Apparent First-order Rate Constants Research Articles

Efficient ofloxacin degradation via peroxymonosulfate activation using an S-scheme MoS2/Co3O4 heterojunction composite under visible light: Performance and mechanistic insights

Sulfate-radical-mediated photocatalysis technology peroxymonosulfate (PMS) activation via visible light irradiation shows great promise for water treatment applications. However, its effectiveness largely depends on the bifunctional performance of photocatalysis and PMS activation provided by the catalysts. In this study, we successfully synthesized a novel S-scheme MoS2/Co3O4 (MC) heterojunction composite by a hydrothermal method and employed it for the first time to activate PMS for ofloxacin (OFX) degradation under visible light irradiation. The MC-5/PMS/Vis system achieved an impressive 85.11% OFX degradation efficiency within 1 min and complete OFX removal within 15 min under optimal conditions, with an apparent first-order kinetics rate constant of 0.429 min-1. Reactive species trapping experiments and electron spin resonance analysis identified 1O2, h+, and •O2- as the primary active species responsible for OFX degradation. Photoelectrochemical analyses and density functional theory calculations indicated the formation of a built-in electric field between MoS2 and Co3O4, which enhanced the separation and migration of photoinduced carriers. Additionally, the Co-Mo interaction further increased the yield of dominant reactive species, thereby boosting photocatalytic activity. This work underscores the potential of visible-light-assisted PMS-mediated photocatalysis using Co3O4-based catalysts for effective pollutant control.

Photolysis of tolfenamic acid in aqueous and organic solvents: a kinetic study.

Tolfenamic acid (TA) is a non-steroidal anti-inflammatory drug that was studied for its photodegradation in aqueous (pH 2.0-12.0) and organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol). TA follows first-order kinetics for its photodegradation, and the apparent first-order rate constants (k obs) are in the range of 0.65 (pH 12.0) to 6.94 × 10-2 (pH 3.0) min-1 in aqueous solution and 3.28 (1-butanol) to 7.69 × 10-4 (acetonitrile) min-1 in organic solvents. The rate-pH profile for TA photodegradation is an inverted V (∧) or V-top shape, indicating that the cationic form is more susceptible to acid hydrolysis than the anionic form of TA, which is less susceptible to alkaline hydrolysis. The fluorescence behavior of TA also exhibits a V-top-shaped curve, indicating maximum fluorescence intensity at pH 3.0. TA is highly stable at a pH range of 5.0-7.0, making it suitable for formulation development. In organic solvents, the photodegradation rate of TA increases with the solvent's dielectric constant and solvent acceptor number, indicating solute-solvent interactions. The values of k obs decreased with increased viscosity of the solvents due to diffusion-controlled processes. The correlation between k obs versus ionization potential and solvent density has also been established. A total of 17 photoproducts have been identified through LC-MS, of which nine have been reported for the first time. It has been confirmed through electron spin resonance (ESR) spectrometry that the excited singlet state of TA is converted into an excited triplet state through intersystem crossing, which results in an increased rate of photodegradation in acetonitrile.

Solvent Polarity and Framework Hydrophobicity of Hf-BEA Zeolites Influence Aldol Addition Rates in Organic Media

Solvent identity and pore polarity are known to influence Lewis acidic catalysis in zeolite pores for a variety of liquid-phase chemistries. We investigated how these parameters alter the rates of self-aldol addition of ethyl pyruvate (EP), a model biomass-derived compound, over hydrophobic and hydrophilic Hf-BEA zeolites in both toluene and acetonitrile solvents. Aldol addition rates are of first order across the entire EP activity range (0.02–0.4) for all four systems, consistent with the nucleophilic attack by the enolate as the rate-determining step and a single adsorbed EP as the most abundant reactive intermediate. Apparent first-order rate constants span 2 orders of magnitude across the four systems; at 363 K, the highest rates were observed over hydrophobic Hf-BEA-F in toluene (kapp = 0.36 (mmol) (mmol closed Hf)−1 (s)−1), while the lowest rates were observed in hydrophilic Hf-BEA-OH in an acetonitrile solvent (kapp = 0.0026 (mmol) (mmol closed Hf)−1 (s)−1). Apparent reaction enthalpies and entropies for each system, estimated using non-ideal transition-state theory, revealed that despite the substantial rate constant variation across the four systems, apparent enthalpies for Hf-BEA-F in both solvents and Hf-BEA-OH in acetonitrile were within the error of each other (∼70 kJ mol–1). Reactions performed using Hf-BEA-OH with toluene featured a higher apparent enthalpic barrier of 83.8 kJ mol–1. The differences between the systems are attributed to hydrogen-bonding interactions between the EP molecules and polar silanol nests during catalysis in toluene using Hf-BEA-OH, which hinder EP adsorption to the active site in the hydrophilic framework. These hydrogen-bonding interactions are not present when acetonitrile is used as the solvent, as acetonitrile itself binds to and blocks silanol groups. Equilibrium EP absorption measurements indicate that while both toluene and acetonitrile are present in pores during catalysis, neither solvent forms a tight solvation shell around EP in the pores that must be disrupted prior to EP adsorption. These findings show that aldol addition kinetics are not significantly modified by solvent polarity in hydrophobic frameworks beyond site-blocking effects; however, silanol nests in hydrophilic frameworks significantly alter substrate adsorption to the active site.

Highly efficient electro-peroxone enhanced by oxygen-doped carbon nanotubes with triple role of in-situ H2O2 generation, activation and catalytic ozonation

The oxygen-doped carbon nanotubes coated on the carbon felt acted as cathode to enhance the electro-peroxone (OCNT-EP) process. Owing to the introduction of oxygen-containing functional groups and defect sites, the OCNT modified cathode could achieve in-situ H2O2 generation, activation, and catalytic ozonation in the EP process. The OCNT-EP showed a 2.3-folds apparent first-order rate constant (k) compared with the EP process using CNT cathode (CNT-EP) for atrazine (ATZ) degradation. According to the processes comparison, quenching experiments, electron paramagnetic resonance (EPR) analysis and determination of hydroxyl radical, it was proved that more.OH and 1O2 were generated by the in-situ H2O2 activation and catalytic ozonation in the OCNT-EP process. Especially, this process improved pollutants degradation under acidic condition for the in-situ H2O2 activation and catalytic ozonation, expanding the pH application range of the EP process with a lower energy consumption (0.10 kWh/g ATZ). What’ more, the OCNT modified cathode performed excellent stability with 20 cycle tests, and demonstrated all improved degradation rate (21.7%−78.0%) for various pollutants (carbamazepine, sulfamethazine, phenol and 2,4-dichlorophenol). Therefore, the OCNT-EP process could be considered as a promising and enhanced EP process for wastewater treatment.

Boosted photocatalytic effect of binary AgI/Ag2WO4 nanocatalyst: characterization and kinetics study towards ceftriaxone photodegradation.

In modern chemistry, great interest has been paid to introducing outstanding photocatalysts for degrading organic pollutants. Herein, a highly efficient binary AgI/Ag2WO4 photocatalyst was prepared from AgI and Ag2WO4 nanoparticles (NPs) and characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), and Fourier transform infrared (FT-IR) techniques. In the Scherrer model, the average crystallite sizes of 34.9, 42.0, and 24.1nm were estimated for the AgI, Ag2WO4, and the binary catalyst, while the values were 91, 13, and 85nm by the Williamson-Hall model. FTIR confirmed the presence of W-O-W, O-W-O, Ag-I, and O-Ag-O bonds in the coupled material. DRS results showed absorption edge wavelengths of 451, 462, and 495nm (corresponding to the band gap values of 2.75, 2.68, and 2.51eV) for Ag2WO4, AgI, and AgI/Ag2WO4 catalyst, respectively. Synergistic photocatalytic activity of the coupled system was achieved towards ceftriaxone (CTX) in an aqueous solution (about 33% 10ppm CTX solution was degraded without any optimization in the initial conditions of catal dose 0.3g/L (Ag2WO4:AgI with mole ratio 1:2 and 30min abrasion time), and irrad. time 45min, CCTX). This boosted effect depended on the AgI:Ag2WO4 mole ratio and grinding time for the mechanical preparation of the binary catalyst (optimums: mole ratio of 4:1 and time 30min). The photodegradation kinetics obeyed the Hinshelwood model with the apparent first-order rate constant (k) of 0.013min-1 (t1/2 = 53.30min). Performing the COD on the photodegraded CTX solutions got a Hinshelwood plot with a slope of 0.019min-1 (t1/2 = 36.5min).

A Distinctive Pattern for Substituent Effects on Transition Metal Centers: Enhanced Electron-Donating Capacity of Cationic Palladium Species

A Distinctive Pattern for Substituent Effects on Transition Metal Centers: Enhanced Electron-Donating Capacity of Cationic Palladium Species

Decolorization of Reactive Black 5 Using N-Doped TiO2

Decolorization of Reactive Black 5 (RB5) was investigated by heterogeneous photocatalysis using N-doped TiO2. N-doped TiO2 photocatalysts were synthesized by means of a sol-gel process. X-ray diffraction performed the characterization of synthesized samples, scanning electron microscopy and X-ray photoelectron spectroscopy measurements. Photocatalytic activity of N-doped TiO2 samples was assessed by following decolorization and degradation efficiency of RB5. N-TiO2(3) sample yielded the highest decolorization efficiency. The apparent first-order rate constants for decolorization of RB5 with N-TiO2(X) samples followed the order of N-TiO2(3) > N-TiO2(2) > N-TiO2(4) > N-TiO2(1). Improvement of decolorization efficiency of TiO2 was observed doping with nitrogen. The effect of actual sunlight on decolorization efficiency was also investigated. 96% and 49% of decolorization efficiency levels were attained within 60 minutes of reaction time with outdoor sunlight and fluorescent daylight lamps, respectively.

Degradation pathways and kinetics of chloroacetonitriles by UV/persulfate in the presence of bromide

Chloroacetonitriles (CANs) are highly toxic nitrogenous disinfection by-products (N-DBPs), which frequently appear in water supply systems and have attracted widespread attention. UV/persulfate (PS) is an effective method to degrade CANs. Bromide (Br−) is widespread in aquatic environments and reacts with oxidative radicals to produce secondary reactive bromine species (RBS), which affects the degradation of CANs by UV/PS. It was found that the degradation of CANs was highly inhibited by Br−. The apparent first-order reaction rate constants of monochloroacetonitrile (MCAN), dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) decreased from 2.63 × 10−3, 2.00 × 10−3 and 8.66 × 10−4 s−1 to 2.58 × 10−4, 1.61 × 10−4 and 1.59 × 10−4 s−1, respectively after adding 20 μM of Br−. HO• was the main radicals contributing to the degradation of CANs when the concentration of Br− was less than 10 μM, compared with SO4•− and direct photolysis. When the concentration of Br− was up to 20 μM, the contributions of RBS accounted for 85.7%, 90.7% and 89.9% of the apparent degradation rate constants of CANs, respectively. During the reaction, about 65% of nitrogen atoms were transformed into NO3− by the CC bond cleavage and oxidation. The yields of Cl− by dechlorination reaction accounted for 83.5%, 71.0% and 41.2% of the chlorine contents in MCAN, DCAN and TCAN, respectively. It was verified that CANs react with free bromine (HOBr) to produce bromochloroacetonitrile (BCAN). DCAN and TCAN are hydrolyzed to produce corresponding haloacetamides (HAMs), which are further reacted with HOBr to produce bromodichloroacetic acid (BDCAA). Furthermore, the generation of bromate was also worth noting via the oxidation of Br− in the UV/PS system.

Copper(II)-Doped Carbon Dots as Catalyst for Ozone Degradation of Textile Dyes.

A catalytic ozonation advanced oxidation process (AOP) with a copper(II)-doped carbon dot as catalyst, Cu-CD (using L-cysteine and polyethylene glycol (PEG) as precursors and passivation agents), was developed for textile wastewater treatment (T = 25 °C and pH = 7). Four dyes were analyzed—Methyl Orange (MO), Orange II sodium salt (O-II), Reactive Black 5 (RB-5) and Remazol Brilliant Blue R (RBB-R), as well as a real effluent from the dying and printing industry. The Cu-CD, with marked catalytic ozonation properties, was successfully synthesized by one-pot hydrothermal procedure with a size of 4.0 nm, a charge of −3.7 mV and a fluorescent quantum yield of 31%. The discoloration of the aqueous dye solutions followed an apparent first-order kinetics with the following rate constants (kap in min−1): MO, 0.210; O-II, 0.133; RB-5, 0.177; RBB-R, 0.086. In the presence of Cu-CD, the following apparent first-order rate constants were obtained (kapc in min−1) with the corresponding increase in the rate constant without catalyst (%Inc): MO, 1.184 (464%); O-II, 1.002 (653%); RB-5, 0.709 (301%); RBB-R, 0.230 (167%). The presence of sodium chloride (at a concentration of 50 g/L) resulted in a marked increase of the discoloration rate of the dye solution due to generation of other radicals, such as chlorine and chlorine oxide, resulting from the reaction of ozone and chloride. Taking into consideration that the real textile effluent under research has a high carbonate concentration (>356 mg/L), which inhibits ozone decomposition, the discoloration first-order rate constants without and with Cu-CD (kap = 0.0097 min−1 and kapc = 0.012 min−1 (%Inc = 24%), respectively) were relatively small. Apparently, the Cu-CD, the surface of which is covered by a soft and highly hydrated caramelized PEG coating, accelerates the ozone decomposition and dye adsorption, increasing its degradation.

Kinetics study of the natural split Npu DnaE intein in the generation of bispecific IgG antibodies.

Rapid and efficient bispecific antibody (BsAb) production for industrial applications is still facing many challenges. We reported a technology platform for generating bispecific IgG antibodies, "Bispecific Antibody by Protein Trans-splicing (BAPTS)." While the "BAPTS" method has shown potential in high-throughput screening of BsAbs, further understanding and optimizing the methodology is desirable. A large number of BsAbs were selected to illustrate the conversion efficiency and kinetics parameters. The temperature of reaction makes no significant influence in conversion efficiency, which can reach more than 70% within 2h, and CD3 × HER2 BsAb can reach 90%. By fitting trans-splicing reaction to single-component exponential decay curves, the apparent first-order rate constants at a series of temperatures were determined. The rate constant ranges from 0.02 to 0.11min-1 at 37°C, which is a high rate reported for the protein trans-splicing reaction (PTS). The reaction process is activated rapidly with activation energy of 8.9kcal·mol-1 (CD3 × HER2) and 5.2kcal·mol-1 (CD3 × EGFR). The BsAbs generated by "BAPTS" technology not only had the similar post-translation modifications to the parental antibodies, but also demonstrated excellent in vitro and in vivo bioactivity. The kinetics parameters and activation energy of the reaction illustrate feasible for high-throughput screening and industrial applications using the "BAPTS" approach. KEY POINTS: • The trans-splicing reaction of Npu DnaE intein in "BAPTS" platform is a rapid process with low reaction activation and high rate. • The BsAb generated by "BAPTS" remained effective in tumor cell killing. • The kinetics parameters and activation energy of the reaction illustrate feasible for high-throughput screening and industrial applications using the "BAPTS" approach.

Identification and quantification of distinct active sites in Hf-Beta zeolites for transfer hydrogenation catalysis

Despite the significant progress made in characterizing different framework heteroatom sites that exist in Lewis acidic zeolites with probe molecule adsorption and spectroscopy, methods to reliably quantify site counts remain indefinite and have been primarily limited to Sn and Ti Lewis acid sites. Here, methods to quantify framework Lewis acidic Hf4+ sites in zeolite Beta (Hf-Beta) with two Lewis base titrants (pyridine, deuterated acetonitrile) were developed using infrared (IR) spectroscopy. Lewis acid site counts for Hf-Beta zeolites were validated by measuring integrated molar extinction coefficients (IMECs; ε, cm μmol−1) on Sn-Beta zeolites using identical Lewis base titrants to benchmark site counts with established literature procedures to quantify Lewis acid sites in Beta zeolites from IR spectra. Highlighting the importance of benchmarking active site counts against well-established experimental protocols, IMECs of CD3CN bound to open (ε(Sn; 2316 cm−1): 1.80 ± 0.25) and closed (ε(Sn; 2308 cm−1): 3.76 ± 0.33) Sn sites were ∼ 1.8x larger than those previously reported while total Lewis acid site counts agreed with those measured by pyridine (ε(Sn; 1451 cm−1): 1.58 ± 0.16) on six different Sn-Beta zeolites. IMECs measured for IR peaks reflecting pyridine bound to Lewis acidic Hf sites (ε(Hf; 1448 cm−1): 1.54 ± 0.21) and CD3CN bound to open (ε(Hf; 2313 cm−1): 2.40 ± 0.22) and closed (ε(Hf; 2307 cm−1): 3.55 ± 0.41) Hf sites, gave similar counts for the total number of Lewis acidic sites across six Hf-Beta zeolites (Si/Hf = 100–413). Consistent with previous reports with Sn-Beta catalysts where open Sn sites are responsible for catalytic turnover, apparent first and zero-order MPVO rate constants (0.01–1 M cyclohexanone in 2-butanol; per total Hf, 373 K) correlated with the total number of open Hf sites, per total Hf, but not with the total number of closed Hf sites or total Lewis acid site counts. Measured initial MPVO rates (0.1 M cyclohexanone in 2-butanol, per open Hf, 373 K) were ∼ 25x higher on hydrophobic Hf-Beta-F than on hydrophilic Hf-Beta-OH zeolites. Overall, the apparent first-order MPVO rate constants (2-butanol solvent, per open Hf, 373 K) were ∼ 6x higher on Hf-Beta-F than on Hf-Beta-OH zeolites. The characterization methods reported here enable normalization of MPVO turnover rates on Sn- and Hf-Beta zeolites by their number of open sites. This enables performing quantitative rate comparisons across Lewis acid zeolites of varying active site identity, solvation, and pore topology used in liquid-phase catalysis.

A novel UV based advanced oxidation process with electrochemical co-generation of chlorine and H2O2 for carbamazepine abatement: Better performance, lower energy consumption and less DBPs formation

To promote the performance of traditional UV/chlorine and UV/H2O2 processes, the novel UV based advanced oxidation process with electrochemical co-generation of chlorine and H2O2 (UV/E-Cl&H2O2) was for the first time used for degradation of carbamazepine (CBZ), a refractory antiepileptic drug with resistance to photodegradation and microbial degradation. Compared with UV/E-Cl and UV/E-H2O2 processes, the apparent first-order rate constant of CBZ degradation by UV/E-Cl&H2O2 process increased by 3.87 and 5.84 times respectively with a lower energy consumption (1.12 kWh/m3-log). Meanwhile, the disinfection by-products (DBPs) formation by the novel process was 21.4% less than that by UV/E-Cl process. Under the optimal condition of initial pH 7, applied current 600 mA and 15 mM NaCl, the UV/E-Cl&H2O2 process could almost completely eliminate CBZ within 4 min and obtain 57.8% TOC removal in 1 h. The mechanism of UV/E-Cl&H2O2 was investigated through processes comparison, quenching experiments, EPR analysis and determination of OH concentration. The generated radicals (i.e., OH and reactive chlorine species), especially OH, played a major role in CBZ removal. Besides, the possible degradation pathways of CBZ were proposed and the stability of UV/E-Cl&H2O2 process for CBZ removal was certified based on ten consecutive runs. The degradation of typical pollutants (sulfamethazine, rhodamine B, methylene blue, atrazine and phenol) and treatments in three kinds of real wastewater confirmed the wide application feasibility of the novel process. In summary, this study provides a novel efficient and energy-saving process for removing organic pollutants with promising perspectives..

Visible-light-driven photocatalytic degradation of ofloxacin by g-C3N4/NH2-MIL-88B(Fe) heterostructure: Mechanisms, DFT calculation, degradation pathway and toxicity evolution

In this study, g-C3N4/NH2-MIL-88B(Fe) (MCN-x) heterostructures were successfully prepared using a facile solvothermal method. MCN-x composites exhibit excellent degradation performance toward ofloxacin in aqueous solution under visible light (λ > 420 nm). The photodegradation rate of ofloxacin by MCN-60 under visible light reaches 96.5% in 150 min, and the apparent first-order kinetics rate constant reaches 0.0217 min−1, 3.7 and 4.7 times that of pristine g-C3N4 and NH2-MIL-88(Fe), respectively. This decent photocatalytic performance is principally attributed that the introduction of g-C3N4 can notably promote the separation of photogenerated electron-hole pairs. Besides, the photocatalytic efficiency and structure of the MCN-60 composite basically show no change after three reuse cycles. Furthermore, trapping experiments and ESR analyses confirm that the O2– radical has a more dominant role than OH and holes (h+). The ofloxacin degradation mechanism and pathway are predicted by density functional theory (DFT) calculations and an intermediate analysis. Quantitative structure–activity relationship (QSAR) predictions reveal that the ofloxacin photocatalytic degradation process can reduce toxicity in a step-by-step manner. MOF-based materials have been confirmed to show high potential for practical application in removing emerging pollutants from wastewater.

Digestion of Lipid-Based Formulations Not Only Mediates Changes to Absorption of Poorly Soluble Drugs Due to Differences in Solubilization But Also Reflects Changes to Thermodynamic Activity and Permeability.

The aim of this study was to evaluate the effect of lipid digestion on the permeability and absorption of orally administered saquinavir (SQV), a biopharmaceutics classification system (BCS) class IV drug, in different lipid-based formulations. Three LBFs were prepared: a mixed short- and medium-chain lipid-based formulation (SMCF), a medium-chain lipid-based formulation (MCF), and a long-chain lipid-based formulation (LCF). SQV was loaded into these LBFs at 26.7 mg/g. To evaluate the pharmacokinetics of SQV in vivo, drug-loaded formulations were predispersed in purified water at 3% w/w and orally administered to rats. A low dose (0.8 mg/rat) was employed to limit confounding effects on drug solubilization, and consistent with this design, presolubilization of SQV in the LBFs did not increase in vivo exposure compared to a control suspension formulation. The areas under the plasma concentration-time curve were, however, significantly lower after administration of SQV as MCF and LCF compared to SMCF. To evaluate the key mechanisms underpinning absorption, each LBF containing SQV was digested, and the flux of SQV from the digests across a dialysis membrane was evaluated in in vitro permeation experiments. This study revealed that the absorption profiles were driven by the free concentration of SQV and that this varied due to differences in SQV solubilization in the digestion products generated by LBF digestion. The apparent first-order permeation rate constants of SQV (kapp,total) were estimated by dividing the flux of SQV in the dialysis membrane experiments by the concentration of total SQV on the donor side. kapp,total values strongly correlated with in vivo AUC. The data provide one of the first studies of the effect of digestion products on the free concentration of a drug in the GI fluid and oral absorption. This simple permeation model may be a useful tool for the evaluation of the impact of lipid digestion on apparent drug permeability from lipid-based formulations. These effects should be assessed alongside, and in addition to, the more well-known effects of lipids on enhancing intestinal solubilization of poorly water-soluble drugs.

Development of intensified flat-plate packed-bed solar reactors for heterogeneous photocatalysis.

Solar-driven photocatalysis is a promising water-cleaning and energy-producing technology that addresses some of the most urgent engineering problems of the twenty-first century: universal access to potable water, use of renewable energy, and mitigation of CO2 emissions. In this work, we aim at improving the efficiency of solar-driven photocatalysis by studying a novel reactor design based on microfluidic principles using 3D-printable geometries. The printed reactors had a dimensional accuracy of 97%, at a cost of less than $1 per piece. They were packed with 1.0-mm glass and steel beads coated with ZnO synthesised by a sol-gel routine, resulting in a bed with 46.6% void fraction (reaction volume of ca. 840μL and equivalent flow diameter of 580μm) and a specific surface area of 3200m2m-3. Photocatalytic experiments, under sunlight-level UV-A irradiation, showed that reactors packed with steel supports had apparent reaction rates ca. 75% higher than those packed with glass supports for the degradation of an aqueous solution of acetaminophen; however, they were strongly deactivated after the first use suggesting poor fixation. Glass supports showed no measurable deactivation after three consecutive uses. The apparent first-order reaction rate constants were between 1.9 and 9.5 × 10-4s-1, ca. ten times faster than observed for conventional slurry reactors. The mass transfer was shown to be efficient (Sh > 7.7) despite the catalyst being immobilised onto fixed substrates. Finally, the proposed reactor design has the merit of a straightforward scaling out by sizing the irradiation window according to design specifications, as exemplified in the paper.

Stability and Stabilization of Pabialgin (Cibalgin) Liquid Preparation

Shelf-life time was supposed to be determined for active principles of original Pabialgin® (Cibalgin®) drops (allobarbital, aminophenazone) and for its stabilized liquid formulation using accelerated testing at elevated temperatures. The paper chromatography-spectrophotometric selective method was used for the determination of allobarbital and aminophenazone in presence of themselves as well as solubilisates and antioxidants. The semi-logarithmic Arrhenius equation was used to calculate shelf-life times at ambient temperature, from apparent first-order rate constants, determined at elevated temperatures. Since shelf-life times of allobarbital and aminophenazone in original pabialgin® liquid formulation were not satisfactory certain stabilization attempts were undertaken. First of all, water as a solvent was replaced with glycerol to inhibit a hydrolytic pathway of allobarbital degradation, and some antioxidants were introduced to stabilize photo-oxidation processes involved in the degradation of aminophenazone. It resulted in an unusual increase in shelf-life times of the abovementioned active principles. Aminophenazone is now replaced with propyphenazone in the so-called neo pabialgin P, because it can be transformed into a potentially cancerous nitrosamine. However, propyphenazone is also a derivative of 1-phenyl2,3-dimethylpyrazolone-5 similar to aminophenazone. Therefore, it should be also susceptible to oxidative processes and our findings could be used within the framework of pharmaceutical work to stabilize pabialgin P as well. A new stabilization technology of pabialgin has been successfully patented.

Tryptophan Fluorescence and Time-Lag Hydrolysis of Peptide Bonds during Degradation of β-Lactoglobulin by Trypsin

The opening of protein globules and corresponding exposure of their internal peptide bonds, the so-called demasking effect, is required for successful hydrolysis of peptide bonds by proteases. Under the proteolytic action of trypsin on β-lactoglobulin (β-LG), the evolution of tryptophan fluorescence spectra showed that the demasking process consists of two stages with different demasking rate constants for each stage. It was found that the ratio of these constants depends on the concentration of trypsin and changes are approximately threefold when the concentration of trypsin changes in the range of 0.3–15 mg/L. Simulation of hydrolysis taking into account the demasking effect demonstrated how the apparent first-order rate constants obtained experimentally are related to the true hydrolysis rate constants and demasking parameters. The lag phase in the kinetic curves corresponding to the hydrolysis of various peptide bonds in β-LG was also analyzed. The increased lag times indicated sites that are hydrolyzed by a two-stage demasking mechanism.

Facile one-pot green solvent synergized fluorescence reaction for determination of doxorubicin in presence of paclitaxel; co-administered drug, application to stability study and analysis in bulk, vial and biological fluids

A green, fast, simple, economical, ultra-sensitive and accurate spectrofluorimetric method was described in the article for the estimation of Doxorubicin hydrochloride (DOX), a type II topoisomerase enzyme inhibitor either alone and in the presence of co- administered drug; paclitaxel as adjuvant chemotherapy combination in bulk, pharmaceutical dosage form and biological fluids. The proposed method was based on studying the fluorescence demeanor of DOX in different organized media and solvents. The intrinsic fluorescence was found to be greatly enhanced in acidic ethanolic solution. The maximum intensity of fluorescence was observed at 590 nm after excitation at 475 nm. Different experimental parameters were examined and adjusted involving various organized media, solvent, and pH. The methods was validated according to ICH guidelines. The linearity of the method was accomplished in the range of 7 × 10−4–4.0 µg ml−1. The values of LOD and LOQ were 0.2 and 0.6 ng ml−1 respectively. The present method is extremely sensitive enough for determination of traces of the drug in various biological fluids with excellent % recovery. The proposed method was extended to investigate the stability of DOX following various induced degradation protocols including: acidic, alkaline, oxidative and photolytic. In addition, the kinetics of the degradation of DOX was investigated and the apparent first-order rate constant, half-life times and Quantum yield were calculated.

α-Fe2O3/Cu2O heterostructure: Brief characterization and kinetic aspect of degradation of methylene blue

The α-Fe2O3/Cu2O heterostructure (HS) was prepared via the hydrothermal precipitation method and used in the kinetic study of the methylene blue (MB) photodegradation. The samples were subjected to the photoluminescence spectroscopy (PL) to evaluate the e/h recombination rate and the results showed a significant decrease in PL intensity of the heterostructure with respect to the individual semiconductors. The band gap energy of 2.28 eV for the single Fe2O3 semiconductor was red-shifted to 1.95 eV by introducing Cu2O species. EDX analysis of the heterostructure showed 74.36% (65.66% atomic%) Cu and 22.21% (22.32 atomic%) Fe in weight%. The heterostructure showed an increased photocatalytic activity towards MB molecules with respect to the individual systems. The degradation process obeyed the first order Hinshelwood kinetic model and an apparent first-order rate constant of 0.025 min−1 with a t1/2 value of 27 min was obtained. The degradation extent of MB was confirmed by the chemical oxygen demand (COD) method that of results confirmed about 90% of MB molecules can be removed during the photodegradation process in the applied conditions.

A brief study on the kinetic aspect of the photodegradation and mineralization of BiOI-Ag3PO4 towards sodium diclofenac

Bismuth oxyiodide and silver phosphate nanoparticles (NPs) were synthesized in-situ and mechanically mixed to obtain BiOI-Ag3PO4 nano-composite (NC). A body-centered cubic structure of Ag3PO4 and the tetragonal BiOI were detected in the XRD pattern of NC with a crystallite size of 37 nm (obtained by Scherrer equation). The absorption edge wavelengths (λAE) of 571, 665, and 745 nm were respectively obtained for the Ag3PO4, BiOI, and the NC samples, corresponding to the bandgap energies of 2.17, 1.86 and 1.66 eV, respectively. BiOI, Ag3PO4, and the NC catalysts degraded about 37, 48, and 61% of diclofenac (DCF) molecules, respectively. The composites with the Ag3PO4: BiOI mole ratios of 1:4 and 2:1 showed the highest photocatalytic activities, and the apparent first-order rate constants of 0.0187 and 0.0224 min−1, respectively. The photodegradation of DCF molecules showed an apparent rate constant of 0.024 min−1 corresponds to t1/2 value of 28.9 min. The DCF mineralization also showed an apparent rate constant of 0.029 min−1 which corresponds to t1/2 value of 23.9 min obtained by applying the Hinshelwood model on the results obtained by COD results of the photodegraded DCF solutions.