Hydrogen bonding association of a ruthenium(II) bipyridine barbituric acid guest to complementary 2,6-diaminopyridine amide hosts: guidelines for designing high binding hydrogen bonding cavities in both high-and low-polarity solvents

Abstract

The binding between a ruthenium polypyridine guest RuG2, (where Ru = 4,4'-di-tert-butyl-bpy) 2 Ru (bpy = 2,2'-bipyridine) and G2 = 5-[4-(4'-methyl)-2,2'-bipyridyl]methyl-2,4,6-(1H,3H,5H)-pyrimidinetrione, and a series of host acyl derivatives of 3,5-bis[(6-aminopyrid-2-yl) amino]carbonylpyridine (R/H = n-Pr/H, phenyl/H, CF 3 /H, t-Bu/H, -(CH 2 ) 3 -CO 2 À H) and 3,5-bis[(6-amino-4-isopropoxypyrid-2-yl)amino]carbonylpyridine diacetyl derivative (R/X = CH 3 /i-OPr) was studied by fluorescence and NMR titrations. The RuG2 (which exists in the enolate form in the presence of the hosts) forms a number of H-bonds involving the amide groups of the hosts and the carbonyl groups of the G2 for all the hosts studied. Specific 1:1 association between RuG2 and all the complementary hosts was observed with binding constants, K a (l mol À1 ), for R/H in CH 2 Cl 2 of 3 Â 10 5 (t-Bu/H), 5 Â 10 6 (Ph/H), 3 Â 10 7 (n-Pr/H), 9 Â 10 7 (CF 3 /H) and b10 8 [-(CH 2 ) 3 CO 2 H) and for R/X of 4 Â 10 8 (Me/i-OPr). Similar, but weaker, binding was also observed in solvents of higher donor number such as d 6 -acetone, d 3 -acetonitrile and d 6 -DMSO with R/X = Me/i-OPr host showing the highest binding constant in CH 2 Cl 2 , d 6 -acetone and d 6 -DMSO. Differences in the binding constants of the ruthenium guest RuG2 to these hosts are analyzed in terms of the steric, electronic and solvational changes in the structure of the host amide substituents and the polarity of the solvents used.

An Enolisable Barbiturate with Adjustable Hydrogen‐Bonding Structure for UV/Vis Detection of Nucleic Acid Bases and Related Compounds

“…Thus, for example, for the complexation of different ruthenium(II) bipyridine barbiturates with a 2,6‐diaminopyridine derivative, values of 10–170 M −1 have been reported. In this case, however, there are aggregates stabilised by six hydrogen bonds 23. For the formation of the cytidine‐guanosine three‐hydrogen‐bond complex in DMSO, a value of K A =3.7±0.6 M −1 has been reported 24.…”

Ultrafast Photoinduced Electron Transfer within a Self-Assembled Donor−Acceptor System

“…The photophysical properties of the assembly BAr f − H1 · G2 were studied in DCM. A high binding constant in DCM, which is anticipated to be on the order of 10 5 M -1 , , enables to study the photoinduced processes at low concentrations, while bimolecular processes between the two free components are prevented.…”

“…The host and guest motif were chosen because of the high association constant of the assembly (typically on the order of 10 5 -10 8 M -1 in chlorinated solvents), which can be optimized using different substituents. 34 Furthermore, the complementarity of the host and the guest results in a 1:1 self-assembled complex, avoiding a statistic distribution of species in solution. The noncovalent linked dyad resulting from the self-assembly of H1 and G2 can be compared with the analogous covalent system having a rhenium complex that contains a bipyridine functionalized with a methyl viologen unit.…”

“…The host and guest motif were chosen because of the high association constant of the assembly (typically on the order of 10 5 −10 8 M -1 in chlorinated solvents), which can be optimized using different substituents . Furthermore, the complementarity of the host and the guest results in a 1:1 self-assembled complex, avoiding a statistic distribution of species in solution.…”

Photo-induced processes in dendrimers

“…From these studies, it was clear that the receptor can be a powerful tool to create stable supramolecular assemblies with barbiturates, even in solvents that are competitive for the receptor site [43].…”