Coil-to-globule transition of poly(N-isopropylacrylamide) doped with chiral amino acidic comonomers.
By combined light scattering and circular dichroism measurements (CD), we have investigated the coil-to-globule transition of the thermosensitive polymer poly(N-isopropylacrylamide) (pNIPAAm) copolymerized with a 1/10 fraction of valine- or leucine-derived groups randomly positioned along the chains. The comonomers provide the pNIPAAm chains with chirality, electric charge, and increased hydrophobicity. For valine-derived copolymers, the coil-globule transition is basically unmodified with respect to pNIPAAm, whereas doping with leucine-derived groups significantly lowers the transition temperature and makes the transition discontinuous. We find the CD signal of the chiral comonomers to cleanly depend on the local chain density. We interpret this behavior as an effect of the whole chain conformation on the conformations accessible to the chiral groups.
Lebon
F
F
Dipartimento di Scienze Biomediche e Biotecnologie, Università di Brescia, viale Europa 11, 25123 Brescia, Italy.
Caggioni
M
M
Bignotti
F
F
Abbate
S
S
Gangemi
F
F
Longhi
G
G
Mantegazza
F
F
Bellini
T
T
D000180:Acrylic Resins / Q000737:chemistry*; D000596:Amino Acids / Q000737:chemistry*; D001703:Biophysics / Q000379:methods*; D002627:Chemistry, Physical / Q000379:methods*; D002942:Circular Dichroism; D008027:Light; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry; D011485:Protein Binding; D012542:Scattering, Radiation; D013237:Stereoisomerism; D013696:Temperature; D014633:Valine / Q000737:chemistry
D000180:Acrylic Resins; D000596:Amino Acids; D011108:Polymers; C052970:poly-N-isopropylacrylamide; D014633:Valine