Accessibility of hydroxyl groups in birch kraft pulps quantified by deuterium exchange in D2O vapor

Deuterium exchange in a deuterium oxide (D₂O) atmosphere (95 % relative humidity), quantified by a dynamic vapor sorption (DVS) apparatus, was applied for assessing the accessibility of hydroxyl groups in birch kraft pulps. Achieving the maximum deuteration level exhibited slower kinetics than was earlier reported for experiments with ground wood and bacterial cellulose. The deuterium exchange process followed two parallel phenomena. Applying multiple drying and rewetting cycles gave kinetic information also on the hornification phenomenon occurring during these cycles. Dry birch pulps treated with sodium hydroxide solution of varying alkalinities at elevated temperatures were assessed for their accessible hydroxyl groups by DVS with deuterium exchange. This method was evaluated against deuteration combined with Fourier transform infra-red spectroscopy and water retention value (WRV). DVS measurements were in correlation with WRV and both the methods indicated that an alkaline treatment of dry birch pulp improves cellulose accessibility. The level of irreversible deuteration also decreased as the alkalinity was increased. DVS was shown to provide quantitative information on the accessibility but to be a time-consuming method for the pulp samples. A potential means to decrease the duration of the measurement is increased D₂O exposure by excluding the drying phases.     

Helical concept of the fine structure of cellulose

The helical concept of the fine structure of cellulose as proposed by Manley is discussed. The deuterium exchange experiments with cotton, cotton crystallites, and regenerated cellulose I, in which accessibility was determined by comparing the ratio of the infrared absorbance of the O? D peak to the O? H peak, revealed that the accessibility of cotton linters decreased on acid hydrolysis, whereas it increased on treatment with ethylamine followed by washing with water. This is in contrast to the finding of Manley, who had evaluated the accessibility by a gravimetric D₂O exchange method and had come to the conclusion that acid hydrolysis did not change the accessibility of cellulose and hence cellulose did not contain crystalline and amorphous phases but was all crystalline. On the basis of Manley's protofibril and the accessibility data obtained in this investigation, a concept of the fine structure of cellulose is proposed, in which the role of Manley's protofibril is analogous to the role of individual molecule in the fringe micellar model. This concept explains the properties of cellulose that are otherwise explainable on the currently accepted fringe micellar theory. In addition, it explains the marked shrinkage in the length of cotton and rayon fibers when placed in 16% sodium hydroxide solution.     

Proton Conductor of Propylene Carbonate–Plasticized Carboxyl Methylcellulose–Based Solid Polymer Electrolyte

Carboxyl methylcellulose (CMC) solid polymer electrolytes were prepared by utilizing oleic acid (OA) and different wt.% of propylene carbonate (PC) by using the solution casting technique. An ionic conductivity study of the films was done by using impedance spectroscopy. The highest ionic conductivity gained is 2.52 × 10^?7 S cm^?1 at ambient temperature for sample CMC-OA-PC 10 wt.%. From transference number measurement (TNM), the value of cation diffusion coefficient, D₊, and ionic mobility, μ₊, was higher than the value of anion diffusion coefficient, D_?, and ionic mobility, μ_?. Thus, the results prove that the present samples were proton conductors.     

Can the Theoretical Fitting of the Proton‐Nuclear‐Magnetic‐Relaxation‐Dispersion (Proton NMRD) Curves of Paramagnetic Complexes Be Improved by Independent Measurement of Their Self‐Diffusion Coefficients?

The self‐diffusion (D_c) coefficients of various lanthanum(III) diamagnetic analogues of open‐chain and macrocyclic complexes of gadolinium used as MRI contrast agents were determined in dilute aqueous solutions (3–31 mM ) by pulsed‐field‐gradient (PFG) high‐resolution ¹H‐NMR spectroscopy. The self‐diffusion coefficient of H₂O (D_w) was obtained for the same samples to derive the relative diffusion constant, a parameter involved in the outersphere paramagnetic‐relaxation mechanism. The results agree with an averaged relative diffusion constant of 2.5 (±0.1)×10^?9 and of 3.3 (±0.1)×10^?9 m² s^?1 at 25 and 37°, respectively, for 'small' contrast agents (M_r 500–750 g/mol), and with the value of bulk H₂O (2.2×10^?9 and 2.9×10^?9 m² s^?1 at 25° and at 37°, respectively) for larger complexes. The use of the measured values of D_c for the theoretical fitting of proton NMRD curves of gadolinium complexes shows that the rotational correlation times (τ_R) are very close to those already reported. However, differences in the electronic relaxation time (τ_SO) at very low field and in the correlation time (τ_V) related to electronic relaxation were found.     

Solvent Effects on the NMR Chemical Shifts of Imidazolium-Based Ionic Liquids and Cellulose Therein

The interactions of ionic liquids (IL) with solvents usually used in liquid-state nuclear magnetic resonance (NMR) spectroscopy are studied. The ¹H- and ¹³C-NMR chemical shift values of 1-n-butyl-3-methyl (BM)- and 1-ethyl-3-methyl (EM)-substituted imidazolium (IM) -chlorides (Cl) and -acetates (Ac) are determined before and after diluting with deuterated solvents (DMSO-d₆, D₂O, CD₃OD, and CDCl₃). The dilution offers structural modifications of the IL due to the solvents capacity to ionization. For further investigation of highly viscous cellulose dopes made of imidazolium-based IL, solid-state NMR spectroscopy enables the reproducibility of liquid-state NMR data of pure IL. The correlation of liquid- and solid-state NMR is shown on EMIM-Ac and cellulose/EMIM-Ac dope (10 wt %).     

The effect of pressure and temperature of self-diffusion coefficients in several concentrated deuterium oxide diamagnetic electrolyte solutions

The pressure dependences of the self-diffusion coefficients of deuterium oxide in 4.5m solutions of LiCl–D₂O and CsCl–D₂O (also 7m) and 3.06m CaCl₂–D₂O have been measured by the NMR spin-echo method at 30°C, 60°C, and 90°C. Shear viscosities and densities of these solutions have also been determined over the same range of experimental conditions. The experimental data show that the diffusion constantD decreases with the increasing structure-making ability of the electrolyte cation Ca⁺²>Li⁺. In contrast, the diffusion coefficient for D₂O in the 4.5 and 7m CsCl solutions is equal to that for pure D₂O at 30°C but lower at 60°C and 90°C. It has been found that the Stokes-Einstein equation relates well the diffusion coefficients to shear viscosity in these concentrated electrolyte solutions.     

Self-assembled films from WO3: Electrochromism and lithium ion diffusion

WO₃/chitosan and WO₃/chitosan/poly(ethylene oxide) (PEO) films were prepared by the layer-by-layer method. The presence of chitosan enabled PEO to be carried into the self-assembled structure, contributing to an increase in the Li⁺ diffusion rate. On the basis of the galvanostatic intermittent titration technique (GITT) and the quadratic logistic equation (QLE), a spectroelectrochemical method was used for determination of the “optical” diffusion coefficient (D_op), enabling analysis of the Li⁺ diffusion rate and, consequently, the coloration front rate in these host matrices. The D_op values within the WO₃/chitosan/PEO film were significantly higher than those within the WO₃/chitosan film, mainly for higher values of injected charge. The presence of PEO also ensured larger accessibility to the electroactive sites, in accordance with the method employed here. Hence, this spectroelectrochemical method allowed us to separate the contribution of the diffusion process from the number of accessible electroactive sites in the materials, thereby aiding a better understanding of the useful electrochemical and electrochromic properties of these films for use in electrochromic devices.     

Method for the measurement of diffusion coefficients of labile gas-phase species: The diffusion coefficient of O(3P) in He at 294 K

The dispersion of a pulse of O(³P) atoms in flowing helium has been analyzed by a modification of Taylor's method in order to determine the diffusion coefficient. Atoms of O(³P) were produced in a flowing stream of helium by a pulsed microwave discharge of molecular oxygen. After traversing a known length of the flow tube, the arrival time distribution of the O(³P) atoms was obtained using a mass spectrometer. The value obtained for D₀ at 294 K, where D₀ = D[He], is (2.40 ± 0.06) × 10¹⁹ cm^?1 ·s^?1, which corresponds to a diffusion coefficient of (731 ± 18) cm²/s at 1 torr. In addition to D₀, analysis of the arrival time distributions gives an estimate of the mean flow velocity for O atoms in helium. There was no significant difference between the value of the velocity found this way and that obtained from the mean bulk gas flow measurement. Thus for this system there is no evidence for a chromatographic effect for O(³P) atoms on the walls of the flow tube.     

IR absorption spectroscopy of polarized states of the [D2O...D-OD2]+ ion in crystalline deuterodioxonium perchlorate

Polymorphism of crystalline DClO₄·2D₂O with 99 at % D has been studied by IR absorption spectroscopy. A new phase has been found, which is easy to identify based on some spectral indications: the spectra show a strong broad band at 2125 cm^?1 due to v_s,as(D₃O) vibrations of the deuterodioxonium group and a rather narrow strong band at 2506 cm^?1 due to the v_as(D₂O) vibrations of the neutral molecular group. The continuous band v_as(O...D...O) typical of the intracationic hydrogen bond in D₅O ₂ ⁺ ClO ₄ ^? is absent in this case. These features point to considerable polarization of the deuterooxonium cation [D₂O...D-OD₂]⁺. Its low symmetry is explained by a considerable displacement of the bridging D atom from the center of the strong hydrogen bond to one of the two D₂O molecules induced by asymmetric interactions in the crystal field. The ClO ₄ ^? ions bound by the hydrogen bonds of dioxonium are also in low-symmetry positions. Upon the crystallization of DClO₄·2D₂O with ≥10 at % H, a polymorphic isotope effect is observed: the crystal structure depends on H-D isotope dilution, the conditions of thermal treatment of all samples being the same.     

Oligosaccharide Analogues of Polysaccharides,Part 20 , NMR Analysis of Templated Cellodextrins Possessing Two Parallel Chains: A Mimic for Cellulose I?

Naphthalene‐1‐ethanol and naphthalene‐1,8‐diethanol carrying one or two glycosidically bonded cellodextrin chains, T‐x and T‐x‐x , resp. ( x =1 – 4, 8) were analyzed by NMR spectroscopy. For solutions in (D₆)DMSO and (D₅)pyridine, analysis was based on a comparison of chemical shifts, coupling constants, temperature dependence of OH signals, and ROESY spectra of the singly and doubly substituted T‐x and T‐x‐x . The characteristic strong intrachain inter‐residue O(3)−H⋅⋅⋅O(5′) H‐bond of celluloses was detected in the singly and doubly substituted naphthalenes. Also detected was a weakly persistent flip‐flop H‐bond between HO(2′) and HO(6). Weak interchain interactions were, however, observed only for the units closest to the link of T‐x‐x in (D₆)DMSO and for parallel units of T‐1‐1 and T‐3‐3 in (D₅)pyridine. Interchain interactions in T‐x‐x are stronger in (D₅)pyridine than in (D₆)DMSO and decrease with increasing distance from the link. The solid‐state CP/MAS ¹³C‐NMR spectra of T‐x‐x were compared with those of T‐x and of celluloses. The spectrum of T‐8 and, surprisingly, also of T‐8‐8 strongly resembles that of cellulose II and not that of cellulose I_β, evidencing that a flexible template possessing parallel cellodextrin chains does not impose sufficient constraints on the structure of supramolecular assemblies to mimic cellulose I_β, but leads to a valuable mimic of cellulose II.     

Isotopic fractionation during pretreatment for accelerator mass spetrometer measurement of (D<Subscript>3</Subscript>C)<Subscript>2</Subscript>O containing <Superscript>14</Superscript>C produced by nuclear reaction

A (D₃C)₂O (d₆-acetone) target was irradiated with semi-monoenergetic neutrons generated from ⁹Be(p,n)⁹B reaction with 20 MeV protons to convert ¹³C and oxygen nuclides in the target into ¹⁴C. With both liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS) we measured the (D₃C)₂O (d₆-acetone) liquid targets, which were combustible and easy to afford CO₂ for the AMS measurements. The ¹⁴C yield measured by the LSC method turned out to be 80 times larger than that by the AMS method. This large discrepancy may be attributed to the loss of ¹⁴C atoms during the sample pretreatment in the AMS method such as combustion and cryogenic trapping of CO₂. It means that ¹⁴C newly produced by nuclear reactions can exist in various chemical forms, i.e., C₃D₆O, CO, CO₂, hydrocarbons, etc., and a simple sample pretreatment right after production can cause serious isotopic fractionation. Therefore, using the AMS method, extreme caution in sample pretreatment should be exercised when the ¹⁴C yield produced immediately by nuclear reaction is measured.     

Emission of occluded volatiles during deformation of polycarbonate due to strain-enhanced diffusion

Measurements of the emission of purposely entrained volatiles (Ar and D₂O) during the loading and unloading of a bisphenol-A polycarbonate in vacuum are made by quadrupole mass spectrometry. Transient loading events are accompanied by dramatic increases in emission, reflecting a similar rise in the diffusion constant of the measured species. We attribute this change to an increase in size of molecular voids in the polymer network, which accompany the increase in sample volume under load. The results are interpreted in terms of the Dolittle relation in which the diffusion constant depends exponentially upon v^*/v_f0, the ratio between an activation volume for diffusion and the average size of the relevant voids in the polymer network. Our data suggests that v^*/v_f0 is unusually low in the D₂O-polycarbonate system, which we attribute to a relatively large value of v_f0; this would be consistent with the relatively long distance between flexible links in the polycarbonate structure. © 1994 John Wiley & Sons, Inc.     

HTO as a conservative tracer used for characterization of contaminant migration in porous rock environment

Methodology for diffusion coefficient determination was applied on sandstone samples, using conservative non sorbing tracer. The results proved that methodology, through-diffusion cell design and GoldSim diffusion module can be used for sandstone samples in order to determine important migration parameters, necessary for transport model input. However, rock heterogeneity factor has to be taken into account in any case as it can potentially change rock properties, even within centimeter scale. Effective diffusion coefficient D _e for rock samples was determined. The values fell into the range of 1.0–6.17 × 10⁻¹⁰ m² s⁻¹. Discrepancies in measured and simulated porosity were observed. Statistical analyses revealed that values of diffusion coefficient D _e were in close interrelation to primary mineral (quartz) and cement forming minerals (kaolinite and organic matter).     

Angular dependence of 1H- and 2H-NMR spectra of water and methanol absorbed in cellulose triacetate film

¹H- and ²H-NMR spectra of water (H₂O and D₂O) and methanol (CH₃OD and CD₃OH) absorbed in cellulose triacetate films have been observed as a function of the angle θ between the film surface and the magnetic field. ¹H-NMR signals of H₂O and CH₃OD are doublets and triplets due to dipole interactions, respectively. ²H-NMR signals of D₂O, CD₃OH, and CH₃OD are doublets due to quadrupole splittings. The magnitudes of these splittings change depending on θ. The analysis of the angle-dependent patterns indicates that the motionally averaged axes of the dipole and the quadrupole moments orient in the direction perpendicular to the film surface. The alignment of water and/or methanol molecules originates from the film morphology, which is anisotropic in the perpendicular direction. From the angle dependence of the chemical shift, the volume diamagnetic susceptibility of the film is estimated to be 0.44 ppm.     

Investigation of the change in the fine structure of Valonia cellulose upon wet heating and mercerization

A Valonia cellulose (NV), a cellulose II derived from NV by mercerization (MV), and a cast cellulose II film (F) were deuterated repeatedly (wetting-drying cycle) in vapor phase at 25°C; the integrated deuteration time amounts to 5 × 10⁵ min. A region C, which cannot be attacked by the exchange reaction, exists in NV and MV, amounting to 80 and 18% in the respective samples. In the case of F, it could not be determined exactly due to the too large scattering of the data. On heating in liquid D₂O for 5 or 10 min., OD groups develop within C above 190 and 170°C in NV and MV, respectively. Above 190°C. the exchange is larger in NV than in MV. These OD groups within the pre-existing crystallites begin to disappear after treating with NaOH solution at the concentration at which cellulose begins to be converted to alkali cellulose I. The resistant OD groups developed within the amorphous and intermediate regions are rehydrogenated by the more dilute alkaline solutions.     

Deuterium diffusion in vanadium deuterides (VDx; 0.4?x?0.6) studied by H NMR

Sites and dynamics of deuterium in VD_0.50 as well as in VD_0.40 and VD_0.57 have been studied by means of X-ray diffraction, differential scanning calorimetry and ²H NMR. VD_0.40 consists of the body-centered-cubic (bcc) α_D and body-centered-tetragonal (bct) β_D phases at room temperature and only the octahedral (O) sites are occupied in the β_D phase. On the other hand, in VD_0.50, consisting of the bctβ_D phase at room temperature, the O site is dominantly occupied with a small occupancy of the tetrahedral (T) sites in the β_D phase. VD_0.57 is composed of the bccα′_D (a high-deuterium-concentration phase of the α_D phase) and bctβ_D phases at room temperature, and the occupancy of the T sites is observed. The mean activation energy (E_D) of the deuterium diffusion is much larger for the O sites than for the T sites, and the diffusion is also much slower in the O sites. The mean E_D values for the O sites are almost the same in the β_D phase of VD_0.40 and VD_0.50, although the distribution of the mean residence time is much larger in VD_0.50 than in VD_0.40.     

Feasibility study for the rapid screening of target molecules using translational diffusion coefficients: diffusion-ordered NMR spectroscopy of biological toxins

A panel of 15 biological toxins ranging between ~60–28,000 g/mol was used to evaluate the feasibility of screening aqueous samples for toxin analytes based on their translational diffusion coefficients, D _t. Toxin D _t values were measured by pulsed-field gradient ¹H NMR spectroscopy using a bipolar pulse pair, longitudinal eddy current delay pulse sequence incorporating water suppression to achieve the maximum dynamic range for toxin signals. To collect data for an effective screening protocol, reference D _t values were determined from five independent measurements at both 25 and 37 °C for all toxins in the panel. In the protocol, D _t values are measured at both temperatures for a suspected toxin target in a sample, and for assignment as a potential toxin analyte, the measurements are required to fall within ±0.25 × 10⁻⁶ cm²/s of both reference D _t values for at least one toxin in the panel. Only solution viscosity was found to influence sample D _t measurements appreciably; however, the measurements are easily corrected for viscosity effects by calculating the D _t value of the suspected toxin at infinite dilution. In conclusion, the protocol provides a rapid and effective means for screening aqueous samples for all toxins in the panel, narrowing toxin identification to ≤2 possibilities in virtually all cases.     

Effect of the solvent upon the diffusion coefficient of polydisperse polystyrene and styrene-acrylonitrile copolymer in dilute solution

A laser homodyne spectrometer was used to obtain translational diffusion coefficients for dilute polystyrene and styrene-acrylonitrile copolymer solutions at room temperature. Data were obtained in the concentration range from 0.01 to 2.0 g polymer per 100 cm³ solution for polystyrene in benzene and in decalin; and for copolymer in dimethyl formamide, in methyl ethyl ketone, and in benzene. The samples were polydisperse polystyrenes of weight average molecular weights between 80,000 and 350,000 and polydisperse copolymers of weight average molecular weights between 200,000 and 800,000. The SAN copolymers were random copolymer samples containing 24% by weight acrylonitrile. For each of the systems investigated the concentration dependence of the diffusion coefficient was linear over the concentration range studied, and was expressed as D(c) = D₀(1+k_Dc). Values of D₀ could be explained with a modified Kirkwood-Riseman expression. Values of the parameter k_D obtained from the slopes could be interpreted using the two-parameter theory approach as suggested by Vrentas and Duda. The value of k_D is positive for high-molecular-weight polymers and negative for low-molecular-weight polymers. For a particular polymer, the molecular weight at which k_D changes sign is greater for poor solvents than for good solvents. Observed values of D₀ were 1 × 10^?7 to 7 × 10^?7 cm²/sec.     

Efficient preparation of carbon papers by pyrolysis of iodine-treated Japanese paper

A novel carbon paper has been prepared by pyrolysis from traditional Japanese paper called washi in Japan, which is mainly composed of cellulose microfibers. The washi was iodine-treated before pyrolysis. The effect of iodine-treatment on pyrolysis of the washi was investigated using thermogravimetric analysis. The structural and electrical properties of the carbon papers were also investigated using Raman scattering, X-ray diffraction, electron microscopy, and resistivity measurements. The iodine-treatment prevents cellulose from thermally decomposing and is effective in increasing the carbon yield and retaining its fibrillar structure. Porous carbon papers consisting of many micro and nanofibrils were prepared by the pyrolysis of the iodine-treated washi at 800 °C. Those prepared at 800 °C and then heat-treated at higher temperatures than 1800 °C show electrical conductivities of 3 S cm⁻¹ and 24–27 S cm⁻¹. The degree of crystallinity and the electrical conductivity of the papers are improved by the heat treatment at higher temperatures.     

Hydrogen in Porous Tetrahydrofuran Clathrate Hydrate

The lack of practical methods for hydrogen storage is still a major bottleneck in the realization of an energy economy based on hydrogen as energy carrier. ¹ Storage within solid‐state clathrate hydrates, ² – ⁴ and in the clathrate hydrate of tetrahydrofuran (THF), has been recently reported. ⁵ , ⁶ In the latter case, stabilization by THF is claimed to reduce the operation pressure by several orders of magnitude close to room temperature. Here, we apply in situ neutron diffraction to show that—in contrast to previous reports^{[5, 6]}—hydrogen (deuterium) occupies the small cages of the clathrate hydrate only to 30 % (at 274 K and 90.5 bar). Such a D₂ load is equivalent to 0.27 wt. % of stored H₂. In addition, we show that a surplus of D₂O results in the formation of additional D₂O ice Ih instead of in the production of sub‐stoichiometric clathrate that is stabilized by loaded hydrogen (as was reported in ref. ⁶ ). Structure‐refinement studies show that [D₈]THF is dynamically disordered, while it fills each of the large cages of [D₈]THF?17D₂O stoichiometrically. Our results show that the clathrate hydrate takes up hydrogen rapidly at pressures between 60 and 90 bar (at about 270 K). At temperatures above ≈220 K, the H‐storage characteristics of the clathrate hydrate have similarities with those of surface‐adsorption materials, such as nanoporous zeolites and metal–organic frameworks, ⁷ , ⁸ but at lower temperatures, the adsorption rates slow down because of reduced D₂ diffusion between the small cages.