word of the day: lecithin

The word of the day is lecithin:

Etymology:  < French lécithine (N. T. Gobley 1850, in Jrnl. de Pharm. et de Chim. XVII. 411), < Greek λέκιθος yolk of egg 

Chem. 

a. Any of a group of phospholipids found in plants and animals which are esters of a phosphatidic acid with choline and on hydrolysis yield choline, phosphoric acid, glycerol, and two fatty acids; also used as a generic name for these compounds. 

b. A commercial mixture of lecithin with other phosphatides and often other lipids obtained from natural products and used industrially, esp. that from soya beans. (OED)

i.e., phosphatidylcholine,

(PubChem)
phosphatidylethanolamine,


(PubChem)

etc.


"Physical chemical studies of short-chain lecithin homologues.  I.  Influence of the chain length of the fatty acid ester and of electrolytes on the critical micelle concentration", Tausk et al., Biophysical Chemistry 1:175 (1973)


I guess these days we'd just say "phospholipids"?  Not quite sure what the significance of the choline part of the molecule is that it deserves its own term.

word of the day: obviate

The word of the day is obviate:

Etymology:  < classical Latin obviāt-, past participial stem (compare -ate suffix³) of obviāre to act contrary to, to go against (late 2nd cent. a.d.), in post-classical Latin also to meet (Vulgate), to withstand, oppose, prevent (5th cent.) 

1. trans.  

a. To meet and dispose of; to circumvent, do away with, remove (a difficulty, need, etc.); to prevent or avoid by anticipatory measures.

b. To anticipate, forestall. Obs. rare.

2. trans. To meet, encounter; to withstand, oppose. Obs. 

3. trans. To lie in the way between. Obs. rare.

"The endotherm asymmetry at 13 mole % GD1a suggests a phase transition which is more complex than a simple first order transition.  (Fig. 6 1B, 1C, also see ref. 34.)  It also obviates the possibility that a new species, such as mixed micelles, is formed in the dispersion (as was suggested for egg PC: GD1a dispersions having more than 10 mole% GD1a."

 - Barenholz et al., "Characterization of micellar and liposomsal dispersions of gangliosides and phospholipids", Advances in experimental medicine and biology 125:105 (1980)


Of course, knowing the meaning of this word is not enough to help me decipher this sentence: it would be nice if this paper actually had a Figure 6 1B and 1C.

Molecule of the day: trinitrobenzenesulfonic acid

The molecule of the day is trinitrobenzenesulfonic acid (TNBS).

It's often used to neutralize peptide terminal amino groups, but will react with any primary amine, and can also be used to measure the bilayer integrity of membranes containing phosphatidylethanolamine:

(Sadly, the "submitted" reference appears to have never made it into print.)

Word of the day: eutectic

The word of the day is eutectic:

Etymology:  Greek εὔτηκτος easily melting (εὐ-eu- comb. form + τήκ-ειν to melt) + -ic suffix.

A. adj.

That is a eutectic; of or pertaining to a eutectic or its liquefaction or solidification; eutectic point, the melting-point of a eutectic, or the point representing it in a constitutional diagram. 

B. n.

A mixture which is distinguished from other mixtures of the same constituents in different proportions by having a single temperature at which it melts and freezes, this temperature being lower than the freezing-point of any of the constituents or of any other mixture of them. Also fig.  (OED)

"Two eutectic points are postulated to occur: one at a very low 1,2-DPG concentration and the other at a 1,2-DPG concentration slightly higher than 66 mol%."

 - López-García et al., "The phase behavior of mixed aqueous dispersions of dipalmitoyl derivatives of phosphatidylcholine and diacylglycerol", Biophysical Journal 66:1991 (June 1994)