Amines and amides Flashcards
Amines
An ammonia molecule where one or more hydrogens are substituted by one or more alkyl or aromatic groups
Amines contain a polar N-H bond that can form hydrogen bonds with water
Ammonia (NH3) and amines act as a Brønsted–Lowry base. Nitrogen’s lone electron pair accepts H+ from water to produce an ammonium ion (NH4+) and a hydroxide ion (OH–)
Amines can be cyclic molecules as well, ex. Imidazole, found in cofactors, nucleic acids, proteins
Primary: N linked to one C
Secondary: N linked to two C
Amides
ACID+ AMINE CONDENSATION
Amides are derivatives of carboxylic acids in which a nitrogen group (—NH2) of a primary or secondary amine replaces the hydroxyl (—OH) group of carboxylic acids
The stability in water of amides makes them extremely useful in the biological environment, similarly to esters
In proteins, the individual amino acid components are held together by amide bonds
Amidation
Reaction that produces amides
When a carboxylic acid reacts with ammonia or a primary or secondary amine and a LOT of heat, a nucleophilic substitution can occur
This reaction is disfavored in aqueous solution ( because is accompanied by the release of water)
In order to efficiently produce amides, the reaction is carried out using the anhydride or an acid alogen as the acyl donor ( NO release of water)
Acid hydrolysis of amides
Amides in water undergo hydrolysis to the acid and amine, eventually forming the corresponding salt
Requires a catalyst and heat, or a strong base
Amide hydrolysis is thermodynamically favored. However, the reaction is kinetically disfavored at neutral pH
Imines
The nitrogen analogues of aldehydes and ketones
Aldimines and ketimines are derived from the condensation of aldehydes or ketones with amines
Secondary imines are also called Schiff’s bases ( have a N-hydrocarbon bond)
Main reaction of amino acids
Amino acids with –OH function (Ser, Thr, Tyr)
• React with acids to form esters. Phosphorylated amino acids.
• React with carbohydrate hemiacetals to form O-glycosidic bonds
Amino acid with –NH2 (Lys)
• Can be condensed with an acetyl group (acetyllysine) forming an amide.
• Can react with an aldehyde to form an imine
Amino acid with –SH (Cys)
• Can form thioesters with organic acids
• Two molecules can be oxidized to form a disulfide bond S-S
• Can bind to metal ions such as Zn2+, Cu2+, Fe2+, Fe3+
Two amino acids in water
Yields a salt
Amine neutralization
Add Acid= salt formation
Amines are bases
Amine nucleophilicity
Amines have a lone pair on the electronegative nitrogen atom, and can act as nucleophiles to attack polarized bonds
Amines are more nucleophilic than the corresponding alcohols
Peptide bond hydrolysis
It’s thermodynamically favoured but at room T and pH 7 it’s very slow
With the use of adequate enzymes they can be easily hydrolized:
- proteases
- amidases
Amino acids
Contain at least one amino ( NH2) and one organic acid ( - COOH)
Peptide bond
When the amino and carboxylic groups of two different amino acids can react together
Peptides
Polymer of amino acids
Protein synthesis: the ribosome
Proteins must have a precise amino acid sequence
The machinery performing the process of protein synthesis it’s a ribonucleoprotein complex (RNA+ proteins): RIBOSOME
Native structure of proteins
The polypeptide interacts with the solvent and minimizes the free energy of the system by forming hydrogen bonds and maximizing the entropy
For water soluble proteins, the secondary structure elements undergo a HYDROPHOBIC COLLAPSE to form the protein core ( it then undergoes a small rearrangement to give the native structure)
