ionic composition of body fluids and acid-base balance eva samcová petr tůma
TRANSCRIPT
Life
• Life possesses the properties of replication, catalysis, and mutability (N. Horowitz)
• Biochemistry is the study of life on the molecular level.
Life in aqueous environments
• Nearly all biological molecules assume their shapes (by that their function) in response to the physical and chemical properties of the surrounding water.
• Reactants and products of metabolic reactions, nutrients as well as waste products, depend on water for transport within and between cells.
• The reactivity of many functional groups on biological molecules depend on the relative concentrations of H and OH in the surrounding medium
Water is a polar molecule
• Water molecules form hydrogen bonds.• The angular geometry of the water molecule has
enormous implications for living system.• Van der Waals distance – the distance of closest
approach between two nonbonded atoms.• Hydrogen bonds and other weak interactions
influence biological molecules.• The strength of bonds and weak interactions: ionic
interactions (two charge groups)►hydrogen bonds►van der Waals forces - arise from electrostatic interactions among permanent or induced dipoles (two permanent dipoles, dipole - induced dipole, London dispersion forces)
Life has evolved in water and is still dependent on it.
• electrical dipole – hydrogen bonds– Important in bonds: H-F, H-O, H-N
H2O CH4
Molar mass, g/mol 18 16
Dipole moment, 10-30 C.m 6,2 0
Boiling point, °C 100 -162
Heat of vaporization, kJ/mol
41 8
Dissolving of inorganic substances in water• electrolytic dissociation and hydration
• NaCl → Na+ + Cl-
• KNO3 → K+ + NO3-
• Na2SO4 → 2Na+ + SO42-
Insoluble salts• BaSO4 (s) ↔ Ba2+ (aq) + SO4
2- (aq)• Product of solubility KS
• KS = [Ba2+].[SO42-]
salt KS
BaSO4 1,3.10-10
AgCl 1,8.10-10
Ca3(PO4)2 1.10-26
Dissolving of organic substances in water• Formation of hydrogen
bonds– Alcohols– Monosaccharides
– Carboxylic acids– Length of chain
• Amphipathic substances– Soaps and detergents
• Hydrophobic substances– Oil in water
Constituent Plasma Interstitial fluid
Intracellular fluid
Na+ 142 145 12
K+ 4 4.1 150
Ca2+ 1-2 1-2 <10-6 mol/l*
Mg2+ 0.75-1.5 2
Cl- 103 113 4
HCO3- 25 27 12
Protein 60 25
The normal composition of the major body fluid compartments is approximately as follows (mmol/l, except Ca2+)* Free ionic Ca2+ is very low inside cells, total calcium may be much higher (1-2mmol/l).
Acids and Bases Acid-Base Balance
Brönsted´s theory: Acid – substance which is able to donate H+
(proton) to another substance (proton donors) Base – substance which is able to accept H+ from another substance (proton acceptors)
Acid ↔ conjugate base + H+
Conjugate pairs:HCl ↔ Cl- + H+
NH3 + H+ ↔ NH4+
Relation to water:
HCl + H2O ↔ Cl- + H3O+
NH3 + H2O ↔ NH4+ + OH-
Disociation of water and pH concept• Autoprotolysis of water – ionic product of water
[H3O+] [OH-] = 1.10-14 při 25 °CpH + pOH = 14
• pH = -log[H3O+]
• Acidic solution: [H3O+] > [OH-] pH < 7• Neutral solution: [H3O+] = [OH-] pH = 7• Basic solution: [H3O+] < [OH-] pH > 7
Solutions of strong acids and strong bases
• Strong acids: HCl, HNO3, H2SO4, HClO4
• Strong bases: NaOH, KOH, Ca(OH)2, Ba(OH)2
X log10X
10 000 = 104 4
1 000 = 103 3
100 = 102 2
10 = 101 1
1 = 100 0
0,1 = 10-1 -1
0,01 = 10-2 -2
0,001 = 10-3 -3
0,0001 = 10-4 -4
pH calculation of solutions of strong acids and bases
• Strong acids: HCl, HNO3, H2SO4, HClO4
• Strong bases: NaOH, KOH, Ca(OH)2, Ba(OH)2
• Calculate the pH of 0,001M HCl. What are concentrations of H3O+ and OH- in this solution?
Calculate the pH of 0,01M KOH. What are concentrations of H3O+ a OH- in this solution?
Weak acids and dissociation constant
• electrolytic dissociation of acid
HA + H2O ↔ H3O+ + A- • Dissociation constant of acid KA
pH weak acid solution• pH = ½ pKA - ½ log [HA]
Calculate pH of 0,01M solution of acetic acid KA= 1,75 10-5
AA
A
KpK
HA
AOHK
log
3
Power of acids
Conjugate pair KA pKA α, [%]
HClO4 ClO4- 95
HNO3 NO3- 90-95
HCl Cl- 90-95
H2SO4 HSO4- 60
H3PO4 H2PO4- 7,5 .10-3 2,12 12
HF F- 6,6 .10-4 3,18 10
CH3COOH CH3COO- 1,75 .10-5 4,76 1,3
H2CO3 HCO3- 4,47 .10-7 6,35 0,12
H2S HS- 1,07 .10-7 6,97
H2PO42- HPO4
- 6,20 .10-8 7,21
HCN CN- 6,17 .10-10 9,21 0,07
HCO3- CO3
2- 4,68 .10-11 10,33
HPO42- PO4
3- 4,27 .10-13 12,37
Po
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f a
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Po
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f b
ase
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BasesPower of bases
• strong bases: NaOH, KOH, CsOH, Ca(OH)2,
Ba(OH)2
• weak bases: NH4OH, pyridine, aniline, purine
Dissociation constant of bases KB
B + H2O ↔ BH+ + OH- BOHBH
KB
Báze KB
NaOH
KOH
Ca(OH)2
NH3 1,80 . 10-5
pyridin 1,62 . 10-9
anilin 4,07 . 10-11
Solutions which buffer deviationof pH
Mixture of weak acid and its conjugate salt:• CH3COOH + NaOH → CH3COONa + H2O• CH3COONa + HCl → CH3COOH + NaCl
Hendersonova-Haselbalch equation kyseliny
solipKpH A log
What is result pH of buffer which was prepared by mixing of 200mL 0,1M CH3COOH with 200mL 0,2M CH3COONa? KA=1,75 10-5
Buffers
pH
Physiological buffers
Phosphate buffer • H2PO4
- + H2O ↔ HPO4-2 + H3O+ pK = 7,2
• Buffers intracellulary, in urine, 1% of plasma• Inorganic phosphate, AMP, ADP, ATPBicarbonate buffer• H2CO3 + H2O ↔ HCO3
- + H3O+
• Buffering of blood plasmaProteins• Side chains of amino acids – His, Lys, Arg, Glu, Asp• The most important hemoglobin 30% of buffer capacity
of blood, other proteins only 6%