Long-lived triplet charge-separated state in naphthalenediimide based donor–acceptor systems

1,4,5,8-Naphthalenediimides (NDIs) are widely used motifs to design multichromophoric architectures due to their ease of functionalisation, their high oxidative power and the stability of their radical anion. The NDI building block can be incorporated in supramolecular systems by either core or imide functionalization. We report on the charge-transfer dynamics of a series of electron donor–acceptor dyads consisting of a NDI chromophore with one or two donors linked at the axial, imide position. Photo-population of the core-centred π–π* state is followed by ultrafast electron transfer from the electron donor to the NDI. Due to a solvent dependent singlet–triplet equilibrium inherent to the NDI core, both singlet and triplet charge-separated states are populated. We demonstrate that long-lived charge separation in the triplet state can be achieved by controlling the mutual orientation of the donor–acceptor sub-units. By extending this study to a supramolecular NDI-based cage, we also show that the triplet charge-separation yield can be increased by tuning the environment.

Ultrafast electron transfer from singlet and triplet excited states in equilibrium results in the population of both singlet and triplet charge-separated states.     

Convenient synthesis of N-methylamino acids compatible with Fmoc solid-phase peptide synthesis

N(alpha)-Methylamino acid containing peptides exhibit interesting therapeutic profiles and are increasingly recognized as potentially useful therapeutics. Unfortunately, their synthesis is hampered by the high price and unavaibility of many N(alpha)-methylamino acids. An efficient and practical preparation of N(alpha)-methyl-N(alpha)-(o-nitrobenzenesulfonyl)-alpha-amino acids without extensive purification is described. The procedure is based on the well-known N-alkylation of N(alpha)-arylsulfonylamino esters which was improved by using dimethyl sulfate and DBU as base. Ester cleavage is efficiently achieved by using an S(N)2-type saponification with lithium iodide, avoiding racemization observed with lithium hydroxide hydrolysis. Compatibility of the synthesized N(alpha)-methylamino acids with Fmoc solid-phase peptide synthesis is demonstrated by using normal coupling conditions to efficiently prepare N-methyl dipeptides. The described procedure allows the preparation of N(alpha)-methylamino acids in a very short period of time and a rapid synthesis of N-methyl peptides using Fmoc solid-phase peptide synthesis.     

Synthesis of the C(43)-C(67) fragment of amphidinol 3

[reaction: see text] A synthesis of the C(43)-C(67) fragment of amphidinol 3 (AM3) has been accomplished by a route that features the use of a double allylboration reaction for synthesis of 1,5-diol 4b, which serves as a precursor to dihydropyran 11.     

Copper(II) chloride complexes with multimodal ligands based on the cyclotriphosphazene platform

The reaction of hexakis(2-pyridyloxy)cyclotriphosphazene (L) and hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene (MeL) with copper(ii) chloride afford the complexes [CuLCl(2)], [(CuCl(2))(2)(MeL)], [CuLCl]PF(6) and [Cu(MeL)Cl]PF(6). The single-crystal X-ray structure of [CuLCl(2)] shows the copper ion to be in a square based pyramidal distorted trigonal bipyramidal (SBPDTBP) environment (tau= 0.47) with L acting as a kappa(3)N donor, coordinating via the nitrogen atoms from two non-geminal pyridyloxy pendant arms, a nitrogen atom in the phosphazene ring and two chloride ions. In the dimetallic complex, [(CuCl(2))(2)(MeL)], the geometry about both (symmetry related) copper(ii) centres is also SBPDTBP (tau= 0.57) with a 'N(3)Cl(2)' donor set. In the monocation of [CuLCl]PF(6), L acts as a kappa(5)N donor, bonding to the copper(ii) centre through the nitrogen atoms of four pyridyloxy pendant arms, a phosphazene ring nitrogen atom and a chloride ion to give an elongated rhombic octahedral coordination sphere. The phosphazene ring atoms remain virtually coplanar in all three structures as a consequence of the phenoxy-hinge, which links the pyridine pendant donors to the cyclotriphosphazene platform, allowing the formation of six-membered chelate rings. The spectroscopic (mass spectral, EPR and electronic) and magnetic properties of the complexes are discussed. The EPR and variable temperature magnetic susceptibility results for the dicopper complex, [(CuCl(2))(2)(MeL)], point to a very weak electronic interaction between the metal atoms.     

Electrophoresis in a non-Newtonian fluid: sphere in a spherical cavity

The electrophoretic behavior of a sphere in a non-Newtonian fluid is investigated theoretically by analyzing the phenomenon that occurs in a spherical cavity under the condition of a weak applied electrical field. Non-Newtonian behavior in the liquid phase may be due to, for example, the addition of polymer to a colloidal dispersion to improve its stability. It may also arise from the increase in the volume fraction of the dispersed phase such as the slurry used in chemical mechanical polishing. A Carreau model is adopted to characterize the shear-thinning behavior of the liquid phase. We show that the difference between the mobility of the particle based on the present model and that based on the corresponding Newtonian fluid increases with the decrease in the thickness of a double layer. The shear-thinning nature of the liquid phase has the effect of increasing the mobility.     

Nanostructuring, compositional fluctuations, and atomic ordering in the thermoelectric materials AgPb(m)SbTe(2+m). The myth of solid solutions

The nature of the thermoelectric materials Ag(1-x)Pb(m)SbTe(m+2) or LAST-m materials (LAST for Lead Antimony Silver Tellurium) with different m values at the atomic as well as nanoscale was studied with powder/single-crystal X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. Powder diffraction patterns of different members (m = 0, 6, 12, 18, infinity) are consistent with pure phases crystallizing in the NaCl-structure-type (Fmm) and the proposition that the LAST family behaved as solid solutions between the PbTe and AgSbTe2 compounds. However, electron diffraction and high resolution transmission electron microscopy studies suggest the LAST phases are inhomogeneous at the nanoscale with at least two coexisting sets of well-defined phases. The minority phase which is richer in Ag and Sb is on the nanosized length scale, and it is endotaxially embedded in the majority phase which is poorer in Ag and Sb. Moreover, within each nanodomain we observe extensive long range ordering of Ag, Pb, and Sb atoms. The long range ordering can be confirmed by single crystal X-ray diffraction studies. Indeed, data collections of five different single crystals were successfully refined in space groups of lower symmetry than Fmm including P4/mmm and Rm. The results reported here provide experimental evidence for a conceptual basis that could be employed when designing high performance thermoelectric materials and dispel the decades long belief that the systems (AgSbTe2)(1-x)(PbTe)x are solid solutions.     

Chiral bidentate aminophosphine ligands: synthesis, coordination chemistry and asymmetric catalysis

Chiral aminophosphines Ph2PN(R)(CH2)nN(R)PPh2 1-4 [n= 2, R = CH(CH3)(Ph) 1; n= 3, R = CH(CH2CH3)(Ph) 2, n= 2, R = CH(CH3)(1-naphthyl) 3; n= 2, R = CH(CH3)(C6H11) 4] were synthesized by the reaction of ClPPh2 with the appropriate easily accessible enantiopure amine building blocks. For compounds 1 and 2, the corresponding selenides 5 and 6 were prepared to determine the electronic character of the phosphine moieties. By reaction of 1 with either PdCl2(cod) or PdCl(CH3)(cod) the cis-complexes 7 and 8 were obtained. The molecular structure for complex 7, cis-[PdCl2(1)], was determined by X-ray crystallography. Reaction of PtCl2(cod) with 1 or 2 yielded the corresponding monomeric cis-isomers 9 and 10. The rhodium derivative [RhCl(CO)(1)] (11) was obtained as a mixture of cis and trans-isomers. Preliminary results in the rhodium catalyzed hydroformylation of styrene and vinyl acetate, with ee's up to 51% and high regioselectivities, showed the potential of these chiral aminophosphines for homogeneous catalysis.     

Quantitative analysis of perchlorate in extracts of whole fish homogenates by ion chromatography: comparison of suppressed conductivity detection and electrospray ionization mass spectrometry

The perchlorate anion (ClO ₄ ^– ) is an anthropogenic contaminant of increasing concern in water supplies, and has been shown to disrupt thyroid activity. Most perchlorate analyses are currently carried out by ion chromatography (IC) with suppressed conductivity detection (SCD). While this procedure has been demonstrated to provide acceptable performance for analysis of water samples, the determination of perchlorate in high-conductivity aqueous extracts of plant or animal material is not readily accomplished by IC-SCD unless lengthy cleanup protocols are applied. With the addition of electrospray ionization mass spectrometry (ESI-MS) to IC, it was hypothesized that the interference imposed by various ionic species could be significantly reduced without the need for purification; however, the analysis of perchlorate in relatively unpurified extracts of biologically derived homogenates by IC-ESI-MS has not previously been described in the literature. The research presented here represents a comparison of the capabilities of IC-SCD and IC-ESI-MS to detect perchlorate in reagent water and in crude extracts of perchlorate-exposed fish (threespine stickleback, Gasterosteus aculeatus). ESI-MS was found to compare favorably to SCD for the detection of perchlorate in deionized water, and to exceed SCD performance in perchlorate analysis of fish-derived extracts.