Path integral Monte Carlo simulation of the absorption spectra of an Al atom embedded in helium

We use a multilevel path integral Monte-Carlo (PIMC) method to simulate the arrangement of He atoms around a single Al atom doped in a He cluster. High-level ab initio Al-He pair potentials and a Balling and Wright pairwise Hamiltonian model are used to describe the full potential and the electronic asymmetry arising from the open-shell character of the Al atom in its ground and excited electronic states. Our calculations show that the doping of the Al 3p electron strongly influences the He packing. The results of the PIMC simulation are used to predict the electronic excitation spectrum of an Al atom embedded in He clusters. With inclusion of tail corrections for the ground and excited states potentials, the calculated 3d<--3p spectrum agrees reasonably well with the experimental spectrum. The blueshift of the calculated spectrum associated with the 4s<--3p transition of solvated Al is about 25 nm (2000 cm-1) larger than seen in experiments on Al embedded in bulk liquid He. We predict that the spectrum associated with the 4p<--3p transition will be blueshifted by approximately 7000 cm-1 (nearly 1 eV).     

Migration of Additives from Poly(vinyl chloride) (PVC) Tubes into Aqueous Media

The stability and migration product of medical PVC tubes plasticized with polyadipates were investigated by ageing in phosphate buffer at pH 1.679 and water at different temperatures. Changes in the PVC tubes were studied by water absorption, weight loss, Fourier infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The low molecular weight migration product that was released was extracted and silylanized before gas chromatography/mass spectroscopy (GC/MS) identification and quantification. After 70 days, the weight loss was less than 0.5% and only a small amount of adipic acid migrated when a tube was aged at 37°C in water and phosphate buffer (pH 1.679), and at 70°C in water after 56 days. However, when aged at 70 and 110°C, gradual deactivation of heat stabilizer after 21 days of ageing in buffer solution and separation of plasticizer from PVC matrix occurred. When the tube was aged at 110°C, significant degradation of both polyadipates and PVC were observed. Adipic acid and 1,4-butanediol monomers and oligomers of polyadipate were the major migration products from polyadipates in the water ageing solution, while only a relatively high amount of adipic acid was identified as the main product in the buffer ageing solution.     

Tuning the Reactivity of Isocyano Group: Synthesis of Imidazoles and Imidazoliums from Propargylamines and Isonitriles in the Presence of Multiple Catalysts

The reaction of propargyl amines with tert‐butylisonitrile in the presence of a catalytic amount of both Yb(OTf)₃ and AgOTf afforded imidazoles, whereas the same reaction with primary and secondary alkylisonitriles, as well as arylisonitriles, in the presence of three metal salts [Yb(OTf)₃/AgOTf/KOTf] resulted in the 1,3,4,5‐tetrasubstituted imidazoliums in excellent yields. Both chiral amines and chiral isonitriles can be used to provide corresponding chiral heterocycles without racemization. In this multiple catalytic system, Yb(OTf)₃ catalyzed the insertion of isonitriles to the N? H bond of amines, AgOTf catalyzed the 5‐exo‐dig cyclization of the resulting amidine nitrogen to the tethered triple bond, and KOTf promoted the salt metathesis, thus providing at the same time the counterion to the imidazolium. Against common knowledge, the isocyano group acted in these reactions as a polarized triple bond instead of conventional carbene‐like function.     

聚合物基纳米复合材料性能及理论研究

对近些年来国内外聚合物／MMT纳米复合材料(polymer montmorillonite nanocomposites,PMN)的研究进行了归纳总结,详细讨论了该类材料结晶、流变和力学性能,阐述了合成过程中的热力学、动力学理论和平均场理论,最后对该类材料的制备方法提出展望。     

Synthesis of macrocyclic ligands incorporating sulfur and furan subunits

Abstract

Polyammonium macrocycles containing sulfur and furan units in the macrocyclic ring have been synthesized and studied for ATPase activity. The synthetic methodology involved using tosyl protection for the amines and the formation of macrocyclic Lactams, followed by reduction using borane in THF. Deprotection of the tosylated forms of the macrocycle was accomplished using sodium in butanol for the furan macrocycles, and HBr in HOAc for the sulfur containing macrocycle. The macrocycles were found to be poor catalysts for ATP hydrolysis compared to other similar polyammonium macrocycles.     

Efficient method for the synthesis of chiral pyrrolidine derivatives via ring-closing enyne metathesis reaction

[reaction: see text] A series of new pyrrolidine derivatives were prepared directly in very good yields, from the substrates containing a basic or nucleophilic N atom via ring-closing enyne metathesis reaction under mild reaction conditions. Moreover, the reaction occurs smoothly without the presence of ethylene gas.     

Context-dependent behavior of the enterocin iterative polyketide synthase; a new model for ketoreduction

Heterologous expression and mutagenesis of the enterocin type II polyketide synthase (PKS) system suggest for the first time that the association of an extended set of proteins and substrates is needed for the effective production of the enterocin-wailupemycin polyketides. In the absence of its endogenous ketoreductase (KR) EncD in either the enterocin producer "Streptomyces maritimus" or the engineered host S. lividans K4-114, the enterocin minimal PKS is unable to produce benzoate-primed polyketides, even when complemented with the homologous actinorhodin KR ActIII or with EncD active site mutants. These data suggest that the enterocin PKS requires EncD to serve a catalytic and not just a structural role in the functional PKS enzyme complex. This strongly implies that EncD reduces the polyketide chain during elongation rather than after its complete assembly, as suggested for most type II PKSs.     

Direct and quantitative analysis of underivatized acylcarnitines in serum and whole blood using paper spray mass spectrometry

A simple protocol for rapid quantitation of acylcarnitines in serum and whole blood has been developed using paper spray mass spectrometry. Dried serum and whole blood containing a mixture of ten acylcarnitines at various concentrations were analyzed as spots from paper directly without any sample pretreatment, separation, or derivatization. The composition of the spray solvent was found to be a critical factor: for serum samples, spray solvent of methanol/water/formic acid (80:20:0.1) gave the best signal intensity while for blood samples which contain more matrix components, acetonitrile/water (90:10) was a much more suitable spray solvent. For the paper type and size used, 0.5 μL of sample provided an optimal signal for both serum and whole blood samples. For quantitative profiling, the limits of quantitation obtained from both serum and blood were much lower than the clinically validated cutoff values for diagnosis of fatty acid oxidation disorders in newborn screening. Linearity (R(2) > 0.95) and reproducibility (RSD ~10 %) were achieved in the concentration ranges from 100 nM to 5 μM for the C2 acylcarnitine, and for other acylcarnitines, these values were from 10 to 500 nM. Acylcarnitine profiles offer an effective demonstration of the fact that paper spray mass spectrometry is an appropriate, simple, rapid method with high sensitivity and high reproducibility applicable to newborn screening tests.     

Rapid finding and quantification of the major antioxidant in water extracts of three marine drug organisms from China by online HPLC-DAD/MS-DPPH

A method based on high-performance liquid chromatography (HPLC) with diode array detector coupled with electrospray ionisation-mass spectrometry and an online detection system for radical scavenging was established and used to rapidly find and quantify antioxidant compounds in the water extracts of Hippocampus japonicus Kaup, Hippocampus kuda Bleeker and Syngnathus acus Linnaeus. The online screening results revealed the presence of one major radical scavenging compound identified as hypoxanthine by comparison of mass data and retention time with the standard. Subsequently, the developed HPLC method was applied to quantify hypoxanthine in different H. japonicus, H. kuda and S. acus samples. The results indicated that the developed HPLC method is simple and reliable for the quantification of hypoxanthine with a detection limit at 0.002 μg mL(-1), and a high recovery from 96.3% to 102.1%. This method provides a powerful tool for rapid identification and quantification of free radical scavenging compounds in complex marine natural products.