Manipulation of the Electroosmotic Flow in Glass und PMMA Microchips with Respect to Specific Enzymatic Glucose Determinations

The determination of glucose in microfluidic chips made of glass or PMMA was used as a model for the combination of an enzymatic reaction with the separation of compounds. It was based on the enzymatic oxidation of glucose and the amperometric detection of hydrogen peroxide. Real samples frequently contain compounds, such as ascorbic acid, which may interfere with quantitative glucose determinations. Thus, electrophoretic separation of specific from unspecific signals was envisaged by applying electric fields which are also used to control the flow of liquid via electroosmotic effects. Surface charge densities of the capillaries influence the electroosmotic flow (EOF). They are dependent on the chip material and on the adsorption of components from the background electrolyte. Reversal of the EOF after addition of cetyltrimethylammonium bromide (CTAB) and an increase in EOF after addition of sodium dodecylsulfate (SDS) were observed at lower surfactant concentrations with the PMMA chips rather than with the glass chips. For both chip materials these concentrations were below the critical micelle concentration. Effective separation of H₂O₂ and ascorbic acid was achieved with low CTAB concentrations, which lead to a reduction, but not to a reversal of the EOF. Reversal of the EOF by higher CTAB concentrations or the increase in cathodic EOF by SDS accelerated ascorbic acid transportation and reduced the differences in migration times. Thus, for the specific determination of glucose, glucose oxidase was added together with low CTAB concentrations to the background electrolyte. This avoided interference from ascorbic acid, and data obtained from the analysis of fruit juices showed a good correlation to data obtained from a reference method.     

Unusual Orthogonality in the Cleavage Process of Closely Related Chelating Protecting Groups for Carboxylic Acids by Using Different Metal Ions

Three structurally related relay protecting groups for carboxylic acids that are based on chelating amines have been developed. These protecting groups can easily be introduced by coupling the carboxylic acid and the corresponding amine in the presence of 2‐(1H‐benzotriazole‐1‐yl)‐1,1,3,3‐tetramethyluronium tetrafluoroborate (TBTU). In addition to being stable to a whole array of reaction conditions, these protecting groups are also stable under acidic and basic conditions, allowing them to be used in combination with the ester protection of carboxylic acids. The cleavage of these protecting groups is activated by the chelation of metal ions, involving an unusual coordination of the amide nitrogen. Despite their similarity, cleavage of these protecting groups is possible in both a stepwise and an orthogonal fashion by applying different metal salts.     

GFAAS和ICP-MS对比测定大米中三种重金属含量

分别采用石墨炉原子吸收光谱法(GFAAS)与电感耦合等离子体质谱法(ICP-MS)同时测定大米中铅、镉和铬三种重金属含量,从分析方法的准确度、精密度等方面比较两种方法的优缺点。研究结果表明,两种方法测定结果均能满足分析要求,但ICP-MS法的测定结果更接近样品真实值,操作更加简便。     

The Hydrolysis of Hydroxamic Acid Complexants in the Presence of Non-oxidizing Metal Ions 1: Ferric Ions

Hydroxamic acids (XHAs) are organic compounds with affinities for cations such as Fe³⁺, Np⁴⁺ and Pu⁴⁺ and have been identified as useful reagents in nuclear fuel reprocessing. Acid catalyzed hydrolysis of free XHAs is well known and may impact negatively on reprocessing applications. The hydrolysis of metal-bound XHAs within metal ion-XHA complexes is less understood. With the aid of speciation diagrams, we have modelled UV-visible spectrophotometric kinetic studies of the acid-catalyzed hydrolysis of acetohydroxamic acid (AHA) bound to the model ion Fe(III). These studies have yielded the following information for the hydrolysis of AHA in the Fe(AHA)²⁺ complex at 293 K: (i) the order with respect to [H⁺] during the rate determining step, m=0.97, is the same as for the free ligand, indicating a similarity of mechanisms; and (ii) the kinetic rate parameter, k ₁=1.02×10⁻⁴ dm³⋅mol⁻¹⋅s⁻¹, is greater than that for the free ligand, k ₀=1.84×10⁻⁵ dm³⋅mol⁻¹⋅s⁻¹ for pH>−0.5, a result that is consistent with a Hammett analysis of the system.     

Using Distonic Radical Ions to Probe the Chemistry of Key Combustion Intermediates: The Case of the Benzoxyl Radical Anion

The benzoxyl radical is a key intermediate in the combustion of toluene and other aromatic hydrocarbons, yet relatively little experimental work has been performed on this species. Here, a combination of electrospray ionization (ESI), multistage mass spectrometry experiments, and density functional theory (DFT) calculations are used to examine the formation and fragmentation of a benzoxyl (benzyloxyl) distonic radical anion. Excited 4-carboxylatobenzoxyl radical anions were produced via two methods: (1) collision induced dissociation (CID) of the nitrate ester 4-(nitrooxymethyl)benzoate, ^–O₂CC₆H₄CH₂ONO₂, and (2) reaction of ozone with the 4-carboxylatobenzyl radical anion, ^–O₂CC₆H₄CH₂ ^?. In neither case was the stabilized ^–O₂CC₆H₄CH₂O^? radical anion intermediate detected. Instead, dissociation products at m/z 121 and 149 were observed. These products are attributed to benzaldehyde (O₂ ^-CC₆H₄CHO) and benzene (^–O₂CC₆H₅) products from respective loss of H and HCO radicals in the vibrationally excited benzoxyl intermediate. In no experiments was a product at m/z 120 (i.e., ^–O₂CC₆H₄ ^?) detected, corresponding to absence of the commonly assumed phenyl radical + CH₂=O channel. The results reported suggest that distonic ions are useful surrogates for reactive intermediates formed in combustion chemistry.

The Phosphoenolpyruvate Phosphorylation: A Self-Organized Mechanism with Implications to Understand the RNA Transformations

In this article, we present a study about the non-enzymatic hydrolysis of phosphoenolpyruvate (PEP) by following the reaction course through ³¹P NMR spectroscopy. We have demonstrated that PEP in water exists mainly as a very stable cyclic pentacoordinate phosphorus compound in equilibrium with other cyclic forms. This explains the PEP stability in water. In contrast, after addition of an alcohol to a PEP aqueous solution, other very unstable cyclic pentacoordinated intermediates are formed, which immediately collapse, giving a feasible phosphorylation of the alcohol. It is known that cyclic pentacoordinated phosphorus intermediates are favored over the corresponding acyclic intermediates by a factor of 10⁶–10⁸, and this preference, found also in this study, might be the “driver mechanism” able to overcome the clutter of abiotic chemistry, thus permitting formation of pre-RNA molecules probably with a “self-organized process.”     

Improvement in the Stability of Gabapentin by the Complexation of Gabapentin with Different Metal Ions: a DFT Study

Gabapentin undergoes intramolecular cyclization by alkylamine nucleophilic attacking on carboxylate carbonyl. And the above self-dehydration condensation can produce gabapentin lactam which has some toxic effects. Therefore, in order to decrease the above subsidiary reaction, the effects of several metal ions on the reaction mechanism and the potential barriers of self-dehydration condensation of gabapentin are analyzed. Each molecular structure of gabapentin in the presence of several metal ions is optimized using the density functional theory(DFT) with B3LYP method at the 6-311+G(d,p) basis set level. And its geometric and thermodynamic parameters are also investigated. The calculated results showed that gabapentin can form stable complexes with divalent metal ions and exhibit the highest affinity for small and highly charged metal cations. The binding ability of these metal ions with gabapentin ranks in an order of Fe~(2+) Zn~(2+) Mg~(2+) Ca~(2+) Na~+ K~+. Besides, the potential barriers of subsidiary reaction of gabapentin increase obviously in the presence of several metal ions than that of free gabapentin. This means that the above metal ions can inhibit effectively the intramolecular cyclization of gabapentin.     

Metal Ions Binding to Natural Organic Matter Extracted from Wheat Bran: Application of the Surface Complexation Model

Ions binding to solid organic matter was investigated in this study. A simple surface complexation model, the diffuse double-layer model, was used to describe Pb(II), Cd(II), Zn(II), and Ni(II) binding to a lignocellulosic substrate extracted from wheat bran. The lignocellulosic substrate was represented by two acid sites: a low-pH ("carboxylic") site and a high-pH ("phenolic") site, the phenolic-type sites contributing significantly to the binding behavior, even at relatively low pH. By using the previously determined concentrations of sites and acidity constants, the surface complexation model was applied to Pb, Cd, Zn, and Ni binding as a function of pH in a 0.1 M NaNO(3) medium. The model fits were good over a wide range of pH (2相似文献   

Enzymatic Lysis of Living Microbial Cells: A Universal Approach to Calculating the Rate of Cell Lysis in Turbidimetric Measurements

The data of the turbidimetric measurement for the enzymatic lysis of various living bacterial cells are analyzed. A method for the correct recalculation of the turbidimetric data (–ΔA/Δt) into absolute values of the change in the concentration of living cells (–ΔCFU/Δt) is proposed. The dimensionless efficiency of cell lysis–(1/CFU₀) · ΔCFU/Δt for various bacterial cells is calculated to correctly compare the efficiency of the action of different bacteriolytic factors on various bacterial cells.     

One‐Pot Fabrication of Noble‐Metal Nanoparticles That Are Encapsulated in Hollow Silica Nanospheres: Dual Roles of Poly(acrylic acid)

An efficient and facile one‐pot method was developed to fabricate noble‐metal nanoparticles (NMNs; Au, Pt, PdO and Ag) that were encapsulated within hollow silica nanospheres (HSNs; NMNs@HSNs) with a size of about 100 nm. NMNs@HSNs were afforded in very high yields between 85–95 %. Poly(acrylic acid) (PAA) polyelectrolyte played a dual role in the fabrication process, both as a core template of the HSNs and as a captor of the NMNs through coordination interactions between the COO^? groups on the ammonium polyacrylate (APA) polyanionic chains and the empty orbital of the Au atom. The amount of Au loading in Au@HSNs was easily regulated by varying the volume of the HAuCl₄ solution added. In addition, these rattle‐type particles were successfully applied in the catalytic reduction of 2‐nitroaniline (2‐NA) as a model reaction, thus indicating that the micropores in the silica shell could achieve the transport of small species—with a size smaller than that of the micropores—into the cavity. Thus, these fabricated NMNs@HSNs have promising applications in catalysis.     

Influence of the Structure of the Aminoalkyl Group in Polysiloxane on the Selectivity of Its Interaction with Metal Ions

Russian Journal of Applied Chemistry - Polysiloxanes containing nonchelating 3-aminopropyl and chelating N-(2-aminoethyl)-3-aminopropyl groups with the degree of functionalization of 28 and 24%,...     

The Interactions of Low Oxidation State Transition Metal Clusters with DNA: Potential Applications in Cancer Therapy

A series of ruthenium and platinum clusters have been examined for DNA binding activity in methanol-water and water solutions. The clusters [H₄Ru₄(C₆H₆)₄]²⁺and Ru₃(CO)₉(PTA)₃(PTA=1,3,5-triaza-7-phosphatricyclo[3.3.1.1] decane) proved to be most effective; the former is believed to cross link DNA and the latter possibly intercalates. These clusters are highly water soluble and combined with their DNA damaging activity and size represent potential anticancer drugs.     

Spectral Study of the Effect of Water on the Complex Formation of Photochromic Spiropyrans with Metal Ions in Acetonitrile

Russian Journal of General Chemistry - A comparative spectral study of the complex formation of molecules of nitro-substituted indoline spiropyrans with metal ions in acetonitrile and...     

Conductance Study of 1 : 1 19-Crown-6 Complexes with Various Mono- and Bivalent Metal Ions in Water

Formation constants (ML) of 1 : 1 19-crown-6 (19C6) complexes with mono- (M+) and bivalent metal ions (M2+) were determined in water at 25 °C by conductometry. The KML value of 19C6 for M+ and M2+ decreases in the order Rb+ K+ > Tl+ > Na+ = Ag+ > Li+ Cs+ and Pb2+ > Ba2+ > Sr2+ > Cd2+ > Ca2+, respectively. The selectivity for the neighboring alkali metal ions in the periodic table is lower for 19C6 than for 18-crown-6 (18C6) except for the case of Rb+ and Cs+. The same is true for the alkaline earth metal ions. Generally, the KML values of 19C6 with M2+ are greater than those with M+. For Na+ and the ions which are smaller in size than Na+ (Li+, Ca2+, Cd2+), the KML value is larger for 19C6 than for 18C6, but the contrary holds for all the other ions of larger sizes than Na+. The limiting ionic molar conductivity (°) of the 19C6–K+ complex in water at 25 °C was determined to be 43. Although 19C6 is larger than 18C6, the 19C6–K+ complex is much more mobile in water than the 18C6–K+ complex.     

"Amphiphilic" Cleavage of gamma-Stannyl Ketones with ATPH/RLi: Application to Enone Fragmentation by the Conjugate Addition - Cleavage Sequence

The use of a combined Lewis acid/base system consisting of aluminum tris(2,6-diphenylphenoxide) (ATPH) and MeLi has allowed the electrophilically activated nucleophilic ("amphiphilic") cleavage of C(alpha)-C(beta) bonds in gamma-stannyl ketones. Through combination with the conjugate addition of alpha-stannyl carbanion to enone, this approach constitutes a novel two-step conjugate addition - cleavage sequence that leads to functionalized ketones (see reaction).