1H-NMR Relaxation of Water Molecules in the Aqueous Microcrystalline Cellulose Suspension Systems and Their Viscosity

An intensive study for aqueous microcrystalline cellulose (MCC) suspensions was carried out in view of the relationship between a viscosity and a 1H spin-spin relaxation time (T2) of water. An investigation was carried out for four suspension systems with the different particle size distributions. The proton mole ratio () of bound water against MCC particles and T2 of bound water (T2,b) were evaluated from the T2 values obtained by Carr-Purcell- Meiboom-Gill (C.P.M.G) method and those by solid echo method, respectively. As a result of these analyses, the T2,b value for the aqueous MCC suspension was evaluated as 5 × 10–3 s and it was found that the system having a larger tended to show a higher viscosity. By relating the above results to the observation of the suspensions by an optical microscope, it was concluded that a network formed by MCC particles plays an important role in generating a high viscosity of MCC suspension, and that an averaged mobility of water molecules is sensitively affected by the network structure.     

New intermolecular interaction potential for simulation of water and aqueous solutions in a wide range of state parameters

A new semiempirical method for derivation of additive effective potentials is proposed. Local features of the shape of the potential energy surface of water dimers are approximated by Gaussian functions. Optimum geometric parameters of nonlinear bifurcated and inverted dimers, obtained from quantum-chemical calculations are constants of the new BMW potential. Free parameters of the potential were chosen based on the results of Monte Carlo simulation of the structural and thermodynamic functions of water in a wide range of state parameters (268 K T 673 K, 0.1 MPa p 400 MPa). Calculations revealed rather high concentrations of the bifurcated and inverted dimers in the systems of H-bonds of water models. Clustering of non-tetrahedral fragments of the network of H-bonds is responsible for a microheterogeneous structure of water on the microscopic level.     

A native cellulose microfibril model

To aid in the understanding of cellulose ultrastructure, computer modelling has been employed to create a model of monoclinic (I) native cellulose. This was achieved by building a chain of cellulose, which was used in a two chain unit cell. An energy minimized microfibril model was created from several of these unit cells. A major advantage of this model is that it is a large scale unconstrained, isolated system. Thus, it facilitates the study of surface as well as central chains and provides a working model of a cellulose microfibril. An extensive analysis was carried out of intermolecular non-bond interactions and how they might contribute to the stability of the structure of crystalline native cellulose. 0969--0239 © 1998 Blackie Academic & Professional     

Carboxymethylation of cellulose in unconventional media

Carboxymethylation of cellulose in the new and highly efficient aqueous solvent Ni(tren)(OH)₂, [tren=tris(2aminoethyl)amine] and in melts of LiClO₄· 3H₂O or NmethylmorpholineNoxide (NMMNO), which is now widely applied for cellulose fibre production, was investigated. In case of Ni(tren)(OH)₂, a totally homogeneous carboxymethylation of cellulose with sodium monochloroacetate, in the presence of an aqueous NaOH solution is possible for the first time. Structure analysis by means of HPLC and ¹ HNMR after chain degradation showed results comparable with findings for CMC obtained by the heterogeneous slurry process, that is, a statistic distribution of substituents along the polymer chain and functionalisation of the hydroxyl groups in the order C6 C2 > C3. The etherification of cellulose in a melt of LiClO₄· 3H₂O, a new type of cellulose solvent, was shown to be possible and gave products of a statistic functionalisation pattern as well. In contrast, carboxymethylation starting from solutions of cellulose in NMMNO initiated with solid NaOH particles yields polymers with a nonstatistic distribution of functional groups along the chain, as observed for cellulose ethers prepared in reactive microstrctures starting from solutions of cellulose intermediates in dimethyl sulfoxide as well as of unmodified cellulose dissolved in N,Ndimethyl acetamide/LiCl.     

Molecular dynamics of cyclic and linear poly(dimethylsiloxanes)

Dielectric spectroscopy (10^–1 Hz to 10⁷ Hz) has been employed to study the molecular dynamics of a series of cyclic and linear polydimethylsiloxanes (PDMS) of various molecular weights ranging from 300 to 10 000 g/mol in the temperature range above the glass transition (from 130 K to 190 K). The observed -relaxation depends strongly on both molecular weight and structure of the samples. For linear PDMS oligomers, the -relaxation shifts towards lower temperatures with decreasing molecular weight in good accordance with the Fox-Flory-model. Cyclic PDMS reveals a qualitatively different molecular weight dependence: for a given temperature the -relaxation time increases with decreasing ring length, but has a maximum for small oligomers (degree of polymerizationn6). The shape of relaxation curves and, with it, the relaxation time distribution is independent from length and architecture of the chains The observed experimental findings are in qualitative agreement with dynamic Monte-Carlo simulations.Dedicated to Prof. E.W. Fischer on the occasion of his 65th birthday Fast macht' das WLF ihn krank, jetzt raucht er wieder, Gott sei Dank! (frei nach Wilhelm Busch)     

Heat capacities of diphenyl,p-terphenyl andp-quaterphenyl from 180 K to their melting points

The heat capacities of diphenyl,p-terphenyl andp-quaterphenyl from 180 K to their melting points were measured with a Perkin-Elmer DSC 1B scanning calorimeter. Anomalies were observed in the heat capacity curves forp-terphenyl (from 400 K to the melting point) andp-quaterphenyl (from 190 to 260 K, and from 450 to 540 K). It is assumed that the anomalies near the melting points of the compounds under consideration could be related both to modification of the motion of the phenyl rings (external or/and internal) and to change in the motion of the molecules as a whole (diffusion phase).

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Zusammenfassung Die Wärmekapazitäten von Diphenyl,p-Terphenyl undp-Quaterphenyl wurden im Bereich von 180 K bis zum Schmelzpunkt der Verbindungen mit einem Perkin-Elmer DSC 1B Scanning-Kalorimeter gemessen. Anomalien der Wärmekapazitätskurven wurden beip-Terphenyl (von 400 K bis zum Schmelzpunkt) und beip-Quaterphenyl (von 190–260 K und von 450–540 K) beobachtet. Es wird angenommen, daß die Anomalien nahe der Schmelzpunkte der betreffenden Verbindungen auf Veränderungen der Bewegung der Phenylringe (äußere und/oder innere) und der Moleküle an sich (Diffusionsphase) zurückzuführen sind.

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- 1 , - - 180 . - 400 , - — 190 260 450 540 ., ( ), ( ).

     

Microcrystalline cellulose powders: structure, surface features and water sorption capability

Characterization of an Avicel PH 102 MCC powder through polymerization degree determination, Xray diffraction and N₂ adsorptions at subcritical temperatures is described. Specific characterizations of MCC/H₂O exchange in different environments were performed by means of thermogravimetric weight losses on time/temperature scale and analyses of water adsorption/absorption from saturated vapors at 310K. The reversibility of MCC/H₂O interactions and the influence of different surface area probes on the specific surface area are discussed.     

K X-ray relative transition probabilities for 23≤Z≤33

The K X-ray relative transition probabilities K_b/K_a of some elements for atomic numbers 23Z33 induced by 3 MeV protons were measured. The experimental results are compared with the relativistic Hartree-Fock (RHF) calculations. Good agreements have been obtained considering the experimental error.     

Systematic survey on crystalline features of algal celluloses

Algal cellulose from different origins has been analysed with special reference to the crystalline features, such as allomorphism (I/I or triclinic/monoclinic two- phase model), dimension and uniplanar orientation behaviour of the specific crystallographic plane to the cell wall surface. Three types of cellulose were identified in the algal system: I-rich/broad microfibril/0.6 nm-oriented type; I- dominant/flat-ribbon/0.53 nm-oriented type; and I- dominant/small/random-oriented type. The first type appears to occur in more primitive organisms than the other types. The three types of algal cellulose correlate well with the arrangements of cellulose synthesizing complexes, i.e. multiple-row linear type, consolidated rosette type, and isolated rosette type, respectively. In Chara two types of crystals were found: an I-dominant/ribbon shaped/0.6 nm-oriented type and an I/narrow/random-oriented type. The former type, known to occur in some families of tunicates, was first identified in algal cellulose during this study. Reducing-end staining was successfully applied to microcrystal cellulose samples of Cladophorales and Zygnematales, showing that the cellulose microfibril has a parallel-chain structure for both cellulose I and cellulose I     

Crystalline transformation of native cellulose from cellulose I to cellulose ID polymorph by a ball-milling method with a specific amount of water

We have demonstrated for the first time that a mechano-chemical treatment of native cellulose with a specific amount of water (30 wt%) present ID the cellulose solid state caused the crystalline transformation from cellulose I into cellulose ID polymorph. X-ray diffractometry was used to show that the extent of transformation into cellulose ID increased with milling time. This specific phenomenon can be explained by considering the chain mobility ID the cellulose–water system, because ₁ ^1H measurement shows that cellulose molecules are most mobile when the water content ID around 30 wt%, and thus are favorable for molecular rearrangement under external forces.     

Electrodynamic investigations of conduction processes in humid microcrystalline cellulose tablets

The conduction mechanism in microcrystalline cellulose (MCC) tablets at varying relative humidity (RH) has been investigated by using the techniques of low frequency dielectric spectroscopy and transient current analysis at room temperature. The dependence on RH on the measured conductivity and charge carrier density indicates that a high-power-law-exponent percolation process of cations being conducted on water molecules occupying available 6-OH units on the cellulose chains is the dominating dc conduction mechanism at RH below 3 wt % of moisture content. The experimentally observed decrease in charge carrier mobility with increasing moisture content shows that protons and H3O+ ions that are being blocked at empty 6-OH sites also contribute to the charge transport process in cellulose at low moisture contents.     

Amorphous solid-like distribution of polydisperse particles of colloidal clay and microcrystalline cellulose in deionized suspension

A metallurgical microscope is used to directly observe the amorphous solid-like structures of deionized suspensions of highly polydispersed colloids in sedimentation equilibrium. The colloids used are colloidal clay of bentonite and microcrystalline cellulose (MCC). The two-dimensional distance distribution functions of the amorphous solid-like structures at relatively diluted and concentrated suspensions resemble those of the liquid-like and gas-like structures of monodispersed spheres, respectively. The center-to-center interparticle distances (D) in the amorphous solid-like structures are explained by the effective hard-sphere model; a colloidal particle is coated with electrical double layers. The maximum length of the width of the double layers (Debye length,D ₁) observed is ca. 1n at very dilute suspensions.D andD ₁ continue to decrease as the initial concentration of the particles increases, and from these data rigidities are estimated to be 0.12 and 0.09 Pa for bentonite and MCC suspensions, respectively. The log [viscosity] of bentonite suspensions begins to increase linearly as log [shear rate] decreases with a slope close to –1, which supports the solid-like nature of the suspensions. These experimental results show that electrostatic interparticle repulsion and the elongated Debye-screening length around the particles are both essential for the appearance of the amorphous solid-like structures.     

Fluorometric determination of hydrogen peroxide with peroxidase and 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid

Summary The possibility of the fluorometric determination of hydrogen peroxide using various tetrahydro--carbolines as hydrogen-donating substrates for horseradish peroxidase was examined. A simple and sensitive method has been developed by using 1-methyl-1,2,3,4-tetrahydro--carboline-3-carboxylic acid as a substrate. The fluorescence intensity was proportional to the hydrogen peroxide concentration in the range of 0.05–1 mol/l (30–600 pmol/tube) in the sample solution with a relative standard deviation of 3.8% (0.1 mol/l).     

Comparison of microwave and lower-frequency discharges for plasma polymerization

A plasma sustained by surface waves (SW) has been used to study the deposition rate R of hydrocarbon and fluorocarbon plasma polymer films as a function of excitation frequency f=/2 in the range 12–400 MHz. The SW technique allows one to vary only f while keeping constant all other parameters known to influence R, for example, power density in the plasma P. A plot of R/P at a total pressure of 200 m Torr (27 Pa) displays two plateaus, that at f<30 MHz being about five times lower than that at f100 MHz. This is attributed to the fact that electron energy distribution functions differ fundamentally at radio- (f50 MHz) and microwave (f100 MHz) frequencies, for the gas pressure range considered.     

Conductivity and Electrokinetic Potential of Microcrystalline Cellulose Particles in Aqueous HCl and NaOH Solutions

The conductivity of microcrystalline cellulose (MCC) dispersions in aqueous 10^–5–10^–2 M HCl and NaOH solutions was measured as a function of the particle volume fraction by the conductometry. The dependence of the relative conductivity of MCC particles on pH of equilibrium solutions was determined using the Wagner equation. The electrophoretic mobility of MCC particles in the aforementioned solutions was measured by the microelectrophoresis, and corresponding dependences of the particle potentials on pH of aqueous HCl and NaOH solutions (pH 2–11) were calculated using the Smoluchowski and Henry equations of the electrophoresis theory. It was shown that, in the case of MCC, the Henry equation, which allows for the significant conductivity of the dispersed particles, as compared with the dispersion medium, makes it possible to calculate more accurate potential values and, consequently, to derive the (pH) dependence, which is satisfactorily consistent with the effect of the surface charge and solution ionic strength on the potential in a wide pH range.     

Evaluation of molten inorganic salt hydrates as reaction medium for the derivatization of cellulose

Molten inorganic salt hydrates are highly efficient solvents forcellulose. The carboxymethylation of the polymer dissolved in this new group ofcellulose solvents was investigated. The homogeneous carboxymethylation ofcellulose in molten LiClO₄3H₂O using sodiummonochloroacetate in the presence of NaOH is possible. The formation of CMC wasconfirmed by FT- Raman spectroscopy. Structure analysis by means of HPLC afterchain degradation showed the formation of CMC with a DS of 2 after a shortreaction time of 4 h. The derivatives exhibit a statisticaldistribution of substituents along the polymer chain if prepared in moltenLiClO₄3H₂O as solvent. A substituent distributioninthe order C-6 > C-2 C-3 for anhydroglucose units (AGU) was concludedfrom ¹H-NMR measurements. The synthesis of CMC in the swellingmediumLiClxH₂O (2 x 5) yields polymers with astatistical distribution of functional groups along the chain. The watercontentof the salt melts has a dramatic influence on the DS_CMC.     

Applications of pulse radiolysis and flash photolysis to some problems related to the chemistry of cancer therapy

The semireduced form (Adr) of the anti-tumour agent adriamycin is implicated in cardiotoxic side effects. Adr, prepared by reduction with e _aq ^– and CO ₂ ^– , has pK values at 2.9 and 9.2. In the pH range 6–11, Adr is relatively stable, existing in equilibrium with Adr and the hydroquinone, the latter subsequently losing the sugar within 100 ms. The E ₇ ¹ of Adrais –328 mV, so at equilibrium the reaction O ₂ ^– + AdrO₂ + Adr lies well over to the left. The relative yields of O₂(¹g) formed via energy transfer from triplet excited components of haematoporphyrin derivative, the drug used in photodynamic therapy, have been measured by observations of the phosphorescence emission at 1270 nm. The measurements suggest that the most active component, dihaematoporphyrin ether or ester, is comparatively ineffective itself photodynamically, but may serve as a pool for the more effective haematoporphyrin and hydroxyethylvinylporphyrin to act inside the cancer cell. One-electron oxidation of dopa, through N ₃ ^. or photoionization, leads to the melanin precursor dopachrome via dopasemiquinone and dopaquinone. The latter reacts with cysteine to form cysteinyldopa, a marker for malignant melanoma metastasis. N ₃ ^. —initiated oxidation of cysteinyldopa proceeds via a different mechanism involving the corresponding semiquinone, quinone and a quinone-imine which rearranges to a more stable benzothiazole.     

Solution studies of some technetium complexes containing sulfur ligands

Interactions between technetium and the following series of sulfur ligands are described: 2,5-dimercapto-1,3,4-thiadiazole, 1-methylimidazol-2-thiol, 6,6-dithiodinicotinic acid, 2-amino-6-mercaptopurine and DL--amino-2-thiopheneacetic acid. The complexation reactions have been investigated (species formed,e, stoichiometry, etc.) and the results obtained have been comparatively evaluated with the aim to find relations between structure of the ligands and its complexing activity.