Influence of terminal substituents on the halide anion binding of foldamer-based receptors

Foldamers 1–4 incorporating different terminal substituents have been designed and synthesized for binding halide anions.~1H NMR titration experiments carried out in DMSO-d_6/CDCl_3(15/85, v/v)demonstrated that the short oligo (aryltriazole)s backbone 1 could not bind halide anions unless that amide H-bond donors were incorporated at the termini of the oligomer. Terminal substituents on oligo(aryltriazoleamide)s foldamers 2–4 display a considerable influence on the binding affinities of the foldamers for halide anions. Large steric hindrance of the terminal substituents was found to be unfavorable for binding halide anions, but aromatic π-π interactions between two terminal substituents are capable of stabilizing the conformation of foldamers thus giving rise to an enhancement in the binding strengths. However, the terminal substituents were found to hardly affect the binding selectivity in the studied cases.     

Preparation and application of streptavidin magnetic particles

Two kinds of streptavidin magnetic particles,namely streptavidin GoldMag particles and streptavidin amino terminal particles were prepared by the methods of physical adsorption and covalent interaction respectively.The streptavidin coated on magnetic particle surface,crucial to many applications,was greatly influenced by the choice of the different buffer.Compared with DynalbeadsM-270 streptavidin, the binding capacity for biotin of different streptavidin magnetic particles was determined by enzyme inhibition method,and the coupling capacity and activity of biotinylated oligonucleotide on their sur- face were also analyzed.The results indicated that the streptavidin GoldMag particle prepared by physical adsorption was stable in STE(NaCl-Tris-EDTA)buffer that was frequently used in nucleic acid hybridization and detection.The streptavidin amino terminal particles prepared by covalent interaction could be used both in STE buffer and PBS(phosphate buffered saline)buffer.The biotin binding ca- pacity for 1 mg of streptavidin GoldMag particles and streptavidin amino terminal particles was 4950 and 5115 pmol respectively.The capacity of biotinylated oligonucleotide(24 bp)coupled on 1 mg of GoldMag and amino terminal magnetic particles was 2839 and 2978 pmol separately.These data were about 6-7 times higher than those of DynabeadsM-270 streptavidin.The hybridization results with FITC-labeled complementary probe on magnetic particle surface demonstrated that the oligonucleotide coupled on streptavidin magnetic particles had high biological activity.     

Tuning the helical twisting power of nematic liquid crystals induced by chiral 1, 2-propanediol derivatives using varied substituents

In this study,a novel series of chiral 1,2-propanediol derivatives with different electron-donating and electron-withdrawing groups were synthesized and characterized by FT-IR and ~1H NMR.The helical twisting properties of all the chiral dopants were investigated by doping the chiral dopants into a nematic liquid crystal host(SLC-1717).The results indicate that the donor-acceptor electron effect have a prominent influence on helical twisting property of the chiral nematic phase induced by the chiral dopants. Introducing electron-withdrawing groups into the terminal ends of chiral 1,2-propanediol can decrease the absolute values of the helical twisting power.In addition,the helix inversion temperatures of the induced chiral nematic phase are variational with the change of terminal groups.     

DEGREE OF BRANCHING OF THE HYPERBRANCHED POLYMERS RESULTED FROM AB_2 POLYCONDENSATION WITH SUBSTITUTION EFFECT

The analytical expressions of the various structural units and the average degree of branching for the hyperbranched polymers resulted from AB_2 polycondensation with substitution effect were derived by the kinetic mechanism.The reactivity difference between the B group in linear unit and that in terminal group has great effect on the molecular parameters of the products obtained.The concentration of terminal units has a maximum with the increase of the conversion of A groups(x).The higher the reactivity...     

Facile synthesis and characterization of novel thermo-chromism cholesteryl-containing hydrogen-bonded liquid crystals

Two series of novel cholesteryl-containing H-bonded liquid crystals were prepared through facile self-assembly between cholesteryl isonicotinate(proton acceptor) exhibiting a monotropic cholesteric phase,and the 4-alkoxy-benzoic acid or 4-alkoxy cinnamic acid(proton donor).It was found that the increase of the conjugate length as well as the terminal length can contribute to enhance the interaction of molecules and thus significantly influenced the thermal behaviors of H-bonded LCs.The cholesteric reflec...     

A simple and effective approach to the synthesis of alkynyl selenides from terminal alkynes

Alkynyl selenides were prepared under very mild conditions by reacting terminal alkynes with respective diorganic diselenides in the presence of potassium t-butoxide.The advantages of this protocol include the use of readily available substrates and reagent and good yield of the products.     

INFLUENCES OF MOLECULAR WEIGHT AND BRANCHING PARAMETER OF LACQUER POLYSACCHARIDE ON THE GROWTH OF LEUCOCYTES

A method of determining branching parameter of lacquer polysaccharide wasestablished by acid-base back-titration of terminal uronic acid of branches. The branchingfactors obtained are in agreement with the values determined by colorimetric method withcarbazole and the results estimated by using Zimm-Stockmayer equation from viscositydata. Influences of molecular weights and branching factors of five fractions of lacquerpolysaccharide on the bioactivities were studied. The results show that the polysaccharideshave bioactivities in motivating the growth of leucocytes, and the effect increases with thedecrease of molecular weight and branching factor in the range studied (17×10~4 >M_w>4×10~4).     

Optical 2-benzyl-5-hydroxy-4-oxopentanoic acids against carboxypeptidase A: synthesis, kinetic evaluation and X-ray crystallographic study

<正>2-Benzyl-5-hydroxy-4-oxopentanoic acid 1 and its enantiomers were designed,synthesized and assayed for inhibitory activity against carboxypeptidase A(CPA,EC 3.4.17.1).To verify the role of the terminal hydroxyl group in 1 binding to CPA,2-benzyl-5- benzyloxy-4-oxopentanoic acid 2 was also synthesized and evaluated.The inhibition constants show that both L-1 and D-1 were shown to have strong binding affinity with L-1 being more potent than its enantiomer by 165-fold.On the other hand,the inhibition constant of 2 increases 4-fold comparing with that of 1.In order to explore the exact binding mode of the hydroxyacteyl group of 1 to the active site zinc ion of CPA,we have solved the crystal structure of CPA complexed with L-1 up to 1.85(?) resolution.In CPA·L-1 complex,the phenyl ring is fitted in the substrate recognition pocket at the S′_1 subsite,and the carboxylate forms bifurcated hydrogen bonds with the guanidinium moiety of Arg-145 and Arg-127 and a hydrogen bond with the phenolic hydroxyl of the down-positioned Tyr-248.The carbonyl oxygen of L-1 does coordinate to the active site zinc ion of CPA as expectedly.Unexpectedly,the terminal hydroxyl group of L-1 is engaged in hydrogen bonding with carbonyl oxygen of Ser-197 instead of coordinating to the active site zinc ion.     

Probing Diverse Disulfur Ligands in the Mo_2S_n~(–/0)(n = 4 ～ 8) Clusters: Structural Evolution and Chemical Bonding

Density functional theory(DFT) and coupled cluster theory(CCSD(T)) calculations were employed to investigate the geometric and electronic structures of a range of dinuclear molybdenum sulfide clusters, Mo_2S_n~– and Mo_2S_n(n = 4～8). The results showed that the sulfur atoms tended to occupy the terminal sites of the clusters continuously in the process of sequential sulfidation. After the oxidation state of Mo atoms reached the maximum of +6, diverse disulfur ligands emerged in the sulfur-rich Mo_2S_n~(–/0)(n = 7, 8) clusters. The driving forces of removing a sulfur atom from different S ligands in Mo_2S_n~(–/0)(n = 4～8) clusters, especially from those disulfur units, were evaluated. The corresponding order may provide insight into the pretreatment of fresh MoS_2 catalysts. Vertical detachment energies(VDEs) were predicted according to the Generalized Koopmans' theorem, and then the photoelectron spectra(PES) were simulated. Molecular orbital and spin density values were analyzed to elucidate the chemical bonding and the evolutionary behavior in the dinuclear molybdenum sulfide clusters.     

Degree of branching of the hyperbranched polymers resulted from ab<Subscript>2</Subscript> polycondensation with substitution effect

The analytical expressions of the various structural units and the average degree of branching for the hyperbranched polymers resulted from AB₂ polycondensation with substitution effect were derived by the kinetic mechanism.The reactivity difference between the B group in linear unit and that in terminal group has great effect on the molecular parameters of the products obtained.The concentration of terminal units has a maximum with the increase of the conversion of A groups（x）.The higher the reactivity ratio（r） of linear B group to branched one is,the later the maximum appears and the larger it is.The degree of branching of the hyperbranched polymers obtained is controllable by adjusting the parameters of r and x,which increases with increasing both x and r.     

Mesomorphic behavior of new benzothiazole liquid crystals having Schiff base linker and terminal methyl group

正A homologous series of heterocycles,6-methyl-2-(4-alkoxybenzylidenamino)benzothiazoles,were synthesized and characterized using FT-IR,~1H and ~(13)C NMR and mass spectrometric analysis.Enantiotropic nematic phase was observed for shorter members.Smectic A phase only emerged from octyloxy derivative onwards.The terminal methyl group at the benzothiazole fragment and the Schiff base linkage influenced the mesomorphic behavior of the present series.     

A new synthesis of alkynyl tellurides promoted by CsOH and 4 Å MS

The mixture of cesium hydroxide and terminal alkynes in dry DMF in the presence of 4 A molecular sieves was stirred for 3.0 h at room temperature under N2, then aryltellurenyl bromide in THF was added, and the reaction mixture was stirred for 2.0 h. Alkynyl tellurides were obtained in about 90% yields by flash chromatography.     

Influence of terminal alkyl chain length on helical twisting property of chiral 1,2-propanediol derivatives

In this study,a novel series of chiral 1,2-propanediol derivatives with different terminal alkyl chain length were synthesized and characterized by FT-IR,~1H NMR and DSC.After doped into a nematic liquid crystal host,all the chiral dopants induced chiral nematic liquid crystals exhibiting a helix inversion with temperature variation.The results indicate that terminal alkyl chain length has a prominent influence on helical twisting property of the chiral dopants.With increasing the terminal alkyl chain le...     

AN APPROACH TO SYNTHESIZE POLY(ETHYLENE GLYCOL)-b-POLY(ε-CAPROLACTONE) WITH TERMINAL AMINO GROUP via SCHIFF’S BASE AS AN INITIATOR

A new method to synthesize a degradable terminal amino group-containing copolymer,poly(ethylene glycol)-b- poly(ε-caprolactone)(MPEG-PCL-NH_2),was developed in the following three steps:(1)the ring-opening polymerization (ROP)ofε-caprolactone from the Schiff base prepared from benzatdehyde and ethanolamine(Ph-CH=NCH_2CH_2OH)used as an initiator to obtain heterobifunctional poly(ε-caprolactone)with one terminal Schiff base group and one hydroxyl group (HO-PCL-CH_2CH_2N=CH-Ph);(2)the coupling reaction of two reactive precursors,a hydroxy-terminated HO-PCL- CH_2CH_2N=CH-Ph andα-monocarboxy-ω-monomethoxy poly(ethylene glycol)(CMPEG)to synthesize MPEG-PCL- CH_2CH_2N=CH-Ph;(3)the conversion of the -N=CH-Ph end-group into NH_2 end-group by acidification of acetic acid to obtain MPEG-PCL-NH_2.The structures from the precursors to the terminal amino group-containing copolymer were confirmed by ~1H-NMR and their molecular weights were measured by gel permeation chromatography.The amphiphilic terminal amino group-containing copolymer could self-assemble into micelles in an aqueous system with PCL block as the core and PEG block as the shell.The micelle formation of the terminal amino group-containing block copolymer was studied by fluorescent probe technique and the existence of critical micellar concentration(cmc)confirmed the amphiphilic nature of the resulting copolymer.ESEM and DLS analysis of the micelles revealed a homogeneous spherical morphology and a unimodal size distribution.     

COVALENTLY BONDING CHIRAL POLYURETHANE ON AMINATED SILICA GEL： A NEW STRATEGY TO PREPARE CHIRAL STATIONARY PHASE FOR HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

Two polyurethanes of different molecular weights were prepared by the copolymerization of phenyl diisocyanate and diisopropyl tartrate. The polyurethanes having terminal isocyanate groups were reacted with 3-aminopropyl silica gel to afford two chiral stationary phases. The Mn of the two polyurethanes were 4057 g/mol and 6442 g/mol. The polyurethanes and the corresponding chiral stationary phases were characterized by FT-IR, 1H NMR and elemental analysis. The loading capacities of the polyurethanes on silica gel were 0.68 mmol units/g and 0.61 mmol units/g, respectively. The separation performance and the influence of additives, triethylamine and trichloroacetic acid, on the separation of chiral compounds were investigated by HPLC. The chiral stationary phase prepared from polyurethane with Mn of 4057 g/mol demonstrated better enantioseparation capability than that with Mn of 6442 g/mol. Additionally, it was found that the addition of triethylamine and trichloroacetic acid in the mobile phases significantly improved the enantioseparation for these two chiral stationary phases.     

SKELETON VIBRATIONS AND FORCE FIELD OF TWO ISOMOR-PHIC TRINUCLEAR μ_3-OXOFORMATO COMPLEXES OF IRON AND CHROMIUM

<正> The IR and Raman spectra for two isomorphic trinuclear μ3-oxo-formato complexes of iron and chromium were measured in the range 2000-110 cm-1.The assignments on the vibrations of the bridging and terminal coordinated formic ligands were made from the results of substitution reaction of the latter.A simplified model and a simplified general valence force field were used in normal coordinate analysis.The calculated frequencies agree well with the observed values,with a mean deviation of 1.1% for [Fe3O17C] and 0.9% for [Cr3O17C],confirming our assignments of their vibrational spectra.Two sets of the force constants have been calculated.In terms of the relationship among the vibrational frequencies,structure and some properties of the compounds,the rationality and reliability of the results were discussed.     

~(13)C-NMR STUDY ON THE CHAIN TERMINAL STRUCTURE OF POLY-1,3-PENTADIENE POLYMERIZED WITH RARE EARTH CATALYST

The sequence distribution and the terminal structures of poly-1,3-pentadiene chains obtained by rare earth catalyst and effect of polymerization temperature on microstructure of the polymer have been investigated by ~(13)C-NMR method. According to experimental results it was supposed that terminal active growing chain of the polymer would be four types of anti- and syn-η~3-allyl structures. When polymerization temperature was reduced, the content of cis-1,4-poly-1,3-pcntadiene increases. It can be explained by isomerization between anti- and syn-η~3-allyl. The process forming trans-1,2 unit instead of 3,4-unit were also described.     

Synthesis of Dialkyl-substituted Terminal Olefin

Dialkyl-substituted terminal olefins were synthesized from the coupling reaction of a-olefins which were catalyzed by zirconocene dichloride/methylalumoxane （MAO） catalyst system under mild condition. High yield was gained and no other oligmer was detected. It was found that the ratio of AI/Zr is responsible for the selectivity of product.     

NMR titration and molecular model MOPAC calculation of protonation processes of two MRI ligands

The protonation process of two DTPA bis(amide) derivatives,DTPA-BDMA and DTPA-BDEA,was studied by using 1H NMR titration and MOPAC calculation.Their protonation process was proposed in the order of the central amine,the terminal amines,the central carboxyl,the terminal carboxyl,the other terminal carboxyl and central amine.During the protonation of the terminal amine,there existed a large fraction of proton transfer from the central amine to the other terminal amine.     

Synthesis of N-Aryl-2- （1＇, 6＇-dihydro-6＇-pyridazinone-3＇-carbonyl） Thiosemicarbazides and Their Related Heterocyclic Compounds

1,6-Dihydro-3-hydrozinocarbonyl-6-pyridazinone (compound 2) were prepared from α-ketoglutaric acid and hydrazine hydrate. A series of N-aryl-2-(1‘,6‘-dihydro-6‘-pyridazinone-3‘-carbonyl) thiosemicarbazides 3a-3f were synthesized from the reaction of aryl isothiocyanates with compound 2. The terminal compounds 1,3, 4-thiadiazole, 1,3,4-oxadiazole and 1,2, 4-triazol-5-thione derivatives were cyclized from compounds 3a-3f. Their structures were confirmed by IR,^1H NMR, MS and elemental analyses.