1 Water and Weak Interactions

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1、WaterWaterandWeakInteractionsWaterandWeakInteractionsXianmingDENGSchoolofLifeSciences,XiamenUniversity2013-09-23LehningerPrinciples of Biochemistry 4thEd.DavidL.NelsonMichaelMCoxMichaelM.CoxWonder of life: diversityand complexity(Appearance, habitat, and genetic composition…...)All cells are more a

2、likethan they are differentat the biochemical level.Universal reaction, interaction, ……Biomoleculesare compounds of carbon……"THE CHEMISTRY OF LIFE"Agenda:AnOverviewWeak Interactions in Aqueous Systems Ionization of Water, Weak Acids, andWeakBasesWeakBasesBuuefferinggagastpagainstpH CCageshange

3、s in BiooogcalogicalSystems Water as a Reactant1.Weak Interactions in Aqueous Systems1.1 WaterWateristhemostabundantsubstanceinlivingsystems,makingupmakingup70%ormoreoftheweightofmostorganisms.ormoreoftheweightofmostorganisms.Vital for life,,ywaterisbyfarthemostabundantcompponentofeverycell.Water,

4、 Water, EverywhereMolecular structure of water (Intra-andinter-molecule)1.2 Hydrogen bonding Thlheelectrostatiiicinteractibionbetweenthhhdehydrogenatomoffonewatermoleculeandtheoxygenatomofanotheryieldsthehydrogen bond.Property of hydrogen bondsHydbdrogen bonddsarerelillativelyweakihbddikwithbonddi

5、ssociiiationenergiiesoffabout23 kJ/mol comparedto470 kJ/mol forthecovalenthydroxybond.HdHydrogen bbdondscanbibeeasillybbrokken–particulllifbarlyifbentChemistry (e.g.DNAreplication).aspectsHydrogenbondsHydrogenbondshavedirectionalitieshavedirectionalities.Functional aspectsHydrogen bonding gives w

6、ater its unusual propertiesThhdhehydrogenbonddisinwaterexertasignificantattractiveforce,causingwatertoclingtoitself(Cohesion)andtoothersurfaces(Adhesion).TtTogethhder,adhhiesionanddhicohesionenablbltewatermolllteculestomoveupwarddsthroughnarrowtubesagainsttheforceofgravity-apropertyofwaterknownas

7、capillarity.WatermovesupaplantstemthroughcohesionWatermovesupaplantstemthroughcohesion-tensioninthexylemtensioninthexylem–onlypossiblebecauseofthehydrogenbonds.Watermustgainorlosealargeamountofenergyforits