Hydrogen-bonded networks in crystals built from bis(biguanides) and their salts

Abstract

Biguanide groups and biguanidinium cations incorporate multiple sites that can donate or accept hydrogen bonds. To assess their ability to associate and to direct the formation of extended hydrogen-bonded networks, we examined the structure of crystals of four compounds in which two neutral biguanide groups or the corresponding cations are attached to the 1,4-and 1,3-positions of phenylene spacers. As expected, all four structures incorporate extensive networks of hydrogen bonds and reveal other reliable features. In particular, (1) neutral biguanide groups favor a roughly planar conformation with an intramolecular hydrogen bond, and they associate as hydrogen-bonded pairs, (2) despite coulombic repulsion, biguanidinium cations can also associate as hydrogen-bonded pairs, and (3) the 1,3-phenylenebis(biguanidinium) dication favors a pincerlike conformation that allows chelation of suitable counterions. However, the precise patterns of hydrogen bonding in the structures vary substantially, limiting the usefulness of biguanide and biguanidinium as groups for directing supramolecular assembly. Résumé :Des groupes biguanide et des cations biguanidinium incorporent de multiples sites qui peuvent donner ou accepter des liaisons hydrogène. Dans le but d'évaluer la capacité d'associer et de diriger la formation de réseaux étendus de liaisons hydrogène, on a étudié la structure cristalline de quatre composés dans lesquels deux groupes biguanide neutres, ou les cations correspondants, sont attachés aux positions 1,4-et 1,3-de groupes phénylènes. Comme prévu, les quatre structures permettent d'incorporer des réseaux de liaisons hydrogène et mettent en évidence d'autres caracté-ristiques fiables. En particulier, 1) les groupes biguanide neutres favorisent une conformation pratiquement plane avec une liaison hydrogène intramoléculaire et s'associent sous la forme de paires réunies par des liaisons hydrogène, 2) malgré une répulsion coulombique, les cations biguanidinium peuvent aussi former des paires associées par des liaisons hydrogène et 3) le dication phénylène-1,3-bis(biguanidinium) favorise une conformation en forme de pince qui permet d'effectuer une chélation avec des contre-ions appropriés. Toutefois, les régimes précis des liaisons hydrogène varient d'une façon substantielle, ce qui limite l'utilité des groupes biguanide et biguanidinium comme unités pouvant orienter un assemblage supramoléculaire.

Physical and Chemical Characterization of Poly(hexamethylene biguanide) Hydrochloride

“…After the first heating ramp, a clear glass transition was detected both in cooling and heating, at ~341 K; but no fusion or crystallization occurred, indicating that if crystallization takes place it is a very slow process, needing a very long heat treatment time. The amorphous nature of PHMB agrees with previous reports, but the glass transition disagrees with results obtained from literature [5,7]. One explanation is presence of water, which has a plasticizing effect, and a distinct molecular weight.…”

“…The same properties that makes PHMB effective as biocide also makes it an interesting molecule to technological applications: It is as good a metal chelator as its parent molecule, biguanide [6]; the five conjugated amines can bind to neighboring molecules with multiple hydrogen bonds, which is attractive for supramolecular chemistry [7]; films of PHMB are transparent and very adherent to metal, plastics and glass; it is a proton conductor, potentially applicable to proton exchange membrane fuel cells [8]; finally, it is soluble in both water and alcohol, commonly used as solvents for paints and lacquers [9].…”

Triguanide Derivatives: Synthesis, Crystal Structure and Evaluation of the Proliferation Effect on Some Tumor Cell Lines

“…Specifically, the plane defined by the C1, N1 and N2 atoms (Figure 2) forms an angle of 61.0(1)° with the plane of the rest of the triguanide moiety. A similar feature was observed in previously reported X‐ray structures of the biguanide salts where the angles between the guanidine submoieties lie in the range of 50–67° 24a,24b,26. Nonetheless, the positive charge is highly delocalized along the triguanide chain, as evidenced by the similar lengths of the C–N bonds within the triguanide backbone (Table S4).…”

Cucurbit[7]uril Host–Guest Complexes with Biguanidinium Cations in Aqueous Solution

“…In addition, biguanide can serve as a base and as a ligand for transition‐metal complexes 2a. The biguanide group and its conjugate acid, the biguanidinium cation, have donor and acceptor sites for hydrogen bonding, allowing for the formation of supramolecular complexes and assemblies 2b. The simplest mono(biguanide) drug, metformin hydrochloride (Figure 1), is an orally administered biguanide drug used to lower blood glucose levels in patients with type 2 diabetes 3,4.…”