Chemical and photochemical properties of a ruthenium nitrosyl complex with the N-monosubstituted cyclam 1-(3-Propylammonium)-1,4,8,11-tetraazacyclotetradecane

Abstract

O complexo aminofuncionalizado trans-[Ru(NO)Cl(1-pramcyH)](PF 6 ) 3 (1-pramcyH = 1-(3-propilamônio)-1,4,8,11-tetraazaciclotetradecano) foi sintetizado através da reação do trans-[RuCl(tfms)(1-pramcyH)](tfms) 2 (tfms = trifluorometanossulfonato) com óxido nítrico (NO) em solução aquosa ácida. O complexo foi caracterizado por análise elementar, espectroscópica (UVvis, IV, RMN de 1 H e 13 C) e eletroquímica. Dois valores de pK a (7,0 e 8,2) foram determinados para trans- [Ru(NO) ](PF 6 ) 3 e foram atribuídos a um dos prótons do grupo amina do cyclam e ao propilamônio. A redução do trans- [Ru(NO) ] 3+ leva à saída rápida de cloreto seguida de saída lenta de NO, enquanto a irradiação do complexo em solução aquosa desaerada resulta na labilização fotoquímica do NO. O rendimento quântico para a fotoaquação do NO diminui com o aumento do comprimento de onda de irradiação e com a diminuição do pH, e é observável apenas a l irr < 370 nm. O comportamento do trans- [Ru(NO) ] 3+ é semelhante ao do complexo análogo trans- [Ru(NO) Cl(cyclam)] 2+ , porém difere daquele do complexo com carboxipropil como substituinte.The amine-functionalized trans- [Ru(NO) ](PF 6 ) 3 complex (1-pramcyH = 1-(3-propylammonium)-1,4,8,11-tetraazacyclotetradecane) was synthesized from trans- [RuCl(tfms) (1-pramcyH)](tfms) 2 (tfms = trifluoromethanesulfonate) in acidic aqueous solution in the presence of nitric oxide (NO). The complex was characterized by elemental, spectroscopic (UV-Vis, IR, 1 H and 13 C NMR) and electrochemical analyses. Two pK a values (7.0 and 8.2) were estimated for trans- [Ru(NO) ](PF 6 ) 3 and were assigned to one of the cyclam nitrogen protons and to the protonated aminopropyl group. Reduction of trans- [Ru(NO) ] 3+ results in rapid loss of chloride followed by slower loss of NO, while irradiation of the complex in aqueous deaerated conditions suggests photochemical labilization of NO. The quantum yields for NO photoaquation decrease as the irradiation wavelength increases, being noticeable only at l irr < 370 nm, and increase as pH increases. The behavior of trans- [Ru(NO) ] 3+ , which contains an aminopropyl substituted cyclam, parallels that reported for the analogous complex with the unsubstituted ligand, but differs from that described for the complex in which carboxypropyl is the substituent. Keywords: nitrosyl, ruthenium, nitric oxide donor, substituted cylam, mono-N-functionalized cyclam IntroductionThe discovery of the participation of nitric oxide (NO) in a wide range of physiological processes and pathologies 1 has launched investigations on NO donors, including metal nitrosyl complexes in solution or immobilized in matrices, aiming at the understanding of both fundamental aspects and biological activity for potential applications. Among the NO donors, ruthenium nitrosyl complexes are particularly attractive because they are stable, can be either water soluble or not, deliver NO at different rates upon activation by reduction at biologically accessible Chemical and Photochemical Properties of a Ruthenium Nitrosyl...

The nature of Ru–NO bonds in ruthenium tetraazamacrocycle nitrosyl complexes—a computational study

“…This strategy has been explored using mono-N-substituted cyclam with carboxyor amino-propyl groups. [56][57][58] It should be stressed that controlling the properties of the complex, such as electronic spectra, reduction potential, and specific rate constant of the release of NO, is crucial for biological applications. [15][16][17][18][19][20][21][22][23]37,38,[59][60][61][62][63] Tetraazamacrocycles such as cyclam and its derivatives are fairly flexible; they adopt five different configurations, depending on the spatial alignment of the NH protons (Fig.…”

The versatile ruthenium(II/III) tetraazamacrocycle complexes and their nitrosyl derivatives

“…Despite the presence of the propylammonium group, the electrode reactivity of trans-[Ru(NO)Cl(1-pramcyclam)] 3+ is similar to that of trans-[Ru(NO)Cl(cyclam)] 2+ in aqueous solution or acetonitrile [33]. Thus, the reactions in Scheme 2 apply as well.…”

“…It is well understood that electrochemical data are important not only to characterize but also to understand and predict the reactivities of complexes, as is the case of Ru III/II redox potentials of macrocyclic complexes [21,22,24,25,[32][33][34][35][36]47,[68][69][70]79,[147][148][149]. These values are reasonably close to those of analogous complexes with non-cyclic amines [24,34,148], and are dependent on ring size, increasing slightly as the macrocyclic cavity increases, as can be seen for the [14]aneN4, [15]aneN4, and [16]aneN4 trans-dichlorido complexes whose values are −150, −125, and −95 mV vs NHE, respectively (Table 4).…”

“…For instance, cyclam derivatives with N-appended groups such as polyaromatic chromophores, crown ethers, alkyl chains bearing terminal amides, amines, carboxylic acid, or thiol groups, among others, have been reported [28][29][30]. Although several Co, Cr, Ni and Cu complexes with these N-functionalized ligands have been prepared [9,31], few Ru analogs are known, perhaps because of synthetic difficulties [13,14,32,33]. Furthermore, the presence of a N-appended group may result in structural and property differences for Ru complexes as has been observed for the nitrosyl complexes trans-[Ru(NO)Cl(1-pramcyclam)](PF 6 ) 3 [33], fac-[Ru(NO)Cl 2 ( 3 N 4 ,N 8 ,N 11 (1-carboxypropyl)cyclam)]Cl [13] (Fig.…”

“…4) [43,44]. Ruthenium nitrosyl complexes exhibit favorable properties for biological application as NO delivery agents, such as solubility in water, induced release of NO by chemical, electrochemical or photochemical means, and also thermal stability; notably they do not decompose for years [5,33,34,39,43,[45][46][47]. They also proved to have biological activity .…”