UGEB2380 The Chemistry of Life 2024-25 Lecture Notes PDF

UGEB2380 The Chemistry of Life Academic Year 2024-25 Dr. Sam CK HAU (Department of Chemistry) Cleaning Agents, Personal Care, and Cosmetics Industry of Cleaning Soaps, Shampoos, toothpastes, mouthwashes, cosmetics, moisturisers, and other skin and hair products, laundry detergents, ho...

UGEB2380 The Chemistry of Life Academic Year 2024-25 Dr. Sam CK HAU (Department of Chemistry) Cleaning Agents, Personal Care, and Cosmetics Industry of Cleaning Soaps, Shampoos, toothpastes, mouthwashes, cosmetics, moisturisers, and other skin and hair products, laundry detergents, household cleaners… … Enormous market for personal care and household products - nearly 450 billion US dollars annually and growing 3  Surface Tension A property of liquids that causes them to behave as if the surface is covered by a thin membrane The molecules that make up the liquids exert cohesive, attractive forces between neighbouring molecules At the water’s surface, nearby Water molecules exert large water molecules are below and forces of attraction on to the sides. This produces neighbouring molecules. Within particularly strong attractions of the liquid, the total force of the surface molecules attraction is dispersed in all immediately below them, and direction results in a cohesion of the surface “surface tension” 4 Soaps and Detergents It is believed the Romans discovering the soaps Heating the goat fat with extracts of wood ashes, which contain strong bases, produces soaps Help clean oily and greasy dirt from various substances, including fabrics, dishes, skin and hair 5 How Soap is Made From the hydrolysis of naturally occurring fats and oils in the presence of a base, such as sodium hydroxide The products are an alcohol, and the salt of the carboxylic acid, “Saponification” Sodium salts of fatty acid containing 10-18 carbons make the best soaps H O H O CH3 +NaˉO C CH3 H C O C n H C OH n O O CH3 CH3 H C O C n + 3 NaOH H C OH + +NaˉO C n O O CH3 +NaˉO C CH3 H C O C n H C OH n H H A triglyceride A glycerol Soap Molecules Sodium salts of Fatty acid 6 Effect of Detergents When detergents are added to water, they form a monolayer (a layer of one molecule thick) at the surface 1. Detergent molecules 2. The nonpolar, 3. The polar, hydrophilic disrupt the attractive hydrophobic tails of the heads of the detergent forces among water detergent molecules molecules are attracted molecules at the surface protrude out of the to water molecules and and lower the surface water’s surface, remain embedded tension disassociating among the water themselves from the molecules at the surface water molecules 7 Surfactants and Micelles Substances that accumulate at the surfaces of water and change their surface properties sharply, especially lowering the tension - Surfactants (表⾯活性劑) As detergents accumulate within the body of water, they coalesce into micelles - microscopic spheres of one substance distribute throughout another, with their hydrophobic tails pointing the interior of the micelles, and shielded from contact with water molecules 8 How Detergent Clean Water must be penetrate well in order to wash A detergent lowers water’s surface tension, allowing water to carry the detergent micelles to get into the fabric When micelles reach the embedded dirt, they trap the oily dirt within their hydrophobic interiors; then becomes dispersed or suspended in the soapy water and be rinsed away with fresh water Micelles are covered by carboxylate groups (–CO2ˉ; negatively charged) 9 Types of Surfactants All have a typical molecular structure in common: a long O hydrophobic chain - “Tail” S O and a hydrophilic group - O O Na “Head” -ve charged hydrophilic head If hydrophilic head is Cleaning natural fibers of cotton negatively charged - anionic surfactants N Cl If hydrophilic head is positively charged - cationic surfactants +ve charged hydrophilic head If the molecule do not bear Effective germicides like mouthwashes electrical charges - nonionic OH surfactants O Nonionic Cleaning synthetic fabrics like polyester 10 Cosmetic and Skin Care Improve our appearance - to look good and to smell nice, especially by applying chemicals to our bodies Henna - a hair dye extracted from henna plants of Africa, India and the Middle East Cosmetic derives from the Greek word ‘kosmos’, meaning order, adornment and the universe Anything intended to be applied directly to the human body for “cleansing, beautifying, promoting attractiveness, or alternating the appearance” 11 Cosmetic and Skin Care Can be categorised into 4 main groups - hair-care products; skin-care products; hand, face, and body soaps; and perfumes and colognes One-tenth of the retail cost on the raw materials like detergents, moisturisers, fragrances, solvents … … Other costs are packaging, distribution, marketing, also research and development expenses 12 Cosmetic and Skin Care Among all, two classes of chemicals, aside of water and common solvents Surfactants - critical component of shampoos, soaps, toothpastes, and related products Fragrances - contribute less than 1% to the total weight of all personal care products, but make up about 25% of the total cost of all the raw materials, and the most expensive one 13 Skin Care Skin The largest body’s organ, covering and containing the body, protecting it from damages Regulating body temperature; sensing stimuli provided by the outer world; synthesising compounds like vitamin D Consists of two major layers - dermis (underlying layer, contains nerves, blood vessels, sweat glands, hair follicles) and epidermis (consists of several tiers of cells, a single sheet of cells dividing continuously and pushing upward) 14 Skin Care When the cells in epidermis move toward the outside of the skin, driving along by new cells from beneath, they lose their ability to divide and die eventually Those dead cells become the lifeless, outermost layer of the skin, called the stratum corneum The condition depends mostly on its water content, too much moisture nourishes the growth of fungi and microorganisms; too little dries it out, producing flaking and cracking 15 Skin Lotions Keep the skin soft and moist Prepared by emulsions of two or more liquids that are insoluble in each other If the first ingredient listed is an oil, likely a water-in-oil emulsion with oil content >50%; if listed is water, probably a oil-in-water emulsion with water content >50% Most effective when applied after a bath or shower, while the skin is still damp 16 Antiperspirants and Deodorants The body control its temperature by perspiring or sweating, and the evaporation of the water contained in perspiration can cool the body The eccrine glands cover most of the skin, dense on the forehead, face, palms; secrete a slightly acidic and very dilute solution of inorganic ions, lactic acid, urea and glucose The apocrine glands lie under the arm, in the groin; their odourless secretions attract bacteria to accumulate and degrade to give an unpleasant- smelling products 17 Antiperspirants and Deodorants Antiperspirants are ionic compounds containing aluminium cations (Al3+), like [Al2nCl6-n·xH2O]m Enter skin cells, water is drawn in and the cells swell, causing the ducts of the eccrine glands to squeeze shut, preventing further release of sweat These aluminium compounds reduce the odour associated with the apocrine glands by killing the bacteria Deodorants mask or eliminate odours with pleasant fragrances and with antibacterial agents Colouring Cosmetic Colouring cosmetic - lipsticks, eye colouring, nail polish, and face powder Dyes and pigments in cosmetics can be classified as organic and inorganic Organic - highly conjugated (system of alternating single and double bonds) Inorganic - ions of transition metals (can absorb or scatter light and produce colours) O Eye shadows use largely O inorganic dyes including ultramarine blue, containing aluminium, oxygen, silicon, HO O OH sodium and sulphur; iron oxides of various shades of red, carbon Br Br black and titanium oxide (TiO2) Dibromofluorescein for white colour (D&C Orange #5) Fragrances Perfume - Latin per (through) and fumus (smoke) Cologne is a much more dilute and less expensive version of a perfume Modern perfumes - mixture of various synthetic chemicals and plant extracts, all dissolved as 10~25% solutions in alcohol Volatile and evaporate readily, mixing with the air and allowing us to smell them The rate of evaporation can be variable, depending on their structures but be increased by body warmth 20 Fragrances The mixed fragrances are O designed to reach the nose in three notes H Top Note - first impact, 2-phenylethanal vaporise easily and move to OH nose quickly Heart Note - most noticeable odour 2-phenylethanol End or Base Note - a O residual, longer-lasting scent Top Note carried by earthy substances and lingers Heart Note Base Note Civetone Sunscreen UV radiation from the sun, called the UVA and UVB regions UVA (320-400 nm), less energetic, not cause sunburns UVB (290-320 nm), cause damage over a long term, tissue destruction, associated redness, blistering and peeling Our skin defence by producing the dark pigment melanin to screen out part of the radiation and helps minimise the damage 22 Sunscreens Most are broad-spectrum meaning that provide protection against both UVA and UVB radiation UV absorbers - organic compounds that absorb UV radiation Para-aminobenzoic acid (PABA) but allergenic and O O other risks Avobenzone and O Octocrylene, which often Avobenzone (UVA) containing benzene rings O bonded to carbonyl groups N C O Octocrylene 23 (UVB and short-wave UVA) Sunscreens Most are broad-spectrum meaning that provide protection against both UVA and UVB radiation Scattering agents - inorganic oxides, such as zinc oxide (ZnO) and titanium oxide (TiO2) Scatter or block all the radiation, letting none through to the skin by nanotechnology Usually applied to the nose and the tops of the ears, areas that receive the most direct exposure 24 Sun Protection Factor (SPF) Serves as a measure of its ability to protect against UVB radiation A product with an SPF of 30: it can reduce the amount of UVB radiation reaching the skin by a factor of 30 (after 30 mins in the sun, you would have received the same amount of UV radiation as someone who spent only 1 min in the sun without sunscreen) 25 Hair Care Serves to help protect the skin and regulate body temperature Lifeless structure composed of a protein called Keratin In keratin, the sulphur-containing amino acid (cysteine) dominates the polymer and accounts for about 15% Along the polypeptide chain, the thiol groups (–SH) of cysteines readily form disulphide links (–S–S–) with the neighbouring chains The joined cystine groups give hair strength by connecting and keeping the polypeptide chains aligned Cysteine amino acid on Form links with each neighboring strands of other which help produce keratin structural rigidity NH NH NH NH H2 H2 H2 H2 HC C SH HS C CH HC C S S C CH C C C C O Cysteine Cysteine O O Cystine O 26 Hair Structure Each strand of hair grows from a living root embedded within follicles under the skin Consists of a central core (the cortex), over it is a thin, translucent, scaly sheath (the cuticle) Sebaceous glands lying in the skin near the follicle lubricate with an oily sebum - gives the hair a gross and keeps the scales of cuticle lying flat to prevent the strand from drying out 27 Hair Structure Too much sebum makes the hair feel greasy and dirty; too little sebum makes the hair dry, dull and wild Detergents of shampoo helps to remove the dirt from the hair and scalp, also the accumulated sebum to keep the hair looking clean Conditioners replace part of the lubricant that might be lost in the washing 28 Hair Treatment Permanent wave hair treatment use a reducing agent to cleave the disulphide links, allowing hair to be curled; once the orientation is settled with an oxidising agent, which converts the cysteines back to cystines Hair relaxers use alkaline compounds like lithium hydroxide (LiOH) to disrupt the disulphide links, allowing curly hair to straighten 29