chemical principles exemplified
ROBERT C. PLUMB Worcester Polytechnic Inrtitvta Worcer1.r. Mo~sachussm01609
Drinking Too Fast Can Cause Sudden Death lllustrating principles of chemical dynamics Information provided by C. D. Eskelson Veterans Administration Hospital Tucson, Arizona "I've got five that says you can't guzzle a pint of whisky!" The foolish person who accepts this challenge (most likely when already well loaded), and wins, usually loseshis life. The scenario is acted out with appallingly regularity; death from drinking too fast in response to a challenge is well known among physicians specializing in alcoholism. The chemistry of the phenomenon is interesting and demonstrates the importance of the laws of chemical kinetics. The initial product of alcohol metaholism is acetaldehyde which is subsequently converted to acetate ion. The oxidation involves the enzyme alcohol dehydrogenase (ADH) and the coenzyme nicotinamide adinine dinucleotide (NAD). It is described in the equations below using the Michaelis-Menten theory of enzymatic, kinetics. ADH
+
NAD'
CH,CHO
+
P s
ADH
+
(ADH.NAD+) NADH ADH
+
NADH
+
+
H+ H+
Species in parentheses are complexes. Under the condition that the enzymatic system is saturated with substrate (ethanol) reactions 1 and 2 are thought to go to equilibrium and reaction 3, the hydride transfer step, is taken as the rate controlling step. The second dehydrogenation step is shown in the usual notation for enzyme reactions since we will not be concerned with the kinetics of that step. The rate of ethanol metabolism will he Rate of metabolism = ~ ~ [ ( C ~ H J O H . A D H . N A D + ) ]
I t is estimated that the body contains 6.6 x moles of NAD+ and NADH, so that to metabolize a significant amount of ethanol the NADH must he continuously reoxidized to NAD+; in the steady state the rates of production and consumption of NAD+ must he equal. If the ethanol concentration is larger than the concentration of NAD+-NADH, further increases in the ethanol concentra-
tion have little effect upon the concentration of the enzyme-coenzyme-substrate complex and the rate of metabolism. If ethanol is added to the body faster than i t is metabolized the concentration of alcohol in the hody will increase. 0.35 wt90 alcohol in the blood is sometimes fatal; 0.55 wt% alcohol in the blood is almost always lethal. Alcohol is known to become distributed over the total hody water. A 70 Kg person contains approximately 50 Kg of water. Thus a dosage of from 175 to 275 g of alcohol can cause death. Death is apparently caused by a derangement of the respiratory and cardiac system by interference with the neurotransmitters of the nervous system. A pint of 100 proof liquor contains approximately 185 grams of alcohol. Add this in a few minutes to a hody which already contains one or two tenths of a percent of alcohol and a foolish dare results in a catastrophe.
Saving a Life with Alcohol Illustrating principles of chemical dynamics Contributed by Prof. A. A. Scala Worcester Polytechnic Institute The chemical dynamics responsible for death, in the exemplum above, may he put to good use under different circumstances, to save a life. Occasionally it happens that a child finds a quantity of ethylene glycol, tastes it, and likes the somewhat sweet taste-and drinks it down. Ethylene glycol itself is not poisonous; however its metabolite, oxalate ion, is lethal. The oxidation of ethylene glycol to oxalate ion proceeds by a mechanism parallel to the oxidation of ethanol to acetate, i.e., ~(NAD+.ADH) 4NADH 4ADH 4H' CD4'- + 2~~ CH,OHCH?OH Ethylene glycol poisoning is treated by intravenous feeding of ethanol. The ethanol competitively inhihits the enzymatic oxidation of ethylene glycol to oxalate. The ADH and NAD+ are put to work a t ethanol metabolism and made less available for ethylene glycol metabolism. Ethanol feeding is continued until excretion has reduced the concentration of ethylene glycol to a tolerable level. The concentration of ethanol used and the values of the cquilihrium and rare constants are such that this treatment reduces the fatalits rate hs ahuut SO%. 'l'he witient does. however, have a hangover.
+
+
Footnote to the House Heating Exemplum Suggested by Prof. J. A. Campbell Harvey Mudd College The question of how an increase of temperature in a house affects the energy content of the house was discussed in this column in July 1972. Professor Campbell offers the followine simnle and eleeant nroof that the energy content is nor changed as the h o k e isheated. The ideal gas law expresses the pressure and volume of a Volume 50. Number 5. May 1973 / 365
gas in terms of the number of moles of gas in that volume and the temperature.
From the kinetic theory of gases we have an expression for the translational energy of the gas in a particular volume in terms of the number of moles of gas in that volume and the temperature.
If we combine these we have a simple expression for the
366 / Journalof Chemical Education
energy of a gas in a volume as a function of only the pressure and volume, an expression which does not depend upon the number of moles of gas in that volume or the temperature
Thus, since the volume of the house is constant and the pressure is constant, the translational kinetic energy of the gas in the house remains constant as the temperature is increased. Of course this is true onlv if the arhitrarv zero of enerev -. is chosen as non-interacting particles a t absolute zero, as is conventionally done in the kinetic theory of gases.
