UV spectroscopies

UV spectroscopy has only little sign cance for the direct analysis of essential oils due to the inability to provide uniform information on individual oil components. However, for testing the presence of furanocoumarins in various citrus oils, which can cause photodermatosis when applied externally, UV spectroscopy is the method of choice. The presence of those components can be easily determined due to their characteristic UV absorption. In the European pharmacopoeia, for example, quality assessment of lemon oil, which has to be produced by cold pressing, is therefore performed by UV spectroscopy in order to exclude cheaper distilled oils. 

The UV spectral data of known parent A,B-diheteropentalenes are summarized in Table 9. The analogous thienothiophenes and selenolothiophenes show more absorption maxima in their UV spectra than the other systems. The known progressive shift of absorption to longer wavelengths which is observed in the simple five-membered heterocycles in the sequence furan pyrrole thiophene selenophene is missing since the rings are fused. 

UV spectroscopy has only little significance for the direct analysis of essential oils due to the inability to provide uniform information on individual oil components. However, for testing the presence of furano-coumarins in various citrus oils, which can cause photodermatosis when applied 

Ultraviolet (UV) spectra of some selected furo[3,2-3]- and furo[2,3 ]pyrroles were published and their apparent ionization constants determined by spectrometric titration (Table 5), and correlated with their structures 2001CCC1615 . 

As can be seen from Table 1 the UV-VIS-spectrum recorded in alkaline methanol or ethanol gives us information on the location of hydroxyl groups 19). The values for the UV maximum in alkaline ethanol in Table 1 are recorded for pure hydroxy-anthraquinones not bearing any other substituents. In the case of naturally occurring an-thraquinones which contain other substituents as well, either positive or negative effects due to these substituents on the bathochromic shift are possible. 

The IR spectrum of an anthraquinone gives information on the environment of the carbonyl groups in the 9- and 10-positions. If a peri hydroxyl group is present, the carbonyl absorption band will show a shift to smaller wave numbers due to hydrogen bonding between the peri hydroxyl and the adjacent carbonyl group (120). The presence 

A study of the effect of substitution patterns in oxadiazoles and isoxazoles and their effect on the UV spectra in the lO -lO M concentration range was performed. Hypso-chromic effects and deviations from Beer s law were observed and were believed to be associated with antiparallel, sandwich-type self-association via dipole-dipole interactions. Beer s law is followed when the molecular dipole moments are small or when self-association is sterically hindered. 

Extensive UV absorption data (as well as NMR and IR data) have been reported for a large number of 2,1-benzisoxazolium salts. The salts show three absorption maxima at 270-273, 280 and 335-338 nm (73DIS(B)1434, 71JOC1543). 

To estimate the concentration of an oligonucleotide solution, the absorption is measured at 260 nm. Correct weights of solid oligonucleotides are difficult to obtain due to non-stoichio-metric inclusion of water molecules into the solid. UV spectra of nucleic acids exhibit a pronounced hypochromicity. In double-stranded nucleic acids, base stacking with a distance of about 3.5 A lowers UV-absorption by up to 20% due ii-systems interaction when compared with single-stranded oligomers (Fig. 25). 

Because UV absorption of resist films at the exposing wavelength is a very important parameter that affects lithographic performance, UV measurements of components and resulting resists are critical in photolithography. Furthermore, since UV spectroscopy can be readily carried out on thin films coated on substrates, resist chemistries can be monitored by this technique in some cases. 

For example, conversion of PBOCST to PHOST is accompanied by an increase in absorption at ca. 280 nm (Fig. 170). Furthermore, UV absorbing polymer end groups can sometimes be detected. As mentioned earlier, UV spectroscopy is highly useful in determination of acid concentration when employed in conjunction with an acid sensitive dye. 

The parent heterocycles (Table 13) display a strong band near 220 nm with one additional band at longer wavelengths for thiophene and selenophene, and two for tellurophene. Analogous weak bands reported in the older literature for furan and pyrrole are now generally accepted as arising from autoxidation products. 

Solvent EtOH EtOH, MeOH EtOH EtOH n-hexane 

71PMH(3)79 71PMH(3)79, 71T245 58AK(13)23, 58SA350 58G453 72JCS(P1)199 

The intense 7i-7i-transition in bis(dithiazole) 24 (622 nm) 1998CC1939 is due to the longer wavelength of the corresponding absorption maxima in bis(dithiazoles) 23 (522 nm) and 11 (565 nm) 1998CC1039 . 

4-Chloro-l,2,3-dithiazoles 41 and 42 show strong ultraviolet (UV) absorption at Amax 423—431 nm (logs 3.8—4.0) and a weaker absorption at Amax 330nm (loge3.2-3.3) 1998J(P1)2505 . 

118 3 Analytical Tools for the Analysis and Quantification of Drug-Membrane Interactions 

Similarly, using UV absorption spectroscopy Gracia and Prello [148] studied the influence of membrane chemical composition and drug structure on the localization of benzodiazepines at the lipid-water interface. Their results revealed that the benzodiazepines can be incorporated as an integral part of the bilayer and are not located only at the core, as reported from fluorescence polarization experiments [149]. 

The influence of lipid phase (gel or liquid crystalline), cholesterol content, lipid composition (egg phosphatidylcholine or DPPC), and structure of benzodiazepines determine their localization in the membrane. The strength of benzodiazepine-membrane interaction increases with a decrease in molecular order, molecular packing, and hydration,. The authors point to the pharmacological relevance of theses results because the extent of partitioning of these drags into biomembranes would be coupled to local oscillation of membrane dynamics which may be induced by physiological events.  

Introduction of the nitro group into the azole cycle leads to a significant bathochro-mic shift of the absorption band maximum in the electron spectra. The absorption band of pyrazole is near 210 nm, whereas that of 4-nitropyrazole lies in the 

269-280 nm region and the band of 3(5)-nitropyrazole is observed in the 254-266 nm region [272, 1115-1124] (Table 3.63). It results from it— jt electron transition in the pyrazole ring with contribution of the charge transfer from ir-system to the nitro group. The position of this absorption band strongly depends on the effects of medium and substituents, and on the ionization processes of the molecule. 

In neutral media the band of pyrazole nitro derivatives is in the 250-290 nm region in acid media it is shifted by 30 nm to the short-wave region and in alkaline media a 40 nm shift to the long-wave region occurs [246,1115,1116,1119-1126], These shifts are caused by protonation and deprotonation of nitropyrazoles that is widely used in studying the acid-base properties of nitroazoles since the existence of these shifts allows spectrophotometrical determination of the pand pA s + values of these compounds. 

Solvatochromism and specific features of interaction between nitropyrazoles and amphiprotic solvents have been studied in detail by Prof. Turchaninov s team [1119-1123, 1127]. The dependence on acid-base properties of solvents of the electron transition in 4-nitropyrazole connected with intramolecular charge transfer has been analyzed [1121], Amphiprotic solvents with a pronounced acidic function form with 4-nitropyrazole cyclic solvates. The results of ab initio calculations 6-31G show that a cyclic complex of both 4-nitropyrazole and 3-nitropyrazole with one water molecule is thermodynamically more stable than a linear complex of the same composition by 0.38 and 1.0 kcal/mol, accordingly [1120-1123]  

The solvatochromism of H-complexes of 5-amino-l-methyl-4-nitropyrazole in aprotic protophilic media has been described by Kamlet-Taft empirical parameters. Specific solvation affects only one of the two long-wave bands, namely that corresponding to an electronic transition involving orbital electron density transfer from the H-bound nitrogen atom [1123], 

Oxygen-containing heterocyclic homologues of ethers exhibit two absorption bands, with the exception of oxirane which has only one absorption maximum at 

1713 cm . At the same time, its ionization potential (10.565 eV) is higher than that of dimethyl ether (10.0 eV) (see Section H.3.C.). The energy of the difference between the absorption bands for the higher cyclic ethers almost corresponds to this energy and thus it is probable that the lone p electrons are equally stabilized in oxirane, presumably by hyperconjugation with the methylene groups.  

For a recent listing of the phenanthrene alkaloids, their physical constants and their spectral data, see H. Guinaudeau, M. Leboeuf, and A. Cave, Lloydia, 38, 275 (1975). 

Pontevedrine is a red, crystalline, alkaloid accompanying corunnine in Glaucium flavum Cr. (Papaveraceae). Its structure had been originally formulated as the 5,7-dioxoaporphine 1. However, the isolation of (+ )-cataline from the 

Interestingly, when the benzylic acid rearrangement was run in ethanolic sodium hydroxide, the product was the analog of 4 with an ethoxyl rather than a methoxyl group at C-4. Benzylic rearrangements within this context may have some analogy in nature, since aristolactams are found as natural products. This topic will be discussed in greater detail in Sec. 17.4. 

The orange colored cepharadiones-A and -B, found in Stephania cepha-rantha Y. Hayata (Menispermaceae), were the first 4,5-dioxoaporphines to be fully characterized. The structural assignments were based on the spectral data indicated.  

The mass spectra of cepharadione-A and -B show molecular ions at mje 305 (88) and 321 (100), respectively with intense peaks for the loss of carbon monoxide at mie 211 (100) and 293 (84), respectively.  

The solution must be freshly prepared it becomes dark brown in the presence of air in the course of 30 min. p-Phenylenediamine should be handled with great care and never brought into contact with the skin or even inhaled because it is cancerogenic. 

An ethanolic solution of iron-III-chloride (FeClj, 1%) is a test for phenolic groups (brown, red, wine red or violet coloration) in some cases the colour changes after addition of some drops of water. 

An ethanolic solution of magnesium acetate [Mg(OAc)2, 2%] gives red to violet colorations with quinones having a free hydroxyl group in the p-position. 

A similar diagnostic colour reagent, Dimroth s reagent, is a solution of boric acid (B(0H)3, 2%) in acetic anhydride. Quinones with a P-hydroxyl group give red to violet colours (boroacetate complexes). 

The Beilstein test is a simple but sensitive and reliable test for lichen substances containing chlorine. The compound (Img) is brought on the tip of a freshly glowed copper wire into the flame of a Bunsen burner a deep green flame develops for a moment in the presence of chlorine (or another halogen) in the substance. 

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Most importantly, analysis using UV-spectroscopy also demonstrated that, as anticipated, the elimination reaction of 4.51 is less efficient than that of 4.44. Ag in, addition of copper(II)nitrate significantly suppresses this reaction. 

Instrumental Analysis. It is difficult to distiaguish between the various acryhcs and modacryhcs. Elemental analysis may be the most effective method of identification. Specific compositional data can be gained by determining the percentages of C, N, O, H, S, Br, Cl, Na, and K. In addition the levels of many comonomers can be estabhshed usiag ir and uv spectroscopy. Also, manufacturers like to be able to identify their own products to certify, for example, that a defective fiber is not a competitor s. To facihtate this some manufacturers iatroduce a trace of an unusual element as a built-ia label. 

In solution, lignin is most conveniendy analyzed quaUtatively and quantitatively by uv spectroscopy. Typical absorptivity values, D, at 280 nm for milled wood (MW) lignins and other types of lignins are Hsted ia Table 4. These values are used for quantitative determination of the lignins ia suitable solvents. 

Phosgene in air and in mixture with other gases can be detected by a variety of methods (35). Trace quantities to a lower limit of 0.05 f-lg/L air can be detected by uv spectroscopy (36). Both in and gas chromatography have been used extensively to measure phosgene in air at 1 ppb—1 ppm (7,37,38). Special... 

Chemical Analysis. The presence of siUcones in a sample can be ascertained quaUtatively by burning a small amount of the sample on the tip of a spatula. SiUcones bum with a characteristic sparkly flame and emit a white sooty smoke on combustion. A white ashen residue is often deposited as well. If this residue dissolves and becomes volatile when heated with hydrofluoric acid, it is most likely a siUceous residue (437). Quantitative measurement of total sihcon in a sample is often accompHshed indirectly, by converting the species to siUca or siUcate, followed by deterrnination of the heteropoly blue sihcomolybdate, which absorbs at 800 nm, using atomic spectroscopy or uv spectroscopy (438—443). Pyrolysis gc followed by mass spectroscopic detection of the pyrolysate is a particularly sensitive tool for identifying siUcones (442,443). This technique rehes on the pyrolytic conversion of siUcones to cycHcs, predominantly to [541-05-9] which is readily detected and quantified (eq. 37). 

The field of steroid analysis includes identification of steroids in biological samples, analysis of pharmaceutical formulations, and elucidation of steroid stmctures. Many different analytical methods, such as ultraviolet (uv) spectroscopy, infrared (ir) spectroscopy, nuclear magnetic resonance (nmr) spectroscopy, x-ray crystallography, and mass spectroscopy, are used for steroid analysis. The constant development of these analytical techniques has stimulated the advancement of steroid analysis. 

Tar. Before the development of gas chromatography (gc) and high pressure Hquid chromatography (hplc), the quantitative analyses of tar distillate oils involved tedious high efficiency fractionation and refractionation, followed by identification or estimation of individual components by ir or uv spectroscopy. In the 1990s, the main components of the distillate fractions of coal tars are deterrnined by gc and hplc (54). The analytical procedures included in the specifications for tar bulk products are given in the relevant Standardi2ation of Tar Products Tests Committee (STPTC) (33), ISO (55), and ASTM (35) standards. 

Theoretical methods ranging from the now obsolete HMO studies to ab initio calculations have been used extensively on pyrazoles. Although not emphasized in earlier reviews (66AHC(6)347,67HC(22)l), the most recent publications (B-76MI40402,79RCR289) contain several references to theoretical studies. Some publications related to structural studies are to be found in the following sections, especially in connection with NMR spectroscopy (Section 4.04.1.3.4), UV spectroscopy (Section 4.04.1.3.6), PE spectroscopy (Section 4.04.1.3.9) and tautomerism (Section 4.04.1.5). 

The use of UV spectroscopy as an identification method is continuously decreasing in relative importance compared to the use of NMR or mass spectrometry. However, due to the general validity of Beer s law, it continues to be an appropriate method for quantitative studies such as the measurement of ionization constants (Section 4.04.2.1.3(iv) and (v)) and the determination of tautomeric equilibrium constants (Section 4.04.4.1.5). 

There is very little published information on the UV spectra of 1,2-benzisothiazoles, though more data are available on the 2,1-isomers. The spectra are complex with as many as six maxima above 200 nm. Representative wavelengths of maxima are collected in Table 12. In all cases the most intense bands (e > 15 000) are those at short wavelengths, but all the bands indicated in the table have molar absorptivities greater than 4000, except those of 3-amino-2,l-benzisothiazole. Saccharin absorbs weakly at 350 nm and 277 nm, with intense bands below 230 nm (ethanol solvent) (82UP41700>. It exists as the anion except in acid solutions. The UV spectra of cations formed from 3-amino-2,l-benzisothiazole are discussed in (69CB1961>. Further applications of UV spectroscopy in studying tautomeric... 

Direct proof of an oxaziridine intermediate was achieved in photolysis experiments in an organic glass at 77 K (80JA5643). Oxaziridine (75), formed by photolysis of A/-oxide (74) and evidenced by UV spectroscopy under the above conditions, decomposed at higher temperature to form the imino ether (76) by N—O bond cleavage and C -> O migration of an aryl group. 

In laser-impulse experiments with chlorophenyldiazirine the carbene could be observed by UV spectroscopy. On addition of defined amounts of alkene the rate of cyclopropanation was measured directly. The rate constants with various alkenes were (lO moF s ) 1-hexene, 1.3 ( )-2-pentene, 34 2-methyl-2-butene, 77 2,3-dimethyl-2-butene, 130 (80JA7576>. 

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