relaxation methods
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Relaxation methods. A chemical equilibrium is thrown off-balance, and we measure the rate of reaching the new equilibrium. E.g.: temperature jump,. Revival of the temperature jump method. Measurement of the rate of protein folding:. - PowerPoint PPT PresentationTRANSCRIPT
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Relaxation methods
A chemical equilibrium is thrown off-balance, and we measure the rate of reaching the new equilibrium.
E.g.: temperature jump,
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Measurement of the rate of protein folding:The fluorescence of tryptophane (ns time-scale) is influenced by the polarity of the medium. Protein folding tends to exclude water from the globule. Principle of the measurement: the protein is defolded by cooling, then a temperature jump returns the temperature to physiological conditions. The tryptophane fluorescence is measured on the ms timescale, thus we can follow the change of polarity near the tryptophane.
Revival of the temperature jump method
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Time-correlated single photon counting
Instead of measuring the decay of fluorescence in real time, we measure the time between the excitation and emission, and based on the statistics we estimate the lifetime of the fluorescence.
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Photochemistry of the >C=C< chromophore: cis – transphotoisomerization
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Photostationary state
cis trans
tc
ct
cis
trans
trans
cis
][
][
Stilbene (1,2-diphenylethane), 313 nm:93%cis, 7% trans, since cis 2400 dm3mol-1s-1, trans 16200 dm3mol-1s-1, ct = 0,35, tc = 0,5
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Additive colours
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Substractive colours
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How the human eye works
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Electrocyclization
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Practical example: synthesis of vitamin D
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Stereochemistry of cycloaddition
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Cycloaddition within DNA
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Relative weight of DNA photodamage
Chemistry Relative weight
Thymine dimer 1
Cytozin hydration 0,5
DNA-protein crosslink 0,0017
DNA crosslink 0,00025
Strand break 0,00025
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Photochemistry of proteins
Amino acid Absorbance
at 254 nm
Quantum efficiency
effectiveness
ε·Φ·104
Cystine(-S-S-) 270 0,13 35,1
Tryptophane 2870 0,004 11,5
Phenylalanine 140 0,013 1,8
Thyrozine 320 0,002 0,6
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Correlation between enzyme photoinactivation and cystine content
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Spectrum of the main photoproduct in the lens
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Thephoto-
chemistryof beer:
thiolproductioninduced by light
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