PH-Switchable LCST/UCST-type thermosensitive behaviors of phenylalanine-modified zwitterionic dendrimers. Issue 18 (11th March 2020)

• Record Type: Journal Article
• Authors: Tamaki, Mamiko; Kojima, Chie
• Is Part Of: RSC advances. Volume 10:Issue 18(2020)
• Page Start: 10452
• Page End: 10460
• Publication Date: 2020-03-11
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0ra00499e
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : We synthesized phenylalanine-modified zwitterionic dendrimers as pH- and thermo-responsive polymers. This is the first report of pH-switchable LCST/UCST-type thermosensitive dendrimers. Abstract : Thermosensitive polymers are useful as intelligent materials. Dendrimers have well-defined structures, which can work as multifunctional polymers. In this study, we designed and synthesized various phenylalanine (Phe)-modified zwitterionic dendrimers as pH- and thermo-sensitive polymers. First, polyamidoamine (PAMAM) dendrimers were modified with Phe and succinic anhydride (Suc) to prepare carboxy-terminal Phe-modified dendrimers (PAMAM-Suc-Phe and PAMAM-Phe-Suc). Both these dendrimers showed upper critical solution temperature (UCST)-type thermosensitivity. Interestingly, PAMAM-Phe-Suc demonstrated lower critical solution temperature (LCST)-type thermosensitivity at lower pH, but PAMAM-Suc-Phe did not. This indicates that PAMAM-Phe-Suc can switch LCST/UCST-type thermosensitivity according to the solution's pH. PAMAM-Phe-SO3 Na with sulfonic acid termini also demonstrated LCST/UCST-type thermosensitivity switched by pH, with a higher sensitivity than PAMAM-Phe-Suc. Coacervation occurred during the phase separation. The quaternized dendrimers (QPAMAM-Phe-Suc and QPAMAM-Phe-SO3 Na) and dendrimers conjugating isoleucine or 4-(amino methyl)benzoic acid did not show the unique thermosensitive properties, indicating that the tertiary amines in the dendrimer core and the Phe residues at the termini are indispensable. PAMAM-Phe-SO3 Na could separate a model compound (rose bengal) from an aqueous solution because of its encapsulation ability. This is the first report of pH-switchable LCST/UCST-type thermosensitive dendrimers.