UV absorbance spectra

In an effort to restrict the location of semiconductor nanoparticles in LB films and inhibit aggregation, the formation of CdS in LB films of calixarenes was investigated [195]. Limiting areas of 3.0 nm and 1.8 nm were obtained on 0.5 mM CdCli, compatible with the cross-sectional areas of the calixarenes. Y-type LB fdms were prepared at 25 mN m on glass, quartz, and silicon. The substrates had been made hydrophobic by treatment with a silane vapor. After H2S treatment overnight in sealed jars, UV absorbance spectra and XPS data were obtained. The absorption edge for the CdS particles formed in the calixarene LB films transferred at pH 5.5 was 3.3 eV as compared with 2.7 eV for films formed in cad-... 

Figure 4.36 shows the UV absorbance spectra of diethyl dixanthogen (EX)2, diethyl monothiocarbonate (MTC ) and diethyl thiocarbonate (EPX). The UV adsorption peaks of (EX)2 lie in about 238 nm (strong) and 286 nm (weak). The ratio of adsorption intensity of two peaks is 2. UV peak of MTC lies in about 225 nm (strong), EPX lies in about 348 nm (strong) and 221 nth (weak). 

Fig. 14. Effects of temperature on the absorbance of hemopexin and the N-domain of hemopexin. The unfolding of hemopexin and N-domain in 25 mM sodium phosphate, pH 7.4, was examined using absorbance spectroscopy (N. Shipulina et al., unpublished). The second derivative UV absorbance spectra of the protein moieties were used to follow protein unfolding and the Soret and visible region spectra to monitor the integrity of the heme complexes, as done with cytochrome 6502 (166). The ferri-heme complex is more stable than the apo-protein moiety, but the is slightly lower than that assessed by DSC, indicating that changes in conformation occur before thermodynamic unfolding. Reduction causes a large decrease in heme-complex stabihty, which is proposed to be a major factor in heme release from hemopexin by its cell membrane receptor, and addition of 150 mM sodium chloride enhanced the stabihty of ah forms of hemopexin.

Fig. 14 UV absorbance spectra of 36 in THF with increasing amounts of Ag03SCp3 (a) 0, (b) 0.5, (c) 1.0, (d) 1.5, and (e) 2.0 equiv. Inset Plot of A303M288 versus the number of molar equivalents of Ag03SCp3. A=absorbance (c(36)=6.7xl0 M)...

In the experiments, it was ascertained that laser irradiation had no effect on the UV absorbance spectra of the samples. 

De Schryver and co-workers u> have confirmed Chandross result for the UV absorbance of l,3-bis(2-naphthyl)propane. Nishijima et al.12) have stated that the absorbance spectrum of meso- and dl-2,4-bis(2-naphthyl)pentane and of the compounds l,3-bis(2-naphthyl)A, where A = propane, butane, pentadecane, and 5-phenylpentane, is similar to the absorbance spectrum of 2-ethylnaphthalene. Finally, an unusual result has been obtained by De Schryver et al.13> for the compound bis(l-(2-naphthyl)ethyl)ether. The meso compound gave a lower value of ID/IM, the ratio of excimer to monomer fluorescence intensities, under excitation at 304 nm relative to excitation at 285 nm, while the dl compound had no such excitation dependence. The UV absorbance spectra of these compounds were not reported, however. 

In short, the UV absorbance spectra of diphenyl and dinaphthylalkanes are substantially the same as that of the corresponding alkylarene. There are no major wavelength or intensity shifts of the spectral bands, and no signs of any additional bands at lower energy. Since there are no ground-state dimers present in these model compounds that are detectable by UV absorption, we expect that no such dimers will be found for PS or P2VN in dilute solution. 

The naphthalenophanes that are fully eclipsed, i.e. the sj>n-[2.2](l,4), achiral [2.2](1,5), achiral [3.3](2,6),. n -[3.3](l,4), and syn-[2>,2] A) isomers, share certain traits in absorption and fluorescence. The UV absorbance spectra of these compounds between 260 and 310 nm retain all of the structure shown in the spectra of the open-chain analogs. Also, new absorption shoulders not seen in the open-chain spectra appear strongly at 245 and weakly at 340 nm. The fluorescence peak of these fully eclipsed naphthalenophanes occurs near 22,000 cm-1, as seen in Table 7. This represents a red shift of 2600 cm-1 relative to the solution excimer of the dimethylnaphtha-lenes.71)... 

The riboflavin vitamers all have similar UV absorbance spectra. They all fluoresce naturally, although the quantum yield of FAD s fluorescence is 10 times less than that of riboflavin and FMN... 

Fig. 6.5 UV absorbance spectra of hydrogen peroxide in aqueous solution and in the gas phase [redrawn from Bolton and Cater (1994), p. 472, Figure 3].

The UV absorbance spectra of the transient species H (Xo get 250 nm), OH ( max - 230 nm), HO ( max 231 nm) and 02 ( max 248 nm) were reported by Getqff (1996). These data suggest that the direct photolysis of the intermediary species must also be considered for the evaluation of photo-initiated AOPs. However, this is not important for the OH radical because its concentration is always so low (cf Fig. 6-13) that its photolysis is negligible. 

Figure6.1 Plotoflabetalol UV absorbance spectra showing pH 3, pH 9, and organic calibration lines at 0.05 mm.

Figure 4. UV absorbance spectra of onium salt photoinitiators...

The mechanism for the hydroxylation of aromatic substrates by flavoprotein monooxygenases has been the subject of signiflcant research interest and controversy over the past decade. These enzymes (p-hydroxybenzoate hydroxylase, phenol hydroxylase, and melilotate hydroxylase) catalyze the initial step in the )8-ketoadipic acid pathway, the hydroxylation of substituted phenols into catechols (Scheme 55). Oxygen is required as cosubstrate, which is activated by the reduced FAD cofactor. The complex mechanism for the oxidative half-reaction is thought to consist of at least four steps and three intermediates 239-242) and to involve a controversial 4a,5-ring-opened flavin 242, 249, 250) (Scheme 56). The flavin C4a-hydroperoxy intermediate 64 and flavin C4a-hydroxy intermediate 65 have been assigned the structures shown in Scheme 56 based on the UV absorbance spectra of various model compounds compared with that of the modified enzyme cofactor alkylated at N(5) 243). However, evidence for the intermediacy of various ring-opened flavin species has been tentative at best, as model compounds and model reactions do not support such an intermediate 242). 

Figure 2.14 Near-UV absorbance spectra for aromatic amino acid side chains. When superimposed on the same scale (bottom right panel), the dominant contribution from tryptophan and tyrosine residues becomes more obvious...

Figure 2.15 Typical near-UV absorbance spectra for proteins (lysozyme, ribonuclease) and nucleic acids (DNA, adenine, thymine). Notice how the lysozyme spectrum (6 Trp, 3 Tyr,...

Quantum Yields. Sunlight quantum yields were calculated for the six test compounds from measurements of their photolysis rates In distilled water and from their UV-absorbance spectra using solar Irradlance data from the literature. The method used Is described In Refs. and 21. Yields were determined from the known quantum yield of the p-NA actlnometer using the following formula ... 

Fig. 21.1 The UV absorbance spectra of tribenzo[fl,ccf,/m]per-ylene and dibenzo[ccf,/m]perylene, showing the complexity inherent to the spectra of PAHs.

Fig. 21.2 The UV absorbance spectra of the spectra are not only different from each other, two isomers tetrabenzo[a,cd,//m]perylene and but are very different from those of the two tetrabenzo[fl,cd,j,/m]perylene. Note that these similar structures shown in Fig. 21.1.

In addition, a calibration graph of sulfonate concentration versus ultraviolet absorbance was obtained for each microemulsion prior to adsorption. A small known volume of microemulsion was diluted with methanol ("spectro" grade) to obtain a clear sulfonate stock solution which was used to prepare four still more dilute methanol solutions of varying sulfonate concentration. The UV absorbance spectra of these solutions were measured on a Cary 118 spectrophotometer absorbances were determined at 271 nm for PDM-334 microemulsions and at 259 nm for TRS 10-410 microemulsions. All calibration plots were linear and passed through the origin. 

Although humulone, adhumulone and cohumulone possess the same chromophore, their UV absorbances/spectra are not exactly the same. There are small differences in their molar absorptivities, large enough to introduce significant errors if this factor is neglected. Since the chromophore in cohumulone is present in a smaller... 

Figure 7. UV absorbance spectra of MMA-TBMA-MAA terpolymer with and without photoadd generator (diphenyliodonium triflate). Fihn thickness is 3.75 microns.

Figure 4. UV absorbance spectra of 1000 nm thick films of novolaks, M-cre lic acid type, MP-meta/para, BPA-bis phenol A, and PHS-polyhydro) styrene.

The UV absorbance spectra of silver colloids are shown in Fig. 2 and the absorbance values are given in Table 2. Among the surfactants tested, the SDS showed the highest yield. Depending on the nature of the smfactant, different absorbance patterns were observed. The measurement of the ex-... 

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