按一下以編輯母片標題樣式,按一下以編輯母片,第二層,第三層,第四層,第五層,Chapter 2:,Biomolecules in Water,水做為溶劑之特殊性,非共價作用力,解離常數與,pH,緩衝溶液,Chapter 2:Biomolecules in Wat,水為生物的首選溶劑,Biological solvent:a medium for metabolic reactions,aquaporins:membrane channels for water transport,Essential buffer to regulate temperature and pH:high specific heat capacity and pH-regulating substances dissolved in it,Participant in many biochemical reactions:photosynthesis and hydrolysis of ATP,水為生物的首選溶劑Biological solvent:a,水是威力強大的小分子,水是威力強大的小分子,Weak Chemical Bonds,Non-covalent interactions:,Hydrogen bonds,氫鍵,Ionic interactions,離子交互作用,(,靜電吸引力,),Hydrophobic interactions(,厭水性交互作用,),van der Waals interactions(,凡得瓦爾力,),這些弱的維繫力重要性何在,?,*,Weak Chemical BondsNon-covalen,“,The more complex the system,the weaker are the forces that govern its behavior”,-J.R.Platt,較強,較弱,Forces:,核間力原子力 共價鍵 非共價鍵 重力,_,Structure:,原子核原子 簡單化合物 生物巨分子 宇宙,簡單 複雜,“The more complex the system,The Four Weak Interactions,*,共通特質：,非共價,可逆,專一,The Four Weak Interactions*共通特,The Polar Nature of Water,Given the difference in electronegativity between oxygen and hydrogen(3.5-2.1=1.4)and its shape,water is a polar molecule with a dipole moment of 1.85D,the net charge on oxygen is-0.66 and that on each hydrogen is+0.33,The Polar Nature of WaterGiven,1.Hydrogen Bonds,5%of the bond strength of a O-H(20 vs.460 kJ/mole),Much longer bond distance:0.18 vs.0.096 nm,Highly directional,Based on the dipole moment of water,Account for the unusual properties of water as both substance and solvent,1.Hydrogen Bonds 5%of the b,Common Hydrogen Bonds,*,Peptides,X-H:A,X=Hydrogen bond donor N,O,S A=Hydrogen bond acceptor O,N,Common Hydrogen Bonds*Peptides,Hydrogen bonding in ice,冰為何浮在水上？,Ice crystal:static,Water:dynamic breaking and forming,Hydrogen bonding in ice冰為何浮在水上,重要生物分子間氫鍵,重要生物分子間氫鍵,Hydrogen Bond Strength is Highly Directional,Fig.2-5,Hydrogen Bond Strength is High,2.Ionic Interactions,They are about 5-10%the strength of a carbon-carbon bond(20-40 vs.350 kJ/mole),Ionically stabilized compounds(like NaCl)are readily dissolved in solvents with a high dielectric constant(like water),Why?,F=Q,1,Q,2,/,e,r,2,e,:dielectric constant,r:distance between the charge groups,2.Ionic InteractionsThey are,Solvent Properties of H,2,O,Ionic compounds(e.g.,KCl)and low-molecular-weight polar covalent compounds(e.g.,C,2,H,5,OH and CH,3,COCH,3,)tend to dissolve in water,The underlying principle is electrostatic attraction of unlike charges;the positive dipole of water for the negative dipole of another molecule,etc.,ion-dipole interaction,:,e.g.,KCl dissolved in H,2,O,dipole-dipole interactions,:,e.g.,ethanol or acetone dissolved in H,2,O,dipole induced-dipole interactions,:,weak and generally do not lead to solubility in water,Solvent Properties of H2OIonic,Dipole-Dipole,Ion-Dipole,Dipole-DipoleIon-Dipole,Salts Dissolve in Aqueous“Cages of Hydration”,Fig.2-6,還有什麼因素讓鹽很容易溶於水？,Salts Dissolve in Aqueous“Cag,氧既是非極性，又如何支持生命？,氧既是非極性，又如何支持生命？,3.Hydrophobic Interactions,They are about 2%the strength of a carbon-carbon bond(8 vs.350 kJ/mole),Water becomes highly ordered around hydrophobic groups,Greasy chains stay together to minimize entropy loss by water,3.Hydrophobic InteractionsThe,生化反应之溶剂水课件,生化反应之溶剂水课件,生化反应之溶剂水课件,水的退出有利酵素與受質作用,水的退出有利酵素與受質作用,4.van der Waals Interactions,They are about 1%the strength of a carbon-carbon bond(4 vs.350 kJ/mole),Attraction between atoms by transiently-induced dipoles,Repulsion when the electron clouds bump together,4.van der Waals Interactions,生化反应之溶剂水课件,