Synthesis of the Cellulose Model Compound Methyl 4″-O-Methyl-β-D-Cellotrioside

A high-yield synthetic route towards methyl 4″-O-methyl-β-D -cellotrioside ( 17 ) via cellobioside acceptor 8 and glucosyl fluoride donor 15 was established. The former was synthesized from cellobiose peracetate in 7 steps and 21% overall yield, while the latter was obtained from methyl β-D -glucopyranoside in a 6-step-synthesis with 19% yield. Glycosidation afforded 13% of α-compound besides the desired β-isomer (31%). The target compound, being the higher homologue of the recently prepared 4′-O-methyl-β-D -cellobioside ( 1 ), is required to study by solid-state techniques the hydrogen bond network in cellodextrins and cellulose, and its changes upon swelling and dissolution.     

Copper Corrosion: Comparison between Naturally Aged Papers and Artificially Aged Model Papers

Summary: Copper corrosion on paper works of art is commonly explained by copper ion-catalysed cellulose oxidation, usually reflected by discoloration of pigment and surrounding paper as well as by loss of mechanical strength. In this study, model paper and historic paper samples, both containing copper pigments, were compared using fluorescence labelling of carbonyl groups and subsequent GPC analysis. The historic paper samples did not show any typical sign of copper pigment induced discoloration, but high brittleness. In artificially copper-corroded paper samples the distribution of carbonyl groups in combination with the molecular weight distribution of cellulose clearly indicated the occurrence of oxidative processes. In contrast, only insignificant oxidative damage was detected in the case of the paper fragments from an original work of art, a codex from the 15^th century. Here, mostly degradation by hydrolytic action was revealed. There was no introduction of carbonyl groups into the bulk section of the molecular weight distribution, and the gain in new carbonyl groups corresponded to the number of reducing end groups newly generated by hydrolysis.     

The effect of water on cellulose solutions in DMAc/LiCl

The solution state of cellulose in the system N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) depends on various factors such as cellulose concentration, provenience (cotton, hardwood, softwood) and chemical history (pulping, pretreatment, bleaching) of cellulose, LiCl concentration, activation method, dissolution conditions (time, shaking), and water content. In particular the influencing of the latter has been intensively investigated in our present studies. Working in anhydrous conditions is not practicable for routine size exclusion chromatography (SEC) analysis. Especially in solutions diluted to SEC levels (0.9 wt% LiCl), an aggregation induced by water was observed. Depending on the time of dissolution and on the amount of water, changes in the solution state were observed. In some cases the amount of aggregates increases within a few minutes. This is reflected by a time-dependent increase in the scattering intensity and quantitatively proved by an increase in the aggregation peak in the calculated intensity distributions. With less soluble pulps, traces of water (lower than 0.01 M) can already suffice to induce and promote aggregation. To disturb a “good” stock solution, the concentration of water must be higher than 0.05 M. The aggregates formed correspond to the model of the fringed micelle.     

N-Methylmorpholine-N-oxide (NMMO): hazards in practice and pitfalls in theory

Cellulose - The hazards of handling N-methylmorpholine-N-oxide (NMMO) cannot be described often enough, although it is a rather common (co-)solvent for cellulose. Inaccuracies in the literature...     

Fluorescent cellulose aerogels containing covalently immobilized (ZnS)x(CuInS2)1−x/ZnS (core/shell) quantum dots

Photoluminiscent (PL) cellulose aerogels of variable shape containing homogeneously dispersed and surface-immobilized alloyed (ZnS)_x(CuInS₂)_1?x/ZnS (core/shell) quantum dots (QD) have been obtained by (1) dissolution of hardwood prehydrolysis kraft pulp in the ionic liquid 1-hexyl-3-methyl-1H-imidazolium chloride, (2) addition of a homogenous dispersion of quantum dots in the same solvent, (3) molding, (4) coagulation of cellulose using ethanol as antisolvent, and (5) scCO₂ drying of the resulting composite aerogels. Both compatibilization with the cellulose solvent and covalent attachment of the quantum dots onto the cellulose surface was achieved through replacement of 1-mercaptododecyl ligands typically used in synthesis of (ZnS)_x(CuInS₂)_1?x/ZnS (core–shell) QDs by 1-mercapto-3-(trimethoxysilyl)-propyl ligands. The obtained cellulose—quantum dot hybrid aerogels have apparent densities of 37.9–57.2 mg cm^?3. Their BET surface areas range from 296 to 686 m² g^?1 comparable with non-luminiscent cellulose aerogels obtained via the NMMO, TBAF/DMSO or Ca(SCN)₂ route. Depending mainly on the ratio of QD core constituents and to a minor extent on the cellulose/QD ratio, the emission wavelength of the novel aerogels can be controlled within a wide range of the visible light spectrum. Whereas higher QD contents lead to bathochromic PL shifts, hypsochromism is observed when increasing the amount of cellulose at constant QD content. Reinforcement of the cellulose aerogels and hence significantly reduced shrinkage during scCO₂ drying is a beneficial side effect when using α-mercapto-ω-(trialkoxysilyl) alkyl ligands for QD capping and covalent QD immobilization onto the cellulose surface.     

Sterically crowded tetracyano-para-quinodimethanes: synthesis and structure of 2,3,5,6-tetramethyl-7,7,8,8-tetracyano-para-quino=dimethane

The sterically crowded 2,3,5,6-tetramethyl-7,7,8,8-tetracyano=$\text{para}$-quinodimethane (=1) has been synthesized. The unique sterical structure of (=1) is discussed based on X-ray structure analysis.     

A practical strategy for the synthesis of 2-dialkylamino-4-arylamino-6-aminopyrimidines

Starting from commercially available 4-amino-2,6-dichloropyrimidine, a practical four steps synthesis of 2-dialkylamino-4-arylamino-6-aminopyrimidines was developed. This strategy could introduce a diverse set of secondary amines and arylamines to displace the 2- and 4-chloro groups. The products of this route are otherwise difficult to access. In addition, 6-amino arylation was carried out to demonstrate the reactivity and utility of 2-dialkylamino-4-arylamino-6-aminopyrimidines as building blocks for assembling interesting aminopyrimidine molecules.     

Solid-state NMR studies of methyl celluloses. Part 1: regioselectively substituted celluloses as standards for establishing an NMR data basis

Three methyl celluloses with completely uniform substitution pattern, 2-O-methyl cellulose (1), 3-O-methyl cellulose (2) and 6-O-methyl cellulose (3), were prepared according to the cationic ring opening polymerization approaches starting from substituted 1,2,4-orthopivalate derivatives of d-glucose. These samples allowed for the first time to sort out the methyl substitution effects on solid-state NMR chemical shifts and relaxation. Dipolar dephasing experiments allowed the detection and assignment (¹H, ¹³C) of the methyl groups. In 1 and 2, these resonances overlapped with those of C-6, whereas in 3, the methyl signal experienced a low-field shift into the region of C-2,3,5. ¹³C T₁ experiments were used to verify different relaxation behavior of the carbon sites, particularly the short relaxation time of at the carbon substitution site next to the methyl groups. This effect was used to unambiguously identify the ¹³C chemical shifts of the carbons carrying the methoxyl substituent, although they overlap with all resonances in the C-2,3,5 region. The data obtained for the standard samples with uniform substitution will now be used as the basis for determining methylation patterns and substitution degree in commercial methyl celluloses.