Fingerprinting and simultaneous determination of alkaloids in Picrasma quassioides from different locations by high performance liquid chromatography with photodiode array detection

A simple and sensitive method was developed and validated for profiling and simultaneous quantitation of seven alkaloids (6-hydroxy-β-carboline-1-carboxylic acid, β-carboline-1-carboxylic acid, β-carboline-1-propanoic acid, 3-methylcanthin-5,6-dione, 5-hydroxy-4-methoxycanthin-6-one, 1-methoxycarbony-β-carboline, and 4,5-dimethoxycanthin-6-one) in Picrasma quassioide grown in different locations by high-performance liquid chromatography with photodiode array detection. The analysis was conducted on a Phenomenex Gemini C(18) column at 35°C with mobile phase of 25 mM aqueous ammonium acetate (pH 4.0, adjusted by glacial acetate acid) and acetonitrile. A common fingerprint chromatograph under 254 nm consisting of 27 peaks was constructed for the evaluation of the similarities among 31 P. quassioide samples. Samples from Guangdong and Guangxi Provinces were found to be within group linkage and showed significant difference from that of Jiangxi Province origin by using principal component analysis and hierarchical clustering analysis. In addition, the seven alkaloids were identified by electrospray ionization mass spectrometry and comparing with reference standards and literature data. All of them were determined simultaneously using the established HPLC method. This rapid and effective analytical method could be employed for quality assessment of P. quassioide, as well as pharmaceutical products containing this herbal material.     

One-dimensional lanthanide complexes bridged by nitronyl nitroxide radical ligands with non-chelating nitrogen donors: Structure and magnetic characterization

A series of new lanthanide-radical complexes [{Ln(hfac)3}2(NITPhIM)2] (Ln = Nd (1), Eu (2), Tb (3), Er (4); hfac = hexafluoroacetylacetonate; NITPhIM = 2-[4-(1-imidazole)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been prepared and characterized. Single crystal X-ray diffraction analyses reveal that these complexes are isostructural with one-dimensional chain structures. These consist in Ln(hfac)3 units bridged by the paramagnetic ligands by the means of coordination of their nitronyl nitroxide groups and imidazole rings. Interestingly, each Ln ion is either bound to two nitronyl nitroxide groups or to two imidazole units, and the different Ln centers alternate along the chain. Magnetic studies show that complex 3 exhibits a single-chain magnet behavior.     

Calixarene-supported hexadysprosium cluster showing single molecule magnet behavior

The syntheses, crystal structures, magnetic and luminescent properties of three isomorphous compounds [Ln III 6 (μ 4-O) 2 (C4A) 2-(NO 3 ) 2 (HCOO) 2 (CH 3 O) 2 (DMF) 4 (CH 3 OH) 4 ] (Ln = Gd (1), Tb (2) and Dy (3); H 4 C4A = p-tert-butylcalix[4]arene) are reported. These three compounds are featured with the sandwich-like units constructed by two tail-to-tail calixarene molecules and an in-between Ln III 6 octahedron. The Dy III compound exhibits both single molecule magnet behavior and photoluminescence.     

Electrochemical study on lithium iron phosphate/hard carbon lithium-ion batteries

The electrochemical performances of lithium iron phosphate (LiFePO₄), hard carbon (HC) materials, and a full cell composed of these two materials were studied. Both positive and negative electrode materials and the full cell were characterized by scanning electron microscopy, transmission electron microscopy, charge–discharge tests, and alternating current (a.c.) impedance techniques. Experimental results show that the LiFePO₄/HC full cell exhibits a gradually decreased cell voltage, and it is capable of delivering a reversible discharge capacity of 122.1 mAh g⁻¹ at 0.2-C rate. At the higher rate of 10 C, the efficiency of the full cell remains almost unchanged from that of 0.2 C. Furthermore, the LiFePO₄/HC battery demonstrated a long life of 2,450 cycles with 40% of capacity change at a 10-C high rate. The internal resistance of the full cell is rather low as it is revealed from a.c. impedance measurements. These properties make the LiFePO₄/HC battery an attractive option for high rate and long cycle life power applications.     

Tailoring carrier injection efficiency to improve the carrier balance of solid-state light-emitting electrochemical cells

We study the influence of the carrier injection efficiency on the performance of light-emitting electrochemical cells (LECs) based on a hole-preferred transporting cationic transition metal complex (CTMC) [Ir(dfppz)(2)(dtb-bpy)](+)(PF(6)(-)) (complex 1) and an electron-preferred transporting CTMC [Ir(ppy)(2)(dasb)](+)(PF(6)(-)) (complex 2) (where dfppz is 1-(2,4-difluorophenyl) pyrazole, dtb-bpy is 4,4'-di(tert-butyl)-2,2'-bipyridine, ppy is 2-phenylpyridine and dasb is 4,5-diaza-9,9'-spirobifluorene). Experimental results show that even with electrochemically doped layers, the ohmic contacts for carrier injection could be formed only when the carrier injection barriers were relatively low. Thus, adding carrier injection layers in LECs with relatively high carrier injection barriers would affect carrier balance and thus would result in altered device efficiency. Comparison of the device characteristics of LECs based on complex 1 and 2 in various device structures suggests that the carrier injection efficiency of CTMC-based LECs should be modified according to the carrier transporting characteristics of CTMCs to optimize device efficiency. Hole-preferred transporting CTMCs should be combined with an LEC structure with a relatively high electron injection efficiency, while a relatively high hole injection efficiency would be required for LECs based on electron-preferred transporting CTMCs. Since the tailored carrier injection efficiency compensates for the unbalanced carrier transporting properties of the emissive layer, the carrier recombination zone would be located near the center of the emissive layer and exciton quenching near the electrodes would be significantly mitigated, rendering an improved device efficiency approaching the upper limit expected from the photoluminescence quantum yield of the emissive layer and the optical outcoupling efficiency from a typical layered light-emitting device structure.     

Theoretical studies on the isomerization mechanism of the ortho-green fluorescent protein chromophore

We present a systematic theoretical investigation on the overall ground state and excited-state isomerization reaction mechanism of ortho-green fluorescent protein chromophore (o-HBDI) using the density functional theory and the multireference methods. The calculated results and subsequent analysis suggest the possible isomerization mechanism for o-HBDI. By comparison with experimental observation and detailed analysis, it is concluded that as initiated by the excited-state intramolecular proton transfer reaction, the conical intersection between the ground state and the excited state along the C4-C5 single-bond rotational coordinate is responsible for the rapid deactivation of o-HBDI.     

Ligand field-tuned single-molecule magnet behaviour of 2p-4f complexes

Three new 2p-4f complexes of [Ln(acac)(3)(NIT-2Py)]·0.5NIT-2Py [Ln(III) = Gd(1), Dy(2)] and [Dy(tfa)(3)(NIT-2Py)]·0.5C(7)H(16) (3) (NIT-2Py = 2-(2'-pyridyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; acac = acetylacetonate and tfa = trifluoroacetylacetonate) have been synthesized, and structurally and magnetically characterized. The X-ray structural analysis exhibits that the three complexes show similar mononuclear structures, in which NIT-2Py radical chelates the Ln(III) ion through the oxygen atom of the NO group and the nitrogen atom from the pyridine ring. The static magnetic measurements on the three complexes exhibit ferromagnetic coupling between the lanthanide ion and the radical. Compared to the silence of the out-of-phase ac susceptibility of complex 3, the magnetic relaxation behavior of complex 2 is observed, suggesting single-molecule magnet behavior. The different magnetic relaxation behaviours of 2 and 3 are due to their slightly different crystal structure around the Dy(III) ions. It was demonstrated that the spin dynamic can be modified by the careful adjustment of the ligand field around the metal center.     

Modulating spin dynamics of cyclic LnIII-radical complexes (LnIII = Tb, Dy) by using phenyltrifluoroacetylacetonate coligand

Three novel ring-like compounds formulated as [Ln(Phtfac)(3)(NITpPy)](2) (Ln(III) = Gd 1, Tb 2, Dy 3; HPhtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione; NITpPy = 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide) were synthesized and structurally and magnetically characterized. Three compounds possess cyclic dimer structure in which each pyridine substituted radical links two different metal ions through the oxygen of nitroxide group and the pyridine nitrogen. DC magnetic studies show the Ln(III) ion interacts ferromagnetically with the directly bonding nitronyl nitroxide. Both Tb(III) and Dy(III) clusters show frequency-dependent ac magnetic susceptibilities, indicating single-molecule magnet behavior. It is demonstrated that the β-diketonate coligand may play an important role in determining the magnetic relaxation for the lanthanide-radical system.     

A fluorescence enhancement-based sensor for hydrogen sulfate ion

Sugar-aza-crown ether-based cavitand 1 can act as a selective turn-on fluorescence sensor for hydrogen sulfate ion in methanol among a series of tested anions. Spectroscopic studies, particularly NMR spectroscopy, revealed that the C-H hydrogen bonding between 1,2,3-triazole ring of cavitand 1 and hydrogen sulfate ion is crucial for the high selectivity of the receptor for hydrogen sulfate.     

KF polymerase-based fluorescence aptasensor for the label-free adenosine detection

We have developed a simple, inexpensive, and label-free method for the selective detection of adenosine. Klenow fragment polymerase (KF polymerase) is a commonly-used 5' to 3' DNA polymerase, it also has 3' to 5' exonuclease activity that can digest single-stranded DNA. An adenosine binding DNA aptamer was employed, the aptamer was split into two pieces of single-stranded DNA (aptamer-A1 + aptamer-A2). Without the addition of adenosine, aptamer-A1 and aptamer-A2 existed as single-stranded DNA which could be efficiently degraded by the exonuclease activity of KF polymerase. Much reduced background fluorescence was obtained when SYBR Green dye was added. However, in the presence of adenosine, aptamer-A1 and aptamer-A2 bound to adenosine, and hybridization of the complementary sequences resulted in the formation of a duplex DNA structure, which could initiate DNA polymerization. The addition of SYBR Green dye resulted in a very high fluorescence enhancement, which could be used for the quantification of adenosine.