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121.
Wang Y Urban C Rodríguez-Fernández J Gallego JM Otero R Martín N Miranda R Alcamí M Martín F 《The journal of physical chemistry. A》2011,115(45):13080-13087
Formation of self-assembled chains of tetrathiafulvalene (TTF) on the Cu(100) surface has been investigated by scanning tunneling microscopy and density functional theory calculations that include semiempirical van der Waals (vdW) interaction corrections. The calculations show that the chain structures observed in the experiments can only be explained by including the vdW interactions. The molecules are tilted along the chain in order to achieve maximal intermolecular interaction. The chains are metastable on the surface, which is consistent with the experimental observation that they disappear after annealing. The fact that all TTF chains observed in the experiment are short might be possibly explained by the interplay between the stabilizing vdW molecule-molecule interaction and the destabilizing rearrangement of surface atoms due to the strong molecule-substrate interaction. 相似文献
122.
Murtaza G Badshah A Said M Khan H Khan A Khan S Siddiq S Choudhary MI Boudreau J Fontaine FG 《Dalton transactions (Cambridge, England : 2003)》2011,40(36):9202-9211
A series of N,N',N'-trisubstituted guanidines (1-6) and their copper(II) complexes, [κ(2)(O,N)-C(6)H(5)CONHC(NHC(6)H(4)Cl)NR](2)Cu(ii) (R = iso-propyl (1a), n-butyl (2a), sec-butyl (3a), tert-butyl (4a), benzyl (5a), and para-tolyl (6a)) were synthesized and characterized using elemental analysis, FTIR and NMR spectroscopy. DFT studies were used to assess the location of the protons in the free ligands. However, calculations have shown that, in all cases, hydrogen bonding from either N-H group gives conformations that are very similar in energy. Single crystal XRD studies were used to characterize ligands 1 and 4 and the related complexes 1a and 4a. The structures reveal that these complexes are mononuclear in the solid state and that copper adopts a regular square planar geometry. In both metallic species, the N, N', N'-trisubstituted guanidine ligands chelate the Cu(II) atom using the oxygen and one nitrogen. The synthesized compounds were investigated for urease inhibition using thiourea as a standard drug. Most complexes exhibit a better activity than the respective guanidines and compound 1a was found to be the most active with IC(50) = 9.83 ± 0.07 μM (the IC(50) for thiourea is 21.0 ± 0.1 μM). The species were also screened for their anti-leishmanial activity. However, all of the compounds were devoid of any significant activity. 相似文献
123.
Varela-Álvarez A Sordo JA Piedra E Nebra N Cadierno V Gimeno J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(38):10583-10599
A general mechanism to rationalize Ru(IV) -catalyzed isomerization of the C=C bond in O-allylic substrates is proposed. Calculations supporting the proposed mechanism were performed at the MPWB1K/6-311+G(d,p)+SDD level of theory. All experimental observations in different solvents (water and THF) and under different pH conditions (neutral and basic) can be interpreted in terms of the new mechanism. Theoretical analysis of the transformation from precatalyst to catalyst led to structural identification of the active species in different media. The experimentally observed induction period is related to the magnitudes of the energy barriers computed for that process. The theoretical energy profile for the catalytic cycle requires application of relatively high temperatures, as is experimentally observed. Participation of a water molecule in the reaction coordinate is mechanistically essential when the reaction is carried out in aqueous medium. The new mechanistic proposal helped to develop a new experimental procedure for isomerization of allyl ethers to 1-propenyl ethers under neutral aqueous conditions. This process is an unique example of efficient and selective catalytic isomerization of allyl ethers in aqueous medium. 相似文献
124.
125.
Elisana Afonso Moura Lidiane Pinto Correia Márcia Ferraz Pinto José Valdilânio Virgulino Procópio Fábio Santos de Souza Rui Oliveira Macedo 《Journal of Thermal Analysis and Calorimetry》2010,100(1):289-293
This article had studied the thermal characterization of the raw material and different fluconazole crystals, obtained through
recrystallization with different solvents using thermoanalytical techniques (TG, DTA, DSC-50, DSC Photovisual, DSC-60) and
Pyr-GC/MS. The results confirmed that the fluconazole volatilizes without decomposition until 250 °C. Pyr-GC/MS showed hexachlorobenzene
like impurities in fluconazole raw material. 相似文献
126.
José Luis Martínez-Hernández Marco Arnulfo Mata-Gómez Cristóbal Noé Aguilar-González Anna Ilyina 《Applied biochemistry and biotechnology》2010,160(7):2045-2053
The production of extracellular and mycelia-associated penicillin G acylase (maPGA) with Mucor griseocyanus H/55.1.1 by surface-adhesion fermentation using Opuntia imbricata, a cactus, as a natural immobilization support was studied. Enzyme activity to form 6-aminopencillanic acid (6-APA) from
penicillin G was assayed spectrophotometrically. The penicillin G hydrolysis to 6-APA was evaluated at six different times
using PGA samples recovered from the skim milk medium at five different incubation times. Additionally, the effect of varying
the penicillin G substrate concentration level on the PGA enzyme activity was also studied. The maximum reaction rate, V
max, and the Michaelis constant, K
M, were determined using the Michaelis–Menten model. The maximum levels for maPGA and extracellular activity were found to
be 2,126.50 international unit per liter (IU/l; equal to 997.83 IU/g of support) at 48 h and 755.33 IU/l at 60 h, respectively.
Kinetics of biomass production for total biomass showed a maximum growth at 60 h of 3.36 and 2.55 g/l (equal to 0.012 g of
biomass per gram of support) for the immobilized M. griseocyanus biomass. The maPGA was employed for the hydrolysis of penicillin G to obtain 6-APA in a batch reactor. The highest quantity
of 6-APA obtained was 226.16 mg/l after 40-min reaction. The effect of substrate concentration on maPGA activity was evaluated
at different concentrations of penicillin G (0–10 mM). K
M and V
max were determined to be 3.0 × 10−3 M and 4.4 × 10−3 mM/min, respectively. 相似文献
127.
Dr. José A. González-Delgado Dr. Miguel A. Romero Dr. Francisco Boscá Dr. Jesús F. Arteaga Prof. Dr. Uwe Pischel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(62):14229-14235
The light-gated organocatalysis via the release of 4-N,N-dimethylaminopyridine (DMAP) by irradiation of the [Ru(bpy)2(DMAP)2]2+ complex with visible light was investigated. As model reaction the acetylation of benzyl alcohols with acetic anhydride was chosen. The pre-catalyst releases one DMAP molecule on irradiation at wavelengths longer than 455 nm. The photochemical process was characterized by steady-state irradiation and ultrafast transient absorption spectroscopy. The latter enabled the observation of the 3MLCT state and the spectral features of the penta-coordinated intermediate [Ru(bpy)2(DMAP)]2+. The released DMAP catalyzes the acetylation of a wide range of benzyl alcohols with chemical yields of up to 99 %. Control experiments revealed unequivocally that it is the released DMAP which takes the role of the catalyst. 相似文献
128.
Barco-Bonilla N Romero-González R Plaza-Bolaños P Fernández-Moreno JL Frenich AG Vidal JL 《Analytica chimica acta》2011,693(1-2):62-71
The objective of this study was the optimization and comparison of two extraction methods for the determination of polycyclic aromatic hydrocarbons (PAHs) in wastewater (WW). A distribution study of the target compounds between the aqueous phase and the suspended particulate matter (SPM) has been performed in order to establish whether the analysis of both phases is necessary. In this sense, the feasibility of stir bar sorptive extraction (SBSE) and solid-phase extraction (SPE) for the determination of 24 PAHs in WW samples has been evaluated. The results demonstrated the suitability of SBSE to perform a comprehensive analysis of liquid samples containing high amounts of SPM, such as in the determination of PAHs in WWs. A gas chromatography triple quadrupole mass spectrometry (GC-QqQ-MS/MS) method has been also optimized for the separation and detection of the target compounds, avoiding the co-elution of some groups of isomers, such as benzo[b], [j] and [k] fluoranthenes and indene[1,2,3-cd]pyrene/dibenz[a,h]anthracene. For that purpose, a specific capillary column developed for PAH determination was used. The SBSE procedure was validated and adequate parameters (such as recovery, linearity, precision, limits of detection and quantification) were obtained. Finally, the validated method was applied to the analysis of real samples collected from an experimental WW treatment plant, detecting some PAHs at concentrations in the range 0.007-0.022 μg L(-1). 相似文献
129.
Manzano R Andrés JM Álvarez R Muruzábal MD de Lera ÁR Pedrosa R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(21):5931-5938
A series of chiral thioureas derived from easily available diamines, prepared from α-amino acids, have been tested as catalysts in the enantioselective Michael additions of nitroalkanes to α,β-unsaturated ketones. The best results are obtained with the bifunctional catalyst prepared from L-valine. This thiourea promotes the reaction with high enantioselectivities and chemical yields for aryl/vinyl ketones, but the enantiomeric ratio for alkyl/vinyl derivatives is very modest. The addition of substituted nitromethanes led to the corresponding adducts with excellent enantioselectivity but very poor diastereoselectivity. Evidence for the isomerization of the addition products has been obtained from the reaction of chalcone with [D(3)]nitromethane, which shows that the final addition products epimerize under the reaction conditions. The epimerization explains the low diastereoselectivity observed in the formation of adducts with two adjacent tertiary stereocenters. Density functional studies of the transition structures corresponding to two alternative activation modes of the nitroalkanes and α,β-unsaturated ketones by the bifunctional organocatalyst have been carried out at the B3LYP/3-21G* level. The computations are consistent with a reaction model involving the Michael addition of the thiourea-activated nitronate to the ketone activated by the protonated amine of the organocatalyst. The enantioselectivities predicted by the computations are consistent with the experimental values obtained for aryl- and alkyl-substituted α,β-unsaturated ketones. 相似文献
130.
In this work we have explored the performance of two functions, recently proposed by Ayers [J. Chem. Sci., 2005, 117, 441], with the purpose of quantifying local electron localization. The first function, ζ(h), measures the total fluctuation per electron in the number of electrons at a given position r(1), while the second one, ζ(R), is a local representation of the minimum fluctuation criterion for electron localization. The study is carried out through a set of diatomic molecules that covers a wide range of covalent/polar character. Additionally, we have also calculated the electron localization function and the exchange-correlation hole along the internuclear axis. We have found that, for all the studied molecules, the numerical integration involved in computing ζ(h) did not converge. We think that this is so because the hole correlation calculations are not able to yield its correct asymptotic decaying behavior for large absolute values of the internuclear distances. On the other hand, the calculation of ζ(R) has proved to be feasible, and the information obtained from it has been concluded to be compatible to that rendered by the electron localization function (ELF) and the exchange-correlation density. Moreover, it has been also found that the results for ζ(R) allow to quantify the relative degree of electron localization within different molecular regions. 相似文献