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1.
The acid dissociation constant (pKa) of small, biological molecules is an important physical property used for investigating enzyme mechanisms and inhibitor design. For phosphorus-containing molecules, the 31P nuclear magnetic resonance (NMR) chemical shift is sensitive to the local chemical environment, particularly to changes in the electronic state of the molecule. Taking advantage of this property, we present a 31P NMR approach that uses inorganic phosphate buffer as an internal pH reference to determine the pKa values of the imide and second diphosphate of uridine-5′-diphosphate compounds, including the first reported values for UDP-GlcNAc and UDP-S-GlcNAc. New methods for using inorganic phosphate buffer as an internal pH reference, involving mathematical correction factors and careful control of the chemical shift reference sample, are illustrated. A comparison of the newly determined imide and diphosphate pKa values of UDP, UDP-GlcNAc, and UDP-S-GlcNAc with other nucleotide phosphate and thio-analogs reveals the significance of the monosaccharide and sulfur position on the pKa values.  相似文献   

2.
Single crystals of Y5Re2O12 have been grown, and the crystal structure has been determined by X-ray diffraction. This compound crystallizes in space group C2/m with cell dimensions of a=12.4081(10) Å b=5.6604(5)Å, c=7.4951(6) Å, β=107.837(3)°, Z=2. The final refinement led to R1=0.0238, WR2=0.0459 for 1053 observed reflections with F>4σ(F0). Edge-sharing ReO6 octahedra form infinite linear [ReO2O4/2]n chains along the b direction with alternating short and long Re-Re distances. Three crystallographically independent yttrium atoms surround O2 to form OY4 tetrahedra, which share edges and corners in the ab plane to form a two-dimensional Y5O4 network which separates the [ReO2O4/2]n magnetic chains. This compound is therefore isostructural with the series Ln5Re2O12Ln=Gd-Lu, which have been known since 1969. The average Re oxidation state is +4.5 in the chains and a reasonable, if qualitative MO scheme results in one unpaired electron per Re dimer. Consistent with this, magnetic susceptibility data can be fitted to the one-dimensional antiferromagnetic Heisenberg model with S=1/2 and parameters Jintra/k=−89(1)K, g=2.15(4) and χ(TIP)=5(1)×10−4 emu/mol. There is no sign of long-range magnetic order down to 2 K. These results are contrasted with those for the isostructural Y5Mo2O12.  相似文献   

3.
The subsolidus phase relations of R2O3-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca14−xRxCu24O41 (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca2+xR2−xCu5O10 (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca14−xRxCu24O41 possesses a layered orthorhombic structure and is isostructural to Sr14−xCaxCu24O41. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca2+xR2−xCu5O10 solid solution is isostructural to Ca2+xY2−xCu5O10, the structure of which is based on an orthorhombic “NaCuO2-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels.  相似文献   

4.
A detailed analysis of the 35Cl/37Cl isotope effects observed in the 19.11 MHz 103Rh NMR resonances of [RhCln(H2O)6−n]3−n complexes (n = 3–6) in acidic solution at 292.1 K, shows that the ‘fine structure’ of each 103Rh resonance can be understood in terms of the unique isotopologue and in certain instances the isotopomer distribution in each complex. These 35Cl/37Cl isotope effects in the 103Rh NMR resonance of the [Rh35/37Cl6]3− species manifest only as a result of the statistically expected 35Cl/37Cl isotopologues, whereas for the aquated species such as for example [Rh35/37Cl5(H2O)]2−, cis-[Rh35/37Cl4(H2O)2] as well as the mer-[Rh35/37Cl3(H2O)3] complexes, additional fine-structure due to the various possible isotopomers within each class of isotopologues, is visible. Of interest is the possibility of the direct identification of stereoisomers cis-[RhCl4(H2O)2], trans-[RhCl4(H2O)2], fac-[RhCl3(H2O)3] and mer-[RhCl3(H2O)3] based on the 103Rh NMR line shape, other than on the basis of their very similar δ(103Rh) chemical shift. The 103Rh NMR resonance structure thus serves as a novel and unique ‘NMR-fingerprint’ leading to the unambiguous assignment of [RhCln(H2O)6−n]3−n complexes (n = 3–6), without reliance on accurate δ(103Rh) chemical shifts.  相似文献   

5.
Vacuum ultraviolet (VUV) excitation and photoluminescent (PL) properties of Eu3+ and Tb3+ ion-doped aluminate phosphors, GdCaAl3O7:Eu3+ and GdCaAl3O7:Tb3+ have been investigated. X-ray diffraction (XRD) patterns indicate that the phosphor GdCaAl3O7 forms without impurity phase at 900 °C. Field emission scanning electron microscopy (FE-SEM) images show that the particle size of the phosphor is less than 3 μm. Upon excitation with VUV irradiation, the phosphors show a strong emission at around 619 nm corresponding to the forced electric dipole 5D07F2 transition of Eu3+, and at around 545 nm corresponding to the 5D47F5 transition of Tb3+. The results reveal that both GdCaAl3O7:RE3+ (RE=Eu, Tb) are potential candidates as red and green phosphors, respectively, for use in plasma display panel (PDP).  相似文献   

6.
Fluorine-19 and natural abundance 17O and 183W NMR spectroscopy were employed for the characterization of aqueous solutions of (NH4)2WO2F4 and (NH4)3WO3F3. Dissolution of the (NH4)2WO2F4 complex is accompanied by its partial acid hydrolysis to give the trans(mer)-dimer, [W2O5F6]4−, and unreacted cis-[WO2F4]2−. The cis(fac)-[W2O5F6]4− anion is the major soluble product resulting from the alkaline hydrolysis of (NH4)2WO2F4 along with the isolation of the solid (NH4)2WO3F2. In addition, the edge-bridging dimer, [W2O6F4]4−, and the cyclic trimer, [W3O9F6]6−, are also suggested as hydrolysis products. Decomposition of (NH4)3WO3F3 occurs in aqueous solution to give NH4WO3F.  相似文献   

7.
In attempts to synthesize lanthanide(III) nitride iodides with the formula M2NI3 (M=La-Nd), moisture-sensitive single crystals of the first quaternary sodium lanthanide(III) nitride iodides NaM4N2I7 (orthorhombic, Pna21; Z=4; a=1391-1401, b=1086-1094, c=1186-1211 pm) could be obtained. The dominating structural features are chains of trans-edge linked [NM4]9+ tetrahedra, which run parallel to the polar 21-axis [001]. Between the chains, direct bonding via special iodide anions generates cages, in which isolated [NaI6]5- octahedra are embedded. The IR spectrum of NaLa4N2I7 recorded from 100 to 1000 cm-1 shows main bands at υ=337, 373 and 489 cm-1. With decreasing radii of the lanthanide trications these bands, which can be assigned as an influence of the vibrations of the condensed [NM4]9+ tetrahedra, are shifted toward higher frequencies for the NaM4N2I7 series (M=La-Nd), following the lanthanide contraction.  相似文献   

8.
The phosphors NaGdFPO4:Ln3+ and GdPO4:Ln3+ (for Ln3+=Ce3+ and Tb3+) were prepared by solid-state reaction technique, the VUV-vis spectroscopic properties of the phosphors were investigated, and we vividly compare the luminescence of Ce3+ and Tb3+ in the hosts. For phosphors GdPO4:Ln3+, the band near 155 nm in VUV excitation spectrum is assumed to be the host-related absorption, and for NaGdFPO4:Ln3+ the absorption is moved to longer wavelength, near 170 nm, showing the P-O bond covalency increased after fluoridation. The f-d transitions of Ce3+ and Tb3+ in the host lattices are assigned and corroborated, and it was found that the 5d states are with lower energy in NaGdFPO4:Ln3+ than those in GdPO4:Ln3+. For fluoridation of GdPO4:Ln3+ to NaGdFPO4:Ln3+, the energy change of Ln3+ (Ln=Ce, Tb) 5d states is consistent with that of host-related absorption.  相似文献   

9.
The reactions of [RuH(CO)Cl(PPh3)3] with N,N-bis(salicylidine)-hydrazine (H2bsh) and N,N-bis(salicylidine)-p-phenylene diammine (H2bsp) in presence of KOH in methanol led in the formation of neutral mononuclear complexes with the formulations [RuH(CO)(PPh3)2(L)] (LHbsh or Hbsp). These present the first examples where the ligands H2bsh or H2bsp provide only two of its available donor sites for interaction with the metal centre. The complexes have been characterized by elemental analyses, FAB-MS, IR, 1H, 13C, 31P NMR and electronic spectral studies. Molecular structure of the representative complex [RuH(CO)(PPh3)2(Hbsh)] have been determined by single crystal X-ray analysis.  相似文献   

10.
The development of a disposal technique for the radiotoxic 137Cs in nuclear wastes is one of the most urgent issues in nuclear fuel technology. An effective disposal method of 137Cs is to immobilize it in a synthetic rock (SYNROC) material: cesium titanate hollandite, 137CsxTi8O16 (I4/m, , ). Practical applications of 137CsxTi8O16 have been restricted so far because the conventional synthetic method requires strong chemical reducers and reaction temperatures higher than 1250 °C. In this report, we present a milder preparation method of CsxTi8O16 by electrolysis of a mixture of Cs2MoO4 and TiO2 in ambient atmosphere at 900 °C. The Cs content in the resultant single-crystalline Cs1.35Ti8O16 is competitive with the highest value in polycrystalline Cs1.36±0.03Ti8O16 prepared by the conventional synthetic method. The electrochemical preparation of Cs1.35Ti8O16 is a promising way to immobilize a high quantity of 137Cs ions in a stable form of single-crystalline SYNROC.  相似文献   

11.
Most of the hydrogels deswell more remarkably in F containing solutions than in other monovalent anion containing solutions. However, significant deswelling followed by abnormal reswelling of polymer gel in KF solutions with increasing F concentration was observed in a series of polymer gels consisted of phenyl rings, for instance, poly(styrene sulfonic acid) (PSSA), hydroxypropyl methylcellulose phthalate (HPMCP) and poly(4-vinyl phenol) (P4VPh) gel. Driving force of this phenomenon was studied to reveal the specific interactions involved in the aqueous systems of aromatic polymers. Elemental analysis and XPS results suggest that F is embedded to the gel by the physical adsorption of KF, as well as the interactions between phenyl ring and F. Further theoretical calculations revealed that the interaction may be (phenyl)CH?F(H2O)n interaction, which is stronger than (phenyl)CH?(H2O)n hydrogen bond. This kind of interaction decreases with the increasing water number and it is invalid when the surrounding water number is more than 5 for the phenol-F(H2O)n system. Therefore, we conclude that F could bind to phenyl ring via such (phenyl)CH?F(H2O)n interaction in solutions with low hydrophilicity. The strong polarization effect of F and (phenyl)CH?F(H2O)n interaction are two important driving forces for the reswelling of gels.  相似文献   

12.
The experimental enthalpies of solution ΔsolHm, van’t Hoff enthalpies of sublimation ΔsgHm0 of solid compounds, partial molar volumes V20, and partial molar heat capacities Cp,20 of aqueous solutions of pyrimidine nucleic acid bases and their derivatives, determined previously and collected here, are discussed in terms of calculated structural parameters. Relations have been established between the calorimetric and volumetric properties. Correlations have been developed to relate both the enthalpies of solvation and the partial molar heat capacities to the polar and apolar parts of the accessible molecular surface areas.  相似文献   

13.
Sb/ZSM-5 was obtained by solid-state reaction with the mixture of Sb2O3 and zeolite HZSM-5 under a dry nitrogen flow at 773 K. Characterization of the treated zeolite was undertaken with XRD, 27Al MAS NMR, BET, TGA and FT-IR. The results revealed that part of the antimony oxides migrated into the channels of zeolite, and decreased the Brönsted acid sites in Sb/ZSM-5 remarkably. The other part of antimony oxides together with the amorphous alumino-silicate in the products distributed on the external surface of zeolite ZSM-5 and modified it, while the framework of ZSM-5 in crystal phase was retained. The structure of occluded antimony oxide inside the channels of ZSM-5 was studied by XRD Rietveld method. The result showed that their structure can be described as a chain of non-perfect [Sb5O5(H2O)2]n5n+, which is parallel to the straight channel of ZSM-5. There is about 0.6 [Sb5O5(H2O)2]5+ unit in every cell of the ZSM-5 on an average.  相似文献   

14.
In the system BaF2/BF3/PF5/anhydrous hydrogen fluoride (aHF) a compound Ba(BF4)(PF6) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF4)(PF6) crystallizes in a hexagonal space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å3 at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF4 and PF6 anions. In the analogous system with AsF5 instead of PF5 the compound Ba(BF4)(AsF6) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å3 at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF6 and four F atoms from BF4 anions. When the system BaF2/BF3/AsF5/aHF is made basic with an extra addition of BaF2, the compound Ba2(BF4)2(AsF6)(H3F4) was obtained. It crystallizes in a hexagonal P63/mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å3 at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF4, three AsF6 and three H3F4 anions. All F atoms, except the central atom in H3F4 moiety, act as μ2-bridges yielding a complex 3-D structural network.  相似文献   

15.
A series of spinel-type CoxNi1−xFe2O4 (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) magnetic nanomaterials were solvothermally synthesized as enzyme mimics for the eletroctrocatalytic oxidation of H2O2. X-ray diffraction and scanning electron microscope were employed to characterize the composition, structure and morphology of the material. The electrochemical properties of spinel-type CoxNi1−xFe2O4 with different (Co/Ni) molar ratio toward H2O2 oxidation were investigated, and the results demonstrated that Co0.5Ni0.5Fe2O4 modified carbon paste electrode (Co0.5Ni0.5Fe2O4/CPE) possessed the best electrocatalytic activity for H2O2 oxidation. Under optimum conditions, the calibration curve for H2O2 determination on Co0.5Ni0.5Fe2O4/CPE was linear in a wide range of 1.0 × 10−8–1.0 × 10−3 M with low detection limit of 3.0 × 10−9 M (S/N = 3). The proposed Co0.5Ni0.5Fe2O4/CPE was also applied to the determination of H2O2 in commercial toothpastes with satisfactory results, indicating that CoxNi1−xFe2O4 is a promising hydrogen peroxidase mimics for the detection of H2O2.  相似文献   

16.
We report the synthesis and elementary properties of the Co7Se8−xSx (x=0-8) and Ni7Se8−xSx (x=0-7) solid solutions. Both systems form a NiAs-type structure with metal vacancies. In general, the lattice parameters decrease with increasing x, but in the Ni7Se8−xSx system c increases on going from x=5 to 7. Magnetic susceptibility measurements show that all samples exhibit temperature-independent paramagnetism from 25-250 K. Samples within the Co7Se8−xSx system, as well as Ni7Se8 and Ni7SeS7, were found to be poor metals with resistivities of ∼0.20 and ∼0.06 mΩ cm at 300 K, respectively. The Sommerfeld constant (γ) was determined from specific heat measurements to be ∼13 mJ/molCoK2 and ∼7 mJ/molNiK2 for Co7Se8−xSx and Ni7Se8−xSx, respectively.  相似文献   

17.
Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La4Srn−4TinO3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)5Ti5O17] and [(La,Sr)6Ti6O20] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]p. The n=5 member is similar to the previously reported n=5 member of other AnBnO3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this AnBnO3n+2 series.  相似文献   

18.
The possible inclusion complexes of Cp2NbCl2 into calixarenes hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed by a combination of NMR, ab-initio calculations, thermogravimetric analysis, FTIR, Raman and PXRD. Ab-initio calculations, 1H NMR solution and solid state 13C CP-MAS NMR results demonstrated that p-sulfonic calix[6]arene does form an inclusion complex with Cp2NbCl2. Raman spectroscopy showed, for the inclusion compound of p-sulfonic calix[6]arene-Cp2NbCl2, a band between 500 and 850 cm−1 characteristic of Nb-O vibration. This result suggests that Nb(V) may engage in coordination with the oxygen of the sulfonate group, as part of the host-guest interaction. However, it is important to mention that the niobocene dichloride (Cp2NbCl2) dissolves in water and undergoes oxidation and hydrolysis processes to yield Cp2NbCl2(OH) species. For that reason this band does not exclude that the Nb-O band belongs to Cp2NbCl2(OH). Solid State 13C CP-MAS NMR and solution 1H NMR spectroscopies together with ab-initio results showed that Cp2NbCl2 is included in the p-sulfonic calix[6]arene cavity, with both Cp rings inside the cavity. In contrast, the solution 1H NMR results demonstrated that calix[6]arene does not form inclusion complex with Cp2NbCl2 in CDCl3 solution. Cp2NbCl2 is not included in the calix[6]arene cavity, possibly due to the lack of sulfonate heads which promote Nb-O interactions and assist the inclusion of Cp2NbCl2 into the cavity.  相似文献   

19.
A series of lithium europium double tungsto-molybdate phosphors LiEu(WO4)2−x(MoO4)x (x=0, 0.4, 0.8, 1.2, 1.6, 2.0) have been synthesized by solid-state reactions and their crystal structure, optical and luminescent properties were studied. As the molybdate content increases, the intensity of the 5D07F2 emission of Eu3+ activated at wavelength of 396 nm was found to increase and reach a maximum when the relative ratio of Mo/W is 2:0. These changes were found to be accompanied with the changes in the spectral feature, which can be attributed to the crystal field splitting of the 5D07F2 transition. As the molybdate content increases the emission intensity of the 615 nm peak also increases. The intense red-emission of the tungstomolybdate phosphors under near-UV excitation suggests them to be potential candidate for white light generation by using near-UV LEDs. In this study the effect of chemical compositions and crystal structure on the photoluminescent properties of LiEu(WO4)2−x(MoO4)x is investigated and discussed.  相似文献   

20.
Reaction of [Ru(Cp)(CH3CN)3](PF6) with P(o-tolyl)3 affords [Ru(Cp){(η6-o-tolyl)P(o-tolyl)2}](PF6) (4) in which the P-atom is not coordinated to the metal. The solid-state structure of 4 has been determined. A related reaction with P(p-tolyl)3 reveals a small quantity [Ru(Cp){(η6-p-tolyl)P(o-tolyl)2}](PF6), in solution, but mostly the expected bis-phosphine complex. Reaction of the Ru(IV) dication, [Ru(Cp)(η3-PhCHCHCH2)(DMF)2](PF6)2, with P(o-tolyl)3 gives a mixture of the phosphonium salt, C6H5CHCHCH2P(o-tolyl)3 (9) and the dication [Ru(Cp) (η6-C6H5CHCHCH2P(o-tolyl)3)](PF6)2 (10). Salt 9 forms via attack of the P-atom on the allyl ligand. The latter product results from complexation of 9 via the phenyl group of the former allyl ligand. It would seem that the sterically demanding P(o-tolyl)3 ligand is not readily compatible with the Ru(Cp) fragment, in either the +2 or +4 oxidation state. Detailed NMR studies are reported.  相似文献   

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