The kinetics and mechanisms of the reactions of chromium(III) with pentane-2,4-dione in aqueous solution

The equilibrium, kinetics and mechanism of the reaction of chromium(III) with pentane-2,4-dione (Hpd) have been investigated in aqueous solution at 55°C and ionic strength 0.5 mol dm⁻³ NaClO₄. The equilibrium constant (log β₁) is 10.08(±0.01) while the pK of Hpd is 8.69(±0.01). The kinetics are consistent with a mechanism in which [Cr(H₂0)₆]³⁺ and [Cr(H₂0)₅(OH)]²⁺ react with the enol tautomer of Hpd with rate constants of 1.05(±0.26) × 10⁻² and 2.78(±0.08) × 10⁻¹ dm³ mol⁻¹ s⁻¹ respectively. These rate constants are considerably more rapid than those predicted by the Eigen-Wilkins mechanism. These data are compared with literature values.     

The palladium(II) promoted hydrolysis of the methyl esters of glycyl-L-leucine,glycyl-L-alanine and L-alanylglycine

The palladium(II)-promoted hydrolysis of the methyl esters of glycyl-L-leucine, glycyl-L-alanine and L-alanylglycine have been studied at 25 °C and I=0.1 M in the pH range 4–5. At a 1:1 metal to ligand ratio the peptide esters act as tridentate ligands, donation occurring via the terminal amino group, the deprotonated amide nitrogen, and the carbonyl group of the ester. Due to the high Lewis acidity of Pd(II) rapid hydrolysis of the ester function by water and hydroxide ion occurs. Rate constants k_OH and k_H2O have been obtained for base hydrolysis and water hydrolysis of the coordinated peptide esters at 25 °C. The rate constants for base hydrolysis are 3.4 X 10⁶ M⁻¹ s⁻¹ (L-alaglyOMe), 6.4 X 10⁶ M⁻¹ s⁻¹ (gly-L-alaOMe) and 2.3 X 10⁷ M⁻¹ s⁻¹ (gly-L-leuOMe). Base hydrolysis of the coordinated peptide esters is at least 10⁶ times that of the free unprotonated ligand. Activation parameters have been obtained for both water and base hydrolysis of the Pd(II) complex of methyl L-alanylglycinate and possible mechanisms for the hydrolyses are considered.     

Enhanced hydrolysis of a phosphonate ester by mono-aquo metal cation complexes

The hydrolysis of the ester 2,4-dinitrophenyl- ethyl methylphosphonate has been examined by both stop-flow spectrophotometric and pH-stat techniques. These reactions have been carried out in the presence of several nucleophiles including simple non-labile (w.r.t. substitution) mono-aquo metal ion complexes. Comparison of reaction rates of the metal complexes with sterically hindered organic nucleophiles has led to the conclusion that the metal ions function predominantly as general base catalysts in dilute aqueous solution. Reaction rates for the various nucleophiles studied are tabulated together with solvolysis constants for hydroxide ion and water at 35 °C and I=0.1 mol dm⁻³ (KNO₃). These later two values are respectively 32.7 mol⁻¹ dm³ s⁻¹ and 1.37 x 10⁻⁴ s⁻¹. A Brönsted β value of 0.52 for the phosphonate ester studied has also been derived.     

Determination of pioglitazone hydrochloride by flow injection chemiluminescence tris(2,2′-bipyridyl)ruthenium(II)–silver(III) complex system

A novel flow injection-chemiluminescence (FI–CL) approach is proposed for the assay of pioglitazone hydrochloride (PG-HCl) based on its enhancing influence on the tris(2,2′-bipyridyl)ruthenium(II)–silver(III) complex (Ru(bipy)₃²⁺-DPA) CL system in sulfuric acid medium. The possible CL reaction mechanism is discussed with CL and ultraviolet (UV) spectra. The optimum experimental conditions were found as: Ru(bipy)₃²⁺, 5.0 × 10⁻⁵ M; sulfuric acid, 1.0 × 10⁻³ M; diperiodatoargentate(III) (DPA), 1.0 × 10⁻⁴ M; potassium hydroxide, 1.0 × 10⁻³ M; flow rate 4.0 ml min⁻¹ for each flow stream and sample loop volume, 180 μl. The CL intensity of PG-HCl was linear in the range of 1.0 × 10⁻³ to 5.0 mg L⁻¹ (R² = 0.9998, n = 10) with limit of detection [LOD, signal-to-noise ratio (S/N) = 3] of 2.2 × 10⁻⁴ mg L⁻¹, limit of quantification (LOQ, S/N = 10) of 6.7 × 10⁻⁴ mg L⁻¹, relative standard deviation (RSD) of 1.0 to 3.3% and sampling rate of 106 h⁻¹. The methodology was satisfactorily used to quantify PG-HCl in pharmaceutical tablets with recoveries ranging from 93.17 to 102.77 and RSD from 1.9 to 2.8%.     

Effect of amino acids present at the carboxyl end of succinimidyl residue on the rate constants for succinimidyl hydrolysis in small peptides

Structural alterations of aspartyl and asparaginyl residues in various proteins can lead to their malfunction, which may result in severe health disorders. The formation and hydrolysis of succinimidyl intermediates are crucial in specific protein modifications. Nonetheless, only few studies investigating the hydrolysis of succinimidyl intermediates have been published. In this study, we established a method to prepare peptides bearing succinimidyl residues using recombinant protein l-isoaspartyl methyltransferase and ultrafiltration units. Using succinimidyl peptides, we examined the effect of amino acid residues on succinimidyl hydrolysis at the carboxyl end of succinimidyl residues and determined the rate constant of hydrolysis for each peptide. The rate constant of succinimidyl hydrolysis in the peptide bearing a Ser residue at the carboxyl side (0.50 ± 0.02 /h) was 3.0 times higher than that for the peptide bearing an Ala residue (0.17 ± 0.01 /h), whereas it was just 1.2 times higher for the peptide bearing a Gly residue (0.20 ± 0.01 /h). The rate constant of succinimidyl formation in the peptide bearing a Ser residue [(2.44 ± 0.11) × 10⁻³ /d] was only 1.2 times higher than that for the peptide bearing an Ala residue ([1.87 ± 0.09) × 10⁻³ /d], whereas 5.5 times higher for the peptide bearing a Gly residue [(10.2 ± 0.2) × 10⁻³ /d]. These results show that the Gly and Ser residues at the carboxyl end of the succinimidyl residue have opposing roles in succinimidyl formation and hydrolysis. Catalysis of Ser residue's hydroxyl group plays a crucial role in succinimidyl hydrolysis.     

The uncatalysed and the copper(II) promoted hydrolysis of 4-nitrophenyl L-leucinate

The uncatalysed hydrolysis of 4-nitrophenyl L-leucinate has been studied in detail over a range of pH and temperature at I=0.1 M (KNO₃). Base hydrolysis of the ester is strongly promoted by copper(II) ions. Rate constants have been obtained for the following reactions (where EH⁺ is the N- protonated ester and E is the free base form) EH⁺ + OH⁻ → products E + OH⁻ → products E + H₂O → products CuE²⁺ + OH⁻ → products Base hydrolysis of the copper(II) complex CuE²⁺ is 3.8 × 10⁵ times faster than that of E and 75 times faster than that of EH⁺ at 25 °C and I=0.1 M. Activation parameters for these reactions have been determined and possible mechanisms are considered.     

Studies on the reactions of PtCl2en,cis-Pt(NH3)2Cl2 and their aqua species with adenosine,deoxyadenosine and adenine using ion-pair HPLC

The reactions of PtCl₂en or cis-Pt(NH₃)₂Cl₂ and their aqua species with adenine and adenosine were studied by means of ion-pair HPLC. From the chromatograms, it was found that the first binding site of Pt(II) was the N(7) site of adenine under both acidic and neutral conditions. The rates of Pt(II) binding at the (N7) site of adenosine and deoxyadenosine were measured. The rate constants, k₁, were obtained for the reactions of PtCl₂en or cis-Pt(NH₃)₂Cl₂ with adenosine and deoxyadenosine at pH 3 and 7 over the temperature range 9–25 °C. The k₁ values were 6.8–7.7 × 10⁻⁴ dm³ mol⁻¹ s⁻¹ at 25 °C. For the aqua species, the rate of [cis-Pt(NH₃)₂ClH₂O]⁺ with adenosine N(7) was measured. The rate constants, k₂ which were found to be smaller than those of hydrolysis, k_h, were calculated at pH 3 over the temperature range 25–40 °C. The k₂ value obtained at 25 °C was 1.1 × 10⁻² dm³ mol⁻¹ s⁻¹, 15 time larger than k¹. The activation parameters were also calculated.     

The synthesis and hydrolysis of a series of deoxyfluoro-d-glucopyranosyl phosphates

The synthesis of all four deoxyfluoro-α-d-glucopyranosyl phosphates is described. Rate constants for their acid-catalyzed hydrolysis were determined, and fluorine substitution was shown to have a significant effect in lowering the rate, particularly when the substitution is adjacent to the anomeric center. Relative rate-constants measured in m HClO₄ at 25° are 60.30:1.00:7.05:3.97:16.5 for α-d-glucopyranosyl phosphate and the 2-, 3-, 4- and 6-deoxyfluoro derivatives, respectively. The hydrolysis of 2-deoxy-2-fluoro-α-d-glucopyranosyl phosphate was studied in more detail, and an activation entropy and enthalpy of 4.1 e.u. (m reactant) and 113.5 kJ.mol⁻¹, respectively, were determined for hydrolysis in m HClO₄ at 60° The pH dependence of its hydrolysis was investigated, and rate constants for hydrolysis of the monoanion (k_M = 1.88 × 10⁻⁶ s⁻¹) and neutral (k_N = 6.23 × 10⁻⁵ s⁻¹) species were thus extracted. Hydrolysis of the monoanion is not significantly affected by fluorine substitution, as expected. The ability or inability of several mechanistically distinct enzymes to utilize these fluorinated substrates is rationalized in the light of these findings.     

Transition state stabilization by deaminases: Rates of nonenzymatic hydrolysis of adenosine and cytidine

Nonenzymatic rates of hydrolytic deamination of adenosine and cytidine by acids and bases analogous to side chains of naturally occurring amino acids are compared with the rates of uncatalyzed deamination in water and with the rates of the hydroxide- and hydrogen ion-catalyzed reactions. For adenosine, hydroxide ion is an effective catalyst, with a second-order rate constant of 7.5 × 10⁻⁶ m⁻¹ s⁻¹ at 85°C and an energy of activation of 19.9 kcal/mol. Acid-catalyzed deamination of adenine proceeds with a second-order rate constant of 1.5 × 10⁻⁶ m⁻¹ s⁻¹ at 85°C. At concentrations of 1 m and at pH values corresponding to their respective pK_a values, dimethylamine, acetate, selenide, imidazole, phosphate, and zinc(II) do not enhance the rate of deamination of adenosine beyond that observed in water, and 2-mercaptoethanol produces only a modest rate enhancement. The uncatalyzed rate of adenosine deamination in water is 8.6 × 10⁻⁹ s⁻¹ at 85°C: extrapolation to 37°C and comparison with k_cat for rat hepatoma adenosine deaminase yield a rate enhancement by the enzyme of approximately 2 × 10¹²-fold. 1,6-Dimethyladenosine, the conjugate acid of which has a pK_a value much higher than that of adenosine, is not readily deaminated, suggesting that the uncatalyzed deamination of adenosine does not proceed by hydroxide ion attack on the rare protonated form of adenosine, but rather by attack on the neutral species. Deamination of cytidine is catalyzed most effectively by hydroxide ion, with a second-order rate constant of 4.5 × 10⁻⁴ m⁻¹ s⁻¹ at 85°C and an energy of activation of 28.5 kcal/mol. The uncatalyzed rate of deamination of cytidine in water, which also exhibits an energy of activation of 28.5 kcal/mol, is 8.8 × 10⁻⁸ s⁻¹ at 85°C. Comparison of the rate extrapolated to 25°C with k_cat for bacterial cytidine deaminase gives a rate enhancement for the enzyme of 4 × 10¹¹-fold. The C-5 proton of the pyrimidine ring of cytidine does not exchange with solvent during alkaline hydrolysis, suggesting that deamination under these conditions does not involve prior addition of water across the 5,6 double bond.     

Na+ uptake and extrusion in the cyanobacterium SynechocystisPCC6714 in response to hypersaline treatment. Evidence for transient changes in plasmalemma Na+ permeability

The kinetics of uptake and loss of Na⁺ have been studied using radioisotopic tracer techniques in cells of the cyanobacterium Synechocystis PCC6714 exposed to hyperosmotic stress. Cells transferred from a fresh-water-based medium to NaCl at 300–1000 mmol·dm⁻³ showed net Na⁺ uptake during the first 2 min following transfer, with the intracellular Na⁺ level at 2 min increasing as a direct function of the external NaCl concentration. Further incubation of cells in low-level hypersaline media (350–500 mmol · dm⁻³ NaCl) led to a marked reduction in cell Na⁺ within 20 min, indicating an efficient active Na⁺ extrusion system. In contrast, cells maintained in more extreme hypersaline media showed little (750 mmol · dm⁻³ NaCl) or no (1000 mmol · dm⁻³ NaCl) net Na⁺ extrusion following upshock. Cells grown in a saline medium (with NaCl at 500 mmol · dm⁻³ showed a greatly reduced net Na⁺ uptake after 2 min in media containing higher levels of NaCl. However, net Na⁺ uptake was also observed when these cells were downshocked to media containing 50–200 mmol · dm⁻³ NaCl. This is the first demonstration of downshock-induced Na⁺ accumulation in a microbial cell. Time-courses for Na⁺ extrusion in cells downshocked from 500 mmol · dm⁻³ to 100 mmol · dm⁻³ NaCl were similar to those for cells upshocked from freshwater to 500 mmol · dm⁻³ NaCl, requiring approximately 30 min to reach their lowest values. Net Na⁺ extrusion in upshocked cells was found to be markedly sensitive to the external K⁺ concentration, with limited net Na⁺ extrusion in the absence of external K⁺ and maximal reductions in cell Na⁺ in media containing K⁺ at 1–10 mmol · dm⁻³. Temperature was also shown to affect uptake and loss of cell Na⁺ during upshock: cells maintained at 5°C showed no capacity for net Na⁺ extrusion, while higher temperatures (up to 35°C) led to a progressive reduction in the amount of cell Na⁺ at 2 min following upshock and also in the rate of net Na⁺ extrusion after this time.     

Action of a juvenile hormone analogue on the activity of Periplaneta americana corpora allata in vitro and on juvenile hormone III levels in vivo

The effects of the juvenile hormone (JH) analogue fenoxycarb (ethyl[2-(4-phenoxyphenoxy)-ethyl]carbamate) on the activity of corpora allata (CA) from adult female Periplaneta americana have been investigated. The in vitro biosynthesis of JH III by isolated CA was inhibited by about 85% in the presence of a high concentration (1 × 10⁻⁴ M) of fenoxycarb. However, at lower concentrations (1 × 10⁻⁶ M and 1 × 10⁻⁸ M) no inhibition of JH biosynthesis was apparent. Topical treatment of adult female cockroaches with fenoxycarb (100 μg/insect) did not reduce the subsequent rate of JH III biosynthesis by CA in vitro. By contrast, the same treatment markedly reduced the titre of endogenous JH III in intact cockroaches. These results suggest that CA activity in adult female P. americana may be controlled by negative feedback, and that this system of control is dependent on the maintenance of contact between the CA and nervous or humoral factors in the intact insect. Alternatively, it is possible that treatment with fenoxycarb increases the rate at which endogenous JH is metabolized.     

Exploitation of micellar medium for photochemical-spectrofluorimetric flow-injection determination of fenvalerate

A photochemical flow-injection methodology for the fluorimetric determination of fenvalerate, a nonfluorescent pyrethroid pesticide, is proposed. The sample was irradiated by ultraviolet light inside a reaction coil in a nonstop mode and the photodegradation products were monitored by spectrofluorimetry at λ_exc=277 nm, λ_em=329 nm. The exploitation of a micellar medium resulted in a pronounced fluorescence enhancement with a concomitant tenfold sensitivity improvement. Several surfactants were evaluated, and best results were obtained with sodium dodecylsulphate (SDS). The calibration plot was linear within 2.0×10⁻⁶ and 1.0×10⁻⁵ mol l⁻¹ fenvalerate. The proposed system is very stable, handles 30 samples h⁻¹ and requires only 60 μmol SDS per determination. The detection limit is 5×10⁻⁷ mol l⁻¹. The method was evaluated in the determination of fenvalerate in tap water.     

A re-investigation of the reactions between superoxide anion and metal picolinate complexes

Rate constants for the reactions of superoxide with the α-picolinate ion and its complexes with copper(II), iron(III) and zinc(II), and for the reaction of α-picolinate with the hydrated electron, were measured using pulse radiolysis. The rate constant for the reaction of superoxide with copper(II)picolinate at pH 9 [(4.1 ± 0.4) × 10⁷l mol⁻¹ s⁻¹] was an order of magnitude higher than that determined previously (W. H. Bannister, J. V. Bannister, A. J. F. Searle and P. J. Thornally, Inorg. Chim. Acta, 78, 139 (1983)) using a less direct competitive inhibition method. The corresponding rate constant for iron(III)picolinate [(7.5 ± 1.5) X 10³ l mol⁻¹ s⁻] was an order of magnitude lower than a previous pulse radiolysis determination (same reference as above). We are not able to reconcile these two values for iron(III)picolinate, although a possible source of spuriously high results is contamination with the kinetically active copper(II) complex. The likely roles of iron(III)picolinate and other low molecular weight iron complexes as potential catalysts of an in vivo superoxide-driven Fenton reaction are discussed in the light of present measurements.     

Surface mediated death of unconditioned Tetrahymena cells: Effect of physical parameters,growth factors,hormones, and surfactants

A new form of cell death has been observed. The death occurs at liquid-air interfaces when Tetrahymena cells are grown in a chemically defined medium (CDM) at low inocula. The cells die by lysis at the liquid-air interface (medium surface), which they reach due to negative gravitaxis as well as positive aerotaxis. When the cells are grown in a closed compartment, with no liquid-air interface, the death is not observed, and the cells proliferate. Cloning of cells in CDM is thus possible. The addition of effectors such as NGF (10⁻¹¹ M), EGF (10⁻¹⁰ M), PDGF (10⁻¹⁰ M), and insulin (10⁻¹⁰ M) to cells in CDM prevents the surface mediated death. Since detergents/surfactants like SDS (7 × 10⁻⁵ M), NP-40 (2 × 10⁻⁵ M), Tween 80 (10⁻⁴% w/v), Pluronic F-68 (10⁻⁷ M), and the biosurfactant surfactin (10⁻⁶ M) have the same effect, we suggest that the effectors act by stimulating the cells to exudate surfactant(s) of their own. Furthermore, lyzed cells and exudates from living cells (pre-conditioned medium) prevent the death. In conditions with liquid-air interfaces, certain physical parameters are of great importance for the survival of cells at low inocula. The parameters are the distance to the surface, the temperature, and the inoculum. By increasing the height of the medium, lowering the temperature, and increasing the inoculum of the culture, the survival can be greatly enhanced. There is no evidence for programmed cell death (PCD) or apoptosis. © 1996 Wiley-Liss, Inc.     

Gold nanoparticles‐based fluorescence enhancement of the terbium–levofloxacin system and its application in pharmaceutical preparations

A sensitive fluorescence (FL) technique is proposed for the determination of levofloxacin (LVX). The method is based on the fact that the weak FL signal of the Tb(III)–LVX system is strongly enhanced in the presence of gold nanoparticles. Gold nanoparticles were prepared by the citrate reduction of HAuCl₄ and characterized by transmission electron microscopy (TEM). Levofloxacin and Tb(III) ion form a fluorescence complex in aqueous solution, and its maximum emission wavelength was found at 545 nm. Optimal conditions for the formation of the levofloxacin–Tb(III) complexes were studied. Levofloxacin was detected by measuring the FL intensity, which increases linearly with the concentration of LVX in the range 6.2 × 10⁻¹⁰–2.6 × 10⁻⁸ mol/L. Recovery of the target analytes was > 96% with good quality parameters: linearity (r² > 0.996), limit of detection (LOD) and limit of quantification (LOQ) values 2.1 × 10⁻¹⁰ mol/L and 7.2 × 10⁻¹⁰ mol/L, and run‐to‐run and day‐to‐day precisions with relative standard deviations (RSDs) around 3%. Thus, the proposed method can be successfully applied to the routine determination of levofloxacin in pharmaceutical preparations. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis,characterization and DNA-binding properties of novel dipyridophenazine complex of ruthenium (II) : [Ru(IP)2(DPPZ)]2+

A novel ruthenium(II) complex of dipyridophenazine (DPPZ) with the ancillary ligand imidazole[4,5-f] [1,10]phenanthroline (IP), [Ru(IP)₂(DPPZ)] (PF₆)₂, has been synthesized and characterized by elemental analysis, 1D and 2D ¹H NMR, fast-atom bombardment mass spectra (FABMS), electronic spectroscopy and cyclic voltammetry. The DNA-binding properties of the complex were studied by spectroscopic methods. The intrinsic binding constant, K =2.1 × 10⁷M⁻¹, of the complex to calf thymus DNA has been determined by absorption titration in 5 mmol dm⁻³ Tris-HCl, 50 mmol dm⁻³ NaCl buffer (pH 7.0). The excited state lifetimes and luminescence quenching with [Fe(CN)₆]⁴⁻ as the quencher in the presence of DNA were also tested and mono-exponentiality was observed for the emission decay curves. Viscosity measurements together with the optical titrations unambiguously proved that the complex bound with DNA intercalatively and that the binding affinity to DNA was several times larger than that of the parent complex [Ru(bpy)₂(DPPZ)]²⁺.     

Comparative nuclear magnetic resonance studies of diffusional water permeability of red blood cells from different species. V—Rabbit (Oryctolagus Cuniculus)

• 1.1. The diffusional water permeability (P_d) of rabbit red blood cell (RBC) membrane has been monitored by a doping nuclear magnetic resonance (NMR) technique on control cells and following inhibition with p-chloromercuribenzene sulfonate (PCMBS).
• 2.2. The values of P_d were around 6.3 × 10⁻³ cm/sec at 15°C, 7.0 × 10⁻³cm/sec at 20°C, 8.0 × 10⁻³ cm/sec at 25°C, 9.1 × 10⁻³ cm/sec at 30°C and10.7 × 10⁻³ cm/sec at 37°C.
• 3.3. Systematic studies on the effects of PCMBS on water diffusion indicated that the maximal inhibition was reached in 15 min at 37°C with 0.5 mM PCMBS.
• 4.4. The values of maximal inhibition were around 71–74% at all temperatures.
• 5.5. The basal permeability to water was estimated as 1.6 × 10⁻³cm/sec at 15°C, 2.0 × 10⁻³cm/sec at 20°C, 2.4 × 10⁻³cm/sec at 25°C, 2.6 × 10⁻³cm/sec at 30°C, and 3.1× 10^{−3 cm/secat 37°C}.
• 6.6. The activation energy of water diffusion was around 18 kJ/mol and increased to 27 kcal/mol after incubation with PCMBS in conditions of maximal inhibition of water diffusion.
• 7.7. The membrane polypeptide electrophoretic pattern of rabbit RBCs has been compared with its human counterpart.
• 8.8. The rabbit membrane contained a higher amount of spectrin (bands 1 and 2), while the band 6 (glyceraldehyde-3-phosphate dehydrogenase) was markedly less intense.
• 9.9. Considerable differences in the electrophoretic patterns of the two sources of RBC membranes appeared in the bands migrating in the band 4.5 region and in front of band 7, where some polypeptides were apparent in higher amounts in the rabbit RBC membrane.

     

Synthesis and characterization of triaminecobalt(III) complexes and acid hydrolysis kinetics of fac-[Codpt(H2O)nX3−n]n+ (X = Cl,Br; n = 0,1,2)

The complexes CodptX₃ and [Codpt(H₂O)X₂]ClO₄ (X = Cl, Br; dpt = dipropylenetriamine = NH(CH₂CH₂CH₂NH₂)₂) have been prepared and characterized. Rate constants (s⁻¹) for aqueous solution at 25 °C and μ = 0.5 M (NaClO₄), for the acid-independent sequential ractions.

have been measured spectrophotometrically. For X = Cl: k₁ ⋍ 2 × 10⁻², k₂ = 1.7 × 10⁻⁴ and k₃ = 4.8 × 10⁻⁶, and for X = Br: k₁ ⋍ 2 × 10⁻², k₂ = 5.25 × 10⁻⁴ and k₃ = 2.5 × 10⁻⁵ The primary equation was found to be acid independent, while the secondary and tertiary aquations were acid-inhibited reactions. For the second step, the rate of the reaction was given by the rate equation

where C_t is the complex concentration in the aqua-and hydroxodihalo species, k′₂ is the rate constant for the acid-dependent pathway and K_a is the equilibrium constant between the hydroxo and aqua complex ions. The activation parameters were evaluated, for X = Cl: ΔH^≠₂ = 106.3 ± 0.4 kJ mol⁻¹ and ΔS^≠₂ = 40.2 ± 1.7 J K⁻¹ mol⁻, and for X = Br: ΔH^≠₂ = 91.6 ± 0.4 kJ mol⁻¹ and ΔS^≠₂ = 0.4 ± 1.7 J K⁻¹ mol⁻¹. The results are discussed and detailed comparisons of the reactivities of these complexes with other haloaminecobalt(III) species are presented.     

FeS2 nanosheets–luminol–O2 chemiluminescence method for determination of venlafaxine hydrochloride,imipramine hydrochloride,and cefazolin sodium

This study introduces a novel chemiluminescence (CL) approach utilizing FeS₂ nanosheets (NSs) catalyzed luminol–O₂ CL reaction for the measurement of three pharmaceuticals, namely venlafaxine hydrochloride (VFX), imipramine hydrochloride (IPM), and cefazolin sodium (CEF). The CL method involved the phenomenon of quenching induced by the pharmaceuticals in the CL reaction. To achieve the most quenching efficacy of the pharmaceuticals in the CL reaction, the concentrations of reactants comprising luminol, NaOH, and FeS₂ NSs were optimized accordingly. The calibration curves demonstrated exceptional linearity within the concentration range spanning from 4.00 × 10⁻⁷ to 1.00 × 10⁻³ mol L⁻¹, 1.00 × 10⁻⁷ to 1.00 × 10⁻⁴ mol L⁻¹, and 4.00 × 10⁻⁶ to 2.00 × 10⁻⁴ mol L⁻¹ with detection limits (3σ) of 3.54 × 10⁻⁷, 1.08 × 10⁻⁸, and 2.63 × 10⁻⁶ mol L⁻¹ for VFX, IPM, and CEF, respectively. This study synthesized FeS₂ NSs using a facile hydrothermal approach, and then the synthesized FeS₂ NSs were subjected to a comprehensive characterization using a range of spectroscopic methods. The proposed CL method was effective in measuring the aforementioned pharmaceuticals in pharmaceutical formulations as well as different water samples. The mechanism of the CL system has been elucidated.     

Remediation of Explosive-Contaminated Soils: Alkaline Hydrolysis and Subcritical Water Degradation

Alkaline hydrolysis and subcritical water degradation were investigated as ex-situ remediation processes to treat explosive-contaminated soils from military training sites in South Korea. The addition of NaOH solution to the contaminated soils resulted in rapid degradation of the explosives. The degradation of explosives via alkaline hydrolysis was greatly enhanced at pH ≥12. Estimated pseudo-first-order rate constants for the alkaline hydrolysis of 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated soil at pH 13 were (9.6?±?0.1)×10^?2, (2.2?±?0.1)×10^?1, and (1.7?±?0.2)×10^?2 min^?1, respectively. In the case of subcritical water degradation, the three explosives were completely removed at 200–300°C due to oxidation at high temperatures and pressures. The degradation rate increased as temperature increased. The pseudo-first-order rate constants for DNT, TNT, and RDX at 300°C were (9.4?±?0.8)×10^?2, (22.8?±?0.3)×10^?2, and (16.4?±?1.0)×10^?2, respectively. When the soil-to-water ratio was more than 1:5, the extent of alkaline hydrolysis and subcritical water degradation was significantly inhibited.