POLISH JOURNAL OF CHEMISTRY
Volume 72 Number 8 August 1998
Pages 1871-2036


CONTENTS

Page

INORGANIC CHEMISTRY
1871 Spectroscopic Properties of New Indium(III) Phthalocyanine Complexes
— Janczak J.
1879 Preparation, Crystal Structure and Properties of (Ph4P)2ReCl6.2CH3CN
— Małecka J., Jaeger L., Wagner Ch. and Mroziński J.
1886 Interactions between the Components in the Zr-Ag-In System at 870 K
— Gulay L.D., Zaremba V.I., Stępień-Damm J. and Kalychak Ya.M.
1890 Synthesis, Spectral, Magnetic and X-ray Powder Diffraction Structural Characterization of [Fe(NCS)3(OPPh3)3]
— Ondrejkovicova I., Jorik V. and Mroziński J.
1897 Uptake of Molecular Oxygen by Co(II) Chelates with Peptides in Aqueous Solution. Part X. Diastereoisomeric Dipeptides as Auxiliary Ligands in Oxygen-Free Complexes
— Kufelnicki A. and Świątek M.
ORGANIC CHEMISTRY
1907 New Insertion Reactions of Some Carbenoids into Amide- and Sulfonamide-NH Bonds
— Mlostoń G., Celeda M., Świątek A., Kaegi M. and Heimgartner H.
1915 Flash Vacuum Pyrolysis of 1,3-Thiazole-5(4H)-thiones
— Leśniak S., Mlostoń G. and Heimgartner H.
1921 Reaction of Cyclic Allylic Acetates with Aliphatic Alcohols in the Presence of Cerium(III) Chloride
— Uzarewicz A. and Dresler R.
1931 2,2'-Diselenobisbenzoates and 2,2'-Diselenobisbenzenesulfonates: New Chiral Aryl Dis-elenides
— Palus J., Młochowski J. and Juchniewicz L.
1937 The Reaction of (Methylthio)acetyliron Complex with Pentose Terminal Aldehydes
— Wiśniewski K. and Zamojski A.
PHYSICAL CHEMISTRY
1949 Studies on Mechanism of 2-Pyridinecarboxaldehyde Oxidation by Dichromates in Strongly Acidic Aqueous Solutions. The Unusual Reaction Order on Concentration of the Aldehyde
— Kita E., Kita P. and Uścińska G.
1958 Interaction of Thymidylate Synthase with 5-Fluoro-Substituted DUMP Analogues in View of the Pyrimidine Ring Structure
— Jarmuła A., Cyrański M.K., Leś A., Krygowski T.M. and Rode W.
1963 Calix[4]resorcinarenes as Dynamic Coatings for Modified Stationary RP-18 Phase for HPLC
— Pietraszkiewicz M., Pietraszkiewicz O. and KoŸbiał M.
1971 The Analysis of Resistance Change in Diffusion Controlled Electrode Processes
— Gatner K. and Zięba A.
1981 Solubility of n-Alkanes in Ethyl tert-Butyl Ether
— Domańska U. and Venkatesu P.
CRYSTAL AND MOLECULAR STRUCTURE
1994 The Crystal Structure of Strontium Complex with 3-Aminopyrazine-2-carboxylic Acid
— Leciejewicz J., Ptasiewicz-Bąk H. and Zachara J.
1999 X-ray Structural Investigations of Three 4-Aryl-Substituted [2.2]Paracyclophanes
— Jones P.G. and Kuś P.
2009 Crystal Structure of 2-(1,4,5,6-Tetrahydropyrimidin-2-yl)phthalazinone-1 Hydroiodide
— Główka M.L., Książek W., Staszewska A., Kozłowska K., Ołubek Z. and Krężel I.
2014 Monomeric Molecules in the Isostructural Calcium(II) and Strontium(II) Complexes with Pyrazine-2-carboxylic Acid
— Ptasiewicz-Bąk H., Ostrowski A. and Leciejewicz J.
COMMUNICATIONS
2024 A Microcalorimetry and Spectroscopy Study on the Interaction of Catalase with Cyanide Ion
— Ghadermarzi M., Saboury A.A. and Moosavi-Movahedi A.A.
2030 Stretching the Limits: According to High-Level Ab Initio Calculations C-O Bonds Are Longer than the Central C-C One in Hypothetical 2-Oxabicyclobutane
— Dodziuk H. and Leszczyński J.
2034 New Complex Compounds of Cu(I), Zn(II), Cd(II) and Hg(II) with 3-(2'-Thiothenoyl-amino)dibenzofuran
— Muresan V., Reiss A., Sbirna L.S., Muresan N. and Florea S.


ABSTRACTS


1871-1878

Spectroscopic Properties of New Indium(III)
Phthalocyanine Complexes

by J. Janczak
W. Trzebiatowski Institute of Low Temperature and Structure Research,
Polish Academy of Sciences, Okólna 2 str. P.O.Box 937, 50-950 Wrocław, Poland

(Received February 19th, 1998)

New blue-violet diamagnetic diindium(III) triphthalocyanine and paramagnetic indium(III) diphthalocyanine complexes have been obtained in crystalline form. The UV- -VIS, IR and far IR spectra of the In2Pc3 and InPc2 complexes are presented here for the first time. The spectroscopic data of the both In(III) complexes are discussed in terms of characteristic group frequencies and compared with other phthalocyanines. An empirical vibrational assignment of the observed fundamentals are given. The absorption electronic spectra indicate the proximity of the HOMO and LUMO of the Pc ligand in energy.

1879-1885

Preparation, Crystal Structure and Properties
of (Ph4P)2ReCl6.2CH3CN

by J. Małecka1, L. Jaeger2, Ch. Wagner2 and J. Mroziński1
1Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland
2Faculty of Chemistry, Institute of Inorganic Chemistry, Martin-Luther-University Halle-Wittenberg, D-06099, Halle/Saale, Germany

(Received March 27th, 1998)

(Ph4P)2ReCl6.2CH3CN 1 crystallizes as colourless single crystals from the acetonitrile solution of (Ph4P)2ReCl6 in ether. The crystals are monoclinic in space group P21/c with unit cell constants of a = 9.5507(12) ; b = 19.724(3) ; c = 15.033(2) ; = = 90o; ß = 8.451(14)o; V = 2801.1(7) 3; Z = 2. In the octahedral anion the Re-Cl bond lengths are 2.368 in average. The FIR region indicates two deformation bands (Cl-Re-Cl) at 162 cm-1 (F2g) and 175 cm-1 (F1u) and stretching band niu(Re-Cl) at 309 cm-1 (F1u). For 1 very weak antiferromagnetic super-exchange is observed; the effective magnetic moment at room temperature is 3.57 B.M.

1886-1889

Interactions between the Components
in the Zr-Ag-In System at 870 K

by L.D. Gulay1, V.I. Zaremba1, J. Stępień-Damm2 and Ya.M. Kalychak1
1Inorganic Chemistry Department, Ivan Franko Lviv State University,
Kirila and Methodiya Street 6, 290005 Lviv, Ukraine
2W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna Street 2, PO Box 937, 50-950 Wrocław, Poland

(Received February 18th, 1998; revised manuscript April 8th, 1998)

The interactions between the components in the ternary Zr-Ag-In system were studied. An isothermal section at 870 K was established by X-ray analysis. Two unknown ternary compounds have been found: ZrAg0.4In2.6-AuCu3 structure type (space group Pm3m, a = 4.3644(4) ) and Zr5AgIn3-Hf5CuSn3 structure type (space group P63/mcm, a = 8.735(3) , c = 5.948(2) ). Their crystal structures were determined by powder X-ray analysis.

1890-1896

Synthesis, Spectral, Magnetic and X-ray
Powder Diffraction Structural Characterization
of [Fe(NCS)3(OPPh3)3]

by I. Ondrejkovicova1, V. Jorik1 and J. Mroziński2
1Department of Inorganic Chemistry, Slovak Technical University, 812 37 Bratislava, Slovakia
2Faculty of Chemistry, Wrocław University, F. Joliot-Curie 14, 50-383 Wrocław, Poland

(Received March 3rd, 1998; revised manuscript April 10th, 1998)

The autocatalytic oxidation of PPh3 with dioxygen in the systems containing some iron compound and NCS- anions in acetonitrile leads to the formation of the complex [Fe(NCS)3(OPPh3)3], where OPPh3 is triphenylphosphine oxide. The complex is also formed by direct interaction of Fe(NCS)3 with OPPh3. This high-spin iron(III) complex acts as an oxidation catalyst of PPh3. On the basis of elemental analysis, spectral data and X-ray powder diffraction have been proved that the samples of the complex have not only the same composition but possess the same crystal structure irrespective of the preparation method.

1897-1906

Uptake of Molecular Oxygen by Co(II)
Chelates with Peptides in Aqueous Solution. Part X. Diastereoisomeric Dipeptides as Auxiliary Ligands in Oxygen-Free Complexes

by A. Kufelnicki and M. Świątek
Institute of Chemistry, Faculty of Pharmacy, Medical Academy of ŁódŸ,
ul. Muszyńskiego 1, 90-151 ŁódŸ, Poland

(Received January 26th, 1998; revised manuscript April 20th, 1998)

Co(II) complexes with a group of diastereoisomeric dipeptides consisting of alanine and leucine in various chiral forms have been studied in aqueous solution. The equilibria were determined by potentiometric and spectrophotometric methods, using least-squares fitting procedures. The results were compared with those for glycine dipeptides containing only one asymmetric atom.

1907-1914

New Insertion Reactions of Some Carbenoids
into Amide- and Sulfonamide-NH Bonds

by G. Mlostoń1, M. Celeda1, A. Świątek1, M. Kaegi2 and H. Heimgartner2
1Department of Organic and Applied Chemistry, University of ŁódŸ,
Narutowicza 68, PL-90-136 Łódz, Poland
2Organisch-chemisches Institut der Universitaet Zuerich,
Winterthurerstrasse 190, CH-8057 Zurrich, Switzerland

(Received February 27th, 1998)

In the presence of catalytic amounts of Rh2(OAc)4 in toluene, dimethyl diazomalonate (1) decomposed with evolution of N2 to form a carbenoid of type 8 which reacted with carboxamides 2 and toluenesulfonamide (4) to give 2-(acylamino)- and 2-(sulfonylamino)malonates 3 and 5, respectively. In an analogous reaction, -diazo ketone 6 and 4 yielded N-(2-oxo-1,2-diphenylethyl)toluenesulfonamide (7).

1915-1920

Flash Vacuum Pyrolysis of 1,3-Thiazole-5(4H)-thiones

by S. Leśniak1, G. Mlostoń1 and H. Heimgartner2
1Department of Organic and Applied Chemistry, University of ŁódŸ, Narutowicza 68, PL-90-136 ŁódŸ, Poland
2Organisch-chemisches Institut der Universitaet Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich, Switzerland

(Received March 16th, 1998)

Flash vacuum pyrolysis of 2-phenyl-1,3-oxazol-5(4H)-one (5) at 600oC/1.5.10-3 Torr proceeded via CO2-elimination to give 3-phenyl-2H-azirine (6) as the only detectable product which was isolated in 34% yield. Under similar conditions, 4,4-dimethyl-1,3- thiazole-5(4H)-thiones 7a and 7b yielded isomeric 1,4,2-dithiazole derivatives 8a,b as main products. Desulfurization leads to 2-(2-propylidene)-1,3-thiazetes 9 as minor products, and in the case of 7a, disulfide 10a is formed as a second minor product.

1921-1930

Reaction of Cyclic Allylic Acetates with Aliphatic
Alcohols in the Presence of Cerium(III) Chloride

by A. Uzarewicz and R. Dresler
Faculty of Chemistry, Nicolaus Copernicus University, 87-100 Toruń, Poland

(Received February 5th, 1998; revised manuscript March 30th, 1998)

The reactions of selected allylic acetates with methanol, ethanol, n-propyl alcohol, isopropyl alcohol and tert-butyl alcohol in the presence of catalytic amounts of cerium(III) chloride are described. Allylic alkyl ethers, bis-allylic ethers and 1,3-dienes were obtained depending on the structure of the acetates.

1931-1936

2,2'-Diselenobisbenzoates and
2,2'-Diselenobisbenzenesulfonates:
New Chiral Aryl Diselenides

by J. Palus, J. Młochowski and L. Juchniewicz
Institute of Organic Chemistry, Biochemistry and Biotechnology, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50 370 Wrocław, Poland

(Received March 13th, 1998; revised manuscript April 2nd, 1988)

The synthesis of chiral 2,2'-diselenobisbenzoates (3) from 2-aminobenzoic acid and chiral alcohols was elaborated. Similar method was applied for the preparation of chiral 2,2'-diselenobisbenzenesulfonates (4) from 2-aminobenzenesulfonic acid. Ester 3a was an efficient catalyst for chemoselective hydrogen peroxide oxidation of sulfides into sulfoxides but no stereoselectivity of the reaction was observed.

1937-1948

The Reaction of (Methylthio)acetyliron Complex
with Pentose Terminal Aldehydes

by K. Wiśniewski and A. Zamojski
Institute of Organic Chemistry, Polish Academy of Sciences,
Kasprzaka 44/52, 01-224 Warsaw, Poland

(Received April 2nd, 1998)

The reaction between anion generated from (methylthio)acetyliron complex (1) and four stereoisomeric dialdo-1,4-furanoses was performed. Each aldehyde led to mixtures (6-8) of stereoisomeric aldols. Aldols were separated and their configuration was determined. Decomplexation of these products was studied with oxidative (NCS, Cl2, I2, CuCl2) and reducing (BH3.Me2S and NaBH4) reagents. Sugar derivatives were isolated and their structures were deduced.

1949-1957

Studies on Mechanism of 2-Pyridinecarboxaldehyde
Oxidation by Dichromates in Strongly Acidic Aqueous Solutions. The Unusual Reaction Order
on Concentration of the Aldehyde

by E. Kita, P. Kita and G. Uścińska
Department of Chemistry, N. Copernicus University, 87-100 Toruń, Poland

(Received January 21st, 1998, revised manuscript March 2nd, 1998)

2-Pyridinecarboxaldehyde (pyad) has been oxidized by Cr2O72- ion at pH range 0-1 to 2-pyridinecarboxylic acid (pyac). The produced Cr(III) exists in the form of three complex ions: [Cr(pyac)(H2O)4]2+, [Cr(pyac)2(H2O)2]+ and [Cr(H2O)6]3+. The reaction follows unusual mixed fourth-order rate law: first-order on concentrations of Haq+ and Cr(VI) and second-order on concentration of the aldehyde. Mechanism of the reaction has been discussed.

1958-1962

Interaction of Thymidylate Synthase with
5-Fluoro-Substituted DUMP Analogues in
View of the Pyrimidine Ring Structure

by A. Jarmuła1, M.K. Cyrański2, A. Leś2, T.M. Krygowski2 and W. Rode1
1Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur St., 02-093 Warsaw, Poland
2Department of Chemistry, University of Warsaw, 1 Pasteur St., 02-093 Warsaw, Poland

(Received February 19th, 1998; revised manuscript March 26th, 1998)

To explain the mechanism of the influence of fluorine substituent on the FdUMP activity in thymidylate synthase reaction, the aromaticity based on X-ray determined structures, factor analysis applied to structural data from CSD and ab initio RHF calculations were employed. It was found that fluorine substitution dearomatizes the pyrimidine ring, stabilizing the local double C(5)=C(6) bond and making them more susceptible to nucleophilic addition from the thymidylate synthase side. The effect of local strain occurs in the ipso region in relation to the substituent. The effect is rather asymmetrical: the C(5)=C(6) bond is more strongly affected by the substituent than the C(4)-C(5) bond. This suggests a possibility of a further affinity increase of FdUMP system regarding the enzyme.

1963-1970

Calix[4]resorcinarenes as Dynamic Coatings for
Modified Stationary RP-18 Phase for HPLC

by M. Pietraszkiewicz, O. Pietraszkiewicz and M. KoŸbiał
Institute of Physical Chemistry, Polish Academy of Sciences, 01224 Warsaw, Kasprzaka 44/52, Poland
E-mail: pietrasz@ichf.edu.pl

(Received January 19th, 1998; revised manuscript April 6th, 1998)

Lipophilic calix[4]resorcinarenes, derived from lauryl aldehyde and resorcinol, are strongly adsorbed on the modified silica gel RP-18 during HPLC. This technique leads to the column with an excellent time stability and good reproducibility at the retention characteristics of substituted phenols as analytes.

1971-1980

The Analysis of Resistance Change
in Diffusion Controlled Electrode Processes

by K. Gatner and A. Zięba
Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50-383 Wrocław, Poland
e-mail: gatner@wchuwr.chem.uni.wroc.pl

(Received August 18th, 1997; revised manuscript April 8th, 1998)

The resistance changes in diffusion limited electrode processes are given and compared with experimentally determined by high frequency resistometry (HFR) combined with potentiostatic, galvanostatic and cyclic voltammetry methods. The general shape of resistance-time dependence is similar to current time transients in potentiostatic and potential time transients in galvanostatic experiments. The resistance-potential depen-dence in cyclic resistometry exhibits a sigmoidal shape, similar to the convolutive CV current function. The greatest change of the electrolyte resistance takes place near the electrode surface. High frequency resistometry provides independent parameters to those obtained from other electrochemical methods.

1981-1993

Solubility of n-Alkanes in Ethyl tert-Butyl Ether

by U. Domańska and P. Venkatesu
Warsaw University of Technology, Faculty of Chemistry, Noakowskiego 3, 00-664 Warsaw, Poland
E-mail:ula@ch.pw.edu.pl

(Received February 4th, 1998; revised manuscript April 9th, 1998)

The solid-liquid equilibrium (SLE), of 11 binary mixtures of n-alkanes (octadecane, nonadecane, eicosane, heneicosane, docosane, tricosane, tetracosane, pentacosane, hexa-
cosane, heptacosane, octacosane) in ethyl tert-butyl ether, (ethyl 1,1-dimethylethyl ether, ETBE) have been determined from 275 K to the melting temperature of n-alkane. Results of solubility are compared with values calculated by Wilson, NRTL and UNIQUAC equations utilizing parameters from SLE. The existence of solid-solid first order phase transition in hydrocarbons has been considered in the solubility calculations. The best correlation of the solubility data has been obtained by the NRTL equation, where the average root-mean-square deviation of the solubility temperatures is 0.84 K.

1994-1998

The Crystal Structure of Strontium Complex
with 3-Aminopyrazine-2-carboxylic Acid

by J. Leciejewicz1, H. Ptasiewicz-Bąk1 and J. Zachara2
1Institute of Nuclear Chemistry and Technology, ul. Dorodna 16, 03-195 Warszawa, Poland
2Department of Chemistry, Warsaw University of Technology, Warszawa, Poland

(Received February 10th, 1998; revised manuscript March 6th, 1998)

In the crystals of trans-diaquobis(mu-3-aminopyrazine-2-carboxylato-N,O,O,O)strontium(II) the Sr ion is eightfold coordinated: by two aminopyrazinate (APZA) ligands via their (N,O) bonding moieties [Sr-O 2.5189(15) , Sr-N 2.7280(18) ], two other carboxylate oxygen atoms donated by the adjacent APZA molecules [Sr-O 2.5989(16) ] bridging the Sr(APZA)2 units into molecular ribbons and two water molecules [Sr-O 2.5556(18) ]. The ribbons are interconnected by hydrogen bonds involving the water molecules and the carboxylate oxygens [O-H...O 2.71(1) ], as well as the amino group nitrogen atoms and the heteroring nitrogen atoms [N-H...N 3.08(1) ].

1999-2008

X-ray Structural Investigation
of Three 4-Aryl-Substituted [2.2]Paracyclophanes

by P.G. Jones1 and P. Kuś2
1Institut f<129>r Anorganische und Analytische Chemie, Technische Universitaet Braunschweig,
Postfach 3329, 38023 Braunschweig, Germany
2Department of Chemistry, Silesian University, 9, Szkolna Street, 40-006 Katowice, Poland

(Received March 16th, 1998)

The low-temperature crystal structures of 4-methylphenyl[2.2]paracyclophane (1), C23H22, orthorhombic, Pbca, a = 12.880(2), b = 7.4234(12), c = 34.425(6) , Z = 8; 2,6-dimethylphenyl[2.2]-paracyclophane (2), C24H24, orthorhombic, P212121, a = 8.593(3), b = 12.550(4), c = 15.745(4) , Z = 4, and 2,4,5-trimethylphenyl[2.2]paracyclophane (3), C25H26, monoclinic, P21/c, a = 13.737(2), b = 17.883(2), c = 15.230(2) , ß = 103.423(8), Z = 8 (two independent molecules) have been determined. Surprisingly, only small differences from the normal paracyclophane structure were found in the three sterically hindered species; the paracyclophane rings are mutually rotated and twisted by a few degrees, and the torsion angle between paracyclophane and aryl rings is slightly increased in 2 and 3 compared to 1.

2009-2013

Crystal Structure of
2-(1,4,5,6-Tetrahydropyrimidin-2-yl)phthalazinone-1 Hydroiodide

by M.L. Główka1, W. Książek1, A. Staszewska1,
K. Kozłowska1, Z. Ołubek1 and I. Krężel2
1Institute of General and Ecological Chemistry, Technical University of ŁódŸ,
ul. Żwirki 36, 90-924 ŁódŸ, Poland
2Department of Pharmaceutical Chemistry and Drug Analysis, Medical Academy,
ul. Muszyńskiego 1, 90-151 ŁódŸ, Poland

(Received February 26th, 1998; revised manuscript March 23rd, 1998)

X-ray crystal study of the 2-(1,4,5,6-tetrahydropyrimidin-2-yl)phthalazinone-1 hydroiodide showed different hydrogen bonding network and packing than those observed in the crystals of two other phthalazinones-1, comprising either smaller (4,5-dihydro-
imidazolyl) or larger (4,5,6,7-tetrahydrodiazepinyl) ring substituent in position 2 and having very similar crystal structures.

2014-2023

Monomeric Molecules in the Isostructural
Calcium(II) and Strontium(II) Complexes
with Pyrazine-2-carboxylic Acid

by H. Ptasiewicz-Bąk1, A. Ostrowski2 and J. Leciejewicz1
1Institute of Nuclear Chemistry and Technology, ul. Dorodna 16, 03-195 Warszawa, Poland
2Department of Chemistry, Warsaw University of Technology, Warszawa, Poland

(Received October 15th, 1997; revised manuscript April 7th, 1998)

The crystals of cis-tetraquobis(pyrazine-2-carboxylato-O,N)calcium(II) contain monomeric molecules, in which the calcium ion has a distorted dodecahedral coordination, formed by four water molecules (mean Ca-O = 2.441 , two oxygen atoms from monodentate carboxylic groups of two pyrazinic acid molecules (mean Ca-O = 2.458 ) and two nitrogen atoms located next to the above carboxylic groups (mean Ca-N = 2.619 ). In the crystals of cis-tetraquobis(pyrazine-2-carboxylato-O,N)strontium(II) the coordination of the Sr2+ ion is identical with that of the calcium complex, the corresponding mean distances being Sr-O(water) 2.572 , Sr-O 2.588 , Sr-N 2.751 . The monomeric molecules of both compounds are linked via a network of hydrogen bonds.

2024-2029

A Microcalorimetry and Spectroscopy Study
on the Interaction of Catalase with Cyanide Ion

by M. Ghadermarzi, A.A. Saboury and A.A. Moosavi-Movahedi
Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran

(Received November 12th, 1997; revised manuscript March 18th, 1998)

2030-2033

Stretching the Limits: According to High-Level Ab Initio Calculations C-O Bonds Are Longer than the Central C-C One in Hypothetical 2-Oxabicyclobutane

by H. Dodziuk1 and J. Leszczyński2
1Institute of Organic Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Kasprzaka 44, Poland E-mail: dodziuk@ichf.edu.pl
2Department of Chemistry, Jackson State University, Jackson, Mississipi 39217, USA
E-mail: jerzy@tiger.jsums.edu
(Received January 27th, 1998; revised manuscript April 9th, 1998)

2034-2036

New Complex Compounds of Cu(I), Zn(II), Cd(II) and Hg(II) with 3-(2'-Thiothenoylamino)dibenzofuran

by V. Muresan, A. Reiss, L.S. Sbirna, N. Muresan and S. Florea
Faculty of Sciences, University of Craiova, 1100 - Craiova, Romania
(Received September 15th, 1997; revised manuscript April 28th, 1998)


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