Transcript Raman Spectroscopy - Harlem Children Society

Raman
Spectroscopy
Anatasia Gangadin
Dr. Ronald Birke
City College of New York
What is Spectroscopy?
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The study of how 'species' (i.e.,
atoms, molecules, solutions) react
to light. Some studies depend on
how much light an atom absorbs.
The electromagnetic radiation
absorbed, emitted or scattered by
the molecule is analyzed.
Typically, a beam of radiation
from a source such as a laser is
passed through a sample, and the
radiation exiting the sample is
measured. Some, like Raman,
depend on a molecule's vibrations
in reaction to the light.
Sir Chandrashekhara Venkata Raman
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November 7, 1888-November 21,
1970
Won the Noble Prize in 1930 for
Physics
Discovered the "Raman Effect"
Besides Discovering the Raman
Effect, He studied extensively in
X-Ray Diffractions, Acoustics,
Optics, Dielectrics, Ultrasonics,
Photo electricity, and colloidal
particles.
SERS vs. Raman
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During charge transfer,
some vibrations will be
altered due to a molecule's
interaction with the
surface, resulting in some
of the SER bands being
shifted in respect to the
normal Raman Spectrum.
SER spectra of a different
small peptides and proteins
were obtained from a
roughened surface using a
Raman spectrometer.
Why Raman?
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In Raman spectroscopy, by
varying the frequency of the
radiation, a spectrum can be
produced, showing the intensity
of the exiting radiation for each
frequency. This spectrum will
show which frequencies of
radiation have been absorbed by
the molecule to raise it to higher
vibrational energy states.
What Exactly Is Being Measured?
METHANE
When Light hits a
sample, It is Excited,
and is forced to vibrate
and move. It is these
vibrations which we are
measuring.
Stokes vs. Anti Stokes
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Atoms are at a certain energy
level at any given time.
As a laser light hits the atom, it is
excited and reaches a higher level
of energy, and then is brought
back down.
If an atom is at a given energy
level, it can be excited then fall
below the original level.
Anti-stokes spectrum are mirror
spectrums of Stokes Raman
Spectrums
Using Stokes/Peaks to Determine
Vibrations
How To carry Out a Raman
Experiment
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An insulated conductor was
soldered to a piece of pure silver
which was the embedded into a
chemically resistant resin, leaving
one face exposed.
1 micro liter of sample solution
was placed on the roughened
surface.
The Sample is put through an
Oxidation Reduction Cycle.
Raman Instruments
Results of Other Raman Studies
Proposing a Structure
Histidine
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One of the common natural amino
acids.
Nutritionally, histidine is considered
an essential Amino Acid, but mostly
only in children.
In Catalytic Triads, the basic nitrogen
of histidine is used to extract a proton
from Serine, Threonine or Cysteine.
Histidine is also used as a ‘Proton
Shuttle’
Our Experiment
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To obtain an acceptable SERS
Spectrum of Histidine
Comparison of Spectrum to
IR and Raman Spectrum
Proposing a structure for
Histidine
Solid Histadine
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Wavelength
10500
10000
9500
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1
101
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Wavelength
1201 1301
1401 1501 1601
1701 1801
1901
Histadine
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Wavenumber
2200
Series2
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Wavelength
1101
1201
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1401
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Citations And References
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Stewart, Fredricks, Surface Enhanced Raman Spectroscopy of
Peptides and Proteins absorbed on a Silver Surface on an
electrochemically Prepared Silver Surface, Spectrochima
Acta, Part A, 55, 1999, pg. 1615-1640
Roth, Hope, Fredricks, et al. Simple Technique for measuring
Surface Enhanced Fourier Transform Raman Spectra of
Organic Compounds. Applied Spectroscopy, Vol. 47, 11,
1993.
Habucchi, Cotlet, Gronheind, et al. Single Molecule Surface
Enhanced Resonance Raman Spectroscopy of the Enhanced
Green Fluorescent Protein. Journal of the American
Chemical Society, 2003, Vol. 125, pg. 8446-8447
Acknowledgements
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Dr. Sat Bhattacharya
HCS
Dr. Ronald Birke
Professor Tudor
Fen Xu
City College of New York