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In this study, we investigated reversible intermolecular proton shifting (IPS) coupled with spin transition (ST) in a novel FeII complex. The host FeII complex and the guest carboxylic acid anion were connected by intermolecular hydrogen bonds (IHBs). We extended the intramolecular proton transfer coupled ST phenomenon to the intermolecular system. The dynamic phenomenon was confirmed by variable‐temperature single‐crystal X‐ray diffraction, neutron crystallography, and infrared spectroscopy. The mechanism of IPS was further validated using density functional theory calculations. The discovery of IPS‐coupled ST in crystalline molecular materials provides good insights into fundamental processes and promotes the design of novel multifunctional materials with tunable properties for various applications, such as optoelectronics, information storage, and molecular devices. [ABSTRACT FROM AUTHOR]

The structure of a recently found hyperhydrated form of sodium chloride (NaCl·13H2O and NaCl·13D2O) has been determined by insitu single‐crystal neutron diffraction at 1.7 GPa and 298 K. It has large hydrogen‐bond networks and some water molecules have distorted bonding features such as bifurcated hydrogen bonds and five‐coordinated water molecules. The hydrogen‐bond network has similarities to ice VI in terms of network topology and disordered hydrogen bonds. Assuming the equivalence of network components connected by pseudo‐symmetries, the overall network structure of this hydrate can be expressed by breaking it down into smaller structural units which correspond to the ice VI network structure. This hydrogen‐bond network contains orientational disorder of water molecules in contrast to the known salt hydrates. An example is presented here for further insights into a hydrogen‐bond network containing ionic species. [ABSTRACT FROM AUTHOR]

In structural biology, peptide bonds, fundamental linkages between hundreds of amino acids, of which a protein molecule is composed, have been commonly treated as a plane structure just as Linus Pauling et al. proposed. In this paper, a site‐specific peptide bond relaxation mechanism by deuterons whose localization has been suggested by neutron crystallography is proposed. Such deuteron was observed as an arm of neutron scattering length density protruding from the carbonyl oxygen atoms in the main chain in the omit map drawn by neutron crystallography of human lysozyme. Our comprehensive study using x‐ray and neutron diffraction and 15N chemical shifts of individual amide nitrogen atoms within the same peptide bond strongly suggests the relaxation of the electronic resonance structure because of site‐specific modulation by protons/deuterons localized on the electron orbital of the carbonyl oxygen. All experimental data used in this examination were obtained at room temperature, which is preferable for enzymatic activity. Such a close interaction between the electron resonance structure of a peptide bond and the exchangeable protons/deuterons well agreed with that observed in an intermediate state in an amide hydrolytic reaction simulated by the ab‐initio calculation including water molecules. [ABSTRACT FROM AUTHOR]

The application of single-crystal neutron diffraction (SCND) to observe proton-transfer phenomena in crystalline compounds exhibiting unusual protonation states or proton dynamics has garnered significant research interest in recent years. However, proton tautomerism, which results in different protonation states before and after proton transfer, has never been observed using the SCND technique. Thus, to observe the proton tautomerism phenomenon by SCND measurements, we developed an iron(II) complex that forms a large crystal and exhibits a proton-transfer-coupled spin transition (PCST). The presence of the two types of proton tautomers was determined by conventional analysis of the proton position by X-ray crystallography, infrared spectroscopy, and density functional theory calculations. Finally, our results confirmed that proton tautomerism was successfully observed for the first time using variable-temperature SCND measurements. [ABSTRACT FROM AUTHOR]

The ongoing global outbreak of coronavirus disease has necessitated the use of ultraviolet (UV) disinfection techniques to reduce viral transmission in public places. The previously used UV wavelength is harmful to the human body, the wavelength range from 200 to 235 nm, often referred to as far‐UVC light, has attracted attention as a novel disinfection wavelength range that can be used in a safe manner. However, the currently used light sources have practical problems, such as an expensive cost, a low efficiency, and short lifetimes. Therefore, environmentally friendly solid‐state light sources with a lower cost, higher efficiency, and longer lifetimes are demanded. Here, an efficient mercury‐free far‐UVC solid‐state light source is presented. This light source demonstrates intense 230 nm emission with a narrow spectral width of 30 nm and a long lifetime of more than 1000 h. These characteristics can be achieved by graphene nanostructure field emitters and wide‐bandgap magnesium aluminate phosphors. By using this light source, the efficient disinfection of Escherichia coli is demonstrated. The light sources presented here facilitate future technologies for preventing the spread of infectious diseases in a safe and convenient manner. [ABSTRACT FROM AUTHOR]

The development in the crystal structure analysis of synthetic polymers using the hybridized combination of wide-angle X-ray and neutron diffraction (WAXD and WAND, respectively) techniques has been reviewed with many case studies performed by the authors. At first, the technical development was reviewed, in which the usage of high-energy synchrotron X-ray source was emphasized for increasing the total number of the observable diffraction peaks, and several examples were introduced. Secondly, the usage of the WAND method was introduced, in which the successful extraction of hydrogen atomic positions was described. The third example is to show the importance for the hybrid combination of these two diffraction methods. The quantitative WAXD data analysis gave the crystal structures of at-poly(vinyl alcohol) (at-PVA) and at-PVA-iodine complex. However, the thus-proposed structure models were found not to reproduce the observed WAND data very much. The reason came from the remarkable difference in the atomic scattering powers of the constituting atomic species between WAXD and WAND phenomena. The introduction of statistical disorder solved this serious problem, which reproduced both of the observed WAXD and WAND data consistently. The more systematic combination of WAXD and WAND methods, or the so-called X-N method, was applied also to the quantitative evaluation of the bonded electron density distribution along the skeletal chains, where the results about polydiacetylene single crystals were presented as the first successful study. Finally, the application of WAND technique in the trace of structural changes induced under the application of external stress or temperature was described. The future perspective is described for the development of structural science of synthetic polymers on the basis of the combined WAXD/WAND techniques. [ABSTRACT FROM AUTHOR]

Structural changes of the raffinose crystal on dehydration from the pentahydrate to the tetrahydrate were investigated by single‐crystal time‐of‐flight neutron diffraction. It was revealed that during the dehydration, rearrangement occurs in the hydrogen bonds related to the lost water molecule, while the symmetry of the crystal structure is retained. The hydrogen‐bonding status of raffinose pentahydrate and tetrahydrate were discussed comprehensively according to Jeffrey's hydrogen‐bonding classification. It was shown that the water molecules are hydrogen bonded to the surrounding molecules by moderate O—H...O hydrogen bonds and weak C—H...O hydrogen bonds, and the number of these two types of hydrogen bonds determines the water molecules that are removed by dehydration. The lattice constant c showed a significant decrease on dehydration and further dehydration leads to loss of crystallinity of the raffinose crystals. [ABSTRACT FROM AUTHOR]

Single-crystal neutron diffraction provides direct information about crystal structures such as hydrogen positions and magnetic structures. However, in-situ experiments conducted under high pressure entail technical difficulties such as attenuation correction, masking of parasitic diffraction, and limitations of sample volumes and accessible directions. For this study, we improved diamond anvil cells with a tubular frame made of Zr-based bulk metallic glass and nano-polycrystalline diamond anvils for single-crystal neutron diffraction. The thicker tubular frame was confirmed through experimentation as stably generating 4.5 GPa. Its feasibility for neutron diffraction was assessed at the Laue-TOF diffractometer at the BL18 (SENJU) beamline in the MLF J-PARC using time-resolved two-dimensional detectors covering wide solid angles. In addition to ambient-pressure measurements of NH4Cl, diffraction patterns of a high-pressure phase of ice were also collected in-situ. The obtained intensities are of refinable quality sufficient for structure analysis. [ABSTRACT FROM AUTHOR]

The chiral 1,2-bis(ethoxycarbonyl)ethyl group was partly inverted to the opposite configuration when the crystal of [(R)-1,2-bis(ethoxycarbonyl)ethyl](pyridine)bis(dimethylglyoximato)cobalt-(III) was exposed to xenon lamp, and finally the racemic group was produced with retention of the single crystal form. The above rotation is a good example of hula-twist rotation in the process of photoisomerization of polyenes such as rhodopsin.

X‐ray diffraction, neutron diffraction, and theoretical calculations were used to investigate the relationship between the optical properties and degree of protonation in acid‐base complexes. We prepared five acid‐base complexes by using a pyridine‐modified pyrrolopyrrole derivative and salicylic acid. Two of the prepared acid‐base complexes were polymorphs of guest‐free crystals with green emission; the other three were guest‐inclusion crystals with yellow emission containing CH2Cl2, CH2Br2, or C2H4Cl2. The presence or absence of guests caused the emission to change color, altering the hydrogen bond strength between the acid‐base complexes. Accurate N⋅⋅⋅H distances between the pyridyl moiety and the carboxy group over the temperature range 123 to 273 K were 1.40 Å for the guest‐free crystals and 1.25 Å for the guest‐inclusion crystals. Our findings contribute to a better understanding of the complex relationship between photofunction and proton dynamics in acid‐base complexes. [ABSTRACT FROM AUTHOR]

Multiple transition phenomena in divalent Eu compound EuAl4 with the tetragonal structure were investigated via the single-crystal time-of-flight neutron Laue technique. At 30.0 K below a charge-density-wave (CDW) transition temperature of TCDW = 140 K, superlattice peaks emerge near nuclear Bragg peaks described by an ordering vector \(\boldsymbol{q}_{\text{CDW}} = (0,0,\delta _{c})\) with δc ∼ 0.19. In contrast, magnetic peaks appear at \(\boldsymbol{q}_{2} = (\delta _{2},\delta _{2},0)\) with δ2 = 0.085 in a magnetic-ordered phase at 13.5 K below TN1 = 15.4 K. By further cooling to below TN3 = 12.2 K, the magnetic ordering vector changes into \(\boldsymbol{q}_{1} = (\delta _{1},0,0)\) with δ1 = 0.17 at 11.5 K and slightly shifts to δ1 = 0.194 at 4.3 K. No distinct change in the magnetic Bragg peak was detected at TN2 = 13.2 K and TN4 = 10.0 K. The structural modulation below TCDW with qCDW is characterized by the absence of the superlattice peak in the (0 0 l) axis. As a similar CDW transition was observed in SrAl4, the structural modulation with qCDW could be mainly ascribed to the displacement of Al ions within the tetragonal ab-plane. Complex magnetic transitions are in stark contrast to a simple collinear magnetic structure in isovalent EuGa4. This could stem from different electronic structures with the CDW transition between two compounds. [ABSTRACT FROM AUTHOR]

An all-solid-state Li-ion secondary battery is a promising device that provides a solution to existing energy problems. However, it remains far from practical application mainly because of the lack of our basic understanding of the conduction mechanism of Li ions in Li-rich superionic conductors used as solid electrolytes in place of liquid electrolytes for conventional batteries. Herein, we studied the crystalline compound Li10GeP2S12 with the largest Li-ion conductivity thus far via a novel route based on a combination of single-crystal neutron diffraction experiments at low temperature and first-principles calculations, and found that a correlated migration of the densely packed Li ions governs the overall Li-ion conduction. The correlated migration mechanism provides us with guidelines on how to design efficient superionic conductors for more efficient batteries. [ABSTRACT FROM AUTHOR]

A spin‐contrast‐variation neutron powder diffractometry technique that extracts the structure factor of hydrogen atoms, i.e. the contribution of hydrogen atoms to a crystal's structure factor, has been developed. Crystals of l‐glutamic acid were dispersed in a d‐polystyrene matrix containing 4‐methacryloyloxy‐2,2,6,6,‐tetramethyl‐1‐piperidinyloxy to polarize their proton spins dynamically. The intensities of the diffraction peaks of the sample changed according to the proton polarization, and the structure factor of the hydrogen atoms was extracted from the proton‐polarization‐dependent intensities. This technique is expected to enable analyses of the structures of hydrogen‐containing materials that are difficult to determine with conventional powder diffractometry. [ABSTRACT FROM AUTHOR]

The crystal structure of an X-type hexaferrite Sr2Co2Fe28O46 was investigated by the x-ray and neutron diffraction methods for a single crystal. Sr2Co2Fe28O46 has the crystal structure described as a space group R \(\bar{\text{3}}\) m (Z = 3) and its lattice constants are a = 5.9165(2) Å and c = 84.1395(33) Å at 843 K. Co ions are almost localized in the octahedral site (9d) in the middle of S*S* blocks. In addition, the adjacent octahedral and tetrahedral sites to 9d site contain the significant number of Co2+. [ABSTRACT FROM AUTHOR]

Magnetism in EuNiIn4 is studied using specific heat, magnetic susceptibility, magnetization, 151Eu Mössbauer spectroscopy, and neutron diffraction experiments. The specific heat exhibited two magnetic transitions at TN1 = 15.2 K and TN2 = 14.3 K at zero magnetic field. An antiferromagnetic ground state of EuNiIn4 was observed to have a uniaxial magnetic anisotropy along the b axis using magnetic susceptibility and 151Eu Mössbauer spectroscopy. Further, single crystal neutron diffraction experiments illustrated that this antiferromagnetic structure in the ground state is characterized by the commensurate propagation vector \(\boldsymbol{{q}} = (1/2,1/2,1/2)\) , which reveals no distinct anomaly at TN2. The magnetization curve along the b axis at 2 K was observed to exhibit four successive magnetic field-induced transitions up to 50 kOe, following which it increased linearly, resulting in saturated magnetization of 7 μB/f.u. above 195.2 kOe, as expected of Eu2+ free ions. The magnetic phase diagram for H ∥ b in EuNiIn4 was found to have unique characteristics with five magnetic states in low magnetic fields. [ABSTRACT FROM AUTHOR]

Combination of high-resolution neutron and X-ray crystallography were used to analyze the serine proteases, the structure of porcine pancreatic elastase to resolve the problems associated with catalytic activity. The data obtained provide insight into the interaction between His57 and Asp102 which result in short but conventional hydrogen bond also described as short ionic hydrogen bond.

An adamantanoid (H2O)(sub 10) cluster is formed, within the hydrophobic cavity of a self-assembled coordination cage, which is termed 'molecular ice' as this structure is the smallest unit of naturally occurring Ic-type ice. The x-ray structural analysis, coupled with neutron diffraction study, reveals that the molecular ice is not simply formed by filling the void space but is a result of specific H2O:...pi interaction within the cage.

The two-dimensional quadratic lattice magnet, bis(glycolato)cobalt(ii) ([Co(HOCH2CO2)2]), showed antiferromagnetic ordering at 15.0 K and an abrupt increase in magnetisation at H = 22 600 Oe and 2 K, thereby acting as a metamagnet. Heat capacity measurements revealed that the associated entropy change ΔS around the transition temperature was evaluated to be 6.20 J K−1 mol−1 and that the Co(ii) ion had the total angular momentum of J = 1/2 at low temperatures. Neutron diffraction studies suggested that the magnetic moment vectors of the Co(ii) ions had an amplitude of 3.59μB and were not aligned in a fully antiparallel fashion to those of their neighbours, which caused canting between the magnetic moment vectors in the sheet. The canting angle was determined to be 7.1°. Canting induced net magnetisation in the sheet, but this magnetisation was cancelled between sheets. The magnetisations in the sheets were oriented parallel to the magnetic field at the critical magnetic field. [ABSTRACT FROM AUTHOR]

The STARGazer data‐processing software is used for neutron time‐of‐flight (TOF) single‐crystal diffraction data collected using the IBARAKI Biological Crystal Diffractometer (iBIX) at the Japan Proton Accelerator Research Complex (J‐PARC). This software creates hkl intensity data from three‐dimensional (x, y, TOF) diffraction data. STARGazer is composed of a data‐processing component and a data‐visualization component. The former is used to calculate the hkl intensity data. The latter displays the three‐dimensional diffraction data with searched or predicted peak positions and is used to determine and confirm integration regions. STARGazer has been developed to make it easier to use and to obtain more accurate intensity data. For example, a profile‐fitting method for peak integration was developed and the data statistics were improved. STARGazer and its manual, containing installation and data‐processing components, have been prepared and provided to iBIX users. This article describes the status of the STARGazer data‐processing software and its data‐processing algorithms. In this article, the status of the STARGazer data‐processing software and its data‐processing algorithms are described in detail. The STARGazer data‐processing software is used for neutron time‐of‐flight single‐crystal diffraction data collected using the IBARAKI Biological Crystal Diffractometer. [ABSTRACT FROM AUTHOR]

Apatite-type rare-earth silicates are attractive materials with extensive applications such as in solid-oxide fuel cells due to their extremely high oxide-ion conductivity below 600 °C. The presence of interstitial (excess) oxygens has been believed to be responsible for the high conductivity of apatite-type materials. On the contrary, the present study clearly reveals the presence of Si vacancies □ instead of interstitial oxygens in La-rich La9.565(Si5.826□0.174)O26 using single-crystal neutron and X-ray diffraction analyses, density measurements and ab initio electronic calculations. Higher mobility (i.e., lower activation energy) of oxide ions along the c axis is a major reason for the high oxide-ion conductivity of La9.565(Si5.826□0.174)O26 when compared with that of La9.333Si6O26. Excess La cations yield overbonded channel oxygens, leading to their highly anisotropic atomic displacements and high oxygen mobility along the c axis. This novel finding of the overbonding effect without interstitial oxygens will open a new window for the design of better ion conductors. [ABSTRACT FROM AUTHOR]

SENJU is a new single-crystal time-of-flight neutron diffractometer installed at BL18 at the Materials and Life Science Experimental Facility of the Japan Accelerator Research Complex (J-PARC). The diffractometer was designed for precise crystal and magnetic structure analyses under multiple extreme sample environments such as low temperature, high pressure and high magnetic field, and for diffraction measurements of small single crystals down to 0.1 mm3 in volume. SENJU comprises three choppers, an elliptical shape straight supermirror guide, a vacuum sample chamber and 37 scintillator area detectors. The moderator-to-sample distance is 34.8 m, and the sample-to-detector distance is 800 mm. The wavelength of incident neutrons is 0.4-4.4 Å (first frame). Because short-wavelength neutrons are available and the large solid angle around the sample position is covered by the area detectors, a large reciprocal space can be simultaneously measured. Furthermore, the vacuum sample chamber and collimator have been designed to produce a very low background level. Thus, the measurement of a small single crystal is possible. As sample environment devices, a newly developed cryostat with a two-axis (ω and ϕ axes) goniometer and some extreme environment devices, e.g. a vertical-field magnet, high-temperature furnace and high-pressure cell, are available. The structure analysis of a sub-millimetre size (0.1 mm3) single organic crystal, taurine, and a magnetic structure analysis of the antiferromagnetic phase of MnF2 have been performed. These results demonstrate that SENJU can be a powerful tool to promote materials science research. [ABSTRACT FROM AUTHOR]

A newly synthesized one-dimensional (1D) hydrogen-bonded (H-bonded) rhodium(II)-η5-semiquinone complex, [Cp*Rh(η5- p-HSQ-Me4)]PF6 ([ 1]PF6; Cp*=1,2,3,4,5-pentamethylcyclopentadienyl; HSQ=semiquinone) exhibits a paraelectric-antiferroelectric second-order phase transition at 237.1 K. Neutron and X-ray crystal structure analyses reveal that the H-bonded proton is disordered over two sites in the room-temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF6− ion. The relative permittivity εb′ along the H-bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of 13C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low-temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10−4-10−6 s in the temperature range of 240-270 K. DFT calculations predict that the protonation/deprotonation of [ 1]+ leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π-bonded rhodium fragment, producing the stable η6-hydroquinone complex, [Cp*Rh3+(η6- p-H2Q-Me4)]2+ ([ 2]2+), and η4-benzoquinone complex, [Cp*Rh+(η4- p-BQ-Me4)] ([ 3]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [ 2]2+ and [ 3], which would be generated in the H-bonded chain. [ABSTRACT FROM AUTHOR]

Transthyretin (TTR) is a tetrameric protein. TTR misfolding and aggregation are associated with human amyloid diseases. Dissociation of the TTR tetramer is believed to be the rate-limiting step in the amyloid fibril formation cascade. Low pH is known to promote dissociation into monomer and the formation of amyloid fibrils. In order to reveal the molecular mechanisms underlying pH sensitivity and structural stabilities of TTR, neutron diffraction studies were conducted using the IBARAKI Biological Crystal Diffractometer with the time-of-flight method. Crystals for the neutron diffraction experiments were grown up to 2.5 mm3 for four months. The neutron crystal structure solved at 2.0 Å revealed the protonation states of His88 and the detailed hydrogen-bond network depending on the protonation states of His88. This hydrogen-bond network is involved in monomer-monomer and dimer-dimer interactions, suggesting that the double protonation of His88 by acidification breaks the hydrogen-bond network and causes the destabilization of the TTR tetramer. Structural comparison with the X-ray crystal structure at acidic pH identified the three amino acid residues responsible for the pH sensitivity of TTR. Our neutron model provides insights into the molecular stability related to amyloidosis. [ABSTRACT FROM AUTHOR]

The IBARAKI biological crystal diffractometer, iBIX, is a high-performance time-of-flight neutron single-crystal diffractometer for elucidating mainly the hydrogen, protonation and hydration structures of biological macromolecules in various life processes. Since the end of 2008, iBIX has been available to users' experiments supported by Ibaraki University. Since August 2012, an upgrade of the 14 existing detectors has begun and 16 new detectors have been installed for iBIX. The total measurement efficiency of the present diffractometer has been improved by one order of magnitude from the previous one with the increasing of accelerator power. In December 2012, commissioning of the new detectors was successful, and collection of the diffraction dataset of ribonucrease A as a standard protein was attempted in order to estimate the performance of the upgraded iBIX in comparison with previous results. The resolution of diffraction data, equivalence among intensities of symmetry-related reflections and reliability of the refined structure have been improved dramatically. iBIX is expected to be one of the highest-performance neutron single-crystal diffractometers for biological macromolecules in the world. [ABSTRACT FROM AUTHOR]

The article reports on the Ibaraki biological crystal diffractometer (IBIX) for protein crystallography, a next-generation neutron source that is installed at the Japan Proton Accelerator Research Complex in December 2008. The IBIX performed according to expectation when it is used to analyze a sampling of organic crystals at an accelerator power of 120 kilowatts. The facility plans to operate the IBIX at one megawatt to improve its efficiency.

The article reports on the use of X-ray diffraction data and neutron crystallography to determine the structure of the porcine pancreatic elastase and human immunodeficiency virus protease. The protein crystal lattice is engineered to improve the symmetry by introducing a leucine interface in the helical region of the human pancreatic ribonuclease and the mutant is crystallized. The hydrophobic interface and the mutant crystals are both observed.

Cover Feature: Insights into Proton Dynamics in a Photofunctional Salt-Cocrystal Continuum: Single-Crystal X-ray, Neutron Diffraction, and Hirshfeld Atom Refinement (Chem. Eur. J. 71/2021) Acid-base complex, fluorescence, Hirshfeld atom refinement, neutron diffraction, proton dynamics Keywords: acid-base complex; fluorescence; Hirshfeld atom refinement; neutron diffraction; proton dynamics EN acid-base complex fluorescence Hirshfeld atom refinement neutron diffraction proton dynamics 17724 17724 1 12/22/21 20211220 NES 211220 B Hydrogen bonding is a fundamental interaction in daily life b and plays an important role in chemical, physical, and biochemical processes. [Extracted from the article]

2-Dimensional X-ray and neutron diffraction patterns have been successfully measured for deuterated and hydrogenated polyoxymethylene (POM) samples obtained by γ-ray induced solid-state polymerization reaction. More than 700 reflections were collected from the X-ray diffraction data at - 150 °C by utilizing a high-energy synchrotron X-ray beam at SPring-8, Japan, from which the crystal structure of POM has been refined thoroughly including the extraction of hydrogen atomic positions as clearly seen in the difference Fourier synthesis map. As the first trial the nonuniform (9/5) helical model was analyzed with the reliability factor (R factor) 6.9%. The structural analysis was made also using the X-ray reflections of about 400 observed at room temperature (R 8.8%), and the thermal parameters of constituent atoms were compared between the low and high temperatures to discuss the librational thermal motion of the chains. The 2-dimensional neutron diffraction data, collected for the deuterated and hydrogenated POM samples using an imaging plate system specifically built-up for neutron scattering experiment, have allowed us to pick up the D and H atomic positions clearly in the Fourier synthesis maps. Another possible model, (29/16) helix, which was proposed by several researchers, has been also investigated on the basis of the X-ray diffraction data at - 150 °C. The direct method succeeded in extracting this (29/16) model straightforwardly. The R factor was 8.6%, essentially the same as that of (9/5) helical model. This means that the comparison of the diffraction intensity between the data collected from the full-rotation X-ray diffraction pattern and the intensity calculated for both the (9/5) and (29/16) models cannot be used for the unique determination of the superiority of the model, (9/5) or (29/16) helix. However, we have found the existence of 001 and 002 reflections which give the longer repeating period 55.7 Å. Besides there observed a series of meridional 001 reflections forbidden for (9/5) helical model. These additional evidences support the nonuniform (29/16) helical model as the most plausible chain conformation of POM crystal. [ABSTRACT FROM AUTHOR]

The crystal structure analysis with neutron diffraction can clearly make a distinction between the deuterium and hydrogen atoms although they cannot be distinguished by X-ray diffraction analysis. Applying the neutron diffraction analysis for the crystalline-state photoisomerization, in which a deuterium atom is replaced with the other hydrogen atom without degradation of the single crystal form, the mechanisms of the hydrogen atom transfer in the photoisomerization of several organic and organometallic compounds have been made clear. In the first example, the photoinversion of the chiral 1-cyanoethyl group bonded to the cobalt atom in a cobaloxime complex proceeded keeping the deuterium atom in this original position. For the larger alkyl group than the 1-cyanoethyl group in the second example, the chiral 1,2-bis(ethoxycarbonyl)ethyl group was also inverted to the opposite configuration in the same mechanism as that of the smaller 1-cyanoethyl group. The deuterium atom bonded to the chiral carbon atom was completely kept in its original position. For the 2-1 photoisomerization of the 2-cyanoethyl group in the third example, the C1-carbon atom of the produced 2-cyanoethyl radical after Co–C bond cleavage makes a bond with the Co atom, following the transformation of one of the deuterium atoms bonded to the C1-carbon atom to the neighboring C2-carbon atom to become a methyl group. For the 3-1 photoisomerization, the reaction proceeds in the two steps, 3-2 and 2-1 isomerizations. The chirality of the produced 1-cyanopropyl group depends on the asymmetric environment surrounding the 3-cyanopropyl group in the crystal structure before irradiation. For the four-membered ring formation in the fifth example, the hydrogen atom of one of the benzyl groups is extracted by one of the olefin carbon atoms of the cyclohexenyl group and the benzyl carbon atom makes a bond with another olefin carbon to form a thiolactam. The deuterium atom of the benzyl groups is transferred to the intramolecular cyclohexene carbon to occupy the equatorial position of the produced cyclohexyl ring. In the sixth example, the 4-cyanobutyl group of a cobaloxime complex was found to be isomerized to the 1-cyanobutyl group with retention of the single crystal form. The structure analysis of the photo-irradiated crystal by neutron diffraction revealed that the isomerization from 4- to 1-cyanobutyl group proceeded in the ‘alkyl turn’ route. The size and the shape of the reaction cavity for the cyanobutyl group clearly suggest that the alkyl turn mechanism is favorable with retention of the single crystal form. The steric repulsion from the atoms surrounding the reactive cyanobutyl group in the crystal causes such a strange reaction process. [ABSTRACT FROM AUTHOR]

Reports on the findings of a study where the H atoms bonded to the chiral C atoms (stereogenic center) of the 1-cyanoethyl groups in two cobalt complexes, [(R)-1-cyanoethyl]bis(dimethylglyoximato)(pyridine)cobalt(III) (2) and [(R,S)-1-cyanoethyl]bis(dimethylglyoximato)(piperidine)-cobalt(III) (3) were replaced with D atoms. Irradiation of the crystals of two cobalt complexes with a xenen lamp.

Single crystal neutron diffraction analysis of photo-exposed (3-cyanopropyl-d2a.a)-[(R)-1-phenylethylamine-d11]bis(di-methylglyoximato-d14)cobalt(III) was carried out in order to clarify the mechanism of the crystalline-state photoisomerization of the 3-cyanopropyl group bounded to the Co atom in some cobaloxine complexes. Before irridation the two H atoms bonded to the C¹ atom of the 3-cyanopropyl group were exchangedd with the D atoms such as - CH2CH2CD2CN. On exposure to a xenom lamp, the cell dimensions of the crystal were gradually exchanged. After 7 d exposure the change became insignificantly small. The structure was analyzed by neutron diffraction. The 3-cyanopropyl group was transformed to the 1-cyanopropyl group such as - CD(CN)C-(H½,D½)2 with retention of the single-crystal form. This indicates that one of the D atoms bonded to C¹. The other atoms of the complex either position bonded to C². The other atoms of the complex remained unchanged. These results indicate that photoisomerization proceeded in two steps: the 3-cyanopropyl group was isomerized to the 2-cyanopropyl group in the first place and then the 2-cyanopropyl group was transformed to the 1-cyanopropyl group. Moreover, it was made clear that the second-step isomerization ws irreversible, since one of the D atoms was retained. The disordered structure at C² is estimated to be caused by the interconversion between the 1-cyanopropyl group produced and its dehydrogenated olefin after the photoisomerization. [ABSTRACT FROM AUTHOR]

Porcine pancreatic elastase (PPE) resembles the attractive drug target leukocyte elastase, which has been implicated in a number of inflammatory disorders. In order to investigate the structural characteristics of a covalent inhibitor bound to PPE, including H atoms and the hydration by water, a single crystal of PPE for neutron diffraction study was grown in D2O containing 0.2 M sodium sulfate (pD 5.0) using the sitting-drop vapour-diffusion method. The crystal was grown to a size of 1.6 mm3 by repeated macroseeding. Neutron diffraction data were collected at room temperature using a BIX-3 diffractometer at the JRR-3 research reactor of the Japan Atomic Energy Agency (JAEA). The data set was integrated and scaled to 2.3 Å resolution in space group P212121, with unit-cell parameters a = 51.2, b = 57.8, c = 75.6 Å. [ABSTRACT FROM AUTHOR]

We developed and employed a profile fitting method for the peak integration of neutron time-of-flight diffraction data collected by the IBARAKI Biological Crystal Diffractometer (iBIX) at the Japan Proton Accelerator Research Complex (J-PARC) for protein ribonuclease A and α-thrombin single crystals. In order to determine proper fitting functions, four asymmetric functions were evaluated using strong intensity peaks. A Gaussian convolved with two back-to-back exponentials was selected as the most suitable fitting function, and a profile fitting algorithm for the integration method was developed. The intensity and structure refinement data statistics of the profile fitting method were compared to those of the summation integration method. It was clearly demonstrated that the profile fitting method provides more accurate integrated intensities and model structures than the summation integration method at higher resolution shells. The integration component with the profile fitting method has already been implemented in the iBIX data processing software STARGazer and its user manual has been prepared. [ABSTRACT FROM AUTHOR]

The single-crystal neutron diffraction revealed that in the process of photo-induced β-thiolactam formation from N,N-dibenzyl-1-cyclohexenecarbothioamide a deuterium atom bonded to the benzyl carbon atom is transferred to the intramolecular cyclohexene carbon to occupy the equatorial position of the produced cyclohexyl ring. [ABSTRACT FROM AUTHOR]