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1.
A new extension of the generalized topological indices (GTI) approach is carried out to represent “simple” and “composite”
topological indices (TIs) in an unified way. This approach defines a GTI-space from which both simple and composite TIs represent
particular subspaces. Accordingly, simple TIs such as Wiener, Balaban, Zagreb, Harary and Randić connectivity indices are
expressed by means of the same GTI representation introduced for composite TIs such as hyper-Wiener, molecular topological
index (MTI), Gutman index and reverse MTI. Using GTI-space approach we easily identify mathematical relations between some
composite and simple indices, such as the relationship between hyper-Wiener and Wiener index and the relation between MTI
and first Zagreb index. The relation of the GTI-space with the sub-structural cluster expansion of property/activity is also
analysed and some routes for the applications of this approach to QSPR/QSAR are also given. 相似文献
2.
Pavlina Simeonova Costel Sarbu Thomas Spanos Vasil Simeonov Stefan Tsakovski 《Central European Journal of Chemistry》2006,4(1):68-80
The present paper deals with the application of classical and fuzzy principal components analysis to a large data set from
coastal sediment analysis. Altogether 126 sampling sites from the Atlantic Coast of the USA are considered and at each site
16 chemical parameters are measured. It is found that four latent factors are responsible for the data structure (“natural”,
“anthropogenic”, “bioorganic”, and “organic anthropogenic”). Additionally, estimating the scatter plots for factor scores
revealed the similarity between the sampling sites. Geographical and urban factors are found to contribute to the sediment
chemical composition. It is shown that the use of fuzzy PCA helps for better data interpretation especially in case of outliers. 相似文献
3.
The nitrocubane substitution network shows the pattern by which single nitro-substitutions starting from cubane lead ultimately
to octanitrocubane. Of the 22 member species, densities have been experimentally measured for only 8, and we utilise these
to estimate the densities of the other 14 members. The network is viewed as a partially ordered set (or poset), which is used for posetic interpolative methods, which in turn differ from conventional QSAR/QSPR procedures based directly
on molecular structures. The posetic methods utilised are the “cluster-expansion” and the “splinoid” ones, which turn out
to be stable procedures as assessed by the leave-one-out cross-validation technique. 相似文献
4.
Summary An analytical evaluation of an HPLC method with diode array detection to separate and quantify polyphenolic compounds from
pears has been made. The method was applied to the quantitative analysis of phenolics from five pear horticultural cultivars
(“Agua”, “Blanquilla”, “Conference”, “Pasagrana” and “Decana”) in both peel and pulp matrices and evaluated for precision
and accuracy. Precision was taken as the reproducibility in peak area of the polyphenols of interest as well as in the slope
of calibration graphs. Values ranged 2–5%. Accuracy was evaluated by recovery of all polyphenolic compounds from both peel
and pulp in all pears investigated. Accuracy values ranged 92–102%, and were independent of the polyphenolic structure, horticultural
cultivar and matrix. Identification was by comparing retention times and UV spectra with those of standards when commercially
available. When not available commercially, provisional identification was according to spectral characteristics as well as
from isolation and hydrolysis data. Application of the method revealed differences between peel and pulp in all cases studied;
the higher levels of phenolics were found in the peels. “Decana” and “Pasagrana” cultivars showed the highest phenolic content
compounds whereas “Conference” showed the lowest. 相似文献
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A. F. Pozharskii O. V. Ryabtsova N. V. Vistorobskii Z. A. Starikova 《Russian Chemical Bulletin》2000,49(6):1097-1102
Tertiary alcohols containing the 4,5-bis(dimethylamino)-1-naphthyl group were synthesized. The carbocations that formed from
α-methyl-containing alcohols in an acidic medium underwent smooth El elimination to give the corresponding unsaturated derivatives
of the “proton sponge” in good yields. At the same time, the carbocation generated from 4-(α-hydroxybenzhydryl)-1,8-bis(dimethylamino)naphthalene
was converted into a benzo-[a]fluorene derivative as a result of a complex reaction which has been previously unknown in the chemistry of “proton sponges.”
The structure of the latter derivative was established by X-ray diffraction analysis.
For Part 26, see Ref. 1; this paper simultaneously presents Part 5 of the series “Resonance-stabilized α-naphthylmethyl carbocations
and derived spiro compounds;” for Part 4, see Ref. 2.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1103–1108, June, 2000. 相似文献
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Alejandro Marcó Ramon Companyó Roser Rubio Maite Pueyo Eugeni Vilalta 《Mikrochimica acta》2007,159(3-4):387-393
The estimation of uncertainty in organic elemental analysis for C, H, N and S is reported. Both “bottom up” and “top down”
strategies are used for uncertainty calculations. The bottom up approach used the results of C, H, N, and S obtained from
the homogeneity study of two pure chemicals (toluene-4-sulfonamide and 4(6)-methyl-2-thiouracil). Two calibration systems,
K factor and calibration curve, were applied in this study and no significant differences were obtained. For the “top down”
approach, we used the data obtained from a proficiency test on both pure chemicals from among 45 Spanish laboratories. Both
approaches are compared and discussed below. 相似文献
11.
A hypothesis on the correlation between the origin of “cold” (∼53 K) water molecules released by a growing crack and a low
(∼123 K) temperature of stretched and then thermoelastically cooled polymer chains that ruptured at the crack top is advanced.
A mechanism behind the formation of “cold” water molecules is suggested. It includes their “soft” desorption due to mechanical
action onto thermoelastically cooled side groups with adsorbed cooled water molecules from an unloading wave that is induced
by the rupture of the main chain and that travels along it. 相似文献
12.
Elfriede Simon M. G. Weller Reinhard Niessner 《Analytical and bioanalytical chemistry》1998,360(7-8):824-826
The aim of the described method was the characterization of a “atrazine-mercaptopropionic acid” humic acid conjugate, which
was required for the calibration of immunoassays to determine bound residues. In order to estimate the amount of bound triazine,
an oxidative nucleophilic substitution reaction of the covalently linked “atrazine-mercaptopropionic acid” to a new triazine
derivative “atrazine-methoxyethanol” was performed. This cleavage product was quantified by gas chromatography. The conditions
for this cleavage procedure were optimized and applied to the “atrazine-mercaptopropionic acid” humic acid conjugate and to
a humic acid blank. The amount of bound “atrazine-mercaptopropionic acid” was calculated to 16.6 ± 2.5 μmol triazine per gram
humic acid, which is equivalent to 0.39 ± 0.07% atrazine.
Received: 7 August 1997 / Accepted: 12 September 1997 相似文献
13.
Aleksander Astel Grażyna Głosińska Tadeusz Sobczyński Leonard Boszke Vasil Simeonov Jerzy Siepak 《Central European Journal of Chemistry》2006,4(3):543-564
The sustainable development rule implementation is tested by the application of chemometrics in the field of environmental
pollution. A data set consisting of Cd, Pb, Cr, Zn, Cu, Mn, Ni, and Fe content in bottom sediment samples collected in the
Odra River (Germany/Poland) is treated using cluster analysis (CA), principal component analysis (PCA), and source apportionment
techniques. Cluster analysis clearly shows that pollution on the German bank is higher than on the Polish bank. Two latent
factors extracted by PCA explain over 88 % of the total variance of the system, allowing identification of the dominant “semi-natural”
and “anthropogenic” pollution sources in the river ecosystem. The complexity of the system is proved by MLR analysis of the
absolute principal component scores (APCS). The apportioning clearly shows that Cd, Pb, Cr, Zn and Cu participate in an “anthropogenic”
source profile, whereas Fe and Mn are “semi-natural”. Multiple regression analysis indicates that for particular elements
not described by the model, the amounts vary from 4.2 % (Mn) to 13.1 % (Cr). The element Ni participates to some extent to
each source and, in this way, is neither pure “semi-natural” nor pure “anthropogenic”. Apportioning indicates that the whole
heavy metal pollution in the investigated river reach is 12510.45 mg·kg−1. The contribution of pollutants originating from “anthropogenic sources” is 9.04 % and from “semi-natural” sources is 86.53
%. 相似文献
14.
Attygalle AB Nishshanka U Weisbecker CS 《Journal of the American Society for Mass Spectrometry》2011,22(9):1515-1525
The diagnostic value of the “ortho effect” for unknown identification by mass spectrometry is well known. Here, we report
the existence of a novel “meta effect,” which adds to the repertoire of useful mass spectrometric fragmentation mechanisms.
For example, the meta-specific elimination pathway described in this report enables unequivocal identification of meta isomers
from ortho and para isomers of carboxyanilides. The reaction follows a specific path to eliminate a molecule of meta-benzyne, from the anion produced after the initial decarboxylation of the precursor. Consequently, in the CID spectra of
carboxyanilides, a peak for the (R-CO-NH)– anion is observed only for the meta isomers. For example, the peaks observed at m/z 58, 86, 120, 128, and 170 from acetamido-, butamido-, benzamido, heptamido-, and decanamido-benzoates, respectively, were
specific only to the spectra of meta isomers. 相似文献
15.
Abrar Hussain James L. Melville Jonathan D. Hirst 《Journal of computer-aided molecular design》2010,24(1):1-15
Actin-binding natural products have been identified as a potential basis for the design of cancer therapeutic agents. We report
flexible docking and QSAR studies on aplyronine A analogues. Our findings show the macrolide ‘tail’ to be fundamental for
the depolymerisation effect of actin-binding macrolides and that it is the tail which forms the initial interaction with the
actin rather than the macrocycle, as previously believed. Docking energy scores for the compounds were highly correlated with
actin depolymerisation activity. The 3D-QSAR models were predictive, with the best model giving a q
2 value of 0.85 and a r
2 of 0.94. Results from the docking simulations and the interpretation from QSAR “coeff*stdev” contour maps provide insight
into the binding mechanism of each analogue and highlight key features that influence depolymerisation activity. The results
herein may aid the design of a putative set of analogues that can help produce efficacious and tolerable anti-tumour agents.
Finally, using the best QSAR model, we have also made genuine predictions for an independent set of recently reported aplyronine
analogues. 相似文献
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Rusakova N. P. Turovtsev V. V. Orlov Yu. D. 《Russian Journal of Applied Chemistry》2011,84(9):1626-1628
For functional groups containing oxygen and sulfur atoms qualitative relationships were obtained and a row of electronegativities
was set up within the limits of the “quantum theory of atoms in molecules.” Possibilities of forecasting composition-property
correlations on a specified basis were discussed. 相似文献
19.
A. V. Harms 《Accreditation and quality assurance》2009,14(6):307-311
A novel graphical method (‘Kiri plots’) for the presentation of proficiency test exercise results is presented. The Kiri plot
visualises the evaluation of the proficiency test results based on three statistical tests (the z score, the zeta score and the relative uncertainty outlier test) by defining six zones including a central “in agreement”
zone. 相似文献
20.
It is well known that the two graph invariants, “the Hosoya index” and “the Merrifield–Simmons index” are important ones in
structural chemistry. The extremal hexagonal chains with respect to the Hosoya index and Merrifield–Simmons index are determined
by Gutman and Zhang (J. Math. Chem., 12 (1993) 197–210, 27 (2000) 319–329 and J. Sys. Sci. Math. Sci., 18 (4) (1998) 460–465).
In this paper, we will consider a type of the pericondensed hexagonal system. The double hexagonal chains with maximal Hosoya
index and minimal Merrifield Simmons index are determined. 相似文献