Calorimetric studies on ice II reveal a surprising HO/DO isotope effect. While the ice II to ice Ic transition is endothermic for HO, it is exothermic for DO samples. The transition enthalpies are +40 and -140 J/mol, respectively, where such a sign change upon isotope substitution is unprecedented in ice research. To understand the observations we employ force field calculations using two water models known to perform well for HO ice phases and their vibrational properties. These simulations reveal that the isotope effect can be traced back to zero-point energy. q-TIP4P/F fares better and is able to account for approximately three-fourths of the isotope effect, while MB-pol only catches approximately one-third. Phonon and configurational entropy contributions are necessary to predict reasonable transition enthalpies, but they do not have an impact on the isotope effect. We suggest to use these calorimetric isotope data as a benchmark for water models.
Download full-text PDF |
Source |
|---|---|
| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7528406 | PMC |
| http://dx.doi.org/10.1021/acs.jpclett.0c02368 | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Structural Changes in Semi-Crystalline Ethylene-Based Ionomers During the Heating Process.
Polymers (Basel)
December 2024
Graduate School of Organic Materials Science, Yamagata University, 4-3-16 Jonan, Yonezawa 992-8510, Japan.
Article Synopsis
- The study explored how different ionic groups in ethylene-based ionomers affect their behavior when heated, focusing on carboxylic acid groups neutralized by Zn and Na ions.
- Differential scanning calorimetry (DSC) showed two endothermic peaks during heating, with the best melting enthalpy occurring at specific Na/Zn ratios, indicating optimal crystallite growth with both ions.
- X-ray scattering techniques revealed temperature-dependent phase transitions of the crystals, and expansions of ionic aggregates were linked to the melting of polyethylene crystals, highlighting the relationship between ionic composition, microstructure, and thermal properties.
Thermal Characterization and Heat Capacities of Seven Polyphenols.
Molecules
January 2025
FEQx Lab, Department of Chemical Engineering, University of Vigo, 36310 Vigo, Spain.
Polyphenolic compounds are key elements in sectors such as pharmaceutics, cosmetics and food; thus, their physicochemical characterization is a vital task. In this work, the thermal behavior of seven polyphenols (-resveratrol, -polydatin, kaempferol, quercetin, myricetin, hesperidin, and (-)-epicatechin) was investigated with DSC (differential scanning calorimetry) and TGA (thermogravimetric analysis). Melting temperatures, enthalpies of fusion and decomposition temperatures were determined, and heat capacities were measured in the temperature range from 283.
View Article and Find Full Text PDFThermally Induced Phenomena in Amorphous Nifedipine: The Correlation Between the Structural Relaxation and Crystal Growth Kinetics.
Molecules
January 2025
Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, nam. Cs Legii 565, 532 10 Pardubice, Czech Republic.
The particle size-dependent processes of structural relaxation and crystal growth in amorphous nifedipine were studied by means of non-isothermal differential scanning calorimetry (DSC) and Raman microscopy. The enthalpy relaxation was described in terms of the Tool-Narayanaswamy-Moynihan model, with the relaxation motions exhibiting the activation energy of 279 kJ·mol for the temperature shift, but with a significantly higher value of ~500 kJ·mol being obtained for the rapid transition from the glassy to the undercooled liquid state (the latter is in agreement with the activation energy of the viscous flow). This may suggest different types of relaxation kinetics manifesting during slow and rapid heating, with only a certain portion of the relaxation motions occurring that are dependent on the parameters of a given temperature range and time frame.
View Article and Find Full Text PDFProtein dynamics underlies strong temperature dependence of heat receptors.
Proc Natl Acad Sci U S A
January 2025
Department of Physiology and Biophysical Sciences, State University of New York at Buffalo, Buffalo, NY 14214.
Ion channels are generally allosteric proteins, involving specialized stimulus sensor domains conformationally linked to the gate to drive channel opening. Temperature receptors are a group of ion channels from the transient receptor potential family. They exhibit an unprecedentedly strong temperature dependence and are responsible for temperature sensing in mammals.
View Article and Find Full Text PDFTransition Boundary from Laminar to Turbulent Flow of Microencapsulated Phase Change Material Slurry-Experimental Results.
Materials (Basel)
December 2024
Department of Mechanical and Power Engineering, Koszalin University of Technology, Raclawicka Street 15-17, 75-620 Koszalin, Poland.
An ice slurry or an emulsion of a phase change material (PCM) is a multiphase working fluid from the so-called Latent Functional Thermal Fluid (LFTF) group. LFTF is a fluid that uses, in addition to specific heat, the specific enthalpy of the phase change of its components to transfer heat. Another fluid type has joined the LFTF group: a slurry of encapsulated phase change material (PCM).
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!