Experimental Determination of Melting Properties of Biological Compounds for Better Solubility Predictions

了解生物分子的溶解性对于设计和优化氨基酸、肽、蛋白质和药物的生产是至关重要的。产品纯度、溶液中生物分子的过饱和度以及合适溶剂的选择都取决于溶解度。在许多情况下，温度、pH值、共溶剂和共溶质的种类和浓度等参数对生物分子溶解度影响的数据还不够充分，因此溶解度行为建模引起了化学工程科学的研究兴趣。然而，用热力学模型预测纯溶解度的结果仍然不令人满意。这主要是由于对生物分子的熔化性质的数据错误或不可用造成的。用常规方法测定生物分子的熔融特性，如熔融温度TSL、熔融焓hSL或热容cpSL，常常由于生物分子在低于TSL的温度下分解而失败。应用基团贡献法估计熔融特性可能会产生很高的不确定性，甚至是不一致的数据。近几年来，发展了快速扫描芯片量热法（FSC），用于实验测定熔融特性（TSL、hSL、cpSL）。这对生物分子来说特别重要，因为这些化合物在熔化前会分解。应用非常高的加热速率（<10 Mio. K/s）与传统方法（<1 K/s）相比，可以显著减少高温分解时间。因此，分解发生在更高的温度下。与此相反，熔化仅略微依赖于加热速率。这允许相变和熔化特性的实验测定。在这个项目中，FSC将进一步发展，以确定生物分子（氨基酸，肽，蛋白质）的TSL，hSL和cpSL的定量数据。由于二肽的溶解性和熔化特性还没有得到很好的研究，因此二肽的化合物类应是本项目的重点。FSC确定的熔化特性将被用作预测固液平衡的热力学模型的输入。这将允许根据温度和pH值预测生物分子在溶剂和溶剂混合物中的溶解度。为了达到这一目标，必须将平衡热力学和实验量热学这两个互补的研究领域结合起来，这两个领域属于申请该项目的Christoph Held和Andreas乌尔姆的研究能力。

Knowledge about solubility of biomolecules is crucial for the designand optimization of production of amino acids, peptides, proteins, andpharmaceuticals. Product purity, supersaturation ratios ofbiomolecules in solution as well as choice of a suitable solventdepend on solubility. In many cases, data on the influence ofparameters like temperature, pH-value, kind and concentration of cosolventsand co-solutes on biomolecule solubility are insufficient.Modeling solubility behavior has thus attracted research interest inchemical engineering science. However, the results of pure solubilitypredictions using thermodynamic models are still not satisfying. Thisis mainly caused by wrong or not available data of the meltingproperties of the biomolecules. The experimental determination ofmelting properties such as melting temperature TSL, melting enthalpyhSL, or heat capacities cpSL with conventional methods often failscaused by decomposition of the biomolecules at temperatures belowTSL. Application of group-contribution methods that might be used toestimate melting properties might yield to very high uncertainties oreven to non-consistent data. In the last years, the new method FastScanning Chip Calorimetry (FSC) has been developed in order todetermine melting properties (TSL, hSL, cpSL) experimentally. This isof special importance for biomolecules, as these compoundsdecompose before melting. Applying of very high heating rates (< 10Mio. K/s) allows reducing the time for decomposition at hightemperatures dramatically compared to conventional methods (< 1K/s). Decomposition thus takes place at much higher temperatures. Incontrast, melting depends only slightly on heat rate. This allows phasechange and experimental determination of melting properties. In thisproposed project, FSC will be further developed in order to determinequantitatively data for TSL, hSL and cpSL for biomolecules (aminoacids, peptides, proteins). The compound class of dipeptides shall bewithin closer focus of this project as solubility and melting propertiesof dipeptides are not well investigated. The melting properties whichwill be determined by FSC will be used as input into thermodynamicmodels for the prediction of solid-liquid equilibria. Thiswill allowpredicting the solubility of biomolecules in solvents and solventmixtures depending on temperature and pH-value. In order to reach the goal, the complementary research fields equilibriumthermodynamics and experimental calorimetry have to be combined.These fields belong to the research competences of Christoph Heldand Andreas Wurm, who are applying for this project.