In order to compare the density functional theory (DFT) and the method with the molecular valence connectivity index of the 3rd order (
) in the estimation of stability constants log β
, we used ...copper(II) complexes with thioflavin-based intercalation compounds designed for application in Alzheimer’s disease. Correlation of ten log β
values calculated by DFT with
yielded r=0.988 and S.E.=0.85. The correlations of indices I
, HOMA and
with log β
, and the intercorrelations between the indices revealed the crucial influence of
on the prediction of the stability of these complexes.
Izabrali smo komplekse bakra(II) s interkalacijskim spojevima temeljenima na tioflavinu, koji su namijenjeni za liječenje Alzheimerove bolesti, kako bismo usporedili teoriju funkcionala gustoće (DFT) s metodom molekularnog valencijskog indeksa 3. reda (
) za procjenu vrijednosti konstanti stabilnosti log β
. Korelacija deset vrijednosti log β
izračunatih metodom DFT s
indeksom dala je r=0,988 i S.E.=0,85. Korelacije indeksa ING, HOMA i
s vrijednostima log β
te međukorelacije indeksa pokazuju bitan utjecaj
na predviđanje stabilnosti istraživanih kompleksa.
Linear model for estimation of the second, K2, and overall, β2, stability constant of cadmium(II) binary and ternary bis-complexes with five aliphatic χ-amino acids based on valence connectivity ...index of the 3rd order (3χv) was developed. Set of amino acids included glycine, alanine, 2-aminobutanoic, 2-aminopentanoic (norvaline) and 2-aminohexanoic acid (norleucine), which by bonding to the cadmium(II) gave 25 K2 and 15 β2 values. For estimation of log β2, the model gave r = 0.940, and the S.E.cv = 0.10, and for the two subsets of log K2 constants the model yielded r = 0.936 and 0.842, and S.E.cv = 0.09. The complex CdGG was excluded from all regressions.
Rad se bavi razvojem pojma elementa od antičkih vremena (Empedoklo, Aristotel) preko razdoblja alkemije i rane kemije (Paracelsus, Petar Bono, Boyle) te početaka moderne kemije (Lavoisier, ...Mendeljejev) do suvremenih shvaćanja utemeljenih na atomskoj teoriji. Pokazuje se da pojam elementa ima dva značenja, elementarne (jednostavne) tvari i elementa u užem smislu; dok se prvi pojam razvijao prateći napredak metoda kemijske analize, za razumijevanje drugog pojma, pojma elementa, bilo je nužno steći dublji uvid u narav kemijskih promjena.
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Models for estimation of the first （K1）, second （K2）, and overall stability constant （β2） of copper（II） chelates with naturally occurring amino acids, based on the valence connectivity index of the ...3rd order （3Xr）, were improved by introduction of a square term and a new graph representation for mono-complexes （MLCor）. The models gave SE = 0.07, 0.05--0.07 and 0.05--0.08 for lg Ki, lg K2 and lg ,62 constants, respectively; models that encompass both bi- nary and ternary bis-complexes included indicator variable. We also validated our models on the test set which in- cluded two mono-, two binary and two ternary Cu（II） chelates with a-aminobutanoic acid and a-aminopentanoic acid, not included into the calibration. The absolute differences between experimental and predicted stability con- stants were in the range of 0.01--0.16.
Linear models for estimation of the first (K 1), second (K 2), and overall stability constant (β2) based on the valence connectivity index of the third order (3 χ v) were developed and checked on ...four sets of copper(II) chelates (with diamines, N-alkylated glycines, and naturally occurring amino acids, including their mixed complexes). Univariate models were valid when log K 1 and log K 2 values were linearly correlated, i.e., when there was no interaction between chelate rings. The univariate models proved applicable for estimation of all three stability constants of complexes with diamines and N-alkylated glycines, but for complexes with amino acids additional terms were needed (bivariate models). Models reproduced stability constants with an error usually less than 0.3 log K units.
The interdependence between the side of apical coordination of H2O and steric crowding at the apical positions was investigated on a set of 34 copper(II) bis‐complexes with N‐ and N,N‐substituted ...amino acids. As a measure of steric crowding, overlapping volumes V* were used, calculated using a modified overlapping spheres method. Steric crowding around the apically bonded ligand was the same for this set of complexes as for the copper(II) bis‐complexes with naturally occurring amino acids, with the optimal occupied volume values between 1 and 1.5 Å3. The interdependence between the length of the apical bond and distortion of the coordination polyhedron was also studied. The apical bond length showed sigmoidal dependence on the magnitude of distortion.
The ovelall stability constants
β
1 of copper(II) and nickel(II) chelates with dipeptides were estimated from its constituents,
K
1 and
K
a. The chelate rings were treated as separate units in the ...model with the valence connectivity index of the 3rd order (
3
χ
v
).
The estimation of the overall stability constants
β
1 of copper(II) and nickel(II) chelates with dipeptides was performed by using the model with the valence connectivity index of the 3rd order (
3
χ
v
). It was done by dividing
β
1 to its constituting constants
K
1 and
K
a, and subsequently by dividing the basic set into subsets or treating the chelate rings as separate units. Altogether 15 copper(II) and eight nickel(II) chelates with dipeptides were investigated. Six models for the estimation of log
K
1 and p
K
a were checked, most of them by usage of indicator variables (for differentiation of copper(II) and nickel(II) complexes or subclasses of ligands). Estimates of log
β
1 gave the range of
rms values from 0.19 to 0.27. For the best model, errors of estimates were less than 0.34.
Metal je loše definiran pojam, točnije podjela na metale i nemetale nije, strogo govoreći, znanstvena (kemijska) nego tradicionalna. U radu se razmatraju opća svojstva elemenata nastojeći pronaći ...kriterije za određivanje njihove kako metalne tako i nemetalne naravi. “Metalni” spojevi nemetala i “metalni” spojevi nemetala te dublje razumijevanje pojma elektronegativnosti ukazuju međutim na činjenicu kako metalna narav elementa nije apsolutna, nego relativna, ovisna o elementu s kojim ulazi u kemijsku vezu.
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The interdependence between the side of apical coordination (H2O, >C=O, dimethyl sulfoxide and Cl−) and steric crowding at the apical positions was investigated for a set of 20 copper(II) bis ...complexes with naturally occurring amino acids. As a measure of steric crowding the overlapping volumes, V*, were used, calculated by the modified overlapping spheres method. It was found that the apically coordinated side of a complex is more hindered by the side‐chain atoms. In addition, if both sides are apically coordinated, the apical bond is shorter at the more crowded side. The interdependence between the length of the apical bond and distortion of the coordination polyhedron was also studied. The apical bond length shows sigmoidal dependence on the magnitude of distortion, and is also dependent on the kind of distortion (square‐pyramidal or tetrahedral).
Prebrojavanje konstitucijskih (strukturnih) izomera alkana lijepa je vježba kojom učenik stječe osjećaj za raznolikost kemijske strukture te ovladava vještinom pisanja kemijskih formula i sustavnih ...imena kemijskih spojeva. U članku je predložena jednostavna shema sustavnog prebrojavanja izomera temeljena na maksimalnoj dužini alifatskog lanca. Zadatak se može izvesti slaganjem šibica ili drugih štapića. U članku je dana konstrukcijska shema do molekule nonana (35 izomera).
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