Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations


Presentation on theme: "Ultraviolet-Visible (UV-VIS) Spectroscopy Gives information about conjugated  electron systems."— Presentation transcript:

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

2 gaps between electron energy levels are greater than those between vibrational levels gap corresponds to wavelengths between 200 and 800 nm Transitions between electron energy states  E = h  E = h

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

4 UV and Visible light cause only two kinds of electronic transitions Only organic compounds with  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 Most stable  -electron configuration  -Electron configuration of excited state          * Transition in cis,trans-1,3-cyclooctadiene HOMO LUMO  E = h  E = h

6  * Transition in Alkenes HOMO-LUMO energy gap is affected by substituents on double bond as HOMO-LUMO energy difference decreases (smaller  E), max shifts to longer wavelengths

7 Substituent Effects Methyl groups on double bond cause max to shift to longer wavelengths C C H H H H C C H H CH 3 max 170 nm max 170 nm CH 3 max 188 nm max 188 nm

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

9 Effect of Conjugation on max

10

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

12 What is carvone’s max ? 236 nm

13 The Beer–Lambert Law The molar absorptivity of a compound is a constant that is characteristic of the compound at a particular wavelength A = log(I / I 0 ) c = concentration of substance in solution l = length of the cell in cm  = molar absorptivity A = cl 

14 Wavelength, nm max 230 nm max 230 nm  max 2630 Molar absorptivity (  ) UV Spectrum of cis,trans-1,3-cyclooctadiene

15 Substituent Effects max 217 nm (conjugated diene) max 217 nm (conjugated diene) H C CHH C C H H H C C H CH 3 H H C C H3CH3CH3CH3CH C C H H max 263 nm conjugated triene plus two methyl groups max 263 nm conjugated triene plus two methyl groups

16 Both the max and  increase as the number of conjugated double bonds increases

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

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

19

20

21

22

23 The Visible Spectrum and Color

24 Vision Biological / Physiological response to light stimuli

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 fovea 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

29 Visual pathway from retina to V1

30 Optical imaging of orientation map

31 Retinotopic map 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 a b c a b c object retina Project orderly to LGN and V1

32 The Retina & Photoreceptive Cells

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

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

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

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

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

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?.....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 Lycopene max 505 nm max 505 nm orange-red pigment in tomatoes

41

42

43

44

45

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”

51

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

53 Vision exercise

54 Terpenes Terpenes are natural products that form from a pyrophosphate and are structurally related to isoprene. H2CH2CH2CH2C C CH 3 CH CH 2 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." headtail tail head

57 Isoprene Links Heads or Tails?

58 Common Carbon Backbone

59

60

61 Terpenes ClassNumber of carbon atoms Monoterpene10 Sesquiterpene15 Diterpene20 Sesterpene25 Triterpene30 Tetraterpene40 Classification of Terpenes

62 Terpenes Representative Monoterpenes  -Phellandrene (eucalyptus) Menthol (peppermint) Citral (lemon grass) OH OH

63 Terpenes Representative Monoterpenes  -Phellandrene (eucalyptus) Menthol (peppermint) Citral (lemon grass) OH OH

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

65 Terpenes Representative Sesquiterpenes  -Selinene (celery) H

66 Terpenes Representative Sesquiterpenes  -Selinene (celery) H

67 Terpenes Representative Sesquiterpenes  -Selinene (celery)

68 Terpenes Representative Diterpenes Vitamin A OH

69 Terpenes Representative Diterpenes Vitamin A OH

70 Terpenes Representative Diterpenes Vitamin A

71 Common Terpenes

72 Limonene

73

74


Download ppt "Ultraviolet-Visible (UV-VIS) Spectroscopy Gives information about conjugated  electron systems."

Similar presentations


Ads by Google