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Near the cells where oxygen is used, its chemical potential is significantly lower than near the lungs. Even though there is no gaseous oxygen near these cells, it is customary to express the abundance of oxygen in terms of the partial pressure of gaseous oxygen that would be in equilibrium with the blood. Using the independent-site model just presented, with only oxygen present, calculate and plot the fraction of occupied heme sites as a function of the partial pressure of oxygen. This curve is called the Langmuir adsorption isotherm ("isotherm" because it's for a fixed temperature). Experiments show that adsorption by myosin follows the shape of this curve quite accurately.

Short Answer

Expert verified

Fraction of occupied heme states as a function of partial pressure of oxygen is correctly calculated and plotted in graph to obtain the curve.

Step by step solution

01

Step 1. Formula

Gibb's Factor is given by formula:

Gibb'sFactor=e-[(E(s)-N(s))kT]

Where, T is temperature, kis Boltzmann's constant,is chemical potential, N(s)is number of state satoms, E(s)is statesenergy.

We consider the system as single donor atom. So, three cases are possible:

(1) Unoccupied state

Here, state energy and number of atoms are both equal to zero.

So, in formula (1) we put N=0and E=0.

So, localid="1647110725971" Gibb'sFactor=e-[(0-0)kT]

localid="1647110803077" =e0

localid="1647110809090" =1

02

Step 2. Case Discussion

Second case possible is:

(2) States with two ionization

Here, state energy is -1and number of atoms is 1.

In formula (1) we put E=-1and N=1.

Gibb'sFactor=e-[(-1-)kT]

=e[(1+)kT]

The degeneracy is 2because there are two independent states of electron.

So, Gibb'sFactor=2e[(1+)kT]

So, grand partition function is:

Z=1+2e[(1+)kT]

03

Step 3. Potential Formula

We can say that probability of ionization of donor atom is:

Pion=1Z

We put Z=1+2e[(1+)kT]in above equation,

Pion=11+2e[(1+)kT]

Formula of chemical potential is:

localid="1647112562133" =-kTlnVZinNQ

We know that ideal gas equation is given by:

PV=NkT

So, VN=kTP

We put value of kTPas VNin above chemical potential formula:

So, =-kTlnkTZinPQ

So, e-kT=kTZinPQ

04

Step 4. Finding Probability

Heme site is occupied by Oxygen O2, the probability is:

P=e-(-)kTZ

In above formula we put localid="1647113657590" Z=1+e-(-)kT

localid="1647113747407" P=e-(-)kT1+e-(-)kT

=11+e(-)kT

=11+[e()kTe(-)kT]

In above equation we put, e(-)kT=kTZinPQ

localid="1647114360985" P=11+[e()kTkTZinPQ]

=11+PoP

We can write Po=kTZinQekT

Therefore, Heme site is occupied by Oxygen O2Probability is:

P=11+kTZinPQekT

05

Step 5. Calculation

For a box of width 1cm, we will find temperature at which translation motion of O2molecule freezes, the formula for quantum length is:

lQ=h2蟺尘办罢

Putting the values of variables in above expression, the volume is:

Q=h2蟺尘办罢3

Q=6.6310-34Js2(321.6610-27kg)(1.3810-23J/K)(310K)3

=5.3810-33m3

Now, we will calculate value of Po

Po=(1.3810-23J/K)(310K)(223)(5.410-33m3)e-0.7eV(8.61710-5eV)(310K)

=738.33Pa1atm105pa

=0.00738atm

06

Step 6. Table and Graph

We make table for Pressure pagainst fraction of pressure PPo+P

P
PPo+P
1
0.9926
2
0.9963
3
0.9975
4
0.9981
5
0.9985
6
0.9987
7
0.9989
8
0.9990
9
0.9991
10
0.9992

We can now draw graph between fraction of occupied heme sites and oxygen partial pressure.

This graph curve is called Langmuir Adsorption Isotherm.

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Most popular questions from this chapter

In Problem 7.28you found the density of states and the chemical potential for a two-dimensional Fermi gas. Calculate the heat capacity of this gas in the limit role="math" localid="1650099524353" kTF路 Also show that the heat capacity has the expected behavior when kTF. Sketch the heat capacity as a function of temperature.

For a system of fermions at room temperature, compute the probability of a single-particle state being occupied if its energy is

(a) 1eVless than

(b) 0.01eVless than

(c) equal to

(d) 0.01eVgreater than

(e) 1eVgreater than

Consider any two internal states, s1 and s2, of an atom. Let s2 be the higher-energy state, so that Es2-Es1= for some positive constant. If the atom is currently in state s2, then there is a certain probability per unit time for it to spontaneously decay down to state s1, emitting a photon with energy e. This probability per unit time is called the Einstein A coefficient:

A = probability of spontaneous decay per unit time.

On the other hand, if the atom is currently in state s1 and we shine light on it with frequency f=/h, then there is a chance that it will absorb photon, jumping into state s2. The probability for this to occur is proportional not only to the amount of time elapsed but also to the intensity of the light, or more precisely, the energy density of the light per unit frequency, u(f). (This is the function which, when integrated over any frequency interval, gives the energy per unit volume within that frequency interval. For our atomic transition, all that matters is the value of u(f)atf=/h) The probability of absorbing a photon, per unit time per unit intensity, is called the Einstein B coefficient:

B=probability of absorption per unit timeu(f)

Finally, it is also possible for the atom to make a stimulated transition from s2down to s1, again with a probability that is proportional to the intensity of light at frequency f. (Stimulated emission is the fundamental mechanism of the laser: Light Amplification by Stimulated Emission of Radiation.) Thus we define a third coefficient, B, that is analogous to B:

B'=probability of stimulated emission per unit timeu(f)

As Einstein showed in 1917, knowing any one of these three coefficients is as good as knowing them all.

(a) Imagine a collection of many of these atoms, such that N1 of them are in state s1 and N2 are in state s2. Write down a formula for dN1/dt in terms of A, B, B', N1, N2, and u(f).

(b) Einstein's trick is to imagine that these atoms are bathed in thermal radiation, so that u(f) is the Planck spectral function. At equilibrium, N1and N2 should be constant in time, with their ratio given by a simple Boltzmann factor. Show, then, that the coefficients must be related by

B'=BandAB=8hf3c3

Consider a system of five particles, inside a container where the allowed energy levels are nondegenerate and evenly spaced. For instance, the particles could be trapped in a one-dimensional harmonic oscillator potential. In this problem you will consider the allowed states for this system, depending on whether the particles are identical fermions, identical bosons, or distinguishable particles.

(a) Describe the ground state of this system, for each of these three cases.

(b) Suppose that the system has one unit of energy (above the ground state). Describe the allowed states of the system, for each of the three cases. How many possible system states are there in each case?

(c) Repeat part (b) for two units of energy and for three units of energy.

(d) Suppose that the temperature of this system is low, so that the total energy is low (though not necessarily zero). In what way will the behavior of the bosonic system differ from that of the system of distinguishable particles? Discuss.

In analogy with the previous problem, consider a system of identical spin0bosonstrapped in a region where the energy levels are evenly spaced. Assume that Nis a large number, and again let qbe the number of energy units.

(a) Draw diagrams representing all allowed system states from q=0up to q=6.Instead of using dots as in the previous problem, use numbers to indicate the number of bosons occupying each level.

(b) Compute the occupancy of each energy level, for q=6. Draw a graph of the occupancy as a function of the energy at each level.

(c) Estimate values of and Tthat you would have to plug into the Bose-Einstein distribution to best fit the graph of part(b).

(d) As in part (d) of the previous problem, draw a graph of entropy vs energy and estimate the temperature at q=6from this graph.

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