Spectroscopic and PM5 semiempirical studies of new hydrazone of gossypol with 3,6-dioxaheptylhydrazine

A new hydrazone of gossypol with 3,6-dioxaheptylhydrazine (GHDO) has been synthesised and its structure has been studied by FT-IR, ¹H NMR, ¹³C NMR as well as PM5 semiempirical methods. All the studies have provided clear evidence of the existence of GHDO in the solution in the N-imine–N-imine tautomeric form. The structure and the spectroscopic behaviour of this tautomer are discussed in details. It is shown the structure of GHDO is strongly stabilised by different types of intramolecular hydrogen bonds. In two of them the oxygen atoms of the oxaalkyl chains are also engaged. The strongest intramolecular hydrogen bond is formed between the O₇H proton and N₁₆ atom from the hydrazone group.     

Spectroscopic studies and PM5 semiempirical calculations of new hydrazone of gossypol with 3,6,9-trioxadecylhydrazine

A new hydrazone of gossypol with 3,6,9-trioxadecylhydrazine (GHTO) has been synthesised and its structure has been studied by ¹H NMR, ¹³C NMR, FT-IR spectroscopy and PM5 semiempirical methods. The results have shown that the newly synthesised hydrazone exists in solution in the N-imine–N-imine tautomeric form, stabilized by several intramolecular hydrogen bonds among which the O₇H N₁₆ intramolecular hydrogen bond is the strongest. The structure of GHTO is visualized by the PM5 semiempirical calculations.     

Complexes of Schiff base of gossypol with n-butylamine and some monovalent or bivalent cations studied by ESI MS, NMR, FT-IR as well as PM5 semiempirical methods

A Schiff base of gossypol with n-butylamine [GSBN] was shown to be capable of complexation of 2H⁺, Li⁺, Ca²⁺ and Ba²⁺ cations. This process of complex formation was studied by ESI mass spectrometry, ¹H and ¹³C NMR and FT-IR spectroscopy as well as by PM5 semiempirical method. It was found that gossypol Schiff base can form a 1:2 complex with H⁺ and 1:1 complexes with Li⁺, Ca²⁺ and Ba²⁺ cations. In all complexes the Schiff base of gossypol with metal cations exists in enamine-enamine tautomer, whereas in the 1:2 complex with H⁺ the imine-imine tautomer was found. The metal cations are coordinated through oxygen atoms of the O₁H(O₁,H) hydroxyl groups and a lone pair of an N-atom. The structures of these complexes were calculated by PM5 semiempirical method and discussed.     

X-ray,FT-IR,ESI MS and PM5 studies of Schiff base of gossypol with allylamine and its complexes with alkali metal cations and perchlorate anion

Crystals of the Schiff base derivative of gossypol with allylamine (GSBAL) were grown and subsequently examined by X-ray diffraction and FT-IR methods. The crystal space group is C2/c with a = 16.057(1) Å, b = 14.112(1) Å, c = 27.185(2) Å, β = 99.371(5)? and Z  = 8. In the crystal, GSBAL exists in the enamine–enamine tautomeric form. The FT-IR spectral features of the crystals are in agreement with the X-ray data indicating that both parts of the molecule are similarly intramolecular hydrogen-bonded but different intermolecular hydrogen-bonded, although the molecule is symmetrically substituted. On the basis of the electrospray ionization mass spectrometry (ESI MS) experiments, it has been shown for the first time that Schiff base of gossypol forms complexes with the perchlorate anion and metal cations simultaneously. The ESI MS spectra of the 1:1:1 mixtures of GSBAL:GOS:M⁺, in the positive and negative ion detection mode, have indicated the preferential formation of the 1:1 complexes of GSBAL with M⁺ (Li, Na or K) and ClO₄ ^? over the respective complexes forming between GOS and the metal cation or the anion. The PM5 semiempirical calculations have allowed visualization of the most energetically favourable structures of these two types of GSBAL complexes.     

Spectroscopic, semiempirical and X-ray structural study of the 2:1 complex of a cyclic diamide of o-phthalic acid with water molecule

Cyclic diamide of o-phthalic acid with 3,6-dioxa-octyl-1,8-diamine (CPhDA) was synthesised by a new method and its hydrate structure has been studied by X-ray diffraction, FT-IR, NMR and PM5 semiempirical methods. The crystal of this compound is orthorhombic, space group Pbcn, with a = 16.7033(11), b = 8.8823(5), c = 19.6182(12) and Z = 8. The IR spectrum of the crystal is consistent with the results obtained by the X-ray study and provides spectroscopic evidence for the formation of the H-bonded complex with water molecules. The calculated structure of the complex and the structural parameters are comparable with those determined by the X-ray method.     

Crystal structure of Schiff base derivative of gossypol with 3,6,9-trioxa-decylamine

Crystals of the Schiff base derivative of gossypol with 3,6,9-trioxa-decylamine were examined using X-ray diffraction, FT-IR and CPMAS spectroscopy. The Schiff base crystallizes as a racemate in the space group C2/c with a=24.390(5), b=12.026(2), c=14.810(3) Å, β=102.78(3)°, and Z=4. The results of the FT-IR, and CPMAS study of the crystals are in agreement with the X-ray data. The FT-IR spectrum of the crystals shows that the OH groups at position 1,1′ and 6,6′ as well as the N₁₆-H proton are involved in weak intermolecular and intramolecular hydrogen bonds, respectively. The FTIR and CP-MAS spectral behaviour is in agreement with the crystallographic results demonstrating the existence of the enamine-enamine tautomeric form of the Schiff base studied.     

Intramolecular hydrogen bonds and hydrogen-bonded systems in di-Schiff bases of 4-methyl-isophthalaldehyde with 4-substituted anilines

Three di-Schiff bases of 2-hydroxy-5-methyl-isophthalaldehyde with 4-R-anilines (R=H, CH₃, OCH₃) and their 1:1 complexes with HClO₄ were studied by FT-IR, ¹H, and ¹³C NMR spectroscopy in acetonitrile and [²H₃]acetonitrile solutions, respectively. In di-Schiff bases intramolecular OH…N hydrogen bonds have been detected; however, they show no proton polarizability. Hydrogen-bonded systems with fast proton fluctuation and large proton polarizability have been found in the 1:1 complexes of di-Schiff bases with HClO₄.     

异双Schiff碱及其稀土配合物的合成、机理与波谱

利用2,6-二氨基己酸(赖氨酸)具有两端不对称结构的－NH~2基,合成了一端与水杨醛,另一端与2,4-二羟基苯甲醛缩合形成空间结构不对称的异双Schiff碱及其与稀土元素配合物。以元素分析、热分析、摩尔电导、红外光谱、EPR以及^1HNMR,^1^3C-^1HCOSY谱、固体高分辨^1^3C谱等表征,研究了这类不对称Schiff碱的形成机理和配位方式。     

Crystal structure of Schiff base derivative of 2,2′-dihydroxybiphenyl-3-carbaldehyde with n-butylamine

Crystals of the Schiff base derivative of 2,2′-dihydroxybiphenyl-3-carbaldehyde with n-butylamine were examined using X-ray diffraction, FT-IR and CPMAS spectroscopy. Their space group is with a=8.377(2), b=12.214(2), c=14.774(3) Å, =76.62(3)°, β=81.34(3)°, γ=86.62(3)° and Z=4. The unit cell contains two symmetry-independent zwitterions. The hydrogen atom of the protonated N atom of the Schiff base is linked to the oxygen atom of the carbonyl group at position 2, which in turn is linked to the hydroxyl group by a short hydrogen bond [molecule A: NO=2.614(3), OO=2.520(3) Å; molecule B: NO=2.594(4), OO=2.526(3) Å]. The OHO⁻H⁺N bifurcated intramolecular hydrogen bonds are crystallographically asymmetric. The results of the FT-IR, ¹H, ¹³C, ¹⁵N NMR and CPMAS study of the crystals are in agreement with the X-ray data. Instead of a continuous absorption, only a broad band is found indicating relatively low proton polarizability in the two types of the cooperative relatively short intramolecular hydrogen bonds. The ¹⁵N NMR chemical shift indicates the protonation of the Schiff base.     

Synthesis and spectroscopic properties of Schiff bases derived from 3-hydroxy-4-pyridinecarboxaldehyde

A series of six new Schiff bases has been prepared by reacting aniline and 4-R-substituted anilines (R=CH₃, OCH₃, Br, Cl, NO₂) with 3-hydroxy-4-pyridinecarboxaldehyde. The ¹H, ¹³C, ¹⁵N and ¹⁷O NMR data of these compounds are used to discuss the tautomerism. ¹⁵N NMR and ¹⁷O NMR chemical shifts established the tautomer existing in solution as the hydroxy/imino. ¹³C CPMAS NMR confirms that the same tautomer is found in the solid state. The stabilities of the tautomeric forms have been approached using density functional calculations (B3LYP/6-31G**) in the gas phase. In all cases the neutral hydroxy/imino with E configuration is more stable than the oxo/enamino form (by ∼22 kJ mol⁻¹) and significantly more stable than the betaine (by ∼75 kJ mol⁻¹).     

NMR studies on a palladium(II) complex containing an incompletely coordinated facultative pentadentate Schiff base ligand

Palladium(II) dichloride reacts with 1,10‐bis(2‐pyrrolyl)‐2,5,9‐triaza‐1,9‐decadiene to give a [Pd(C₁₅H₂₀N₅)]Cl complex in which the ligand is four‐coordinated, leaving one pyrrole group dangling. By using COSY, gHSQC, gHMBC connectivities and NOE experiments it has been concluded that one linkage isomer exists in DMSO solution, in spite of the fact that different sets of N atoms of potentially pentadentate ligand might be involved in coordination, and that the three chelate rings in the complex cation are arranged in a sequence: five‐membered, six‐membered, five‐membered which is different from that (5–5–6) found by x‐ray studies on the related [Ni(C₁₅H₂₀N₅)]Cl compound. NMR studies allowed an unambiguous assignment of all ¹H and ¹³C NMR resonances for the complex. Results of x‐ray structural analysis of [Pd(C₁₅H₂₀N₅)](CH₃COO)H₂O supported the five‐membered, six‐membered, five‐membered ring sequence in the [Pd(C₁₅H₂₀N₅)]⁺ complex cation and show an E (trans) orientation of the dangling pyrrole group with respect to the metal center. Copyright © 2002 John Wiley & Sons, Ltd.     

Structural characterization of monomeric and oligomeric arylamides by solution and solid‐state NMR spectroscopy

An extensive study of both liquid‐ and solid‐state NMR spectroscopy was undertaken in order to elucidate the structural features of a phenyleneterephthalamide oligomer (OPTA) and of some related diarylamides. 1D‐ and 2D‐COSY measurements allowed us to assign completely the proton signals of the title compounds in solution, while 1D‐, 2D‐HETCOR and 2D‐COLOC measurements were used to assign ¹³C resonances. Solid‐state ¹³C NMR experiments, by conventional cross‐polarization (CP) at different contact times and with the dipolar dephased CP technique, were used to characterize these molecules in the solid state. Such techniques allowed us to differentiate among different carbon atoms; in the resulting spectra it was then possible to observe the selective appearance of signals from protonated and quaternary carbon atoms. It was also ascertained that the limited structural mobility of the insoluble OPTA, existing as a single monophasic species, can be explained in terms of hydrogen‐type bonds present in the solid state. Copyright © 2002 John Wiley & Sons, Ltd.     

NMR studies of novel Schiff bases derived from L-alpha-amino methyl esters and 3-hydroxypyridin-4-carboxaldehyde

Schiff bases of 3-hydroxypyridin-4-carboxaldehyde and L-alpha-amino esters as well as those derived from the structurally related amines lacking the ester function have been synthesised. In two cases a tetrahydro-1H-imidazo[4,5-c]pyridine was formed as a by-product. (1)H, (13)C, (15)N-NMR spectral data and density functional theory (DFT) calculations established the structure of all compounds.     

Full multinuclear resonance analysis of 4-amino-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane

The complete assignment of 19F, 1H and 13C NMR spectra for a monosubstituted octafluoro[2.2]paracyclophane derivative is described for the first time. The unambiguous assignments were achieved through the combination of 19F--1H HOESY, 1H COSY and 19F COSY techniques and then further confirmed employing a complementary approach using a Karplus-dependent 3JCF interaction. Interesting aspects of the coupling patterns for various JHH, JHF, JCF and JFF interactions are also discussed.     

Syntheses and characterization of a new class of mono‐ and heterodinuclear derivatives of boron derived from Schiff bases

Reactions of 2‐isopropoxy‐1, 3, 2‐ benzodioxaborole with equivalent amounts of Schiff base ligands having two hydroxyl groups ( 1a–3a ) yield mononuclear derivatives with one residual hydroxy group. The reactions of these mononuclear derivatives with hexamethyldisilazane in a 2:1 ratio yield heterodinuclear derivatives. All these newly synthesized derivatives have been characterized by elemental analyses and molecular weight measurements. Tentative structures have been proposed on the basis of IR and NMR (¹H, ¹³C, ¹¹B,²⁹Si)spectral data and Fab‐mass studies. Schiff bases and their corresponding mono‐ and heterodinuclear derivatives of boron have also been screened for antifungal activities. Copyright © 2010 John Wiley & Sons, Ltd.     

Deuterium isotope effects on 13C NMR chemical shifts of some α-(2-hydroxyaryl)-N-phenylnitrones (Schiff base N-oxides)

The deuterium isotope effect on the ¹³C NMR chemical shifts of some α-2-hydroxyaryl-N-phenylnitrones (Schiff base N-oxides) was studied. The existence of an intramolecular hydrogen bond with the proton localized on the phenolic oxygen atom was evidenced. Exceptionally large isotope effects ΔC-2(D) and ΔC-α(D) suggest that the substitution of the proton of the OH group by deuterium leads to a weakening of the hydrogen bond and some conformational changes in the molecule. This conclusion was drawn on the basis of a comparison of the deuterium isotope effects of Schiff base N-oxides and parent Schiff bases. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis and complete assignment of the 1H and 13C NMR signals of new acetamido and aminoflavonoid derivatives

The complete ¹H and ¹³C NMR assignment of 9 acetamidochalcones, 18 acetamidoflavones, 18 aminoflavones, 9 acetamidoflavonols and 9 aminoflavonols has been performed using one‐ and two‐dimensional NMR techniques including COSY, HMQC and HMBC experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

Palladium(II)‐dppe‐arylazoimidazole Complexes: Synthesis and Spectroscopic Charecterization

Reaction of [Pd(dppe)Cl2/Br2] with AgOTf in a dichloromethane medium followed by ligand addition led to [Pd(dppe)(OSO2CF3)2] and then [Pd(dppe)(RaaiR’)](OSO2CF3)2 [RaaiR’＝p-R-C6H4-NN-C3H2-NN-1-R’, (1—3), abbreviated as a N,N’-chelator, where N(imidazole) and N(azo) are represented by N and N’, respectively; R＝H (a), Me (b), Cl (c) and R’＝Me (1), CH2CH3 (2), CH2Ph (3), OSO2CF3 is the triflate anion, dppe＝1,2-bis- (diphenylphosphinoethane)]. 31P NMR confirmed that due to the two phosphorus atom interaction in the azoimine symmetrical environment one sharp peak was formed. The 1H NMR spectral measurements suggest that azo-imine links with lot of phenyl protons in the aromatic region. 13C NMR spectrum, 1H-1H COSY and 1H-13C HMQC spectrum assign the solution structure and stereo-retentive conformation in each complex.     

Deuterium isotope effects on 15N chemical shifts of double Schiff bases in the solid state and solution

The proton transfer equilibrium in a series of double Schiff base derivatives of trans‐1,2‐diaminocyclohexane in solution and the solid state was studied by means of ¹⁵N NMR spectroscopy and analysis of the deuterium isotope effect on the chemical shifts Δ¹⁵N(D). The presence of a proton transfer equilibrium in the N‐2‐hydroxynaphthylidene moieties of the Schiff bases studied in the solid state at room temperature was evidenced. The results confirmed the interrelation of the two hydrogen bonds in double Schiff base derivatives of trans‐1,2‐diaminocyclohexane. Copyright © 2003 John Wiley & Sons, Ltd.     

The tautomerism of Omeprazole in solution: a 1H and 13C NMR study

The tautomerism of 5(6)-methoxy-2-([(4-methoxy-3,5-dimethyl-2-pyridinyl)methyl] sulfinyl)-1H-benzimidazole (omeprazole) was determined in solution, K(T) = 0.59 in THF at 195 K, in favor of the 6-methoxy tautomer. The assignment of the signals was made by comparison with its two N-methyl derivatives in acetone-d6 and through theoretical calculations of the absolute shieldings (GIAO/DFT/6-311++G**).