Azobenzene-Containing Polypeptides

UV Light-induced Conformational Transitions in Azobenzene-containing Polypeptides... 

The role of the supramolecular order of LBK films on the photoreorientation of azobenzene moieties upon polarized irradiation was investigated in detail. It was found that the photo(re)orientation proceeds reaclily in disordered, spin-coated films of azobenzene polymer 34 or azobenzene-containing polypeptide 38, whereas the photoreorientation is hindered in highly ordered LBK films of these polymers. In the case of polyacrylaerylat 34 and polypeptides 38 with shorter spacers (n = 2), the photoreorientation proceeds readily after the structure of the LBK film has been randomized by UV irradi-... 

F. Ciardelli, O. Pieroni, A. Fissi, and J. L. Houben. Azobenzene-containing polypeptides Photoregulation of conformation in solution, Biopolymers 23, 1423-1437 (1984). 

Higuchi M, Minoura N, Kinoshita T. 1995b. Photo responsive behavior of a monolayer composed of an azobenzene containing polypeptide in the main chain. Colloid Pol Sci 273(11) 1022 1027. 

Investigation of light-induced conformational changes has also been extended to solid films of azobenzene-containing poly(L-aspartate)s, but no conformational change was induced by photoisomerization of the azobenzene units. This was probably due to the limited mobility of the polypeptide chains in the films. 57 ... 

The photochromic behaviour of azobenzene-containing poly(L-lysine) has also been reported in the monolayer state [19]. When the polypeptide monolayer is kept at constant area, alternate irradiation with visible and ultraviolet light produces reversible changes ( 25%) of the surface pressure of the monolayer. 

M. Higuchi, N. Minoura, T. Kinoshita, Photocontrol of micellar structure of an azobenzene containing amphiphilic sequential polypeptide, Chem. Lett. 23, 227-230 (1994). 

The conformational behavior can be quite different in aqueous solution. Below pH 5, a sample of poly(L-glutamic acid) containing about 30 mol% azobenzene units adopts a P-structure that is not affected by light. Above pH 7, the polypeptide is random coil and the conformation is, once more, not affected by the photoisomerization of the azo side chains. However, at pH values in the range 5-7 (close to the pK of the conformational transition), irradiation causes a remarkable diminishing of the ordered structure, which is completely reversed in the dark.120,221... 

Poly(L-lysine) containing azobenzene units linked to the side chains by means of a sulfonamide function (Scheme 4, Structure VI), was obtained by treating poly(L-lysine) with p-phenylazobenzenesulfonyl chloride. The poly(a-amino acid) was modified quantitatively conversion to the azo-lysine units of VI was effectively 100%. The azo-modified polypeptide was soluble in HFP, in which it exhibited an intense photochromism attributed to the trans-cis photoisomerization of the azobenzene units. Like other sulfonated azobenzene compounds, 33 azosulfonyl-modified polymers of L-lysine were found to be very stable in their tis form, and no thermal decay was observed at room temperature over periods of times as long as several weeks. Interconversion between the two forms at room temperature could only be effected by irradiation at appropriate wavelengths. This behavior allowed the authors to purify the trans and cis forms of the model compound NE-azobenzenesulfonyl-L-lysine (VII) by chromatography, and to measure the absorption spectra of the two pure photoisomers. 

A photochromic polymer containing azobenzene units has also been prepared by modification of a naturally occurring microbial poly(E-L-lysine) (Scheme 5, Structure IX), and investigated by means of absorption and circular dichroism spectroscopy.1431 The structure of this polymer, however, does not correspond to those of polypeptides, which are poly(amide)s of a-amino acids, and therefore the results cannot be discussed in terms of the typical polypeptide structures (a-helix, P-structure, random coil) and their standard CD spectra. 

Analogous membranes have been prepared from poly(L-glutamic acid) containing about 14 mol % azobenzene-sulfonate groups in the side chains (Scheme 3, Structure IV). 25 109 The polypeptide was adsorbed onto a porous support and the hydro-... 

When azobenzenes are attached to polypeptides, photochromic reactions of azobenzenes can induce the change in helical properties of the polypeptides, which may be detected by CD spectrum as well as optical rotation. For 4-phenylazophen-ylamine-condensed poly(y-glutamic acid) A-9 containing up to 80 mol% of 4-phenylazophenylamide side chain, UV irradiation in organic solvents, such as... 

A detailed investigation of photochromism, conformation and CD properties was carried out in recent years on poly(L-glutamic acid) having various contents of azobenzene groups in the side chains. In trimethylphosphate (TMP), the azo-polypeptides exhibited the a-helix CD pattern. In water at acid pH, the polymers containing 16 mol % and 21 mol % azobenzene groups adopted the a-helix structure while a P-structure was present in a 36 mol % azo-polypeptide. 

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