Basic Aqueous Media Research Articles

4‐Cyano‐6,7‐dimethoxycarbostyrils with Solvent‐ and pH‐Independent High Fluorescence Quantum Yields and Emission Maxima

AbstractHighly fluorescent and stable 6,7‐dimethoxy‐2‐oxoquinoline‐4‐carbonitriles (11) were synthesized starting from appropriate 4‐hydroxyquinolones 3 via reactive 4‐chloroquinolones 8 by using toluenesulfinates as catalysts. In contrast to the well‐described 4‐trifluoromethyl‐substituted analogues 18, N‐substituted derivatives 11 fluoresce in water, polar, and apolar solvents in a narrow 430–440‐nm window with almost constant quantum yield of 0.5. Equal excitation is possible in the broad double maximum between 385 and 410 nm yielding identical data between pH 1 and 11. These properties could lead to a broadly usable fluorescence standard. N‐Alkylation with bromoacetate yields ester 13 in good yields. Reactive succinimidoyl (OSu) ester 15 was prepared by saponification to acid 14. With amino acids or peptides, linking to labeled derivatives 17 was achieved under mild conditions in slightly basic aqueous media. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis of efficient and reusable palladium catalyst supported on pH-responsive colloid and its application to Suzuki and Heck reactions in water

An efficient and reusable pH-responsive colloid supported palladium catalyst was synthesized by loading 3-nm Pd nanoparticles into the pH-responsive colloid of core–shell microspheres of poly[styrene- co-2-(acetoacetoxy)ethyl methacrylate- co-methyl acrylic acid] (PS- co-PAEMA- co-PMAA). The colloidal scaffold of the core–shell microspheres, which contained a pH-responsive shell of PMAA segment and a coordinative core of PAEMA and PS segments, was synthesized by one-stage soap-free emulsion polymerization in water. The pH-responsive colloid supported palladium catalyst was dispersed in basic aqueous medium like a homogeneous catalyst, and also could be simply separated and recovered like a heterogeneous one just by adjusting pH of the aqueous medium. The pH-responsive colloid-supported palladium catalyst proved to be efficient and reusable for the Suzuki and Heck reactions performed in water.

Alternate Method for the Synthesis of N‐Alkyl/aralkyl‐2‐(α‐hydroxy Alkyl/aralkyl)benzimidazoles via Regiospecific Acetylation

Acetylation of 1H‐2‐(α‐hydroxyalkyl/aryl)benzimidazoles 2 with Ac2O results in the regiospecific formation of O‐acetoxy derivative 3, which on alkylation with alkylating agents in nonaqueous media under phase‐transfer catalytic conditions affords N‐alkyl derivatives 4. The latter, on hydrolysis in an aqueous basic medium, results in the title compounds 5 in good yields in high purity. Alternatively, 5 can also be obtained by reduction of 1‐substituted‐2‐acetyl/benzoylbenzimidazoles 8 using NaBH4.

Hydrothermal Synthesis of Electrochemically Active LiMnPO4

Abstract Highly crystalline olivine-structured LiMnPO4 was prepared by a simple hydrothermal method in a basic aqueous medium at 200 °C for 10 h. The particle shape of the as-prepared LiMnPO4 was plate-like with the thickness of 100–200 nm. A capacity of 68 mA h g−1 was reversibly achieved between 3 and 4.5 V vs. Li+/Li.

Comparative evaluation of a bioluminescent bacterial assay in terrestrial ecotoxicity testing

Despite the widespread and successful use of luminescence-based bioassays in water testing, their applications to soils and sediments is less proven. In part this is because such bioassays have mainly been carried out in an aqueous-based medium and, as such, favour contaminants that are readily water-soluble. In this study, aqueous solutions and soils contaminated with heavy metals (HM), polar organic contaminants and hydrophobic organic contaminants (HOCs) were tested using a range of luminescence-based bioassays (Vibrio fischeri, Escherichia coli HB101 pUCD607 and Pseudomonas fluorescens 10586r pUCD607). For the first two chemical groups, the assays were highly reproducible when optimised extraction procedures were employed but for HOCs the bioassay response was poor. Quantitative structure-activity relationships (QSARs) obtained from aqueous solutions had a linear response although correlation for the chemicals tested using bacterial bioassays was significantly less sensitive than that of sublethal tests for Tetrahymena pyriformis. Bacterial and Dendrobaena veneta bioassay responses to extracts from HM amended soils showed that a clear relationship between trophic levels could be obtained. There is no doubt that the wide range of bioluminescent-based bioassays offers complementary applications to traditional testing techniques but there is a significant need to justify and optimise the extraction protocol prior to application.

Synthetic Application of PVP-stabilized Au Nanocluster Catalyst to Aerobic Oxidation of Alcohols in Aqueous Solution under Ambient Conditions

Abstract Gold nanoclusters (φ = 1.3 nm) stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) were found to show a high catalytic activity toward the aerobic oxidation of alcohols. Various kinds of primary and secondary alcohols were converted to the corresponding carboxylic acids and ketones, respectively, in basic aqueous media at 300–360 K under air.

Kinetic study of the promazine oxidation to promazine 5-oxide by trisoxalatocobaltate(III) in basic aqueous media

The kinetics of the oxidation of promazine by trisoxalatocobaltate(III) were studied in the presence of a large excess of the cobalt(III) in tris buffer solution using u.v.–vis spectroscopy ([CoIII] = (0.6 − 2) × 10−3M, [ptz] = 6 × 10−5M, pH = 6.6–7.8, I = 0.1 M (NaCl), T = 288−308 K, l = 1 cm). The reaction proceeds via two consecutive reversible steps. In the first step, the reaction leads to formation of cobalt(II) species and a stable cationic radical. In the second step, cobalt(III) is reduced to cobalt(II) ion and a promazine radical is oxidized to the promazine 5-oxide. Linear dependences of the pseudo-first-order rate constants (k1 and k2) on [CoIII] with a non-zero intercept were established for both redox processes. Rates of reactions decreased with increasing concentration of the H+ ion indicating that the promazine and its radical exist in equilibrium with their deprotonated forms, which are reactive reducing species. The activation parameters for reactions studied were as follows: ΔH≠ = 44 ± 1 kJ mol−1, ΔS≠ = −100 ± 4 JK−1 mol−1 for the first step and ΔH≠ = 25 ± 1 kJ mol−1, ΔS≠ = −169 ± 4 J K−1 mol−1 for the second step, respectively. Mechanistic consequences of all the results are discussed.

MnO Octahedral Nanocrystals and MnO@C Core−Shell Composites: Synthesis, Characterization, and Electrocatalytic Properties

We present a simple and facile synthesis of MnO octahedral nanocrystals and MnO@C core-shell composite nanoparticles. The synthesis is accomplished by a single-step direct pyrolysis of cetyltrimethylammonium permanganate in specially made Let-lock union cells. The products are characterized by HRSEM, HRTEM, Raman spectroscopy, and cyclic voltammetry (CV). The product consists mainly of octahedral MnO nanocrystals and MnO coated with carbon (MnO@C). The core-shell particles are observed only when the core size is smaller than 150 nm. The shape of the nanocrystals can be controlled by varying parameters such as reaction temperature and duration. As the temperature increases from 600 to 800 degrees C, the octahedral MnO crystals observed are without any carbon shell. The effect of time and temperature on the octahedral MnO nanocrystal formation is described. The electrocatalytic activities of the products are studied for oxygen reduction reaction in aqueous basic medium and are compared with bulk MnO. The MnO nanocrystals and core-shell composites exhibit higher activity than that of bulk MnO.

The Active Role of the Water Solvent in the Regioselective CO Hydrogenation of Unsaturated Aldehydes by [RuH2(mtppms)x] in Basic Media

The regioselective hydrogenation of cinnamaldehyde in basic aqueous media catalyzed by [RuH2(mtppms)x] [x = 3,4; mtppms = meta-sulfonatophenyl-diphenylphosphine] is analyzed by means of theoretical calculations. The water solvent is modeled by the inclusion of a (H2O)3 cluster in addition to a continuum model. Two Ru complexes are evaluated as active species for the reduction process: the major identified species [RuH2P4] and the related phosphine dissociated complex [RuH2P3]. Several reaction mechanisms are computationally evaluated, and their analysis suggests that the reaction takes place in several steps. The first hydrogenation process takes place by means of a hydrogen transfer from the metal catalyst, whereas the second hydrogenation process is performed by a water solvent molecule. This mechanism can account for the selectivity of the CO versus CC double bond reduction experimentally observed under basic reaction conditions and can be directly related to the mechanism found in acidic media, where...

Synthesis of amphiphilic polysaccharides by micellar catalysis

Amphiphilic polymers are prepared by chemical modification of dextran, a neutral bacterial polysaccharide consisting of α-1,6 linked glucose units. Hydrocarbon groups are attached to the polysaccharide chains by reacting dextran with aliphatic or aromatic 1,2-epoxides in a basic aqueous medium. Because of the low water-solubility of the epoxides, the reaction medium is biphasic with the organic epoxide emulsified in the continuous aqueous phase. It is shown that dextran modification is no longer possible with epoxides having very low water-solubility. The addition of a cationic surfactant appears to make chemical modification possible even with highly hydrophobic epoxides (1,2-epoxydodecane or 1,2-epoxyoctadecane). The reaction mechanism is discussed taking into account the characteristics of the reactants involved and especially the effect of surfactant (nature and amount).

N‐Carboxymethylated 6,7‐Dimethoxy‐4‐trifluoromethylcarbostyrils as Fluorescence Markers for Amino Acids, Peptides, Amino Carbohydrates and Amino Polysaccharides

AbstractThe highly fluorescent 6,7‐dimethoxy‐3‐trifluoromethylcarbostyril 2 was regioselectively carboxymethylated with bromoacetates 4 at N‐1 to give esters of type 5 in good yield. After saponification to 8, succinimidoyl (OSu) esters 9 were prepared. Dyestuffs 9 were reacted in slightly basic aqueous media under mild conditions with free amino acids, esters and peptides to give the fluorescently labeled amino acid derivatives 11 and 13 in good yields. Similarly, aminoglucose and chitosane reacted to form the fluorescently labeled carbohydrates 15 and 17. Fluorescence quantum yields of 0.3–0.4, their photostability and a pH‐independence between 3 and 10 make this class of compounds useful for linking to biological samples in aqueous media.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Eco-efficient Catalytic Hydrodechlorination of Carbon Tetrachloride in Aqueous Cyclodextrin Solutions

An eco-efficient process of catalytic hydrodechlorination of carbon tetrachloride into methane and chloride salts has been developed in aqueous basic medium at room temperature. The organic pollutants are trapped in water by cyclodextrins (CDs) via the formation of inclusion complexes and dechlorinated by a supported heterogeneous palladium catalyst. Catalytic investigations demonstrate that CDs act as efficient CCl4 solubilizers and, much more interesting, as protective molecules against side reactions.

Reversible binding of molecular dioxygen to CoTSPP electrodeposited films from aqueous basic media

The oxidative electrodeposition of CoTSPP (tetrakis 4-sulfonatophenyl Co porphyrin) on ITO electrode from NaOH 0.1 M aqueous solution has been studied, and cyclic voltammetry, spectroelectrochemistry, UV–Vis and reflection-FTIR spectroscopies have been used to analyze the composition of such a film. Our experimental data lead us to propose that electrodeposited CoTSPP films are composed by ( OH ) 2 Co ( III ) O 2 - and the porphyrin ring as radical cation. Futhermore, the Co(OH) 2 species is formed from the reduction of the film in oxygen absence. However, the properties of these films do not match with those corresponding to Co(II) hydroxide films, since the electrodeposited CoTSPP is able to absorb atmospheric oxygen to form Co ( III ) O 2 - species. Moreover, in oxygen absence, the Co(II) may interact with the porphyrin radical cation to regenerate CoTSPP.

Synthesis of Diazeniumdiolates from the Reactions of Nitric Oxide with Enolates

[reaction: see text] Reactions of nitric oxide with enolates derived from aliphatic methyl ketones containing alpha-methylene or alpha-methine groups and with enolates derived from alpha,alpha'-dimethylene or alpha,alpha'-dimethine ketones yield mono- or bis(diazeniumdiolate) products. Diazeniumdiolation occurs in the following order: alpha-methine > alpha-methylene > alpha-methyl. The amount of the base used alters the extent of diazeniumdiolation and the course of the reaction. Mono- and bis(diazeniumdiolate)-substituted methyl ketones are cleaved in the presence of excess base before and after the subsequent diazeniumdiolation of the alpha-methyl group. Similar to the trihalogenated methyl groups in the base-assisted halogenation reactions of methyl ketones, the bis(diazeniumdiolate)-substituted alpha-methylene and alpha-methyl groups act as leaving groups in the presence of excess base. The reaction of nitric oxide with a (approximately 20:80, cis/trans) mixture of 2,6-cyclohexananone yields the cis and trans isomers of 2,6-dimethylcyclohexanone-2,6-bis(diazeniumdiolate) in 12.9% and 57.6% yield. Single-crystal X-ray diffraction data determined for potassium cis-2,6-dimethylcyclohexanone-2,6-bis(diazeniumdiolate), cis-14b, reveal that the N(2)O(2-) substituent is planar with considerable delocalization of a double bond over the anionic four-atom group. Except for one of the diazeniumdiolate products, namely, potassium propanoate 2,2-bis(diazeniumdiolate), 8b, all are stable in neutral and basic aqueous media. Compound 8b slowly decomposes in neutral aqueous solution releasing nitrous oxide and nitric oxide gases but is stable in basic aqueous media. Differential scanning calorimetry data measured for the diazeniumdiolate products indicate that they decompose exothermally with most of them undergoing explosive decomposition at moderately high temperatures (181-274 degrees C).

Synthesis and pH-Dependent micellization of a novel block copolymer containing s-Triazine linkage

Novel pH-sensitive moieties containing an s-triazine ring were synthesized with sulfonamide and secondary amino groups. The synthesized pH-sensitive moieties were used for the synthesis of a pH-sensitive amphiphilic ABA triblock copolymer. The pH-sensitive triblock copolymer was composed of diblock copolymers, methoxy poly(ethylene glycol)-poly (e-caprolactone-co-D,L-lactide) (MPEG-PCLA), and pH-sensitive moiety. These copolymers could be dissolved molecularly in both acidic and basic aqueous media at room temperature due to secondary amino and sulfonamide groups. The synthesized s-triazine rings containing pH-sensitive compounds were characterized by1H-NMR,13C-NMR, and LC/MSD spectral data. The synthesized diblock and triblock copolymers were also characterized by1H-NMR and GPC analyses. The critical micelle concentrations at various pH conditions were determined by fluorescence technique using pyrene as a probe. Furthermore, the micellization and demicellization study of the triblock copolymer was done with pH-sensitive groups. The sensitivity towards pH change was further established by acid-base titration.

Synthesis and Evaluation of Insulin−Human Serum Albumin Conjugates

A series of human insulin maleimido derivatives with short and long linkers was synthesized by exploiting the variations in the pK(a) values and environment of the three amino groups present in the protein. The syntheses were accomplished in organic solvent because of maleimide's instability in basic aqueous media. The derivatives thus obtained were conjugated to the free thiol on Cys34 of human serum albumin (HSA) and purified. A structure-activity relationship based on in vitro receptor binding and activation results for this series of insulin-HSA conjugates showed that the best compounds were attached at the B1 position of insulin with either short or long linkers. Two conjugates were administered subcutaneously to streptozotocin-induced diabetic rats and found to possess blood glucose normalizing activity up to 8 h post-administration. The return to diabetic plasma glucose levels was not observed within the time frame of the experiment (48 h). In comparison, the insulin-treated group's normalization activity lasted 2 h and returned to a diabetic level at 8 h. The onset of the conjugate activities were delayed by 1 h when compared to the activity of human insulin. The study results led to the identification of CJC-1575 as a potent and long lasting human insulin analogue.

Ligand-Assisted Reduction of Osmium Tetroxide with Molecular Hydrogen via a [3+2] Mechanism

Osmium tetroxide is reduced by molecular hydrogen in the presence of ligands in both polar and nonpolar solvents. In CHCl3 containing pyridine (py) or 1,10-phenanthroline (phen), OsO4 is reduced by H2 to the known Os(VI) dimers L2Os(O)2(mu-O)2Os(O)2L2 (L2 = py2, phen). However, in the absence of ligands in CHCl3 and other nonpolar solvents, OsO4 is unreactive toward H2 over a week at ambient temperatures. In basic aqueous media, H2 reduces OsO4(OH)n(n-) (n = 0, 1, 2) to the isolable Os(VI) complex, OsO2(OH)4(2-), at rates close to that found in py/CHCl3. Depending on the pH, the aqueous reactions are exergonic by deltaG = -20 to -27 kcal mol(-1), based on electrochemical data. The second-order rate constants for the aqueous reactions are larger as the number of coordinated hydroxide ligands increases, k(OsO4) = 1.6(2) x 10(-2) M(-1) s(-1) < k(OsO4(OH)-) = 3.8(4) x 10(-2) M(-1) s(-1) < k(OsO4(OH)2(2-)) = 3.8(4) x 10(-1) M(-1) s(-1). The observation of primary deuterium kinetic isotope effects, k(H2)/k(D2) = 3.1(3) for OsO4 and 3.6(4) for OsO4(OH)-, indicates that the rate-determining step in each case involves H-H bond cleavage. Density functional calculations and thermochemical arguments favor a concerted [3+2] addition of H2 across two oxo groups of OsO4(L)n and argue against H* or H- abstraction from H2 or [2+2] addition of H2 across one Os=O bond. The [3+2] mechanism is analogous to that of alkene addition to OsO4(L)n to form diolates, for which acceleration by added ligands has been extensively documented. The observation that ligands also accelerate H2 addition to OsO4(L)n highlights the analogy between these two reactions.

Indirect evidences of desulfurization of a thiosemicarbazonecopper(II) system in aqueous basic medium

A basic aqueous solution of the [{Cu(L)(NO 3)} 2] compound (HL = C 8H 10N 4S, pyridine-2-carbaldehyde 4N-methylthiosemicarbazone) at pH = 11 is acidified to pH = 5 by addition of diluted nitric acid yielding the [{Cu(L)} 2(NO 3)](OH) · 5H 2O ( 1) complex. The structure of 1 contains a bidentate Cu–ON(O)O–Cu nitrato bridge. However, a 1:2 copper:thiosemicarbazone ratio in the Cu II / HL / NO 3 - system leads to the attainment of the [{Cu(L)(H 2O)}{Cu(L)(SO 4)}] · 5H 2O ( 2) compound. The monodentate sulfato group in 2 arises from the desulfurization of thiosemicarbazone ligands. In both cases, the crystal structures consist of dinuclear non-centrosymmetric entities where the thiosemicarbazone sulfur atoms act as bridges between copper(II) ions in distorted square-pyramidal environments.

Ni(ii)1,4,8,11-tetraazacyclotetradecane electrocatalytic films prepared on top of surface anchored PAMAM dendrimer layers. A new type of electrocatalytic material for the electrochemical oxidation of methanol

Gold electrodes, previously prepared with surface anchored PAMAM dendrimers, were further modified with a Ni-containing tetraazamacrocycle resulting in a novel electrocatalytic material which proved to be particularly efficient for the electrochemical oxidation of methanol in basic aqueous medium.

Direct Evidence of Controlled Structure Reorganization in a Nanoorganized Polypeptide Multilayer Thin Film

Aspects of poly(l-lysine) (PLL) and poly(l-glutamic acid) (PLGA) multilayer thin film assembly, physical properties of the films, and changes in film structure on pH shift have been studied by far-UV circular dichroism spectroscopy (CD), ultraviolet spectroscopy (UVS), ellipsometry, quartz crystal microbalance (QCM), and atomic force microscopy (AFM). We show that CD can be used to assess the secondary structure content of a polypeptide multilayer film deposited on quartz substrates by electrostatic layer-by-layer assembly (LbL). Measurements have revealed that, under conditions where PLL and PLGA displayed a random coillike conformation in solution, the polypeptides formed predominantly β-sheet structures in multilayer films fabricated by LbL. A substantial conformational change occurred on exposure of such films to a strongly acidic (pH ≤ 2.5) or strongly basic (pH ≥ 12.0) aqueous medium, from β-sheet to predominantly α-helical structure. pH shift thus may be a useful postpreparation approach for stimuli-responsive modification of the surface roughness, porosity, and permeability of preassembled polypeptide films or structures made from such films, e.g., microcapsules.