Flashcards in lecture 9- Circular dichroism spec Deck (57)
Circular dichroism occurs
when a molecule differentially absorbs left and right circularly polarised light
Light produced by natural sources?
Unpolarised light waves are randomly
orientated around the beam axis
passing light through a filter will select for ?
Just one of those directions
Polarisation filters are made of?
are made of long chains of organic molecules, arranged in parallel to each other.
When light passes through the filter, the filter absorbs?
components of electric fields that are parallel to the direction in which the organic molecules are arranged.
light that comes out would have its electric field oscillating along one direction
Reflection also causes
a partial linear polarization in the direction parallel to the reflected surface.
What light is polarised in polaroid sunglasses?
light coming from glares off the roads or from a water surface is polarized
Sunglasses (polaroid) have what type of filter?
Glares when wearing polaroid sunglasses
A large portion of the light produced by a glare is unable to travel through the sunglasses
Light can be polarised by which two ways?
Linearly or circularly polarised
All polarised light states can be described by?
sum of two linearly polarised states at right angles to each other
How can we get Circularly polarised light from the sum of two linearly polarised states?
using a second filter, causes quarter wave retardation
The quarter-wave retardation plate is made of?
a sheet of birefringent (double refracting) material
Thickness of the polarised light entering the phase such that ?- circularly polarised
- Horizontally and vertically polarized light entering in phase will emerge from the retardation plate 1/4 of a wavelength out of phase.
Circularly polarised light can be ?
right or left handed
how do you get plane polarised light?
When you add together left-handed and right-handed circularly polarised light
if a sample absorbs one more that the other, what kind of light do you get
elliptically polarised light.
L and R beams have different amplitudes
What properties must a molecule have in order to create circular dichroism ?
- Ability to absorb light (chromophore)
- Asymmetric / contain CHIRAL residues
-----Contain a peptide bond
------Contain aromatic residues in asymmetric environments
------Contain DNA bases in asymmetric environments
Chiral molecules have pairs of ??
Enantiomers - non super impossible mirror images
D AND L
Light source for CD spec?
purpose of a photo elastic modulator and what it actually is?
normally a quartz crystal subjected to an oscillating electric field.
to form left and right polarised light- plane polarised light
Frequency of the light passing though the photo elastic modulator ?
what is kept constant in. a CD spec kit
What is detected by a photomultiplier ?
differential absorption of left and right polarised light
When light is detected by a photomultiplier??- units
converted into ellipticity (units millidegrees)
is the unit of circular dichroism and is defined as the tangent of the ratio of the minor to major elliptical axis