Position Of Deuterium Atoms Research Articles

Kinetically Protected Carbon-Bridged Oligo(p-phenylenevinylene) Derivatives for Blue Color Amplified Spontaneous Emission

Abstract Carbon-bridged oligo(p-phenylenevinylene)s (COPVn with repeating unit n = 1–6) have demonstrated great success as laser dyes for thin-film organic lasers. The excellent photostability observed in the longer homologues is, however, not present in the blue-emitting shorter compounds COPV1 and COPV2, attributed to the unprotected terminal positions that can degrade by photoreaction in the excited state. Here we report the synthesis of various COPV1 and COPV2 derivatives functionalized at the terminal positions with two types of sterically bulky protecting substituents: Tip (2,4,6-triisopropylphenyl) and tert-butyl (t-Bu) groups. Such molecular designs aim at preventing such photodegradation processes and thus to improve their stability. The efficacy of kinetic isotope effect for stabilization is also examined for COPV2, by the addition at terminal positions of deuterium atoms. Absorption, photoluminescence (PL), including PL quantum yield, and amplified spontaneous emission (ASE) studies have been conducted in polystyrene films doped with each of the derivatives. Significant and slight improvements of the ASE photostability are observed for the compounds with Tip groups and deuterium, respectively. Installation of substituents slightly affects the ASE wavelength within the blue spectral region, that is 385–413 nm and 462–474 nm, for COPV1 and COPV2, respectively.

Neutron and X-ray Crystal Structures of a Perdeuterated Enzyme Inhibitor Complex Reveal the Catalytic Proton Network of the Toho-1 β-Lactamase for the Acylation Reaction

The mechanism by which class A β-lactamases hydrolyze β-lactam antibiotics has been the subject of intensive investigation using many different experimental techniques. Here, we report on the novel use of both neutron and high resolution x-ray diffraction to help elucidate the identity of the catalytic base in the acylation part of the catalytic cycle, wherein the β-lactam ring is opened and an acyl-enzyme intermediate forms. To generate protein crystals optimized for neutron diffraction, we produced a perdeuterated form of the Toho-1 β-lactamase R274N/R276N mutant. Protein perdeuteration, which involves replacing all of the hydrogen atoms in a protein with deuterium, gives a much stronger signal in neutron diffraction and enables the positions of individual deuterium atoms to be located. We also synthesized a perdeuterated acylation transition state analog, benzothiophene-2-boronic acid, which was also isotopically enriched with (11)B, as (10)B is a known neutron absorber. Using the neutron diffraction data from the perdeuterated enzyme-inhibitor complex, we were able to determine the positions of deuterium atoms in the active site directly rather than by inference. The neutron diffraction results, along with supporting bond-length analysis from high resolution x-ray diffraction, strongly suggest that Glu-166 acts as the general base during the acylation reaction.

Direct Determination of the Hydrogen Bonding Arrangement in Anhydrous β-Chitin by Neutron Fiber Diffraction

The hydrogen bonding arrangement in anhydrous β-chitin, a homopolymer of N-acetylglucosamine, was directly determined by neutron fiber diffraction. Data were collected from a sample prepared from the bathophilous tubeworm Lamellibrachia satsuma in which all labile hydrogen atoms had been replaced by deuterium. Initial positions of deuterium atoms on hydroxyl and acetamide groups were directly located in Fourier maps synthesized using phases calculated from the X-ray structure and amplitudes measured from the neutron data. The hydrogen bond arrangement in the refined structure is in general agreement with predictions based on the X-ray structure: O3 donates a hydrogen bond to the O5 ring oxygen atom of a neighboring residue in the same chain; N2 and O6 donate hydrogen bonds to the same carbonyl oxygen O7 of an adjacent chain. The intramolecular O3···O5 hydrogen bond has the most energetically favorable geometry with a hydrogen to acceptor distance of 1.77 Å and a hydrogen bond angle of 171°.

Neutron diffraction study of aluminous hydroxide δ-AlOOD

We have determined the position of deuterium atoms in δ-AlOOD by neutron powder diffraction at ambient pressure. As previously reported by theoretical and experimental studies, the deuterium atoms are located in the tunnel formed by the chains of AlO6 octahedra. The data are best fit with the P21 nm structure, producing bond lengths of D–O1 of 1.552(2) A, O2–D of 1.020(2) A and O1–O2 of 2.571(2). This study confirms that the hydrogen bond is asymmetric at ambient conditions in agreement with recent single-crystal synchrotron study for δ-AlOOH.

Crystal structures of high-pressure phases in the alumina-water system: II. Powder X-ray diffraction study of a new dense aluminum deuteroxide, δ-Al(OD)3

In this study we report the solution of the structure of δ-Al(OD)3. The crystal structure was determined using powder X-ray diffraction and direct methods, while the positions of deuterium atoms were estimated by difference-Fourier methods and MEM/Rietveld analysis. In the A-site deficient hydroxy-perovskite-type structure of δ-Al(OD)3, we find two types of one-dimensional H-bonding network.

On the variation of the structure of liquid deuterium fluoride with temperature.

The structure of liquid deuterium fluoride has been measured using pulsed neutron diffraction and high energy x-ray diffraction techniques as a function of temperature. The neutron experiments were performed at T=296+/-2 K, 246+/-2 K, and 193+/-2 K and the x-ray measurements carried out at 296+/-2 K and 195+/-2 K. The x-ray pair correlation functions, which are dominated by fluorine-fluorine interactions, show the first peak at approximately 2.53+/-0.05 A remains very nearly invariant with decreasing temperature. Peaks around 4.5 and 5.0 A also appear at both temperatures in the x-ray data. In contrast, the intermolecular peaks in the total neutron pair correlation function show that significant systematic local structural changes occur as the temperature is lowered. The first intermolecular peak position shortens from 1.64+/-0.05 A at 296 K to 1.56+/-0.05 A at 195 K. Although there are overlapping contributions from the intermolecular hydrogen-fluorine and hydrogen-hydrogen correlations, it is clear that the temperature dependent structural changes are largely due to a rearrangement of the deuterium atom positions in the fluid. By comparison with partial structure factor data the hydrogen bonds appear to become more linear at lower temperatures.

The Mechanism of NaBH4 Addition to Aldehydes: A Labeling Experiment

In order to determine the sources of hydrogens in NaBH4 reductions of aldehydes, a series of reductions were carried out using differentially deuterated reagents and solvents. Thus, benzaldehyde was subjected to four different reduction protocols: reaction with NaBH4 followed by HCl, reaction with NaBD4 followed by HCl, reaction with NaBH4 followed by DCl, and reaction with NaBD4 followed by DCl. Products were isolated and analyzed by GC-MS. The results showed four different compounds were produced differing in the number and/or position of deuterium atoms and indicated that hydrogens in the reduced product came from NaBH4 and the acid work up.

The crystal structure of Sr(OD) 2

The crystal structure of Sr(OD) 2 has been determined from a Reitveld refinement of time-of-flight neutron diffraction data, and the deuterium atom positions have been determined for the first time. The structure is orthorhombic: Pnma, a = 9.8269(5) Å, b = 3.9051(2) Å, c = 6.0733(3) Å, V = 233.06 Å 3, D x = 3.466 g cm −3, R wp = 3.93%, R p = 2.95%, reduced X 2 = 4.774 for 81 variables. Although the data were collected at 12 K, the H atoms have large thermal parameters suggesting the possibility of some disorder. Relationships of the structure to the structures of YOOH, SrBr 2, SrI 2, and SrBr 2 · H 2O are discussed.

A Comparison of Neutron Diffraction and Molecular Dynamics Structures: Hydroxyl Group and Water Molecule Orientations in Trypsin

A comparison is presented of experimentally observed hydroxyl and water hydrogen atoms in trypsin determined from neutron density maps with the results of a 140 ps molecular dynamics simulation. Experimental determination of hydrogen and deuterium atom positions in molecules as large as proteins is a unique capability of neutron diffraction. The comparison addresses the degree to which a standard force-field approach can adequately describe the local electrostatic and van der Waals forces that determine the orientations of these hydrogen atoms. The molecular dynamics simulation, based on the all-atom AMBER force-field, allowed free rotation of all hydroxyl groups and movement of water molecules making up a bath surrounding the protein.The neutron densities, derived from 2.1 Å 2H 2O-H 2O difference Fourier maps, provide a database of 27 well-ordered hydroxyl hydrogen atoms. Virtually all of the simulated hydroxyl orientations are within a standard deviation of the experimentally observed positions, including several examples in which both the simulation and the neutron density indicate that a hydroxyl group is shifted from a “standard” rotamer. For the most highly ordered water molecules, the hydrogen distributions calculated from the trajectory were in good agreement with neutron density; simulated water molecules that display multiple hydrogen-bonding networks had correspondingly broadened neutron density profiles. This comparison was facilitated by development of a method to construct a pseudo 2 Å density map based on the hydrogen atom distributions from the simulation. This method is particularly useful for statically disordered water molecules, in which the average location assigned from a trajectory may represent a site of relatively low occupancy. The degree of disorder of internal water molecules is shown to result primarily from the electrostatic environment surrounding that water molecules as opposed to the cavity size available to the molecule.

Determination of isotopic purity and position in deuterated methyl behenate

AbstractIn the course of preparing peanut oil type triglycerides for metabolism studies, methyl esters of deuterated behenic acid, a saturated 22‐carbon fatty acid, with zero, two, and six deuterium atoms were synthesized. The specific positions of deuterium atoms and the completion of deuteration in the products were characterized by gas chromatography/mass spectrometry methods.

Neutron powder diffraction study of 239PuD x

A neutron powder diffraction study has been carried out on several deuterids of Plutonium (PuD 2.25,PuD 2.33, PuD 2.65) to determine the positions of deuterium atoms in the host metal f.c.c. lattice. It has been found that vacancies occur in the tetrahedral sites. Moreover, with increasing deuterium concentration, octahedral interstitial deuterium atoms are displaced from their ideal positions. These results can be explained by the formation of clusters. Finally, at low temperature, these compounds become ferromagnetically ordered. An ordered magnetic moment μ 0≈0.8 μ B has been measured on all compounds.

The deuterium-atom positions in deuterated molybdic acid, MoO3.2D2O, by powder neutron diffraction

The deuterium-atom positions in deuterated molybdic acid, MoO3.2D2O, by powder neutron diffraction

Synthese d'Analogues Deuteries des (5α) Androstanediol ‐ 3ξ, 17β

AbstractSix deuterated androstanediols were synthetised. The position of deuterium atoms on the molecule were checked by mass spectrometry and 1H or 13c nuclear magnetic resonance. The per cent of d0, d1,… dn‐molecules were calculated.The use of such labelled molecules in the fields of isotopic dilution‐mass fragmentography as carriers and/or internal standards is discussed.

Use of the neutron time-of-flight technique for structure investigations

The application of a time-of-flight neutron diffractometer for crystallographic investigations, designed on the basis of a pulsed neutron source, is discussed. The procedure for obtaining integrated intensities and introducing corrections is described. The results of a test experiment with perdeuteronaphthalene are given. The deuterium atom positions in the structure of La2Mg3(NO3)12.24D2O are also refined and compared with those obtained using X-ray diffraction techniques. The observed systematic differences in bond lengths and valence angles are explained by the differences between the 'X-ray' and 'neutron' coordinates of the light atoms.

Determination of Interstitial Deuterium Locations in Niobium by Channeling

AbstractChanneling provides a new technique for determining the lattice positions of deuterium atoms in single crystals at low concentrations. In the present investigation the D(d,p)T reaction yield was measured around the 〈100〉 and the 〈111〉 incidence directions of a 300 keV deuteron beam penetrating through niobium loaded with 2 atomic percent deuterium. In combination with flux and energy distribution calculations of the channeled deuterons the conclusion was reached that at 150 K the dissolved deuterium atoms are located at tetrahedral lattice sites. Measurements at room temperature indicate that deuterium at 295 K occupies the same sites.

Recherches dans la série des cyclitols XXXVII Etude par spectrométrie de masse

AbstractLow resolution mass spectra of cyclohexane‐triols, ‐tetrols, ‐pentols and ‐hexols and of some of their deuterium labelled derivatives have been measured. The results indicate that for some geometrical isomers quantitative differences between ion intensities are significant, allowing to deduce the stereochemistry of the molecule from its mass spectrum. In all these compounds the electron impact induced elimination of water occurs mainly by interaction between OH groups. There is a correlation between the relative abundance of (M – H2O)+ and (M −2 H2O)+ ions and the number of axial hydroxyls in the more stable conformation of the molecule. Difficulties encountered in deducing fragmentation patterns, and determination of number and position of deuterium atoms in the molecule of ms‐inositol are discussed.