title: Alkali Metal Ion Complexes with Phosphates, Nucleotides, Amino Acids, and Related Ligands of Biological Relevance. Their Properties in Solution.
abstract: Alkali metal ions play very important roles in all biological systems, some of them are essential for life. Their concentration depends on several physiological factors and is very variable. For example, sodium concentrations in human fluids vary from quite low (e.g., 8.2 mmol dm(-3) in mature maternal milk) to high values (0.14 mol dm(-3) in blood plasma). While many data on the concentration of Na(+) and K(+) in various fluids are available, the information on other alkali metal cations is scarce. Since many vital functions depend on the network of interactions occurring in various biofluids, this chapter reviews their complex formation with phosphates, nucleotides, amino acids, and related ligands of biological relevance. Literature data on this topic are quite rare if compared to other cations. Generally, the stability of alkali metal ion complexes of organic and inorganic ligands is rather low (usually log K < 2) and depends on the charge of the ligand, owing to the ionic nature of the interactions. At the same time, the size of the cation is an important factor that influences the stability: very often, but not always (e.g., for sulfate), it follows the trend Li(+) > Na(+) > K(+) > Rb(+) > Cs(+). For example, for citrate it is: log K ML = 0.88, 0.80, 0.48, 0.38, and 0.13 at 25 °C and infinite dilution. Some considerations are made on the main aspects related to the difficulties in the determination of weak complexes. The importance of the alkali metal ion complexes was also studied in the light of modelling natural fluids and in the use of these cations as probes for different processes. Some empirical relationships are proposed for the dependence of the stability constants of Na(+) complexes on the ligand charge, as well as for correlations among log K values of NaL, KL or LiL species (L = generic ligand).
authors: Dipartimento di Scienze Chimiche, Università di Messina, Viale F. Stagno d'Alcontres, 31, I-98166, Messina, Italy.
authors: Francesco
authors: F
authors: Crea
authors: Dipartimento di Scienze Chimiche, Università di Messina, Viale F. Stagno d'Alcontres, 31, I-98166, Messina, Italy.
authors: Concetta
authors: C
authors: De Stefano
authors: Dipartimento di Scienze Chimiche, Università di Messina, Viale F. Stagno d'Alcontres, 31, I-98166, Messina, Italy.
authors: Claudia
authors: C
authors: Foti
authors: Dipartimento di Scienze Chimiche, Università di Messina, Viale F. Stagno d'Alcontres, 31, I-98166, Messina, Italy.
authors: Gabriele
authors: G
authors: Lando
authors: Dipartimento di Scienze Chimiche, Università di Messina, Viale F. Stagno d'Alcontres, 31, I-98166, Messina, Italy.
authors: Demetrio
authors: D
authors: Milea
authors: Dipartimento di Scienze Chimiche, Università di Messina, Viale F. Stagno d'Alcontres, 31, I-98166, Messina, Italy. ssammartano@unime.it.
authors: Silvio
authors: S
authors: Sammartano
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D001826:Body Fluids / Q000737:chemistry*; D002412:Cations; D006801:Humans; D008024:Ligands; D008672:Metals, Alkali / Q000737:chemistry*; D009711:Nucleotides / Q000737:chemistry*; D009942:Organometallic Compounds; D010710:Phosphates / Q000737:chemistry*; D012996:Solutions; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D002412:Cations; D008024:Ligands; D008672:Metals, Alkali; D009711:Nucleotides; D009942:Organometallic Compounds; D010710:Phosphates; D012996:Solutions
keywords: Empirical relationships; Formation constants; Models; Speciation; Thermodynamic parameters