Vision and reflection on Mining Software Repositories research in 2024
UV-visible spectroscopy - 2021
1. Ph.D.Ahmed Metwaly
Ultraviolet/visible spectroscopy
ORCID account
Email: ametwaly@azhar.edu.eg
1
• Associate Professor of Pharmacognosy , faculty of Pharmacy, Al-Azhar University
• Senior research fellow, Liaoning University of Traditional Chinese Medicine, China (20118-2019)
• Visiting scholar, School of Pharmacy, University of Mississippi, USA (2012-2014)
3. Electromagnetic Radiation
Electromagnetic radiation consist of discrete packets of energy
which are called as photons.
A photon consists of an oscillating electric field (E) & an
oscillating magnetic field (M) which are perpendicular to each
other.
4.
5. Electromagnetic Radiation
Frequency (ν):
It is defined as the number of times electrical field radiation oscillates
in one second.
The unit for frequency is Hertz (Hz).
1 Hz = 1 cycle per second
Wavelength (λ):
It is the distance between two nearest parts of the wave in the same
phase i.e. distance between two nearest crest or troughs.
7. Electromagnetic Radiation
The visible spectrum constitutes a small part of the total radiation spectrum.
Most of the radiation that surrounds us cannot be seen, but can be detected by
instruments.
8. Ultraviolet and Visible Spectroscopy:
The ultraviolet and visible (UV/Vis) radiation is that region of EMR (electromagnetic
radiation) or spectrum whose wavelengths range from 10-800 nm.
The (UV/Vis) region can be divided into three types of radiation that are
1. Vacuum UV; λ = 10-200 nm
2. Near UV; λ = 200-400 nm
3. Visible radiation; λ = 400-800 nm
14. Principles of Spectroscopy
The principle is based on the measurement of spectrum of a
sample containing atoms / molecules.
Spectrum is a graph of intensity of absorbed or emitted
radiation by sample verses frequency (ν) or wavelength (λ).
Spectrometer is an instrument design to measure the
spectrum of a compound.
18. Five Basic Optical Instrument Components
1) Source – A stable source of radiant energy at the desired wavelength (or range).
2) Wavelength Selector – A device that isolates a restricted region of the EM
spectrum used for measurement (monochromators, prisms & filters).
3) Sample Container – A transparent container used to hold the sample (cells,
cuvettes, etc).
4) Detector/Photoelectric Transducer – Converts the radiant energy into a useable
signal (usually electrical).
5) Signal Processor & Readout – Amplifies or attenuates the transduced signal and
sends it to a readout device as a meter, digital readout, chart recorder, computer,
etc.
24. LIGHT SOURCES
Various UV radiation sources are as follows
a. Deuterium lamp
b. Hydrogen lamp
c. Tungsten lamp
d. Xenon discharge lamp
e. Mercury arc lamp
Various Visible radiation sources are as follow
a. Tungsten lamp
b. Mercury vapour lamp
c. Carbonone lamp
SAMPLE COMPARTMENT
25. SUMMARY
Types of source, sample holder and detector for various EM region
REGION SOURCE SAMPLE
HOLDER
DETECTOR
Ultraviolet Deuterium lamp Quartz/Fused
silica
Phototube, PM
tube, diode array
Visible Tungsten lamp Glass/Quartz Phototube, PM
tube, diode array
26. Beer Lamberts Law:
Beer Lamberts Law:
A = ε b c
A=absorbance
ε =molar absorbtivity with units of L /mol.cm
b=path length of the sample (cuvette)
c =Concentration of the compound in solution, expressed
in mol /L
27.
28. Chromophore
Chromophore: covalently unsaturated groups responsible for electronic
absorption
e.g. NO2, N=O, C=O, C=N, C≡N, C=C, C=S, etc
Auxochrome
The functional groups attached to a chromophore which modifies the ability of the
chromophore to absorb light , altering the wavelength or intensity of absorption.
OR
The functional group with non-bonding electrons that does not absorb radiation in
near UV region but when attached to a chromophore alters the wavelength &
intensity of absorption.
29. Factors affecting UV/Vis absorption:
The position and intensity of an absorption band of a chromophore may be modified by
substituent groups attached to the chromophore, type of solvent, degree of conjugation and
stereochemical effect.
Bathochromic (Red) shift: The shift of absorption to a longer wavelength.
Hypsochromic ( Blue) shift: The shift of absorption to a shorter wavelength.
Hyperchromic effect: The increase in absorption intensity.
Hypochromic effect: The decrease in absorption intensity.
30. Application of UV/vis spectroscopy:
Chrysophanol, λ max (EtOH) nm: 224, 254, 288, 432,
By addition of one drop of 5% NaOH, a bathochromic shift will occurs; 232, 250,
330, 500.
Ferulic acid, λ max (MeOH) nm: 230, 279.
Vanillic acid, λ max (MeOH) nm: 252, 291, 328.
Iridoids and secoiridoids, λ max (MeOH) nm: 236; characteristics for enol-ether
system conjugated with carbonyl group (-OCO-C=CH-O-).
UV Aspect of Flavonoids:
31. • When absorption maxima (λmax) of a
compound shifts to longer wavelength, it is
known as bathochromic shift or red shift.
• The effect is due to presence of an auxochrome
or by the change of solvent.
• e.g. An auxochrome group like –OH, -OCH3
causes absorption of compound at longer
wavelength.
• Bathochromic Shift (Red Shift)
1
32. • In alkaline medium, p-nitrophenol shows red
shift. Because negatively charged oxygen
delocalizes more effectively than the unshared
pair of electron.
p-nitrophenol
λmax = 255 nm λmax = 265 nm
• Bathochromic Shift (Red Shift)
1
OH
N
+ O
-
O
OH
-
Alkaline
medium
O
-
N
+ O
-
O
33. • When absorption maxima (λmax) of a
compound shifts to shorter wavelength, it is
known as hypsochromic shift or blue shift.
• The effect is due to presence of an group
causes removal of conjugation or by the
change of solvent.
• Hypsochromic Shift (Blue Shift)
2
34. • Aniline shows blue shift in acidic medium, it
loses conjugation.
Aniline
λmax = 280 nm λmax = 265 nm
• Hypsochromic Shift (Blue Shift)
2
NH2
H
+
Acidic
medium
NH3
+
Cl
-
35. • When absorption intensity (ε) of a compound is
increased, it is known as hyperchromic shift.
• If auxochrome introduces to the compound, the intensity
of absorption increases.
Pyridine 2methylpyridine
λmax = 257 nm λmax = 260 nm
ε = 2750 ε = 3560
• Hyperchromic Effect
3
N N CH3
36. • When absorption intensity (ε) of a compound is
decreased, it is known as hypochromic shift.
Naphthalene 2-methyl naphthalene
ε = 19000 ε = 10250
CH3
• Hypochromic Effect
4
37. Wavelength ( λ )
Absorbance
(
A
)
Shifts and Effects
Hyperchromic shift
Hypochromic shift
Red
shift
Blue
shift
λmax