Thermodynamics of sulfate anion binding by macrocyclic polyammonium receptors
The interaction of SO42− with polyammonium cations derived from fourteen polyamines (5 polyazacycloalkanes, 2 polyazacyclophanes, 3 phenanthrolinacyclophanes, 2 dibenzenacyclophanes and 2 acyclic polyamines) in aqueous solution has been studied by means of potentiometric and microcalorimetric techniques. Only 1 : 1 receptor–anion complexes have been found in solution. Complexed species of considerable stability are formed, although the two acyclic polyamines (dimethylpentaethylenehexaamine and dimethylhexaethyleneheptaamine) and the smallest phenanthrolinacyclophane do not interact with the anion. The complexation reactions are endothermic, or almost athermic, and promoted by invariably fav…
Dinuclear Zn II Complexes of Polydentate Polyamines as Minimalist Models of Hydrolytic Reactions
The synthesis of the novel macrocycle 2,6,9,12,16-pentaaza[17](2,9)(1,10)phenanthrolinophane (L3) is reported. Speciation studies on the systems ZnII−L3 and ZnII−L2 (L2 =2,6,10,13,17,21-hexaaza[22]metacyclophane) performed in aqueous solution show the formation of mono- and dinuclear ZnII complexes. In the two systems, the dinuclear complexes readily hydroxylate, with the hydroxo species being the main ones in solution at relatively low pH values. This feature makes these complexes promising hydrolytic agents for carboxy and phosphate esters. The hydrolytic ability of the L1−L3 dinuclear complexes toward the carboxy and phosphate ester bond was tested by addition of p-nitrophenyl acetate (N…
Potential ATPase mimics by polyammonium macrocycles: Criteria for catalytic activity
Abstract A series of polyammonium macrocycles, ranging in size from the 18-membered ring [18]aneN6 to the 36-membered [36]aneN12 were examined as potential ATPase mimics. The rates of hydrolysis of ATP were followed at pH 3.0 and 7.0 using 31P NMR and HPLC techniques. Stability constants as a function of degree of protonation, distribution curves for the ligands as a function of pH, and distribution curves for the mixed species of nucleotides, inorganic phosphate, and macrocycle were also determined. All of the macrocycles catalyzed the hydrolysis of ATP to some extent compared to noncatalyzed hydrolysis. A critical dependence on macrocyclic ring size was observed, with [21]aneN7 being the …
Proton coordination by polyamine compounds in aqueous solution
Abstract The present article is concerned with proton transfer reactions in aqueous solution of open-chain, macrocyclic and macropolycyclic or cage compounds having nitrogen atoms as protonation sites in the molecular framework, although several compounds with additional different donors will be considered. The main purpose of this review is to collect some significant examples of proton transfer processes in order to show how the electronic properties and molecular topology of polyamines affect the thermodynamic parameters of their protonation equilibria.
Proton and metal binding by cyclen-based highly rigid cryptands.
The basicity properties of the two cryptands L1 and L2, featuring, respectively, a dibenzofuran or a diphenyl ether moiety bridging the 1,7 positions of a 1,4,7,10-tetraazacyclododecane macrocycle (cyclen) have been studied by means of potentiometric, UV-vis and fluorescence emission measurements. Both ligands show a high basicity in the first protonation step, the first basicity constant of L1 being too high to be measured in aqueous solution. The crystal structure of {[HL1]L1}(+) shows that the NH(2)(+) group is involved in an intramolecular hydrogen bonding network, which justifies the observed high basicity in solution. (1)H, (13)C NMR, UV-vis and fluorescence emission measurements show…
The Role of Macrocyclic Receptors in Organization of Metal Centers
The coordination properties of saturated aza or oxa-aza macrocyclic receptors are strictly dependent on their molecular topology. In order to rationalize the relationship between structural features and binding characteristics of such molecules we have studied the coordination behavior of different macrocyclic or macropolycyclic oxa-aza ligands towards metal cations. Depending on molecular topology, a variety of inorganic chemical species can be lodged inside the receptor’s cavity, such as simple metal ions, complexed inorganic anions, partially hydrated metal cations or binuclear assemblies.
Effect of Nitrogen Methylation on Cation and Anion Coordination by Hexa- and Heptaazamacrocycles. Catalytic Properties of These Ligands in ATP Dephosphorylation
The stability constants of the complexes formed by 1,10-dimethyl-1,4,7,10,13,16-hexaazacyclooctadecane (L) and 1,4,7-trimethyl-1,4,7,10,13,16,19-heptaazacyclohenicosane (L1) with Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Pb(2+), as well as that for the formation of PbL2(2+) (L2 = 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane), were determined by means of potentiometric (pH-metric) titrations in 0.15 mol dm(-)(3) NaClO(4) at 298.1 +/- 0.1 K. The enthalpy changes for the formation of Cu(2+) complexes with L and L1 were measured by means of microcalorimetry. These thermodynamic data were compared with those previously reported for L2, 1,4,7,10,13,16-hexaazacyclooctadecane (L3), and 1,4,…
Cascade complex formation by phosphate in the cobalt(II)/[30]aneN10 anaerobic system
Abstract The interaction of phosphate with the mono- and binuclear cobalt(II) complexes of [30]aneN 10 (1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane) has been studied by potentiometry in 0.15 mol dm −3 NaClO 4 solution at 298.15 K under anaerobic conditions. The stable species [CoH 2 ([30]aneN 10 )PO 4 ] + , [CoH 4 ([30]aneN 10 )PO 4 ] 3+ , [Co 2 H([30]aneN 10 )PO 4 ] 2+ , [Co 2 H 2 ([30]aneN 10 )PO 4 ] 3+ and [Co 2 H 3 ([30]aneN 10 )PO 4 ] 4+ , where the phosphate anion is directly bound to the metal ions or acts as a second sphere ligand, are formed and their stability constants have been determined. The results obtained allowed for the selection of suitable conditions for the study…
Interaction of Zn(II) and Cd(II) with Large Polyazacycloalkanes in dmso/H2O (80:20 vol./vol.). A potentiometric Study.
Abstract A potentiometric study on the interaction at 25 °C and 0.15 mol dm −3 between large polyazacycloalkanes of the series [3 k ]aneN k and Zn(II) and Cd(II) ions in dmso:H 2 O (80:20 vol./vol.) is reported. The protonation behavior of the free macrocycles and coordination trends are compared with those previously observed in aqueous solution. The main features observed in the mixed solvent are: similar protonation behavior of the free polyamines, greater tendency to form binuclear and protonated complexes and a lower tendency to bear hydrolytic reactions.
Thermodynamic study of the interaction of long open-chain polyazaalkanes with cobalt(II) and nickel(II) ions
Complexation equilibria between the open-chain terminally methylated polyamines 1,14-bis(methylamino)-3,6,9,12- tetraazatetradecane (L1), 1,17-bis(methylamino)-3,6,9,12,15-pentaazaheptadecane (L2), 1,20-bis(methylamino)- 3,6,9,12,15,18-hexaazaicosane (L3) and 1,23-bis(methylamino)-3,6,9,12,15,18,21-heptaazatricosane (L4) with Co2+ and Ni2+ have been studied by means of potentiometric and spectrophotometric methods in 0.15 mol dm−3 NaClO4 aqueous solution at 298.15 K The stability constants for the complexes formed have been determined from e.m.f, data. All these ligands form mononuclear ML2+ complexes of similar stability with Co2+ and Ni2+. Binuclear Co2L44+, Ni2L34+ and Ni2L44+ are also f…
Cation and Anion Coordination Chemistry of Palladium(II) with Polyazacycloalkanes. Thermodynamic and Structural Studies
The interaction of PdCI2 4 - with the macrocyclic ligands of the series [3k]aneNk has been studied both in solution and in the solid state. [18]aneN6 and [21]aneN7 form both mono- and binuclear Pd2+ complexes, whose stability constants have been determined in 0.5 mol dm-3 NaCI at 298.15 K. [21]aneN7 also forms, in solution, a trinuclear species in which an amino group deprotonates to bridge two Pd2+ ions, as observed in the solid state. The crystal structure of the complexes [Pd2([18]aneN6)Cl2][CIO4]2 and [Pd3[21]aneN7)CI3][CIO4]2 ⋅ H2O have been solved by single crystal X-ray analysis. C12H30N6CI4O8Pd2: monoclinic, space group C2/m, a = 10.876(2), b = 18.117(2), c = 7.043(2) A, s = 113.78(…
Polyfunctional recognition of pyridinedicarboxylate anions with macrocyclic polyamine receptors containing heteroaromatic groups.
The interaction of the biologically relevant anions deriving from the six pyridinedicarboxylic acids (H2PDC) with two macrocyclic receptors containing a pentamine chain and a bipyridine (1) or a phenanthroline (2) moiety, as well as with the aliphatic analogue [21]aneN7 (3), was studied by means of spectroscopic methods (UV-vis, NMR) and potentiometric titrations affording the stability constants of the adducts formed. All three receptors form stable complexes with the substrates thanks to the formation of several salt bridges and hydrogen bond contacts, as observed in the crystal structure of the H8[3(2,6-PDC)4] x H2O x 0.5 EtOH solid compound. Additional pi-stacking interactions between t…
ChemInform Abstract: Proton Coordination by Polyamine Compounds in Aqueous Solution
Abstract The present article is concerned with proton transfer reactions in aqueous solution of open-chain, macrocyclic and macropolycyclic or cage compounds having nitrogen atoms as protonation sites in the molecular framework, although several compounds with additional different donors will be considered. The main purpose of this review is to collect some significant examples of proton transfer processes in order to show how the electronic properties and molecular topology of polyamines affect the thermodynamic parameters of their protonation equilibria.