No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Hydrazones from hydroxy naphthaldehydes and N-aminoheterocycles: Structure and stereodynamics
Abstract
Schiff bases derived from 2-hydroxy-1-naphthaldehyde, or 1-hydroxy-2-naphthaldehyde, and different saturated N-aminoheterocycles have been prepared. Their structures have been elucidated in both solution and the solid state, including unequivocal X-ray diffraction analyses. Experimental data evidence the presence of imine (or hydrazone) structures as the most stable tautomers, while all attempts to switch to enamine (or enhydrazine) structures based on electronic and steric considerations were unsuccessful. A complete conformational analysis assisted by DFT calculations at B3LYP/6-31G∗ and M06-2X/6-311++G∗∗ levels has been performed on each series of representative structures.Graphical abstract
... Introduction. Schiff bases produced by condensation reaction of aromatic amines and aromatic aldehydes; which are versatile ligands furnishing imine N and other donor sites are responsible for a wide range of biological and chemical applications [1][2][3][4][5][6][7]. Past several decades have seen a great number of reports describing the synthesis of Schiff bases with interesting structural aspects and their biological perspective as well [8]. ...
... Difference of symmetric and asymmetric vibrations of the carbonyl group i.e. Δν(C_O asym \C_O sym ) provided valuable information about the coordination mode of COOH group in the complexes (2)(3)(4)(5)(6)(7). The values of Δν less than 200 cm −1 indicate the monodentate coordination mode of carboxylic group [21]. ...
Six new transition metal complexes derived from the reaction of 4(4-(dimethylamino) benzylideneamino) benzoic acid and Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) cations, were prepared, isolated and characterized by a range of spectral and analytical methods including UV/Vis, FT IR, NMR, MS, powder XRD, TGA and SEM. The complexes were formed with the deprotonation of the ligand and presented typical six-coordinated octahedral geometry. In addition, the biological activity was evaluated by conducting in vitro anti-bacterial, anti-fungal and anti-leishmanial screenings. All the complexes were found more active than the ligand, while complex 7 revealed biological significance.
... Introduction. Schiff bases produced by condensation reaction of aromatic amines and aromatic aldehydes; which are versatile ligands furnishing imine N and other donor sites are responsible for a wide range of biological and chemical applications [1][2][3][4][5][6][7]. Past several decades have seen a great number of reports describing the synthesis of Schiff bases with interesting structural aspects and their biological perspective as well [8]. ...
... Difference of symmetric and asymmetric vibrations of the carbonyl group i.e. Δν(C_O asym \C_O sym ) provided valuable information about the coordination mode of COOH group in the complexes (2)(3)(4)(5)(6)(7). The values of Δν less than 200 cm −1 indicate the monodentate coordination mode of carboxylic group [21]. ...
Heterocyclic 3-acetyl coumarin with hydrazide derivatives and their metal complexes are a substantial family of pharmaceutical drugs used to treat infection, anti-inflammatory issues, diabetes, and neurological disorders in the field of medicinal chemistry. Cyclization of 5- floro-2-furaldehyde, ethyl acetoacetate, and urea or thiourea by LaCl3.7H2O, addition of hydrazine to form amine derivatives were performed, and respective Schiff base derivatives (L1, L2) were produced by adding acetyl coumarin in an ethanolic solution at ambient temperature. New ligands and its complexes of the V (IV), Fe (III) and Mn (II) ions were characterized using (FT-IR, UV, MS) and nuclear magnetic resonance (1H-NMR) as well as elemental analysis (CHN). The synthesized complexes chelate with ligands L1, L2 via (N, O2) atoms. The structural geometry of the complexes was illustrated in the solid phase using FT-IR and UV-VIS spectroscopy, elemental analysis (CHNS), and flame atomic absorption, in addition to magnetic susceptibility and conductivity measurement. The antibacterial activity of the newly prepared ligands and their metal complexes was evaluated against Pseudonomous aerugionosa as a gram negative and Bacillus subtilis as a gram positive microorganism. Moreover, the antifungal activity against two fungi Aspergillus flavus, and Saccharomyces cerevisiae was studied for all compounds. The coordinated ligands significantly increased their bactericidal and fungicidal action compared to the free ligands, which did not exhibit any activity against the selected fungal and bacterial strains. The results focused on the synergetic relationship between the metal ion and the ligand, in addition to the structural variation.
In this work, Schiff base ligand (L) has been synthesized by condensation reaction of N-amino quinoline-2-one with 4-chlorobenzaldehyede in ethanol, for 5 hours. The synthesized ligand was characterized using ( ¹³ C, ¹ H NMR), (U.V-Vis), X-ray diffraction (XRD), (FT-IR), (C.H.N) elemental analysis, atomic force microscope (AFM) and melting point. The chromium complex was obtained by (2:1) (L: M) molar ratio and then characterized by FT-IR, UV-Vis, molar conductivity, magnetic susceptibility measurements, AFM, XRD and flame atomic absorption technique (FAA). The results confirmed an octahedral geometry of chrome ion (III). Drop casting techniques was used to prepare nano-thin films of the synthesized compounds. The aim of this study was to fabricate solar cells using the prepared nano-thin films. To achieve, the morphological, structural and optical properties of the nano-thin films were studied, and then they were precipitated on the silicon slides. The fabricated solar cells showed a high efficiency promising to be used for improving silicon solar cells.
Tautomerism plays a pivotal role in structural stabilization and reactivity. Herein we investigate in detail, aided by DFT simulations, the case of gossypol, a naturally-occurring atropisomeric dialdehyde showing promising properties as male contraceptive and antineoplasic agent. Its toxicity linked to reactive aldehydo groups can be reduced through amino conjugation. The occurrence of either imino or enamino structures is puzzling indeed and a clear-cut rationale is missing yet. N-enamine–N-enamine structures are prevalent or exclusive tautomers for Schiff bases from gossypol, while their corresponding hydrazones only possess N-imine–N-imine structures both in solution and the solid state. The modification of interactions between the lone pairs on the nitrogen atoms by altering the steric hindrance of the non-iminic nitrogen can favor enamine tautomers. This assumption has now been confirmed and, in solid state, hydrazones from N-aminopiperidine and their trans-2,6-dimethylderivative present bis-imine and bis-enamine structures, respectively. In solution, these compounds exist in equilibrium between both structures. The tautomerization mechanism, analysis of axial chirality and aromaticity in such H-bonded pseudorings are discussed as well.
This paper extends previous studies on hydrazones derived from hydroxyl naphthaldehydes to aromatic N-aminoheterocycles (exemplified herein by triazole derivatives), in an attempt to freeze enamine structures either by altering the electronic properties of the non-iminic nitrogen or through steric hindrance leading to coplanar dispositions between the lone pairs. By comparing experimentally obtained results (NMR in solution and crystal data) to computationally simulated ones (via DFT calculations in the gas phase and CHCI3), the structures of the preferential conformers and tautomers can be confidently assigned. All data are consistent with enhanced stability of imine forms with respect to their enamine counterparts. DFT calculations have the ability to identify the orbital interactions responsible for electron delocalization and the energy of intramolecular hydrogen bonding. In addition, all transition structures for conformational and tautomeric equilibria are located and characterized.
De-N-alkylation of iminium salts to aromatic azines, not necessarily those directly related in structure, occurs under exceptionally mild conditions. Several mechanistic pathways may be followed, among which the facile oxidation of N-alkylhydrazones of aromatic aldehydes appears to be a key step.
Reactions of 2,4-dinitrophenylhydrazine with salicylaldehyde, pyridine-2-carbaldehyde and 2-aminobenzophenone in methanol result in the hydrazone Schiff base ligands salicylaldehyde-, pyridine-2-carbaldehyde-, and 2-aminobenzophenone-2,4-dinitrophenylhydrazone, respectively. Crystals of salicylaldehyde-2,4-dinitrophenylhydrazone are monoclinic, space group P2 1/c, a = 13.820(3), b = 4.3515(9), c = 25.159(7) Å, β= 123.01(2)° with Z = 4. The molecular packing is mostly a zigzag or herring-bone pattern. " 2007 Verlag der Zeitschrift für Naturforschung.
Publisher Summary X-ray data can be collected with zero-, one-, and two-dimensional detectors, zero-dimensional (single counter) being the simplest and two-dimensional the most efficient in terms of measuring diffracted X-rays in all directions. To analyze the single-crystal diffraction data collected with these detectors, several computer programs have been developed. Two-dimensional detectors and related software are now predominantly used to measure and integrate diffraction from single crystals of biological macromolecules. Macromolecular crystallography is an iterative process. To monitor the progress, the HKL package provides two tools: (1) statistics, both weighted (χ 2 ) and unweighted (R-merge), where the Bayesian reasoning and multicomponent error model helps obtain proper error estimates and (2) visualization of the process, which helps an operator to confirm that the process of data reduction, including the resulting statistics, is correct and allows the evaluation of the problems for which there are no good statistical criteria. Visualization also provides confidence that the point of diminishing returns in data collection and reduction has been reached. At that point, the effort should be directed to solving the structure. The methods presented in the chapter have been applied to solve a large variety of problems, from inorganic molecules with 5 A unit cell to rotavirus of 700 A diameters crystallized in 700 × 1000 × 1400 A cell.
The results of studies of light-created chemiluminescence are described systematically. Conditions for the transformation of a dark chemical reaction into a chemiluminescence reaction are considered. Examples of photosensitised and photoinduced processes as well as of analytical applications are given.
Schiff bases N-(2-hydroxy-3-nitrobenzalidene)4-aminomorpholine (1) and N-(2-hydroxy-1-naphthylidene)4-aminomorpholine (2) were synthesized from the reaction of 4-aminomorpholine with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy-1-naphthaldehyde. Compounds 1 and 2 were characterized by elemental analysis, IR, 1H NMR, 13C NMR and UV–Visible techniques. The UV–Visible spectra of the Schiff bases with OH group in ortho position to the imino group were studied in polar and nonpolar solvents in acidic and basic media. The structures of compounds 1 and 2 have been examined cyrstallographically, for two compounds exist as dominant form of enol-imines in both the solutions and solid state. The title compounds 1 and 2 crystallize in the monoclinic space group P21/c and P21/n with unit cell parameters: a=8.410(1) and 11.911(3), b=6.350(9) and 4.860(9), c=21.728(3) and 22.381(6) Å, β=90.190(1) and 95.6(2)°, V=1160.6(3) and 1289.5(5) Å3, Dx=1.438 and 1.320 g cm−3, respectively. The crystal structures were solved by direct methods and refined by full-matrix least squares. The antimicrobial activities of compounds 1 and 2 have also been studied. The antimicrobial activities of the ligands have been screened in vitro against the organisms Escherichia coli ATCC 11230, Staphylococcus aureus ATCC 6538, Klebsiella pneumoniae UC57, Micrococcus luteus La 2971, Proteus vulgaris ATCC 8427, Pseudomonas aeruginosa ATCC 27853, Mycobacterium smegmatis CCM 2067, Bacillus cereus ATCC 7064, Listeria monocytogenes ATCC 15313, Candida albicans ATCC 10231, Kluyveromyces fragilis NRRL 2415, Rhodotorula rubra DSM 70403, Debaryomyces hansenii DSM 70238 and Hanseniaspora guilliermondii DSM 3432.
We present two new hybrid meta exchange- correlation functionals, called M06 and M06-2X. The M06 functional is parametrized
including both transition metals and nonmetals, whereas the M06-2X functional is a high-nonlocality functional with double
the amount of nonlocal exchange (2X), and it is parametrized only for nonmetals.The functionals, along with the previously
published M06-L local functional and the M06-HF full-Hartree–Fock functionals, constitute the M06 suite of complementary functionals.
We assess these four functionals by comparing their performance to that of 12 other functionals and Hartree–Fock theory for
403 energetic data in 29 diverse databases, including ten databases for thermochemistry, four databases for kinetics, eight
databases for noncovalent interactions, three databases for transition metal bonding, one database for metal atom excitation
energies, and three databases for molecular excitation energies. We also illustrate the performance of these 17 methods for
three databases containing 40 bond lengths and for databases containing 38 vibrational frequencies and 15 vibrational zero
point energies. We recommend the M06-2X functional for applications involving main-group thermochemistry, kinetics, noncovalent
interactions, and electronic excitation energies to valence and Rydberg states. We recommend the M06 functional for application
in organometallic and inorganometallic chemistry and for noncovalent interactions.
Simultaneously with the chemiluminescent reaction of salicylaldehyde hydrazone (G) oxidation by hypochlorite, the competing chemiluminescent reaction of G with the hydroxide ion occurs in alkaline media. The former reaction is accompanied by green chemiluminescence, whereas the latter, with blue chemiluminescence. The estimation of the rate constant for the bimolecular reaction G + OH– gives the value 2105 l mol–1 s–1. The necessary condition for appearance of chemiluminescence upon interaction of G with OH– is the preliminary illumination of the solution of G with light at a wavelength of 400–540 nm, which is accompanied by the formation of an acoplanar quinonoid isomer of G interacting with the hydroxide ion. The height of the energetic barrier for transition of G molecules from the illuminated to the dark state is 18 kcal mol–1.
Cited By (since 1996): 6085, Export Date: 25 August 2011, Source: Scopus
In the title compound, C(14)H(14)N(2)O(3)S, the conformation is stabilized by an intra-moleclar O-H⋯N hydrogen bond and the dihedral angle between the aromatic ring planes is 79.55 (18)°. In the crystal structure, inter-molecular N-H⋯O hydrogen bonds lead to [100] chains of mol-ecules.
The two independent mol-ecules in the asymmetric unit of the title compound, C(15)H(16)N(2)O(3)S, are each linked by an N-H⋯O(sulfon-yl) hydrogen bond into a linear chain that runs along the shortest axis of the triclinic unit cell. The hydr-oxy groups are engaged in intra-molecular hydrogen bonding and the amino N atom shows pyramidal coordination.
This simple, rapid, sensitive fluorometric method for determining magnesium is based on formation of a fluorescent complex of magnesium with 2-hydroxy-1-naphthaldehyde salicyloyl-hydrazone in alkaline ethanolic medium (lambda ex = 420 nm, lambda em = 460 nm). The detection limit of the method is 0.05 microgram/L (2 nmol/L) and the relative standard deviations (CVs) are 0.8%, 1.1%, and 2.5% at magnesium concentrations of 50, 5.0, and 0.50 microgram/L, respectively. The standard curve is linear from 0 to 250 micrograms/L (0-10 mumol/L). We investigated the chemistry of the reaction, and have applied the method to determine magnesium in 100-fold-diluted, otherwise untreated serum samples. Within-run CVs for the method were 1.7%, 1.1%, and 1.3% at mean magnesium concentrations of 15.7, 26.4, and 36.2 mg/L, respectively. Day-to-day CVs were 2.7%, and 3.6% at mean magnesium concentrations of 10.1 and 25.5 mg/L, respectively. Samples from 96 hospitalized patients in intensive-care units were analyzed by the proposed method (y) and by an automated colorimetric method involving Magon sulfonate reagent (x). Linear regression analysis of the results yielded: y = 1.01x - 0.04 (r = 0.982, Sxy = 0.90).
The title compound, C 14H 12N 4O 6·C 3H 7NO, was prepared by the reaction of 2-hydroxy-3-methoxybenzaldehyde and 2,4-dinitrophenylhydrazine in N,N-dimethylformamide. In the crystal structure, the molecule of 2-hydroxy-3-methoxy-benzaldehyde-2,4-dinitrophenylhydrazone is approximately planar, with a mean deviation of non-H atoms from the plane of 0.109 Å. The crystal packing is stabilized by O-H⋯O and N-H⋯O hydrogen bonds and aromatic packing interactions. © 2005 International Union of Crystallography Printed in Great Britain - all rights reserved.
Crystals of salicylaldehyde-4-morpholinothiosemicarbazone, , are orthorhombic with space group Pna21. Unit-cell dimensions are a = 11.85(5), b = 15.45(5) c = 7.18(3) with z = 4. Three-dimensional intensity data were collected from the multiple-film equi-inclination Weissenberg photographs taken with radiation. The intensities were estimated visually. The structure was solved by Patterson and Fourier methods and refined by the block-diagonal least-squares methods until the final R value becomes 0.11 for the 1064 observed independent reflections. The morpholine ring has a chair form. The rest atoms of salicylaldehyde-4-morpholinothiosemicarbazone molecule excluding morpholine ring and sulfur atom approximately lie on a plane. The hydroxyl group of the salicylaldehyde and the nitrogen atom of the thiosemicarbazone form an intramolecular hydrogen bond, , of 2.67. The short intermolecular distances all appear to be normal van der Waals contacts.
A possible explanation of the alpha effect, i.e. enhanced reactivity of nucleophiles possessing a lone pair adjacent to the reactive center is offered, based on the theory of charge and frontier controlled reactions. The enhanced reactivity results from an orbital splitting that raises the energy of the highest filled orbital of the nucleophile and increases the frontier controlling effect. Accordingly, it should be observed only in reactions involving a large covalent bond formation component in the rate determing step. Experimental data seem to confirm these conclusions.
The title compound, C22H16N2O2, exists as the phenol-imine form in the crystal, and there are strong intramolecular O-H···N hydrogen bonds with an O···N distance of 2.575(3)Å. The asymmetric unit contains only one-half of the molecule. The C=N bond distance is 1.290(2)Å and the C=N-Ni bond angle is 113.6(2)°. The configuration about the N-N bond is anti(1E). It belongs to the space group P21/n with cell parameters a = 8.5690(7), b = 6.1116(3), c = 16.0107(14)Å, β = 91.161(7)°. 2006
The crystallographic characterization of N-(2-hydroxy-benzylideneamino)benzamide, C14H12N2O2, reveals quasi coplanarity of the whole molecular skeleton, localization of the double bonds in the central -C=N-N-C=O chain, which has an E configuration with respect to the double bond of the hydrazone bridge, and an amide trans,s-cis configuration around the single N-N bond. The molecules are held together by hydrogen bonds linking them into layers along [100] direction.
The crystals of C 8 H 9 N 3 O 2 .C 2 H 4 O 2 consist of a one-to-one ratio of salicylaldehyde semicarbazone and acetic acid. Each molecule of salicylaldehyde semicarbazone is joined to an acetic acid molecule by a double hydrogen bond. This arrangement is very similar to the typical carboxylic acid dimer. The crystal structure exhibits a three-dimensional network of hydrogen bonds involving all of the possible hydrogen-bond donors and acceptors in both molecules.
Two molecules of the title compound, C14H13ClN2O3S, are linked by two N—H⋯Osulfonyl hydrogen bonds about a center of inversion to furnish a hydrogen-bonded dimer.
The molecule of the Schiff base in the crystal structure of the title compound, C8H9N3O2S·0.5H2O, interacts with symmetry-equivalent molecules and with the water molecule, which lies on a twofold rotation axis, to give a three-dimensional hydrogen-bonded network structure.
The review surveys the present state of research on the conformation, isomerism, and intramolecular interactions of molecules of the immense class of organic compounds containing a hydrazone group. A list of 221 references is included.
Proton tautomerization of salicylideneanilines in the solid state and in solution is reviewed, mainly focusing on the zwitterionic character of the NH form and its stabilization in the solid state and in solution at low temperature. The essential role of aggregation of molecules in proton tautomerization is emphasized.
The two symmetry-independent molecules of the title compound, C13H11ClN2O3S, are linked by N-H center dot center dot center dot Os (s = sulfonyl) and N-H center dot center dot center dot O-h (h = hydroxy) hydrogen bonds to furnish a chain that propagates along the a axis of the monoclinic unit cell.
Two molecules of the title compound, C14H13ClN2O3S, are linked by two N-H center dot center dot center dot O-sulfonyl hydrogen bonds about a center of inversion to furnish a hydrogen-bonded dimer.
Hydrogen bonding in salicylaldehyde-4-phenylthiosemicarbazone (1) has been studied by using experimental (NMR, Raman and UV spectroscopies) and quantum chemical (DFT) methods. It has been demonstrated that 1 adopted the hydroxy-thione tautomeric form in solution as found also in the solid state and previously indicated by secondary deuterium isotope effects. Apart from the intra-molecular hydrogen bonds new interactions between 1 and solvent molecules were formed as well. Changes in NMR chemical shifts and calculations have pointed towards a formation of inter-molecular three-centered hydrogen bonds in each of the studied complexes involving OH and NH groups of 1 and associated solvent molecules. Stabilization energies of intra-molecular hydrogen bonds were found to decrease with the increase of the solvent polarity. Two-dimensional NOESY spectra indicated conformational changes in solution with respect to the structure observed in the solid state. These were accounted for by a relatively low barrier of the rotation of the NN single bond thus enabling a molecule to posses a higher conformational flexibility in solution with portions of skewed conformations. The results presented here can help in a better understanding of the role hydrogen bonds can play in bioactivity of related thiosemicarbazone derivatives and their metal complexes.
Low-temperature, high-resolution X-ray studies of charge distributions in the three Schiff bases, the dianil of 2-hydroxy-5-methylisophthaldehyde, 3,5-dinitro-N-salicylidenoethylamine and 3-nitro-N-salicylidenocyclohexylamine, have been carried out. These structures exhibit interesting weak interactions, including two extreme cases of intramolecular hydrogen bonds that are ionic N(+)-H...O- and neutral O-H...N in nature. These two types of hydrogen bond reflect differences in geometrical parameters and electron density distribution. At the level of geometry, the neutral O-H...N hydrogen bond is accompanied by an increase in the length of the C(1)-O(1) bond, opening of the ipso-C(1) angle, elongation of the aromatic C-C bonds, shortening of the C(7)-N(2) bond and increased length of the C(1)-C(7) bond, relative to the ionic hydrogen bond type. According to the geometrical and critical point parameters, the neutral O-H...N hydrogen bond seems to be stronger than the ionic ones. There are also differences between charge density parameters of the aromatic rings consistent with the neutral hydrogen bond being stronger than the ionic ones, with a concomitant reduction in the aromaticity of the ring. Compounds with the ionic hydrogen bonds show a larger double-bond character in the C-O bond than appears in the compound containing a neutral hydrogen bond; this suggests that the electronic structure of the former pair of compounds includes a contribution from a zwitterionic canonical form. Furthermore, in the case of ionic hydrogen bonds, the corresponding interaction lines appear to be curved in the vicinity of the hydrogen atoms. In the 3-nitro-N-salicylidenocyclohexylamine crystal there exists, in addition to the intramolecular hydrogen bond, a pair of intermolecular O...H interactions in a centrosymmetric dimer unit.
The directional components of the barrier to rotation in hydrazine are investigated. The repulsion of the lone pairs appears to be significant, favoring the form with perpendicular lone pairs over the syn and anti forms.[/p]
The anils of salicylaldehyde comprise a chemical system which exhibits the properties of solid-state photochromism and thermochromism, and therefore are interesting for practical applications. In this paper the topochemical factors responsible for these properties are explored, together with the mechanism of the photochromic process and the nature of the colored anil molecule. For a better understanding of these problems the search incorporates solution and flash photolysis studies. Finally, new developments in which anils are used in different matrices like polymers, Langmuir-Blodgett films and cyclodextrins are reviewed, together with a number of potential applications.
The compound, 2-hydroxyacetophenone methanesulfonylhydrazone (apmsh) has been synthesized and its crystal structure has been investigated by X-ray analysis. The compound crystallizes in the monoclinic space group P21/c and the following unit cell parameters: a = 20.9496(15) Å, b = 4.9849(4) Å, c = 10.2300(8) Å; α = 90°, β = 98.2750(10)°, γ = 90°; V = 1057.21(14) Å3 and Z = 1. The molecular geometry of the apmsh in the ground state has been calculated using the restricted Hartree–Fock with HF/6-31G** and density functional method with B3LYP/6-31G** basis set. The optimized bond lengths and bond angles obtained by using B3LYP/6-31G** are in better agreement with the experimental values than those by using RHF/6-31G**. The conformers located at minima by PM3 semi-empirical calculation were re-optimized by using B3LYP/6-31G** method. Quantum-chemical calculations indicate that enol-imine tautomeric form is favored and the most stable conformer in gas phase is approximately 6 kcal/mol stable than next conformer.
Despite the remarkable thermochemical accuracy of Kohn–Sham density-functional theories with gradient corrections for exchange-correlation [see, for example, A. D. Becke, J. Chem. Phys. 96, 2155 (1992)], we believe that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional containing local-spin-density, gradient, and exact-exchange terms is tested on 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total atomic energies of first- and second-row systems. This functional performs significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
We present a new continuum solvation model based on the quantum mechanical charge density of a solute molecule interacting with a continuum description of the solvent. The model is called SMD, where the "D" stands for "density" to denote that the full solute electron density is used without defining partial atomic charges. "Continuum" denotes that the solvent is not represented explicitly but rather as a dielectric medium with surface tension at the solute-solvent boundary. SMD is a universal solvation model, where "universal" denotes its applicability to any charged or uncharged solute in any solvent or liquid medium for which a few key descriptors are known (in particular, dielectric constant, refractive index, bulk surface tension, and acidity and basicity parameters). The model separates the observable solvation free energy into two main components. The first component is the bulk electrostatic contribution arising from a self-consistent reaction field treatment that involves the solution of the nonhomogeneous Poisson equation for electrostatics in terms of the integral-equation-formalism polarizable continuum model (IEF-PCM). The cavities for the bulk electrostatic calculation are defined by superpositions of nuclear-centered spheres. The second component is called the cavity-dispersion-solvent-structure term and is the contribution arising from short-range interactions between the solute and solvent molecules in the first solvation shell. This contribution is a sum of terms that are proportional (with geometry-dependent proportionality constants called atomic surface tensions) to the solvent-accessible surface areas of the individual atoms of the solute. The SMD model has been parametrized with a training set of 2821 solvation data including 112 aqueous ionic solvation free energies, 220 solvation free energies for 166 ions in acetonitrile, methanol, and dimethyl sulfoxide, 2346 solvation free energies for 318 neutral solutes in 91 solvents (90 nonaqueous organic solvents and water), and 143 transfer free energies for 93 neutral solutes between water and 15 organic solvents. The elements present in the solutes are H, C, N, O, F, Si, P, S, Cl, and Br. The SMD model employs a single set of parameters (intrinsic atomic Coulomb radii and atomic surface tension coefficients) optimized over six electronic structure methods: M05-2X/MIDI!6D, M05-2X/6-31G, M05-2X/6-31+G, M05-2X/cc-pVTZ, B3LYP/6-31G, and HF/6-31G. Although the SMD model has been parametrized using the IEF-PCM protocol for bulk electrostatics, it may also be employed with other algorithms for solving the nonhomogeneous Poisson equation for continuum solvation calculations in which the solute is represented by its electron density in real space. This includes, for example, the conductor-like screening algorithm. With the 6-31G basis set, the SMD model achieves mean unsigned errors of 0.6-1.0 kcal/mol in the solvation free energies of tested neutrals and mean unsigned errors of 4 kcal/mol on average for ions with either Gaussian03 or GAMESS.
Two different tautomeric forms of a new Schiff base, C(17)H(19)N(3)O(2).C(17)H(19)N(3)O(2), are present in the crystal in a 1:1 ratio, namely the enol-imine form 4-(1-{[4-(dimethylamino)benzylidene]hydrazono}ethyl)benzene-1,3-diol and the keto-amine form 6-[(E)-1-{[4-(dimethylamino)benzylidene]hydrazino}ethylidene]-3-hydroxycyclohexa-2,4-dien-1-one. The tautomers are formed by proton transfer between the hydroxy O atom and the imine N atom and are hydrogen bonded to each other to form a one-dimensional zigzag chain along the crystallographic b axis via intermolecular hydrogen bonds.
A simple procedure for preparing uncontaminated salicylaldehyde hydrazone is outlined. The condensation reaction of salicylaldehyde and hydrazine in 2:1 molar ratio usually gives initially a mixture of the three geometrical isomers of salicylaldazine: one isomer is bright yellow, another is cream, the third is light pink. The earlier reports of Feigl and of Terentev et al. on the use of salicylaldehyde in the detection of hydrazine have been found to be misleading and the later report of Jain et al. incomplete. A detailed account is now given and improved salicylaldehyde tests for hydrazine are recommended. The structure given by Jain et al. for the copper(II) complex of salicylaldehyde hydrazone is confirmed by means of infrared spectroscopy and microanalysis. Preliminary studies on the copper(II) complex of salicylaldazine are reported.
Two different compounds, salicylaldehyde hydrazone and salicylaldazine, are formed by the condensation of salicylaldehyde and hydrazine, as shown by the difference in their melting points, solubilities, elemental analysis and infrared spectra. The earlier work of Feigl and Terentev et al. on the use of these compounds in detection of hydrazine has been reviewed and found to be misleading; the resulting confusion has been resolved.
A correlation-energy formula due to Colle and Salvetti [Theor. Chim. Acta 37, 329 (1975)], in which the correlation energy density is expressed in terms of the electron density and a Laplacian of the second-order Hartree-Fock density matrix, is restated as a formula involving the density and local kinetic-energy density. On insertion of gradient expansions for the local kinetic-energy density, density-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calculations on a number of atoms, positive ions, and molecules, of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent.
Previous studies have demonstrated that 2-hydroxy-1-naphthaldehyde isonicotinoyl hydrazone (NIH) and several other aroylhydrazone chelators possess anti-neoplastic activity due to their ability to bind intracellular iron. In this study we have examined the structure and properties of NIH and its FeIII complex in order to obtain further insight into its anti-tumour activity. Two tridentate NIH ligands deprotonate upon coordination to FeIII in a meridional fashion to form a distorted octahedral, high-spin complex. Solution electrochemistry of [Fe(NIH–H)2]+ shows that the trivalent oxidation state is dominant over a wide potential range and that the FeII analogue is not a stable form of this complex. The fact that [Fe(NIH–H)2]+ cannot cycle between the FeII and FeIII states suggests that the production of toxic free-radical species, e.g. OH.
or O2.
–, is not part of this ligand's cytotoxic action. This suggestion is supported by cell culture experiments demonstrating that the addition of FeIII to NIH prevents its anti-proliferative effect. The chemistry of this chelator and its FeIII complex are discussed in the context of understanding its anti-tumour activity.
N-(4-tert-butylbenzoyl)-2-hydroxy-1-naphthaldehyde hydrazone (BBNH) inhibits both the DNA polymerase and ribonuclease H (RNase H) activities of the human immunodeficiency virus type 1 reverse transcriptase. In this study, we show that BBNH binding impacts on the stability of the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) heterodimer. The Gibbs free energy of dimer dissociation of HIV-1 RT is decreased in the presence of increasing concentrations of BBNH, resulting in a loss in stability of 3.8 kcal mol(-1). To evaluate whether this observed phenomenon was mediated by BBNH binding to one or more sites in RT, we synthesized a variety of BBNH analogs and identified (4-t-butylbenzoyl)-2-hydroxy-1-salicylyl hydrazone (BBSH) and (4,N,N-dimethylaminobenzoyl)-2-hydroxy-1-naphthyl hydrazone as specific inhibitors of RT DNA polymerase or RT RNase H activity, respectively. Interestingly, only BBSH provided significant destabilization of the HIV-1 RT dimer. The identification of these specific inhibitors, in combination with other biochemical data, suggests a model in which two molecules of BBNH bind per RT heterodimer. In this regard, only the binding of hydrazone molecules in the DNA polymerase domain activity elicits the observed destabilization of the HIV-1 RT heterodimer.
Although density functional theory is widely used in the computational chemistry community, the most popular density functional, B3LYP, has some serious shortcomings: (i) it is better for main-group chemistry than for transition metals; (ii) it systematically underestimates reaction barrier heights; (iii) it is inaccurate for interactions dominated by medium-range correlation energy, such as van der Waals attraction, aromatic-aromatic stacking, and alkane isomerization energies. We have developed a variety of databases for testing and designing new density functionals. We used these data to design new density functionals, called M06-class (and, earlier, M05-class) functionals, for which we enforced some fundamental exact constraints such as the uniform-electron-gas limit and the absence of self-correlation energy. Our M06-class functionals depend on spin-up and spin-down electron densities (i.e., spin densities), spin density gradients, spin kinetic energy densities, and, for nonlocal (also called hybrid) functionals, Hartree-Fock exchange. We have developed four new functionals that overcome the above-mentioned difficulties: (a) M06, a hybrid meta functional, is a functional with good accuracy "across-the-board" for transition metals, main group thermochemistry, medium-range correlation energy, and barrier heights; (b) M06-2X, another hybrid meta functional, is not good for transition metals but has excellent performance for main group chemistry, predicts accurate valence and Rydberg electronic excitation energies, and is an excellent functional for aromatic-aromatic stacking interactions; (c) M06-L is not as accurate as M06 for barrier heights but is the most accurate functional for transition metals and is the only local functional (no Hartree-Fock exchange) with better across-the-board average performance than B3LYP; this is very important because only local functionals are affordable for many demanding applications on very large systems; (d) M06-HF has good performance for valence, Rydberg, and charge transfer excited states with minimal sacrifice of ground-state accuracy. In this Account, we compared the performance of the M06-class functionals and one M05-class functional (M05-2X) to that of some popular functionals for diverse databases and their performance on several difficult cases. The tests include barrier heights, conformational energy, and the trend in bond dissociation energies of Grubbs' ruthenium catalysts for olefin metathesis. Based on these tests, we recommend (1) the M06-2X, BMK, and M05-2X functionals for main-group thermochemistry and kinetics, (2) M06-2X and M06 for systems where main-group thermochemistry, kinetics, and noncovalent interactions are all important, (3) M06-L and M06 for transition metal thermochemistry, (4) M06 for problems involving multireference rearrangements or reactions where both organic and transition-metal bonds are formed or broken, (5) M06-2X, M05-2X, M06-HF, M06, and M06-L for the study of noncovalent interactions, (6) M06-HF when the use of full Hartree-Fock exchange is important, for example, to avoid the error of self-interaction at long-range, (7) M06-L when a local functional is required, because a local functional has much lower cost for large systems.