Supramolecular assemblies and molecular recognition of amphiphilic schiff bases with barbituric acid in organized molecular films

A bolaform Schiff base, N,N'-bis(salicylidene)-1,10-decanediamine (BSC10), has been synthesized and its interfacial hydrogen bond formation or molecular recognition with barbituric acid was investigated in comparison with that of a single chain Schiff base, 2-hydroxybenzaldehyde-octadecylamine (HBOA). It has been found that while HBOA formed a monolayer at the air/water interface, the bolaform Schiff base formed a multilayer film with ordered layer structure on water surface. When the Schiff bases were spread on the subphase containing barbituric acid, both of the Schiff bases could form hydrogen bonds with barbituric acid in situ in the spreading films. As a result, an increase of the molecular areas in the isotherms was observed. The in situ H-bonded films could be transferred onto solid substrates, and the transferred multilayer films were characterized by various methods such as UV-vis and FT-IR spectrosopies. Spectral changes were observed for the films deposited from the barbituric acid subphase, which supported the hydrogen bond formation between the Schiff bases and barbituric acid. By measuring the MS-TOF of the deposited films dissolved in CHCl3 solution, it was concluded that a 2:1 complex of HBOA with barbituric acid and a 1:2 complex of BSC10 with barbituric acid were formed. On the other hand, when the multilayer films of both Schiff bases were immersed in an aqueous solution of barbituric acid, a similar molecular recognition through the hydrogen bond occurred. A clear conformational change of the alkyl spacer in the bolaform Schiff base was observed during the complex formation with the barbituric acid.     

Substitution controlled molecular orientation and nanostructure in the Langmuir-Blodgett films of a series of amphiphilic naphthylidene-containing Schiff base derivatives

Three amphiphilic Schiff bases containing naphthylidene group, N-octadecyl-2'-hydroxy-naphthalenylideneamine (HNOA-1), N-(4'-octadecyloxy)-2'-hydroxy-naphthalenylideneaniline (HNOA-2), and N-(4'-N-octadecylbenzamide)-2'-hydroxy-naphthalenylideneaniline (HNOA-3), were designed and their interfacial assemblies were investigated. These amphiphiles have different substitution groups in the Schiff base moiety. It was observed that HNOA-1, being in lack of second aromatic ring, formed multilayer films at the air/water interface, while the other two compounds, with another aromatic ring and some hydrophilic groups, can be spread as monolayers on water surface. All of Schiff bases could coordinate with Cu(Ac)2 in situ in the spreading films. Both the spreading films from water and aqueous Cu(Ac)2 subphases were transferred onto solid substrates and their surface morphologies as well as molecular packing modes were investigated by a series of methods such as atomic force microscopy, Fourier transform infrared spectra and X-ray diffraction. Depending on the different substitutions, these amphiphiles showed different orientations in the Langmuir-Blodgett films. Particularly, during the process of complex formation at the air/water interface, great conformational change of the alkyl chain was observed for HNOA-2 in comparison with that of other compounds. In addition, nanofiber structures were observed for the Cu(II)-complexed HNOA-1 and HNOA-2 films.     

Supramolecular Assembly and Headgroup Effect in Interfacial Organized Films (I): A Study of Some Bolaamphiphiles

Two bola form Schiff bases derivatives with different substituted head groups have been designed and their interfacial phase behaviors and coordination with Cu(II) ions were investigated. It has been found that while one molecule with benzene headgroup formed dotted aggregations at the air/water interface, another with naphthyl moiety as head group formed crystalline multilayer films on water surface. When on the sub phase containing Cu(II) ions, both of the Schiff bases can coordinate with Cu(II) in situ in the spreading films with the obvious conformational change of alkyl chains. The in situ Cu(II)-coordinated films could be transferred onto solid substrates and subsequently characterized by various spectroscopic methods such as UV-vis and Fourier transform infrared spectra as well as the morphological character with atomic force microscopy measurement. In comparison, the ex situ coordination process at the liquid/solid interface have also been investigated by continuous spectral measurement. Depending on the different head groups, these amphiphiles showed different aggregation behaviors in the Langmuir-Blodgett films. Particularly, during the coordination process of ligand with Cu(II) ions in organized molecular films, great conformational change of the alkyl chains was observed. At the same time, a rational explanation about the head group effect on regulating the aggregation behaviors was discussed.     

溶剂和分子结构对席夫碱分子在有机凝胶中的荧光增强和超分子手性的影响

研究了在有机胶凝剂中掺杂的席夫碱化合物的结构和性质. 实验发现, 虽然席夫碱分子单独不能在有机溶剂中形成凝胶, 当其与一种胶凝剂N,N’-双十八烷基-L-Boc-谷氨酸混合时, 它们在二甲基亚砜或甲苯中形成透明的有机凝胶. 与相应的溶液相比, 观察到在有机凝胶中的荧光增强现象, 并且这一增强与席夫碱的结构有密切关系. 在二甲基亚砜的有机凝胶中, 观察到带有长烷基链的席夫碱具有诱导手性. 表明通过凝胶的形成, 胶凝剂的手性能传递到带有长链的席夫碱上.     

Supramolecular Assembly and Headgroup Effect in Interfacial Organized Films (II): A Study of Some Single Chain Amphiphiles

Some single chain Schiff bases amphiphiles with different substituted headgroups have been designed and their interfacial phase behaviors and coordination with Cu(II) ions were investigated. It has been found that depending on the size of aromatic headgroups, the formed nanostrucures showed obvious differences, indicating different aggregation behaviors in the Langmuir-Blodgett films. The spreading Cu(II)-coordinated films could be transferred and subsequently characterized by spectral methods and morphological measurement. In addition, during the coordination process of ligand with Cu(II) ions in organized molecular films, some conformational change of long alkyl chains was observed. The present work showed clearly the headgroup effect of amphiphiles on regulating the aggregation behaviors in Langmuir-Blodgett films.     

几个新型呋喃氨基腈衍生物的合成及抗菌活性

用5-甲基-4-乙氧羰基呋喃氨基腈与芳醛反应制得Schiff碱,再采用NaBH4还原Schiff碱,得到3个新型5-甲基-4-乙氧羰基呋喃氨基腈衍生物.利用核磁共振谱(1H NMR)、红外光谱(IR),质谱(EI-MS)表征了产物的结构;并初步测定了产物的抗菌活性.结果表明,目标化合物的抗菌活性一般.     

Effect of Solvent and Molecular Structure on the Enhanced Fluorescence and Supramolecular Chirality of Schiff Bases in Organogels

The structures and properties of some Schiff base compounds doped in organogels were investigated. It was found that although individual Schiff bases could not form organogels with organic solvents, they can gel by mixing with an organogelator, N,N′-bisoctadecyl-L-Boc-glutamic-diamide, which formed transparent organogels in dimethyl sulfoxide (DMSO) or toluene (Tol). The enhancement of doping Schiff bases fluorescence in the organogel was observed in comparison with that of the corresponding solution. Furthermore, in the DMSO organogel, the induced chirality was obtained from the doping Schiff base with long alkyl chain. In contrast, the Schiff bases without long alkyl chain could not form supramolecular chiral assemblies in organogel. It was suggested that through gel formation the chirality of the gelator could be transferred to the Schiff base through hydrophobic interaction among the long alkyl chains.     

Molecular structures and stability constants of gossypol and its aza-derivative complexes with silver(I) cations studied by potentiometric, ESI MS, NMR, and AM1d semiempirical methods

Stability constants of complexes formed by gossypol and by ten of its Schiff bases with Ag (+) cations were determined by the potentiometric method. The potentiometric and ESI MS experiments indicate the formation of AgL (+) and Ag 2L (2+) complexes between the Schiff bases G1-G7 and Ag (+) cations as well as the formation of AgL (+), Ag 2L (2+), AgL 2 (+) and Ag 3L 2 (3+) complexes between the Schiff bases G8-G10 and Ag (+) cations. The highest stability constant was found for the AgL (+) complex of G8 Schiff base and the lowest one for the AgL (+) complex of G molecule. The (13)C NMR spectra of mixtures between G and AgClO 4 as well as G1-G10 and AgClO 4 indicate that the complexation of the Ag (+) cations is exclusively realized by the aldehyde-aldehyde tautomer of gossypol and by the enamine-enamine form of gossypol Schiff bases, respectively. We show that the main coordination sites for the Ag (+) metal cations are either the oxygen or the nitrogen atoms of the amine parts of the Schiff bases of gossypol. The energetically most favorable structures of the Ag (+) complexes with gossypol (G) or with the gossypol Schiff bases (G1-G10) were calculated and visualized by the AM1d method at an semiempirical level of theory.     

INVESTIGATION INTO THE SPECTROSCOPY AND PHOTOISOMERIZATION OF A SERIES OF POLY (ETHYLENE GLYCOL) PEPTIDE SCHIFF BASES OF 11-cis RETINAL

Abstract— The 11-cis and all-trans isomers of a series of poly(ethylene glycol)-oligopeptide - Schiff bases as models for rhodopsin were synthesized and studied. Absorption data for certain of the PEG-peptide Schiff bases demonstrated that no intramolecular hydrogen-bonding (or protonation) occurs between the Schiff base and an acidic amino acid residue, as was previously thought. Photoisomerization of the 11-cis protonated and unprotonated Schiff bases were examined using both steady state and laser flash techniques. Also with 355 nm excitation (and additionally 532 nm in one case), an approximate 40% increase in quantum yield of isomerization (φ) occurred for all protonated PEG-peptide Schiff bases compared to the H⁺-n-butylamine counterparts (in methanol). In one case, a > 100% increase in φ was found in dichloromethane. These data show that PEG-oligopeptide Schiff bases are still further improved models for rhodopsin compared to their n-butylamine analogs.     

Fabrication of chiral Langmuir-Schaefer films of achiral amphiphilic Schiff base derivatives through an interfacial organization

Supramolecular chirality in the Langmuir-Schaefer (LS) films of two achiral amphiphilic Schiff bases, 2-(2'-benzimidazolyliminomethyl)-4-octadecyloxyphenol (BSC18) and 2-(2'-benzthiazolyliminomethyl)-4-octadecyloxyphenol (TSC18), was investigated. Both of these amphiphiles could form LS films from the water surface or coordinate with Ag(I) in the subphase to form Ag(I)-coordinated LS films. Although both of these amphiphiles were achiral, TSC18 formed a chiral LS film from the water surface, while BSC18 formed a chiral Ag(I)-coordinated LS film from the aqueous AgNO3 subphase. The supramolecular chirality in these LS films was suggested to be due to a cooperative stereoregular pi-pi stacking of the functional groups together with the long alkyl chains in a helical sense. The relationship between the chirality of the LS films and the molecular structures of TSC18 and BSC18 as well as their H-bond or coordination behaviors was discussed. The Schiff base films showed a reversible color change upon exposure to HCl and NH3 gas alternatively; however, the supramolecular chirality was irreversible during these processes.     

First Example of Schiff Bases Containing Poly(Acryl Amid) in the Synthesis and Characterization

A novel polymeric‐Schiff base derived from the condensation reaction poly(acryl amid) and indole‐3‐carboxaldehyde has been synthesized and their Co(II) and Ni(II) complexes have been prepared. Mol ratio of acrylamid group and Schiff bases group was estimated by means of height of ‐CH multiple peaks and –CH=N‐ peak in ¹H‐NMR spectrum. The studied substances were characterized by molar conductance, magnetic susceptibility, electronic and IR spectral studies. In addition, main units have been suggested with elemental analysis for these substances, and than the weight average molecular weight (M_w) has been suggested. The number average molecular weight (M_n) was determined with a vapor pressure osmometer. Polydispersity index (PDI) found to be ca 1.7 from M_w/M_n for poly‐Schiff bases and their Co(II) and Ni(II) complexes. PAA‐Schiff bases were found to have the highest thermal stablility compared to that of the Co(II) and Ni(II) complexes. The conductivities of the PAA‐Schiff bases and their complexes were measured by the four‐probe technique and were found in the range 10^?5?10^?6 S cm^?1.     

Synthesis, potentiometric and antimicrobial studies on metal complexes of isoxazole Schiff bases

The metal complexes of Cu(II), Ni(II) and Co(II) with Schiff bases of 3-(2-hydroxy-3-ethoxybenzylideneamino)-5-methyl isoxazole [HEBMI] and 3-(2-hydroxy-5-nitrobenzylidene amino)-5-methyl isoxazole [HNBMI] which were obtained by the condensation of 3-amino-5-methyl isoxazole with substituted salicylaldehydes have been synthesized. Schiff bases and their complexes have been characterized on the basis of elemental analysis, magnetic moments, molar conductivity, thermal analysis and spectral (IR, UV, NMR and Mass) studies. The spectral data show that these ligands act in a monovalent bidentate fashion, co-ordinating through phenolic oxygen and azomethine nitrogen atoms. Chelates of Co(II), Ni(II) appear to be octahedral and Cu(II) appears to be distorted octahedral. To investigate the relationship between formation constants of binary complexes and antimicrobial activity, the dissociation constants of Schiff bases and stability constants of their binary metal complexes have been determined potentiometrically in aqueous solution at 30+/-1 degrees C and at 0.1 M KNO3 ionic strength and discussed. Antimicrobial activities of the Schiff bases and their complexes were screened. The structure-activity correlation in Schiff bases and their metal(II) complexes are discussed, based on the effect of their stability constants. It is observed that the activity enhances upon complexation and the order of activity is in accordance with stability order of metal ions.     

无长链席夫碱衍生物单分子膜和LB膜

在银离子的诱导下,两种含有苯并咪唑、没有长链取代基的席夫碱衍生物可以形成稳定的单分子膜,此单子分子膜可以用水平拉膜法转移到固体表面形成ＬＢ膜、ＬＢ膜的紫外吸收光谱和光电子能谱研究表明,Ａｇ（Ⅰ）离子被络合进行了单分子膜中。     

Structural investigation on phenyl‐ and pyridin‐2‐ylamino(methylene)naphthalen‐2(3H)‐one. Substituent effects on the NMR chemical shifts

Schiff bases bearing phenyl and pyridyl groups were synthesized by condensation of appropriate amines with 2‐hydroxynaphthaldehyde. These Schiff bases were obtained as colored crystalline solids. The proton NMR spectra of these compounds showed a doublet for the NH protons indicating a keto tautomer for these Schiff bases. The pyridyl‐substituted Schiff bases containing hydroxyl moiety were found to show the most downfield shift for the NH protons in DMSO solvent, and this was rationalized due to the formation of a six‐ and five‐membered ring using hydrogen bonds for these two compounds. Correspondingly, the olefinic proton of the Schiff bases is also found to be a doublet due to coupling to the amine proton. These Schiff bases exhibited thermochromic properties. Detailed NMR spectral analysis for both the phenyl‐ and pyridyl‐substituted Schiff bases is presented. Copyright © 2010 John Wiley & Sons, Ltd.     

Polymeric Schiff Bases. III. Some Prototype Exchange Reactions of Schiff Bases

The amine moiety in Schiff bases can be exchanged quantitatively by another amine to yield new Schiff bases if the volatility of the replacing amine is lower than the derived amine, thereby allowing the latter to distilled from the reaction mass. This amine exchange was shown to be quantitative also for diamines and di-Schiff bases. Similarly, quantitative conversions were found for aldehydes and acetal exchanges with Schiff bases for both monofunctional and difunctional reactants. The bis exchange, involving two complementary Schiff bases, was quantitative also when the reactants were so selected that one of the new derived Schiff bases could be removed by distillation. The bis exchange was demonstrated with mono and di-Schiff bases.

Mechanisms are suggested for these Schiff base exchange reactions: attempts to isolate the proposed intermediates physically were unsuccessful; however spectroscopic evidence indicates the formation of intermediate compounds.

The Schiff base exchanges involving polyfunctional reactants are of interest in the synthesis of polymers.     

Enrichment of copper and nickel with solid phase extraction using multiwalled carbon nanotubes modified with Schiff bases

The behaviour of some Schiff bases in the presence of metal ions is very selective in complex formation. In this study, new, selective and easily prepared adsorbent materials have been developed. Multiwalled carbon nanotubes (MWCNTs) are quite suitable as supporting material for preparation of new solid phase adsorbents modified with Schiff bases due to their selective nature. Different Schiff bases were designed and synthesised as adsorbent agents for Ni(II) and Cu(II) ions, according to the literature, and MWCNTs were modified with these Schiff bases. The modification of CNTs was performed by adsorption from the alcoholic solution of Schiff base. The measurements of Ni(II) and Cu(II) ions were carried out using ICP-MS. Different parameters such as pH, model and eluent solution flow rates, eluent type, amount of ligand, sample volume and effect of foreign ions, which have an effect upon recovery of analytes, were investigated. The obtained results indicated that enrichment can be done with six modified adsorbent materials for Cu(II) at pH 9 and two modified adsorbent materials for Ni(II) at pH 8. It was concluded that four adsorbent materials were selective only for the enrichment of Cu(II). Merely one modified adsorbent material was noneligible for the enrichment of Cu(II) and Ni(II). The solid phase adsorbents prepared by modification with two of the Schiff bases used in this study showed an enrichment factor of 80 for both metal ions, whereas the solid phase adsorbents prepared by modification with four of the Schiff bases showed an enrichment factor of 40 for Cu(II) ions. The confirmation of the developed method was tested with certified reference materials with satisfactory results.     

Synthetic studies of carbapenem and penem antibiotics. II. Synthesis of 3-acetyl-2-azetidinones by (2 + 2) cycloaddition of diketene and Schiff bases.

It was found that (2 + 2) cycloaddition reaction of diketene with Schiff bases was effectively promoted by imidazole as a catalyst to afford 3-acetyl-2-azetidinone derivatives 4. As an application of this new method, a practical asymmetric synthesis of 4 and its conversion into (3S,4S)-4-carboxy-1-(di-p-anisylmethyl)-3-[(R)-1-hydroxyethyl]-2- azetidinone, which is a key intermediate for the synthesis of carbapenem and penem antibiotics, were accomplished.     

Structural and energetic consequences of the formation of intramolecular hydrogen bonds

Formation of intramolecular hydrogen bonds leads to structural modifications in the whole molecule, which are discussed on the basis of B3LYP/6-31G(d,p) calculations. The energy and the structure of various hydrogen-bonded and open conformers are considered for two groups of ortho-substituted phenols–N-dimethylaminomethylphenols (Mannich bases) and N-methylbenzylideneamines (Schiff bases). The energy of intramolecular hydrogen bond formation in Mannich bases was corrected for non-bonded interactions within the molecules, based on a thermodynamic cycle. Structural data were used to estimate the fraction of the ortho-quinoid (keto) form in particular tautomers. It is shown that proton transfer in Schiff bases leads to an increase of this fraction to about 40%, while opening of the hydrogen bond in the proton transferred form increases the keto fraction to 70%.     

Microwave-assisted synthesis and biological activity of new Schiff bases derived from dimers of 4-amino-3-[3-(1-benzyl)indole]-5-thiomethyl-1,2,4-triazole

An expeditious method with microwave irradiation has been developed for synthesis of novel Schiff bases from dimers of 4-amino-3-[3-(1-benzyl)indole]-5-thiomethyl-1,2,4-triazole. Its distinct advantages are short reaction times and good conversion. The structures of these new Schiff bases were established by ¹H NMR, IR, and mass spectroscopy, and elemental analysis. The antibacterial activity of ten novel Schiff bases against three bacterial strains was studied by the disk diffusion method. Preliminary results indicated that some of the compounds had strong antibacterial activity.     

Novel Ru - K/Carbon Nanotubes Catalyst for Ammonia Synthesis

Since 1970s alkali metal-promoted ruthenium was found to be an active catalyst forammonia synthesis under atmospheric pressure, ruthenium catalysts come to beconsidered as a second-generation-catalyst for ammonia synthesis after the iron-basedcatalyst'-=. We have reported the activity of ammonia synthesis of ruthenium-basedcatalysts on various supports previously and found that fullerene was the best support'.Recently, we used the carbon nanotubes, which have metallic or semiconductingproperti…