Hi Frank
I mean that, in my opinion, the term "enthalpic interaction" is not appropriate to describe the hydrophobic effect, since the latter is mainly driven by changes in the (system) entropy, not enthalpy. Table1 of the cited paper reports the thermodynamic functions for transferring some nonpolar solutes from a few organic solvents to water. The author says that: "The data collected in Table 1 clearly show that the thermodynamic barrier to the solution process is entropic rather than enthalpic". Also, after a brief description of two theoretical models (the cavity-based model and the clathrate cage model) the author states: "It is important to point out that both the cavity-based model and the clathrate cage model rest upon the fact that the hydrophobic effect is entropy, not enthalpy driven. The models differ only in how they explain the source of the entropy loss." Best Stefano Le 2018-09-19 14:41, Frank von Delft a écrit : > Hi Stefano - could you elaborate? > > Certainly the medicinal chemists go on a great deal about how deltaH balances > deltaS and how it's bloody hard to know what is what even when you try to > measure it. Which is what that abstract also goes on about. > > On 19/09/2018 10:54, Stefano Trapani wrote: > > Le 2018-09-19 11:59, Frank von Delft a écrit : > > I believe medicinal chemists do indeed talk about "enthalpic interactions". > Frank > > Not a good choice either (à mon avis ...) > > > > THE REAL REASON WHY OIL AND WATER DON'T MIX > > Todd P. Silverstein > Journal of Chemical Education 1998 _75_ (1), 116 > > DOI: 10.1021/ed075p116 > > https://pubs.acs.org/doi/abs/10.1021/ed075p116 [2] > > Stefano > > On 19/09/2018 10:40, Stefano Trapani wrote: > > Le 2018-09-18 19:31, Daniel M. Himmel, Ph. D. a écrit : > > (where hydrophobic interactions result from van der Waals forces in an > aqueous environment). > > Hi > > I am not sure that, if one is to give a concise definition of hydrophobic > "interactions", this would be a convenient one, because it may lead someone > to identify vdW forces as the main factor that maintains apolar aggregated > molecules together in aqueous environment. I have seen many students (and > PhD's) believing to the equality: hydrophobic 'forces'=vdW forces (and not > understanding, for example, that the side chains of a Ser and an Ile can also > establish vdW interactions). > > It is true that apolar groups that aggregate establish van der Waals > interactions (like any molecule in contact with another one) but these > microscopic (real) forces are not (as far as I know) the main reason of > aggregation in aqueous environment. > > The hydrophobic effect seem to be of a mainly entropic nature (and it has > much more to do with hydrogen bonds than van der Waals forces): > > https://en.wikipedia.org/wiki/Hydrophobic_effect#Cause [3] > > https://en.wikipedia.org/wiki/Entropic_force#Hydrophobic_force [4] > > Being mainly of an entropic nature, hydrophobic "contacts" are not the direct > result of real microscopic "forces" that act between apolar groups. The terms > "forces" and "interactions" in widely used expressions like "hydrophobic > forces" and "hydrophobic interactions" are somehow misleading. > > Best > > --- > Stefano Trapani > > Maître de Conférences > http://www.cbs.cnrs.fr/index.php/fr/personnel?PERS=Stefano%20Trapani [1] > ------------------------------------- > Centre de Biochimie Structurale (CBS) > 29 rue de Navacelles > 34090 MONTPELLIER Cedex, France > > Tel : +33 (0)4 67 41 77 29 > Fax : +33 (0)4 67 41 79 13 > ------------------------------------- > Université de Montpellier > CNRS UMR 5048 > INSERM UMR 1054 > ------------------------------------- > > -- > This message has been scanned for viruses and > dangerous content by MAILSCANNER [5], and is > believed to be clean. > > ------------------------- > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 [6] -- This message has been scanned for viruses and dangerous content by MAILSCANNER [5], and is believed to be clean. -- This message has been scanned for viruses and dangerous content by MAILSCANNER [5], and is believed to be clean. -- This message has been scanned for viruses and dangerous content by MAILSCANNER [5], and is believed to be clean. Links: ------ [1] http://www.cbs.cnrs.fr/index.php/fr/personnel?PERS=Stefano%20Trapani [2] https://pubs.acs.org/doi/abs/10.1021/ed075p116 [3] https://en.wikipedia.org/wiki/Hydrophobic_effect#Cause [4] https://en.wikipedia.org/wiki/Entropic_force#Hydrophobic_force [5] http://www.mailscanner.info/ [6] https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1
