Sustained antimicrobial activity and reduced toxicity of oxidative biocides through biodegradable microparticles.

The spread of antibiotic-resistant pathogens requires new treatments. Small molecule precursor compounds that produce oxidative biocides with well-established antimicrobial properties could provide a range of new therapeutic products to combat resistant infections. The aim of this study was to investigate a novel biomaterials-based approach for the manufacture, targeted delivery and controlled release of a peroxygen donor (sodium percarbonate) combined with an acetyl donor (tetraacetylethylenediamine) to deliver local antimicrobial activity via a dynamic equilibrium mixture of hydrogen peroxide and peracetic acid. Entrapment of the pre-cursor compounds into hierarchically structured degradable microparticles was achieved using an innovative dry manufacturing process involving thermally induced phase separation (TIPS) that circumvented compound decomposition associated with conventional microparticle manufacture. The microparticles provided controlled release of hydrogen peroxide and peracetic acid that led to rapid and sustained killing of multiple drug-resistant organisms (methicillin-resistant Staphylococcus aureus and carbapenem-resistant Escherichia coli) without associated cytotoxicity in vitro nor intracutaneous reactivity in vivo. The results from this study demonstrate for the first time that microparticles loaded with acetyl and peroxygen donors retain their antimicrobial activity whilst eliciting no host toxicity. In doing so, it overcomes the detrimental effects that have prevented oxidative biocides from being used as alternatives to conventional antibiotics. STATEMENT OF SIGNIFICANCE: The manuscript explores a novel approach to utilize the antimicrobial activity of oxidative species for sustained killing of multiple drug-resistant organisms without causing collateral tissue damage. The results demonstrate, for the first time, the ability to load pre-cursor compounds into porous polymeric structures that results in their release and conversion into oxidative species in a controlled manner. Until now, the use of oxidative species has not been considered as a candidate therapeutic replacement for conventional antibiotics due to difficulties associated with handling during manufacture and controlling sustained release without causing undesirable tissue damage. The ultimate impact of the research could be the creation of new materials-based anti-infective chemotherapeutic agents that have minimal potential for giving rise to antimicrobial resistance.

Unusual stability and carbon acidity of a dicationic carbon species.

1,1'-Methylenebis(pyridinium) dication (MDP) is an unusual ion with two formal positively charged substituents attached to a central carbon, yet it is remarkably stable to hydrolysis at pH < 8. However, above this pH it undergoes a biphasic reaction liberating two equiv of pyridine sequentially. The rate of the first phase is second order in hydroxide ion, while that of the second is pH-independent. The first phase is also accompanied by the generation of a chromophore at 366 nm, which has been identified as a pyridine-ring-opened unsaturated iminoaldehyde formed by an ANRORC-type mechanism. This intermediate then undergoes ring closure to give the second equiv of pyridine and formaldehyde. Below pD 8 there is a very slow alternative pathway for degradation that is first order in hydroxide ion, liberates only one equiv of pyridine, and forms N-(hydroxymethyl)pyridinium ion. Deuterium exchange of the central methylene in D2O is faster than the breakdown of MDP and is predominantly OD(-)-catalyzed with a small amount of buffer catalysis. The estimated pKa of MDP dication in H2O, 21.2 at 25 °C and I = 1.0 M (KCl), is unexpectedly high but is about 9 units lower than that for the monocationic N-methylpyridinium ion. Deuterium exchange also occurs at the 2 and 6 positions of the pyridinium rings, but at a lower rate that is first order in deuteroxide ion and competitive with the breakdown of MDP only below pD 11.

The relative hydrolytic reactivities of pyrophosphites and pyrophosphates.

The pH-rate profiles for the hydrolysis of pyrophosphate (PP(V)) and pyrophosphite (PP(III), pyro-di-H-phosphonate) are a complex function of pH, reflecting the different ionic species and their relative reactivities. PP(III) is more reactive than PP(V) at all pHs and only PP(III) shows a hydroxide-ion reaction at high pH, so it is 10(10)-fold more reactive than PP(V) in 0.1 M NaOH. The pK(a2) of PP(III) ~0.44, so the dominant species at pH's > 1 is the di-anion PP(III)(2-). Although there is no observable (NMR or ITC) binding of Mg(2+) to the PP(III) di-anion there is a modest increase in the rate of hydrolysis of PP(III) by Mg(2+). PP(III) is neither a substrate nor an inhibitor of pyrophosphatase, the enzyme that efficiently catalyses the hydrolysis of PP(V).