<unk>  is a hygroscopic, colorless to yellow-brown, oily liquid, that is readily soluble in alcohol, ether or light petroleum. It is miscible with water in its neutral amine base form between 60 °C and 210 °C. It is a dibasic nitrogenous base, having Kb1=1×10−6, Kb2=1×10−11. It readily forms ammonium salts with acids that are usually solid and water-soluble. Its flash point is 95 °C and its auto-ignition temperature is 244 °C.<unk>  is readily volatile (vapor pressure 5.5 Pa at 25 °C) On exposure to ultraviolet light or various oxidizing agents,<unk>  is converted to<unk>  oxide,<unk> c acid (niacin, vitamin B3), and methylamine.<unk>  is chiral and hence optically active, having two enantiomeric forms. The naturally occurring form of<unk>  is levorotatory with a specific rotation of αD=–166.4° ((−)-nicotine). The dextrorotatory form, (+)-nicotine is physiologically less active than (−)-nicotine. (−)-nicotine is more toxic than (+)-nicotine. The salts of (−)-nicotine are usually dextrorotatory; this conversion between levorotatory and dextrorotatory upon protonation is common among alkaloids. The hydrochloride and sulfate salts become optically inactive if heated in a closed vessel above 180 °C. Anabasine is a structural isomer of<unk> , as both compounds have the molecular formula . Structure of protonated<unk>  (left) and structure of the counterion benzoate (right). This combination is used in some vaping products to increase<unk>  delivery to the lung. Pod mod electronic cigarettes use<unk>  in the form of a protonated<unk> , rather than free-base<unk>  found in earlier generations. Biosynthesis<unk>  biosynthesis The biosynthetic pathway of<unk>  involves a coupling reaction between the two cyclic structures that comprise<unk> . Metabolic studies show that the pyridine ring of<unk>  is derived from niacin <unk> c acid) while the pyrrolidine is derived from N-methyl-Δ1-pyrrollidium cation. Biosynthesis of the two component structures proceeds via two independent syntheses, the NAD pathway for niacin and the tropane pathway for N-methyl-Δ1-pyrrollidium cation. The NAD pathway in the genus<unk> otiana begins with the oxidation of aspartic acid into α-imino succinate by aspartate oxidase (AO). This is followed by a condensation with glyceraldehyde-3-phosphate and a cyclization catalyzed by quinolinate synthase (QS) to give quinolinic acid. Quinolinic acid then reacts with phosphoriboxyl pyrophosphate catalyzed by quinolinic acid phosphoribosyl transferase (QPT) to form niacin mononucleotide (NaMN). The reaction now proceeds via the NAD salvage cycle to produce niacin via the conversion of<unk> mide by the enzyme<unk> midase. The N-methyl-Δ1-pyrrollidium cation used in the synthesis of<unk>  is an intermediate in the synthesis of tropane-derived alkaloids. Biosynthesis begins with decarboxylation of ornithine by ornithine decarboxylase (ODC) to produce putrescine. Putrescine is then converted into N-methyl putrescine via methylation by SAM catalyzed by putrescine N-methyltransferase (PMT). N-methylputrescine then undergoes deamination into 4-methylaminobutanal by the N-methylputrescine oxidase (MPO) enzyme, 4-methylaminobutanal then spontaneously cyclize into N-methyl-Δ1-pyrrollidium cation. The final step in the synthesis of<unk>  is the coupling between N-methyl-Δ1-pyrrollidium cation and niacin. Although studies conclude some form of coupling between the two component structures, the definite process and mechanism remains undetermined. The current agreed theory involves the conversion of niacin into 2,5-dihydropyridine through 3,6-dihydronicotinic acid. The 2,5-dihydropyridine intermediate would then react with N-methyl-Δ1-pyrrollidium cation to form enantiomerically pure (−)-nicotine. Detection in body fluids<unk>  can be quantified in blood, plasma, or urine to confirm a diagnosis of poisoning or to facilitate a medicolegal death investigation. Urinary or salivary cotinine concentrations are frequently measured for the purposes of pre-employment and health insurance medical screening programs. Careful interpretation of results is important, since passive exposure to cigarette smoke can result in significant accumulation of<unk> , followed by the appearance of its metabolites in various body fluids.<unk>  use is not regulated in competitive sports programs.
Nicotine
Heroin
Cannabis 
Cannabis
Cocaine
Cocaine 
Benzyl alcohol
Methamphetamine