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Author Topic: Calcium to phosphate bonds  (Read 4370 times)

Offline Simon

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Calcium to phosphate bonds
« on: 03/11/2004 10:52:45 »
Hi, great site you've got here. Just a quick question:

 If I have a calcium 2+ in a protein's active site, and an oxygen from a phophate ion completing the calcium's coordination sphere, would I expect the angle between the calcium/oxygen/phosphorous to be about 109 degrees? Seems my memory of undergraduate chemistry is not as good as it should be!

Simon


 

Offline Ylide

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Re: Calcium to phosphate bonds
« Reply #1 on: 04/11/2004 07:53:07 »
Bond angles from VSEPR theory only apply to covalent bonds.  Calcium binds phosphate ionically, which is non-directional, i.e. no specific angle there.





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Offline Simon

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Re: Calcium to phosphate bonds
« Reply #2 on: 04/11/2004 11:03:02 »
Thanks for your reply. Do you know why this might be? My logic tells me that lone pair electrons will generally try to stay away from each other even when being strongly attracted by a positive charge, and hence one might expect to see at least a compromise! If there is fairly good directionality with hydrogen bonds to carbonyl oxygens, possibly due to the sp2 hybridisation of the oxygen, is there any rhyme or reason in more delocalised species?

Simon
 

Offline Ylide

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Re: Calcium to phosphate bonds
« Reply #3 on: 04/11/2004 16:42:34 »
Ionic species are not sharing obitals in the way that covalents ones are.  The attraction is solely from coulomb forces.  Since there are no orbitals to orient the atoms, there is no directionality.  

The atoms will of course try to assume a position of lower energy, but that is not to say that there is only one position that is the lowest overall energy, as in covalent bonds.  



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Offline Simon

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Re: Calcium to phosphate bonds
« Reply #4 on: 05/11/2004 17:26:12 »
Do the d orbitals of phosphorous have any effect on where the electrons end up?

Simon
 

Offline Ylide

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Re: Calcium to phosphate bonds
« Reply #5 on: 06/11/2004 09:46:48 »
I'm not sure what you mean...which electrons?  The electrons of a particular energy level will move about the space represented by their orbitals...

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Offline Simon

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Re: Calcium to phosphate bonds
« Reply #6 on: 09/11/2004 20:21:58 »
quote:
Originally posted by Ylide

I'm not sure what you mean...which electrons?  The electrons of a particular energy level will move about the space represented by their orbitals...



 I was just wondering if the position of the electrons in the d orbitals of the phosphorus atom would in any way force the electrons in the oxygens away from the phosphorus/oxygen bond and hence localise the charge on the other side of the oxygen atoms.

Simon
 

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Re: Calcium to phosphate bonds
« Reply #6 on: 09/11/2004 20:21:58 »

 

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