Proline is a non-essential, optically active, and imino acid, which means it has a secondary amine as part of its structure, setting it apart from other common amino acids that have a primary amine. It's classified as a non-polar or hydrophobic amino acid due to its cyclic structure, making it unique among the 20 standard amino acids. Proline plays a crucial role in collagen formation, the main structural protein in animals, giving tissues their strength and stability. Its rigid ring structure makes it highly influential in protein folding and stability, often found in the active sites of enzymes and at the turns of alpha-helices in proteins. Unlike most amino acids, proline does not participate in the alpha helix formation because of its inability to form the hydrogen bond needed, making it a significant factor in protein conformation.

The term "neutral amino acid" can be somewhat ambiguous without specifying the context or the particular amino acid being discussed. Generally, amino acids have a central carbon atom (α-carbon) bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable R group. At physiological pH (around 7.4), most amino acids exist as zwitterions, which means they carry both positive and negative charges but are overall electrically neutral. However, this does not mean that all amino acids are chemically neutral in terms of their properties. For example, some amino acids like glycine, alanine, serine, and valine are considered nonpolar (or hydrophobic) and do not readily interact with water. Others, such as asparagine and glutamine, are polar (or hydrophilic) but uncharged at physiological pH. In contrast, some amino acids, like lysine, arginine, and histidine, are positively charged, while aspartate and glutamate are negatively charged. So, while most amino acids are electrically neutral due to the presence of equal numbers of positive and negative charges, their chemical properties can vary widely.

Epoxy resin often emits a strong smell during its curing process, primarily due to the volatile organic compounds (VOCs) it releases. To mitigate this odor, ensure proper ventilation in the workspace by opening windows and using fans to circulate fresh air. Additionally, employing air purifiers with activated carbon filters can help absorb and neutralize the smell. It's also beneficial to wear a respirator mask specifically designed to filter out VOCs for personal protection. If the smell persists on the cured resin, washing the surface with a mixture of warm water and mild detergent, then rinsing and drying it thoroughly, can reduce odor. For items that can't be washed, placing them outdoors in a shaded area for several days might help dissipate the smell without causing damage from direct sunlight. Always adhere to the manufacturer's safety guidelines and use products in well-ventilated areas.