The powder form of N6-Cbz-L-lysine exhibits typical physical characteristics of organic protected amino acids, described across the following dimensions for appearance, particle properties, and physical state:
I. Macroscopic Appearance and Color
Color Characteristics: Pure samples typically appear as white to off-white powder with uniform color, free of visible impurities or spots. Improper storage (e.g., moisture, light exposure) may cause slight yellowing without affecting the main structure.
Luster: The powder surface shows subtle crystalline luster with faint reflectivity under natural light, resulting from light scattering by the regular arrangement of molecular crystals.
II. Particle Properties and Microscopic Morphology
Particle Morphology: Optical microscopy reveals powder particles mostly as needle-like or prismatic crystals, related to the rigidity of the benzyloxycarbonyl (Cbz) benzene ring and the extensibility of the lysine side chain in the molecular structure. Crystals have clear edges and distinct angles, with no obvious agglomeration under dry conditions.
Particle Size Distribution: Hand-ground or mechanically crushed powder has a particle size of ~50–200 μm, with uniformity influenced by preparation processes (e.g., spray drying yields finer powder at ~10–50 μm). Uncrushed original crystals may be larger, up to 0.5–1 mm.
Flowability and Hygroscopicity: The powder shows moderate flowability. Intermolecular hydrogen bonding may cause particle adhesion and reduced flowability after slight moisture absorption. In environments with humidity >60%, the powder surface deliquesces easily, forming small agglomerates.
III. Physical State and Tactile Properties
Texture and Touch: The powder is fine and dry, with no rough granular feel when rubbed between fingers, exhibiting the typical touch of organic crystal powders (distinct from the sandy texture of inorganic salts).
Compressibility: Under external pressure, the powder can be compacted into flakes, demonstrating certain compressibility due to intermolecular forces (e.g., hydrogen bonds, van der Waals forces) in its crystal structure.
Solubility-Related Characteristics: Containing polar groups (carboxyl, amino) and non-polar benzyl groups, the powder dissolves in polar solvents (water, methanol) but not in non-polar solvents (diethyl ether, n-hexane), dispersing rapidly upon contact with soluble media.
IV. Factors Influencing Powder Morphology
Preparation Processes:
Crystallization from organic solvents (e.g., ethanol-water mixtures) yields larger particles via slow cooling, while rapid crystallization produces fine powders.
Freeze-drying results in more 疏松 powder with uniform particle size distribution and lower hygroscopicity.
Storage Conditions:
Exposure to humidity causes hygroscopic caking, destroying crystal morphology and potentially darkening the color.
High temperatures (>60°C) or intense light lead to partial decomposition of the Cbz protecting group, yellowing the powder and increasing particle hardness.
V. Correlation Between Purity and Powder Morphology
High-purity N6-Cbz-L-lysine features white, uniform particles without agglomerates or discolored grains. Impurities (e.g., unreacted L-lysine, Cbz-Cl by-products) may render the powder slightly gray, with uneven particle sizes and even oily agglomerates.
Purity analysis via infrared spectroscopy (IR) or thin-layer chromatography (TLC) shows clear characteristic peaks for pure powder (e.g., benzene ring skeleton vibration of the Cbz group, amino stretching vibration), free of interfering impurity peaks, reflecting the regularity of its crystal structure.
N6-Cbz-L-lysine powder is typified by white, needle-like crystals, integrating physical properties of polar and non-polar groups. Its particle state, flowability, and hygroscopicity are closely linked to preparation techniques and storage environments. The stability of powder morphology serves as an important indicator for judging purity and applicability. In fields such as drug synthesis and peptide preparation, physical properties must be maintained by controlling crystallization conditions and storage environments.
