Kinetic and equilibrium studies of the acid dissociation of the cobalt(II) complexes of N,N'-dialkyl- 1,10-phenanthroline-2,9-dimathanamine ligands

1999 ◽  
Vol 77 (9) ◽  
pp. 1471-1475 ◽  
Author(s):  
Hongwei Sun ◽  
Zhifen Zhou ◽  
Huakuan Lin ◽  
Guanghua Zhao ◽  
Shourong Zhu ◽  
...  
Keyword(s):  
Linear Relationship ◽  
Key Words ◽  
Dissociation Rate ◽  
Acid Dissociation ◽  
Stopped Flow ◽  
Isokinetic Temperature ◽  
Dissociation Kinetics ◽  
Equilibrium Studies ◽  
Complexation Property ◽  
Kinetics Of

The complexation property and the acid dissociation kinetics of four N,N'-dialkyl-1,10-phenanthroline-2,9-dimathanamine complexes with cobalt(II) were studied using a pH meter and a stopped-flow spectrophotometer. In 6.6 × 10-3~0.5 mol dm-3 HCl (I = 0.5 mol dm-3 HCl + NaCl), the dissociation rate follows the law kobs = kK2[H+]/(1 + K2[H+]). The acid dissociation can be rationalized in terms of a four-step kinetic process involving two rapid pre-equilibrium protonations and rate-determining cleavage of the Co(II)-N(phenanthroline) bond. The temperature dependence of the rate was determined, and the appropriate thermodynamic parameters were obtained. The linear relationship between ΔH not equal and ΔS not equal suggests that an isokinetic temperature, Tiso of 282 ± 2 K exists. Key words: N,N'-dialkyl-1,10-phenanthroline-2,9-dimathanamine, complexation property, acid dissociation kinetics, mechanism, cobalt(II) complex.

Kinetic and Equilibrium Studies of the Reactions of Cyanide Ion with 1,3,5-Trinitrobenzene, 2,4,6-Trinitroanisole, and 2,4,6-Trinitrotoluene in Isopropanol

1974 ◽  
Vol 52 (1) ◽  
pp. 8-17 ◽  
Author(s):  
Leong Huat Gan ◽  
Albert Richard Norris
Keyword(s):  
Standard Enthalpy ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Stopped Flow ◽  
Cyanide Ion ◽  
Equilibrium Studies ◽  
Kinetics Of Formation ◽  
Kinetics Of

Equilibrium constants for the formation of 1:1 cyanide ion σ-complexes with 1,3,5-trinitrobenzene, 2,4,6-trinitroanisole, and 2,4,6-trinitrotoluene have been determined spectrophotometrically over a range of temperatures. Standard enthalpy (ΔH0) and entropy (ΔS0) changes associated with each reaction have been evaluated. The kinetics of formation of the σ-complexes have been investigated by means of a stopped-flow technique and the activation parameters characterizing the formation of each complex have been determined. Evidence is presented which indicates the cyanide ion – 2,4,6-trinitroanisole σ-complex formed in isopropanol contains the cyanide ion bonded exclusively at the C-3 position.

Acid dissociation kinetics of the deprotonated nickel(II)-tetraglycinamide complex

1980 ◽  
Vol 19 (2) ◽  
pp. 497-500 ◽  
Author(s):  
John M. T. Raycheba ◽  
Dale W. Margerum
Keyword(s):  
Acid Dissociation ◽  
Dissociation Kinetics ◽  
Kinetics Of

Dissociation kinetics of metal complexes in aqueous acid. III. The effects of methyl substitution and chelate ring size on the rates of dissociation of copper(II) triazamacrocyclic complexes

1984 ◽  
Vol 37 (11) ◽  
pp. 2243 ◽  
Author(s):  
PG Graham ◽  
DC Weatherburn
Keyword(s):  
Chelate Ring ◽  
Acid Dissociation ◽  
Ring Size ◽  
Dissociation Kinetics ◽  
Methyl Substitution ◽  
First Order ◽  
Aqueous Acid ◽  
Kinetics Of ◽  
Chelate Ring Size ◽  
Acid Dependence

The acid dissociation kinetics of mono copper(II) complexes of the ligands 2-methyl-1,4,7-triazacyclononane, mznn ; 1,4,7-triazacycloundecane, zaud ; 1,4,7-triazacyclododecane, zadd ; and 1,5,9-triazacyclotetradecane, zted were studied in aqueous solution over a range of acid concentra- tions (0.025-0.5 mol 1-1), I1.0 (NaN03). Cu(mznn)2+ displays a first-order dependence on [H+] with kH (298 K) 26 1. mol-1 s-1. The other complexes show an acid dependence at low [H+] but become independent of acid at higher concentrations. The acid-independent rate constants k1 were determined to be Cu(zaud)2+, 67 s-1 (280 K); Cu(zadd)2+, 45 s-1 (298 K); Cu(zted)2+ 50 s-1 (298 K). The results are compared with those obtained with other copper(II) triazamacro- cyclic complexes.

scholarly journals Identification of key components in the irreversibility of salmon calcitonin binding to calcitonin receptors

2000 ◽  
Vol 166 (1) ◽  
pp. 213-226 ◽  
Author(s):  
JM Hilton ◽  
M Dowton ◽  
S Houssami ◽  
PM Sexton
Keyword(s):  
Salmon Calcitonin ◽  
Time Course ◽  
Alpha Helix ◽  
Structural Features ◽  
Dissociation Rate ◽  
Human Calcitonin ◽  
Dissociation Kinetics ◽  
Binding Competition ◽  
Calcitonin Receptors ◽  
Kinetics Of

This study investigates the poor reversibility of salmon calcitonin (sCT) binding to rat and human calcitonin receptors. Efficacy of CT and analogue peptides in (125)I-sCT binding competition and cAMP assays was compared with the dissociation kinetics of (125)I-labelled peptides. Assessment was performed on cells stably expressing either rat or human calcitonin receptors. Dissociation kinetics of the antagonists, sCT(8-32) and AC512, revealed that binding was rapidly and completely reversible at the receptors, despite high affinity binding, suggesting that poor reversibility required the active conformation of the receptor. G protein coupling was not essential as the dissociation kinetics of (125)I-sCT binding to cell membranes did not significantly alter in the presence of GTP gamma S. Time course experiments established that the transition to irreversibility was slow, while the reversible component of binding appeared to involve a single population of either receptor states or binding sites. Pre-bound (125)I-human CT dissociated rapidly from the receptors, indicating that not all agonists bound irreversibly. To identify structural features of sCT that contribute to its poor reversibility, dissociation kinetics of sCT analogues with various structural modifications were examined. Increasing truncation of N-terminal residues of sCT analogues led to a corresponding increase in the rate of peptide dissociation. Salmon CT peptides which had been substituted at the N-terminus by 13-21 residues of human CT (hCT) were equipotent with sCT in binding competition and cAMP accumulation assays but exhibited a dissociation rate similar to hCT. In contrast, despite lower affinity and efficacy at the receptors, the chimeric analogue sCT(1-16)-hCT(17-32) displayed poorly reversible binding, similar to sCT. Analysis of the dissociation kinetics of sCT analogues with differing alpha-helix forming potential indicated that the ability to form alpha-helical secondary structure was an important factor in the rate of ligand dissociation. We hypothesise that poor reversibility results from a conformational change in the receptor and/or ligand and that this is dependent, at least in part, on interaction with residues constrained within the alpha-helix of the peptide.

Dissociation kinetics of DNA-anthracycline and DNA-anthraquinone complexes determined by stopped-flow spectrophotometry

1985 ◽  
Vol 34 (6) ◽  
pp. 733-736 ◽  
Author(s):  
Bijukumar M. Gandecha ◽  
Jeffrey R. Brown ◽  
Michael R. Crampton
Keyword(s):  
Stopped Flow ◽  
Dissociation Kinetics ◽  
Kinetics Of

scholarly journals The kinetics of antibody binding to membrane antigens in solution and at the cell surface

1980 ◽  
Vol 187 (1) ◽  
pp. 1-20 ◽  
Author(s):  
D W Mason ◽  
A F Williams
Keyword(s):  
Cell Surface ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Surface Antigens ◽  
Dissociation Rate ◽  
Simple Relationship ◽  
Dissociation Kinetics ◽  
Cell Surface Antigens ◽  
Dissociation Rate Constants ◽  
Kinetics Of

The reaction kinetics of 125I-labelled mouse monoclonal antibodies binding to three cell-surface antigens of rat thymocytes (Thy-1.1, W3/25) were studied. The differences between bivalent and univalent interactions were determined by using antibody in the F(ab′)2 or Fab′ form and by using antigen in polymeric or monomeric forms. Association rate constants (k+1), dissociation rate constants (k-1) and equilibrium constants were determined. Also, the dissociation kinetics of rabbit antibodies against rat Thy-1 antigen were studied. The major findings were as follows. (i) With F(ab′)2 antibody there was no simple relationship between antigen density at the cell surface and extent of bivalent binding. Extensive univalent binding was observed unless the antibody had a high k-1 for the univalent interaction, in which case all binding was bivalent. (ii) k+1 values were similar for F(ab′)2 or Fab′ antibody, and for the different antibodies were in the range 0.8 × 10(5)–1.1 × 10(6) M-1.s-1. These differences were sufficient to affect the interpretation of serological assays with the different antibodies. (iii) Antibody bound bivalently dissociated much more slowly than that bound univalently. However, the k-1 values for the univalently bound antibody were sufficiently low in most cases that the lifetime of the univalent complex was similar to or greater than the time needed for the assay. Thus the results could be interpreted on the basis of irreversible reactions. The overall conclusion from the study is that for an understanding of the binding of antibody to cell-surface antigens the kinetics of the interaction are of major importance and theories based on equilibrium binding are inappropriate.

Acid dissociation kinetics of the copper(II) complex of a 15-membered mixed N3O2 donor macrocycle

1994 ◽  
Vol 19 (5) ◽  
pp. 559-560 ◽  
Author(s):  
Robert W. Hay ◽  
Mansour M. Hassan ◽  
David E. Fenton ◽  
Brian P. Murphy
Keyword(s):  
Acid Dissociation ◽  
Dissociation Kinetics ◽  
Kinetics Of
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