共查询到20条相似文献,搜索用时 15 毫秒
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Katrin Petzold Katrin Schwikal Wolfgang Günther Thomas Heinze 《Macromolecular Symposia》2005,232(1):27-36
The hemicellulose xylan is a polysaccharide that occurs in nature in enormous amount in various one year- and perennial plants having different structures and molecular masses. Versatile ways to generate bio-based functional polymers result from the chemical modification of this biopolymer. In our research, xylans from various resources like birch-, beech-, and eucalyptus wood and from oat husk, rye bran, and corn cob were used to investigate the important method of carboxymethylation in detail. Different activation procedures were elaborated to synthesize carboxymethyl xylan. One step reactions lead to products with a degree of substitution (DS) from 0.13 to 1.22 in dependence on the molar ratio of anhydroxylose unit (AXU) to reagent. Two step syntheses yielded DS values up to 1.65. Carboxymethyl xylans are water soluble at a DS of 0.3. The solutions have different clearness depending on the provenience. NMR spectroscopy and HPL chromatography were applied to characterize the carboxymethyl xylans in detail. 相似文献
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《Analytical letters》2012,45(15):3049-3058
ABSTRACT Waxy (essentially amylose-free) maize starch was chemically modified to varying degrees by treatment with 3-chloro-2-hydroxypropyltrimethyl ammonium chloride (CHPTAC), and the degree of cationic modification was determined by a standard wet chemistry method. FT-Raman spectra of the modified starches were taken, and a characteristic Raman band ~761 cm?1 was found. This 761 cm?1 Raman band's intensity depended on the level of cationic modification of the starch. The ratio of intensity of the ~761 cm?1 band to a ~715 cm?1 C-C stretch Raman band (used as an internal standard) was plotted versus the amount of cationic modification derived by titration analysis, and a linear fit was obtained with a correlation of 0.998. The FT-Raman spectroscopy method presented here demonstrates a rapid non-destructive way to determine the level of cationic modification of waxy maize starch, and should be suitable for use with cationic modified starches of any amylose content. 相似文献
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Dr. Lucas Frédéric Bibiana Fabri Dr. Laure Guénée Dr. Francesco Zinna Prof. Lorenzo Di Bari Prof. Jérôme Lacour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(56):e202201853
In essentially one-pot, using Ir- and Pd-catalysis, tris(arene)-functionalized cationic [4]helicenes are synthesized with full regioselectivity and enantiospecificity starting from a trivial precursor (17 examples). This poly-addition of aryl groups improves key optical properties, that is, fluorescence quantum yields and lifetimes. Electronic circular dichroism and circularly polarized luminescence signatures are observed up to the far-red domain, in particular with additional arenes prone to aggregation. 相似文献
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Ralf Giernoth Patrick Huebler Joachim Bargon 《Angewandte Chemie (International ed. in English)》1998,37(18):2473-2475
The catalyst-bound intermediate 1 is detected in the homogeneous hydrogenation of styrene derivatives in the presence of cationic RhI catalysts 2 . The detachment from the catalyst of the ethylbenzene 3 formed turns out to be slow and possibly rate-determining in some cases. 相似文献
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利用水相连续法实现了纳米纤维素晶体(NCC)的高碘酸钠氧化及阳离子化,然后将阳离子化纳米纤维素晶体(CDAC)悬浮液与壳聚糖(CTS)醋酸溶液混合,并采用流延法制得壳聚糖-纳米纤维素(CTS-CDAC)复合膜。采用红外光谱(FT-IR)、透射电镜(TEM)、X射线衍射(XRD)、Zeta电位及粒径分析表征了改性前后NCC的结构与性能,并研究了制得的CDAC悬浮液与CTS醋酸溶液混合时的相容性及CTS-CDAC复合膜中CDAC质量分数对复合膜力学性能、水溶胀性的影响。结果表明:CDAC悬浮液与CTS醋酸溶液混合时相容性良好,CDAC在CTS基质中分散均匀,CTS-CDAC复合膜的力学性能较纯CTS膜明显提高。当复合膜中CDAC的质量分数为12%时,拉伸强度达到最高。另外,CTS-CDAC复合膜在水中的溶胀度较纯CTS膜明显降低,稳定性变好。 相似文献
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Pavol Ondrisek Dr. Margaux Elie Marion Pupier Dr. Adiran de Aguirre Dr. Amalia I. Poblador-Bahamonde Dr. Céline Besnard Prof. Jérôme Lacour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(15):e202104405
Cationic triangulenes, and related helicenes, constitute a rich class of dyes and fluorophores, usually absorbing and emitting light at low energy, in the orange to red domains. Recently, to broaden the scope of applications, regioselective late-stage functionalizations on these core moieties have been developed. For instance, with the introduction of electron-donating groups (EDGs), important bathochromic shifts are observed pushing absorptions towards or in the near-infrared (NIR) spectral domain while emissive properties disappear essentially completely. Herein, to upset this drawback, acetylene derivatives of cationic diazaoxa triangulenes (DAOTA) and [4]helicenes are prepared (16 examples). Contrary to other EDG-functionalized derivatives, C≡C− functionalized products remain broadly fluorescent, with red-shifted absorptions (Δλabs up to 25 nm) and emissions (Δλem up to 73 nm, ΦPL up to 51 %). Quite interestingly, a general dynamic stereoisomerism phenomenon is evidenced for the compounds derived from achiral DAOTA cores. At low temperature in 1H NMR spectroscopy (218 K), N−CH2 protons become diastereotopic with chemical shifts differences (Δδ) as high as +1.64 ppm. The signal coalescence occurs around 273 K with a barrier of ∼12 kcal mol−1. This phenomenon is due to planar chiral conformations (Sp and Rp configurations), induced by the geometry of the alkyl (n-propyl) side-chains next to the acetylenic substituents. Ion pairing studies with Δ-TRISPHAT anion not only confirm the occurrence of the chiral conformations but evidence a moderate but definite asymmetric induction from the chiral anion onto the cations. Finally, DFT calculations offer a valuable insight on the geometries, the corresponding stereodynamics and also on the very large difference in NMR for some of the diastereotopic protons. 相似文献
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Aleksandra Markovic Dr. Leon Buschbeck Prof. Dr. Thorsten Klüner Prof. Dr. Jens Christoffers Prof. Dr. Gunther Wittstock 《ChemistryOpen》2019,8(9):1176-1182
Derivatives of 2,5-diaminoterephthalate (DAT) are efficient fluorescence dyes that are also redox-active, thus allowing for the electrochemical manipulation of spectral properties. The electrochemical behaviour of seven DAT derivatives was studied by cyclic voltammetry in dichloromethane. In the absence of a proton donor, DATs should be oxidized in two one-electron steps. The first step is usually quasi-reversible while the second step is either quasi-reversible or irreversible. Some electrochemical properties such as the formal potentials and the ratio between the anodic and the cathodic current were determined from the cyclic voltammograms. Correlation between the formal potential of first oxidation and the absorption or the fluorescence emission wavelengths are established for this specific type of dyes. These correlations were confirmed with density functional theory calculations. 相似文献
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Patrícia M. Dias Dalva L. A. De Faria Vera R. L. Constantino 《Journal of inclusion phenomena and macrocyclic chemistry》2000,38(1-4):251-266
In the present work, the interaction between5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine (TMPyP) and its metallated form(CoTMPyP) with three cationic clays was investigatedby X-ray diffraction (XRD), UV-VIS and resonance Ramanspectroscopies. Sodium montmorillonites K10 and KSFand a synthetic fluorohectorite (FHT) containingdifferent macrocycle loadings, were prepared by an ionexchange reaction. In nonsaturated KSF and FHT, theCoTMPyP molecule assumes a flat orientation, relativeto the host layers, giving rise to at least twoabsorption bands in the Soret region (ca. 445 and 465 nm)assigned to adsorbed and intercalated CoTMPyP,respectively. For the delaminated K10 sample, a broadband centered around 456 nm, indicates a majorcontribution from the metalloporphyrin on the clayexternal surfaces. The electronic spectra of FHTsamples containing increasing amounts of CoTMPyPshow bands red shifted even when a small amount ofporphyrin is used, suggesting that the electroniclevels of the macrocycle are more affected by theinteraction with the clay than by the metalloporphyrindistortion inside the galleries. The resonance Ramanspectra obtained for all CoTMPyP samples presentedonly minor shifts in peak positions and band width,with the exception of the FHT saturated sample, wherethe bands are clearly broader when compared to otherloadings, suggesting that porphyrin aggregation isoccurring. In the case of TMPyP, the bands at ca. 430and 468 nm were assigned to nonprotonated andprotonated molecules, respectively. This assignment issupported by resonance Raman spectroscopy, which alsoshowed the 2 mode (ca. 1550 cm-1) to bethe most sensitive peak to protonation. 相似文献
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Dr. Selina Beatrice van der Meer Theresa Seiler Christin Buchmann Georgia Partalidou Dr. Sophia Boden Dr. Kateryna Loza Dr. Marc Heggen Dr. Jürgen Linders Dr. Oleg Prymak Prof. Dr. Cristiano L. P. Oliveira Prof. Dr. Laura Hartmann Prof. Dr. Matthias Epple 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(4):1451-1464
Ultrasmall gold nanoparticles (diameter about 2 nm) were surface-functionalized with cysteine-carrying precision macromolecules. These consisted of sequence-defined oligo(amidoamine)s (OAAs) with either two or six cysteine molecules for binding to the gold surface and either with or without a PEG chain (3400 Da). They were characterized by 1H NMR spectroscopy, 1H NMR diffusion-ordered spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy. The number of precision macromolecules per nanoparticle was determined after fluorescent labeling by UV spectroscopy and also by quantitative 1H NMR spectroscopy. Each nanoparticle carried between 40 and 100 OAA ligands, depending on the number of cysteine units per OAA. The footprint of each ligand was about 0.074 nm2 per cysteine molecule. OAAs are well suited to stabilize ultrasmall gold nanoparticles by selective surface conjugation and can be used to selectively cover their surface. The presence of the PEG chain considerably increased the hydrodynamic diameter of both dissolved macromolecules and macromolecule-conjugated gold nanoparticles. 相似文献
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Stefan Wild Michael Fickert Aleksandra Mitrovic Vicent Lloret Christian Neiss Jos Alejandro Vidal‐Moya Miguel ngel Rivero‐Crespo Antonio Leyva‐Prez Katharina Werbach Herwig Peterlik Mathias Grabau Haiko Wittkmper Christian Papp Hans‐Peter Steinrück Thomas Pichler Andreas Grling Frank Hauke Gonzalo Abelln Andreas Hirsch 《Angewandte Chemie (International ed. in English)》2019,58(17):5763-5768
The chemical bulk reductive covalent functionalization of thin‐layer black phosphorus (BP) using BP intercalation compounds has been developed. Through effective reductive activation, covalent functionalization of the charged BP by reaction with organic alkyl halides is achieved. Functionalization was extensively demonstrated by means of several spectroscopic techniques and DFT calculations; the products showed higher functionalization degrees than those obtained by neutral routes. 相似文献
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以淀粉和三甲基环氧丙基氯化铵为原料,在三氯化铝催化作用下,制备了阳离子淀粉,最佳反应条件为:淀粉 50g,三甲基环氧丙基氯化铵 10g,三氯化铝 0. 74g, 50%乙醇 60mL,反应温度 50℃,反应时间 17h. 相似文献
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以对硝基苯酚为原料,经偶氮,Williamson醚化和季铵化反应合成了一种疏水基中间含偶氮苯基团的阳离子表面活性剂,其结构经1H NMR,IR和元素分析表征. 相似文献
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Elisabete Curti Douglas de Britto Srgio Paulo Campana‐Filho 《Macromolecular bioscience》2003,3(10):571-576
N,N,N‐trimethylchitosan (TMC) was prepared by reacting purified chitosan with iodomethane, in the presence of sodium hydroxide, water and sodium iodide, at room temperature. The reaction medium was N‐methyl‐2‐pyrrolidone. Different samples of TMC were obtained by adding to the reaction medium a fixed volume (5.5 mL) of aqueous NaOH solutions at different concentrations (15, 20, 30 and 40 wt.‐%) and carrying out the reactions for 9 or 24 h. The features observed in the 1H and 13C NMR spectra of these chitosan derivatives, in respect of the chemical shift, number and relative intensity of the signals, depended strongly on the excess of NaOH and H3CI added to the reaction medium, but when the lowest excess was employed, the characteristics of the derivative were not affected by the reaction time to the same extent. The average degree of quaternization of these N‐methylated derivatives of chitosan ranged from 10.5% to 44.8%, according to the reaction conditions. Increasing the excess of NaOH, in reactions carried out for 9 h, resulted in TMC samples with progressively higher content of trimethylated sites however, the reaction yields were correspondingly lower and O‐alkylation was favored in these cases.