Sublimation thermodynamics of nucleobases derived from fast scanning calorimetry

© 2020 the Owner Societies. The five fundamental units of the genetic code: Uracil (U), thymine (T), cytosine (C), adenine (A) and guanine (G) are known for extremely low vapor pressure and low thermal stability at elevated temperatures. Therefore, application of conventional techniques for the determination of sublimation enthalpies and vapor pressures fails to provide accurate results. Recently, a Fast Scanning Calorimetry method (FSC) for vapor pressure determination was developed for investigation of extremely low volatile, as well as for thermally unstable molecular and ionic molecules. This success has encouraged application of the FSC method for determination of vapor pressures and sublimation enthalpies of the five nucleobases, where available literature data are in disarray. The thermodynamic data of the nucleobases available in the literature were collected, evaluated, and combined with our experimental results to reconcile available experimental data. The set of evaluated thermochemical data on the five nucleobases was recommended as the benchmark properties for these thermally labile compounds

Application of the Flash DSC 1 and 2+ for vapor pressure determination above solids and liquids

In this work, we adapted a procedure for vapor pressures determination utilizing a fast scanning chip calorimeter to the case of a stagnant gas phase. The validity of the developed procedure was checked by comparing the vapor pressures determined in this work for several polyaromatic, heteroaromatic, and long-chain compounds with reliable vapor pressure data available in the literature. The results of the comparison show that the commercial Flash DSC 1 and the Flash DSC 2+ (Mettler Toledo, Switzerland) can be used for a reliable appraisal of the vapor pressures in a wide temperature range, which allows using these devices without additional technical changes as a source of comprehensive and internally consistent information about the energy of phase transitions