Synthesis of thermoresponsive polystyrene-based comb-type grafted poly( N -isopropylacrylamide)

Narrowly distributed polystyrene-g-p(N-isopropylacrylamide) (PSt-g-PNIPAM) was prepared by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using the brominated polystyrene as macroinitiator and CuCl combined with hexamethyltriethylenetetramine as catalyst. Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed the structure of PSt-g-PNIPAM. The gel permeation chromatography (GPC) showed that the graft copolymer had a single distribution peak with molecular weight, M _n (g/mol) of 19815 g/mol (using polystyrene as the standard). Differential scanning calorimetry (DSC) revealed that due to both effects of hydrophobic isopropyl groups and hydrogen bonds in the amide group, the glass transition temperature (T _g) of PSt-g-PNIPAM enhanced 16.0°C compared to the T _g of the polystyrene.     

稀土乙酰丙氨酸咪唑配合物的合成及光谱性质

稀土元素由于特殊的外层电子构型,在与不同类型配体配位时,呈现出丰富多彩的配位行为和结构,其配合物,特别是有机配合物,由于具有发光性强、选择性好的特点,在发光、激光材料创制、结构探针、荧光免疫分析及生物传感器等领域的研究和应用引起广泛关注.氨基酸、肽是各种生物大分子的基本组成单元,咪唑存在于组氨酸、羧肽酶、血红蛋白等生物分子中参与配位或"变构效应"成为活性部位结构,唑环有丰富的能级,其作为含N富电子体系可与稀土离子形成既有生物活性,又有优良光学性能的配合物.     

Study on structural properties and solution dynamics of zinc complexes with the (N,N-dimethylaminomethyl)ferrocenyl ligand

The reaction of {C,N-[Fe(η⁵-C₅H₅)(η⁵-C₅H₃(CH₂NMe₂)-2)]}Li, (FcN)Li, with zinc chloride affords the diorganozinc complex (FcN)₂Zn (1). In solution, 1 appears as a mixture of rac and meso diastereomers, whereas in the solid state it crystallizes solely as a rac diastereomer. The ratio of rac/meso diastereomers in solution is solvent-, temperature- and concentration-dependent, consistent with an intermolecular exchange between diastereomers. An intramolecular dynamic phenomenon involving dissociation and recoordination of Zn---N bonds was also observed. The reaction of 1 with zinc chloride yields the monoorganozinc compound (FcN)ZnCl (2) as a slightly soluble yellow microcrystalline powder.     

Synthesis, characterization and thermal behaviour of ortho-metallated Pd(II) complexes containing N-benzoylthiourea derivatives

The synthesis and characterization (elemental analysis, ¹H and ¹³C NMR spectroscopy and single crystal X-ray diffraction) of the first ortho-metallated Pd(II) complexes containing N-benzoyl thiourea ligands are described. Four of these compounds showed liquid crystal properties which were investigated by mean of DSC and polarised light microscopy and their mesogenic properties are compared to those of ortho-metallated imine Pd(II) complexes with other types of co-ligands.     

Preparation of substituted ionic carbohydrate polymers and their interactions with ionic surfactants

The formation of micelles of hexadecyltrimethylammonium chloride (CTAC) and sodium dodecylsulfate (SDS) in aqueous solutions containing charged polysaccharides was studied by steady-state and time-resolved fluorescence measurements using pyrene as a photophysical probe. Micropolarity studies using the I₁/I₃ ratio of the vibronic emission bands of pyrene and the behaviour of the I_E/I_M ratio between the excimer and monomer emissions show the formation of hydrophobic domains. The interactions between the polyelectrolytes and surfactants of opposite charge lead to the formation of induced pre-micelles at surfactant concentrations lower than the critical micellar concentration (cmc) of the surfactants. At similar concentrations, the I_E/I_M ratio shows a peak. This aggregation process is assumed to be due to electrostatic attractions. At higher surfactant concentrations, near the critical micellar concentration, micelles with the same properties as those found in pure aqueous solution are formed. On the other hand, systems containing polyelectrolytes and surfactants of the same charge do not show this behaviour at low concentrations. The presence of long alkyl chains bound to the polyelectrolytes also induces the formation of free micelles at concentrations somewhat below the aqueous cmc.     

Solubilization of benzene and cyclohexane in aqueous solutions of hexadecyltrimethylammonium bromide: a deuterium magnetic resonance study

Quadrupole splittings in the ²H NMR spectrum from C₆D₆ and C₆D₁₂ solubilized in aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) have been observed in the hexagonal liquid crystalline phase (E) as well as in the concentrated micellar phase (L₁). The order parameter that is obtained for solubilized C₆D₆ is more than two orders of magnitude greater than previously reported from measurements of linear dichroism spectra. Various possibilities for the nature of the solubilization sites are discussed.     

New ionic liquid for inorganic cations analysis by capillary electrophoresis: 2-hydroxy- N , N , N -trimethyl-1-phenylethanaminium bis(trifluoromethylsulfonyl)imide (phenylcholine NTf2)

The potentialities of new ionic liquids (ILs) based on choline were evaluated as an electrophoretic medium in capillary electrophoresis for the analysis of alkaline and alkaline earth cations (Li⁺, K⁺, Na⁺, Cs⁺, Mg²⁺, Ba²⁺, Ca²⁺, and Sr²⁺) with indirect UV detection. Two types of capillaries were tested: an untreated fused silica and fused silica coated with a film of polyvinylalcohol. The coated capillary proved to be the best adapted for the metal ions studied. Moreover, it appeared that the nature of the ionic liquid anion influenced the baseline stability, and the bis(trifluoromethylsulfonyl) imide (NTf₂ ⁻) anion seemed to be the most efficient. These preliminary studies led us to synthesize a new ionic liquid, 2-hydroxy-N,N,N-trimethyl-1-phenylethanaminium NTf₂ (phenylcholine NTf₂). This liquid was able to act as the running electrolyte and probe, generating the background signal in indirect UV light and consequently simplifying the electrophoretic medium. Excellent baseline stability, good reproducibility, as well as good sensitivity of detection were obtained with this new ionic liquid. Thus, 510,000 plates/meter for Li⁺ with 40 mM IL were successfully obtained. The optimal concentration of IL was 20 mM with a detection limit ranging from 28 μg L⁻¹ for Li⁺ to 1,000 μg L⁻¹ for Cs⁺. This method (phenylcholine NTf₂ with polyvinylalcohol capillary) was applied to analyze different commercial source and mineral waters. Finally, the potentiality of this ionic liquid in nonaqueous capillary electrophoresis was explored. The use of phenylcholine NTf₂ with a fused silica capillary, in pure methanol medium and in the presence of acetic acid, made it possible to obtain separation selectivity different from that obtained in aqueous medium.     

Analysis of dimeric cyanine–nucleic acid dyes by capillary zone electrophoresis in N,N-dimethylacetamide as non-aqueous organic solvent

A method based on capillary zone electrophoresis is presented for the determination of the purity of commercial dimeric cyanine dyes (TOTO, YOYO, BOBO, all -1 and -3 species, LOLO-1, POPO-1) that are common as fluorescent probes for nucleic acid staining. These dyes are tetracharged cations, and have a strong tendency to interact with negatively charged centres, where they are rapidly adsorbed, especially from aqueous solutions. Thus anionic sites at the capillary wall must be avoided, and aqueous buffers are not suitable. The method introduced here avoids both complications, using non-aqueous N,N-dimethylacetamide as solvent, and suppressing the dissociation of silanol groups at the capillary surface due to selection of acidic separation conditions (20 mmol/l perchloric acid as background electrolyte). The present method enables the determination of the purity of all 10 dyes in less than 15 min. The selectivity of the method allows separation of at least five main and differentiating a number of unresolved minor contaminants as demonstrated in detail for TOTO-3 as an example. Quantitation (with 100% normalisation of the peak areas) of nine lots of this dye results in a purity between 33 and 87%.     

Oxidation of secondary alcohols byN-methylmorpholine-N-oxide (NMO) catalyzed by atrans-dioxo ruthenium(VI) complex or perruthenate complex: A kinetic study

Thetrans-dioxo ruthenium (VI) complex, [P(C₆H₅)₃C₆H₅CH₂]⁺[Ru(O)₂OAcCl₂] or tetrapropylammonium perruthenate catalyzes the oxidation of secondary alcohols to ketones byN-methylmorpholine-N-oxide (NMO). Kinetic studies showed the formation of a complex between catalyst and substrate (alcohol) as the first step in the mechanism.     

Preparation of the individual compact single-chain globular particulates of Poly(N-isopropylacrylamide)

The compact single-chain (SC) particulates of Poly(N-isopropylacrylamide) (PNIPAM), which have been formed above its lower critical solution temperature in an aqueous solution containing the surfactant of sodium n-dodecyl sulfate (SDS), were recovered from the solution by freeze-drying. Under scanning electron microscopy, the compact particulate appears as a spherical or elliptical particulate individually dispersed in SDS, which acts as a solid solvent to prevent agglomeration. The conformation of the compact SC particulates of PNIPAM dispersed in SDS had been studied by the solid-state high-resolution ¹³C NMR spectroscopy. The ¹³C spin-lattice relaxation time T ₁ of the SC sample was determined in comparison with that of the original one. It was found that the T ₁ of the methyl carbon in the isopropyl group of the SC sample was about 45% higher than that in the original multichain sample, which revealed the differences in the motion of the methyl group in the different condensed states and illuminated the characteristic conformation of the compact SC globular particulates of PNIPAM.     

DMA水溶液的1H NMR研究

测量了N,N-二甲基乙酰胺(DMA)水溶液体系不同温度下全浓度范围的¹H NMR数据, 对体系中的缔合情况进行了讨论, 应用化学缔合模型求得了各缔合平衡常数K和缔合平衡的ΔH. 结合N,N-二甲基甲酰胺(DMF)和N-甲基乙酰胺(NMA)水溶液的研究结果, 发现酰胺自身结构和酰胺浓度是影响酰胺水溶液性质的主要因素.     

Interaction of cellulose with amine oxide solvents

Cellulose I, mainly as ramie or as Avicel microcrystalline cellulose, has been monitored by optical microscopy and by ¹³C CPMAS NMR, over the course of its dissolution in hot N-methylmorpholine N-oxide solvent. Its interaction with the near-solvent N-ethylmorpholine N-oxide and related non-solvents has also been investigated. NMR shows that N-methylmorpholine N-oxide partly converts crystalline cellulose I into amorphous solid cellulose. The changes in chemical shift imply increased flexibility at the glycosidic bonds. In contrast, N-ethylmorpholine N-oxide converts cellulose I to cellulose III_I, without dissolution. Microscopy shows that the ramie fibres swell laterally, and at least some also shorten longitudinally, during dissolution. Model studies using methyl--d-glucopyranose show no evidence from ¹³C chemical shifts for different modes of binding with different solvents. However, N-methylmorpholine N-oxide binds more strongly to methyl--d-glucopyranose in DMSO than does N-ethylmorpholine N-oxide, whereas N-ethylmorpholine N-oxide binds better to H₂O. Also, ¹³C T ₁ values for aqueous cellobioside show increasing rotational freedom of the –CH₂OH sidechains as N-methylmorpholine N-oxide is added. Together, these observations imply the initial penetration of solvents and near-solvents between the molecular cellulose sheets. Subsequently, N-methylmorpholine N-oxide breaks H-bonds, particularly to O-6, just sufficiently to loosen individual chains and then dissolve the sheets.     

New liquid-crystalline complex C12DMAO/LaIII with the nematic phase

The results of the synthesis and characteristics of the new lyotropic lanthanide-containing liquid-crystalline systems possessing the nematic phase based on the zwitterionic surfactant, N,N-dimethyldodecylamine oxide (C₁₂DMAO), in the aqueous-decanol environment are presented. The phase diagrams are constructed. The formation of the La-O coordination bonds in the liquid-crystalline complex C₁₂DMAO/La^III is confirmed by IR spectroscopy.     

Synthesis and reactivity of neodymium(III) amido-tethered N-heterocyclic carbene complexes

The reaction of the heteroleptic Nd(III) iodide, [Nd(L′)(N″)(μ-I)] with the potassium salts of primary aryl amides [KN(H)Ar′] or [KN(H)Ar^*] affords heteroleptic, structurally characterised, low-coordinate neodymium amides [Nd(L′)(N″)(N(H)Ar′)] and [Nd(L′)(N″)(N(H)Ar^*)] cleanly (L′ = t-BuNCH₂CH₂[C{NC(SiMe₃)CHNt-Bu}], N″ = N(SiMe₃)₂, Ar′ = 2,6-Dipp₂C₆H₃, Dipp = 2,6-Prⁱ₂C₆H₃, Ar^* = 2,6-(2,4,6-Prⁱ₃C₆H₂)₂C₆H₃). The potassium terphenyl primary amide [KN(H)Ar^*] is readily prepared and isolated, and structurally characterised. Treatment of these primary amide-containing compounds with alkali metal alkyl salts results in ligand exchange to give alkali metal primary amides and intractable heteroleptic Nd(III) alkyl compounds of the form [Nd(L′)(N″)(R)] (R = CH₂SiMe₃, Me). Attempted deprotonation of the Nd-bound primary amide in [Nd(L′)(N″)(N(H)Ar^*)] with the less nucleophilic phosphazene superbase Bu^tNP{NP(NMe₂)₃}₃ resulted in indiscriminate deprotonations of peripheral ligand CH groups.     

Starch Derivatives of High Degree of Functionalization 11: Studies on Alternative Acylation of Starch with Long-chain Fatty Acids Homogeneously in <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl acetamide/LiCl

Starch materials of different amylose content were allowed to react with saturated and unsaturated fatty acids of varying chain length from C₁₄ to C₁₈ under homogeneous conditions applying the solvent N,N-dimethyl acetamide in combination with LiCl. As reagent the corresponding acid chlorides and, alternatively, carboxylic acids in situ activated with toluene-4-sulfonyl chloride and N,N′-carbonyldiimidazole (CDI) were studied. Using fatty acid chlorides (FACl) and toluene-4-sulfonyl chloride-activated acids an almost complete substitution of the starch occurs. By in situ activation of the fatty acids with CDI, products with a degree of substitution up to 2 were obtained, which, in particular, represents a simple and very mild procedure.     

Polystyrene latex particles coated with crosslinked poly(N-isopropylacrylamide)

Thermoresponsive colloidal particles were prepared by seeded precipitation polymerization of N-isopropylacrylamide (NIPAM) in the presence of a crosslinking monomer, N,N-methylenebisacrylamide (MBA), using polystyrene latex particles (ca. 50 nm in diameter) as seeds in aqueous dispersion. Phase transitions of the prepared poly(N-isopropylacrylamide), PNIPAM, shells on polystyrene cores were studied in comparison to colloidal PNIPAM microgel particles, in H₂O and/or in D₂O by dynamic light scattering, microcalorimetry and by ¹H NMR spectroscopy including the measurements of spin–lattice (T1) and spin–spin (T2) relaxation times for the protons of PNIPAM. As expected, the seed particles grew in hydrodynamic size during the crosslinking polymerization of NIPAM, and a larger NIPAM to seed mass ratio in the polymerization batch led to a larger increase of particle size indicating a product coated with a thicker PNIPAM shell. Broader microcalorimetric endotherms of dehydration were observed for crosslinked PNIPAM on the solid cores compared to the PNIPAM microgels and also an increase of the transition temperature was observed. The calorimetric results were complemented by the NMR spectroscopy data of the ¹H-signal intensities upon heating in D₂O, showing that the phase transition of crosslinked PNIPAM on polystyrene core shifts towards higher temperatures when compared to the microgels, and also that the temperature range of the transition is broader.     

X-ray Crystal and Ab Initio Structures of 3′,5′-di-O-Acetyl-N(4)-Hydroxy-2′-Deoxycytidine and Its 5-Fluoro Analogue: Models of the N(4)-OH-dCMP and N(4)-OH-FdCMP Molecules Interacting with Thymidylate Synthase

The crystal and molecular structures of the 3′,5′-di-O-acetyl-N(4)-hydroxy-2′-deoxycytidine molecule and its 5-fluoro congener have been determined by X-ray single crystal diffraction. The 3′,5′-di-O-acetyl-N(4)-hydroxy-5-fluoro-2′-deoxycytidine molecule crystallizes in the space group C2 with the following unit cell parameters: a = 21.72 Å, b = 8.72 Å, c = 8.61 Å, and β = 90.42^∘. 3′,5′-di-O-acetyl-N(4)-hydroxy-2′-deoxycytidine also belongs to the monoclinic space group C2 and the unit cell parameters are: a = 39.54 Å, b = 8.72 Å, c = 22.89 Å, and β = 95.26^∘. The non-fluorine analogue demonstrates a rare example of crystal structure with five symmetry-independent molecules in the unit cell. All the molecules in both crystal structures have the sugar residue anti oriented with respect to the base, as well as have the N(4)-OH residue in cis conformation relatively to the N(3)-nitrogen atom. In addition to the molecular geometries from X-ray experiment, the optimized molecular geometries have been obtained with the use of theoretical ab initio calculations at the RHF/6-31G(d) level. The corresponding geometric parameters in the molecules of 3′,5′-di-O-acetyl-N(4)-hydroxy-2′-deoxycytidine and its 5-fluoro congener have been compared. The differences including the C(5)=C(6) bond shortening and C(4)—C(5)—C(6) angle widening in the fluorine analogue are discussed in this paper in relation to the molecular mechanism of enzyme, thymidylate synthase, inhibition by N(4)-hydroxy-2′-deoxycytidine monophosphate and its 5-fluoro congener.     

Synthesis, XRD structure and properties of diaqua(p-toluidine-N,N-di-3-propionato)copper(II) dihydrate [Cu(p-Tdp)(H2O)2]·2H2O

The copper(II) complex [Cu(p-Tdp)(H₂O)₂]·2H₂O, where p-Tdp is the anion of p-toluidine-N,N-di-3-propionic acid (or N,N-di(2-carboxyethyl)-p-toluidine), has been synthesized and characterized by X-ray diffraction. Three crystallographically independent [Cu(p-Tdp)(H₂O)₂] molecules have a similar structure. The Cu atoms have a square pyramidal environment (4+1) with a small trigonal bipyramidal distortion. The ortho-H atom of the benzene ring blocks up the sixth coordination position of the Cu polyhedron. The basal plane is formed by the donor atoms of the tridentate ligand and by the water molecule (average bond length Cu---N 2.03, Cu---O 1.93, Cu---O_w 2.00 Å), the apex is occupied by another water molecule (Cu---O_w 2.27 Å). The Cu atoms are located 0.20–0.30 Å out of the mean planes of the four basal atoms towards the apical O_w atom. The IR and electronic absorption spectra of p-Tdp and the title compound have been described. UV–Vis reflectance spectra shows that the complex has the same square pyramidal geometry in the crystal state and in solution. The protonation constants of the ligand log K₁=6.87(2), log K₂=3.75(2), log K₃=2.57(2) and stability constants log K_CuH(p-Tdp)=2.13(5), log K_Cu(p-Tdp)=6.38(3) were determined by pH-titration at 25.0 °C and I=0.1 M KNO₃.     

Comparative study on interaction of bovine serum albumin with dissymmetric and symmetric gemini surfactant by spectral method

The interaction between bovine serum albumin (BSA) with N, N′-bis(dimethylalkyl) ethylammonium dibromide (C₁₂C₂C_m, m = 8, 12) was investigated by spectral methods. It can be seen that C₁₂C₂C₈ and C₁₂C₂C₁₂ mainly interact with tryptophan residues of BSA from synchronous fluorescence spectra. Fluorescence, far-UV, and near-UV circular dichrosim spectra of BSA are changed by addition of dissymmetric and symmetric gemini surfactant. For surfactant solution, the polarity of the microenvironment surrounding pyrene is lower while the fluorescence lifetime of it is longer and the microviscosity is higher in the presence of BSA than those in the absence of BSA. But compared with C₁₂C₂C₁₂, C₁₂C₂C₈ has lower binding ability with BSA due to the shorter hydrophobic tail and lower symmetry.     

Interaction and Scale of Mixing in Cellulose Acetate/Poly(<Emphasis Type="Italic">N</Emphasis>-vinyl Pyrrolidone-co-vinyl Acetate) Blends

Binary blends and pseudo complexes of cellulose acetate (CA) with vinyl polymers containing N-vinyl pyrrolidone (VP) units, poly(N-vinyl pyrrolidone) (PVP) and poly(N-vinyl pyrrolidone-co-vinyl acetate) [P(VP-co-VAc)], were prepared, respectively, by casting from mixed polymer solutions in N,N-dimethylformamide as good solvent and by spontaneous co-precipitation from solutions in tetrahydrofuran as comparatively poor solvent. The scale of miscibility and intermolecular interaction were examined for the blends and complexes by solid-state ¹³C-NMR spectroscopy. It was revealed that the formation of complexes was due to a higher frequency of hydrogen-bonding interactions between the residual hydroxyl groups of CA and the carbonyl groups of VP residues in the vinyl polymer component. From measurements of CP/MAS spectra and proton spin-lattice relaxation times (T_1ρ^H) in the NMR study, the existence of the hydrogen-bonding interaction was also confirmed for the miscible blends and the homogeneity of the mixing was estimated to be substantially on a scale within a few nanometers.