This chapter talks about interest in the liquid-liquid interface that is concerned with the topic of emulsions, which is closely related to the study of food science. It explains that the liquid-liquid interface consists of liquid drops dispersed in another liquid, which are normally thermodynamically unstable and are usually stabilized by the adsorption of an emulsifier. It also considers the movement of a solute from one liquid phase to another. This is important with processes such as liquid-liquid extraction in the chemical industry and in many biological situations. The chapter highlights the role of membranes that can be significant in solute transport and is an essential feature of many biological processes. It reviews emulsions that are concerned with water or an aqueous solution as one phase and a water-insoluble organic liquid as the other phase.
Chapter
The liquid–liquid interface: emulsions; membranes
Chapter
The chemicals of biological systems
This chapter provides a background on the chemistry processes that take place in the cells of living organisms, noting that cells consist of a semipermeable membrane that encloses an aqueous solution rich in a diverse range of chemicals. It describes cells as sophisticated machines that undertake a wide range of chemistry in an organized fashion. It also refers to the chemicals present in cells that appear to have been selected by the processes of evolution for their chemical utility. The chapter shows that many cellular processes can be understood in simple molecular terms. It introduces a series of examples to exemplify principles that are important for understanding the chemistry of cells.
Chapter
Lipids: cells as compartments
This chapter examines the molecular components of the membranes enclosing compounds, looking at compartments of living organisms that are bounded by semipermeable membranes. It discusses how organic compounds are immiscible with water and tend to associate in aqueous solution, which is exploited by cells with the use of compounds and lipids to form the basic structures of cell membranes. It also develops an awareness of the intrinsic chemistry of phospholipids. The chapter analyses the membranes found in biological systems. These are formed by the spontaneous association of relatively small organic molecules called lipids. It explains that membrane structures arise because of the amphiphilic nature of lipid molecules, wherein one end is hydrophilic and the remainder is a hydrophobic tail.
Chapter
Acid–base Equilibrium
This chapter explains the acid-base equilibrium. This involves the transfer of protons in line with the Brønsted–Lowry theory. A strong acid or strong base is fully ionized in an aqueous solution, while weak acids or bases are only partially ionized in an aqueous solution. Acid-base titrations measure the unknown concentration of one solution by reaction with another standard solution with a familiar concentration. The chapter also notes how indicators are typically water-soluble weak organic acids with varying colours at different pH values. It explores the alternative theory of acid-base reactions proposed by Gilbert Lewis: a Lewis acid is an electron-pair acceptor, while a Lewis base is an electron-pair donor.
Chapter
Coordination chemistry
This chapter begins by discussing coordination chemistry in aqueous solution, and then moves on to the more varied coordination chemistry that is seen in non-aqueous solution. It covers the complexes of f-elements, excluding those with Ln- or An-carbon bonds. The chapter also highlights the importance of chelating and macrocyclic ligands in f-element coordination chemistry, particularly in aqueous solution. Both lanthanoids and actinoids are generally considered as hard Lewis acids, and so their coordination chemistry is dominated by hard O and N donor ligands. Bonding is highly ionic in most cases, resulting in labile complexes that can have highly irregular coordination geometries dictated by ligand steric factors. Large ionic radii result in high coordination numbers, except where ligands are exceptionally sterically demanding.
Chapter
Aqueous solution species
This chapter focuses on two particular aspects of the chemistry of the second and third row d-block metals in aqueous solution: species present in solution and redox behaviour. It explores the increase in electron withdrawing power of the metal centre which is associated with an increase in oxidation state and is reflected in the fact that the hexaaqua ion of vanadium does not exist in a solution. It also discusses the loss of protons through the polarization of O-H bonds in coordinated water. This leads to the formation of hydroxo ligands and the concomitant generation of dinuclear species. The chapter describes the dramatic effect that the change in ligand has on the relative case of iron(III) reduction. It mentions the use of potential diagrams as a valuable method of displaying the redox behaviour of different species containing a particular element.
Chapter
Acids and Bases
This chapter begins by outlining definitions of acids and bases based on Johannes N. Brønsted and Gilbert N. Lewis. Substances that taste sour have long been known as acids. Bases, on the other hand, are compounds which counteract or neutralize acids. The chapter then reviews the dissociation of a Brønsted acid in aqueous solution. It also presents the two important properties of buffer solutions. First, they allow us to prepare an aqueous solution of a desired pH using a weak acid and its conjugate base (a salt of the acid). The second important property of a buffer solution is that its pH will remain approximately constant if relatively small amounts of a further acid or base are added. Next, the chapter focuses on the factors which affect acid and base strengths. It also analyzes the basicity of organic compounds and the solvent effects on acid-base reactions.
