Complexing behavior of rutin and quercetin

1991 ◽  
Vol 69 (12) ◽  
pp. 1994-2001 ◽  
Author(s):  
Graciela M. Escandar ◽  
Luis F. Sala
Keyword(s):  
Aqueous Solution ◽  
Transition Metal ◽  
Stability Constant ◽  
Key Words ◽  
Stability Constants ◽  
Metal Ion ◽  
Spectrophotometric Methods ◽  
Equilibrium Reactions ◽  
Rutin Aglycone ◽  
Rutin And Quercetin

The equilibrium reactions between rutin, 3-[6-O-(6-deoxy-α-L-mannopyranosyl)-(β-D-glucopyranosyl)oxy]-2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4H-1-benzopyran-4-one, and quercetin (rutin aglycone) with iron(III), copper(II), cobalt(II), and nickel(II) have been studied by potentiometric and spectrophotometric methods in aqueous solution. All measurements were carried out at t = 20 °C and μ = 0.10 M, and the corresponding stability constants were calculated by applying computational methods. The interactions between the proposed cations with both biological ligands and other related ones are compared, with simultaneous postulation of the probable structures. Key words: chelate stability constants of rutin, chelate stability constants of quercetin, transition metal ion interaction with flavonoids, stability constant determinations, potentiometric and spectrophotometric studies.

Transferrin binding of Al3+ and Fe3+.

1987 ◽  
Vol 33 (3) ◽  
pp. 405-407 ◽  
Author(s):  
R B Martin ◽  
J Savory ◽  
S Brown ◽  
R L Bertholf ◽  
M R Wills
Keyword(s):  
Stability Constant ◽  
Blood Plasma ◽  
Stability Constants ◽  
Metal Ion ◽  
Equilibrium Dialysis ◽  
Ion Binding ◽  
Metal Ion Binding ◽  
Quantitative Studies ◽  
Intensity Changes ◽  
The Stability

Abstract An understanding of Al3+-induced diseases requires identification of the blood carrier of Al3+ to the tissues where Al3+ exerts a toxic action. Quantitative studies demonstrate that the protein transferrin (iron-free) is the strongest Al3+ binder in blood plasma. Under plasma conditions of pH 7.4 and [HCO3-]27 mmol/L, the successive stability constant values for Al3+ binding to transferrin are log K1 = 12.9 and log K2 = 12.3. When the concentration of total Al3+ in plasma is 1 mumol/L, the free Al3+ concentration permitted by transferrin is 10(-14.6) mol/L, less than that allowed by insoluble Al(OH)3, by Al(OH)2H2PO4, or by complexing with citrate. Thus transferrin is the ultimate carrier of Al3+ in the blood. We also used intensity changes produced by metal ion binding to determine the stability constants for Fe3+ binding to transferrin: log K1 = 22.7 and log K2 = 22.1. These constants agree closely with a revision of the reported values obtained by equilibrium dialysis. By comparison with Fe3+ binding, the Al3+ stability constants are weaker than expected; this suggests that the significantly smaller Al3+ ions cannot coordinate to all the transferrin donor atoms available to Fe3+.

The affinity of aldehydic compounds to complex formation. Nickel(II) and cobalt(II) complexes with 2-pyridinecarboxaldehyde

1977 ◽  
Vol 55 (14) ◽  
pp. 2613-2619 ◽  
Author(s):  
M. S. El-Ezaby ◽  
M. A. El-Dessouky ◽  
N. M. Shuaib
Keyword(s):  
Complex Formation ◽  
Aqueous Solutions ◽  
Stability Constants ◽  
Metal Ion ◽  
Experimental Conditions ◽  
Complex Species ◽  
Spectrophotometric Methods ◽  
Complex Equilibria ◽  
The Stability ◽  
Hydroxy Groups

The interactions of Ni(II) and Co(II) with 2-pyridinecarboxaldehyde have been investigated in aqueous solutions at μ = 0.10 M (KNO3) at 30 °C. The stability constants of different complex equilibria have been determined using potentiometric methods. Spectrophotometric methods were also used in the case of the nickel(II) – 2-pyridinecarboxaldehyde system. It was concluded that nickel(II) and cobalt(II), analogous to copper(II), enhance hyrdation of 2-pyridinecarboxaldehyde prior to deprotonation of one of the geminal hydroxy groups. Complex species of 1:1 as well as 1:2 metal ion to ligand composition exist under the experimental conditions used.

scholarly journals Interaction of Ampicillin and Amoxicillin with Mn2+: A Speciation Study in Aqueous Solution

Molecules ◽  
2020 ◽  
Vol 25 (14) ◽  
pp. 3110
Author(s):  
Claudia Foti ◽  
Ottavia Giuffrè
Keyword(s):  
Aqueous Solution ◽  
Stability Constants ◽  
Metal Ion ◽  
Formation Constants ◽  
Enthalpy Change ◽  
Ligand Concentration ◽  
Empirical Parameter ◽  
Speciation Study ◽  
Potentiometric Measurements ◽  
The Stability

A potentiometric and UV spectrophotometric investigation on Mn2+-ampicillin and Mn2+-amoxicillin systems in NaCl aqueous solution is reported. The potentiometric measurements were carried out under different conditions of temperature (15 ≤ t/°C ≤ 37). The obtained speciation pattern includes two species for both the investigated systems. More in detail, for system containing ampicillin MLH and ML species, for that containing amoxicillin, MLH2 and MLH ones. The spectrophotometric findings have fully confirmed the results obtained by potentiometry for both the systems, in terms of speciation models as well as the stability constants of the formed species. Enthalpy change values were calculated via the dependence of formation constants of the species on temperature. The sequestering ability of ampicillin and amoxicillin towards Mn2+ was also evaluated under different conditions of pH and temperature via pL0.5 empirical parameter (i.e., cologarithm of the ligand concentration required to sequester 50% of the metal ion present in traces).

Stability constants of metal ion complexes formed with N3-deprotonated uridine in aqueous solution

2003 ◽  
Vol 6 (1) ◽  
pp. 90-93 ◽  
Author(s):  
Bernd Knobloch ◽  
Carla P Da Costa ◽  
Wolfgang Linert ◽  
Helmut Sigel
Keyword(s):  
Aqueous Solution ◽  
Stability Constants ◽  
Metal Ion ◽  
Metal Ion Complexes

Solution properties of metal ion complexes formed with the antiviral and cytostatic nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]-2-amino-6-dimethylaminopurine (PME2A6DMAP)

2014 ◽  
Vol 92 (8) ◽  
pp. 771-780 ◽  
Author(s):  
Raquel B. Gómez-Coca ◽  
Astrid Sigel ◽  
Bert P. Operschall ◽  
Antonín Holý ◽  
Helmut Sigel
Keyword(s):  
Aqueous Solution ◽  
Stability Constants ◽  
Metal Ion ◽  
Present System ◽  
Therapeutic Effects ◽  
Solution Properties ◽  
Acidity Constants ◽  
Nucleotide Analogue ◽  
Ether Oxygen ◽  
The Stability

The acidity constants of protonated 9-[2-(phosphonomethoxy)ethyl]-2-amino-6-dimethylaminopurine (H3(PME2A6DMAP)+) are considered, and the stability constants of the M(H;PME2A6DMAP)+ and M(PME2A6DMAP) complexes (M2+ = Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, or Cd2+) were measured by potentiometric pH titrations in aqueous solution (25 °C; I = 0.1 mol/L, NaNO3). In the M(H;PME2A6DMAP)+ species, H+ and M2+ (mainly outersphere) are at the phosphonate group; this is relevant for phosphoryl-diester bridges in nucleic acids because, in the present system, there is no indication for a M2+–purine binding. This contrasts, for example, with the complexes formed by 9-[2-(phosphonomethoxy)ethyl]adenine, M(H;PMEA)+, where M2+ is mainly situated at the adenine residue. Application of log [Formula: see text] vs. [Formula: see text] plots for simple phosph(on)ate ligands, R–PO32− (R being a residue that does not affect M2+ binding), proves that all M(PME2A6DMAP) complexes have larger stabilities than what would be expected for a M2+–phosphonate coordination. Comparisons with M(PME–R) complexes, where R is a noncoordinating residue of the (phosphonomethoxy)ethane chain, allow one to conclude that the increased stability is due to the formation of five-membered chelates involving the ether–oxygen of the –CH2–O–CH2–PO32− residue: the percentages of formation of these M(PME2A6DMAP)cl/O chelates, which occur in intramolecular equilibria, vary between 20% (Sr2+, Ba2+) and 50% (Zn2+, Cd2+), up to a maximum of 67% (Cu2+). Any M2+ interaction with N3 or N7 of the purine moiety, as in the parent M(PMEA) complexes, is suppressed by the (C2)NH2 and (C6)N(CH3)2 substituents. This observation, together with the previously determined stacking properties, offers an explanation why PME2A6DMAP2– has remarkable therapeutic effects.

Measurement of the interaction of aqueous copper(II) with a model amyloid-β protein fragment — Interference from buffers

2011 ◽  
Vol 89 (12) ◽  
pp. 1429-1444 ◽  
Author(s):  
Michael H. Benn ◽  
Arvi Rauk ◽  
Thomas W. Swaddle
Keyword(s):  
Aqueous Solution ◽  
Stability Constant ◽  
Stability Constants ◽  
Amyloid Β ◽  
Buffer System ◽  
Amyloid Β Protein ◽  
Buffer Solution ◽  
Solution Ph ◽  
Physiological Importance

For the formation of a complex of Cu2+ with the amyloid-β (Aβ) proxy N-α-dihydrourocanylhistamine (L) in unbuffered aqueous solution (pH ∼ 5.7, 25.0 °C), UV spectrophotometric measurements give a stability constant of 3.8 × 105 L mol–1. This stability constant is within the lower limit of the range of stability constants reported in the literature for complexes of Aβ with Cu2+ — as expected, in view of the smaller number of coordination sites in L. Computer modeling indicates that the Cu2+–L complex is CuL(H2O)22+, with terdentate L bound to Cu2+ via two Nπ atoms and the O atom of the peptide link. Attempts to make stability constant measurements for Cu2+ with L in aqueous solution buffered with Tris/TrisH+/ClO4– to pH near 7.2 were unsuccessful because the Tris base when in large excess over CuL2+ promoted its dissociation to Cu2+ + L by scavenging free Cu2+ as Cu(Tris)(TrisH–1)+, or when in roughly equimolar concentrations formed a ternary adduct, CuL(Tris)2+. The interactions of Cu2+ with Tris buffer were re-examined spectrophotometrically and with the aid of computations that show that the most stable Cu2+–Tris complexes are the syn- and anti-isomers of Cu(Tris)22+, but in the experimental pH ranges these are present as Cu(Tris)(TrisH–1)+. Since Cu2+(aq) is strongly complexed by almost any base capable of forming a buffer system with near-physiological pH, stability constants reported for Cu2+–Aβ complexes in any buffer solution should be regarded with skepticism unless interactions of the buffer with Cu2+ and with CuAβ2+ are taken quantitatively into account. Moreover, in vivo, biological buffers will reduce the physiological importance of Aβ–Cu2+ complexes by competing with Aβ for Cu2+.

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