Controllable self-assembly of organic-inorganic amphiphiles containing Dawson polyoxometalate clusters

An organic-inorganic molecular hybrid containing the Dawson polyoxometalate, ((C(4)H(9))(4)N)(5)H[P(2)V(3)W(15)O(59)(OCH(2))(3)CNHCOC(15)H(31)], was synthesized and its surfactant-like amphiphilic properties, represented by the formation of bilayer vesicles, were studied in polar solvents. The vesicle size decreases with both decreasing hybrid concentration and with increasing polarity of the solvent, independently. The self-assembly behavior of this hybrid can be controlled by introducing different counterions into the acetonitrile solutions. The addition of ZnCl(2) and NaI can cause a gradual decrease and increase of vesicular sizes, respectively. Tetraalkylammonium bromide is found to disassemble the vesicle assemblies. Moreover, the original counterions of the hybrid can be replaced with protons, resulting in pH-dependent formation of vesicles in aqueous solutions. The hybrid surfactant can further form micro-needle structures in aqueous solutions upon addition of Ca(2+) ions.     

Mapping the synthesis of low nuclearity polyoxometalates from octamolybdates to Mn-Anderson clusters

A comprehensive study of the isomer-independent synthesis of TRIS ((HOCH(2))(3)CNH(2)) Mn-Anderson compounds from Na(2)MoO(4)·2H(2)O, via the corresponding octamolybdate species, is presented. Three octamolybdate salts of [Mo(8)O(26)](4-) in the β-isomer form, with tetramethylammonium (TMA), tetraethylammonium (TEA) and tetrapropylammonium (TPA) as the counter cation, were synthesised from the sodium molybdate starting material. Fine white powdery products for the three compounds were obtained, which were fully characterised by elemental analysis, TGA, solution and solid state Raman, IR and ESI-MS, revealing a set ratio of Na and organic cations for each of the three compounds; (TMA)(2)Na(2)[Mo(8)O(26)] (1), (TEA)(3)Na(1)[Mo(8)O(26)] (2) and (TPA)(2)Na(2)[Mo(8)O(26)] (3), and the analyses also confirmed that the three compounds all consisted of the octamolybdate in the β-isomeric form. ESI-MS analyses of 1, 2 and 3 show similar fragmentation for these β-isomers compared to the previously reported study for the α-isomer ((TBA)(4)[α-Mo(8)O(26)]) (A) in the synthesis of ((TBA)(3)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)]) (B), and compounds 1, 2 and 3 were successfully used to synthesise equivalent TRIS Mn-Anderson compounds: (TMA)(3)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)] (4), (TEA)(3)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)] (5) and (TPA)(2)Na(1)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)] (6), as well as Na(3)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)] (7). This is the first example where symmetric organically-grafted Mn-Anderson compounds have been synthesised in DMF from anything but the {Mo(8)O(26)} α-isomer.     

Organic-soluble lacunary {M(2)(P(2)W(15))(2)} polyoxometalate sandwiches showing a previously unseen αββα isomerism

New polyoxometalate 'sandwiches' have been formed where two [P(2)W(15)O(56)](12-) lacunary Dawson clusters encapsulate two transition metal ions to give clusters with the general formula [M(II)(2)(P(2)W(15)O(56))(2)](20-) (where M = Mn, Co, and Ni respectively), [Fe(III)(2)(P(2)W(15)O(56))(2)](18-), and [Cu(II)(4)(P(2)W(15)O(56))(2)](16-). The Mn, Co, and Ni clusters exhibit a hitherto unseen αββα isomeric geometry and all five compounds are associated with tetrabutylammonium cations which allow for their dissolution in non-aqueous solvent.     

Cation induced structural transformation and mass spectrometric observation of the missing dodecavanadomanganate(IV)

The heteropolyvanadate cluster [(n-C(4)H(9))(4)N](4)[Mn(IV)V(12)O(34)]·2CH(3)CN has been isolated by cation exchange from K(10)[(Mn(IV)V(11)O(32))(2)]·20H(2)O. The structural transformation has been confirmed by X-ray single crystal structure determination and cryospray ionization mass spectrometry measurements.     

Electromagnetically Induced Transparency and optical pumping processes formed in Cs sub-micron thin cell

The Electromagnetically Induced Transparency (EIT) effect in a Λ-system formed by Cs atoms (6S_1/2 ? 6P_3/2 ? 6S_1/2) confined in an extremely thin cell (ETC) (atomic column thickness L varies in the range of 800 nm –3 µm is studied both experimentally and theoretically. It is demonstrated that when the coupling laser frequency is in exact resonance with the corresponding atomic transition, the EIT resonance parameters weakly depend on L, which allows us to detect the effect at L = λ = 852 nm. EIT process reveals a striking peculiarity in case of the coupling laser detuned by Δ from the atomic transition, namely the width of the EIT resonance rapidly increases upon an increase in Δ (an opposite effect is observed in centimeter-scale cells). The strong broadening of the EIT resonance for large values of detunings Δ is caused by the influence of atom-wall collisions on dephasing rate of coherence. The influence of the coupling laser on the velocity selective optical pumping/saturation resonances formed in ETC has been also studied. The theoretical model well describes the observed results.     

Morphogenesis of polyoxometalate cluster-based materials to microtubular network architectures

Pressed pellets of polyoxometalate (POM)-based materials are shown to undergo morphogenesis to produce microtubular network architectures without the need for a large single crystal precursor. The compression of the POM material into a pellet lowers the solubility sufficiently to allow tube initiation and growth from POMs that would otherwise be too soluble in their native crystalline state, thus yielding hollow, highly controllable, tubes of diameter 10-100 μm.     

Enhancing the emergence rate of coherent wavefronts from ocean ambient noise correlations using spatio-temporal filters

Extracting coherent wavefronts between passive receivers using cross-correlations of ambient noise (CAN) provides a means for monitoring the seismoacoustic environment without using active sources. However, using cross-correlations between single receivers can require a long recording time in order to extract stable coherent arrivals from CAN. This becomes an issue if the propagation medium fluctuates significantly during the recording period. To address this issue, this article presents a general spatio-temporal filtering procedure to enhance the emergence rate for coherent wavefronts extracted from time-averaged ambient noise correlations between two spatially separated arrays. The robustness of this array-based CAN technique is investigated using ambient shipping noise recorded over 24?h in the frequency band [250-850 Hz] on two vertical line arrays deployed 143?m apart in shallow water (depth 20?m). Experimental results confirm that the array-based CAN technique can significantly reduce the recording duration (e.g., from 22?h to 30?min) required for extracting coherent wavefronts of sufficient amplitude (e.g., 20?dB over residual temporal fluctations) when compared to conventional CAN implementations between single pairs of hydrophones. These improvements of the CAN technique could benefit the development of noise-based ocean monitoring applications such as passive acoustic tomography.     

Zero-term rank preservers

We obtain characterizations of those linear operators that preserve zero-term rank on the m×n matrices over antinegative semirings. That is, a linear operator T preserves zero-term rank if and only if it has the form T(X)=P(B∘X)Q, where P, Q are permutation matrices and B∘X is the Schur product with B whose entries are all nonzero and not zero-divisors.