An Efficient Method for Determination of the Degree of Substitution of Cellulose Esters of Long Chain Aliphatic Acids

The determination of the degree of substitution (DS) of fatty acid cellulose esters, representing a broad range of substituents (C₆, C₁₂, C₁₈ and C₂₂), was performed by alkaline hydrolysis of the ester groups and the quantification of fatty acids by gas chromatography-mass spectrometry (GC-MS) as their trimethylsilyl derivatives. The method was optimized and compared with established techniques for the DS determination (elemental analysis and alkaline hydrolysis/titrimetry). The results demonstrated that alkaline hydrolysis/GC-MS is a rapid, reliable and powerful method for analysis of fatty acid cellulose esters, particularly when different acyl substituents are present.     

Dynamic mechanical investigations of different substituted cellulose o-silyl ethers

In contrast to many cellulose derivatives, the cellulose O-silyl ethers with bulky side groups exhibit scarcely a change in glass transition temperature by a variation of the degree of substitution (DS) or degree of polymerization (DP) or by introducing phenyl carbamate groups for the remaining hydroxyls along the main chain. However, a substitution of these hydroxyls by flexible acetate groups lowers the glass transition temperature considerably. The secondary dispersion (relaxation) behavior is strongly influenced by the various substituents and can be correlated to specific motions of the molecules. The dynamic mechanical properties are also dependent on the kind of preconditioning of the samples.     

纤维素苯基氨基甲酸酯的均相合成及其手性拆分性能评价

认识多糖类手性拆分材料的结构性能关系对于构建新型高效手性固定相具有重要指导意义。该文中,以1-烯丙基-3-甲基咪唑氯离子液体为介质,合成了系列不同结构的纤维素苯基氨基甲酸酯,进而考察了取代度、取代基团种类和位置对产物手性拆分性能的影响。结果表明,随着取代度的增加,纤维素苯基氨基甲酸酯对于绝大部分手性分子的拆分效果提高;苯环上取代基团的种类和位置对纤维素苯基氨基甲酸酯手性拆分性能影响显著,弱吸电子基团氯基和给电子基团甲基在合适的位置能显著增强纤维素苯基氨基甲酸酯的手性拆分性能;纤维素3-甲基-4-氯苯基氨基甲酸酯、3,5-二氯苯基氨基甲酸酯和2-甲基-5-氯苯基氨基甲酸酯对一些手性分子的拆分效果优于纤维素3,5-二甲基苯基氨基甲酸酯。     

Determination of the degree of substitution (DS) of mixed cellulose esters by elemental analysis

Equations for transforming the results of elemental analysis (EA) into degree of substitution (DS) values for aliphatic cellulose esters were developed. The equations allow one to determine the DS of cellulose derivatives bearing not only one but also two different acyl substituents. Error transmission studies revealed that the accuracy of the DS-values for a pure sample depends on both the number of carbon atoms in the substituents and on the uncertainty of the EA, especially from the hydrogen content. This method provides accurate DS-values (±0.10 in most cases) if H-content determinations are within ±0.1%.     

Catalytic Kinetic Polarographic Determination of Trace Amount of Indium

The method of polarography for determination of trace In(III) had been reported by reference(l-2), However, The method of catalytic kinetic polarography has not been reported. Author discovered that trace indium(III) cold catalyze the discoloring oxidizing reaction of methyl orange by potassium bromate in 0.03mol/L H₂SO₄——0.25mol/L NH₃.H₂O supporting electrolyte, methyl orange exhibits a sensitive polarography wave at -0.45V(vs.SCE), The change in methyl orange concentration is traced by polarography. Hence, a new catalytic kinetic polarography method for determination of trace indium has been established. The method was used to determined trace indium in pure metallic zine with satisfactory results.     

Effect of Molecular Structure on the GasPermeability of Cellulose Aliphatate Esters简

In this work, four kinds of cellulose aliphatate esters, cellulose acetate （CA）, cellulose propionate （CP）, cellulose butyrate （CB） and cellulose acetate butyrate （CAB） are synthesized by the homogeneous acylation reactions in cellulose/AmimC1 solutions. These cellulose aliphatate esters are used to prepare gas separation membranes and the effects of molecular structure, such as substituent type, degree of substitution （DS） and distribution of substituents, on the gas permeability are studied. For CAs, as the DS increases, their gas permeabilities for all five gases （02, N2, CH4, CO and CO2） increase, and the ideal permselectivity significantly increases first and then slightly decreases. At similar DS value, the homogenously synthesized CA （distribution order of acetate substituent： C6 〉 C3 〉 C2） is superior to the heterogeneously synthesized CA （distribution order of acetate substituent： C3 〉 C2 〉 C6） in gas separation. With the increase of chain length of aliphatate substituents from acetate to propionate, and to butyrate, the gas permeability of cellulose aliphatate esters gradually increases. The cellulose mixed ester CAB with short acetate groups and relatively long butyrate groups exhibits higher gas permeability or better permselectivity than individual CA or CB via the alteration of the DS of two substituents.     

Carbamoylation Applied for Structure Determination of Cellulose Derivatives

Carbamoylation of cellulose esters (CE) and investigation of the mixed derivatives obtained with NMR spectroscopy represents a useful analytical tool for the determination of the degree of substitution (DS) and analysis of the distribution of substituents on the level of the anhydroglucose unit (AGU). Especially the carbethoxymethylcarbamoylation and the ethylcarbamoylation of CE combined with ¹H NMR spectroscopy are efficient and inexpensive ways to gain information on the over-all DS and partial DS values in position 2, 3, and 6 of the AGU. Complete subsequent phenylcarbamoylation can be achieved even for CE with bulky substituents, e.g., adamantanecarboxylic acid esters. In addition to NMR experiments the carbamoylated CE were studied by HPLC after complete chain degradation. Carbethoxymethylcarbamoylation has turned out to be the most useful tool for this path. Chromatograms comparable to carboxymethylated cellulose (CMC) were obtained, which can be exploited to calculate the mole fractions of the basic building units (un-, mono-, di- and tri-substituted glucoses) of the polymer. Comparison with statistic calculations gave a first hint on the distribution of substituents along the polymer chain. For a commercial cellulose diacetate a statistic pattern of substitution was determined.     

钴-二氮菲一硫脲体系的极谱催化波

In 8*10^-^7M phenanthroline-0.02M thiourea medium (ethanolamine buffer, pH =8.3), by using Na2SO3 to remove dissolved oxygen, cobalt ion can produce a sensitive catalytic wave with a peak shape on dc polarography. Ep=1.62V (vs. S.C.E.), detection limit is 1 X 10^-^1^0M. There is a linear dependence of peak height on cobalt concentration over a range of 2 X 10^-^1^0 - 4 X 10^-^8 M. Common ions which are not more than 1000-fold of Co^2^+ do not interfere the determination of cobalt, except Ni^2^+ and As^3^+ which are permitted to only 125 and 300-fold respectively. Good results are obtained in determining traces of cobalt in various samples by this method.     

Effect of substituent distribution on water solubility of O-methylcellulose

The effect of substituent distribution on the water solubility of O-methylcellulose (MC) was re-examined to elucidate the lower limit of the degree of substitution (DS) in water-soluble MC. To this end, a series of 2,3-MCs which are regioselectively substituted at the C-2 and C-3 hydroxyl groups were prepared by homogeneous methylation. It was found that the lower limit for the DS value of water-soluble 2,3-MC was almost the same as that for MCs having even distributions of substituents along the cellulose chain as well as in the anhydroglucose units. This revised version was published online in August 2006 with corrections to the Cover Date.     

Adsorbing colloid flotation separation and polarographic determination of Mo(VI) in water

A method is described for the flotation and determination of Mo(VI) in water at ng/ml levels. Mo(VI) is preconcentrated and separated by adsorbing colloid flotation employing aluminium(III) hydroxide as collector and sodium lauryl sulphate as surfactant at pH 5.3 ± 0.1. The molybdenum content in the froth is estimated by using the catalytic wave of Mo(VI) in the presence of nitrate by charging current compensated d.c. polarography (CCCDCP) or differential pulse polarography (DPP). The effect of variables such as pH, ionic strength, concentration of collector and surfactant, time of stirring and gas flow-rate on the recovery of Mo by flotation is reported. The effects of various cations and anions on the flotation and determination of Mo are studied. This method is employed for the determination of molybdenum in natural fresh water samples.     

Electrochemical reduction of isonicotinic amide in a strong acid medium

Isonicotinic amide was studied by dc and DP polarography and linear sweep cyclic voltammetry in a strong acid medium (pH < 3). Tafel slopes and reaction orders were obtained at potentials corresponding to the foot of the polarographic wave.In a very strong acidic medium the process occurs through the formation of a protonated gem-hydroxylamine which is transformed into the aldehyde via a substitution by water, which is the rate-determining step. For 0 < pH < 3, the gem-hydroxylamine formed after two reversible electron transfers can eliminate an ammonia molecule in two ways: (a) proton-catalysed substitution by water followed by the formation of a hydrated aldehyde; and (b) non-catalysed elimination to form the free aldehyde. The limiting current of the wave is partially controlled by these concurrent chemical reactions and. consequently, the process appears as ECE.     

THE UNIFORMITY OF DISTRIBUTION OF SUBSTITUENTS ALONG THE CHAIN OF CARBOXYMETHYL CELLULOSE SYNTHESIZED IN TWO-PHASE MEDIUM C6H66——C2H5OH

 Based on the property that carboxymethylcellulose (CMC ) can be de-graded to anhydroglucose residues by cellulase, the rate constant (K) of enzymatic degra-dation of CMC synthesized in the benzene-ethanol medium has been determined. Further-morel experimental equation K = 2.71× 10^-2(DS)^-1.2 reflecting the relationship betweenK and the degree of substitution (DS) is correlated and used to describe chemical mi-crostructure uniformity of the distribution of substituents along chains effectively. Chain structure parameters of enzymatic degradation products of CMC — the number of chain breaks and the percentage of glucose released have been also measured.Average length of substituted and unsubstituted chain segments are calculated simultaneously.Through the study of static and dynamic procedures of enzymatic degradation,the method to characterize the distribution of substituents of CMC along the chain has been improved.     

Substituent influences on the stability of the ring and chain tautomers in 1,3-O,N-heterocyclic systems: characterization by 13C NMR chemical shifts, PM3 charge densities, and isodesmic reactions

Substituent effects on the stabilities of the ring and chain forms in a tautomeric equilibrium of five series of 2-phenyloxazolidines or -perhydro-1,3-oxazines possessing nine different substitutions at the phenyl moiety have been studied with the aid of 13C NMR spectroscopy and PM3 charge density and energy calculations. Reaction energies of the isodesmic reactions, obtained from the calculated energies of formation, show that electron-donating substituents stabilize both the chain and ring tautomers but the effect is stronger on the stability of the chain form than on that of the ring form. The 13C chemical shift changes induced by the phenyl substituents (SCS) were analyzed by several different single and dual substituent parameter approaches. The best correlations were obtained by equation SCS = rhoFsigmaF + rhoRsigmaR. In all cases the rhoF values and in most cases also the rhoR values were negative at both the C=N and C-2 carbons, indicating a reverse behavior of the electron density. This concept could be verified by the charge density calculations. The 13C chemical shifts of the C=N and C-2 carbons show a normal dependence on the charge density (q(tot)), but the charge density shows a reverse dependence on substitution. Correlation analysis of the 13C chemical shifts, solvent effect (CDCl3 vs DMSO-d6) on the NMR behavior as well as the effect of substituents on the electron densities and on the stabilities of the ring and chain tautomers show that the substituent dependence of the relative stability of the ring and chain tautomers in equilibrium is governed by several different electronic effects. At least intramolecular hydrogen bonding between the imine nitrogen and the hydroxyl group as well as polarization of the C=N bond seem to contribute in the chain form. Stereoelectronic and electrostatic effects are possible to explain the increase in stability of the ring form by electron-donating substituents.     

Hydroxypropyl-substituted β-cyclodextrins: influence of degree of substitution on the thermodynamics of complexation with tauroconjugated and glycoconjugated bile salts

The effect of the degree of substitution (DS) on the ability of hydroxypropylated β-cyclodextrin (HPβCD) to form inclusion complexes with six different bile salts, found within the intestinal tracts of rats, dogs, and humans, was studied by isothermal titration calorimetry. The composition and molecular structure of the cyclodextrin samples were characterized by MALDI-TOF mass spectrometry together with 1D and 2D-NMR, and some of the complexes were studied by 2D ROESY NMR. The stability and structure of the complexes were mainly determined by the position of hydroxyl groups on the bile salts and depended relatively little on the number of hydroxypropyl side chains on the CDs. The enthalpy and entropy of complexation exhibited a strong linear increase as the DS increased from 0 to 1, and a pronounced enthalpy-entropy compensation was observed. These observations are interpreted as an increased release of ordered water from the hydration shells of the bile salts, caused by the hydroxypropyl substituents on the rim of the CD. It is estimated that each CD hydroxypropyl substituent dehydrates a hydrophobic surface area of approximately 10 ?(2).     

抗癌药物博莱霉素伏安行为及其反应机理研究

博莱霉素（ＢＬＥＯ）Ａ５在０．０５ｍｏｌ／Ｌ Ｈ２ＳＯ４溶液中出现两个还原波，峰电位分别为ＥＰ１＝－０．８３Ｖ和ＥＰ２＝－１．０９Ｖ（ｖｓ．，Ａｇ／ＡｇＣｌ）。用线性扫描与循环伏安法、恒电位库仑法、脉冲极谱、交流极谱等手段研究体系的伏安行为及反应机理。实验表明，Ｐ１为ＢＬＥＯＡ５分子中嘧啶环第一步两电子还原的吸附波，Ｐ２为嘧啶环第二、三步还原和催化氢还原的具有吸附性的重叠波。     

Photoinduced shape fixity and thermal-induced shape recovery properties based on polyvinyl alcohol bearing coumarin

In this paper, polyvinyl alcohol (PVA) bearing coumarin with different degrees of substitution (DS) are synthesized by esterifying hydroxyl of PVA with 7-carboxylmethoxycoumarin. The grafted polymer has photosensitive property and presents photocrosslinking due to the photodimerization between pendant coumarin groups, which affords PVA–coumarin sample photoinduced shape fixity properties. PVA–coumarin can be cross-linked after being illuminated under UV light of 360 nm; this provides the possibility that the sample has shape memory properties only if the cross-linking extent is suitable. The shape memory properties were induced by thermal as most shape memory polymer do. In fact, the shape fixity and recovery has strong relationship with DS, irradiation time, and thickness of sample. The effect of DS on the grafted polymer structure and properties has been studied by differential scanning calorimetry, thermogravimetric analysis, and UV spectra.     

Determination of Mo(VI) in tap-water and sea-water by differential-pulse polarography and co-flotation

A new method is described for the microdetermination of Mo(VI) in natural waters and sea-water by differential-pulse polarography based on the catalytic wave caused by Mo(VI) in nitrate medium following preconcentration by co-flotation on Fe(III) hydroxide. In the case of sea-water samples, hexadecyltrimethylammonium bromide (HTAB) was used together with octadecylamine as the surfactant. For the analysis of natural water samples only HTAB is needed. Molybdenum in the range 0.7-5.7 ng/ml has been determined.     

DIFFUSION MEASUREMENTS IN MICROEMULSIONS

We have carried out diffusion coefficient measurements in both aqueous micelles and microemulsions using the techniques of palaeography and quasielastic light scattering (QLS) The former method involves the determination of the diffusion coefficient of an electroactive oil soluble probe at a polarizable microelectrode. For high water content microemulsions, both methods yield the same diffusion coefficients, which can be identified as the self diffusion coefficient For cetyltrimethylammonium bromide (CTAB) micelles, both methods yield the same result at the salt (NaBr) concentration at which the QLS measurements are independent of CTAB concentration. In more concentrated microemulsions, QLS data gave diffusion coefficients in agreement with polarography only for a sodium cetyl sulfate (SCS) system at 65-75 wt % water. For the SCS microemulsions at 60% water, and CTAB microemulsion at 60-75% water, the QLS data yielded rapid, nonexponential decays. However, consistent polarographic diffusion coefficients could still be obtained, By using probes of varying chain length (oil solubility), it has been demonstrated that these CTAB and SCS microemulsions containing butanol and pentanol cosurfactants respectively, are not cosolubilized systems but do contain distinct hydrophilic and hydropobic regions.     

Current dips in polarography and cyclic voltammetry associated with electrochemical inducement of chemical reactions: Aromatic nucleophilic substitution

In electrochemically induced chemical reactions, such as aromatic nucleophilic substitution, current dips are frequently observed in cases where the product wave is negative to the reactant wave. The dips then appear following the reactant wave at the foot of the product wave. Such phenomena have been found for electrochemically induced aromatic substitutions in organic solvents or in liquid ammonia. They can be observed both in cyclic voltammetry and classical polarography. A mechanistic and kinetic model is presented which accounts for the formation of these current dips in the context of the two techniques. The effect of the experimental parameters on the shape, magnitude and location of the dip is discussed. It is shown that the main cause for the appearance of the current dips is the occurrence of an autocatalytic process triggered by a solution electron transfer between the reduced form of the product and the reactant. It does not involve surface phenomena, although the current—potential curves resemble those found in the case of self-inhibition deriving from reactant adsorption or passivation phenomena. The similarity in the experimental manifestation of both types of phenomena also appears through the observation of hysteresis in the potential—current curves obtained in galvanostatic conditions for electrochemically induced reactions.     

Mode of action of acetylesterases associated with endoglucanases towards water-soluble and -insoluble cellulose acetates

A screening of commercial enzyme preparations for the capability ofcellulose acetate (CA) deacetylation revealed that such enzyme activity ismore common than could be anticipated. Enzyme-aided deacetylation of celluloseacetate was clearly a function of the degree of substitution (DS). Celluloseacetates up to a DS of 1.4 were deacetylated by a large number of enzyme mixes.Interestingly, none of the investigated enzyme preparations had the capabilityfor complete cellulose acetate deacetylation. Definitely most hydrolasepreparations investigated in our study deacetylated cellulose acetate with nopreference for a certain position, as could be confirmed by NMR spectroscopy.However, one acetyl esterase had a clear preference for the C2- andC3-positions, leaving the acetyl substituents at the C6-position intact.