L-Cystine Dihydrochloride is the hydrochloride salt of L-cystine, formed by the reaction of L-cystine with hydrochloric acid. It is described in terms of properties, performance characteristics, and applications as follows:

I. Properties

1. Physical Properties

Appearance: Typically a white or off-white crystalline powder, odorless or with a slight characteristic odor.

Solubility: Easily soluble in water, with significantly better aqueous solubility than free L-cystine due to the ionic nature of the hydrochloride salt, which enhances interactions with water molecules. Poorly soluble in organic solvents such as ethanol and ether.

Molecular Formula and Weight: C₆H₁₂N₂O₄S₂·2HCl, with a molecular weight of 313.22.

Melting Point: Decomposes upon heating; the decomposition temperature varies slightly depending on purity, generally above 200°C.

2. Chemical Properties

Stability: Relatively stable under dry, light-protected, and room-temperature conditions. However, it may decompose under high temperature, humidity, or strong oxidative environments, especially due to the reactivity of the disulfide bond.

Acidity: Due to the hydrochloride groups, its aqueous solution is acidic.

Reactive Properties: The disulfide bond (-S-S-) in the molecule exhibits certain reactivity, capable of being reduced to form thiol groups (-SH), or participating in oxidation reactions. The amino and carboxyl groups retain the typical reactivity of amino acids, such as esterification and peptide bond formation.

II. Performance Characteristics

Excellent Water Solubility: Compared to the poorly soluble free-form L-cystine, the dihydrochloride form shows greatly enhanced solubility in water due to ionic dissociation, making it more suitable for use in liquid formulations and easier for the body or biological systems to absorb and utilize.

Good Biocompatibility: As an amino acid derivative, it is highly compatible with biological systems and can participate in normal metabolic processes once in the body, showing high safety within reasonable dosage ranges.

Sulfur-Containing Characteristics: The molecule contains sulfur, an essential trace element for the human body, involved in the synthesis of various biologically active compounds (such as glutathione, coenzyme A, etc.), which makes it particularly significant in nutritional supplementation.

Moderate Stability: It can be stably stored under normal conditions but should be protected from strong light, high temperatures, moisture, and strong oxidizing agents to prevent structural degradation or spoilage.

III. Applications

1. Pharmaceutical and Nutritional Supplementation

Nutritional Fortifier: Used in the preparation of amino acid injections and oral nutritional formulations to supplement essential sulfur-containing amino acids in patients undergoing surgery, critical illness, or those who cannot eat normally, helping maintain nitrogen balance and protein synthesis in the body. It is especially suitable for individuals needing additional sulfur intake.

Adjunct in Liver Disease Treatment: Cystine participates in liver detoxification processes. Its dihydrochloride form can serve as a supportive ingredient in improving liver function and is included in certain hepatoprotective preparations.

Hair and Skin Health Products: As a key structural component of hair and skin, cystine dihydrochloride is used in hair growth products, hair care formulations, or skin nutrition supplements to help maintain healthy hair and skin conditions.

2. Food Industry

Food Additive: Can be used as a nutritional fortifier in health foods or specialized dietary products (such as infant formulas, sports nutrition foods), enhancing amino acid content and improving the overall nutritional value of food.

3. Biochemical and Research Fields

Culture Media Component: Used in microbial fermentation or cell culture media as a cystine nutrient source to support growth and reproduction. It can also be used as a biochemical reagent for amino acid metabolism research, enzyme activity assays, and especially in studies involving disulfide bond-related biochemical reactions.

L-Cystine Dihydrochloride, with its excellent water solubility, good biocompatibility, and sulfur content, holds significant application value in the fields of medicine and nutrition, the food industry, and scientific research.