Characterization of Autocatalytic Reactions in Modified Cellulose/NMMO Solutions by Thermal Analysis and UV/VIS Spectroscopy

The thermal stability of cellulose/N-methylmorpholine-N-oxide (NMMO) solutions were investigated using UV/VIS spectrometry with a temperature programming cuvette and caloric measurements by means of the Systag calorimeter RADEX (mini-autoclave). Both analytical methods allow to characterize the influences of stabilizers and additives. With the temporal course of the optical density, temperature and pressure thermal runaway reactions with gas evolution and accumulation of chromophoric degradation products were recognized. Kinetic model calculations compared with UV/VIS measurements demonstrate the existence of autocatalytic reactions in cellulose/NMMO solutions. Varying the heating rate autocatalysis can be proved by dynamic caloric measurements as well.     

Efficient synthesis of cellulose furoates in 1-<Emphasis Type="Italic">N</Emphasis>-butyl-3-methylimidazolium chloride

The ionic liquid 1-N-butyl-3-methylimidazolium chloride ([C₄mim]⁺Cl⁻) was investigated as reaction media for the homogeneous acylation of cellulose with 2-furoyl chloride in the presence of pyridine. The preparation of cellulose furoate depending on the reaction conditions, the cellulose type and the pyridine content was studied. Cellulose furoates with a degree of substitution in the range from 0.46 to 3.0 were accessible, i.e., under mild conditions, with a low excess of reagent and in a short reaction time. The products were characterized by elemental analysis, perpropionylation, ¹H- and ¹³C NMR spectroscopy and FTIR spectroscopy. Thomas Heinze is the member of the European Polysaccharide Network of Excellence (EPNOE), www.epnoe.eu     

Der Stoffwechsel von Verbindungen mit Dreifachbindung. VI. Stoffwechselverhalten von Alkincarbonsäuren und Alkindicarbonsäuren

Metabolism of Acetylenic Monocarboxylic and Dicarboxylic Acids Feeding of acetylenic monoacids with chain length of 11 to 18 C-atoms to rats led to excretion of dicarboxylic acids with retained triple bonds. 10-Octadecynoic acid led to the formation of metabolites with even and odd number of C-atoms, suggesting in addition to established ω- and β-oxidation an α-oxidative pathway.     

Highly Soluble and Green Indigo Dyes: 4,4′,7,7′‐Tetraalkoxy‐5,5′‐diaminoindigotins

Two new types of 4,4′,7,7′‐tetraalkoxyindigotins, 1a – f and 2a – f along with the new N‐substituted indigotins 4e – f , were synthesized from dinitrobenzaldehydes 5a – f , which were prepared from 2‐hydroxy‐5‐methoxybenzaldehyde ( 7 ) via dialkoxybenzaldehydes 6a – f (Scheme). The new dialkoxyindigotin 3g was obtained from dialkoxybenzaldehyde 6g via nitrobenzaldehyde 8g . The 1,4‐dialkoxy‐2,3‐dinitrobenzenes 9 were isolated as by‐products. The 4,4′,7,7′‐tetraalkoxy‐5,5′‐diaminoindigotins 1 are soluble in organic solvents, and their solutions are green, which is highly uncommon for indigotins and is primarily caused by electronic effects of substituents, steric effects playing a minor role. The indigotins 1 produce a strong red shift of the longest‐wavelength absorption and negative solvatochromism indicating the predominance of polar resonance structures in the ground state. Tautomeric structures were excluded. These indigotins are valuable compounds for technical applications, for synthetic purposes, and for analytical studies. SANS (Small‐angle neutron scattering) experiments showed that certain 4,4′,7,7′‐tetraalkoxy‐5,5′‐diaminoindigotins 1 form rod‐like aggregates in solution. The similarly substituted 4,4′,7,7′‐tetraalkoxy‐5,5′‐dinitroindigotins 2 are far less soluble. They produce red monoanions (preferably dimers) and bluish‐purple dianions in organic solvents.     

FOURIER TRANSFORM INFRARED SPECTROELECTROCHEMISTRY OF THE BACTERIOCHLOROPHYLL a ANION RADICAL

Abstract— Fourier transform infrared (FTIR) difference spectroscopy of the electrochemically generated anion radical of bacteriochlorophyll a was used to follow the molecular changes upon one-electron reduction. An IR spectroelectrochemical cell was constructed, allowing in situ electrolysis in connection with spectroscopic investigations from 200 to 10 000 nm. FTIR difference spectra of the BChl a anion formation in THF d₈ at U =+0.9 V (as determined by ferrocene calibration) were obtained. After complete formation of the radical, the reverse process was followed. Comparison of visible and IR spectra of the reduction and re-oxidation processes indicates that more than 90% of the BChl a anion could be formed with 90% of it being reversible. The main IR absorbance changes are observed for the conjugated and even for the non-conjugated C=O groups of BChl a . These results demonstrate the use of the combination of FTIR spectroscopy and electrochemistry for the characterization of radicals of the isolated pigments and of their in vivo bonding to the protein environment.