Ch10: N- and P-Containing Compounds

Amino Acids

Dipolar molecules

Amino group, carboxyl group, R group, and H attached to a-C

Amino Acids: Amphoteric

Act as acid and base

Acidic carboxyl deprotonate for neg charge

Basic amino protonate for pos charge

Zwitterion

Dipolar amino acid ion at neutral pH

Amino Acids: Condensation Reaction

Form peptide bonds → Polypeptides

Polypeptides

Base unit of proteins

Amino Acids: Hydrolysis

Cleave peptide bond

Catalyzed by strong acid/base

Peptide Bond: Partial Double-Bond

From resonance

Limit rotation about N and carbonyl C bond

Increase rigidity and stability

Strecker Synthesis: Reactants (4)

Aldehyde/ketone, NH4Cl, KCN, H2O

Strecker Synthesis: Reaction Types (3)

Condensation (imine formation) → Step 1

Nu addition (-CN addition) → Step 1

Hydrolysis → Step 2

Strecker Synthesis: Step 1

**Aldehyde/Ketone + NH4Cl + KCN → Imine → Aminonitrile**

Carbonyl O protonated to increase carbonyl C electrophilicity

NH3 attack form imine

CN- nucleophilic addition to imine C form aminonitrile

Strecker Synthesis Step 1: Aminonitrile

Amino (-NH2) + Nitrile (-C≡N)

Strecker Synthesis: Step 2

**Aminonitrile → Imine → Amino Acid (Carboxylic acid group)**

Nitrile N protonated to increase nitrile C electrophilicity

H2O attack form imine and hydroxyl moieties on same C

H2O attack form amino acid with carboxylic acid group (accelerate with acid and heat)

Strecker Synthesis Step 2: Amino Acids

Racemic mixture

Gabriel (Malonic-Ester) Synthesis: Reactants (4)

Potassium phthalimide, diethyl bromomalonate, alkyl halide, H2O

(acid and base catalysts)

Gabriel Synthesis: Reaction Types (3)

2 x SN2, hydrolysis, decarboxylation

Gabriel Synthesis: Amino Acid

Racemic mixture

Phosphate Group/Inorganic Phosphate (Pi)

Form high-energy bonds in ATP

P in buffered mixture of hydrogen phosphate and dihydrogen phosphate

Phosphodiester Bonds

DNA backbone

Link sugar moieties

Contain Pi

Pyrophosphate (PPi)

Released by DNA polymerase

Provide energy for new phosphodiester bond

Hydrolyzed to 2 Pi in aqueous solutions

Organic Phosphate

C-containing molecules with phosphate groups

ATP, GTP, DNA nucleotides

Phosphoric Acid Buffer

3 acidic H with varying pKa

In strongly acidic conditions (H3PO4)

Dihydrogen Phosphate

In mildly acidic conditions (H2PO4 -)

Lose first H (pKa = 2.15)

Hydrogen Phosphate

In weakly basic solutions (HPO4 2-)

Lose second H (pKa = 7.20)

Phosphate

In strongly basic solutions (PO4 3-)

Lose third H (pKa = 12.32)

Phosphate: Physiological pH (7.4)

Dihydrogen phosphate and hydrogen phosphate predominate

Phosphate/Pyrophosphate Cleavage

P repulsion from neg charge and stability from resonance

Cleaving = release high energy