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71.
Daniilia S Minopoulou E Andrikopoulos KS Karapanagiotis I Kourouklis GA 《Analytica chimica acta》2008,611(2):239-249
The purpose of this study is to clarify important details about a Cumaean Sibyl painting that is preserved in a private collection. This work, bearing neither signature nor date, has never undergone conservation. It was executed after Domenichino's Cumaean Sibyl, a work known to have been used as a model by many 18th century painters.Investigation of the anonymous artist's painting technique and identification of its constituent materials were facilitated by employing optical microscopy (OM), scanning electron microscopy (SEM/EDS), FTIR and microRaman spectroscopies and high performance liquid chromatography with diode array detection (HPLC-DAD). The painter's palette comprised lead white, yellow ochre, lead-antimonate yellow (Naples yellow), cinnabar, cochineal lake, madder lake, haematite, Prussian blue and carbon black.The detection of Prussian blue (synthesized in 1704 and widely used as artist's pigment after 1750) was decisive in establishing the work's authenticity for, as such, it cannot be attributed either to Domenico Zampieri (1581-1641) or to his apprentices. In addition, the identification of Naples yellow, which prevailed in the period from 1750 to 1850, supports this statement. Nevertheless, its elaborate painting technique strongly suggests an artist greatly influenced by the Renaissance masters. A comparison of its stylistic features with those of the Cumaean Sibyl of Angelica Kauffmann (1741-1807), a prolific 18th century artist known to have studied and to have copied Domenichino's Sibyl, reveals significant similarities between the two in composition and palette. The unsigned Sibyl, therefore, could well be by Kauffmann. 相似文献
72.
We have performed a series of highly accurate calculations between CO2 and the 20 naturally occurring amino acids for the investigation of the attractive noncovalent interactions. Different nucleophilic groups present in the amino acid structures were considered (α-NH2, COOH, side groups), and the stronger binding sites were identified. A database of accurate reference interactions energies was compiled as computed by explicitly-correlated coupled-cluster singles-and-doubles, together with perturbative triples extrapolated to the complete-basis-set limit. The CCSD(F12)(T)/CBS reference values were used for comparing a variety of popular density functionals with different basis sets. Our results show that most density functionals with the triple-zeta basis set def2-TZVPP align with the CCSD(F12)(T)/CBS reference values, but errors range from 0.1 kcal/mol up to 1.0 kcal/mol. 相似文献
73.
Charge exchange in ion–surface collisions may be influenced by surface adsorbates to alter the charge state of the scattered projectiles. We show here that the positive‐ion yield, observed during ion scattering on metal surfaces at low incident energies, is greatly enhanced by adsorbing electronegative species onto the surface. Specifically, when beams of N+ and O+ ions are scattered off of clean Au surfaces at hyperthermal energies, no positive ions are observed exiting. Partial adsorption of F atoms on the Au surface, however, leads to the appearance of positively charged primary ions scattering off of Au, a direct result of the increase in the Au work function. The inelastic energy losses for positive‐ion exits are slightly larger than the corresponding ionization energies of the respective N and O atoms, which suggest that the detected positive ions are formed by surface reionization during the hard collision event. 相似文献
74.
Dr. Yunxi Yao Prof. Konstantinos P. Giapis 《Angewandte Chemie (International ed. in English)》2016,55(38):11595-11599
Most Eley–Rideal abstraction reactions involve an energetic gas‐phase atom reacting directly with a surface adsorbate to form a molecular product. Molecular projectiles are generally less reactive, may dissociate upon collision with the surface, and thus more difficult to prove that they can participate intact in abstraction reactions. Here we provide experimental evidence for direct reactions occurring between molecular N2+ and O2+ projectiles and surface‐adsorbed D atoms in two steps: first, the two atoms of the diatomic molecule undergo consecutive collisions with a metal surface atom without bond rupture; and second, the rebounding molecule abstracts a surface D atom to form N2D and O2D intermediates, respectively, detected as ions. The kinematics of the collisional interaction confirms product formation by an Eley–Rideal reaction mechanism and accounts for inelastic energy losses commensurate with surface re‐ionization. Such energetic hydrogenation of dinitrogen may provide facile activation of its triple bond as a first step towards bond cleavage. 相似文献
75.
Synthesis of (R)-dihydropyridones as key intermediates for an efficient access to piperidine alkaloids 总被引:2,自引:0,他引:2
Tzanetou EN Kasiotis KM Magiatis P Haroutounian SA 《Molecules (Basel, Switzerland)》2007,12(4):735-744
The efficient transformation of D-glucal to (2R)-hydroxymethyldihydropyridinone 5 in seven steps and 35 % overall yield is reported. Dihydropyridone 5 constitutes a versatile chiral building block for the synthesis of various piperidine alkaloids. In this regard, 5 was converted to piperidinol 13 and piperidinone 15, that may be further elaborated for the syntheses of (+)-desoxoprosophylline (1) and deoxymannojirimycin (3) or D-mannolactam (4), respectively. 相似文献
76.
Thalassinos K Jackson AT Williams JP Hilton GR Slade SE Scrivens JH 《Journal of the American Society for Mass Spectrometry》2007,18(7):1324-1331
Novel software has been developed to aid the interpretation of tandem mass spectrometry (MS/MS) data from synthetic polymers. The software is particularly focused toward aiding the end-group determination of these materials by significantly speeding up the interpretation process. This allows information on the initiator and/or chain transfer agents, used to generate the polymer, and the mechanism of termination to be inferred from the data much more rapidly. The software allows the validity of hypothesized structures to be rapidly tested by automatically annotating the data file using previously proposed fragmentation rules for synthetic polymers. Low-energy collision-induced dissociation (CID) data from methacrylate, styrene, and polyether oligomers are used as example data for the software. Exact-mass CID information was used to aid the understanding of the dissociation mechanism of the polymers. The software can use exact-mass data to provide more confidence in the results. The MS/MS results indicate that the fragmentation pathways are those previously proposed for these polymers. 相似文献
77.
Maria Tsoukka Konstantinos E. Litinas Demetrios N. Nicolaides Dimitra J. Hadjipavlou‐Litina 《Journal of heterocyclic chemistry》2007,44(3):529-534
78.
Georgios Patermarakis Konstantinos Moussoutzanis Nikolaos Nikolopoulos 《Journal of Solid State Electrochemistry》1999,3(4):193-204
A new method has been developed capable of describing the incorporation of electrolyte anions along the pore wall surface
and across both the barrier layer and the pore wall oxide after the establishment of the steady state of growth of porous
anodic Al2O3 where other methods cannot be applied to obtain reliable results. The knowledge of the nature/composition of anodic oxides
as regards the incorporation of species like electrolyte anions is of specific importance for both the understanding of the
electrochemical mechanism of oxide production and growth and the scientific and technological applications of porous anodic
Al2O3 films. The method consists of the selection and use of a suitable catalytic probe reaction on porous anodic oxides at thicknesses
varying from a value near zero up to the maximum limiting thickness and the treatment of the experimental reaction rate results
by a properly developed mathematical formalism. This method was employed in anodic Al2O3 films prepared in H2SO4 anodizing electrolyte at a constant bath temperature and different current densities using as a probe reaction the decomposition
of HCOOH on these oxides, which is almost exclusively a dehydration reaction, at relatively high reaction temperatures, 350 °C
and 390 °C, where the effect of other species except SO4
2− incorporated in the oxide on the reaction rate is eliminated. It has been shown that the fraction of the intercrystallite
surfaces occupied by SO4
2− follows a parabola-like distribution. It has a significant value at the pore base surface, depending on the current density,
then it passes through a maximum along the pore wall surface and across both the barrier layer and the pore walls near the
pore bases at positions depending on the current density and then becomes almost zero at the mouths of the pores of the oxide
with the maximum limiting thickness and at both the Al2O3/Al interface and cell boundaries. The maximum value of the surface coverage is almost independent of the current density
and is always near 1, showing an almost complete saturation of intercrystalline surfaces at these positions. The above distribution
of surface coverage predicts a qualitatively similar distribution of the SO4
2− bulk concentration across both the barrier layer and pore wall oxide around the pore bases. The method may be improved and
developed further either for a more detailed investigation of the above films or to investigate films prepared in other pore-forming
electrolytes.
Received: 30 July 1998 / Accepted: 30 September 1998 相似文献
79.
Konstantinos Chondroudis Debojit Chakrabarty Enos A. Axtell Mercouri G. Kanatzidis 《无机化学与普通化学杂志》1998,624(6):975-979
The reaction of one equivalent of In with a molten flux of (Ph4P)2Se5 and P2Se5 (1 : 2), at 250 °C gave the (Ph4P)[In(P2Se6)] ( I ). Stoichiometric elemental synthesis at 750 °C produced the Cs5In(P2Se6)2 ( II ). The thin, yellow crystals of ( I ), and the irregular, dark orange crystals of ( II ), appear to be air- and water-stable. Compound ( I ) crystallizes in the monoclinic space group C2/c (no. 15) and at 23 °C: a = 23.127(7) Å, b = 6.564(1) Å, c = 19.083(3) Å, β = 97.42(2)°, V = 2873(1) Å3, Z = 4, final R/Rw = 4.4/5.2%. Compound ( II ) crystallizes in the tetragonal space group P42/m (no. 84) and at 23 °C: a = b = 13.886(1) Å, c = 7.597(2) Å, V = 1464.9(3) Å3, Z = 2, final R/Rw = 3.9/5.1%. Compound ( I ) contains infinite [In(P2Se6)]nn– with a structure related to that of K2FeP2Se6. Compound ( II ) contains the discrete [In(P2Se6)2]5– which can be viewed as a fragment of the [In(P2Se6)]nn– chain. 相似文献
80.
Probing hemoglobin structure by means of traveling-wave ion mobility mass spectrometry 总被引:1,自引:0,他引:1
Charlotte A. Scarff Vibhuti J. Patel Konstantinos Thalassinos James H. Scrivens 《Journal of the American Society for Mass Spectrometry》2009,20(4):625-631
Hemoglobin (Hb) is a tetrameric noncovalent complex consisting of two α- and two β-globin chains each associated with a heme group. Its exact assembly pathway is a matter of debate. Disorders of hemoglobin
are the most common inherited disorders and subsequently the molecule has been extensively studied. This work attempts to
further elucidate the structural properties of the hemoglobin tetramer and its components. Gas-phase conformations of hemoglobin
tetramers and their constituents were investigated by means of traveling-wave ion mobility mass spectrometry. Sickle (HbS)
and normal (HbA) hemoglobin molecules were analyzed to determine whether conformational differences in their quaternary structure
could be observed. Rotationally averaged collision cross sections were estimated for tetramer, dimer, apo-, and holo-monomers
with reference to a protein standard with known cross sections. Estimates of cross section obtained for the tetramers were
compared to values calculated from X-ray crystallographic structures. HbS was consistently estimated to have a larger cross
section than that of HbA, comparable with values obtained from X-ray crystallographic structures. Nontetrameric species observed
included apo- and holo- forms of α- and β-monomers and heterodimers; α- and β-monomers in both apo- and holo- forms were found to have similar cross sections, suggesting they maintain a similar fold
in the gas phase in both the presence and the absence of heme. Heme-deficient dimer, observed in the spectrum when analyzing
commercially prepared Hb, was not observed when analyzing fresh blood. This implies that holo-α-apo-β is not an essential intermediate within the Hb assembly pathway, as previously proposed. 相似文献