Photocontrol of the Structure and Functions of a Polypeptide Membrane Composed of Poly(L-glutamic acid) Containing Pararosaniline Leucocyanide Groups in the Side Chains

Abstract

ABSTRACT:A photo-responsive polypeptide membrane composed of poly(L-glutamic acid) (PGA) containing 38.3 mo!% pararosaniline leucocyanide (rose(CN)) groups in the side chains was prepared. The ultraviolet (UV) light irradiation could produce cationic side chains along the polypeptide backbone resulting from a photodissociation of rose(CN) side chains in the membrane, which arises an electrostatic repulsive forces among the cationic side chains. This increased electrostatic repulsive force destabilized the oc-helical structure of the rose(CN}-PGA in the membrane. As a result, the membrane functions of rose(CN)-PGA, such as membrane potential and transport properties, were strongly dependent on UV light irradiation_, especially, the permeability of KCl through the rose(CN)-PGA membrane was much increased by a factor of 16 upon UV irradiation. The photoinduced changes of the membrane functions were reversible and consistent with the photoinduced conformational changes of rose(CN)-PGA membrane.KEY WORDS Photoresponsive Polypeptide / Membrane / Pararosaniline Leucocyanide Side Chain / Photoinduced Conformational Change / Photoinduced Membrane Potential Change / Photoinduced Permeability Change/ Photo-responsive polymeric materials are primary concerns in the development of information technology. Many studies of photoinduced effects on polymers have been published, such as photochromism in polymer matrices, 1 photoinduced transitions of polymer conformation,2-4 photo-viscosity effect5 -7 and so on. However, there are few studies on photoinduced changes of functions of polymer membranes containing photochromic groups incorporated as pendant groups in the polymer chains.In previous studies, we showed that the transport properties of polypeptide membranes are strongly dependent upon the backbone conformation of the polypeptides, e.g., pH-induced conformational change of poly(Lglutamic acid), 8 redox-controlled conformational changes of poly(L-cystein). 9 Recently, we also reported the photo-induced conformational changes of poly(L-glutamic acid) containing azobenzenesulfonate 10 and pararosaniline leucohydroxide moieties, 11 respectively, in the side chains. The conformation of the membrane composed of poly(L-glutamic acid) containing pararosaniline leucohydroxide moieties in the side chains was changed by a pH increase resulting from the photoproduction of OH-ions from the leucohydroxide moieties in the membrane phase.

Light Responsive Polymer Membranes: A Review

“…A further improvement in the photo-responsiveness of PGA membranes was obtained by using triarylmethane leucocyanide groups (pararosaniline leucocyanide moieties) in the side chains [ 45 ]. Upon UV irradiation, pararosaniline leucocyanide groups photo-dissociate and the electrostatic repulsion among cationic side chains induces the α-helix → random coil transition of PGA membranes with 38.3% parosaniline leucocyanide moieties at pH 5.3.…”

Photoswitchable Polypeptides

“…[110] Irradiation of the membranes with UV light at pH values in the range 5±9 induced large variations in hydration and membrane potential. [114] For a membrane prepared at pH 5.3 from a polymer containing 38 mol% of photochromic groups, exposure to UV light induced large variations in the degree of swelling, membrane potential, and the permeation coefficient of KCl through the membrane. It was suggested that the trans®cis isomerization of the azo chromophores might result in a higher degree of dissociation of the unmodified COOH side chains, which should be the key factor responsible for the photoresponse effects.…”