HISTORICAL REVIEW

1820

J.-B. Biot and F. Savart collaborated on the theory of magnetism. Their eponymous law (formulated in 1820) describes the motion of a charge in a magnetic field.

1872

Ernst Abbe formulated his wave theory of microscopic imaging. In 1878, he was able to correlate resolution and wavelength of light mathematically. A few years later, through the company Zeiss, he commercialized the first ever lenses to have been designed based on sound optical theory and the laws of physics.

1873

In the second half of the nineteenth century, J. C. Maxwell established the laws of electromagnetism. His equations first appeared in fully developed form in his book Electricity and Magnetism (1873).

1897

J. J. Thomson discovered electrons by demonstrating cathode rays were actually units of electrical current made up of negatively charged particles of subatomic size. For these investigations, he won the Nobel Prize for physics in 1906.

1924

In his doctoral thesis, de Broglie theorized that matter has the properties of both particles and waves. He received the 1929 Nobel Prize for physics. The particle–wave duality was confirmed experimentally for the electron a few years later by C. J. Davisson and L. H. Germer, and by G. P. Thomson. Thomson and Davisson jointly shared the Nobel Prize in physics in 1937.

1926

H. Busch described a lens to focus electrons. H. Ruska subsequently built the first working electron microscope in 1930 (Nobel Prize in 1986). Ruska's 1931 paper contains for the first time the term “electron microscopy.” The principle behind this type of microscope has not varied significantly since.

1932

Fritz Zernike invented the phase-contrast light microscope, which uses a quarter-wave plate. He was awarded the 1953 Nobel Prize for physics for this work, which opened up the study of transparent biological materials. The feasibility of a scanning electron microscope was demonstrated by Knoll in 1935, and the first prototype was built by M. Van Ardenne three years later. By the late 1930s, electron micrographs of recognizable value to biologists were being published. In 1942, S. E. Luria obtained the first high-quality electron micrograph of a bacteriophage.

1940s

The negative staining technique came into extensive use in the 1940s, although it was only in 1955 that C. E. Hall recognized, and deliberately used, phosphotungstic acid as a negative stain. In 1959, S. J. Singer used ferritin-coupled antibodies to detect cellular molecules.

HISTORICAL REVIEW

1897

J. J. Thomson made the first measurement of the mass-to-charge ratio of elementary particle “corpuscles,” which later became known as electrons. This can fairly be considered as the birth of mass spectrometry.

1918–1919

A. Dempster and F. Aston developed the first mass spectrographs. Photographic plate was used as the array detector. The instruments were used for isotopic relative abundance measurements.

1951

W. Pauli and H. Steinwedel described the development of a quadrupole mass spectrometer. The application of superimposed radio-frequency and constant potentials between four parallel rods acted as a mass separator in which only ions within a particular mass range perform oscillations of constant amplitude and are collected at the far end of the analyzer.

1959

K. Biemann was the first to apply electron ionization mass spectrometry to the analysis of peptides. Later it was shown that for sequence determination, peptides had to be derivatized prior to analysis by a direct probe.

1968–1970

M. Dole was the first to bring synthetic and natural polymers into the gas phase at atmospheric pressure. This was done by spraying a sample solution from a small tube into a strong electric field in the presence of a flow of warm nitrogen, to assist desolvation. First experiments on lysozyme demonstrated the phenomenon of multiple charging.

1974

D. Torgerson introduced plasma desorption mass spectrometry. This technique uses 252Cf fission fragments to desorb large molecules from a target. It was the first of the particle-induced desorption methods to demonstrate that gas-phase molecular ions of proteins could be produced from a solid matrix.

1974

B. Mamyrin made the most important contribution to the development of time-of-flight (TOF) mass spectrometry. He constructed the so-called reflectron device, which had been proposed by S. Alikanov in 1957. The reflectron essentially improves mass resolution in the TOF mass spectrometer.

1978

N. Commisarow and A. Marshall adapted Fourier transform methods to ion cyclotron resonance spectrometry and built the first Fourier transform mass instrument. Since that time, interest in this technique has increased exponentially, as has the number of instruments.

HISTORICAL REVIEW

The discovery of biological macromolecules is tightly interwoven with the history of physical chemistry, which formally emerged as a discipline in 1887, when the journal founded by Jacobus Van't Hoff and Wilhelm Ostwald, Zeitschrift für Physikalische Chemie, was first published. Interestingly, the first papers were concerned with reactions in solution, because biological processes essentially take place in the aqueous environment inside living cells.

The nineteenth-century discoveries of solution properties that led to our knowledge about biological macromolecules are described briefly in the Introduction. We must also mention the Grenoble chemist François-Marie Raoult (1886), who formulated the freezing-point depression law that made it possible to determine the molecular weight of dissolved substances, and Hans Hofmeister (1895), a medical doctor and physiologist who was interested in the diuretic and laxative effects of salts, and classified them according to how they modified the solubility of protein in aqueous solutions. The Hofmeister series was later established as a ranking order of the “salting-out,” or precipitating, efficiency of ions. Gilbert Newton Lewis introduced the concepts of activity in 1908, and of ionic strength, with Merle Randall in 1921. In 1911, Frederick George Donnan published a paper on the membrane potential developed during dialysis of a non-permeating electrolyte. Peter Debye and Erich Hückel (1923) proposed a theory for electrolyte solutions. In recent decades, modern methods, such as dynamic light scattering and small-angle neutron scattering, developed for the characterization of polymers, and especially polyelectrolytes, have contributed significantly to our current understanding of biological macromolecules in solution.

There is now a growing interest in the behavior of proteins in non-aqueous solvents and even in vacuum, mainly in the context of biotechnology, but also with respect to whether or not water is essential to life. Proteins, as active biological particles, have evolved in the presence of water, however, and, to a large extent, cannot be considered separately from their aqueous environment. We recall that even crystals of biological macromolecules contain an appreciable amount of solvent and should be considered as organized macromolecular solutions.

HISTORICAL REVIEW

1924

W. Pauli proposed the theoretical basis for NMR spectroscopy. He suggested that certain atomic nuclei have properties of spin and magnetic moment and, as a consequence, exposure to a magnetic field leads to splitting of their energy levels. W. Gerlach and O. Stern observed the splitting in atomic beam experiments, providing proof for the existence of nuclear magnetic moments.

1938

I. I. Rabi and colleagues first observed NMR by applying electromagnetic radiation in atomic beam experiments. Energy was absorbed at a sharply defined frequency, causing a small but measurable deflection of the beam. Rabi received the Nobel Prize for physics in 1944.

1946

Research groups led by F. Bloch and E. M. Purcell reported the observation of proton NMR in liquid water and solid paraffin wax. Bloch and Purcell shared the 1953 Nobel Prize for physics.

1946

F. Bloch suggested a new method of excitation using a short radio-frequency pulse and in 1949 E. L. Hahn showed that this did indeed produce a free precession signal. Hahn also established that pulse sequences could be used to generate additional information in the form of a spin echo. For many years, however, these methods were of little use to chemists because of the complexity of the signal obtained. In 1956, I. J. Lowe and R. E. Norberg pointed out that the time-domain signal and the frequency-domain spectrum are related by Fourier transformation. The first high-resolution multichannel Fourier transform NMR spectrum was measured by R. R. Ernst and W. A. Anderson.

1950

W. G. Proctor and F. C. Yu observed two unexpected 14N resonance frequencies for NH4NO3. At about the same time, W. C. Dickinson noticed similar effects for 19F in several compounds. In 1951, J. T. Arnold and colleagues introduced the term chemical shift following the observation of several resonance peaks for 1H in ethanol, with the relative intensity in each peak corresponding to the relative number of protons in each chemical environment.

1951

H. S. Gutowsky and D. W. McCall suggested that interactions between spins of neighboring nuclei were responsible for multiple resonance lines. In 1951, N. F. Ramsey and E. M. Purcell proposed the concept of indirect spin–spin coupling or scalar coupling. It was found that in certain cases spin coupling failed to produce the expected multiplets, leading to the development of the concept of chemical exchange.