202 Biographical Memoirs With Higher School Certificate distinctions in physics and chemistry, and credits in pure and applied mathematics, Haydon proceeded to King’s College London, where he graduated in 1951 with First Class Honours in the B.Sc. chemistry course. The bulk of the teaching had not come up to Mr Price’s exceptional standards, and he found himself bored by organic chemistry, both at the university and at the ICI Dyestuffs Division, Blackley, where he spent six weeks engaged on a minor research project during one vacation. However, the lectures given by Professor (later Sir) Eric Rideal, F.R.S., were altogether different in quality. Rideal imparted very little useful information, and covered the blackboard several layers deep with equations of which he rarely gave both sides: his students used to photograph the board, and analyse it later. This highly stimulating course shifted Haydon’s attention decisively from organic to physical and surface chemistry, and settled the initial direction of his research.
Denis Arthur Haydon 203 it over as Plummer Professor of Biophysics in Cambridge, Haydon was moved to a new sub-department of Biophysics located in a wing of the Physiological Laboratory. In 1974 he was promoted to Reader in Surface and Membrane Biophysics, and in 1980 to an ad hominem Chair as Professor of Membrane Biophysics. He gave lectures in Part II of the Natural Sciences Tripos, on surface chemistry to the chemists, and on membrane biophysics to the physiologists and biochemists.
Denis Arthur Haydon 205 oceanography with biology at Southampton, and is studying for a Ph.D. in Texas on mathematical modelling of the food web; and Rosalind, who is reading history at York. Denis and Primrose agreed to separate in 1982, and the marriage was dissolved in 1986.
206 Biographical Memoirs that such an approach could be applied to unicellular organisms in order to characterize the charges on their surfaces, but except in the case of protons, where the dependence of mobility on pH had been examined, it had not so far been applied using other types of ion. Haydon therefore looked for a suitable system to work with, and decided on Escherichia , which could readily be cultured and subjected to electrophoresis.
Denis Arthur Haydon 207 The properties of lipid bilayers The background to Haydon’s long and important set of studies on the fundamental properties of lipid bilayers was that in the early 1960s, the question was constantly being raised as to whether or not the bilayer was a significant structural feature of a biological membrane. The available evidence was derived mainly from electron microscopy, and to outsiders and insiders alike the subject was bedeviled by controversy and problems of artefacts. After first writing a valuable theoretical paper with Janet Taylor (34) to set the stage, Haydon and his collaborators embarked on the task of verifying his speculations experimentally.
208 Biographical Memoirs In a paper of seminal importance (37) describing experiments performed in collaboration with Tetsuya Hanai and Janet Taylor, many of the basic questions were answered, and it was shown how the membrane thickness and structure could be deduced from measurements of electrical capacitance and resistance when combined with surface chemistry which Haydon described with his usual modesty as ‘straightforward’. The electrical capacity was a subject of particular interest, because of its close relationship to the thickness of the bilayer, and a series of papers by Haydon, Hanai and Taylor (49-52) were concerned with the factors that affected it. Their demonstration ‘at a rather trivial level’ that the capacity was proportional to area (51) was followed up by showing that the polar phosphatidylcholine groups did not contribute appreciably to the capacity at most frequencies, though for the lowest ones a correction of the order of 5% had to be applied. In collaboration with C.T. Everitt (58) the effect of the ionic double layer was considered, and it was found that only at ionic strengths less than about 1 mM would the double-layer capacity have any influence on the measured quantity. This was an important conclusion because it meant that all the rest of the capacity was related to the layer of hydrocarbon, and the system could be treated as a parallel plane condenser filled with hydrocarbon. All the hydrocarbons had dielectric constants falling within the narrow range of 1.9-2.1 and it was therefore possible to use capacity to obtain fairly accurate estimates of membrane thickness. When the amount of solvent was low, such estimates agreed well with those deduced from X-ray diffraction on liquid crystal stacks of the same phospholipid. The capacity measurements also yielded thicknesses in good agreement with the admittedly less reliable results of determining light reflectance. The whole question of membrane thickness and geometric parameters was re-examined in 1982 by Jim Dilger, Len Fisher and Haydon (125) in a critical review which remains the standard authority on the subject.