リボフラビン

外観

赤黄色, 結晶性粉末～粉末

定義

本品は、ビタミンB2であり、次の化学式で表される。

溶解性

水に難溶。エタノール, エーテルに殆ど不溶。アルカリに可溶。水に極めて溶けにくく、エタノールにほとんど溶けない。

解説

7,8-dimethyl-10-D-ribitylisoalloxazine．C17H20N4O6(376.37)．ビタミン B2 ともいう．動物の成長促進因子．現在は2-アミノ-4,5-ジメチル-1-リビチルアミノベンゼンとアロキサンとの縮合により生産されている．黄色の結晶性粉末．分解点280 ℃．[α]²⁵_D－112°(0.1 mol L－1 水酸化ナトリウム)，－122°(水)．λmax 220～225，267，374，475 nm(0.1 mol L－1 塩酸)．pK1 3.57，pK2 9.50(35 ℃)．熱に対して安定であるが，紫外線により強い緑色の蛍光を発して不可逆的に分解し，アルカリ性ではルミフラビンに，中性や酸性ではルミクロムになる．水溶液は黄緑色の蛍光を発し，還元すると無色のロイコフラビンになり，空気にさらして酸化するとふたたびフラビンに戻る．リボフラビンは，アミノ酸オキシダーゼ，NADHデヒドロゲナーゼ，キサンチンオキシダーゼなどでFADまたはFMNの形で補酵素として機能し，細胞呼吸，水素および電子伝達に重要な作用をしている．この欠乏症としては，口唇の障害，口角炎，顔面の局所性脂漏性皮膚炎，特殊な舌炎，眼球機能障害などがある．[CAS 83-88-5]
森北出版「化学辞典（第2版）

用途

光学分割剤。

健康への影響

ビタミンB複合体に含まれる耐熱性の成長促進因子で、ビタミンB2の別名。ビタミンGともよばれた。黄褐色の結晶で、水にわずかに溶け、光により分解する。牛乳、肝臓、卵黄のほか、酵母や米糠(こめぬか)に多く含まれる。牛乳中の蛍光物質として19世紀末にすでに知られていた。1933年、ドイツの生化学者R・クーンが結晶分離してフラビンと命名し、同じころO・H・ワールブルクは酵母の黄色呼吸酵素の配合団として同一物質を取り出した。生化学的には2種のフラビン補酵素、すなわちフラビンモノヌクレオチド（FMN）とフラビンアデニンヌクレオチド（FAD）の構成成分として重要である。いずれもフラビン酵素の補酵素として多くの酸化還元反応系に関与する。還元状態では無色、酸化されると黄色となる。細菌、カビ、植物はリボフラビンを合成できるが、動物はできず、したがってビタミンとして摂取する必要があり、ヒトでは1日1.5～2.5ミリグラムとされる。欠乏症は皮膚炎、発育不良、口角炎、舌や目などの異常であり、ネズミでの実験的欠乏症では成長の停止、視力や神経系の障害、生殖能力の喪失がみられる。工業的には微生物の培地から精製され、また化学合成によっても得られる。ラクトフラビン、オボフラビン、ヘパトフラビンなどとよばれたものは、すべてリボフラビンと同一物質である。

化粧品の成分用途

皮膚コンディショニング剤

効能

ビタミンB2補充薬

説明

A water-soluble B fraction was found in the 1920s to contain a yellow, fluorescent growth factor called riboflavin in England and vitamin G in the United States. In the early 1930s, several groups found the coenzyme forms of riboflavin 50-phosphate (flavin mononucleotide) and the further conjugate with adenylic acid (flavin adenine dinucleotide).

化学的特性

VITAMIN B2 (Riboflavin). Some earlier designations for this substance included vitamin G, lactoflavin, hepatoflavin, ovoflavin, verdoflavin. The chemical name is 6,7-dimethyl-9-d-l’ribityl isolloxazine. Riboflavin is a complex pigment with a green fluorescence.

物理的性質

Riboflavin is moderately soluble in water (10–13 mg/dl) and ethanol but insoluble in ether, chloroform, and acetone. It is soluble but unstable under alkaline conditions.
The catalytic functions of riboflavin are carried out primarily at positions N-1, N-5, and C-4 of the isoalloxazine nucleus. In addition, the methyl group at C-8 participates in covalent bonding with enzyme proteins. The flavin coenzymes are highly versatile redox cofactors because they can participate in either one- or two electron redox reactions
Riboflavin antagonists include analogs of the isoalloxazine ring (e.g., diethylri boflavin, dichlororiboflavin) and the ribityl side chain (e.g., d-araboflavin, d-galactoflavin, 7-ethylriboflavin).

使用

riboflavin (Vitamin B2) is used in skin care preparations as an emollient. It can be found in sun care products as a suntan enhancer. Medicinally, it is used for the treatment of skin lesions.

定義

ChEBI: D-Ribitol in which the hydroxy group at position 5 is substituted by a 7,8-dimethyl-2,4-dioxo-3,4-dihydrobenzo[g]pteridin-10(2H)-yl moiety. It is a nutritional factor found in milk, eggs, malted barley, liver, kidney, heart, and leafy vege ables, but the richest natural source is yeast. The free form occurs only in the retina of the eye, in whey, and in urine; its principal forms in tissues and cells are as flavin mononucleotide and flavin-adenine dinucleotide.

一般的な説明

The conflicting results were eventually found to be due,in part, to deficiencies in study animals not just of vitamin B₂,but also vitamin B₃ (niacin), the cause of human forms of pellagra,and/or vitamin B₆ (pyridoxine), another cause of dermatitis.Likewise, treatments with vitamin B₂ were inconsistentbecause the early sources of this vitamin contained otherB vitamins. Vitamin B₂ was eventually isolated from eggwhites in 1933 and produced synthetically in 1935. Thename riboflavine was officially accepted in 1960; althoughthe term was in common use before then. In 1966, IUPACchanged it to riboflavin, which is in common use today.Riboflavin is synthesized by all green plants and by mostbacteria and fungi. Therefore, riboflavin is found, at least insmall amounts, in most foods. Foods that are naturally highin riboflavin include milk and other dairy products, meat,eggs, fatty fish, and dark green vegetables.
Chemically, riboflavin is an N-glycoside of flavin, alsoknown as lumichrome, and the sugar, ribitol .Flavin is derived from the Latin word flavus for “yellow”because of the yellow color of its crystals and yellow fluorescenceunder UV light. Riboflavin is heat stable but easilydegraded by light. Its systematic names are 7,8-dimethyl-10-ribitylisoalloxazine and 7,8-dimethyl-10-(D-ribo-2,3,4,5-tetrahydroxypentyl)isoalloxazine.

臨床応用

Severe riboflavin deficiency is known as ariboflavinosis, andtreatment or prevention of this condition is the only provenuse of riboflavin. Ariboflavinosis is most commonly associatedwith multiple vitamin deficiency as a result of alcoholismin developed countries. Because of the large numberof enzymes requiring riboflavin as a coenzyme, deficienciescan lead to a wide range of abnormalities. In adults seborrheicdermatitis, photophobia, peripheral neuropathy, anemia, andoropharyngeal changes including angular stomatitis, glossitis,and cheilosis, are often the first signs of riboflavin deficiency.In children, cessation of growth can also occur. As the deficiencyprogresses, more severe pathologies develop untildeath ensues. Riboflavin deficiency may also produce teratogeniceffects and alter iron handling leading to anemia.

安全性プロファイル

Poison by intravenous route. Moderately toxic by intraperitoneal and subcutaneous routes. Mutation data reported. When heated to decomposition it emits toxic fumes of NOx.

環境運命予測

Physicochemical Properties
Riboflavin has the appearance of a yellow to orange amorphous solid and imparts an orange color to the B vitamin tablets. Riboflavin has a melting point of 290°C, a density of 1.65, and a refractive index of 135°. The pKa is 9.888 and log P is 0.095. Riboflavin has solubility in water of 0.1 g l^-1.
Exposure Routes and Pathways
The route of exposure is oral. Dietary sources of riboflavin and its coenzymes include broccoli, spinach, asparagus, enriched flour, yeast, eggs, milk, cheese, mackerel, trout, poultry, liver, and kidneys.
Toxicokinetics
Riboflavin, which is only moderately water soluble, is absorbed from the gastrointestinal tract but is limited to about 27 mg at any one time from an oral dose given to an adult. Hence, mega doses would not be expected to increase significantly the total amount absorbed. It is hepatically metabolized, protein bound, and widely distributed to tissue; however, little is stored in the liver, spleen, heart, and kidneys. Riboflavin is excreted renally as metabolites, which have been oxidatively cleaved in the ribityl side chain and converted to hydroxymethyls in the ring methyl functions. Riboflavin in excess of daily body needs is excreted unchanged in the urine. Riboflavin exhibits biphasic pharmacokinetics with initial and terminal half-lives of 1.4 and 14 h, respectively.

純化方法

It crystallises from H2O as a yellow-orange powder in three different forms with differing amounts of H2O. It melts if placed in an oil bath at 250o, but decomposes at 280o if heated at a rate of 5o/minute. It is also purified by crystallisation from 2M acetic acid, then extracted with CHCl3 to remove lumichrome impurity. [Smith & Metzler J Am Chem Soc 85 3285 1963.] Its solubility in H2O is 1g in 3-15L depending on the crystal structure. Its solubility in EtOH at 25o is 4.5mg in 100mL. Store it in the dark because it is decomposed to lumichrome by UV light. [Pearson The Vitamins vol V pp1-96 1967 and vol VII pp 1-96 1972, Gy.gy and Pearson eds, Academic Press, Beilstein 26 IV 2542.]