Ligand absorption

Luminescence spectroscopy provides simple access to the splitting of the ground multiplet but this technique is not always accessible due to nonradiative decay and strong ligand absorptions as encountered, for example, in the [Ln(Pc)]-/0 systems. For these reasons, alternative spectroscopic tools should be available for magnetochemists. The use of INS as a spectroscopic probe for molecular magnetic systems has recently been reviewed by Guidi [36], Amoretti et al. [37]... 

Electronic spectra of metalloproteins find their origins in (i) internal ligand absorption bands, such as n->n electronic transitions in porphyrins (ii) transitions associated entirely with metal orbitals (d-d transitions) (iii) charge-transfer bands between the ligand and the metal, such as the S ->Fe(II) and S ->Cu(II) charge-transfer bands seen in the optical spectra of Fe-S proteins and blue copper proteins, respectively. Figure 6.3a presents the characteristic spectrum of cytochrome c, one of the electron-transport haemoproteins of the mitochondrial... 

NaCl, KBr or polythene mulls. Assignment uncertain because of ligand absorption in this region. cbzim = benzimidazole. 2-Mebzim = 2-methylbenzimidazole. em = 1,3-diaminopropane. Him = imidazole. 8 Meim = methylimidazole. bigH = higuanide. 

The complexes have yellow to red colours and the electronic spectra are dominated by intense ligand absorptions. A weak band ususally found in the range 18000 to 21000 cm-1 has been assigned to the 4A2g— AT2g transition and provides an approximate value for A. 

A few observations of photosubstitution in lanthanide complexes have been reported. Irradiation into the f—f bands of [Pr(thd)3], [Eu(thd)3] and [Ho(thd)3] (thd is the anion of 2,2,6,6-tetramethyl-3,5-heptanedione) results in substitution of thd by solvent.153 The proposed mechanism involves intramolecular energy transfer from an f—f excited state to a reactive IL excited state which is responsible for the observed ligand loss. Photosubstitution has also been observed upon direct excitation into the ligand absorption bands of [Tb(thd)3].154... 

The photo substitution pathway probably involves intramolecular energy transfer from an f-f excited state to an intraligand state leading to the dissociation of ligand thd from the complex. Excitation of ligand absorption bands of Tb(thd)3 also leads to the same substitution reaction [111],... 

Size can also be a factor determining which endocytotic pathways are involved in ligand absorption. For example, in nonphagocytotic cells, latex beads with diameters less than 200 nm were taken up by the clathrin-dependent pathway, and latex beads with diameters between 200 and 500 nm were taken up by a caveolin-dependent process. Similarly, absorption of DNA-polycation complexes showed clear size dependence sizes greater than 200 nm were internalized by macropinocytosis. Intermediate size... 

In the following discussion, we analyze some factors responsible for the Eu3+ and Tb3+ luminescence intensity, that is the efficiencies of the ligand absorption, of the ligand-metal energy transfer, and of the metal luminescence. Furthermore, we compare the intensities of the metal luminescence... 

Ligand localized 7r r ES are common to complexes having large aromatic ligands. Absorption and emission bands attributed to nn states shift to the red with increasing P [6]. For example, fluorescence maxima from the ligand centered states of the tetraphenyl porphyrin complexes Mg(TPP) and Zn(TPP) display shifts ranging from —34 cm VlOO MPa in methanol to —94 cm /fOO MPa in chloroform with... 

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