Vortex counter-current chromatography

A novel counter-current chromatographic system is developed by mounting a vortex column on a type-I coil planet centrifuge. The column is fabricated from a high-density polyethylene disk (16 cm diameter and 5 cm thick) by making multiple holes of various diameters (3-12.5 mm) each arranged in a circle and connected with narrow transfer ducts. The performance of this vortex column is tested with three different two-phase solvent systems with a broad range in hydrophobicity. The results indicated that the smallest diameter column (3mm diameter, 120 units with 42.8 ml capacity) yielded the best separation with the height equivalent to a theoretical plate of 2 cm compared with 20 cm required by the conventional multilayer coil column of high-speed CCC. By avoiding the use of an Archimedean Screw Force, the system shows a low column pressure which would permit safe operation of a large preparative column without a risk of leakage of solvent and column damage.     

Contribution of spin and anisotropy to single molecule magnet behavior in a family of bell-shaped Mn11Ln2 coordination clusters

The synthesis, structures, and magnetic properties of a family of isostructural "bell-shaped" heterometallic coordination clusters [Mn(III)(9)Mn(II)(2)La(III)(2)(μ(4)-O)(7)(μ(3)-O)(μ(3)-OH)(2)(piv)(10.8)(O(2)CC(4)H(3)O)(6.2)(NO(3))(2)(OH(2))(1.5)(MeCN)(0.5)]·12CH(3)CN·2H(2)O (1) and [Mn(III)(9)Mn(II)(2)Ln(2)(μ(4)-O)(7)(μ (3)-O)(μ(3)-OH)(2)(piv)(10.6)(O(2)CC(4)H(3)O)(6.4)(NO(3))(2)(OH(2))]·nCH(3)CN·H(2)O (Ln = Pr(III), n = 8 (2); Ln = Nd(III), n = 10 (3); Ln = Eu(III), n = 17 (4); Ln = Gd(III), n = 13 (5); piv = pivalate) are reported. The complexes were obtained from the reaction of [Mn(III)(2)Mn(II)(4)O(2)(piv)(10)(4-Me-py)(2.5)(pivH)(1.5)] and Ln(NO(3))(3)·6H(2)O in the presence of 2-furan-carboxylic acid (C(4)H(3)OCOOH) in CH(3)CN. Compounds 1-5 are isomorphous, crystallizing in the triclinic space group P1 with Z = 2. The Mn(III) and Mn(II) centers together form the shell of the bell, while the two Ln(III) centers can be regarded as the bell's clapper. The magnetic properties of 1-4 reveal dominant antiferromagnetic interactions between the magnetic centers leading to small spin ground states; while those of 5 indicate similar antiferromagnetic interactions between the manganese ions but with unusually strong ferromagnetic interactions between the Gd(III) ions leading to a large overall spin ground state of S = 11-12. While ac and dc magnetic measurements confirmed that Mn(11)Gd(2) (5) is a single-molecule magnet (SMM) showing hysteresis loops at low temperatures, compounds 1-4 do not show any slow relaxation of the magnetization, indicating that the S = 7 spin of the ferromagnetic Gd(2) unit in 5 is a necessary contribution to its SMM behavior.     

Novel lanthanide-based polymeric chains and corresponding ultrafast dynamics in solution

Two types of structurally related one-dimensional coordination polymers were prepared by reacting lanthanide trichloride hydrates [LnCl(3)·(H(2)O)(m)] with dibenzoylmethane (Ph(2)acacH) and a base. Using cesium carbonate (Cs(2)CO(3)) and praseodymium, neodymium, samarium, or dysprosium salts yielded [Cs{Ln(Ph(2)acac)(4)}](n) (Ln = Pr (1), Nd (2), Sm (3), Dy (4)) in considerable yields. Reaction of potassium tert-butoxide (KOtBu) and the neodymium salt [NdCl(3)·(H(2)O)(6)] with Ph(2)acacH resulted in [K{Nd(Ph(2)acac)(4)}](n) (5). All polymers exhibit a heterobimetallic backbone composed of alternating lanthanide and alkali metal atoms which are bridged by the Ph(2)acac ligands in a linear fashion. ESI-MS investigations on DMF solutions of 1-5 revealed a dissociation of all the five compounds upon dissolution, irrespective of the individual lanthanide and alkali metal present. Temporal profiles of changes in optical density were acquired performing pump/probe experiments with DMF solutions of 1-5 via femtosecond laser spectroscopy, highlighting a lanthanide-specific relaxation dynamic. The corresponding relaxation times ranging from seven picoseconds to a few hundred picoseconds are strongly dependent on the central lanthanide atom, indicating an intramolecular energy transfer from ligands to lanthanides. This interpretation also demands efficient intersystem crossing within one to two picoseconds from the S(1) to T(1) level of the ligands. Magnetic studies show that [Cs{Dy(Ph(2)acac)(4)}](n) (4) has slow relaxation of the magnetization arising from the single Dy(3+) ions and can be described as a single-ion single molecule magnet (SMM). Below 0.5 K, hysteresis loops of the magnetization are observed, which show weak single chain magnet (SCM) behavior.     

Salen-based coordination polymers of iron and the rare earth elements

Reaction of N,N'-bis(4-carboxysalicylidene)ethylenediamine (H(4)L) with iron(III) chloride and lanthanide nitrates resulted in the coordination polymers of composition {[Ln(2)(FeLCl)(2)(NO(3))(2)(DMF)(5)]·(DMF)(4)}(n) (Ln = Y, Eu, Gd, Tb, Dy). The polymers consist of iron-salen-based moieties having carboxylate linkers connected to rare earth atoms in a 1D chain structure. Thus, the iron-salen complex acts as a "metalloligand". Because of the twisting of the chains, porous structures are formed and possess large free void space. The magnetic studies of selected compounds exhibit weak intramolecular antiferromagnetic interactions of Ln-Ln. At 3, 30, and 80 K, the M?ssbauer spectra of the iron-dysprosium compound show a strongly asymmetric quadrupole doublet with isomer shift and quadrupole splitting values typical for Fe(III) ions in high spin state. In addition, an anomalous temperature dependence of both isomer shift and quadrupole splitting has been observed.     

Pressure distributions in a static physical model of the uniform glottis: entrance and exit coefficients

Pressure distributions for the uniform glottis were obtained with a static physical model (M5). Glottal diameters of d=0.005, 0.0075, 0.01, 0.02, 0.04, 0.08, 0.16, and 0.32 cm were used with a range of phonatory transglottal pressures. At each pressure and diameter, entrance loss and exit coefficients were determined. In general, both coefficients decreased in value as the transglottal pressure or the diameter increased. Entrance loss coefficients ranged from 0.69 to 17.6. Use of these coefficients with the measured flow rates in straightforward equations accurately reproduced the pressure distributions within the glottis and along the inferior vocal fold surface.