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Changes of phase: background theory
Published in Michael de Podesta, Understanding the Properties of Matter, 2020
In fact, the phase diagram of water is not so simple as indicated in Figure 10.16(c). In different regimes of temperature and pressure there are at least ten known crystal structures of the solid phase of water (ice). The common crystal structure (known as ice Ih) collapses under the application of pressure (≈2 × 108 Pa at −40 °C) to form ice II, which is denser than liquid water at that pressure. This changes the slope of solid–liquid coexistence curve from its initial negative slope to the more common positive slope. The experimental phase diagram is shown in Question 28 in Chapter 12.
Examples of Phase Transitions
Published in Teunis C. Dorlas, Statistical Mechanics, 2021
The usual ice is called ice I, but under high pressures this is unstable and transforms into ice II or ice III, etc. These transformations occur at the bottom of glaciers. Note a peculiarity of water, namely that the melting temperature Tf decreases with increasing pressure.
Host–guest and guest–guest interactions in noble gas hydrates
Published in Molecular Physics, 2018
Surinder Pal Kaur, C. N. Ramachandran
The research activities on noble gas hydrates got the attention for the first time after the discovery of argon hydrates by Villard et al. in 1896 [23]. Later on, Londono et al. showed that hydrates of helium in ice-II structure can be obtained by applying a pressure of 0.28–0.48 GPa on helium gas in water [24]. With the aid of differential thermal analysis, Dyadin et al. investigated the formation of ice II clathrate hydrates of helium (He), neon (Ne), argon (Ar) and krypton (Kr) from their respective aqueous solution [25]. Abbondondola et al. [26] studied the rate of absorption of hydrogen, argon and xenon into sII propane hydrate and found that hydrogen due to its smaller size diffuses more in the hydrates. In another study, the same research group reported that a mixture of xenon (Xe) and propane forms sII hydrate [27]. They also observed that the presence of Xe accelerates the formation of propane hydrate. Using the three phase coexisting curves of Kr and Xe hydrates, Sugahara et al. studied about the thermodynamic stability boundaries of these hydrates up to a pressure of 445 MPa [28]. They observed that Kr hydrate exhibits a structure transition from sII to sH around 414 MPa, in contrast to Xe hydrate (sI), for which no phase transition was observed. Falenty et al. [29] studied about the role of host–guest interaction on the stability of the hydrates as well as on the limit of meta-stability of ice XVI structure by emptying Ne atoms from sII clathrate hydrates. They reported that empty crystal structures possess negative thermal expansion due to the absence of host–guest interactions.
Five new cobalt(II) complexes based on indazole derivatives: synthesis, DNA binding and molecular docking study
Published in Journal of Coordination Chemistry, 2019
Bing-Fan Long, Qin Huang, Shu-Long Wang, Yan Mi, Meng-Fan Wang, Ting Xiong, Shu-Cong Zhang, Xian-Hong Yin, Fei-Long Hu
Single-crystal X-ray diffraction measurements reveal that 3 crystallizes in space group C2/c. The coordination model of 3 is shown in Figure 2. The central ion Co2+ is coordinated to five nitrogen atoms from two 2,2′-bipy ligands and one indazole ligand and one oxygen atom from carboxyl group of indazole acid (Scheme 1, B). The lattice water molecules form a ten-membered ring. It must be remarked that the complex molecules are binding to each water cluster by hydrogen bonds. All the complex molecules are alternately linked through O1 from the COOH group. In this way, five independent lattice water molecules held together forming a ten-membered ring and the rings are further linked by hydrogen bonds to form a 1D hydrogen-bonded water tape by the edge-sharing model. As shown in Supplementary Information Figure S5, 1D nano-channels were formed along the c axis. These water tapes are located in the gaps of the thick 2D networks which act as hosts to stabilize the water tapes. The detailed structure of the water tape is shown in Figure 3. This water network is combined by central symmetry water rings. The rings are further connected by O7 atom with the corner sharing model (Figure 3). Carboxyl groups provide potential hydrogen bonding intermolecular interactions, beside the coordination ability towards metal ions. Within the water tape, the O…O distances are in the range of 2.81–2.90 Å with an average of 2.84 Å, which is comparable to that observed in the ice II phase 2.77–2.84 Å [18a, 19a, 19b, 20]. The O…O…O angles vary from 168.92° to 169.37°. The carboxyl group that acts as hydrogen-bond acceptor towards the water molecules via both of O2 and O1 atom, O2 exhibits delocalized π-system with nearly identical C-O distances.
Innovative tools for atrial fibrillation ablation
Published in Expert Review of Medical Devices, 2020
Laura Rottner, Daniela Waddell, Tina Lin, Andreas Metzner, Andreas Rillig
More recently, patients with persistent AF are also increasingly treated with a CB-based catheter ablation [9]. Besides showing that CB-ablation is a reasonable first-line strategy for patients with persistent AF, the recently published Cryo4persistent study demonstrated a significant improvement in patients’ quality of life following CB ablation in persistent AF [37]. In regards to safety and efficacy of PVI using CB versus RF ablation with a contact-force sensing catheter in patients with persistent AF, the FIRE And ICE II Trial is promising to produce additional reliable data in the near future.