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81.
Zora?Popovi?Email author Gordana?Pavlovi? Vibor?Roje Nadja?Do?li? Dubravka?Matkovi?-?alogovi? Ivan?Leban 《Structural chemistry》2004,15(6):587-598
Three Schiff-bases of the Ar—CH—N—Ar type were synthesized from 2-hydroxy-1-naphthaldehyde and o- (1), m- (2), and p-nitroaniline (3) in order to investigate the shift of the keto-amine/enol-imine tautomeric equilibrium that arises by the introduction of the electron-withdrawal nitro group. The compounds have been investigated experimentally, in the solid state and in the solution, by IR, NMR, UV spectroscopy, and X-ray single crystal analysis, and theoretically by using density functional theory (DFT). The tautomeric equilibrium is strongly shifted towards the keto-amine form despite of the nitro group position at N-phenyl ring in the solid state of molecular structures of 1, 2, and 3 (especially indicated by C—O and C—N bond distances). The keto-amine tautomeric form of the compounds is characterized by a strong, resonance assisted hydrogen bond (RAHB) of the N—H O type (the N O distances are 2.530(8), 2.554(2) and 2.555(5) Å in 1, 2, and 3, respectively). The molecules are assembled in the crystalline state into a 3D HB network (1), centrosymmetrical dimers (2) or infinite chains (3) by the C—H O intermolecular hydrogen bonds. In contrast, UV/VIS spectra of the chloroform solution of the title compounds reveal predominance of the enol-imine form. The molecular geometries and relative stabilities of the compounds determined by using DFT find good agreement with the experimental data. 相似文献
82.
The Schiff base N,N-bis(2-hydroxy-3-methoxyphenylmethylidene)-2,6-pyridinediamine has been synthesized and characterized in the solid state and in solution using X-ray analysis, IR, UV/Vis, and NMR spectroscopy. Crystal data: C21H19N3O4, M
r = 377.39, orthorhombic, space group Pnc2, a = 4.9288(8), b = 8.8873(19), c = 20.870(5) Å, V = 914.19(20) Å3, Z = 2, R = 0.0387, R
w = 0.0530, 1845 independent reflections, 778 with I > 2(I). There are two intramolecular hydrogen bonds O—H-N between the hydroxyl and imino groups of 2.622(3) Å. The enolimine form is found in the solid state and is also the predominant tautomeric form in solution. Comparison of the title compound with the structurally related N,N-bis(salicylidene)-2,6-pyridinediamine and N,N-bis(salicylidene)-2,3-pyridinediamine is given. 相似文献
83.
Silylcobalt tetracarbonyls were reacted with various amines (B) in non-polar solvents to form silylammonium tetracarbonylcobaltate contact ion pairs formulated as [BSiR
3
+
, −Co(CO)4]. The compounds were characterized by IR and multinuclear magnetic resonance spectroscopy both in solution and in solid state.
Their properties are analogous to the known ion pairs [BH+, −Co(CO)4] and to amine adducts of halosilanes as well. 相似文献
84.
Dubravka Matkovi‐alogovi Jasminka Popovi Zora Popovi Igor Picek
eljka Soldin 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(1):m39-m40
The title compound, [HgBr(C7H4NO4)(H2O)], was obtained by the reaction of an aqueous solution of mercury(II) bromide and pyridine‐2,6‐dicarboxylic acid (picolinic acid, dipicH2). The shortest bond distances to Hg are Hg—Br 2.412 (1) Å and Hg—N 2.208 (5) Å; the corresponding N—Hg—Br angle of 169.6 (1)° corresponds to a slightly distorted linear coordination. There are also four longer Hg—O interactions, three from dipicH? [2.425 (4) and 2.599 (4) Å within the asymmetric unit, and 2.837 (4) Å from a symmetry‐related molecule] and one from the bonded water molecule [2.634 (4) Å]. The effective coordination of Hg can thus be described as 2+4. The molecules are connected to form double‐layer chains parallel to the y axis by strong O—H?O hydrogen bonds between carboxylic acid groups of neighbouring molecules, and by weaker hydrogen bonds involving both H atoms of the water molecule and the O atoms of the carboxylic acid groups. 相似文献
85.
Ilija Čorić Dalibor Milić Dubravka Matković-Čalogović Linda Tomašković 《Structural chemistry》2009,20(1):73-80
Nitration of α-resorcylic acid (3,5-dihydroxybenzoic acid) to 3,5-dihydroxy-2-nitrobenzoic acid (1) and 3,5-dihydroxy-4-nitrobenzoic acid (2), their separation, and crystallization is described. Crystal structures of 1, 1 · 3H2O, and 2 were determined by X-ray single-crystal diffraction analysis and compared with DFT-calculated structures. An intramolecular
hydrogen bond between the nitro group and o-hydroxyl group(s) occurs in all investigated structures. Intermolecular hydrogen bonds and π···π stacking interactions determine
the molecular packing. Additionally, N···O interactions have a crucial role in arrangement of the molecules in the crystal
structures of 1 and 2. DFT calculations in the gas phase and in the solution reveal that minor product 2 is a more stable regioisomer than 1, the major product in the nitration reaction. 相似文献
86.
Mirta Rub
i Ivica ?ilovi Marina Cindri Dubravka Matkovi‐alogovi 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(10):o570-o573
The molecular structures of two salicylaldehyde thiosemicarbazone derivatives, namely salicylaldehyde 4‐phenylthiosemicarbazone, C14H13N3OS, (I), and 4‐methoxysalicylaldehyde 4‐phenylthiosemicarbazone, C15H15N3O2S, (II), both of potential pharmacological interest, are found in the keto (thione) tautomeric form. The first compound represents a second triclinic polymorph of composition β‐C14H13N3OS. Although both polymorphs crystallize in the same space group (P), the α‐polymorph [Seena, Kurup & Suresh (2008). J. Chem. Crystallogr. 38 , 93–96] differs from the β form in its unit‐cell volume at 293 K. The molecules in the crystal structures of (I) and (II) are linked into centrosymmetric R22(8) dimers by hydrogen bonds of the N—H...S=C type. These dimers are connected through π–π stacking and T‐shaped C—H...π interactions into three‐dimensional networks. 相似文献
87.
Dubravka Jembrih Manfred Schreiner Momtchil Peev Peter Krejsa Christian Clausen 《Mikrochimica acta》2000,133(1-4):151-157
Art Nouveau (Tiffany, Loetz) and modern (Jack Ink, Strini Art Glass) iridescent glass fragments were characterized using
energy dispersive X-ray fluorescence analysis (EDXRF) and energy dispersive X-ray microanalysis in a scanning electron microscope
(SEM/EDX) in combination with factor analysis in order to obtain clustring. A character istic of Tiffany glass fragments is
leaded bulk glass, whereas in the case of Loetz K-Ca-Si bulk glass could be determined. Modern glass fragments show a high
amount of Na (7 wt% in the bulk of Jack Ink) and 0.6–1.5 wt% Sr in the bulk of Strini Art Glass. The contents of Si and Ca
are similar to Loetz glass. Furthermore, the differences in the structure of the glass artifacts could be determined. The
cross-sections of Tiffany show a layered structure of the bulk without a specific surface layer whereas the cross-sections
of Loetz glass reveal a homogeneous bulk material with one or two homogeneous surface layers in the BE-image. In the case
of the Jack Ink a homogeneous bulk glass and an inhomogeneous multilayered surface could be determined. Strini Art Glass show
a homogeneous bulk glass and a homogeneous surface layer in the backscattered electron image. 相似文献
88.
Zora Popović Dubravka Matković-Čalogović Jasminka Popović Ivan Vicković Marijana Vinković Dražen Vikić-Topić 《Polyhedron》2007
Novel mercury(II) compounds of 3-hydroxypicolinic acid (HpicOH; IUPAC name: 3-hydroxy-2-pyridinecarboxylic acid) were synthesized and characterized. HgCl(picOH) (1) and HgBr2(HpicOH) (2) were obtained as reaction products from the reaction of the corresponding mercury(II) halide with HpicOH, irrespective of the molar ratio of the reactants. From the reaction of HpicOH and mercury(II) acetate, Hg(picOH)2 (3) was obtained, while mercury(II) nitrate monohydrate gave the 1/1 solvate with water Hg(picOH)2 · H2O (3a). Infrared, 1H and 13C NMR spectroscopic data were analyzed for complexes 1, 2 and 3. X-ray crystal structure analysis of 1 and 2 revealed their polymeric nature and different coordination modes of HpicOH. In 1 the deprotonated picolinic acid is N,O-chelating and bridging, while in 2 HpicOH is a O-monodentate weakly bound ligand. Compound 1 consists of HgCl(picOH) moieties with two linear covalent bonds, Hg–N 2.143(4) and Hg–Cl 2.298(1) Å, and four additional Hg?O contacts (2.460(3)–2.904(3) Å) in which both oxygen atoms from the carboxylic group are bridging and involved in coordination to three neighboring mercury atoms, thus forming infinite layers. The coordination of mercury is 2 + 4. 2 consists of {HgBr2(HpicOH)} moieties, which are linked into chains by means of mercury to bromine secondary long range interactions. The coordination sphere of mercury can be described as irregular 2 + 3 formed by two covalently bonded bromine atoms (Hg–Br 2.277(1) and 2.366(1) Å), two bridging bromine atoms (Hg?Br 3.309(1) and 3.247(1) Å) and by the HpicOH ligand attached to mercury in the zwitterionic form via the carboxylic oxygen atom (Hg?O 2.602(7) Å). 相似文献
89.
Anamarija Peter Jana ic
labur Jona uri Sandra Voa Dubravka Dujmovi Purgar Lato Pezo Neven Voa 《Molecules (Basel, Switzerland)》2021,26(13)
Invasive plant species (IAS), with their numerous negative ecological, health, and economic impacts, represent one of the greatest conservation challenges in the world. Reducing the negative impacts and potentially exploiting the biomass of these plant species can significantly contribute to sustainable management, protect biodiversity, and create a healthy environment. Therefore, the main objective of this study was to evaluate the nutritional potential, phytochemical status, and antioxidant capacity of nine alien invasive plant species: Abutilon theophrasti, Amaranthus retroflexus, Ambrosia artemisiifolia, Datura stramonium, Erigeron annuus, Galinsoga ciliata, Reynoutria japonica, Solidago gigantea, and Sorghum halepense. Multivariate statistical methods such as cluster and PCA were performed to determine possible connections and correlations among selected IAS depending on the phytochemical content. According to the obtained results, R. japonica was notable with the highest content of vitamin C (38.46 mg/100 g FW); while E. annuus (1365.92 mg GAE/100 g FW) showed the highest values of total polyphenolic compounds. A. retroflexus was characterized by the highest content of total chlorophylls (0.26 mg/g) and antioxidant capacity (2221.97 µmol TE/kg). Therefore, it can be concluded that the selected IAS represent nutrient-rich plant material with significant potential for the recovering of bioactive compounds. 相似文献
90.
Whole grain cereals are an important source of bioavailable lignans, the group of compounds with potential anti-cancerogenic, antioxidant, anti-proliferative, pro-apoptotic, and antiangiogenic properties. The aim of this work was to develop a sensitive method for determination of wheat bran lignans. The analysis of lignans secoisolariciresinol, hydroxymatairesinol, lariciresinol, matairesinol, pinoresinol, syringaresinol is based on derivatization with pentafluoropropionic anhydride (PFPA) and gas chromatography-electron capture detection (GC-ECD), using styrene glycol as internal standard. To our knowledge, this is the first time that EC detection has been used for lignan analysis. The results show that the technique is reproducible and sensitive enough for detecting lignans in wheat at parts-per-billion (ppb) levels, except for hydroxymatairesinol. The method developed showed good recovery (85-105%) and precision (4-20%) for five types of lignans and thus represents a simpler and more affordable alternative to state-of-the-art wheat lignan liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. 相似文献