The reactivity of the sulfur‐containing nucleoside 4‐thio‐(2′‐deoxy)‐thymidine usually abbreviated as 4‐thio‐thymidine, (S4‐TdR) under Fenton conditions, ie, in the presence of H2O2 and catalytic amounts of Fe(II), was investigated by UV‐vis spectroscopy and electrospray ionization single and tandem mass spectrometry (ESI‐MS and MS/MS). S4‐TdR hydroxylated on the S atom was found to be a key reaction intermediate, ultimately leading to (2′‐deoxy)‐thymidine usually abbreviated as thymidine, (TdR) as the main reaction product. This finding was in accordance with the outcome of the reaction between S4‐TdR and H2O2, previously investigated in our laboratory. On the other hand, the additional presence of ?OH radicals, induced by the Fe(II)/H2O2 combination, led to the increased generation of another interesting S4‐TdR product, already observed after its reaction with H2O2 alone, ie, the covalent dimer including a S? S bridge between two S4‐TdR molecules. More importantly, multihydroxylated derivatives of S4‐TdR and TdR were detected as peculiar products obtained under Fenton conditions. Among them, a product bearing an OH group both on the methyl group linked to the thymine ring and on the C5 atom of the ring was found to prevail. The results obtained during this study, integrated by those found previously in our laboratory, indicate 4‐thiothymidine as a promising molecular probe for the recognition, through a careful characterization of its reaction products, of the prevailing species among reactive oxygen species (ROS) corresponding to singlet‐state oxygen, hydrogen peroxide, and hydroxylic radical. 相似文献
The efficiency of activated carbons prepared from corncob, to remove asphaltenes from toluene modeled solutions, has been studied in this work. The activating agent effect over carbonaceous solid preparation , and also temperature effect on the asphaltenes adsorption on the prepared activated carbons, was studied. The asphaltene adsorption isotherms were determined, and the experimental data were analyzed applying the Langmuir, Freundlich, Redlich–Peterson, Toth and Radke–Prausnitz and Sips models. Redlich–Peterson model described the asphaltenes isotherm on the activated carbons better. The asphaltenes adsorption capacities at 25° for activated carbons were: 1305 mg g?1, 1654 mg g?1 and 559.1 mg g?1 for GACKOH, GACKP and GACH3PO4, respectively. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° were also evaluated from the adsorption isotherms in asphaltene solutions from toluene solutions, and it was found that the adsorption process was spontaneous and exothermic in nature. Kinetic parameters, reaction rate constant and equilibrium adsorption capacities were evaluated and correlated for each kinetic model. The results show that asphaltene adsorption is described by pseudo-second-order kinetics, suggesting that the adsorption process is chemisorption. The adsorption calorimetry was used to analyze the type of interaction between the asphaltenes and the activated carbons prepared in this work, and their values were compared with the enthalpic values obtained from the Clausius–Clapeyron equation.
Dexketoprofen [(2S)‐2‐(3‐benzoylphenyl)propanoic acid], C16H14O3, is the S‐enantiomer of ketoprofen, a nonsteroidal anti‐inflammatory drug (NSAID) that has analgesic, antipyretic and anti‐inflammatory properties, and finds applications for the short‐term treatment of mild to moderate pain. A new crystalline phase of dexketoprofen is reported. Its solid‐state structure was determined by single‐crystal X‐ray diffraction (SCXRD). The molecular structure of the two independent molecules found in the asymmetric unit of this new phase ( DXKP‐β ) were compared to those of the already known crystal form of dexketoprofen ( DXKP‐α ) and with the S‐enantiomer of the racemic compound. The three different conformers of dexketoprofen found in DXKP‐α and DXKP‐β were then investigated by computational methods. The optimized structures are very close to the corresponding starting geometries and do not differ significantly in energy. The crystal packing of DXKP‐β was studied by means of Hirshfeld surface (HS) analysis; interaction energies were also calculated. A comparison with DXKP‐α shows close similarities between the two crystal forms, i.e. in both cases, molecules assemble through the catemer O—H…O synthon of the carboxylic acid stabilized by additional C—H…O contacts and, accordingly, the interaction energies, as well as the contributions to the HS area, are very similar. Finally, the thermal behaviour of the two polymorphs of dexketoprofen was assessed by means of XRD (both from single crystal and microcrystalline powder) and differential scanning calorimetry (DSC); both crystal forms are stable under the experimental conditions adopted (air, 300–350 K for DXKP‐α and 300–340 K DXKP‐β ) and no solid–solid phase transition occurs between the two crystal forms in the investigated temperature range (from 100 K up to ca 350 K). 相似文献
Metoprolol {systematic name: (RS)‐1‐isopropylamino‐3‐[4‐(2‐methoxyethyl)phenoxy]propan‐2‐ol}, C15H25NO3, is a cardioselective β1‐adrenergic blocking agent that shares part of its molecular skeleton with a large number of other β‐blockers. Results from its solid‐state characterization by single‐crystal and variable‐temperature powder X‐ray diffraction and differential scanning calorimetry are presented. Its molecular and crystal arrangements have been further investigated by molecular modelling, by a Cambridge Structural Database (CSD) survey and by Hirshfeld surface analysis. In the crystal, the side arm bearing the isopropyl group, which is common to other β‐blockers, adopts an all‐trans conformation, which is the most stable arrangement from modelling data. The crystal packing of metoprolol is dominated by an O—H…N/N…H—O pair of hydrogen bonds (as also confirmed by a Hirshfeld surface analysis), which gives rise to chains containing alternating R and S metoprolol molecules extending along the b axis, supplemented by a weaker O…H—N/N—H…O pair of interactions. In addition, within the same stack of molecules, a C—H…O contact, partially oriented along the b and c axes, links homochiral molecules. Amongst the solid‐state structures of molecules structurally related to metoprolol deposited in the CSD, the β‐blocker drug betaxolol shows the closest analogy in terms of three‐dimensional arrangement and interactions. Notwithstanding their close similarity, the crystal lattices of the two drugs respond differently on increasing temperature: metoprolol expands anisotropically, while for betaxolol, an isotropic thermal expansion is observed. 相似文献
The increased levels of cyclic nucleotides (cGMP and cAMP) in enterocytes trigger intracellular mechanisms of ion and fluid secretion into the lumen, causing secretory diarrhea. Twelve novel pyridopyrimidines derived from 5-(3,5-bistrifluoromethylphenyl)-1,3-dimethyl-5,11-dihydro-1H-indeno[2,1 : 5,6]pyrido[2,3-d]pyrimidine-2,4,6-trione (FPIPP) were synthesized and evaluated on intracellular cyclic nucleotide accumulation. All compounds had no effect on either cyclic nucleotide basal levels or on pre-contracted aortic rings. The metabolic activity and viability in T84 cells, assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) and the LDH (lactate dehydrogenase) assays, respectively, were not affected by incubation with the compounds (50 μM). Compound VI almost abolished cGMP accumulation (94 % inhibition) induced by STa toxin in T834 cells and significantly reduced (69 %) forskolin-induced cAMP accumulation in Jurkat cells. Compound VI was active in an in vivo model for diarrhea in rabbits. These results prompted us to perform a microscopic histopathological analysis of intestinal tissues, showing that only compound VI preserves the intestine without significant pathological changes and with a decreased inflammatory pattern in comparison to FPIPP. In vitro stability test revealed that compound VI is resistant to oxidation promoted by atmospheric oxygen. 相似文献
Four‐way junctions (4WJs) are supramolecular DNA assemblies comprising four interacting DNA strands that in biology are involved in DNA‐damage repair. In this study, a new mononuclear platinum(II) complex 1 was prepared that is capable of driving the crystallization of the DNA oligomer 5′‐d(CGTACG)‐3′ specifically into a 4WJ‐like motif. In the crystal structure of the 1 –CGTACG adduct, the distorted‐square‐planar platinum complex binds to the core of the 4WJ‐like motif through π–π stacking and hydrogen bonding, without forming any platinum–nitrogen coordination bonds. Our observations suggest that the specific molecular properties of the metal complex are crucially responsible for triggering the selective assembly of this peculiar DNA superstructure. 相似文献
It is known that the asymptotic decay (|r|→∞) of the electron density n(r) outside a molecule is informative about its first ionization potential I0. It has recently become clear that the special circumstance that the Kohn–Sham (KS) highest-occupied molecular orbital (HOMO) has a nodal plane that extends to infinity may give rise to different cases for the asymptotic behavior of the exact density and of the exact KS potential [P. Gori-Giorgi et al., Mol. Phys. 114, 1086 (2016)]. Here we investigate the consequences of such a HOMO nodal plane for the effective potential in the Schrödinger-like equation for the square root of the density, showing that for atoms and molecules it will usually diverge asymptotically on the plane, either exponentially or polynomially, depending on the coupling between Dyson orbitals. We also analyze the issue in the external harmonic potential, reporting an example of an exact analytic density for a fully interacting system that exhibits a different asymptotic behavior on the nodal plane. 相似文献
Boron neutron capture therapy (BNCT) is a binary radiation therapy used to treat malignant brain tumours. It is based on the nuclear reaction (10B + n th --> [11B*] --> alpha + 7Li + 2.79 MeV) that occurs when 10B captures a thermal neutron to yield alpha particles and recoiling 7Li nuclei, both responsible of tumour cells destruction by short range and high ionization energy release. The clinical success of the therapy depends on the selective accumulation of the 10B carriers in the tumour and on the high thermal neutron capture cross-section of 10B. Magnetic resonance imaging (MRI) methods provide the possibility of monitoring, through 10B nuclei, the metabolic and physiological processes suitable to optimize the BNCT procedure. In this study, spatial distribution mapping of borocaptate (BSH) and 4-borono-phenylalanine (BPA), the two boron carriers used in clinical trials, has been obtained. The BSH map in excised rat brain and the 19F-BPA image in vivo rat brain, representative of BPA spatial distribution, were reported. The BSH image was obtained by means of double-resonance 10B-editing 1H-detection sequence, named M-Bend, exploiting the J-coupling interaction between 10B and 1H nuclei. Conversely, the BPA map was obtained by 19F-BPA using 19F-MRI. Both images were obtained at 7 T, in C6 glioma-bearing rat brain. Our results demonstrate the powerful of non conventional MRI techniques to optimize the BNCT procedure. 相似文献