Using the steady-state and time-resolved fluorescence anisotropy, the mobility of 5-(dimethylamino)naphthalene-1-sulfonyl (dansyl) fluorophore in homologous 1-[2-acetamido-3-(1H-indol-3-yl)propanamido]-n-[5-(dimethylamino)naphthalene-1-sulfonamido]alkanes 1 was studied in binary solvents glycerol-water. Steady-state fluorescence data were evaluated by the generalized Perrin equation and the micro-Brownian motion of dansyl fluorophore was described by means of average characteristics (rotational relaxation times) of the rotational relaxation spectrum. The rotational relaxation time of "fast" motions caused by torsional vibrations of single bonds within the rotational-isomeric states decreases with increasing number of methylene groups in homologous compounds. The rotational relaxation time of "slow" motions due to conformational changes of the chain between the tryptophane and dansyl fluorophore remains at first approximately constant with increasing number of methylene groups but increases considerably for long aliphatic chains. The observed decrease in the rate of conformational changes of a long aliphatic chain is probably due to intramolecular interaction of parts of the methylene chain in a medium with high water content. The values of activation enthalpy ∆H≠ and activation entropy ∆S≠ calculated from experimental data corroborate such interpretation. Time-resolved anisotropy of dansyl fluorophore at a particular binary solvent composition confirmed the shape of rotational relaxation spectrum and the measured rotational correlation times have been discussed. The time-dependent decays of anisotropy supported our previous interpretation in terms of intramolecular association of the long aliphatic chain in polar medium.
使用稳态和时间分辨荧光各向异性,研究了5-(二甲氨基)萘磺酰(丹磺)荧光物质在同系列1-[2-乙酰胺基-3-(1H-吲哚-3-基)丙酰胺基]-n-[5-(二甲氨基)萘磺酰胺基]烷烃1中在二元溶剂甘油-水中的运动性。稳态荧光数据通过广义Perrin方程进行评估,丹磺荧光物质的微布朗运动通过旋转弛豫谱的平均特性(旋转弛豫时间)描述。由于同系列化合物中甲基烷基数目增加而引起的由单键扭转振动引起的“快速”运动的旋转弛豫时间随之减少。由于色氨酸和丹磺荧光物质之间链条的构象变化引起的“慢速”运动的旋转弛豫时间,起初随着甲基烷基数目的增加大致保持恒定,但对于长链脂肪烃来说会显著增加。观察到长链脂肪烃构象变化速率的减少可能是由于在水含量较高的介质中甲基链部分之间的分子内相互作用所致。从实验数据计算得到的活化焓ΔH≠和活化熵ΔS≠的值支持这种解释。在特定二元溶剂组成下,丹磺荧光物质的时间分辨各向异性证实了旋转弛豫谱的形状,并讨论了测得的旋转相关时间。各向异性的时间依赖衰减支持了我们先前在极性介质中关于长链脂肪烃分子内缔合的解释。