detergents Cleaning agents: chemicals with both hydrophobic (averse to water) and hydrophilic (water-attracted) properties that can dissolve fats and oils.

dextran A polysaccharide of bacterial origin.

dialysis/diafiltration Membrane ultrafiltration in which a large solute (such as a protein) is washed or dialyzed with another solution; for example, changing buffer conditions without affecting protein concentration.

differential scanning calorimetry Analytical method that independently measures the rate of heat flow to a sample against a reference standard of the same temperature. Data are obtained by monitoring the differential heat flow as a function of temperature. DSC can measure heat capacities, phase transitions, dehydration, and heats of reaction.

diluent A chemically inert substance added to a solution to increase the volume and reduce the concentration; a diluting agent.

dimer A polymer made up of two identical molecules. When three monomers link up, the resultant polymer is called a trimer. Larger polymers are usually referred to by placing a number before the "-mer" suffix: 4-mer, 5-mer, 6-mer, and so on.

dissociation constant A specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into its component ions. The dissociation constant is usually denoted K _d and is the inverse of the affinity constant. Dissociation constants are commonly used to describe how tightly a ligand (such as a drug) binds to a protein. Such binding is usually non-covalent, i.e., no chemical bonds are made or broken. Since the binding is usually described by a two-state process P + L = C the corresponding dissociation constant is defined K _d = [P][L]/[C] where [P], [L] and [C] represent the concentrations of the protein, ligand and bound complex, respectively. The dissociation constant has the units of molar (M), and corresponds to the concentration of ligand [L] at which the binding site on the protein is half occupied, i.e., when the concentration of protein with ligand bound [C] equals the concentration of protein with no ligand bound [P]. The smaller the dissociation constant, the more tightly bound the ligand is; for example, a ligand with a nanomolar (nM) dissociation constant binds more tightly than a ligand with a micromolar (μM) dissociation constant.

disulfide bond A covalent bond formed between sulfur atoms of different cysteines in a protein; such bonds (links, bridges) help hold proteins together

divalent cations Cations with a net positive charge of +2.

DIW Deionized water, very pure water in which contaminants have been ionized and removed by special filtration.

DMSO Dimethysulfoxide; a common cryoprotectant used to cryopreserve cells and tissues.

Using the scanning electron microscope.