Reminiscences of N. K. Adam

1 Reminiscences of N . K. Adam JAMES F. DANIELLI T h e Department of L i f e Sciences, Worcester Polytechnic Institute, Worcester, Mass. 01609 and T h e Center for Theoretical Biology, State University of N e w York, Amherst, N . Y . 14226

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N.

K. Adam was unlike anyone else I have ever met. Most people can be said to resemble a number of others, and by making such com parisons one obtains useful insights. No such comparison could be made with N. K. which had validity or value. His scientific work lay almost entirely in surface chemistry, essen tially in the study of monolayers. He took up the study of monolayers, following the remarkable contribution made by Irving Langmuir. The field at that time needed afirstclass experimentalist who could work with rigour and dispassionate exactness. N. K. was the ideal man for this. Judging from his behaviour, his work and his writing, he was con vinced that, provided the correct experiments were done, the phenomena of nature can be shown to arise from a few simple principles. This ascetic attitude was shown in his writing, in which, by the accurate use of simple words and simple sentences, he conveyed meaning with unusual clarity. All his writings on surface chemistry had this characteristic. Although i n many ways a sober and austere person, he also had a capacity for humour and gaiety which delighted his companions, and which endeared him to his students. M y undergraduate year composed a song about the faculty which was of noteworthy lewdness i n some cases: the verse about N . K. was a mild good humoured comment about his use of a windy equation to which I shall refer later. I shall never forget his telling me of his own involvement, when he was an undergraduate at Cambridge, i n a competition to see who could sit longest bare-bottomed on a block of ice. I had the good fortune to attend his lectures on surface chemistry during my freshman year at University College London, i n 1929. Questioning the validity of some data resulted i n an invitation to spend the Summer of 1930 i n his laboratory. This splendid opportunity resulted i n my working for my doctoral thesis under his guidance, with occasional help from G . S. Hartley. One of the first principles of research he instilled in me was that, when one's experimental findings are not quite those 1

Goddard; Monolayers Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

MONOLAYERS

2


(ZOO

SOO

2

4 F

6 d y n e s per c m .

8

to

"The Physics and Chemistry of Surfaces"

Figure 1.

Behaviour

of the diesters of aa> dibasic esters (1)

anticipated, the proper course is not to minimise, but to maximise, the discrepancies, because by so doing new discoveries are made. This opportunity to work under his guidance enabled me to appreciate his excellence i n the laboratory. As can be seen by looking at the first edition of his book "The Physics and Chemistry of Surfaces", his initial endeavour as a surface chemist was to survey the range of phenomena exhibited by monolayers, using the surface balance which George Jessop and he invented. These results he then endeavoured to explain i n terms of the molecular structures of the substances concerned. One of the tools he found useful was the evidence on the shapes and sizes of organic molecules made available by Lawrence Bragg's X-ray diffraction data. This was reflected i n a chapter on X-ray diffraction studies which was included i n the first edition. B y the time the second edition was prepared


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DANiELLi

Reminiscences

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X-ray diffraction methods were very well known and the chapter could be omitted. The first paper on the film balance was published from Cambridge. Soon thereafter he moved to the Department of Chemistry at University College London, the head of which was F . G . Donnan, of "Donnan Equilibrium" fame. Here he enjoyed a period of intensive research, in good company, always with several research students.

The results he obtained with the film balance confirmed and greatly extended the results obtained by Langmuir. Several of the more inter esting sets of data are set out in Figures 1-5. Figure 1 shows the behaviour of the diesters of αω dibasic esters. These molecules he supposed would lie flat at the air—water interface, and, therefore, there would be little lateral cohesion between molecules. Thus, he argued that the molecules should obey the gas equation: FA

=

RT.

This equation was received with joy and hilarity by successive genera-


4

MONOLAYERS


r j Temperature

7·*·

.5

30

35

4

0

.

er molecule

4

*

A

55

A


Figure 3.

Behaviour of myristic acid at different temperatures

(1)

tions of ribald students, and eventually was written as: FA

= kT,

which diminished the noise levels i n his lectures. As can be seen from Figure 1, at infinite dilution the value of FA does tend closely to the value of 400 postulated for a perfect gas. In Figure 2 is shown the data for molecules which have only one polar area, at one end of a hydrocarbon chain. In monolayers of such molecules the chains lie more or less perpendicular to the plane of the surface, with a cross-sectional area primarily determined b y the non-polar chain, secondarily modified by the nature of the polar groups. Such films are coherent liquids or solids when the chain length is sufficiently great. W i t h shorter chains he found interesting transitions. Figure 3 shows the behaviour of myristic acid [ C H ( C H ) i 2 C O O H ] at different temperatures; these films consist of two phases, one stable at low surface pressure, and one at high pressure, with a transition region. A t very low pressures these films approximate to a gaseous state, as shown in Figure 4. The behaviour of molecules i n monolayers shown i n Figures 3 and 4 involved the existence of coherent phases in which the area per molecule was much greater 3

2



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than the minimum cross-section of a hydrocarbon chain. H e , therefore, called these "expanded films". Their nature has interested many surface chemists since Adam's studies were made: yet no very satisfactory theory of these films has yet emerged. The general conclusion, which emerged from these studies, was that, for substances containing one polar group, at sufficiently low temperature and sufficiently high surface pressure, condensed films were formed i n which the cross-sectional area per molecule agreed well with that pre dicted from molecular models and from X-ray diffraction data. Molecules with two polar groups, spaced widely apart formed gaseous films. Thus, the principle emerged from these early studies that, provided the physical state of a film was understood, approximate molecular cross-sectional areas could be obtained from monolayer data. When I became one of N . K.'s research students, he suggested that a study of steroids should be made. H e had made a few preliminary studies, finding that monolayers of cholesterol and a few other steroids were stable and suitable for serious study. This was an interesting period

Ο

Figure

500

4.

looo

Myristic

1500 1000 1500 3000 3500 4000 4500 Areas per molecule Sq.A "The Physics and Chemistry of Surfaces"

acid films approximating pressure (1)

a gaseous state at very low


6

MONOLAYERS


in steroid chemistry. The structure of the hydrocarbon nucleus was i n dispute. Work on the structure of vitamin D indicated a close relationship of this substance to the steroids. In the work we did on sterols, we used the principles outlined above to find molecular cross-sectional areas (see Figure 5 ). This enabled us to confirm one of several proposed structures


Figure 5.

Molecular

cross-sectional areas of sterols ( 1 )

for the steroid nucleus, and to show that the orientation of steroids in films was a function of the position of the polar groups. A t this point we examined films of oestrogens, then recently isolated but of unknown struc ture. Figure 6 shows typical results obtained with oestrogens i n mono layers. From results such as these we were able to measure the dimensions of the oestrogens, and show that they were probably steroids. Simultane ously J. D . Bernai made X-ray diffraction studies on the same molecules, and came to the same conclusions. Ν. K. was a generous supervisor, ensuring that his students received recognition for their achievements. Work with him involved a good deal of fun. One unforgettable incident arose when he was asked to look into the blocking of ships' salt-water circulation pipes by growth of mussels,



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Adam

etc. within the pipes. Several tins of mussels attached to pipes, well sealed, were stored i n his laboratory for some months. Finally, he got around to opening one. The stench which emerged emptied the top floor of the laboratory. The last occasion on which I worked with h i m was i n 1936, when he was asked by the Royal Society to study oil pollution, already a menance to sea birds. Tar on the beaches could conveniently be studied by exam ining the feet and bottoms of holiday makers. But oil on the water re quired more strenuous exercise. Ν. K . persuaded me to row him round Plymouth bay and Plymouth harbour: whilst I got the exercise, he was very contentedly measuring the surface tension of the water! In 1937, Ν. K . moved to the University College of Southampton, and his subse quent work is reviewed in the article by M . C. Phillips in this volume. The work done by Adam & Langmuir on monolayers has had many repercussions. Not least was that it was from these two great men that I drew the concepts which enabled me to develop the basic principles of cell membrane structure in the 1930's. These defined cell membranes has having a lipid bilayer as their continuous phase, sandwiched between two protein layers, and penetrated by hydrophobic proteins. There are now some thousands of biologists studying these membranes, and the source of concepts remains in the work of Adam and Langmuir. I wish we knew as much about the protein components as we do about the lipids. Looking back on the last sixty years of monolayer studies, the greatest impact was made by Langmuir and Adam. Langmuir's grasp of the

.„

.„

100 130 160 190 220

Area per molecule, sq. A "The Physics and Chemistry of Surfaces'

Figure 6.

Typical

results obtained with oestrogens in monolayers


(1)


8

MONOLAYERS

properties of matter led to development of necessary theory. Adam's precision in experimentation revealed the boundaries of monolayer studies and provided reliable data which set standards in the field. A d a m was not comfortable with theory, and relied upon others, particularly Hartley and Guggenheim, in evaluating theory. Though in general a tolerant and kindly person, he was intolerant of humbug and was of great intellectual honesty. To his close associates his intellectual honesty was perhaps the most valued of his attributes. Only a fool tried to put anything over on Ν. K . A l l of us knew that, asked to read a draft paper, he would examine it with the keenest eye, and what passed his eye would pass any editor. H e set a high ethical standard, shared his knowledge, and was incapable of the rather shady practices shown i n e.g. "The Double Helix". I do not pretend that he was devoid of human weaknesses. When tired or overworked, he was often reluctant to consider new ideas. But in my experience, Ν. K . was one of the easiest men to get along with, given intellectual honesty. H e was never concerned to prove something—rather to find out whether it was right or wrong. One of the principles he instilled into his students was not to gloss over deviations from expected results. Rather to find out how to magnify the deviations, since this is the way new discoveries are made. I wish he were still with us. Literature Cited 1. A d a m , Ν. K . , " T h e Physics and Chemistry of Surfaces," T h e Clarendon Press, Oxford, E n g l a n d , 1930. RECEIVED January 24,

1975.


Reminiscences of N. K. Adam

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