 10(-7) cm(2)/s for 0.91 mM Pb2+ and (2.84-9.39) x 10(-7) cm(2)/s for 0.35 mM Pb2+. Lead binding in the sensor gel is slightly less avid than in solution. This is attributed, in part, to the demonstrated affinity of the ligand 4-acryloylamidobenzo-18-crown-6 to the gel. Diffusion coefficients determined for the sensor gel were found to be location dependent. This is attributed to heterogeneities in the crown concentration in the gel. Analysis of diffusion coefficients and rate constants show that diffusion and not chemical relaxation will limit the time response of the material.     

Immobilization of crown ether carboxylic acids on silica gel and their use in column concentration of alkali metal cations from dilute aqueous solutions

Eight crown ethers with pendent carboxylic acid groups are immobilized on silica gel and utilized for column concentration of alkali metal cations from dilute aqueous solutions. The column concentration selectivity and efficiency are found to be strongly influenced by (1) the cavity size of the crown ether unit, (2) conformational positioning of the proton-ionizable side arm with respect to the crown ether cavity, and (3) capping of residual silanol surface groups with trimethylsilyl functions. By use of a chromatographic stripping technique, selective column concentration of Na(+), K(+), (Rb(+) and Cs(+)), and Cs(+) by different functionalized silica gels has been achieved.     

Al_2O_3对稀土配合物掺杂有机改性凝胶玻璃结构及荧光性能的影响

以γ-缩水甘油氧基三甲氧基硅烷作为有机改性先驱体,采用原位合成技术,用溶胶-凝胶法制备稀土离子(Eu3+或Tb3+)、配位体β-二酮噻吩甲酰三氟丙酮或苯甲酸及协同体1,10-菲啰啉共掺的两种有机改性二氧化硅玻璃,测量它们的发射光谱和红外光谱,并进行X射线衍射分析和扫描电镜观察,探讨Al2O3的掺量对凝胶玻璃结构及性能的影响。结果表明:Al3+对稀土离子发射峰的位置没有明显的影响,并使凝胶在室温时的荧光减弱,但它能使稀土离子及原位合成的配合物在较高温度保持相对稳定,提高凝胶玻璃的热稳定性和荧光强度;在制备较实用的具有较强荧光的含稀土离子的凝胶玻璃时,要根据实际需要选取适宜掺量的Al2O3。     

两种冠醚环化二硫纶配体的Ni配合物的合成、结构及光电性质研究

以配体Ia、Ib和Ni(dbbpy)Cl_2(dbbpy=4,4′-二-叔丁基-2,2′-联吡啶)反应,合成了两种新型冠醚环化二硫纶配体的Ni(Ⅱ)配合物1和2。经~1 H NMR、IR、MS和元素分析表征了二者的结构,并解析了其晶体结构,初步测定了其光电响应性质。结果表明,配合物2对Li~+有较明显的响应,ΔE_1~(1/2)=35mV(30倍Li~+),对碱金属离子Na~+和K~+均无明显响应。同时配合物1和2在室温下均有明显的溶剂变色现象。     

Monolithic bioreactor immobilizing trypsin for high-throughput analysis

A miniaturized trypsin reactor was prepared by coating a trypsin-containing gel on a porous silica monolith. The trypsin-encapsulated gel was prepared by the sol-gel method. The sol-gel reaction was optimized so that the sol solution containing trypsin forms a thin film on the sol-gel monolith. The trypsin was encapsulated into the gel matrix without losing its activity. The silica monolith was fabricated to fit into a 96-well microtiter plate well and could then be easily removed. The trypsin-immobilized monolith was reacted in the 96-well microtiter plate. After the reaction, the monolith was removed, and the enzymatic activity was measured. The large surface area of the monolith enabled the immobilized trypsin to achieve a high catalytic turnover rate. Furthermore, the kinetic parameter of the immobilized trypsin indicates the absence of diffusional limitations. The durability and repeatability of the fabricated trypsin-coated monolith was tested and found to be satisfactory. The encapsulated trypsin exhibits an increased stability even after continuous use compared with that in free solution. Furthermore, this on-plate bioreactor was applicable to the digestion of protein with multiple cleavage sites.     

Preparation and luminescence properties of sol-gel hybrid materials incorporated with europium complexes

Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)₃·phen: where HTTA = 1-(2-thenoyl)-3,3,3-trifluoracetone and phen = 1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu³⁺, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu³⁺ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate or ethyl methacrylate, the inorganic/polymer hybrid materials containing Eu(TTA)₃·phen have also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)₃·phen.     

Integration of on-line protein digestion, peptide separation, and protein identification using pepsin-coated photopolymerized sol-gel columns and capillary electrophoresis/mass spectrometry

A miniaturized pepsin reactor was prepared inside a fused-silica capillary (i.d. 75 microm) by coating a pepsin-containing gel on a photopolymerized porous silica monolith. The pepsin-encapsulated film was prepared by a sol-gel method. The sol-gel reaction was optimized so that the sol solution containing pepsin forms a thin film on the photopolymerized sol-gel (PSG) monolith that was initially fabricated at the inlet of the capillary. Pepsin was encapsulated into the gel matrix without losing its activity. The large surface area of the PSG monolith enabled the immobilized pepsin to achieve a high catalytic turnover rate, and the porous nature of the PSG promotes penetration of large molecular proteins into the column. The immobilized pepsin-digested peptides and proteins, and the resulting mixture of peptide fragments, could be directly separated in the portion of the capillary where no PSG monolith exists. The durability and repeatability of the fabricated pepsin-coated column was tested and found to be satisfactory. An acidic solution consisting of 0.5 M formic acid was used as the running buffer, because it suppresses the adsorption of proteins or peptides on the inner surface of the capillary as well as enables direct connection of the output of the capillary electrophoresis column to a mass spectrometer. The on-line digestion of insulin chain beta and lysozyme provides identification of the proteolytic peptides. Recovery was achieved for 100% of the insulin chain beta amino acid sequence and 73% of the lysozyme amino acid sequence.     

Porous MAl2O4:Eu (Eu), Dy (M = Sr, Ca, Ba) phosphors prepared by Pechini-type sol-gel method: The effect of solvents

In this work, a series of porous Eu²⁺-doped alkaline earth aluminates phosphors including MAl₂O₄:Eu²⁺ (Eu³⁺), Dy³⁺ (M = Sr, Ca, Ba) have been prepared by Pechini-type sol-gel approach, using citric acid as chelating ligand and ethylene glycol (or H₂O) as solvent. The as-obtained samples were characterized by means of XRPD, FESEM and PL techniques. MAl₂O₄:Eu²⁺, Dy³⁺ (M = Sr, Ca, Ba) phosphors were prepared in a reducing atmosphere (H₂/Ar, 20 + 80%) while MAl₂O₄:Eu³⁺, Dy³⁺ (M = Sr, Ca, Ba) phosphors were obtained in air. Upon changing the molar ratio of citric acid to total metal cations concentration in ethylene glycol can produce spherical phosphors and the higher molar ratio favors the formation of spherical ones. Otherwise, irregular shaped phosphors occur when conducting the reaction in pure H₂O. The irregular shaped phosphors have higher emission intensity than those spherical ones observed with the help of excitation spectra, emission spectra and decay curves.     

Preparation and Luminescence Properties of Terbium-Sal Complex In-situ Synthesized in Silica Matrix by a Two-Step Sol-Gel Process

1.IntroductionThesol-gelmethodhasbeenprovedtobeaverypromisingrouteforpreparinghostmaterialsforencapsulatingopticallyactivespecies.Sofarthismethodwasmainlyusedtosyfithesizemonolithicgelsorfilmscontainingorganicdyeswithvariousopticalfunctions[1].Recentlymuchattentionhasbeenpaidtothetransparentgelsemployedasthemediaofor-ganicdyestoproducelaser.However,thephotode-compositionoftheorganicdyeslimitstheirapplicationlifetime.Therefore,itisofgreatimportancetoexploreotherluminescentspeciesastheopticalma…     

Metal ion-sensitive holographic sensors

Holographic sensors for Na+ and K+ have been fabricated from crown ethers incorporated into polymeric hydrogels. The methacrylate esters of a homologous series of hydroxyether crown ethers were synthesized and copolymerized with hydroxyethyl methacrylate and the cross-linker ethylene dimethacrylate (3 mol %) to form stable hydrogel films (approximately 10 m thick) containing covalently bound (0-97 mol %) 12-crown-4, 15-crown-5, and 18-crown-6 pendant functionalities. The films were transformed into silver-based volume holograms using a diffusion method coupled with a holographic recording using a frequency-doubled Nd:YAG laser. The resulting holographic reflection spectrum was used to characterize the shrinkage and swelling behavior of the holograms as a function of polymer composition and the nature and concentration of alkali, alkaline earth, and NH4+ ions in the test media. Optimized film compositions containing 50 mol % crown ether showed substantial responses (< or = 200 nm) within 30 s at ion concentrations of < or = 30 mM, which could be rationalized on the basis of the known complexation behavior of the crown ethers. An 18-crown-6 holographic film was shown to be able to quantitate K+ concentrations over the physiologically relevant range. It was virtually unaffected by variations in the Na+ background concentration within the normal physiological variation (approximately 0.13-0.15 M) and shows promise for developing simple, low-cost K+ sensors for medical applications.     

Luminescence properties of nano-sized Sr2MgSiO5: Eu2+, Mn2+ phosphors prepared by the sol-gel method

Nano-sized Sr2MgSiO5:Eu2+, Mn2+ phosphor was synthesized by the sol-gel method. The preparation conditions of the precursor were determined. The effect of Eu2+ and Mn2+ content on the luminescence intensity was studied. X-ray diffraction (XRD), photoluminescence spectra (PL), and photoluminescence excitation spectra (PLE) were used to characterize the samples. The results showed that the excitation bands ranged from 250 to 450 nm, and their peaks positioned around 365 nm. The emission spectrum consists of three bands: blue, green, and red, respectively. The blue and green emission bands originate from the center of the Eu2+, while the red emission band is attributed to the energy transfer from Eu2+ to Mn2+. White light can be obtained by mixing the three emission colors. The experiment results show that the Sr2MgSiO5:Eu2+, Mn2+ is a single host phosphor with superior properties for use in white light emitting diodes (white LED).     

Observation of room-temperature 5D1 luminescence of an organoeuropium complex encapsulated in sol-gel glass

In comparing emissions of the inorganic Eu3+ salts (chloride or nitrate) to organoeuropium complexes doped into optically transparent sol-gel glass, previous studies have indicated that changes in the local chemical environment by chelation or variation of the ligand or gel matrix compositions were found to leave the main spectral features of Eu3+ essentially unchanged; complexation just increases the emission intensity of europium and leads to broadening and splitting of the peaks. In all cases studied and irrespective of the excitation energy, the observable emission peaks result only from relaxations out of the 5D0 excited state of Eu3+ to the first five levels of the 7F ground manifold. The present research examines the luminescence behavior of EuCl3 and Eu-TETA (TETA is the macro cycle, 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraaceticacid) doped into a sol-gel host; in addition to emissions from the 5D0, emission from the 5D1 excited state of Eu3+ is observed for the first time.     

On-line trypsin-encapsulated enzyme reactor by the sol-gel method integrated into capillary electrophoresis

A novel trypsin-encapsulation technique using the sol-gel method was developed for the preparation of an on-line enzyme reactor integrated into capillary electrophoresis. Trypsin was encapsulated in tetramethoxysilane-based hydrogel, and its enzymatic activity was evaluated using alpha-N-benzoyl-L-arginine ethyl ester and two peptides (bradykinin and [Ter8]-bradykinin). The enzyme encapsulation was carried out in a single step under mild conditions within a capillary, and 1.5-cm gel was formed at the inlet of the capillary. The resultant monolithic reactor showed excellent enzymatic activity, which was approximately 700 times higher than that in free solution, without stopping the flow. Separation of the unreacted substrates and products in the same capillary also showed high selectivity, and sample size in this system decreased 3 orders of magnitude from conventional tryptic reaction schemes. The encapsulated trypsin maintains its substrate specificity even in a sol-gel matrix. Furthermore, the encapsulated trypsin exhibits increased stability even after continuous use compared to that in free solution.     

Chromatographic probing of electrostatic potential

Electrostatic potential in the vicinity of the surface of a cation-exchange resin has been evaluated by modeling chromatographic retention. Binary mixtures of K+ and its crown ether complex in methanol are used as mobile phases, and two types of solutes, that is, cationic and crown ether probes, have been examined. The cationic probes show the sigmoidal retention changes with increasing concentration of a crown ether incorporated into the mobile phase, whereas crown ether probes give retention maximums. The model derived from the Poisson-Boltzmann theory well explains these specific changes in probe retention and gives the electrostatic potential at the closest approach of each probe molecule. The closest approaches for probe molecules correlate well with their molecular sizes. In addition, changes in retention of cationic probes also correlate well with the electrostatic potential changes at the closest approaches of probe molecules, indicating that simple sensing of the electrostatic potential is feasible using probe retention. The reduction of crown ether complexation occurs in the vicinity of the cation-exchange resin surface and causes the specific retention behaviors of crown ether probes in the mobile-phase systems composed of K+ and its complex with a modifier crown ether.     

Effect of crown ethers on the ion-exchange behavior of alkaline Earth metals. Toward improved ion-exchange methods for the separation and preconcentration of radium

The effect of selected crown ethers on the uptake of alkaline earth cations by sulfonic acid and diphosphonic acid-based cation-exchange resins from hydrochloric acid media is examined. The effect observed is shown to vary with the hydrophobicity of the crown ether. Water-soluble crown ethers enhance the sorption of certain cations, thereby improving the selectivity of the resin for other alkaline earths over calcium ion, an apparent result of a synergistic interaction between crown ether present in the resin phase and the ionic functional groups of the resin. In the presence of more hydrophobic crown ethers, a decrease in cation sorption is often observed, a result of the exclusion of the crown ether from the resin phase and the formation of cation-crown complexes in the solution phase. The result can be a reversal of the selectivity sequence ordinarily exhibited by the resin.     

Eu3+掺杂的硼酸锶系列荧光体的合成及其发光性能

采用溶胶-凝胶法和高温固相反应法合成了Eu^3 掺杂的SrB4O7、SrB2O4、Sr2B2O5、Sr3B2O6荧光体．荧光光谱测试结果表明在不同基质中Eu^3 的荧光发射是有区别的，Sr2B2O5：Eu^3 、Sr3B2O7：Eu^3 发射峰在610nm左右的红光区，SrB2O4：Eu^3 的发射峰在593nm的橙色区，而SrB4O7：Eu^3 则表现出了Eu^2 离子的特征峰，产生这种区别主要是由Eu^3 所处的配位环境不同造成的．荧光体SrB4O7：Eu^3 、SrB2O4：Eu^3 、Sr2B2O5：Eu^3 、Sr3B2O6：Eu^3 的最佳掺杂浓度为2％左右．     

A lipophilic sol-gel matrix for the development of a carbonate-selective electrode

Organic-inorganic hybrid sol-gel matrixes were used as hosts for trifluoroacetyl-p-decylbenzene (TFADB), a traditional ionophore for carbonate. The sol-gel precursor was prepared by the reaction of (3-isocyanopropyl)triethoxysilane with ethylene glycol. Hexadecyltrimethoxysilane (HDTMOS) was employed as a co-precursor. An appropriate amount of tridodecylmethylammonium chloride (TDMAC) and 2-nitrophenyloctyl ether (NPOE) were used as membrane components. On mixing with an acidic catalyst, the sol-state precursors slowly gelled, yielding a membrane in which the active components, TFADB and TDMAC, were encapsulated. Infrared, (1)H, and (29)Si MAS NMR spectrometers were employed to monitor the sol-gel process and the degree of polymerization. The performances of the sol-gel membrane-based electrodes were compared to those of TFADB-based poly(vinyl chloride) (PVC) membrane electrodes. Membranes with a molar ratio of TFADB:TDMAC (1:0.14) showed extended lifetime and stable baseline potential. The response slope toward carbonate was approximately 27 mV/decade between 10(-)(5) and 10(-)(3.5) M at 18 degrees C. Interestingly, selectivity toward carbonate over salicylate and other lipophilic anions was improved, clearly deviating from the Hofmeister selectivity pattern. Responses toward small inorganic anions including chloride and sulfate were negligible. The selectivity coefficients measured by the matched potential method in 0.1 M tris-sulfuric acid buffer, pH 8.75, were log = -0.3, log = -4.2, and log = -2.5.     

Effect of Structural Variation within Lipophilic Lariat Ether Phosphonic Acid Monoesters on the Selectivity and Efficiency of Competitive Alkali Metal Cation Extraction into Chloroform

Lipophilic lariat ether phosphonic acid monoethyl esters with systematic crown ether ring size variation from 12-crown-4 to 24-crown-8 are utilized for competitive alkali metal cation extractions from aqueous solutions into chloroform. Effective alkali metal cation extraction from weakly acidic, neutral, and basic aqueous solutions is achieved. With 4, 5, and 6 oxygens in the crown ether rings, selectivities for Li(+), Na(+), and K(+), respectively, are observed. An 18-crown-6 phosphonic acid monoester exhibits excellent extraction selectivity for K(+) with K(+)/Li(+) and K(+)/Na(+) > 100. The lipophilic group attachment site, as well as the crown ether ring size, is shown to influence the extraction selectivity for the lariat ether phosphonic monoesters.     

三维花状Sr2MgSi2O7∶Eu2+蓝色发光材料及其发光性能

采用溶胶-凝胶法,以葡萄糖为表面活性剂,成功地合成了三维花状的Sr2MgSi2O7∶Eu2+蓝色荧光粉。利用X射线衍射仪、扫描电镜、荧光光谱仪对产物的结构、形貌和发光性能进行了分析。结果表明,添加适量的葡萄糖对产物的结构无影响,但可改变产物的形貌和提高发光性能。当葡萄糖含量为0.03g/mL时,焙烧后的产物由无规则的块状形貌转变成颗粒形态为花瓣状的特征形貌。所得发光材料在355nm波长的紫外光激发下获得波长为469nm的明亮蓝光,而且发光强度最高。     

La_(0.60)Sr_(0.40-x)K_xMnO_3系列材料的磁电阻效应

利用溶胶-凝胶法(sol-gel)制备了多晶类钙钛矿型稀土锰氧化物La0.60Sr0.40-xKxMnO3(x=0.00,0.15,0.20,0.30)。发现K+取代部分Sr2+后,可使样品的居里温度降至室温附近,并且使样品的室温磁电阻比替代前明显增大。在1.8T的磁场下,x=0.30的样品磁电阻峰值为21%,相应的峰值温度为304K。而母体La0.60Sr0.40MnO3的磁电阻峰值仅为6.4%,峰值温度为373K。可见K+离子替代使室温附近样品的庞磁电阻效应有了明显的改善。