A multinuclear NMR study on the microscopic ionization constants of adenosine-5′-triphosphate in aqueous solution

A ¹H, ¹³C and ³¹P NMR study of adenosine-5′-triphosphate has been performed as a function of pH. The examination of the chemical shifts allowed the proposal of an ionization scheme in which the third deprotonation takes place both on the adenine ring and on the phosphate group in a ratio of about 2:1. Furthermore, an analysis of carbon relaxation times supports this mechanism of ionization and confirms that the adenine ring binds the proton both on the NH₂ group and the N₇ nitrogen atom.     

Spectrophotometric determination of α-naphthol, β-naphthol,and oxine in aqueous solution

Diazotized orthanilic acid reagent has been devised as a novel chromogen for the trace determination of α-naphthol, β-naphthol, and oxine in aqueous solution. The developed method is characterized by simplicity and rapidness and does not resort to either temperature control or solvent extraction.     

Poly(oxyethylene)–cation interactions in aqueous solution: a molecular dynamics study

We have performed molecular dynamics simulations of a poly(oxyethylene) (POE) chain with 15 ethylene oxide units in an aqueous solution in the presence of potassium cations for 1 ns. The effect of the potassium ions on the POE aqueous solution characteristics are examined for the energetics, the hydration, the chain conformation and dynamics, and the solvent structure in comparison to those in the absence of cations. The POE's helical conformation is considerably distorted by complex formations with K⁺, and a significant perturbation of the POE hydration by K⁺ is observed. The competition between the K⁺–water and the K⁺–POE associations is found to be heavily shifted toward the latter. Furthermore, the POE–water pair interaction energy drastically decreases upon addition of K⁺. The observations, along with the decreased chain flexibility, point to the salting-out of POE salt aqueous solutions.     

A critical study of the application of ultraviolet spectroscopy to the self-association of adenine,adenosine and 5′-AMP in aqueous solution

UV spectra of adenine, adenosine and 5′-AMP in aqueous solution have been measured over the concentration range 1 × 10⁻⁶−5 × 10⁻² M. The apparent molar absorptivity of these compounds changes upon concentration, showing two hypochromic effects at c < 5 × 10⁻³ M and c &>; 5 × 10⁻³ M, respectively, which may be explained in terms of self-association.A method for calculating self-association constants from these experimental data is developed, based on an association model in which the first hypochromic effect is interpreted in terms of formation of dimers, with an equilibrium constant K₂, and the second effect is interpreted in terms of formation of polymers, with an equilibrium constant K_n. The value of K₂ is of the order of magnitude of 10⁴ for the three compounds. The value of K_n is dependent on the model chosen for the analysis of the second effect, having an order of magnitude of 10².The features of the self-association model are discussed, as well as the method for calculating self-association parameters from experimental data.     

Poly（vinylpyridine） adsorbent for the removal of SIPA from its aqueous solution

Poly(vinylpyridine) WH-225 resin was prepared and characterized.Compared with the commercial hypercrosslinked adsorbent NDA-100 and macroporous adsorbent XAD-4 resins,the newly synthesized poly(vinylpyridine) WH-225 resin exhibited the highest adsorption capacity toward SIPA from aqueous solution.     

Thermochemical study of the reactions of acid–base interaction in an aqueous solution of α-aminobutyric acid

The heat effects of the interaction between a solution of α-aminobutyric acid and solutions of HNO₃ and KОН are measured by means of calorimetry in different ranges of рН at 298.15 K and values of ionic strength of 0.25, 0.5, and 0.75 (KNO₃). The heat effects of the stepwise dissociation of the amino acid are determined. Standard thermodynamic characteristics (Δ_r H ⁰, Δ_r G ⁰, and Δ_r S ⁰) of the reactions of acid–base interaction in aqueous solutions of α-aminobutyric acid are calculated. The connection between the thermodynamic characteristics of the dissociation of the amino acid and the structure of this compound is considered.     

Degradation of anthracene, pyrene and benzo[a]-anthracene in aqueous solution by chlorine dioxide

Polycyclic aromatic hydrocarbons (PAHs) constitute an important group of micropollutants, which are known to be mutagenic, carcinogenic and/or co-carcinogenic and relatively persistent in the environment. The effects of chlorine dioxide (ClO2) on the degradation of anthracene (ANTH), pyrene (PYR) and benzo[a]anthracene (BaA) in aqueous solution were investigated using high performance liquid chromatography (HPLC). In preliminary experiments, it was observed that ClO2 could remove these three PAHs effectively within a short time. Several factors including reaction time, the concentration of ClO2 and pH of the reaction mixture influencing the degradation ratio of PAHs have been studied by batch experiments. The results showed that the degradation ratio of PAHs was affected by reaction time and the concentration of ClO2 instead of pH. The degradation ratio of ANTH, PYR and BaA could reach their maximum as approximately 99.0%, 67.5% and 89.5%, respectively, under the condition as follows: reaction time 30, 60 and 120 min, the concentration of ClO2 0.1, 0.4 and 0.5 mmol·L-1, and pH 7.2. ANTH was selected as the representative to study the reaction mechanism with ClO2. The oxidation products formed in the reaction of ANTH with ClO2 were tentatively identified by gas chromatography-mass spectrometry (GC-MS), and the results showed that the main product was 9, 10-anthraquinone, which could be biodegraded more easily and quickly than ANTH. Through analyzing the reaction properties of ANTH and ClO2, the possible pathway for the ANTH-ClO2 reaction was proposed based on the theory of single electron transfer (SET).     

Chemical relevance of the copper(II)—l-carnosine system in aqueous solution: A thermodynamic and spectrophotometric study

The copper(II)—l-carnosine (L⁻) system has been re-investigated in aqueous solution, at I = 0.1 mol dm⁻¹, different temperatures (5⩽t⩽45°C) and with metal to ligand ratios ranging from 3:1 to 1:3. Both potentiometry and visible spectrophotometry were employed. From an overall consideration of all experiments, [CuLH]²⁺, [CuL]⁺, [CuLH₋₁]°, [Cu₂L₂H₋₂]° and [Cu₂LH₋₁]²⁺ were recognized as the species which provide the best interpretation of experimental data. The complex formation constants, determined at different temperatures, allowed us to obtain reliable values of ΔH° and good estimates of ΔC°_p. From visible spectrophotometric measurements, carried out at different pH and metal to ligand ratios, it was possible to calculate the electronic spectrum of each complex formed in solution. A structure is also proposed for each species, on the basis of thermodynamic and spectral results.     

Thermochemical study of coordination equilibria in the zinc(II)-β-alanine-water system in aqueous solution

The heats of formation of β-alanine (HAla) complexes with Zn²⁺ ion at temperatures of 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 mol/l (KNO₃) were determined by calorimetry; the heats of dilution of a zinc nitrate solution in supporting electrolyte solutions were found for introduction of appropriate corrections. The standard heats of complexation in the zinc(II)-β-alanine-water system were determined. The standard thermodynamic characteristics of zinc(II) complexation with β-alanine and standard enthalpies of formation of ZnAla⁺ and ZnAla₂ complex species were calculated.     

Poly(ethylene oxide) irradiated in the solid state,melt and aqueous solution—a DSC and WAXD study

Interactions of the aggregate state of poly(ethylene oxide), PEO, and γ-irradiation conditions (total dose, atmosphere) on its thermal and crystalline properties were investigated by DSC and WAXD taking into account sample molecular mass and form. In PEO irradiated in the solid state and in the presence of oxygen, chain scission dominated over concurrent crosslinking up to 200 kGy, particularly in PEO powders, due to a large surface being in contact with air. In solid samples the degree of crystallinity and crystallite size increased with the dose up to 50 kGy, probably not just due to partial crystallization upon degradation of amorphous phase, but to recrystallization of broken tie molecules. The least changes in crystallinity and phase transformation temperatures occurred in solid films. A substantial decrease in crystallinity and transformation temperatures without the initial crystallinity increase was achieved in samples that were amorphous on irradiation, at temperatures above the PEO melting temperature and in aqueous solutions. Radiation crosslinking of the PEO aqueous solution in an inert atmosphere is the most suitable way to obtain a lower degree of crystallinity and phase transformation temperatures while preserving mechanical properties.     

The mechanism and pathway of the ozonation of 4-chlorophenol in aqueous solution

Chlorophenols (CPs) have been widely used in dif- ferent formulations as preservatives, herbicides, insec- ticides, bactericides and solvents. Parts of chlorophe- nols were released to the natural environment during the usage. As a result, many water sources were con- taminated with CPs[1,2]. Furthermore, they also can be formed during the disinfection of phenol containing water by chlorination. Several CPs are recognized as the priority pollutants by the United States EPA (En- vironmenta…     

Triphenylphosphine-catalyzed isomerization of alkynyl ketones in aqueous solution

An efficient isomerization of alkynyl ketones to(E,E)-diene ketones was developed.The reaction catalyzed by 20 mol% triphenylphosphine in aqueous media gave the desired products in good yields.     

Multinuclear NMR study of lanthanide(Ⅲ)complexes of 1,2-PDTA in aqueous solution

The complexation oflanthanide(Ⅲ) cations with 1,2-propanediaminetetraacetate (1,2-PDTA)in aqueous solution has been investigated by ~(23)Na,~(35)Cl,~2H and ~(17)O NMR shift measurements.It hasbeen shown that the contact shifts are dominant for ~(17)O,~(35)Cl and ~2H (only for the heavier lanthanideseries) and the pseudocontact shifts are dominant for ~(23)Na.It is suggested that the 1,2-PDTA ligandis bound pentadentately via the two nitrogens and the three carboxylates for the lighter lanthanidecomplexes,hexdentately via the two nitrogens and the four carboxylates for the heavier ones.Thenumbers of the water coordinated were determined.The small amount of chloride anion in innercoordination sphere was observed.     

Behaviour of β2-microglobulin in the electrical double layer of the mercury/solution interface

β₂-Microglobulin (β₂-m) is a small globular protein (12000 Da) which exists as a monomer in numerous body fluids. Data published on the electrochemical behaviour of β₂-m are scarce. In this paper an attempt was made to ge more information on the structure of the double layer at mercury/solution interface in the presence of β₂-m. Using phase selective ac polarography the capacitive current-potential (C-E) curve was analysed as the function of various β₂-m concentration, pH of medium, temperature, denaturation agent concentration etc. The data obtained are discussed particularly from the aspect of folding/unfolding state of the protein studied.     

γ-Ray induced catalytic properties of the silica nanoparticles dispersed in the aerated aqueous solution

Silica nanoparticles (NPs) dispersed in an aerated aqueous solution containing Ag⁺ were irradiated to a dose of 10 kGy using ⁶⁰Co γ-rays. The typical surface plasmon band of Ag NPs was observed around 400 nm, indicating that even in the presence of dissolved oxygen the reduction of Ag⁺ occurred by silica NPs. Transmission electron microscopy images indicated that Ag NPs formed on the surface of the silica NPs. The subtraction spectra showed broad absorption around 500 nm with the absorbance depending on the dose. The electrons generated by charge separation from silica NPs with a size of about 12 nm reduce Ag⁺ to Ag⁰ and form (Ag⁰) _n species on the silica NPs, and the type of (Ag⁰) _n species formed depended on the silica NP, and Ag⁺ contents, and the dose. In the co-presence of organic molecules on the silica NP such as rhodamine, the absorbance of the surface plasmon band of both Ag NPs and rhodamine decreased, indicating the electrons to participate in the reductive decomposition of rhodamine molecules adsorbed on the silica NP. Furthermore, in the case when the silica NPs contained fluorescein molecules, the fluorescein molecules were also decomposed, indicating that the fluorescein molecules adsorbed on the inner surface of the silica NPs. The addition of I₂ as an oxidative reagent prevented the decomposition of the fluorescein molecules, indicating that electrons are the main species emitted from irradiated silica NPs.     

Characterization of the inclusion complex of β-cyclodextrin with sorbic acid in the solid state and in aqueous solution

Crystal structure of β-cyclodextrin (β-CD) complexes with sorbic acid, usually as food preservative, has been determined by single-crystal X-ray diffraction at 113 K. The space group of β-cyclodextrin-sorbic acid complex is P1 with unit cell dimensions of a = 15.284(3) Å, b = 15.402(3) Å, c = 17.981(4) Å, α = 99.67(3)°, β = 112.83(3)°, γ = 102.48(3)° and Z = 1. The result indicates that the β-CD molecules form head-to-head dimers which pack in the intermediate mode. Each dimer contains two guest molecules whose methyl groups are located at the dimer interface while the carboxyl groups protrude from the β-CD primary faces. Water molecules (25.5) are distributed outside the cyclodextrin cavity over 31 sites. Furthermore, nuclear magnetic resonance spectroscopy (¹H NMR) has been employed to investigate the inclusion behavior between the host β-CD and guest sorbic acid in aqueous solution. The results obtained enabled us to structurally characterize the β-CD inclusion complex with sorbic acid.     

The nature of the [TTF]˙+···[TTF]˙+ interactions in the [TTF]2(2+) dimers embedded in charged [3]catenanes: room-temperature multicenter long bonds

The properties of tetrathiafulvalene dimers ([TTF](2)(2+)) and the functionalized ring-shaped bispropargyl (BPP)-functionalized TTF dimers, [BPP-TTF](2)(2+), found at room temperature in charged [3]catenanes, were evaluated by M06L calculations. The results showed that their isolated [TTF](2)(2+) and [BPP-TTF](2)(2+) dimers are energetically unstable towards dissociation. When enclosed in the 4(+)-charged central cyclophane ring of charged [3]catenanes (CBPQT(4+)), [TTF](2)(2+) and [BPP-TTF](2)(2+) dimers are also energetically unstable with respect to leaving the CBPQT(4+) ring; since the barrier for the exiting process is only about 3 kcal mol(-1), that is, within the reach of thermal energies at room temperature (neutral [TTF](2)(0) dimers are stable within the CBPQT(4+) ring). However, the [BPP-TTF](2)(2+) dimers in charged [3]catenanes cannot exit, because this would imply breaking the covalent bonds of the BPP-TTF(+) macrocycle. Finally, it was shown that the [TTF](2)(2+), [BPP-TTF](2)(2+) dimers, and charged [3]catenanes are energetically stable in solution and in crystals of their salts, in the first case due to the interactions with the solvent, and in the second case mostly due to cation-anion interactions. In these environmental conditions at room temperature the TTF units of the [BPP-TTF](2)(2+) dimers make short contacts, thus allowing their SOMO orbitals to overlap: a room-temperature multicenter long bond is formed, similar to those previously found in other [TTF](2)(2+) salts and their solutions.