Crystallography

We can realise the representations of the group SL(2,R) on the unit disc. This is due to an isomorphism between the group SL(2,R) and the group SU(1,1). The discrete series representations for the group SL(2,R)given by\pi_{n}(g)\varphi(z)=\varphi (\frac{d z-b}{a-cz} )(a-c z)^{-n},    where  n  is an integer number,is on the Bergman space where n>2 .Lang studies the discrete series on the group  in the upper half-plane and on the unit disc.  For n=1, the SL(2,R) representation is called the mock discrete series. The representation space of the mock discrete series is the Hardy space.In this article we describe the  SL(2,R) representation on the Dirichlet space.

DFT studies of desoxydinucleoside monophosphate complexes with Na-ions (dDMPs), using DGAUSS and ADF software reveal that the characteristic B-type conformation of DNA duplexes is initially predisposed in single strand in the form of a local minimum. Such predisposition may be important for biological functioning of DNA by facilitating an addition of new nucleotide in the processes of DNA duplication and restoration of double helix after unwinding. The computational results demonstrate the important contribution of intra-strand interactions to conformational stability and sequence-dependent variability of B-DNA duplexes. The main characteristics of the ''canonical" BI conformations, such as the regions of torsion angles of sugar-phosphate backbone, C2 0 -endo or very close to C2 0 -endo sugar puckerings, and nearly parallel base-ring arrangements are already present in the single strand and are universal for all 16 dDMPs. The dihedral angle between the bases does not depend on the extent of their overlap, which suggests the major contribution of sugar-phosphate backbone to formation of these minima. The study reveals characteristic sequence dependence of the base arrangements. Namely, an extensive base-ring overlap takes place for all purine-purine and purine-pyrimidine sequences, and negligible ring overlap is observed in all pyrimidine-purine and pyrimidine-pyrimidine sequences. These arrangements closely resemble the geometrical characteristics of BI DNA in duplex crystals. Preliminary results of search for other energy minima related to helical DNA structures revealed the existence of BII-like minima for some dDMPs.

The products of the solid-state reactions between potassium metal and tetracene (K:Tetracene, 1:1, 1.5:1, and 2:1) are fully structurally characterized. Synchrotron X-ray powder diffraction shows that only K 2 Tetracene forms under the reaction conditions studied, with unreacted tetracene always present for x < 2. Diffraction and 13 C MAS NMR show that K 2 Tetracene has a crystal structure that is analogous to that of K 2 Pentacene, but with the cations ordered on two sites because of the influence of the length of the hydrocarbon on possible cation positions. K 2 Tetracene is a nonmagnetic insulator, thus further questioning the nature of reported superconductivity in this class of materials.

Layered two-anion compounds are of interest for their diverse electronic properties. The modular nature of their layered structures offers opportunities for the construction of complex stackings used to introduce or tune functionality, but the accessible layer combinations are limited by the crystal chemistries of the available anions. We present a layered three-anion material, Bi4O4Cu1.7Se2.7Cl0.3, which adopts a new structure type composed of alternately stacked BiOCuSe and Bi2O2Se-like units. This structure is accessed by inclusion of three chemically distinct anions, which are accommodated by aliovalently substituted Bi2O2Se0.7Cl0.3 blocks coupled to Cu-deficient Bi2O2Cu1.7Se2 blocks, producing a formal charge modulation along the stacking direction. The hypothetical parent phase Bi4O4Cu2Se3 is unstable with respect to its charge-neutral stoichiometric building blocks. The complex layer stacking confers excellent thermal properties upon Bi4O4Cu1.7Se2.7Cl0.3: a room-temperature t...

MAYIS 2003 tarihinde yayınlanan makale düzenlenerek tekrar yayınlanmıştır. Öz Kaymalı yatak malzemesi olarak bakır esaslı alaşımlardan pirinç ve özellikle bronz yaygın bir şekilde kullanılmaktadır. Bu alaşımlar kaymalı yataklardan beklenen özellikleri sağlamaktadırlar. İyi bir tribolojik performansa sahip bu malzemeler, kaymalı yataklarda iyi sonuçlar vermektedir. Bu çalışmada; CuSn10 bronzu ile CuZn30 pirincinden üretilen kaymalı yatakların sürtünme ve aşınma özellikleri belirlenip, birbiriyle karşılaştırılmıştır. Karşı aşındırıcı olarak SAE 1050 çelik mil kullanılmıştır. Deneyler radyal kaymalı yatak aşınma test cihazında 20 N yük, 1500 d/dak ve 2.5 saatte yapılmıştır. Sonuç olarak, kuru ortamda yapılan deneylerde yüksek sürtünme katsayısı ve ağırlık kaybı, yağlı ortamda ise çok daha düşük elde edilmiştir. Anahtar Kelimeler: Tribolojik özellikler, Bakır esaslı yataklar, Aşınma

MAYIS 2003 tarihinde yayınlanan makale düzenlenerek tekrar yayınlanmıştır. Kaymalı yatak malzemesi olarak bakır esaslı alaşımlardan pirinç ve özellikle bronz yaygın bir şekilde kullanılmaktadır. Bu alaşımlar kaymalı yataklardan beklenen özellikleri sağlamaktadırlar. İyi bir tribolojik performansa sahip bu malzemeler, kaymalı yataklarda iyi sonuçlar vermektedir. Bu çalışmada; CuSn10 bronzu ile CuZn30 pirincinden üretilen kaymalı yatakların sürtünme ve aşınma özellikleri belirlenip, birbiriyle karşılaştırılmıştır. Karşı aşındırıcı olarak SAE 1050 çelik mil kullanılmıştır. Deneyler radyal kaymalı yatak aşınma test cihazında 20 N yük, 1500 d/dak ve 2.5 saatte yapılmıştır. Sonuç olarak, kuru ortamda yapılan deneylerde yüksek sürtünme katsayısı ve ağırlık kaybı, yağlı ortamda ise çok daha düşük elde edilmiştir . Anahtar Kelimeler: Tribolojik özellikler, Bakır esaslı yataklar, Aşınma

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The crystal and molecular structure of the complex formed by the ionized bistartro‐[18]‐crown‐6 receptor molecule 1 with the ethylenediammonium cation, is described. The macrocycle is roughly planar, the carboxy groups of each tartaric acid residue being in a diaxial relationship and extending above and below this plane. This conformation allows ‘lateral’ interactions with bound species to occur.The substrate is sandwiched between two macrocycles, with one of its NH heads anchored to the polyether core, and the other one in contact with the two carboxy groups of the neighboring molecule.

First principle study of cyclic compound has a great interest because their products are very much useful in biological and clinical applications. In this work, Density functional theory (DFT) and Time dependent DFT calculations have been performed to study structural, electronic and vibrational properties of Tyramine (a neuromodulator) at B3LYP/3-21G level employing Gaussian 09 software. All the theoretical calculations were carried out to study the equilibrium geometries, vibrational spectra, molecular electrostatic potential (MEP), highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and UV-Vis spectra of the title compound. Also, the molecular docking analysis of Tyramine against two different proteins (Trace amine-associated receptor 1 and Dopamine D 2 receptor) was carried out using AutoDock Vina. The scaled values of calculated vibrational frequencies were used for vibrational assignments on the basis of the potential energy distribution (PED). The structure activity relation has been interpreted by mapping MEP and Time dependent DFT method has been adopted to elucidate electronic properties. Graphical representation of frontier molecular orbital for both gaseous and solvent phase provides valuable insight into the nature of reactivity, stability and some of the structural and physical properties of the title molecule. Also, the calculated HOMO and LUMO energy values show that the charge transfer occurs within the molecule. Further, the title molecule shows good potentiality for binding against Trace amine-associated receptor 1 (1TQN) with binding affinity-6 kcal/mol The binding site of the Tyramine is found to be amine (NH 2) group.

K␤ x-ray spectra of metallic vanadium and its compounds ͑V 2 O 3 , VO 2 , V 2 O 5 , VC, VN, VCl 2 , NH 4 VO 3 , and VOSO 4 ϫ 5H 2 O͒ induced in thick targets by 3 MeV proton beams were measured by using wavelength dispersive ͑WD͒ x-ray spectrometer. In addition to the main K␤ 1,3 x-ray line, "satellites" or second order contributions like K␤Ј, K␤Љ, K␤ٞ, and K␤ 2,5 were clearly resolved. Intensities and positions of these lines relative to the K␤ 1,3 x-ray line have been extracted by fitting the spectra and corrected for x-ray sample self-absorption. The influence of the oxidation states and vanadium-ligand bond distances in studied compounds on relative intensities and positions of K␤Љ, K␤ 2,5 , and ͑K␤Љ + K␤ 2,5 ͒ x-ray lines ͑relative to K␤ 1,3 + K␤Ј͒ has been studied and discussed. The obtained results indicate that the strength of the K␤Љ and K␤ 2,5 transition probability per vanadium-ligand pair decreases exponentially with increasing vanadium-ligand distance, in agreement with the observation reported by Bergman et al. for K␤Љ relative intensity in a number of Mn oxide compounds ͓U.

K␤ x-ray spectra of metallic vanadium and its compounds ͑V 2 O 3 , VO 2 , V 2 O 5 , VC, VN, VCl 2 , NH 4 VO 3 , and VOSO 4 ϫ 5H 2 O͒ induced in thick targets by 3 MeV proton beams were measured by using wavelength dispersive ͑WD͒ x-ray spectrometer. In addition to the main K␤ 1,3 x-ray line, "satellites" or second order contributions like K␤Ј, K␤Љ, K␤ٞ, and K␤ 2,5 were clearly resolved. Intensities and positions of these lines relative to the K␤ 1,3 x-ray line have been extracted by fitting the spectra and corrected for x-ray sample self-absorption. The influence of the oxidation states and vanadium-ligand bond distances in studied compounds on relative intensities and positions of K␤Љ, K␤ 2,5 , and ͑K␤Љ + K␤ 2,5 ͒ x-ray lines ͑relative to K␤ 1,3 + K␤Ј͒ has been studied and discussed. The obtained results indicate that the strength of the K␤Љ and K␤ 2,5 transition probability per vanadium-ligand pair decreases exponentially with increasing vanadium-ligand distance, in agreement with the observation reported by Bergman et al. for K␤Љ relative intensity in a number of Mn oxide compounds ͓U.

This study is devoted to the physicochemical and mineralogical characterizations of palygorskite from Marrakech High Atlas, Morocco. The raw clay and its Na ? -saturated \2 lm fraction were characterized using chemical, structural, and thermal analytical techniques. Measurements of specific surface area and porous volume are reported. The clay fraction was found to be made up of 95 % of palygorskite and 5 % of sepiolite. An original feature of this palygorskite is its deficiency in zeolitic H 2 O. The half-cell structural formula of its dehydrated form was determined on the basis of 21 oxygens to be (Si 7.92 Al 0.08 )(Mg 2.15 Al 1.4 Fe 0.4 Ti 0.05 h 1 )(Ca 0.03 Na 0.08 K 0.04 )O 21 , while the hydrated form could be formulated as (Si 7.97 Al 0.03 )(Mg 2.17 Al 1.46 Fe 0.40 Ti 0.05 )(Ca 0.03 Na 0.07 K 0,03 ) O 20.18 (OH) 1.94 (OH 2 ) 3.88 Á2.43 H 2 O. These formulas show that the (Al 3? ?Fe 3? )/Mg 2? ratio is around 0.84, revealing a pronounced dioctahedral character. Further, inside its octahedral sheet, it was determined that the inner M 1 sites are occupied by vacancies, whereas the M 2 sites are shared between 90 % of trivalent cations (78 % for Al 3? and 22 % for Fe 3? ), 7.5 % of Mg 2? , and 2.5 % of Ti 4? , all of them linked to 1.94 of structural hydroxyls. The two remaining Mg 2? by half-cell occupy edge M 3 sites and are coordinated to 3.88 molecules of OH 2 . Channels of this palygorskite are deficient in zeolitic H 2 O since they contain only 2.43 H 2 O molecules. A correlation was found between these results and the observation of very intense and well-resolved FTIR bands arising from dioctahedral domains (mainly Al 2 OH, Fe 2 OH, and AlFeOH) along with very small responses from a trioctahedral domain (Mg 3 OH). Accordingly, a schematic representation of the composition of the octahedral sheet was proposed. The cation exchange capacity, specific surface area, and total pore volume were also assessed to be ca. 21.2 meq/100 g, 116 m 2 /g, and 0.458 cm 3 /g, respectively.

ErFeO 3 single crystal 7 mm in diameter and up to 70 mm in length has been grown by the floating zone technique using a four-mirror image furnace. Particular attention was given to the surface morphology of different cross-sections of the single crystal perpendicular to the growth direction. There are many cracks, bubbles, and precipitations on the cross-sections of the crystal observed by scanning electron microscopy. The thermal stress induced by the high growth rate might play an important role in the formation of the cracks. The bubbles might be mainly caused by high growth rate and the voids within the sintered feed rod. The energy-dispersive X-ray spectroscopy analysis indicates that there is Fe deficiency in the crystal especially in the precipitations.

Photocatalytic activity of most metal oxides is restricted to the ultraviolet (UV) range of solar spectrum due to their large band gap. Since UV accounts for only 5% of the solar spectrum, designing metal oxide semiconductors with capability of absorbing visible light has been widely attempted. The large band gap of metal oxides can be reduced by various methods like doping with metallic or non-metallic ions, however a better photocatalytic activity can not be achieved necessarily by these methods due to fast recombinations of electron and hole. In recent years, authors have paid attention to the high pressure phases of metal oxides, which theoretically possess narrow band gaps, being able to absorb visible light. In this review, high pressure phases of well-known metal oxides like titania (TiO 2 ), zirconia (ZnO), and yttria (Y 2 O 3 ) have been stabilized by applying a severe plastic deformation method, and photocatalytic properties of them have been evaluated.

Severe plastic deformation using high-pressure torsion (HPT) is successfully applied at room temperature to partially stabilized ZrO 2 . X-ray diffraction and Raman spectroscopy analyses reveal that appreciable strain is introduced in the sample and a phase transformation with a coherent interface occurs from the metastable tetragonal phase to the monoclinic phase during HPT. The fraction of the stress-induced monoclinic phase increases with straining, reaches a saturation level. Transmission electron microscopy shows that nanograins of high dislocation density but with no twins are formed during HPT.

The assembly, orientation, and structural features of nanoscale tubes composed of cyclic peptides, formed at the air-water interface, were detected by grazing incidence X-ray diffraction (GIXD). The peptide cyclo-[(L-Phe-D-N-MeAla-) 4 ] (1) exhibits two-dimensional crystallinity in which the plane of the peptide ring is parallel to the water interface. The peptide cyclo-[(L-Trp-D-Leu) 3 -L-Ser-D-Leu] (2) forms predominantly planar aggregates composed of several tubes, lying with their long axes parallel to the air-water interface. In contrast, the peptide cyclo-[(L-Trp-D-Leu) 4 ] (3) exhibits a very low tendency to form ordered two-dimensional arrays of nanotubes. Films of peptides 2 and 3 as well as their mixtures with the phospholipid DPPA were transferred onto a solid support and visualized by scanning force microscopy (SFM).

by pulsed laser melting and rapid thermal annealing (RTA). As a three terminal scanning tunneling microscopy technique, BEEM can image both the surface topography and the local hot electron transport. Using ion implantation through a lithographically patterned mask and varying subsequent processing conditions, we have made locally confined GaNxAs1-x dots with different activated nitrogen concentrations. By analyzing BEEM images of the quantum dots, we study giant bandgap bowing effects on the Schottky barrier height. We will also discuss the effects of different implanted nitrogen concentrations, laser fluences and RTA conditions on the conduction band structures of these quantum dots.

We will present two dimensionally patterned GaN x As 1-x nanostructures fabricated in a GaAs matrix using nitrogen ion implantation followed by pulsed laser melting and rapid thermal annealing (RTA). The arbitrarily patterned GaN x As 1-x regions are investigated by ballistic electron emission microscopy (BEEM), a three terminal scanning tunneling microscopy technique. BEEM can image both the surface topography and the local hot electron transport. Using ion implantation through a lithographically patterned mask and varying subsequent processing conditions such as nitrogen concentrations and laser fluences, we have made locally confined GaN x As 1-x dots. By analyzing BEEM images of the quantum dots, we study giant bandgap bowing effects on the Schottky barrier height. We will also discuss the effects of different implanted nitrogen concentrations, laser fluences and RTA conditions on the conduction band structures of GaN x As 1-x .

The edgewise interactions of anions with phenylalanine (Phe) aromatic rings in proteins, known as anion-quadrupole interactions, have been well studied. However, the anion-quadrupole interactions of the tyrosine (Tyr) and tryptophan (Trp) rings have been less well studied, probably because these have been considered weaker than interactions of anions hydrogen bonded to Trp/Tyr side chains. Distinguishing such hydrogen bonding interactions, we comprehensively surveyed the edgewise interactions of certain anions (aspartate, glutamate, and phosphate) with Trp, Tyr, and Phe rings in high-resolution, nonredundant protein single chains and interfaces (protein-protein, DNA/RNA-protein, and membrane-protein). Trp/Tyr anion-quadrupole interactions are common, with Trp showing the highest propensity and average interaction energy for this type of interaction. The energy of an anion-quadrupole interaction (-15.0 to 0.0 kcal/mol, based on quantum mechanical calculations) depends not only on the...

In the title compound, C 18 H 20 O 4 S, the thiophene and benzene rings are oriented at a dihedral angle of 10.83 (11) . The central chain makes dihedral angles of 1.86 (13) and 9.25 ( ) with the benzene and thiophene rings, respectively. In the crystal, molecules are linked through weak intermolecular C-HÁ Á ÁO interactions.interactions are also observed between the benzene rings with a centroid-centroid distance of 3.6832 (12) A ˚. The slippage between the benzene rings is 0.956 A ˚.

Scanning tunneling microscopy (STM) has been used to characterize the surface structure of cleaved single crystals of Bi2,2Srl,8CuOy and Bi, Sr,&u,#~.,O,. Images of Bi2,2Srl,8Cu0, exhibit a one-dimensional superstructure with a modulation period of 25.1 f 0.3 1. The atomic structure in these images is ordered and shows no evidence of local distortions due to Sr2+ substitution and/or extra oxygen in the BiO layer. Substitution of Fe in the CuO layer of this material caused substantial changes in the superstructure and the BiO layer atomic structure. The superstructure period in Bi2,2Srl,8Cu,,, F%,,OY determined from the analysis of STM images and two-dimensional Fourier transform power spectra, 22.8 f 1 .O 1, was smaller and less regular than that observed for Bi2,2Sr1,8C~Oy samples. In addition, the atomic structure of the Fe-substituted material exhibited significant disorder. These results are discussed in terms of lattice mismatch and bonding between the BiO and the Cu(Fe)O layers of this material. (

Electronic and geometric structures of Ca(II) and Zn(II) complexes with porphyrazine (Pz) and tetrakis(1,2,5-thiadiazole)porphyrazine (TTDPz) were investigated by density functional theory (DFT) calculations and compared. The perimeter of the coordination cavity was found to be practically independent on the nature of a metal and a ligand. According to the results of the natural bond orbital (NBO) analysis and quantum theory of atoms in molecules (QTAIM) calculations, Ca-N bonds possess larger ionic contributions as compared to Zn-N. The model electronic absorption spectra obtained with the use of time-dependent density functional theory (TDDFT) calculations indicate a strong bathochromic shift (~70 nm) of the Q-band with a change of Pz ligand by TTDPz for both Ca and Zn complexes. Additionally, CaTTDPz was synthesized and its electronic absorption spectrum was recorded in pyridine and acetone.

Peculiarities of the molecular geometry, electronic structure and spectral properties of heterocyclic subphthalocyanines analogues containing electron-deficient heterocycles have been considered using DFT and TD DFT methods. Subporphyrazine with annulated 1,2,5-selenadiazole rings was prepared and characterised for the first time and molecular parameters of the 1,2,5-thiadiazole analogue have been determined by single crystal X-ray diffraction. The theoretical results are compared with the experimental data and the effect of heteroatom substitution in benzene rings of subphthalocyanines on spectral-luminescence properties was revealed. Fusion of pyrazine, 1,2,5thiadiazole or 1,2,5-selenadiazole rings instead benzene fragments leads to considerable stabilization of the frontier π-molecular orbitals of subporphyrazine macrocycle. The HOMO-LUMO gap is increased when pyrazine or 1,2,5thiadiazole rings are fused, but becomes narrower in the presence of 1,2,5-selenadiazole rings. The intense Q band observed in the visible region (530 -575 nm) originate from the lowest ππ* transition (2a 2 →1e*) and its energy follows the changes in HOMO-LUMO gap. Two transitions (2a 1 →1e* and 1a 1 →1e*) contribute predominantly to closely lying excited states (B 1 , B 2 ) responsible for the intense Soret band in the of subphthalocyanine and its pyrazine and 1,2,5-thiadiazole analogues. For the Se-analogue the energy of the 2a 1 →1e* transition is decreased and B 1 band is shifted bathochromically shifted to 342 nm. Fusion of π-electron-deficient 1,2,5-chalcogenadiazole rings leads to appearance of the less intense band at 390 (S) or 408 nm (Se) due to electronic transition from HOMO 2a 2 to 2e* orbital localized on predominantly on peripheral heterocyclic fragments (CT band). The heavy atom effect of chalcogens decreases the fluorescence quantum yield in heterocyclic subphthalocyanines analogues, but promotes the intersystem crossing and strongly enhances the singlet oxygen quantum yield for 1,2,5-selenadiazole fused subporphyrazine (Φ ∆ = 0.98 in CH 2 Cl 2 ).

Co-cyclization of 1,2,5-thiadiazole-3,4-dicarbonitrile and 3,6-diamyloxyphthalodinitrile in the presence of magnesium or lithium amylate in amyl alcohol leads to mixtures containing the Mg derivatives of the symmetrical species tetrakis(1,2,5-thiadiazolo)porphyrazine, (S 4 )PzH 2 , and tetrakis(1,4-diamyloxybenzo)porphyrazine, (A 4 )PzH 2 , and the low-symmetry macrocycles bearing peripheral 1,2,5-thiadiazole and 1,4-diamyloxybenzene rings in the ratio 1:3, 2:2 (cis and trans), and 3:1, that is, (SA 3 )PzH 2 , (S 2 A 2 )PzH 2 , (SASA)PzH 2 , and (S 3 A)PzH 2 , respectively. The basic Mg materials were converted to the corresponding free-base macrocycles by treatment with CF 3 COOH. The species were separated from the mixtures by chromatography, either as Mg complexes or demetalated materials. With results on (S 4 )PzH 2 and (SA 3 )PzH 2 in hand, including crystallographic work on the latter, a general chemical physical investigation has been carried out of all the symmetrical and unsymmetrical free-base macrocycles. The structures of the species (S 2 A 2 )PzH 2 and (A 4 )PzH 2 . were elucidated by single-crystal X-ray crystallography. The effect of the progressive variation of the macrocyclic structure along the series, from the symmetrical (S 4 )PzH 2 to its symmetrical partner (A 4 )PzH 2 via the low-symmetry 3:1, 2:2 (cis and trans), and 1:3 macrocycles, was studied by IR, 1 H NMR, and UV/Vis linear and nonlinear (optical limiting) measurements. The results are interpreted on the basis of intra-and intermolecular interactions between the electron-deficient 1,2,5thiadiazole and the electron-donating 1,4-diamyloxybenzene moieties.

We describe extensive studies on a family of perovskite oxides that are ferroelectric and ferromagnetic at ambient temperatures. The data include x-ray diffraction, Raman spectroscopy, measurements of ferroelectric and magnetic hysteresis, dielectric constants, Curie temperatures, electron microscopy (both scanning electron microscope and transmission electron microscopy (TEM)) studies, and both longitudinal and transverse magnetoelectric constants α33 and α31. The study extends earlier work to lower Fe, Ta, and Nb concentrations at the B-site (from 15%–20% down to 5%). The magnetoelectric constants increase supralinearly with Fe concentrations, supporting the earlier conclusions of a key role for Fe spin clustering. The room-temperature orthorhombic C2v point group symmetry inferred from earlier x-ray diffraction studies is confirmed via TEM, and the primitive unit cell size is found to be the basic perovskite Z = 1 structure of BaTiO3, also the sequence of phase transitions with i...

Twelve members of the Ho 2 À y Nd y Zr 2 O 7 series, prepared using conventional solid state methods, have been characterised by neutron powder diffraction. Ho 2 Zr 2 O 7 has a defect fluorite structure whereas Nd 2 Zr 2 O 7 is found to adopt the ordered pyrochlore structure with the composition induced fluoritepyrochlore transformation occurring near y¼ 1. Rietveld analysis on the neutron data for all the compositions reveals an increase in lattice parameter as a function of y across the entire series, with a small discontinuity associated with the transformation. The neutron profile results suggest that domains of pyrochlore-type initially begin to form before crystallising into a separate phase, and therefore that anion and cation ordering processes are distinct. There is a strong correlation between the extent of disorder in the anion sublattice and the x-parameter of 48f oxygen. These results point the way to a better understanding of the stability observed in pyrochlore structures.

The zirconates Ln 2 Zr 2 O 7 (Ln = lanthanoid) have been studied using a combination of Zr L-edge X-ray absorption near edge structure (XANES) and synchrotron X-ray and neutron powder diffraction methods. These studies demonstrate that as the size of the lanthanoid cation decreases, the local structure evolves smoothly from the ideal pyrochlore toward the defect fluorite rather than undergoing an abrupt transformation. The Zr L-edge spectrum is found to be extremely sensitive to changes in the local coordination environment and demonstrates an increase in local disorder across the pyrochlore oxides. The sensitivity of the XANES measurements enables us to identify the progressive nature of the transition that could not be detected using bulk diffraction techniques.

EPR studies have been carried out on a Fe 3ϩ -doped LaCaAlO 4 single crystal at the X band ͑9.6 GHz͒ at room, liquid-nitrogen, and liquid-helium temperatures to study the effect of substitutional disorder that results when Ca 2ϩ and La 3ϩ ions substitute at the same site in this crystal. The variation of the observed Fe 3ϩ EPR linewidth as a function of the orientation of the external magnetic field with respect to the crystallographic c axis is found to be consistent with that reported previously for the Fe 3ϩ ion in YCaAlO 4 single crystal. This provides a confirmation of the disorder model proposed in oxide single crystals to explain the angular dependency of the linewidth behavior caused by statistical distribution of R 3ϩ ͑R denotes rare-earth ion͒ and Ca 2ϩ ions, situated in the same crystallographic position. The details of the manifestation of disorder in LaCaAlO 4 on EPR spectra have been provided. In addition, the EPR line positions have been exploited to estimate the Fe 3ϩ spin-Hamiltonian parameters in LaCaAlO 4 at 295, 77, and 4.2 K. The superposition model has been applied to calculate the Fe 3ϩ zero-field splitting parameter b 2 0 in RCaAlO 4 (RϭY, La) isostructural crystals, leading to the value of the intrinsic parameter b ¯2(R 0 )ϭϪ119Ϯ1 GHz for R 0 ϭ1.784 Å. The liquid-helium temperature spectrum has been used to determine the absolute sign of the b 2 0 parameter, which is negative.

X-band (,9.8 GHz) EPR studies on a single crystal of pentacalcium-oxide trialuminate (5CaO´3Al 2 O 3 ) doped with Eu 21 were carried out at 4.2, 77.4 K and in the range 120±300 K. The site symmetry, as revealed by the angular variation of the EPR spectrum, was found to be nearly axial. The Eu 21 spin-Hamiltonian parameters were estimated from the positions of the EPR lines at various temperatures. The absolute sign of the zero-®eld splitting parameter, B 2 0 , was determined to be positive from the relative intensities of lines at liquid-helium temperature. The resolved Eu 21 hyper®ne (HF) structure was observed only for a few ®ne-structure EPR lines, and only at some orientations of the external magnetic ®eld. HF-interaction constants for the 151 Eu and 153 Eu isotopes were estimated from an analysis of the partly resolved HF structure.

, La(III), Sm(III), Gd(III), x = 2/3, 3/4, a = valency of metal ion) have been synthesized by fusion technique. The infra-red spectral studies of these complex polymetaphosphate derivatives have been carried out in KBr in the range 400-4000 cm -1 on a FTIR Spectrophotometer. The spectra of these complex polymetaphosphate derivatives show broad bands which may be ascribed to their amorphous polymeric character.

Structures of nanoparticles in Fe-16Cr-4.5Al-0.3Ti-2W-0.37Y 2 O 3 ͑K3͒ and Fe-20Cr-4.5Al-0.34Ti-0.5Y 2 O 3 ͑MA956͒ oxide dispersion strengthened ͑ODS͒ ferritic steels produced by mechanical alloying ͑MA͒ and followed by hot extrusion have been studied using high-resolution transmission electron microscopy ͑HRTEM͒ techniques to understand the formation mechanism of nanoparticles in MA/ODS steels. The observations of Y-Al-O complex-oxide nanoparticles in both ODS steels imply that decomposition of Y 2 O 3 in association with internal oxidation of Al occurred during mechanical alloying. While the majority of oxide nanoparticles formed in both steels is Y 4 Al 2 O 9 , a few oxide particles of YAlO 3 are also observed occasionally. These results reveal that Ti ͑0.3 wt %͒ plays an insignificant role in forming oxide nanoparticles in the presence of Al ͑4.5 wt %͒. HRTEM observations of crystalline nanoparticles larger than ϳ2 nm and amorphous or disordered cluster domains smaller than ϳ2 nm provide an insight into the formation mechanism of oxide nanoparticle in MA/ODS steels, which we believe from our observations involves solid-state amorphization and recrystallization. The role of nanoparticles in suppressing radiation-induced swelling is revealed through TEM examinations of cavity distributions in ion-irradiated Fe-14Cr and K3-ODS ferritic steels. HRTEM observations of helium-filled cavities ͑helium bubbles͒ preferably trapped at nanoscale oxide particles and clusters in ionirradiated K3-ODS are presented.

Introduction. The viral inflammatory protein II (vMIP-II) is a mammalian chemokine homolog encoded by Kaposi's sarcoma-associated herpesvirus (KSHV). Chemokines constitute the largest family of cytokines that play important roles in immune responses. The main biological function of chemokines is to mediate the recruitment of leukocytes to the site of inflammation and their activation. The activity of chemokines is effected by binding to the G-protein coupled chemokine receptors present on various subpopulations of leukocytes such as monocytes, macrophages, basophils, eosinophils, and lymphocytes. Based on the positions of the first two conservative cysteine residues, chemokines are classified into four subfamilies: CXC, CC, CX3C, and C. As a viral chemokine, vMIP-II shows a broad spectrum of binding to CXC, CC, and CX3C chemokine receptors. In particular, vMIP-II binds to both CXCR4 and CCR5, which are the only two major coreceptors of human immunodeficiency virus Type 1 (HIV-1). Although most mammalian chemokines are agonists to their corresponding receptors, vMIP-II is in most cases an antagonist to its receptors including CXCR4 and CCR5. 2 All ligands of CXCR4 and CCR5 show anti-HIV activity in vitro by competing with HIV-1 for the binding of the coreceptors though some are more potent than others. The structural basis of the interaction between chemokines and their receptors was subjected to intense investigation in recent years. However, many of the details are still not known. Here, we report the crystal structure of vMIP-II in two crystal forms different from previously reported and discuss the structural features that are possibly related to the binding affinity and specificity. Abbreviations: vMIP-II, viral macrophage inflammatory protein-II; MCP-2, monocyte chemoattractant protein-2; CXCR4, CXC chemokine receptor 4; CCR5, CC chemokine receptor 5; RMSD, root mean square deviations.

The three-dimensional structure of the repeating units of Haemophilus influenzae types c and f capsular polysaccharides (CPS) have been investigated by molecular dynamics simulations. The models consist of disaccharides joined by phosphodiester linkages, explicit water, and sodium as the counterion. Four 1 ns simulations were performed for each type, with either different starting conformations or different methods to handle long-range truncation effects, namely, Ewald summation or force shift truncation. For the average properties investigated, the choice of the method did not make any significant difference. Limited flexibility was observed close to the sugar residues, whereas at the phosphorus atom, the torsions showed major transitions. For comparison, 3 J H,P was measured on CPS material. On the basis of these spin-spin couplings, only small changes are required in the models of the disaccharide repeating unit to agree with data on the CPS. In addition, hydrogen bonding and radial and spatial distribution functions were analyzed to obtain a picture of solvent ordering around the disaccharides.

Molecular dynamics simulations in vacuum and solution have been carried out on 2′‐α‐L‐fucosyllactitol, a model for blood group H in conjunction with two‐dimensional nmr measurements on the same compound. Three independent starting conformations for the dynamics were chosen from low energy conformations obtained by a ϕ/ψ grid search. Nine 5 ns vacuum simulations of the trisaccharide were performed, employing three different ways to treat electrostatic interactions for each starting conformation: distance‐dependent dielectric with ε = r, constant dielectric with ε = 1, or constant dielectric with ε = 80. In vacuum, transitions of ϕ and ψ for the α‐L‐Fuc‐(1 → 2)‐β‐D‐Gal element occur in a cooperative manner. The virtual distance obtained for H1 in fucose to H2 in galactose from nuclear Overhauser effect spectroscopy experiments agree with one of the conformations of the trisaccharide in one of the three 100 ps aqueous simulations (ϕ/ψ ca. −100°/150°), indicating this may be a dominant ...

The length of weak dative bonds in donor functionalized organo aluminum alkoxides [R 2 AlϪOϪR'ϪY] 2 (Y ϭ NR 2 , OR, SR) show a temperature dependence in the solid state that is distinctively different from the common effect of libration. This observation is interpreted as being caused by thermal excitation. The

Using quantum chemical calculations, spectroscopic methods, and molecular docking analysis, this work explores the electronic, structural, vibrational, and biological characteristics of CAFI. Intramolecular hydrogen bonding between the methyl and C = O groups (with bond lengths less than 3 Å) was detected, affirming molecular stability. Corresponded with the theoretical expectations, FT-IR and UV spectra corroborating CAFI's chemical stability. Frontier molecular orbital study indicated HOMO-LUMO energy gaps between 4.227 eV (gas) and 4.792 eV (ethanol), underscoring charge transfer activity. Molecular docking revealed CAFI as the most potent binder to proteins that stimulate kidney function, with a binding energy of-4.08 kcal/mol and sustained hydrogen bonding connections. ADMET analysis confirmed CAFI's drug-likeness, indicating advantageous absorption, distribution, metabolism, and toxicity characteristics. These findings indicate CAFI as a potential treatment candidate for the regulation of renal function.

Multi-component high-entropy (TiCrAl0.5NbCu)CxNy coatings targeting applications requiring medium-to-high friction and wear-resistant surfaces were fabricated through the co-sputtering of elemental targets in an Ar + CH4 + N2 reactive atmosphere using a hybrid HiPIMS/DCMS technique. Two sets of samples were fabricated: (a) (TiCrAl0.5NbCu)Cx high-entropy carbides (HEC) and (b) (TiCrAl0.5NbCu)CxN0.13 high-entropy carbonitrides (HECN), 0 ≤ x ≤ 0.48. The structural, mechanical, tribological, and corrosion resistance properties were thoroughly investigated. The metallic sample exhibits a single BCC structure that changes to FCC via an intermediary amorphous phase through the addition of C or N to the content of the films. The crystallinity of the FCC phases is enhanced and the density of the films decreases down to 5.5 g/cm3 through increasing the carbon fraction up to 48%. The highest hardness of about 16.9 GPa and the lowest wear rate of about 5.5 × 10−6 mm3/Nm are presented by the sam...

Polymorphs of Zn(2-nIm) 2 (compound 1) and Co(2-nIm) 2 (compounds 2 and 3) (2-nIm = 2nitroimidazole) have been prepared by two routes: solvothermal synthesis and recrystallisation of ZIF-65(Zn/Co). Compounds 1 and 2 are isostructural, with a tetrahedrallyconnected framework topology related to, but different from, that of tridymite (lonsdaleite). Single crystal X-ray diffraction analysis showed that in compound 1 (Pccn, Z = 8; a = 8.462(8) Å, b = 14.549(15) Å, c = 18.799(18) Å, V = 2314(4) Å 3 ) there is rotational disorder for two of the three crystallographically-distinct linker types, which has been investigated computationally and by solid-state NMR spectroscopy. Detailed adsorption studies on a sample of 1 prepared by recrystallisation show 1.1 mmol g -1 uptake of CO 2 at 0.1 bar (25 °C) with high affinity for CO 2 over CH 4 and N 2 (adsorption enthalpies of 39.5, 26.0 and 18.5 kJ mol -1 , respectively). A cobalt analogue (compound 2) with improved water stability (but lower porosity) has also been prepared. Changing the conditions of synthesis and recrystallisation gives rise to a cobalt 2-nitroimidazolate (Co(2-nIm) 2 , compound 3), which has a layered structure (I4 1 /amd, a = 6.025(18) Å, c = 26.95(8) Å, V = 978.3(5) Å 3 ) containing sheets of tetrahedrally-connected Co 2+ cations composed of four membered rings, without porosity.