pH-Switchable LCST/UCST-type thermosensitive behaviors of phenylalanine-modified zwitterionic 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/UCSTtype thermosensitivity according to the solution's pH. PAMAM-Phe-SO 3 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-SO 3 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-SO 3 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. 72 254 8190; Tel: +81 72 254 8190 † Electronic supplementary information (ESI) available: Experimental section; summary of synthesized dendrimers with different generations; NMR and FT-IR spectra of synthesized dendrimers; the pH titration proles; and temperature-dependent transmittance curves of obtained dendrimers under various conditions. See

A Naked‐eye Colorimetric pH and Temperature Sensor Based on Gold Nanoparticle‐Loaded Stimuli‐Sensitive Dendrimers

“…PAMAM-Phe-Suc, PAMAM-Phe, and PAMAM-Suc were synthesized, as described in our previous reports. [24][25][26] The pH and temperature sensitivities of PAMAM-Phe-Suc, PAMAM-Phe, and PAMAM-Suc (1 mg/ml) were previously reported and are listed in Table 1. PAMAM-Suc without Phe showed no thermosensitive properties at any solution pH.…”

“…Interestingly, the terminal groups largely affected the thermosensitive behaviors. [24][25][26] In particular, the amino-terminal Phemodified dendrimer (PAMAM-Phe) exhibited lower critical solution temperature (LCST)-type thermosensitivity at high pH, [24] whereas the carboxy-terminal Phe-modified dendrimer (PAMAM-Phe-Suc) exhibited both upper critical solution temperature (UCST)-and LCST-type thermosensitivity, which could be switched by pH. [26] In the present study, we prepared dual stimuli-responsive AuNP-based sensors from PAMAM-Phe and PAMAM-Phe-Suc with unique pH and temperature-sensitive properties (Figure 1).…”

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“…Notwithstanding the LCST, the engineering of nanomaterials might be utilized to adjust drug release kinetics, especially with huge changes in the surface area as a result of the modified porosity and geometries or inclusion of metallic nanoparticles. Some parameters such as polymer concentration and molecular weight or pH can impact the LCST and UCST behaviors of thermoresponsive polymers [49][50][51].…”

“…In a recent study, Tamaki et al obtained thermoresponsive polymers by different phenylalanine (Phe)-modified zwitterionic dendrimers [50]. They obtained carboxyterminal Phe-modified dendrimers polyamidoamine (PAMAM) and succinic anhydride (Suc) (PAMAM-Suc-Phe and PAMAM-Phe-Suc) utilizing PAMAM dendrimers modified with Phe and Suc.…”

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“…[ 5 ] This progress prompted the systems with two or more thermoresponsive behaviors have been increasing in popularity based on their diverse applications. [ 6–9 ] Most of the thermoresponsive systems reports the employment of two or more LCST‐type transitions to block copolymers, whereas a relatively little progress has been made toward the development of systems that exhibit both LCST‐ and UCST‐type transitions (i.e., S–I–S or I–S–I). Block copolymers of poly(ethylene glycol) and poly(acrylamide‐ co ‐acrylonitrile) display S–I–S type dual thermoresponsive behaviors (LCST at low temperatures and UCST at high temperatures) with a phase transition behavior from micelles to reverse micelles.…”