Shirke Sonali, Ludescher Richard D
Department of Food Science, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520, USA.
Carbohydr Res. 2005 Dec 12;340(17):2661-9. doi: 10.1016/j.carres.2005.08.015. Epub 2005 Oct 5.
We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in thin films of either maltose or maltitol to investigate the physical properties of these amorphous pure sugar matrixes. Intensity decays collected as a function of emission wavelength over the range from 640 to 720 nm were analyzed using a stretched exponential kinetic model in which the lifetime (tau) and the stretching exponent (beta) were the physically relevant parameters. The lifetimes varied systematically with emission wavelength in both matrixes. Analysis of the temperature dependence of the lifetime at each wavelength provided an estimate of the activation energy for nonradiative quenching of the triplet state; the activation energy also varied with emission wavelength. In addition, time-resolved emission spectra exhibited a blue shift with time following excitation. These data support a photophysical model in which probes are distributed among sites that vary in terms of overall molecular mobility and in which sites with lower rates of dipolar relaxation also have lower rates of collisional quenching of the erythrosin triplet state. The amorphous matrix of both maltose and maltitol in both the glass and the melt state is thus characterized by dynamic site heterogeneity in which different sites vary in terms of their overall molecular mobility.
我们利用分散在麦芽糖或麦芽糖醇薄膜中的赤藓红B（四碘荧光素）的磷光来研究这些无定形纯糖基质的物理性质。在640至720 nm范围内，作为发射波长函数收集的强度衰减，使用拉伸指数动力学模型进行分析，其中寿命（tau）和拉伸指数（beta）是物理相关参数。在两种基质中，寿命均随发射波长系统地变化。对每个波长下寿命的温度依赖性分析提供了三重态非辐射猝灭活化能的估计值；活化能也随发射波长而变化。此外，时间分辨发射光谱在激发后随时间呈现蓝移。这些数据支持一种光物理模型，其中探针分布在整体分子迁移率不同的位点之间，并且其中偶极弛豫速率较低的位点对赤藓红三重态的碰撞猝灭速率也较低。因此，玻璃态和熔融态的麦芽糖和麦芽糖醇的无定形基质的特征在于动态位点异质性，其中不同位点的整体分子迁移率不同。
