BIOPHYSICAL METHODS

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• BIOPHYSICAL METHODS

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• Analysis of Bio molecules
• UV and Visible Light
• Spectroscopy NMR and ESR
• Circular dichorism
• X ray diffraction
• Mass Spectroscopy
• Surface plasmon Resonance

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ELECTROMAGNETIC SPECTRUM
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ELECTROMAGNETIC SPECTUM
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UV SPECTRUM
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VISIBLE SPECRUM
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INFRARED SPECRTUM
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Quantitative UV

• Quantitative UV/vis is used to determine the
  concentration of an analyte usually in an aqueous
  solution.

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• In order to be able to do this, the analyte must
  absorb in the UV/vis region.

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• Beer's Law is a linear relationship between
  absorbance and concentration.
• A a b c, where c is concentration, A is
  absorbance, b is path length (usually 1 cm) and a
  is the molar absorbtivity.
• Beer's law is linear.

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UV Analysis - General Theory

• UV ANALYZERS
• The UV region consists of wavelengths from 200 to
  400 nanometers (nm).
• The visible region extends from 400 to 800 nm,
  and the near IR (NIR) region covers 0.8 to 2.50
  micrometers (jm).

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• The UVVIS-NIR is a relatively small part of the
  electromagnetic radiation spectrum, and the
  shorter the wavelength the more penetrating the
  radiation.
• The region where a compound absorbs radiation
  depends on the energy of the molecular
  transitions.

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• High-energy electronic transitions are observed
  in the low-wavelength UV/VIS regions.
• Moderate-energy vibrational and rotational
  transitions are observed in the high-wavelength
  IR region.

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• The Main Components of UV Analyzers
• 1. Source-provides radiation for the spectral
  region being measured
• 2. Mono chromator-a device used to select narrow
  bands of wavelengths

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• 3. Sample cell-contains the sample at an
  appropriate path length
• 4. Detector-a device which measures transmitted
  energy and converts it into electrical energy
• 5. Readout device-provides a means of recording
  the measurement results

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Radiation Sources

• The function of the source is to provide
  radiation of sufficient energy to
  makemeasurements in the region of spectral
  interest.

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• The cadmium, mercury, and zinc vapor sources that
  are used in the UV region are emission line
  sources.
• The output of these sources provides radiation
  as narrow discrete emission lines at a
  high-energy level

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• Mercury vapor lamps are often used because of
  their long service life.
• Deuterium arc sources provide a broad band of UV
  radiation at all of the wavelengths in the UV
  region.

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• The energy of the deuterium source is relatively
  lower than the energy of the mercury source.

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• The two sources used in the visible and NIR
  regions are tungsten filaments and quartz-halide
  lamps.

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• Two types of UV energy sources are used
• broad and discrete line emission sources.
• The broad emission source provides energy in a
  broad wavelength band, and narrow-band filters
  are used to isolate the wavelengths of interest.

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• These sources provide all wavelengths in the
  region but usually have a low-emission, or
  low-energy level, at any given wavelength.
• Sources of this type include hydrogen, or
  deuterium, discharge lamps tungsten lamps and
  tungsten-iodine lamps.

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• Discrete line sources use gas discharge lamps
  with narrow lines of emission.
• These sources emit radiation energy at various
  discrete wavelengths at a high-energy level
• The wavelengths that are not desired are
  filtered, leaving only the wavelength of interest

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• Tungsten-iodine cycle lamps can be used down to
  300 nm
• Mercury vapor lamps are the most useful UV
  sources due to their high intensity and long life
  
• Medium-pressure mercury lamps can operate down to
  300 nm
• Zinc discharge lamps are useful due to their 214
  nm emission line

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The Mono chromator

• Dispersive and nondispersive mono chromator are
  used in photometric analysis

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• A monochromator is an optical device that
  transmits a mechanically selectable narrow band
  of wavelengths of light or other radiation chosen
  from a wider range of wavelengths available at
  the input. The name is from the Greek roots
  mono-, single, and chroma, colour, and the Latin
  suffix -ator, denoting an agent.

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MONO CROMATOR
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SPCTROPHOTOMETER
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• Spectrophotometers are dispersive instruments and
  photometers are non-dispersive instruments.
• The function of the mono-chromator is to disperse
  light from a source and selectively pass a narrow
  spectral band to the sample and detector

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• Spectrophotometers are dispersive devices that
  are used to scan across a spectrum of
  wavelengths.
• They can be used to make measurements at several
  wavelengths
• This capability allows for the analysis of
  multiple components with a spectrophotometer.

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• Photometers are non-dispersive devices which
  exclude a large amount of spectral radiation.
• Photometers are used to make measurements at
  selected discrete wavelengths.

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• The measurement wavelength filter is selected to
  match the absorption band of the component being
  analyzed.

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• The ratio of the transmitted light at the
  reference and measured wavelengths is measured by
  the photometer.
• Normally, photometers are used to measure a
  single component in a process stream.

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The Sample Cell

• The purpose of the sample cell is to contain a
  representative sample from the process stream.

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• Stainless steel is the material most commonly
  used for cell bodies
• Other metals such as Monel, Hastelloy, and
  titanium are also used.
• Plastic cell bodies made of Teflon or Kynar are
  used in some applications
• Quartz, sapphire, and glass cell windows are
  used in the UV-VIS-NIR spectral regions.

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Detectors

• Several types of detectors are used in process UV
  analyzers, including phototubes, photomultiplier
  tubes, and photocells.

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• The photoelectric effect is used in the vacuum
  phototube to produce a current proportional to
  the energy striking the tube cathode
• The photomultiplier tube offers very sensitive
  detection of UV and visible light but large
  radiation energy levels will damage the
  light-sensitive surface

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• The photocell (photovoltaic) is a semiconductor
  light detector of the barrier layer type
• A current is developed proportional to the light
  intensity but, the current output is not linear
  with the energy level

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• Photomultiplier tubes (PMT) have traditionally
  been used in UV/VIS instruments.
• The photoelectric effect is used in the PMT to
  produce a current proportional to the radiation
  striking the cathode of the tube.

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PHOTOMULTIPLIER
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• A recent development in photometric analyzers is
  the use of photodiode arrays (PDA).
• The PDA detectors are used throughout UV-VIS-NIR
  regions.
• A large number of discrete detectors are located
  in a very close space in the PDA
• This array of diode detectors allows for all of
  the wavelengths to be measured simultaneously.

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PHOTODIODE ARRAY
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Readouts

• Analog meters, digital meters, strip chart
  recorders, and video display tubes (VDTs) are
  examples of readout devices used in photometers
  and spectrophotometers

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ANALOGUE METER
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DIGITAL METER
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STRIP CHART RECORDER
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VIDEO DISPLAY TUBE
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Scanning Spectrophotometers

• Scanning spectrophotometers are dispersive
  devices that normally utilize diffraction
  gratings to scan across a spectral region
• Scanning devices can be used for multiple
  component applications
• . Scanning spectrophotometers can be used in the
  UV, visible, and NIR regions

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DIFFRACTION GRATING
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DIFFRACTION GRATING
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SCANNING SPECTROPHOTOMETER
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Spectrometer

• A spectrograph is an optical instrument used to
  measure properties of light over a specific
  portion of the electromagnetic spectrum,
  typically used in spectroscopic analysis to
  identify materials

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SPECTROMETER
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UV / VISIBLE SPECTROMETER
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• Spectrometer is a term that is applied to
  instruments that operate over a very wide range
  of wavelengths, from gamma rays and X-rays into
  the far infrared
• If the region of interest is restricted to near
  the visible spectrum, the study is called
  spectrophotometry.

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Circular dichroism

• Circular dichroism (CD) is the differential
  absorption of left- and right-handed circularly
  polarized light.
• A CD Spectrometer is an instrument that records
  this phenomenon as a function of wavelength

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CIRCULAR DICHORISM
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CIRCULAR DICHORISM
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• CD can be used to help determine the structure
  of macromolecules (including the secondary
  structure of proteins and the handedness of DNA).
• CD was discovered by the French physicist Aimé
  Cotton in 1896.

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Interaction of circularly polarized light with
matter

• The electric field of a light beam causes a
  linear displacement of charge when interacting
  with a molecule, whereas the magnetic field of it
  causes a circulation of charge
• These two motions combined result in a helical
  displacement when light impinges on a molecule

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• The two types of circularly polarized light are
  absorbed to different extents
• In a CD experiment, equal amounts of left and
  right circularly polarized light of a selected
  wavelength are alternately radiated into a
  (chiral) sample
• One of the two polarizations is absorbed more
  than the other one, and this wavelength-dependent
  difference of absorption is measured, yielding
  the CD spectrum of the sample.

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Application to biological molecules

• In general, this phenomenon will be exhibited in
  absorption bands of any optically active
  molecule.
• As a consequence, circular dichroism is exhibited
  by biological molecules, because of their
  dextrorotary and levorotary components

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• Even more important is that a secondary structure
  will also impart a distinct CD to its respective
  molecules.
• Therefore, the alpha helix of proteins and the
  double helix of nucleic acids have CD spectral
  signatures representative of their structures
• The far-UV (ultraviolet) CD spectrum of proteins
  can reveal important characteristics of their
  secondary structure

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• CD spectra can be readily used to estimate the
  fraction of a molecule that is in the alpha-helix
  conformation, the beta-sheet conformation, the
  beta-turn conformation, or some other (e.g.
  random coil) conformation

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• It can reveal important thermodynamic information
  
• CD a valuable tool for verifying that the protein
  is in its native conformation
• Visible CD spectroscopy is a very powerful
  technique to study metalprotein interactions

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• CD gives less specific structural information
  than X-ray crystallography and protein NMR
  spectroscopy
• for example, which both give atomic resolution
  data
• However, CD spectroscopy is a quick method that
  does not require large amounts of

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• CD can be used to survey a large number of
  solvent conditions, varying temperature, pH,
  salinity, and the presence of various cofactors.

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Nuclear magnetic resonance

• Nuclear magnetic resonance (NMR) is the name
  given to a physical resonance phenomenon
  involving the observation of specific quantum
  mechanical magnetic properties of an atomic
  nucleus in the presence of an applied, external
  magnetic field

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NMR OVER VIEW
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MAGNETIC RESONANCE
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• Many scientific techniques exploit NMR phenomena
  to study molecular physics, crystals and
  non-crystalline materials through NMR
  spectroscopy
• NMR is also routinely used in advanced medical
  imaging techniques, such as in magnetic resonance
  imaging (MRI).

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• All nuclei that contain odd numbers of nucleons
  have an intrinsic magnetic moment and angular
  momentum, in other words a spin gt 0.
• The most commonly studied nuclei are 1H
• A key feature of NMR is that the resonance
  frequency of a particular substance is directly
  proportional to the strength of the applied
  magnetic field

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• If a sample is placed in a non-uniform magnetic
  field then the resonance frequencies of the
  sample's nuclei depend on where in the field they
  are located
• The principle of NMR usually involves two
  sequential steps

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• The alignment (polarization) of the magnetic
  nuclear spins in an applied, constant magnetic
  field H0.
• The perturbation of this alignment of the nuclear
  spins by employing an electro-magnetic, usually
  radio frequency (RF) pulse

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• The required perturbing frequency is dependent
  upon the static magnetic field (H0) and the
  nuclei of observation.

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• The two fields are usually chosen to be
  perpendicular to each other as this maximises the
  NMR signal strength
• The resulting response by the total
  magnetization (M) of the nuclear spins is the
  phenomenon that is exploited in NMR spectroscopy
  and magnetic resonance imaging

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• NMR phenomena are also utilized in low-field NMR,
  NMR spectroscopy and MRI in the Earth's magnetic
  field (referred to as Earth's field NMR), and in
  several types of magnetometers.

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NMR spectroscopy

• NMR spectroscopy is one of the principal
  techniques used to obtain physical, chemical,
  electronic and structural information about
  molecules due to either the chemical shift Zeeman
  effect, or the Knight shift effect, or a
  combination of both, on the resonant frequencies
  of the nuclei present in the sample

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• It is a powerful technique that can provide
  detailed information on the topology, dynamics
  and three-dimensional structure of molecules in
  solution and the solid state
• Thus, structural and dynamic information is
  obtainable

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NMR SPECTROPHOTOMETER
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High magnetic field (800 MHz, 18.8 T) NMR
spectrometer being loaded with a sample.
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• Nuclear magnetic resonance spectroscopy, most
  commonly known as NMR spectroscopy, is the name
  given to a technique which exploits the magnetic
  properties of certain nuclei
• Many types of information can be obtained from an
  NMR spectrum

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• It can, among other things, be used to study
  mixtures of analytes, to understand dynamic
  effects such as change in temperature and
  reaction mechanisms
• It is an invaluable tool in understanding protein
  and nucleic acid structure and function. It can
  be applied to a wide variety of samples, both in
  the solution and the solid state.

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The NMR sample is prepared in a thin-walled glass
tube - an NMR tube.
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• When placed in a magnetic field, NMR active
  nuclei (such as 1H or 13C) absorb at a frequency
  characteristic of the isotope.
• The resonant frequency, energy of the absorption
  and the intensity of the signal are proportional
  to the strength of the magnetic field

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• For example, in a 21 tesla magnetic field,
  protons resonate at 900 MHz. It is common to
  refer to a 21 T magnet as a 900 MHz magnet,
  although different nuclei resonate at a different
  frequency at this field strength.

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• In the Earth's magnetic field the same nuclei
  resonate at audio frequencies. This effect is
  used in Earth's field NMR spectrometers and other
  instruments.

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Chemical shift

• Depending on the local chemical environment,
  different protons in a molecule resonate at
  slightly different frequencies

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• Since both this frequency shift and the
  fundamental resonant frequency are directly
  proportional to the strength of the magnetic
  field, the shift is converted into a
  field-independent dimensionless value known as
  the chemical shift

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• By understanding different chemical environments,
  the chemical shift can be used to obtain some
  structural information about the molecule in a
  sample

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Correlation spectroscopy

• Correlation spectroscopy is one of several types
  of two-dimensional nuclear magnetic resonance
  (NMR) spectroscopy
• This type of NMR experiment is best known by its
  acronym, COSY

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CORRELATION SPECTROSCOPY
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• Other types of two-dimensional NMR include
  J-spectroscopy, exchange spectroscopy (EXSY),
  Nuclear Overhauser effect spectroscopy (NOESY),
  total correlation spectroscopy (TOCSY) and
  heteronuclear correlation experiments, such as
  HSQC, HMQC, and HMBC

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Solid-state nuclear magnetic resonance

• A variety of physical circumstances does not
  allow molecules to be studied in solution, and at
  the same time not by other spectroscopic
  techniques to an atomic level

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• Applications in which solid-state NMR effects
  occur are often related to structure
  investigations on membrane proteins, protein
  fibrils or all kinds of polymers, and chemical
  analysis in inorganic chemistry, but also include
  "exotic" applications like the plant leaves and
  fuel cells.

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Electron paramagnetic resonance

• Electron paramagnetic resonance (EPR) or electron
  spin resonance (ESR) spectroscopy is a technique
  for studying chemical species that have one or
  more unpaired electrons, such as organic and
  inorganic free radicals or inorganic complexes
  possessing a transition metal ion

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• The basic physical concepts of EPR are analogous
  to those of nuclear magnetic resonance (NMR), but
  it is electron spins that are excited instead of
  spins of atomic

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• EPR was first observed in Kazan State University
  by a Soviet physicist Yevgeny Zavoisky in 1944,
  It was developed independently at the same time
  by Brebis Bleaney at Oxford University.

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EPR spectrometer
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• In principle, EPR spectra can be generated by
  either varying the photon frequency incident on a
  sample while holding the magnetic field constant,
  or doing the reverse

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EPR applications

• EPR spectroscopy is used in various branches of
  science, such as chemistry and physics, for the
  detection and identification of free radicals and
  paramagnetic centers

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• EPR is a sensitive, specific method for studying
  both radicals formed in chemical reactions and
  the reactions themselves
• For example, when frozen water (solid H2O) is
  decomposed by exposure to high-energy radiation,
  radicals such as H, OH, and HO2 are produced.
  Such radicals can be identified and studied by
  EPR

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• Organic and inorganic radicals can be detected
  in electrochemical systems and in materials
  exposed to UV light
• Medical and biological applications of EPR also
  exist
• Specially-designed nonreactive radical molecules
  can attach to specific sites in a biological
  cell, and EPR spectra can then give information
  on the environment of these so-called spin-label
  or spin-probes.

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• EPR also has been used by archaeologists for the
  dating of teeth.
• Radiation damage over long periods of time
  creates free radicals in tooth enamel, which can
  then be examined by EPR and, after proper
  calibration, dated

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• Radiation-sterilized foods have been examined
  with EPR spectroscopy, the aim being to develop
  methods to determine if a particular food sample
  has been irradiated and to what dose.

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X-ray scattering techniques

• This is an X-ray diffraction pattern formed when
  X-rays are focused on a crystalline material, in
  this case a protein
• Each dot, called a reflection, forms from the
  coherent interference of scattered X-rays passing
  through the crystal.

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X RAY SCATTERING
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• X-ray scattering techniques are a family of
  non-destructive analytical techniques which
  reveal information about the crystallographic
  structure, chemical composition, and physical
  properties of materials and thin films

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• These techniques are based on observing the
  scattered intensity of an X-ray beam hitting a
  sample as a function of incident and scattered
  angle, polarization, and wavelength or energy.

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X-ray diffraction techniques

• X-ray diffraction finds the geometry or shape of
  a molecule using X-rays.
• X-ray diffraction techniques are based on the
  elastic scattering of X-rays from structures that
  have long range order

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X RAY DIFFRACTION
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• Single-crystal X-ray diffraction is a technique
  used to solve the complete structure of
  crystalline materials, ranging from simple
  inorganic solids to complex macromolecules, such
  as proteins.

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• Powder diffraction (XRD) is a technique used to
  characterize the crystallographic structure,
  crystallite size (grain size)
• Powder diffraction is commonly used to identify
  unknown substances, by comparing diffraction data
  against a database maintained by the
  International Centre for Diffraction Data

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• Thin film diffraction and grazing incidence X-ray
  diffraction may be used to characterize the
  crystallographic structure and preferred
  orientation of substrate-anchored thin films

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• High-resolution X-ray diffraction is used to
  characterize thickness, crystallographic
  structure, and strain in thin epitaxial films. It
  employs parallel-beam optics
• X-ray pole figure analysis enables one to analyze
  and determine the distribution of crystalline
  orientations within a crystalline thin-film
  sample

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Compton scattering

• Compton scattering or the Compton effect is the
  decrease in energy (increase in wavelength) of an
  X-ray or gamma ray photon, when it interacts with
  matter
• Compton scattering usually refers to the
  interaction involving only the electrons of an
  atom

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COMPTON SCATTERING
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• The Compton effect was observed by Arthur Holly
  Compton in 1923
• Arthur Compton earned the 1927 Nobel Prize in
  Physics for the discovery.

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X-ray Raman scattering

• X-ray Raman scattering (XRS) is non-resonant
  inelastic scattering of x-rays from core
  electrons
• .
• It is analogous to Raman scattering, which is a
  largely-used tool in optical spectroscopy, with
  the difference being that the wavelengths of the
  exciting photons fall in the x-ray regime and the
  corresponding excitations are from deep core
  electrons

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Mass spectrometry (MS)

• Mass spectrometry (MS) is an analytical technique
  for the determination of the elemental
  composition of a sample or molecule
• It is also used for elucidating the chemical
  structures of molecules, such as peptides and
  other chemical compounds

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MASS SPECTROMETRY
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MASS SPECTROMETER
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• The MS principle consists of ionizing chemical
  compounds to generate charged molecules or
  molecule fragments and measurement of their
  mass-to-charge ratios

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Typical MS procedure

• 1) a sample is loaded onto the MS instrument, and
  
• 2) the components of the sample ionized by one of
  a variety of methods (e.g., by impacting them
  with an electron beam), which results in the
  formation of charged particles (ions),

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• 3) directing the ions into a electric and/or
  magnetic fields
• 4) computation of the mass-to-charge ratio of the
  particles based on the details of their motion of
  the ions as they transit through electromagnetic
  fields

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• 5) detection of the ions, which in step 4) were
  sorted according to m/z.

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• MS instruments consist of three modules 1.An ion
  source, which can convert gas phase sample
  molecules into ions
• A mass analyzer, which sorts the ions by their
  masses by applying electromagnetic fields

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• A detector, which measures the value of an
  indicator quantity and thus provides data for
  calculating the abundances of each ion present

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• The technique has both qualitative and
  quantitative uses
• These include identifying unknown compounds,
  determining the isotopic composition of elements
  in a molecule, and determining the structure of a
  compound by observing its fragmentation

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Main steps of measuring with a mass spectrometer
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• Other uses include quantifying the amount of a
  compound in a sample or studying the fundamentals
  of gas phase ion chemistry
• MS is now in very common use in analytical
  laboratories that study physical, chemical, or
  biological properties of a great variety of
  compounds.

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Tandem mass spectrometry

• A tandem mass spectrometer is one capable of
  multiple rounds of mass spectrometry, usually
  separated by some form of molecule fragmentation

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TANDEM MASS SPECTROMETER
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• For example, one mass analyzer can isolate one
  peptide from many entering a mass spectrometer.
• A second mass analyzer then stabilizes the
  peptide ions while they collide with a gas,
  causing them to fragment by collision-induced
  dissociation (CID).
• A third mass analyzer then sorts the fragments
  produced from the peptides

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• There are various methods for fragmenting
  molecules for tandem MS, including
  collision-induced dissociation (CID), electron
  capture dissociation (ECD), electron transfer
  dissociation (ETD), infrared multiphoton
  dissociation (IRMPD) and blackbody infrared
  radiative dissociation (BIRD).

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• An important application using tandem mass
  spectrometry is in protein identification

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• An important type of Tandem mass spectrometry is
  Accelerator Mass Spectrometry (AMS), which uses
  very high voltages, usually in the mega-volt
  range, to accelerate negative ions into a type of
  tandem mass spectrometer.
• One of the most important applications of this
  technique is radiocarbon dating.

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Mass spectrum analysis

• Since the precise structure or peptide sequence
  of a molecule is deciphered through the set of
  fragment masses, the interpretation of mass
  spectra requires combined use of various
  techniques

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• Usually the first strategy for identifying an
  unknown compound is to compare its experimental
  mass spectrum against a library of mass spectra

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• Computer simulation of ionization and
  fragmentation processes occurring in mass
  spectrometer is the primary tool for assigning
  structure or peptide sequence to a molecule

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• Another way of interpreting mass spectra involves
  spectra with accurate mass
• A computer algorithm called formula generator
  calculates all molecular formulas that
  theoretically fit a given mass with specified
  tolerance.

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Applications

• Isotope dating and tracking
• Mass spectrometer to determine the 16O/18O and
  12C/13C isotope ratio on biogenous carbonate

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• Pharmacokinetics
• Pharmacokinetics is often studied using mass
  spectrometry because of the complex nature of the
  matrix (often blood or urine) and the need for
  high sensitivity to observe low dose and long
  time point data

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• Protein characterization
• Mass spectrometry is an important emerging method
  for the characterization of proteins. The two
  primary methods for ionization of whole proteins
  are electrospray ionization (ESI) and
  matrix-assisted laser desorption/ionization
  (MALDI).

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• Space exploration
• As a standard method for analysis, mass
  spectrometers have reached other planets and
  moons. Two were taken to Mars by the Viking
  program

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CHANDRAYAN
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High Resolution Mass Spectrometer
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• Respired gas monitor
• Mass spectrometers were used in hospitals for
  respiratory gas analysis beginning around 1975
  through the end of the century

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Surface plasmon resonance

• The excitation of surface plasmons by light is
  denoted as a surface plasmon resonance (SPR) for
  planar surfaces or localized surface plasmon
  resonance (LSPR) for nanometer-sized metallic
  structures.

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• This phenomenon is the basis of many standard
  tools for measuring adsorption of material onto
  planar metal (typically gold and silver) surfaces
  or onto the surface of metal nanoparticles.
• It is behind many color based biosensor
  applications and different lab-on-a-chip sensors.

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• Surface plasmons, also known as surface plasmon
  polaritons, are surface electromagnetic waves
  that propagate in a direction parallel to the
  metal/dielectric (or metal/vacuum) interface
• Since the wave is on the boundary of the metal
  and the external medium , these oscillations are
  very sensitive to any change of this boundary,
  such as the adsorption of molecules to the metal
  surface.

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• In order to excite surface plasmons in a resonant
  manner, one can use an electron or light beam
  (visible and infrared are typical
• The incoming beam has to match its impulse to
  that of the plasmon

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• In the case of p-polarized light (polarization
  occurs parallel to the plane of incidence), this
  is possible by passing the light through a block
  of glass to increase the wavenumber and achieve
  the resonance at a given wavelength and angle

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SPR Emission

• When the surface plasmon wave hits a local
  particle or irregularity -like on a rough
  surface-, part of the energy can be reemitted as
  light
• This emitted light can be detected behind the
  metal film in various directions

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Applications

• Surface plasmons have been used to enhance the
  surface sensitivity of several spectroscopic
  measurements including fluorescence, Raman
  scattering, and second harmonic generation

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• in their simplest form, SPR reflectivity
  measurements can be used to detect molecular
  adsorption, such as polymers, DNA or proteins,
  etc

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Magnetic Plasmon Resonance

• Recently, there has been an interest in magnetic
  surface plasmons
• These require materials with large negative
  magnetic permeability, a property that has only
  recently been made available with the
  construction of metamaterials.