33. XRay crystallography Flashcards
Bragg diffraction equation
2 x d x sin (O) = n x lamda
Upper mass limit of ESI
100kDa
What is the upper mass limit of MALDI?
300kDa
What is the precision of mass measurement for ESI?
0.005%-0.05%
What is the precision of mass measurement for MALDI?
0.05%-0.1%
What is the sensitivity of ESI?
0.5 pmol
What is the sensitivity of MALDI?
0.1 pmol
F = q * E + q * v * B
What is this equation? Explain parameters
Lorentz force Q : charge on the particle E : electric field B : magnetic field V : velocity of the particle
TOF equation
t = (d/sqrt2U) * sqrt (m/q)
Wavelength range of x-rays
10^-8 to 10^-12 metres
Frequency range of X-rays
10^6 to 10^20 hertz
What are the 2 types of difraction?
- Fresnel
- Fraunhaufer
What is a mono crystal?
crystal lattice of the entire sample is unbroken and continuous
5 steps of X-ray crystallography
- Crystalization of the sample
- diffraction + interference
- Detection
- Calculation of lattice spacing
- Construction of electron density map + atomic model
What information do we get from interference pattern?
- angle of diffraction
- intensity of spot (pptional to the number of electrons in the plane)
What is the interference maxima?
Site of amplification (constructive interference)
What is mass spectrometry?
Determining the chemical composition of a sample by analyzing the spectra of the mass of atoms in a gas phase
3 components of mass spectrometer
ion source
analyser
detector
What does ESI stand for?
electrospray ionization
What is the result of ESI?
a continuous stream of ionized, accelerated molecules
What does MALDI stand for?
Matrix assisted laser desorption / ionization
What is desorption?
release of an absorbed substance from a surface
What are 3 important characteristic of the matrix the sample is absorbed into?
- small molecular weight
- contains tiny cations
- highly absorbtive of laser light
What happens to the matrix when the laser hits it?
irradiated spot becomes heated and vibrationally excited. matrix molecules carry analyte molecules inton the gas phase. Analyte molecules are ionized by being protonated / deprotonated
What is the Lorentz force?
forced exerted on a charged particle moving through both an electric and a magnetic field
Principle of the magnetic method for mass analysis
ions are deflected by a magnetic field according to their masses. The lighter they are, the more deflected they will be.
What is the time of flight method?
Ions with a larger m/z ratio will reach a lower speed if accelerated with the same voltage
What technique is most used in proteomics?
Tandem mass spectrometry (2 or more mass analyzers connected together)
Which enzyme is missing in phenylketonuria?
phenylalanine hydroxylase
