An EPR investigation of room temperature radiation damage and molecular motion in the ferroelectric phosphates

Several types of paramagnetic centers have been detected in the room temperature irradiated KH₂PO₄, KD₂PO₄, KH₂PO₄KH₂AsO₄, KD₂PO₄KD₂AsO₄ and in the newly discovered ferroelectric NaTh₂(PO₄)₃. Comparative studies of temperature dependence in the EPR spectra show that as in KH₂PO₄-type crystals, the ferroelectric phase transition in NaTh₂(PO₄)₃ crystals also seems to be related to the motion of the PO₄ units. The results help to clarify some earlier observed anomalies on the effects of γ-irradiation on dielectric properties of KH₂PO₄ and in particular, show that the extent of the damage can be controlled by changing the impurity content of the unirradiated samples.     

An AC electrokinetic technique for collection and concentration of particles and cells on patterned electrodes

We report an electrohydrodynamic effect arising from the application of alternating electric fields to patterned electrode surfaces. The AC fields were applied to dilute suspensions of latex microspheres enclosed between a patterned silicon wafer and an ITO-coated glass slide in a small chamber. The latex particles became collected in the center of the conductive "corrals" on the silicon wafer acting as bottom electrode. The particle collection efficiency and speed depended only on the frequency and strength of the field and were independent of the material properties of the particles or the electrodes. The leading effect in the particle collection process is AC electrohydrodynamics. We discuss how the electrohydrodynamic flows emerge from the spatially nonuniform field and interpret the experimental results by means of electrostatic and hydrodynamic simulations. The technique allows three-dimensional microfluidic pumping and transport by the use of two-dimensional patterns. We demonstrate on-chip collection of latex particles, yeast cells, and microbes.     

Observation of symmetry lowering and electron localization in the doublet-states of a spin-frustrated equilateral triangular lattice: Cu3(O2C16H23) x 1.2C6H12

Cu3(O2C16H23)6.1.2C6H12, containing a Cu36+ core in an equilateral triangle geometry, has been found to be a versatile model system for investigating the spin-frustration phenomenon in a triangular lattice. It affords well-resolved EPR spectra from both of the two possible (Stotal = 1/2 and 3/2) spin states of the Cu36+ core. From 295 to 100 K, the spectra consist of a triplet, but with the central line overlapped by an additional, sharp peak, which replaces the triplet at 30 K and below. The triplet was thus assigned to the excited state with Stotal = 3/2, located at 324 +/- 5 K ( approximately 225 cm-1), with the zero-field parameters D = -535 G, E = 0, g parallel = 2.209 and g perpendicular = 2.057. The singlet was attributed to the Stotal = 1/2 state, with gxx = 2.005, gyy = 2.050, gzz = 2.282, and, surprisingly, a hyperfine splitting arising from a single Cu2+ nucleus, with Azz = 157 G. The detailed magnetic measurements on a three-electron, equilateral triangular system, and the observation of symmetry lowering in the doublet ground state, should be of broad theoretical and experimental interest in molecular magnetism.     

Structure, electrochemistry, and magnetism of the iron(III)-substituted Keggin dimer, [Fe6(OH)3(A-alpha-GeW9O34(OH)3)2]11-

The iron(III)-substituted tungstogermanate [Fe6(OH)3(A-alpha-GeWO34(OH)3)2]11- (1) has been synthesized and characterized by IR, elemental analysis, SQUID magnetometry, electron paramagnetic resonance (EPR), and electrochemistry. Single-crystal X-ray analysis was carried out on Cs4Na7[Fe6(OH)3(A-alpha-GeW9O34(OH)3)2] x 30H2O, which crystallizes in the monoclinic system, space group C2/m, with a = 36.981(4) A, b = 16.5759(15) A, c = 16.0678(15) A, beta = 95.311(3) degrees, and Z = 4. Polyanion 1 consists of two (A-alpha-GeW9O34) Keggin moieties linked via six Fe3+ ions, leading to a double-sandwich structure. The equivalent iron centers represent a trigonal prismatic Fe6 fragment, resulting in virtual D3h symmetry for 1. Electrochemistry studies revealed that 1 is stable in solution from pH 3 to at least pH 7. In pH = 3 media the reduction of the six Fe3+ centers was featured by a single voltammetric wave for most supporting electrolytes used. In that case, whatever the scan rate from 1000 mV x s(-1) down to 2 mV x s(-1), no splitting of the single Fe-wave of 1 was observed. The acetate medium induced a partial splitting of the wave, and this separation is enhanced with increasing pH. Remarkable efficiency of 1 in the electrocatalytic reduction of nitrite, nitric oxide, and nitrate is demonstrated. Magnetic susceptibility (chi) measurements indicate a diamagnetic (S(T) = 0) ground state, with an average J = -12 cm(-1) and g = 2.00. EPR studies confirm that the ground state is indeed diamagnetic, since the EPR signal intensity steadily decreases without any line broadening as the temperature is lowered and becomes unobservable below about 50 K. The signal is a single broad peak at all frequencies (90-370 GHz), ascribed to the thermally accessible excited states. Its g(iso) is 1.992 51, as expected for a high-spin Fe3+-containing species, and supports the chi data analysis.     

Confined Water in Amyloid‐Competent Oligomers of the Prion Protein

Conformational switching of the prion protein into the abnormal form involves the formation of (obligatory) molten‐oligomers that mature into ordered amyloid fibrils. The role of water in directing the course of amyloid formation remains poorly understood. Here, we show that the mobility of the water molecules within the on‐pathway oligomers is highly retarded. The water relaxation time within the oligomers was estimated to be ≈1 ns which is about three orders of magnitude slower than the bulk water and resembles the characteristics of (trapped) nano‐confined water. We propose that the coalescence of these obligatory oligomers containing trapped water is entropically favored because of the release of ordered water molecules in the bulk milieu and results in the sequestration of favorable inter‐chain amyloid contacts via nucleated conformational conversion. The dynamic role of water in protein aggregation will have much broader implications in a variety of protein misfolding diseases.     

Estimation of L-dopa from Mucuna pruriens LINN and formulations containing M. pruriens by HPTLC method

A selective, precise, and accurate high-performance thin-layer chromatographic (HPTLC) method has been developed for the analysis of L-dopa in Mucuna pruriens seed extract and its formulations. The method involves densitometric evaluation of L-dopa after resolving it by HPTLC on silica gel plates with n-butanol-acetic acid-water (4.0+1.0+1.0, v/v) as the mobile phase. Densitometric analysis of L-dopa was carried out in the absorbance mode at 280 nm. The relationship between the concentration of L-dopa and corresponding peak areas was found to be linear in the range of 100 to 1200 ng/spot. The method was validated for precision (inter and intraday), repeatability, and accuracy. Mean recovery was 100.30%. The relative standard deviation (RSD) values of the precision were found to be in the range 0.64-1.52%. In conclusion, the proposed TLC method was found to be precise, specific and accurate and can be used for identification and quantitative determination of L-dopa in herbal extract and its formulations.     

Thin-Layer Chromatographic Enantioseparation of (RS)-Etodolac Using Indirect Approach

JPC – Journal of Planar Chromatography – Modern TLC - Enantioseparation of (RS)-etodolac was achieved by an indirect approach. Extraction of the drug (RS)-etodolac (Etd) was done from...     

[bmim]OH: An efficient catalyst for the synthesis of mono and bis spirooxindole derivatives in ethanol at room temperature

A rapid and efficient, one pot synthesis of spirooxindole derivatives has been attempted by threecomponent reaction of isatin, malononitrile and carbonyl compound possessing a reactive α-methylene group by using task specific ionic liquid, 1-butyl-3-methyl imidazolium hydroxide [bmim]OH as a catalyst. The important features of this methodology are straight forward route in short reaction time at room temperature and avoid any hazardous organic solvent, toxic catalyst, tedious purification step. Interestingly, this protocol is not only limited to mono-systems but also to the synthesis of newer bisspirooxindole system. The separation of the product and reusability of the catalyst are easy with excellent yield. The [bmim]OH catalyst system could be reused up to five recycles without appreciable loss of activity.