Search

Synthesis and photophysical characterisation of [Ln(hfac)3DPEPO] complexes (with Ln = Eu, Tb, Yb, Nd, Gd) has been carried out to investigate the factors responsible for the variation in total photoluminescence quantum yield within this family of emissive lanthanide complexes. Electronic absorption and emission spectroscopy, in conjunction with DFT calculations of the excited state of the Eu complex, elucidate the role of each ligand in the sensitisation of the lanthanide through the antenna effect. The X-ray crystal structure of [Gd(hfac)3DPEPO] has been determined and shows an 8-coordinate environment around the Gd and a ten-membered chelate ring involving the DPEPO ligand. Total photoluminescence quantum yields were measured to be 6%, 1% and 2% for Ln = Tb, Nd and Yb, respectively, in comparison with around 80% for Ln = Eu. The lower quantum yield for Nd and Yb, compared with Eu, can be attributed to more efficient quenching of the excited Ln state by high-energy oscillations within the ligands, whereas the lower quantum yield for Tb is assigned to a combination of poor energy transfer from the ligand excited state to the Tb and longer radiative lifetime. [ABSTRACT FROM AUTHOR]

Four new sterically hindered pyridines, L1-L4-containing amido substituents at the 2-position act as efficient solvent extractants for [CoCl4]2− or [ZnCl4]2− from acidic chloride solutions through protonation of the pyridino N-centre to form the neutral outer-sphere complexes [(LH)2MCl4]. These ionophores show very high selectivity for chlorometallate anions over chloride ion and are readily stripped to liberate the free-metal chlorides without the formation of inner-sphere complexes [ML2Cl2]. Single-crystal X-ray structure determinations of [(L2H)2CoCl4] and [(L2H)2ZnCl4] (L2=2-(4,6-di- tert-butylpyridin-2-yl)- N, N′-dihexylmalonamide) coupled with 1H NMR spectroscopy and DFT calculations on L2H+ and other complexes of [ZnCl4]2− confirm that the pyridinium NH group does not address the outer co-ordination sphere of the metallanion, but rather forms a hydrogen bond to the pendant amide groups and thus pre-organizes the ligand to present both CH and amido NH hydrogen-bond donors to the [MCl4]2− ions. The selectivity for chlorometallates over chloride ions shown by this class of extractants arises from their ability to present several polarized CH units towards the charge-diffuse ions [MCl4]2−, whereas the smaller, 'harder' chloride anion prefers to be associated with the amido NH hydrogen-bond donors. [ABSTRACT FROM AUTHOR]

The development of methods for measuring the efficiency of gas-plasma decontamination has lagged far behind application. An approach to measuring the efficiency of protein removal from solid surfaces using fluorescein-labelled bovine serum albumin and epifluorescence scanning (EFSCAN) is described. A method for fluorescently labelling proteins, which are adsorbed and denatured on metal surfaces, has been developed. Both approaches have been used to evaluate the efficiency of radio frequency (RF) gas-plasma decontamination protocols. Examples with 'real' surgical instruments demonstrate that an argon-oxygen RF gas-plasma treatment can routinely reduce the protein load by about three orders of magnitude beyond that achieved by current decontamination methods. [ABSTRACT FROM AUTHOR]

The decontamination of a range of "in-use" stainless steel surgical instruments by conventional hospital reprocessing techniques was studied, using scanning electron microscopic (SEM) and energy dispersive X-ray spectroscopic (EDX) analyses, with results obtained when an Ar: O2 RF gas-plasma treatment step was added to the cleaning cycle. In some cases, protein contaminants were still retained on instruments subjected to conventional cleaning and sterilization after seven cleaning cycles. No retention of contamination was evident on the surfaces of instruments that were subjected to gas-plasma cleaning. The efficacy of the plasma decontamination is significantly improved by hydration of the tissue residues immediately before exposure to the plasma. The reasons for this are not known, but it is suggested that the production of excited OH radicals and H atoms within the tissue matrix may play some part. Deposition of fluorescently labeled protein from physiological saline solution shows that protein is incorporated into salt crystals formed on stainless steel surfaces. This protein is resistant to plasma etching, but it is shown that water treatment results in improved cleaning. A combination of effects including physical "cracking" of the salt crystals under vacuum and dissolution of the inorganic matrix, which could possibly be accelerated by dipolar heating of the aqueous phase, may be responsible. [ABSTRACT FROM AUTHOR]

We explore the structure, torsional frequencies and electronic properties of the gas phase 4-cyanobiphenyl molecule, a prototypical liquid crystal core fragment, in its ground and first excited singlet electronic states. We employ a methodology which combines ab initioquantum mechanical calculations and fluorescence spectroscopy of laser-desorbed, jet-cooled molecules. The aim is to test the predictive power of parameter-free calculations of structure and dynamics in an experimental environment which is similar to the computational conditions of low thermal activation and negligible intermolecular interaction. Both spectroscopic and computational results indicate that very large molecular conformational changes accompany the optical pi → pi* transition. These are found to have a significant influence on the molecular flexibility and electronic polarity. [ABSTRACT FROM AUTHOR]

Abstract: A new multicolor pH-dependent fluorophore was synthesized via Pd-mediated cross-coupling chemistry of the mono-triflate of fluorescein with p-hydroxyphenylboronic acid. The novel indicator, named anthofluorescein, is highly sensitive to pH changes between 7 and 10 and displays a green to red fluorescence shift, making it a valuable candidate for biological studies. [Copyright &y& Elsevier]