Decoding nitric oxide release rates of amine-based diazeniumdiolates

Mechanisms of nitric oxide generation in living systems

In modern chemical and biochemical studies, special attention is paid to molecular systems capable of generating nitric oxide (NO), which is one of the most important signalling molecules in the body and can trigger a whole cascade of reactions. Despite the importance of this molecule, the mechanisms of its formation in living organisms remain a subject of debate. This review combines the most important methods of releasing NO from endogenous and exogenous sources. The history of endogenous NO donors dates back more than 150 years, since the synthesis of nitroglycerin, which remains the standard vasodilator today, even though it is known that it and many other similar compounds lead to the development of a nitrate tolerance. Particular awareness is devoted to the mechanisms of NO formation without the participation of enzymes, since these methods are most important for creating exogenous sources of NO as drugs. The study of NO formation methods is centred on both the creation of new NO donors and understanding the mechanisms of tolerance to them.

The HNO- radical anion: A proposed intermediate in diazeniumdiolate synthesis using nitric oxide and alkoxides

The strategy of synthesizing diazeniumdiolates (X-N(O)=NO^-) through the coexistence of nitric oxide and alkoxides (RO^-) was introduced by Wilhelm Traube 120 years ago. Today, despite the wide use of diazeniumdiolate derivatives to release nitric oxide in the treatment of cancer, the first step of the reaction mechanism for diazeniumdiolate synthesis remains a mystery and is thought to be complex. We have studied the gas-phase reactions of nitric oxide with alkoxides at room temperature. An electron-coupled hydrogen transfer is observed, and the radical anion HNO^- is the only ionic product in these reactions. HNO^- can further react with nitric oxide to form N₂O and HO^-.

Managing bacterial biofilms with chitosan-based polymeric nitric oxides: Inactivation of biofilm bacteria and synergistic effects with antibiotics

In this study, we developed a new approach in the preparation of chitosan-based polymeric nitric oxides. Chitosan film (unreacted chitosan) reacted with glutaraldehyde to introduce aldehyde groups onto the material surface (glutaraldehyde-treated chitosan). Glutaraldehyde-treated chitosan reacted with a small-molecule nitric oxide donor, 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene, to covalently immobilize nitric oxide–releasing moieties onto the polymer (chitosan-based polymeric nitric oxide). Chitosan-based polymeric nitric oxide showed sustained release of nitric oxide. The activation energies and rate constants of nitric oxide release were determined. The released nitric oxide provided potent antimicrobial effects against Gram-positive and Gram-negative bacteria living in biofilms, and the chitosan-based polymeric nitric oxide film showed added/synergistic effects with common antibiotics. At 4°C, the chitosan-based polymeric nitric oxide could be stored for more than 1 month, without significantly losing nitric oxide–releasing capabilities. Furthermore, chitosan-based polymeric nitric oxide showed excellent biocompatibility with mammalian cells, pointing to great potentials of the new materials for a wide range of biomedical applications.

Aminolysis of an N-diazeniumdiolated amidine as an approach to diazeniumdiolated ammonia

Recent theoretical studies have suggested that the parent diazeniumdiolate ion, H₂N–N(O)=NO^– (“diazeniumdiolated ammonia”), might be stable enough to be isolated and that it could potentially serve as a uniquely advantageous prodrug form of bioactive nitroxyl (HNO). Here, we report on an attempt to isolate its O²-benzylated derivative by aminolysis of the C=N bond in PhC(NH₂)=N–N(O)=NOBn. The reaction proved remarkably sluggish in comparison to aminolysis of unsubstituted benzamidine, and the desired product could not be isolated, apparently because of base sensitivity of the NH₂ group. Consistent with this interpretation, O-benzylhydroxylamine and N₂O were recovered from the reaction mixture in high yields, along with N,N′-dibutylbenzamidine. Theoretical calculations rationalize the observed slow aminolysis by demonstrating that the diazeniumdiolate group greatly suppresses the electrophilicity of the adjacent C=N carbon center, rendering attack at that position endothermic. The data provide significant insights into the challenges inherent to the pursuit of diazeniumdiolated ammonia.

A comparative study of NONOate based NO donors: spermine NONOate is the best suited NO donor for angiogenesis

Nitric oxide (NO) is a known modulator of angiogenesis. The NONOate subfamily of NO donors has long been used in experimental and clinical studies to promote angiogenesis. However, no studies have been conducted yet to compare the angiogenesis potential of these NO donors in respect to their pattern of NO release. We hypothesize that having different pattern of NO release, each of the NO donors in NONOate subfamily can promote key stages of angiogenesis in differential manner. To verify our hypothesis, NO donors with half life ranging from seconds to several hours and having very different pattern of NO release were selected to evaluate their efficacy in modulating angiogenesis. Endothelial tube formation using EAhy926 cells was maximally increased by Spermine NONOate (SP) treatment. SP treatment maximally induced both ex vivo and in vivo angiogenesis using egg yolk and cotton plug angiogenesis models respectively. Experiment using chick embryo partial ischemia model revealed SP as the best suited NO donor to recover ischemia driven hampered angiogenesis. The present study elaborated that differential release pattern of NO by different NO donors can modulate angiogenesis differentially and also suggested that SP have a unique pattern of NO release that best fits for angiogenesis.