Quantum Size Effect and very localized random laser in ZnO@mesoporous silica nanocomposite following a two-photon absorption process

ZnO@mesoporous silica nanocomposite was prepared by the impregnation of a CMI-1 material in a Zn(NO₃)₂ solution followed by calcination under O₂. Intensive characterization was carried out by N₂ adsorption–desorption measurements, scanning and transmission electron microscopy. The optical properties of the ZnO@mesoporous silica nanocomposite were studied by photoluminescence spectroscopy. Quantum Size Effect was firstly demonstrated by subjecting the sample to a 254 nm excitation light, and was further confirmed by using a 680 nm excitation laser beam, which implies a two-photon absorption process. By focusing the 680 nm laser beam on different places in the sample, a very localized random laser effect, also induced by a two-photon absorption process, was detected.     

Atypical Lone Pair–π Interaction with Quinone Methides in a Series of Imido‐Ferrociphenol Anticancer Drug Candidates

Ferrociphenols, especially those possessing a heterocycle at the terminus of an aliphatic chain, display strong anticancer activity through a novel redox mechanism that generates active metabolites such as quinone methides (QMs). X‐ray crystallography and UV/Vis spectroscopy reveal that the specific lone pair (lp)–π interaction between a carbonyl group of the imide and the quinone motif of the QM plays an important role in the exceptional cytotoxic behaviour of their imido‐ferrociphenol precursors. This intramolecular lp–π interaction markedly enhanced the stability of the QMs and lowered the pK_a values of the corresponding phenol/phenolate couples. As the first example of such a non‐covalent interaction that stabilizes QMs remotely, it not only expands the scope of the lp–π interaction in supramolecular chemistry, but also represents a new mode of stabilization of a QM. This unprecedented application of lp–π interactions in imido‐ferrociphenol anticancer drug candidates may also have great potential in drug discovery and organocatalyst design.     

The Fe2(NO)2 Diamond Core: A Unique Structural Motif In Non‐Heme Iron–NO Chemistry

Non‐heme high‐spin (hs) {FeNO}⁸ complexes have been proposed as important intermediates towards N₂O formation in flavodiiron NO reductases (FNORs). Many hs‐{FeNO}⁸ complexes disproportionate by forming dinitrosyl iron complexes (DNICs), but the mechanism of this reaction is not understood. While investigating this process, we isolated a new type of non‐heme iron nitrosyl complex that is stabilized by an unexpected spin‐state change. Upon reduction of the hs‐{FeNO}⁷ complex, [Fe(TPA)(NO)(OTf)](OTf) ( 1 ), the N‐O stretching band vanishes, but no sign of DNIC or N₂O formation is observed. Instead, the dimer, [Fe₂(TPA)₂(NO)₂](OTf)₂ ( 2 ) could be isolated and structurally characterized. We propose that 2 is formed from dimerization of the hs‐{FeNO}⁸ intermediate, followed by a spin state change of the iron centers to low‐spin (ls), and speculate that 2 models intermediates in hs‐{FeNO}⁸ complexes that precede the disproportionation reaction.     

Long term changes in the distribution and delta(15)N values of individual soil amino acids in the absence of plant and fertiliser inputs

The long-term 'biodegradation' on soil amino acids was examined in the control plots of '42 parcelles' experiment, established in 1928 at INRA, Versailles (France). None of the plots is cultivated, but is kept free of weeds, and mixed to a depth of 25 cm twice yearly. Topsoil (0-10 cm depth) samples collected in 1929, 1963 and 1997 were subjected to acid hydrolysis (6 N HCl) for comparison. The distribution and delta(15)N natural abundance of 20 individual amino acids in the soils were determined, using ion chromatography (IC) and gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The total N and amino acid-N (AA-N), respectively, decreased by 54 % and 73 % in the period from 1929 to 1997. The average N loss was comparable for 1929-1963 (period 1) and 1963-1997 (period 2), but AA-N loss was three times faster in the former period. This significant reduction in total AA-N content was mirrored in the individual amino acids, which decreased by 74 % +/- 1 % (ranging 58-89 %) between 1929 and 1997. The bulk delta(15)N values generally increased from 1929 to 1997, mainly associated with comparable or even higher increase of delta(15)N of the non-AA-N in the soil. The residence time (t(1/2), time in which half of N was lost from a specific soil pool) was ca. 65 +/- 5 years for the bulk soil, and comparable for periods 1 and 2. However, between periods 1 and 2 it decreased from 128 to 41 years in the non-AA pool, but increased from 59 to 92 years in the AA-N pool. Proline and amino acids that appear early in soil microbial metabolic pathways (e.g. glutamic acid, alanine, aspartic acid and valine) had relatively high delta(15)N values. Phenylalanine, threonine, glycine and leucine had relatively depleted delta(15)N values. The average delta(15)N value of the individual amino acids (IAAs) increased by 1delta unit from 1929 to 1997, associated with a similar rise from 1929 to 1963, and no change thereafter till 1997. However, the delta(15)N values of phenylalanine decreased by more than 7delta(15)N units between 1929 and 1997. The delta(15)N shift of IAAs from 1929 to 1963 and from 1929 to 1997 was not influenced by the relative amount of N remaining compared with the 1929 soil concentrations. The only exception was phenylalanine which showed decreasing delta(15)N associated with its decreasing concentration in the soil. We conclude therefore that in the absence of plant and fertiliser inputs, no change in the delta(15)N value of individual soil amino acids occurs, hence the original delta(15)N values are preserved and diagnostic information on past soil N (cycling) is retained. The exception was phenylalanine, its delta(15)N decreased with decreasing concentration from 1929 to 1997, hence it acted as a 'potential' marker for the land use changes (i.e. arable cropping to a fallow). The long term biological processing and reworking of residual amino acids resulted in a (partial) stabilisation in the soil, evidenced by reduced N loss and increased residence time of amino acid N during the period 1963-1997.     

Interexperimental and interindividual variations of DNA repair capacities after UV-B and UV-C irradiations of human keratinocytes and fibroblasts

DNA repair plays a central role in the cellular response to UV. In this work we have studied the response of skin cells (i.e. fibroblasts and keratinocytes) from the same or from different individuals after both ultraviolet-B (UV-B) and ultraviolet-C (UV-C) irradiations using the comet assay to characterize the specific cellular response to UV-induced DNA damage. Cells were irradiated with increasing doses of UV-B or UV-C. To study the UV dose dependency of initial steps of DNA repair, namely recognition and incision at DNA damage level, the comet assay was performed, under alkaline conditions, 60 min after UV irradiation to allow detection of DNA strand breaks. Comparative analysis of tail moment values after UV exposure of cells from the same or from different individuals showed interexperimental and interindividual variations, implying that repeated assays are necessary to characterize the individual DNA repair capacity. With increasing doses of UV in keratinocytes, a plateau was rapidly reached after irradiation, whereas in fibroblasts a linear dose-effect relationship was observed. These interindividual variations associated with cellular specificity in DNA response may be of significance in skin cell and individual susceptibility toward UV-induced carcinogenesis.     

The reaction of GeCl4 with primary and secondary phosphines

Reaction of GeCl4 and CyPH2 leads to a range of products from which crystals of [CyPH3]+[GeCl3]- have been obtained. The major intermediate in this reaction, Cy(H)PGeCl3, can be obtained as the dominant product only when an excess of GeCl4 is used in the preparation. Similarly, crystals of [Ph2PH2]+[GeCl3]- have been obtained from reaction of Ph2PH and GeCl4(1 : 1). The structures of both primary and secondary phosphonium cations are reported. Aerosol-assisted and low-pressure chemical vapour deposition experiments using Cy(H)PGeCl3 as precursor lead to the deposition of thin films containing both germanium and phosphorus, contaminated with large amounts of oxygen. GeP has been identified as components of the film from bandgap measurements.     

Spatial and temporal feedback control of traveling wave solutions of the two-dimensional complex Ginzburg-Landau equation

Previous work has shown that Benjamin-Feir unstable traveling waves of the complex Ginzburg-Landau equation (CGLE) in two spatial dimensions cannot be stabilized using a particular time-delayed feedback control mechanism known as ‘time-delay autosynchronization’. In this paper, we show that the addition of similar spatial feedback terms can be used to stabilize such waves. This type of feedback is a generalization of the time-delay method of Pyragas [K. Pyragas, Continuous control of chaos by self-controlling feedback, Phys. Lett. A 170 (1992) 421-428] and has been previously used to stabilize waves in the one-dimensional CGLE by Montgomery and Silber [K. Montgomery, M. Silber, Feedback control of traveling wave solutions of the complex Ginzburg Landau equation, Nonlinearity 17 (6) (2004) 2225-2248]. We consider two cases in which the feedback contains either one or two spatial terms. We focus on how the spatial terms may be chosen to select the direction of travel of the plane waves. Numerical linear stability calculations demonstrate the results of our analysis.     

Effect of metals on herbicides-alpha-synuclein association: a possible factor in neurodegenerative disease studied by capillary electrophoresis

The aggregation of alpha-synuclein in the dopaminergic neurons of the substantia nigra is a critical step in the Parkinson's disease (PD). The etiology of the disease is unknown but recent epidemiological and experimental studies have renewed interest in the hypothesis that environmental factors, especially herbicides and metals, have a role on the pathogenesis of PD. For the first time, the association constants of alpha-synuclein with five herbicides have been calculated using a capillary electrophoresis (CE) method. In addition, the effect of a number of metals on this binding has been investigated. It appears that the herbicides preferentially bind to a partially folded intermediate conformation of alpha-synuclein induced by manganese, aluminium, cadmium, copper and zinc. Then, metal increases the synuclein-herbicide association. However, this study shows contrasting actions with the antibiotic rifampicin and magnesium addition leading to a decrease of the alpha-synuclein-herbicide interaction even if other metals are present in the bulk solvent. Considering epidemiological studies, all these results suggest an underlying molecular basis for PD and related body diseases.     

Spatially resolved Suzuki coupling reaction initiated and controlled using a catalytic AFM probe

Appropriately modified proximal probes can be utilized in the spatially resolved chemical coupling of surface-bound and solution-phase reagents. Herein we report a chemically specific Suzuki coupling reaction between a surface-confined aryl bromide and boronic acid reagents in solution achieved using a catalytic AFM probe.