Good to excellent stereoselectivity has been found in the addition reactions of Grignard and organozinc reagents to N-protected aziridine-2-carboxaldehydes. Specifically, high syn selectivity was obtained with benzyl-protected cis, tert-butyloxycarbonyl-protected trans, and tosyl-protected 2,3-disubstituted aziridine-2-carboxaldehydes. Furthermore, rate and selectivity effects of ring substituents, temperature, solvent, and Lewis acid and base modifiers were studied. The diastereomeric preference of addition is dominated by the substrate aziridines' substitution pattern and especially the electronic character and conformational preferences of the nitrogen protecting groups. To help rationalize the observed stereochemical outcomes, conformational and electronic structural analyses of a series of model systems representing the various substitution patterns have been explored by density functional calculations at the B3LYP/6-31G* level of theory with the SM8 solvation model to account for solvent effects. 相似文献
A family of ZnII‐based metal–organic coordination polymers (MOCPs) [Zn(L)(imid)2] ( 1 ), [Zn(L)(2,2′‐bpy)] ( 2 ), [Zn2(L)2(Py)3] ( 3 ), [Zn(L)(DPP)]?DMF ( 4 ), [Zn(L)(DPEA)] ( 5 ), [Zn2(L)2(4,4′‐bpy)] ( 6 ), [Zn(L)(3,4′‐DPEE)]?DMF ( 7 ), and [Zn3(L)3(3,4′‐DPEE)2]?DMF ( 8 ) (L=dithieno[3,2‐b:2′,3′‐e]benzene‐2,6‐dicarboxylic acid, imid=imidazole, bpy=bipyridine, Py=pyridine, DPP=1,3‐di(pyridin‐4‐yl)propane, DPEA=1,2‐di(pyridin‐4‐yl)ethane, and DPEE=(E)‐3,4′‐(ethene‐1,2‐diyl)dipyridine) have been rationally designed and generated in the solvothermal reaction systems of the new conjugated thiophene derivative L, Zn(ClO4)2?6 H2O, and seven different aromatic N‐donor co‐ligands separately. These N‐donor compounds were carefully selected and employed in the crystal preparation of the eight MOCPs as structure‐directing co‐ligands owing to their structural specialties and habitual coordination fashions. Among these MOCPs, compounds 1 – 3 are 1D polymers with different chain structures. Compounds 4 , 7 , and 8 are 2D structures, in which 4 has two sets of twofold interpenetrating layers, whereas 7 and 8 are both built from three independent sheets. Compounds 5 and 6 are 3D frameworks, in which 5 exhibits a fivefold interpenetrating diamondoid network, whereas 6 shows a typical twofold interpenetrating pillared layer structure with nanoscale channels. The photoluminescent properties of these MOCPs, including excitation, emission, and radiactive lifetime, have also been investigated to help us tentatively understand their structure–property relationships. 相似文献
Effects of temperature on self‐interaction of human‐like collagen (HLC) were investigated by hydrophobic interaction chromatography, calorimetric measurement, and sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) analysis. Results show that three types of interaction roles may exist between HLC molecules at 3–50°C, which were divided into three narrower temperature ranges. In temperature range from 3–22°C, hydrogen bonding plays a key role in the formation of a gelatinous aggregate. In the range of 22–38°C, hydrophobic bonds accompanied by hydrogen bonds are involved in the formation compact aggregates. When temperature is above 38°C the hydrophobic effect formed in the HLC monomer results in the loss of its ability to self‐interact. 相似文献
A static and exhaustive extraction mode of hollow fiber-supported liquid membrane was developed for field sample passive pretreatment of environmental water samples. The extraction device was prepared by immobilizing dihexyl ether in the wall of a polypropylene hollow fiber membrane (60 cm length, 50 μm wall thickness, and 280 μm id) as liquid membrane and filling the fiber lumen with 0.1 M NaOH as acceptor, and closing the two ends of the fiber with an aluminum foil. Passive extraction was conducted by immersing the device into 15 mL water samples modified with 0.01 M HCl and 20% m/v NaCl. Model analytes including 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol were transferred into acceptor with extraction efficiencies over 79% in 10 h at room temperature, and determined by high-performance liquid chromatography. The proposed method has the enrichment factor of 394-498 and LOD of 0.3-0.4 μg/L for the three chlorophenols. Humic acid and salinity in the environmentally relevant range had no significant influence on the extraction, and chlorophenols in various environmental waters were determined with spike recoveries between 71.6 and 120%. The static passive extraction nature benefited field sample pretreatment without power, whereas the exhaustive extraction mode effectively eliminated the sample matrix effects. 相似文献
A series of amphiphilic multi‐armed PPn copolymers were prepared by ROP of Phe‐NCA with PEI‐25k as a macroinitiator. The particle size of the PPn/DNA complexes was about 100 nm and the zeta potentials were below 20 mV. An MTT assay demonstrated that all the PPn copolymers had lower cytotoxicity compared to PEI‐25k. In vitro gene transfection studies were also conducted in HeLa, 293 and CT 26 cells. The optimal quantity of hydrophobic phenylalanine segments in PP80 led to higher transfection efficiency in various cell lines based on this study. The results indicate that PP80 was the best candidate for gene delivery among these PPn copolymers.
A simple, low cost, fast and sensitive method is reported for the determination of the four endocrine disrupting chemicals (EDCs) 4-tert-butylphenol, 4-tert-octylphenol, bisphenol A and 17β-estradiol using pentafluoropyridine as the derivatizing reagent. These EDCs were determined by simultaneous extraction and derivatization in a solid phase analytical derivatization (SPAD) technique without the aid of any phase transfer catalyst (PTC) or an ion-pair mechanism. Recoveries of analytes as their tetrafluoropyridyl derivatives from water ranged from 71% for 4-tert-butylphenol to 106% for 17β-estradiol; from urine they ranged from 61% for 17β-estradiol to 91% for 4-tert-octylphenol; and from humic acids solution the ranged from 59% for 17β-estradiol to 104% for 4-tert-octylphenol in humic acid solutions. Calibration curves were constructed from a matrix of human male urine in the range 1-40 ng/mL and had coefficients of correlation greater than 0.99. For 4-tert-butylphenol, bisphenol A and 17β-estradiol the limits of quantitation were 5 ng/mL and for 4-tert-octylphenol it was 1 ng/mL. This method was applied to determine EDCs and detected 4-tert-octylphenol, bisphenol A and 17β-estradiol in concentrations comparable to those found in the literature. The method offers advantages in speed of analysis, reduced reagent and specificity of derivatization. 相似文献