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2014-09-14
1
Acid Base lecture 15-16 September 2014Agnes Rinaldo-Matthis
1. Introduction to pH
2. Acid base concept -calculations
3. Buffert -calculations
4. Titration
5. Physiologic pH regulation -calculations
6. Measure pH?
-Read: Kemiboken från gymnasiet, Harvey & Ferrier, sid 6-9, Kompendiet Syra-Bas
Introduction to pH
2014-09-14
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2M HCl -0.30.1 M HCl 1Coca Cola 2.3Schampo 5-6active/resting muscle 6.1/6.9Saliva 6.4-7Blood (venous) 7.32-7.38Blood (arteriell) 7.37-7.43
•The cell has low amounts of H+, around 10-7 M, =>pH=7 same as 0,0001 mM. (compare with [Na+]=140 mM in the cell)
Introduction to pH
pH describes the concentration of H+ or H3O+ in water solution.
The lower the pH, the greater the hydronium ion concentration.
Introduction to pH
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pH = -Log[H+]
It is easier to think in log of concentrations but it takes practice!!
Introduction to pH
Example : If the pH of a solution is 3.4, what is the hydronium ion concentration?
[H3O+] = 10-pH = 10-3.4 = 0.000398 M=3.98x10-4 M
• Neutral water has a tendency to ionizeH2O <-> H+ + OH-
• The free proton is associated with a water molecule to form the hydronium ion
H3O+
• High ionic mobility due to proton jumping
Introduction to pH
Where does the H+ come from?
Dissociation of H2O
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Proton Jumping
• Hydronium ion migration; hops by switching partners at 1012 per second
Introduction to pH Dissociation of H2O
Acid Base lecture 15-16 September 2014Agnes Rinaldo-Matthis
1. Introduction to pH
2. Acid base concept -calculations
3. Buffert -calculations
4. Titration
5. Physiologic pH regulation -calculations
6. Measure pH?
2014-09-14
5
Relationship between pH and [H+] / [OH-] concentration
2. Acids and bases
• Acidic if [H+] > 10-7 M• Basic if [H+] < 10-7 M
H2O <-> H+ + OH-
• Acid is a substance that can donate a proton.• Base is a substance that can accept a proton.• Conjugate acid base pair
HA + H2O H3O+ + A-/OH-
Acid1 Base2 Conjugate ConjugateAcid2 Base1
or
HA A- + H+
Acid1 Conjugate ConjugateBase2 Acid
2. Acids and bases Lowry definition
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– The stronger acids are those that loose their hydrogen ions more easily than other acids.
– Similarly, the stronger bases are those that hold onto hydrogen ions more strongly than other bases.
2. Acids and bases Relative strength of acids and bases
Strong acid undergoes complete dissociationEx. HCl
HCl + H2O Cl- + H3O+
2. Acids and bases Relative strength of acids and bases
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Strong acid undergoes complete dissociationEx. HCl
HCl + H2O Cl- + H3O+
HCl H3O+ Cl-
2. Acids and bases Relative strength of acids and bases
Weak acid undergoes partial dissocationEx. Acetic acid
HA + H2O A- + H3O+
2. Acids and bases Relative strength of acids and bases
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HA HA
H+ A-
Weak acid undergoes partial dissocationEx. Acetic acid
HA + H2O A- + H3O+
2. Acids and bases Relative strength of acids and bases
A solution of strong acids and bases (ex HCl och KOH)
H+ + Cl- + K+ + OH- H2O + K+ + Cl-
If we take same amount of HCl as KOH it becomes neutral = neutralisation,
otherwise it becomes acidic or basic.
Neutralisation2. Acids and bases
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A weak acid is not completely proteolysed Equilibrium to the left.
around 1% of HAc will react.
The relative stability of the acid form as compared to its conjugated base formDetermines if it is a weak or a strong acid.
If the acid form is stable = the proton is not lost easily = weak acid(ex HAc)
If the base form is stable = the proton will easily be lost = strong acid (ex HCl)
HAc + H2O Ac- + H3O+
Proteolysis of a weak acid
Weak acids/bases2. Acids and bases
Determine pH in a solution
HAc + H2O Ac- + H3O+
HCl + H2O Cl- + H3O+
Strong acid, equilibrium shifted to the right,completely shifted as for HCl
Weak acid, at equilibrium there is still acid left ex Acetic acid HAc where 1% of HAc will react.
Easy!
Difficult!
How can we calculate pH in a solution of a weak acid?
Weak acids/bases2. Acids and bases
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• Law of mass action (massverkans lag): Therate of a chemical reaction is proportional to theconcentrations of the reacting substances.
and
• experimental values of Ka (acid base constant) is used to determine pH in a solution of a weak acid.
Law of Mass action
Calculate pH in a solution of a weak acid.We need:
2. Acids and bases
at equilibriumsame rates
2 delreaktioner:
Vid jämvikt är v1=v2 dvs Som kan omformuleras till
[Ac-] · [H3O+]k1
[HAc] · [H2O]k2
= där k1/k2 =Ka (syrakonstanten)
Ac- + H3O+HAc + H2O
1) HAc + H2O
HAc + H2O2) Ac- + H3O+
Ac- + H3O+ v1=k1 [HAc] · [H2O]
v2= k2 [Ac-] · [H3O+]
k1[HAc] · [H2O] = k2[Ac-] · [H3O+]
k1
k2
Law of Mass action2. Acids and bases
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at equilibriumsame rates
2 reactions:
Vid jämvikt är v1=v2 dvs Som kan omformuleras till
[Ac-] · [H3O+]k1
[HAc] · [H2O]k2
= där k1/k2 =Ka (syrakonstanten)
Ac- + H3O+HAc + H2O
1) HAc + H2O
HAc + H2O2) Ac- + H3O+
Ac- + H3O+ v1=k1 [HAc] · [H2O]
v2= k2 [Ac-] · [H3O+]
k1[HAc] · [H2O] = k2[Ac-] · [H3O+]
k1
k2
Law of Mass action2. Acids and bases
at equilibriumsame rates
2 reactions:
At equilibrium v1=v2
[Ac-] · [H3O+]k1
[HAc] · [H2O]k2
= där k1/k2 =Ka (Acid constant)
Ac- + H3O+HAc + H2O
1) HAc + H2O
HAc + H2O2) Ac- + H3O+
Ac- + H3O+ v1=k1 [HAc] · [H2O]
v2= k2 [Ac-] · [H3O+]
k1[HAc] · [H2O] = k2[Ac-] · [H3O+]
k1
k2
Law of Mass action2. Acids and bases
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Law of Mass Action
Ka betecknar syrakonstant och har ett specifickt värde för varje syra, ex. stort värde på Ka, stark syra
K = [H2O] = 55,6 M
Ka =
I utspädd lösning är H2O ungefär konstant ca 55M och kan inneslutas i jämvikts- konstanten och man får:
[Ac-] · [H3O+]
[HAc] · [H2O]
[Ac-] · [H3O+]
[HAc]
Law of Mass action2. Acids and bases
Ka is the acid constant and it has a specific value for each acid, ex. large value of Ka, strong acid
K = [H2O] = 55,6 M
Ka =
In water H2O is considered constant and can be included in the equilibrium constant K.
[Ac-] · [H3O+]
[HAc] · [H2O]
[Ac-] · [H3O+]
[HAc]
Law of Mass Action
Acid constant2. Acids and bases
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1. An acid with stable conj. Base has a tendency to loose its proton and its equil. Is shifted to the right and we get a large Ka.
1. A weak acid with a unstable conj. Base has a small tendency to loose its proton and equilibrium is shifted to the left – small Ka.
Ka = [Ac-] · [H3O+]
[HAc]
HAc + H2O Ac- + H3O+
Acid constant, Ka
and analogous to the pH terminology the pKa = -lgKa
Acid constant, Ka2. Acids and bases
Which are the experimental values of Ka?
Acid constant, Ka2. Acids and bases
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Ka describes acid strengthHA + H2O A- + H3O+
[A-] · [H3O+]
[HA]Ka =
Syra Ka pKa
•HCl 1 · 107 -7•H2SO4 1 · 103 -3•H3PO4 6,3 · 10-3 2,2
•Mjölksyra 1,6 · 10-4 3,8•ß-OH-smörsyra 4,0 · 10-5 4,4•Acetic acid 1,7 · 10-5 4,76
stark
svag
(-lg Ka)
Acid constant, Ka2. Acids and bases
Base constant
Law of Mass action for bases
A strong base has a tendency to take up protons the equilibrium is shifted to the right and Kb is large. A small Kb is a weak base – lower tendency to take up a proton.
and analogous to the pH terminology the pKb = -lgKb
HAc + OH-Ac- + H2O
Kb = [HAc] · [OH-]
[Ac-]
Base constant, Kb2. Acids and bases
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Kb describes base strengthA- + H2O HA + OH-
[HA] · [OH-]
[A-]Kb =
Base Kb pKb
•OH- (lut) 8,7 · 101 -1,74•CO3
2- (soda) 2,5 · 10-4 3,7•NH3 1,74 · 10-5 4,76
•HCO3- (bikarbonat) 1,26 · 10-8 7,9
•acetate 5,75 · 10-10 9,24
strong
weak
(-lg Kb)
Base constant, Kb2. Acids and bases
For conjugated acid-base pair: pKa + pKb = 14
HAc / Ac- : 4,76 + 9,24 = 14
H2O / OH- : 15,74 + (-1,74) = 14
H3O+ / H2O : -1,74 + 15,74 = 14
H2CO3 / HCO3- : 6,1 + 7,9 = 14
Acid/Base constant2. Acids and bases
Kb can be calculated from its conjugated acid Ka value:Kb=Kw/Ka
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Now we know Law of Mass actionAnd some experimental values of Ka
So now we can calculate pH in a solution of a weak acid!
2. Acids and bases
Protolysis of a weak acidEx. 0.1 mol acetic acid (CH3COOH) in 1 liter H2O
HAc + H2O Ac- + H3O+
2:a grade equation ....Make two approximations:1) X << 0,12) X >> 10-7
[Ac-] · [H3O+]
[HAc]Ka =
X · (X+10-7)
0,1-XKa =
Before equil. 0,1 noll 10-7
After equil. 0,1 - X X X + 10-7
Weak acids 2. Acids and bases
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Protolysis of a weak acidEx. 0.1 mol acetic acid (CH3COOH) in 1 liter H2O
HAc + H2O Ac- + H3O+
Before equil. 0,1 noll 10-7
After equil. 0,1 - X X X + 10-7
Weak acids
[Ac-] · [H3O+]
[HAc]Ka =
X · (X+10-7)
0,1-XKa =
2. Acids and bases
Protolysis of a weak acidEx. 0.1 mol acetic acid (CH3COOH) in 1 liter H2O
HAc + H2O Ac- + H3O+
Before equil. 0,1 noll 10-7
After equil. 0,1 - X X X + 10-7
Weak acids
[Ac-] · [H3O+]
[HAc]Ka =
X · (X+10-7)
0,1-XKa =
Ka = X · X Ka
HAc=1,7.10-5
0,1
2. Acids and bases
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Protolysis of a weak acidEx. 0.1 mol acetic acid (CH3COOH) in 1 liter H2O
HAc + H2O Ac- + H3O+
Before equil. 0,1 noll 10-7
After equil. 0,1 - X X X + 10-7
Weak acids
[Ac-] · [H3O+]
[HAc]Ka =
X · (X+10-7)
0,1-XKa =
Ka = X · X Ka
HAc=1,7.10-5
0,1
1,74 · 10-5 = X2
0,1
2. Acids and bases
Protolysis of a weak acidEx. 0.1 mol acetic acid (CH3COOH) in 1 liter H2O
HAc + H2O Ac- + H3O+
Before equil. 0,1 noll 10-7
After equil. 0,1 - X X X + 10-7
Weak acids
[Ac-] · [H3O+]
[HAc]Ka =
X · (X+10-7)
0,1-XKa =
Ka = X · X Ka
HAc=1,7.10-5
0,1
1,74 · 10-5 = X2
0,1
X = 1,32 · 10-3 M = [H3O+]
pH = 2,88
2. Acids and bases
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[H3O+] · [OH-]
[H2O] · [H2O]K =
H2O + H2O H3O+ + OH-
[H3O+] · [OH-]
10-14 M2 Kw= ion product of water
Kw =
Kw =
Waterconcentrationenis constant 55.5 M
K is the dissociation constantK becomes Kw
b) base H2O + H+ H3O+
a) acid H2O H+ + OH-
An amphoteric species is a molecule or ion that can react as an acid as well as a base. For ex water.
Amphoteric species2. Acids and bases
pKw = -lg 1x10-14 = pH + pOH = 14
Neutral water OH- = H3O+
Kw = (H3O+)(OH-) = (10-7)(10-7) = 10-14
Therefore the pH is 7 In pure water
pKw = pH + pOH
Kw = Ion product of water
-log10
Ion product of water2. Acids and bases
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a) HSO4- + H2O SO4
2- + H3O+
b) HSO4- + H2O H2SO4 + OH-
c) HPO42- + H2O PO4
3- + H3O+
d) HPO42- + H2O H2PO4 + OH-
e) H2PO4- + H2O HPO4
2- + H3O+
f) H2PO4- + H2O H3PO4 + OH-
g) HCO3- + H2O CO3
2- + H3O+
h) HCO3- + H2O H2CO3
2- + OH-
Ex. of other amphoteric species
Vätesulfat
Monovätefosfat
Divätefosfat
vätekarbonat
Amphoteric species2. Acids and bases
Acid Base lecture 15-16 September 2014Agnes Rinaldo-Matthis
1. Introduction to pH
2. Acid base concept -calculations
3. Buffert -calculations
4. Titration
5. Physiologic pH regulation -calculations
6. Measure pH?
2014-09-14
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Observation
If you add 0.01 ml of 1M HCl to 1000 ml of water pH 7, the pH of the water drops from 7 to 5!!
i.e 100 fold increase in H+ concentration: Log = 2 change.
Problem:Biological properties change with small changes in pH, usually less than 1 pH unit.
How does a system prevent fluctuations in pH?
Buffer solutionsA buffer consists of corresponding pairs of weak acids and weak bases
HA H+ + A-
Weak acid proton conjugated base
A buffer solution is keeping the pH relatively constant when strong acid or base is added
3. Buffer
A buffer keeps the pH constant during dilution with water.
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• The buffer capacity is largest
at the pKa.
3. Buffer
By definition the pK is the pH where [HA] = [A-] : 50% dissociated
3. Buffer
pKa of Tris buffer is 8.08 the buffering range is 7.1 - 9.1
By definition the pK is the pH where [HA] = [A-] : 50% dissociated
Tris buffer
X
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1) Choose a buffer that can buffer at the pH interval.
Check pKa for conj. acid, should be close to desired pH.
Acetat buffer, can buffer at pH=4,76 ± 1,5
HAc + H2O Ac- + H3O+
2) The higher conc. of ([HAc] + [Ac-]), the better buffering capacity.
3. Buffer Make a buffer
Example of different conjugate acid base pairs.
Fig 1-11pH 7
3. Buffer Make a buffer
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How to make a buffer solution
1) Mix a weak acid with its corresponding weak base2) Mix weak acid with a strong base3) Mix weak base with stron acid
4) Or, first mix buffer as solid add water to desired volumeand then adjust the pH by adding acid or base to the pH you want
3. Buffer Make a buffer
HAc + H2O Ac- + H3O+
Exempel: Make 0,2 M acetatbuffert in 1L H2O .
Conjugate acid and base added in similar amounts –best buffering capacity at 50:50
3. Buffer
Take 0,1 mol 0,1 mol (same as 0.1 M in 1 L water)
Make a buffer
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How can we determine the pH in a buffer?Example: HAc + H2O Ac- + H3O+
3. Buffer
0,1 M 0,1 M
Buffer equation
We use the buffer equation:A variant of Law of Mass action
-Can only be used to calculate pH in buffers.
-Only valid if 1/30 < base/acid < 30
pH = pKa+ lg [Ac-]
[HAc]
3. Buffer Buffer equation
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Deduction of the buffer equationHAc + H2O Ac- + H3O+
[Ac-] · [H3O+]
[HAc]Ka =
lg Ka = lg [Ac-] + lg [H3O+] – lg [HAc]
-lg [H3O+] = -lg Ka+ lg [Ac-] – lg [HAc]
pH = pKa+ lg [Ac-]
[HAc]
3. Buffer
Taking the logaritm
Replacement
Law of Mass action
Buffer equation!(Hendelson-Hasselbach)
0,1 M 0,1 M
Buffer equation
HAc + H2O Ac- + H3O+
Exempel: 0,2 M acetatbuffert (0,1 mol HAc, 0,1 mol Ac-, 1 liter H2O)
pH = pKa+ lg 0,1
0,1
pH = 4,76
Tillför 1 liter vatten
0,1 0,1
HAc + H2O Ac- + H3O+
0,05 0,05
pH = pKa+ lg 1
pH = pKa+ lg 0,05
0,05
pH = 4,76
pH = pKa+ lg 1
3. Buffer
How does pH change in a buffer upon dilution
Buffer equation
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pH=4,28
HAC/Ac- 50:50
x
3. Buffer
Vid pKa är HAC/Ac- 50:50
AfteradditionHCl
x
ekvivalens-punkt
When the buffer isbuffering, the equilibrium is changed:
Buffer equation
Ac-
x ekvivalens-punkt
When the buffer is buffering, the equilibrium is shifted:
HAc + OH- Ac- + H2O
x
x
EftertillsatsHCl
EftertillsatsOH-
3. Buffer Buffer equation
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Acid Base lecture 15-16 September 2014Agnes Rinaldo-Matthis
1. Introduction to pH
2. Acid base concept -calculations
3. Buffert -calculations
4. Titration
5. Physiologic pH regulation -calculations
6. Measure pH?
Titration is a common laboratory method to determine the unknown concentration of an identified analyte.
Take a weak acid HAc, add or titrate NaOH while monitoring pH (x-axis) amount NaOH added (y-axis).
4. Titration
Buffer capacity: highest at pKa
The buffer effect can be seen in a titration curve.
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pH=4.76
Ac-
HAC/Ac- 50:50
x equivalens-point
pKa-punkt
Best buffertkapacitet Half-equivalenspointpKa ± 1,5
Titration of a weak acid with a strong base.
4. Titration
At the equivalenspointamount base added = amount mole acid at start
At pKa HAc/Ac 50:50
Distribution curves for acetate and acetic acid
pKa = 4.76Best buffer capacityHAc/Ac 50:50
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Ex. Titration curve for the amino acid alanine
2 groups on alanine that can be deprotonated, 2 pKa´s
-COOH / -COO- pKa1-NH3
+ / -NH2
pKa2
4. Titration
Often characteristic for an acid -good analytical method.
Ex. 20 ml HCl is titrated with 16 ml of 0.1 M NaOH to the equivalenspoint. What is the concentration of HCl?
An acid with one proteolytic step is titrated against a strong base. At the equivalenspoint , the n(acid) in the solution is the same as the amount (n) of base added.How much base do we have? We use n=cv => 0.1M x 0.016 L = 1.6 x 10-3 mol = 0.0016 molAt the equivalenspoint the n(acid) = n(base) => Which means that n(acid)=0.0016 mol. What is the concentration of acid? c = n/v = 0.0016 mol / 0.02 L = 0.08 M.
Answer: The concentration of theHCl solution is 80 mM.
4. Titration
equivalenspoint
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Acid Base lecture 15-16 September 2014Agnes Rinaldo-Matthis
1. Introduction to pH
2. Acid base concept -calculations
3. Buffert -calculations
4. Titration
5. Physiologic pH regulation -calculations
6. Measure pH?
6 7 8[H3O+]:
[OH-]:
10-6M 10-7M 10-8M
10-8M 10-7M 10-6M
Life
normal,arteriellblood
4. Physiologic pH regulation
Normal value blood pH 7.4Blood (venous) 7.32-7.38Blood (arteriell) 7.37-7.43
How can we keep the pH so constant?
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Our body uses 3 different systems to keep the pH constant:
1) Buffers in body fluids (the first minutes)Phosphatbuffer (in the cell)Proteins (albumin,Hemoglobin) in the cellBicarbonate buffer (blood, plasma)
2) Regulate breathing (adjust pCO2)3) Long term regulation via kidneys
5. Physiologic pH regulation Buffers in body fluids
Our body uses 3 different systems to keep the pH constant:
1) Buffers in body fluids (the first minutes)Phosphatbuffer (in the cell)Proteins (albumin,Hemoglobin) in the cellBicarbonate buffer (blood, plasma)
2) Regulate breathing(justera pCO2)3) Long term regulation via kidneys
5. Physiologic pH regulation
Bicarbonate most significant buffer in bloodFormed from gaseous CO2
Buffers in body fluids
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Buffers in body fluids
H2PO4- + H2O HPO4
2- + H3O+
korr. syra korr. bas
Phosphatebuffert
CO2 + 2H2O H2CO3 + H2O HCO3- + H3O+
korr. syra korr. bas
Bicarbonatebuffer
protH + H2O prot- + H3O+
korr. syra korr. bas
Proteins, (ex. albumin, Hb) buffrande förmåga -Histidin
Buffering at pH= 7
5. Physiologic pH regulation
H3PO4 + H2O H2PO4- + H3O+
korr. syra korr. bas
!Two of the ions are amphoteric species!
Can loose protons 3 times= 3 proteolytic steps
H2PO4- + H2O HPO4
2- + H3O+
korr. syra korr. bas
HPO42- + H2O PO4
3- + H3O+
korr. syra korr. bas
5. Physiologic pH regulation Phosphate buffer
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Phosphate buffer
H3PO4 + H2O H2PO4- + H3O+
At pKa best buffer capacity
H2PO4- + H2O HPO4
2- + H3O+
HPO42- + H2O PO4
3- + H3O+
5. Physiologic pH regulation
What kind of phosphate ions do we have in the cell?
5. Physiologic pH regulation
Many phosphate groups on molecules in the, t ex ATP, ADP, AMP, P-creatine.
Phosphate buffer
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When a protein acts as a buffer, only a few amino acids areresponsible
Ex of proteins that can act as a buffer: Albumin och Hemoglobin
5. Physiologic pH regulation Proteins as a buffer
Amino acids that can buffer:
korr. syra korr. bas
korr. syra korr. bas
+
-
When the amino acid is buffering, the charge will change!
5. Physiologic pH regulation
Histidin
Cystein
Proteins as a buffer
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When Histidin-side chain buffer, it will take up a proton.
It becomes positively charged.
The new + gives a new electrostatic interaction with a neighbouring -
Structure will change.
Maybe even the function of the protein?
The protein structure canchange due to pH
+
H3O+
5. Physiologic pH regulation
pH sensitive protein is protected by otherproteins, and other buffers
ProteinXexposed
ProteinX
ProteinX
H3O+
ProteinX
ProteinX
H3O+
ProteinProtein
ProteinProtein
Protein
ProteinProtein
ProteinProtein
ProteinProtein
Protein
H2PO4-/HPO4
2-
ProteinX
ProteinX
H3O+
ProteinProtein
ProteinProtein
Protein
ProteinProtein
ProteinProtein
ProteinProtein
Protein
H2PO4-/HPO4
2-
H2PO4-/HPO4
2-
H2PO4-/HPO4
2-
H2PO4-/HPO4
2-
H2PO4-/HPO4
2-
H2PO4-/HPO4
2-
H2PO4-/HPO4
2-ProteinXprotected
5. Physiologic pH regulation Proteins as a buffer
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Good with overlapping buffersOne buffer Mix of buffers
Buf
fert
kapa
cite
t
5. Physiologic pH regulation Proteins as a buffer
Bicarbonate buffer
H2CO3 + H2O HCO3- + H3O+
Conjugate acid. Conjugate base
First proteolytic step important.
2 proteolytic steps
HCO3- + H2O CO3
2- + H3O+
Conjugate acid Conjugate base
5. Physiologic pH regulation
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H2CO3 + H2O HCO3- + H3O+
Conj. Acid conj.. base
Dihydrogen carbonate (kolsyra) (H2CO3) can exist in waterbut will quickly become CO2 bubbles.
The acid in bicarbonate buffer consists of H2CO3 and CO2(d) together.
CO2(d) + 2H2O H2CO3 + H2O HCO3- + H3O+
conj. acid conj. base
In body fluids
5. Physiologic pH regulation Bicarbonate buffer
The concentration of dissolved CO2, is proportional to the partial pressure for CO2 (pCO2).
Water with dissolved , dihydrogen carbonateand CO2
H2CO3
H2CO3
H2CO3
H2CO3
CO2
CO2
CO2
CO2CO2CO2 is dissolved in water
[CO2] + [H2CO3] = 0,23 · pCO2kPa, mM
5. Physiologic pH regulation Bicarbonate buffer
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Buffer formula for bicarbonate buffer
CO2 + 2H2O H2CO3 + H2O HCO3- + H3O+
conjugate acid Conjugate base
pH = pKa+ lg [base]
[acid]
pH = pKa+ lg [HCO3
-]
[CO2] + [H2CO3]
[CO2] + [H2CO3] = 0,23 ·pCO2
pH = pKa+ lg [HCO3
-]
0,23 · pCO2
Henderson Hasselbalch´s formula
5. Physiologic pH regulation Bicarbonate buffer
Our body uses 3 different systems to keep the pH constant:
1) Buffers (the first minutes)Phosphatbuffert (in the cell)Proteiner (albumin,Hemoglobin) in the cellCarbonate buffert (blood, plasma)
2) Regulate breathing Acids are formed during metabolism. In tissues CO2 forms - transported to lungs as HCO3
-. CO2 can be released in lungs. If problems with lungs: can get acidosis.
1) Long term regulation via kidneys
5. Physiologic pH regulation Regulate pH by breathing
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Gas transport
O2 is transported from the lung to the tissues and CO2 formed in tissues is transported back to the lung. The transport of these gases is coupled to pH:
.
Gases affecting pH
O2
O2
O2
O2Hemoglobin transport O2.It has 4 Heme groups
5. Physiologic pH regulation
pH, CO2, O2 and BPG (2,3-bisfosfoglycerat) attenuates Hb´s affinity for O2
Relaxed form Tense formBinds O2 releases O2
+[H+]
+[CO2]
+BPG
Low O2 affinityHigh O2 affinity
Low pH
Hemoglobin5. Physiologic pH regulation
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Bohr effekt:An increase of CO2 and a decrease in pH results in
reduced affinity of Hb for O2.
Tissue= Low pH, High CO2
O2 affinity decrease andis released to tissuesShift right
Lungs: High pH, Low CO2 and O2
affinity increases, Shift left
5. Physiologic pH regulation
Our body uses 3 different systems to keep the pH constant:
1) Buffers (the first minutes)Phosphatbuffert (in the cell)Proteiner (albumin,Hemoglobin) in the cellCarbonate buffert (blood, plasma)
2) Regulate breathing Acids are formed during metabolism. In tissues CO2 forms - transported to lungs as HCO3-. CO2 can be released in lungs. Problems with lungs: can get acidosis.
1) Long term regulation via kidneys
5. Physiologic pH regulation
During normal metabolism of food – we produce acids - excreted via urine. The kidneys excrete/retain H+ and HCO3
-. If you are acidotic, your kidneyswill try to excrete H+ and retain HCO3
-.
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Acid Base lecture 15-16 September 2014Agnes Rinaldo-Matthis
1. Introduction to pH
2. Acid base concept -calculations
3. Buffert -calculations
4. Titration
5. Physiologic pH regulation -calculations
6. Measure pH?
pH paper: acid base form have different light absorbance
pH meter:
Measures the voltage produced by the solution, compares it with the voltage of a known standard solution, and uses the difference in voltage to calculate the pH.
In vivo: measure in plasma or urine. Difficult to measure inside the cell, microelektrodes.
6. Measuring pH
Recommended