The theoretical models based on valence connectivity index of the 3rd order, 3χv, have been discussed in terms of their ability to predict stability of coordination compounds. The key factors for the ...success are: (1) the choice of reliable experimental data for the calibration of the model, (2) writing an appropriate constitutional formula (i.e. graph) of the complex, and (3) development of proper form of regression function. If these requirements were met, it is possible to obtain theoretical results comensurable with the experimental ones, i.e. of the sufficient quality to evaluate experimental methods or to propose the best values for stability constants.
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Catalysis in the Primordial World Raos, Nenad; Bermanec, Vladimir
Kemija u industriji; časopis kemičara i tehnologa Jugoslavije,
11/2017, Letnik:
66, Številka:
11-12
Journal Article
Recenzirano
Odprti dostop
Catalysis provides orderly prebiotic synthesis and eventually its evolution into autocatalytic (self-reproduction) systems. Research on homogeneous catalysis is concerned mostly with random peptide ...synthesis and the chances to produce catalytic peptide oligomers. Synthesis of ribose via formose reaction was found to be catalysed by B(OH)4−, presumably released by weathering of borate minerals. Oxide and clay mineral surfaces provide catalytic sites for the synthesis of oligopeptides and oligonucleotides. Chemoautotrophic or iron-sulphur-world theory assumes that the first (pioneer) organisms developed by catalytic processes on (Fe/Ni)S particles formed near/close hydrothermal vents. The review provides an overlay of possible catalytic reactions in prebiotic environment, discussing their selectivity (regioselectivity, stereoselectivity) as well as geological availability of catalytic minerals and geochemical conditions enabling catalytic reactions on early Earth.
We developed a model for the stability (log β(ZnLB)) of Zn(2+) mixed complexes (N = 16) with 2-aminobenzamide (L) and four amino acids (B) glycine, alanine, valine, and phenylalanine at 300, 310, ...320, and 330 K. The model was based on the quadratic regression function of the molecular valence connectivity index of the third order, (3)χ(v), yielded S.E. = 0.02. We also developed an overall model for K(1), K(2) and β(ZnLB) of the same system at all of the four temperatures (N= 48). This model yielded S.E. = 0.05.
Relativna atomska masa – što je to? Raos, Nenad
Kemija u industriji; časopis kemičara i tehnologa Jugoslavije,
2021, Letnik:
70, Številka:
5-6
Journal Article
Recenzirano
Odprti dostop
Pojam relativne atomske mase pojavljuje se u dva značenja: prvo proizlazi iz zakona stalnih masenih omjera („atomska težina“), a drugo, novije, iz definicije mola, kao Avogadrova broja atoma ...(čestica). U članku je opisana kako povijest određivanja „atomske težine“ (Dalton, Berzelius, Stas) tako i povijest njezina definiranja (prema vodiku, kisku ili nuklidu 12C). Dva značenja relativne atomske mase utjecala su i na način rješavanja stehiometrijskih zadataka.
There are two basic understandings of relative atomic mass. The first (“atomic weight”) stems from the law of constant and multiple mass proportions and has no reference to the size and the absolute mass of atoms. “Atomic weights” were defined and measured in the 19th Century, and at that time atoms and molecules were just hypothetical particles. However, in the 20th Century, it became possible to measure the number and mass of atoms, and relative atomic mass was defined in reference to the mass and number of atoms,
i.e.
Avogadro constant and mole. This also resulted in the change of reference unit,
A
r(H) = 1 or
A
r(O) = 16, for
A
r(12C) = 12, and the way of teaching of stoichiometry (calculations
via
n
A instead of using proportionality principle). This article also describes the history of “atomic weight” determination by gravimetric analysis, especially the work of J. J. Berzelius and J. S. Stas.
This paper presents models for the estimation of stability constants (
K
1
and
β
2
) of nickel(II), copper(II) and zinc(II)
mono
- and
bis
-complexes with 5 Schiff bases (salicylideneglycine, ...salicylidenealanine, salicylideneserine, salicylidenephenylalanine, and salicylidenetyrosine). The models were based on the molecular-graph theory and valence molecular connectivity index of the 3
rd
order,
3
χ
v
, derived from it. Univariate linear models were developed for each metal separately, while in the common models for two and three metals, the indicator variable,
In
, was introduced. The standard error of models for the log
K
1
constant was less than 0.12, while for log
β
2
models, the S.E. did not exceed 0.14.
Stability constants of copper(II) chelates with amino acids and diaminoethanes were correlated to the 3rd valence connectivity indices,
3
χ
v
, of the corresponding complexes. The first and second ...stability constants were fairly well reproduced, yielding an error of the estimate around 0.3 log
K units.
3
χ
v
=
∑
path
{
δ
(
i
)
δ
(
j
)
δ
(
k
)
δ
(
l
)
}
-
0.5
Topological analysis was applied for the estimation of stability constants (
β
1 and
β
2) for sets of copper(II) mono-, ML, and bis-complexes, ML
2, with bidentate ligands, namely 1,2-diaminoethanes (
N
=
14), aliphatic amino acids and their
N-alkylated derivatives (
N
=
11), and naturally occurring amino acids (
N
=
9). A set consisting of 16 mixed (ternary) copper(II) bis-complexes with naturally occurring amino acids was also taken into account. The log
β values were correlated on the connectivity index
3
χ
v
of the ligands and their mono- or bis-complexes, with or without water coordination, yielding the best results for the model with two additionally bonded water molecules. An improvement of the method was obtained by proposing an additional ligand coordination in some complexes, especially in the set of mono- (
r
=
0.888) and bis-complexes (
r
=
0.786) of naturally occurring amino acids. The error of the estimate is 0.01–0.14 and 0.01–0.33 log
β units for mono- and bis-complexes, respectively. The estimation of log
β
2 for mixed amino acid complexes (MLA) was performed by bivariate linear regression using composite indices, obtained by addition or subtraction of the
3
χ
v
indices for two chelate rings, ML and MA. This regression gave
r
=
0.801 and the reproduction of experimental data 0.01–0.33 log
β units.
Logarithms of stability constants, log K₁ and log β₂, of the first transition series metal mono- and bis-complexes with any of four aliphatic amino acids (glycine, alanine, valine and leucine) ...decrease monotonously with third order valence connectivity index, ³χv, from Cu²+ to Mn²+. While stability of the complexes with the same metal is linearly dependent on ³χv, stability constants of Mn²+, Fe²+, Co²+, and Ni²+complexes with the same ligand show a quadratic dependence on ³χv. As Cu²+ complexes deviate significantly from quadratic functions, models for the simultaneous estimation of the stability constants, yielding r = 0.999 (S.E. = 0.05) and r = 0.998 (S.E. = 0.11), for log K₁ and log β₂, respectively, were developed only for Mn²+, Fe²+, Co²+, and Ni²+ complexes with amino acids.
The principal aim of our research was to develop theoretical models for estimating stability constants of coordination compounds, focusing on chelates of heavy metals, Cu(II) and Ni(II), with ...bioligands (amines, amino acids and peptides). We tried to solve the problem using graph-theoretical models. We also encountered a specific problem for coordination compounds - the choice of the constitutional formula, that is graph, of the complex species.
Prikazani su načini rješavanja problema procjene konstanta stabilnosti bakrovih(II) i niklovih(II) kelata s aminima, aminokiselinama i peptidima primjenom graf-teorijskih modela. Osebujni problem za koordinacijske spojeve je izbor konstitucijske formule, tj. grafa kompleksnoga spoja, pa su stoga iskušani modeli temeljeni na formuli liganda i više oblika konstitucijske formule kompleksa. Pokazalo se da se najbolji rezultati postižu valencijskim indeksom povezanosti trećeg reda, 3χv. Iskušani su modeli temeljeni na kombinacijama indeksa izvedenih iz molekularnih segmenata. Takvi su se modeli pokazali osobito uspješnima za procjenu stabilnosti miješanih kompleksa.
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