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Abstract

An improved model of the screening effect is suggested. Mutual ≪shielding≫ of chromophores from light due to competition for the incident photon can take place in molecular aggregates and macromolecules. From a common point of view, it could be interpreted as in ≪interaction≫ of the absorption dipol moment transitions. Screening leads to a decrease in the extinction coefficient. The largest decrease is observed in the maximum of the absorption band. This is demonstrated with chromophores of adenine, tyrosine, tryptophan, retinol, porphyrin and anthracene. The model enables prediction of hypochromic spectra or evaluation of the quantity of chromophores in an aggregate or macromolecule.

New fluorescent derivatives of oligopropylamines

“…Self-association of the dye molecules is often accompanied by a hypochromic effect in UVVis spectra. [10][11][12][13][14][15] Spectra of mono-NBD derivatives of OPAs are similar to the known NBDamines 5 and contain two main bands near 350 and 500 nm (Table 1, Figure 1) irrespective of pH values. A decrease of absorbance at 500 nm was observed for NBD-N2H at pH 10 only.…”

“…[5][6][7] and from Ref. 8 for 13 C NMR of NBD ring. The NBD-tagged OPAs show basic properties and titration of NBD-N3 hydrochloride from acidic medium (an excess of HCl was added to adjust pH = 2) proceeds with three inflections which correspond to removal of the corresponding proton from the amine.…”

Hypochromicity in red blood cells: an experimental and theoretical investigation

“…The doublet at 547 and 575 nm showed good overlap between the whole and lysed red cell spectra. The differences in intensity have been attributed to molecular hypochromicity by several authors [24,25]. …”

“…Historically, certain strongly absorbing chromophores capable of close association have been shown to exhibit molecular hypochromism , a reduction in the absorption when the molecules are in close proximity of one another [20]. The phenomenon has been suggested to be present in strongly absorbing biological constituents such as chlorophyll [21,22], polynucleotides [23], and hemoglobin [24,25]. In the most well studied system, polynucleotides, the molecular hypochromic effect has been explained in terms of absorptive distortions due to molecular dipolar interactions [21] or the physical overlap of π orbitals of stacked chromophores [26].…”

“…Multiwavelength spectra is generally a more powerful tool compared to single wavelength analysis since given its greater information content, it offers the ability to elucidate multiple parameters for the characterization of a suspended system. Optical scattering analyses of erythrocytes have typically been limited to a single wavelength [32] or to a small number of select wavelengths [17,33,34], while multiwavelength representations have been reported as diffuse spectra [24,25]. Diffuse spectra results from the acquisition of a large amount of scattered light in colloidal systems and is typically defined by a wide angle of acceptance of the detector [35].…”