Figure 1 Delocalization of a positive charge
over the guanidinium group of Arginine

Figure 2 Arginine Amino Acid

Arginine        

                                                        

Arginine is one of 20 naturally occurring amino acids. It removes ammonia from the body and is important in both cell division and the healing of wounds. If taken as an oral supplement, Arginine can aid as a precursor to the synthesis of nitric oxide and urea, as well as lower blood pressure. It also plays a small role in the treatments of alcoholic hepatitis, advanced cirrhosis, and erectile dysfunction. It is found in the Lysine polypeptide, which binds free sugar molecules so they can react with proteins. This provides an anti-glycation effect.

Arginine is a white crystalline powder. Its molecular weight is 174g, it melts at 235˚C, and has an isoelectric point of 10.75. Its functional groups include four amines, a guanidinium group and one carboxylic acid. Amines absorb between 3300 and 3400 cm^-1 on the IR spectrum. The C=O bond of the carboxylic acid absorbs at about 1710 cm^-1 and the O-H absorption occurs from 2500-3500 cm^-1. The pK_a value for the carboxylic acid is approximately 5. The guanidinium group has a pK_a of 12.48. The nitrogen atoms of this group delocalize a positive charge. Figure 1 shows the guanidinium group. Figure 2 is larger picture of Arginine and is a more accurate depiction of the molecule, having a hydrogen atom bound to the oxygen in the carboxyl group.

http://en.wikipedia.org/wiki/Arginine

http://www.sciencelab.com/msds.php?msdsId=9927439

¹Smith, J. Organic Chemistry. 2^nd ed.; McGraw-Hill, 2008, pp 700, 974.

http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/proteins.htm