Søren Peder Lauritz Sørensen life and biography

Søren Peder Lauritz Sørensen (9 January 1868 - 12 February 1939), a Danish biochemist, suggested a convenient way of expressing acidity – the negative logarithm of hydrogen ion concentration (pH). Soren Peter Lauritz Sorensen, a Danish biochemist, is the man who established the concept of pH, defining it as pH = -log[H+]. He was born in Havrevjerg near Slaglese in Denmark as as son of an owner farmer (Soren’s father – Hans Sorensen and Soren’s mother – Kirstine Katrine Sorensen)

Soren Peter Lauritz Sorensen first began to study medicine at the University of Copenhagen, but soon moved to chemistry. He graduated from the University of Copenhagen in 1881, and for following ten years he worked on inorganic syntheses under Prof. S.M. Jorgensen (1837-1914) at the Technical University of Denmark in Copenhagen. Sorensen obtained his Ph.D. in 1899.
Soren Peter Lauritz Sorensen was maried with Anna Louise Willumsen on 18 November 1892 and they had four children: Inge Sorensen, Viggo Sorensen, Arthur Sorensen, Annelise Sorensen.
Sorensen’s work and life were connected with Carlsberg Laboratory in Copenhagen. J.C. Jacobsen (1811-1887), the founder of the Carlsberg Brewery in Copenhagen, established the Carlsberg Laboratory in 1876. Professor J. Kjeldahl (1849-1900) became the first head of the Chemical Department of the Laboratory and worked until his tragic death in July 1900. Professor. S.P.L. Sorensen was invited as the successor of Prof. J. Kjeldahl in 1901. It was at this laboratory that Prof. Sorensen carried out numerous pioneering works by his elaborate experimental technique in the field of biochemistry.
While at the Carlsberg Laboratories, Sorensen started to study amino acids, proteins and enzymes. In earlier stage his researches are categorized in the following four domains: (1) electrometric method of determining hydrogen ion concentration, (2) preparation of pH buffer solutions, (3) colorimetric method of measuring pH, and (4) application of these procedures to study on enzymes and proteins. The results in these fields by his group were summarized in amino acids and protein.
Their brilliant achievements were published in 17 reports from the Laboratory. Some of these became a classic work in the real sense of the word and continued materials for many papers, i.e., serving as a foundation of protein chemistry.
It is noted that he studied on coagulation of proteins on heating and then succeeded in crystallizing the protein egg alubumin by ammonium sulphate precipitation (1936). The Carlsberg Laboratory became renowned as one of the world’s most productive centers of study in the field of biochemistry, attracting many chemists all over the world. Sorensen subsequently became a leader in the application of thermodynamics to proteins chemistry, and in this work he was assisted by his second wife, Margrethe Hoyrup Sorensen.
Because hydrogen ion concentration played a key role in enzymatic reactions he devised a simple way of expressing it. By taking a negative logarithm of hydrogen ion concentration a convenient scale can be established; this is the well-known pH value. Numerical values based on this unit, now universally in use, give an indication of the acidity of solutions. He also developed buffer solutions to maintain constant pH of solutions (Sorensen buffers).

Historical background for pH:
In the late 1880’s, Svante Arrhenius proposed that acids were substances that delivered hydrogen ion to the solution. He has also pointed out that the law of mass action could be applied to ionic reactions, such as an acid dissociating into hydrogen ion and a negatively charged anion. This idea was followed up by Wilhelm Ostwald, who calculated the dissociation constants (the modern symbol is Ka) of many weak acids.
Ostwald also showed that the value of the constant is measure of an acid’s strength. By 1894, the dissociation constant of water (today called Kw) was measured to the modern value of 1×10-14. In 1904, H. Friedenthal recommended that the hydrogen ion concentration be used to characterize solutions. He also pointed out that alkaline (modern word = basic) solutions could also be characterized this way since the hydroxyl concentration was always (1×10-14 / the hydrogen ion concentration). Many consider this to be the real introduction of the pH scale.
The context for the introduction of pH was the slow changeover from the old color-change tests for indicating the degree of acidity or basicity to electrical methods. In the latter, the current generated in an electrochemical cell by ions migrating to oppositely charged electrodes was measured, using a highly sensitive (and delicate) galvanometer. Until Sorensen developed the pH scale, there was no widely accepted way of expressing hydrogen ion concentrations.
His scale removes the awkward negative power for hydrogen ion concentrations that range over orders of magnitude: from about ~12 M at the high end to ~10-15 M at the low end. Instead Sorensen suggested that the power could be represented by a pH scale in which 7 is neutral, and 1 and 14 are the extremes of acidity and alkalinity, respectively.

pH introduced into the science:
The pH scale was quickly accepted by the biochemical research community in their studies of the facinating ability of living tissues to “buffer” against excessive acidity or alkalinity. Largely due to the German medical chemist Leonor Michaelis (1875-1949), who published a book on hydrogen ion concentration in 1914, wider community of chemists finally adopted the pH scale. The use of pH became even more widespread in 1935 when Arnold Beckman (b. 1900) developed and sold a simple portable direct-reading pH meter.
The letters pH are an abbreviate for “pondus hydrogenii” (translated as potential hydrogen) meaning hydrogen power as acidity is caused by a predominance of hydrogen ions (H+). Dr. Sorensen has been credited as the founder of the modern pH concept.
In Sorensen ’s original paper, pH is written as PH. According to the Compact Oxford English Dictionary, the modern notation “pH” was first adopted in 1920 by Leland Clark (inventor of the Clark oxygen electrode) for typographical convenience. “p-Functions” have also been adopted for other concentrations and concentration-related numbers. For example, “pCa = 5.0″ means a concentration of calcium ions equal to 10-5 M, and pKa = 4.0 means an acid dissociation constant equal to 10-4.

Sorensen retired from the post of the director of the chemical section of Carlsberg Laboratories in 1938. Professor Sorensen, gifted with rare talent as a chemist with a fervent hope for progress of human welfare and peace, passed away peacefully on Feburary 12, 1939, Charlottenlund, Denmark.

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