Water&PH 2new

Aqueous Solutions:Water&pH

and by Drs. Selma Yilmaz and Kamer Kilinc

Water on Earth moves continuallythrough the water cycle of evaporationand transpiration (evapotranspiration),condensation, precipitation, and runoff,usually reaching the sea. Evaporationand transpiration contribute to theprecipitation over land.

Water: The solvent of life

Aqueous Solutions: The cell

Most of the major components in cells (proteins, DNA andpolysaccharides) are also dissolved in water.

Water movement

c)

d)

Biomedical Importance-I Water is the predominant chemical component of iving organisms and ideal biological solvent.

Water covers 71% of the Earth's surface. Only 2.5% of the Earth's water isfreshwater, and 98.8% of that water is in ice and groundwater. Less than0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an evensmaller amount of the Earth's freshwater (0.003%) is contained withinbiological bodies and manufactured products

The total amount of water in a man of average weight (70 kilograms)is approximately 40 litres, averaging 57 percent of his total body weight.Intracellular fluid (2/3 of body water, extracellular fluid (1/3 of bodywater) In a newborn infant, this may be as high as 75 percent of the bodyweight, but it progressively decreases from birth to old age, most of thedecrease occurring during the first 10 years of life.

Also, obesity decreases the percentage of water in the body,sometimes to as low as 45 percent ref.: Arthur Guyton 's Textbook of Medical Physiology

Biomedical Importance-II Water is the chemical substances with chemical formula H2O .

One molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom.

Biomedical Importance-II

Waters peculiar physical properties, including the ability to solvate a wide range of organic and inorganic molecules, derive from waters dipolar structure and exceptional capacity for forming hydrogen bonds.

The manner in which water interacts with a solvated biomolecule influences the structure of each. An excellent nucleophile, water is a reactant or product in many reactions.

Biomedical Importance-III

Water has a slight tendency to dissociate into hydroxide ions and protons.

The acidity of a solution is generally reported using logarithmic pH scale.

Bicarbonate and other buffers normally maintain the pH of extracellular fluid between 7.35 and 7.45.

Suspected disturbances of acid-base balance are verified by measuring the pH of arterial blood and the CO2 content of venous blood.

Biomedical Importance-V

Causes of acidosis (blood pH 7.45) may follow vormiting of acidic gastric contents. The main cause of respiratory alkalosis is hyperventilation, resulting in a loss of carbon dioxide.

Soda lime

Suspected disturbances of acid-base balance:Acidosis and Alkalosis

Biomedical Importance-VI

Regulation of water balance(the flow of water in and outof a system)

depends upon

the hypothalamicmechanismson antidiuretic hormone(ADH),on retention orexcretion of water bythe kidneys, andon evaporative loss.

Biomedical Importance-VIII Diabetes insipidus (DI): A condition characterized by excessive thirstand excretion of large amounts of severely diluted urine, with reductionof fluid intake having no effect on the concentration of the urine.

Nephrogenic diabetes insipidus (NDI): A form of diabetes insipidus, is primarily due to kidney or nephron dysfunction caused by an insensitivity of the kidneys or nephrons to ADH.

Biomedical Importance-VIII Nephrogenic diabetesinsipidus (NDI) resultsfrom the unresponsivenessof renal tubularosmoreceptorsto antidiuretic hormone,

leading to a decrease inthe ability of kidney toconcentrate urine byremoving free water oradjust the subtle changesin extracellular fluidosmolarity.

Water Is An IdealBiological Solvent

Water molecule forms dipole.

Water molecule forms hydrogenbonds.

Water Is An Ideal Biological Solvent

A water is an irregular, slightly skewed tetrahedron with an oxygenat its center.

The water molecule has a bent geometry with an O-H bond distanceof 0.958 and an H-O-H bond angle of 104.5o Ideal tetrahedral angle is 109.5o.

The large electronegativity difference between H and O gives a 33%ionic character on the O-H bond as is indicated by waters dipolemoment of 1.85 debye units.

Water Is An Ideal Biological SolventWater is a strong dipole

Water is dipole.

A water molecule is polarbecause of the unequalsharing of the electrons ina bent structure.

Water Is An Ideal Biological SolventWater is a strong dipole

Water, a strong dipole,has a high dielectricconstant.

The stronglyelectronegative oxygenatom pulls electrons awayfrom the hydrogen nuclei,leaving them with a partialpositive charge, while itstwo unshared electron pairsconstitute a region oflocal negative charge.

Water has a high dielectric constant As quantitatively described by Coulombs law,the strength of interaction (F) between oppositely charged particles isinversely proportionate to the electric constant () of the surroundingmedium.

Water has a high dielectric constant,therefore greatly decreasesthe force of attraction betweencharged and polar species relative towater-free environments withlower dielectric constant.

Its strong dipole and high dielectricconstant enable waterto dissolve large quantities ofcharged compounds such as salt.

Water molecules can form hydrogen bonds Water has a slight tendency to dissociate into hydroxide ionsand protons.The ability of water to ionize, while slight, is of central importancefor life. Since water can act both as an acid and as a base, its ionizationmay be represented as an intermolecular proton transfer that formsa hydronium ion (H3O+) and a hydroxide ion (OH):

H2O+H2O = H3O+ + OH-

H3O+ (the hydronium ion) is abbreviated H; a bare proton has nostable existence in aqueous solution.

The transferred proton is actually associated with a cluster ofwater molecules.

Water molecules can form hydrogen bonds

A partially unshielded hydrogennucleus covalently bound to anelectron-withdrawing oxygen ornitrogen atom can interact withan unshared electron pair onanother oxygen or nitrogenatom to form a hydrogen bond.

Since water moleculescontain both of thesefeatures, hydrogenbonding favors the self-association of watermolecules into orderedarrays (Figure 22).

....

.... ....

.... ....

........

.... ....

.... .... ....

Structure of Water

Structure ofwater


The boiling point of water (and all other liquids) is dependent on theatmospheric pressure. Mt. Everest water boils at 68 C, sea level water boils at 100 C at sealevel.Water deep in the ocean near geothermal vents can reach temperaturesof hundreds of degrees and remain liquid.


Hydrogen bonding profoundly influences the physical properties of water and accounts for its exceptionally high viscosity, surface tension, and boiling point.

On average, each molecule in liquid water associates through hydrogenbonds with 3.5 others.

These bonds are both relatively weak and transient, with a half-life of one microsecond or less.

Rupture of a hydrogen bond in liquid water requires only about4.5 kcal/mol, less than 5% of the energy required to rupture acovalent OH bond.

Water molecules can formhydrogen bonds

Hydrogen bonding enables water to dissolve many organicbiomolecules that contain functional groups which canparticipate in hydrogen bonding.

The oxygen atoms of aldehydes, ketones, and amides,for example, provide lone pairs of electrons that can serveas hydrogen acceptors.


Alcohols and amines can serve both as hydrogen acceptors andas donors of unshielded hydrogen atoms for formation of hydrogenbonds (Figure 23).

Pure water has a low electrical conductivity, but this increases with thedissolution of a small amount of ionic material such as sodium chloride.

It is not only hydrogen bond acceptors or donors that dissolve well inwater. In contrast to most organic liquids, water is an excellent solvent forionic compounds. Substances like NaCl are very stable. They readily dissolvein water. This is caused by dipolar nature of water. Dipoles interact with ions,so cations and anions in aqueous solution are hydrated. They are surroundedby shells of water molecules, called hydration shells.

High solubility of NaCl is caused by two factors:

1. The formation of hydration shells is energetically and thermodynamicallyfavorable.

2. High dielectric constant of water decreases the charge-charge interactionbetween Na and Cl ions.

Substances that are readily dissolved in water are hydrophilic or water-loving substances.

Water as a Solvent

Solvation of ions by oriented water molecules

Water as a Solvent Nonpolar and nonionic compound does not dissolve in water.

Substances like aliphatic and aromatic hydrocarbons, therefore, arecalled hydrophobic or water-fearing compounds.

A most interesting and important class of molecules are the ones thatexhibit both hydrophilic and hydrophobic properties simultaneously.Such amphipathic compounds have a hydrophilic or polar headgroup and a hydrophobic tail usually a hydrocarbon.

When one attempts to dissolve them in water, such compounds formpeculiar structures. They form a monolayer on the water surface, withonly the head groups immersed.

If the mixture is vigorously stirred, micelles (spherical structuresformed by a single layer of molecules) or bilayer vesicles may form. Insuch cases the hydrocarbon tails lie in a roughly parallel array. In thisstructure they interact via Van der Waals forces and hydrophobicinteractions. The polar or ionic heads are strongly hydrated. Mostimportant to biochemistry is the fact that amphipathic molecules formthe basis of the biological membrane.

Water as Solvent

INTERACTION WITHWATER

INFLUENCES THESTRUCTURE

OF BIOMOLECULES

Covalent & Noncovalent Bonds Stabilize Biologic Molecules Biomolecules Fold to Position Polar & Charged Groups on Their Surfaces Hydrophobic Interactions Electrostatic Interactions van der Waals Forces Multiple Forces Stabilize Biomolecules

1. The covalent bond is the strongest force that holdsmolecules together.

2. Noncovalent forces, while of lesser magnitude, makesignificant contributions to the structure, stability, andfunctional competence of macromolecules in living cells.

These forces, which can beeither attractive or repulsive,involve interactions bothwithin the biomolecule andbetween it andthe water that formsthe principal component ofthe surrounding environment.

Bond Energies for Atoms of Biologic Significance

Covalent & Noncovalent Bonds Stabilize Biologic Molecules

The covalent bond is the strongest force that holdsmolecules together.

A covalent bond is a chemical bond that involves thesharing of electron pairs between atoms. The stablebalance of attractive and repulsive forces between atomswhen they share electrons is known as covalent bonding.

Covalent Bonds Stabilize Biologic Molecules

Covalent Bonds

Non-Covalent Interactions-1

1. Charge-Charge + - -NH3+ -OOC- 1/r

q+ q-q+ q-

q+ q-2. Charge-Dipole + H2O +H3N-1/r2

3. Dipole-Dipole H2O H2O 1/r3

q+ q-

q+ q- +

q+ q-

4.Charge-Induced dipole

5.Dipole-Induced dipole

- + 1/r4

1/r5

-NH3+

- +H2O

Type of interaction Model ExampleDependence of Energy on Distance

q+ q-

q- q+- +

1/r6+ -

6. Dispersion

7. Van der Waals interactions:a. Attractionb. Repulsion 1/r12

8. Hydrogen bonds

q- q+

Acceptor donor

C=O H-N

Non-Covalent Interactions-2

Type of interaction Model ExampleDependence of Energy on Distance

Most biomolecules are amphipathic; that is, they possess regionsrich in charged or polar functional groups as well as regions withhydrophobic character.

Amphiphile (from the Greek amphis: both and philia: love,friendship):

A chemical compound possesing both

hydrophilic (water-loving, polar, ionically charged) and hydrophobic (lipophilic, fat-loving, nonpolar) properties.

Such a compound is called amphiphilic or amphipathic.

Common amphiphilic substances are soaps and detergents.

Biomolecules Fold to Position Polar &Charged Groups on Their Surfaces

Proteins tend to fold with the R-groups of amino acids withhydrophobic side chains in the interior. Aminoacids with chargedor polar amino acid side chains (eg, arginine,glutamate, serine)generally are present on the surface in contact with water.

A similar pattern prevails in a phospholipid bilayer, where thecharged head groups of phosphatidyl serine orphosphatidylethanolamine contact water while their hydrophobic fatty acyl sidechains cluster together, excluding water.

This pattern maximizes the opportunities for the formation ofenergetically favorable chargedipole, dipoledipole, and hydrogenbonding interactions between polar groups on the biomolecule andwater.

It also minimizes energetically unfavorable contacts between waterand hydrophobic groups.

Biomolecules Fold to PositionPolar & Charged Groups on Their Surfaces

Amphiphiles Form Micelles and Bilayers

A Phospholipid

The most important reaction of amino acids isthe formation of a peptide bond (shaded).

Hydrophobic interaction refers to thetendency of nonpolar compounds toself-associate in an aqueousenvironment.

Self-association minimizes energeticallyunfavorable interactions betweennonpolar groups and water.

While the hydrogens of nonpolar groupssuch as the methylene groups of hydro-carbons do not form hydrogen bonds,they do affect the structure of the waterthat surrounds them.

Hydrophobic Interactions

Water molecules adjacent to a hydrophobic group are restricted inthe number of orientations (degrees of freedom) that permit themto participate in the maximum number of energetically favorablehydrogen bonds.

Maximal formation of multiple hydrogen bonds can be maintainedonly by increasing the order of the adjacent water molecules, withan accompanying decrease in entropy.


It follows from the second law of thermodynamics,

the optimal free energy of a hydrocarbonwater mixture is afunction of both maximal enthalpy (from hydrogen bonding) andminimum entropy (maximum degrees of freedom).

Thus,nonpolar molecules tend to form droplets in order to minimizeexposed surface area and reduce the number of watermolecules affected.

Similarly, in the aqueous environment of the living cell the hydrophobicportions of biopolymers tend to be buried inside the structure of themolecule, or within a lipid bilayer, minimizing contact with water.


Fatty acidDetergent

Phospholipid

Hydrophylic groups

WATER

liposome

Micelles

WATER

Interactions between charged groups help shape biomolecular structure.

Electrostatic interactions between oppositely charged groups within orbetween biomolecules are termed salt bridges.

Salt bridges are comparable in strength to hydrogen bonds but act overlarger distances.

Electrostatic Interactions/Ionic Bonds

Electrostatic Interactions

Ionic interactions: Negatively charged groups, such as the carboxylate group (-COO-) in the side chain of aspartate or glutamate, can interact with positively charged groups, such as the amino group (-NH3+) in the side chain of lysine (see Figure 2.11)

van der Waals forces arise from attractionsbetween transient dipoles generated by therapid movement of electrons of all neutralatoms. Significantly weaker than hydrogenbonds but potentially extremely numerous,van der Waals forces decrease as the sixthpower of the distance separating atoms.Thus, they act over very short distances,typically 24 .

Van der Waals Forces

Multiple ForcesStabilize Biomolecules

The DNA double helix illustrates the contribution of multiple forces to thestructure of biomolecules..These noncovalent interactions includehydrogen bonds between nucleotide bases (WatsonCrick base pairing)and van der Waals interactions between the stacked purine andpyrimidine bases.

Most of the major componentsin cells (proteins, DNA andpolysaccharides) are alsodissolved in water.

Multiple Forces StabilizeBiomolecules

The DNA double helix illustrates thecontribution of multiple forces to thestructure of biomolecules.

Multiple Forces Stabilize Biomolecule

Water is an excellent nucleophile

Metabolic reactions often involve the attack by lone pairs ofelectrons residing on electron-rich molecules termednucleophiles upon electron-poor atoms called electrophiles.

Metabolic reactions often involve the attack by lone pairs ofelectrons residing on electron-rich molecules termednucleophiles upon electron-poor atoms called electrophiles.

Nucleophiles (nucleus-loving): electron-rich molecules,nucleophiles donate electrons, Lewis bases, reacts withpositively (or partially positively) charged atoms(electrophiles)

Electrophiles (electron-loving): electron-poor atoms,positively charged atoms, electrophiles reacts with sourcesof electrons (nucleophiles)


Nucleophiles and electrophiles do not necessarily possessa formal negative or positive charge.

Water, whose two lone pairs of sp3 electrons bear a partialnegative charge, is an excellent nucleophile.

Other nucleophiles of biologic importance include theoxygen atoms of phosphates, alcohols, and carboxylicacids; the sulfur of thiols; the nitrogen of amines; and theimidazole ring of histidine.

Common electrophiles include the carbonyl carbons inamides, esters, aldehydes, and ketones and the phosphorusatoms of phosphoesters.

Water is an excellent nucleophileNucleophilic attack by water generally results in the cleavage of theamide, glycoside, or ester bonds that hold biopolymers together.

Hydrolysis ( Greek: hydro-: "water",and lysis : "separation") usuallymeans the cleavage of chemical bonds by the addition of water.

This process is termed hydrolysis. Where a carbohydrate is broken intoits component sugar molecules by hydrolysis (e.g. sucrose beingbroken down into glucose and fructose), this is termed saccharification.Generally, hydrolysis or saccharification is a step in the degradation of asubstance.


Conversely, when monomer units are joined together toform biopolymers such as proteins or glycogen, water is aproduct, for example, during the formation of a peptide bondbetween two amino acids:


In the cell, protein catalysts called enzymesaccelerate the rate of hydrolytic reactionswhen needed.

Proteases catalyze the hydrolysis of proteinsinto their component amino acids, whilenucleases catalyze the hydrolysis of thephosphoester bonds in DNA and RNA.

Many Metabolic Reactions InvolveGroup Transfer

D-G + A A-G + D

Many Metabolic ReactionsInvolve Group Transfer

Given the nucleophilic character of water and itshigh concentration in cells,

why are biopolymers such as proteins and DNArelatively stable?

And how can synthesis of biopolymers occur in anaqueous environment?

Central to both questions are the properties ofenzymes.

Many Metabolic ReactionsInvolve Group Transfer

In the absence of enzymic catalysis, evenreactions that are highly favoredthermodynamically do not necessarily takeplace rapidly.

Precise and differential control of enzymeactivity and the sequestration of enzymesin specific organelles determine under whatphysiologic conditions a given biopolymerwill be synthesized or degraded.

Newly synthesized biopolymers are notimmediately hydrolyzed, in part becausethe active sites of biosynthetic enzymessequester substrates in an environmentfrom which water can be excluded.

WATER, ACIDS, BASES AND BUFFERS

Water has a slight tendency to transfer the proton that forms a hydroniumion (H3O+) and a hydroxide ion (OH):

H2O+H2O = H3O+ + OH-

H3O+ (the hydronium ion) is abbreviated H; a bare proton has no stableexistence in aqueous solution.

The transferred proton is actually associated with a cluster of watermolecules.

WATER DISSOCIATES INTO HYDROXIDE IONS ANDPROTONS-1

WATER DISSOCIATES INTO HYDROXIDE IONS ANDPROTONS-1

At one instant WATER is an ion; an instant later WATER is part of a water molecule.

WATER DISSOCIATES INTO HYDROXIDE IONS ANDPROTONS

For dissociation of water,r dissociation of water,

where the brackets represent molar concentrations (strictlyspeaking, molaractivities) and K is the dissociation constant.

Since 1 mole (mol) of water weighs 18 g,1 liter (L) (1000 g) of water contains 1000 / 18 = 55.56 mol.Pure water thus is 55.56 molar.

The molar concentration of H+ ions (or of OH ions) existence in purewater

is the product of the probability (1.8 ~ 109 ) x the molar concentration ofwater (55.56 mol/L ) = 1.0 ~ 107 mol/L.

The result is (1.8 ~ 109 ) x (55.56 mol/L ) = 1.0 ~ 107 mol/L.

We can now calculate K for pure water:

WATER DISSOCIATES INTO HYDROXIDE IONS ANDPROTONS

The term pH was introduced in 1909 by Sorensen, who definedpH as the negative log of the hydrogen ion concentration: pH = - log [H+]This definition, while not rigorous, suffices for many biochemicalpurposes.To calculate the pH of a solution: 1. Calculate the hydrogen ion concentration [H+]. 2. Calculate the base 10 logarithm of [H+]. 3. pH is the negative of the value found in step 2.

For example, for pure water at 25 C, pH=-log 10-7 = 7

This value is also known as the power (English), puissant(French), or potennz (German) of the exponent, hence the useof the term p.

pH IS THE NEGATIVE LOG OF THE HYDROGEN ION CONCENTRATION

log10 X (10 to the X) is X = log (10X) = X

The pH scale

log10 (10 to the X) is X = log10 (10X) = X

log1/10= log10-1= -1log 0.1= -1log10-2= -2

The following examples illustrate how to calculate the pHof acidic and basic solutions.

Low pH values correspond to highconcentrations of H+ and high pH valuescorrespond to low concentrations of H+.

Solutions with a higher concentration of H+than occurs in pure water have pH valuesbelow 7 and are acidic. Solutionscontaining molecules or ions that reducethe concentration of H+ below that of purewater have pH values above 7 and arebasic or alkaline.

The pH scale

pHLow pH values correspond to high [ H+] andhigh pH values correspond to low [ H+].

Acids are proton donors and bases are proton acceptors.

Strong acids (eg, HCl, H2SO4) completely dissociate intoanions and cations even in strongly acidic solutions (low pH).Weak acids dissociate only partially in acidic solutions.Similarly, strong bases (eg, KOH, NaOH)but not weakbases (eg, Ca[OH]2)are completely dissociated at high pH.

Many biochemicals are weak acids.

Exceptions include phosphorylated intermediates, whosephosphoryl group contains two dissociable protons, the first of which is strongly acidic.

Minireview-1

Minireview-2

Minireview-3

The titration curve of acetic acid

Figure 1.3. The titration curve of acetic acid.

The molecular species that predominateat low pH (acetic acid) and high pH (acetate)are shown.

At low pH (high [H+]), the molecule isprotonated, and has zero charge.

As alkali added, [H+] decreases, (H+) and(OH-) forms H2O,acetic acid dissociates and loses itsproton, and the carbonyl group becomesnegatively charged.

Acids in the Blood of a Healthy Individual.

The Hendersen-Hasselbach Equation-1

The Hendersen-Hasselbach Equation-2

log1/10=log10-1=-1log 0.1=-1log10-2=-2

The Hendersen-Hasselbach Equation

Dissociation of Weak Acids

CH3COOH CH3COO- + H+(HA) (A-)

Henderson-Hasselbach Equation

[H+] = Ka [HA][A-]

pH = pKa + log[A-] Conjugated base[HA] Acid

Ka = [H+] [A-]

[HA]

-log [H+] = -log Ka - log [HA][A-]

Some weak acids or basesacid Conjugated base pK

H-COOH HCOO- + H+ 3.75

CH3-COOH CH3COO- + 4.76

CH3CHCOOH CH3CHCOO- + H+ 3.86OH OH

H3PO4 H++H2PO4- H++HPO4= H+ PO43-2.34 6.86 12.4

H2CO3 H+ + HCO3- CO32- + H+3.8 10.2

C6H5OH C6H5O + H+ 9.89

N H4 NH3 + H+ 9.25 +

A buffer is an aqueous solution consisting of a mixture of aweak acid and its conjugate base or a weak base and itsconjugate acid.

Its pH changes very little when a small amount of strong acidor base is added to it and thus it is used to prevent changes inthe pH of a solution.

Buffer solutions are used as a means of keeping pH at anearly constant value in a wide variety of chemical applications.

Many life forms thrive only in a relatively small pH range sothey utilize a buffer solution to maintain a constant pH.

One example of a buffer solution found in nature is blood.

BUFFERS-1

Because of reversible and partial dissociation, weak acids and theirconjugated base forms can act as proton donors and proton acceptors:

CH3COOH CH3COO- + H+

NaOH Na+ + OH- H2O

By the same mechanism, weak bases can act as buffers.

CH3COOH CH3COO- + H+

HCl Cl- + H*

The Mechanism of Buffer Action

Figure 1.9. The titration curve of aceticacid.

The molecular species that predominateat low pH (acetic acid) and high pH(acetate) are shown.

At low pH (high [H+]), the molecule isprotonated, and has zero charge.

As alkali added, [H+] decreases, (H+) and(OH-) forms H2O,acetic acid dissociates and loses itsproton, and the carbonyl group becomesnegatively charged.

BUFFERS

A buffer is any mechanism that resists changes in acidity (pH). Thebody has two types of buffers:

Chemical buffers/ Physiological buffers - substances that bindhydrogen ion and removes it from solution, as its concentrationbegins to rise, and releases hydrogen ion as the concentration of asolution begins to fall.

Physiological organ buffers - systems that control the bodysoutput of acids, bases or carbon dioxide.

The four major chemical buffer systems of the body are thebicarbonate, phosphate, hemoglobin and protein systems.

Major Chemical Buffers in the biology/biochemistry laboratory

Acid form pKaCacodylic acid 6.2

BISTRIS 6.5

PIPES 6.8

Imidazole 7.0

HEPES 7.6

Tris 8.3

Major Chemical Buffers in Human Body/Physiological Buffers

Buffer ConjugateAcid

Conjugate Base Main buffering Site

Hemoglobin HHb Hb- erythrocytes

Proteins HProt Prot- Intracellular,extracellular

Phosphate H2PO4- HPO42- Intracellular

Bicarbonate CO2 H2CO3- HCO3- Extracellular

1. Hemoglobin

2. Proteins

3. Phosphate buffer system

4. Carbonic acid / Bicarbonate system

Non-bicarbonatebuffers

Chemical Buffers in Human Body/Physiological Buffers

Carbonic acid-Bicarbonate Buffer systemH2CO3 H+ + HCO3- pK1 = 3.8HCO3- H+ + CO32- pK2 = 10.2

CO2 + H2O H2CO3 H+ + HCO3-CA

HCO3- / H2CO3 ratio is 20/1

pK(apperent) = [HCO3-] [H+]

H2CO3= 6.1

7.4 = 6.1 + log [HCO3-]

[H2CO3]

Phosphate Buffer System

H2PO4- H+ + HPO42-

HPO42- / H2PO4 = 4/1

* Major intracellular inorganic buffer.

*H2PO4 excretion in urine is important for the regulation of blood pH.

pK = 6.8

7.4 = 6.8 + log HPO42-

H2PO4-

Plasma Red blood cells CO2

H2O

H2CO3

H+ + HCO3-

HCO3-

O2 release

Cl- Tissu

e m

etab

olis

m

CO2

O2

CO2 + H2O H2CO3

HCO3- + H+Cl-

HHb

Carbamino Hb

H2PO4-

HPO4=

HbO2

O2

CA

Plasma Red blood cellsCO2

H2O

H2CO3

H+ + HCO3-

HCO3-

O2 diffusion

Cl- Alve

ols

CO2

O2

CO2 + H2O H2CO3

HCO3- + H+Cl-

HHb

Carbamino Hb

H2PO4-

HPO4=

HbO2

O2

CA

Hydrochloric Acid

Hydrochloric acid (HCl), also called gastric acid, is secreted byparietal cells of the stomach into the stomach lumen, where thestrong acidity denatures ingested proteins so they can be degradedby digestive enzymes.

When the stomach contents are released into the lumen of the smallintestine, gastric acid is neutralized by bicarbonate secreted frompancreatic cells and by cells in the intestinal lining.

Proteins can be either positively or negatively charged based on the pH ofthe surrounding solution. Amino acids that make up proteins may be positive,negative, neutral, or polar in nature, and together give a protein its overallcharge.

At a pH below their pI (isoelectric point), proteins carry a net positive charge;at a pH above their pI, they carry a net negative charge.

Effects of pH on Proteins

Protein denaturation

If there is an increase in the pH of the surrounding solution and it becomes toobasic, the amino acid bonds will break and the protein will be denatured. Thesame is true if there's increased acidity.


Clinical Causes of Acid-Base DisordersMetabolic acidosis Respiratory acidosis Metabolic alkalosis Respiratory alkalosis

Diabetes mellitus(ketoacidosis)

Chronic obstructiveairways disease

Vomiting (loss ofhydrogen ion)

Hyperventilation (anxiety,fever)

Lactic acidosis Severe asthma Nasogastric suction Lung diseasesassociated withhyperventilation

Renal failure (inorganicacids)

Cardiac arrest hypokalemia Anemia

Severe diarrhea (loss ofbicarbonate)

Depression of respiratorycenter (drugs, opiates)

i.v. Administration ofbicarbonate (after cardiacarrest)

Salicylate poisoning

Renal and intestinal lossof HCO3-

Weaknes of respiratorymuscles

Impairment of renal H+excretion

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Water&PH 2new