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Hans Kuhn (chemist)

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Hans Kuhn
Hans Kuhn in 1975

Hans Kuhn (born 5 December 1919) is a Swiss chemist. He is professor emeritus for physical chemistry and former scientific director at the Max Planck Institute for Biophysical Chemistry (Karl Friedrich Bonhoeffer Institute) in Goettingen.[1]

Biography

Curriculum

Hans Kuhn was born in Berne, Switzerland. He studied chemistry at the ETH Zürich and at the University of Basel at which he did the doctorate under the guidance of Werner Kuhn (not related) and received his habilitation in 1946. In 1947, he worked as a postal doctoral fellow with Linus Pauling at Caltech in Pasadena and in 1950 with Niels Bohr in Copenhagen.


In 1951, he became professor at the University of Basel. As a professor and director of the Institute of Physical Chemistry he was appointed in 1953 to the Philipps University of Marburg. At the Max Planck Institute for Biophysical Chemistry in Goettingen he was from 1971 to 1984 director of the department 'Molecular Systems Assembly'.

Fritz Peter Schäfer, Peter Fromherz, Horst-Dieter Försterling, Viola Vogel and Dietmar Möbius were among Hans Kuhn's students. Erwin Neher was member in his department 'Molecular Systems Assembly'.

Hans Kuhn got married to Elsi Hättenschwiler 1948. Their four children are Elisabeth, Andreas, Eva and Christoph. Elsi died 2004.

Scientific Research

Hans Kuhn began to work for his doctorate by investigating decoiling of a random coiled chain molecule in a flowing viscous solvent. Werner Kuhn suggested him to replace the random coil by a dumbbell-model. Hans Kuhn was fascinated by the model's simplicity and by its great success in theoretically analyzing a broad variety of experiments in quantitative terms. This experience and his postdoctoral work with Linus Pauling and Niels Bohr, supported this fascination for powerful simple models and was determining for his life's work in research.[2]

Polymer molecules were described as chains of statistical chain elements. [3] The preferential statistical elements were defined in 1943.[4] Today the preferental element is called Kuhn length, in the recent textbook Principles of Physical Chemistry it is simply called statistical chain element.[5] Hans Kuhn made expriments with macroscopic models of random coils to describe the behavior in flowing liquids more accurately than based on the dumbbell-model.[6]

Polyene: potential energy (atomic troughs neglected) and π-electron density. a) Instability of equal bonds. b) Stabilized by alternation of single and double bonds (bondlength consistent with π-electron density (BCD)-approximation).

Hans Kuhn developed the electron gas model leading to a quantitative theoretical understanding of the light absorption of organic dyes later called free electron model (FEMO).[7] In Pauling's lab Hans Kuhn was trying to understand the color of polyenes by describing π-electrons as particles in a box and he was greatly disappointed - it did not work. Later, when applying the model to cyanine dyes he observed a quantitative agreement with experiment. He saw the reason why he had failed in polyenes: an instability when assuming equal bonds leads to an alternation between single- and double-bonds. This followed from the agreement between measured and theoretically predicted absorption spectra.[8] Later it was justified by determining the condition for self-consistency between assumed bond lengths and corresponding theoretical π-electron density distribution.[9] The box-model and its improvements developed into a theory on the light absorption of organic dyes.[10] The effect of a lattice distortion in one dimension was considered with periodic Bloch wave functions used in Solid-state physics and later called Peierls instability.[11][12] The particular properties of conducting polymers are based on the theoretical relation between bond alternation and equalization. In Marburg Hans Kuhn developed (shortly before the age of digital computers) with Fritz Peter Schäfer an analogue computer to solve the 2-dimensional Schrödinger equation.[13] This room-filling analogue computer was applied by Kuhn's research group to calculate bond lengths in π-electron systems.[14][15][16][17][18][19]


Separating and contacting (from a to b and from b to c) in atomic precision. Monolayer of a blue fluorescent dye (donor) on a glass slide partially covered by a monolayer of a red fluorescent dye (acceptor) fixed at a PVA-polymer layer. Energy transfer from donor to acceptor at contact. Courtesy Dietmar Möbius. Reproduced with permission, Wiley-VCH Verlag.[20]
(a) Modeling emergence of first replicating strand (oligomer R). (b)Very particular location on the prebiotioc planet. Arrow: small region, very particular cyclic change of temperature and many other special conditions given by chance just here. (c) Evolution of increasingly complex self-reproducing forms by populating increasingly unfavorable regions.

In the beginning of the 1960ies Hans Kuhn saw a new paradigm in chemistry: the synthesis of single molecules which fit structurally into each other in such a way that they form functional units (supramolecular machines).[21][22][23] His research group constructed simple prototypes of supramolecular functional units by advancements of the Langmuir–Blodgett films which are known today under the name Langmuir–Blodgett-Kuhn-films (LBK-films) or Langmuir–Blodgett-Kuhn-(LBK)-layers. The many different techniques to manipulate systems of monolayers were developed in close cooperation of Hans Kuhn and Dietmar Möbius. Thus the layers should be called Langmuir–Blodgett-Möbius-Kuhn -(LBMK)-layers.

In close correspondance to the objective of constructing supramolecular functional units he (now at the Max Planck Institute for Biophysical Chemistry in Goettingen) approached theoretically the origin of life: modelling a hypothetical chain of many small physical-chemical steps which are a priori in harmony with thermodynamics that leads to the biological machine. Some steps are of partcular significance, such as the step initiating the transition from a multiplcation and translation apparatus into a multiplcation, transcription and translation apparatus.[24][25][26][27][28][29] This genetic apparatus agrees in the basic structure and in the mechanism with the biological multiplication and translation apparatus. The skill of the experimentalist building supramolecular machines is replaced in life's origin by very particular conditions given by chance in a very particular location on the prebiotic earth or elsewhere in the universe.

The unifying paradigm has led to construct supramolecular machines and to invent a pathway leading to the genetic apparatus. This required thinking in terms of strongly simplifying theoretical models describing complex situations. The variety of methods that had to be developed caused a divergence - supramolecular chemistry, molecular electronics, systems chemistry, nano-technology. Future research will be based on integrating these topics. Having in mind this coherence is stimulating and will be useful. In Hans Kuhn's view these topics should be included in a modern textbook on physical chemistry.

During his retirement Hans Kuhn developed (with his son Christoph and with Horst Dieter Försterling) his early work on π-electron density (a precursor of the Density functional theory (DFT)) to a very useful approximation called BCD method (bondlength consistent with total π-electron density method) and contributed in understanding Photosynthesis of Purple bacteria , the proton pump of Halobacterium, and the ATP synthase motor.[5]

Honours and awards

The items of this list are accessible [30].

Bibliography

  • The Electron Gas Theory of the Color of Natural and Artificial Dyes. by Hans Kuhn in Progress in the Chemistry of Organic Natural Products ed. Laszlo Zechmeister 16, 169 (1958) and ibid. 17, 404 (1959).
  • Praxis der Physikalischen Chemie. Grundlagen, Methoden, Experimente by Horst-Dieter Försterling and Hans Kuhn, 3rd Edition, Wiley-VCH, Weinheim (1991) (ISBN 3-527-28293-9).
  • Monolayer assemblies. In Investigations of Surfaces and Interfaces by Hans Kuhn and Dietmar Möbius in Physical Methods of Chemistry Series eds. Bryant William Rossiter and Roger C. Baetzold, Part B, Chapter 6, Vol. 9B, 2nd Edition, Wiley, New York (1993).
  • Principles of Physical Chemistry by Hans Kuhn, Horst-Dieter Försterling and David H. Waldeck, 2nd Edition, Wiley, Hoboken (2009) (ISBN 978-0-470-08964-4)

References

  1. ^ http://www.mpibpc.mpg.de/inform/25years/History.html History of the Max Planck Institut for Biophysical Chemistry in Goettingen.
  2. ^ H. Kuhn: Fascination in Modeling Motifs, Chapter 6 in R. Jaenicke and G. Semanza (Eds.) Selected Topics in History of Biochemistry: Personal Recollections VI (Comprehensive Biochemistry Vol 41) Elsevier Science 2000.
  3. ^ W. Kuhn: Ueber die Gestalt fadenförmiger Moleküle in Lösungen Kolloid Zeitschrift 68:2 (1934).
  4. ^ W. Kuhn and H. Kuhn: Die Frage nach der Aufrollung von Fadenmolekülen in strömenden Lösungen Helv. Chim. Acta 26:1394 (1943).
  5. ^ a b Principles of Physical Chemistry by Hans Kuhn, Horst-Dieter Försterling and David H. Waldeck, 2nd Edition, Wiley, Hoboken (2009).
  6. ^ H. Kuhn: Viscosity, sedimentation, and diffusion of long-chain molecules in solution as determined by experiments on large scale models. J. Colloid Sci. 5:331 (1950).
  7. ^ H. Kuhn: Elektronengasmodell zur quantitativen Deutung der Lichtabsorption von organischen Farbstoffen J. Helv. Chim. Acta 31:1441 (1948).
  8. ^ H. Kuhn: A quantum mechanical theory of light absorption of organic dyes and similar compound J. Chem. Phys. 17:1198 (1949).
  9. ^ name=Egm> F. Bär, W. Huber, G. Handschig, H. Martin and H. Kuhn: "Nature of the free electron gas model. The case of the polyenes and polyacetylenes." J. Chem. Phys. 32, 470 (1960).
  10. ^ H. Kuhn: Neuere Untersuchungen über das Elektronengasmodell organischer Farbstoffe. Werner Kuhn, Basel, zum 60. Geburtstag gewidmet. Angew. Chem. 71:93–101 (1958).
  11. ^ R. E. Peierls: Zur Theorie der elektrischen und thermischen Leitfähigkeit von Metallen Ann. Phys. 4:121-148 (1930).
  12. ^ R. E. Peierls: Quantum theory of solids Clarendon, Oxford (1955).
  13. ^ F.P. Schäfer: "Analogrechner und Registrierautomat zur Ermittlung der stationären Wellenfunktionen und Energieniveaus eines Teilchens in einem zweidimensionalen Potentialfeld", Dissertation Marburg (1960).
  14. ^ H. Kuhn: Analogiebetrachtungen und Analogrechner zur quantenmechanischen Behandlung der Lichtabsorption der Farbstoffe Chimia 15:53-62 (1961)
  15. ^ F. F. Seelig, W. Huber, H. Kuhn: Analogiebetrachtungen und Analogrechner zur Behandlung der Korrelation von π-Elektronen Zeitschrift für Naturforschung 17a:114–121 (1962).
  16. ^ H.D. Försterling, W. Huber and H. Kuhn: Projected electron density method of π-electron systems I. Electron distribution in the ground state. Int. J. Quant. Chem. 1, 225 (1967).
  17. ^ H.D. Försterling and H. Kuhn: "Projected electron density method of π-electron systems II. Excited states." Int. J. Quant. Chem. 2, 413 (1968).
  18. ^ H. Kuhn, W. Huber, G. Handschig, H. Martin, F. Schäfer, and F. Bär: "Nature of the Free Electron Model. The Simple Case of the Symmetric Polymethines." J. Chem. Phys., 32, 467 (1960)
  19. ^ Cite error: The named reference Egm was invoked but never defined (see the help page).
  20. ^ D. Möbius: "Manipulieren in molekularen Dimensionen" Chemie in unserer Zeit 9:173-182 (1975).
  21. ^ H. Kuhn: "Versuche zur Herstellung einfacher organisierter Systeme von Molekülen" Verhandlungen der Schweizerischen Naturforschenden Gesellschaft, 245–66 (1965)
  22. ^ H. Bücher, K.H. Drexhage, M. Fleck, H. Kuhn, D. Möbius, F.P. Schäfer, J. Sondermann, W. Sperling, P. Tillmann and J. Wiegand: "Controlled transfer of excitation energy through thin layers", Molecular Crystals 2:199 (1967)
  23. ^ H. Kuhn, D. Möbius: "Systems of monomolecular layers-assembling and physico-chemical properties" Angew. Chem. Int. Ed. Engl, 10:620–37 (1971).
  24. ^ H. Kuhn: "Self-organization of molecular systems and evolution of the genetic apparatus", Angew. Chem. Int. Ed. Engl. 11:798–820 (1972)
  25. ^ H. Kuhn: "Model consideration for the origin of life. Environmental structure as stimulus for the evolution of chemical systems", Naturwissenschaften 63:68–80 (1976)
  26. ^ H. Kuhn, J. Waser: "Molecular self-organization and the origin of life", Angew. Chem. Int. Ed. Engl. Edit. 20:500–20 (1981).
  27. ^ H. Kuhn, J. Waser: "A model of the origin of life and perspectives in supramolecular engineering" in: J.-P.Behr (editor): "Lock-and-key principle", Chichester: Wiley 247–306 (1994)
  28. ^ H. Kuhn, C. Kuhn: "Diversified world: drive of life's origin?!", Angew. Chem. Int Ed. Engl. 42:262–6 (2003)
  29. ^ H. Kuhn: "Origin of life — Symmetry breaking in the universe: Emergence of homochirality" Current Opinion in Colloid & Interface Science 13:3–11 (2008).
  30. ^ http://www.phys-chem.com/design/Hans_Kuhn's_Honours.jpg items of awards

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