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Introduction to Fluorescence and Photophysics
Published in Mary-Ann Mycek, Brian W. Pogue, Handbook of Biomedical Fluorescence, 2003
The absorption process involves interaction of the molecule in the ground state with a photon to promote an electron from a lower energy to a higher energy molecular orbital. The absorbance (A) of a sample is proportional to the concentration (c, in molarity M; Beer’s law) of absorbing species in a sample of pathlength ℓ (cm) traversed by the light and is generally independent of the intensity of the excitation light (Lambert’s law), although the latter may not hold under high-intensity laser irradiation. In transparent media the pathlength is simply the thickness of the sample, but it is more complex to determine in opaque or highly scattering materials. This results in the common expression of the Beer-Lambert law shown in Eq. (1). The molar absorption coefficient (ε in M−l cm−1) is the proportionality factor and its magnitude reflects the probability of the absorption of a photon of a given energy by the molecule. The absorption spectrum of a compound is constructed by plotting ε as a function of excitation wavelength. (
Biomedical Applications in Probing Deep Tissue Using Mid-Infrared Supercontinuum Optical Biopsy
Published in Lingyan Shi, Robert R. Alfano, Deep Imaging in Tissue and Biomedical Materials, 2017
Water is present in biological cells and tissue. The isolated water molecule (effectively water vapor) has three fundamental vibrational modes (see Figs 8.2(a)–(c)). These modes are: symmetrical stretching (υ1); asymmetrical stretching (υ3) and bending (υ2); the latter changes the H–O–H angle [5(c)]. MIR absorption spectra of liquid-water are more complex than that of isolated water molecules, due to hydrogen-bonding-based inter-molecular interactions in the liquid state. As introduced above, the molar absorptivity, ε (i.e. molar absorption coefficient), is defined as absorbance (A = ln Io (incident light intensity)/I (transmitted light intensity)) per mole of absorbing species and per cm path length (traditional units, non-SI). For liquid-water [9], at 25°C, the most strongly absorbing vibrational band is centered at 3404 cm–1 (2.94 μm; ε = 99.9 ± 0.8 M–1cm–1) and comprises three components: (i) second overtone (2υ2) at ∼3250 cm–1 (∼3.08 μm) of the bending mode (i.e. of the fundamental υ2 at 1644 cm–1 (6.08 μm wavelength)); (ii) enhanced by Fermi resonance with the υ1 symmetric stretching vibration at ∼3450 cm–1 (2.90 μm) and, finally, (iii) the third component is the υ3 asymmetrical stretching vibrational mode at ∼3600 cm–1 (2.78 μm). The fundamental υ2 bending vibrational absorption at 1644 cm–1 (6.08 μm wavelength) has ε = 21.8 ± 0.3 M–1cm–1. A broad absorption band in the range ∼500–800 cm–1 (∼12–20 μm wavelength) is due to librations: a collective, concerted normal mode (υL) involving many water molecules. There is also observed in MIR absorption spectra of liquid water a small combination band of bending and libration vibrations (υ2 + υL) at 2127 cm–1 (4.70 μm) [9]. It should be noted that there are likely to be changes incurred in both band position and intensity where water molecules are hydrogen- bonded to biomolecules, such as to the amide residue (–N–H—O(H)2) instead of, or as well as, to other water molecules, and also in conditions of extreme pH and/or in the presence of polar molecules.
Nickel(II)-PPh3 complexes of substituted benzophenone thiosemicarbazones: Electrochemistry, structural analysis, and antioxidant properties
Published in Journal of Coordination Chemistry, 2020
The compounds were tested by the normal CUPRAC methods at ambient conditions [11, 22]. Trolox (TR) was utilized as the standard reference compound for all antioxidant capacity studies. The slope of the linear calibration curve was evaluated to calculate the molar absorption coefficient (ɛ). In order to estimate the TEAC coefficients, the ratio between each of εcompound and εTR was used in Table 4. The TEACCUPRAC of the ligands and complexes were calculated as 3.16, 1.42, 2.00, and 4.82 for L1H2, L2H2, L3H2, and L4H2, respectively. Amongst all the compounds, it was revealed that the highest TEACCUPRAC coefficient was 4.82 for L4H2. The reason for this behavior is attributed to the ligand (L4H2) containing two different hydroxyl groups located on the phenolic structure. The highest antioxidant potential of L4H2 is linked to its electron donation ability based on the electron-transfer mechanism. The TEACCUPRAC values for nickel(II) complexes (1–4) were 0.93, 0.54, 1.61, and 2.95, respectively. These complexes exhibit less antioxidant capacity compared to their own ligands, indicating the coordination of metal ion to the hydroxyl group located at the meta-position of phenolic ring.
Preparation of fragrant collagen fibers by cross-linking with β-cyclodextrin and inclusion of l-menthol: characterization, release behavior and reusability evaluation
Published in The Journal of The Textile Institute, 2022
Huitao Wen, Xin Zheng, Guofei Yu, Yining Chen, Nianhua Dan, Zhengjun Li, Weihua Dan
The apparent stability constant Ka value was calculated from UV-vis data using the modified Hildebrand-Benesi equation Eq. (4) (Benesi & Hildebrand, 1949; Najlaoui et al., 2015; Zhang et al., 2008). where [CD]0 and [MEN]0 are the initial concentrations of β-CD and l-menthol, mol/L, respectively. Ka is the apparent stability constant for MEN/CD-COLF inclusion complex, L/mol. ε is the molar absorption coefficient, L/mol. And ΔA is the change value of the absorbance of the l-menthol by the addition of CD-COLF-II.