Synthesis, Characterisation and Antimicrobial Activity of Novel Phosphine Stablised Silver (1) Dicarboxylate Complexes

The α, ω-dicarboxylic acids HOOC-(CH2)n-COOH (where n = 1-11) reacted smoothly with [Ag(CH3COO)] to yield 11 novel silver dicarboxylate complexes. These silver dicarboxylates were reacted with triphenylphosphine (PPh3) in 1:2.5, 1:4 and 1:6 molar ratios resulting in the isolation of 30 novel silver dicarboxylate triphenylphosphine derivatives. X-ray crystal structures for nine of these complexes were determined showing a variation in the structural motifs across the series with mononuclear, dinuclear, polynuclear and polymeric species being generated. When the 11 novel silver dicarboxylate complexes were reacted with bis-(diphenylphosphino)methane (dppm) in a 1:2 molar ratio 11 novel complexes were isolated. The complexes were isolated as powders and 8 of them formulated as [Ag2(dicarboxylate)(dppm)4] with the remainder having just three dppm ligands in their formulae. The only crystals isolated from this series precipitated from the mother liquor of the reaction involving dodecanedicarboxylic acid (dddaH2), which formulated as {Ag2(dppm)2(ddda)(H2O)}n and whose structure comprises a linear polymer in which centrosymmetric Ag2(dppm)2 units are linked by diacid anions. The 11 novel silver dicarboxylate complexes were reacted with bis-(diphenylphosphino)ethane (dppe) in a 1:2 molar ratio using the same procedure employed for the dppm reactions to yield 11 novel complexes which again were isolated as powders and formulated as either [Ag2(dicarboxylate)(dppe)4] or [Ag2(dicarboxylate)(dppe)3]. All of the complexes were found to have limited solubilities and the phosphine derivatives were all relatively light stable compared to simple silver salts such as AgNO3. The metal free dicarboxylic acids and phosphine based ligands are relatively poor antifungals and display no antibacterial activity. The 11 silver dicarboxylate complexes are potent in-vitro anti-Candida agents but only five of them displayed good antibacterial activity, although it was significantly less than that of AgNO3. Furthermore, unlike the activity of AgNO3 these five complexes displayed some discrimination towards the Grampositive (S. aureus /MRSA) and Gramnegative (E.coli) bacteria suggesting that these complexes do not act on microbial cells in the same way as AgNO3. All of the PPh3 complexes exhibited significant antifungal activity against the Candida albicans cells although their activity is, on average, over ten times less than that of the equivalent silver dicarboxylate. Only 5 of these complexes are active against the bacterial cells tested. Three of these complexes display higher antibacterial activity (comparable to that of AgNO3) than antifungal activity, a trend not previously observed. The dppm and dppe derivatives all exhibited significant antifungal activity against the Candida albicans cells. However, most of their activities are again significantly less than that of the equivalent silver dicarboxylate. Only three of these complexes display any activity against the bacterial cells tested and one of them exhibits good activity against the Grampositive MRSA but it is inactive against the Gramnegative E.coli