Ionic composition of body fluids and acid-base balance Eva Samcová Petr Tůma

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 H2OH2OCH 4 Molar mass, g/mol1816 Dipole moment, C.m6,20 Boiling point, °C Heat of vaporization, kJ/mol 418

Dissolving of inorganic substances in water electrolytic dissociation and hydration NaCl → Na + + Cl - KNO 3 → K + + NO 3 - Na 2 SO 4 → 2Na + + SO 4 2- Insoluble salts BaSO 4 (s) ↔ Ba 2+ (aq) + SO 4 2- (aq) Product of solubility K S K S = [Ba 2+ ].[SO 4 2- ] saltKSKS BaSO 4 1, AgCl1, Ca 3 (PO 4 )

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

Composition of Body Fluids Organic substances Glucose Amino Acids Urea

ConstituentPlasmaInterstitial fluid Intracellular fluid Na K+K Ca <10-6 mol/l* Mg Cl HCO Protein6025 The normal composition of the major body fluid compartments is approximately as follows (mmol/l, except Ca 2+ )mmol/l * Free ionic Ca 2+ is very low inside cells, total calcium may be much higher (1-2mmol/l).mmol/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 + NH 3 + H + ↔ NH 4 + Relation to water: HCl + H 2 O ↔ Cl - + H 3 O + NH 3 + H 2 O ↔ NH OH -

Disociation of water and pH concept Autoprotolysis of water – ionic product of water [H 3 O + ] [OH - ] = při 25 °C pH + pOH = 14 pH = -log[H 3 O + ] Acidic solution: [H 3 O + ] > [OH - ]pH < 7 Neutral solution: [H 3 O + ] = [OH - ]pH = 7 Basic solution:[H 3 O + ] 7

Solutions of strong acids and strong bases Strong acids: HCl, HNO 3, H 2 SO 4, HClO 4 Strong bases: NaOH, KOH, Ca(OH) 2, Ba(OH) 2 Xlog 10 X = = = = = ,1 = ,01 = ,001 = ,0001 =

pH calculation of solutions of strong acids and bases Strong acids: HCl, HNO 3, H 2 SO 4, HClO 4 Strong bases: NaOH, KOH, Ca(OH) 2, Ba(OH) 2 Calculate the pH of 0,001M HCl. What are concentrations of H 3 O + and OH - in this solution? Calculate the pH of 0,01M KOH. What are concentrations of H 3 O + a OH - in this solution?

Weak acids and dissociation constant electrolytic dissociation of acid HA + H 2 O ↔ H 3 O + + A - Dissociation constant of acid K A pH weak acid solution pH = ½ pK A - ½ log [HA] Calculate pH of 0,01M solution of acetic acid K A = 1,

Power of acids Conjugate pairKAKA pK A α, [%] HClO 4 ClO HNO 3 NO HClCl H 2 SO 4 HSO H 3 PO 4 H 2 PO 4 - 7, ,1212 HFF-F- 6, ,1810 CH 3 COOHCH 3 COO - 1, ,761,3 H 2 CO 3 HCO 3 - 4, ,350,12 H2SH2SHS - 1, ,97 H 2 PO 4 2- HPO 4 - 6, ,21 HCNCN - 6, ,210,07 HCO 3 - CO , ,33 HPO 4 2- PO , ,37 Power of acids Power of bases

Bases Power of bases strong bases: NaOH, KOH, CsOH, Ca(OH) 2, Ba(OH) 2 weak bases: NH 4 OH, pyridine, aniline, purine Dissociation constant of bases K B B + H 2 O ↔ BH + + OH - BázeKBKB NaOH KOH Ca(OH) 2 NH 3 1, pyridin1, anilin4,

Solutions which buffer deviation of pH Mixture of weak acid and its conjugate salt: CH 3 COOH + NaOH → CH 3 COONa + H 2 O CH 3 COONa + HCl → CH 3 COOH + NaCl Hendersonova-Haselbalch equation What is result pH of buffer which was prepared by mixing of 200mL 0,1M CH 3 COOH with 200mL 0,2M CH 3 COONa? K A =1, Buffers

Physiological buffers Phosphate buffer H 2 PO H 2 O ↔ HPO H 3 O + pK = 7,2 Buffers intracellulary, in urine, 1% of plasma Inorganic phosphate, AMP, ADP, ATP Bicarbonate buffer H 2 CO 3 + H 2 O ↔ HCO H 3 O + Buffering of blood plasma Proteins Side chains of amino acids – His, Lys, Arg, Glu, Asp The most important hemoglobin 30% of buffer capacity of blood, other proteins only 6%

Dissociation of phosphoric acid