New supramolecular architectures using hydrogen bonding

Abstract

Several new multiply hydrogen bonded complexes have been studied to determine their strength and the specificity with which they form. While many factors contribute to the stability of multiply hydrogen bonded complexes, it appears that the arrangement of the hydrogen bond donor and acceptor groups is a particularly good predictor of binding strength. The results are consistent with W. L. Jorgensen’s secondary electrostatic hypothesis. The heterocyclic recognition units that have been synthesized may serve as the basis for constructing new synthetic hosts or new self-assembling systems.

Self-Association without Regard to Prototropy. A Heterocycle That Forms Extremely Stable Quadruply Hydrogen-Bonded Dimers

“…Because the chemical shifts did not change and no new peaks appeared, only a lower limit to the dimerization constant, K dimer >10 7 M -1 , could be estimated. This is among the largest stability constants reported to date for a neutral, hydrogen-bonded species. ,, …”

“…In addition, a titration study carried out under conditions where dimerization of 6 ( 7 ) and 11 were minimal gave K assoc = 3033 M -1 (5% DMSO- d 6 /CDCl 3 ). That complex 9 ( 10 )· 11 is as robust as the aforementioned dimers is unexpected when solely considering secondary hydrogen-bond interactions. , This finding could indicate a preference for conformers 9 and 10 or that there are inherently stronger primary interactions in 9 · 11 and 10 · 11 . Preliminary computational studies support the latter.…”

“…There is a continuing challenge to develop a diverse set of molecular subunits for supramolecular assembly . Along these lines, we have a long-standing interest in heterocycles capable of forming robust hydrogen-bonded complexes in solution. , The use of heterocycles in this manner can, however, be complicated by prototropy . Although undesirable protomers are often converted to the desired form by complexation, the observed association constants ( K assoc ) are lowered, and the information content can be compromised.…”

“…Although undesirable protomers are often converted to the desired form by complexation, the observed association constants ( K assoc ) are lowered, and the information content can be compromised. For example, complex 1 · 2 , containing an AAA·DDD (A, D = hydrogen-bond acceptor and donor) motif, is the strongest, neutral triply hydrogen-bonded complex known. , However, its stability is lowered because in addition to the desired 1,4-dihydro form ( 2 ), a significant portion of the dihydropyridine monomer exists as the noncomplementary 3,4-dihydro form ( 3 ) in chloroform- d (CDCl 3 ) 2a …”

A Molecular Replication Process Drives Supramolecular Polymerization

“…This hydrogen-bonding pattern is self-complementary and allows the formation of homodimers in solution that are sufficiently stable ( K a ≈ 2 × 10 7 M –1 ) to drive − supramolecular polymerization. Polymers that rely on homodimerization of this recognition element have received significant attention. − However, this heterocyclic skeleton suffers − from a number of issues. First, the synthesis − of heterocylic ring systems that contain large numbers of contiguous hydrogen-bond donors or acceptors can be problematic.…”