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

Using fast scanning calorimetry to study solid-state cyclization of dipeptide L-leucyl-L-leucine

© 2020 Elsevier B.V. The possibility of using fast scanning calorimetry (FSC) to study the kinetics of the solid-state cyclization of dipeptide was demonstrated in the present work for the first time. The activation energy and Arrhenius constant of the cyclization of L-leucyl-L-leucine (Leu-Leu) were estimated. FSC data obtained at heating rates from 18,000 to 54,000 K min−1 were evaluated by non-isothermal kinetics. The dependence of the specific heat capacity cp on temperature was determined for linear and cyclic Leu-Leu dipeptides using differential scanning calorimetry (DSC) and FSC. The application of FSC allows studies of solid-state reactions for expensive substances and compounds synthesized in very small amounts

Hexamorphism of Dantrolene: Insight into the Crystal Structures, Stability, and Phase Transformations

Dantrolene represents yet another interesting example of abundant molecular crystal polymorphism existing in at least six different neat polymorphs, three of which can be obtained via crystallization (I-III) and an additional three (IV- VI) via solid-state dehydration from three different monohydrates (MH-I-MH-III). The reasons for polymorph formation were rationalized by analyzing the crystal structures of the polymorphs and hydrates used in their preparation. The thermodynamic relations among the polymorphs were established from calorimetric data, solubility measurements, and lattice energy calculations

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

Long-chain linear alcohols: Reconciliation of phase transition enthalpies

© 2020 Elsevier Ltd Thermodynamics of phase transitions of long-chain linear alcohols were revised by means of complementary experimental techniques: transpiration, differential scanning calorimetry (DSC), fast scanning calorimetry (FSC), and solution calorimetry (SC). Absolute vapor pressure temperature dependencies for heptadecanol-1 and octadecanol-1 were measured by the transpiration and FSC methods. The validity and accuracy of the FSC experimental setup towards reliable vapor pressure measurement was established. It was shown that vaporization enthalpies for heptadecanol-1 and octadecanol-1 obtained by FSC and transpiration method are in good agreement. The SC approach was used for estimation of sublimation/vaporization enthalpies of linear alcohols. Energetics of the phase transitions found with the SC-approach agree well with that from conventional methods and they are consistent with each other

Smart control of calixarene polymorphic states

© The Royal Society of Chemistry. An efficient strategy of polymorph screening is offered for tert-butylthiacalix[4]arene tetrasubstituted with phenacyloxy groups (1), which is based on saturation of its guest-free solid samples and inclusion compounds with guest vapors inducing solid-solid phase transition, complete or partial exchange or repulsion of included guests. The offered approach makes the preparation of polymorphs more reproducible and predictable as the performed phase transitions are under mostly thermodynamic control even when giving metastable forms. Smart transformation of calixarene states was demonstrated where stable and metastable polymorphs are formed in a kind of on/off switching. Guest repulsion or solid-phase exchange with another guest vapor gives a guest-free form directly, or a less stable inclusion compound is prepared that can release guests by drying under milder conditions without host collapse to a stable packing. In total, seven polymorphs of 1 were identified and characterized. Single-crystal data reveal the polymorphophore features of 1, which help to control its polymorphic state. The observed control of polymorphic transitions contributes to the comprehension of their causes and mechanism. The elaborated procedures enable an effective screening of polymorphs through a standardized treatment of the target compound on a click basis with a flexible variation of conditions, which may be scaled up to find more crystal forms. This journal i

2D monomolecular nanosheets based on thiacalixarene derivatives: Synthesis, solid state self-assembly and crystal polymorphism

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Synthetic organic 2D materials are attracting careful attention of researchers due to their excellent functionality in various applications, including storage batteries, catalysis, thermoelectricity, advanced electronics, superconductors, optoelectronics, etc. In this work, thiacalix[4]arene derivatives functionalized by geranyl fragments at the lower rim in cone and 1,3-alternate conformations, that are capable of controlled self-assembly in a 2D nanostructures were synthesized. X-ray diffraction analysis showed the formation of 2D monomolecular-layer nanosheets from synthesized thiacalix[4]arenes, the distance between which depends on the stereoisomer used. It was established by DSC, FSC, and PXRD methods that the obtained macrocycles are capable of forming different crystalline polymorphs, moreover dimethyl sulphoxide (DMSO) is contributing to the formation of a more stable polymorph for cone stereoisomer. The obtained crystalline 2D materials based on synthesized thiacalix[4]arenes can find application in material science and medicine for the development of modern pharmaceuticals and new generation materials