1. Ultraviolet-Visible (UV-VIS) Spectroscopy
Gives information about conjugated p electron systems 1

2. Transitions between electron energy states
gaps between electron energy levels are greater than those between vibrational levels
gap corresponds to wavelengths between 200 and 800 nm
DE = hn 2

3. X-axis is wavelength in nm (high energy at left, low energy at right)
Conventions in UV-VIS
X-axis is wavelength in nm (high energy at left, low energy at right)
lmax is the wavelength of maximum absorption and is related to electronic makeup of molecule— especially p electron system
Y axis is a measure of absorption of electromagnetic radiation expressed as Absorbance or molar absorptivity (e) 3

4. UV and Visible light cause only two kinds of electronic
transitions
Only organic compounds with p electrons can absorb
energy in the UV/Visible region
A visible spectrum is obtained if visible light is absorbed
A UV spectrum is obtained if UV light is absorbed

5. pp* Transition in cis,trans-1,3-cyclooctadiene
LUMO
y3*
DE = hn y2
HOMO y1
Most stable p-electron configuration
p-Electron configuration of excited state 5

6. pp* Transition in Alkenes
HOMO-LUMO energy gap is affected by substituents on double bond
as HOMO-LUMO energy difference decreases (smaller DE), lmax shifts to longer wavelengths 5

7. Methyl groups on double bond cause lmax to shift to longer wavelengths
Substituent Effects
Methyl groups on double bond cause lmax to shift to longer wavelengths H H H
CH3 C C H
CH3 H H
lmax 170 nm
lmax 188 nm 5

8. A chromophore is the part of a molecule which absorbs
UV or visible light

9. Effect of Conjugation on lmax

11. Substituent Effects
Extending conjugation has a larger effect on lmax; shift is again to longer wavelengths H H H H C C H C H H H H H
lmax 170 nm
lmax 217 nm 5

12. 236 nm
What is carvone’s max?

13. The Beer–Lambert Law A = cle A = log(I / I0)
c = concentration of substance in solution
l = length of the cell in cm
e = molar absorptivity
The molar absorptivity of a compound is a constant that
is characteristic of the compound at a particular
wavelength

14. UV Spectrum of cis,trans-1,3-cyclooctadiene
2000
Molar absorptivity (e)
lmax 230 nm
emax 2630
1000
Wavelength, nm 4

15. lmax 217 nm (conjugated diene)
Substituent Effects H C
lmax 217 nm (conjugated diene) C H
CH3
H3C
lmax 263 nm conjugated triene plus two methyl groups 5

16. Both the lmax and e increase as the number of
conjugated double bonds increases

17. An auxochrome is a substituent in a chromphore that
alters the lmax and the intensity of the absorption

18. Uses of UV/Vis Spectroscopy
Measure the rates of a reaction
Determine the pKa of a compound
Estimate the nucleotide composition of DNA

19. Figure Number: 08-08
Title: Figure 8.8
Caption: Nitroethane anion formation can be monitored by UV at 240 nm.
Notes: The rate of proton removal from nitroethane can be measured by monitoring the nitroethane anion formed by the reaction.

20. Figure Number: 08-09
Title: Figure 8.9
Caption: Pyruvate concentration can be monitored by UV at 340 nm.
Notes: The rate of reduction of pyruvate by NADH can be measured by monitoring pyruvate disappearance at 340 nm.

21. Figure Number: 08-10
Title: Figure 8.10
Caption: The absorbance of an aqueous solution of phenol at 287 nm as a function of pH.
Notes: The absorption at 287 nm is due to the presence of phenoxide ion (the conjugate base of phenol). When half of the phenol has been converted into phenoxide, the concentrations of phenol and phenoxide are equal. At this point, pH = pKa.

22. Figure Number: 08-11
Title: Figure 8.11
Caption: The absorbance of a solution of DNA at 260 nm as a function of the temperature of the solution.
Notes: Single-stranded DNA absorbs at 260 nm because nonbonding electrons on nitrogen atoms, which are normally tied up in hydrogen bonding together complementary strands of DNA, are free to undergo n --> p* transitions in single-stranded DNA. When the temperature has risen to the point that half of the DNA is single-stranded, DNA is said to be at its "melting" temperature, Tm.

23. The Visible Spectrum and Color

24. Biological / Physiological response
Vision
Biological / Physiological response
to light stimuli 1

25. The Eye and Vision

26. The Eye and its Neurological Wiring

27. Vision: Receptive Field (RF)
Definition: the area of the retina (or visual field) in which light signals evoke responses
It’s a property of the cell, not a cell or a part of the cell
It depends largely on the synaptic inputs to the cell and to some degree the biophysical property of the cell itself

28. Projection from retina to LGN
fixation point
Nasal RGC: axons crossover, project to contralateral LGN
Temporal RGC: axons stay on the same side (ipsilateral)
Left visual field: right LGN, right V1
Right visual field: left LGN, left V1
fovea

29. Visual pathway from retina to V1

30. Optical imaging of orientation map

31. Retinotopic map c b a a b c neighboring cells have neighboring RF
retinotopic map is true in the retina, LGN and V1, but it gets fuzzy as you move on to higher visual areas c
Project orderly to LGN and V1 b a a b c
object
retina

32. The Retina & Photoreceptive Cells

33. Different cells in the retina The Basic Retinal Circuit
Back of eye
6. Pigment cells
1. Receptor Cells
(Graded potential)
(input)
2. Bipolar Cells
3. Ganglion Cells
(action potential)
(Output)
4. Horozontal Cells
(Graded potential)
5. Amacrine Cells
(Graded/action potential)
Structure of the eye
Front of eye 2

34. light
Fovea: high spatial resolution
Periphery: low spatial resolution

35. Direct pathway: Photo receptor  Bipolar  RGC
+: excitatory synapse, preserve response direction
-: inhibitory synapse, flip response direction
Direct pathway is responsible to the RF center

36. Indirect pathway
Indirect pathway mediated by horizontal is responsible to the RF surround
There are other indirect pathway mediated by amacrine cells

37. Summary of retinal circuit
Direct pathway
Indirect pathway
Pathways mediated by amacrine cells

38. The Nobel Prize in Physiology or Medicine 1981:
Roger W.Sperry: for his discoveries concerning the functional specialization of the cerebral hemispheres
David H. Hubel & Torsten N. Wiesel: for their discoveries concerning information processing in the visual system

39. Terpenes in Vision Can diet affect sight
Terpenes in Vision Can diet affect sight?.....It might depend on what you’re looking at.
Color vision vs. B&W: Rods vs. Cones
The Photochemical Process
Lycopenes
Carotenes
Vitamin A
Retinol / Retinal
Humans only see in B&W at night, but some animals like the nocturnal hawkmoth see color. Nature, , 2002

40. orange-red pigment in tomatoes
Lycopene
orange-red pigment in tomatoes
lmax 505 nm 5

46. Cis-Trans Isomerization & Vision

47. B&W Chemistry Step One: Oxidation

48. B&W Chemistry Step Two: Trans -> Cis Isomerization

49. B&W Chemistry Step Three: “Hooked on Opsin”

50. B&W Chemistry Step Four: “Flash”

52. B&W Chemistry Step Five: “Repeat Process”

53. Vision exercise

54. Isoprene (2-methyl-1,3-butadiene)
Terpenes
Terpenes are natural products that form from a pyrophosphate and are structurally related to isoprene.
H2C C
CH3 CH
CH2
Isoprene (2-methyl-1,3-butadiene)

55. The Isoprene Unit
An isoprene unit is the carbon skeleton of isoprene (ignoring the double bonds)
Two isoprene units:

56. The Isoprene Unit The isoprene units are joined "head-to-tail." head

57. Isoprene Links Heads or Tails?

58. Common Carbon Backbone

61. Terpenes Class Number of carbon atoms Monoterpene 10 Sesquiterpene 15
Classification of Terpenes
Class Number of carbon atoms
Monoterpene 10
Sesquiterpene 15
Diterpene 20
Sesterpene 25
Triterpene 30
Tetraterpene 40

62. a-Phellandrene (eucalyptus)
Terpenes
Representative Monoterpenes OH O H
a-Phellandrene (eucalyptus)
Menthol (peppermint)
Citral (lemon grass)

63. a-Phellandrene (eucalyptus)
Terpenes
Representative Monoterpenes OH O H
a-Phellandrene (eucalyptus)
Menthol (peppermint)
Citral (lemon grass)

64. a-Phellandrene (eucalyptus)
Terpenes
Representative Monoterpenes
a-Phellandrene (eucalyptus)
Menthol (peppermint)
Citral (lemon grass)

65. Terpenes
Representative Sesquiterpenes H
a-Selinene (celery)

66. Terpenes
Representative Sesquiterpenes H
a-Selinene (celery)

67. Terpenes
Representative Sesquiterpenes
a-Selinene (celery)

68. Terpenes
Representative Diterpenes OH
Vitamin A

69. Terpenes
Representative Diterpenes OH
Vitamin A

70. Terpenes
Representative Diterpenes
Vitamin A

71. Common Terpenes

72. Limonene

73. Limonene