Synthesis of saccharidic polymer colloids via free radical mini‐emulsion polymerization

Polymer colloids based on 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐α‐D ‐glucofuranose (3‐MDG) and butyl acrylate (BA) were prepared via free radical mini‐emulsion polymerization. The kinetic and colloidal features of the copolymerization were investigated. The final particle size (D) of the sugar latexes is inversely proportional to the concentration of the anionic emulsifier (sodium dodecyl sulphate, SDS) and the non‐ionic one (alkyl polyglucoside, APG). It was also found that D is independent of the concentration of either the water‐soluble initiator (potassium persulfate, KPS), or the oil‐soluble initiator (2,2′‐azobisisobutyronitrile, AIBN). The rate of mini‐emulsion polymerization is lower in comparison with the conventional emulsion polymerization under the same conditions. The polymerization rate (R_p) and the total number of particles (N_p) are proportional to the 0.72th and 0.93th power of the SDS, and to the 1.40th and 2.22th of the APG concentration. Following reaction orders, 0.79/0.06 were obtained for R_p/N_p versus the concentration of KPS, and 0.22/?0.01 for AIBN, respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

On the conformational stability and dimerization of phosphotransferase enzyme I from Escherichia coli

The activity of enzyme I (EI), the first protein in the bacterial PEP:sugar phosphotransferase system, is regulated by a monomer–dimer equilibrium where a Mg²⁺-dependent autophosphorylation by PEP requires the homodimer. Using inactive EI(H189A), in which alanine is substituted for the active-site His189, substrate binding effects can be separated from those of phosphorylation. Whereas 1 mM PEP (with 2 mM Mg²⁺) strongly promotes dimerization of EI(H189A) at pH 7.5 and 20 °C, 5 mM pyruvate (with 2 mM Mg²⁺) has the opposite effect. A correlation between the coupling of N- and C-terminal domain unfolding, measured by differential scanning calorimetry, and the dimerization constant for EI, determined by sedimentation equilibrium, is observed. That is, when the coupling between N- and C-terminal domain unfolding produced by 0.2 or 1.0 mM PEP and 2 mM Mg²⁺ is inhibited by 5 mM pyruvate, the dimerization constant for EI(H189A) decreases from >10⁸ to <5 × 10⁵ or 3 × 10⁷ M⁻¹, respectively. With 2 mM Mg²⁺ at 15–25 °C and pH 7.5, PEP has been found to bind to one site/monomer of EI(H189A) with K_A′10⁶ M⁻¹ (ΔG′=−33.7±0.2 kJ mol⁻¹ and ΔH=+16.3 kJ mol⁻¹ at 20 °C with ΔC_p=−1.4 kJ K⁻¹ mol⁻¹). The binding of PEP to EI(H189A) is synergistic with that of Mg²⁺. Thus, physiological concentrations of PEP and Mg²⁺ increase, whereas pyruvate and Mg²⁺ decrease the amount of dimeric, active, dephospho-enzyme I.     

An Alternative Method for Anomeric Deacetylation of Per-acetylated Carbohydrates

An alternative method for anomeric deacetylation of fully acetylated carbohydrates has been developed using imidazole in methanol.     

Determination of Total Sugar in Tobacco by Near-Infrared Spectroscopy and Wavelet Transformation-Based Calibration

Based on wavelet transformation (WT) and mutual information (MI), a simple and effective procedure is proposed for multivariate calibration of near-infrared spectroscopy. In such a procedure, the original spectra of the training set are first transformed into a set of wavelet representations by wavelet prism transform. Then, the MI value between each wavelet coefficient variable and the dependent variable is calculated, resulting in a MI spectrum; by retaining a subset set of coefficients with higher MI, an update training set consisting of wavelet coefficients is obtained and reconstructed/converted back to the original domain. Based on this, a partial least square (PLS) model can be constructed and optimized. The optimal wavelet and decomposition level are determined by experiment. A NIR quantitative problem involving the determination of total sugar in tobacco is used to demonstrate the overall performance of the proposed procedure, named RPLS, meaning PLS in reconstructed original domain coupled with MI-induced variable selection in wavelet domain (RPLS). Three kinds of procedures, that is, conventional full-spectrum PLS in original domain (FPLS), PLS in original domain coupled with MI-induced variable selection (OPLS), and direct PLS in MI-based wavelet coefficients (WPLS), are used as reference. The result confirms that it can build more accurate and robust calibration models without increasing the complexity.     

碳糖苷合成的新进展

本文介绍了近几年来有关碳糖苷合成的最新进展, 包括亲电取代、亲核糖取代、过渡金属催化、异头碳自由基反应、重排和环加成反应以及糖环形成反应等。     

毛细管色谱直接进样法测定白酒中高碳脂肪酸乙酯的研究

介绍了采用ＦＦＡＰ键合毛细管柱直接进样测定白酒中５种高碳脂肪酸乙酯的方法，操作简捷，定量准确，检测限低达０４ｍｇ／Ｌ。用该法测定了各种香型近９０个白酒样品。改变色谱条件后，在一次直接进样分析中除能测定高碳脂肪酸乙酯外，而且还能对白酒中醇、酯、醛、酮以及有机酸等５２种香味组分进行定量测定，结果重现性良好。     

Synthesis of bridged sugar amino acids: a new entry into conformationally locked δ- and ε-amino acids

The synthesis of three methylene bridged sugar amino acids is described. Key transformations in the synthetic strategy are a CO-insertion on fully protected ribose, an aldol condensation with formaldehyde and an oxetane forming cyclisation step. A novel Leu-enkephalin analogue containing the δ-SAA 1 was prepared using standard solution phase peptide chemistry.     

Synthesis and Conformational Analysis of Cyclic Homooligomers from Pyranoid ε‐Sugar Amino Acids

New pyranoid ε‐sugar amino acids were designed as building blocks, in which the carboxylic acid and the amine groups were placed in positions C2 and C3 with respect to the tetrahydropyran oxygen atom. By using standard solution‐phase coupling procedures, cyclic homooligomers containing pyranoid ε‐sugar amino acids were synthesized. Conformation analysis was performed by using NMR spectroscopic experiments, FTIR spectroscopic studies, X‐ray analysis, and a theoretical conformation search. These studies reveal that the presence of a methoxy group in the position C4 of the pyran ring produces an important structural change in the cyclodipeptides. When the methoxy groups are present, the structure collapses through interresidue hydrogen bonds between the oxygen atoms of the pyran ring and the amide protons. However, when the cyclodipeptide lacks the methoxy groups, a U‐shape structure is adopted, in which there is a hydrophilic concave face with four oxygen atoms and two amide protons directed toward the center of the cavity. Additionally, we found important evidence of the key role played by weak electrostatic interactions, such as the five‐membered hydrogen‐bonded pseudocycles (C₅) between the amide protons and the ether oxygen atoms, in the conformation equilibrium of the macrocycles and in the cyclization step of the cyclic tetrapeptides.     

Separation of complex sugar mixtures on a hydrolytically stable bidentate urea‐type stationary phase for hydrophilic interaction near ultra high performance liquid chromatography

A stationary phase bearing both bridged bis‐ureido and free amino groups (USP‐HILIC‐NH₂–2.5SP) for high‐speed hydrophilic interaction liquid chromatography separations was prepared using a one‐pot two‐step procedure starting from 2.5 μm totally porous silica particles. Highly polar compounds, such as polyols, hydroxybenzoic acids, and sugars, were successfully analyzed in shorter times and with higher peak efficiency, when compared to results obtained with a bidentate urea‐type column packed with 5 μm particles. Increased sugarophilicity and better peak shape were attested for the USP‐HILIC‐NH₂–2.5SP column (100 × 3.2 mm id) when compared with two commercially available UHPLC columns, namely an acquity BEH amide packed with totally porous 1.7 μm microparticles and a HILIC Kinetex column packed with core–shell 2.6 μm particles. Finally, the new column was employed in the separation of complex mixture of sugars (mono‐, di‐, and oligosaccharides) and in the analysis of beer samples. The resulting chromatograms showed good selectivity and overall resolution, while the catalyzing effect of the free amino moieties resulted in excellent peak shapes and in the absence of split peaks due to sugar anomerization phenomena.     

真空离心浓缩/气相色谱-质谱联用法测定白酒中6种邻苯二甲酸酯类增塑剂

建立了测定白酒中6种邻苯二甲酸酯类增塑剂的真空离心浓缩/气相色谱-质谱联用(GC-MS)分析方法。样品经真空离心浓缩,正己烷提取,取上层正己烷,4000r/min离心5min,采用GC-MS测定,外标法定量。在0.10～5.00μg/mL范围内,相关系数r20.992,样品在0.10～2.00 mg/kg范围内加标,平均回收率在88.83%～111.67%之间,相对标准偏差(RSD)为4.85%～11.35%,检出限(LOD)在0.02～0.05 mg/kg之间。采用该方法对16个白酒样品进行测定,结果表明该法简便、快速、结果准确可靠、灵敏度高,能够满足白酒中6种邻苯二甲酸酯增塑剂检测需求。