Activation Parameters ΔH Research Articles

Moderation of the Electronic Structure of Phosphamides to Execute the Catalytic Appel Reaction Bypassing Phosphine.

A set of structurally analogous, albeit electronically distinct, phosphamides (1aa-10aa) is prepared, and the effect of the electronic amendment due to p-substitution has been tested for the conversion of alcohols to halides via the Appel reaction. The -OMe-substituted diphosphamide (8aa) remains the most active, providing ∼96% conversion of alcohols to halides with a TON of 11 in moderate reaction conditions with a large substrate scope. Halide formation follows a pseudo-first-order rate with a constant rate (kobs) of 7.13 × 10-5 s-1. Temp-dependent kinetics and Eyring analyses reveal the activation parameters ΔH‡ of 28.95 (±1.6) kcal mol-1, ΔS‡ of -70.02 (±0.4) cal K-1 mol-1, and ΔG‡298 of 49.81 (±1.2) kcal mol-1. The deuterium labeling study highlights the O-H dissociation of the alcohol as the rate-determining step, while the Hammett analysis with p-substituted benzyl alcohols indicates a positive charge accumulation at the phosphorus center during the Appel reaction. The HOMO-LUMO energy and NPA analyses show that p-OMe substitutions in 8aa make the "P═O" bond more ionic and corresponding aminophosphine is nucleophilic, which are favorable for the Appel reaction. In situ detection of the Appel salt, [R3PX]CX3 and alkoxy phosphonium cation [R3POR]X, validates the reaction pathway mediated by the phosphamides.

Pt–Ni–Co trimetallic nanoparticles anchored on graphene oxide: An effective catalyst for ammonia-borane hydrolysis and direct electrooxidation of ammonia-borane in alkaline solution

In this study, graphene oxide supported platin, nickel and cobalt trimetallic nanoparticles (PtNiCo@GO) were prepared by the impregnation/reduction method. The catalytic performances of PtNiCo@GO catalysts prepared with different atomic ratios were investigated for hydrogen production and electro-oxidation of ammonia-borane (AB). For hydrolysis of ammonia-borane, Pt0.8Ni0.1Co0.1@GO catalyst exhibited higher catalytic activity than Pt0.6Ni0.2Co0.2@GO, Pt0.4Ni0.3Co0.3@GO, and Pt0.2Ni0.4Co0.4@GO. The hydrogen generation rate and turnover frequency values were found to be 540 mL min−1g−1 and 42.8 min−1, respectively, in the experiment conducted at 35 °C, 0.5 mmol AB, and 50 mg Pt0.8Ni0.1Co0.1@GO catalyst. The activation parameters (Ea, ΔH#, and ΔS#) in the catalytic hydrolysis of AB were obtained at 42.22 kJ/mol, 31.95 kJ/mol and −114.82 J/(mol × K), respectively. The effects of the PtNiCo@GO catalyst on AB electro-oxidation were made at a scanning rate of 100 mV/s in the potential range of - 1V/+1V against Ag/AgCl, and chronoamperometry measurements were made at constant potentials of - 0.2V, 0.1V and 0.4V. For cyclic voltammetry and chronoamperometry measurements, 5 mM [Fe(CN)6]3/4 (1 M KCl) redox probe and 1 M NaOH + 50 mM AB solution were used.

Redox reaction of a RuIII(pic)3 complex with cysteine: Spectral, kinetic and biological studies

The kinetics of the reduction of [RuIII(pic)3] (pic− = picolinate) with cysteine leading to the formation of the corresponding red coloured [RuII(pic)3]− complex (λmax = 466 nm, εmax = 12000 M−1 cm−1) was studied by using stopped-flow and rapid scan spectrophotometry. The time course of the reaction was followed at 466 nm as a function of cysteine concentration, pH and temperature. Kinetic data (k = 291 ± 4 M−1 s−1 at 25 °C and pH 8.4) and activation parameters (ΔH≠ = 36 ± 1 kJ mol−1 and ΔS≠ = −78 ± 3 J mol−1 deg−1) are interpreted in terms of a mechanism involving rate-determining outer-sphere electron transfer between Ru(III) and the cysteine. Inhibition of bacterial growth (Klebsiella pneumonia and Staphylococcus aureus) by the [RuIII(pic)3] complex both in absence and presence of cysteine has been examined, and the results show a positive effect of cysteine addition on the anti-bacterial activity of the complex for S.aureus.

Co(II)-N4 Catalysts for the Coupling of CO2 with Epoxides into Cyclic Carbonates: Catalytic Activity, Computational and Kinetic Studies.

In this study, we synthesized and characterized a series of cobalt(II) complexes bearing linear tetradentate N4 ligands. These Co(II)-N4 complexes proved to be efficient catalysts for the cycloaddition reaction between carbon dioxide and epoxides even at room temperature and 1 bar pressure of carbon dioxide without the need for solvents or cocatalysts. Furthermore, when combined with (triphenylphosphoranylidene)ammonium chloride (PPNCl) as a cocatalyst, the Co-N4 catalysts exhibited an impressive turnover frequency of up to 41,000 h-1 for coupling of epichlorohydrin/CO2. These Co(II)-N4 catalysts were found to have excellent stability and reusability, retaining their catalytic activity after they were recycled seven times. Density functional theory (DFT) calculations provided a comprehensive mechanism for the cycloaddition reaction, indicating that the rate-determining step is the epoxide ring opening, in both the presence and absence of PPNCl. Further kinetic studies allow us to determine the activation parameters (ΔH‡, ΔS‡, and ΔG‡ at 25 °C) of the coupling reaction using the Eyring equation. The Gibbs free activation energy obtained from the kinetic studies was in close agreement with that of the DFT calculations. The substituent effect on the cycloaddition reaction of CO2 with various substituted styrene oxides was also examined for the first time.

Enzyme mimicking activity of the Ru(pic)3 complex in the oxidation NADH coenzymes: kinetic and mechanistic studies

Mimicking the enzymatic oxidation of NADH and obtaining mechanistic insight into the electron transfer reaction pertinent to the redox inter-conversion of NADH/NAD+ couple is a long-term challenge in biological and energy-related chemistry. The kinetics and mechanism of the oxidation of NADH by [RuIII(pic)3] (pic– = picolinate anion) has been studied spectrophotometrically and kinetically in aqueous solution at pH 7.0 (MES buffer). The reaction was followed over time at 466 nm (metal to ligand charge transfer band of [RuII(pic)3]–). The rate of NADH oxidation was found to be first-order with respect to Ru(III)-complex concentration. The values of the observed rate constant (k obs) increased linearly with increase in the concentration of NADH. The rate of the reaction was independent of the ionic strength of the reacting solution. Activation parameters (ΔH≠ = 56 ± 1 kJ mol−1 and ΔS≠ = −65 ± 3 J.deg−1 mol−1) were determined from the temperature dependence studies (15-35 °C) of the reaction. Kinetic data and activation parameters are interpreted in terms of a mechanism involving outer-sphere electron transfer.

Kinetic studies on the persulfate oxidation of methylene blue in the absence and presence of silver(I) as a catalyst in aqueous and micellar media

AbstractThe kinetics and mechanism of the oxidative decolorization of methylene blue (MB+) as a cationic dye by persulfate using silver(I) catalyst in aqueous acidic medium were studied. The effects of different parameters like [H+], [Ag+], reactant concentration, micelles, and temperatures were investigated. The kinetic data showed that the oxidative decolorization of [MB]+ by persulfate obeyed pseudo‐first‐order kinetics by taking a large excess of [S2O82−] over [MB+]. The observed rate constant increases with increasing of [H+]. A plausible mechanism for the silver(I) enhanced decolorization of [MB]+ by persulfate is suggested which is consistent with the experimental rate law. The effect of micelles such as SDS and Triton X‐100 on the reaction rate is investigated. The rate of reaction decreases with increasing [SDS] but is not affected by Triton X‐100. The mechanism of the electron transfer process between [MB]+ and S2O82– proceeds through an outer‐sphere mechanism. Thermodynamic activation parameters ΔH* and ΔS* were calculated. The experimental data may be useful for the layout of wastewater treatment containing various types of dyes.

Bioactivity, molecular docking and anticancer behavior of pyrrolidine based Pt(II) complexes: Their kinetics, DNA and BSA binding study by spectroscopic methods

The complex [Pt(AEP)Cl2]; C-1 (where, AEP = 1-(2-Aminoethyl) pyrrolidine) and its hydrolyzed diaqua form cis-[Pt(AEP)(H2O)2]2+; C-2 were synthesized for their bioactivity and in vitro kinetic study with bioactive thiol group (-SH) containing ligands (like; L- cysteine and N-ac-L- cysteine) for their biological importance for 'drug reservoir' activity. The Thermal Gravimetric Analysis (TGA) was executed to confirm about the weight loss due to coordinated water molecules at high temperature range. At pH 4.0, the substitution behavior of C-2 with the thiols was studied in pseudo-first order reaction condition. The interaction mechanism of thiols with complex C-2 to their corresponding thiol substituted C-3 [Pt(AEP)(L-cys)] and C-4 [Pt(AEP)(N-ac-L-cys)] (where L-cys = L-cysteine and N-ac-L-cys = N-ac-L- cysteine) were proposed from their thermodynamical activation parameters (ΔH≠ and ΔS≠), which were obtained from Eyring equation. DNA and BSA binding activity of the complexes C-1 to C-4 were investigated by gel electrophoresis technique, spectroscopic titration and viscosity methods. The binding activity of the complexes with DNA and BSA was evaluated using a theoretical approach molecular docking study. The drug-like nature of the complexes is supported by the prediction of activity spectra for substance (PASS) from 2D structure of the Pt(II) complexes. Structural optimization, HOMO-LUMO energy calculation, Molecular electrostatic potential surface, NBO and TD-DFT calculation were executed by using density functional theory (DFT) with Gaussian 09 software package to pre-assessment of biological activity of the complexes. DFT-based descriptors were determined from the HOMO-LUMA energy to be related with the ability of binding affinity of Pt(II) complexes towards DNA and BSA to the formation of their corresponding adducts. The anticancer property of the design complexes were examined on HCT116 (colorectal carcinoma) cancer cell lines and as well as human normal cell NKE (Normal Kidney Epithelial) and compared with the recognised anticancer drug cisplatin. The Reactive Oxygen Species (ROS) production was assessed by DCFDA assay in presence of the Pt(II) complexes.

Pumice-Supported Ruthenium nanoparticles as highly effective and recyclable catalyst in the hydrolysis of methylamine borane

Pumice-supported Ruthenium nanoparticles were prepared by the impregnation-reduction method and investigated for hydrogen production in the methylamine borane (MeAB) hydrolysis reaction. The catalytic properties of this highly active Ru/Pumice catalyst were analyzed in terms of temperature (from 298 K to 328 K), substrate ([MeAB]) amount, metal loadings ([Ru]), and recyclability. In addition, the characterization of the obtained catalyst was investigated by inductively-coupled plasma optical emission spectroscopy (ICP-OES), powder X-ray diffraction (P-XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) imaging/spectroscopic techniques. The Ru/Pumice catalyst showed a superior initial TOF value (83.15 min−1 or 4989.30 h−1) in the MeAB hydrolysis reaction, and also the activation parameters (Ea, ΔH#, and ΔS#) from the Arrhenius and Eyring-Polonyi equations were found to be 42.4 kJ/mol, 39.8 kJ/mol, and −110.07 J/mol.K, respectively.

Effect of the dried limes (Citrus aurantifolia) on the caffeine kinetic extraction in black tea leaves (kinetic and thermodynamic study)

ABSTRACT. The kinetic and thermodynamic parameters were studied for the extraction of caffeine in black tea leaves and tea leaves containing antioxidant dried limes (Citrus aurantifolia). Caffeine is widely used in human consumption and is present in any liquid suitable for drinking except water. However, the health and environmental demerits make it significant to reduce caffeine to much less concentration or decaffeination. Therefore, the effect of the dried antioxidant Citrus aurantifolia on caffeine concentration followed by pseudo-first-order reaction, kinetic parameters (pseudo-first-order rate constant (k), equilibrium absorbance (A∞)), and thermodynamic activation parameters, the activation energy (Ea), change in enthalpy of activation (ΔH#), the change in entropy of activation (ΔS#) and change in activation Gibbs free energy (ΔG#) was calculated at four different temperatures 30, 60, 80, and 100 °C. Using the spectroscopic method the activation energy of the caffeine concentration in free black tea leaves solution (Ea = 13.32 kJmol-1) was higher than the black tea leaves mixed with lime solution (Ea = 9.89 kJmol-1), the higher collision of molecules A-factor (1.96 min-1), and large correlation factor (R2 = 0.95). The thermodynamic activation parameters ΔH#, ΔS#, and ΔG# demonstrate less heat absorption, irreversible, and more spontaneous interaction of lime with caffeine.
 
 KEY WORDS: Caffeine, Tea leaves, Citrus aurantifolia, Thermodynamic parameters, Kinetic
 Bull. Chem. Soc. Ethiop. 2022, 36(3), 697-705. 
 DOI: https://dx.doi.org/10.4314/bcse.v36i3.18

Corrosion inhibitor of carbon steel in 3.5%NaCl solution with Schiff base compounds

In this work, synthesized N4,N4`-bis(2, 3, 4 nitro benzylidene) biphenyi-4-4`-diamine(B1-B3) , was tested as an inhibitors in controlling the corrosion of carbon steel in NaCl 3.5% solution by using open circuit potential (OCP),at four different temperatures (293, 303, 313 and 323 K). Furthermore, the surface morphology was investigated using the Atomic force microscopy (AFM). The effect of using different Schiff bases and temperature was also investigated. Schiff bases was synthesized and characterized via using. Fourier Transform Infrared Spectroscopy (FT-IR)and Atomic Force Microscope (AFM) characterized . The experimental results shown that Schiff bases can consider as an excellent corrosion inhibitors for carbon steel in NaCl 3.5% solution, by presence of Schiff bases the corrosion of carbon steel was significantly suppressed. The inhibition efficiency is decreased with the increases of temperature. Kinetic and thermodynamic activation parameters (Ea, A, ΔH*, ΔS* and ΔG*) were calculated.

Characterization of the glutathione-dependent reduction of the peroxiredoxin 5 homolog PfAOP from Plasmodium falciparum.

Peroxiredoxins use a variety of thiols to rapidly reduce hydroperoxides and peroxynitrite. While the oxidation kinetics of peroxiredoxins have been studied in great detail, enzyme‐specific differences regarding peroxiredoxin reduction and the overall rate‐limiting step under physiological conditions often remain to be deciphered. The 1‐Cys peroxiredoxin 5 homolog PfAOP from the malaria parasite Plasmodium falciparum is an established model enzyme for glutathione/glutaredoxin‐dependent peroxiredoxins. Here, we reconstituted the catalytic cycle of PfAOP in vitro and analyzed the reaction between oxidized PfAOP and reduced glutathione (GSH) using molecular docking and stopped‐flow measurements. Molecular docking revealed that oxidized PfAOP has to adopt a locally unfolded conformation to react with GSH. Furthermore, we determined a second‐order rate constant of 6 × 105 M−1 s−1 at 25°C and thermodynamic activation parameters ΔH ‡, ΔS ‡, and ΔG ‡ of 39.8 kJ/mol, −0.8 J/mol, and 40.0 kJ/mol, respectively. The gain‐of‐function mutant PfAOPL109M had almost identical reaction parameters. Taking into account physiological hydroperoxide and GSH concentrations, we suggest (a) that the reaction between oxidized PfAOP and GSH might be even faster than the formation of the sulfenic acid in vivo, and (b) that conformational changes are likely rate limiting for PfAOP catalysis. In summary, we characterized and quantified the reaction between GSH and the model enzyme PfAOP, thus providing detailed insights regarding the reactivity of its sulfenic acid and the versatile chemistry of peroxiredoxins.

Kinetics of halide exchange in cyclopentadienylruthenium bis(triarylphosphine)halides

The kinetics of halide exchange in cyclopentadienylruthenium bis(triarylphosphine) halide complexes CpRu(PAr3)2X (1a X = Cl, 1b X = Br, 1c X = I; X′= Cl, Br, Ar = C6H5, 2 Ar = p-CH3OC6H4, X = Cl, X′= Br and 3 Ar = p-FC6H4, X = Cl, X′ = Br) have been measured and the results interpreted with respect to two possible mechanisms: halide dissociation vs phosphine dissociation. Halide exchange between nBu4NX′ and 1–3 in fluorobenzene under pseudo-first order conditions is found to be first order in 1–3. Relative rates of halide exchange follow the order: 1a > 1b > 1c > 2 ≈ 3 with activation parameters ΔH† = 117 ± 6 kJ/mol and ΔS† = 44 ± 18 J/mol-K (1a, X′ = Br) and ΔH† = 120 ± 14 kJ/mol ΔS† = 50 ± 45 J/mol-K (1b, X′ = Cl). Plots of kobs vs [X′–] for 1 and 2 are consistent with a two-term rate law where kobs = (k1 + k2[X′–]) while reactions of 3 are independent of the halide concentration. The rate data are consistent with phosphine dissociation as the rate determining step followed by a slightly faster reaction with halide ions where the dissociated phosphine competes effectively with halide for the open coordination site in a CpRu(PAr3)X intermediate.

Kinetic and thermodynamic comparative study of quince bio-waste slow pyrolysis before and after sustainable recovery of pectin compounds

This work aims to study and compare the kinetic and thermodynamic behavior of pyrolysis of quince waste (QW) and pectin-free quince waste (PFQW) after extraction. The pectin extraction with acid treatment had a yield of 3.2 ± 0.1% (dry basis, db). Pyrolysis experiments were conducted in a macro-TG reactor at three heating rates (5, 10, and 15 °C/min) and temperatures in the range 27–900 °C under a nitrogen atmosphere. A better fit of the experimental data was achieved by modeling the reactions by a multi-step mechanism considering three different parallel reactions for thermal decomposition of hemicelluloses, cellulose, and lignin. The results indicated that the Flynn-Wall-Ozawa (FWO) method provided the best R2, MSE, and AAD values. The resulting values of the thermodynamic activation parameters ΔH, ΔG, and ΔS were 53.28–89.36 kJ/mol, 114.54–155.01 kJ/mol, and −0.17–(−0.04) kJ/(mol K) for pyrolysis of QW, and 29.97–90.68 kJ/mol, 99.42–158.86 kJ/mol, and −0.23 – (−0.01) kJ/(mol K) for PFQW. According to bioenergy indicators, PFQW presented good characteristics as a biofuel feedstock due to its high energy density values. The kinetic and thermodynamic parameters indicated greater reactivity of PFQW to pyrolysis compared to QW, showing that in addition to obtaining a product with added value, such as pectin, the extraction process generates a solid residue that is easier to treat under a thermochemical platform. The novelty of the paper focuses on the influence of the pretreatment of quince bio-waste (by extracting pectin compounds) on reactivity to pyrolysis, providing valuable kinetic and thermodynamic information.

Experimental and theoretical investigation of inhibition behavior of bisflavanol for Q235 steel in hydrochloric acid solution

Bis-8,8′-catechinylmethane, known as bisflavanol (BF), from cacao liquor was synthesized here as effective, eco-friendly, especially edible corrosion inhibitor for Q235 steel in HCl. The result of gravimetric measurements showed that the inhibition efficiency of BF at 0.1 mM was 92.42%, while catechin at 0.2 mM was 78.28%, reflecting a synergistic effect between the two catechin moieties of BF. Activation parameters ΔG0 ads, Ea, ΔH* and ΔS* were evaluated and discussed. Surface morphological analyses (SEM, EDX and AFM) showed that a film of inhibitor was formed on the surface of Q235 steel. XPS, Fukui function and MD simulations were used to study the corrosion inhibition performance of FP in HCl, predict the interaction between FP and Q235 steel, and verify the experimental results.

H2 production from the hydrolytic dehydrogenation of methylamine-borane catalyzed by sulfonated reduced graphene oxide-aided synthesis of ruthenium nanoparticles

A new catalyst was prepared using sulfonated reduced graphene oxide support with a large surface area containing ruthenium nanoparticles (Ru@rGO-SO3H). The developed Ru@rGO-SO3H catalyst was used in the hydrogen production process from the hydrolytic dehydrogenation of methylamine-borane (MeAB). Sulfonated reduced graphene oxide and the developed catalyst were characterized by Raman and FT-IR spectroscopies, ICP-OES, XRD, XPS, TEM, TEM-EDX, SEM and SEM-EDX techniques. The average particle size of Ru nanoparticles, which were homogeneously distributed on the sulfonated reduced graphene oxide surface, was found as 2.2 ± 0.2 nm. After analyzing the effect of nanocatalyst and substrate concentrations on the catalytic reaction, reactions were realized at different temperatures, the efficiency of the Ru@rGO-SO3H nanocatalyst in initial turnover frequency (TOFinitial) and the activation parameters (Ea, ΔH# and ΔS#) were calculated. According to the data obtained, the TOFinitial value was calculated as 5300.86 h− 1 (88.35 min− 1). Ea, ΔH# and ΔS# values were also calculated as 53.83 kJ/mol, 50.73 kJ/mol and −51.55 J/mol.K, respectively. Finally, when the reusability performance results of the catalyst are evaluated, it is found that the catalyst is very stable and retains its initial effectiveness to a great extent (>95%) after the 5th reuse.

Anticancer activity and cell death mechanism of Pt(II) complexes: Their in vitro bio-transformation to Pt(II)-DNA adduct formation and BSA binding study by spectroscopic method

Pt(II) complex cis-[Pt(PEA)(OH2)2] X2, C-2 (where, PEA = 2-Pyridylethylamine and X = ClO4− or NO3–) was synthesized by hydrolysis of cis-[Pt(PEA)Cl2] C-1. Glutathione (GSH) and DL-penicilamine (DL-pen) substituted complexes cis-[Pt(PEA)(GSH)],C-3 and cis-[Pt(PEA)DL-pen)]X C-4 were synthesized and characterized by spectroscopic methods. Kinetic studies were traced on complex C-2 with the thiols, GSH and DL-pen. Pt(II)-Sulfur adduct formation mechanisms of the substituted products C-3 and C-4 were established from the kinetic investigation. At pH 4.0, C-2 - thiols interactions follow two consecutive steps: the first step is dependent, and the second is independent of [thiol]. The association equilibrium constant (KE), substitution rate constants for both steps (k1 & k2), and activation parameters (ΔH‡ and ΔS‡) have been assessed to propose the mechanism. Agarose gel electrophoresis mobilization pattern of DNA with complexes was performed to visualize the interaction nature. CT-DNA and BSA binding activities of the complexes have been executed by electronic, fluorescence spectroscopy, and viscometric titration methods. Evaluation of thermodynamic parameters (ΔH0, ΔS0, and ΔG0) from BSA binding constants was executed to propose the driving forces of interaction between these species. A molecular docking study was performed to evaluate the binding mode of complexes with BDNA strands. Anticancer activity of the complexes C-1 to C-4 was explored on both A549 and HEp-2 cell lines, compared with approved anticancer drugs cisplatin, carboplatin, and oxaliplatin. All these complexes were tested by NBT assay on normal cell line skeletal muscle cells (L6 myotubes) to observe the adverse effects compared to recognized anticancer medications. The ultimate aim is to explore the role of anticancer agents on cell death mechanism, which has been performed by flow-cytometer on HEp-2 cell lines.

An Azophosphine Synthetic Equivalent of Mesitylphosphaazide and Its 1,3-Dipolar Cycloaddition Reactions.

Dibenzo-7-phosphanorbornadiene-substituted diazene MesN2PA (1, where Mes = mesityl, A = anthracene, or C14H10), a synthetic equivalent of mesitylphosphaazide (MesN2P) and anthracene, was synthesized by treatment of [Ph3BPA][Na(OEt2)2] with [MesN2]OTf (OTf = CF3SO3-) in thawing tetrahydrofuran (14% isolated yield). Treatment of 1 with unsaturated molecules cyclooctyne, [Na(dioxane)2.5][OCP] (phosphaethynolate), and Ad-C≡P (Ad = adamantyl) results in the corresponding [3 + 2] phosphaazide-(phospha)alkyne cycloadducts, with concomitant loss of anthracene in 65%, 49%, and 38% isolated yield, respectively. Structural data for the phosphaethynolate cycloadduct ([3][Na(12-crown-4)2]) were obtained in a single-crystal X-ray diffraction study. A diazatriphosphole was generated by combining 1 with P2A2, a thermally activated anthracene-based molecular precursor to diphosphorus (P2). Thermolysis (33-65 °C) of 1 in benzene-d6 leads to anthracene extrusion. This process has a unimolecular kinetic profile and proceeds with activation parameters of ΔH⧧ = 21.6 ± 0.3 kcal/mol and ΔS⧧= -4.9 ± 0.8 cal/(mol K).

Role of ionic surfactants on the plasmonic oxidative dissolution of silver nanoparticles by ferric ions

Effects of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) on the optical sensing of AgNPs toward ferric ions were investigated spectrophotometrically in an aqueous media. Surface Plasmon resonance (SPR) intensity of AgNPs was decreases after addition of ferric ions at room temperature. CTAB and SDS, respectively, catalyzed and inhibited the oxidative dissolution rates of AgNPs. The redox reaction between AgNPs and Fe3+ ions proceeds through the complex formation. The reaction follows first-, and fractional-order kinetics with AgNPs and Fe3+ ions, respectively. CTAB catalytic role was explained with micellar pseudo-phase model, and associated parameters were estimated. The activation parameters (Ea, ΔH#, and ΔS#) were found to be 23.7 kJ/mol, 16.6 kJ/mol, −226 J/K/mol, and 16.5 kJ/mol, 13.5 kJ/mol, −238 J/K/mol for aqueous and CTAB assisted dissolution of AgNPs. SDS coordinated with Fe3+ through electrostatic interactions in pre-, and post-micellar region, which in turn reduces the electron gaining tendency of Fe3+, and overall rates of sensing reaction decreases.

A side-on Mn(III)-peroxo supported by a non-heme pentadentate N3Py2 ligand: synthesis, characterization and reactivity studies.

A mononuclear manganese(iii)-peroxo complex [MnIII(N3Py2)(O2)]+ (1a) bearing a non-heme N,N'-dimethyl-N-(2-(methyl(pyridin-2-ylmethyl)amino)ethyl)-N'-(pyridin-2-ylmethyl)ethane-1,2-diamine (N3Py2) ligand was synthesized by the reaction of [Mn(N3Py2)(H2O)](ClO4)2 (1) with hydrogen peroxide and triethylamine in CH3CN at 25 °C. The reactivity of 1a in aldehyde deformylation using 2-phenyl propionaldehyde (2-PPA) was studied and the reaction kinetics was monitored by UV-visible spectroscopy. A kinetic isotope effect (KIE) = 1.7 was obtained in the reaction of 1a with 2-PPA and α-[D1]-PPA, suggesting nucleophilic character of 1a. The activation parameters ΔH‡ and ΔS‡ were determined using the Eyring plot while Ea was obtained from the Arrhenius equation by performing the reaction between 288 and 303 K. Hammett constants (σp) of para-substituted benzaldehydes p-X-Ph-CHO (X = Cl, F, H, and Me) were linear with a slope (ρ) = 3.0. Computational study suggested that the side-on structure of 1a is more favored over the end-on structure and facilitates the reactivity of 1a.

Investigation of Aniline and N,N-Dimethylaniline as Acidic Corrosion Inhibitor: a Structure–Efficiency Relationship Study

In this study, aniline and N,N-dimethylaniline was evaluated as corrosion inhibitor for the A3 steel in 5% HCl solution, by the way of gravimetric measurements, and the structure-efficiency relationship was studied. With the result under different concentration and temperature, from 303 to 343 K, the inhibition efficiency of the two inhibitors was compared. The adsorption of aniline and N,N-dimethylaniline on the A3 steel is figured out conforming Langmuir type isotherm. From the comparison of the thermodynamic activation parameters (ΔG, ΔH, ΔS and Ea), it reveals that aniline is easier to absorb on the steel, which can be attributed to the stereochemistry of the two compounds.