Water; required for life (Introduction)

by David Turell , Tuesday, April 09, 2019, 21:38 (1845 days ago) @ David Turell

Another very complex article filled with dense equations about water's properties:

https://inference-review.com/article/water-and-its-mysteries#footnote-1

"There are very few things that modern science does not understand. One of them is consciousness; the other is water.1 In the case of consciousness, the hard problem is designing good experiments; in the case of water, finding a theory that explains its properties.

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"Strange. A decrease in temperature suggests a decrease in the average speed of molecules in water; and this, in turn, suggests a decrease in volume as molecules are attracted to one another. With water, the opposite is observed. A decrease in speed induces repulsion between water molecules and not attraction.

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"What makes water unique for biology is this wide palette of minima or maxima between –42°C and 100°C. It remains a theoretical challenge to explain why large mean square fluctuations in entropy, volume, and temperature, and small mean square fluctuations in pressure are observed as the average speed of water molecules decreases.

"Chemists are not without clues. A first: all thermodynamic response functions seem to diverge toward a singular temperature of about 228 K at ambient pressure. A second: all water anomalies are linked to the existence of hydrogen bonds (H-bonds) between water molecules. The idea of performing molecular dynamics simulations in order to predict phase diagrams is, if not inevitable, then, at least, natural. Under simulation, H-bonds are characterized by a van der Waals component ε describing the universal attraction between molecules, a directional component J describing the decrease in potential energy specific to hydrogen bonding (two-body interactions), and a component Jc describing the cooperative character of H-bonds (three-body interactions).

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Comment: There are two forms of water, low and high density:

"It follows that LDW has a more rigid tetrahedral structure based on linear H-bonds than HDW. Recent experiments have shown that a high-pressure phase ice VIII transforms to a low-density liquid under rapid and complete release of pressure at 140–165 K.14 X-ray scattering data suggests that the structure of this liquid was very similar to that of low-density amorphous ice, with no variation of the spectrum with temperature consistent with a fully developed tetrahedral network. By contrast, deeply supercooled water showed a spectrum that displayed strong temperature dependences. These changed continuously due to structural fluctuations between HDW and LDW, and caused water anomalies around the Widom line.

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"What pushes water molecules to form two liquids of different densities having quite different local structures and dynamics? This is not yet understood. Water anomalies reflect the properties of hydrogen bonding, and it is just the question why hydrogen bonds exist in the first place that remains unclear. This problem has already been treated in this journal, and the key point seems to be the capability of water molecules to undergo electronic self-excitations using vacuum virtual energy.19 Quantum field theory allowing direct coupling between matter and photons predicts that two different shapes could be expected for water molecules. When the water molecule is not excited by the vacuum’s virtual energy, it adopts an almost spherical shape that is perfectly suited for strong van der Waals interactions typical of HDW-type liquids. On the other hand, self-excitation toward Rydberg states localized onto the oxygen atom using the vacuum’s virtual energy leads to the tetrahedral structure typical of hydrogen bonding. It is this second tetrahedral shape that displays a strong cooperative behavior associated with quantum coherence typical of the other, LDW type of liquid."

Comment: Vital for life and not understood. I've left out the complex physics discussions