Cholesterol interaction with recombinant human sterol carrier protein-2

The interaction of human recombinant sterol carrier protein-2 (SCP-2) with sterols was examined. Two independent ligand binding methods, Lipidex 1000 binding of [³H]cholesterol and a fluorescent dehydroergosterol binding assay, were used to determine the affinity of SCP-2 for sterols. Binding analysis indicated SCP-2 bound [³H]cholesterol and dehydroergosterol with aK _d of 0.3 and 1.7 μM, respectively, and suggested the presence of a single binding site. Phase fluorometry and circular dichroism were used to characterize the SCP-2 sterol binding site. Alterations in dehydroergosterol lifetime, SCP-2 tryptophan lifetime, and SCP-2 tryptophan quenching by acrylamide upon cholesterol binding demonstrated a shielding of the SCP-2 tryptophan from the aqueous solvent by bound sterol. Differential polarized phase fluorometry revealed decreased SCP-2 tryptophan rotational correlation time upon cholesterol binding. Circular dichroism of SCP-2 indicated that cholesterol elicited a small decrease in SCP-2 alpha helical content. The data suggest that SCP-2 binds sterols with affinity consistent with a lipid transfer protein that may act either as an aqueous carrier or at a membrane surface to enhance sterol desorption.     

Synthesis,Crystal Structure of Tetra-Nuclear Macrocyclic Cu(II) Complex Material and Its Application as Catalysts for A3 Coupling Reaction

A novel tetra-nuclear macrocyclic Cu(II) complex has been synthesized by the reaction of cupric acetate monohydrate with N-acetyl-l-phenylalanine and 4,4-bipyridine in water/ethanol (v:v = 1:1) solution, and characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The results show that the Cu(II) complex belongs to monoclinic, space group P ₂₁ with a = 14.993(3) Å, b = 14.831(3) Å, c = 22.262(4) Å, β = 99.37(3)°, V = 4884.2(16) Å³, Z = 2, D _c  = 1.420 μg m^?3, μ = 0.942 mm^?1, F(000) = 2,160, and final R ₁ = 0.0701, ωR ₂ = 0.1905. The molecules form three dimensional tubular structures by the interaction of hydrogen bonds and π–π interaction. The A³ coupling reaction of phenylacetylene, aldehyde and amine (piperidine) in the presence of Cu(II) complex as an efficient heterogeneous catalyst has been studied. The catalyst displayed high activity and afforded the corresponding propargylamines with excellent yields. The Cu(II) complex catalyst was reused three times without significant loss of its catalytic activity.     

Metal–Organic Framework Based on Pyridine-2,3-Dicarboxylate and a Flexible Bis-imidazole Ligand: Synthesis, Structure, and Photoluminescence

A novel metal–organic framework {[Zn(2,3-pydc)(bbi)]·0.5CH₃CN·2H₂O} _n (2,3-pydc = pyridine-2,3-dicarboxylate, bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) (1), was prepared under hydrothermal conditions and characterized by elemental analyses, IR and X-ray diffraction. Crystal data for 1 are monoclinic, space group C2/c, a = 19.685(2) Å, b = 14.332(1) Å, c = 16.930(2) Å, β = 121.205(2)°, U = 4085.3(6) Å³, Z = 4. The results reveal that the Zn(II)-atom is five-coordinated with two O-atoms and three N-atoms forming a distorted trigonal bipyramidal geometry. The Zn(II) atoms are bridged by 2,3-pydc and bbi ligands, leading to a three-dimensional network. The Zn···Zn separations are 8.277 Å [through the 2,3-pydc bridge] and 12.638 Å [through the bbi bridge]. Additionally, 1 shows strong fluorescence in the solid state at room temperature.     

1D Coordination Polymer from Tetraaza Macrocyclic Nickel(II) Complex and 1,2,3,4-Cyclobutanetetracarboxylic Acid

The self assembly of [Ni(L)]Cl₂·2H₂O (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) and 1,2,3,4-cyclobutanetetracarboxylic acid (H₄cbtc) acid generates a 1D coordination and 2D hydrogen-bonded polymer [Ni(L)(H₂cbtc)₂·3H₂O] _n (1). Complex 1 is characterized by X-ray crystallography, spectroscopy and magnetic susceptibility. Each nickel(II) ion has a distorted octahedral coordination environment with the four secondary amines of the macrocycle in which two carboxylate anions of the H₂cbtc^2? ligand have assembled around each nickel center. The compound crystallizes in the triclinic system P-1 with a = 9.715(3) Å, b = 12.891(5) Å, c = 13.903(6) Å, α = 72.64(2)°, β = 75.70(3)°, γ = 73.27(3)°, V = 1566.6(10) ų, Z = 2. The electronic spectrum of 1 indicates a high-spin octahedral environment. The magnetic behavior of 1 reveals a weak intramolecular antiferromagnetic interaction with J = ?1.23(1) cm^?1.     

Lipid specificity and location of the sterol carrier protein-2 fatty acid-binding site: A fluorescence displacement and energy transfer study

Although it was recently recognized that sterol carrier protein-2 (SCP-2) interacts with fatty acids, little is known regarding the specificity of SCP-2 for long-chain fatty acids or branched-chain fatty-acid-like molecules. Likewise the location of the fatty-acid binding site within SCP-2 is unresolved. A fluorescent cis-parinaric acid displacement assay was used to show that SCP-2 optimally interacted with 14–22 carbon chain lipidic molecules: polyunsaturated fatty acids > monounsaturated, saturated > branched-chain isoprenoids > branched-chain phytol-derived fatty acids. In contrast, the other major fatty-acid binding protein in liver, fatty-acid binding protein (L-FABP), displayed a much narrower carbon chain preference in general: polyunsaturated fatty acids > branched-chain phytol-derived fatty acids > 14- and 16-carbon saturated > branched-chain isoprenoids. However, both SCP-2 and l-FABP displayed a very similar unsaturated fatty-acid specificity profile. The presence and location of the SCP-2 lipid binding site were investigated by fluorescence energy transfer. The distance between the SCP-2 Trp⁵⁰ and bound cis-parinaric acid was determined to be 40 Å. Thus, the SCP-2 fatty-acid binding site appeared to be located on the opposite side of the SCP-2 Trp⁵⁰. These findings not only contribute to our understanding of the SCP-2 ligand binding site but also provide evidence suggesting a potential role for SCP-2 and/or L-FABP in metabolism of branched-chain fatty acids and isoprenoids.     

Synthesis,Structure and Fluorescence Spectra Study of a Supramolecular Zinc(II) Complex

A new structural supramolecular zinc(II) complex (1), [Zn(H₂O)₆]²⁺[Zn(4,4′-bipy)(SO₄)₂(H₂O)₂]^2?[Zn(4,4′-bipy)(SO₄)(H₂O)₃] is synthesized in mixed solvent system at room temperature. The complex was characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. Structural analyses reveal that the complex is crystallized in the triclinic system with P1 space group. Cell parameters: a = 7.3145 (15) Å, b = 11.194 (2) Å, c = 11.442 (2) Å, α = 72.48 (3)°, β = 73.78 (3)°, γ = 83.39 (3)°, V = 857.3 (3) ų. Zn atoms (Zn1, Zn2 and Zn3) are all six-coordinated, however, the coordination environments of them are different. Owning to the abundant intro- and inter- hydrogen bonding interactions, the adjacent molecular units were connected to form a 2D supramolecular chain, and the two adjacent chains were furthermore linked to form a 3D supermolecular network structure via the hydrogen bonds. In addition, it is found that the complex has potential applications as fluorescent-emitting materials due to the strong fluorescence.     

Synthesis and structural refinement of fully dehydrated fully Zn<Superscript>2+</Superscript>-exchanged zeolite Y (FAU), |Zn<Subscript>35.5</Subscript>|[Si<Subscript>121</Subscript>Al<Subscript>71</Subscript>O<Subscript>384</Subscript>]-FAU

The single-crystal structure of |Zn_35.5|[Si₁₂₁Al₇₁O₃₈₄]-FAU per unit cell, a = 24.794(1), dehydrated at 673 K and 1 × 10^?6 Torr, has been determined by single-crystal X-ray diffraction techniques in the space group \( Fd\bar{3}m \) at 294(1) K. The structure was refined using all intensities to the final error indices (using the 930 reflections for which F _o > 4σ(F _o)) R ₁ = 0.0448 (based on F) and wR ₂ = 0.1545 (based on F ²). About 35.5 Zn²⁺ ions per unit cell are found at an unusually large number of crystallographic distinct positions, six. The 0.5 Zn²⁺ ion per unit cell is located at the center of double 6-ring (D6R, site I; Zn(I)-O(3) = 2.642(3) Å and O(3)-Zn(I)-O(3) = 81.23(12) and 98.77(12)°). Two different site-I′ positions (in the sodalite cavities opposite D6Rs) are occupied by 14 and 3 Zn²⁺ ions per unit cell, respectively; these Zn²⁺ ions are recessed 0.67 Å and 1.02 Å, respectively, into the sodalite cavities from their 3-oxygens plane (Zn(I′a)-O(3) = 2.094(3) Å, Zn(I′b)-O(3) = 2.23(5) Å, O(3)-Zn(I′a)-O(3) = 110.32(12)°, and O(3)-Zn(I′b)-O(3) = 100.9(30)°). Site-II′ positions (in the sodalite cavities opposite S6Rs) are occupied by 6 Zn²⁺ ions, each of which extends 0.63 Å into the sodalite cavities from their 3-oxygens plane (Zn(II′)-O(2) = 2.164(3) Å and O(2)-Zn(II′)-O(2) = 112.00(12)°). Twelve Zn²⁺ ions are found at two nonequivalent sites II (in the supercage) with occupancies of 7 and 5 ions, respectively; these Zn²⁺ ions are recessed 0.52 Å and 0.96 Å, respectively, into the supercage from their 3-oxygens plane (Zn(IIa)-O(2) = 2.138(12) Å, Zn(IIb)-O(2) = 2.28(4) Å, O(2)-Zn(IIa)-O(2) = 114.2(10)°, and O(2)-Zn(IIb)-O(2) = 103.7(25)°).     

Lanthanide(III) 1,4-Phenylenediacetate Complexes: The Relation Between the Structure and Thermal Properties

The series of isostructural lanthanide coordination polymers with the empirical formula [Ln₂(PDA)₃(H₂O)]·2H₂O, where PDA = 1,4-phenylenediacetate anion = [C₈H₈(COO)₂]^2?; Ln = La-Lu(III), and Y(III) were produced in the reaction of LnCl₃·nH₂O with ammonium salt of 1,4-phenylenediacetic acid in water solution. The compounds were characterised structurally using powder X-ray diffraction, elemental and thermogravimetric analyses as well as FT-IR spectroscopy. Thermogravimetric analyses show that in the range 60–170 °C the dehydration process occurs. The thermal stability of dehydrated compounds, Ln₂(PDA)₃ increased from about 200–350 °C in the whole series of complexes. Single-crystal X-ray diffraction analysis for the Gd(III) complex revealed that the compound crystallizes in the monoclinic P2₁/c space group with a = 21.863(2) Å, b = 10.035(1) Å, c = 13.854(1) Å, β = 91.53(1)° and V = 3,038.5(4) ų. The complex contains one-dimensional gadolinium-carboxylato chains, which are connected with the –CH₂–C₆H₄–CH₂– spacers of PDA ligand to the three-dimensional metal–organic framework.     

A Flexible Hexacarboxylate-Samarium(III) Metal–Organic Framework: Synthesis, Structure and Spectroscopic Properties

A new flexible triazine-based polycarboxylate metal–organic framework, [Sm₂(TTHA)(H₂O)₄]·9H₂O (I) (TTHA = 1,3,5-triazine-2,4,6-triamine hexaacetate), has been synthesized under hydrothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis and FT-IR spectroscopy. Crystal data for I are monoclinic C2/c, a = 12.6974(13) Å, b = 16.7309(12) Å, c = 14.8076(15) Å, β = 91.452(8)°, V = 3,144.7(5) Å³. Each Sm^III ion is 9-coordinate in a distorted tri-capped trigonal prismatic geometry; but, the principal inorganic building block is {Sm₂O₁₆}, which comprises two of these polyhedra that share an edge. The complex exhibits a three-dimensional open-framework structure of approximately 31 % void volume, which comprises two types of channels oriented in three directions; [0 0 1], [1 1 0] and [?1 1 0]. The network can be simplified into either the cooperite (pts) or anatase (ant) topologies depending on the choice of nodes. The UV–Vis spectra of the compound are dominated by the absorption of the TTHA ligand. Thermogravimetric analysis shows that the loss of channel and coordinated water upon heating occurs in two distinct steps.     

1D Ladder-Like Structure Motif Assembled from Edge-Sharing Rhombic Squares of Sm2Mo2 Based on [Mo(CN)8]4− and Sm3+ Ions as Building Blocks

Novel bimetallic 4d–4f complex, {Cs[Sm(MeOH)₃(DMF)(H₂O)Mo(CN)₈] · H₂O} _n (1) (DMF = N,N′-dimethylformamide) has been synthesized and structurally characterized. The crystal analyses shown that 1 exhibit a one-dimension (1D) infinite chain structure, which adopts a 1D ladder-like structure motif assembled from edge-sharing rhombic squares of Sm₂Mo₂, and that is the first structurally characterized example of a 1D ladder structure based on the [Mo(CN)₈]^4? and Sm³⁺ building blocks. The complex 1 crystallizes in triclinic, space group P-1, with a = 9.905(2), b = 10.333(2), c = 13.562(3) Å, α = 82.00(3)°, β = 86.62(3)°, γ = 65.76(3)°, V = 1253.5(4) Å³ and Z = 2. The magnetic behavior of 1 has also been studied in this paper.     

Synthesis,Characterization, Crystal Structure and Antimicrobial Evaluation of a Novel –M–X–M–X– Type Infinite Chain 1D Cu(II) Complex with Eflornithine Hydrochloride Hydrate as Ligand

A novel –M–X–M–X– type infinite chain 1D copper(II) complex of Eflornithine, Dichloro-[2-amino-5-ammonio-2-(difluoromethyl)pentanoate]copper(II) hydrate, [Cu(C₆H₁₂F₂N₂O₂)Cl₂]·H₂O 1 has been synthesized and characterized by elemental analysis, spectroscopic techniques (UV/Vis and FT-IR), TGA and X-ray diffraction. Single-crystal X-ray diffraction analysis of the complex 1 showed the structure to be monoclinic with space group Cc, a = 13.1295(15) Å, b = 12.1859(14) Å, c = 8.1927(9) Å, β = 118.359(3) Å, V = 1153.5(2) Å³, Z = 4. The complex exhibits a quadratic planar coordination of the Cu-atom. The Cu(II) centre is coordinated by two chloride atoms, an oxygen atom of the carboxyl- and a nitrogen atom of the amino-group, respectively, forming a quadratic planar geometry. The terminal amino group of the ligand is protonated to form NH₃ ⁺ while the carboxylic moiety is deprotonated to form Zwitterionic eflornithine ligand, with the coordination of the metal at the nitrogen atom of the second amino group. The compound has –M–X–M–X– infinite 1D chain polymeric structure. Two neigbouring Cu(EFL)Cl chain units are bridged by an Cl^? ion, forming a –Cu–Cl–Cu–Cl– linear chain structure along C-axis. The antibacterial activities of the complex on Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) were investigated and found to be active at higher concentration than the parent ligand.     

A Novel Boat-Shaped Rare Earth Complex with a 3-D Interlinked Structure of Pr(III) and 1,2,4,5-Benzenetetracarboxylic Acid

A novel boat-shaped praseodymium (III)-carboxylate polymeric complex [Pr(Hbtec)]_n (H₄btec = 1,2,4,5-benzenetetracarboxylic acid) with 3-D interlinked structure, which contains nine-coordinate rare earth metal centers, simplified as PRCPC, has been synthesized under hydrothermal conditions. The frames interlinked with each other and formed a unique boat-like alignment. PRCPC that was obtained was characterized by differential thermal analysis/thermogravimetry (DTA/TG), single crystal X-ray diffraction, elemental analysis and FTIR spectral analysis. Analysis of the single-crystal X-ray diffraction confirms that PRCPC crystallizes in triclinic symmetry with space group (P ? 1), where a = 7.325(3), b = 8.162(3), c = 8.791(3) Å, α = 65.345(4), β = 86.015(4), γ = 84.203(5)°, V = 475.0(3) Å³, Z = 2, R1 = 0.0201, wR2 = 0.0505. PRCPC exhibits high thermal stability and its supramolecular frame remains stable without any change under heat treatment to 510°C.     

Microwave Assisted Crystal Growth of a New Organic—Decavanadate Assembly: [V10O27(OH)] · 2(C6N2H14) · (C6N2H13) · (C6N2H12) · 2H2O

Microwave synthesis was used to grow single crystals of a new organic–inorganic supramolecular assembly, [V₁₀O₂₇(OH)] · 2(C₆N₂H₁₄) · (C₆N₂H₁₃) · (C₆N₂H₁₂) · 2H₂O, in a very short time compared to the conventional solution technique. In order to generate crystals suitable for single crystal experiments, an equimolar mixture of reactants and a few hours of microwave heating are required. Although non-merohedral twinning is an inherent problem, the crystal structure can be solved and refined in the orthorhombic space group Pna2 ₁ with a = 20.972(4) Å, b = 10.3380(14) Å, c = 20.432(3) Å, Z = 4, with an excellent result, R(F²) = 0.0431. The assembly is hydrogen bond-assisted and built up of the monoprotonated decavanadate and 1,4-diazabicyclo[2.2.2]octane of various degrees of protonation. The number and location of protons on both the inorganic and organic motifs govern the formation of the extensive hydrogen bonding network, which in turn regulates the assembly architecture.     

An Interesting Complex: [Cd(l -trp) (d-trp)] n

A novel coordination polymer [Cd(l-trp) (d-trp)] _n (where l-trp and d-trp are l-tryptophan and d-tryptophan or (S)-2-amino-3-(3-indolyl)propionic acid and (R)-2-amino-3-(3-indolyl)propionic acid) was prepared by a solvent-thermal method and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. The compound(monoclinic space group P2(1)/c with a = 19.759(2) Å, b = 5.2496(10) Å, c = 9.7594(16) Å, β = 97.2760(10)°, Z = 2) shows a two-dimensional plane structure. The crystallized coordination polymer has a centrosymmetric space group. Each Cd²⁺ ion coordinates with a pair of racemes, and the complex is a mesomer. Although l-trp was used, both l-trp and d-trp appear in the complex.     

Thresholds for Sterol-Limited Growth of Daphnia magna: A Comparative Approach Using 10 Different Sterols

Arthropods are incapable of synthesizing sterols de novo and thus require a dietary source to cover their physiological demands. The most prominent sterol in animal tissues is cholesterol, which is an indispensable structural component of cell membranes and serves as precursor for steroid hormones. Instead of cholesterol, plants and algae contain a variety of different phytosterols. Consequently, herbivorous arthropods have to metabolize dietary phytosterols to cholesterol to meet their requirements for growth and reproduction. Here, we investigated sterol-limited growth responses of the freshwater herbivore Daphnia magna by supplementing a sterol-free diet with increasing amounts of 10 different phytosterols and comparing thresholds for sterol-limited growth. In addition, we analyzed the sterol composition of D. magna to explore sterol metabolic constraints and bioconversion capacities. We show that dietary phytosterols strongly differ in their potential to support somatic growth of D. magna. The dietary threshold concentrations obtained by supplementing the different sterols cover a wide range (3.5–34.4 μg mg C^?1) and encompass the one for cholesterol (8.9 μg mg C^?1), indicating that certain phytosterols are more efficient in supporting somatic growth than cholesterol (e.g., fucosterol, brassicasterol) while others are less efficient (e.g., dihydrocholesterol, lathosterol). The dietary sterol concentration gradients revealed that the poor quality of particular sterols can be alleviated partially by increasing dietary concentrations, and that qualitative differences among sterols are most pronounced at low to moderate dietary concentrations. We infer that the dietary sterol composition has to be considered in zooplankton nutritional ecology to accurately assess potential sterol limitations under field conditions.     

One-pot template synthesis and crystal structure of two new polyaza copper(II) complexes

A new 14-membered hexazamacrocyclic copper(II) complex [Cu(H₂L¹)](ClO₄)₄(L¹=1,8-bis(2-aminoethyl)-1,3,6,8,10,13-hexaazacyclotetradecane) has been prepared by the one-pot reaction of ethylenediamine and formaldehyde in the presence of the Cu(II) ion. The crystal structure of [Cu(H₂L¹)](ClO₄)₄ was determined by X-ray diffraction. It crystallizes in the triclinic space group P−1 with a=12.118(2) Å, b=12.438(2) Å, c=12.466(2) Å, α=102.26(1)°, β=112.82(1)°, γ=111.51(1)°, and Z=2. The coordination geometry around the copper(II) ions is axially elongated octahedral with four nitrogen atoms of the macrocycle [Cu–N 2.012(7) Å for Cu(1) and 2.013(6) Å for Cu(2), average value] and two oxygen atoms of two ClO₄⁻ anions [Cu–O=2.550 Å for Cu(1) and 2.601(6) Å for Cu(2)]. [CuL²](ClO₄)₂(L²=3,7-bis(2-aminoethyl)-1,3,5,7-tetraazabicyclo[3,3,2]decane) with a novel tetraazabicyclic ligand was obtained from the same reaction system as an additional product. Crystal structure of [CuL²](ClO₄)₂: monoclinic space group Cc, a=16.393(3) Å, b=8.8640(18) Å, c= 13.085(3) Å, β=105.01(3)°, and Z=4.     

Improvement of the Structural Model for the M1 Phase Mo�CV�CNb�CTe�CO Propane (Amm)oxidation Catalyst

An improved structural model for the M1 phase in the Mo?CV?CNb?CTe?CO propane (amm)oxidation catalyst has been refined after accounting for a molybdenum-substituted-V₂O₅ impurity and by making adjustments based on aberration-corrected imaging results. The newly refined unit cell has Pba2 symmetry with a = 21.134(1) Å, b = 26.647(1) Å, c = 4.0140(2) Å, and Z = 4, in good agreement with our earlier findings (DeSanto et al. Top Catal 23:23 [20], DeSanto et al. Z Kristallogr 219:152 [22]). From the newly refined occupancies, the formula unit is {TeO}_0.86(1)·Mo_7.48(6)V_1.52(6)NbO₂₈. As in the earlier models, V is concentrated in sites that link the pentagonal rings of M1. Careful analysis of bond valences, in combination with the electroneutrality constraint, suggest that the linking sites S3, S4, and S7 all have mixed Mo/V occupancies and valences (d ¹/d ⁰). Furthermore, these sites may contain a mix of Mo⁵⁺ and V⁵⁺, which is consistent with the proposed catalytic mechanism in which V⁵⁺ plays an important role in propane activation.     

Crystal and Supramolecular Structure of a Novel Organotin Sulphate: {[(Ph3Sn)2SO4]2 · (H2O)3} · 2EtOH

A novel sulphate of organotin was synthesized by the reaction of triphenyltin chloride with silver sulphate. The structure of {[(Ph₃Sn)₂SO₄]₂ · H₂O)₃} · 2EtOH has been determined by X-ray crystallography. The crystal data parameters are as follows: monoclinic, space group Cc, a = 14.146(6), b = 23.844(11), c = 23.777(11) Å, Z = 4. The title compound displays a dimeric tetra-tin nuclear structure. The geometry about tin is trigonal bipyramidal with a trans-O₂SnC₃ stereochemistry about the metal. Hydrogen bonding between the oxygen atoms of the anion and the solvate water produces a graphite-like 3D network lattice.     

A solvothermal synthesis of a novel 1D ladder-like (NH3CH2CH2NH3)AgAsS4 containing N–H⋯S hydrogen bonding

A one-dimensional compound (NH₃CH₂CH₂NH₃)AgAsS₄ with ladder-like chains was synthesized solvothermally. This compound crystallizes in the monoclinic system, space group C2/c, with a=13.5805(8) Å, b=6.5331(3) Å, c=22.7711(9) Å, α=90°, β=106.42(3)°, γ=90°, Z=8. The rare type hydrogen bonding of N–H⋯S and electrostatic force hold the anionic chains together.