Fluorescent Molecular Thermometers Based on Polymers Showing Temperature-Induced Phase Transitions and Labeled with Polarity-Responsive Benzofurazans
作者:Seiichi Uchiyama、Yuriko Matsumura、A. Prasanna de Silva、Kaoru Iwai
DOI:10.1021/ac0346914
日期:2003.11.1
Poly(N-isopropylacrylamide) in aqueous solution undergoes a phase transition at ∼32 °C. The fluorescence properties of benzofurazans are affected by solvent polarity. We combine these two characteristics for the first time to develop sensitive fluorescent molecular thermometers. Five fluorescent monomers having a benzofurazan skeleton were synthesized, and the copolymers of N-isopropylacrylamide (NIPAM) and a small quantity of the fluorescent monomer were obtained to investigate their fluorescence properties. With increase in temperature, the copolymers in water showed the temperature-induced phase transition at ∼32 °C and the fluorescence intensities of the copolymers concurrently increased. Especially, for the copolymer of 4-N-(2-acryloyloxyethyl)-N-methylamino-7-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole and NIPAM, the fluorescence intensity at 37 °C was 13.3-fold that seen at 29 °C. The sensitive range of temperature of these fluorescent molecular thermometers is changed by the replacement of the NIPAM units by N-isopropylmethacrylamide or N-n-propylacrylamide units in the copolymers. The basis of these fluorescent molecular thermometers is the decrease in the microenvironmental polarities near the main chains of the copolymers with increasing temperature, as confirmed from the maximum emission wavelengths of the benzofurazan units in the copolymers. The responses from the copolymers to the change in temperature are reversible and exactly repeatable during at least 10 cycles of heating and cooling.
水溶液中的聚(N-异丙基丙烯酰胺)在 ∼32 °C 时发生相变。苯并呋喃的荧光特性受溶剂极性的影响。我们首次将这两种特性结合起来,开发出了灵敏的荧光分子温度计。我们合成了五种以苯并呋喃为骨架的荧光单体,并得到了 N-异丙基丙烯酰胺(NIPAM)与少量荧光单体的共聚物,以研究它们的荧光特性。随着温度的升高,水中的共聚物在 ∼32 °C处出现了温度诱导的相变,共聚物的荧光强度也随之增加。特别是 4-N-(2-丙烯酰氧乙基)-N-甲基氨基-7-N,N-二甲基氨基磺酰基-2,1,3-苯并噁二唑和 NIPAM 的共聚物,在 37 °C 时的荧光强度是 29 °C 时的 13.3 倍。将共聚物中的 NIPAM 单元替换为 N-异丙基甲基丙烯酰胺或 N-正丙基丙烯酰胺单元,可改变这些荧光分子温度计的灵敏温度范围。这些荧光分子温度计的基础是共聚物主链附近的微环境极性随着温度的升高而降低,共聚物中苯并呋喃单元的最大发射波长证实了这一点。共聚物对温度变化的反应是可逆的,在至少 10 个加热和冷却周期中都可以准确重复。