Synthesis and Structural Characterization of Silver(I) and Gold(I) Complexes with 2-Mercaptonicotinic Acid (H2mna) and Triphenylphosphine Ligands, and Their Antimicrobial Activities. Crystal Structures of Monomeric, 3- and 4-Coordinate Silver(I) Complexes [Ag(Hmna)(PPh3)2] and [Ag(Hmna)(PPh3)3] in the Solid State

Abstract

Two types of silver(I)-triphenylphosphine complexes with 2-mercaptonicotinic acid (H2mna) were prepared as [Ag(Hmna)(PPh3)n] (1, n = 2; 2, n = 3); their crystal structures determined by single-crystal X-ray diffraction. These complexes were obtained from reactions of the precursor, [Ag(Hmna)]n, with less excess (3 equiv) and large excess (20 equiv) amounts of PPh3, respectively. Complex 1 was also obtained from a reaction among another precursor [AgCl(PPh3)3], H2mna and aqueous NaOH. The coordination geometry of 1 was a trigonal pyramid with an AgSP2 core; there was a weak interaction between the silver(I) center and the pyridine nitrogen atom, while that of 2 was a distorted tetrahedron with an AgSP3 core. In both 1 and 2, the carboxyl group was protonated and its oxygen atoms did not participate in the coordination. In contrast to the formation of 1 and 2, a related complex, [Ag(Hmba)(PPh3)3] 4 (H2mba = 2–mercaptobenzoic acid), has been obtained from a reaction of [Ag(Hmba)]n with a stoichiometric amount (3 equiv) of PPh3. On the other hand, the gold(I) complex, [Au(Hmna)(PPh3)] 3, with a 2-coordinate AuSP core, was prepared by a stoichiometric reaction among [AuCl(PPh3)], H2mna and aqueous NaOH. Complex 3 in the solid state showed a supramolecular array based on a repetition of hydrogen-bonding interactions between the carboxyl group and the pyridine nitrogen atom, also being contrasted to the related complex, [Au(Hmba)(PPh3)] 5, with a hydrogen-bonding dimer structure in the solid state. In CHCl3, both 1 and 2 were present as several equilibrium species due to a successive dissociation of PPh3 ligands, while 3 was present as an almost monomer. The antimicrobial activities in aqueous media of 1—5, evaluated by minimum inhibitory concentration (MIC), were also tested.

Silver coordination compounds: A new horizon in medicine

“…The choice of saccharinate as the co-ligand followed the observation that silver(I) species bearing N,O-donors seem to target bacterial proteins containing thiol groups in their active sites. The soft character of sulfur-containing groups makes them apt to coordinate the equally soft silver(I) centers, so that the more labile N,O-donors are easily replaced by the thiol groups [6,[67][68][69]. It was also noticed that the easier the ligand is replaced, the wider the spectrum of antimicrobial activity [70].…”

Synthesis and antimicrobial activities of gold(I) sulfanylcarboxylates

“…In this last field, the compounds under investigation include a major collection of the type R 3 PAuL, in which the gold atom is coordinated to a phosphine ligand and L is an O- [26,27], N- [28,29], Cl- [30] or S- [29,[31][32][33][34][35] 2 ], Na 3 [Au(mna) 2 ] (H 2 mna 02-mercaptonicotinic acid) [13] and the cationic complexes [Au(L) 2 ](NO 3 ) 3 (L01-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea) [34]. For the latter ligand, compounds of the type [Au(L)]Br, [Au(L)] SCN and [Au(L)]Cl were also prepared [34] and the coexistence of an S-donor ligand and a Cl ligand was also described for [LAuCl] (where L 02,3-diphenyl-1,3,4-thiadiazolium-5-thiolato-S exo ) [36].…”

Pt(II) and Ag(I) complexes with acesulfame: Crystal structure and a study of their antitumoral, antimicrobial and antiviral activities

“…The mechanism of antimicrobial activity of Ag(I) complexes has been scarcely reported, although three possible mechanisms for inhibition of bacteria growing by aqueous Ag(I) ions was proposed: (i) interference with the electron transport system; (ii) DNA-binding; and (iii) interaction with the cell membrane [13,16]. Nomiya and co-workers [13,17,18] suggested that Ag(I) complexes with good leaving groups, especially those containing N/O donor atoms, are able to target some bacterial proteins which possess S containing ligands in their active sites. The molecules containing N/O donor atoms are easily replaced in the silver coordination sphere by S-ligands found in the bacterial proteins active sites.…”