Prodan is a
fluorescent
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, ...
dye (a
naphthalene derivative) used as a membrane probe with environment-sensitive coloration,
as well as a non-covalently bonding probe for
proteins.
Prodan was proposed as a membrane dye by Weber and Farris in 1979. Since then, multiple derivatives have been introduced, such as
lypophilic
Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipop ...
Laurdan (derivative of
lauric acid
Lauric acid, systematically dodecanoic acid, is a saturated fatty acid with a 12-carbon atom chain, thus having many properties of medium-chain fatty acids. It is a bright white, powdery solid with a faint odor of bay oil or soap. The salts and ...
) and thiol-reactive Badan (
bromoacetic acid derivative) and Acrylodan.
Being a
push-pull dye, Prodan has a large excited-state
dipole moment and consequently high sensibility to the polarity of its environment (solvent or
cell membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...
, including the physical state of surrounding
phospholipids
Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids t ...
). Usually it is concentrated at the surface of the membrane, with some degree of penetration. Excited-state relaxation of prodan is sensitive to whether the linkage between phospholipid hydrocarbon tails and the
glycerol
Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
backbone is of ether or ester type. Therefore, many studies exploited this sensitivity to explore coexisting lipid domains in dual-wavelength ratio measurements, to detect non-bilayer lipid phases, to map membrane structure changes.
However, Prodan presence itself is found to change the structure of membranes.
In proteins, Prodan and Badan are quenched by non-covalent bonding with tryptophan and the oxidation of it by excited Prodan/Badan.
Absorption of Prodan lies in the UV range (361 nm in methanol),
but
two-photon excitation techniques have been successfully applied. Fluorescence wavelength is highly sensitive to the polarity of the environment. For example, the emission wavelength shifts from 380 nm in
cyclohexane to 450 nm in
DMFA to 498 nm in
methanol to 520 nm in
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
.
Cyclic voltammetry
Cyclic voltammetry (CV) is a type of potentiodynamic electrochemical measurement. In a cyclic voltammetry experiment, the working electrode potential is ramped linearly versus time. Unlike in linear sweep voltammetry, after the set potential is r ...
shows a reversible reduction peak at —1.85 V in
acetonitrile and a quasi-reversible one at —0.88 in aqueous buffer (pH 7.3) (vs.
NHE
The standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute electrode potential is estimated to be at 25 °C, but to form a basis ...
). Contrariwise, excited-state reduction potential is +1.6 V in the acetonitrile and +0.6 V in water (vs. NHE).
Photostability of Prodan and Laurdan in low-polaritry environments is limited due to undergoing an
intersystem crossing Intersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different spin multiplicity.
Excited Singlet and Triplet States
When an electron in a molecule with a singlet ground ...
in the excited state, with subsequent reactions with triplet oxygen (this also diminishes its quantum yield, which is 0.95 in
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
but only 0.03 in cyclohexane).
References
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Fluorescent dyes
Naphthalenes
Dimethylamino compounds