Monthly Archives: March 2015

Assignment 18 March 2015

In Canada, major sources of SOx mostly come from non-ferrous smelters, then coal-fired generators. Major source of NOx is motor vehicles. Half of East Canada’s wet sulphate deposition come from US whereas 10% of wet sulphate deposition in North-Eastern US come from Canada. Acid rain has affected Canada’s ecology and water quality.

In the UK, the country is a considerable emitter of acidic pollution compared to other countries. Most UK SO2 come from power stations and other industries whereas the largest source of NOx is road transport.

In Europe, during the 1970s and 1980s, with the use of tall chimneys in industry and power generation increasing, acid deposition became a particularly prevalent problem. It is found that the amounts of SO2 and NO being emitted are different from acidic pollution deposited. Some countries were emitting small quantities of pollutants yet deposition was observed to be several times greater.

Implications of Stereoisomerism in Drugs to Society

Introduction

Stereochemistry may seem like a trivial subject because there are no major differences between stereoisomers. In nature however, especially in the biological system like a human body, these minor changes may have severe consequences.

Explanation

In society, many drugs are composed of a single stereoisomer of a compound, and while one stereoisomer may have positive effects on the body, another stereoisomer may be toxic. Due to this, one of the key roles of organic chemists consists of synthesizing compounds consisting of a single stereoisomer.

In some instances, toxicity has been linked to one member of a pair of isomers. This pair need not be the active isomer for the substance to be toxic. For example, granulocytopenia is related to the d-isomer of levodopa and vomiting is caused by the d-isomer of levamisole.

Shown below is another example – the binding of Ibuprofen, a common pain reliever. While one stereoisomer of the compound has the right three-dimensional shape to bind to the protein receptor, the other does not and can not bind, and is therefore ineffective as a pain reliever.

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One of the most common examples of the impact of stereochemistry cites back to the thalidomide disaster. Thalidomide is a pharmaceutical drug, first prepared in 1957 in Germany, prescribed for treating morning sickness in pregnant women. The drug was discovered to be teratogenic (able to disturb the growth and development of an embryo or fetus), causing serious genetic damage to early embryonic growth and development, leading to limb deformities in babies. In the human body however, thalidomide undergoes racemization: even if only one of the two enantiomers is administered as a drug, the other enantiomer is produced as a result of metabolism. Thus, it would be incorrect to state that one of the stereoisomer is safe while the other is teratogenic. Thalidomide is currently used for the treatment of other diseases, notably cancer and leprosy. Strict regulations and controls have been enabled to avoid its use by pregnant women and prevent developmental deformations. This disaster was a driving force behind requiring strict testing of drugs before making them available to the public.

Therefore, the importance of stereochemistry in biological systems extends to more than just drugs and medicines. The human body, for example, can only create and digest carbohydrates and amino acids of a certain stereochemistry. Thus, all of our proteins that make up our hair, skin, organs, brain, and tissues, are composed of a single stereoisomer of amino acids. Moreover, our bodies can make and digest starch (found in potatoes and bread) but not cellulose (found in wood and plant fibers), even though both are just polymers of glucose of different stereochemistry.

References:

http://www.chemhelper.com/biostereo.html

http://en.wikipedia.org/wiki/Stereochemistry

The Chemical Concept of Stereoisomers

Introduction

Isomerism in a chemical compound is the existence of different arrangements of atoms with the same chemical formula. There are 2 kinds of isomerism:

Structural Isomerism, where isomers of different structures arise from

  • Different position of carbon chains
  • Different position of functional groups
  • Different functional groups

Stereoisomerism, where isomers have the same structure and sequence of atoms, but different spatial arrangement. There are 2 kinds of stereoisomers:

  • Geometric isomers are centered about a C=C bond. These are also known as cis-trans isomers
  • Optical Isomers are centered about chiral carbon.

Our team will focus on stereoisomerism(in particular, optical isomerism) and how it can change the effects of drugs.

Explanation

A chiral molecule is centered about a chiral carbon that has 4 different functional groups attached to it and cannot be superimposed with its mirror image. The concept is similar to how our left and right hands are mirror images of each other but not superimposable. Two mirror images of such a molecule are known as enantiomers, and a mixture containing equal amounts of both enantiomers is known as a racemic mixture.

Enantiomers are often named by R/S system. To name enantiomers by the R/S system, the viewer needs to orientate the molecule such that the functional group with the lowest priority, according to the Cahn–Ingold–Prelog priority rules, is pointed away from the viewer. The R-enantiomer is the one with the priority of the remaining 3 functional groups decrease in a clockwise direction and the S-enantiomer is the one that decreases in an anti-clockwise direction.

The +/- system of naming is also often used, in reference to the direction in which the enantiomers rotate polarised light.

To appreciate how stereoisomerism affects drugs, we have to first consider that biological molecules often react with each other via the “lock-and-key” mechanism. As a result, if a molecule is able to fit another reactant molecule, its enantiomer may not due to a different 3-D spatial arrangement. This will lead to the enantiomer being an inactive compound or a compound that reacts differently.

References

Stereochemistry in Drug Action, Jonathan McConathy, Ph.D. and Michael J. Owens, Ph.D. Link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC353039/

Unit 8 Lecture Slides 48-49.

Meeting Minutes 15 Mar 2015

Virtual Location: Google Docs 

Time and duration: 4pm, 2 hours

Team members who attended and members who missed the meeting with clarification on their reasons for missing it.

Attended:

Andrew Fung

Jaslyn

Andrew Teng

Andreas dwi putra

Ardyanto widjojo

Anshuman subsequently followed up with tasks from 6-7pm

Topics discussed (briefly)

Chemical Concept

-Focus on optical isomers

Implications on Society

-Find examples of enantiomers in drugs that have different effects on the human body

Tasks to be done before the next meeting and who has been assigned/agreed on doing them.

Brainstorm on video

Problems arising if any

NIL

Plan of action

Chemical Concept and Implications to Society to be filled.

Meeting was adjourned.