首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 32 毫秒
1.
2.
We use cryogenic ion vibrational spectroscopy to characterize the structure and fluxionality of the magic number boron cluster B13+. The infrared photodissociation (IRPD) spectrum of the D2‐tagged all‐11B isotopologue of B13+ is reported in the spectral range from 435 to 1790 cm−1 and unambiguously assigned to a planar boron double wheel structure based on a comparison to simulated IR spectra of low energy isomers from density‐functional‐theory (DFT) computations. Born–Oppenheimer DFT molecular dynamics simulations show that B13+ exhibits internal quasi‐rotation already at 100 K. Vibrational spectra derived from these simulations allow extracting the first spectroscopic evidence from the IRPD spectrum for the exceptional fluxionality of B13+.  相似文献   

3.
Singlet oxygen (1O2) plays an important role in oxidative stress in all types of organisms, most of them being able to mount a defense against this oxidant. Recently, zinc finger proteins have been proposed to be involved in its cellular detection but the molecular basis of this process still remains unknown. We have studied the reactivity of a Zn(Cys)4 zinc finger with 1O2 by combinations of spectroscopic and analytical techniques, focusing on the products formed and the kinetics of the reaction. We report that the cysteines of this zinc finger are oxidized to sulfinates by 1O2. The reaction of the ZnS4 core with 1O2 is very fast and efficient with almost no physical quenching of 1O2. A drastic (ca. five orders of magnitude) decrease of the Zn2+ binding constant was observed upon oxidation. This suggests that the Zn(Cys)4 zinc finger proteins would release their Zn2+ ion and unfold upon reaction with 1O2 under cellular conditions and that zinc finger sites are likely targets for 1O2.  相似文献   

4.
Zn11Rh18B8 and Zn10MRh18B8 with M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Si, Ge and Sn are obtained by reaction of the elemental components in sealed tantalum tubes at 1500 K. They crystallize tetragonally with Z = 2 in the spacegroup P4/mbm with lattice constants a = 1771.2(2) pm, c = 286.40(4) pm for Zn11Rh18B8 and in the range a = 1767.65(9) pm, c = 285.96(3) pm (Zn10NiRh18B8) to a = 1774.04(9) pm, c = 286.79(2) pm (Zn10SnRh18B8) for the quaternary compounds. According to powder photographs all compounds are isotypic. Struture determinations based on single crystal X-ray data were performed with Zn11Rh18B8, Zn10FeRh18B8 and Zn10NiRh18B8. The structure of Zn11Rh18B8 is related to the Ti3Co5B2 type. Along the short axis planar nets of rhodium atoms composed of triangles, squares, pentagons and elongated hexagons alternate with layers containing the boron and zinc atoms. The rhodium atoms form trigonal prisms centered by boron atoms, two kinds of tetragonal and pentagonal prisms centered by zinc atoms and elongated hexagonal prisms containing pairs of zinc atoms. In the quaternary compounds Zn10MRh18B8 the zinc atoms in one sort of tetragonal prisms are replaced by M atoms.  相似文献   

5.

The oxidation of 1,2-C2B10H12 (1) with 100% nitric acid was studied in two solvents (CH2C12 and CCl4). Under the action of superacid (CF3SO3H), the compound 9-HO-1,2-C2B10H11 (2) gives the onium cation 9-H2O+-1,2-C2B10H11 involved in the salt [9-H2O+-1,2-C2B10Hn]-CF3SO3?, as demonstrated by uB NMR spectroscopy. The experimental and simulated uB NMR spectra of the cation 9-H2O+-1,2-C2B10H11 are in satisfactory agreement with each other. In the presence of a base, compound 2 is transferred from an ethereal solution to an aqueous alkaline solution giving the anion 9-O?- 1,2-C2B10H11. The structure of compound 2 was confirmed by 1H, 11B, 11B1H, 11B-11B COSY NMR spectroscopy, IR spectroscopy, and gas chromatography mass spectrometry and was additionally established by X-ray diffraction.

  相似文献   

6.
Molecular dynamics (MD) simulations for Zif268 (a zinc‐finger‐protein binding specifically to the GC‐rich DNA)‐d(A1G2C3G4T5G6G7G8C9A10C11)2 and TATAZF (a zinc‐finger‐protein recognizing the AT‐rich DNA)‐d(A1C2G3C4T5A6T7A8A9A10A11G12G13)2 complexes have been performed for investigating the DNA binding affinities and specific recognitions of zinc fingers to GC‐rich and AT‐rich DNA sequences. The binding free energies for the two systems have been further analyzed by using the molecular mechanics Poisson‐Boltzmann surface area (MM‐PBSA) method. The calculations of the binding free energies reveal that the affinity energy of Zif268‐DNA complex is larger than that of TATAZF‐DNA one. The affinity between the zinc‐finger‐protein and DNA is mainly driven by more favorable van‐der‐Waals and nonpolar/solvation interactions in both complexes. However, the affinity energy difference of the two binding systems is mainly caused by the difference of van‐der‐Waals interactions and entropy components. The decomposition analysis of MM‐PBSA free energies on each residue of the proteins predicts that the interactions between the residues with the positive charges and DNA favor the binding process; while the interactions between the residues with the negative charges and DNA behave in the opposite way. The interhydrogen‐bonds at the protein‐DNA interface and the induced intrafinger hydrogen bonds between the residues of protein for the Zif268‐DNA complex have been identified at some key contact sites. However, only the interhydrogen‐bonds between the residues of protein and DNA for TATAZF‐DNA complex have been found. The interactions of hydrogen‐bonds, electrostatistics and van‐der‐Waals type at some new contact sites have been identified. Moreover, the recognition characteristics of the two studied zinc‐finger‐proteins have also been discussed. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011  相似文献   

7.
Synthesis, 11B NMR, Vibrational Spectra, and Crystal Structure of (PPh4)[1-(NO)B10H9] By reaction of (n-Bu4N)2[B10H10] in aqueous acetonitrile with NO2 a reaction mixture is formed from which [1-(NO)B10H9] has been isolated by ion exchange chromatography on diethylaminoethyl(DEAE) cellulose. The X-ray structure determination of (PPh4)[1-(NO)B10H9] (triclinic, space group P1, a = 7.6553(11), b = 13.179(2), c = 14.122(3) Å, α = 69.853(13), β = 82.445(14), γ = 87.230(13)°, Z = 2) reveals the coordination of the NO group via N in an apical position of the B10 cluster with B1–N = 1.457(5) and N–O = 1.101(4) Å. The 11B NMR spectrum exhibits the characteristic feature (1 : 1 : 4 : 4) of a in 1 position substituted B10 cluster with a strong downfield shift of the ipso-B atom at +6.5 ppm. The IR and Raman spectra show a strong NO stretching vibration at 2219 cm–1.  相似文献   

8.
Preparation and Characterization of Thiocyanate Derivatives of the Hydroborate Anions B10H102? and B12H122? The reaction of B10H102? or B12H122? with (SCN)2 in dichloromethane yields mixtures of thiocyanatohydroborates from which the pure isomers 1-and 2-(SCN)B10H92?, 1, 10-(SCN)2B10H82?, and 1-(SCN)B12H112? are isolated by ion exchange chromatography on diethylaminoethyl cellulose. The structures are determined by 11B and 11B{1H}NMR spectroscopy. There are characteristic chemical shifts due to apical and equatorial substituents, respectively. In B10H102? the substitution at apical positions is prefered. The IR and Raman spectra are similar to those of isosteric halogeno derivatives in the region of ν(BH) and of the borate cages. Because of the high frequencies of ν(CN): 2120–2140 cm?1 S coordination of SCN? is supposed.  相似文献   

9.
The closo‐undecaborate A2[B11H11] (A = NBzlEt3) can be halogenated with excess N‐chlorosuccine imide, bromine or iodine, respectively, to give the perhalo‐closo‐undecaborates A2[B11Hal11] (Hal = Cl, Br, I). The chlorination in the 11 : 1 ratio of the reagents yields A2[B11HCl10], whose subsequent iodination makes A2[B11Cl10I] available. The three type [B11Hal11]2– anions show only one and the two type [B11Cl10X]2– anions (X = H, I) only two 11B NMR peaks in the ratio 10 : 1, thus exhibiting the same degenerate rearrangement of the octadecahedral B11 skeleton as is well‐known for [B11H11]2–. The crystal structure analysis of A2[B11Br11] and A2[B11I11] reveals a rigid octadecahedral skeleton in the solid state, up to 330 K, whose B–B bond lengths deviate more or less from the idealized C2v gas phase structure, but are in good accordance with the distances of A2[B11H11]. Electrochemical experiments elucidate the mechanism of the known oxidation of [B11H11]2– to give [B22H22]2–: A first one‐electron transfer is followed by the dimerization of the [B11H11] monoanion, whereas neutral B11H11, a presumably most reactive species, does not play a role as an intermediate. The electrochemical oxidation of [B11Hal11]2– anions also starts with a one‐electron transfer, which is perfectly reversible only in the case of Hal = Br. There is no electrochemical indication for the formation of [B22Hal22]2–. The neutral species B11Hal11 should be a short‐lived, very reactive species.  相似文献   

10.
The first mixed calcium zinc borate with a new fundamental building block (FBB) [B8O17], Ca1.13Zn0.87B8O14 has been successfully synthesized. It exhibits two independent interpenetrating three-dimensional B−O anion networks constructed by [B8O17] groups, enriching the structural diversity of B−O configurations. In particular, the UV-Vis-NIR diffuse-reflectance spectrum shows that it has a short UV cutoff edge (<195 nm).  相似文献   

11.
The doping of graphene molecules by borazine (B3N3) units may modify the electronic properties favorably. Therefore, the influence of the substitution of the central benzene ring of hexa‐peri‐hexabenzocoronene (HBC, C42H18) by an isoelectronic B3N3 ring resulting in C36B3N3H18 (B3N3HBC) is investigated by computational methods. For comparison, the isoelectronic and isosteric all‐B/N molecule B21N21H18 (termed BN) and its carbon derivative C6B18N18H18 (C6BN), obtained by substitution of a central B3N3 by a C6 ring, are also studied. The substitution of C6 in the HBC molecule by a B3N3 unit results in a significant change of the computed IR vibrational spectrum between 1400 and 1600 cm?1 due to the polarity of the borazine core. The properties of the BN molecule resemble those of hexagonal boron nitride, and substitution of the central B3N3 ring by C6 changes the computed IR vibrational spectrum only slightly. The allowed transitions to excited states associated with large oscillator strengths shift to higher energy upon going from HBC to B3N3HBC, but to lower energy upon going from BN to C6BN. The possibility of synthesis of B3N3HBC from hexaphenylborazine (HPB) using the Scholl reaction (CuCl2/AlCl3 in CS2) is investigated. Rather than the desired B3N3HBC an insoluble and X‐ray amorphous polymer P is obtained. Its analysis by IR and 11B magic angle spinning NMR spectroscopy reveals the presence of borazine units. The changes in the 11B quadrupolar coupling constant CQ, asymmetry parameter η, and isotropic chemical shift δiso(11B) with respect to HPB are in agreement with a structural model that includes B3N3HBC‐derived monomeric units in polymer P. This indicates that both intra‐ and intermolecular cyclodehydrogenation reactions take place during the Scholl reaction of HPB.  相似文献   

12.
Preparation and Spectroscopic Characterization of the Monofluorohydro-closo-borates [B6H5F]2? and [B12H11F]2? By treatment of [B6H6]2? with 1-(chloromethyl)-4-fluoro-1,4-diazabicyclo[2.2.2]octane-bis(tetrafluoroborate)in acetonitrile monofluorohydro-closo-hexaborate [B6H5F]2? ( 1 ) is formed in good yields. [B12H12]2? reacts with unhydrous HF yielding the monofluorododecaborate [B12H11F]2? ( 2 ). These compounds are separated by ion exchange chromatography on diethylaminoethyl(DEAE) cellulose from by-products. The 11B nmr spectra exhibit the characteristic patterns (1 : 4 : 1) of a monosubstituted B6 octahedron and (1 : 5 : 5 : 1) of a monosubstituted B12 icosahedron with strong downfield shifts of the ipso-B nuclei at +9.3 ppm ( 1 ) and at +9.0 ppm ( 2 ). The 19F nmr spectra reveal quartets at ?212 ppm ( 1 ) and ?209 ppm ( 2 ) proving a B? F bonding. In the i.r. spectra, for ( 1 ) in the Raman spectrum too, cage vibrations depending on the F substituent at 1195 ( 1 ) and at 1182/1154 cm?1 ( 2 ) are observed. The Raman spectra show the B6F stretching mode at 535 cm?1 and the B12F stretching vibration at 445 cm?1.  相似文献   

13.
closo-Undecaborates were synthesized by the deprotonation of B11H13(SMe2) with LitBu in thp or K[BHEt3] in thf, [Li(thp)3]2[B11H11] and K2[B11H11] being obtained in 83 and 93% yield, respectively. K2[B11H11] can be transformed into A2[B11H11] with the corresponding ammonium chlorides in aqueous solution (A = [NMe3Ph], [NBzlEt3], [N(PPh3)2]). The crystal structure analysis of [Li(thp)3]2[B11H11] (space group P21/c) reveals a rather distorted octadecahedron for the [B11H11]2– anion, whereas the corresponding octadecahedron in [NBzlEt3]2[B11H11] (space group P212121) exhibits a structure close to C2v symmetry, expected for the free anion. The protonation of [B11H11]2– at low temperature gives [B11H12], whose structure could be elucidated by NMR methods; it is formed, apparently, by the opening of the B1–B4 edge of [B11H11]2– in the course of its known degenerate skeletal rearrangement, followed by the protonation of the B2–B4 edge. The reaction of [B11H12] with a second molecule of the acid HX (X = CF3COO) gives nido-[B11H13X]. The addition of BH3 to [B11H11]2– yields closo-[B12H12]2– under loss of H2. Two [B11H11]2– units are fused by the aid of FeCl3, with the known anion [B22H22]2– as the product, whose 11B-NMR signals could completely be assigned on the basis of Cs symmetry. The compound [NBzlEt3][N(PPh3)2][B22H22] crystallizes in the space group Pna21.  相似文献   

14.
15.
It is shown that fat-soluble vitamins A and E and water-soluble vitamins B (B1, B2, B6, and B12) can be separated by high-performance thin-layer chromatography using fractional elution. Benzene was used as the first mobile phase, and a 0.02 M aqueous micellar solution of sodium dodecyl sulfate was the second eluant.  相似文献   

16.
Preparation, 11B, 13C, 1H NMR and Vibrational Spectra of Monoethoxyhydro-closo-dodecaborate(2–), and the Crystal Structure of [(C5H5N)2CH2][B12H11(OC2H5)] By treatment of Na2[B12H12] with dry HF in ethanol Na2[B12H11(OC2H5)] is formed which has been separated by ion exchange chromatography on diethylaminoethyl(DEAE) cellulose from the starting compound and by-products. The X-ray structure determination of [(C5H5N)2CH2][B12H11(OC2H5)] (monoclinic, space group P21/m, a = 9.1906(3), b = 12.6612(8), c = 9.3640(12) Å, β = 112.947(6)°, Z = 2) reveals the complete ordering of the anion sublattice. The 11B nmr spectrum exhibits the characteristic feature (1:5:5:1) of a mono substituted B12 cage with a strong down-field shift of ipso-B at +6.5 ppm. In the 13C nmr spectrum a triplet at 67.9 ppm of the methylene group and a quartet at 19.5 ppm of the methyl group is observed. Correspondingly, the 1H nmr spectrum shows two multiplets at 3.7 and 1.3 as expected for an ethoxy substituent, and a multiplet at 2.1 ppm due to the protons of the boron cluster. The i.r. and Raman spectra exhibit strong CH stretching vibrations between 2 963 and 2 863 cm?1, and in the i.r. spectrum the CO and BO stretching frequencies of the B? O? C bridge are observed at 1 175 and 1 140 cm?1.  相似文献   

17.
Preparation, 11B NMR, Vibrational Spectra, and Crystal Structure of [(C5H5N)2CH2][1-(O2N)B10H9] By reaction of [B10H10]2? in aqueous acetonitrile with a saturated solution of NO2 in dichloromethane [1-(O2N) · B10H9]2? and [B10H9(NO)B10H9]3? are formed which can be separated by ion exchange chromatography on diethylaminoethyl(DEAE) cellulose from the starting compound. The X-ray structure determination of [(C5H5N)2CH2][1-(O2N)B10H9] (triclinic, space group P1 , a = 7.1530(9), b = 8.3753(8), c = 15.198(2) Å, α = 96.00(1), β = 95.48(1), γ = 95.60(1)°, Z = 2) reveals the coordination of the NO2 group via N with a B1? N distance of 1.535(5) Å and an O2? N? O1 angle of 119.3(3)°. The 11B NMR spectrum exhibits the characteristic feature (1 : 1 : 4 : 4) of an apical monosubstituted B10 cluster with a strong downfield shift of the ipso-B atom at +13.4 ppm. The IR and Raman spectra show strong NO stretching vibrations at 1381 und 1420 cm?1.  相似文献   

18.
《先进技术聚合物》2018,29(1):641-648
To explore the component synergistic effect of boron/phosphorus compounds in epoxy resin (EP), 3 typical boron compounds, zinc borate (ZB), boron phosphate (BPO4), and boron oxide (B2O3), blended with phosphaphenanthrene compound TAD were incorporated into EP, respectively. All 3 boron/phosphorus compound systems inhibited heat release and increased residue yields and exerted smoke suppression effect. Among 3 boron/phosphorus compound systems, B2O3/TAD system brought best flame‐retardant effect to epoxy thermosets in improving the UL94 classification of EP composites and also reducing heat release most efficiently during combustion. B2O3 can interact with epoxy matrix and enhance the charring quantity and quality, resulting in obvious condensed‐phase flame‐retardant effect. The combination of condensed‐phase flame‐retardant effect from B2O3 and the gaseous‐phase flame‐retardant effect from TAD effectively optimized the action distribution between gaseous and condensed phases. Therefore, B2O3/TAD system generated component synergistic flame‐retardant effect in epoxy thermosets.  相似文献   

19.
Li47B3P14N42, the first lithium nitridoborophosphate, is synthesized by two different routes using a Li3N flux enabling a complete structure determination by single‐crystal X‐ray diffraction data. Li47B3P14N42 comprises three different complex anions: a cyclic [P3N9]12−, an adamantane‐like [P4N10]10−, and the novel anion [P3B3N13]15−. [P3B3N13]15− is the first species with condensed B/N and P/N substructures. Rietveld refinement, 6Li, 7Li, 11B, and 31P solid‐state NMR spectroscopy, FTIR spectroscopy, EDX measurements, and elemental analyses correspond well with the structure model from single‐crystal XRD. To confirm the mobility of Li+ ions, their possible migration pathways were evaluated and the temperature‐dependent conductivity was determined by impedance spectroscopy. With the Li3N flux route we gained access to a new class of lithium nitridoborophosphates, which could have a great potential for unprecedented anion topologies with interesting properties.  相似文献   

20.
Structural Investigations on Cs2[B12H12] The crystal structure of Cs2[B12H12] has been determined from X‐ray single‐crystal data collected at room temperature. Dicesium dodecahydro‐closo‐dodecaborate crystallizes as colourless, face‐rich crystals (cubic, Fm 3; a = 1128.12(7) pm; Z = 4). Its synthesis is based on the reaction of Na[BH4] with BF3(O(C2H5)2) via the decomposition of Na[B3H8] in boiling diglyme, followed by subsequent separations, precipitations (with aqueous CsOH solution) and recrystallizations. The crystal structure is best described as anti‐CaF2‐type arrangement with the Cs+ cations in all tetrahedral interstices of the cubic closest‐packed host lattice of the icosahedral [B12H12]2–‐cluster dianions. The intramolecular bond lengths are in the range usually found in closo‐hydroborates: 178 pm for the B–B and 112 pm for the B–H distance. Twelve hydrogen atoms belonging to four [B12H12]2– icosahedra provide an almost perfect cuboctahedral coordination sphere to the Cs+ cations, and their distance of 313 pm (12 ×) attests for the salt‐like character of Cs2[B12H12] according to {(Cs+)2([B12H12]2–)}. The 11B{1H}‐NMR data in aqueous (D2O) solution are δ = –12,70 ppm (1JB–H = 125 Hz), and δ = –15,7 ppm (linewidth: δν1/2 = 295 Hz) for the solid state 11B‐MAS‐NMR.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号