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.
diastereomer A stereoisomer (one of two or more molecules with the same atoms in the same order but different three-dimensional shapes)
having two or more chiral centers that is not a mirror image of another stereoisomer of the same compound; glucose, galactose,
and mannose are all diastereomers.
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
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
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
divalent cations Cations with a net positive charge of +2.
Deionized water, very pure water in which contaminants have been ionized and removed by special filtration.
Dimethysulfoxide; a common cryoprotectant used to cryopreserve cells and tissues.
Deoxyribonucleic acid, the nucleic acid based on deoxyribose (a sugar) and the nucleotides G, A, T, and C. Double-stranded DNA has a corkscrew-ladder
shape (the "double helix") and is the primary component of chromosomes, which thus carry inheritable characteristics of life.
(See nucleotides, nucleic acids.)
Using the scanning electron microscope.