Structural characterization and antibacterial activity of oligoguanidine (polyhexamethylene guanidine hydrochloride)

Polyguanidine oligomers, particularly polyhexamethylene biguanide (PHMB) oligomer, are used extensively and safely as disinfectants and biocides. The antibacterial activity of PHMB is attributed to its interaction with cellar membrane components. However, the detailed molecular structures and components of polyguanidine oligomers are still vague and remain to be learned. In this paper, polyhexamethylene guanidine oligomer (PHMG) was prepared by polycondensation of hexamethylenediamine and guanidine hydrochloride, and its molecular structure and components were analyzed in detail using an electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Seven types of molecular structures of PHMG were determined, including three linear types and four cyclic or branched ones, and their relative contents varied with reaction conditions. Furthermore, the relationship between the antibacterial activity and weight-average molecular weight (Mw) of PHMG was investigated. The results showed that an aqueous solution of PHMG (Mw > 640) at a concentration as low as 1.0 ppm exhibited an antibacterial rate above 90.0%.