wk16b-application of metal complexes [compatibility mode]

8/14/2019 Wk16b-Application of Metal Complexes [Compatibility Mode]

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Co3+(aq) + e-Co2+(aq) E = +1.82 V

4 Co3+(aq) + 2 H2O(l)4 Co2+(aq) + 4 H+ + O2(g), Ecell = +0.59 V

But:

Co3+(aq) + NH3(aq)[Co(NH3)6]2+(aq) Kf = 4.5.10

33

and

[Co(NH3)6]3+(aq) + e-[Co(NH3)6]

2+(aq) E = +0.10 V


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Photo ra h : Fixin a Photo ra hic Film

Blackandwhite.

FinelydividedemulsionofAgBr onmodifiedcellulose.

PhotonsoxidizeBr toBrandreduceAg+toAg.

6 4 2

ReactsonlyatthelatentimagesitewheresomeAg+is

presentandconvertsallAg+ toAg. Negativeimage.

FixerremovesremainingAgBr.

AgBr(s)+2S2O3

(aq) [Ag(S2O3)2]

(aq)+Br

(aq)

Printthenegative


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Chelates:

ComplexesofSpecialInterest

complexeswithmonodentateligands.

The increase in entro durin chelation is animportantfactorinthestabilitiesofchelates.

[Ni(NH3)6]2+(aq) + EDTA4-(aq)

[NiEDTA]2-(aq) + 6 (NH3)6(aq) K = 8 x 109


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SequesteringMetalCations

tetrasodiumEDTA


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totieitupinaformthateffectively

.

EDTA(ethylenediaminetetraaceticacid)is

common yuse oseques erme a ons n

solution. Chelationtherapy,usingEDTA,is

sometimesusedtotreatheavymetalion

poisoning.


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AMetalEDTACom lex

Hexadentate

ligand completely surrounds

and isolates the metalion.


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SequesteringMetalCations

SomeLogvalues:10.6(Ca2+),18.3(Pb2+), 24.6(Fe3+).


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chloro h l aporphyrin


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(an enzyme that lacks its metal center or prosthetic

groups)


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Why is CO lethal?

Hemoglobin (Hb) is the main chemical component of red

blood cells, carrying oxygen from the lungs to the body

,

concentration to low concentration.

This transportation is accomplished by the formation of

the oxygen-hemoglobin complex, oxyhemoglobin (HBO2)

Hb(aq) + O2(g) HbO2 (aq)

K=[HbO2]

[Hb] PO2


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In the absence of Hb the amount of O in blood is low.Because of the formation of the HbO2 complex, the amount

of O2 in blood is increased by a factor of 70.

Hb(aq) + O2(g) HbO2 (aq)

LeChateliers principle predicts that in regions of high O2

partial pressure, the Hb-HbO2 equilibrium is shifted to ther g , w c s e case n e ungs

In re ions of low O artial ressure, the e uilibrium shifts

to the left, resulting in a breakup of the HbO2 complex,releasing O2 to the bodys tissues.


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Hb(aq) + CO(g) HbCO (aq)

K(CO)=[HbCO]

[Hb] PCO

K(CO) > (KO2 )

Which means that CO binds more tightly to Hbcompared to O2

When Hb is exposed to both O2 and CO, there is

competition for the Hb, and the following reaction takesplace:

HbO2 (aq) + CO(g) HbCO(aq) + O2 (g)


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The relative amounts of HbCO and HbO de end on thepartial pressures of CO and O2.

Since K(CO) > K(O2), K for the competition reaction is

>1

In fact at 38o

C, the value of K is 210 and so the positiono e equ r um s rong y avors e orma on o e

HbCO complex, with CO displacing O2 from the HbO2complex .

However, the process is reversible - from LeChateliers

principle, a large partial pressure of O2 will result in the

equilibrium of the competition reaction to favor the

HbO2 complex.


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wk16b-application of metal complexes [compatibility mode]

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