The time course of the heat effects in rapid chemical changes. Part II.—Some reactions of acids, bases, amino-acids and proteins

Abstract

During the last 20 years the time relationships of the rapid heat changes in muscle and nerve have been the subject of exhaustive study, by Hill, Hartree, Meyerhof and many of their collaborators. The changes involved in such processes have turned out to be dependent both on physical factors and on the heat effects of a number of separate rapid chemical reactions. Hitherto, however, there seems to have been but little attempt, either by physical chemists or by physiologists, to study the time relationships involved in the heat effects of individual rapid chemical reactions themselves. Investigators, for instance, have contented themselves with measuring the total heat of such reactions, merely by mixing together in thermos flasks, or other suitable calorimeters, the reagents required, and by noting the temperature changes which ensue over the period subsequent to mixing. Since, as a rule, observations of this kind have to be extended over a period of some minutes in order to ensure that the heat liberated in the change is uniformly distributed through the calorimeter and its contents, no information is obtained as to whether the heat change under investigation is complete within say one minute or within the merest fraction of a second. Such information ought in certain cases to prove to be of great interest to chemistry, but of its importance in physiology when attempts are made to assess the rôle of separate chemical reactions in the rapid changes known to occur in muscle, nerve and blood there would seem to be no question. Recently a method has been worked out for this purpose, and a description of its experimental details and testings have been described fully above. It is sufficient to state here that the method has made it possible to mix together completely within a period of 0∙001 second or less the reagents, whose interaction it is desired to study, and to measure accurately the total heat evolved within a period of only 0·01 to 0·002 second after the reaction has been started by mixing the reagents. It has been shown that the total temperature change involved in such heat effects can be measured to an accuracy of 0·001°C., whilst in the case of “time” reactions in which the evolution or absorption heat takes place gradually over a period of 0·01 second or more the temperature changes between instants of time t 1 and t 2 can be determined almost to a further place of decimals, viz., 0·0001°C. to 0·0002°C. The present paper is of a preliminary kind and contains a description of the first applications of the method to the following rapid reactions: (α) the neutralisations of typical acids and bases (strong and weak); (β) the reactions of the simplest amino-acid, glycine, with acids, bases and buffers; (γ) the reactions of the blood proteins with acids and bases; and (δ) a single experiment on the reaction between carbon monoxide and hæmoglobin. It was to be anticipated that of the above reactions only those of carbonic acid with bases, of bicarbonate with acid, and of hæmoglobin with carbon monoxide, would fail to show completion of the heat change within 0·01 to 0·015 second. The experimental observations confirmed this expectation.