Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, University of Messina and C.I.R.C.M.S.B V.le F. Stagno D'Alcontres, 31-98166 Messina, Italy.
CNR - ISMN Istituto per lo Studio dei Materiali Nanostrutturati c/o Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, University of Messina, V.le F. Stagno D'Alcontres, 31-98166 Messina, Italy.
Int J Mol Sci. 2020 Jun 3;21(11):4001. doi: 10.3390/ijms21114001.
Under acidic conditions and at high ionic strength, the zinc cation is removed from its metal complex with 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) thus leading to the diacid free porphyrin, that subsequently self-organize into J-aggregates. The kinetics of the demetallation step and the successive supramolecular assembly formation have been investigated as a function of pH and ionic strength (controlled by adding ZnSO). The demetallation kinetics obey to a rate law that is first order in [ZnTPPS] and second order in [H], according to literature, with = 5.5 ± 0.4 M s at 298 K (IS = 0.6 M, ZnSO). The aggregation process has been modeled according to an autocatalytic growth, where after the formation of a starting seed containing porphyrin units, the rate evolves as a power of time. A complete analysis of the extinction time traces at various wavelengths allows extraction of the relevant kinetic parameters, showing that a trimer or tetramer should be involved in the rate-determining step of the aggregation. The extinction spectra of the J-aggregates evidence quite broad bands, suggesting an electronic coupling mechanism different to the usual Frenkel exciton coupling. Resonance light scattering intensity in the aggregated samples increases with increasing both [H] and [ZnSO]. Symmetry breaking occurs in these samples and the J-aggregates show circular dichroism spectra with unusual bands. The asymmetry g-factor decreases in its absolute value with increasing the catalytic rate , nulling and eventually switching the Cotton effect from negative to positive. Some inferences on the role exerted by zinc cations on the kinetics and structural features of these nanostructures have been discussed.
在酸性条件和高离子强度下，锌阳离子会从其与 5,10,15,20-四(4-磺基苯基)卟啉(TPPS)的金属配合物中被去除，从而导致二酸游离卟啉，随后自组装成 J-聚集体。作为 pH 和离子强度（通过添加 ZnSO 来控制）的函数，已经研究了脱金属步骤和随后的超分子组装形成的动力学。根据文献，脱金属动力学遵循一级反应规律，即 [ZnTPPS]呈一级，[H]呈二级，在 298 K 时， = 5.5 ± 0.4 M s（IS = 0.6 M，ZnSO）。根据自催化生长模型，对聚集过程进行了建模，其中在形成含有 卟啉单元的起始种子后，速率随时间呈幂次变化。在各种波长下对消光时间轨迹进行全面分析，可以提取出相关的动力学参数，表明三聚体或四聚体应该参与到聚集的速率决定步骤中。J-聚集体的消光谱显示出相当宽的带，表明电子耦合机制不同于通常的弗伦克尔激子耦合。聚集样品中的共振光散射强度随[H]和[ZnSO]的增加而增加。这些样品中发生了对称破缺，J-聚集体显示出具有异常带的圆二色性光谱。不对称 g 因子的绝对值随催化速率 的增加而减小，从负值变为正值，从而使科顿效应发生反转。讨论了锌阳离子对这些纳米结构的动力学和结构特征所起的作用的一些推论。
