J. Serb. Chem. Soc. 63(7) 491-496 (1998)
UDC 513.83.084:535.32:62.001.57
JSCS-2553
Original scientific paper
Buckley-type relations for Wiener-type
structure-descriptors
IVAN
GUTMAN
Faculty of Science, University of Kragujevac,
P.O.Box 60, YU-34000 Kragujevac, Yugoslavia
(Received 9
February 1998)
The Wiener
index (W) of the molecular graph (G) of a Cn-alkane and of the
respective line graph (L(G)) are related as W (L(G)) = W(G)-n(n-1)/2,
a formula first discovered by Buckley. In this work similar relations are
established for a variety of other distance-based structure-descrptors, used in
QSPR and QSAR studies of organic compounds.
Key words: line
graph, distance-based topological indices, Wiener index, reciprocal Wiener
index, Harary index, hyper-Wiener index.
J. Serb. Chem. Soc. 63(7) 497-504 (1998)
UDC 513.83.084.535.32:547.2
JSCS-2554
Origin scientific paper
Defining Cluj matrices and Cluj matrix
invariants
IVAN
GUTMAN and MICREA V. DIUDEA*
Faculty of Science, University of Kragujevac,
P.O.Box 60, YU-34000 Kragujevac, Yugoslavia and
*Department
of Chemistry, "Babes-Bolyai" University, R-3400 Cluj, Romania
(Received
11 February 1998)
Rigorous
and generally applicable definitions are put forward for the Cluj matrices and
their invariants. The Cluj matrices were recently conceived as a kind of generalization
of the Wiener-matrix-concept to cycle-containing molecular graphs. Whereas for
acyclic graphs the elements of the Wiener matrix have a direct and intuitively
clear structural interpretation, in the case of cycle-containing systems
several ambiguities are encountered which need to be resolved. Our analysis
reveals that, when constructing Cluj matrices, one has to choose between
several equally plausible options. In other words, the actual, already existing
definition is just one among several possible ways in which Cluj-type matrices
can be designed.
Key words: topological
indices, Wiener matrix, Cluj matrix, Cluj index.
J. Serb. Chem. Soc. 63(7) 505-517 (1998)
UDC 543.42/.45:62.001.57
JSCS-2555
Original scientific paper
Critical reexamination of the existing types of
profiles for spectral band shape analysis
VLADIMIR
M. PETRUSEVSKI and LJUPCO PEJOV
Institute of Chemistry, Faculty of Natural
Sciences and Mathematics, The "Sv. Kiril i Metodij" University,
Arhimedova
5, 91000 Skopje, Macedonia
(Received
17 February 1998)
The
knowledge of the true type of the shape of a spectral band (type of profile) is
very important in virtually all areas where spectroscopy is used both as a tool
and as the principal method of investigation. Basically, it enables accurate
quantitative investigations to be undertaken. Quantum-mechanical arguments lead
to the conclusion that spectral bands should be of Lorentzian (Cauchy) type.
Collision broadening results in the same type of profile. Doppler broadening
is, on the other hand, the bases of Gaussian band shapes, as are interactions
of the dispersive type. However, spectral bands are, very often, neither
Lorentzian nor Gaussian. Quite a number of other types of profiles has been
mentioned in the literature to date. The agreement between the experimental and
fitted spectra is sometimes impressive. This, however, does not imply that the
band shape is really of the assumed particular type. One should always be
cautious: i) when good agreement results from the use of functions with a large
number of adjustable parameters and ii) when it appears as a result of fitting
with functions that have no physical significance at all. The types of profiles
used so far are critically analysed.
Key words:
spectra, profile types, band-shapes, curvefitting.
J. Serb. Chem. Soc. 63(7) 519-527 (1998)
UDC 543.544.4:541.135.27
JSCS-2556
Original scientific paper
The log k pair linearity rule as a method of
studying RPP mobile phase scales
TOMISLAV
J. JANJIC, GORDANA VUCKOVIC and MILENKO B. CELAP
Faculty of Chemistry, University of Belgrade,
P. O. Box 158, YU-11001 Belgrade, Yugoslavia
(Received
19 February 1998)
A new
method is proposed by which it can be established if there is a common RPP
scale of solvents for one group of examined compounds, being separated by the
same series of solvents, and if by this method it can also be estimated. The
method is illustrated by literature data obtained using C18 columns and solvents
containing methanol or acetonitrile as modifiers and various aqueous phases. In
most cases a good linear dependence (r = 0.9980 - 0.9990) was established
between the experimentally determined log k values of the examined
substances and the obtained RPP values.
Key words: C18 column chromatography,
Log k pair linearity rule, RPP mobile phase scale.
J. Serb. Chem. Soc. 63(7) 529-536 (1998)
UDC 66.063.61.001.4:541.653.3
JSCS-2557
Original scientific paper
Emulsion inversion point (EIP) as a parameter
in the selection of emulsifier
S.
GASIC, B. JOVANOVIC* and S. JOVANOVIC*
Institute for Plant Protection and Environment,
Teodora Drajzera 9, YU-11000 Belgrade and
*Faculty
of Technology and Metallurgy, University of Belgrade, P.O.Box 494, YU-11001
Belgrade, Yugoslavia
(Received
10 March 1998)
In this
work the method of emulsion inversion point (EIP) was applied to the chosen
system of nonionic emulsifiers and oil phases. Two homologous series of
nonionic emulsifiers were used: nonylphenolpolyglycolethers with 2-30 moles of
bound ethylene oxide and polyglycolethers of fatty alcohols (C16-C18) with 2-23 moles of
bound ethylene oxide. Compounds of different chemical structures were used as
the oil phases: liquid paraffin, xylene, cyclohexane, n-hexane and
isooctane. The results were shown in relation to the corresponding
hydrophilic-lipophilic balance (HLB) values. The obtained results indicated
that it is possible and useful to apply stated method for the selection of a
suitable emulsifier, with certain limitations. The application of this method
is especially important when the "required" HLB value of the oil
phase is unknown.
Key words: emulsifier
selection, nonionic emulsifiers, phase inversion.
J. Serb. Chem .Soc. 63(7) 537-543 (1998)
UDC 541.135.2:543.251
JSCS-2558
Original scientific paper
The determination of the optimum current wave
in reversing current metal electrodeposition
K.
I. POPOV, T. M. KOSTIC, E. R. STOJILKOVIC,* N. D. NIKOLIC** and M. G.
PAVLOVIC**
Faculty of Technology and Metallurgy,
University of Belgrade, Karnegijeva 4, YU-11000 Belgrade,
*Faculty
of Agriculture, University of Belgrade, Nemanjina 6, YU-11080 Zemun-Belgrade
and
**ICTM
Institute of Electrochemistry, University of Belgrade, Njegoseva 12, YU-11000
Belgrade, Yugoslavia
(Received
17 February, revised 24 March 1998)
The
experimental procedure for the determination of the optimum reversing current
wave, producing uniformlly distributed polycrystalline deposits, is given.
First, deposition at the maximum current density for different periods of RC
wave was carried out. The period was increased until a smooth polycrystalline
deposit was obtained in the middle of the electrode. Subsequently, the
deposition current density was decreased by increasing the anodic-to-cathodic
time ratio, in order to obtain a suitable metal distribution on a macroprofile.
Key words:
reversing current, optimum current wave, metal electrodeposition.
J. Serb. Chem. Soc. 63(7) 545-553 (1998)
UDC 661.634.2:661.961.13
JSCS-2559
Original scientific paper
Phosphoric acid as a source of hydrogen in
cathodic hydrogen evolution
VEDRANA
MARINOVIC and ALEKSANDAR DESPIC*
Institute of Technical Sciences of the Serbian
Academy of Science and Arts, Knez Mihajlova 35, YU-11001 Belgrade, and
*Institute of Electrochemistry ICTM, Njegoseva 12, YU-11001 Belgrade,
Yugoslavia
(Received
20 January, revised 1 April 1998)
Cathodic
hydrogen evolution on silver was studied from aqueous solutions of phosphoric
acid at different pH values. A theoretical analysis was carried out to
calculate the abundance of the four species (undissociated H3PO4, H2PO4-, HPO42- and PO43-) as a function of pH,
using literature values of the dissociation constants. It was found that in
some pH range each of the species exists in virtually 100% abundance. Hence,
the kinetics of hydrogen discharge from the two acid anions could be
investigated separately. A diagnostic criterion, established to determine the
hydrogen donors, indicates that the first dissociation step of the acid is so
fast that the equilibrium concentration of hydronium ion is maintained up to
very high current densities of dicharge and, hence, at low pH up to 2, this ion
is the source of hydrogen. Contrary to this, at higher pH the equilibrium
concentration of hydronium ions is so low that the two acid anions take over
acting as hydrogen donors.
Key words:
cathodic hydrogen evolution, phosphoric acid.
J. Serb. Chem. Soc. 63(7) 555-564 (1998)
UDC 661.931:541.135.52/546.431' 654'' 732'''/
JSCS-2563
Original scientific paper
Oxygen evolution at La1-xBaxCoO3 perovskite-type
electrodes
SVETLANA
MITROVSKI and DRAGUTIN M. DRAZIC*
ICTM-Centre for Catalysis and Chemical
Engineering, Njegoseva 12, YU-11000 Belgrade and
*ICTM -
Centre for Electrochemistry, Njegoseva 12, YU-11000 Belgrade, Yugoslavia
(Received
17 March 1998)
Perovskite
oxides of the type La1-xBaxCoO3 (x = 0.1, 0.2, 0.4)
and La0.8Bax0.2CoO3were synthesized and
tested as oxygen anodes in 1 mol dm-3 NaOH solution at room temperature. The
electrodes were prepared by pressing and sintering the synthesized perovskite
powders. The roughness factors of the electrodes were determined by
Hg-porosimetry and by double layer capacitance measurements. The ones
determined by Hg-porosimetry, rs, were found to be in the range 42<rs<1500, while the ones
determined from the double layer capacitance, rDL, were found to be in
the range 11<rDL<470. No correlation
between the composition of the oxides and the roughness factors was found,
whereas the ratio rDL/rs remained approximately
constant and amounted to around 0.3 (+10%) for all the electrodes. The
behaviour of the electrodes in the oxygen evolution reaction (OER) was studied.
All the electrodes showed Tafel slopes of about 60 mV dec-1, whereas the activity
in the OER, expressed using the corresponding roughness factors, increased with
increasing x and was almost one order of magnitude higher for the Ba-
than the Ca-substituted perovskite, for the same degree of substitution, x
= 0.2. The enhanced activity of the perovskites with higher Ba content was
attributed to the higher Co4+ ions content, together with the higher specific activity
of these active centres for the OER, determined by cyclic voltammetry.
Key words: perovskite,
oxygen evolution, reaction mechanism.
J. Serb. Chem. Soc. 63(7) 565-572 (1998)
UDC 547.918+546.791:541.428.49:535.243
JSCS-2561
Original scientific paper
Spectrophotometric investigation of the
uranil(II)-hesperidin complex in 70% methanol
VESNA
KUNTIC, MARA KOSANIC, DUSAN MALESEV, ZORICA RADOVIC and UBAVKA MIOC*
Faculty of Pharmacy, University of Belgrade,
Vojvode Stepe 450, Belgrade and
*Faculty
of Physical Chemistry, Studentski trg 12-16, Belgrade, Yugoslavia
(Received
13 December 1997, revised 11 February 1998)
The
composition and stability constant of the UO2(II)-hesperidin complex were determined
by suitable spectrophotometric methods and pH-metric measurements. It was found
that the uranil ion and hesperidin form a 1:2 complex in which the uranil ion
is linked to the hesperidin molecule through the carbonyl and the 5-hydroxyl
group. The relative stability constant, log K2, ranged from 5.77 at
pH 4.0 to 7.00 at pH 6.0. The conditions for the spectrophotometric
determination of hesperidin, by means of reaction of the complex formation
reaction, were investigated. Beer's law was obeyed up to 2.0×10-5 mol dm-3 hesperidin.
Key words: complex,
hesperidin, uranilnitrate, spectrophotometric methods.
J. Serb. Chem. Soc. 63(7) 573-583 (1998)
UDC 546.562 723:543.062.661.242.2/541.135.52/
JSCS-2562
Original scientific paper
Determination of copper(II) and iron(III) by
EDTA using pyrite electrode
M.
M. ANTONIJEVIC, R. P. MIHAJLOVIC* and B. V. VUKANOVIC
Technical Faculty Bor, University of Belgrade,
P.O.Box 50, YU-19210 Bor,
*Faculty
of Science, University of Kragujevac, YU-34000 Kragujevac, Yugoslavia
(Received
24 July 1997, revised 27 February 1998)
The
results obtained in the potentiometric titrations of copper(II) and iron(III)
with standard EDTA solutions are presented. Titrations of copper(II), at pH
values in the range from 8.11 to 10.99 (ammonia buffer), and of iron(III), at
pH values from 3.59 to 5.65 (acetate buffer), were performed. The titration
end-point (TEP) was detected with an indicator electrode from natural
crystalline pyrite as an electrochemical sensor. The results obtained in the
potentiometric titrations with the pyrite electrode were compared with those
obtained using a platinum electrode (Fe3+) and a Cu-ISE (Cu2+). Accurate and
reproducible results with good agreement were obtained, but higher potential
changes at the TEP were obtained using the pyrite electrode. In the course of
the titration the potential was established in less than one minute, whereas at
the TEP in about 2-3 min. The potential changes at the TEP were in the range
from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the
formed complex. The highest potential changes, ranging from 160 to 200 mV, were
obtained in the titration of iron(III) at pH value of 3.59. Reverse titrations
were also performed and accurate and repoducible results were obtained. The
influence of the hetrogeneity of the pyrite on the accuracy of the results was
investigated.
Key words:
pyrite sensor, complexometric titrations, EDTA.
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