light-controlled conversion between monomeric and dimeric forms by the choice of the appropriate wavelengths. Several applications are based on this kind of reversible photo linker without absorption in the visible range. But which is the best molecule from the coumarin family for such an application? Within this study, we compared the photochemical cleavage behavior of twelve coumarin-type cyclobutane dimers. In
Thermal [2 + 2] Cycloreversion of a Cyclobutane Moiety via a Biradical Reaction
作者:J. Liese、N. Hampp
DOI:10.1021/jp111577j
日期:2011.4.14
“forbidden” thermally triggered [2 + 2] cycloreversion of the cyclobutane ring. The quantum efficiency of the photochemical cleavage is about 1%. The thermal cycloreversionreaction is independent from solvent and occurs at low activation energies of about 13 kcal/mol, even in the solid state. The radical scavenger and EPR results are further supported by the finding, that the reaction products are solely the
1,1-Dimethylnaphthalenon-dimers as photocleavable linkers with improved two-photon-absorption efficiency and hydrolytic stability
作者:Julia Liese、Norbert A. Hampp
DOI:10.1016/j.jphotochem.2009.11.005
日期:2010.1
Coumarins are well known for reversible dimer formation with wavelengths greater than 300 nm and dimer cleavage below 300 nm. In a photochemical [2+2]-cycloaddition a cyclobutane ring is formed. Formation as well as cleavage of the cyclobutane ring may be accomplished by a single-photon-absorption as well as by a two-photon-absorption triggered reaction. The coumarin system is of interest for various kinds of applications, ranging from drug delivery for ophthalmic implants to optical data storage. However, the two-photon-absorption coefficient of coumarin dimers is rather low falling in the range of 1 GM in the visible range. We present here a substitute for the coumarin dinner system which not only has an about one order of magnitude higher two-photon-absorption coefficient, but also overcomes several other problems of the coumarin dimer system. Coumarines and in particular coumarine dimers have a very limited solubility in common solvents and are susceptible to hydrolysis of the lactone ring, which leads to an undesired complexity in the photochemical cleavage reaction. The 1,1-dimethylnaphtalenone dimers introduced here show excellent stability, lead only to a single cleavage product,and have a two-photon-absorption coefficient of about 10 GM at 532 nm. These properties make the 1,1-dimethylnaphtalenone dimers a superior substitute over the well-known coumarin dimers in particular in applications where two-photon-absorption induced photocleavage is required. (C) 2009 Elsevier B.V. All rights reserved.
Synthesis and photocleavage of a new polymerizable [2+2] hetero dimer for phototriggered drug delivery
作者:Julia Liese、Norbert A. Hampp
DOI:10.1016/j.jphotochem.2011.02.021
日期:2011.4
release group. The linker–drug conjugate was photochemically polymerized into a HEMA/MMA copolymer. Photo-triggered drug release from the polymer via single-photon-absorption as well as two-photon-absorption in solution were carried out. The detachment of 5-FU from the polymer and its release from the polymer were monitored in the polymer as well as in the aqueous medium and multidose drug release was