X-ray Structure Determination Research Articles

A Phosphine-Oxide Cobalt(II) Complex and Its Catalytic Activity Studies toward Alcohol Dehydrogenation Triggered Direct Synthesis of Imines and Quinolines.

Herein, a new pincer-like amino phosphine donor ligand, H2L1, and its phosphine-oxide analog, H2L2, were synthesized. Subsequently, cobalt(II) complexes 1 and 2 were synthesized by the reaction of anhydrous Co(II)Cl2 with ligands H2L1 and H2L2, respectively. The ligands and complexes were fully characterized by various physicochemical and spectroscopic characterization techniques. Finally, the identity of the complexes 1 and 2 was confirmed by single crystal X-ray structure determination. The phosphine ligand containing complex 1 was converted to the phosphine oxide ligand containing complex 2 in air in acetonitrile solution. Both complexes 1 and 2 were investigated as precatalysts for alcohol dehydrogenation-triggered synthesis of imines in air. The phosphine-oxide complex 2 was more efficient than the phosphine complex 1. A wide array of alcohols and amines were successfully reacted in a mild condition to result in imines in good to excellent yields. Precatalyst 2 was also highly efficient for the synthesis of varieties of quinolines in air. As H2L2 in 2 has side arms that can be deprotonated, we investigated complex 2 for its base (KOtBu) promoted deprotonation events by various spectroscopic studies and DFT calculations. These studies have shown that mono deprotonation of the amine side arm attached to the pyridine is quite feasible, and deprotonation of complex 2 leads to a dearomatized pyridyl ring containing complex 2a. The mechanistic investigations of the catalytic reaction, by a combination of experimental and computational studies, have suggested that the dearomatized complex, 2a acted as an active catalyst. The reaction proceeded through the hydride transfer pathway. The activation barrier of this step was calculated to be 26.5 kcal/mol, which is quite consistent with the experimental reaction temperature under aerobic conditions. Although various pincer-like complexes are explored for such reactions, phosphine oxide ligand-containing complexes are still unexplored.

Thiosalicylanilide complexes of nickel(II), palladium(II) and platinum(II)

Reactions of the complexes cis-[PtCl2(PPh3)2], [PtCl2(dppf)] {dppf = Fe(C5H4PPh2)2}, [PdCl2(PPh3)2], [PdCl2(dppe)] (dppe = Ph2PCH2CH2PPh2) and [NiCl2(dppe)] with thiosalicylanilide (HSC6H4CONHPh, H2-1a) and its substituted derivatives H2-1b to H2-1d (where H2-1b = p-Cl-HSC6H4CONHPh, H2-1c = p-CH3-HSC6H4CONHPh, and H2-1d = m-OCH3-HSC6H4CONHPh) gave a series of square-planar MS2P2-type complexes. The complexes were characterised by ESI MS, 1H and 31P{1H} NMR, FTIR, and microelemental analyses, and in some cases by single crystal X-ray crystallography. The predominant coordination mode is through bonding of deprotonated thiol group of two ligands. However, the tendency to form complexes with a single, chelating S,N- and S,O-donor ligand was observed by 31P{1H} NMR in some reactions. In addition, cis/trans isomerisation was observed in some complexes by 31P{1H} NMR and confirmed by X-ray structure determinations on trans-[Pt(H-1b)2(PPh3)2] and trans-[Pd(H-1b)2(PPh3)2]. A comparison of the energetics of the reaction systems involving [Pt(1b)(PPh3)2]/[Pt(H-1b)2(PPh3)2], [Pt(1d)(PPh3)2]/[Pt(H-1d)2(PPh3)2] and [Pd(1b)(dppe)]/[Pd(H-1b)2(dppe)] using Density Functional Theory (DFT) revealed that the MS2P2 systems [Pt(H-1b)2(PPh3)2], [Pt(H-1d)2(PPh3)2] and [Pd(H-1b)2(dppe)] have lower Gibbs free energies than the S,N-chelate systems [Pt(1b)(PPh3)2], [Pt(1d)(PPh3)2] and [Pd(1b)(dppe)], and are thermodynamically favoured. Intermolecular interactions quantified and visualized on Hirshfeld surfaces for trans-[Pt(H-1b)2(PPh3)2], [Pt(H-1d)2(PPh3)2].H2O, and [Pd(H-1a)2(dppe)] revealed the dominant contribution of H···H contacts to crystal packing.

Further Insight into the Manganese(II) 2,2′-Bipyridine-1,1′-dioxide Homoleptic Complex: Single-Crystal X-ray Structure Determination of the Perchlorate Salt and DFT Calculations

The homoleptic cationic complex formed by reacting suitable manganese(II) salts with 2,2′-bipyridine-1,1′-dioxide (bipyO2) has been subjected to several studies in the past because of its peculiar absorption and electrochemical features. Here, the first single-crystal X-ray structure determination of a [Mn(bipyO2)3]2+ salt is reported, where the charge of the cation is balanced by perchlorate anions. The hydrated salt [Mn(bipyO2)3](ClO4)2 crystallizes in the monoclinic system (P21/n space group) and the asymmetric unit contains three cationic complexes and six perchlorate anions. The environment of the manganese(II) ions is best described as octahedral, with scarce variations among the three cations in the asymmetric unit. The bipyO2 ligands exhibit κ2 coordination mode, forming seven-membered metallacycles. The X-ray outcomes have been used as the starting point for DFT and TDDFT calculations, aimed to elucidate the charge transfer origin of the noticeable absorption in the visible range. The MLCT nature is confirmed by the hole and electron distributions associated with the spin-allowed transitions. DFT calculations on the related manganese(III) complex indicate that the geometry of [Mn(bipyO2)3]2+ changes only slightly upon oxidation, in agreement with the reversible electrochemical behaviour experimentally observed.

Unusual Stabilisation of Remarkably Bent Tetra-Cationic Tetra-radical Intermolecular Fe(III) μ-Oxo Tetranuclear Complexes.

A hitherto unknown series of air stable, π-conjugated, remarkably bent tetra-cation tetra-radical intermolecular Fe(III) μ-oxo tetranuclear complex, isolated from the dication diradical diiron(III) porphyrin dimers, has been synthesised and spectroscopically characterised along with single crystal X-ray structure determination of two such molecules. These species facilitate long-range charge/radical delocalisation through the bridge across the entire tetranuclear unit manifesting an unusually intense NIR band. Assorted spin states of Fe(III) centres are stabilised within these unique tetranuclear frameworks: terminal six-coordinate iron centres stabilise the admixed intermediate spin states while the central five-coordinate iron centres stabilise the high-spin states. Variable temperature magnetic susceptibility measurements indicated strong antiferromagnetic coupling for the Fe(III)-O-Fe(III) unit while the exchange interactions between the Fe centres and the porphyrin π-cation radicals are weaker as supported both by magnetic data and DFT calculations. The nature of orbital overlap between the SOMOs of Fe(III) and π* orbital of the porphyrin was found to rationalise the observed exchange coupling, establishing such a complex magnetic exchange in this tetranuclear model with a significant bioinorganic relevance.

Diverse Reactivity of Amidinate-Supported Boron Centers with the Hypersilyl Anion and Access to a Monomeric Secondary Boron Hydride.

Diverse reactivity of the bulky tris(trimethylsilyl)silyl substituent [Si(SiMe3)3], also known as the hypersilyl group, was observed for amidinate-supported dichloro- and phenylchloroborane complexes. Treatment of the dichloroborane with potassium tris(trimethylsilyl)silyl led to the activation of the backbone β-carbon center and formation of saturated four-membered heterocyclic chloroboranes R'{Si(SiMe3)3}C(NR)2BCl [R' = Ph, R = Cy (3); R' = Ph, R = iPr (6); R' = tBu, R = Cy (8)], whereas the four-membered amidinate hypersilyl-substituted phenyl borane 4 {PhC(NCy)2B(Ph)[Si(SiMe3)3]} was observed for the case of an amidinate-supported phenylchloroborane. The highly deshielded 11B NMR spectroscopic resonance and the distinct difference in the 29Si NMR spectrum confirmed the presence of a σ-donating hypersilyl effect on compounds 3, 6, and 8. Reaction of 3 with the Lewis acid AlCl3 led to the formation of complex 11 in which an unusual cleavage of one of the C-N bonds of the amidinate backbone is observed. Nucleophilic substitution at the boron center of saturated chloroborane 3 with phenyllithium generated the phenylborane derivative 12, whereas the secondary monomeric boron hydride 13 was observed after treatment with alane (AlH3). All compounds (2-13) have been fully characterized by NMR spectroscopy and single-crystal X-ray structure determination studies.

Na3Ge2P3: A Zintl Phase Featuring [P3Ge-GeP3] Dimers as Building Blocks.

Recently, ternary lithium phosphidotetrelates have attracted interest particularly due to their high ionic conductivities, while corresponding sodium and heavier alkali metal compounds have been less investigated. Hence, we report the synthesis and characterization of the novel ternary sodium phosphidogermanate Na3Ge2P3, which is readily accessible via ball milling of the elements and subsequent annealing. According to single crystal X-ray structure determination, Na3Ge2P3 crystallizes in the monoclinic space group P21/c (no. 14.) with unit cell parameters of a = 7.2894(6) Å, b = 14.7725(8) Å, c = 7.0528(6) Å, β = 106.331(6)° and forms an unprecedented two-dimensional polyanionic network in the b/c plane of interconnected [P3Ge-GeP3] building units. The system can also be interpreted as differently sized ring structures that interconnect and form a two-dimensional network. A comparison with related ternary compounds from the corresponding phase system as well as with the binary compound GeP shows that the polyanionic network of Na3Ge2P3 resembles an intermediate step between highly condensed cages and discrete polyanions, which highlights the structural variety of phosphidogermanates. The structure is confirmed by 23Na- and 31P-MAS NMR measurements and Raman spectroscopy. Computational investigation of the electronic structure reveals that Na3Ge2P3 is an indirect band gap semiconductor with a band gap of 2.9 eV.

Structures of LIG1 provide a mechanistic basis for understanding a lack of sugar discrimination against a ribonucleotide at the 3'-end of nick DNA

Human DNA ligase 1 (LIG1) is the main replicative ligase that seals Okazaki fragments during nuclear replication and finalizes DNA repair pathways by joining DNA ends of the broken strand breaks in the three-steps of ligation reaction. LIG1 can tolerate the RNA strand at the upstream of the nick, yet an atomic insight into the sugar discrimination mechanism by LIG1 against a ribonucleotide at the 3'-terminus of nick DNA is unknown. Here, we determined X-ray structures of LIG1/3'-RNA-DNA hybrids and captured the ligase during pre- and post-step 3 the ligation reaction. Furthermore, the overlays of 3'-rA:T and 3'-rG:C step 3 structures with step 2 structures of canonical 3'-dA:T and 3'-dG:C uncover a network of LIG1/DNA interactions through Asp570 and Arg871 side chains with 2'-OH of the ribose at nick showing a final phosphodiester bond formation and the other ligase active site residues surrounding the AMP site. Finally, we demonstrated that LIG1 can ligate the nick DNA substrates with preinserted 3'-ribonucleotides as efficient as Watson-Crick base-paired ends in vitro. Together, our findings uncover a novel atomic insight into a lack of sugar discrimination by LIG1 and the impact of improper sugar on the nick sealing of ribonucleotides at the last step of DNA replication and repair.

Functional Model of Compound II of Cytochrome P450: Spectroscopic Characterization and Reactivity Studies of a FeIV-OH Complex.

Herein, we show that the reaction of a mononuclear FeIII(OH) complex (1) with N-tosyliminobenzyliodinane (PhINTs) resulted in the formation of a FeIV(OH) species (3). The obtained complex 3 was characterized by an array of spectroscopic techniques and represented a rare example of a synthetic FeIV(OH) complex. The reaction of 1 with the one-electron oxidizing agent was reported to form a ligand-oxidized FeIII(OH) complex (2). 3 revealed a one-electron reduction potential of -0.22 V vs Fc+/Fc at -15 °C, which was 150 mV anodically shifted than 2 (Ered = -0.37 V vs Fc+/Fc at -15 °C), inferring 3 to be more oxidizing than 2. 3 reacted spontaneously with (4-OMe-C6H4)3C• to form (4-OMe-C6H4)3C(OH) through rebound of the OH group and displayed significantly faster reactivity than 2. Further, activation of the hydrocarbon C-H and the phenolic O-H bond by 2 and 3 was compared and showed that 3 is a stronger oxidant than 2. A detailed kinetic study established the occurrence of a concerted proton-electron transfer/hydrogen atom transfer reaction of 3. Studying one-electron reduction of 2 and 3 using decamethylferrocene (Fc*) revealed a higher ket of 3 than 2. The study established that the primary coordination sphere around Fe and the redox state of the metal center is very crucial in controlling the reactivity of high-valent Fe-OH complexes. Further, a FeIII(OMe) complex (4) was synthesized and thoroughly characterized, including X-ray structure determination. The reaction of 4 with PhINTs resulted in the formation of a FeIV(OMe) species (5), revealing the presence of two FeIV species with isomer shifts of -0.11 mm/s and = 0.17 mm/s in the Mössbauer spectrum and showed FeIV/FeIII potential at -0.36 V vs Fc+/Fc couple in acetonitrile at -15 °C. The reactivity studies of 5 were investigated and compared with the FeIV(OH) complex (3).

Reduction of Germanium Oxides-The Mixed-Valence Germanates A2Ge4O7 (A = Na, K).

We report on the synthesis of two-layered alkali germanates, Na2Ge4O7 and K2Ge4O7. Both compounds were synthesized by using the ammonothermal method at 823 K and 100 MPa. Under these conditions, germanium is partially reduced from the +IV state to +II, forming mixed-valence compounds with the rarely observed [Ge(II)O3]4- unit. The valence state was verified by X-ray photoelectron spectroscopy (XPS) and was accompanied by theoretical calculations alongside vibrational spectroscopy and single-crystal X-ray structure determination. The compounds crystallize in the trigonal space groups (Na2Ge4O7: P3̅c1 and K2Ge4O7: P3̅m1) and feature layers of corner sharing [Ge(II)O3]4- and [Ge(IV)2O7]6- units forming [Ge(II)2Ge(IV)2O7]2- polyanions. These layers are separated by alkali metal ions. The compounds are colorless insulators with band gaps of 4.0-4.2 eV. According to the Robin-Day classification, both compounds can be described as class I materials, where the valences are trapped on specific sites.

Stereoselective synthesis and X-ray structure determination of novel 1,2-dihydroquinolinehydrazonopropanoate derivatives

A novel series of 1,2-dihydroquinolinhydrazonopropanoate have been synthesized via a convenient aza-Michael addition reaction between hydrazinylquinolinones and ethyl propiolate in ethanol under refluxing temperature. The structures for all obtained products were confirmed with FTIR, NMR spectrums, as well as mass spectrometry. In addition, the monoclinic structure for compounds 8a, 8c, and 8d was also confirmed via X-ray crystallography analyses. The E-configuration for the obtained products was confirmed form the X-ray analysis. On the other hand, the crystal packing shows that the intermolecular and hydrogen bonds between atoms are parallel to the bc plan.

Triflate's bigger brother: The unprecedented tribrate anion, [Br3 CSO3

The synthesis of the unprecedented [Br3 CSO3 ]- anion starts with the bromination of phenylmethanesulfonate, C6 H5 OSO2 CH3 , with KOBr leading to C6 H5 OSO2 CBr3 . The formation of the [CBr3 ] moiety has been proved, also by an X-ray structure determination of the compound (triclinic, P-1, a=685.9(2), b=698.1(2), c=1190.2(3) pm, α=93.99(1)°, β=97.42(1)°, γ=94.45(1)°). The ester C6 H5 OSO2 CBr3 can be split under basic conditions. The resulting acid provides access to the yet unknown tribromomethanesulfates ("tribrates"). K[Br3 CSO3 ] ⋅ H2 O, the first tribrate known so far has been characterized comprehensively, including an X-ray structure determination (monoclinic, C2/c, a=2267.1(2), b=1282.25(8), c=2618.2(2) pm, β=111.266(2)°), vibrational spectroscopy and theoretical calculations. Moreover, the thermal analysis shows that, after loss of the crystal water, the tribrate decomposes between 530 and 630 K.

Solving protein structures by combining structure prediction, molecular replacement and direct-methods-aided model completion.

Highly accurate protein structure prediction can generate accurate models of protein and protein-protein complexes in X-ray crystallography. However, the question of how to make more effective use of predicted models for completing structure analysis, and which strategies should be employed for the more challenging cases such as multi-helical structures, multimeric structures and extremely large structures, both in the model preparation and in the completion steps, remains open for discussion. In this paper, a new strategy is proposed based on the framework of direct methods and dual-space iteration, which can greatly simplify the pre-processing steps of predicted models both in normal and in challenging cases. Following this strategy, full-length models or the conservative structural domains could be used directly as the starting model, and the phase error and the model bias between the starting model and the real structure would be modified in the direct-methods-based dual-space iteration. Many challenging cases (from CASP14) have been tested for the general applicability of this constructive strategy, and almost complete models have been generated with reasonable statistics. The hybrid strategy therefore provides a meaningful scheme for X-ray structure determination using a predicted model as the starting point.

Structure and photochemistry of di-tert-butyldiphosphatetrahedrane.

Di-tert-butyldiphosphatetrahedrane (tBuCP)2 (1) is a mixed carbon- and phosphorus-based tetrahedral molecule, isolobal to white phosphorus (P4). However, despite the fundamental significance and well-explored reactivity of the latter molecule, the precise structure of the free (tBuCP)2 molecule (1) and a detailed analysis of its electronic properties have remained elusive. Here, single-crystal X-ray structure determination of 1 at low temperature confirms the tetrahedral structure. Furthermore, quantum chemical calculations confirm that 1 is isolobal to P4 and shows a strong largely isotropic diamagnetic response in the magnetic field and thus pronounced spherical aromaticity. A spectroscopic and computational study on the photochemical reactivity reveals that diphosphatetrahedrane 1 readily dimerises to the ladderane-type phosphaalkyne tetramer (tBuCP)4 (2) under irradiation with UV light. With sufficient thermal activation energy, the dimerisation proceeds also in the dark. In both cases, an isomerisation to a 1,2-diphosphacyclobutadiene 1' is the first step. This intermediate subsequently undergoes a [2 + 2] cycloaddition with a second 1,2-diphosphacyclobutadiene molecule to form 2. The 1,2-diphosphacyclobutadiene intermediate 1' can be trapped chemically by N-methylmaleimide as an alternative [2 + 2] cycloaddition partner.

Structural consequences in differently substituted haloarylcarboxylates and non-covalent interactions on crystal packing and biological efficacy of copper(II) complexes with N,N,N′,N′-tetramethylethylenediamine N-donor ligand

In this work, we reported four new copper(II) halo-benzoate complexes (2-chloro-4-nitrobenzoate (2-Cl-4-NO2-BZ), 3,5-DICBZ, 2-chloro-5-nitrobenzoate (2-Cl-5-NO2-BZ), 3,5-difluoro benzoate (3,5-DIFBZ), and 3,5-dichlorobenzene (3,5-DICBZ) respectively in complexes 1–4) with N,N,N’,N’- tetramethylethylene diamine (temed) N-donor ligand in order to study the interesting coordination features and biological evaluation of such complexes under ambient reaction conditions. All the complexes 1–4 were characterized by elemental analyses, and spectroscopic techniques, including FT-IR, UV–vis, and EPR etc. Single crystal X-ray structure determination (SCXRD) of complexes revealed the distorted octahedral geometry in all complexes. Notably, the halobenzoate ligands exhibited a bidentate chelation mode in complexes 1 and 2, while they showed a monodentate mode in complex 3. In complex 4, the carboxylate ligand exhibited both monodentate as well as bidentate coordination. Furthermore, detailed packing analyses of complexes 1–4 highlighted the significance of halogen bonding in lattice stabilization besides hydrogen bonding and π∙∙∙π interactions as evidenced by Hirshfeld surface analyses and crystal analysis. Moreover, packing analyses displayed that complex 1 exhibited a layered or wave-like arrangement, while complex 2 featured a helical arrangement supported by a supramolecular halogen-bonded network guided by Cl∙∙∙O interactions. Complex 3 displayed a zig-zag layered arrangement with a stacking topology, and Complex 4 showcased a ribbon-like arrangement stabilized by F∙∙∙F and Cl∙∙∙Cl halogen bonding interactions. Furthermore, sigma hole on halogen atoms has also been examined (which play an important role in halogen bonding) by electrostatic-potential isosurfaces. In order to exploit the biological efficacy of complexes 1–4 owing to the inherent biological activity of copper metal, molecular docking analyses against gram +ve bacteria i.e. S. epidermidis (PDB ID; 8DO6), B. subtilis (1QD9), as well as two gram -ve bacteria, namely, P. aeruginosa (5WZE) and S. dysenteriae (1DM0), have also been carried out. Interestingly, values of docking scores and inhibition constant of all complexes 1–4 (with a maximum binding score (inhibition constant) of -9.8 kcal/mol (0.063 µMol) in 1 against 8DO6 and 1DM0) revealed higher biological efficacy than that of standard drugs.

Synthesis, structure, preliminary antimicrobial and antimalarial studies of 1,1′-(piperazine-1,4-diyl)bis(2-phenylethan-1-one) and its lanthanide, Ce(III), Pr(III), and Nd(III) complexes

A dione ligand, 1,1′-(piperazine-1,4-diyl)bis(2-phenylethan-1-one) derived from the reaction of phenylacetylchloride with piperazine and the lanthanides, Ce(III), Nd(III), and Pr(III) complexes of general formula [LnL(NO3)2]NO3 were synthesized. The compounds were characterized by conventional NMR, Mass Infra-Red and UV–vis spectroscopic techniques, melting point, elemental analysis, conductivity, thermogravimetric analysis, magnetic susceptibility, and single X-ray structure determination of the ligand. In vitro, antimicrobial studies indicated that the ligand is active against Staphylococcus aureus, Bacillus Sublitis, Salmonella typhi, and Streptococcus pneumonae. The Ce(III) and Pr(III) complexes were active against all the microorganisms except A. Niger and Pseudomonas aeruginosa whereas the Ce(III) complex showed activity against Staphylococcus aureus, Bacillus Sublitis, and Streptococcus pneumonae. The In vivo anti-plasmodial assay of infected rats indicated that the ligand and Nd(III), Pr(III) complexes have high antiplasmodial potency in comparison to the antimalarial medicine Artesunate. In corroboration with findings on the enhanced antimicrobial properties of the complexes, binding energies from molecular docking correlated strongly with the inhibition zone diameter for Staphylococcus aureus and density functional theoretical studies suggest the presence of the metals account for the improved properties in the following order: Nd(III) > Pr(III) > Ce(III).

Structural and biochemical analysis of the PARP1-homology region of PARP4/vault PARP.

PARP4 is an ADP-ribosyltransferase that resides within the vault ribonucleoprotein organelle. Our knowledge of PARP4 structure and biochemistry is limited relative to other PARPs. PARP4 shares a region of homology with PARP1, an ADP-ribosyltransferase that produces poly(ADP-ribose) from NAD+ in response to binding DNA breaks. The PARP1-homology region of PARP4 includes a BRCT fold, a WGR domain, and the catalytic (CAT) domain. Here, we have determined X-ray structures of the PARP4 catalytic domain and performed biochemical analysis that together indicate an active site that is open to NAD+ interaction, in contrast to the closed conformation of the PARP1 catalytic domain that blocks access to substrate NAD+. We have also determined crystal structures of the minimal ADP-ribosyltransferase fold of PARP4 that illustrate active site alterations that restrict PARP4 to mono(ADP-ribose) rather than poly(ADP-ribose) modifications. We demonstrate that PARP4 interacts with vault RNA, and that the BRCT is primarily responsible for the interaction. However, the interaction does not lead to stimulation of mono(ADP-ribosylation) activity. The BRCT-WGR-CAT of PARP4 has lower activity than the CAT alone, suggesting that the BRCT and WGR domains regulate catalytic output. Our study provides first insights into PARP4 structure and regulation and expands understanding of PARP structural biochemistry.

Ethoxylate Polymer-Based 96-Well Screen for Protein Crystallization

Crystallization is the limiting step in X-ray structure determination of biological macromolecules. As crystallization experiments can be largely automatized, the diversity of precipitant solutions is often the determinant factor to obtain crystals of high quality. Here, we introduce a 96-well screening kit of crystallization conditions, centered on three ethoxylate-based organic polymers as precipitants and various additional compounds to promote crystal formation. This crystallization screen was tested on various non-standard proteins from bacteria and archaea. Structure determination succeeded for seven out of thirteen targets based on crystals that frequently diffracted to a higher resolution than those obtained with commercially available screening kits. Crystallization hits were rarely similar among the three ethoxylate-based organic polymers and, in comparison, with already available crystallization screens. Hence, the presented crystallization screen is an efficient tool to complement other screens and increase the likelihood of growing crystals suitable for X-ray structure determination.

X-ray structures of Enterobacter cloacae allose-binding protein in complexes with monosaccharides demonstrate its unique recognition mechanism for high affinity to allose

d-Allose is an aldohexose of the C3-epimer of d-glucose, existing in very small amounts in nature, called a rare sugar. The operon responsible for d-allose metabolism, the allose operon, was found in several bacteria, which consists of seven genes: alsR, alsB, alsA, alsC, alsE, alsK, and rpiB. To understand the biological implication of the allose operon utilizing a rare sugar of d-allose as a carbon source, it is important to clarify whether the allose operon functions specifically for d-allose or also functions for other ligands. It was proposed that the allose operon can function for d-ribose, which is essential as a component of nucleotides and abundant in nature. Allose-binding protein, AlsB, coded in the allose operon, is thought to capture a ligand outside the cell, and is expected to show high affinity for the specific ligand. X-ray structure determinations of Enterobacter cloacae AlsB (EtcAlsB) in ligand-free form, and in complexes with d-allose, d-ribose, and d-allulose, and measurements of the thermal parameters of the complex formation using an isothermal titration calorimeter were performed. The results demonstrated that EtcAlsB has a unique recognition mechanism for high affinity to d-allose by changing its conformation from an open to a closed form depending on d-allose-binding, and that the binding of d-ribose to EtcAlsB could not induce a completely closed form but an intermediate form, explaining the low affinity for d-ribose.

The synthesis of novel lanthanum hydroxyborate at extreme conditions.

The novel structure of lanthanum hydroxyborate La2B2O5(OH)2 was synthesized by the reaction of partially hydrolyzed lanthanum and boron oxide in a diamond anvil cell under high-pressure/high-temperature (HPHT) conditions of 30GPa and ∼2,400K. The single-crystal X-ray structure determination of the lanthanum hydroxyborate revealed: , a = 6.555(2)Å, c = 17.485(8)Å, Z = 6, R1 = 0.056. The three-dimensional structure consists of discrete planar BO3 groups and three crystallographically different La ions: one is surrounded by 9, one by 10, and one by 12 oxygen anions. The band gap was estimated using ab initio calculations to be 4.64eV at ambient pressure and 5.26eV at 30GPa. The current work describes the novel HPHT lanthanum hydroxyborate with potential application as a deep-ultraviolet birefringent material.

Cocrystal of Codeine and Cyclopentobarbital

The two-component compound formed by codeine and cyclopentobarbital was produced using grinding techniques and through evaporation from alcoholic solutions. The cocrystal nature of this phase was established unequivocally through single crystal X-ray structure determination. The asymmetric unit contains one formula unit. In the cyclopentobarbital molecule, the cyclopentenyl ring is disordered over two positions related by a rotation of approximately 180° about its C—C bond to the pyrimidine ring. The two NH groups of the cyclopentobarbital molecule form N—H⋯N and N—H⋯O bonds to piperidine and hydroxyl groups, respectively, belonging to different codeine molecules. In addition, the hydroxyl and methoxy groups of neighboring codeine molecules are linked by O—H⋯O interactions, resulting in a H-bonded framework structure of codeine and cyclopentobarbital molecules. The cocrystal was also characterized using thermal analysis, X-ray powder diffraction and IR spectroscopy.