Chapter 7 Chemistry of Life and Green Chemistry

Chapter 7 Chemistry of Life and Green Chemistry and the Ten Commandments of Sustainability, 3 rd Edition Stanley E. Manahan Chem. Char 2011 For questions, contact: Stanley E. Manahan manahans@missouri. edu 1

2 7. 1 Green Biochemistry is the science of chemical proceses that occur in living organisms Green biochemistry is biochemistry devoted to sustainability Biochemistry is essentially “green” because organisms have evolved to exist sustainably The conditions under which biochemical processes occur are inherently green • Moderate temperature • Avoid toxic substances • Avoid corrosive and reactive chemicals Importance of biochemistry in green science and technology • Ability of organisms to make a variety of materials • Role of biochemistry in understanding toxicity

3 Environmental Biochemistry • Effects of chemical species on biochemical processes • The nature of environmental species made biochemically • Biodegradation of environmental chemicals Affinity or non-affinity of substances for water as related to their biochemical behavior Hydrophilic substances are “water-loving” Hydrophobic substances are “water-hating” • Traverse cell membranes • Undergo bioaccumulation • Many hydrocarbons and organohalides are hydrophobic Detoxification of hydrophobic substances • Makes hydrophobic substance more hydrophilic • More water-soluble • More readily eliminated (through urine)

7. 2 Biochemistry and the Cells Representations of prokaryotic cells (left), eukaryotic animal cells (center), and eukaryotic plant cells (right).

5 LIFE CHEMICALS Biochemistry is the chemistry of life processes. Living organisms produce biochemicals • Carbohydrates • Proteins • Lipids • Nucleic acids Many biochemicals are large macromolecules

6 7. 3 CARBOHYDRATES Biomolecules consisting of carbon, hydrogen, and oxygen Glucose is a monosaccharide Table sugar, C 12 H 22 O 11 is a disaccharide Starch is a polysaccharide, a biopolymer of glucose Generation of glucose by photosynthesis: 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 Carbohydrates and green chemistry • Capture of solar energy • Solar energy to chemical energy • Glucose fermentation to ethanol • Glucose as raw material for chemical synthesis

7 Figure 7. 3 Segment of a molecule of cellulose, a very high molecular mass macromolecule that makes up most of plant biomass Cellulose is a green raw material with many current and potential uses • Hydrolyzed to glucose that can serve as a raw material for chemical synthesis or fermented to ethanol alcohol

7. 4 Proteins Composed of carbon, hydrogen, nitrogen, oxygen, and small amounts of sulfur Polymers of amino acids • Glycine is the simplest amino acid and the others have various groups substituted for the H in glycine designated by the arrow below Protein structure is very important • Altered adversely by denaturation processes Figure 7. 4. Bonding of three amino acids with loss of water to produce a segment of a protein polymer. 8

9 7. 5 Lipids: Fats, Oils, and Hormones Characterized by solubility in organic solvents Bioaccumulate substances not soluble in water Important sources of raw materials, such as biodiesel fuel

Figure 7. 6 Important glands that secrete hormones directly into the bloodstream. Some hormones are lipids. 10

7. 6 Nucleic Acids Nucleic acids are biological macromolecules that store and pass on the genetic information that organisms need to reproduce and synthesize proteins. • Deoxyribonucleic acid (DNA) • Ribonucleic acid (RNA) Three major constituents (see next slide) • A nitrogenous base • A sugar • Inorganic phosphate DNA consists of two strands of material counterwound around each other in an alpha-helix held together by hydrogen bonds between complementary nitrogenous bases 11

12 Figure 7. 7 Structural formulas of segments of nucleic acid polymers

13 Figure 7. 8 Representation of DNA double helix structure A: adenine C: cytosine G: guanine T: thymine ---: hydrogen bonds

Importance of DNA in Green Biochemistry and Sustainability • Hazards of chemical substances to DNA, including cancer caused by altered DNA • Genetic engineering and recombinant DNA technology • Transgenic organisms to produce crops with unique characteristics, synthesize pharmaceuticals, and make a variety of useful raw materials 14

7. 7 Enzymes Enzyme action may require coenzymes Enzyme action can be adversely affected by toxic substances or harsh conditions Enzymes are useful in green applications such as chemical synthesis or waste treatment • Function under inherently mild conditions • Perform processes that cannot be carried out otherwise 15

Immobilized Enzymes in Green Chemistry Typically uses enzymes held on a solid phase over which reactants flow Living cells, usually of bacteria, can be held on a solid phase and use made of their enzymes • An important example is the trickling filter for wastewater treatment in which a film of bacterial and protozoa cells form a film on solids (typically rock) exposed to air over which the wastewater flows • Genetic engineering enables transfer of genes from other organisms to bacteria enabling enzymatic processes to occur with immobilized enzymes 16

Effects of Toxic Substances on Enzymes inhibited, altered or destroyed by toxic substances • Example: “Sulfur-seeking” heavy metals (Pb 2+, Hg 2+) that bind with – SH groups on enzyme active sites causing them to malfunction • Example: Inhibition of acetylcholinesterase enzyme required for nerve function by Sarin organophosphate nerve gas 17

7. 8 Biochemical Processes in Metabolism Organisms act on substances performing metabolism • Alteration of biomolecules • Synthesis of biomolecules (anabolism) • Breakdown of biomolecules (catabolism) Energy-yielding processes • Respiration in which organic substances undergo catabolism • Oxic requiring molecular O 2 • Anoxic in absence of O 2 • Fermentation differing from respiration in not requiring an electron transport chain • Photosynthesis in which light energy captured by plant and algae chloroplasts is converted to chemical energy in the form of carbohydrates (glucose) Heterotrophic organisms metabolize biochemicals for energy, material Autotrophic organisms use chemical or light energy and use CO 2 as a carbon source 18

Figure 7. 10. Adenosine triphosphate involved with energy transfer in living organisms 19

7. 9 Biochemistry of Toxic Substances and Toxicological Chemistry Two major aspects of biochemistry as it relates to green chemistry and toxic substances 1. Biochemical changes in a toxic substance in an organism • Detoxification of substances • Conversion of nontoxic compounds to toxic ones 2. Biochemical mode of action of toxic substances through which they exert a toxic effect Toxicological chemistry deals with the chemical nature and reactions of toxic substances • Origins • Uses • Chemical aspects of exposure, fates, and disposal Toxicological chemistry addresses the relationships between the chemical properties and molecular structures of molecules and their toxicological effects 20

Figure 7. 11 Illustration of the definition of toxicological chemistry 21

22 Biochemistry of Toxicants and Protoxicants Toxicants are toxic (poisonous) substances Protoxicants are substances that can be metabolically converted to toxic substances Xenobiotic compounds are those that are normally foreign to living systems Toxicants and protoxicants in general are acted upon by enzymes that normally act upon endogenous substrates (those normally present in organisms) • Example: Enzyme that oxidizes endogenous cysteamine to cystamine also oxidizes xenobiotic N and S compounds Intermediary xenobiotic metabolism produces transient substances • Intermediary metabolites can be biochemically very reactive • Are often the species through which a toxic effect is exerted

Phase I and Phase II Reactions A phase I reaction normally introduces a functional group onto a compound Figure 7. 12. Phase I conversion of benzene to phenol with production of reactive intermediate benzene epoxide (normally the toxic agent) 23

24 Figure 7. 13. A Phase II reaction in which phenol is conjugated with glucuronide, an endogenous conjugating agent

Biochemical and Toxic Effects of Toxicants Figure 7. 14. The dynamic phase of toxicant action in which a toxicant interacts with an endogenous receptor leading to biochemical changes that adversely affect an organism 25

Toxicological Chemistry and the Endocrine System 26 Environmental exposure to substances that have the potential to disrupt the crucial endocrine gland activities that regulate the metabolism and reproductive functions of organisms • Estrogenic substances that act like female hormone estrogen • Example: 17 a-ethinylestrdiol used in oral contraceptives • Xenoestrogens are synthetic compounds that are estrogenic • Examples: Bisphenol A and phthalic acid ester plasticizers The practice of green chemistry minimizes the production and use of xenoestrogens and attempts to prevent their introduction into the environment