A caveat: I have come into this mid-thread and am not the original author. I
couldn't help but try to straighten out some of this funky chemistry.
In article <3f0dvs$4eh at nof.abdn.ac.uk>, opt018 at nof.abdn.ac.uk (opt018) writes:
> Hao Xiao (haoxiao at cc.UManitoba.CA) wrote:
> : Four major forces are involved.
>> : London disperse forces: like moon (Ag) and earth (Ab), can not be too close
hmmm... This implies that gravity is involved Ag-Ab complexes. A simple
description is probably more illustrative. When non-polar molecules like for
example a molecule of He are bumping around with other molecules, the protons
can momentarily be attracted to another He atoms electrons. This creates a
momentary dipole. Some nonpolar molecules like NH3 can actually have permanent
dipoles or charge separations. It is this electrostatic attraction that
results in bonding. The gravitional force is more than a billion times weaker
than this interaction and would be negligable in an ag-ab complex
>>> : Hydrophorbic force: act like your ruber sticker on the glass wall. you squeeze
Hydrophobic force is a peculiar attaction based on the principle of "Like
likes Like" The above example is actually electrostatic attraction. Glass has a
net - charge and rubber an effective net positive charge since it is an
insulator. In fact this example will not work underwater as a ag-ab complex
can be envisioned as occuring.
A better example is the idea of mixing oil with water. A protein
molecule has "oily" parts and "watery" parts all along the same polymer. The
"oily" (hydrophobic) parts of the ag will tend to stick near the oily parts of
the antibody and the "watery" (hydrophilic) parts likewise
>> : Hydrogen and ionic bonding: act like your magnet sticker. Such forces
Hydrogen bonding is an extreme case of ionic bonding. It is what gives water
its remarkable properties and is classifies as a force in its own right.
Electrostatic interactions are much weaker but still quite strong. These are
cases where one molecule has a strong charge and the other a strong charge of
the opposite polarity but cannot either a)abstract the electron or b) force a
covalent bond where the electrons are shared by both molecules.
> -----
>> Nice explainations.
...hmmm
>> ----
>> Question 1: Can London disperse force and Hydrophorbic force coexist in the same
> Ag/Ab complex pair?
Absolutely! Ag-Ab complexes rely on all four of these interactions. One alone
would probably not be enough to overcome the jostling of random thermal motion.
>> Question 2: You mentioned that you can increase the affinity by slightly
> increase the Ag size, simply because 'more water molecules are squeezed out'.
> Does this contradict the fact that Ab only recognize a certain fragment of Ag
> specifically, no matter how big the Ag size is?
Nope. By increasing any one of the forces, in this case hydrophobicity, you
can make the ag stick even better to the antibody.
>> Question 3: What is the forth major force? :-)
Hydrophobic and electrostatic count as two differnt forces in this situation.
>>> Thanks a lot.
>>>> --------------------
>> Yours
>> Y-F D. Cheng, MB ChB
> Dept Ophthalmology
> Univ Aberdeen
> UK
>> <opt018 at aberdeen.ac.uk>
> <http://www.abdn.ac.uk/~opt018/cheng.html>
Allen Black
Dept. of Pathology
Univ. of Newcastle
mdcabl at cc.newcastle.edu.au
