Peter B. Wyatt

Quenching of Er(III) luminescence by ligand C–H vibrations: Implications for the use of erbium complexes in telecommunications

The authors have quantified the quenching of the luminescence lifetime of Er3+ ions in organic complexes due to the presence of CH vibrational oscillators as a function of their distance from the ion. They have shown that any hydrogen atoms within a sphere of at least 20A from an erbium ion will cause sufficient quenching to prohibit its use in telecommunications applications.

Dietary flavonoids inhibit the anticancer effects of the proteasome inhibitor bortezomib

Dietary flavonoids have many health-promoting actions, including anticancer activity via proteasome inhibition. Bor-tezomib is a dipeptide boronate proteasome inhibitor that has activity in the treatment of multiple myeloma but is not effective in chronic lymphocytic leukemia (CLL). Although CLL cells are sensitive in vitro to bortezomib-induced apoptosis when cultured in medium, the killing activity was blocked when cultured in 50% fresh autologous plasma. Dietary flavonoids, quercetin and myricetin, which are abundant in plasma, inhibited bortezomib-induced apoptosis of primary CLL and malignant B-cell lines in a dose-dependent manner. This inhibitory effect was associated with chemical reactions between quercetin and the boronic acid group, -RB(OH)2, in bortezomib. The addition of boric acid diminished the inhibitory effect of both quercetin and plasma on bortezomib-induced apoptosis. The protective effect was also reduced when myeloma cell lines, but not B-cell lines, were preincubated with quercetin, indicating a direct effect of quercetin on myeloma cells. At high doses, quercetin itself induced tumor cell death. These data indicate that dietary flavonoids limit the efficacy of bortezomib, whereas supplemental inorganic boric acid is able to reverse this. The complex interactions between quercetin, tumor cells, and bortezomib mean caution is required when giving dietary advice to patients.

Elucidating the role of hyperfine interactions on organic magnetoresistance using deuterated aluminium tris(8-hydroxyquinoline)

Measurements of the effect of a magnetic field on the light output and current through an organic light-emitting diode made with deuterated aluminum tris(8-hydroxyquinoline) have shown that hyperfine coupling with protons is not the cause of the intrinsic organic magnetoresistance. We suggest that interactions with unpaired electrons in the device may be responsible.

Cooperative Infrared to Visible Up Conversion in Tb3+, Eu3+, and Yb3+ Containing Polymers

The conversion of IR photons to higher energies is widely employed in lasers, imaging, and biology. Mechanisms based on nonlinear properties of the interaction between matter and radiation [ 1 ] are longstanding techniques to achieve this, but usually require very high excitation powers. Up-conversion (UC) processes, which occur when IR-excited centers populate a higher-energy emitting state, [ 2 ] represent a promising linear Hamiltonian alternative. This process can be extremely effi cient and allows a number of photonic and solar cell applications, [ 3 ] all of them currently based on inorganic materials. Consequently there are diffi culties with their processability, which, together with the low concentration of emitters required to avoid inter-ion quenching of the luminescence, [ 4 ] present serious operational limits. Here, we present and analyze the design rules for the observation of intense cooperative UC [ 5 ]

Electro-organic reactions. Part 41. Diels-Alder reactions of o-quinodimethanes from the cathodic reduction of α, α′-dibromo-1,2-dialkylbenzenes

Abstract Cathodic reduction of α, α′-dibromo-1,2-dialkylbenzenes in DMF containing Et4N+ Br− as supporting electrolyte, in the presence of dienophiles (e.g. maleic anhydride derivatives), yielded Diels-Alder adducts of o-quinodimethanes. Selective reduction of the benzylic dibromides was often possible even when their irreversible cyclic voltammetric reduction peak potentials were more negative than the Eo values for the anhydrides. This might be a consequence of redox catalysis, with the anhydrides having a dual role as mediators and dienophiles.

Studies of the kinetics of the reduction of chromate by glutathione and related thiols

The reduction of chromate by glutathione, its mono- and diethyl esters, L-cysteine, 2-mercapto-propionic acid and mercapto-succinic acid has been studied. The empirical rate law kobs = ab[Thiol]2/(1 + b[Thiol]) is obeyed by all of these thiols, at neutral pH. No evidence could be obtained for a first-order pathway in glutathione under these conditions. These observations are used to comment on the stability of intermediates potentially important in explaining chromate toxicity.

Luminescent zinc(II) complexes of fluorinated benzothiazol-2-yl substituted phenoxide and enolate ligands.

Zn(II) complexes of the following new, fluorine-containing, benzothiazole-derived ligands have been synthesized and characterized crystallographically: 2-(3,3,3-trifluoro-2-oxopropyl)benzothiazole (3), 4,5,6,7-tetrafluoro-2-(3,3,3-trifluoro-2-oxopropyl)benzothiazole (4), 4,5,6,7-tetrafluoro-2-(2-hydroxyphenyl)benzothiazole (12), 2-(3,4,5,6-tetrafluoro-2-hydroxyphenyl)-4,5,6,7-tetrafluorobenzothiazole (13), and 2-(3,4,5,6-tetrafluoro-2-hydroxyphenyl)benzothiazole (16); the Cu(II) complex of ligand 4 is also reported. These are analogs of the important photo- and electroluminescent material [Zn(BTZ)(2)](2), where H-BTZ = 2-(2-hydroxyphenyl)benzothiazole. DFT calculations indicate that HOMO and LUMO energy levels in these materials are substantially lowered by fluorination. The fluorinated ZnL(2) complexes are mononuclear (in contrast to the dinuclear, nonfluorinated material [Zn(BTZ)(2)](2)). They easily sublime and show broad visible photoluminescence. A common crystallographic feature is the existence of pairs of fluorinated ZnL(2) molecules related by inversion centers, with their π systems facing one another.

ADDITION TO ACTIVATED IMINES OF ENOLATES FROM CHIRAL N-ACYLOXAZOLIDINONES

Abstract The lithium and titanium enolates of N-acyloxazolidinones 1a–c add in their chelated forms to PhCHNTs, to give stereoselectively the β-amino acid derivatives 3a-c and 4a-c. The relative configurations of the newly created chiral centres were established by conversion to the trans (8a-c) or cis (9a, c) β-lactams. Absolute stereochemistry was assigned by correlation with known compounds 10a and tent-11a, together with an X-ray crystal structure determination on 9a. The use of the lithium enolate of 1a at −78 °C gave only a 1.4:1 ratio of anti product 3a to syn product 4a, but this ratio was improved to >5: 1 by the use of the chlorotitanium enolate of 1a at −55 °C or below. Similar results were obtained by using the chlorotitanium enolate of 1b, but for the chlorotitanium enolate of the N (phenylacetyl)oxazolidinone 1c the proportion of syn product 4c to anti product was significantly greater, consistent with a kinetically controlled reaction involving the si face of the chelated (Z)-enolate and the competing alternative transition states TS3 (reaction on si face of imine) and TS7 (reaction on re face of imine).

2-(penta-1,3-dienyl)oxazolidines: synthesis of hydroxylated piperidines by a stereoselective diels-alder Reaction

Abstract Hexa-2,4-dienal condensed with (-)-ephedrine to give predominantly the oxazolidine 4 , which underwent a stereoselective Diels-Alder reaction with benzyl nitrosoformate to give the cycloadducts 9 and 10 in a ca 5:2 ratio. Further transformations of 9 to give the optically active mono- and tri- hydroxypiperidine derivatives 11 and 15 have also been performed.

Nonradiative de-excitation mechanisms in long-lived erbium(III) organic compounds ErxY1-x[(p-CF3-C6F4)2PO2]3.

We have performed a spectroscopic study of ErxY1-x[(p-CF3-C6F4)2PO2]3 aimed at understanding nonradiative de-excitation mechanisms. These fluorinated compounds have a long lifetime for the erbium 4I13/2-->4I15/2 emission at lambda approximately 1540 nm, but the lifetime increases with decreasing x. We have studied the lifetime as a function of morphology, temperature, and high hydrostatic pressure. We have demonstrated the occurrence of energy migration and calculated the corresponding activation energy. Moreover, using high pressure techniques, we provide evidence that cross-relaxation involving energy transfer from an excited erbium in the 4I13/2 promoting a neighbor in the same state to 4I9/2 is the dominant mechanism at ambient conditions for short erbium-erbium distances. The model explains the observed dynamics of excited states in the series and is tested against the Yb[(p-CF3-C6F4)2PO2]3 compound.