Sulfuric acid absorbance spectrum

Most of the thiazoles studied absorb in the ultraviolet above 254 nm, and the best detection for these compounds is an ultraviolet lamp (with plates containing a fluorescent indicator). Other indicator systems also exist, among which 5% phosphomolybdic acid in ethanol, diazotized sulfanilic acid or Pauly s reagent (Dragendorff s reagent for arylthiazoles), sulfuric anisaldehyde, and vanillin sulfuric acid followed by Dragendorff s reagent develop alkylthiazoles. Iodine vapor is also a useful wide-spectrum indicator. 

The sulfuric acid treated aliquot representing the blank forms a cyclic ether anhydroerythromycin.10 The alkaline treatment causes the formation of an unsaturated ketone (9-keto-10-ene) having its absorbance maximum as a shoulder at 236 nm. (e 6000).n i2 Thus, any other UV absorbing species are measured with the blank and subtracted from the absorbance before calculation of the erythromycin concentration. A typical spectrum is shown in Figure 4. 

The 2Fe2S (S, acid-labile sulfur) ferredoxins have a redox active binuclear center, with each of the two iron atoms attached to the protein by two cysteinyl sulfur ligands and connected by two inorganic acid-labile sulfur ligands. At cty-ogenic temperatures these clusters are EPR detectable, with characteristic features in the vicinity of g = 1.94. Spinach ferredoxin has principal g values of 2.03, 1.96, and 1.88 and a broad absorbance spectrum with a weak maximum around 420 nm, giving these proteins a reddish brown color which bleaches on reduction. Ferredoxins are low potential electron carriers chloroplast ferredoxins function in photosynthetic electron transfer, but related proteins such as adrenal ferredoxin are involved in steroidogenic electron transfer in mitochondria in tissues which produce steroid hormones. 

Fig. 7.105. Differential IR spectrum of platinum-aqueous sulfuric acid interface containing 0.1 M methanol at 0.1 V (vs. SHE) in the sequence from 0.0 to 0.8 V (vs. SHE). Absorbance maxima were found at 2150 (peak A), 1620 (peak B). 1185 (peak C), and 1050 cm (peak D). (Reprinted from K. C. Chan-drasekaran, J. C. Wass, and J. O M. Bockris, J. Electrochem. Soc. 137(2) 519, 1990. Reproduced by permission of The Electrochemical Society, Inc.)...

FIGURE 2.S Ultraviolet absorption spectrum obtained clopidogrel bisulfate, dissolved at a concentration of 5.5 /rg/ml in methanol that had been acidified with sulfuric acid. The inset spectrum represents an expansion of the absorbance scale. 

The ultraviolet absorption spectrum of cimetidine in 0.1N aqueous sulfuric acid is shewn in Figure 3. A summary of the ultraviolet absorbance characteristics obtained in several solvents is shewn in Table 1. 

Record the ultraviolet absorption spectrum of this solution in 1 cm cells on a suitable spectrophotometer fran 320 to 210 nm using 0.1N sulfuric acid as a blank. Measure the absorbance difference (M) between the absorbance at 218 nm (maximum) and that at 260 nm. 

The UV-vis absorption spectra of 4.201 and 4.202 recorded in chloroform are characterized by the presence of broad, relatively weak absorbance bands in the 300-450 nm spectral region (only). The spectrum of 4.201 in sulfuric acid, however, is considerably different. Under these conditions, the absorbance bands become both bathochromically shifted and are more intense. These findings were rationalized by assuming that treatment of 4.201 and 4.202 with sulfuric acid generates the dicationic enol-tautomeric species 4.203 and 4.204. 

Crystals from water + acetone, mp 196-200". [alff -47,5 (c = 2, 2% NaOH) -26.0 (c = 2, 10% HCI). pK, -- 3.8 pKj — 6.2. aM (molar absorbancy) 15.4 X I03 at 259 nm (pH 7.0). Readily sol in boiling water. The compound is readily deaminated by nitrous acid to form inosinic acid less rapidly hydrolyzed than 3 -adenylic acid by sulfuric acid. Furfural is formed only in traces On distillation with 20% HCI, cf. Levene, Bass, Nucleic Acids (New York, 1931) pp 230-232. Absorption spectrum Kalckar. foe. cir. thERap cat-. Nutrient. 

When sublimed, anthraquinone forms a pale yellow, crystalline material, needle-like in shape. Unlike anthracene, it exhibits no fluorescence. It melts at 286 0 and boils at 379 —38UC. At much higher temperatures, decomposition occurs. Anthraquinone has only a slight solubility in alcohol or benzene and is best recrystaUized from glacial acetic acid or high boiling solvents such as nitrobenzene or dichlorobenzene. It is very soluble in concentrated sulfuric acid. In methanol, uv absorptions of anthraquinone are at 250 nm (e = 4.98), 270 nm (4.5), and 325 nm (4.02) (4). In the ir spectrum, the double alljdic ketone absorbs at 5.95 am (1681 cm ), and the aromatic double bond absorbs at 6.25 im (1600 cm ) and 6.30 Jm (1587 cm ). 

In concentrated sulfuric acid, the ultraviolet absorbance spectrum of dexamethasone undergoes a bathochromic shift characteristic of a number of steroids. Spectral data reported for dexamethasone include ... 

Copper phthalocyanine blue pigments are soluble in concentrated sulfuric add. The solutions are quite stable at room temperature for several hours. The sample preparation for this analysis is quite simple. The pigment sample (3-5 mg) is weighed on a microbalance and then dissolved in concentrated sulfuric acid by stirring and/ or sonication. After complete dissolution the sample is diluted to a known volume and the Visible to Near IR spectrum is scanned from 400 to 900 run. Based on the absorbance and weight concentration of the sample and that of the reference pure standard at the wavelength of maximum absorption (Imax). the amount of pigment in the sample is determined. 

Chloro-naphthalene and 1-methyl-naphthalene can also be used for dissolution of copper phthalocyanine blue pigments. This is particularly useful for plastic matrices where sulfuric acid is not recommended. The solubility in these solvents is limited to about 10 mg/L (10 ppm). The use of a microbalance is necessary for weighing low mg amounts. Figure 21.4 shows the visible spectrum of copper phthalocyanine blue at a concentration of 7 mg/L in 1-methyl-naphtahlene (absorbance at 677 nm is 2.1). 

TLC plate adsorbents (e.g., silica gel, alumina and so on) usually contain small amounts of substances which migrate with the development solvent along the plate towards the solvent front. Solvents such as methanol cause migration of adsorbent impurities almost completely to the solvent front, whereas non-polar solvents such as -hexane do so to a lesser extent. These impurities adsorbed in the UV region of the spectrum but do not appear to absorb much in the infrared region the impurities also produce a char when the plate was sprayed with sulfuric acid and heated to about 170 °C, indicating that they contain organic matter. 

The substitution of a bromine atom on a nucleic acid base (e.g. 8Br-adenosine) provides the base with significant absorption in the 300 nm region. The RR spectrum of the brominated species can then be specifically excited by 300 nm irradiation [59]. The brominated bases are in effect RR labels but there are rare naturally occurring bases with significant absorption in the near UV, these are sulfur substituted analogs absorbing from 300-360 nm. For example Nishimura, Tsuboi and coworkers [60] obtained RR spectra of the single 4-thiouridine which occurs in a number of tRNAs. 

Absorption studies of amino acids in the UV region go back to the mid-thirties [15]. An overview on this subject appeared as early as 1952 [16]. Only the aromatic amino acids, phenylalanine, tyrosine and tryptophan, absorb in a conveniently observed region (Fig. 6). The weakest of them is phenylalanine, revealing at least 6 absorption bands it has a molecular absorption coefBcient of fimoi 0.195 X 10 at 257 nm. The UV-spectrum of tyrosine is strongly dependent on pH in the presence of 0.1 N HCl (protonated hydroxyl group) Sj oi = 1-34 x 10 at the maximum, (l x 275 nm) in 0.1 N NaOH (phenolate) = 2.33 x 10 at 293 nm. The absorption of tryptophan, is nearly independent of the pH it shows a maximum at 280 nm with = 5.55 x 10 and a second maximum (shoulder) at 288 nm of = 4.55 x 10. These parameters have often been used in the quantitative analysis of peptides. The sulfur-containing side chains show weak absorption below 250 nm and are of interest only in rare special cases. 

---