Bifunctional cinchona alkaloids-catalyzed asymmetric [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones

A highly enantioselective [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones was realized with readily available cinchona alkaloids as the catalysts. Using this reaction, a series of highly functionalized δ-lactones with adjacent α-quaternary-β-tertiary stereocenters were obtained in high yields (up to 97%) and with good-to-excellent enantioselectivities (up to 97% ee).     

Control and Optimization of <Emphasis Type="Italic">Clostridium tyrobutyricum</Emphasis> ATCC 25755 Adhesion into Fibrous Matrix in a Fibrous Bed Bioreactor

The great performance of a fibrous bed bioreactor (FBB) is mainly dependent on the cell adhesion and immobilization into the fibrous matrix. Therefore, understanding the mechanism and factors controling cell adhesion in the fibrous matrix is necessary to optimize the FBB setup and further improve the fermentability. The adhesion behavior of a strain of Clostridium tyrobutyricum isolated from an FBB was studied, which was proven to be affected by the different environmental conditions, such as growth phase of cells, pH, ionic strength, ionic species, and composition of media. Our results also suggested that electrostatic interactions played an important role on bacteria adhesion into the fibrous matrix. This study demonstrated that the compositions of fermentation broth would have a significant effect on cell adhesion. Consequently, a two-stage glucose supply control strategy was developed to improve the performance of FBB with higher viable cell density in the operation of the FBB setup.     

Electrospray ionization tandem mass spectrometric characterization of DNA adducts formed by bromobenzoquinones

Bromobenzoquinones (BBQs) represent a class of reactive metabolites of various aromatic contaminants with bromine-containing substituents, including bromobenzene, bromophenols, polybrominated diphenyl ethers (PBDEs). Recently, 2,6-dibromobenzoquinone also has been detected directly from drinking water. The alternation of the genome caused by covalent binding of chemicals or their metabolites to DNA provides a viable mechanism for carcinogenicity. In the present study, electrospray ionization coupled with ion trap mass spectrometry (ITMS), triple quadrupole MS or quadrupole time-of-flight MS was applied for the analysis of DNA adducts formed by BBQs. The study demonstrated 2-monobromobenzoquinone and 2,6-dibromobenzoquinone could covalently bind to deoxyguanosine (dG) and DNA in vitro. The chemical structures of the DNA adducts were confirmed by accurate mass values, collision-induced fragmentation tandem mass spectra as well as isotopic patterns. Generally, the reaction mechanism for the DNA adduction involved Michael addition between the electron-deficient carbon from the quinone and the nucleophilic exocyclic nitrogen from the dG followed by reductive cyclization with loss of a small molecule such as H(2)O, or HBrO. It was of particular interest to note that some adducts were generated from the reaction of one dG molecule with two BBQ molecules. The obtained results provided new information for assessing the potential cancer risk associated with bromobenzene, bromophenols, PBDEs and BBQs.     

Asymmetric iodoamination of chalcones and 4-aryl-4-oxobutenoates catalyzed by a complex based on scandium(III) and a N,N'-dioxide ligand

Highly diastereo‐ and enantioselective iodoamination of chalcones, 4‐aryl‐4‐oxobutenoates, and a trifluoro‐substituted enone has been accomplished in the presence of a chiral N,N′‐dioxide/[Sc(OTf)₃] complex (0.5–2 mol %), delivering the desired vicinal anti‐α‐iodo‐β‐amino carbonyl compounds regioselectively in high yields (up to 97 %) and with excellent diastereoselectivities (>99:1 d.r.) and enantioselectivities (up to 99 % ee). Enantiopure syn‐α‐iodo‐β‐amino products could also be obtained from the isomerization of particular iodo compounds. TsNHX species (X=Cl, Br, I), generated from the reactions between the halo sources and TsNH₂, were further confirmed as the active species in the haloamination reactions involved in the formation of the key halonium ion intermediates. A typical haloamination dependency was observed, with reactivity decreasing in the order NBS>NIS?NCS.     

Towards a fully synthetic MUC1-based anticancer vaccine: efficient conjugation of glycopeptides with mono-, di-, and tetravalent lipopeptides using click chemistry

The membrane‐bound tumor‐associated glycoprotein MUC1 is aberrantly glycosylated in cancer cells compared with normal cells, and is therefore considered an attractive target for cancer immunotherapy. However, tumor‐associated glycopeptides from MUC1 do not elicit a sufficiently robust immune response. Therefore, antitumor vaccines were developed, which consist of MUC1 glycopeptides as the B epitopes and immune‐stimulating toll‐like receptor 2 (TLR 2) lipopeptide ligands. These fully synthetic vaccine candidates were prepared by solid‐phase synthesis of the MUC1 glycopeptides. The Pam₃Cys lipopeptide, also synthesized on solid‐phase, was C‐terminally coupled to oligovalent lysine cores, which N‐terminally incorporate O‐propargyl oligoethylene glycol acyl side chains. The MUC1 glycopeptides and lipopeptide lysine constructs were then conjugated by click chemistry to give oligovalent synthetic vaccines. Oligovalent glycopeptide–lipopeptide conjugates are considered more immunogenic than their monovalent analogues.     

One-step synthesis of silver/dopamine nanoparticles and visual detection of melamine in raw milk

In this work, we propose a simple, sensitive and reliable assay for melamine in raw milk with dopamine-stabilized silver nanoparticles (AgNPs) as a colorimetric reader. Dopamine can reduce Ag(+) and functionalize the produced AgNPs to form monodispersed AgNPs. The coexisting melamine in reaction solution could bind dopamine through Michael addition and Schiff base reactions, which leads to the aggregation of AgNPs and induces a colorimetric response. The one-step assay is simple, rapid and highly sensitive. The color-change is quantitatively correlated with the concentration of melamine in the range of 10 ppb to 1.26 ppm, which is below the safety limit in China (1.0 ppm) and EU (2.0 ppm). The coexisting substances including phenylalanine, dl-leucine, l-glutamate, sulfanilic acid, Mg(2+), galactose, lysine, urea and glucose do not affect the determination of melamine. The colorimetric sensor can be used for rapid monitoring of raw milk quality.     

Coexistence of magnetic and electric orderings in the metal-formate frameworks of [NH4][M(HCOO)3

A family of three-dimensional chiral metal-formate frameworks of [NH(4)][M(HCOO)(3)] (M = Mn, Fe, Co, Ni, and Zn) displays paraelectric to ferroelectric phase transitions between 191 and 254 K, triggered by disorder-order transitions of NH(4)(+) cations and their displacement within the framework channels, combined with spin-canted antiferromagnetic ordering within 8-30 K for the magnetic members, providing a new class of metal-organic frameworks showing the coexistence of magnetic and electric orderings.     

Dynamic pH junction-sweeping for on-line focusing of dipeptides in capillary electrophoresis with laser-induced fluorescence detection

In this paper, we developed a simple and effective on-line focusing technique combining dynamic pH junction and sweeping by capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. Dynamic pH junction-sweeping is defined when the sample has a different buffer pH (dynamic pH junction condition) and is devoid of micelles (sweeping condition) relative to the background electrolyte (BGE). This hyphenated focusing mode was applied to the sensitive and selective focusing of four dipeptides: Tyr-Phe, Tyr-Leu, Trp-Gly, and Ala-Gln. Picomolar detectability of these dipeptides by CE-LIF detection was demonstrated through effective focusing of large sample volumes (up to 39% capillary length) using the dual pH junction-sweeping focusing mode. 25 mmol L(-1) sodium dihydrogen phosphate, pH 2.5 was used as the sample matrix, and 100 mmol L(-1) borate, 21 mmol L(-1) sodium dodecylsulfate (SDS), 16 mmol L(-1) Brij35, pH 9.0 as the background solution (BGS). The concentration detection limits (S/N = 3) of the four dipeptides were in the range of 1.0-5.0 pmol L(-1). The developed method has been successfully used for the determination of dipeptides in human serum samples.     

Nitrate enhanced electrochemiluminescence determination of tris(2,3-dibromopropyl) isocyanurate with a gold nanoparticles-modified gold electrode

Tris(2,3-dibromopropyl) isocyanurate (TBC) is a heterocyclic hexabrominated flame retardant, which cannot be degraded even over a long time and may be a potential environmental pollutant. In this paper, TBC is for the first time as far as we know determined by silver nitrate-enhanced electrochemiluminescence (ECL) using a gold nanoparticles (AuNPs)-modified gold electrode. In our experiments, TBC was found to have the characteristics of increasing the ECL intensity of Ru(bpy)(3)(2+), and the ECL signal was proportional to the concentration of TBC. Based on this, we have successfully developed a novel, fast and sensitive method for the analysis of TBC. The main influencing factors including the volume ratio of acetonitrile and water, and the concentration of Ru(bpy)(3)(2+) were investigated in detail. Compared with using a bare gold electrode in MeCN without AgNO(3), the limit of detection is remarkably lowered by 20 times and the linear range is expanded by 5 times by using the AuNPs-modified gold electrode and AgNO(3). Under the optimal conditions, a limit of detection of 5.0 × 10(-8) M (S/N = 3) is achieved with a linear range of 1.0 × 10(-7) to 5.0 × 10(-5) M. The mechanism of the ECL enhancement of the system is also investigated.