Solvent Effect on the Photolysis of Riboflavin

The kinetics of photolysis of riboflavin (RF) in water (pH 7.0) and in organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol, ethyl acetate) has been studied using a multicomponent spectrometric method for the assay of RF and its major photoproducts, formylmethylflavin and lumichrome. The apparent first-order rate constants (k_obs) for the reaction range from 3.19 (ethyl acetate) to 4.61 × 10⁻³ min⁻¹ (water). The values of k_obs have been found to be a linear function of solvent dielectric constant implying the participation of a dipolar intermediate along the reaction pathway. The degradation of this intermediate is promoted by the polarity of the medium. This indicates a greater stabilization of the excited-triplet states of RF with an increase in solvent polarity to facilitate its reduction. The rate constants for the reaction show a linear relation with the solvent acceptor number indicating the degree of solute–solvent interaction in different solvents. It would depend on the electron-donating capacity of RF molecule in organic solvents. The values of k_obs are inversely proportional to the viscosity of the medium as a result of diffusion-controlled processes.KEY WORDS: dielectric constant, kinetics, photolysis, riboflavin, solvent effect, viscosity     

Effect of Ascorbic Acid on the Degradation of Cyanocobalamin and Hydroxocobalamin in Aqueous Solution: A Kinetic Study

The degradation kinetics of 5 × 10⁻⁵ M cyanocobalamin (B₁₂) and hydroxocobalamin (B_12b) in the presence of ascorbic acid (AH₂) was studied in the pH range of 1.0–8.0. B₁₂ is degraded to B_12b which undergoes oxidation to corrin ring cleavage products. B_12b alone is directly oxidized to the ring cleavage products. B₁₂ and B_12b in degraded solutions were simultaneously assayed by a two-component spectrometric method at 525 and 550 nm without interference from AH₂. Both degrade by first-order kinetics and the values of the rate constants at pH 1.0–8.0 range from 0.08 to 1.05 × 10⁻⁵ s⁻¹ and 0.22–7.62 × 10⁻⁵ s⁻¹, respectively, in the presence of 0.25 × 10⁻³ M AH₂. The t_1/2 values of B₁₂ and B_12b range from 13.7 to 137.5 h and 2.5–87.5 h, respectively. The second-order rate constants for the interaction of AH₂ with B₁₂ and B_12b are 0.05–0.28 × 10⁻² and 1.10–30.08 × 10⁻² M⁻¹ s⁻¹, respectively, indicating a greater effect of AH₂ on B_12b compared to that of B₁₂. The k_obs–pH profiles for both B₁₂ and B_12b show the highest rates of degradation around pH 5. The degradation of B₁₂ and B_12b by AH₂ is affected by the catalytic effect of phosphate ions on the oxidation of AH₂ in the pH range 6.0–8.0.KEY WORDS: ascorbic acid, cyanocobalamin, degradation, hydroxocobalamin, kinetics, two-component spectrometry     

Photodegradation of Moxifloxacin in Aqueous and Organic Solvents: A Kinetic Study

The kinetics of photodegradation of moxifloxacin (MF) in aqueous solution (pH 2.0–12.0), and organic solvents has been studied. MF photodegradation is a specific acid-base catalyzed reaction and follows first-order kinetics. The apparent first-order rate constants (k_obs) for the photodegradation of MF range from 0.69 × 10⁻⁴ (pH 7.5) to 19.50 × 10⁻⁴ min⁻¹ (pH 12.0), and in organic solvents from 1.24 × 10⁻⁴ (1-butanol) to 2.04 × 10⁻⁴ min⁻¹ (acetonitrile). The second-order rate constant (k₂) for the [H⁺]-catalyzed and [OH⁻]-catalyzed reactions are 6.61 × 10⁻² and 19.20 × 10⁻² M⁻¹ min⁻¹, respectively. This indicates that the specific base-catalyzed reaction is about three-fold faster than that of the specific acid-catalyzed reaction probably as a result of the rapid cleavage of diazabicyclononane side chain in the molecule. The k_obs-pH profile for the degradation reactions is a V-shaped curve indicating specific acid-base catalysis. The minimum rate of photodegradation at pH 7–8 is due to the presence of zwitterionic species. There is a linear relation between k_obs and the dielectric constant and an inverse relation between k_obs and the viscosity of the solvent. Some photodegraded products of MF have been identified and pathways proposed for their formation in acid and alkaline solutions.KEY WORDS: acid-base catalysis, kinetics, moxifloxacin, photodegradation, rate–pH profile, solvent effect     

Azaguanine: A Theoretical Study of Its Tautomerism and Protonation in the Gas Phase and Aqueous Solution

The tautomerism and protonation of 8-azaguanine (azaG) have been studied by means of ab initio methods, both in the gas phase and in aqueous solution. An elimination procedure to choose the most stable tautomeric forms, based on AM1 and HF/6–31G* energies, has been applied. Tautomers azaG(1,9), azaG(1,7) and azaG(9,15) have been selected and their energies calculated at MP2/6–311++G**//HF/6–31G* level. Self-consistent reaction field IPCM, based on polarizable continuum model (PCM), has been applied to study the solvent effects. The stability order in the gas phase is azaG(1,7) = azag(1,9) > azaG(9,15), whereas in solution the order becomes azaG(1,7) > azaG(1,9) > azaG(9,15), the latter being just 0.76 kcal/mol over azaG(1,7). The calculations of proton affinities allowed to unambiguously determine the preferred sites of protonation of these species.     

石油焦基高比表面积活性炭对水中Pb2+离子吸附性能的研究

以石油焦基为原料,采用KOH活化法制取高比表面积活性炭。考察了高比表面积活性炭吸附水中Pb^2 时,pH值、Pb^2 浓度、吸附时间和活性炭用量等因素对Pb^2 吸附量和水中Pb^2 残余浓度的影响。实验结果表明：高比表面积活性炭在适宜条件下对Pb^2 具有较大的吸附量和良好的再生效果。为高比表面积活性炭在废水中的实际应用提供了理论依据。     

Solubility of Drugs in Aqueous Polymeric Solution: Effect of Ovalbumin on Microencapsulation Process

Microencapsulation of water-soluble drugs using coacervation-phase separation method is very challenging, as these drugs partitioned into the aqueous polymeric solution, resulting in poor drug entrapment. For evaluating the effect of ovalbumin on the microencapsulation of drugs with different solubility, pseudoephedrine HCl, verapamil HCl, propranolol HCl, paracetamol, and curcuminoid were used. In addition, drug mixtures comprising of paracetamol and pseudoephedrine HCl were also studied. The morphology, encapsulation efficiency, particle size, and in vitro release profile were investigated. The results showed that the solubility of the drug determined the ratio of ovalbumin to be used for successful microencapsulation. The optimum ratios of drug, ovalbumin, and gelatin for water-soluble (pseudoephedrine HCl, verapamil HCl, and propranolol HCl), sparingly water-soluble (paracetamol), and water-insoluble (curcuminoid) drugs were found to be 1:1:2, 2:3:5, and 1:3:4. As for the drug mixture, the optimum ratio of drug, ovalbumin, and gelatin was 2:3:5. Encapsulated particles prepared at the optimum ratios showed high yield, drug loading, entrapment efficiency, and sustained release profiles. The solubility of drug affected the particle size of the encapsulated particle. Highly soluble drugs resulted in smaller particle size. In conclusion, addition of ovalbumin circumvented the partitioning effect, leading to the successful microencapsulation of water-soluble drugs.     

Calcium Acetate or Calcium Carbonate for Hyperphosphatemia of Hemodialysis Patients: A Meta-Analysis

Background

High levels of serum phosphorus both at baseline and during follow-up are associated with increased mortality in dialysis patients, and administration of phosphate binders was independently associated with improved survival among hemodialysis population. Calcium-based phosphate binders are the most commonly used phosphate binders in developing countries for their relatively low costs.

Objectives

To compare the efficacy and safety between calcium carbonate and calcium acetate in the treatment of hyperphosphatemia in hemodialysis patients.

Methods

PubMed, EMBASE, Cochrane Library, Google scholar and Chinese databases (Wanfang, Weipu, National Knowledge Infrastructure of China) were searched for relevant studies published before March 2014. Reference lists of nephrology textbooks and review articles were checked. A meta-analysis of randomized controlled trials (RCTs) and quasi-RCTs that assessed the effects and adverse events of calcium acetate and calcium carbonate in adult patients with MHD was performed using Review Manager 5.0.

Results

A total of ten studies (625 participants) were included in this meta-analysis. There was insufficient data in all-cause mortality and cardiovascular events for meta-analysis. Compared with calcium carbonate group, the serum phosphorus was significantly lower in calcium acetate group after4 weeks’ administration (MD -0.15 mmol/L, 95% CI -0.28 to -0.01) and after 8 weeks’ administration (MD -0.25 mmol/L, 95% CI -0.40 to -0.11). There was no difference in serum calcium levels or the incidence of hypercalcemia between two groups at 4 weeks and 8 weeks. No statistical difference was found in parathyroid hormone (PTH) levels or serum calcium by phosphorus (Ca x P) product. There was significantly higher risk of intolerance with calcium acetate treatment (RR 3.46, 95% CI 1.48 to 8.26).

Conclusions

For hyperphosphatemia treatment, calcium acetate showed better efficacy and with a higher incidence of intolerance compared with calcium carbonate. There are insufficient data to establish the comparative superiority of the two calcium-based phosphate binders on all-cause mortality and cardiovascular end-points in hemodialysis patients.     

Entropies of Redox Reactions between Proteins and Mediators: The Temperature Dependence of Reversible Electrode Potentials in Aqueous Buffers

The temperature dependencies of the reversible electrode potentials for a number of charge transfer reactions of redox mediators were used to evaluate the corresponding charge transfer entropies in Tris–HCl (pH 8) buffer. The redox mediator thermodynamic data, along with reaction enthalpy data for mediator redox protein electron transfer, were used to evaluate the charge transfer entropy for the cytochrome c redox couple [(cytc)_ox/(cytc)_red] in Tris–HCl (pH 8) buffer and were found to be equal to −16 cal/°K mol. Reversible electrode potentials at 298°K for the redox mediator half-reactions were observed to vary from −528 to +657 mV (vs NHE). Charge transfer entropies were observed to depend upon the structure of the redox mediators and to vary from −13.8 to −29.7 cal/°K mol for a closely related series of organic dications (viologens) and a value of −43.6 cal/°K mol was observed for the [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻couple under the same conditions. A procedure for determining charge transfer entropies of protein redox couples which cannot be studied by direct electrochemical methods is outlined. The factors contributing to the magnitude of the charge transfer entropies are discussed.     

Kinetic Study of the Inhibition of Linoleic Acid Oxidation in Aqueous Media by Phenolic Compounds

The antioxidant activity of several phenolic compounds has been evaluated in terms of the inhibition of the lipid oxidation. The extent of linoleic acid oxidation was monitored by the absorption of the conjugated diene hydroperoxydes formed as a result of oxidation. The antioxidant activity of phenolic compounds was evaluated in aqueous media consisting of negatively-charged micelles of sodium dodecyl sulfate (SDS) or positively-charged micelles of hexadecyl trimethylammonium bromide (HDTBr). 2,2′-azobis-(2-amidinopropane)-dihydrochloride (ABAP) was employed as the oxidation initiator. The assayed phenolic compounds showed good antioxidant efficiency, closely related to the presence of hydroxyl groups and the electron delocalization within the structure, which may stabilize the formed phenoxyl radicals. The kinetic analysis revealed that the oxidizability of linoleic acid was 10-fold higher in SDS than in HDTBr media, which could indicate that oxidation is favoured in negatively charged SDS micelles regarding to positive HDTBr medium. Furthermore, a greater antioxidant efficiency of phenolic compounds was found in HDTBr than in SDS micelles.     

Material Balance and Additional Effect of Second Organic Solutes in the Radiolysis of Aqueous Methionine Solution

The gamma-radiolysis of methionine in 10^?3 m aqueous solution was studied. From the yield vs. dose plots, the following values were obtained: G(?Methionine)=3.0, G(Methionine sulfoxide)=0.30, G(α- Aminobutyric acid)=0.46, G(3-Methylthio propylamine)=0.59, G(Methional)=0.08, G(Carboxylic acid)=0.24, G(Mercaptan + Disulfide)=0.6l, G(Ammonia)=1.48, and G(Carbon dioxide)=1.45. From these results, it was concluded that major reaction was deamination and decarboxylation by OH radical attack.

Addition of methanol as the second solute at concentration above 4 × 10^?3 m could not lower G(Methionine sulfoxide), suggesting the reaction of methionine with secondary radical produced from methanol.

Existence of similar reaction was suggested in the radiolysis of methionine in aqueous pork extract.     

Studies on Radiation Chemistry of Halogenophenols in Aqueous Solution

In relation to the bactericidal action of γ-irradiated halogenophenol solution, radiolysis of p-bromophenol in the aqueous system under anaerobic condition was investigated. Several phenolic compounds could be isolated from the radiolysis products, and three of them were elucidated for their structures. One of them was hydroquinone and the other two were assigned as new asymmetrical dimers, 5-bromo-2,4′-dihydroxybiphenyl and 2-bromo-5,4′-dihydroxybiphenyl, which were confirmed by the syntheses of their methyl ethers.     

Correction for Irrelevant Absorption in Multicomponent Spectrophotometric Assay of Riboflavin, Formylmethylflavin, and Degradation Products: Kinetic Applications

In the spectrophotometric assay of multicomponent systems involved in drug degradation studies, some minor or unknown degradation products may be present. These products may interfere in the assay and thus invalidate the results due to their absorption in the range of analytical wavelengths. This interference may be eliminated by the application of an appropriate correction procedure to obtain reliable data for kinetic treatment. The present study is based on the application of linear and non-linear irrelevant absorption corrections in the multicomponent spectrophotometric assay of riboflavin and formylmethylflavin during the photolysis and hydrolysis studies. The correction procedures take into account the interference caused by minor or unknown products and have shown considerable improvement in the assay data in terms of the molar balance. The treatment of the corrected data has led to more accurate kinetic results in degradation studies.     

Complexes of Tungsten(VI) with Mucic Acid: a Spectrophotometric and Polarimetric Study in Aqueous Solution

Spectrophotometric work on mucic acid-W(VI) system shows the formation of three different oxoanion complexes in aqueous solution; their stability is dependent upon pH. One of the complexes is monomeric tungstodimucate and the other two are 2/2 species. An anomalous cryoscopic behaviour, similar to that of W(VI) tartaric system, has been observed for the dimeric complex formed at higher pH. The stoichiometries and conditional dissociation constants have been polarimetrically determined by means of competitive reactions between the mucic and tartaric ligands. ¹H and ¹³C NMR spectra have been interpreted for the similar complex species of both mucic and tartaric acids.     

Photolysis of Low-Brominated Diphenyl Ethers and Their Reactive Oxygen Species-Related Reaction Mechanisms in an Aqueous System

To date, no report was concerned with participation of reactive oxygen species in waters during photolysis of low-brominated diphenyl ethers (LBDEs). Herein, we found that electron spin resonance (ESR) signals rapidly increased with increasing irradiation time in the solution of LBDEs and 4-oxo-TMP solutions. But this phenomenon did not occur in the presence of NaN₃ (¹O₂ quencher) demonstrating generation of ¹O₂ in process of LBDEs photolysis. The indirect photolytic contribution rate for BDE-47 and BDE-28 was 18.8% and 17.3% via ¹O₂, and 4.9% and 6.6% via ·OH, respectively. Both D₂O and NaN₃ experiments proved that the indirect photolysis of LBDEs was primarily attributable to ¹O₂. The bimolecular reaction rate constants of ¹O₂ with BDE-47 and BDE-28 were 3.12 and 3.64 × 10⁶ M^-1 s^-1, respectively. The rate constants for BDE-47 and BDE-28 (9.01 and 17.52 × 10⁻³ min^-1), added to isopropyl alcohol, were very close to those (9.65 and 18.42 × 10⁻³ min^-1) in water, proving the less indirect photolytic contribution of ·OH in water. This is the first comprehensive investigation examining the indirect photolysis of LBDEs in aqueous solution.     

Reduction of Deoxynivalenol in Barley by Treatment with Aqueous Sodium Carbonate and Heat

Naturally contaminated lots of Canadian barley containing either 18.4 or 4.3 μg/g deoxynivalenol (DON) were heated at 80 °C, with small amounts of water or 1 M sodium carbonate solution to study the rate of DON reduction. Samples were heated in sealed polypropylene containers for periods of up to 8 days. In the 18.4 μg/g DON barley, rapid reductions were observed: with no solutions added, DON declined to 14.7 μg/g after 1 day, and to 4.9 μg/g after 8 days solely due to heat; with water at 10 mL/100 g barley, DON levels reached 3.7 μg/g after 8 days; with 1 M sodium carbonate solution added at 10 mL/100 g barley, DON declined to 4.7 μg/g after 1 day, and to 0.4 μg/g after 8 days; with 20 mL/100 g barley, DON declined to 1.4 μg/g after 1 day and to near-zero levels after 8 days. In the 4.3 μg/g DON barley, more gradual reductions were evident: with no solutions added, DON declined to 2.9 μg/g after 8 days solely due to heat; with water at 10 mL/100 g barley, DON levels reached 2.3 μg/g after 8 days; with 1 M sodium carbonate solution added at 10 mL/100 g barley, DON declined to 2.7 μg/g after 1 day, and to near-zero levels after 8 days; with 20 mL/100 g barley, DON declined to 1.4 μg/g after 1 day and to near-zero levels after 3, 5 and 8 days.     

The Effect of Riboflavin on Hypertension induced by High Salt Diet in the Rat

The effect of riboflavin on development of hypertension in rats given a high salt diet was studied. Large doses of riboflavin prevented both elevation of blood pressure and rise of cholesterol levels in the serum. The increase in liver monoamine oxidase activity of the rats fed riboflavin was confirmed.     

金顶侧耳多糖及其化学修饰产物水溶液构象的圆二色谱测定

金顶侧耳多糖及其化学修饰产物水溶液构象的圆二色谱测定张丽萍,张翼伸（东北师范大学生物系,长春１３００２４）我们曾对金顶侧耳多糖ＰＣ－３的分离纯化、糖链结构确定、ＰＣ－３及其化学修饰产物有无抗病毒活性进行过研究［１,２］。本文将简要报导ＰＣ－３及其衍生...