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Circular Dichroism. 2011161059 김재범. Polarization. Polarization( 편광 ). - 편광 : 파동의 진동이 그 평면상의 특정 방향으로 놓이게 되는 것 - 빛은 물질과 반응하여 편광상태가 바뀔 수 있음. Linearly polarized light( 선형 편광 ). 선형편광 = 편광방향이 바뀌지 않음 궤도가 한 면 위에 있음. Linearly polarized light( 선형 편광 ).

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circular dichroism

Circular Dichroism




- 편광 : 파동의 진동이 그 평면상의 특정 방향으로 놓이게 되는 것

- 빛은 물질과 반응하여 편광상태가 바뀔 수 있음

linearly polarized light
Linearly polarized light(선형 편광)
  • 선형편광 = 편광방향이 바뀌지 않음
  • 궤도가 한 면 위에 있음
linearly polarized light1
Linearly polarized light(선형 편광)
  • 선형편광을 적절히 조합하면 임의의 방향의 선형편광이나원형편광도 만들어 낼 수 있다.
circularly polarized light
Circularly polarized light(원형편광)

Left circularly polarized(LCP) light

Right circularly polarized(RCP) light

optical activity chirality
광학 이성질성(Optical activity, Chirality)
  • 탄소 주위의 4개의 작용기가 모두 다른 비대칭 탄소를 가지고 있으므로 서로 거울 상은 되지만 겹쳐지지 않는 이성질체
  • 다른 이성질체와 달리 결정 모양, 비중, 끓는점 등 물리적 성질은 모두 일치
  • 그러나 편광 된 빛을 흡수하는 정도가 달라 광학 이성질체의 결정이나 용액에 편광 된 빛을 통과시키면 편광 면을 회전 시키는 정도가 좌, 우에 각각 다르게 나타난다.
circular dichroism3
Circular Dichroism이란?
  • 우회전 편광의 흡수도
  • ≠ 좌회전 편광의 흡수도
  • → 파동의 형태가 타원이 됨!
circular dichroism4
Circular Dichroism이란?
  • Optical rotation
  • Ellipticity(θ)

minor axis/major axis

circular dichroism5
Circular Dichroism이란?
  • Ellipticity(θ)

θ = 32.98 CD(ΔA)

ΔA=좌형 원형 편광 세기 – 우형 원형 편광 세기

  • Molar ellipticity

[θ] = 100 θ / C l

C= molar 농도, I= path length(cm)

circular dichroism6
Circular Dichroism이란?
  • [θ]=3298Δε

- Δε= ΔA /C I

the difference in absorption for a

1M solution in a 1cmcuvette,

→ [θ]=3298ΔA

application to biology1
Application to Biology
  • Near UV CD (250 - 350 nm)
    • Near-UV CD spectroscopy is dominated by Phe, Tyr, Trpand disulfides
    • Aromatic residue → asymmetric → exhibit CD
application to biology2
Application to Biology
  • Far UV CD (180 - 250 nm)
    • amide group : most abundant CD chromophore in proteins
    • In secondary structure conformations; backbone and the amide bond chromophores are

“regular, organized, asymmetric”

application to biology3
Application to Biology
  • 전자 전이

bonding orbital( , )

→anti-bonding orbital(*, *)

  • The intensity and energy of these transitions depends on φ and ψ

→ by “secondary structure”

application to biology4
Application to Biology
  • Far UV-CD of random coil:
    • positive at 212 nm (π->π*)
    • negative at 195 nm (n->π*)
  • Far UV-CD of β-sheet:
    • negative at 218 nm (π->π*)
    • positive at 196 nm (n->π*)
  • Far UV-CD of α-helix:
    • Excitation coupling of the π->π* transitions leads to positive (π->π*)(perpendicular) at 192 nm and negative (π->π*)(parallel) at 209 nm
    • negative at 222 nm is red shifted (n->π*)
application to biology5
Application to Biology
  • Determination of secondary structure of proteins that cannot be crystallized
  • Investigation of the effect of drug binding on proteinsecondary structure
  • Study of the effects of environment on protein structure
  • Study of ligand-induced conformational changes
application to biology6
Application to Biology
  • 광우병진단
    • 정상적인 cellular prionprotein“alpha-helix”
    • 광우병에걸린 scrapieprion protein은

“beta sheet structure”

  • 빠르다! 간단하다!
  • 복잡한 준비과정 X
  • 용액 상태로도 측정 가능!
  • 샘플의 양이 적어도 OK
  • 어떤 크기의 거대분자든지 측정 가능!
  • 공통점, 차이점을 정량화 X
  • 특정 buffer components가 방해요인이 될 수 있음
  • 편광 된 빛이 asymmetric medium을 통과하면 optical rotation이 일어남(Ellipticity)
    • Ellipticity를 측정하여 Ellipticity크기와 경향을 diagram으로 나타낸 것이 “Circular Dichroism”
  • Near UV CD (250-350 nm)
    • dominated by Phe, Tyr, Trpand disulfides
  • Far UV CD (180-250 nm)
    • In secondary structure conformations, the backbone and the amide bond chromophores are arranged in regular, organized, asymmetric patterns
    • → Random coil, β-sheet, α-helix