The oxidation of alkanes and arylalkanes by KMnO(4) in CH(3)CN is greatly accelerated by the presence of just a few equivalents of BF(3), the reaction occurring readily at room temperature. Carbonyl compounds are the predominant products in the oxidation of secondary C-H bonds. Spectrophotometric and kinetics studies show that BF(3) forms an adduct with KMnO(4) in CH(3)CN, [BF(3).MnO(4)](-), which is the active species responsible for the oxidation of C-H bonds. The rate constant for the oxidation of toluene by [BF(3).MnO(4)](-) is over 7 orders of magnitude faster than by MnO(4)(-) alone. The kinetic isotope effects for the oxidation of cyclohexane, toluene, and ethylbenzene at 25.0 degrees C are as follows: k(C6H12)/k(C6D12) = 5.3 +/- 0.6, k(C7H8)/k(C7D8) = 6.8 +/- 0.5, k(C8H10)/k(C8D10) = 7.1 +/- 0.5. The rate-limiting step for all of these reactions is most likely hydrogen-atom transfer from the substrate to an oxo group of the adduct. A good linear correlation between log(rate constant) and C-H bond energies of the hydrocarbons is found. The accelerating effect of BF(3) on the oxidation of methane by MnO(4)(-) has been studied computationally by the Density Functional Theory (DFT) method. A significant decrease in the reaction barrier results from BF(3) coordination to MnO(4)(-). The BF(3) coordination increases the ability of the Mn metal center to achieve a d(1) Mn(VI) electron configuration in the transition state. Calculations also indicate that the species [2BF(3).MnO(4)](-) is more reactive than [BF(3).MnO(4)](-). 相似文献
Treatment of the allenylcarbene complex OsCl2(=CPh-CH=C=CHPh)(PPh3)2 with (PPh3)AuCCR in the presence of HNEt3Cl in CH2Cl2 produces osmabenzynes Os(CC(R)=C(CH2Ph)CH=CPh)Cl2(PPh3)2. 相似文献
Tissue engineering involves culturing, growing and assembling cells and newly generated matrix in polymeric scaffolds. To achieve a functional tissue in vitro, the cell-scaffold constructs are subjected to various stimulations during an incubation phase, which mimics the in vivo environment. In order to monitor the progression of tissue formation, there is a need for on-line and non-destructive methods of monitoring at the cellular and biomolecular level, for example, the assessment of scaffold degradation alongside the measure of matrix production. This study presents a proof of concept for monitoring scaffold degradation on-line within a culture environment. Using a mesoporous silica based approach, a pH sensitive fluorescent probe, fluorescein isothiocyanate (FITC), was incorporated into degradable polymeric scaffolds made from poly(L-lactic acid) which has a slow degradation rate, and poly(lactide-co-glycolide) which has a rapid degradation rate. The fluorescent probe was incorporated into thin films and three dimensional porous scaffolds demonstrating the capabilities of monitoring on-line. Following incubation, the intensity of fluorescence in the rapidly degrading scaffolds reduced with culture time in comparison to slow degrading polymeric scaffolds when observed qualitatively using fluorescent microscopy. The relationship between pH and fluorescent intensity was assessed, and the use of this technique for monitoring by-products via the solid scaffold by microscopy or through culture medium by a luminescence spectrometer is discussed. This study demonstrates that endowing scaffolds with a sensing element could provide an on-line and non-destructive monitoring method for tissue engineering. 相似文献
Summary: A new strategy was developed to prepare disorderly exfoliated nanocomposites, in which a soft siloxane surfactant with a weight‐average molecular weight ( ) of 1 900 was adopted to modify the clay. The modified clay slurry was then mixed with silicone rubber by hand, and exfoliation was achieved. The proposed mechanism thereof was verified by TEM and XRD. The physical entanglement of the soft siloxane surfactant plays a vital role in the diffusion and intercalation of the matrix molecules during the compounding of the slurry‐polymer mixture. This simple method is applicable to other silicone‐based materials reinforced by clay.
TEM micrograph of silicone rubber/clay‐sil nanocomposite. 相似文献
Neurofurans (NeuroFs) and dihomo‐isofurans (dihomo‐IsoFs) are produced in vivo by non‐enzymatic free‐radical pathways from docosahexaenoic and adrenic acids, respectively. As these metabolites are produced in minute amounts, their analyses in biological samples remain challenging. Syntheses of neurofuran and dihomo‐isofurans described are based on a pivotal strategy, thanks to an enantiomerically enriched intermediate, which allowed, for the first time, access to both families: the alkenyl and enediol. Owing to this formation, quantitation of specific NeuroF and dihomo‐IsoFs in biological samples was attainable. 相似文献
The development of molecular frameworks derived from binuclear platinum(II) aromatic Schiff base (salphen) complexes and their supramolecular chemistry have been undertaken. A series of axially rotating (Pt‐salphen)2 luminophores, tethered in a cofacial manner by a rigid linker (xanthene, 1 ; dibenzofuran, 2 ; biphenylene, 3 ), was synthesized in which the O(salphen) groups are potentially amenable for guest‐binding. The molecular structures of 1 and 3 have been determined by X‐ray crystallography, revealing intra‐ and intermolecular π‐stacking interactions, as well as contrasting syn ( 1 ) and anti ( 3 ) configurations, for the (Pt‐salphen)2 moiety. All complexes are luminescent in solution at room temperature. Their photophysical and solvatochromic properties have been examined, and the emissions are assigned to mixed triplet O(p)/Pt(d)→π*(diimine) excited states. The red‐shifted fluid emissions and lower quantum yields of 1 and 3 , relative to 2 , are ascribed to enhanced intramolecular π‐stacking interactions. Photophysical changes and selective responses to metal ions (particularly Pb2+) have been investigated by using various spectroscopic methods and DFT calculations, and through comparative studies with control complexes. A plausible binding mechanism is proposed based on occupation of the O(salphen)‐binding cavity, which induces perturbation of intramolecular π–π interactions, and hence the self‐quenching and emission properties, of the (Pt‐salphen)2 unit. 相似文献