Continued fractions with three limit points

On page 45 in his lost notebook, Ramanujan asserts that a certain q-continued fraction has three limit points. More precisely, if A_n/B_n denotes its nth partial quotient, and n tends to ∞ in each of three residue classes modulo 3, then each of the three limits of A_n/B_n exists and is explicitly given by Ramanujan. Ramanujan's assertion is proved in this paper. Moreover, general classes of continued fractions with three limit points are established.     

Simultaneous determination of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone in rat plasma by liquid chromatography-tandem mass spectrometry: application to a pharmacokinetic study of a standardized fraction of Salvia miltiorrhiza, PF2401-SF

A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the simultaneous determination of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone, the active components of Salvia miltiorrhiza in rat plasma, was developed. After liquid-liquid extraction with tariquidar as an internal standard, tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone were eluted from an Atlantis dC18 column within 5 min with a mixture of methanol and ammonium formate (10 mm, pH 6.5; 85:15, v/v). The analytes were detected by an electrospray ionization tandem mass spectrometry in the selected reaction monitoring (SRM) mode. The standard curves were linear (r=0.999) over the concentration range of 0.25-80 ng/mL for tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone in rat plasma. The coefficients of variation and the relative errors of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone for intra- and inter-assay at four quality control (QC) concentrations were 1.1-5.1% and -4.0-6.0%, respectively. The lower limit of quantification for tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone was 0.25 ng/mL from 100 microL of plasma. This method was successfully applied to the pharmacokinetic study of tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone after oral administration of PF2401-SF, the standardized fraction of Salvia miltiorrhiza enriched with tanshinone I, dihydrotanshinone I, tanshinone IIA and cryptotanshinone to male Sprague-Dawley rats.     

Chejuenolides A and B, new macrocyclic tetraenes from the marine bacterium Hahella chejuensis

Two new 17-membered carbocyclic tetraenes, chejuenolides A and B (1 and 2), have been isolated from the EtOAc extract of the marine bacterium Hahella chejuensis by various chromatographic methods. The structures and relative configurations of 1 and 2 were mainly determined by analysis of the NMR spectroscopic data, and their absolute configurations were assigned by application of modified Mosher method.     

Chemical synthesis of gold nanowires in acidic solutions

High aspect ratio gold nanowires with single crystalline surface have long been a missing piece in the toolbox of plasmonics metal nanostructures. Such wires are now made with a room temperature, surfactant assisted chemical synthesis in acidic aqueous solution. The diameters and lengths of the multiply twinned gold nanowires can be tuned by varying the amount of seed particles and acid in the growth solution. Nanowires with diameters around 35 nm and lengths up to 10 micron were made with a low seed concentration in pH approximately 1 solution.     

Crystal forms of a capsaicin derivative analgesic DA-5018

DA-5018 is a new capsaicin derivative and has analgesic effect. The objective of this work was to investigate the existence of polymorphs and pseudopolymorphs of DA-5018 and the transformation of crystal forms. Eight crystal forms of DA-5018 have been isolated by recrystallization and characterized by powder X-ray diffractometry (PXRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TG). The PXRD and DSC patterns of the eight crystal forms were different respectively. In the dissolution studies in simulated intestinal fluid at 37±0.5°C, the solubility of Form 2 was the highest. And the solubility in water decreased in rank order: Form 2>Form 3>Form 1>Form 5>Form 7>Form 4>Form 6>Form 8. Eight crystal forms were shown to have a good physical stability at room temperature for 60 days.     

Phase-field Determination of NaSICON Materials in the Quaternary System Na2O−P2O5−SiO2−ZrO2: The Series Na3Zr3–xSi2PxO11.5+x/2

Two types of solid electrolytes have reached technological relevance in the field of sodium batteries: ß/ß”-aluminas and NaSICON-type materials. Today, significant attention is paid to room-temperature stationary electricity storage technologies and all-solid-state Na batteries used in combination with these solid electrolytes are an emerging research field besides sodium-ion batteries. In comparison, NaSICON materials can be processed at lower sintering temperatures than the ß/ß”-aluminas and have a similarly attractive ionic conductivity. Since Na₂O−SiO₂−ZrO₂−P₂O₅ ceramics offer wider compositional variability, the series Na₃Zr_3–xSi₂P_xO_11.5+x/2 with seven compositions (0≤x≤3) was selected from the quasi-quaternary phase diagram in order to identify the predominant stability region of NaSICON within this series and to explore the full potential of such materials, including the original NaSICON composition of Na₃Zr₂Si₂PO_l2 as a reference. Several characterization techniques were used for the purpose of better understanding the relationships between processing and properties of the ceramics. X-ray diffraction analysis revealed that the phase region of NaSICON materials is larger than expected. Moreover, new ceramic NaSICON materials were discovered in the system crystallizing with a monoclinic NaSICON structure (space group C2/c). Impedance spectroscopy was utilized to investigate the ionic conductivity, giving clear evidence for a dependence on crystal symmetry. The monoclinic NaSICON structure showed the highest ionic conductivity with an optimum ionic conductivity of 1.22×10⁻³ at 25 °C for the composition Na₃Zr₂Si₂PO₁₂. As the degree of P⁵⁺ content increases, the total ionic conductivity is initially enhanced until x=1 and then decreases again. Simultaneously, the increasing amount of phosphorus leads a decrease in the sintering temperatures for all samples, which was confirmed by dilatometry measurements. The thermal and microstructural properties of the prepared samples are also evaluated and discussed.     

Electronic and steric effects controlling efficiencies of photoaddition reactions of fullerene C60 with N-α-trimethylsilyl-N-alkyl-N-benzylamines

Single electron transfer (SET)-promoted photoaddition reactions between fullerene C₆₀ and both various alkyl (Me, Et, i-Pr, t-Bu)- and para-substituted (p-Me, p-OMe, p-F, p-CF₃) arene ring containing, N-α-trimethylsilyl-N-alkyl-N-benzylamines were explored to gain information about photoproduct profiles and how the electronic and steric nature of the amine substrates influence reaction efficiencies. The results show that visible light (λ > 540 nm) irradiation of 10% EtOH-toluene solutions containing C₆₀ and N-α-trimethylsilyl-N-alkyl-N-benzylamines produce 1-aminomethyl-1,2-dihydrofullerenes as a sole photoproduct. In addition, SET-promoted photoaddition reactions of unsubstituted and para-electron donating group substituted arene ring containing N-α-trimethylsilyl-N-alkyl-N-benzylamines take place to give photoproducts more efficiently than those containing para-electron withdrawing group substituted arene rings. Moreover, although steric factors are less significant than the electronic nature of the amine substrates in governing reaction efficiencies, sterics do play a significant role in photoreactions of electron deficient amine substrates.     

Solid state of a new COX-2 inhibitor CG100649

CG100649 [4-(3-(3-Fluorophenyl)-5,5-dimethyl-4-oxo-4,5-dihydrofuran-2-yl)-benzenesulfonamide, polmacoxib, Acelex™] is a new NSAID used to treat osteoarthritis. It inhibits the enzymes carbonic anhydrase and COX-2. The objective of this work was to investigate the existence of polymorphs of CG100649 and the solubility of different crystal forms of CG100649. Four crystal forms of CG100649 (Forms 1–4) have been isolated by recrystallization and characterized by differential scanning calorimetry and powder X-ray diffractometry. In dissolution studies in pH 6.8 ± 0.05 buffer at 37 ± 0.5 °C, the solubility of Form 1 was the highest, and the dissolution rate at 30 min in water decreased in rank order: Form 3 > Form 2 > Form 4. After storage for one month at 2 °C and 24% relative humidity, all crystal forms were not transformed.

     

Cryopreservation of dormant herbaceous peony (Paeonia lactiflora pall.) shoot-tips by desiccation

A simplified technique for the cryoprotection of dormant shoot-tips was developed for the germplasm conservation of herbaceous peony (Paeonia lactiflora Pall.). The highest post-thaw regrowth level was obtained from shoot-tips desiccated by air drying for 5 h. The post-thaw regrowth of P. lactiflora. var. 'Mikang' was the highest (74.9 percent) among the five genotypes tested. The regeneration level after cryopreservation was highest (66approximate74%; average of 70 percent) for dormant shoot-tips collected from November to February. Shoot tips which were dissected from non-dormant buds in late March, however, showed very low post-thaw regrowth. Post-thaw regrowth of shoot-tips was promoted in MS medium containing 1 mg 1(-1) of gibberellic acid (GA3) and 0.5 mg 1(-1) of N(6)-benzyladenine (BA). The elongated shoots were rooted on a 1/4 MS medium containing 0.1 mg 1(-1) of beta-naphthalene acetic acid (NAA). In addition, random amplified polymorphic DNAs (RAPDs) assays suggested that the cryostorage treatment used here preserved the genetic fidelity of the peony dormant shoot-tips. This cryopreservation method appears to be promising for the conservation of herbaceous peony germplasm.