Chromophoric compounds

Certain disease states also produce alterations in the skin s optical properties. Alterations of the skin s surface, such as by psoriatic plaques, decrease transmitted fight. The effect may be lessened by application of oils whose refractive index is similar to that of skin (Anderson and Parrish, 1981). Disorders such as hyperbilirubinemia, porphyrias, and blue skin nevi result in increased absorption of visible light due to accumulation or altered distribution of endogenous chromophoric compounds. 

Fig. 3. (a) chemical structure of the synthetic chromophore compound 1-28 compared to that of the protein (R1 and R2 correspond to amino-acids which link the chromophore to the rest of the protein), (b) Differential transmission spectrum, at magic angle and for different pump-probe delays, of 1-28 in dioxan solution (6 pg/ml) excited in the conditions described in the caption of fig. 1. 

Detection of amino acids is typically by UV absorption after postcolumn reaction with nin-hydrin. Precolumn derivatization with ninhydrin is not possible, because the amino acids do not actually form an adduct with the ninhydrin. Rather, the reaction of all primary amino acids results in the formation of a chromophoric compound named Ruhemann s purple. This chro-mophore has an absorption maximum at 570 nm. The secondary amino acid, proline, is not able to react in the same fashion and results in an intermediate reaction product with an absorption maximum at 440 nm. See Fig. 5. Detection limits afforded by postcolumn reaction with ninhydrin are typically in the range of over 100 picomoles injected. Lower detection limits can be realized with postcolumn reaction with fluorescamine (115) or o-phthalaldehyde (OPA) (116). Detection limits down to 5 picomoles are possible. However, the detection limits afforded by ninhydrin are sufficient for the overwhelming majority of applications in food analysis. 

Experiments on model solutions demonstrate that chromophoric compounds, such as Fe(III) oxalato complexes, may act as primary photore-... 

From the preceding discussions, it should be clear that photochemistry within all phases of the atmosphere is a major driver of chemical transformations in relatively short time scales. With increasing knowledge of the ever-widening array of chromophoric compounds emitted and produced in the atmosphere, there is definitely room for much more fundamental research into primary and secondary photochemical reactions of relevance. In particular, the role of humic-like substances in aerosol, cloud and ice phases needs to be studied. 

Figure 1.19a shows the partial amplitudes of p-C 1PX for this component as a function of the detection wavelength. First, considering only the mono-chromophoric compound p-ClPj (Fig. 1.19a [ ]) with a t2 of 6.3 ps, a change of sign of the partial amplitude can be observed. Taking into account the shape and the positive/negative behavior of this kinetic component, it is attributed to a vibrational relaxation in the electronically excited state of the peryleneimide chromophore. 

Diffusion controlled processes for H+/Lewis acid generation upon both OP and TP excitation can be of minor importance if the onium compound comprises a part of the TP chromophore. Compound 179 is such a chromophore. This compound combines a distyrylbenzene with end capped amino groups. The latter bears a sulfonium group in m-position. OPA of 179 occurs at 392 nm (e = 5.5 x 104 M em ). TPA was investigated between 705 and 850 nm. The TPA cross section of 179 is 690 GM (Fig. 3.68a). Furthermore, the quantum yield of OP initiated generation of H+ is about 0.5, while the quantum yield for fluorescence is significantly less (f = 0.013) [137, 225]. 

NLO properties are provided by including chromophore compounds, such as an azo-t)q)e dye, which can absorb photon radiation. The chromophore may also provide adequate charge generation. Alternatively, a sensitizer may be added to provide or boost the mobile charge required for photorefractive properties. 

Melting points and heats of fusion and decomposition were compared for the two methods. Particular attention was paid to the fusion endotherm to ascertain whether the glass capillary method accurately measured the transition. Results of this comparison as well as tiie decomposition exotherms are given in Table I for several NLO chromophores. Compounds were included just to show the reproducibility of the glass capillary method and the comparison with conventional aluminum pans at least in the case of the melting endotherm. 

Figure 11.1.1. The origin of two types of solvatochromic shifts in the spectra of chromophoric compounds.

La Course WR and Owens GS (1996) Pulse electrochemical detection of non chromophoric compounds following capillary electrophoresis. Electrophoresis 17 310-318. 

O. N. Witt assumed that coloured compounds contain atomic groupings which he called chromophors. Compounds containing chromophors he called chromogens although coloured they are not dyestuffs and have no affinity to tissues. Nitrobenzene is coloured but is not a dye. To produce dyes, the presence of groups such as OH or NHg is also necessary, which Witt later called auxochromes, Witt named as chromophors only the groups NO2, — N=N—, and CO occurring twice in quinones. ... 

A useful strategy in the design of new polymeric materials for electronic applications is the incorporation of a chromophore unit into the conjugated backbone of the polymer. One such class of chromophoric compounds that have gained interest over the past decade is represented by diketopyrrolopyrrole (DPP) derivatives. The chromophoric properties are attributed to the intramolecular charge transfer (ICT) between the aryl substituents at the 3- and 6- positions to the electron deficient lactam units. Tieke et al have reported an... 

Among the fundamental photophysical and photochemical processes, electron transfer has a high priority. Porphyrins and metalloporphyrins form one of the most promising series of chromophoric compounds for designing suitable redox systems as described above, since they have intense visible absorption bands and the can be varied by the substituents and the central metal ions. The redox properties are also easily regulated according to purpose. In recent intensive studies on electron transfer by various approaches from the viewpoints of theory. 

Mes and coworkers compared TDA, DLS, HDC, and SEC and showed that all four methods can be used effectively to determine diffusion coefficients of systems with low polydispersities by measuring a series of styrene acrylonitrile (SAN) copolymers. Although these are polymeric systems, it is possible to apply the findings to supramolecular ensembles. The characterization of samples of low polydispersity was achieved best with TDA and DLS, since they both allow the rapid and absolute determination of the diffusion coefficient. However, TDA has the disadvantage that it is subject to interference due to the presence of low-molecular-mass chromophoric compounds. DLS, on the other hand, is influenced much more by the polydispersity of the sample than TDA. Furthermore, the use of DLS enables direct measurements of the Z-average diffusion coefficient of a polydisperse sample but requires a relatively large amount of the sample and is concentration dependent. Unlike TDA, DLS is especially suited for the analysis of high-molecular-mass systems, such as supramolecular systems, and is not disturbed by the presence of low-molecular-mass impurities. 

Extended DPQ chromophores, compounds 118-120, have been investigated by Anzenbacher and coworkers. The effect of using 5,8-aryl substituents on the fluorescence was twofold with a red-shift in the emission maximum and an increase in the quantum yield. These modifications of the DPQ design also lead to an increase in binding affinity toward anions. Fluoride is bound strongly by all hosts (e.g., 118 Ka = 51 300 in acetonitrile) however, pyrophosphate was bound very strongly = 93 700 in acetonitrile). The addition of fluoride or pyrophosphate leads to the appearance of a new absorbance band at 500-550 nm and a decrease in the band at 400-450 mn. Besides a colorimetric response, fluorescence quenching is also observed. 

Chromophore Compound, or parts of a compound that absorb UV or visible light. 

A major problem in pharmaceutical analysis is the analysis of aliphatic amines. Because they are non-chromophoric compounds, UV detection is only possible at very low wavelengths (<200nm) which are prone to interferences by matrix and eluant components. Moreover, amines rmdergo interactions with free... 

Oxygenated carotenoids require a more polar solvent system, and the acetone content should be adjusted to 30-45% to effect acceptable separation. A combination of oxygenated sites and double bond positioning determines the retention, and the highly oxygenated violaxanthin is less sorbed than expected, mainly because of the short chromophore. Compounds that differ only within the ring system, such as lutein/zeaxanthin and taraxanthin/antheraxanthin, are clearly separated. 

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