Schiff bases of pyridoxal 5'-phosphate and 5'-deoxypyridoxal with phenylglycine derivatives and their metal complexes

Abstract

Potentiometric p [H] measurements are employed to evaluate protonation constants, metal complex stabilities, and Schiff base (SB) formation constants in solutions containing pyridoxal 5'-phosphate (PLP) 5'-deoxypyridoxal (DPL), phenylglycine and its derivatives, and divalent transition-metal ions at 25 O C and at an ionic strength of 0.100 M (KN03). Protonation constants for phenylglycine (PG), (4-methoxyphenyl)glycine (MPG), and (4-sulfophenyl)glycine (SPG) indicate that these synthetic amino acids are more acidic than glycine and other natural amino acids. Stability constants are reported for 1:l and 1:2 complexes of Mn2', Co*', Ni2', Cu2+, and Zn2+ with PG, MPG, and SPG. Hydrolysis of these metal ions complicates the study of the nature of the metal complex formed at high p [H]. The vitamin B6 derivatives, pyridoxal 5'-phosphate and 5'-deoxypyridoxal, were found to form only 1:l metal complexes. The equilibrium constants for the formation of Schiff bases by PLP and DPL with PG, MPG, and SPG are reported. The monoprotonated form of the Schiff base was found to be the most stable species in each of the systems studied. The equilibrium constants are reported for protonated 1:l Cu(I1)-Schiff base complexes, CuSBH,"+ and for 1:l and 2:1 Schiff base complexes of Mn(II), Co(II), Ni(II), and Zn(I1). The formation of a number of hydroxometal Schiff base chelates in alkaline solutions is observed. The equilibrium constants determined are employed to calculate the distribution of complex species as a function of p [H] in solutions containing these ligands and the metal ions identified above.The transfer of a nitrosyl ligand between neutral and oxidized iron and cobalt metalloporphyrins in dichloromethane solutions was investigated by electrochemistry and FTIR or ESR spectroelectrochemistry. The transfer of NO from (P)Co(NO) to (P)Fe, from [(P)Co(NO)]' to (P)FeC104, and from [(P)Fe(NO)]+ to (P)Co was demonstrated for complexes where P = the dianion of tetraphenylporphyrin (TPP), meso-tetrakis(2,4,6-trimethylphenyl)porphyrin (TMP), or octaethylporphyrin (OEP). The driving force in these reactions is related to both the nature and oxidation state of the central metal in (P)M(NO) or [(P)M(NO)]+, where M = Fe or Co, and follows the order (P)Fe(NO) > (P)Co(NO) > [(P)Fe(NO)]' > [(P)Co(NO)]'.

Kinetic Selectivity and Thermodynamic Features of Competitive Imine Formation in Dynamic Covalent Chemistry

“…Pyridoxalp hosphate (2)w as chosen as aldehyde reactanti n view of its role as coenzymef or aw ide range of different reactions, [52,[54][55][56] involving amino acids and other biological pro-cesses. [57][58] It has also been used in dynamic covalents ystems.…”

Oxovanadium(iv and v) and copper(ii) complexes of N-salicyl-glycylglycine and N-salicyl-glycylglycylglycine

“…13 In 1 and 2 intramolecular H-bonding is possible between the phenolic O atom and the amine H atoms. By comparison with the corresponding acidity constants of H 2 salGly (pK 2 = 8.16, I = 0.2 M), 13 salicylaldehyde (pK = 8.13, I = 0.15 M) and salicylamide (pK = 8.89, I = 3.0 M), 42 and Schiff bases derived from pyridoxal-5Ј-phosphate (and derivatives) and phenylglycine (and derivatives) (pK = 7.1-7.3, I = 0.10 M), 43 we suggest that the pK values of ca. 7.4-7.6 may be ascribed to the phenolic protons.…”

Pyridoxal Based Fluorescent Chemosensor for Detection of Copper(II) in Solution With Moderate Selectivity and Live Cell Imaging

“…Pyridoxal moiety imparts a physiological feasibility as it is the biologically active form of vitamin B 6 , pyridoxal 5-phosphate (PLP) and a versatile enzyme cofactor responsible for amino acid metabolism in organisms ranging from bacteria to human . Several metal complexes of Schiff bases derived from pyridoxal and amino acids/polyamines have been reported [51][52][53][54][55][56][57][58][59][60][61][62]. Recently, a new Schiff base was generated by condensing equimolar pyridoxal with 2-aminoethyl pyridine and its vanadium and copper complexes were prepared [63,64].…”