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SUMMARY:Is water responding symmetrically to charge?
DTSTART:20150528T163000
DTEND:20150528T173000
DTSTAMP:20260510T044926Z
UID:adf9834870c6b3e31b87e3139254f6106c79bb656186af42a39da91c
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Sylvie Roke\nLaboratory for fundamental BioPhotonics\, E
 PFL\nBeing positive is best in all human affairs. For charges in an aqueou
 s environment\, being negative might be better. A number of biological\, c
 hemical and physical phenomena show indirect evidence that water may have 
 a preference for negative charge\, for example:\nLipid membranes\, macromo
 lecules and their interfaces are either neutral or negatively charged – 
 why did biology choose for negative membranes?\nThe hydrophobic/water surf
 ace carries a negative charge\nThe point of zero charge of most interfaces
  occurs at very low pH\nThe dynamics of water reorientation and H-bond exc
 hange is different around positive and negative ions\nHofmeister effects a
 re more pronounced for negatively charged ions than for positively charged
  ones\nHere\, we have quantified the differences between the hydration-she
 ll and hydrophobic/water interfacial structure induced by two ions of virt
 ually identical size\, shape\, and chemical structure\, but with opposite 
 charge. We find that the water structures around the two isolated ions\, a
 s well as the influences of these two ions on the (weakly charged) hydroph
 obic/water interface are dramatically different: Anions are preferentially
  hydrated and induce greater orientation order on water near hydrophobic i
 nterfaces. Cations have far fewer and weaker pi-H bonds than the anions an
 d strongly reduce the orientational order of water near a hydrophobic inte
 rface. The observations can be explained by the cooperative (anions)\, and
  non-cooperative (cations) interplay of H-bonding and electrostatic intera
 ctions. Our results imply a preference for water interfaces to be negative
 ly charged\, which explains nature’s choice to prefer negative rather th
 an positive charge.
LOCATION:CH G1 495 https://plan.epfl.ch/?room==CH%20G1%20495
STATUS:CONFIRMED
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