Journal of the Serbian Chemical Society

Published by Serbian Chemical Society
Print ISSN: 0352-5139
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Keywords: a,-epoxy acids, pK a -values, LFER, transmission coefticients, Synthesis of trans--aroylepoxyacrylic acids. INTRODUCTION The applications of pK a values are extremely diverse, ranging from the most fundamental ones, e.g., calculating the distribution functions in a given pH-interval, to exploring the transportation of substances through cell membrane. Therefore, the knowl- edge of the pK a value of a substance is essential for various investigations in pharmacology, physiology, in structural, environmental, preparative and analytical studies and for industrial purposes, etc. l In the field of physical organic chemistry, the polar effects of substituents on the ionisation of acids 2 have been frequently studied
 
The electrochemical deposition and dissolution of copper in 0.0025 M CuSO4 + N,N-dimethylformamide + 0.5 M KClO4 solution was examined by the rotating disc and potentiodynamic methods. Both platinum and copper were used as working electrodes. A wide polarization range –1 to +2 V vs. SCE, and several temperatures between 25 and 55°C were encompased. The Cu/electrolyte interface was found to be permanently out of equilibrium, as a consequence of the development of a passivating layer. In accordance with the classic theory of a copper electrode in acidified aqueous solutions, the cathodic and anodic Tafel lines of metallic copper define a unique value of the exchange current density, however, their slopes do not correspond to the classic theory.
 
The crystal structure of 14-oxo-13, 14-seco-5a-cholest-13(18)-en-3b-yl acetate (2), obtained (in addition to the (E)- D12-isomer 3) by oxidative fragmentation of the C(13)-C(14) bond of 14a-hydroxy-5a-cholestten-3b-yl acetate (1), was determined by X-ray analysis. In addition, the configurations of the acetoxy derivatives 4-6, formed by the thermal lead tetraacetate oxidation of 1, were deduced from the relevant 1H-NMR parameters.
 
In this study the transfer coefficient of evaporation heat of the refrigerant 1,1,1,2-tetrafluoroethane (R-134a) in a vertical plate heat exchanger was experimentally investigated. The results are presented as the dependancy of the mean heat transfer coefficient for the whole heat exchanger on the mean vapor quality. The influences of mass flux, heat flux and flow configuration on the heat transfer coefficient were also taken into account and a comparison with previously published experimental data and literature correlations was made.
 
Comparison of the frictional factors for PHE and S&T heat exchangers.
Influence of plate corrugation angle on the j factor and the frictional factor.
Refrigerant cycle. 
Experimental results for the pressure drop during the evaporation of the refrigerant 1,1,1,2-tetrafluoroethane (R-134a) in a vertical plate heat exchanger are presented in this paper. The influences of mass flux, heat flux and vapor quality on the two-phase pressure drop are specially analyzed and compared with previously published experimental data and literature correlations. All results are given in graphical form as the dependency of the frictional pressure drop on the mean vapor quality.
 
The evaporation heat transfer coefficient of the refrigerant R-134a in a vertical plate heat exchanger was investigated experimentally. The area of the plate was divided into several segments along the vertical axis. For each of the segments, the local value of the heat transfer coefficient was calculated and presented as a function of the mean vapor quality in the segment. Owing to the thermocouples installed along the plate surface, it was possible to determine the temperature distribution and vapor quality profile inside the plate. The influences of the mass flux, heat flux, pressure of system and the flow configuration on the heat transfer coefficient were also taken into account and a comparison with literature data was performed.
 
X-Ray crystal structure analysis of the complex [Cu(tpth)(phen)(H2O)]n, where tpht is the dianion of terephthalic acid and phen is 1,10-phenanthroline, showed that two crystallographically different, but chemically identical tpht ions with monodentately coordinated COO groups exist; both tpht ions act as bridging ligands forming zigzag chains. The Cu(II) ions are in a deformed trigonal bipyramidal environment consisting of two N atoms from phen, two O atoms from different tpht ligands and one O atom from coordinated H2O molecule. The crystal data are as follows: C20H14CuN2O5, Mr = 425.87, triclinic system, space group P 1, a = 9.007(5), b = 10.557(5), c = 11.554(5) Å, a = 114.343(5), b = 92.942(5), g = 114.516(5) º, V = 877.3(7) Å3, Z = 2, F(000) = 434, rx = 1.612 g cm-3, m = 1.281 mm-1, R1 = 0.0280 for 4363 reflections with I > 2s(I), wR2 = 0.0785 for 5104 independent reflections and 254 refined parameters. Some of data were compared with isostructural Co(II) and Zn(II) complexes having the same ligands.
 
Diastereoisomers of {PdCl 2 [(S,S)-(i-Pr) 2 eddip]} (1). 
Molecular structure of {PdCl[(S,S)-(i-Pr)eddip]} (2). The dashed lines represent H-bonds. TABLE III. Selected experimentally found bond lengths (Å) and angles (°) in the molecular structure of 2 and the calculated values (2c) for the diastereoisomers of 2 Bond Compound 2 (R,R)-anti-2c (R,S)-anti-2c (S,R)-anti-2c (S,S)-anti-2c Pd-N2 1.995(5) 2.039 2.045 2.032 2.034 Pd-O4 2.019(5) 2.003 2.012 2.002 2.006 Pd-N1 2.047(6) 2.078 2.077 2.079 2.055 Pd-Cl 2.325(1) 2.344 2.340 2.350 2.353 C1-O1 1.190(1) 1.234 1.234 1.241 1.243 C1-O2 1.314(1) 1.374 1.376 1.353 1.351 C4-O2 1.441(1) 1.495 1.500 1.495 1.497 C7-O3 1.216(8) 1.242 1.242 1.242 1.243 C7-O4 1.316(8) 1.334 1.337 1.336 1.337 C10-N2 1.476(8) 1.494 1.502 1.494 1.504 C11-N1 1.508(8) 1.502 1.500 1.515 1.508 N2-Pd-N1 86.3(2) 86.5 85.5 87.2 86.5 N2-Pd-Cl 177.1(1) 177.2 178.3 176.8 175.2 O4-Pd-N1 167.7(2) 168.9 166.2 169.8 169.1 O4-Pd-Cl 95.2(1) 98.2 97.8 98.6 101.6 N1-Pd-Cl 96.6(1) 92.2 95.4 91.5 88.8 N2-C10-C11 108.2(6) 108.4 110.6 109.6 111.5 
The reaction of K2[PdCl4] with (S,S)-(i-Pr)2eddip diester (diiso-propyl (S,S)-2,2’-(1,2-ethanediyldiimino)dipropanoate) resulted in {PdCl2[(S,S)-(i-Pr)2eddip-κ2N,N’]} (1) and {PdCl[(S,S)-(i-Pr)eddip-κ2N,N’,κO]} (2) with one hydrolyzed ester group. The compounds were characterized by spectroscopic methods and it was proved that the reaction is diastereoselective (1H- and 13C-NMR) in the case of 2 (one diastereoisomer of four possible). The structure of 2 was determined by X-ray diffraction analysis, indicating that the product is the (R,R)-N,N’ configured isomer. In contrast, the reaction yielding 1 produced two of three possible diastereoisomers. DFT calculations support the formation of two diastereoisomers of 1 and of one diastereoisomer of 2.
 
A novel series of complexes of the type [M(C28H18N6)X2], where M=Co(II), Ni(II), Cu(II) or Zn(II) and X = Cl-, NO3- or CH3COO-, were synthesized by template condensation of isatin and 1,2-diaminobenzene in methanolic medium. The complexes were characterized with the help of various physico–chemical techniques, such as elemental analyses, molar conductance measurements, magnetic measurements, and NMR, infrared and far infrared spectral studies. The low value of molar conductance indicates them to be non-electrolytes. Based on various studies, a distorted octahedral geometry may be proposed for all the complexes. All the synthesized macrocyclic complexes were also tested for their in vitro antibacterial activity against some pathogenic bacterial strains. The MIC values shown by the complexes against these bacterial strains were compared with those of the standard antibiotics linezolid and cefaclor. Some of the complexes showed good antibacterial activities.
 
2-Chloro-4H-pyrido[1,2-a]pyrimidin-4-one (1) was utilized as a synthone precursor to prepare novel heterotricyclic systems. 2-Azido and 2-hydrazino derivatives (2 and 3) were obtained by nucleophilic replacement evolving compound 1. The hydrazine derivative 3 was transformed into the azido derivative 2 by nitrosation. Treatment of compound 3 with [bis(methylthio)methylene]malononitrile afforded 2-pyrazolylpyridopyrimidine 4. When compound 1 was reacted with 5-amino-3-(methylthio)-1H-pyrazole-4-carbonitrile, the same compound 4 was obtained with no evidence for the production of (pyrazolyl-amino)pyridopyrimidine 5 or pyrazolodipyridopyrimidine 6. Poly-functionalized dipyridopyrimidine 8 was obtained by reaction of compound 1 with 2-[(methylthio)-(phenylamino)methylene]propanedinitrile. Cyanoguanidine was reacted with compound 1 to afford N-pyridopyrimidinylguanidine 9, which was subjected to cyclization reaction, in presence of piperidinium acetate, to give pyridopyrimidopyrimidine 10.
 
Chemical speciation of Pb(II), Cd(II), Hg(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of L-glutamic acid was studied at 303 K in 0–60 vol. % 1,2-propanediol–water mixtures, whereby the ionic strength was maintained at 0.16 mol dm-3. The active forms of the ligand are LH3+, LH2 and LH–. The predominant detected species were ML, ML2, MLH, ML2H and ML2H2. The trend of the variation in the stability constants with changing dielectric constant of the medium is explained based on the cation stabilizing nature of the co-solvents, specific solvent–water interactions, charge dispersion and specific interactions of the co-solvent with the solute. The effect of systematic errors in the concentrations of the substances on the stability constants is in the order alkali > > acid > ligand > metal. The bioavailability and transportation of metals are explained based on distribution diagrams and stability constants.
 
Structures of the ligands 1-(p-chlorobenzyl)-2-(p-chlorophenyl)benzimidazole (L 7 ) and 1-[p-(dimethylamino)benzyl]-2-[p-(dimethylamino)phenyl]benzimidazole (L 10 ).
The possible geometry of the complexes.  
The reaction of the polymeric carbonyl complex [RuCl2(CO)2]x with 2-monosubstituted and 1,2-disubstituted benzimidazoles and 1,4-bis(benzimi-dazol-2-yl)benzene (L9) in 2-methoxyethanol produces various coloured complexes of the formulae [Ru(CO)2Cl2(L)2]•xH2O (L = 1-(o-hydroxybenzyl)-2-(o-hydroxyphenyl)benzimidazole (L1), 1-(o-hydroxyphenyl)benzimidazole (L4), 1-(p-hydroxyphenyl)benzimidazole (L5), 1-(p-chlorobenzyl)-2-p-chlorophenyl)benzimidazole (L7), 1-[1-(dimethylamino)benzyl]-2-[1-(dimethylamino)phenyl]benzimidazole (L10), x = 0; L = 2-benzylbenzimidazole (L8), 1,4-bis(benzimidazol-2-yl)benzene (L9), x = 2; L = 1-(o-chlorobenzyl)-1-(o-chlorophenyl)benzimidazole (L6); x = 3), [Ru(CO)2Cl(L2)3]Cl•3H2O and [Ru(CO)2(L3)4]Cl2•3H2O (L2 = 1-(>m-hydroxybenzyl)-2-(m-hydroxyphenyl)-benzimidazole; L3 = 1-(p-hydroxybenzyl)-2-(p-hydroxyphenyl)benzimidazole). The complexes were characterized by elemental analysis, conductivity measurements, as well as infrared, electronic, 1H- and 13C-NMR spectral studies.
 
Scheme 1. Synthesis of 1,2-dihydro-1-aryl-3H-naphth[1,2-e][1,3]oxazin-3-ones.
A phosphomolybdic acid catalysed novel method for the synthesis of 1,2-dihydro-1-aryl-3H-naphth[1,2-e][1,3]oxazin-3-one derivatives by a one-pot, three-component reaction of β-naphthol, aromatic aldehydes and urea in excellent yields is described.
 
Mechanism of formation of the 3,5-anhydro ring. 
The reactivity of the oxetane ring in 3,5-anhydro-1,2-O-cyclohexylidene-a-D-xylofuranose (1) was exemplified by its regiospecific nucleophilic opening. The action of concentrated hydrobromic or hydroiodic acid on 1 resulted in the exclusive formation of the 5-deoxy-5-halo derivatives, while the action of acetyl chloride or acetyl bromide yielded the corresponding 3-O-acetyl-5-deoxy-5-halo derivatives in 70 – 90 % yield. Under strongly acidic reaction conditions, the protection of the cyclohexylidene acetal function remained intact.
 
Preparation of the ligand Na[H 2 B(BTz) 2 ].
Preparation of the MCl 2 py 2 complexes.
Preparation of the complexes M[H 2 B(BTz) 2 ] 2 py 2 .
The preparation of sodium dihydrobis(1,2,3-benzotriazolyl)borate was realised by refluxing one mole of sodium borohydride with two moles of 1,2,3-benzotriazole in toluene over a period of 12 h. Its complexes with MCl2·py2 [whereM=Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and py=pyridine] were characterized by elemental analysis as well as magnetic, spectroscopic and conductivity measurements. On the basis of these studies, it is proposed that the geometry of all the complexes is octahedral. The ligand field parameters 10 Dq, B and b show extensive overlap between the M–L orbital. The molar conductance of 10-3 M solutions of the complexes in DMSO suggest them to be non-ionic in nature.
 
1,2,3-Trimethylbenzimidazolium iodide and its analogue salts with one or two substituents on benzene ring (X = NO2, Br,Cl, CH3) are, due to the reactivity of the 2-methyl group, able to react with para-substituted aromatic aldehydes (X = OH, OCH3, CH3, NMe2, NO2) using piperidine as a catalyst. 1-Methyl-2-styrylbenzimidazole iodomethylates were obtained and their structure elucidated by means of NMR and IR spectroscopy. The compounds are interesting as hemicyanine dyes. They lend themselves to studies based on electronic absorption spectroscopy and they have potential practical applications linked to their photosensitive properties.
 
On the basis of quantum chemical (PM3 and RHF/6-31G*) study, the regioselectivity of the bromination of 1-oxo-1,2,3,4-tetrahydronaphthalene (1) and 6,7-dimethyl-1-oxo-1,2,3,4-tetrahydronaphthalene (2) at their alicyclic and aromatic fragments was quantum chemically substantiated and confirmed experimentally. It was found that the above compounds undergo aromatic at the a-methylene position. The conditions for bromination at the positions 5, 8 of benzannelated ring were established. For the first time, non- and 2,2’-dibromosubstituted with respect to the oxo group bis(6,7-dimethyl-1-oxo-1,2,3,4-tetrahydronaphth-2-yl) sulphides (7, 8a, b) were obtained. The latter were found to show promise as stabilizing agents for the storage of cholera sera.
 
The ligands (L1: R=H; L2:R=CH 3 ; L3: R=Cl)  
Tautomeric equilibrium of the benzimidazole moiety.
Suggested structural formulas for the complexes of L1-L3 with CdCl 2 and HgCl 2 (R = H, CH 3 , Cl; M = Hg; R = CH 3 , Cl; M = Cd).
The bimetallic complexes of 1,4-bis-(5-H/methyl/chloro-1H-benzimidazol-2-yl)-1,2,3,4-butanetetraols (L1–L3) with CdCl2 and HgCl2 were synthesized and characterized by elemental analysis, molar conductivity, as well as IR and 1H-NMR spectroscopy. The ligands coordinate to the metal ion through all of the hydroxyl oxygen atoms as tetradentate in the Hg(II) complexes of L1–L3 and in the Cd(II) complexes of L2 and L3. In theCd2(L1)Cl4 complex, the ligand acts as tetradentate through the benzimidazole nitrogen atoms and the two oxygen atoms of the hydroxyl groups near the imidazole ring.
 
The packing diagrams show intermolecular hydrogen bonding and π-stacking interactions in the crystal of (1).  
The intermolecular contacts involving the functional groups of the cation in GOLFIW. CONCLUSIONS
The intermolecular contacts involving the functional groups of the cation in GOLFIW. CONCLUSIONS The (C 13 H 15 N 2 ) 2 [ZnCl 4 ]·H 2 O complex of distorted tetrahedral geometry was obtained in the reaction of ZnCl 2 with tacrine hydrochloride. The contacts surrounding the cations in the present structure and in the structures of C 13 H 15 N 2 Cl·H 2 O 24 and C 13 H 15 N 2 [B(Ph) 4 ]·CH 3 CN 25 reported elsewhere have been analyzed in detail. The prominent structural feature of [ZnCl 4 ] 2– is the variation in the Zn–Cl bond lengths. The Zn–Cl bond length increases with increasing the number of intermolecular hydrogen bonds that involve the ligand atom. Supplementary data. Cambridge Crystallographic Data Center, CCDC No. 695064, contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).  
The main aim of this study was to investigate the relationship between mIn the reaction of ZnCl2 with tacrine hydrochloride in water novel tetracoordinated (C13H15N2)2[ZnCl4]×H2O complex was obtained and characterized by elemental analysis, molar conductivity and X-ray analysis. The complex crystallizes in the space group P-1 of the triclinic crystal system. The structure contains two crystallographically different molecules of protonated tacrine present as counter cations, the [ZnCl4]2- complex anion and one water solvent molecule. The counter cations slightly differ in the puckering of the cyclohexene ring. The molecules of protonated tacrine are involved in different intermolecular hydrogen bonds. In the crystal, the hydrogen bonding generates a 3D assembly. In the crystal, p×××p stacking interactions between the rings of protonated tacrine were evidenced. The [ZnCl4]2- complex anion has a distorted tetrahedral geometry. Three out of the four Cl atoms are involved in intermolecular hydrogen bonding. The intermolecular H-bond interactions involving the Cl atoms affect the Zn–Cl bond lengths.
 
Structural formulae for (a) 3-amino-1,2,4-triazole, (b) 4-amino-1,2,4-triazole, (c) 2-mercaptothiazoline and (d) 2-mercaptopyridine.
Infrared spectra for: (a) 2-mercaptothiazoline, (b) CuCl 2 ·(2mct)·H 2 O, (c) CuCl 2 ·2(2mct)·2.5H 2 O and (d) CuCl 2 ·3(2mct)·2H 2 O.
Infrared spectra for: (a) 2-mercaptopyridine, (b) CuCl 2 ·(2mcp) and (c) CuCl 2 ·2(2mcp)·H 2 O.
Schematic representation of the proposed coordinative features for: (a) 3amt and (b) 4amt adducts.  
Thermogravimetric (TG) and differential TG (DTG) curves for: (a) CuCl 2 ·2(2mcp) and (b) CuCl 2 ·2(2mcp)·H 2 O.  
The adducts CuCl2·(3amt), CuCl2·2(3amt)·2H2O, CuCl2·3(3amt), CuCl2·(4amt), CuCl2·2(4amt), CuCl2·3(4amt)·2H2O, CuCl2·(2mct)·H2O, CuCl2·2(2mct)·2.5H2O, CuCl2·3(2mct)·2H2O, CuCl2·(2mcp) and CuCl2·2(2mcp)·H2O, where 3-amino-1,2,4-triazole = 3amt, 4-amino-1,2,4-triazole = 4amt, 2-mercaptothiazoline = 2mct and 2-mercaptopyridine = 2mcp, were synthesized by a solid state route and characterized by CHN elemental analysis and infrared spectroscopy. A thermogravimetric study was also performed. It was verified that 4amp is a molecule with a higher ability to act as a bridging ligand in comparison with 3amp. It was also found that, for all compounds, the mono adducts were the most thermally stable ones. Such a fact is in agreement with a higher ionic and covalent character of the metal–ligand bond in surch compounds.
 
Scheme 1. The starting compounds 3-arylsydnones 1a-d, the intermediates 3-aryl-5-methyl-1,3,4-oxadiazolin-2-ones (6a-d) after 1,3-dipolar cycloaddition, and the final product 3'-substituted-2-aryl-5-methyl-5'-thioxo-[4,4'-bi-4H-1,2,4-triazol]-3(1'H, 2H)-ones (10a-l).
Asimple and high yieldingmethod for the integration of two 1,2,4-triazole rings (10a–l) has been developed starting from 3-arylsydnones (1a–d). Confirmation for the structures of the newly synthesised compounds was provided by their physical, analytical and spectral data (IR, 1H NMR, 13C NMR and MS).
 
Transition metal complexes of 5-bromosalicylidene-4-amino-3-mercapto-1,2,4-triazine-5-one with metal precursors, such as Cu(II), Ni(II), Co(II) and Pd(II), were synthesized and characterized by physico–chemical and spectroscopic techniques. All the complexes are of the ML type. Based on analytical, spectral data and magnetic moments, the Co(II) and Ni(II) complexes were assigned octahedral geometries, while the Cu (II) and Pd(II) complexes square planar. A study on the catalytic oxidation of benzyl alcohol, cyclohexanol, cinnamyl alcohol, 2-propanol and 2-methyl-1-propanol was performed with N-methylmorpholine-N-oxide (NMO) as co-oxidant. All the complexes and their parent organic moiety were screened for their biological activity on several pathogenic bacteria and were found to possess appreciable bactericidal properties.
 
Alkylation of the 5-{4-[(4-bromophenyl)sulfonyl]phenyl}-4-(3/4-me¬thylphenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thiones 3a,b with various alkylation agents, i.e., ethyl bromide, phenacyl bromide and ethyl chloroacetate, afforded the S-substituted 1,2,4-triazoles 4-6a,b. The structures of these new compounds were elucidated by elemental analysis and IR, UV, 1H-NMR, 13C-NMR and MS spectroscopy. The newly synthesized products were tested for their antibacterial effects.
 
The acid-base behaviour of 4-phenyl-5-(4-R-benzyl)-1,2,4-triazoline-3-thione (1(R = OH); 2(R = OC2H5)) was studied in aqueous sulfuric acid and sodium hydroxide solutions. Three ionisation equilibria of compound 1 (pKBH3+ = –4.64, pKBH2 = 7.50, pKBH– = 10.06) and two ionisation equilibria of compound 2 (pKBH2+ = –4.82, pKBH = 7.45) were found. The first equilibrium belongs to the protonation of 1,2,4-triazoline-3-thione, while the second belongs to the dissociation of the same part of the molecule. The third equilibrium represents the dissociation process of the phenolic OH group of compound 1. The kinetics of hydrolysis of compounds 1 and 2 were studied in high concentrated sulfuric acid solutions. The hydrolysis follows an irreversible first-order consecutive reaction path.
 
The stability constants of the 1:1 binary complexes of Ni(II) and Co(II) with 3-amino-1,2,4-triazole (AT), leucine (Leu) and glutamic acid (Glu), and the 1:1:1 ternary complex of them and the protonation constants of the ligands were determined potentiometrically at a constant ionic strength of I = 0.10molL-1 (NaClO4) in aqueous solutions at 15.0 and 25.0 ºC. The thermodynamic parameters DGf0, DHf0 and DSf0 are reported for the formation reactions of the complexes. The enthalpy changes of all the complexations were found to be negative but the entropy changes positive. While the driving force for the formation of the Ni(II), Co(II) – AT complexes is the enthalpy decrease, the driving force for the ternary complexes of AT is the entropy increase.
 
Structure of the ligand.
Plots of ln(ln 1/y) vs. 1/T for the first degradation process of A, [Nb(GMT)Cl 5 ]; B, [Nb(BIAMT)Cl 5 ] and C, [Nb(BEAMT)Cl 5 ].
Metal complexes of niobium(V) with 3-substituted-4-amino-5-mercapto-1,2,4-triazole Schiff bases have been synthesized in dry chloroform under a nitrogen atmosphere. They were characterized by elemental analysis, molar conductance, electronic, infrared, 1H-NMR spectroscopy and thermal studies. Parameters, such as energy of activation (Ea), enthalpy (DH#), entropy (DS#) and Gibbs energy (DD#), were computed from the thermal decomposition data. Based on the spectral and thermal studies, a coordination number of seven is proposed.
 
Metal complexes of some divalent metal ions (Co, Ni, Cu and Zn) with 3-(a-acetylethylidenehydrazino)-5,6-diphenyl-1,2,4-triazine (AHDT) as a Schiff-base have been investigated potentiometrically and spectrophotometrically and found to have the stoichiometric formulae 1:1 and 1:2 (M:L). The formation constants of the proton-ligand and metal-ligand complexes have been determined potentiometrically at different temperatures (10, 20, 30, 40 and 50°C) at an ionic strength of 0.1 M KNO3 in 75% (v/v) dioxane-water solution. The standard thermodynamic parameters, viz. DG°, DH°, and DS°, for the proton-ligand and the stepwise metal-ligand complexes have been evaluated.
 
A space-filling presentation of the structure projected along the [110] direction showing 3D Cu(II)-btc open framework and channels containing H 2 tn 2+ ions. (Lattice H 2 O molecules, H 2 tn 2+ ions and H atoms are omitted for clarity.)  
Crystal structure analysis of the title complex, (H3NC3H6NH3)[Cu{C6H2(COO)4}]·2H2O, showed that the structure is built up from Cu(II) and tetradentate 1,2,4,5-benzenetetracarboxylate( 4–) (btc) ions forming a 3D open-framework with two different channels extending parallel to the 110/1,–1,0 and 001 directions. The first,wider channels accommodate 1,3-propanediammonium cations, whereas the second ones are filled with H2O molecules. The Cu(II) ions are in a tetrahedrally distorted square-planar environment consisting of four carboxylate O atoms from four different btc ligands. The four uncoordinated O atoms from the same carboxylate groups are placed around Cu(II) at longer distances (~2.8Å), forming a distorted sphenoid. The complex crystallizes in the orthorhombic space group Cc2m with a = 8.887(1), b = 11.493(2), c = 16.457(3) Å, V = 1680.9(5) Å3 and Z = 4. Final agreement indices are: R1 = 0.0303 for 1012 reflections with I > 2s(I), wR2 = 0.0493 for 1317 independent reflections and 123 refined parameters. The compound was also characterized by IR spectroscopy and TG/DSC analysis.
 
A three-dimensional QSAR pharmacophore model for antimalarial activity of steroidal 1,2,4,5-tetraoxanes was developed from a set of 17 substituted antimalarial derivatives out of 27 analogues that exhibited remarkable in vitro activity (below 100 ng/mL) against sensitive and multidrug-resistant Plasmodium falciparum malaria. The pharmacophore, which contains two hydrogen bond acceptors (lipid) and one hydrophobic (aliphatic) feature, was found to map well onto the potent analogues and many other well-known antimalarial trioxane drugs including artemisinin, arteether, artesunic acid, and tetraoxanes. The presence of at least one hydrogen bond acceptor in the trioxane or the tetraoxane moiety appears to be necessary for potent activity of this class of compounds. Docking calculations of some of these compounds with heme are consistent with the above observation as the proximity of the heme iron to the oxygen atom of the trioxane or the tetraoxane moiety favors potent activity of the compounds. Electron transfer from the oxygen of trioxane or the tetraoxane appears to be crucial for mechanism of action of the compounds. This information together with the pharmacophore should enable search for new peroxide containing antimalarial candidates from databases and custom designed synthesis of more efficacious and safer analogues.
 
An intramolecular steroidal 1,2,4,5-tetraoxane has been synthesised in six steps starting from methyl 3-oxo-7a,12a-diacetoxy-5b-cholan-24-oate. The synthesised 1,2,4,5-tetraoxane has moderate in vitro antimalarial activity against P. falciparum strains (IC50 (D6) = 0.35 mg/mL; IC50 (W2) = 0.29 mg/mL).
 
(a) Crystal packing showing the pseudo-layers of the complex units and lattice solvent molecules, as well as channels extending along the b-axis; (b) an enlarged view showing the content of channels as obtained by the crystal structure analysis (top), and a possible arrangement of the disordered H 2 O and DMSO molecules (bottom).
A view of the centrosymmetric binuclear complex unit with the atomic numbering scheme (displacement ellipsoids are drawn at the 50 % probability level). For the sake of clarity, only the asymmetric part of the lattice solvent molecules is shown and the hydrogen atoms are omitted. Symmetry code: (i)-x+1,-y+1,-z+2.
The crystal structure of the complex [Ni2 (btc)(dipya)2(H2O)6]×6H2O·DMSO (btc = tetra-anion of 1,2,4,5-benzenetetracarboxylic acid, dipya = 2,2’-dipyridylamine) was refined in the triclinic system, space group P , using low temperature (170 K) X-ray diffraction data. The compound consists of binuclear complex entities and la­ttice solvent molecules making pseudo-layers parallel to the 101 plane and channels parallel to the b-axis. The observed structural features were compared with the pre­viously reported results and formula [Ni2(btc)(dipya)2(H2O)6]×4H2O based on room temperature X-ray diffraction data. A possible arrangement of the disordered lattice solvent molecules located in the structural channels is described and discussed. It is concluded that the layout of these molecules is non-centrosymmetric, although the remaining and main part of the structure is centrosymmetric.
 
The molecular structure and conformational analysis of 1,2,7-thiadiazapane conformers were investigated by density functional theory (DFT) calculations at the B3LYP/cc-pVDZ level of theory. Four twist-chair (TC), six twist-boat (TB), two boat (B), two chair (C) and four twist (T) conformers were identified as minima and transition states for 1,2,7-thiadiazepane. The TC1 conformer is the most stable conformer and the twist-chair conformers are predicted to be lower in energy than their corresponding boat and chair conformations. DFT predicts a small barrier to pseudo-rotation and a remarkable activation barrier for the conformational interconversion of the twist-chair conformers to their corresponding boat conformers. The simplest conformational process and the one with the lowest barrier is the degenerate interconversion of the twist-chair 3 (TC3) conformation with itself via the Cs symmetric chair (C2) transition state. The calculated strain energy barrier for this process is 2.41 kJ mol-1. The highest conformational interconversion barrier is between TC2 and twist-boat 3 (TB3) forms, which was found to be 75.62 kJ mol-1.
 
Scheme 1.
The syntheses of cis-3a,4,7,7a-tetrahydroisoindole-1,3-dione derivatives and some cyclic diimides were performed by the reaction of different aromatic and aliphatic amines and diamines with cis-1,2,3,6-tetrahydrophthalic anhydride and maleic anhydride on montmorillonite K-10 under microwave irradiation and solvent-free conditions. The desired attractive products were obtained in high yields and characterized by elemental analysis aswell as by IR and 1H-NMR spectroscopy.
 
A series of 1,3-bis-substituted-5,5-dimethylhydantoins was synthesized using the reaction of 5,5-dimethylhydantoin with the corresponding alkyl halide in the presence of trimethylamine as catalyst and sodium hydroxide, according to a modified literature procedure. The experimental investigation included modification of the synthetic procedure in terms of starting materials, solvent, temperature, isolation techniques, as well as purification and identification of the products. The absorption spectra of the 1,3-bis-substituted-5,5-dimethylhydantoins were recorded in twelve solvents in the range 200–400 nm. The effects of the solvent polarity and hydrogen bonding on the absorption spectra were interpreted by means of linear solvation energy relationships using a general equation of the form n = n0 + sp* + aa + bb and by two-parameter models presented by the equation n = n0 + sp* + aa, where p* is a measure of the solvent polarity/polarisability, a is the scale of the solvent hydrogen bond donor acidities and b is the scale of the solvent hydrogen bond acceptor basicities. The solvent and substituent effects on the electronic absorption spectra of the investigated hydantoins is discussed.
 
Graphical presentation of the dependence of the Kovats retention indices on temperature for 2,4-pentanedione (a) and 2,4-nonanedione (b) on a DB-5 capillary column.
Dependence of the activation enthalpy on the number of carbon atoms for linear (u) and branched (s) alkyl 1,3-diketones.
A series of alkyl 1,3-diketones were used to study the temperature dependence of the Kovats retention indices in the temperature range 130–190 ºC (403–463 K). The temperature dependence is described by the empirical equation I = B + B/T + ClnT. On the basis of this equation, the activation enthalpy, DH#, and the chemical potential of the partitioning of one methylene group between the two phases of the chromatographic system, Dmp(CH2), were calculated. Also, the Kovats retention indices – boiling point correlations (linear and reciprocal) for alkyl 1,3-diketones were studied and Dmp(CH2) was calculated.
 
Room temperature Mössbauer spectrum of FePO-DAP.  
TG/DTG curves of FePO-DAP.  
1,3-Diaminopropane (DAP) was used as a structure-directing agent for the hydrothermal synthesis of an organically templated iron phosphate. During crystallization at 180 ºC, iron phosphate (FePO-DAP) with a layered structure was formed after one day. Longer crystallization yielded a mixture of FePO-DAP and leucophosphite, raising the question whether a transformation of FePO-DAP to leucophosphite occurs, or wheter DAP decomposes under hydrothermal conditions resulting in leucophosphite formation. Lattice energy and free energy calculations strongly support the supposition that a decomposition of DAP occurs prior to the formation of leucophosphite.
 
Propylimino derivatives of seven 5-arylidene-2,4-dioxotetrahydro-1,3-thiazoles, through the intermediate 2-thiono-5-arylidene-4-oxotetrahydro-1,3-thiazoles, were synthesized as new potential biologically active compounds. Log P was calculated for both possible tautomeric forms. The IR, 1H-NMR and 13C-NMR spectra, as well as M + in the MS are given for synthesized compounds.
 
The regiochemistry of the reaction between cycloimmonium ylides and ethyl propiolate.
Reaction scheme of the 1,3 dipolar cycloaddition of 1-methylphthalazinium ylides to ethyl propiolate.
In this paper, a comparative study of the reaction of 1-methylpihthalazinium ylides with nonsymmetrically activated alkynes in a solid media by classical heating and under microwaves is presented. The reactants were impregnated on a mineral support (Al2O3 – KF) or irradiation were brought into catalytic conditions through interphase solide – liquid transfer in the absence of a solvent and were then subjected to microwave. The reaction of 1-methylphthalazinium ylides with nonsymmetrically activated alkynes on a mineral support and in phase transfer catalysis under microwave irradiation is a regioselective reaction and results in larger yields in a shorter time than under classical conditions.
 
Structures of aripiprazole and bifeprunox, atypical antipsychotics. 
Schematic representation of 5-{2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl}-1H-benzimidazole interaction with key amino acids in the binding site of the D 2 dopamine receptor. 
Eight new compounds with halogen atom introduced into the benzimi­dazo­le-2-thione dopaminergic pharmacophore of 5-[2-(4-arylpiperazin-1-yl)ethyl]-1,3-dihy­dro-2H-benzimidazole-2-thiones with the arylpiperazine part of the molecule being selected according to known structure–affinity requirements, have been syn­thesized. All the new compounds were evaluated for the in vitro binding affinity at the dopa­mine (DA) D1 and D2 and serotonin 5-HT1A receptors by the competitive radioas­says, performed on synaptosomal membranes prepared from fresh bovine caudate nuclei and hippocampi. All the new compounds were strong competitors for the bin­d­ing of the radioligands to the D2 and 5-HT1A receptors, with the most active of them having 34 and 170 time higher affinity than non-halogenated congeners in the D2 DA receptor radioassays (compounds 9.1b and 9.2b, respectively). Diver­gently, the­se compounds were without significant affinities for the D1 DA receptors.
 
Structure of Hnan.  
Structure of the metal complexes of Hnan (M = Ni(II), Cu(II), Zn(II)).  
The coupling of diazotized 1-aminonaphthalene with 1,3-dicarbonyl compounds (acetylacetone, methylacetoacetate and acetoacetanilide) yielded a new series of bidentate ligand systems (HL). Analytical, IR, 1H-NMR and mass spectral data indicate that the compounds exist in the intramolecularly hydrogen bonded keto-hydrazone form. With Ni(II), Cu(II) and Zn(II), these potential monobasic bidentate ligands formed [ML2] type complexes. The IR, 1H-NMR and mass spectral data of the complexes are consistent with the replacement of the chelated hydrazone proton of the ligand by a metal ion, thus leading to a stable six-membered chelate ring involving the hydrazone nitrogen and the hydrogen bonded carbonyl oxygen. The Ni(II) and Zn(II) chelates are diamagnetic, while the Cu(II) complexes are paramagnetic. In the metal complexes of the naphthylazo derivatives of acetylacetone and methylacetoacetate, the acetyl carbonyl is involved in coordination, whereas in the chelates of the naphthylazo derivative of acetoacetanilide, the anilide carbonyl is bonded with the metal ion.
 
Phenesterine. 
New functionally substituted 5-arylidene-2,4-dioxotetrahydro-1,3-thiazole-3-carboxylic acid cholesteryl esters were synthesized from 2,4-dioxotetrahydro-1,3-thiazole and evaluated for their in vitro cytotoxicity against several human tumor cell lines and one normal lung fibroblast cell line.
 
Metal complexes of a 20-membered tetraazamacrocycle 2,12-dimethyl-3,13-di-n-propyl-1,4,11,14-tetraazacycloeicosa-1,3,11,13-tetraene (L) of the type [MLX2]X (M = Cr(III), Fe(III); X = NO3) [CoLNO3]NO3, [NiL(NO3)2], [CuL]Cl2 and [ZnLCl2] have been prepared by 2 + 2 cyclocondensation of 2,3-hexanedione with 1,6-diaminohexane in the presence of metal ions as templates. These complexes were characterized by elemental analyses, conductances, IR and electronic spectra and magnetic measurements.
 
2+2 Cyclocondensation of 1,7-diaminoheptane with a-diketones, viz. 2,3-butanedione, 3,4-hexanedione or 4,4’-dimethylbenzil, in the presence of Mg2+, Ca2+, Sr2+ and Ba2+ ions as templates yields a series of complexes of the type [ML(X2)] (where L = N4 macrocycle having a 22-membered ring and X = Cl or NCS). The resulting complexes were characterized by elemental analysis, conductance measurements and IR and 1H-NMR spectral studies.
 
IR spectra of dye 4a, 4b and 4c.  
A series of monoazo disperse dyes based on 2-amino-5-mercapto-1,3,4-thiadiazole was prepared by coupling with various N-arylmaleimides. The dyeing performance of these dyes was assessed on nylon fabric. The dyes were found to give yellow to brown colour shades on dyeing with good depth and levelness on nylon fabric. The dyebath exhaustion, fixation and fastness properties of the dyes were also determined. The dyed fabric showed moderate to good light fastness and very good to excellent fastness to washing, rubbing, perspiration and sublimation. The IR and visible range spectral properties of the dyes were also determined.
 
Ligand.
Tautomeric forms of the ligand.
Proposed structure of [MLCl 2 (H 2 O)], where M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II).
Scheme 1. Preparation of the ligand.
A new ligand 5-[6-(5-mercapto-1,3,4-oxadiazol-2-yl)pyridin-2-yl]-1,3,4-oxadiazole-2-thiol (L) and its Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes were synthesized. The authenticity of the ligand and its transition metal complexes were established by elemental analyses, conductance and magnetic susceptibility measurements, as well as spectroscopic (IR, 1H- and 13C-NMR, electronic, mass, ESR) and thermal studies. The IR and 1H-NMR spectral studies revealed the existence of the ligand in the thiol form in the solid state, whereas in the thione form in the dissolved state. The magnetic and electronic spectral studies suggest an octahedral geometry for all the complexes. The ligand acts as a tridentate ligand coordinating through the pyridine nitrogen and the nitrogen atoms (N-3' and N-3'') of the two oxadiazole rings. Antimicrobial screening of the ligand and its metal complexes were determined against the bacteria Escherichia coli and Bacillus cirroflagellosus, as well as against the fungi, Aspergillus niger and Candida albicans.
 
The clean cyclization of chalcones (1a–c/2a–c) with hydrazine hydrate under microwave irradiation afforded pyrazolines derivatised with sydnone (3d–i/4d–i), which underwent 1,3-dipolar cyclo-addition with acetic anhydride to form pyrazolines appended with 1,3,4-oxadiazoles (5g–l/6g–l). The newly synthesized compounds were confirmed by spectral and elemental analyses. In comparison to classical heating, the results indicate that microwave irradiation affords higher yields, shorter reaction times (4–12 min) and cleaner reactions.
 
Some hitherto unknown novel bismesoionic compounds, 3-[4/3-(5H/substituted- 2-sulphido-1,3,4-thiadiazolium-4-carbonyl)phenyl]sydnones 5a–d and 6a-d and 4-[4-(5H/substituted-2-sulphido-1,3,4-thiadiazolium)benzoyl]-5H/substituted-1,3,4-thiadiazolium-2-thiolates 9a–d have been synthesized from 3-[(hydrazinocarbonyl)phenyl] sydnones 1 and 2. Afew of these compounds exhibited in vitro antitubercular activity and also antimicrobial activity higher than the employed reference drugs.
 
A novel series of 1-(4-phenoxyphenyl)-3-[5-(substituted aryl)-1,3,4-oxadiazol-2-yl]propan-1-one was synthesized by reaction of 3-(4-phenoxybenzoyl)propionic acid with several aryl acid hydrazides in phosphorus oxychloride. The structures of the compounds were supported by IR, 1H- and 13C-NMR, MS data and elemental analysis results. These compounds were tested for their anti-inflammatory, analgesic, ulcerogenic and lipid peroxidation actions. A few compounds were found to have very good anti-inflammatory activity in the carrageenan-induced rat paw edema test, while a fair number of the compounds showed significant analgesic activity in the acetic acid-induced writhing test. These new compounds showed very low ulcerogenic action with reduced malondialdehyde content (MDA), which is one of the by-products of lipid peroxidation.
 
In order to find new and potent drug candidates for the treatment of Helicobacter pylori infections‚ in this study attention was focused on the synthesis and anti-H. pylori activity of a series of 5-(5-nitrofuran-2-yl)-1,3,4-thiadiazoles containing piperazinyl functionality at the C-2 position of the 1,3,4--thiadiazole ring. The synthesis of 1-[5-(5-nitrofuran-2-yl)-1,3,4-thiadiazol-2--yl]piperazine derivatives 3a–h and pyrrolidine derivative 3i was achieved with a versatile and efficient synthetic route via 2-chloro-5-(5-nitrofuran-2-yl)-1,3,4--thiadiazole. The inhibitory activity of the new derivatives 3a–i against twenty clinical H. pylori strains was evaluated by the disc diffusion method and compared with the commercially available standard drug metronidazole. Resulting biological data indicated that most compounds exhibited strong inhibitory activity even at doses lower than 2 μg/disc (average zone of inhibition >20 mm) while metronidazole had little or no growth inhibition at this dose. Compound 3c containing the N-benzoylpiperazin-1-yl moiety showed the most potent inhibitory activity.
 
Optimization of the reaction conditions
An efficient and practical synthesis of 1,3,5-trisubstituted 2-pyrazoline structures was achieved through cyclization of phenylhydrazine with ,-unsaturated ketones (chalcones) using methanoic acid (formic acid) as catalyst under thermal condition.
 
Top-cited authors
Ivan Gutman
  • University of Kragujevac
Slobodan Milonjic
  • Vinča Institute of Nuclear Sciences, Belgrade University, Belgrade, Serbia
Vele Tešević
  • University of Belgrade
Sumitra Chanda
  • Saurashtra University
D. Ž. Mijin
  • Faculty of Technology and Metallurgy, University of Belgrade