Characterization of cellulose and cellulose derivatives in solution by high resolution 13C-NMR spectroscopy

Exploitation of reactivity and selectivity in cellulose functionalization using unconventional media for the design of products showing new superstructures

A variety of new cellulose solvents was investigated toward their potential as media for the functionalization of the polyglucane. Thus, mixtures of dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF), N-methylmorpholine-N-oxide (NMMNO)/DMSO, melts of LiClO(4).3H(2)O, and aqueous solutions of Ni(tren)(OH)(2) [tren = tris(2-aminoethyl)amine] were applied as reaction media. In case of the new solvent, DMSO/TBAF its usefulness for derivatization reactions including the etherification with sodium monochloroacetate and the acylation with vinyl esters of carbonic acids was studied. The structural features of the products were analyzed by means of (1)H NMR spectroscopy (after depolymerization or peresterification), (13)C NMR spectroscopy, and HPLC after complete hydrolytic chain degradation. The results were compared with those obtained from derivatives prepared using the solvent N,N-dimethylacetamide (DMAc)/LiCl and conventional, heterogeneous synthesis. It can be shown that in case of carboxymethylation reactions the reaction medium applied has a drastic influence both on the course of reaction and on the structural features of the products. A highly efficient tool was found to be atomic force microscopy (AFM), showing remarkable differences in the superstructures of the differentially synthesized derivatives.

Preparation, characterization, and tabletting properties of a new cellulose-based pharmaceutical aid

A new cellulose-based tabletting excipient, hereinafter referred to as UICEL, has been developed by treating cellulose powder with an aqueous solution of sodium hydroxide (conc. > or = 5N) and subsequently precipitating it with ethyl alcohol. UICEL is similar in structure to Avicel PH-102, a commercial direct compression excipient commonly referred to as microcrystalline cellulose (MCC). It, however, shows the cellulose II lattice, while Avicel PH-102 belongs to the cellulose I polymorphic form. As produced, UICEL consisted of a mixture of aggregated and non-aggregated fibers. The degrees of polymerization (DP) and crystallinity (DC) of UICEL, determined by the viscosity and powder X-ray methods, were 189-207 and 47-58%, respectively. Avicel PH-102, by comparison, showed an aggregated structure with DP and DC values corresponding to 248 and 76.9%, respectively. Compared to Avicel PH-102, UICEL shows higher true density, bulk density, tap density, Carr's index and Hausner ratio values. The mean deformation pressure (P(y)) values calculated from the linear portion of the Heckel plots for UICEL and Avicel PH-102 were about 104 and 87 MPa, respectively, suggesting that UICEL is less ductile than Avicel PH-102. The hardness values of UICEL tablets increased nearly linearly with increasing compression pressures. Comparatively, Avicel PH-102 formed stronger tablets. Irrespective of the compression pressure used, all UICEL tablets disintegrated within 15 s, whereas Avicel PH-102 tablets of comparable strengths remained intact for over 12 h. In conclusion, the results show that UICEL can be used as a direct compression excipient, especially in the design and development of fast-disintegrating tablets.

Comparative analysis of partial structures of a peat humic and fulvic acid using one- and two-dimensional nuclear magnetic resonance spectroscopy

Nuclear magnetic resonance (NMR) resonance integrals obtained from one-dimensional NMR spectra provide semiquantitative contents of humic constituents with limited resolution in structural detail. When supplemented by connectivity information available from homo- and heteronuclear two-dimensional NMR spectra a more reliable assignment of humic substructures becomes available. This is demonstrated with a comparative one- and two-dimensional NMR analysis of a fulvic and a humic acid obtained from Eriophorum peat. An example of a detailed analysis of the proton chemical shift region normally attributed to carbohydrates shows substantial contributions from amino acids, amino and desoxy sugars, and highly oxidized aliphatic chains of intermediate length. The very good resolution of structural detail by a combined analysis of all NMR spectra shows that the effect of the fractionation procedure on the composition and chemical structure of humic materials is very significant. The comparison of the partial structures comprising humic acid (HA) and fulvic acid (FA) of the peat humic materials studied indicates that FA is diagenetically downstream of HA, favoring the biopolymer degradation (BD) model of humification.

Determination of substituents distribution in carboxymethylpullulans by NMR spectroscopy

The distribution of carboxymethyl substituents in the alpha-(1 --> 6)-linked maltotriosyl repeating units of a carboxymethylpullulan (CMP) series was investigated by high resolution NMR spectroscopy on very short oligomers (DPn = 1.2-1.5) obtained by acid hydrolysis. A series of 2D NMR experiments on parent pullulan, hydrolysed pullulan and CMP was used to assign the proton and carbon chemical shifts of CMP acid hydrolysates. The degree of substitution (DS) and the relative distribution of -CH2COONa groups at OH-2, OH-3, OH-4 and OH-6 of glucose residues (DSi) were determined from 1H NMR measurements. From a set of CMP samples, widely different in degree of substitution, it was observed that the substitution at C-2 is predominant and decreases according to the order C-2 > C-3 > C-6 > C-4. Taking into account the availability of each OH group in the parent pullulan, an order of relative reactivity of hydroxyl groups is defined according to the relation: Ri = DSi/ni, where ni is the number of free OH groups in a maltotriose unit (MTU) for a given site C-i, the reactivity order was found to be OH-2 > OH-4 > OH-6 > OH-3.

Characterisation of the substituent distribution in hydroxypropylated potato amylopectin starch

The distribution of substituents in hydroxypropylated potato amylopectin starch (amylose deficient) modified in a slurry of granular starch (HPPAPg) or in a polymer 'solution' of dissolved starch (HPPAPs), was investigated. The molar substitution (MS) was determined by three different methods: proton nuclear magnetic resonance (1H NMR) spectroscopy, gas-liquid chromatography (GLC) with mass spectrometry, and a colourimetric method. The MS values obtained by 1H NMR spectroscopy were higher than those obtained by GLC-mass spectrometry analysis and colourimetry. The relative ratio of 2-, 3-, and 6-substitution, as well as un-, mono-, and disubstitution in the anhydroglucose unit (AGU) were determined by GLC-mass spectrometry analysis. Results obtained showed no significant difference in molar distribution of hydroxypropyl groups in the AGU between the two derivatives. For analysis of the distribution pattern along the polymer chain, the starch derivatives were hydrolysed by enzymes with different selectivities. Debranching of the polymers indicated that more substituents were located in close vicinity to branching points in HPPAPg than in HPPAPs. Simultaneous alpha-amylase and amyloglucosidase hydrolysis of HPPAPg liberated more unsubstituted glucose units than the hydrolysis of HPPAPs, indicating a more heterogeneous distribution of substituents in HPPAPg.