Lecture 24 - Spectroscopy

Lecture 24 - Spectroscopy - Hydrophobic Interactions CH4...

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Hydrophobic Interactions Oil and water don’t mix, called the hydrophobic effect . Methane Hydrate Entropically unfavorable to dissolve non-polar molecule in H 2 O. Non-polar molecules forced together (oil droplet) to minimize interaction with H 2 O. H 2 O would rather interact with itself rather than interact with non-polar molecule. CH 4 (g) + H 2 O(l) CH 4 --- H 2 O (aq) Δ G > 0 & Δ S < 0 CH 4 --- non-polar solvent CH 4 --- H 2 O Δ G > 0
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Hydophobic Effect Hydrophobic interactions cause non-polar solutes to “clump” together to minimize contact with water. This effect is one of the major factors in protein folding! F354 L355 L327 C N R – CH 3 (l) + H 2 O(l) R – CH 3 --- H 2 O (aq) Δ G > 0 & Δ S < 0
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Hydrogen Bonds Hydrogen Bonds H-bonds form when proton shared between two electronegative atoms such as N, O, or F (i.e. electrostatic attraction). Individual H-bonds are weak (~5-40 kJ/mol), but play an essential role in biology. X-ray structures show H-bonds have some covalent character. δ+ δ− δ−
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Hydrogen Bonds Vary in Strength H-bonds range from weak (~5 kJ/mol) to very strong (40 kJ/mol): F—H :F (40 kJ/mol) O—H :N (29 kJ/mol) O—H :O (21 kJ/mol) N—H :N (13 kJ/mol) N—H :O (8 kJ/mol) Collectively responsible for structure of DNA and RNA | | | | | | | | | | | | | | | 109° δ+ δ− O – H ||| :N H 109° O – H ||| :O H 109° .. H δ−
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Hydrogen Bonds in Nucleic Acid Structure Watson-Crick Base Pairs: 00244 . 0 ) 300 314 . 8 / 5000 3 exp( ) exp( ] [ ] , [ 1 = × × = Δ = K mol K J mol J RT E G C G C pair base free
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Hydrogen Bonds in Proteins ( α -helix) α -Helix Hemoglobin 4 1 2 3
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β -sheet Class I MHC (Major Histocompatibility Complex) Hydrogen Bonds in Proteins ( β -sheet)
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β -turn Anti-parallel β -sheet
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Lecture 24 - Spectroscopy - Hydrophobic Interactions CH4...

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