The School of Biomedical Sciences Wiki - User contributions [en]

Buffer

2018-11-24T04:26:23Z

180658035:

By definition, a buffer is a substance (usually a weak acid and its conjugate base) which is added to a sample to avoid changes in its ph. An example of a buffer would be an amino acid as it has a carboxyl group and an amine group. The name for this type of buffer with both a positive ion and negative ion in its molecule is called a zwitter ion. A buffer must contain the chemical species for “neutralizing” added amounts of [[Acid|acid]] or [[Base|base]]. For example, if a buffer was a solution of a [[Weak acid|weak acid]] and its conjugate [[Base|base]] it would contain [[Acetic acid|acetic acid]] and [[Sodium acetate|sodium acetate]] or a [[Weak base|weak base]] and conjugate acid it would contain [[Ammonia|ammonia]] and [[Ammonium chloride|ammonium chloride]]. If there is a lot of acid or alkali added then the buffer will not be able to cope with such a change and will no longer able to maintain the pH.

Buffers are most effective in the range [[PH]] = pK’a ± 1. Outside the range the [[Concentration|concentration]] of either the [[Acid|acid]] or the conjugate [[Base|base]] is too small to effectively resist the effect of added [[Hydrogen|hydrogen]] or [[Hydroxide|hydroxide]] [[Ion|ions]].

== '''Examples of buffers that are found in the blood<ref>Lawrie Ryan and Roger Norris. Cambridge International AS and A Level Chemistry Coursebook. 2nd ed. In: Chapter 21: Further aspects of equilibria, page 315. United Kingdom: University Printing House, Cambridge CB2 8BS.</ref>''' ==

*Hydrogencarbonate ions, HCO3-  
*Haemoglobin and plasma proteins
*Dihydrogenphosphate (H2PO4-) and hydrogenphosphate (HPO42-) ion.

 

 

=== References ===

<references />

Buffer

2018-11-24T04:14:22Z

180658035:

By definition, a buffer is a substance (usually a weak acid and its conjugate base) which is added to a sample to avoid changes in its ph. An example of a buffer would be an amino acid as it has a carboxyl group and an amine group. The name for this type of buffer with both a positive ion and negative ion in its molecule is called a zwitter ion. A buffer must contain the chemical species for “neutralizing” added amounts of [[Acid|acid]] or [[Base|base]]. For example, if a buffer was a solution of a [[Weak acid|weak acid]] and its conjugate [[Base|base]] it would contain [[Acetic acid|acetic acid]] and [[Sodium acetate|sodium acetate]] or a [[Weak base|weak base]] and conjugate acid it would contain [[Ammonia|ammonia]] and [[Ammonium chloride|ammonium chloride]]. If there is a lot of acid or alkali added then the buffer will not be able to cope with such a change and will no longer able to maintain the pH.

Buffers are most effective in the range [[PH]] = pK’a ± 1. Outside the range the [[Concentration|concentration]] of either the [[Acid|acid]] or the conjugate [[Base|base]] is too small to effectively resist the effect of added [[Hydrogen|hydrogen]] or [[Hydroxide|hydroxide]] [[Ion|ions]].

== '''Examples of buffers that are found in the blood<ref>SlideShare. Buffer in the blood. 2013 [cited 24/11/2018]; Available from: https://www.slideshare.net/tohapras/buffer-in-the-blood</ref>''' ==

*Hydrogencarbonate ions, HCO3-  
*Haemoglobin and plasma proteins
*Dihydrogenphosphate (H2PO4-) and hydrogenphosphate (HPO42-) ion.

 

 

=== References ===

<references />

Sterioisomers

2018-11-24T03:18:01Z

180658035:

Stereoisomers are [[Molecules|molecules]] that have the same [[Molecular formula|molecular formula]], but have a different [[Spatial arrangement|spatial arrangement]]. This means that they are arranged differently in space, despite the fact the [[Atom|atoms]] are bonded in the same order. In order for this to occur, the molecule must contain a [[Carbon|carbon]] that is bonded to four different groups, This is called a [[Chiral centre|chiral centre]], or an [[Asymetric carbon|asymmetric carbon]]. Sterioisomers can be divided into further groups according to the specific spatial arrangements. 

== Enantiomers ==

[[Enantiomers|Enantiomers]] are stereoisomers that are non-superimposable mirror images of each other. They are usually described as having [[D isomer|D]] or [[L isomer|L]] configuration. Often one configuration exists more frequently in nature, for example the L form of most [[Amino acid|amino acids]] is more prominant in nature, possibly because they are slightly more soluble than the D form. You can differentiate between the two forms by investigating the direction in which they rotate polarised light. 

== Diastereoisomers ==

Molecules that have multiple asymmetric carbons are called [[Diastereoisomers|diastereoisomers]]. These are not mirror images of each other. A common example is a [[Monosaccharide|monosaccharide]] that has a carbon chain of three or more, such as [[Glucose|glucose]]. The number of possible stereoisomers is equal to 2n, where n is the number of asymmetric carbons in the molecule. There are two further types of diastereoisomers - [[Epimers|epimers]] and [[Anomers|anomers]]. Epimers are two diastereoisomers that differ at only one of the multiple asymmetric carbons, whereas anomers are cyclic molecules that differ at a new asymmetric carbon that is formed as a result of the ring formation. E-Z or cis-trans isomerism is another type of diastereoisomers, resulting from the restricted rotation around a [[Double bond|double bond]] <ref>Biochemistry, 7th Edition, Jeremy M. Berg, John L. Tymoczko, Lubert Stryer, W. H. Freeman and Company, New York, 2012, chapter 11- page 331, chapter 2 - page 27.</ref>.  

=== References ===

<references />