Pseudo-first Order Reaction Conditions Research Articles

Mechanistic approach to the antioxidant activities of metal-associated superoxide with Trolox

Trolox-C (TXC) is a water-soluble analogue of α-tocopherol that reduces the metal-bound superoxo complex (SOC), [(NH3)5Co(µ-O2)Co(NH3)5]5+in water–ethanol media. In aqueous-acid media ([H+] = 0.02–0.70 mol/L), TXC quantitatively reduces SOC under the pseudo first-order reaction condition where the concentration of TXC, [TXC], was at least 10 times or more than that of [SOC]. Variations in media ionic strength suggest for the reaction between two cationic species, and a positive kinetic isotope effect ( kH/ kD < 1) indicates for a pre-equilibrium step of protonation of the pyran-oxygen of TXC. Both TXC and the protonated TXC, i.e., TXCH, are the potential reductants under the experimental range of media acidity. The reduction of SOC takes place through the single-electron transfer and the kinetic analysis yields the value for second-order rate constants for TXC and TXCH as 9.7 and 3.6 × 103 (mol/L)−1s−1at 15 °C.

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.

The Catalytic Influence of Polymers and Surfactants on the Rate Constants of Reaction of Maltose with Cerium (IV) in Acidic Aqueous Medium

Kinetics of the reaction of maltose with cerium ammonium sulfate were analyzed spectrophotometrically by observing the decrease of the absorbance of cerium (IV) at 385 nm in the presence and absence of polyethylene glycols (600, 1500, and 4000) and polyvinylpyrrolidone (PVP), in addition to anionic micelles of sodium dodecyl sulfate (SDS), cationic micelles of cetyltrimethylammonium bromide (CTAB) and non-ionic micelles of Tween 20 surfactants. Generally, there is little literature about using the polymers (PEGs and PVP) as catalysts in the oxidation-reduction reactions. Therefore, the major target of this work was to investigate the influence of the nature of polymers and surfactants on the oxidation rates of maltose by cerium (IV) in acidic aqueous media, as well as employing the Piszkiewicz model to explain the catalytic effect. The kinetic runs were derived by adaptation of the pseudo first-order reaction conditions with respect to the cerium (IV). The reaction was found to be first-order with respect to the oxidant and fractional-order to maltose and H2SO4. The reaction rates were enhanced in the presence of polymer and micellar catalysis. Indeed, the surfactants were found to work perfectly close to their critical micelle concentrations (CMC). Electrostatic interaction and H-bonding appear to play an influential role in binding maltose molecules to polymer/surfactant micelles, while oxidant ions remain at the periphery of the Stern layer within the micelle.

Kinetic Study of the Pyridine-Catalyzed Selenolactonization of 4-Pentenoic Acid

The kinetics and mechanism of the pyridine-catalyzed cyclofunctionalization of 4-pentenoic acid by means of PhSeX (X = Cl, Br) have been investigated spectrophotometrically, under pseudo-first order reaction conditions. The influence of the reaction temperature, the type of cyclization reagent and used catalyst on the reaction rate and mechanism was examined. The obtained data have showed that rate constants go on increasing as the temperatures go up and with use of PhSeCl as reagent. Also, the reaction rate is directly depended on the type of the catalyst used—stronger bases with higher tendency for hydrogen bond formation (DN) are promoting reaction in more efficient way.

Facile synthesis of poly (benzylamine) brushes stabilized silver nanoparticle catalyst for the abatement of environmental pollutant methylene blue

Abstract A novel type of polymer brushes as a stabilizing agent was synthesized by benzylamine at room temperature. The synthesized polymer brushes can act as an excellent stabilizing agent and the method of synthesis is also a simple one. Three different types of magnetically recoverable nano-catalysts were prepared through individual immobilization of silver nanoparticles (Ag NPs) onto the surface of Fe3O4 NPs, Fe3O4-OA NPs and Fe3O4-PBA NPs viz., Fe3O4-Ag NPs, Fe3O4-OA-Ag NPs, Fe3O4-PBA-Ag NPs catalysts, respectively. The synthesized catalysts were characterized by XRD, 1H NMR, GPC, Raman, FT-IR, UV-vis, VSM, SEM and HR-TEM. The catalytic potential of the newly prepared catalyst was examined through the reduction/degradation of methylene blue by NaBH4 under pseudo-first order reaction condition. The apparent rate constant (Kapp) and TOF of Fe3O4-Ag NPs, Fe3O4-OA-Ag NPs, Fe3O4-PBA-Ag NPs are 2.0 × 10−2 s−1, 3.3 × 10−2 s−1, 15.6 × 10−2 s−1 and 5.0 × 10−3 s−1, 83.3 × 10−3 s−1, 285.7 × 10−3 s−1 respectively. Among the catalysts, based on Kapp value, catalytic activity of Fe3O4-PBA-Ag NPs (15.6 × 10−2 s−1) is eight times higher than Fe3O4-Ag NPs (2.0 × 10−2 s−1). The Fe3O4-PBA-Ag NPs catalyst was tested to estimate the material stability up to seven runs without losing catalytic activity by recovery catalysts. This new method of prepared catalysts is expanded for the application of magnetic recoverable nano-catalysts in various industrially important reactions because of its simple preparation method along with its recyclable capacity and high activity.

Facile synthesis of core-shell nanocomposites Au catalysts towards abatement of environmental pollutant Rhodamine B

Magnetically recoverable Au nanoparticles immobilized/stabilized on core-shell nanocomposites are synthesized by the combination of suspension polymerization as well as surface initiator atom transfer radical polymerization (SI-ATRP) methods. The magnetic core-shell supported Au nanocatalysts are namely Fe3O4-PAC-AuNPs, Fe3O4-PVBC-g-PAC-AuNPs, Fe3O4-HEA-AuNPs, and Fe3O4-PVBC-g-HEA-AuNPs. Among all the catalysts, Fe3O4-PVBC-g-PAC-Au NPs exhibited an excellent activity in the reduction of Rhodamine B with an apparent rate constant of 10.77 × 10−3 s−1 and TOF value of 47.62 × 10−3 s−1 under pseudo-first order reaction condition. Further, Fe3O4-PVBC-g-PAC-Au NPs has an outstanding activity and recyclability without applying any external magnetic field. This new approach provides an exciting potential way in the preparation of recyclable metal nano-catalysts with high catalytic activity.

Optimizing the Gas Absorption/Chemical Reaction Method for Measuring Air–Water Interfacial Area in Porous Media

The gas-absorption/chemical-reaction (GACR) method developed in Chemical Engineering to measure gas-fluid interface in reactor systems is adapted for natural porous geologic media. Several series of column experiments were conducted using model glass beads and a natural sand to determine optimal operational conditions for measuring air-water interfacial area with the adapted method. The impacts of operational variables were investigated, including liquid and gas volumetric flow rates, solution concentration, and temperature. The results show that the magnitude of the measured air-water interfacial area is dependent upon all of these variables to greater or lesser degrees. Larger fluid flow rates promote distribution and mixing of the fluids, enhancing absorption and reaction. Increasing the concentration of NaOH in solution reduced the relative utilization of NaOH, promoting pseudo first-order reaction conditions. The results elucidate the optimal operational conditions for application of the method to geomedia systems.

New nanohybrids from poly(propylene imine) dendrimer stabilized silver nanoparticles on multiwalled carbon nanotubes for effective catalytic and antimicrobial applications

ABSTRACTFive types of multiwalled carbon nanotubes noncovalently functionalized with poly (propylene imine) dendrimer (PPI (G2))-silver nanoparticle hybrids were prepared by varying the [Ag+] load from 2 to 6 mM. These nanohybrids were characterized with FTIR, UV-Vis, FESEM, EDS, HRTEM and Raman analyses. The catalytic potential was studied through the reduction of 4-nitrophenol as a model reaction under pseudo first-order reaction conditions. The calculated kobs value (16.94 × 10−2 min−1) reveals that the 4 mM [Ag+] loaded catalyst showed higher efficiency than with rest of the catalysts. Further, the in vitro antimicrobial activities of all nanohybrids were inspected against Pseudomonas aeruginosa and Staphylococcus aureus.

Surface Properties and Photocatalytic Activities of the Colloidal ZnS:Mn Nanocrystals Prepared at Various pH Conditions.

Water-dispersible ZnS:Mn nanocrystals (NC) were synthesized by capping the surface with mercaptoacetic acid (MAA) molecules at three different pH conditions. The obtained ZnS:Mn-MAA NC products were physically and optically characterized by corresponding spectroscopic methods. The UV-Visible absorption spectra and PL emission spectra showed broad peaks at 310 and 590 nm, respectively. The average particle sizes measured from the HR-TEM images were 5 nm, which were also supported by the Debye-Scherrer calculations using the X-ray diffraction (XRD) data. Moreover, the surface charges and the degrees of aggregation of the ZnS:Mn-MAA NCs were determined by electrophoretic and hydrodynamic light scattering methods, indicating formation of agglomerates in water with various sizes (50–440 nm) and different surface charge values accordingly the preparation conditions of the NCs (−7.59 to −24.98 mV). Finally, the relative photocatalytic activities of the ZnS:Mn-MAA NCs were evaluated by measuring the degradation rate of methylene blue (MB) molecule in a pseudo first-order reaction condition under the UV-visible light irradiation. As a result, the ZnS:Mn-MAA NC prepared at the pH 7 showed the best photo-degradation efficiency of the MB molecule with the first-order rate constant (kobs) of 2.0 × 10−3·min−1.

A shock tube study of CH3OH + OH → Products using OH laser absorption

The rate coefficient for the reaction of methanol (CH3OH) with the hydroxyl (OH) radical was determined in reflected shock wave experiments at temperatures of 961–1231K and pressures of 1.18–1.48atm. Pseudo-first order reaction conditions were achieved with mixtures of CH3OH and tert-butyl hydroperoxide (TBHP) diluted in argon. Rapid thermal decomposition of TBHP at high temperatures was used as a fast OH radical source, and OH time-histories were measured using laser absorption of OH radicals near 306.7nm. The rate coefficient of the title reaction was found from best-fit comparison of simulated OH profiles with measured data, using simulations from the Wang et al. USC-Mech II reaction mechanism (2007). A detailed uncertainty analysis was performed, with estimated uncertainties of −10%/+17% at 961K and −12%/+18% at 1231K. The current results agree well with the results of Vandooren and Van Tiggelen (1981), Hess and Tully (1989), and Xu and Lin (2007). The three-parameter Arrhenius expression k1(210–1231K)=5.71×104T2.62exp(343/T[K]) cm3mol−1s−1 is recommended from a fit to the combined data of Hess and Tully (1989), Jiménez et al. (2003), Dillon et al. (2005), and the current work.

Identification of Serpin Determinants of Specificity and Selectivity for Furin Inhibition through Studies of α1PDX (α1-Protease Inhibitor Portland)-Serpin B8 and Furin Active-site Loop Chimeras

α1-Protease inhibitor Portland (α1PDX) is an engineered serpin family inhibitor of the proprotein convertase (PC), furin, that exhibits high specificity but limited selectivity for inhibiting furin over other PC family proteases. Here, we characterize serpin B8, a natural inhibitor of furin, together with α1PDX-serpin B8 and furin-PC chimeras to identify determinants of serpin specificity and selectivity for furin inhibition. Replacing reactive center loop (RCL) sequences of α1PDX with those of serpin B8 demonstrated that both the P4-P1 RXXR recognition sequence as well as the P1'-P5' sequence are critical determinants of serpin specificity for furin. Alignments of PC catalytic domains revealed four variable active-site loops whose role in furin reactivity with serpin B8 was tested by engineering furin-PC loop chimeras. The furin(298-300) loop but not the other loops differentially affected furin reactivity with serpin B8 and α1PDX in a manner that depended on the serpin RCL-primed sequence. Modeling of the serpin B8-furin Michaelis complex identified serpin exosites in strand 3C close to the 298-300 loop whose substitution in α1PDX differentially affected furin reactivity depending on the furin loop and serpin RCL-primed sequences. These studies demonstrate that RCL-primed residues, strand 3C exosites, and the furin(298-300) loop are critical determinants of serpin reactivity with furin, which may be exploited in the design of specific and selective α1PDX inhibitors of PCs.

Kinetics of Reversible Consecutive Reactions

Rate equations are exactly solved for the reversible consecutive reaction of the first-order and the time- dependence of concentrations is analytically determined for species in the reaction. With the assumption of pseudo first-order reaction, the calculation applies and determines the concentration of product accurately and explicitly as a function of time in the unimolecular decomposition of Lindemann and in the enzyme catalysis of Michaelis-Menten whose rate laws have been approximated in terms of reactant concentrations by the steady-state approximation. Mechanisms and rate laws of most chemical reactions can be described based on reversible, consecutive or parallel processes whose reaction rates are determined in detail as functions of time provided that they consist of the first-order or pseudo first-order steps. Concentrations in terms of time for species involved in these simple processes are easily obtained mathematically and the exact results are found in usual chemical kinetics texts. However many realistic reac- tions in fact contain the variety of combinations of the three rudimentary processes aforementioned and this complicates solving rate equations analytically and makes it difficult determining time-dependence of rates accurately. Approxi- mate methods thus have been developed and introduced to handle these reactions. A typical example is the steady-state approximation (SSA) which is often used to describe reactions in which reversible processes are combined with consecutive steps. It has been developed from the first-order reversible consecutive reaction which is represented by . If the rate of consumption of B is much greater than its rate of formation in the reaction scheme, the concentration of B may be presumed to change little with time and can be estimated in terms of reactant concentration from the assumption. The overall rate of reac- tion is then evaluated using the approximate concentration without detailed integration of rate equations. This simple but efficient technique is widely applied in reactions consist- ing with many steps to determine rates approximately. Ex- amples are the unimolecular decomposition known for Lin- demann mechanism and the enzyme catalysis of Michaelis- Menten. 1 The rate of reaction , if it is obtained fully as a function of time, can be extended under the pseudo first-order reaction condition to precisely determine the time-dependent behavior of reactions obeying mechanism of Lindemann or of Michaelis-Menten. Analytical solution to the rate equations of these reactions, however, has not been reported and the detailed time-dependence of concentrations is not known yet within the author's knowledge. In this work, rate equations of the first-order reversible consecutive reaction are exactly solved and two sample calculations are performed with different set of rate con- stants to show how concentrations depend on time in detail. The derivations are applied to reactions of the named mech- anisms to calculate concentrations of products analytically and are used to check the approximate rate laws by SSA for validity and limitations. Then a brief summary concludes the article.

Acid-catalyzed decomposition of stable 1-(2,1-benzisothiazol-3-yl)-3-phenyltriazenes

Abstract The acid-catalyzed decomposition of unusually stable 1-(2,1-benzisothiazol-3-yl)-3-phenyltriazenes in either aqueous perchloric acid or an aqueous mixture of perchloric and acetic acid was studied under pseudo-first order reaction conditions at 25 °C. Different products were obtained according to substitution on nitrogen N-3. For a triazene carrying hydrogen, the corresponding 3-amino-2,1-benzisothiazole and benzenediazonium salts were formed whereas in the case of substitution by an alkyl group (methyl and n-butyl) the 2,1-benzisothiazole-3-diazonium salt and N-alkylaniline were obtained. The observed rate constant (kobs) of the acid-catalyzed decomposition increased, initially, nonlinearly with increasing concentration of acid. Subsequently, kobs decreased slightly and at high acid concentration, increased steeply once again. An A-SE2 mechanism in which protonation of the triazene nitrogen proceeds simultaneously with cleavage of the N–N bond is proposed. Tautomerism of 1-(2,1-benzisothiazol-3-yl)-3-phenyltriazene was investigated using 1H NMR spectroscopy.

Kinetics of binding the mRNA cap analogues to the translation initiation factor eIF4E under second-order reaction conditions

The kinetics of binding of five analogues of the 5′-mRNA cap, differing in size and electric charge, to the eukaryotic initiation factor eIF4E, at 20 °C, pH 7.2, and ionic strength of 150 mM, were measured, after mixing solutions of comparable concentrations of the reagents, in a stopped-flow spectrofluorimeter. The registered stopped-flow signals were fitted using an efficient software package, called Dyna Fit, based on a numerical solution of the kinetic rate equations for assumed reaction mechanisms. One-, two-, and three-step binding models were considered. The quality of fits for these models were compared using two statistical criteria: Akaike's Information Criterion and Bayesian Information Criterion. Based on resulting probabilities of the models, it was concluded that for all investigated ligands a one-step binding model has essentially no support in the experimental observations. Our conclusions were also analysed from the perspective of kinetic transients obtained for cap–eIF4E systems under the so called pseudo-first order reaction condition, which result in the linear correlation of the observed association rate constant with ligand concentration. The existence of such a linear correlation is usually considered as proof of a one-step binding mechanism. The kinetic and optical parameters, derived from fitting a two-step cap-binding model with the DynaFit, were used to simulate kinetic transients under pseudo-first order reaction conditions. It appeared that the observed association rate constants derived from these simulated transients are also linearly correlated with the ligand concentration. This indicated that these linear dependencies are not sufficient to conclude a one-step binding.

Mechanism of the axial ligand substitution reactions on the head-to-tail alpha-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex with olefins.

Reactions of the head-to-tail alpha-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex having equivalent two platinum atoms, Pt(N(3)O), with p-styrenesulfonate and 4-penten-1-ol were studied kinetically. Under the pseudo first-order reaction conditions in which the concentration of the Pt(III) dinuclear complex is much smaller than that of olefin, a consecutive basically four-step reaction was observed for the reaction with p-styrenesulfonate, but for the reaction with 4-penten-1-ol, the reaction was three step. The olefin pi-coordinates to one of the two equivalent Pt atoms in the first step (step 1), followed by the second pi-coordination of another olefin molecule to the other Pt atom (step 2). In the next step (step 3), the nucleophilic attack of water to the first pi-coordinated olefin initiates its pi-sigma bond conversion on the Pt atom, and the second pi-bonding olefin molecule on the other Pt atom is released. Finally, dissociation of the alkyl group on the Pt(N(3)O) and reduction of the Pt(III) dinuclear complex to the Pt(II) dinuclear complex occur (step 4). The first water substitution with olefin (step 1) consists of two paths, the reaction of the diaqua dimer complex (path a) and the reaction of the aquahydroxo dimer complex (path b), whereas the second substitution (step 2) proceeds through three reaction paths: the normal path of the direct substitution of H(2)O (path c), the path of the coordinated OH(-) substitution (path d), and the path via the coordinatively unsaturated five-coordinate intermediate (path e). The reaction with p-styrenesulfonate proceeds through paths c, d, and e, whereas the reaction with 4-penten-1-ol proceeds through paths c and d. The third step (step 3) for the reaction with p-styrenesulfonate involves the coordinatively unsaturated intermediate, but that for the 4-pentene reaction does not. The reactivities of the HH dimer and HT dimer with olefins are compared and discussed.

Mechanism of ketone and alcohol formations from alkenes and alkynes on the head-to-head 2-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex.

Reactions of the head-to-head 2-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex having nonequivalent two platinum atoms, Pt(N(2)O(2)) and Pt(N(4)), with p-styrenesulfonate, 2-methyl-2-propene-1-sulfonate, 4-penten-1-ol, and 4-pentyn-1-ol were studied kinetically. Under the pseudo first-order reaction conditions that the concentration of the Pt(III) dinuclear complex is much smaller than that of olefin, a consecutive basically four-step reaction was observed: the olefin pi-coordinates preferentially to the Pt(N(2)O(2)) in the first step (step 1), followed by the second pi-coordination of another olefin molecule to the Pt(N(4)) (step 2). In the next step (step 3), the nucleophilic attack of water to the coordinated olefin triggers the pi-sigma bond conversion on the Pt(N(2)O(2)), and the second pi-bonding olefin molecule on the Pt(N(4)) is released. Finally, reductive elimination occurs to the alkyl group on the Pt(N(2)O(2)) to produce the alkyl compound (step 4). The first water substitution with olefin (step 1) occurs to the diaqua and aquahydroxo forms of the complex, whereas the second substitution (step 2) proceeds either on the coordinated OH(-) on the Pt(N(4)) (path a) or on the coordinatively unsaturated five-coordinate intermediate of the Pt(N(4)) (path b), in addition to the common substitution of H(2)O (path c). The reactions of p-styrenesulfonate and 2-methyl-2-propene-1-sulfonate proceed through paths b and c, whereas the reactions of 4-penten-1-ol and 4-pentyn-1-ol proceed through paths a and c. This difference reflects the difference of the trans effect and/or trans influence of the pi-coordinated olefins on the Pt(N(2)O(2)). The pentacoordinate state in path b is employed only by the sulfo-olefins, because these exert stronger trans effect. The steps 3 and 4 reflect the effect of the axial alkyl ligand (R) on the charge localization (R-Pt(IV)(N(2)O(2))-Pt(II)(N(4))) and delocalization (R-Pt(III)(N(2)O(2))-Pt(III)(N(4))-OH(2)); when R is p-styrenesulfonate having an electron withdrawing group, the charge localization in the dimer is less pronounced and the water molecule on the Pt(N(4)) atom is retained (R-Pt(III)(N(2)O(2))-Pt(III)(N(4))-OH(2)) in the intermediate state. In both routes, the alkyl group undergoes nucleophilic attack of water, and the oxidized products are released via reductive elimination.

Absorption of CO2 in a sterically hindered amine: modeling absorption in a mechanically agitated contactor

Abstract The absorption of dilute CO 2 into aqueous solutions of a sterically hindered amine, 2-amino-2-methyl-1-propanol (AMP), is modeled in the mechanically agitated contactor under the fast pseudo first-order reaction condition using the kinetic data for CO 2 –AMP presented elsewhere by this study group [A.K. Saha, S.S. Bandyopadhyay, A.K. Biswas, Kinetics of absorption of CO 2 into aqueous solutions of 2-amino-2-methyl-1-propanol, Chem. Eng. Sci. 50 (1995) 3587–3598.] Experimental results of absorption studies in the mechanically agitated contactor at 288 and 301.5 K over ranges of CO 2 partial pressure (5–15 kPa) and amine concentration (1–2 kmol m −3 ) are in excellent agreement with the results predicted from the numerical model, confirming the validity of the mathematical model proposed, and the kinetic data and the mechanism presented earlier by this study group for the CO 2 –AMP system [A.K. Saha, S.S. Bandyopadhyay, A.K. Biswas, Kinetics of absorption of CO 2 into aqueous solutions of 2-amino-2-methyl-1-propanol, Chem. Eng. Sci. 50 (1995) 3587–3598.] The maximum deviation between the predicted and experimental values of liquid-phase CO 2 loading with time was within 3%.

The reaction of glutamic acid and trinitrobenzenesulfonic acid—kinetic study and analytical application

Some kinetic aspects of the reaction of glutamic acid (GLU) and Trinitrobenzenesulfonic acid (TNBS) were studied spectrophotometrically (420 nm), under pseudo-first order reaction conditions. The effect of GLU, TNBS, SO 2− 3 and H + had been investigated. Working curves for the initial rates IR versus [GLU] are linear in the range 7.5–30.0 mM. The regression equation is IR = (8 ± 8)E − 6 + (39 ± 0.5)·[GLU] and the correlation coefficient r = 0.9998. The limit of quantitation is 1.5 μM GLU and the relative standard deviation of the method 1.2%. The kinetics of the interfering TNBS hydrolysis reaction in alkaline range of pH, as well as the effect of sulfite concentration on the main reaction, are also presented. The analytical application of the reaction for the kinetic spectrophotometric assay of GLU and other aminoacids, as well as TNBS, is presented and the relevant advantages and disadvantages of the method are discussed.

Kinetic studies on the formation of acridine-linked DNA triple helices

We have used DNase I footprinting to measure the rate of intermolecular triple helix formation at the target sites A 6G 6 · C 6T 6 and G 6A 6 · T 6C 6 with the acridine-linked oligonucleotides Acr-T 5C 5, and Acr-C 5T 5 respectively. Under pseudo first-order reaction conditions we find that the reactions are slow, with half-lives of several minutes. The rates are dependent on the concentration of the third strand oligonucleotide and yield bimolecular association rate constants of 300 M −1 · s −1 for Acr-T 5C 5 binding to A 6G 6 · C 6T 6 and 2000 M −1 · s −1 for the interaction of Acr-C 5T 5 with G 6A 6 · T 6C 6.