Riboflavin properties

Riboflavin forms fine yellow to orange-yeUow needles with a bitter taste from 2 N acetic acid, alcohol, water, or pyridine. It melts with decomposition at 278—279°C (darkens at ca 240°C). The solubihty of riboflavin in water is 10—13 mg/100 mL at 25—27.5°C, and in absolute ethanol 4.5 mg/100 mL at 27.5°C it is slightly soluble in amyl alcohol, cyclohexanol, benzyl alcohol, amyl acetate, and phenol, but insoluble in ether, chloroform, acetone, and benzene. It is very soluble in dilute alkah, but these solutions are unstable. Various polymorphic crystalline forms of riboflavin exhibit variations in physical properties. In aqueous nicotinamide solution at pH 5, solubihty increases from 0.1 to 2.5% as the nicotinamide concentration increases from 5 to 50% (9). 

Riboflavin is heat-stable in the absence of light, but extremely photosensitive. It has a high degree of natural fluorescence when excited by UV light. This property can be used for detection and determination. Two coenzymes (Fig. 2), flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), are derived from riboflavin. 

Table 4. Chemical structure and spectroscopical and photophysical properties of riboflavin (RF) in aqueous phosphate buffer pH 7.4 (Valle et al, 2011).

Another example of ACE analyses of solute-bilayer interactions was described by Roberts et al. (50), who observed retardation of riboflavin by liposomes. Analyses technically similar to liposomal ACE have been performed with mixed bile salt/phosphatidylcholine/fatty acid micelles (95). The partitioning of basic and acidic drugs depended on the acid-base properties of the drug and on the shape and charge of the mixed micelles. 

The 8a-modified flavins show some remarkable physical properties which differ from those of common flavins. Since these properties are very helpful in the identification of modified 8a-substituted flavocoenzymes originating from biological materials the physical properties are presented briefly here. Compared to riboflavin (Scheme 2, (7), R = H) the visible light absorption properties of (2) to... 

Another Japanese research group isolated two riboflavin derivatives from the culture filtrate of Schizophyllum commune and called these natural products Schizo-flavin 1 and 2 The physical and chemical properties of these compounds are... 

Riboflavin (vitamin B2) 6,7-dimethyl-9-(D-l-ribityl)isoalloxazine (63), was discovered as a coloring matter in milk in 1879, but its importance was not then realized. Deficiency causes lesions of the eye and of the angle of the mouth. Riboflavin is phosphorylated by adenosine triphosphate (ATP) to give riboflavin 5 -phosphate (flavinadenine mononucleotide, FMN) and then flavinadenine dinucleotide (FAD) (64 R = riboflavin). These function as prosthetic groups in a number of flavoproteins which are dehydrogenation catalysts by virtue of the oxidation-reduction properties of the isoalloxazine system. 

The attention of biochemists was first attracted to flavins as a result of their color and fluorescence. The study of spectral properties of flavins (Fig. 15-8) has been of importance in understanding these coenzymes. The biochemical role of the flavin coenzymes was first recognized through studies of the "old yellow enzyme"144 145 which was shown by Theorell to contain riboflavin 5 -phosphate. By 1938, FAD was recognized as the coenzyme of a different yellow protein, D-amino acid oxidase of kidney tissue. Like the pyridine nucleotides, the new flavin coenzymes were reduced by dithionite to nearly colorless dihydro forms (Figs. 15-7 and 15-8) revealing the chemical basis for their function as hydrogen carriers. 

P Nielsen, P Rauschenbach, A Bacher. Preparation, properties and separation by high-performance liquid chromatography of riboflavin phosphates. Methods Enzymol 122G 209-220, 1986. 

Riboflavin (vitamin I 2) is an important chemical species that occurs in many complex biologically related samples. The substance is chiral and strongly fluorescent and the coupling of these molecular properties into the FDCD-HPLC detection system greatly enhances both the specificity and the limit of detection capabilities of the method. In the specific case of riboflavin an HPLC system using FDCD detection where excitation is done at 325nm with a HeCd-laser a detection limit of 170 pg of riboflavin [30] is attainable. This level is about 10 times better than what is possible with a laser excitation -transmission CD-HPLC system [29]. 

Facilitated diffusion involves carrier-mediated transport down a concentration gradient. The existence of the carrier molecules means that diffusion down the concentration gradient is much greater than would be expected on the basis of the physicochemical properties of the drag. A much larger number of substances are believed to be transported by facilitated diffusion than active transport, including vitamins such as thiamine, nicotinic acid, riboflavin and vitamin B6, various sugars and amino acids. 

Chlorophyll studies of adducts with various biological molecules are also known (bovine plasma albumin and (3-carotene [195], quinone riboflavin [196], and NADH [173]. Mitsui et al. [196] have shown that in porphyrin complexes of viologen the counterion (I-, C1-, Br-) affects the electron transfer process by reduction of the electron-accepting properties of viol-... 

Rhodoapirillum rubrum succinate dehydrogenase of, 254-255 transhydrogenase of, 66, 69, 213 energy and, 73, 74 molecular properties, 69,71 preparation, 68 reconstitution and, 78 Riboflavin... 

A comparison of the photodynamic properties of H2(4-TRPyP) and its zinc metalated derivative, Zn(4-TRPyP) with the methylene blue and riboflavin photosensitizers also was carried out (240) using 2 -deoxyguanosine as a model compound (169, 241, 242). Riboflavin is a typical type 1 photosensitizer, while methylene blue exhibits a type If behavior. The selectivity measured by the ratio of the amount of photoproducts generated by type Il/type I mechanisms was 0.4 for riboflavin, and 2.3,3.6, and 5.6 for H2 TRPyP, methylene blue, andZn(4-TRPyP), respectively, showing that Zn(4-TRPyP) is the most specific type If photosensitizer of the series. 

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