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991.
Pantarotto D Briand JP Prato M Bianco A 《Chemical communications (Cambridge, England)》2004,(1):16-17
Functionalised carbon nanotubes are able to cross the cell membrane and to accumulate in the cytoplasm or reach the nucleus without being toxic for the cell up to 10 [micro sign]M. 相似文献
992.
The kinetics of the inversion of configuration of a family of chiral oxonium ions, that is, O-protonated 1-aryl-1-methoxyethanes [YMe+], were investigated in two different gaseous media (in CH3X with X=F and X=Cl) at 720 torr of pressure and in the temperature range: 25-140 degrees C. The activation parameters of the [YMe+] inversion reaction were found to obey two different isokinetic relationships (IKR), depending on the nature and the position of the substituents in the oxonium ions and on the nature of the bulk gas employed. The observation of two IKR for the same family of reactions was related to a switchover in the resonant vibrational energy exchange between the reactants' critical mode, active in the transition state (omega), and the discrete vibrational levels v of the bulk gas. In CH3F, this vibrational-vibrational coupling switchover concerns the out-of-plane C-F...H-O bending) the phi family) and the H3C-F stretching (the gamma family) modes in the proton-bound [CH3F.YMe+] complex. In CH3Cl, the coupling switchover concerns the out-of-plane C-Cl...H-O bending (the phi family) and the H3C-Cl methyl group rocking (the gamma family) modes in the proton-bound [CH3Cl.YMe+] complex. The [YMe+] activation dynamics also determine the inversion dynamics. The [YMe+]ret<==>[YMe+]inv isomerization for the phi family involves the same "thermodynamically most favorable" transition state in both the CH3F and the CH3Cl media, whereas the same process for the gamma family proceeds through different, dynamically favored transition states. 相似文献
993.
Boiocchi M Bonizzoni M Fabbrizzi L Foti F Licchelli M Taglietti A Zema M 《Dalton transactions (Cambridge, England : 2003)》2004,(4):653-658
The nickel(II) complex with an open chain tetramine containing a piperazine fragment (1) displays an unusual resistance to demetallation in acidic solution and exhibits a lifetime of about five minutes in a solution 0.1 M in HClO4 and 7.0 M in NaClO4. Sluggishness with respect to the demetallation is ascribed to the occurrence of the boat-to-chair conformational conversion of the piperazine fragment, which implies the passage through the highly energetic half-boat transition state. The use of a high concentration of the inert electrolyte induces a 'salting out' effect on both thermodynamics (stability of metal complexes is enhanced) and kinetics (resistance to demetallation is increased). 相似文献
994.
Tegoni M Dallavalle F Belosi B Remelli M 《Dalton transactions (Cambridge, England : 2003)》2004,(9):1329-1333
The equilibria of copper(II) with (S)-glutamic-gamma-hydroxamic acid (H2L) were investigated in aqueous solution by different techniques: glass electrode potentiometry; calorimetry; VIS and CD spectrophotometry; and ES-MS. An unexpected pentacopper(II) 12-metallacrown-4 [Cu5L4H(-4)](2-) was detected, analogous to those well known formed by alpha- and beta-aminohydroxamic acids, but of lower stability. Another five species were found: [CuLH]+; [CuL2H2]; [Cu2L2]; [CuL2H]-; and [CuL2]2-. Their structures are proposed based on both spectroscopic and calorimetric data. 相似文献
995.
Tagmatarchis N Arcon D Prato M Shinohara H 《Chemical communications (Cambridge, England)》2002,(24):2992-2993
High-resolution 13C NMR has been used to structurally characterize a single isomer possessing C2 molecular symmetry as well as an inseparable mixture of other isomers of [92]fullerene, produced from dysprosium arc-burned soot, separated and isolated via multi-stage recycling HPLC. 相似文献
996.
997.
Full quantitative multiple-scattering analysis of X-ray absorption spectra: application to potassium hexacyanoferrat(II) and -(III) complexes 总被引:1,自引:0,他引:1
Hayakawa K Hatada K D'Angelo P Della Longa S Natoli CR Benfatto M 《Journal of the American Chemical Society》2004,126(47):15618-15623
A recently developed method to the full quantitative analysis of the XAS spectra extending from the absorption edge to the high-energy region is presented. This method is based on the use of two independent approaches to the analysis of the EXAFS and XANES data, the well-known GNXAS and the newly developed MXAN procedures. Herein, we report the application of this technique to two iron complexes of known structure where multiple-scattering effects are prominent, the potassium hexacyanoferrat(II) and -(III) crystals and aqueous solutions. The structural parameters obtained from refinements using the two methods are equal and compare quite well with crystallographic values. Small discrepancies between the experimental and calculated XANES spectra have been observed, and their origin has been investigated in the framework of non-muffin-tin correction. The ligand dependence of the theoretical spectra has been also examined. Analysis of the whole energy range of the XAS spectra has been found to be useful in elucidating both the type of ligands and the geometry of iron sites. These results are of particular use in studying the geometrical environment of metallic sites in proteins and complexes of chemical interest. 相似文献
998.
Dondi D Fagnoni M Molinari A Maldotti A Albini A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(1):142-148
Alkyl radical obtained by irradiation of tetrabutylammonium decatungstate in acetonitrile in the presence of cycloalkanes (C5H10, C6H12, C7H14) are efficiently trapped by electrophilic alkenes (acrylonitrile, isopropylydenmalonitrile, isopropylydencyanoacetate) to give the corresponding alkylated aliphatic nitriles. The reaction can be carried out up to complete conversion of the alkene with reasonable (in most cases 60-65 %) yields. Addition of the radicals to the alkene is followed by electron transfer from reduced decatungstate regenerating the sensitizer (turn over number up to 60). Steady-state measurements, EPR evidence, deuteration experiments and attempted intramolecular trapping of the adduct radical support the mechanistic proposal. 相似文献
999.
Adamus G Montaudo MS Montaudo G Kowalczuk M 《Rapid communications in mass spectrometry : RCM》2004,18(13):1436-1446
A series of aliphatic copolyesters was obtained from (R,S)-beta-butyrolactone and two isomeric hydroxy acids, 6-hydroxyhexanoic and (R,S)-2-hydroxyhexanoic acids. The reactions were conducted in bulk without catalyst. Electrospray ionization tandem mass spectrometry (ESI-MSn) was used for molecular characterization of these copolyester oligomers. The mass spectra of the copolyesters studied have enabled identification of their molecular structures including chemical nature of the end groups (hydroxyl and carboxylate). The compositions of the oligocopolyesters and their sequence distributions were determined based on measurement of the relative intensities of the individual oligocopolyester peaks in the ESI mass spectra. The mass spectra (MS1) provided information on composition and sequence distribution, and small deviations from Bernoulli statistics were detected. The arrangement of co-monomer structural units along the oligopolyester chains was verified by MS/MS experiments and investigation of the fragmentation pathways. 相似文献
1000.
In this paper we describe a family of locally conformal Kähler metrics on class 1 Hopf surfaces H a,ß containing some recent metrics constructed in [GO98]. We study some canonical foliations associated to these metrics, in particular a 2-dimensional foliation E a,ß that is shown to be independent of the metric. We prove with elementary tools that E a,ß has compact leaves if and only if a m=ß n for some integers m and n, namely in the elliptic case. In this case we prove that the leaves of E a,ß explicitly give the elliptic fibration of H a,ß, and we describe the natural orbifold structure on the leaf space. 相似文献