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The kinetics of the chlorination of leucine, isoleucine, and valine (BCAAs) was studied in excess HOCl by stopped-flow and spectrophotometric methods (25 ◦C, I = 1.0 M NaClO 4). The intermediates and products were identified and monitored by 1H NMR spectroscopy. It was established that these reactions are fully analogous and proceed according to distinct mechanisms under alkaline and neutral conditions. At high pH, the formation and subsequent rate determining decomposition of N -monochloroamino acid control the process. The decomposition occurs via competing pH-independent and OH−-assisted reaction paths and the sequence of chlorination, dichlorination and decarboxylation steps leads to the formation of N -chloroimines and their carbanionic forms, which are in fast acid – base equilibria. The dechlorination of the carbanions yields nitriles as the main products. The hydration of the N -chloro imines produces chloramine and aldehydes which are involved in further oxidation reactions with HOCl. The formation of chloroform and chloroacetaldehyde was confirmed in each system. At pH 7.0, the N -chloro derivatives of BCAAs form immediately and are converted into the corresponding N , N -dichloro species within a few seconds after mixing the reactants. In this reaction, the reactive form of the oxidant is Cl 2 O. The first-order decomposition of the dichloroamino acids occurs on stopped-flow timescale (k = 0.5 – 0.7 s−1) and yields N -chloroimines which slowly decompose with a characteristic first-order rate constant on the order of a few times 10−5 s−1. The main products are the corresponding nitriles that account for about 80% and 60% of the original amounts of amino acids under neutral and alkaline (c OH − = 5.00 × 10−2 M) conditions, respectively. Aldehydes, carboxylic acids, chloroform and NCl 3 were also identified as by-products. The results unequivocally confirm that harmful chlorinated species may form from amino acids long after the chlorination step in water treatment technologies that deteriorates the quality of the finished water. In source waters, amino acids account for about 75% of the total dissolved nitrogen. Therefore, it is an essential issue how the reactions of these compounds with hypochlorite ion can be controlled to avoid the formation of toxic compounds. The compounds formed from BCAAs are considered to be harmful both under alkaline and neutral conditions (chloroacetaldehyde, chloroform, nitriles). However, some of the intermediates have extended lifetime in these systems and they may also react with other components of raw water during water treatment processes. [Display omitted] • The products and the main intermediates have been identified. • At high pH, the formation of N , N -dichloroamino acids does not occur. • At pH∼7, the reactions of monochloroamino acids with Cl 2 O yield dichloroamino acid. • Detailed mechanisms are postulated for the interpretation of the results. • Nitriles as main products and chlorinated by-products have been identified. [ABSTRACT FROM AUTHOR]

Superoxide dismutase (SOD) enzymes are pivotal in regulating oxidative stress. In order to model Ni containing SOD enzymes, the results of the thermodynamic, spectroscopic and SOD activity studies on the complexes formed between nickel(II) and a NiSOD related peptide, CysCysAspLeuProCysGlyValTyr–NH2 (wtCC), are reported. Cysteine was introduced to replace the first histidine residue in the amino acid sequence of the active site of the NiSOD enzyme. The novel peptide exhibits 3 times higher metal binding affinity compared to the native NiSOD fragment. This is due to the presence of the first cysteine in the coordination sphere of nickel(II). At physiological pH, the (NH2,S–,S–,S–) coordinated complex is the major species. This coordination mode is altered when one thiolate group is replaced by an amide nitrogen of the peptide backbone above pH 7.5. The nickel complexes of wtCC exhibit similar SOD activity to that of the complex formed with the active site fragment of the native NiSOD. The reaction between the complexes and the superoxide anion was studied by the sequential stopped-flow method. These studies revealed that the nickel(II) complex is always in excess over the nickel(III) complex during the dismutation process. However, the nickel(III) species is also involved in a relatively fast degradation process. This unambiguously proves that a protective mechanism must be operative in the NiSOD enzyme which prevents the oxidation of the sulfur atom of cysteine in the presence of O2−. The results provide new possibilities for the use of NiSOD mimics in bio- and industrial catalytic processes. [ABSTRACT FROM AUTHOR]

The light source of a photometer may induce chemical reactions in photosensitive reactive systems. Diode-array spectrophotometers are particularly suitable for producing such phenomena. This paper provides an overview on how this equipment can be used as a photoreactor. The principles of various techniques to control the intensity and spectral region of the illuminating light are discussed in detail. It will be shown that the quantum yields of various photochemically induced redox reactions can be determined by exploiting specific features of diode-array spectrophotometers. Kinetic coupling between primary photo - chemical and secondary thermally activated reaction steps are utilized to explore intimate details of composite redox reactions. Key aspects of the method applied are demonstrated via the photoreactions of 2,6-dichloro-1,4-benzoquinone (DCQ), the photoinduced autoxidation of S(IV) and a photochemically activated redox reaction of the chlorate ion. [ABSTRACT FROM AUTHOR]

The overall six-electron oxidation of water soluble porphyrin FeIIITPPS by hydrogen peroxide and peroxomonosulfate ion was studied by the stopped-flow method with UV-vis detection. A three-step consecutive reaction was observed with two intermediates: FeIIITPPS → Int1 → Int2 → products. The products were identified as the iron(III) complex of the biliverdin analog formed from TPPS and 4-sulfobenzoic acid. All the rate constants with both oxidizing agents were determined. Intermediate Int1 is proposed to be the species (TPPS•+)FeIV=O. Although no unambiguous proposal for the structure of Int2 can be made, it is most probably the product of the four-electron oxidation of the original FeIIITPPS, contains an iron-oxo center and has a dissociable proton with a pΚ of around 3.1. In spite of the protolytic equilibria occuring in the pH region 2-4, the kinetic observations do not show pH dependence. [ABSTRACT FROM AUTHOR]

The effect of dissolved oxygen on the acid-dependent disproportionation of dithionate ion (S2O62-) and its oxidation with a number of reagents (I2, Br2, I3-, Br3-, IO3-, BrrO3-, IO4-, MnO4-, Cr(VI), Ce(VI), and H2O2) were studied. Dithionate ion is remarkably inert at room temperature, and heating to elevated temperatures (50-90 °C) was necessary to observe detectable reaction rates in all of these processes. It was confirmed that dithionate ion is never oxidized directly; its redox reactions are zeroth-order with respect to the oxidizing agent and proceed through disproportionation and subsequent fast oxidation of the sulfur(IV) formed. The effect of dissolved oxygen is attributable to its reaction with sulfur(IV) produced in the disproportionation. This autoxidation occurs only with a catalyst. Cerium(III) and iodide ions were shown to catalyze the autoxidation, and their effect on the kinetic traces was studied. In a few cases, highly unusual kinetic traces, such as straight lines with sharp break points, inverted parabolas, and a combination of these, were detected and successfully interpreted in terms of simple kinetic and stoichiometric considerations. [ABSTRACT FROM AUTHOR]

The kinetics and mechanism of the chlorine(III)-HOBr reaction were studied by the stopped-flow method under acidic conditions, pH 1.0-3.0, in 1.0 M NaCIO4 and at 25.0 °C. The overall redox process occurs in two consecutive steps via the formation of the BrClO2 intermediate. The electron transfer reactions are coupled with bromine hydrolysis, the formation of the tribromide ion, and the protolytic equilibrium of chlorine(III). On the basis of simultaneous evaluation of the kinetic traces, the following rate constants were obtained for the redox steps: HClO2 + HOBr ↔ BrClO2 + H2O, k3 = (3.34 ± 0.02) × 104 M-1 S-1, , k-3 = (3.5 ± 1.3) × 10³ s-1; BrCIO2- ↔ 2CIO2 + Br-, k4 = (2.9 ± 1.0) × 107 M-1 s-1. The second step was practically irreversible under the conditions applied, and the value of k-4 could not be determined. The equilibrium constant for the formation of BrClO2, K3 = 9.5 M-1, was calculated from the kinetic results, and it was confirmed that this species is a very powerful oxidant. The redox potential was also estimated for the BrOlO2 + e- = Br- + ClO2 reaction: ∈0 ∼ 1.70 V. [ABSTRACT FROM AUTHOR]

Stability constants of the complexes formed in the reaction of [Pd(bpma)]2+ [bpma=bis(pyridin-2-ylmethyl)amine] with monodentate nitrogen and thioether ligands including uridine, MeUH, cytidine, MeC, EtGH, AcHis, AcHm, AcLys and AcMet were determined by potentiometric method. The coordination chemistry of [Pd(bpma)]2+ shows a significant similarity to that of [Pd(terpy)]2+, but it is different from [Pd(dien)]2+. The formation of hydroxo and dinuclear complexes is especially enhanced in the case of [Pd(bpma)]2+ and [Pd(terpy)]2+, but the affinity of palladium(II) ions for the coordination of thioether residues is reduced in the presence of pyridine nitrogen atoms. Stopped-flow kinetic measurements reveal that the substitution reactions of the thioether ligand AcMet are much faster than those of the N-donor cytidine. The presence of the two pyridyl residues significantly enhances the kinetic reactivity of [Pd(bpma)]2+ as compared to that of [Pd(dien)]2+. The Pd–S(thioether) bonded species can be important intermediates in multicomponent systems, but the equilibrium state is characterised by the formation of Pd–N bonded species. The complex [Pd(bpma)NO3]NO3 has been prepared in solid state and its structure was elucidated by single crystal X-ray diffraction method. [Copyright &y& Elsevier]

The kinetics of the complex formation between oxovanadium(IV) and maltol was studied by the stopped-flow method at 25 °C in 0.2 M KCl. The formation of the bis-complex is about an order of magnitude faster than that of the mono-complex under the same conditions. The results confirm that parallel paths are operative in these reactions via the acid (HA) and base (A−) forms of the ligand. The relevant rate constants were determined and mechanistic implications of the results are also discussed. It is concluded that the oxovanadium(IV) ion can easily form the thermodynamically most favorable complexes in ligand rich environments such as biological liquids. [Copyright &y& Elsevier]

Studies the kinetics and mechanisms of ligand substitution reactions of the iron hydroxo dimer with various inorganic ligands. Confirmation of transient formation of particular di- and tetranuclear complexes; Catalytic effect of arsenic on the hydrolytic reaction of iron; Establishment of the appropriate rate laws.

In this paper, the kinetic study of the reaction between substituted 1,4-benzoquinones (RBQs) and Na2SO3 (S(IV)) is presented in aqueous solutions at different pH values and reagent concentrations. The stoichiometry of the reaction is 1:2 RBQs:S(IV) and one equivalent of chloride ion was also detected as a product when using mono- (2-CBQ) or dichloro-benzoquinones (2,5-DCBQ; 2,6-DCBQ) as reactants. This shows that reductive dehalogenation occurs instead of simple reduction to the corresponding substituted 1,4-hydroquinones (RBQHs) and quinone bisulfites are formed, analogously to the addition of bisulfite ion to carbonyl compounds. Various sulfonated quinones have been identified as products by electrospray mass spectrometry. Kinetic traces at different wavelengths were obtained by the stopped-flow technique with spectrophotometric detection, a kinetic fitting program (ZiTa) was used to fit a multi-step model to the data. A detailed mathematical evaluation of the reaction scheme was carried out under non-pseudo-first order conditions showing that our model can be fitted with a double exponential function even when none of the reagents are in large excess. [ABSTRACT FROM AUTHOR]

The kinetics and mechanism of the cis dihydroxylation of cis‐1,2‐dichloroethylene, trans‐1,2‐dichloroethylene, and trichloroethylene by osmium tetroxide was studied systematically in aqueous solution. The stoichiometry of the process was determined based on the principle of continuous variation of reactant ratios with spectrophotometric detection. The results always showed 1:1 stoichiometry, which is in agreement with dihydroxylation. All three reactions were found to proceed in two distinct steps. The first step occurred on a time scale of seconds and was associated with a minor change in absorbance and was identified as the formation of a 1:1 adduct between the two reagents, which is the osmium(VI) ester that plays a decisive role in catalytic applications. This species is formed in an equilibrium that is very much shifted toward the reactants, so the osmium(VI) complex is a short‐lived intermediate of the process, which is detected kinetically, but its concentration is never high enough for structural characterization. The second reaction is accompanied by major spectral changes; it involves the formation of the final products. Our results clearly show that it is possible to detect the intermediate of the process by careful kinetic studies. It is also possible that the same strategy might be successful in other OsO4‐dependent dihydroxylation processes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Static SFE combined with aerogel adsorption is used to protect aroma materials. • Hydrophilic and hydrophobic silica aerogels showed different selectivities. • Trace compounds were enriched to an analytically significant level. • Extracted components competed with each other for the active sites on the surface. • Static SFE gives higher number of components and cleaner extracts. Abstract Static supercritical fluid extraction has been used to concentrate the aroma materials of common herbs and spices. The technique has provided a higher number of components and cleaner extract than the one-step ethanol maceration. The one-step supercritical fluid extraction of the aroma compounds has been combined with their in situ adsorption in hydrophilic and hydrophobic silica aerogels. The extracts have been analyzed by a GC–MS technique and 55 aroma compounds have been identified. Most of the compounds have been adsorbed in both polar and apolar silica aerogels with no direct connection with the surface polarity. However, previously undetected compounds enriched to an analytically significant level, while others competed with each other for the active sites on the surface. Functionalized silica aerogels can be used as a new type of aroma storage materials and as selective and tuneable adsorbents for the extraction and enrichment of potentially active components from a complex matrix. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The decomposition of N -chloro- α -alanine is a multistep process. • The rate of decomposition increases by increasing the pH. • The sole product is acetaldehyde under neutral – slightly alkaline conditions. • In highly alkaline solution, pyruvate ion is the main and N -acetyl- α -alanine is the secondary product. Abstract N -chloro-amino acids are readily formed in chlorination water treatment technologies. These reactions are also important in biological systems where HOCl plays an important role in the defense mechanism against invading pathogens. The intermediates and the products formed are of primary concern because they may have significant biological activities. In order to clarify intimate details and resolve discrepancies in the literature, the decomposition kinetics of N -chloro- α -alanine (MCA) was studied in the neutral – alkaline pH range by UV–vis spectrophotometry and 1H-NMR method. In contrast to earlier reports, the decomposition reaction proceeds via two distinct reaction paths: k obs1 = k OH [OH−] + k , where k OH = (1.38 ± 0.02) × 10−2 M−1s−1 and k = (2.95 ± 0.09) × 10−4 s−1. In slightly alkaline solution, the sole product is acetaldehyde. Under alkaline conditions, the main product is pyruvate ion, however, N -acetyl- α -alanine is also formed in a subsequent reaction sequence. A detailed kinetic model is postulated which involves the rate determining dissociation of MCA into Cl− and ethanimine which produces acetaldehyde in further reaction steps. Via the OH− assisted path, first a carbanion is formed which undergoes dechlorination and produces iminopropionate ion. This species is transformed into pyruvate ion through hydration and deamination steps. [ABSTRACT FROM AUTHOR]

The chlorination of the two simplest amino acids at HOCl excess was studied by stopped-flow, conventional spectrophotometric and time resolved 1H NMR kinetic methods at 25 °C. These reactions show distinct characteristics under neutral and alkaline conditions. At high pH, the common feature of the two systems is that the N -dichloroamino carboxylate ion does not form and the overall process is controlled by the initial decomposition of the N -monochloro derivative. Under such conditions, carbanions form in equilibrium acid – base processes and open alternative reaction paths, resulting in enhanced complexity of the corresponding mechanisms. In the case of α-alanine, the formation of acetonitrile and N -chloro acetamide as main products; acetate ion, acetaldehyde, chloroacetaldehyde, chloroform as byproducts; acetamide and N -chloro ethanimine as intermediates was confirmed. In the case of glycine, the final products are formamide and OCN−. Under neutral conditions, monochloroamino acid forms immediately upon mixing the reactants, and subsequently it is converted into dichloroamino acid by Cl 2 O in a fast process. In considerably slower further reaction steps, acetonitrile and acetate ion form as final products in the α-alanine system, while the chlorination of glycine proceeds to full mineralization. The detailed mechanisms suggested for these reactions postulate the formation of various imines and N -chloro imines which are involved in decarboxylation, dechlorination, hydration and hydrolytic reaction steps. [Display omitted] • The chlorination mechanisms of glycine and alanine at HOCl excess is explored. • Antagonistic products and intermediates were identified in these systems. • At high pH, the formation of N , N -dichloroamino acid does not occur. • At pH ∼ 7, Cl 2 O chlorinates monochloroamino acid to produce dichloroamino acid. • The CH 3 group on the α-carbon atom profoundly alters the chlorination mechanism. [ABSTRACT FROM AUTHOR]

Mesoporous silica aerogels covalently functionalized with Cu(II) complexes of cyclen (1,4,7,10-tetraazacyclododecane) and cyclam (1,4,8,11-tetraazacyclotetradecane), denoted as CuAM12 and CuAM14, respectively, have been first prepared. Monolithic materials were synthesized from alkoxysilane-anchored macrocyclic complexes and TMOS through the base catalyzed sol-gel method followed by a supercritical CO 2 drying. Presence of organic moieties in the silica structure was confirmed by FT-IR measurements, the amount of incorporated copper was determined by ICP-OES technique, resulting in 1.310 ± 0.028 and 2.060 ± 0.025 wt% copper for CuAM12 and CuAM14, respectively). Surface morphology was characterized by nitrogen adsorption/desorption porosimetry and scanning electron microscopy. Catalytic activities of the aerogels CuAM12 and CuAM14 were evaluated by oxidation of phenol with eco-friendly reagent hydrogen peroxide, without buffering or using organic co-solvents. Control experiments using unbound macrocyclic complexes in the homogenous phase were also conducted. Surprisingly, results revealed that the functionalized aerogels' turnover frequencies (TOF) were approximately 7–15 times higher than that of the free complexes in the homogeneous phase. The increase was attributed to the confinement effect. Reusability studies showed that the catalysts remained active even after four cycles completed. Certain reduction of catalytic activity was observed in the repeated cycles, which was the combined effect of poor mechanical properties of the aerogel, splitting-off and leaching of the less-bound surface macrocycles, and extensive adsorption of the oxidation products. [ABSTRACT FROM AUTHOR]

It is often challenging to follow fast surface adsorption processes with sufficient time resolution. Here we report a convenient UV–Vis spectrophotometry based method to study the fast kinetics of an archetypical surface process: the adsorption of MB on quartz. The test object was a commercial quartz cuvette. About 3.3% of the dye was adsorbed from a 34 μM solution at pH 7 in 10 min. Biphasic kinetics was observed for the depletion of MB under continuous stirring at 1000 rpm. A kinetic model was postulated for the interpretation of time resolved spectral changes. This model assumes the reversible adsorption of MB on the surface which is followed by the isomerization of the binding mode. The overall process is kinetically first order with respect to MB, thus dimer formation, which was previously proposed to be favored on quartz, can be ruled out. The experimental adsorption isotherm is consistent with the formation of an adsorption monolayer from single molecules. The UV–vis absorbance spectrum of adsorbed MB does not show any blue shift. With the simplest experimental setup, it is shown that the dimerization of MB is not exceptionally favored on quartz surface. [ABSTRACT FROM AUTHOR]

This work reports an experimental study of the hydrogen/deuterium exchange in the basic aqueous solutions of trichloroethylene, trans-1,2-dichloroethylene, and cis-1,2-dichloroethylene using 1H NMR as a monitoring method. 1,1-Dichlorethylene was also investigated but found not to exchange hydrogen isotopes with water. The kinetics of isotope exchange features two different pathways, the first is first order with respect to hydroxide ion, whereas the second is second order. The first pathway is interpreted as a straightforward bimolecular reaction between chloroethylene and hydroxide ion, which leads to the deprotonation of chloroethylene. The second pathway involves a transition state with the association of one molecule of the chloroethylene and two hydroxide ions. It is shown that the second pathway could involve the formation of a precursor complex composed of one chloroethylene molecule and one hydroxide ion, but a direct termolecular elementary reaction is also feasible, which is shown by deriving a theoretical highest limit for the rate constants of termolecular reactions in solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanoscale structural features of hydrated hybrid aerogels by NMR and SANS. • Nanoscale architecture of hybrid backbone is conserved in water. • Size distribution of water-filled pores measured by NMR cryoporometry. • Wetting mechanism and chemical environment of water revealed by NMR relaxometry. • Extensive hydration of PVA dictates the wetting of the hybrid skeleton. Mesoporous borosilicate – polyvinyl alcohol (PVA) hybrid aerogels show positive bioactivity when interacting with dental pulp stem cells. The surface characteristics and the nanostructures of the hydrated aerogel particles are important in determining the biological response. This study reports the comparative structural characterization of pristine and stepwise hydrated hybrid aerogels, and proposes a qualitative mechanism for the wetting and pore-filling processes of these mesoporous materials. Nuclear magnetic resonance (NMR) relaxometry and cryoporometry revealed the extensive hydration of PVA macromolecules in the hybrid skeleton when contrasted to the wetting of pure silica aerogels. In spite of this extensive hydration, the open and permeable pore-structure of the hybrid borosilicate-PVA aerogels are preserved even when completely filled with liquid water. The conservation of the nanoscale architecture of the hybrid aerogels upon wetting was further confirmed by SANS. Finally, it was shown that the incorporation of microcrystalline hydroxyapatite into the hybrid skeleton does not alter the advantageous morphological features and wetting mechanism of the hybrid aerogels. The rough nanostructured skeleton is advantageous for cell binding and ensures facile mass transport through the particles in aqueous suspensions. [ABSTRACT FROM AUTHOR]

The significance of persulfide species in hydrogen sulfide biology is increasingly recognized. However, the molecular mechanisms of their formation remain largely elusive. The obvious pathway of the reduction of biologically abundant disulfide moieties by sulfide was challenged on both thermodynamic and kinetic grounds. Using DTNB (5,5′-dithiobis-(2-nitrobenzoic acid), also known as Ellman's reagent) as a model disulfide we conducted a comprehensive kinetic study for its reaction with sulfide. The bimolecular reaction is relatively fast with a second-order rate constant of 889 ± 12 M −1 s −1 at pH = 7.4. pH dependence of the rate law revealed that the reaction proceeds via the bisulfide anion species with an initial nucleophilic thiol-disulfide exchange reaction to give 5-thio-2-nitrobenzoic acid (TNB) and TNB-persulfide with a pH independent second-order rate constant of 1090 ± 12 M −1 s −1 . However, kinetic studies and stoichiometric analyses in a wide range of reactant ratios together with kinetic simulations revealed that it is a multistep process that proceeds via kinetically driven, practically irreversible reactions along the disulfide → persulfide → inorganic polysulfides axis. The kinetic model postulated here, which is fully consistent with the experimental data, suggests that the TNB-persulfide is further reduced by sulfide with a second-order rate constant in the range of 5 × 10 3  – 5 × 10 4  M −1 s −1 at pH 7.4 and eventually yields inorganic polysulfides and TNB. The reactions of cystine and GSSG with sulfide were found to be significantly slower and to occur via more complicated reaction schemes. 1 H NMR studies suggest that these reactions also generate Cys-persulfide and inorganic polysulfide species, but in contrast with DTNB, in consecutive equilibrium processes that are sensitive to changes in the reactant and product ratios. Collectively, our results demonstrate that the reaction of disulfides with sulfide is a highly system specific process from both thermodynamic and kinetic aspects, which together with the considerable steady-state concentrations of the reactants in biological systems signifies physiological relevance. [ABSTRACT FROM AUTHOR]

The kinetics and mechanism of the reaction between dissolved oxygen and sulfur(IV) was studied in aqueous acidic medium using co-catalysts peroxodisulfate and silver(I) ions. The presence of both catalysts was required to observe measurable rates in the studied process. The reaction rate was determined through following the UV-absorption of hydrated sulfur dioxide, and the trends were determined as a function of pH, reactant and catalyst concentrations. Individual kinetic curves under conditions where dissolved oxygen was the limiting reagent were close to zeroth-order. A chain mechanism with four chain carriers, sulfite, sulfate, peroxomonosulfate ion radical and silver(II) ion, is proposed to interpret all the kinetic and stoichiometric findings, and an explicit formula was obtained for the rate law. The role of the co-catalysts is to produce chain carriers, whereas silver(I) and silver(II) ions also participate in chain propagation steps. Further supporting evidence for the proposed mechanism was gained in laser flash photolysis studies, which showed that sulfate ion radical reacts quite rapidly with silver(I) ion. [ABSTRACT FROM AUTHOR]

Mesoporous silica aerogels have a wide range of potential applications in biotechnology, the food industry, pharmacy and medicine. Understanding the nature of the interactions of biomolecules with these porous nanostructured materials is essential for achieving optimum performance in the targeted applications. In this study, the well-characterized bovine serum albumin (BSA) was chosen as a model protein to probe protein–aerogel interactions in the solution phase. Aqueous BSA was mixed with suspended silica aerogel microparticles, and the colloid system was monitored on-line by UV–vis spectrophotometry and turbidimetry. The global mathematical analysis of the time-resolved data reveals that the fast sorption of the protein on the aerogel microparticles follows a multistep binding mechanism. The extensive sorption of the protein eventually induces the aggregation of the covered aerogel due to the alteration of the electrical double layer of the particles. The interaction of BSA and silica aerogel is the strongest between pH = 4 and 5, because their native surface charges are the opposite in this pH range, as indicated by their respective zeta potentials. [ABSTRACT FROM AUTHOR]

The article focuses on the effects of ethylene glycol grades which was investigated by the elemental analysis of pitfall-trapped insect samples. The aim of the study is explore the condition of insect samples remains suitable for further elemental analysis after trapping with undiluted ethylene glycol. It also presents the statistical data of the effects of trapping fluid on elemental concentration.

Abstract: Insects often used as accumulation indicators of hazardous elements. Pitfall traps with ethylene glycol as trapping fluid are frequently used to collect insects. We studied the effect of glycol and preservation with ethanol on the elemental composition of hand collected firebugs. Control samples were stored in a freezer and the following treatments were used: insect kept in trapping fluid for 2weeks, and for 1month, trapping fluid for 2weeks plus 2weeks in ethanol, and trapping fluid for 1month plus ethanol for 1month. Insects kept in trapping fluid gained mass with respect to control: 26% for the short trapping and 37% for the long trapping. Preservation in ethanol reversed this effect in each case. Trapping fluid did not alter the dry mass. A significant loss in dry mass only occurred in the long trapping plus long preservation treatment. We analysed the concentration of eight elements: Ca, Cu, K, Mg, Mn, Na, Sr and Zn. We found significant difference in the concentrations of elements among the four treatments in the case of all elements, except magnesium and zinc. Our results indicate the potential of both certain trapping fluids as well as preservation in ethanol influencing the concentration of certain elements in insects. Live trapping for collection and storage in under freezing conditions for preservation could be a more reliable method if quantitative analytical studies are to be performed, when invertebrates are used as indicators of the presence and concentrations of hazardous substances in the environment. [Copyright &y& Elsevier]

Silica-gelatin hybrid aerogel of 24 wt% gelatin content is an advanced functional material suitable for the high performance selective adsorption of aqueous Hg(II). The remediation efficacy of this adsorbent was tested under realistic aquatic conditions by exposing cultures of Paramecium caudatum to Hg(II) and monitoring the model cultures by time-lapse video microscopy. The viability of Paramecium was quantified by analyzing the pixel differences of the sequential images caused by the persistent movement (motility) of the cells. The viability of Paramecium displays a clear exposure-response relationship with Hg(II) concentration. Viability decreases with increasing Hg(II) concentration when the latter is higher than 125 μg L−1. In the presence of 0.1 mg mL−1 aerogel adsorbent, the viability of the cells decreases only at Hg(II) concentrations higher than 500 μg L−1, and 220 min survival time was measured even at 1000 μg L−1 Hg(II). The effective toxicity of Hg(II) is lower in the presence of the aerogel, because the equilibrium concentration of aqueous Hg(II) is low due to adsorption, thus Paramecium cells do not uptake as much Hg(II) as in the un-remediated cultures. Video imaging of Paramecium cultures offers a simple, robust and flexible method for providing quantitative information on the effectiveness of advanced materials used in adsorption processes for water treatment. [Display omitted] • Paramecium caudatum used as bioindicator of Hg(II) toxicity. • Paramecium cultures monitored by time lapse video microscopy imaging. • Quantitative exposure-effect relationship established for Hg(II) toxicity. • Silica-gelatin aerogel effectively protects Paramecium from Hg(II). [ABSTRACT FROM AUTHOR]

The kinetics and mechanism of the photoinitiated and iodide ion-catalyzed aqueous autoxidation of sulfur(IV) has been studied in a diode-array spectrophotometer using the same light beam for excitation and detection. Light absorption of both the iodide ion and sulfur(IV) contribute to the initiation of a highly efficient radical chain reaction, the overall rate of which depends on the reactant and catalyst concentrations, the pH, and the light intensity in a complex manner. To interpret all the experimental findings, an elaborate scheme is proposed, in which the chain carriers are SO3-•, SO4-•, SO5-•, I•, and I2-•. There are three termination steps, each of them is second-order with respect to the chain carriers. Model calculations and nonlinear fitting have been used to show that the proposed scheme gives an excellent quantitative interpretation of the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: The [(CN)5Pt–Tl(edta)]4− complex, having direct metal–metal bond, has been prepared in solution by two different reactions: (a) dissolution of [(CN)5Pt–Tl](s) in aqueous solution of edta ligand, (b) from Pt(CN)4 2− and Tl(edta)(CN)2− reactants. The decomposition reaction is greatly accelerated by cyanide and significantly inhibited by edta. It proceeds through the [(CN)5Pt–Tl(CN)3]3− intermediate. This complex decomposes to Pt(CN)4 2− and Tl(CN)4 −. To complete the reaction, Tl(CN)4 − and edta4− react in relatively fast equilibrium step(s) giving Tl(edta)(CN)2−. The formation of [(CN)5Pt–Tl(edta)]4− complex can proceed via two different pathways depending on the ratio of the cyanide and the edta ligand. The ‘direct path’ at excess of edta means the formation of a [(CN)4Pt…Tl(CN)(edta)]4− intermediate followed by the release of the cyanide from the Tl-center than the coordination of a cyanide from the bulk to the Pt-center of the intermediate. The ‘indirect path’ dominates in the absence of extra edta and the formation of the Pt–Tl bond happens between Pt(CN)4 2− and Tl(CN)4 − as studied earlier in our laboratories. [Copyright &y& Elsevier]

The photoinitiated and cerium(III)-catalyzed aqueous reaction between sulfite ion and oxygen has been studied in a diode-array spectrophotometer using the same light beam for excitation and detection. Cerium(III) is identified as the photoactive absorbing species, and the production of cerium(IV) initiates a radical chain reaction. To interpret all the experimental findings, a simple scheme is proposed, in which the additional chain carriers are sulfite ion radical (SO3-·, sulfate ion radical (SO4-·), and peroxomonosulfate ion radical (SO5-·, The overall rate of oxidation is proportional to the square root of the light intensity per unit volume, which is readily interpreted by the second-order termination reaction of the proposed scheme. It is also shown that the reaction proceeds for an extended period of time in the dark following illumination, and a quantitative analysis is presented for this phase as well. The postulated model predicts that cerium(III) should have a cocatalytic or synergistic effect on the autoxidation of sulfite ion in the presence of other catalysts. This prediction was confirmed in the iron(III)-sulfite ion-oxygen system. The experimental method and the mathematical treatment used might be applicable to a wide range of photoinduced chain reactions. [ABSTRACT FROM AUTHOR]

Formation kinetics of the metal-metal bonded binuclear [(CN)5Pt-TI(CN)]- (1) and the trinuclear [(CN)5Pt-TI-Pt-(CN)5]3- (2) complexes is studied, using the standard mix-and-measure spectrophotometric method. The overall reactions are Pt(CN)42- + TI(CN)2+ ⇄ and Pt(CN)42- + [(CN)5Pt-TI(CN)]- ⇄ 2. The corresponding expressions for the pseudo-first-order rate constants are kobs = (k1[TI(CN)2+] + k-1)[TI(CN)2+] (at TI(CN)2+ excess) and kobs = (k2b[Pt(CN)42-] + k-2b)[HCN] (at Pt(CN)42- excess), and the computed parameters are k1 = 1.04 ± 0.02 M-2 s-1, k-1 = k1k1 = 7 x 10-5 M-1 s-1 and k2b = 0.45 ± 0.04 M-2 s-1, K2b = 26 ±6 M-1, k-2b = k2b/K2b = 0.017 M-1 s-1, respectively. Detailed kinetic models are proposed to rationalize the rate laws. Two important steps need to occur during the complex formation in both cases: (i) metal-metal bond formation and (ii) the coordination of the fifth cyanide to the platinum site in a nucleophilic addition. The main difference in the formation kinetics of the complexes is the nature of the cyanide donor in step ii. In the formation of [(CN)5Pt-TI(CN)]-, TI(CN)2+ is the source of the cyanide ligand, while HCN is the cyanide donating agent in the formation of the trinuclear species. The combination of the results with previous data predict the following reactivity order for the nucleophilic agents: CN- > TI(CN)2+ > HCN. [ABSTRACT FROM AUTHOR]

Studies the formation kinetics of the metal-metal bonded [(CN)[sub 5]PtTl(CN)[sub 3]][sup 3] complex from Pt(CN)[sub 4][sup 2-] and Tl(CN)[sub 4][sup -]. Use of the standard mix-and-measure spectrophotometric technique and stopped-flow method; Actual concentration ratio; Pseudo-first-order rate constant.

[Display omitted] • Kinetic and stoichiometric studies on new catalysts in the chlorate process. • Decomposition of hypochlorous acid at elevated temperature. • YCl 3 catalyzes the decomposition via the formation of O 2. • Y 2 O 3 and Te(OH) 6 slightly accelerate the chlorate production. • Te(OH) 6 is a more active catalyst than Y 2 O 3 but inferior compared to Cr(VI). By pursuing the aim of identifying new types of catalysts in the electrolytic production of NaClO 3 from NaCl (chlorate process), we report a detailed study on the decomposition of hypochlorous acid accelerated by yttrium(III) chloride (YCl 3), yttrium(III) oxide (Y 2 O 3) and telluric acid (Te(OH) 6) at 80 °C. The results were compared with those obtained in the uncatalyzed and chromium(VI) catalyzed reactions. In general, the decomposition of HOCl occurs via two competing paths toward the formation of ClO 3 − or O 2. In the case of YCl 3 , the decomposition proceeds via the oxygen path over the entire studied pH range. Y 2 O 3 slightly catalyzes the chlorate path under acidic conditions, however the noted catalytic effect is probably due to the "self-buffering" of the reaction mixture (Y 2 O 3 suspension). Although, a real catalytic process takes place in the presence of Te(OH) 6 , a significant pH-effect is also observed which is most likely associated with the acid–base equilibria of telluric acid. pH dependent studies demonstrate that the optimum pH of decomposition is at around 6.7–6.9 in this case. The comparison of the results obtained in the presence of chromium(VI) and Te(OH) 6 reveals that the former is a more active catalyst. On the basis of kinetic and stoichiometric results, it is reasonable to assume that Te(OH) 6 may be utilized as an alternative catalyst in the chlorate process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phenanthroline-mono- N -oxides form stable complexes with copper(II) and nickel(II) ions. • The introduction of hydrophobic methyl substituents leads to selective metal binding. • The structures of the complexes were thoroughly characterized. Thorough equilibrium and spectroscopic studies are reported on the complexes formed between copper(II) or nickel(II) and derivatives of phenanthroline-mono- N -oxides (1,10-phenanthroline-1- N -oxide (phenO), 2,9-dimethyl-1,10-phenanthroline-1- N -oxide (DMPO) and 3,4,7,8-tetramethyl-1,10-phenanthroline-1- N -oxide (TMPO)). PhenO exhibits excellent metal binding ability, both copper(II) and nickel(II) form bis complexes in which the ligands coordinate to the metal ions via the (N,O) donor set. In the case of copper(II), a square-pyramidal complex forms, where the phenO-s coordinate at the corners of the square and the remaining site is occupied by the water molecule. The bis complex formed between nickel(II) and phenO possesses square-planar geometry in solution, however, the Ni(II) ion exhibits a distorted octahedral geometry in solid phase. DMPO forms relatively stable complexes with copper(II), but the coordination of this ligand to nickel(II) could not be confirmed. Because of precipitate formation in the entire studied pH range (pH = 2.0 – 11.0), well defined complexes could not be identified in the copper(II) – TMPO system. In contrast, this ligand forms stable water soluble nickel(II) complexes. The noted selectivity of these ligands in complex formation reactions is explained by considering the plasticity of copper(II), the rigid, square-planar geometry of nickel(II) and the enhanced steric repulsion of the methyl substituents of DMPO. [ABSTRACT FROM AUTHOR]

Detailed equilibrium, spectroscopic and superoxide dismutase (SOD) activity studies are reported on a nickel complex formed with a new metallopeptide bearing two nickel binding loops of NiSOD. The metallopeptide exhibits unique nickel binding ability and the binuclear complex is a major species with 2×(NH2,Namide,S−,S−) donor set even in an equimolar solution of the metal ion and the ligand. Nickel(III) species were generated by oxidizing the NiII complexes with KO2 and the coordination modes were identified by EPR spectroscopy. The binuclear complex formed with the binding motifs exhibits superior SOD activity, in this respect it is an excellent model of the native NiSOD enzyme. A detailed kinetic model is postulated that incorporates spontaneous decomposition of the superoxide ion, the dismutation cycle and fast redox degradation of the binuclear complex. The latter process leads to the elimination of the SOD activity. A unique feature of this system is that the NiIII form of the catalyst rapidly accumulates in the dismutation cycle and simultaneously the NiII form becomes a minor species. [ABSTRACT FROM AUTHOR]

The paper aims at exploring the prerequisites for a beneficial knowledge transfer between manufacturing plants of multinational companies (MNCs), by taking the characteristics of the knowledge sending and knowledge receiving plant into consideration. This research seeks to understand how efforts undertaken by manufacturing plants, and how collaborative tools and coordination mechanisms influence a successful knowledge transfer. The study includes thirteen case studies conducted in manufacturing plants from four different European countries (i.e., Switzerland, Romania, Albania, and Macedonia). Given the exploratory nature of this study, the authors used a qualitative research approach. The main method of data collection involved multiple semi-structured interviews at manufacturing plants, uniformly applied in each country in order to observe general patterns across different cases. Their results show that the personal interaction between knowledge sending and receiving plants is more important for a successful knowledge transfer than information systems or prior related knowledge. [ABSTRACT FROM AUTHOR]

1,10-Phenanthroline mono-N-oxide (phenO) is a product of the decomposition of tris( 1,10-phenanthroline)iron(III), Fe(phen)33+, and has a slight autocatalylic effect on the overall reaction. The mechanism is proposed to involve Fe(phen)34+ as a minor intermediate. The addition of phenO significantly influences the kinetic teatures of the decomposition of Fe(phen)33+ and the oxidation of Fe(phen)32+ by HSO5-. The autocatatytic decomposition explains the difficulties in the preparation of Fe(phen)33+ and may contribute to exotic kinetic phenomena studied using Fe(phen)33+/Fe(phen)33+ as a supposedly innocent indicator. [ABSTRACT FROM AUTHOR]

The visible region of the electronic absorption spectra of Cu(II) complexes was studied by time-dependent density functional theory (TD-DFT). The performance of twelve functionals in the prediction of absorption maxima (λ max) was tested on eleven compounds with different geometry, donors and charge. The ranking of the functionals for λ max was determined in terms of mean absolute percent deviation (MAPD) and standard deviation (SD) and it is as follows: BHandHLYP > M06 ≫ CAM-B3LYP ≫ MPW1PW91 ~ B1LYP ~ BLYP > HSE06 ~ B3LYP > B3P86 ~ ω-B97x-D ≫ TPSSh ≫ M06-2X (MAPD) and BHandHLYP > M06 ~ HSE06 > ω-B97x-D ~ CAM-B3LYP ~ MPW1PW91 > B1LYP ~ B3LYP > B3P86 > BLYP ≫ TPSSh ≫ M06-2X (SD). With BHandHLYP functional the MAPD is 3.1% and SD is 2.3%, while with M06 the MAPD is 3.7% and SD is 3.7%. The protocol validated in the first step of the study was applied to: i) calculate the number of transitions in the spectra and relate them to the geometry of Cu(II) species; ii) determine the coordination of axial water(s); iii) predict the electronic spectra of the systems where Cu(II) is bound to human serum albumin (HSA) and to the regions 94–97 and 108–112 of prion protein (PrP). The results indicate that the proposed computational protocol allows a successful prediction of the electronic spectra of Cu(II) species and to relate an experimental spectrum to a specific structure. A time-dependent density functional theory protocol to simulate the electronic absorption spectra in the visible region of Cu(II) complexes was validated and applied to determine the coordination of axial water(s) and predict the spectra of bioinorganic systems formed by copper with human serum albumin and prion protein fragments. Unlabelled Image • Electronic spectra of Cu(II)-bioligand systems were studied by computational methods. • BHandHLYP and M06 showed the best performance in the prediction of the spectra. • The expected and experimental results were compared. • The coordination of axial water(s) in Cu(II) complexes was determined. • The protocol can predict the Cu(II) spectra of human serum albumin and prion fragments. [ABSTRACT FROM AUTHOR]

In this study, the formation of 17 N -chloramines from proteinogenic amino acids and HOCl was studied by direct kinetic method in the pH = 3–13 range. Thus, the uncertainties associated with the indirect methods used in some of the previous studies were eliminated. Each reaction proceeds according to an overall second order kinetics: v = − k [HOCl][R–NH 2 ] and the rate constants are several times 107 M−1s−1. A very slight correlation was found between the lg k and the p K AA of the amino acids. The results make possible to predict the reactivity order of the amino acids toward HOCl under various conditions. A comparison of the parameters of activation indicates that the presence of a bulky substituent on the side chain close to the α -carbon atom decreases the strength of bonding between the reactants and make the structure more diffuse in the transition state. The chlorination of histidine proceeds via two pH dependent paths presumably leading to the formation of N -chloramine and a side chain chlorinated product. The latter compound may be involved in fast subsequent trans-chlorination reactions. The results presented here resolve earlier discrepancies in the literature and are relevant in chlorination water treatment technologies as well as in the interpretation of in vivo processes involving the formation of N -chloro amino acids in a wide pH range. Image 1 • The kinetics of the N -chlorination of 17 amino acids was studied as a function of pH. • The reactive species are HOCl and the R–NH 2 form of the amino acids. • The amino and the imidazole groups of histidine are chlorinated in parallel steps. • A direct comparison of the rates of chlorination of amino acids is reported. [ABSTRACT FROM AUTHOR]

Monochloramine is a widely employed agent in water treatment technologies. However, its utilization has some drawbacks like the transformation of the active species into the undesired dichloramine. Although it is more pronounced in acidic solutions, the features of this reaction have still remained largely unexplored in the pH < 4 region. In this study the decomposition of monochloramine is examined under such conditions by using kinetic and computational methods. Fast kinetics measurements have convincingly showed that the disproportion into dicloramine is relatively fast and can be studied without any interference from side reactions. By varying the pH, the deprotonation constant of monochloramine has been determined by UV spectroscopy (Ka = 0.023 ± 0.005 M for I = 1.0 M NaClO4, and T = 25.0 °C). Dichloramine formation via monochloramine disproportion was found to follow second-order kinetics. The computations have provided the reaction mechanism and its free energy profile in accord with the proposed kinetic model. This involves the reaction between the protonated and unprotonated forms of monochloramine, with a rate constant k = 335.3 ± 11.8 M−1 s−1, corresponding to an activation free energy barrier of 14.1 kcal mol−1. The simulations predicted a barrier of 14.9 kcal mol−1 and revealed a key short-lived chlorine-bridged intermediate which yields dichloroamine and ammonium ion through a deprotonation-coupled chlorine shift. [ABSTRACT FROM AUTHOR]

• ZrO 2 and YSZ aerogels derived by combining sol-gel method and supercritical drying. • Evolution of crystallinity was observed by in-situ XRD measurements up to 1200 °C. • Phase transformation of zirconia (ZrO 2) is affected by crystallite size growth. • Yttria-stabilized zirconia (YSZ) aerogel forms stable single-phase t -ZrO 2 at 455 °C. Monolithic, structurally stable zirconia (ZrO 2) aerogels can be used in high temperature applications and as medical implants. The macroscopic properties of these solids can be fine-tuned by the appropriate thermal treatment of the amorphous aerogels. Herein, we investigate the thermally induced phase transitions of ZrO 2 and yttria-stabilized zirconia (YSZ) monolithic aerogels. All aerogels were produced by an acid-catalyzed sol-gel technique and subsequent supercritical drying (SCD). A complete reaction mechanism is proposed for the formation of the wet gel network. Also, the phase transformations taking place during calcination were followed as function of temperature by in-situ X-ray diffraction measurements. Composition and size of the forming crystallites were calculated from the XRD data. Phase transition is controlled by the temperature-dependent growth of crystallite size during calcination up to 1200 °C. Both tetragonal and monoclinic zirconia form in pure ZrO 2 aerogels, and a single tetragonal phase forms in YSZ aerogels. [ABSTRACT FROM AUTHOR]

Equilibrium and detailed spectroscopic characterization of zinc(ii) complexes with NiSOD binding loop and their related model fragments are reported in the whole investigated pH-range. The zinc(ii) complexes of L1 (HCDLPCGVY-NH2), L2 (Ac-HCDLPCGVY-NH2) and L3 (HCDLACGVY-NH2) and the nickel(ii) and zinc(ii) complexes of L4 (HCDLPCG-NH2) were studied by pH-potentiometric and several spectroscopic methods. The results indicated that the macrochelate coordinated zinc(ii) complexes are dominant in a whole pH-range and the side chain donors of the peptides are involved in the metal binding. Therefore, the deprotonation and coordination of the peptide backbone occur only in a strongly alkaline solution. The acetylation of the peptide amino terminus (L2) significantly enhances the zinc(ii) binding ability compared to the corresponding nickel(ii) complexes. L2 complexes of zinc(ii) are 2 or 3 orders of magnitude more stable than the corresponding nickel(ii) complexes. This effect clearly shows the crucial role of the terminal amino group in the nickel binding for the NiSOD enzyme. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Methotrexate functionalized silica-gelatin hybrid aerogel (SGM) was synthesized by the sol–gel method and co-gelation. The drug methotrexate (MTX) is covalently linked to the collagen molecules of the hybrid aerogel backbone by amide-bond. The characteristic MTX content of the functionalized hybrid aerogel is ca. 6 wt% by the dry weight. The micronization of SGM aerogel in water yields cell sized (d = 10–20 µm) particles. The cytotoxicity of these microparticles against tumor cell lines (SCC VII and HL-60) is unprecedentedly high, it is approximately equivalent to that of an equal dose of free (dissolved) MTX, as proved by in vitro experiments. Thus, the activity of MTX is intact after aerogel functionalization, and the mass specific cytotoxicity of SGM is high enough for medical applications. Drug release studies verified that MTX cannot be liberated from this drug delivery system solely by chemical hydrolysis, however, collagenase enzymatic activity releases MTX from the functionalized hybrid aerogel. The cytotoxicity of SGM towards various cancerous and non-cancerous cell lines correlates with the collagenase activities of cells. Therefore, conjugation with the hybrid aerogel provides a controlled release system for the antineoplastic agent MTX. The morphology of the delivery vehicle was chosen to adapt the size of cancer cells; thus the metastatic pathways of the tumor cells can get flooded. [ABSTRACT FROM AUTHOR]

Iron(III)-crosslinked alginate aerogel beads ( d  = 3–5 mm) were prepared and loaded with ibuprofen by using the technique of adsorptive deposition from supercritical CO 2 . Additional formulations were prepared where the aerogels were co-impregnated by ibuprofen and ascorbic acid. The release of ibuprofen from the Fe(III)-alginate is much faster in pH = 7.4 (PBS) than in pH = 2.0 (HCl), which can be explained by the faster dissolution and higher swelling of the alginate matrix in PBS. By decreasing the size of the beads and using a higher G content alginate the release rate could be slightly increased. A marked acceleration of drug release was achieved in both HCl and PBS by incorporating ascorbic acid into the Fe(III)-alginate aerogel preparations. The explanation is that in aqueous media ascorbic acid in situ reduces the crosslinking Fe(III) to Fe(II). The latter does not interact strongly with alginate, which promotes the hydration of the chains, thus the erosion and dissolution of the carrier matrix. [ABSTRACT FROM AUTHOR]

An important reaction step in the industrial production of NaClO3 (electrochemical chlorate process) is the thermal decomposition of HOCl/OCl− to yield ClO3− and Cl−. It is widely accepted that this reaction is accelerated by aqueous chromium(vi) species. A detailed kinetic study was conducted under industrially relevant conditions, i.e. at high ionic strength (6.0 M) and elevated temperature (80 °C), to investigate this phenomenon. The decomposition of hypochlorous acid was followed in the presence of Cr(vi) or phosphate (PO43−) or without any additive. In addition to the beneficial pH buffering effect of Cr(vi), the CrO42− form of chromium(vi) was found to slightly catalyze the decomposition of hypochlorous acid. The overall rate of HOCl decomposition can be expressed as −dcHOCl/dt = kdec[HOCl]2[OCl−] + kcat[HOCl]2[CrO42−]. The corresponding rate constants were determined, kdec = 9.4 ± 0.1 M−2 s−1 and kcat = 4.6 ± 0.8 M−2 s−1, and mechanistic interpretation of the catalytic rate law is given. The contribution of the catalytic path to the overall rate of decomposition changes from ca. 30% at pH = 8 to ca. 70% at pH = 6. [ABSTRACT FROM AUTHOR]

The complexation behavior of reactive and nonreactive N-substituted 1-amino-5-isocyanonaphthalene (ICAN) derivatives was studied in the presence of Ag(I) ions by UV–vis, steady-state and time resolved fluorescence measurements. The effect of ligand, solvent and counterion is covered. The equilibrium constants were found to be K AgL ∼ 10 6 M −1 in dioxane and water. Complex formation results a significant, solvent dependent (30–59 nm) batochromic shift of the emission maximum. This shift is accompanied by a switch-off effect in the case of the unreactive ligands, while in the case of the acrylated derivative (ACAIN) significant intensity enhancement was detected. Based on spectroscopic results only 1:1 AgL complex could be detected in solution at low concentrations c AgL <10 −4 M, while at higher concentrations pure 1:2 AgL 2 formed which was characterized by ESI–MS, IR and NMR methods The structure and optical behavior of the complexes are discussed based on high-level quantum chemical calculations. It is shown that the complexation of ACAIN can be used for the selective detection and quantification of silver(I) ions from aqueous media. In addition, the fluorescene switch-off in the case of MICAN yields a significant contrast enhancement in biolabeling applications as is shown on fixated HaCat cells.s [ABSTRACT FROM AUTHOR]

Silica-gelatin hybrid aerogels, introduced recently as drug delivery devices, were investigated for biocompatibility with SCC tumor cells by a time-lapse video-microscopy technique. The particles proved to be not only non-toxic in nature, but the cells migrated towards them. Fluorescently labeled hybrid aerogels were synthesized by covalently binding fluorescein isothiocyanate either to the amino groups of gelatin molecules, or to the amine-functionalized silica backbone prior to sol-gel polycondensation and co-gelation steps. Scanning electron microscopy and fluorescence spectroscopy characterization of pristine and labeled aerogels showed identical structures and spectra, while fluorescence lifetimes were 10% shorter than that of the free fluorescein, due to covalent attachment. Migration plots based on time-lapse video recordings showed that the cells exhibited a directive migration nearby the aerogel particles. No signs of apoptosis or necrosis were observed at any phases of the cell cycle in the presence of the silica-gelatin aerogel particles, indicating that the hybrid aerogels are biocompatible materials, and may be used as drug delivery matrices in living organisms. [ABSTRACT FROM AUTHOR]

The kinetics of the oxidation of various 1,10-phenanthroline derivatives by peroxomonosulfate ion was studied in detail. The results confirmed that all of these reactions are second order, i.e. first order with respect to each reactant. The large negative activation entropies (ΔS‡∼−130 J mol−1 K−1) imply that these reactions proceed via oxygen atom transfer. Under acidic conditions, the protonation of the mono-N-oxides leads to the formation of an internal hydrogen bond which prevents the oxidation of the second nitrogen atom, i.e. the formation of di-N-oxides. Apart from the kinetic studies, the acid dissociation constants of the studied phen derivatives were also determined by pH-potentiometric titration or combined pH-potentiometry and spectrophotometry. The correlation between the pKa-s of the phenanthroline derivatives and the logarithm of the rate constant of the mono-N-oxidation reaction is linear with the exception of 2,9-dimethyl-1,10-phenanthroline (DMP). Such a correlation strongly suggests that the protonation and mono-N-oxidation of the substrates are governed by the electronic effects of the substituents. In the case of DMP, the significantly slower than expected reaction rate indicates that steric effects may also play an important role in the N-oxidation reactions. [ABSTRACT FROM AUTHOR]

The recovery of palladium compounds from aqueous solutions containing other metal salts is a challenging task of environmental technology. One solution is the development of selective sorbents by the appropriate design of surface functionality. For this purpose, a mesoporous, polycarboxylate (pyromellitic acid monoamide) functionalized silica-gelatin aerogel was prepared by the sol-gel method and supercritical drying. It is characterized using low voltage scanning electron microscopy (LV-SEM), N 2 -sorption porosimetry, small angle neutron scattering (SANS), infrared spectroscopy (FT-IR), solid-state nuclear magnetic resonance spectroscopy (ssNMR) and X-ray photoelectron spectroscopy (XPS). Its aqueous phase Zeta potential was investigated as a function of pH. The aerogel has excellent selectivity for binding Pd(II) around pH = 2.0 in the simultaneous presence of Pt(II), Pt(IV) and six other metal ions with a very high sorption capacity of 369 mg g−1 at pH = 2.3. The quantitative recovery of Pd(II) and the regeneration of the sorbent is possible using 5 mM methionine. The mechanism of binding is the reversible surface complexation of Pd(II) via the O-atoms of the adjacent carboxylate groups of the aerogel, as shown by XPS. This high stability coordination mode accounts for the excellent selectivity of the sorbent, and prevents the reduction of Pd(II). [Display omitted] • Polycarboxylate functionalized aerogel with well controlled surface chemistry. • High selectivity toward Pd(II) against Pt(II), Pt(IV) and six other metal ions. • Sorption capacity for Pd(II) is 369 mg g−1 at pH = 2.3. • Sorption equilibrium establishes in 2 h. • Quantitative recovery of Pd(II) and sorbent regeneration by 5 mM methionine. [ABSTRACT FROM AUTHOR]

[Display omitted] • High SOD activity of Cu(II) complexes upon covalent immobilization in aerogel. • EPR and SANS show the molecular level separation of the complexes in the aerogel. • EPR data show the formation of new coordination modes in the aerogel. • Chemical environment, coordination mode, separation alter reactivity of complexes. • SOD mimetic aerogels form stable microparticles in water. The copper(II) complexes of 1,4,7,10-tetraazacyclododecane (cyclen) and 1,4,8,11- tetraazacyclotetradecane (cyclam) were covalently immobilized in mesoporous silica aerogels by the sol–gel method using functionalized silica precursors. The modified macrocyclic precursors are characterized by mass spectrometry (MS) and solution phase nuclear magnetic resonance (NMR) spectroscopy. The supercritically dried aerogels are characterized using low voltage scanning electron microscopy (LV-SEM), N 2 -sorption porosimetry, infrared spectroscopy (FT-IR), electron paramagnetic resonance spectroscopy (EPR) and contrast variation small angle neutron scattering (SANS). The suspended aerogel particles act as nanoenzymes, because they have significant SOD activities, dramatically higher than the corresponding dissolved Cu(II) complexes. The most important factors responsible for the altered reactivities due to the covalent immobilization of the complexes were elucidated based on the compiled results of the characterization methods. These are: i) the formation of new chemical environments and Cu(II) coordination modes; ii) the effective separation of the active Cu(II) centers in the aerogels; and iii) the confinement effect operative in the nanoporous network. As a perspective, the present functionalized aerogel microparticles can be developed into passive targeting antioxidant pharmaceutical agents administered locally or subcutaneously. [ABSTRACT FROM AUTHOR]

Specific features of a silica-gelatin aerogel (3 wt.% gelatin content) in relation to drug delivery has been studied. It was confirmed that the release of both ibuprofen (IBU) and ketoprofen (KET) is about tenfold faster from loaded silica-gelatin aerogel than from pure silica aerogel, although the two matrices are structurally very similar. The main goal of the study was to understand the mechanistic background of the striking difference between the delivery properties of these closely related porous materials. Hydrated and dispersed silica-gelatin aerogel has been characterized by NMR cryoporometry, diffusiometry and relaxometry. The pore structure of the silica aerogel remains intact when it disintegrates in water. In contrast, dispersed silica-gelatin aerogel develops a strong hydration sphere, which reshapes the pore walls and deforms the pore structure. The drug release kinetics was studied on a few minutes time scale with 1 s time resolution. Simultaneous evaluation of all relevant kinetic and structural information confirmed that strong hydration of the silica-gelatin skeleton facilitates the rapid desorption and dissolution of the drugs from the loaded aerogel. Such a driving force is not operative in pure silica aerogels. [ABSTRACT FROM AUTHOR]

The direct photodegradation of 2,4,6-trichlorophenol (TCP) by UV–vis light was studied in aqueous solution in order to analyze the mechanism of the photochemical process and to determine the kinetic parameters including the quantum yield. Based on initial rate studies at different overall volumes and illumination patterns, it was proved that the rate of the process is directly proportional to the intensity of irradiating light. A significant, but moderate acceleration of the reaction rate with increasing temperature was revealed between 5.0 and 35.0 °C, which could be interpreted readily by assuming that the excited state of TCP is involved in two competing processes. High pressure liquid chromatography and mass spectrometry provided us information on the nature of the intermediates and the products formed. 2,6-Dichloro-1,4-benzoquinone, 3,5-dichloro-2-hydroxy-1,4-benzoquinone and 2,6-dihclorohydroxyquinone were detected as products and/or intermediates, and there were also hints of the formation of 3,5-dichlorobenzene-1,2-diol and 3,5-dichloro-1,2-benzoquinone. A possible degradation mechanism is proposed to interpret the kinetic findings. [ABSTRACT FROM AUTHOR]

This paper confirms the unexpected formation of 1,10-phenanthroline-N,N′-dioxide (phenO2) when 1,10-phenanthroline (phen) is oxidized by peroxomonosulfate ion (PMS) in a neutral aqueous solution. The kinetics of oxidation of phen by PMS features a complex pH dependence. In 1.00 M H2SO4, 1,10-phenanthroline-mono-N-oxide (phenO) is the sole product of the reaction. The rate of the N-oxidation is highly dependent on pH with a maximum at pH ∼6.7. The formation of phenO occurs via two parallel pathways: the rate constant of the oxidation of phen (k = 3.1 ± 0.1 M-1 s-1) is significantly larger than that of Hphen+ [k = (4.1 ± 0.3) × 10-3 M-1 s-1] because the two N atoms are open to oxidative attack in the deprotonated substrate while an internal hydrogen bond hinders the oxidation of the protonated form. With an excess of PMS, four consecutive oxidation steps were found in nearly neutral solutions. In the early stage of the reaction, the stepwise oxidation results in the formation of phenO, which is converted into phenO2 in the second step. The formation of phenO2 was confirmed by ¹H NMR and ESI-MS methods. The results presented here offer the possibility of designing an experimental protocol for preparing phenO2. [ABSTRACT FROM AUTHOR]