Pegylation of 1,4,8,11-tetraazacyclotetradecane (cyclam) and its Cu(II) complexation

Two novel star-like cyclam derivatives appended with four amino groups and four PEG-arms have been synthesised. The complex formation of cyclam and the two cyclam derivatives with Cu(II) has been studied by UV-vis and time-resolved laser-induced fluorescence (TRLFS) measurements outlining 1:1 complexes between cyclam ligands and Cu(II). By TRLFS measurements a quench effect of the Cu(II) on the fluorescence of the ligand was also found to determine the complex formation between Cu(II) and the ligands.     

Dissociation Kinetics of Aqua[(1SR, 4RS, 7RS, 8SR, 11RS, 14RS)-5,5,7,12,12,14-Hexamethyl-1,4,8,11-Tetraazacyclotetradecane]Copper(II) (Red) Cation in Strongly Acidic,Aqueous Media

In order to investigate the effect of structure variation upon complex dissociation rate constants, the kinetics of the dissociation of (C·rac·5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)copper(II) (red) cation has been examined spectrophotometrically at 25.0°C in 0.1–5.0 M HNO₃. The cleavage of the second copper-nitrogen bond is proposed as the rate-determining step for this reaction. The possible pathways for the cleavages of the copper-nitrogen bonds, the factors influencing the dissociation rates, and the factors affecting the relative importance of each of these possible pathways are considered.     

Solvent effects on the spectroscopic and photophysical properties of the trans-(1,4,8,11-tetraazacyclotetradecane)diisothiocyanatochromium(III) ion, trans-[Cr(cyclam)(NCS)(2)]+

The spectroscopy and photophysics of trans-[Cr(cyclam)(NCS)2]+ (where cyclam is 1,4,8,11-tetraazacyclotetradecane) were studied in a range of solvents. The cyclam NH stretching vibration [nu(NH)] wavenumber correlates with the Gutmann donor number, whereas the thiocyanate CN stretching vibration [nu(CN)] wavenumber correlates with the Snyder solvent strength (P') scale. These results signify that there is a difference in the solvent interactions with the two types of ligands. The energy of the ligand-to-metal charge transfer absorption maximum between 310 and 320 nm and the energy of the spin-forbidden (doublet-quartet) absorption and emission bands above 700 nm correlate with the nu(CN) wavenumber. This establishes the dominant role of solvent effects at the NCS- ligand in "tuning" the energy of these spectroscopic features. Quantum yields phirx for photosubstitution are <0.02 at 54 degrees C and <0.002 at 22 degrees C, demonstrating that photochemical reaction is a very minor pathway. The effects of solvent and temperature on the nonradiative decay of the doublet excited-state were investigated by observing the time-resolved phosphorescence between 700 and 750 nm. Below 30 degrees C, the lifetimes are relatively temperature-independent, whereas at higher temperatures, a strong Arrhenius-type dependence is observed. Values for the preexponential factor (A) and the activation energy (Ea) are solvent-dependent and follow a Barclay-Butler-type correlation. These observations are consistent with a dominant back-intersystem crossing pathway for nonradiative decay in the higher-temperature region. From trends observed between ln(A) and the nu(CN) frequency, it appears that solvent effects at the thiocyanate ligand play a dominant role in influencing the rate of nonradiative decay in the high-temperature region.     

Structure,solvatochromism, and solvation of trans-[CoIII(cyclam)(NCS)2](NCS) and the structure of [CoII(Me4cyclam) (NCS)]2[Co(NCS)4]MeOH

The structures of trans-[CoIII(cyclam)(NCS)2](NCS) and of [CoII(Me4cyclam)(NCS)]2[Co(NCS)4]·MeOH have been established by X-ray diffraction methods. The solvatochromic behavior of the trans-[Co(cyclam)(NCS)2]+ cation in several binary aqueous solvent mixtures is reported. Transfer chemical potentials for this complex from H2O into MeOH-H2O mixtures have been established from solubility measurements on its thiocyanate salt. The solvatochromic behavior of this cation is discussed in the context of other solvatochromic inorganic complexes; its transfer chemical potentials are discussed in relation to those of other cobalt(III) complexes.