Rate Of Exchange Reaction Research Articles

Study of the Electroless Deposition of Pd on Cu-Modified Graphite Electrodes by Metal Exchange Reaction

The electroless deposition of Pd on Cu-modified graphite electrodes using a metal exchange reaction was investigated. The modification procedure consisted in the electrodeposition of Cu on the graphite electrode, subsequently replaced by Pd at open circuit in a Pd-containing solution. The influence of experimental conditions on the exchange reaction rate, the chemical state and the distribution of Cu and Pd on the electrode surface are highlighted. The resulting deposits were studied using cyclic voltammetry, atomic absorption spectroscopy, scanning electron microscopy, energy-dispersive X-ray, and X-ray photoelectron spectroscopy. The last technique confirmed the spontaneous oxidation of Cu by the Pd complexes adsorbed on the electrode surface and also demonstrated that Pd/Cu atomic ratio increases by increasing the PdCl2 concentration. An increase of the Pd electroactive surface area, estimated by cyclic voltammetry, was observed by increasing the initial Cu loading, the exchange reaction time or the PdCl2 concentration. It was also demonstrated that the metal exchange reaction leads to the formation of a Cu core enveloped by a Pd shell for every PdCl2 concentration investigated here. The corrosion rate for the corrosion of copper by a Pd complex was determined and compared with that of the corrosion of copper by oxygen. On the basis of our observations, a general model to describe the Cu−Pd exchange process and the resulting electrode surface composition was proposed.

The effect of glucosyl-β-cyclodextrin on the hydrogen–deuterium exchange rate constant of the peptide bonds of chicken egg white lysozyme in a D 2O solution

FT-IR spectroscopy revealed that the hydrogen–deuterium (H–D) exchange reaction rate of the peptide hydrogen atoms of chicken egg white lysozyme in a deuterated aqueous solution was significantly accelerated in the presence of glucosyl-β-cyclodextrin at 55 °C. The addition of methyl α- d-glucopyranoside, which has no inclusion ability, rather decelerated the H–D exchange reaction rate at the same temperature. The H–D exchange rate constant of lysozyme was evaluated by the time dependence of the absorbance ratio of the amide II infrared band against the amide I’. The H–D exchange rate constant was not influenced by the addition of glucosyl-β-cyclodextrin at 45 °C, however, it became twice larger than that in the absence of the cyclodextrin at 55 °C. These results strongly suggest that peptide bonds of lysozyme become exposed to the aqueous medium due to the inclusion by glucosyl-β-cyclodextrin to accelerate the H–D exchange rate.

Enhanced DNA strand exchange on positively charged liposomes

The mechanism of DNA strand exchange, performed in vivo by proteins in the RecA family, is, despite extensive studies, still not understood in detail. We are therefore investigating a model system, using the surface of a lipid vesicle, to systematically study the effect of individual parameters on the rate of the strand exchange reaction. DNA oligonucleotides are accumulated on the surface of cationic liposomes and the strand exchange is monitored using FRET. We show that in the presence of lipid vesicles containing 35% cationic lipid the strand exchange takes place with a significantly enhanced rate and improved yield, compared to in bulk without liposomes. The highest rate is observed at a charge ratio where the positive surface charge is matched by the negative charges from DNA, and thus all double- and single-stranded DNA can be bound to the liposome surface. The DNA duplex is destabilized on the positively charged surface and with the accumulation of complementary single strands in close proximity a fast exchange is facilitated. We also show that when aggregation of liposomes is minimized by incorporation of a PEG-modified lipid, the strand exchange is still efficient, although with a lower rate than for the unmodified system. We conclude that the liposome model system, with the possibility to systematically vary the surface composition, is a promising platform for further studies of DNA strand exchange reactions.

Pre-Steady-State Kinetic Studies of the Reductive Dehalogenation Catalyzed by Tetrachlorohydroquinone Dehalogenase

Tetrachlorohydroquinone dehalogenase catalyzes two successive reductive dehalogenation reactions in the pathway for degradation of pentachlorophenol in the soil bacterium Sphingobium chlorophenolicum. We have used pre-steady-state kinetic methods to probe both the mechanism and the rates of elementary steps in the initial stages of the reductive dehalogenation reaction. Binding of trichlorohydroquinone (TriCHQ) to the active site is followed by rapid deprotonation to form TriCHQ-2 and subsequent formation of 3,5,6-trichloro-4-hydroxycyclohexa-2,4-dienone (TriCHQ*). Further conversion of TriCHQ* to 2,6-dichlorohydroquinone (DCHQ) proceeds only in the presence of glutathione. Conversion of TriCHQ to DCHQ during the first turnover is quite rapid, occurring at about 25 s-1 when the enzyme is saturated with TriCHQ and glutathione. The rate of subsequent turnovers is limited by the rate of the thiol-disulfide exchange reaction required to regenerate the free enzyme after turnover, a reaction that is intrinsically less difficult, but is hampered by premature binding of the aromatic substrate to the active site before the catalytic cycle is completed.

Stereospecific Proton Transfer by a Mobile Catalyst in Mammalian Fructose-1,6-bisphosphate Aldolase

Class I fructose-1,6-bisphosphate aldolases catalyze the interconversion between the enamine and iminium covalent enzymatic intermediates by stereospecific exchange of the pro(S) proton of the dihydroxyacetone-phosphate C3 carbon, an obligatory reaction step during substrate cleavage. To investigate the mechanism of stereospecific proton exchange, high resolution crystal structures of native and a mutant Lys(146) --> Met aldolase were solved in complex with dihydroxyacetone phosphate. The structural analysis revealed trapping of the enamine intermediate at Lys(229) in native aldolase. Mutation of conserved active site residue Lys(146) to Met drastically decreased activity and enabled trapping of the putative iminium intermediate in the crystal structure showing active site attachment by C-terminal residues 360-363. Attachment positions the conserved C-terminal Tyr(363) hydroxyl within 2.9A of the C3 carbon in the iminium in an orientation consistent with incipient re face proton transfer. We propose a catalytic mechanism by which the mobile C-terminal Tyr(363) is activated by the iminium phosphate via a structurally conserved water molecule to yield a transient phenate, whose developing negative charge is stabilized by a Lys(146) positive charge, and which abstracts the C3 pro(S) proton forming the enamine. An identical C-terminal binding mode observed in the presence of phosphate in the native structure corroborates Tyr(363) interaction with Lys(146) and is consistent with transient C terminus binding in the enamine. The absence of charge stabilization and of a mobile C-terminal catalyst explains the extraordinary stability of enamine intermediates in transaldolases.

Recovery of labeled CO2 from acetate in severely burned children

The purpose of this study was to determine the fractional recovery rate of labeled CO(2) in the breath of severely burned children. This information is needed to perform tracer studies of substrate oxidation using carbon-labeled fatty acids. Nine children, ages 4-14 yr with massive burns participated in the study. All experiments were performed 7 days post burn after an overnight fast. A primed (60 micromol/kg), constant (2.0 micromol.kg(-1).min(-1)) infusion of [1,2-(13)C]acetate was given during a 4-h basal period and during a 4-h hyperinsulinemic euglycemic clamp. A priming dose (150 micromol/kg) of NaH(13)CO(3) was given at the beginning of the study. Breath samples were collected every 10 min during the last 40 min of each period. Indirect calorimetry was performed during the last 30 min of each period. The isotopic enrichment of (13)CO(2) was determined by isotope ratio-mass spectrometry, and total CO(2) excretion was measured by indirect calorimetry. The fractional recovery of acetate label was 0.89 +/- 0.05 and 0.88 +/- 0.04 during the basal state and clamp, respectively. We conclude that the fractional recovery of labeled acetate in severely burned children is approximately three times the recovery of a nonburned adult and similar to the value in exercising adults. The high recovery rate reflects the rapid turnover of the TCA cycle in burned children relative to the rate of exchange reactions. Minimal correction of expired CO(2) data is needed in this circumstance to quantify fatty acid oxidation using (13)C-labeled fatty acids.

Theoretical investigation of exchange and recombination reactions in O(P3)+NO(Π2) collisions

We present a detailed dynamical study of the kinetics of O(3P)+NO(2Pi) collisions including O atom exchange reactions and the recombination of NO2. The classical trajectory calculations are performed on the lowest 2A' and 2A" potential energy surfaces, which were calculated by ab initio methods. The calculated room temperature exchange reaction rate coefficient, kex, is in very good agreement with the measured one. The high-pressure recombination rate coefficient, which is given by the formation rate coefficient and to a good approximation equals 2kex, overestimates the experimental data by merely 20%. The pressure dependence of the recombination rate, kr, is described within the strong-collision model by assigning a stabilization probability to each individual trajectory. The measured falloff curve is well reproduced over five orders of magnitude by a single parameter, i.e., the strong-collision stabilization frequency. The calculations also yield the correct temperature dependence, kr proportional, T-1.5, of the low-pressure recombination rate coefficient. The dependence of the rate coefficients on the oxygen isotopes are investigated by incorporating the difference of the zero-point energies between the reactant and product NO radicals, DeltaZPE, into the potential energy surface. Similar isotope effects as for ozone are predicted for both the exchange reaction and the recombination. Finally, we estimate that the chaperon mechanism is not important for the recombination of NO2, which is in accord with the overall T-1.4 dependence of the measured recombination rate even in the low temperature range.

Slowdown of H/D Exchange Reaction Rate and Water Dynamics in Ionic Liquids: Deactivation of Solitary Water Solvated by Small Anions in 1-Butyl-3-Methyl-Imidazolium Chloride

The H/D exchange reaction and the rotational dynamics of heavy water (D2O) are studied at 50 degrees C in the ionic liquid, 1-butyl-3-methylimidazolium chloride ([bmim][Cl]), in the [D2O] range of 3-55 M. The initial H/D exchange rates are observed as 1.0 x 10(-7), 4.5 x 10(-6), 1.0 x 10(-5), 4.1 x 10(-5), 1.1 x 10(-4), and 3.7 x 10(-4) s(-1), respectively, at [D2O] of 2.8, 7.1, 8.1, 11, 15, and 25 M. The rate is very slow and less than 10(-5) s(-1) at [D2O] below approximately 7 M. It steeply increases to the order of 10(-4)s(-1) for 7 M < [D2O] < 10 M, and linearly increases with [D2O] in the more water-rich region. The intercept of the linear region at [D2O] = approximately 9 M is interpreted by considering that each chloride anion deactivates 1.6 equiv water molecules due to the strong solvation. Correspondingly, the rotational correlation time of D2O at [D2O] < 7 M is 1 order of magnitude larger than that in water-rich conditions.

Oxygen Exchange Reaction between CO2-CO Gas and Molten Oxide Containing Iron Oxide

Oxygen exchange reaction rates between CO2-CO gas and molten oxides containing iron oxide have been measured by isotope exchange technique with 18O at 1773K with PCO2/PCO=1. Measured results represent that the oxygen exchange reaction rates show the maximum values at the beginning of the reaction and sharply decrease within approximately 20 s, and then gradually decrease with the reaction time proceeds. These changes indicate that the rate-limiting step would change from the dissociative adsorption of oxygen on the surface of molten oxide in the initial stage of reaction to the mass transfer of oxide ion from the surface to the inside of molten oxide in the following stage. Based on the kinetic analysis of the oxygen exchange process, CO2 dissociation rate constant, CO2 re-formation rate constant and the mass transfer coefficient of oxide ion in molten oxides were calculated for the FeOx-CaO and FeOx-SiO2 systems. Addition of CaO and SiO2 to molten oxide increases and decreases the oxygen exchange reaction rate, respectively.

Alkyne Exchange Reactions of Silylalkyne Complexes of Tantalum: Mechanistic Investigation and Its Application in the Preparation of New Tantalum Complexes Having Functional Alkynes (PhC⋮CR (R = COOMe, CONMe2))

Silylalkyne complexes of tantalum with the general formula TaCl3(R1C⋮CR2)L2 (1, R1 = R2 = SiMe3, L2 = DME; 2, R1 = SiMe3, R2 = Me, L2 = DME; 6, R1 = R2 = SiMe3, L = py; 7, R1 = SiMe3, R2 = Me, L = py) reacted with an internal alkyne to give corresponding alkyne complexes via an alkyne exchange reaction. These silylalkyne complexes were newly prepared and structurally characterized. Kinetic measurements revealed that the rates of the exchange reactions of the DME complexes 1 and 2 were first-order dependent on the concentration of the complex and the reaction proceeded via dissociative pathway. The exchange reaction rates of the bis(pyridine) complexes 6 and 7 were slower. In contrast to the DME complexes, the exchange reaction of 6 proceeded via an associative interchange pathway, and the exchange mechanism for 7 was an associative pathway. During the exchange, two pyridine ligands coordinated strongly to the tantalum center and the intermediate is proposed to be a bis(alkyne) complex. New tantalum comple...

Modelling the budget of middle atmospheric water vapour isotopes

Abstract. A one-dimensional chemistry model is applied to study the stable hydrogen (D) and stable oxygen isotope (17O, 18O) composition of water vapour in stratosphere and mesosphere. In the troposphere, this isotope composition is determined by "physical'' fractionation effects, that are phase changes (e.g. during cloud formation), diffusion processes (e.g. during evaporation from the ocean), and mixing of air masses. Due to these processes water vapour entering the stratosphere first shows isotope depletions in D/H relative to ocean water, which are ~5 times of those in 18O/16O, and secondly is mass-dependently fractionated (MDF), i.e. changes in the isotope ratio 17O/16O are ~0.52 times of those of 18O/16O. In contrast, in the stratosphere and mesosphere "chemical'' fractionation mechanisms, that are the production of HO due to the oxidation of methane, re-cycling of H2O via the HOx family, and isotope exchange reactions considerably enhance the isotope ratios in the water vapour imported from the troposphere. The model reasonably predicts overall enhancements of the stable isotope ratios in H2O by up to ~25% for D/H, ~8.5% for 17O/16O, and ~14% for 18O/16O in the mesosphere relative to the tropopause values. The 17O/16O and 18O/16O ratios in H2O are shown to be a measure of the relative fractions of HOx that receive the O atom either from the reservoirs O2 or O3. Throughout the middle atmosphere, MDF O2 is the major donator of oxygen atoms incorporated in OH and HO2 and thus in H2O. In the stratosphere the known mass-independent fractionation (MIF) signal in O3 is in a first step transferred to the NOx family and only in a second step to HOx and H2O. In contrast to CO2, O(1D) only plays a minor role in this MIF transfer. The major uncertainty in our calculation arises from poorly quantified isotope exchange reaction rate coefficients and kinetic isotope fractionation factors.

On the hexamethyldisiloxane dissociation paths in a remote Ar-fed expanding thermal plasma

In this paper we present primary hexamethyldisiloxane (HMDSO) molecule dissociation paths in a remote argon-fed expanding thermal plasma, where the HMDSO dissociation is initiated by charge exchange reactions with argon ions followed by dissociative recombination reactions with electrons. Investigation of the argon/HMDSO plasma chemistry by means of cavity ring down spectroscopy and threshold ionization mass spectrometry has allowed the detection and identification of radical species, such as CHx, SiCxHy and SiCHxO, and oligomerization products. The charge exchange reaction rate constant between argon ions and HMDSO molecules has been found to be equal to (4 ± 2) × 10−16 m3 s−1. This reaction has a dissociative character, i.e. the dissociation occurring at the Si–C and Si–O bonds accompanied by the abstraction of radicals, e.g. CH3 and OSi(CH3)3. Under the experimental conditions investigated, the ions produced via charge exchange reactions lead to negligible ion-induced oligomerization routes. Instead, they undergo recombination reactions with electrons, leading to Si–O bond dissociation and further abstraction of methyl radicals.

Comparison of gas‐phase acidities of some carbon acids with their rates of hydron exchange in methanolic methoxide

AbstractHydron exchange reaction rates, kexch M−1s−1, using methanolic sodium methoxide are compared with gas‐phase acidities, ΔG kcal/mol, for four 9‐YPhenylfluorenes‐9‐iH, seven YC6H4CiH(CF3)2, seven YC6H4CiHClCF3, and C6F5iH. Fourteen of the fluorinated benzylic compounds and pentafluorobenzene result in near unity experimental hydrogen isotope effects that suggest substantial amounts of internal return associated with the exchange process. Although the reactions of 9‐phenylfluorene have experimental isotope effects that appear to be normal in value, they do not obey the Swain–Schaad relationship. This suggests that they occur with small amounts of internal return. The entropies of activation, ΔS‡, are +12 to +14 eu, for the benzylic compounds and different significantly from those for the 9‐YPhenylfluorenes, ΔS‡ of −8 to −12 eu. The ΔS‡ ∼ 1 eu for the reactions of pentafluorobenzene falls between the other compounds. Density functional calculations using B3LYP/6‐31+G(d,p) are reported for the reactions of CH3O−(HOCH3)3 with C6F5H, C6H5CH(CF3)2, C6H5CHClCF3, and 9‐phenylfluorene. Copyright © 2006 John Wiley &amp; Sons, Ltd.

The recovery of labeled acetate in severely burned children 7 days after injury

Introduction A correction factor for acetate recovery must be measured for estimation of fatty acid oxidation in severely burned children. The purpose of the study was to determine the fractional recovery rate of labeled CO2 in the breath during the infusion of an acetate tracer in the basal state and during a hyperinsulinemic clamp. Methods Twelve children, aged 4 to 14 years with massive burns (total body surface area burned 61.2 ± 15.7 %), and admitted to the hospital within 4 days post-burn, participated in the study. All experiments were performed 7 days post-burn after an overnight fast. A primed (45 μmol/kg), constant (1.5 μmol·kg−1·min−1) infusion of [1,2-13C] acetate was given during a four hour basal period and during a four hour hyperinsulinemic-euglycemic clamp. A priming dose (150 μmol/kg) of NaH13CO3 was given at the beginning of the study. Breath samples were collected every 10 minutes during the last 40 minutes of each period. Indirect calorimetry was performed during the last 20 minutes of each period with a sensor medic metabolic cart. The isotopic enrichment of 13CO2 was determined by isotopic ratio-mass spectrometry. Results The fractional recovery of acetate label (i.e. the acetate correction factor) was 0.89 ± 0.05, and 0.91 ± 0.04, during the basal state and clamp, respectively. Conclusion The fractional recovery of labeled acetate in severely burned children is approximately three times the recovery of a non-burned adult, and close to the value of 1.0 in exercising adults. The high recovery rate reflects the rapid turnover of the TCA cycle in burned children relative to the rate of exchange reactions.

Sono-electroplating of Tin Film From Ti(IV)-EDTA Bath

SnCl4 and EDTA-4Na were dissolved in a 2 mol/dm3 CH3COOH - 2 mol/dm3 CH3COONa buffer solution, and was adjusted to pH4.1 by adding 2 mol/dm3 CH3COOH or 2 mol/dm3 CH3COONa solutions. 100 cm3 of the electrolyte was used. In the stationary state, Sn film was not deposited below 100 mA/cm2, and Sn film deposited in the range of 200 to 1000 mA/cm2. However, thickness was not obtained 1 μm. In the sonication, electrodeposited film obtained 5 ∼ 20 μm in the range of 200 to 1000 mA/cm2. Electrodeposition was carried out smoothly, because the mass transfer accelerated with ultrasonic agitation and Sn ion was supplied to electrode surface. Best conditions of sono-electroplating were 0.10 mol/dm3 SnY, pH 4.0, 298 K and 300 mA/cm2. The mass transfer and crystallization processes were most affected with micro-jet and shock wave pressure in the range of 200 ∼ 400 mA/cm2. Exchange current density and reaction rate constant in the sonication increased compared with that in the stationary and vibration states. As for this, an electron reaction becomes fast by the micro-jet or shock wave pressure. Reduction became difficult to break out as sonication was with powerful agitation. The deposited film was smooth and dense surface in the sonication compared with that in the stationary states by the shock wave pressure. [DOI: 10.1380/ejssnt.2006.574]

Use of Conductivity Relaxation Experiments to Evaluate Surface-Exchange Catalysts

Gas permeation through dense mixed ionic and electronic conductors (MIEC) depends on bulk transport of ionic and electronic species and the rates of surface chemical reactions. Decreasing the membrane thickness, decreases membrane resistance and enhances the permeation flux. However, below a critical thickness enhancements in flux can only occur due to improvement in the surface exchange reaction rates. The electrical conductivity relaxation (ECR) technique has been used to study oxygen surface exchange on bare and surface exchange catalyst-coated dense composite MIEC materials, comprising Gd 0.08 Sr 0.88 Ti 0.95 Al 0.05 O 3±δ (GSTA) and Gd 0.2 Ce 0.8 O 1.9 (GDC). The results show that ECR is an effective method for screening surface exchange catalysts.

Oxygen Exchange Reaction between CO2-CO Gas and Molten Oxide Containing Iron Oxide

Oxygen exchange reaction rates between CO 2 -CO gas and molten oxides containing iron oxide have been measured by isotope exchange technique with 18 O at 1 773 K with P CO2 /P CO =1. Measured results represent that the oxygen exchange reaction rates show the maximum values at the beginning of the reaction and sharply decrease within approximately 20s, and then gradually decrease with the reaction time proceeds. These changes indicate that the rate-limiting step would change from the dissociative adsorption of oxygen on the surface of molten oxide in the initial stage of reaction to the mass transfer of oxide ion from the surface to the inside of molten oxide in the following stage. Based on the kinetic analysis of the oxygen exchange process, CO 2 dissociation rate constant, CO 2 re-formation rate constant and the mass transfer coefficient of oxide ion in molten oxides were calculated for the FeO x -CaO and FeO x -SiO 2 systems. Addition of CaO and SiO 2 to molten oxide increases and decreases the oxygen exchange reaction rate, respectively.

β3 Tyrosine Phosphorylation and αvβ3-mediated Adhesion Are Required for Vav1 Association and Rho Activation in Leukocytes

Integrin alpha(v)beta(3)-mediated adhesion of hematopoietic cells to vitronectin results in activation of the Rho GTPases. Mutation of beta(3) tyrosine residue 747, previously shown to disrupt cell adhesion, results in sustained activation of Cdc42 and diminished Rac and Rho activity. We investigated the role of the hematopoietically restricted guanine nucleotide exchange factor Vav1 in alpha(v)beta(3)-mediated adhesion. We find that Vav1, a guanine nucleotide exchange factor for Rac and Rho, associates with alpha(v)beta(3) upon cell adhesion to vitronectin and that this association requires beta(3) tyrosine phosphorylation. Expression of exogenous Vav1 demonstrates that Y160F, but not wild type or the Vav1Y174F mutant, inhibits Rac and Rho activation during alpha(v)beta(3)-mediated cell adhesion to vitronectin. Cells expressing Vav1Y160F exhibit a sustained Cdc42 activation similar to nonphosphorylatable beta(3) mutants. In addition, cytoskeletal reorganization and cell adhesion are severely suppressed in Vav1Y160F-transfected cells, and Vav1Y160F fails to associate with beta(3) integrins. Furthermore, Vav1 itself is selectively phosphorylated upon tyrosine 160 after alpha(v)beta(3)-mediated adhesion, and the association between Vav1 and beta(3) occurs in specific response to adhesion to substrate. These studies describe a phosphorylation-dependent association between beta(3) integrin and Vav1 which is essential for cell progression to a Rho-dominant phenotype during cell adhesion.

Increasing the Reactivity of an Artificial Dithiol−Disulfide Pair through Modification of the Electrostatic Milieu

The thiol-disulfide exchange reaction plays a central role in the formation of disulfide bonds in newly synthesized proteins and is involved in many aspects of cellular metabolism. Because the thiolate form of the cysteine residue is the key reactive species, its electrostatic milieu is thought to play a key role in determining the rates of thiol disulfide exchange reactions. While modest reactivity effects have previously been seen in peptide model studies, here, we show that introduction of positive charges can have dramatic effects on disulfide bond formation on a structurally restricted surface. We have studied properties of vicinal cysteine residues in proteins using a model system based on redox-sensitive yellow fluorescent protein (rxYFP). In this system, the formation of a disulfide bond between two cysteines Cys149 and Cys202 is accompanied by a 2.2-fold decrease in fluorescence. Introduction of positively charged amino acids in the proximity of the two cysteines resulted in an up to 13-fold increase in reactivity toward glutathione disulfide. Determination of the individual pK(a) values of the cysteines showed that the observed increase in reactivity was caused by a decrease in the pK(a) value of Cys149, as well as favorable electrostatic interactions with the negatively charged reagents. The results presented here show that the electrostatic milieu of cysteine thiols in proteins can have substantial effects on the rates of the thiol-disulfide exchange reactions.

Kinetics of formation and dissociation of lanthanide(iii) complexes with the 13-membered macrocyclic ligand TRITA4−

The tetraazamacrocyclic ligand TRITA(4-) is intermediate in size between the widely studied and medically used 12-membered DOTA(4-) and the 14-membered TETA(4-). The kinetic inertness of GdTRITA(-) was characterized by the rates of exchange reactions with Zn(2+) and Eu(3+). In the Zn(2+) exchange, a second order [H(+)] dependence was found for the pseudo-first-order rate constant (k(0)=(4.2 +/- 0.5) x 10(-7) s(-1); k'=(3.5 +/- 0.3) x 10(-1) M(-1)s(-1), k" =(1.4 +/- 0.4) x 10(3) M(-2)s(-1)). In the Eu(3+) exchange, at pH <5 the rate decreases with increasing concentration of the exchanging ion, which can be accounted for by the transitional formation of dinuclear GdTRITAEu(2+) species. At physiological pH, the kinetic inertness of GdTRITA(-) is considerably lower than that of GdDOTA(-)(t(1/2)= 444 h (25 degrees C) vs. 3.8 x 10(5) h (37 degrees C), respectively). However, GdTRITA(-) is still kinetically more inert than GdDTPA(2-), the most commonly used MRI contrast agent (t(1/2)= 127 h). The formation reactions of LnTRITA(-) complexes (Ln = Ce, Gd and Yb) proceed via the rapid formation of a diprotonated intermediate and its subsequent deprotonation and rearrangement in a slow, OH(-) catalyzed process. The stability of the LnH(2)TRITA* intermediates (log K(LnH2L*)= 3.1-3.9) is lower than that of the DOTA-analogues. The rate constants of the OH(-) catalyzed step increase with decreasing lanthanide ion size, and are about twice as high as for DOTA-complexes.