de Petris Giulia, Festa Maria Rosa, Galantini Luciano, Giglio Edoardo, Leggio Claudia, Pavel Nicolae Viorel, Troiani Anna
Dipartimento di Chimica, Research Center SOFT-INFM-CNR, and Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Università di Roma, P. le Aldo Moro 5, 00185 Roma, Italy.
J Phys Chem B. 2009 May 21;113(20):7162-9. doi: 10.1021/jp9010586.
This paper deals with electrospray ionization mass spectrometry (ESIMS), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) measurements in order to provide information on the existence, aggregation, composition, and structure of the two-component aggregates of sodium glycocholate (NaGC) and sodium glycodeoxycholate (NaGDC) in the gas and solution phases. Five samples, containing 100% NaGC and 100% NaGDC, and NaGDC/NaGC molar ratios of 3 (75D), 1 (50D), and 1/3 (25D), have been analyzed by ESIMS in positive-ion detection mode starting from 10(-3) and 10(-2) M total bile salt concentration in aqueous solutions. Generally, dimers or trimers prevail in the 100% NaGC or NaGDC samples, respectively, as observed in the preceding one-component ESIMS measurements and in agreement with the proposed micellar aggregate structures in aqueous solution. Moreover, it is observed that the composition of multimers in the samples 75D, 50D, and 25D deviates from the one expected on the basis of a random association of the monomers, the NaGDC contribution generally prevailing on the NaGC one. It happens also under the same percentage condition (50D sample), in agreement with a greater aggregation ability of NaGDC with respect to NaGC. SAXS and DLS data were recorded on six samples containing a NaGC+NaGDC 40 mM total concentration, one bile salt having 40, 32, 24, 16, 8, and 0 mM concentration and the other the complementary one, keeping constant the NaCl concentration (0.6 M). The NaGDC 40 mM sample presents SAXS curves in agreement with a cylindrical shape of the aggregates as shown in a previous paper. For the bile salt mixtures, the progressive decrease of the sizes and change of the aggregate morphology, toward a globular-like geometry, are observed by increasing the NaGC fraction, thus confirming the hypothesis about the ability of trihydroxy salts to inhibit the growth of dihydroxy salt aggregates. Fits on the basis of cylindrical model can be accomplished for all the SAXS spectra, however, when the extracted cylinder parameters are used to estimate theoretical hydrodynamic radii a reasonable agreement is obtained only for the samples at high fraction of NaGDC (NaGDC>or=24 mM).
本文进行了电喷雾电离质谱（ESIMS）、小角X射线散射（SAXS）和动态光散射（DLS）测量，以便提供有关气相和溶液相中甘氨胆酸钠（NaGC）和甘氨脱氧胆酸钠（NaGDC）两组分聚集体的存在、聚集、组成和结构的信息。五个样品，分别含有100% NaGC和100% NaGDC，以及NaGDC/NaGC摩尔比为3（75D）、1（50D）和1/3（25D），已通过ESIMS在正离子检测模式下进行分析，起始水溶液中总胆汁盐浓度为10⁻³和10⁻² M。一般来说，在100% NaGC或NaGDC样品中分别以二聚体或三聚体为主，如之前的单一组分ESIMS测量中所观察到的，并且与水溶液中提出的胶束聚集体结构一致。此外，观察到75D、50D和25D样品中多聚体的组成偏离了基于单体随机缔合所预期的组成，NaGDC的贡献通常超过NaGC。在相同百分比条件下（50D样品）也会发生这种情况，这与NaGDC相对于NaGC具有更强的聚集能力一致。SAXS和DLS数据记录在六个总浓度为40 mM的NaGC + NaGDC样品上，一种胆汁盐浓度为40、32、24、16、8和0 mM，另一种为互补浓度，同时保持NaCl浓度恒定（0.6 M）。如前一篇论文所示，40 mM的NaGDC样品呈现的SAXS曲线与聚集体的圆柱形形状一致。对于胆汁盐混合物，通过增加NaGC的比例，观察到聚集体尺寸逐渐减小且形态向球状几何形状转变，从而证实了关于三羟基盐抑制二羟基盐聚集体生长能力的假设。然而，基于圆柱形模型对所有SAXS光谱进行拟合时，当使用提取的圆柱参数来估计理论流体动力学半径时，仅对于高比例NaGDC（NaGDC≥24 mM）的样品才能获得合理的一致性。
