Vitamins absorption spectra

Fluorescent probes are divided in two categories, i.e., intrinsic and extrinsic probes. Tryptophan is the most widely used intrinsic probe. The absorption spectrum, centered at 280 nm, displays two overlapping absorbance transitions. In contrast, the fluorescence emission spectrum is broad and is characterized by a large Stokes shift, which varies with the polarity of the environment. The fluorescence emission peak is at about 350 nm in water but the peak shifts to about 315 nm in nonpolar media, such as within the hydrophobic core of folded proteins. Vitamin A, located in milk fat globules, may be used as an intrinsic probe to follow, for example, the changes of triglyceride physical state as a function of temperature [20]. Extrinsic probes are used to characterize molecular events when intrinsic fluorophores are absent or are so numerous that the interpretation of the data becomes ambiguous. Extrinsic probes may also be used to obtain additional or complementary information from a specific macromolecular domain or from an oil water interface. 

Wald, et. al97,98. performed a set of experiments during the 1940 s that purported to demonstrate the formation of rhodopsin from either retinene, (now known as retinal) or Vitamin A, and a native protein. While their work involved materials showing a peak absorption at 500 nm, this is the wavelength of peak isotropic absorption of a large number of dipolar retinoids. Such a peak is not exclusive to the chromophoies of vision. Neither is it relevant to the anisotropic absorption spectrum of the chromophores of vision. 

In a previous study we have found that, at low temperature, PS-I electron transfer is largely blocked away from A, and that the state (P-700+, A, ) decays with a half-time of 130us. Analysis of the absorption spectrum of that state showed that A, is presumably a quinone radical anion (Brettel et al, 1986). Chemical analysis, following separation by HPLC, has shown that phylloquinone (a naphthoquinone also named vitamin Kj) is the only quinone present in PS-I. We have found 2 moles of phylloquinone per PS-I. Extraction with dry hexane does not change the electron transfer reactions this treatment only extracts only one phylloquinone per PS-I (Biggins and Mathis, 1987). 

Ultraviolet absorption spectrum of vitamin A shows a maximum near 328 nm, which was used extensively as a means for both identification and determination of the vitamin in the... 

The absorption spectrum of interferants is commonly linear, but nonlinear interferant absorption has been reported. A number of mathematical techniques have been developed to correct for nonlinear interfering absorption. Most of the correction techniques are based on assuming that the interferents have an absorption profile that can be represented by some mathematical function. The simpler correction techniques, such as the geometric correction technique(s), assume a linear interferant absorption profile. A basic approach to the technique can be seen from the three-point geometric correction technique, a modification of which has found applicability to the analysis of vitamin A in fish oils. Higher-order functions have also been used to describe the interfering absorption, and in these cases more involved formulas have been developed. 

Quite often, the absorption data of the derivatives or degradation products of a compound of unknown structure have lead to the ultimate structure determination of the parent compound. Recently, the degradation product of vitamin Big, 5 6-dimethylbenzimmazoIe, was identified by its ultra-violet absorption spectrum4. The structure of vitamin Bx (thiamine) was elucidated by comparison of the spectra of its sodium sulphite fission products" with the spectra of model compounds11. The crude structure of vitamin Kx was found by the use of spectral data. The absorption spectrum of vitamin IC, has the following bands 249 my (e 19,000), 260 mju. (f 18,000) and 325 my... 

Needles. + HjO from AoOEt-MeOH. M.p. l52-3°. [a] ) — 109 in CHCI3. Absorption spectrum and colour reactions similar to ergo-sterol.. Irradiation —> vitamin EL. 

The identification of fragment B of the vitamin molecule gave less trouble. It was recognized as a thiazole derivative by Clarke and Gurin . On oxidation with nitric acid it yielded 4-methylthiazole-5-carboxylic acid (VI), a compound that had already been synthesized in 1890. It appeared to contain an aliphatic hydroxyl group which could be replaced by chlorine without much change in the U.V. absorption spectrum, so it could be reconstructed as having structure VII. 

As an example to prove how valuable absorption data can be, one can dte the example of vitamin K whose structure was determined the use of its spectral data. Tbe absorption spectrum of vitamin Kj has the following absorption maxima 249 nm, 260 nm, and 325 nm. The maxima aroimd 250-330 nm are characteristic of a naphthaqumone. Chemical manipulation and comparison of spectra with several model compounds indicated that the positions of the absorption maxima were similar to those of 2,3-dialkyl-1, 4-naphthaquinone. The structure of vitamin K, determined later is as below ... 

Andresen (1954) reports the isolation of a vitamin Bi2 protein complex with an absorption spectrum practically identical with the purest fraction described by Wijmenga et al. (1954). Ultracentrifugation data showed that the two products had the same sedimentation constant. Andresen s product, unlike that of Wijmenga et al., was clinically active when administered to patients with pernicious anemia in relapse. The daily oral dose in the two cases described was 1.2 mg. and 2.4 mg. of the complex, corresponding to 10 fig., and 20 fig. of vitamin B12 (microbiologically determined). 

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