Deuterium Exchange Method Research Articles

Wood-Water Relations Affected by Anhydride and Formaldehyde Modification of Wood.

The moisture uptake of wood is influenced by accessible hydroxyl groups acting as sorption sites and the water-available cell wall space. To what extent do these mechanisms control the moisture uptake in wood needs to be addressed. For this purpose, we modified sorption site density and cell wall space by wood treatments with acetic anhydride or formaldehyde and investigated their effects on moisture uptake. Chemical changes at the cell wall level caused by the treatments were first determined by confocal Raman imaging. Following this, the deuterium exchange method was used to gravimetrically measure the hydroxyl accessibility, while the moisture uptake and the consequent swelling of the wood were determined by dynamic measurements of mass and dimensions within the hygroscopic range. The results showed that the effectiveness in reducing the moisture content of untreated wood across the hygroscopic range differed between the anhydride- and formaldehyde-modified wood. We also observed a poor correlation of accessible hydroxyl concentration in formaldehyde-modified wood with weight percentage gain and water uptake. Moreover, the dynamic mass and dimension analysis indicated that the reduction in swelling in formalized wood was affected by an unidentified mechanism in addition to reduced moisture content.

Water vapor sorption mechanism of furfurylated wood

Furfurylation could have a significant influence on wood hygroscopicity. However, moisture sorption and its mechanism of furfurylated wood are not fully understood. The aim of this study was to clarify the effect of furfurylation on sorption behavior and the mechanism of moisture sorption for furfurylated wood. Water vapor sorption isotherms were derived from dynamic vapor sorption apparatus and analyzed employing Hailwood–Horrobin model. Simultaneously, fiber saturation point and accessible hydroxyl groups were determined by NMR cryoporometry and deuterium exchange method, respectively. Results indicated that compared with control sample, furfurylated samples with different weight gain percents (WPGs) exhibited a little difference in reduced equilibrium moisture content (EMCR) throughout RH range. Specifically, an increase below 30% RH and above 60% RH, and a reduction at 30–60% RH in EMCR of the furfurylated samples were showed, when compared with that of control sample. EMCR of 69% WPG displayed no distinguishable difference with that of 23% WPG over the whole RH range. Fiber saturation point increased with enhanced WPGs. However, accessible OH groups possessed a reduction with increased WPGs. The hygroscopic mechanism of furfurylated wood was associated with not only accessible OH groups but also other effects. This work could provide valuable guidance to control moisture-related properties of furfurylated wood.

Accessibility of hydroxyl groups in furfurylated wood at different weight percent gains and during Rhodonia placenta decay

Deuterium exchange was used to measure accessible hydroxyl (OH) groups in furfurylated wood at different weigh percent gains (WPGs) and at different levels of mass loss caused by exposure to the brown-rot fungus Rhodonia placenta. The results from the deuterium exchange method showed that OH accessibility in furfurylated samples did not change with increasing WPGs. However, OH accessibility in furfurylated samples increased significantly after initiation of decay at commercial treatment level (mean WPG 32%), which is attributed to degradation of crystalline cellulose regions and formation of new OH groups in lignin and the furfuryl alcohol polymer.

Time-resolved total reflection detects mass transfer along thickness direction of bulk Nafion® film

To elucidate a bulk membrane (Nafion®) with respect to channel connectivity or mass transfer (water or ions) through the channels, we propose to utilize time-resolved neutron reflectivity and deuterium exchange method. We performed the experiment on time-of-flight spectrometer iMATERIA at pulsed neutron spallation source J-PARC in Tokai, Japan. To exchange water (D2O or H2O) in the film during RF measurements, we specially designed a sample environment with Si substrates. A bulk film (50 μm thickness) is sandwiched by Si substrate (5 mm thickness) and Al mesh plate. The incident neutron incomes from edge of Si substrate and reflects at a front surface of bulk film. When we exchange water (D2O or H2O), water flows through Al mesh and starts to diffuse in the film. When exchanged water reaches to a front surface of the film, critical angle for total reflection (or critical wave number) changes, according to the chemical composition and therefore the averaged coherent scattering length (bav) at the front surface. Consequently, diffusion coefficient is determined from time-dependence in bav.

An Effective Deuterium Exchange Method for Neutron Crystal Structure Analysis with Unfolding-Refolding Processes.

A method of hydrogen/deuterium (H/D) exchange with an unfolding-refolding process has been applied to hen egg-white lysozyme (HWL), and accurate evaluation of its deuteration was carried out by time-of-flight mass spectroscopy. Neutron crystallography requires a suitable crystal with enough deuterium exchanged in the protein to decrease incoherent scattering from hydrogens. It is very expensive to prepare a fully deuterated protein, and therefore a simple H/D exchange technique is desirable for this purpose. Acid or base addition to protein solutions with heating effectively increased the number of deuterium up to more than 20 % of that of all hydrogen atoms, and refolded structures were determined by X-ray structure analysis at 1.8 Å resolution. Refolded HWL had increased deuterium content in its protein core and its native structure, determined at atomic resolution, was fully preserved.

What Can Study of Oligomerization of Proteins in the Process of Oncogenesis Bring Us?

Many cellular proteins form oligomers. The equilibrium between monomeric and oligomeric states of these proteins is important for the regulation of protein activity. Modulation of the oligomerization equilibrium could be an interesting approach in the development of new therapeutic agents. This review summarizes information about protein oligomerization and modulation of this process, demonstrating the role of oligomerization in oncogenesis by tumor suppressor protein p53, which forms tetrameric structure. Today, many studies focus on finding compounds that stabilize its tetramers. Among the methods for studying oligomerization, we present hydrogen/ deuterium exchange method coupled with mass spectrometry which is suitable for the detection of protein-protein interaction and analysis of oligomerization dynamics.

Aliphatic Hydrocarbon Spectra by Helium Ionization Mass Spectrometry (HIMS) on a Modified Atmospheric-Pressure Source Designed for Electrospray Ionization

Chemical-ionization techniques that use metastable species to ionize analytes traditionally use a flat pin or a sharp solid needle onto which the high potential needed to generate the discharge plasma is applied. We report here that direct analysis of samples containing volatile and semivolatile compounds, including saturated and unsaturated aliphatic hydrocarbons, can be achieved on any electrospray-ionization mass spectrometer by passing helium though the sample delivery metal capillary held at a high potential. In the helium plasma ionization source (HPIS) described here, the typical helium flow required (about 20-30 mL/min), was significantly lower than that needed for other helium-ionization sources. By this procedure, positive ions were generated by nominal hydride ion removal from molecules emanating from heated saturated hydrocarbons as large as tetratetracontane (C(44)H(90)), at capillary voltages ranging from 2.0 to 4.0 kV. Unsaturated hydrocarbons, on the other hand, underwent facile protonation under much lower capillary voltages (0.9 to 2.0 kV). Although saturated and monounsaturated hydrocarbons bearing the same number of carbon atoms generate ions of the same m/z ratio, a gas-phase deuterium exchange method is described to ascertain the identity of these isomeric ions originating from either protonation or hydride abstraction mechanisms. Moreover, mass spectrometric results obtained by exposing unsaturated hydrocarbons to D(2)O vapor in an HPIS-MS instrument confirmed that the proton donor for ionization of unsaturated hydrocarbons is protonated water.

Difference of the Crystal Structure of Cellulose in Wood after Hydrothermal and Aging Degradation: A NIR Spectroscopy and XRD Study

The change of crystalline structure in hydrothermally treated hinoki wood was investigated by means of Fourier-transform near-infrared spectroscopy in combination with a deuterium exchange method and X-ray diffraction. The results were compared with analogous data of dry-exposed archeological wood taken from an old wooden temple. Although the decomposition of the amorphous regions in cellulose and hemicelluloses, which corresponds to an increase of the degree of crystallinity, was observed for both, archeologically and hydrothermally treated wood, the increase of crystallite thickness was confirmed only for hydrothermally treated wood. The increase of the average size of crystallites corresponds well to the measured decrease of the deuteration accessibility of the crystalline regions. As the accessibility of the crystalline regions decreased for both, D(2)O and t-butanol, it is assumed that due to the expansion of the crystalline domains by hydrothermal treatment several elementary fibrils are arranged at distances below 0.3 nm.

Near-infrared spectroscopic analysis of aging degradation in antique washi paper using a deuterium exchange method

The diffusion process of deuterated water (D 2O) in washi (Japanese traditional paper) was investigated by means of a deuterium exchange method and Fourier-transform near-infrared (FT-NIR) transmission spectroscopy. The samples were the modern (AD 2003) hand-made washi and those from an archival collection of cultural artifacts (AD 1791 and 1615). Four absorption bands were identified in the NIR spectral range from 7200 to 6000 cm −1 which are due to OH groups in the amorphous, semi-crystalline and two types of crystalline regions of cellulose. The accessibility of D 2O increased with decreasing state of order of cellulose, and the saturation accessibility increased with the age of the samples. It was suggested that during aging hemicellulose, which forms a composite with cellulose in paper, was progressively hydrolyzed, resulting in the expansion of inter-molecular distance between cellulose chains. The oldest sample showed a low diffusion rate compared with the others. SEM observation of the textile structures indicated that the oldest sample had two layers due to beating. It was estimated that the tight surface layer blocked the diffusant in the initial stage of the diffusion process.

Functionalization of SBA-15 by an acid-catalyzed approach: A surface characterization study

The functionalization of a mesoporous ordered silica, SBA-15, by a grafting strategy has been successfully achieved. The derivatized SBA-15 products with trimethylmethoxy silane, vinyltrimethoxy silane and octyltrimethoxy silane have been characterized by BET analysis, DRX analysis, thermogravimetric analysis and NMR techniques. The use of p-toluenesulfonic acid as catalyst and the azeotropic distillation of the alcohol generated in the hydrolysis and condensation of the silanes allowed the incorporation of high amounts of organic loading in shorter times as compared to conventional toluene reflux method. The surface of the resulting materials has been thoroughly analyzed and the concentration of total and residual silanols and silane molecules attached on the surface has been quantitatively determined. Being the as-modified SBA-15 materials hydrophobic as a rule, the accessibility of the residual silanol population, evaluated by a deuterium exchange method and subsequent cross-polarization NMR analysis, depends on the nature of the surface organic layer.

Near-infrared spectroscopic observation of the ageing process in archaeological wood using a deuterium exchange method

The ageing degradation of the fine wood structure of dry-exposed archaeological wood was investigated by Fourier transform near-infrared spectroscopy with the aid of a deuterium exchange method. The archaeological wood sample was taken from an old wooden temple in Japan (late 7th century), which has been designated as a UNESCO world heritage site. Comparing the analytical results with those of a modern wood sample of the same species, the ageing process of archaeological wood was clarified as a change in the state of order on a macromolecular structural level. It can be concluded from NIR spectra that the amorphous region, and partially semi-crystalline region, in cellulose, hemicellulose, and lignin decreased by the ageing degradation, whereas the crystalline region in cellulose was not affected by the ageing. The accessibility of the diffusant to effect H/D-exchange was monitored by an OH-related absorption band obtained from FT-NIR transmission spectroscopy and characteristically varied with the ageing process of the wood samples, the absorption bands characteristic of a specific state of order and the diffusion agent. Finally, we proposed a morphological model to describe the variation of the fine structure of the microfibrils in the cell wall with ageing degradation. The state of microfibrils changed loosely by ageing, so that elementary fibrils were arranged loosely under 5 A, whereas several elementary fibrils in the modern wood were arranged in very close proximity under 3 A to each other.

Quantitative determination of surface silanol groups in silicagel by deuterium exchange combined with infrared spectroscopy and chemometrics

Concentration of silanol groups on silica gel surface has been quantitatively determined using the deuterium exchange method. Simple and effective procedures have been used in pre-sample drying, deuterium exchange and extraction of resulting isotopic mixture from the exchange reaction. Each of four silica gel samples with varying surface area has been subjected to pre-drying to remove adsorbed water and then quantitatively mixed with deuterium oxide in a steel bomb for isotopic exchange. The resulting D(2)O/water mixture was then extracted by applying high pressure using infrared pellet press. The infrared spectrum of the isotopic mixture was measured and the composition was then determined by a multivariate calibration model established between infrared profiles of water in D(2)O standard mixtures and their composition. The results show that the silanol group concentration determined agrees with the values reported in the literature.

Usefulness of the hydrogen–deuterium exchange method in the study of drug metabolism using liquid chromatography-tandem mass spectrometry

The usefulness of the hydrogen–deuterium (H-D) exchange method in the study of drug metabolism was investigated. Metabolite samples of denopamine and promethazine prepared in vitro were introduced to a triple stage quadrupole tandem mass spectrometer via a high performance liquid chromatography (HPLC) system using a deuterated mobile phase. Mass spectra by various ionization modes and collisionally induced dissociation (CID) mass spectra were obtained. A metabolite of denopamine was observed to have a shift of 7 mass units by the H-D exchange method, and this shift proved to be a glucuronidated metabolite. Discrimination between N- or S-oxide formation and hydroxylation observed in the metabolism of promethazine was also easily accomplished by this method. In this manner, the structures of the metabolites were elucidated unequivocally by determining the number of labile hydrogen atoms by the use of the H-D exchange method, since various reactions in drug metabolism are accompanied by an increase or a decrease in the number of labile hydrogen atoms. Additional information on the structures was obtained by analysis of the CID spectra of the molecular ion species. Thus, the combination of the H-D exchange method and tandem mass spectrometry was found to be very useful for the study of drug metabolism.

Cluster chemical ionization and deuterium exchange mass spectrometry in supersonic molecular Beams

A cluster-based chemical ionization method has been developed that produces protonated molecular ions from molecules introduced through a supersonic molecular beam interface. Mixed clusters of the analyte and a clustering agent (water or methanol) are produced in the expansion region of the beam, and are subsequently ionized by "fly through" electron impact (EI) ionization, which results in a mass spectrum that is a combination of protonated molecular ion peaks together with the conventional EI fragmentation pattern. The technique is presented and discussed as a tool complementary to electron impact ionization in supersonic molecular beams. Surface-induced dissociation on a rhenium oxide surface is also applied to simplify the mass spectra of clusters and reveal the analyte spectrum. The high gas flow rates involved with the supersonic molecular beam interface that enable the easy introduction of the clustering agents also have been used to introduce deuterating agents. An easy-to-use, fast, and routine on-line deuterium exchange method was developed to exchange active hydrogens (NH, OH). This method, combined with electron impact ionization, is demonstrated and discussed in terms of the unique information available through the EI fragmentation patterns, its ability to help in isomer identification, and possible applications with fast gas chromatography-mass spectrometry in supersonic molecular beams.

Hydrogen-Bond Detection in Peptides by 1H-Nuclear Magnetic Resonance through a Hydrogen–Chlorine Exchange Reaction

Abstract NMR spectroscopy is a versatile method for the conformational analysis of peptides and proteins. The hydrogen–chlorine exchange of amide NH protons is detected by 1H NMR and used as a method to distinguish between intramolecularly hydrogen-bonded and solvent-exposed NH moieties. The method has been applied to hydrogen bond detection in naturally occurring antibiotic peptides, such as gramicidin S, and CH3CONH–X (X = alkyl- or aryl-) derivatives. The deuterium exchange method was compared with this method in parallel experiments. In the case of chlorine exchange, in contrast to deuterium exchange, the hydrogen-bonded amide protons are replaced much faster than their solvent-exposed counterparts and the duration of the experiments is considerably less. It is highly possible that the hydrogen–chlorine exchange reaction under the present experimental conditions, in the dark and at room temperature, proceeds through an electrophilic polar mechanism.

Proton nuclear magnetic resonance study of human interleukin 6: Chemical modifications and partial spectral assignments for the aromatic residues

Partial assignments for the 1H-NMR resonances of the aromatic residues in human interleukin 6 (IL-6) are reported. The homonuclear Hartmann-Hahn spectrum clearly shows all connectivities for the histidine, tyrosine and tryptophan residues that exist in IL-6. Using a deuterium exchange method, the imidazole proton resonances of His-16 and His-165 have been assigned. Iodination of the tyrosine residues led to the assignment of Tyr-32. Photo-chemically induced dynamic nuclear polarization data have shown that His-16, Tyr-32 and Trp-158 are exposed to solvent, whereas His-165, Tyr-98 and Tyr-101 are buried. Iodination of Tyr-32 gave no significant effect on IL-6 activity, suggesting that Tyr-32 is not responsible for IL-6 activity.

Confirmation and application of transmission near infrared absorption technique for absolute quantitation of functional groups on silica gel

A transmission near infrared (NIR) technique has been demonstrated to be useful for the qualitative and quantitative measurements of silica surface functionalities. Confirmation of this method's quantitative capabilities has been performed using a newly developed deuterium-exchange method and the more established methods of tritium radiosotopic exchange and carbon analysis. This NIR technique has been utilized for the evaluation of surface modification reactions for reducing the silanol content of modified silicas. This effort led to the development of “direct butylation” as a promising method for deactivation of porous silica surfaces. Complementary surface characterization information was obtained using solid state NMR, BET adsorption, mercury intrusion porosimetry and gas chromatography.

Diffusion of water into phenylon C4

The diffusion of water into the aromatic polyamide, Phenylon C4, has been studied. It was shown that the sorption isotherm of the water is described by a Langmuir equation. The water concentration necessary to fill the surface with a monomolecular layer corresponds to the amide group concentration in the accessible volume (accessibility was determined by a hydrogen→deuterium exchange method). The sorption-diffusion characteristics of the Phenylon are compared with similar data for aliphatic PAs.

Quantitative evaluation for the role of beta 146 His and beta 143 His residues in the Bohr effect of human hemoglobin in the presence of 0.1 M chloride ion.

Two different methods were used to determine the number of Bohr protons released upon oxygenation of human hemoglobin (Hb A) and Hb A lacking beta 146 His (des-His Hb A) at the pH ranging from pH 5.0 to 9.0 in the presence of 0.1 M Cl- at 25 degrees C. One is the direct differential titration method, the other is based on the measurement of oxygen affinity as a function of pH. The results obtained for Hb A or des-His Hb A with two methods were completely mutually consistent. The number of Bohr protons released from des-His Hb A upon oxygenation at pH 7.5 was about 44% less than that from Hb A, while at pH 5.5 the number of Bohr protons taken up by des-His Hb A was 20% greater than that by Hb A. The differences in the number of Bohr protons between Hb A and des-His Hb A could not be simply ascribed to the lack of beta 146 His from Hb A. The pK alpha values, which were determined by the deuterium exchange method using 1H NMR, were 8.0 for beta 146 His of deoxy-Hb A and 6.5 for that of CO Hb A, while those of beta 143 His were 5.2 for deoxy-Hb A and 6.0 for CO Hb A. From these pK alpha values, in addition to those of alpha 1 Val proposed for the modified CO and deoxy-Hb A with carbamylated beta chains by Van Beek and De Bruin (Van Beek, G. M., and De Bruin, S. H. (1980) Eur. J. Biochem. 105, 353-360), it became evident that almost all (about 92%) of the alkaline Bohr protons released upon oxygenation of Hb A in the presence of 0.1 M Cl- could be accounted for by the protons from these 2 residues, although the involvement of other histidine residues could not be denied. About half the acid Bohr protons from Hb A, which corresponds to the higher pH part (above pH 5.0) of the acid Bohr effect, could be explained by the involvement of beta 143 His residue. The residual acid Bohr effect in the more acidic pH region was presumably contributed by an amino acid residue with pK alpha values of 4.05 and 5.95 for the deoxy- and CO Hb A, respectively, although the amino acid residue was unspecified.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination of water adsorption sites in wood by a hydrogen–deuterium exchange

IT is important in the field of forest products science to know the sorption mechanism of water in wood. Adsorption of water onto hygroscopic natural polymers, such as wood and cellulose, is thought to depend entirely on the hydroxyl groups on the surface1. The mechanism of water adsorption in wood can therefore be studied by evaluating the quantity and the state of the adsorption sites, hydroxyl groups. Until now, in order to measure the number of adsorption sites of water in wood, it has been usual to draw a sorption isotherm from which the adsorbed area can be calculated assuming monomolecular layer adsorption according to the BET theory2. Little is known of the sorption mechanism on the molecular level, however. We report here the use of a hydrogen–deuterium exchange method to determine the adsorption sites of water in wood. Hydrogen–deuterium exchange is a well established method which has been widely used to determine hydroxyl group accessibility3,8,9.