Glycine

• BPGlycine
• JPGlycine
• Ph. Eur.Glycine
• USP–NFGlycine

Aminoacetic acid; aminoethanoic acid; glycocoll; Gly; E640

Aminoacetic acid · [56-40-6]

UNII TE7660XO1C · PubChem CID 750

C2H5NO2 · 75.07

pH adjuster, buffering agent, Stabiliser, lyoprotectant

Typical concentrations: — · Dosage forms: Sterile (parenteral/ophthalmic)

Used as a buffering agent, bulking agent and protein stabiliser in parenteral products, particularly freeze-dried formulations, where it is often combined with mannitol or sucrose. It is also used in antacid and effervescent formulations, as a sweetening and flavour-modifying agent, and in oral rehydration and nutritional products.

White, odourless, crystalline powder or crystals with a sweetish taste. It is the simplest amino acid and, having no chiral centre, is optically inactive.

pKa

≈ 2.3 (carboxyl) and ≈ 9.6 (amino), at 25 °C

Isoelectric point

≈ 6.0

Melting point

decomposes above about 230 °C

Solubility

freely soluble in water (about 1 in 4 at 25 °C); very slightly soluble in ethanol; practically insoluble in ether

Polymorphism

α, β and γ forms; commercial material is normally the α form

Stable as a solid. Store in a well-closed container in a cool, dry place. In freeze-drying, glycine crystallises readily during freezing or annealing, which gives a strong cake; incomplete crystallisation can leave amorphous glycine that crystallises later and destabilises proteins.

As a primary amine it can undergo Maillard reaction with reducing sugars. Incompatible with strong oxidising agents.

Produced commercially by amination of chloroacetic acid with ammonia, or by the Strecker synthesis from formaldehyde, hydrogen cyanide and ammonia, followed by purification by crystallisation.

A naturally occurring amino acid regarded as non-toxic at excipient levels. Absorption of large volumes of glycine irrigating solution during urological surgery can cause fluid overload, hyponatraemia and visual and neurological disturbances; this relates to its use as an irrigant rather than as an excipient.

Observe normal precautions for the quantity handled; eye protection and gloves are recommended.

Accepted as a food additive in Europe (E640). Included in the FDA Inactive Ingredient Database (injectable preparations; oral products) and in parenteral and non-parenteral medicines licensed in Europe.

Alanine; histidine; mannitol; sodium glycinate.

Sodium phosphate–glycine combinations should be used with care in frozen protein solutions, because selective crystallisation of buffer components can shift the pH during freezing. In lyophilised products, the glycine-to-protein ratio and the freezing and annealing programme largely determine whether glycine acts as a crystalline bulking agent or remains partly amorphous.