Cd Sites Research Articles

Screening of mimetic peptides for CD14 binding site with LBP and antiendotoxin activity of mimetic peptide in vivo and in vitro

The study was aimed at screening out the mimetic peptides from the binding site of lipopolysaccharide binding protein and CD 14, and then observing if the mimetic peptide will inhibit in vitro LPS-induced inflammatory reaction and function as an anti-endotoxin in the model of LPS-induced acute lung injury. Human monocytic cell line (U937) was used in vitro. Thirty three-month-old SD rats were used. Phage display peptide library was adapted to screen mimetic peptide sequences. U937 cells were exposed to treatment with LPS and rhLBP and then were incubated with MP12 at three different concentrations after they were induced and differentiated by PMA. LPS intravenous injection was used to establish a model of rat acute lung injury which was later treated with intravenous injection of MP12. We successfully obtained the mimetic peptide of lipopolysaccharide-binding protein and CD 14 binding site, the gene sequence of which is FHRWPTWPLPSP (MP12). MP12 can markedly inhibit LPS induced TNF-alpha expression. MP12 can evidently increase PaO(2) of rats with acute lung injury and also increase the survival rate of these rats. MP12 (FHRWPTWPLPSP) has the same function as mimetic of lipopolysaccharide-binding protein and CD 14 binding site. The application of MP12, both in vitro and in vivo, confers the biological activity required to antagonise LBP/CD14 and block LPS inflammatory signals, and it can markedly enhance PaO(2) of rats suffering from acute lung injury and also enhance their survival rate.

Leucine 85 Is an Important Determinant of Divalent Ion Affinity in Rat β-Parvalbumin (Oncomodulin)

Despite 69% sequence identity with chicken parvalbumin 3 (CPV3), rat beta-parvalbumin (beta-PV) exhibits a substantially lower Ca(2+) affinity (DeltaDeltaG degrees ' = 2.0 kcal/mol). This difference largely reflects the disparate behavior of the respective CD sites. Replacement of the rat beta-PV codon with the CPV3 codon at positions 49, 50, and 57-60 produces virtual sequence identity with the CPV3 CD site. However, the resulting protein exhibits a modest (0.5 kcal/mol) improvement in Ca(2+) affinity, implying that sequence differences beyond the binding site modulate divalent ion binding behavior. The solution structure of Ca(2+)-free rat beta-PV suggested that Leu-85, phenylalanine in CPV3, might be an important determinant. Therefore, the impact of the L85F mutation on divalent ion affinity was examined in rat beta-PV, in the variant harboring all six of the aforementioned CD site mutations, and in the intermediate CD site variants. We find that the identity of residue 85, located within the E helix, strongly influences divalent ion affinity in the mammalian beta-PV isoform and that its impact is mediated by interactions with residues in the CD site. In the wild-type protein, L85F primarily affects the EF site. By contrast, in the presence of the six CD site mutations, L85F also improves the CD site performance, yielding a protein with Ca(2+) affinity rivaling that of CPV3 and markedly enhanced Mg(2+) affinity as well. The impact of L85F on CD site Ca(2+) affinity is particularly sensitive to the identities of residues 59 and 60. Interestingly, however, significant improvement in CD site Mg(2+) affinity also requires mutation of additional CD site residues.

Bismuth-induced deep levels and carrier compensation in CdTe

First-principles calculations show that Bi on Cd site in CdTe can be either a donor ${\text{Bi}}_{\text{Cd}}^{+}$ or an acceptor ${\text{Bi}}_{\text{Cd}}^{\ensuremath{-}}$, depending on the Fermi level. The ${\text{Bi}}_{\text{Cd}}^{\ensuremath{-}}$ can bind a substitutional O $({\text{O}}_{\text{Te}})$ with large binding energy of 1.40 eV. The calculated $(0/\ensuremath{-})$ transition level for ${\text{Bi}}_{\text{Cd}}^{\ensuremath{-}}{\text{-O}}_{\text{Te}}$ complex is in good agreement with experimentally observed deep hole trapping level. Bi can also substitute Te to form an acceptor. The amphoteric nature of Bi in CdTe results in the pinning of the Fermi level and the high resistivity. The transition of the CdTe samples from semi-insulating to $p$ type at high Bi doping levels is explained by the formation of secondary phase that contains Bi and Te.

Observation of Local Fields at 111Cd(←111In) Sites in Aluminum-Doped ZnO

Observation of Local Fields at ¹¹¹Cd(←¹¹¹In) Sites in Aluminum-Doped ZnO

Self-assembled one-pot synthesis of red luminescent CdS:Mn/Mn(OH) 2 nanoparticles

We report a novel method of growing red luminescent (635 nm) Mn-doped CdS (CdS:Mn) nanoparticles capped by an inorganic shell of Mn(OH) 2. CdSO 4, Na 2S 2O 3 and Mn(NO 3) 2 were used as the precursors, and thioglycerol (C 3H 8O 2S) was employed as the capping agent and also the catalyst of the reaction. Using these materials resulted in very slow rate of the reaction and particles growth. The self-assembled one-pot process was performed at pH of 8 and Mn:Cd ratio of 10, and took about 10 days for completion. CdS:Mn nanoparticles are slowly formed in the first day of the process; however, the luminescence is weak. After 7 days, the solution turns white turbid through the formation of additional particles, which precipitate on the walls on the next day. At this stage, a relatively strong red luminescence at 635 nm appears from transparent solution of the CdS:Mn nanoparticles. The white deposit on the walls turns to dark-brown color and luminescence increases on the 9th day. Finally, the CdS:Mn nanoparticles agglomerate and precipitate out of the solution on 10th day. X-ray diffraction and optical spectroscopy showed crystalline phase CdS nanoparticles with an average size of 3.6 nm. We explain the luminescence enhancement based on the formation of a Mn(OH) 2 shell on the surface of the CdS:Mn nanoparticles during the precipitation stage. This can passivate the S dangling bonds located on the particles surface. As the surface Cd sites are previously capped with thioglycerol molecules, a complete surface passivation is achieved and results in emergence of high-intensity luminescence.

Crystal Structure of Escherichia coli MazG, the Regulator of Nutritional Stress Response

MazG is a nucleoside triphosphate pyrophosphohydrolase that hydrolyzes all canonical nucleoside triphosphates. The mazG gene located downstream from the chromosomal mazEF "addiction module," that mediated programmed cell death in Escherichia coli. MazG activity is inhibited by the MazEF complex both in vivo and in vitro. Enzymatic activity of MazG in vivo affects the cellular level of guanosine 3',5'-bispyrophosphate (ppGpp), synthesized by RelA under amino acid starvation. The reduction of ppGpp, caused by MazG, may extend the period of cell survival under nutritional stress. Here we describe the first crystal structure of active MazG from E. coli, which is composed of two similarly folded globular domains in tandem. Among the two putative catalytic domains, only the C-terminal domain has well ordered active sites and exhibits an NTPase activity. The MazG-ATP complex structure and subsequent mutagenesis studies explain the peculiar active site environment accommodating all eight canonical NTPs as substrates. In vivo nutrient starvation experiments show that the C terminus NTPase activity is responsible for the regulation of bacterial cell survival under nutritional stress.

Two Adjacent Docking Sites in the Yeast Hog1 Mitogen-Activated Protein (MAP) Kinase Differentially Interact with the Pbs2 MAP Kinase Kinase and the Ptp2 Protein Tyrosine Phosphatase

Functional interactions between a mitogen-activated protein kinase (MAPK) and its regulators require specific docking interactions. Here, we investigated the mechanism by which the yeast osmoregulatory Hog1 MAPK specifically interacts with its activator, the MAPK kinase Pbs2, and its major inactivator, the protein phosphatase Ptp2. We found, in the N-terminal noncatalytic region of Pbs2, a specific Hog1-binding domain, termed HBD-1. We also defined two adjacent Pbs2-binding sites in Hog1, namely, the common docking (CD) domain and Pbs2-binding domain 2 (PBD-2). The PBD-2 docking site appears to be sterically blocked in the intact Hog1 molecule, but its affinity to Pbs2 is apparent in shorter fragments of Hog1. Both the CD and the PBD-2 docking sites are required for the optimal activation of Hog1 by Pbs2, and in the absence of both sites, Hog1 cannot be activated by Pbs2. These data suggest that the initial interaction of Pbs2 with the CD site might induce a conformational change in Hog1 so that the PBD-2 site becomes accessible. The CD and PBD-2 docking sites are also involved in the specific interaction between Hog1 and Ptp2 and govern the dynamic dephosphorylation of activated Hog1. Thus, the CD and the PBD-2 docking sites play critical roles in both the activation and inactivation of Hog1.

Effects of Cd 2+ on AMPA receptor-mediated synaptic transmission in rat hippocampal CA1 area

Cadmium (Cd 2+) is a common pollutant that causes a wide variety of toxic effects on the central nervous system. However, the mechanism of Cd 2+ neurotoxicity remains to be elucidated. In the present study, we examined the effects of Cd 2+ on AMPA receptor-mediated synaptic transmission and short-term synaptic plasticity in hippocampal CA1 area, using whole-cell patch clamp technique. Cd 2+ significantly inhibited the peak amplitude of evoked EPSCs (eEPSCs) in a concentration-dependent manner and enhanced the short-term synaptic plasticity including paired-pulse facilitation and frequency facilitation. Cd 2+ also decreased the frequency and amplitude of spontaneous EPSCs (sEPSCs) but had no effect on those of miniature EPSCs (mEPSCs). These effects of Cd 2+ may involve a presynaptic mechanism of blockade of action potential-sensitive, calcium-dependent release of glutamate. In addition, Cd 2+ prolonged the decay time of both sEPSCs and mEPSCs, which suggested a postsynaptic action site of Cd 2+. This study demonstrates that Cd 2+ impairs the Schaffer collateral-commissural-CA1 glutamatergic synaptic transmission and short-term plasticity in rat hippocampal slices, which may be a possible contributing mechanism for the Cd 2+-induced neurotoxic effects.

Interactions of cadmium(II) ions with adenosine as well as adenosine-5′-monophosphate and diamine or triamines in the ternary systems

The mode of coordination in complexes formed in the systems Cd(II)/Ado/di- or triamine and Cd(II)/AMP/di- or triamine has been established on the basis of the equilibrium and spectral investigation. The overall stability constants (log β) and equilibrium constants of formation (log K e) of the complexes formed in the above systems have been determined. In the species, the main interaction centres are the nitrogen atoms N(1) or N(7) of the purine ring of Ado and AMP, while in the nucleotide also the oxygen atoms of the phosphate group and donor nitrogen atoms of the polyamine (PA) molecule. The effect of polyamine on the coordination dichotomy has been ascertained. For example, the presence of polyamine in the ternary system is responsible for involvement of only N(7) of the nucleoside in the metallation in Cd(Ado)H(Put), while in the binary system Cd(II)/Ado, the N(1)/N(7) dichotomy occurs in the whole pH range studied. Polyamine can also affect the character of the phosphate group of the nucleotide. The phosphate group, inactive in the binary system Cd(II)/AMP, after introduction of the polyamine becomes engaged in the interactions, e.g. in the complex Cd(AMP)H(dien). In Cd(AMP)H(en) and Cd(AMP)H(Put) no participation of the oxygen atom of the phosphate group has been found. This group is involved in weak interactions with a protonated amine group PA located in the outer coordination sphere. On the other hand, in the Cd(AMP)H(3,3-tri) complex the phosphate group is the only site of Cd(II) bonding. In this species the donor nitrogen atoms N(1) and N(7) of the nucleotide are outside the inner coordination sphere and involved in noncovalent interactions with protonated amine group from 3,3-tri.

Solution structure of Ca2+‐free rat β‐parvalbumin (oncomodulin)

Relative to other parvalbumin isoforms, the mammalian beta-parvalbumin (oncomodulin) displays attenuated divalent ion affinity. High-resolution structural data for the Ca(2+)-bound protein have provided little insight into the physical basis for this behavior, prompting an examination of the unliganded state. This article describes the solution structure and peptide backbone dynamics of Ca(2+)-free rat beta-parvalbumin (beta-PV). Ca(2+) removal evidently provokes significant structural alterations. Interaction between the D helix and the AB domain in the Ca(2+)-bound protein is greatly diminished in the apo-form, permitting the D helix to straighten. There is also a significant reorganization of the hydrophobic core and a concomitant remodeling of the interface between the AB and CD-EF domains. These modifications perturb the orientation of the C and D helices, and the energetic penalty associated with their reversal could contribute to the low-affinity signature of the CD site. By contrast, Ca(2+) removal causes a comparatively minor perturbation of the E and F helices, consistent with the more typical divalent ion affinity observed for the EF site. Ca(2+)-free rat beta-PV retains structural rigidity on the picosecond-nanosecond timescale. At 20 degrees C, the majority of amide vectors show no evidence for motion on timescales above 20 ps, and the average order parameter for the entire molecule is 0.92.

THE CRYSTAL STRUCTURE OF KUDRIAVITE, (Cd,Pb)Bi2S4

The crystal structure of kudriavite, (Cd,Pb)Bi 2 S 4 , a new mineral species, was solved from single-crystal X-ray-diffraction data and refined to R = 4.9% (4.3% for a model with split mixed-cation sites). Lattice parameters are a 13.095(1), b 4.0032(3), c 14.711(1) A, β 115.59(1)°, V 695.6(1) A 3 . The structure is equivalent to that of synthetic CdBi 2 S 4 , space group C 2/ m , Z = 4, and represents a pavonite homologue, N = 3. It is built of three-octahedron-thick columns of (311)PbS-like slabs combined by “unitcell twinning” in a quasi-mirror-glide succession. The slabs, which are intrinsically of the same topology, differ in the coordination state of bordering cations because of the relative positions of the adjacent layers. In the slabs of type I (the “non-accreting” slab common to all pavonite homologues), the central columns of octahedra are flanked by half-octahedral (square-pyramidal) coordinations completed to split-octahedra by the addition of two S atoms from the adjacent slab. The central columns of octahedra in the slabs of type II (of varying thickness, i.e. , “accreting” in pavonite homologues) are flanked by octahedral coordinations involving a S atom from the adjacent slab. The observed chemical Cd ↔ Pb and Bi ↔ In substitutions are, according to the crystal-chemical analysis, structurally limited to Bi-containing sites. They are distributed predominantly in the boundary coordinations of the type-I slabs, and the central octahedra of the type-II slabs, with Pb preferentially entering the former, and In the latter. The marginal octahedral sites of the type-II slabs, and the central octahedral sites of the type-I slabs, have been refined as pure Bi and Cd sites, respectively. The crystal-chemical analysis suggests that the observed 1:1 Pb:Cd ratio in natural kudriavite represents the upper limit for the substitution of Pb in the structure. A limit of the In substitution is not possible to determine from the present data, but it most probably is less than In:Bi = 1:3. The ratio observed in type kudriavite is less than 1:10.

Interaction of salinity and cadmium stresses on mineral nutrients, sodium, and cadmium accumulation in four barley genotypes.

Interaction of salinity (NaCl) and cadmium (Cd) on growth, mineral nutrients, Na and Cd accumulation in four barley genotypes differing in salt tolerance was studied in a hydroponic experiment. Cd, NaCl and their combined stresses reduced Ca and Mg concentrations in roots and shoots, K concentration in shoots, increased K and Cu concentrations in roots relative to control, but had non-significant effect on micronutrients Cu, Fe and Mn concentrations in shoot. The three stresses reduced accumulation of most tested nutrients in both roots and shoots, except NaCl and NaCl+Cd stresses for root K and shoot Cu accumulation in salt tolerant genotypes. The salt tolerant genotypes did not have higher nutrient concentration and accumulation than the sensitive ones when exposed to Cd and NaCl stresses. In conclusion, the affecting mechanism of Cd stress on nutrients was to some extent different from salinity stress, and the NaCl+Cd stress was not equal to additional Cd and NaCl stresses, probably due to the different valence and competitive site of Na(+) and Cd(2+). NaCl addition in the Cd-containing medium caused remarkable reductions in both Cd concentration and accumulation, with the extent of reduction being also dependent on genotypes. The salt-tolerant genotypes had lower Na concentration than sensitive ones.

Cationic, neutral and anionic metal(II) complexes derived from 4-oxo-4H-pyran-2,6-dicarboxylic acid (chelidonic acid)

The structures of five metal complexes containing the 4-oxo-4H-pyran-2,6-dicarboxylate dianion illustrate the remarkable coordinating versatility of this ligand and the great structural diversity of its complexes. In tetraaquaberyllium 4-oxo-4H-pyran-2,6-dicarboxylate, [Be(H(2)O)(4)](C(7)H(2)O(6)), (I), the ions are linked by eight independent O-H...O hydrogen bonds to form a three-dimensional hydrogen-bonded framework structure. Each of the ions in hydrazinium(2+) diaqua(4-oxo-4H-pyran-2,6-dicarboxylato)calcate, (N(2)H(6))[Ca(C(7)H(2)O(6))2(H2O)2], (II), lies on a twofold rotation axis in the space group P2/c; the anions form hydrogen-bonded sheets which are linked into a three-dimensional framework by the cations. In bis(mu-4-oxo-4H-pyran-2,6-dicarboxylato)bis[tetraaquamanganese(II)] tetrahydrate, [Mn2(C(7)H(2)O(6))2(H2O)(8)].4H2O, (III), the metal ions and the organic ligands form a cyclic centrosymmetric Mn2(C(7)H(2)O(6))2 unit, and these units are linked into a complex three-dimensional framework structure containing 12 independent O-H...O hydrogen bonds. There are two independent Cu(II) ions in tetraaqua(4-oxo-4H-pyran-2,6-dicarboxylato)copper(II), [Cu(C(7)H(2)O(6))(H2O)4], (IV), and both lie on centres of inversion in the space group P1; the metal ions and the organic ligands form a one-dimensional coordination polymer, and the polymer chains are linked into a three-dimensional framework containing eight independent O-H...O hydrogen bonds. Diaqua(4-oxo-4H-pyran-2,6-dicarboxylato)cadmium monohydrate, [Cd(C(7)H(2)O(6))(H2O)2].H2O, (V), forms a three-dimensional coordination polymer in which the organic ligand is coordinated to four different Cd sites, and this polymer is interwoven with a complex three-dimensional framework built from O-H...O hydrogen bonds.

Physical properties of Bi-doped CdTe thin films deposited by cosputtering

The structural, morphological, electrical, and optical properties of CdTe–Bi cosputtered thin films related with composition are presented. The films were grown on Corning glass substrates at room temperature from a CdTe–Bi target. The composition measurements show that the Bi content in the films ranges from x = 0.0 to x = 6.37 at%, depending on the area fraction covered by the Bi piece attached to the CdTe target. The structure of the annealed films was determined from X-ray diffraction measurements. Two kinds of structures were observed, depending on the Bi content: (1) CdTe polycrystalline films containing a small amount of Bi that is probably incorporated in the Cd and Te sites of the CdTe lattice. (2) Amorphization of the polycrystalline films, with higher Bi content. From the experimental results, we concluded that using this deposition method n/p-type Bi-doped CdTe polycrystalline films can be produced with electrical resistivity between 102–103 Ω cm and electron mobility between 101 and 102 cm2 V–1 s–1. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Pd0.213Cd0.787 and Pd0.235Cd0.765 Structures: Their Long c Axis and Composite Crystals, Chemical Twinning, and Atomic Site Preferences

We present single-crystal studies of Pd(0.213)Cd(0.787) and Pd(0.235)Cd(0.765), synchrotron powder studies of Pd(1-x)Cd(x), 0.755> or =x> or =0.800, and LDA-DFT and extended Hückel (eH) calculations on these or related phases. The two single-crystal structures have a, b, and c axis lengths of 9.9013(7), 14.0033(10), 37.063(24) and 9.9251(3), 14.0212(7), 60.181(3) A, respectively and they crystallize in the space groups Ccme and F2mm, respectively (solved as (3+1)-dimensional crystals their most convenient superspace group is Xmmm(00gamma)s00). The structures have two different structural components each with their own separate axis parameters. Powder data shows that the ratio of these separate axes (S/L) varies from 1.615 to 1.64, values near the golden mean (1.618). For Pd(0.213)Cd(0.787), different Pd and Cd site occupancies lead to variation in the R factor from 2.6-3.6 %. The site occupancy pattern with the lowest R factor (among the 26 820 variants studied) is the exact site occupancy pattern predicted by LDA-DFT parameterized eH Mulliken charge populations. The phases can be understood through a chemical twinning principle found in gamma-brass, the parent structure for the above phases (a relation with the MgCu(2) Laves phase is also noted). This twinning principle can be used to account for Cd and Pd site preferences. At the same time there is a clean separation among the Cd and Pd atoms for the two separate chain types at height b=0 and 1/2. These results indicate that Cd:Pd stoichiometry plays a role in phase stability.

Spectroscopic investigations on II–VI-semiconductor nanocrystals and their assemblies

This review points out that (magneto-)optical measurements may help to shine light on the recombination processes taking place in semiconductor nanocrystals. The surface capping with thiols creates a CdS shell around CdTe cores and forms a Cd site that is not fourfold-coordinated at the surface. It is pointed out how specific cappings such as thio-amines and thio-acids assist in coupling NCs and how we may distinguish between NC–NC interactions via electrostatic and covalent linking with the aid of the optical measurements. Furthermore, with static and time-resolved ODMR studies on IR-active core-shell HgTe/Hg x Cd1−x Te(S) particles it is demonstrated how the nature of the recombination emission being associated with a Cd–Hg mixed site is elucidated and by this yielding structural information on the NC core-shell interface. With these examples we show that and how nanomaterials of probable technological interest are studied beneficially with advanced spectroscopic techniques.

Low-Affinity Signature of the Rat β-Parvalbumin CD Site. Evidence for Remote Determinants

Although rat beta-parvalbumin and chicken parvalbumin 3 (CPV3) are identical at 74 of 108 residues, rat beta exhibits perceptibly lower Ca2+ and Mg2+ affinities. At 25 degrees C, in Hepes-buffered saline, at pH 7.4, the overall deltadeltaG degrees ' values are 2.0 and 3.9 kcal/mol, respectively. These differences primarily reflect the disparate behavior of the CD sites in the two proteins. Their respective binding constants for Ca2+, for example, are 1.5 x 10(6) and 2.4 x 10(7) M-1. The extent to which this differential behavior is dictated by local and remote sequence differences is unknown. To explore this question, we performed mutagenesis on rat beta, substituting the corresponding CPV3 codon for residues 49, 50, 57, 58, 59, and 60. The resulting CD site is identical to CPV3 at 27 of 30 positions. The mutations were introduced in four stages, replacing residues 49 and 50 (yielding beta 49/50), then 57 and 58 (beta 49/50/57/58), then 59 (beta 49/50/57/58/59), and finally 60 (beta 49/50/57/58/59/60). Apoprotein stability was examined by scanning calorimetry and chemical denaturation and divalent ion affinity by titration calorimetry. All four variants exhibit elevated Tm values and are between 0.13 and 0.39 kcal/mol more stable at 25 degrees C. Although all four proteins display heightened divalent ion affinity, the increases are small. The maximal deltadeltaG degrees ' values, observed for 49/50/57/58/59/60, are just -0.56 and -0.96 kcal/mol for Ca2+ and Mg2+, respectively. Evidently, structural features beyond the metal ion-binding motif contribute to the unusual divalent ion-binding behavior associated with the rat beta CD site.

Modification of Polypropylene Fibers by Plasma and Preparation of Hybrid Luminescent and Rodlike CdS Nanocrystals/Polypropylene Fibers

A simple method for the preparation of hybrid luminescence and rodlike CdS nanoclusters/poly (propylene-grafted-(2-methylacrylic acid 3-(bis-carboxymethyl amino-2-hydroxy-propyl ester) (GMA-IDA fibers, by plasma induced method following chemical deposition method, is presented in this study. GMA-IDA chelating groups which are grafted onto the poly(propylene) fibers are the coordination sites for chelating Cd+2, on which nano-sized CdS nanocrystals grew. TEM observations demonstrate that the mean diameter of CdS nanocrystals inside the poly(PP-graft-GMA-IDA) fibers alters from 2 nm to 8 nm at various concentrations of S2- solution. Additionally, SEM presents that the CdS nanocrystals on the surface have rod-like structure. The UV-vis absorption spectra provide the information of the absorption edges, band-gaps, and average diameter of CdS nanocrystals, the results of which are coincidence with the TEM observations. Furthermore, the photoluminescence (PL) shows the maximum peaks are 495 nm, 571 nm, 657 nm, and 675 nm corresponding to the mean particle sizes 2.6 nm, 3.5 nm, 4.8 nm, and 7.7 nm, respectively, at an excitation wavelength of 366 nm.

On the crystal structure of the quasicrystalline approximant YbCd 6 at low temperature

The body-centered cubic (space group I m 3 ¯ , No. 204) crystal structure of the quasicrystalline approximant YbCd 6 has been studied by means of single-crystal X-ray diffraction at low temperature. These studies suggest that below 120 K, the disorder in the innermost Cd-shell in YbCd 6 is best modeled with a 1/3 occupied cube-octahedron representing Cd 4-tetrahedron in six possible orientations. The disordered cadmium atoms occupy the Wyckoff position 24 g. Above this temperature, the disorder of the Cd 4-tetrahedra inside the Cd 20-dodecahedra in this “onion”-type structure becomes progressively larger and the Cd site can be further split as to occupy a general position with a Wyckoff letter 48 f. These results are in agreement with the disorder model suggested previously from structure refinements of YbCd 6 at room temperature.

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