Controlled Photochemical Release of Nitric Oxide from O²-Benzyl-Substituted Diazeniumdiolates

Abstract

An investigation of potential photosensitive protecting groups for diazeniumdiolates (R2N-N(O)=NO-) has been initiated, and here the effect of meta electron-donating groups on the photochemistry of O2-benzyl-substituted diazeniumdiolates (R2N-N(O)=NOCH2Ar) is reported. Photolysis of the parent benzyl derivative (Ar = Ph) results almost exclusively in undesired photochemistry-the formation of nitrosamine and an oxynitrene intermediate with very little, if any, photorelease of the diazeniumdiolate. We have been able to use meta substitution to tune the photochemistry of these benzylic systems. The desired diazeniumdiolate photorelease has been shown to become more substantial with stronger pi-donating meta substituents. This effect has been verified by direct observation of the photoreleased diazeniumdiolate with 1H NMR spectroscopy and by NO quantification measurements conducted in high- and low-pH solutions. In addition, the observed rates of NO release are consistent with that expected for normal thermal decomposition of the diazeniumdiolate in aqueous solutions and also show the same pH dependence.

Generation of nitric oxide by photolysis of silver hyponitrite in suspension induced by LMCT excitation

“…The photochemical formation of NO is of special value because it is controlled by light. In addition to organic precursors [8][9][10][11][12], light-sensitive coordination compounds [13][14][15][16][17][18] play an important role. In particular, nitrosyl complexes have been investigated in quite some detail.…”

Photosensitive Precursors to Nitric Oxide

“…Importantly, this precursor overcomes the shortcomings of the previously studied benzyl derivatives [15]. The high efficiency of diazeniumdiolate photorelease is not pH dependent and can be initiated by long wavelength (≥ 350 nm) light, making this diazeniumdiolate precursor potentially well-suited for a range of biological applications.…”

“…Subsequent to the above studies, a series of metasubstituted O 2 -benzyl-substituted diazeniumdiolates was reported as a potential class of photosensitive precursors to diazeniumdiolates [15]. These studies attempted to take advantage of the well established meta-effect of electrondonating and electron-withdrawing groups in benzylic systems [16][17][18].…”

“…Such substitution has been shown to favor the formation of ionic products in photochemical reactions. On the basis of this previous work, a series of O 2 -benzylsubstituted diazeniumdiolates, 5 -9, was prepared and the effect of electron-donating meta substituents on the efficiency of NO release was examined [15]. Results concerning the photochemistry (Rayonet, 300 nm in 90% aqueous acetonitrile) of 5 -9 were interpreted in terms of Path A (undesired) and Path B (desired) shown in (Fig.…”

“…Additionally, da Silva and co-workers have reported a macrocyclic ruthenium nitrosyl complex, trans-[RuCl( [15] aneN 4 )NO] 2+ , where [15]aneN 4 is a tetraazamacrocyclic ligand of 15 members. Following 355 nm laser flash photolysis in aqueous solution, trans-[RuCl( [15]aneN 4 ) NO] 2+ releases NO with a quantum yield of 0.61 [70].…”