Chapter 8

The Chemistry of Medicine and Clothing: Condensation Polymers, Especially Those Containing Nitrogen

Review Questions

  1. Amines are molecules that contain a nitrogen atom bonded to one or more hydrocarbon groups.
  1. Alcohols are molecules in which an oxygen atom is bonded to both a hydrogen atom and a hydrocarbon group. Alcohols are given the general formula R-O-H, and can undergo hydrogen bonding. Amines are molecules in which a nitrogen atom is bonded to one or more hydrocarbon groups. The general formulas for amines bonded to one, two, and three hydrocarbon groups are R-N-H2, R2-N-H, and R3-N, respectively. Those amines with formulas R-N-H2 and R2-N-H resemble alcohols, and can also undergo hydrogen bonding. However, hydrogen bonds containing a nitrogen atom are weaker than those containing an oxygen atom.
  1. Amines correspond to molecule of ammonia, NH3, in which one, two, or all three of the hydrogen atoms are replaced by hydrocarbon groups.
  1. Diamines are amines that contain two amino nitrogen atoms.
  1. Neurotransmitters, many of which are amines, are molecules responsible for transmitting impulses between adjacent nerve cells.
  1. Serotonin is a neurotransmitter required to maintain a positive mood. Chronic deficiencies of serotonin are linked to depression. Serotonin also regulates the body’s temperature. The structure of serotonin is given below.

Dopamine, another neurotransmitter, is responsible for the regulation of mood, movement, and attention. Its structure is given below.

A third neurotransmitter is acetylcholine. (You can obtain additional information from Web resources listed at the end of the chapter.) This neurotransmitter is believed to be responsible for learning and memory. Its structure is given below.

  1. Neurotransmitters are released from the nerve cell from which the impulse is originating and travels across a gap, called a synaptic gap, of a few hundred nanometers to a receptor on an adjacent nerve cell. The neurotransmitter temporarily attaches to the second nerve cell and signals the impulse to travel along that nerve cell. After signal generation, the neurotransmitters are rapidly released and frequently travel back to the original nerve cell for reuse.
  1. Prozac modifies the recycling of the neurotransmitter serotonin in certain nerve cells. It increases the concentration of serotonin in the synaptic gap (or region) by preventing its reuptake. This allows for repeated binding of serotonin to the target receptor and initiation of multiple nerve impulse without requiring the excitation and release of serotonin from the nerve cell of origin.
  1. Pyridine is structurally similar to benzene. In pyridine a nitrogen atom replaces one of the carbon atoms. Also, analogous to benzene, the bonds joining the ring atoms in pyridine alternate between single and double in character. In pyridine, however, the nitrogen atom is not bonded to a hydrogen atom as the nitrogen atom can only take three bonds. The structures of benzene and pyridine are given below.

pyridine

benzene

  1. A stimulant is a chemical substance that stimulates the body’s central nervous system. Stimulants affect the body by temporarily increasing one’s level of alertness and the speed of mental processes. It improves mood by providing a sense of euphoria and decreases fatigue and appetite.
  1. Nicotine is a mild stimulant and it consists of a pyrrolidine ring and a pyridine ring linked by a single bond with a methyl group attached to the nitrogen of the pyrrolidine. Nicotine is addictive because a decrease in its blood levels produces withdrawal symptoms, such as irritability, anxiety, difficulty in concentrating, and restlessness. The structure of nicotine is given below.
  1. The nicotine patch is used by some individuals to help them to quit smoking. This device continuously delivers nicotine to the bloodstream by being absorbed through the skin.
  1. Caffeine is a stimulant that is also classified as an amine. The structure of caffeine is given below.
  1. The half-life of a substance is defined as the length of time required for one half of the total amount of a substance to decompose.
  1. Drug A would be 90% eliminated from the body first because it has a shorter half-life (1 hour versus 10 hours). Since drug A is eliminated faster than drug B, drug A would need to be taken more frequently.
  1. The ammonia molecule consists of a nitrogen atom bonded to three hydrogen atoms. An ammonium ion consists of a nitrogen atom bonded to four hydrogen atoms. In the ammonium ion, nitrogen forms an additional covalent bond to hydrogen by using its pair of nonbonding electrons.
  1. The nitrogen atom in the amine forms a bond to the hydrogen ion, H+, which is extracted from a molecule of water. In the process, a hydroxide ion is released in to the aqueous solution, making it more basic.
  1. Crack cocaine is the name given to the free base form of cocaine. Cocaine, as the free amine, or base, is not very water-soluble. Therefore, in the extraction process, the amine is converted to the corresponding hydrochloride salt, cocaine hydrochloride. In order to produce the free base, the salt is reacted with a substance such as sodium bicarbonate.
  1. An analgesic is a compound that relieves pain. An antipyretic is a substance that relieves fever.
  1. Aspirin (acetylsalicylic acid) is defined as a mild analgesic, whereas codeine, a derivative of morphine, is a much stronger analgesic.
  1. Amides are molecules containing an amino group bonded to a carbonyl carbon. A polyamide is a polymer formed by the condensation of a dicarboxylic acid (a molecule with two –COOH groups) and a diamine (a molecule with two amino groups) with the loss of water.
  1. Condensation polymers are molecules formed by the reaction of two compounds with repeating functional groups with the concurrent loss of a water molecule. Nylon 6,10 is an example of a condensation polymer.
  1. A diacid is molecule containing two carboxylic acid (-COOH) groups. When dicarboxylic acids combine with diamines, water molecules are removed and a polyamide is produced.
  1. –[C(O)-(CH2)5-C(O)-NH-(CH2)10-NH]-
  1. An amino acid is a molecule that contains both an amino group and a carboxylic acid group joined by a carbon chain.
  1. Polyesters are condensation copolymers analogous to the polyamides. These polymers are formed when a diol, or dialcohol, is reacted with a diacid and water is eliminated. This results in the formation of an ester group (-CO-O-) at each linkage point between the diol and the diacid.
  1. The polymer chains in polyamides are parallel to each other due to the high degree of hydrogen bonding between the hydrogen atom of the -NH- group of one chain and the oxygen atom of the carbonyl group on an adjacent chain. As a result of this extensive hydrogen bonding, the chains pack well together and form a very strong material. In contrast, adjacent chains in polyesters cannot undergo hydrogen bonding due to the absence of hydrogen atoms bonded to either nitrogen atoms or oxygen atoms.
  1. The polymer PET or PETE [poly(ethylene terephthalate)] is formed from the condensation of ethylene glycol (HO-CH2-CH2-OH, a dialcohol) with a diacid in which the carboxylic acid groups (-COOH) are separated by a benzene ring.
  1. Polycarbonates, like polyesters, are condensation products of a diacid and a diol. Unlike polyesters, however, polycarbonates contain a diacid, carbonic acid, in which the two –OH groups are bound to the same carbon. This results in the production of two ester linkages with a carbon C=O group between them. The structure of carbonic acid is given below.
  1. Polyethylene glycol has numerous ether oxygens (see structure below). Because these ether oxygens can form extensive hydrogen bonds with water molecules, the material draws moisture and heat away from the individual wearing the fabric by dissolving the water vapor, keeping then cool and dry.

…O-CH2-CH2-O-CH2-CH2-O…

Understanding Concepts

  1. Compound “b” will have the higher boiling point because it has two hydrogen atoms that can participate in hydrogen bonding. Compound “a” lacks hydrogen atoms bound directly to nitrogen. The presence of hydrogen bonds between molecules results in a higher boiling point.
  1. The alcohol will have the higher boiling point. As both molecules have similar chemical weights and structures, the difference in boiling points results from differences in the strength of the hydrogen bonds between the molecules. Since hydrogen bonds containing a nitrogen atom are weaker than the corresponding hydrogen bonds with an oxygen atom, the alcohol will have stronger hydrogen bonds.
  1. Smokers crave cigarettes more often than coffee drinkers crave coffee because the half-life of nicotine is less than that for caffeine. Since the half-lives of nicotine and caffeine are 2 and 4 hours, respectively, nicotine is eliminated from the body faster. This results in lower nicotine levels in the bloodstream and an increased craving for nicotine.
  1. The longer the half-life of a compound, the slower it is eliminated from the body. Thus, caffeine, with a half-life of 4 hours, remains in the body the longest. Cocaine, with a half-life of 0.7 hours, is 90% eliminated first.
  1. If the half-life of a drug is 90 minutes, the concentration would fall to 1/4 of its initial value in two half-life periods, or 180 minutes. The same drug would fall to 1/16 of its initial concentration in four half-life periods, or 360 minutes.
  1. If the half-life of a substance is 1 hour, 1/4 of the substance remains after 2 hours. Similarly, 1/8 of the substance remains after 3 hours, and 1/16 after 4 hours.
  1. If the concentration of a drug in a patient falls to 1/4 of its initial amount after three hours, then it must have been administered two half-life periods ago. Therefore, its half-life must be 1.5 hours (3 hours / 2) or 90 minutes.
  1. If the concentration of a drug was found to be 1/8 of the original dose 3 hours after it was administered, then three half-life periods must have elapsed in that time period. Thus, the half-life of the drug is 1 hour (3 hours / 3 half-life periods or 1 hour / 1 half-life period).
  1. As the ratio of carbon atoms to nitrogen atoms in an amine decreases, its solubility in water increases. Hydrogen atoms bound to carbon atoms are unable to hydrogen bond with water, whereas hydrogen atoms bound to nitrogen atoms are. Thus, the lower the number of carbon atoms per nitrogen atom (or the lower the ratio of carbon atoms to nitrogen atoms), the greater the number of hydrogen bonds per molecule, and the greater its solubility in water. Another way to arrive at this answer is to remember that hydrocarbon molecules tend to be non-polar, while similar compounds containing nitrogen atoms are somewhat polar in character. Thus, the greater the polarity of the molecule, the greater its solubility in water. Similarly, the greater the non-polar character of the molecule, the lower its water solubility will be.
  1. A salt containing a BH+ ion is more soluble than the corresponding neutral B molecule because the ion is stabilized by strong interactions with the nonbonding electrons of the oxygen atoms present in water.
  1. While many drugs contain a polar amino group (-NH2), they are relatively insoluble in water (that is, they are hydrophobic) because of their relatively high C-to-N ratio. Because of their insolubility in water, they are not good drug candidates for intravenous administration. In order to make these drugs more water soluble, they are converted into their ionic form. Ions are more water-soluble because they are strongly stabilized by interactions with the nonbonding electrons of the oxygen atoms of water.
  1. Cocaine hydrochloride cannot be smoked because it is an ionic solid with a high melting point. Its melting point is so high (about 200oC) that it decomposes upon burning.

Injecting the drug results in high concentrations in the bloodstream. When the freebase is smoked, a volatile liquid is produced that quickly vaporizes, is inhaled into the lungs, and is quickly absorbed into the bloodstream producing high concentrations.

  1. The structures of adrenaline and amphetamine are given below.

Adrenaline increases the rate of glycogen breakdown to glucose in the liver and the muscles, thereby increasing the glucose supply in the blood and providing a fast source of energy. Adrenaline also increases the heart and breathing rates to provide more oxygen to the blood.

Amphetamine acts in a similar way to increase heart rate, wakefulness, energy level and drive. Both result in a temporary elevation in mood followed by a period of fatigue and depression.

The effects are similar because the structures of both amines are similar. Both have a benzene ring bonded to a two-carbon chain that is connected to an amino group.

  1. Biochemically, cocaine alters the level of dopamine, a neurotransmitter that helps the body to regulate movement, mood, and attention. It does this by blocking the reabsorption of dopamine onto sites located at the original transmission nerve fiber. This results in an overabundance of dopamine in the synaptic region and an overstimulation of the receptors. However, continued presence of the dopamine molecule in the synapse allows them to be gradually destroyed by enzymes. This loss of dopamine produces both severe depression and an intense craving for more cocaine.
  1. The structures for acetylsalicylic acid, acetaminophen, and ibuprofen are given below

Acetylsalicylic acid:

Acetaminophen:

Ibuprofen:

Acetylsalicylic acid contains a carboxylic acid group and an ester group of acetic acid bonded to a benzene ring. Acetaminophen consists of an amine combined with acetic acid (a carboxylic acid group) on a benzene ring. Ibuprofen contains a carboxylic acid group bonded to a benzene ring. Thus, all three molecules contain a carboxylic acid group and a benzene ring. They have a planar (or flat) region associated with the benzene ring and have similar shapes, sizes, and polarities.

46.The analgesics discussed in the chapter represent a class of drugs known as non-steroidal anti-inflammatory drugs, or NSAIDs. These drugs mainly inhibit the body’s ability to synthesize biomolecules, called prostaglandins, which are made in response to cell injury. The common mechanism of action for NSAIDs is the inhibition of an enzyme known as cyclooxygenase (COX) required for the formation of prostaglandins. This enzyme has two forms, COX-1, which protects the stomach lining, and COX-2, which is required for the formation of prostaglandins. Most NSAIDs inhibit both COX-1 and COX-2. Newer anti-inflammatory drugs only inhibit COX-2, resulting in a decrease in both prostaglandin synthesis and stomach irritation. The COX-2 inhibitors currently available have been approved by the Food and Drug Administration for the treatment of acute pain and arthritis. While more effective in managing pain in these conditions, COX-2 inhibitors have also been associated with an increased risk of heart attacks.

47. Reaction of a diacid and a diol:

Reaction of a monoacid and a diol:

48. Polymerization will form a molecule with the following repeat unit:

–[C(O)-(CH2)4-C(O)-NH-(CH2)7-NH]-

  1. Unlike amines, which contain only amino groups, amino acids are molecules that contain both an amino group and a carboxylic acid group. Thus, polymers of amino acids can be formed by the reaction of the acid –OH group of one amino acid with the amino hydrogen of an adjacent molecule. Similar reactions can be performed with the residual amino and carboxylic acid groups of the dimer.

Synthesizing Ideas

  1. Since CH3CH2CH2NH2 can form hydrogen bonds with water than (CH3)3N, CH3CH2CH2NH2 would be more water-soluble.
  1. No, hydrogen bonding cannot occur in pure amines in which all three atoms bonded to the nitrogen are carbon chains rather than hydrogen. Hydrogen bonding in amine compounds requires the presence of a hydrogen atom that is directly bonded to the nitrogen. The boiling point for the amine (CH3)N will be significantly lower than the boiling point for its isomer CH3CH2CH2NH2. The greater the extent of hydrogen bonding, the higher the boiling point of the molecule.
  1. a) Cocaine contains an amine functional group and two ester groups.

b) Acetylsalicylic acid contains a carboxylic acid group and an ester group.

  1. We are readily able to detect the odors of small diamines because of their volatility (ability to form a gas) and water-solubility. The monomers of nylon 6,6 are chemically bonded together into long polymer chains and are, therefore, unable to become volatile.
  1. a) Prozac modifies the recycling of serotonin, a neurotransmitter. It increases the concentration of serotonin in the synaptic region of the neuron by blocking the recapture of the neurotransmitter by the nerve cell from which the signal originated. Similarly, cocaine blocks the reabsorption of dopamine, another neurotransmitter, onto sites on its nerve fiber of origin, thereby increasing the concentration of dopamine in the synaptic region.

b) Both drugs block the re-uptake or reabsorption of the neurotransmitter.

c) Both molecules have similar structural features. Both contain aromatic rings and amino groups.

d) Prozac produces an overstimulation of the serotonin receptors, and thereby serves as an antidepressant. Cocaine is a powerful stimulant to the central nervous system as it results in the overstimulation of dopamine receptors. Cocaine, by acting as a stimulant, also exhibits anti-depressant activity.

e) Structural features of drugs that would simulate cocaine activity in the body would include the presence of hydroxyl and/or amino functional groups, aromatic rings, and a relatively small molecular structure.