Glycylglycine, also known as diglycine, is a dipeptide composed of two glycine molecules connected by a peptide bond. Its molecular formula is C₄H₈N₂O₃, making it one of the simplest peptide compounds. The following sections elaborate on its properties, characteristics, and applications:

I. Properties of Glycylglycine

Physical Properties:

At room temperature, glycylglycine is a white crystalline powder that is odorless and slightly sweet. It is highly soluble in water, slightly soluble in ethanol, and insoluble in ether and chloroform. Its melting point is approximately 260–262°C. It is stable at high temperatures, although it decomposes under strong heating. Its aqueous solution is mildly acidic with a pH of about 5.5–6.5.

Chemical Properties:

As a dipeptide, it exhibits typical reactivity of peptide bonds and can be hydrolyzed into two glycine molecules under acidic or alkaline conditions. Containing both amino (-NH₂) and carboxyl (-COOH) groups, it behaves as a zwitterion, existing in cationic, anionic, or amphoteric forms depending on the pH. Glycylglycine can also form coordination complexes with metal ions (e.g., copper, nickel), giving it value in coordination chemistry.

II. Characteristics of Glycylglycine

Simple Structure and High Stability:

As one of the simplest dipeptides (glycine–glycine), glycylglycine has a clear molecular structure and superior chemical stability compared to free amino acids. It does not easily degrade under neutral, ambient conditions, making it convenient for storage and use.

Excellent Biocompatibility:

Glycylglycine is a naturally occurring metabolic intermediate in biological systems, often generated during protein hydrolysis. It is non-toxic, highly biocompatible, and exhibits minimal immunogenicity, making it safe for applications in medicine and biomedicine.

Amphoteric Electrolyte Properties:

Due to the presence of both amino and carboxyl groups, glycylglycine has buffering capacity in solution—especially near neutral pH—helping to stabilize the pH of biochemical systems. However, its buffering ability is weaker than that of dedicated buffers like phosphate buffers and is thus more suitable for mild conditions or low-concentration systems.

Controllable Reactivity:

The peptide bond in glycylglycine can be selectively cleaved (e.g., enzymatically or via acid hydrolysis) to release glycine, making it useful both as a peptide model molecule and as a precursor for the controlled release of bioactive compounds.

III. Applications of Glycylglycine

Biomedical and Pharmaceutical Applications:

Glycylglycine is widely used as a tool in biomedical research and as a pharmaceutical intermediate. It serves as a model compound to study peptide structure and function, especially in understanding peptide bond behavior and interactions. In drug development, it can be used to adjust the solubility and stability of peptide-based drugs. Its excellent biocompatibility also makes it suitable as an additive in cell culture media, providing nutrients or maintaining environmental stability.

Biochemical Experiments and Analysis:

Glycylglycine is often used as a buffering agent in biochemical experiments, effective within the pH 5.5–8.0 range, such as in enzyme activity assays and protein purification. It is also used as a standard substance in peptide chromatography (e.g., HPLC), helping calibrate instruments or quantify peptide levels in samples.

Cosmetic Industry:

Thanks to its good water solubility and biocompatibility, glycylglycine is added to skincare products. It can penetrate the stratum corneum to help retain moisture in the skin. Its small molecular size and low irritation potential make it suitable for sensitive skin formulations. Studies also suggest that it may participate in skin metabolic regulation, improving skin health and reducing damage from external environmental factors.

Food and Feed Industry:

As a naturally occurring dipeptide, glycylglycine can be used as a food additive to improve flavor and nutritional profiles. For example, in functional beverages, it may serve as a nutritional enhancer, supplementing amino acid content. In animal feed, it acts as a feed additive to boost protein absorption and promote growth.

Organic Synthesis:

Glycylglycine is used as an intermediate in organic synthesis. It can undergo peptide chain extension to form longer peptides or be modified via its amino or carboxyl groups to introduce new functional groups. This enables the synthesis of specialized derivatives used in dyes, catalysts, and fine chemical products.

Thanks to its simple structure, high biocompatibility, and chemical stability, glycylglycine has important applications in biomedicine, chemistry, personal care, and other industries. Its value is particularly notable in settings requiring mild conditions and biological safety. As peptide research progresses, the scope of its applications continues to expand.