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1.
Organic nanoparticles from a chiral auxiliary, (R)-(+)-1,1'-bi-2-naphthol dimethyl ether (BNDE), with a range of particle sizes from 25 to 100 nm were fabricated through the reprecipitation method. It is found that BNDE nanoparticles exhibit positive exciton chirality in 200-260 nm region in circular dichroism (CD) spectra, which are completely opposite to CD spectra of the dilute solution. The exciton chirality of the particles displays size-dependent behavior; that is, the exciton chirality peaks evolve to the low-energy side with increase in particles size. CD spectra accompanied with UV, fluorescence spectra, lifetime measurements of the excited states, and quantum mechanical calculations reveal that the chirality inversion results from intermolecular exciton coupling between two adjacent BNDE molecules in the nanoparticles, and the bathochromic shift of the peaks is attributed to the increased intermolecular interaction with increasing particle size.  相似文献   

2.
The absolute configuration of phomopsidin, a marine-derived fungal metabolite from Phomopsis sp. isolated at Pohnpei, was determined by the exciton chirality method as 6S, 7S, 8S, 11S, 12R, and 15R. The biosynthetic study using 13C-labeled precursors revealed the origin of all carbon atoms in phomopsidin, which was built by nine acetates and three methyl groups from l-methionine. Inhibitory activities of phomopsidin and its Me ester derivative against microtubule assembly were examined together with the structurally related compounds MK8383, solanapyrones, and tanzawaic acids. Phomopsidin and its (16Z)-isomer (MK8383) showed anti-microtubule activity at IC50 of 5.7 and 8.0 μM, respectively, while the Me ester and other compounds were not active at 100 μM.  相似文献   

3.
A sensitive luminescent bioassay for the simultaneous detection of Salmonella Typhimurium and Staphylococcus aureus was developed using aptamer-conjugated magnetic nanoparticles (MNPs) for both recognition and concentration elements and using upconversion nanoparticles (UCNPs) as highly sensitive dual-color labels. The bioassay system was fabricated by immobilizing aptamer 1 and aptamer 2 onto the surface of MNPs, which were employed to capture and concentrate S. Typhimurium and S. aureus. NaY0.78F4:Yb0.2,Tm0.02 UCNPs modified aptamer 1 and NaY0.28F4:Yb0.70,Er0.02 UCNPs modified aptamer 2 further were bond onto the captured bacteria surface to form sandwich-type complexes. Under optimal conditions, the correlation between the concentration of S. Typhimurium and the luminescent signal was found to be linear within the range of 101–105 cfu mL−1 (R2 = 0.9964), and the signal was in the range of 101–105 cfu mL−1 (R2 = 0.9936) for S. aureus. The limits of detection of the developed method were found to be 5 and 8 cfu mL−1 for S. Typhimurium and S. aureus, respectively. The ability of the bioassay to detect S. Typhimurium and S. aureus in real water samples was also investigated, and the results were compared to the experimental results from the plate-counting methods. Improved by the magnetic separation and concentration effect of MNPs, the high sensitivity of UCNPs, and the different emission lines of Yb/Er- and Yb/Tm-doped NaYF4 UCNPs excited by a 980 nm laser, the present method performs with both high sensitivity and selectivity for the two different types of bacteria.  相似文献   

4.
New transient arenesulfenic acids were involved in the synthesis of enantiopure 2-arylsulfinyl-1,3-dienes, showing central or axial chirality of the substituted arene residue, apart from the chirality related to the stereogenic sulfur atom. Some of the obtained dienes, that is, (Sa,SS)- and (SaRS)-2-(2′-hydroxy-1,1′-binaphthalen-2-sulfinyl)-3-methyl-1,3-butadienes, were subjected to diastereoselective Diels-Alder cycloadditions with N-methylmaleimide. Removal of the arylsulfoxide auxiliary, in the major adduct, was accomplished by reductive cleavage with Raney nickel.  相似文献   

5.
The total syntheses of (+)- and (−)-1,3,4,5-tetragalloylapiitol were achieved in seven steps from d- and l-ribose, respectively. By comparing the optical rotations of both enantiomers with those of the natural product, the absolute configuration at C-3 in the naturally occurring 1,3,4,5-tetragalloylapiitol has been revised to R. The absolute configurations at C-3 in the synthetic (+)- and (−)-1,3,4,5-tetragalloylapiitol were further confirmed by the circular dichroism exciton chirality method.  相似文献   

6.
Xiaohong Hou 《Tetrahedron》2005,61(24):5866-5875
The versatility of the 4-(N,N-dimethylamino)benzoate (DMAB) group embedded in host 1 as a signaling subunit for anion recognition was elucidated in terms of 1H NMR, CD, and fluorescence studies. Host 1 showed 1:1 complexation with monovalent anions and stepwise 1:1 and 2:1 (host 1: anion) complexation with divalent phosphate anions. The binding constants between host 1 and anions were determined by means of 1H NMR titrations in CD3CN (HPO42−: log K1:1=6.2, log K2:1=4.9; H2P2O72−: log K1:1=4.4, log K2:1=1.8; AMP2−: log K1:1>7, log K2:1>5) and the affinity of host 1 toward divalent anions, HPO42−, H2P2O72−, and AMP2−, is stronger than that toward monovalent anions, NO3, BF4, ClO4, HSO4, and PF6. The CD exciton chirality studies of host 1 with divalent anions, HPO42− and AMP2−, revealed that the two DMAB groups in the 2:1 complexes were arranged with negative chirality (counterclockwise). The dual fluorescence behavior of the DMAB group demonstrated not only the complexation stoichiometry but also the role(s) of the lipophilic countercation such as tetrabutylammonium and/or the hydrophilic residue in AMP during anion recognition.  相似文献   

7.
A novel dichloro zinc complex (L1)ZnCl2, where L1 is N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane, has been synthesized and characterized. The dimethyl derivatives, generated in situ from the well characterized dichloro zinc complexes (L1)ZnCl2 and (L2)ZnCl2, where L2 is N,N′-bis-(benzyl)-(R,R)-1,2-diaminocyclohexane, were employed as initiators for the ring opening polymerization (ROP) of rac-lactide (rac-LA). The complexes were found to be highly efficient initiators yielding the polylactide (PLA) with a narrow molecular weight distribution. The catalytic activity and heterotactic selectivity of the Zn(II) complexes were affected by the substituents on the phenyl groups of benzyl moieties in (R,R)-1,2-diaminocyclohexane. The dimethyl derivative of (L2)ZnCl2 produced highly stereocontrolled PLA with Pr = 0.75 at −25 °C.  相似文献   

8.
A concise enantioselective total synthesis of (2S,3′R,7′Z)-N-(3′-hydroxy-7′-tetradecenoyl)-homoserine lactone is described. Key feature of this protocol is a catalytic asymmetric hydrogenation and a prophenol-zinc-catalyzed diazo addition to imine reaction as genesis of chirality. Moreover, flexibility is built in the synthesis to generate enantioenriched analogs using catalytic amount of enantioenriched C2-symmetric ligands.  相似文献   

9.
Fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF-(DOBAA)n-RF] reacted with hibitane in methanol at 90 °C to afford RF-(DOBAA)n-RF oligomeric nanoparticles-encapsulated hibitane in good isolated yields. These fluorinated oligomeric particles-encapsulated hibitane were nanometer size-controlled very fine particles, and were found to exhibit a good dispersibility and stability in a wide variety of traditional organic solvents including fluorinated aliphatic solvents. Each dispersed solution with fluorinated nanoparticles afforded transparent colorless solution. These fluorinated nanoparticles were also found to exhibit a good antibacterial activity, and were applied to the surface modification of traditional organic polymers such as poly(methyl methacrylate).  相似文献   

10.
The crystal chemistry and crystallography of the compounds SrR2CuO5 (Sr-121, R=lanthanides) were investigated using the powder X-ray Rietveld refinement technique. Among the 11 compositions studied, only R=Dy and Ho formed the stable SrR2CuO5 phase. SrR2CuO5 was found to be isostructural with the “green phase”, BaR2CuO5. The basic structure is orthorhombic with space group Pnma. The lattice parameters for SrDyCuO5 are a=12.08080(6) Å, b=5.60421(2) Å, c=7.12971(3) Å, V=482.705(4) Å3, and Z=8; and for the Ho analog are a=12.03727(12) Å, b=5.58947(7) Å, c=7.10169(7) Å, V=477.816(9) Å3, and Z=8. In the SrR2CuO5 structure, each R is surrounded by seven oxygen atoms, forming a monocapped trigonal prism (RO7). The isolated CuO5 group forms a distorted square pyramid. Consecutive layers of prisms are stacked in the b-direction. Bond valence calculations imply that residual strain is largely responsible for the narrow stability of the SrR2CuO5 phases with R=Dy and Ho only. X-ray powder reference diffraction patterns for SrDy2CuO5 and SrHo2CuO5 were determined.  相似文献   

11.
Novel substituted 2-[(2-hydroxyethyl)]aminophenols, MeN(CHR1CR2R3OH)(C6H4-o-OH) (2-5), were synthesized by the reaction of 2-methylaminophenol with corresponding oxiranes. Titano-spiro-bis(ocanes) [MeN(CHR1CR2R3O)(C6H4-o-O)]2Ti 6-9 (2, 6, R1 = H, R2 = R3 = Me; 3, 7, R1 = R2 = Ph (treo-), R3 = H; 4, 8, R1 = Ph, R2 = R3 = H; 5, 9, R1 = R2 = H, R3 = Ph) based on [ONO]-ligands have been synthesized. The obtained compounds were characterized by 1H and 13C NMR spectroscopy and elemental analysis data. The complex [Ti(μ2-O){O-o-C6H4}{μ2-CMe2CH2}NMe]6 (10) was obtained by controlled hydrolysis of 6. Molecular structure of 10 was determined by X-ray structure analysis.  相似文献   

12.
Long-range chirality recognition between the two chiral guest ligands can be tuned based on the helix distances (dLn–Ln = 11.5 and 14.0 Å) of bis-diketonate bridged dinuclear lanthanide complexes (2Th and 3Th, respectively) used as mediators. Both 2Th and 3Th form one-dimensional (1D) helical structures upon terminal binding of two chiral guest co-ligands (LR or LS). Long-range chiral self-recognition is achieved in self-assembly of 2Th with LR and LS to preferentially form homochiral assemblies, 2Th-LR·LR and 2Th-LS·LS, whereas there is no direct molecular interaction between the two guest ligands at the terminal edges. X-ray crystal structure analysis and density functional theory studies reveal that long-range chiral recognition is achieved by terminal ligand-to-ligand interactions between the bis-diketonate ligands and chiral guest co-ligands. Conversely, in self-assembly of 3Th with a longer helix length, statistical binding of LR and LS occurs, forming heterochiral (3Th-LR·LS) and homochiral (3Th-LR·LR and 3Th-LS·LS) assemblies in an almost 1 : 1 ratio. When phenyl side arms of the chiral guest co-ligands are replaced by isopropyl groups (L′R and L′S), chiral self-recognition is also achieved in the self-assembly process of 3Th with the longer helix length to generate homochiral (3Th-L′R·L′R and 3Th-L′S·L′S) assemblies as the favored products. Thus, subtle modification of the chiral guests is capable of achieving over 1.4 nm-range chirality recognition.

Long-range chirality recognition between the two chiral guest ligands can be tuned based on the helix distances (dLn–Ln = 11.5 and 14.0 Å) of bis-diketonate bridged dinuclear lanthanide complexes (2Th and 3Th, respectively).  相似文献   

13.
Neosartorin (1) was isolated from the endophytic fungus Aspergillus fumigatiaffinis. The absolute configuration of 1, including both axial and central chirality elements, was established as (aR,5S,10R,5′S,6′S,10′R) for the first time on the basis of its electronic circular dichroism (ECD) spectra aided with TDDFT–ECD calculations. Neosartorin (1) exhibited substantial antibacterial activity against a broad spectrum of Gram-positive bacterial species including staphylococci, streptococci, enterococci, and Bacillus subtilis with minimal inhibitory concentrations in the range of 4–32 μg/mL. When the toxicity of 1 against eukaryotic cells was measured using a panel of different cancer cell lines such as HELA and BALB/3T3, the average IC50 values exceeded 32 μg/mL.  相似文献   

14.
《Tetrahedron: Asymmetry》1998,9(9):1549-1556
Fumonisins are mycotoxins produced by Fusarium moniliforme (Sheldon) and other related fungi that are common contaminants of corn and other grains throughout the world. The circular dichroism (CD) exciton chirality method was applied to determine the absolute configuration of the terminal part of the backbone of fumonisins. Using the p-dimethylaminobenzoate chromophore, the structure of FB1 was confirmed to be 2S, 3S and 5R, while that of FB3 is described for the first time to be 2S and 3S.  相似文献   

15.
The thermal reactions of fluoroalkanesulfonyl azides RfSO2N3 with pyrazine and its derivatives are studied in detail. All the reactions involved the fluoroalkanesulfonyl nitrene intermediates RfSO3N: which was captured by pyrazine to give the pyrazinium N-fluoroalkanesulfonyl ylides C4NH4N+-NSO2Rf and hydrogen abstraction product RfSO2NH2, but no corresponding N-pyrazinyl fluoroalkanesulfonyl amide derivatives RfSO2NHC4N2H3 were isolated. Excess azides did not afford the bisN-ylide product RfSO2N-+NC4H4N+-NSO2Rf.  相似文献   

16.
Four new C22N2Lycopodium alkaloids, senepodines B-E (2-5), consisting of an octahydroquinoline ring and a quinolizidine ring have been isolated together with senepodine A (1) from the club moss Lycopodium chinense. The relative and absolute stereochemistry of 2-5 were determined by combination of NOESY correlations and chemical transformation, while the absolute configuration of 1 was assigned by exciton chirality method.  相似文献   

17.
18.
4-Phosphoranylidene-5(4H)-oxazolones 1 undergo hydrolysis in THF in the presence of HBF4 at room temperature to give N-acyl-α-triphenylphosphonioglycines 3 (R2 = H) in very good yields. 4-Alkyl-4-triphenylphosphonio-5(4H)-oxazolones 2 react with water in CH2Cl2/THF solution without any acidic catalyst at 0-5 °C in a few days yielding N-acyl-α-triphenylphosphonio-α-amino acids 3 (R2 = Me) or α-(N-acylamino)alkyltriphenylphosphonium salt 4 (R2 = CH2OMe). α-Triphenylphosphonio-α-amino acids 3, on heating up to 105-115 °C under reduced pressure (5 mmHg) or on treatment with diisopropylethylamine in CH2Cl2 at 20 °C undergo decarboxylation to give the corresponding α-(N-acylamino)alkyltriphenylphosphonium salts 4, usually in very good yields.  相似文献   

19.
A set of multidentate ligands have been synthesized and used to stabilize the putative highly electrophilic zinc species initiating ring-opening polymerization (ROP) of cyclohexene oxide (CHO) and propylene oxide (PO). Reaction of the bidentate C2-chiral bis(oxazoline) ligand (R2,R3BOX: R2 = (4S)-tBu, R3 = H (a); R2 = (4S)-Ph, R3 = H (b); R2 = (4R)-Ph, R3 = (5S)-Ph (c)) with Zn(R1)2 (R1 = Et (1), Me (2)) led to the heteroleptic three-coordinate complexes (R2,R3BOX)ZnR1, 1a-c and 2a, which were isolated in 92-96% yield. Next, two pyridinyl-functionalized N-heterocyclic carbene (NHC) ligands have been designed and synthesized: the 1,3-bis(2-pyridylmethyl)imidazolinium salt (d) and the protected NHC adduct 2-(2,3,4,5,6-pentafluorophenyl)-1,3-bis(2-pyridylmethyl)imidazolidine (e). The reaction of ligands d and e with ZnEt2 led directly to the formation of (NHC)ZnEt(Cl) 3d complex with ethane elimination and the adduct (NHC-C6F5(H))ZnEt24e, respectively, in high yield. In situ combinations of selected complexes 1a-c, 3d and 4e with B(C6F5)3 (1 or 2 equivalents) give active systems for ROP, with high productivity (3.3-5.9 106 gpolym. molZn−1 h−1) and high molecular weight (Mn up to 132 103 g mol−1) for CHO polymerization. Although the in situ B(C6F5)3-activated zinc species were not isolated, the sterically demanding BOX ligands (1c > 1b > 1a) and functionalized NHC ligands seem to enhance the stability of highly electrophilic zinc complexes over ligand redistribution, allowing a better control of the cationic ROP as reflected particularly for 3d and 4e complexes by their respective efficiency (42-88%).  相似文献   

20.
Alkyl and dialkylammonium tetrafluoroborate promoted cis-trans isomerization of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane (1) in DMSO-d6 were studied. The isomerization equilibrium constant K are within the range of 3.74-3.30 from 22 to 47 °C. Thermodynamic parameters of ΔH° and ΔS° for the isomerization were −0.95 kcal/mol and −0.59 cal/mol-K respectively. The isomerization rate is first order in [cis-1] and second order in [RnNH4−nBF4]. Both components of RnNH4−n+ and BF4 are essential for the catalytic cis-trans isomerization. The catalytic strength follows the decreasing order of +H3N(CH2)6NH3+>n-C8H17NH3+>n-C16H33NH3+>Me3CNH3+>PhCH2NH3+>Et2NH2+?Ph2CHNH3+, Et3NH+. Inversion region was observed in the plot of ln(kf/T) versus (1/T) with the ceiling located at around 38 °C. The positive activation enthalpy of 9 kcal/mol was estimated at 22-32 °C. The activation enthalpy turns to be slightly negative at T>38 °C.  相似文献   

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