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262 > Lecture 10 Chemistry > Flashcards

Lecture 10 Chemistry Flashcards

1
Q

Threshold E to produce e transitions in water

A

7.4 ev

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2
Q

Depending on the amount of E transferred to the e, the molecule can undergo

A

ionization (E threshold in water 13eV, excitation (7.4 ev), thermal transfer (vibrational rotation)

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3
Q

Average E loss and most probably E loss

A

E straggling

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4
Q

E needed to break C=C

A

4.9 ev

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5
Q

cell composition

A

70-85% H2O, 10-20% protein, 10% carbs, 2-3% lipids

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6
Q

Initial physical event

A

transfer of 7-100 ev to cause ionizations or excitations in H2O molecule

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7
Q

E of subexcitation e in H2O

A

<7.4 ev

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8
Q

The time scale for physical stage

A

10^(-16)s

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9
Q

Species produced at the physical stage of the interaction of particle in water

A

H2O* (excitation), H2O+ (ionization), e (E=7.4 ev)

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10
Q

Prechemical stage

A

initial reactants produce radicals as they diffuse in medium.

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11
Q

what is a radical

A

atom that contains an unpaired e and thus is very reactive (can be neutral or charged)

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12
Q

what is a e aq

A

e captured by water through dipolar interactions, becoming solvated

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13
Q

E needed to break O-H bond

A

5 ev

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14
Q

Name radicals produced in water due to irradiation

A

H2O8=HO. (oxidizer)+ H., H2O+ = H+ + OH., H2O-= H. +OH-, ,and e aq from H2O

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15
Q

what is oxidation

A

the loss of e. e transferred to an oxidizing agent which becomes reduced

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16
Q

Time scale for prechemical stage

A

10^-15-10^-12 s

17
Q

Chemical stage time scale

A

10^-12s

18
Q

Characterize the chemical stage

A

the radicals and ions react with each other HO. +HO. = H2O2, HO. +e aq = OH-, HO. +H. = H2O , H+ + e aq=H. and etc. Most of the reactions remove the chemically reactive species

19
Q

Time when most of the radicals and ions diffuse that far that the further reaction is unlikely

A

10^-6. The chemical stage is over by this time. G value will not change after

20
Q

the formula for radical diffusion

A

D = distance^2/6 time

21
Q

Simulations of the track of charged particle is possible via

A

Monte Carlo method : generation of e, passage model. generations of reactive species, diffusion of species, recombination events.

22
Q

G value

A

Radiochemical yield: # of species produced/100 ev of E loss by charged particle and its secondaries when it stops in water.

23
Q

How different the species produced by a, b, e radiation in 10^-15s in track regions

A

they are the same H2O*, H2O+, e. The difference in the spatial E deposition patterns (track density)

24
Q

Limitation of Fricke dosimeter

A

stong LET dependence

25
Q

Fricke dosimeter characteristics

A

a most useful method to measure # of reactive species in solution;
1mM FeSO4 in 0.8M H2SO4: when irradiated Fe2+ oxidized to Fe3+ which has blue color (spectrophotometer measurement),
D response linear up to 400 Gy and up to 700Gy

26
Q

How many Fe3+ are produced in Fricke dosimeter

A

G= 2G(H2O2)+3G(H.)+G(HO.) if O2 is present, otherwise:

G(H)+G(OH)+2G(H2O2)

27
Q

What is the use of a Fricke dosimeter?

A

to test scavengers and the effect of LET on E deposition as an effect on scavengerable species

28
Q

Direct effect of radiation

A

E deposited into a molecule (DNA): ionization, excitation leading to radicals formation inside the biomolecule. The dose-response relationship is linear

29
Q

Indirect action of radiation

A

ionization of the solvent molecules. Indirect actions are diffusion-limited and the dose-response rate can be complex.

30
Q

Primary species that are responsible for rad damage in DNA

A

HO.

31
Q

For high LET radiations

A

direct action is a predominant mechanism of DNA damage

32
Q

Repair processes of DNA damage

A

Recombination, restoration, repair

33
Q

Recombination of DNA

A

recombination: reaction of nearby radical with the DNA radical to regenerate the original DNA (<10^-11s);

34
Q

Restoration

A

restitution: chem restoration of DNA (no enzyme involved). Some intracellular agents can react with radicals

35
Q

The most important intracellular agent that reacts with radicals

A

gsh glutathione. It donates one H. to the DNA and restores it. <10^-3s

36
Q

Repair stage of DNA

A

cellular enzymes recognize damage and repair DNA within min and hours

37
Q

Scavengers

A

Chemicals that can react with reactive species like HO. can block indirect effects of radiation: can be helpful in estimating the relative contributions of direct and indirect effects; define chemistry, and they showed that 60-70% of all damages from low LET are caused by HO.

38
Q

name several scavenger reactants

A

N2O, O2, Acid

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