chemical structure of L-Ascorbic acidAttack of ascorbic enol on proton to give 1,3-diketone
Find information on thousands of medical conditions and prescription drugs.

Ascorbic acid

Ascorbic acid is an organic acid with antioxidant properties. Its appearance is white to light yellow crystals or powder. It is water soluble. The L-enantiomer of ascorbic acid is commonly known as vitamin C. In 1937 the Nobel Prize for chemistry was awarded to Walter Haworth for his work in determining the structure of ascorbic acid (shared with Paul Karrer, who received his award for work on vitamins), and the prize for Physiology or medicine that year went to Albert Szent-Györgyi for his studies of the biological functions of L-ascorbic acid. more...

Home
Diseases
Medicines
A
8-Hour Bayer
Abacavir
Abamectin
Abarelix
Abciximab
Abelcet
Abilify
Abreva
Acamprosate
Acarbose
Accolate
Accoleit
Accupril
Accurbron
Accure
Accuretic
Accutane
Acebutolol
Aceclidine
Acepromazine
Acesulfame
Acetaminophen
Acetazolamide
Acetohexamide
Acetohexamide
Acetylcholine chloride
Acetylcysteine
Acetyldigitoxin
Aciclovir
Acihexal
Acilac
Aciphex
Acitretin
Actifed
Actigall
Actiq
Actisite
Actonel
Actos
Acular
Acyclovir
Adalat
Adapalene
Adderall
Adefovir
Adrafinil
Adriamycin
Adriamycin
Advicor
Advil
Aerobid
Aerolate
Afrinol
Aggrenox
Agomelatine
Agrylin
Airomir
Alanine
Alavert
Albendazole
Alcaine
Alclometasone
Aldomet
Aldosterone
Alesse
Aleve
Alfenta
Alfentanil
Alfuzosin
Alimta
Alkeran
Alkeran
Allegra
Allopurinol
Alora
Alosetron
Alpidem
Alprazolam
Altace
Alteplase
Alvircept sudotox
Amantadine
Amaryl
Ambien
Ambisome
Amfetamine
Amicar
Amifostine
Amikacin
Amiloride
Amineptine
Aminocaproic acid
Aminoglutethimide
Aminophenazone
Aminophylline
Amiodarone
Amisulpride
Amitraz
Amitriptyline
Amlodipine
Amobarbital
Amohexal
Amoxapine
Amoxicillin
Amoxil
Amphetamine
Amphotec
Amphotericin B
Ampicillin
Anafranil
Anagrelide
Anakinra
Anaprox
Anastrozole
Ancef
Android
Anexsia
Aniracetam
Antabuse
Antitussive
Antivert
Apidra
Apresoline
Aquaphyllin
Aquaphyllin
Aranesp
Aranesp
Arava
Arestin
Arestin
Argatroban
Argatroban
Argatroban
Argatroban
Arginine
Arginine
Aricept
Aricept
Arimidex
Arimidex
Aripiprazole
Aripiprazole
Arixtra
Arixtra
Artane
Artane
Artemether
Artemether
Artemisinin
Artemisinin
Artesunate
Artesunate
Arthrotec
Arthrotec
Asacol
Ascorbic acid
Asmalix
Aspartame
Aspartic acid
Aspirin
Astemizole
Atacand
Atarax
Atehexal
Atenolol
Ativan
Atorvastatin
Atosiban
Atovaquone
Atridox
Atropine
Atrovent
Augmentin
Aureomycin
Avandia
Avapro
Avinza
Avizafone
Avobenzone
Avodart
Axid
Axotal
Azacitidine
Azahexal
Azathioprine
Azelaic acid
Azimilide
Azithromycin
Azlocillin
Azmacort
Aztreonam
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z

Chemistry

Acidity


The hydroxyls (OH) next to the bottom double bond are enols. One enol loses an electron pair, becoming an oxonium group (=OH+), by creating a double bond to the carbon. Simultaneously, the carbon-carbon double bond (between the enols) transfers its electrons to form a double bond to the next (two-oxygen) carbon. To give way, the double bond electrons of the carbonyl are received by the carbonyl's oxygen, to produce an enolate. The oxonium promptly deprotonates to produce a carbonyl, and this loss of protons gives ascorbic acid its acidity. The overall reaction is enol deprotonation to produce an enolate, where the negative charge of the resulting enolate counterion is delocalized over the system of carbonyl (C=O) and the double bond (C=C). This delocalization makes the counterion more stable and less likely to regain the proton.

Tautomerism

Ascorbic acid also rapidly interconverts into two unstable diketone tautomers by proton transfer, although it is the most stable in the enol form. The proton of the enol is lost, and reacquired by electrons from the double bond, to produce a diketone. This is an enol reaction. There are two possible forms, 1,2-diketone and 1,3-diketone.

Uses

Ascorbic acid is easily oxidized and so is used as a reductant in photographic developer solutions (among others) and as a preservative.

Exposure to oxygen, metals, light and heat destroy ascorbic acid, so it must be stored in dark and cold and not in a metal containment.

The oxidized form of ascorbic acid is known as dehydroascorbic acid.

The L-enantiomer of ascorbic acid is also known as vitamin C (the name "ascorbic" comes from its property of preventing and curing scurvy). Primates (including humans) and a few other species in all divisions of the animal kingdom, notably the guinea pig, have lost the ability to synthesise vitamin C and must obtain it in their food.

Ascorbic acid and its sodium, potassium, and calcium salts are commonly used as antioxidant food additives. These compounds are water soluble and thus cannot protect fats from oxidation: for this purpose, the fat-soluble esters of ascorbic acid with long-chain fatty acids (ascorbyl palmitate or ascorbyl stearate) can be used as food antioxidants.

The relevant European food additive E numbers are: E300 ascorbic acid, E301 sodium ascorbate, E302 calcium ascorbate, E303 potassium ascorbate, E304 fatty acid esters of ascorbic acid (i) ascorbyl palmitate (ii) ascorbyl stearate.

Antioxidant mechanism

Ascorbate acts as an antioxidant by being itself available for energeticaly favourable oxidation. Oxidants (scientifically referred to as reactive oxygen species) such as the hydroxyl radical (formed from hydrogen peroxide), contain an unpaired electron and thus are highly reactive and damaging to humans and plants at the molecular level. This is due to their interaction with nucleic acid, proteins and lipids. Reactive oxygen species can 'abstract' a hydrogen from ascorbate, which becomes monodehydroascorbate and soon gains another electron to become dehydroascorbate. The reactive oxygen species are reduced to water while the oxidized forms of ascorbate are relatively stable and unreactive, and do not cause cellular damage.

Read more at Wikipedia.org


[List your site here Free!]


Supplement of a chitosan and ascorbic acid mixture for Crohn's disease. A pilot study - Author Abstract
From Alternative Medicine Review, 5/1/03 by T Tsujikawa

Tsujikawa T, Kanauchi O, Andoh A, et al. Nutrition 2003;19:137-139.

Although the pathogenesis of Crohn's disease remains unclear, dietary fat is thought to exacerbate intestinal inflammation. Chitosan is a water-insoluble dietary fiber, and a chitosan and ascorbic acid mixture has been shown in rats to increase fecal fat excretion without affecting protein digestibility. However, it remains unclear whether a chitosan and ascorbic acid mixture is safe and effective for patients with Crohn's disease. We designed a pilot trial to investigate the tolerability and amount of fat excretion alter the oral administration of a chitosan and ascorbic mixture for inactive Crohn's disease. Eleven outpatients were given seven tablets daily of a chitosan and ascorbic mixture (chitosan was given at 1.05 g/d) for 8 wk. Patients did not interrupt their respective therapies for Crohn's disease. The bowel movements of most patients increased slightly during the study. Nutritional and inflammatory markers in patients did not differ before and after treatment. The chitosan and ascorbic acid mixture significantly increased the fat concentration in the feces during treatment. These results indicated that oral administration of a chitosan and ascorbic acid mixture in patients with Crohn's disease is tolerable and increases fecal fat excretion without affecting disease activity.

COPYRIGHT 2003 Thorne Research Inc.
COPYRIGHT 2003 Gale Group

Return to Ascorbic acid
Home Contact Resources Exchange Links ebay