Category Archives: Chemistry

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds.

Partition Coefficient

A new page has been added with some details on Kpc. Please go and read! Thanks =)

The page can also be accessible via the drop down menus above (under Applications – Analytical)

Please send any notes you wish to donate for publishing on this website to ravenslark@gmail.com

Maxim Yap
HoD Chemistry 2012

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Filed under Analytical Chemistry, Applications of Chemistry, Chemistry, Uncategorized

Molecule of the Month (November 2012) – Varenicline

Now students, it is not a secret. Many students abuse nicotine. If you wish to clear your life of it, now is the time! There are numerous ways, but here is one pharmacological way. There are risks however, so please read carefully. Nonetheless, ENJOY this post =)

Maxim Yap
HoD Chemistry 2012

From Wikipedia, the Free Encyclopedia

Varenicline (trade name Chantix in the USA and Champix in Canada, Europe and other countries, marketed by Pfizer, usually in the form of varenicline tartrate), is a prescription medication used to treat smoking addiction. Varenicline stimulates nicotine receptors more weakly than nicotine does, that is, it is a nicotinic receptor partial agonist. In this respect it is similar to cytisine and different from the nicotinic antagonist, bupropion, and nicotine replacement therapies (NRTs) like nicotine patches and nicotine gum. As a partial agonist it both reduces cravings for and decreases the pleasurable effects of cigarettes and other tobacco products. Through these mechanisms it can assist some patients to quit smoking.

Medical uses

Varenicline is indicated for smoking cessation. It is more effective than NRTs and nicotine agonists. In a 2006 randomized controlled trial sponsored by Pfizer, after one year the rate of continuous abstinence was 10% for placebo, 15% for bupropion and 23% for varenicline.In a 2009 meta-analysis of 101 studies funded by Pfizer, varenicline was found to be more effective than bupropion (odds ratio 1.40) and NRTs (odds ratio 1.56).

A Cochrane systematic review concluded that both varenicline and bupropion improved smoking cessation. More people quit with varenicline than with bupropion, but the difference was not statistically significant.

The FDA has approved its use for twelve weeks. If smoking cessation has been achieved it may be continued for another twelve weeks.

Varenicline has not been tested in those under 18 years old or pregnant women and therefore is not recommended for use by these groups.

Adverse effects

Nausea occurs commonly in people taking varenicline. Other less common side effects include headache, difficulty sleeping, and abnormal dreams. Rare side effects reported by people taking varenicline compared to placebo include change in taste, vomiting, abdominal pain, flatulence, and constipation. In a recent meta-analysis paper by Leung et al, it has been estimated that for every 5 subjects taking varenicline at maintenance doses (1mg twice daily), there will be an event of nausea, and for every 24 and 35 treated subjects, there will be an event of constipation and flatulence respectively. Gastrointestinal side-effects are important factors compromising the compliance of varenicline.

Depression and suicide

In November 2007, the FDA announced it had received post-marketing reports that patients using varenicline for smoking cessation had experienced several serious side-effects, including suicidal ideation and occasional suicidal behavior, erratic behavior, and drowsiness. On February 1, 2008 the FDA issued an alert to further clarify its findings, noting that “it appears increasingly likely that there is an association between Chantix and serious neuropsychiatric symptoms.” It is unknown whether the psychiatric symptoms are related to the drug or to nicotine withdrawal symptoms, although not all patients had stopped smoking. The FDA also recommended that health care professionals and patients watch for behavioral and mood changes.In May 2008, Pfizer updated the safety information associated with varenicline, noting that “some patients have reported changes in behavior, agitation, depressed mood, suicidal thoughts or actions.” While it is unclear whether or not a small subgroup of people develop depression and suicidal ideation as a result of varenicline or smoking cessation itself, there is evidence that varenicline, similar to nicotine, has antidepressant properties and the use of varenicline for smoking cessation leads to a reduced rate of initiation of antidepressant pharmacotherapy.

As of July 1, 2009, the US Food and Drug Administration requires Chantix (varenicline) to carry a black box warning, the agency’s strongest safety warning, due to public reports of side effects including depression, suicidal thoughts, and suicidal actions.

Cardiovascular disease

On June 16, 2011, the FDA issued a safety announcement that Chantix may be associated with “a small, increased risk of certain cardiovascular adverse events in patients who have cardiovascular disease.”

On July 4, 2011, four scientists published a review of double-blind studies in the Canadian Medical Association Journal. They found that varenicline has increased risk of serious adverse cardiovascular events compared with placebo.

Mechanism of action

Varenicline is a partial agonist of the α4β2 subtype of the nicotinic acetylcholine receptor. In addition it acts on α3β4 and weakly on α3β2 and α6-containing receptors. A full agonism was displayed on α7-receptors.

Acting as a partial agonist varenicline binds to, and partially stimulates, the α4β2 receptor without producing a full effect like nicotine. Thus varenicline does not greatly increase the downstream release of dopamine. Due to its competitive binding on these receptors, varenicline blocks the ability of nicotine to bind and stimulate the mesolimbic dopamine system, akin to the action of buprenorphine in the treatment of opioid addiction.

Varenicline also acts as an agonist at 5-HT3 receptors, which may contribute to mood altering effects of varenicline.

Pharmacokinetics

Most of the active compound is excreted renally (92–93%). A small proportion is glucuronidated, oxidated, N-formylated or conjugated to a hexose. The elimination half-life is about 24 hours.

History

Varenicline was discovered at Pfizer through the research aimed at modifying the structure of cytisine.

Varenicline received a “priority review” by the U.S. Food and Drug Administration (FDA) in February 2006, shortening the usual 10-month review period to 6 months because of its demonstrated effectiveness in clinical trials and perceived lack of safety issues. The agency’s approval of the drug came on May 11, 2006. August 1, 2006, varenicline was made available for sale in the United States and on September 29, 2006, was approved for sale in the European Union.

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Filed under Applications of Chemistry, Chemistry, Design and materials, General

Molecule of the Month (March) – Ibuprofen

From Wikipedia:

Ibuprofen (INN); from the nomenclature iso-butyl-propanoic-phenolic acid) is a nonsteroidal anti-inflammatory drug (NSAID) used for relief of symptoms of arthritis, fever, as an analgesic (pain reliever), especially where there is an inflammatory component, and dysmenorrhea.

Ibuprofen is known to have an antiplatelet effect, though it is relatively mild and somewhat short-lived when compared with aspirin or other better-known antiplatelet drugs. In general, ibuprofen also acts as a vasodilator, having been shown to dilate coronary arteries and some other blood vessels. Ibuprofen is a core medicine in the World Health Organization‘s “WHO Model List of Essential Medicines“, which is a list of minimum medical needs for a basic healthcare system.

Ibuprofen was derived from propionic acid by the research arm of Boots Group during the 1960s. It was discovered by Andrew RM Dunlop, with colleagues Stewart Adams, John Nicholson, Vonleigh Simmons, Jeff Wilson and Colin Burrows, and was patented in 1961. Originally marketed as Brufen, ibuprofen is available under a variety of popular trademarks, including Motrin, Nurofen, Advil, and Nuprin.

Chemical Structure of Ibuprofen

Athletes, the young, the old, the sick alike all use Ibuprofen. Can you recall the last time you were prescribed this chemical? Take care though… from personal experience, this drug, as well as most drugs… cause gastric discomfort 😦

Ibuprofen Tablets

Links:
http://en.wikipedia.org/wiki/Ibuprofen
http://www.chem.ox.ac.uk/mom/ibuprofen/ibuprofen.html

Maxim

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Filed under General, Organic Chemistry

Electrochemistry Revision & Reading

Below is an excerpt taken from RavenslarkChem Blogspot site. Echoes from the past will always return… but use them wisely, and you will succeed in the future!
_________________________
From April 11th, 2010

There isn’t much on chemguide about A2 Electrochemistry. You folks are going to have to depend quite heavily on my notes this time. There’s some on AS Electrochemistry on Chemguide, which includes Electrolysis of Brine

Basic pointers regarding the drawing of the experimental setup:
1) Standard Hydrogen Electrode (SHE) is always on the left in diagram
2) Sign of electrode potential as measured from voltmeter = charge of RHS electrode
3) Labeling of direction of flow of electrons is done ONLY on the voltmeter wire

Basic pointers regarding the construction of a cell diagram:
1) (-) on the left; (+) on the right
2) | to denote a boundary between electrode & electrolyte
3) // to denote the salt bridge
4) Either side of a cell diagram will be the solid electrodes
5) Electrons are lost on the left, and gained on the right

N.B. DO NOT CONFUSE THE Cell Diagram with the experimental setup diagram.

If anyone has good links for Electrochemistry A2 please feel free to post!

Update: So far, in class, we’ve gone through the cell diagrams / experimental setup for measuring the electrode potentials for Zn2+/Zn, Cu2+/Cu & Cl2/Cl half-cells.
The class will go home and research on the case for measuring the standard electrode potentials for Cr3+/Cr2+ & Fe3+/Fe2+ systems.

Update (14/4/2010): Pt(s)|Cr2+(aq),Cr3+(aq)//Fe3+(aq),Fe2+(aq)|Pt(s)
AND
Zn(s)|Zn2+(aq)//Cu2+(aq)|Pt(s)

Maxim

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