Ultraviolet photoirradiation

Gray PJ, Philips DR. Ultraviolet photoirradiation of daunomycin and DNA-daunomycin complexes. Photochem Photobiol 1981 (33) 297-303. 

To realize the above system, it is required to design a polymer which reversibly changes the molecular properties, such as hydrophilicity, by the external stimulation. Many molecules are known to be reversibly transformed to other isomers by external stimulation, such as photons, electrons or chemicals. Table 1 lists a few examples. Azobenzene shows the property change by photoirradiation. It isomerizes from the trans to the cis form by ultraviolet irradiation, and the dipole moment increases from 0.5 to 3.1 deb ye. The polar cis form returns to the less polar tram form by visible irradiation. Electrochemical oxidation of ferrocene changes the hydrophilicity. When it is oxidized from Fe(II) to Fe(III), the hydrophilicity increases. The Feflll) state returns to the Fe(II) state by either electrochemical or chemical reduction. Host molecules also change the properties in the presence of suitable guest ions. Benzo[18]crown-6, for example, captures potassium ions in the cavity, and increases the hydrophilicity. 

Photoirradiation and ESR Measurements. The samples of cellulose and cellulose derivatives were packed uniformly into clear fused Suprasil quartz tubes (O.D. 4 mm), which did not produce any ESR signal during the irradiated sequences. The quartz tubes containing the samples were evacuated to a constant pressure (10 6 mm Hg) and sealed. The source of ultraviolet irradiation was a high pressure mercury-xenon compact arc lamp (Conrad Hanovia type 901 BOOH, 200 W) which... 

The second mechanism (2) utilizes the change iMuced in the intramolecular interaction between pendant groups by photoirradiation. The system reported for the first time is polyfmethacrylic acid) with pendant azobenzene groups [4]. In an aqueous solution, the viscosity was found to increase by ultraviolet irradiation (Fig. 2(2a). The trans to cis photoisomerization was considered to decrease the hydro-phobic interaction between the azobenzene chromophor, allowing the polymer coil to expand. 

Even when the azobenzene chromophores are incorporated into the polymer backbone, the dipole moment increase of azobenzene residues by photoirradiation can also induce a change in polymer chain conformation. The solution viscosity of poly(dimethylsiloxane) containing azobenzene residues in the main chain decreased upon ultraviolet irradiation, and the effect was attributed to the trans to cis photoisomerization [9]. The photodecrease of the viscosity depended on the polarity of the solvent. It was 24% in non-polar heptane, but negligible in polar dichloroethane. 

Fig. 4. Viscosities of polyamide (d) in V,JV-di-methylacetamide at 20 °C ( ) in the dark before photoirradiation and (O) under irradiation with ultraviolet light (410 nm > A > 350 nm) [14]...

One example, which exceptionally exhibited a real photochemical contraction effect in the film state, is poly(ethyl acrylate) cross-linked with 4,4 -dimethacryloyl-aminoazobenzene studied by Eisenbach [35]. Figure 14 shows the data. The film contracts upon irradiation with ultraviolet light, which causes the tram to cis isomerization of the azobenzene chromophores, while it expands by irradiation with visible light, which induces the cis to tram isomerization. Both contraction and expansion are induced by photoirradiation. This finding indicates that the structural change of the cross-linking azobenzene chromophores in the polymer network is responsible for the contraction/expansion behavior. However, the observed contraction was very small, being only about 0.15-0.25%. 

The research was initiated by Kato et al. [51] in 1976, who used an acetyl cellulose film containing photochromic spirobenzopyran and phosphatidyl diloride. Figure 23 shows a schematic diagram of the apparatus used for the measurement of the membrane potential. The concentration ratio, y = C1/C2, of the electrolytes in compartments I and II is a parameter to vary the potential in the dark. In the dark before photoirradiation, the membrane exhibited a steady state potential difference Aq> of —28mv. The membrane potential shifted to — lOmv when the membrane was irradiated with ultraviolet light, and it reverted to the initial value upon visible irradiation. The change in the membrane potential was thus reversible. 

Fig. 30. Transmittance changes at 750 nm of a 1 % aqueous solution of poly(7V-isopropylacrylamide) with pendant azobenzene groups (2.7 mol%) when heated at a rate of 2°C/min. (O) before photoirradiation ( ) under photostationary state with ultraviolet irradiation (410 nm > A > 350 nm)...

Figure 4 shows the size and shape changes of the gel before and after photoirradiation. When the whole gel was irradiated with ultraviolet light, both the gel length and diameter expanded by as much as two times(Figure 4B). When the irradiation beam was localized to one side of the rod shaped gel, the gel showed bending motion (Figure 4D).

Figure 4. Photostimulated size and shape changes of polyacrylamide gels having triphenylmethane leucocyanide groups (3.1 mole %) (A) before photoirradiation, (B) the whole gel being irradiated with ultraviolet light, (C)before photoirradiation, (D) upper side of the rod shaped gel being irradiated.

Figure 6. Photostimulated bending motion of a rod shaped acrylamide gel (25 mm in length and 2 mm in section diameter) having 3.1 mole% triphenylmethane leucocyanide groups in an electric field (10 V/cm) in water (A) before photoirradiation, (B)under ultraviolet irradiation, (C) under ultraviolet irradiation, polarity of the electric field being opposite to that in (B).

These results indicate that the zwitterionic azabutadiene intermediates generated from imines 227 or 228 and ketenes undergo a conrotatory ring closure only to produce j5-lactams 229 or 230. This reveals the inapplicability of the Woodward-HofFmann rules to the photoirradiation-induced Staudinger reaction. Second, when acyclic imines 227 were employed, to Z isomerization of the imine moiety in the zwitterionic intermediates occurs, induced by microwave or ultraviolet irradiation. The results also provide direct experimental evidence for the proposed stereochemical process of the microwave and photoirradiation-induced Staudinger reactions, which, in conjunction with the results of Podlech... 

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