Margalit R, Rotenberg M
Biochem J. 1984 Apr 15;219(2):445-50. doi: 10.1042/bj2190445.
The dimerization equilibrium of deuteroporphyrin IX and of mesoporphyrin IX in aqueous solutions were studied by fluorimetric techniques over the 0.01-1 microM concentration range, where dimerization is the dominant aggregation process. Deuteroporphyrin IX was studied at several temperatures over the range 22-37 degrees C, and mesoporphyrin at 25 and 37 degrees C. The magnitudes determined for the dimerization equilibrium constants (25 degrees C, neutral pH, phosphate-buffered saline) are 2.3 X 10(6)M-1 and 5.4 X 10(6)M-1 for the deutero and meso derivatives respectively. The meso, deutero and haemato species tested show a similar temperature effect, namely dimerization decreasing with increasing temperature, indicating the involvement of a negative enthalpy change. Van't Hoff isochore of the dimerization constants determined for deuteroporphyrin IX was linear within the temperature range of 22-37 degrees C, allowing the calculation of the thermodynamic parameters. For deuteroporphyrin dimerization, those were found to be delta G0 = -36. 4kJ X mol-1; delta H0 = -46. 0kJ X mol-1 and delta S0 = -32.2J X K-1 X mol-1 (at neutral pH, 25 degrees C, phosphate-buffered saline), showing the process to be enthalpy-driven. Similar trends have been found for porphyrin species other than those studied here. Our data fit with a hypothesis giving a major role to the solvent in driving porphyrins to aggregate in aqueous solution. The magnitudes and directions of the energetic changes fit better with the expectation of the ' solvophobic force' theory predicting enthalpy-driven association, than with the classic hydrophobic bonding, predicting the association to be entropy-driven.
采用荧光技术研究了水溶液中氘代卟啉IX和中卟啉IX在0.01 - 1微摩尔浓度范围内的二聚平衡，在此浓度范围内二聚是主要的聚集过程。在22 - 37℃的几个温度下研究了氘代卟啉IX，在25℃和37℃下研究了中卟啉。在25℃、中性pH、磷酸盐缓冲盐水中测定的二聚平衡常数分别为：氘代衍生物为2.3×10⁶M⁻¹，中卟啉衍生物为5.4×10⁶M⁻¹。所测试的中卟啉、氘代卟啉和血卟啉物种表现出相似的温度效应，即二聚作用随温度升高而降低，表明涉及负焓变。在22 - 37℃温度范围内，氘代卟啉IX二聚常数的范特霍夫等容线呈线性，从而可以计算热力学参数。对于氘代卟啉二聚作用，这些参数为：ΔG⁰ = -36.4kJ·mol⁻¹；ΔH⁰ = -46.0kJ·mol⁻¹和ΔS⁰ = -32.2J·K⁻¹·mol⁻¹（在中性pH、25℃、磷酸盐缓冲盐水中），表明该过程是由焓驱动的。对于本文未研究的其他卟啉物种也发现了类似趋势。我们的数据符合一种假设，即溶剂在促使卟啉在水溶液中聚集方面起主要作用。能量变化的大小和方向更符合“疏溶剂力”理论预测的焓驱动缔合的预期，而不符合经典疏水键合预测的熵驱动缔合。
