Azo compounds and Schiff 's bases derived from 5-(4-pyridyl)-2-amino-1,3,4-thiadiazole: synthesis,mesomorphic properties and structural study by semi-empirical calculations

The synthesis and liquid crystalline properties of new Schiff 's bases (series 3a-f) and azo compounds (4a-f) incorporating pyridine and 1,3,4-thiadiazole rings are reported. The first homologues in the series of Schiff's bases (3a-c) show a monotropic mesophase and the homologues 3d-f display an enantiotropic SmA phase. The only azo compounds to exhibit liquid crystalline properties are the homologues 4e, f which show a monotropic nematic phase. These series are compared with Schiff's bases and azo compounds analogues (series 5 and 6), previously reported by us and an AM1 study of the structure/mesomorphic property relationship is described.     

Symmetric esters derived from 1,3,4-oxadiazole: synthesis,mesomorphic properties and structural study by semi-empirical calculations

Three homologous series of symmetric esters derived from 2-alkylthio-5-(p -hydroxy)phenyl-1,3,4-oxadiazole (series 3, 4 and 5) were synthesized and their liquid crystalline properties investigated by optical microscopy and differential scanning calorimetry. Depending on the chain length, nematic and smectic C phases were observed in the series 3 ; smectic A and smectic C phases in series 4. None of the homologues of series 5 shows mesomorphic properties. These three series are compared with other previously reported oxadiazoles. A structural study of AM1 semi-empirical calculations is also described.     

Symmetric esters derived from 1,3,4-oxadiazole: synthesis, mesomorphic properties and structural study by semi-empirical calculations

Three homologous series of symmetric esters derived from 2-alkylthio-5-( p -hydroxy)phenyl-1,3,4-oxadiazole (series 3 , 4 and 5 ) were synthesized and their liquid crystalline properties investigated by optical microscopy and differential scanning calorimetry. Depending on the chain length, nematic and smectic C phases were observed in the series 3 ; smectic A and smectic C phases in series 4 . None of the homologues of series 5 shows mesomorphic properties. These three series are compared with other previously reported oxadiazoles. A structural study of AM1 semi-empirical calculations is also described.     

Synthesis, mesomorphic properties and structural study by semi-empirical calculations of amides containing the 1,3,4-thiadiazole unit

The synthesis and liquid crystalline properties of a new series of amides (series 2a-f , 3a-d and 4a-d ) incorporating pyridine and 1,3,4-thiadiazole rings are reported. No homologues of the series 2 show mesomorphic properties. In the series 3 only the highest homologues ( 3d ) displays an enantiotropic SmA mesophase; the compound 3c exhibits a monotropic SmA mesophase, and the homologues 3a , b display no liquid crystal properties. The amides 4b-d display an enantiotropic SmA phases and the first homologue ( 4a ) exhibit only crystalisotropic transition. These series are compared with previously reported Schiff's bases and amide analogues. A structural study by AM1 semi-empirical calculation is also described.     

Synthesis,mesomorphic properties and structural study by semi-empirical calculations of amides containing the 1,3,4-thiadiazole unit

The synthesis and liquid crystalline properties of a new series of amides (series 2a-f,3a-d and 4a-d) incorporating pyridine and 1,3,4-thiadiazole rings are reported. No homologues of the series 2 show mesomorphic properties. In the series 3 only the highest homologues (3d) displays an enantiotropic SmA mesophase; the compound 3c exhibits a monotropic SmA mesophase, and the homologues 3a,b display no liquid crystal properties. The amides 4b-d display an enantiotropic SmA phases and the first homologue (4a) exhibit only crystalisotropic transition. These series are compared with previously reported Schiff's bases and amide analogues. A structural study by AM1 semi-empirical calculation is also described.     

2-氨基-5-[二-(4-氟苯)甲基]硫代-1,3,4-噻二唑席夫碱的微波合成及表征

2,5-二取代-1,3,4-噻二唑具有杀虫、杀菌、除草、调节植物生长以及药理活性等多种功效[1-5],因而该类化合物的研究迄今仍方兴未艾.近年来,很多文献报道含芳环或芳杂环的席夫碱化合物具有很高的生物活性,因而也引起人们的高度重视[6,7].由于氟原子具有模拟效应、电子效应等特殊性质,氟原子与含氟基团的引入有时可使化合物的生物活性倍增,近年也公认含氟化合物对环境的影响最小[8].鉴于不同活性的基团在同一分子中聚集能明显改善化合物的生物活性这一特性,本文将二-(4-氟苯)甲基引入到1,3,4-噻二唑Schiff碱类化合物中,以期实现活性的叠加,有可能发现新型生物活性更好的化合物.该类化合物的合成一般采用常规加热法,但具有反应时间长,收率不高,溶剂使用量大等缺点.     

Synthesis and mesomorphic properties of esters derived from Schiff's bases containing 1,3,4-thiadiazole

Two homologous series of esters derived from Schiff's bases containing the 1,3,4-thiadiazole unit (series 3 and 5) were synthesized and their liquid crystalline properties investigated by optical microscopy and differential scanning calorimetry. Depending on the position occupied by the carbonyl group, the smectic A phase was observed in series 3 and nematic phase in series 5.     

Synthesis and mesomorphic properties of esters derived from Schiff's bases containing 1,3,4-thiadiazole

Two homologous series of esters derived from Schiff's bases containing the 1,3,4-thiadiazole unit (series 3 and 5) were synthesized and their liquid crystalline properties investigated by optical microscopy and differential scanning calorimetry. Depending on the position occupied by the carbonyl group, the smectic A phase was observed in series 3 and nematic phase in series 5.     

Disperse dyes derived from 2-amino-5-mercapto-1,3,4-thiadiazole

Some novel heterocyclic monoazo dyes based on 2-amino-5-mercapto-1,3,4-thiadizole have been synthesized by coupling with various N-phenylacrylamide derivatives. The dyeing performance of these dyes was assessed on polyester fabrics. IR and visible spectra of the dyes were examined. The percentage dye bath exhaustion, fixation, and various fastness properties of the dyes were also determined. These dyes were found to give brownish-orange to reddish-pink shades on dyeing with good depth, levelness, and brightness on fabric. The dyed fabric showed a good to excellent fastness to washing, rubbing, perspiration, and sublimation.     

New polycatenar Schiff bases derived from 1,3,4-thiadiazole: synthesis,mesomorphism and luminescence behaviour

Two new series of columnar liquid crystal materials based on tetra- and hexacatenar Schiff bases were synthesised by reaction of 4-aminophenyl-1,3,4-thiadiazole derivatives with terephthalaldehyde (series 2a–f) and with 2,5-thiophenedicarbaldehyde (series 3a–f). The mesomorphic properties of these compounds were studied by differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (XRD). The mesomorphic behaviour was found to be dependent on the nature of the central ring (benzene in series 2a–f, thiophene in series 3a–f), on length and on number of alkoxy chains. Both tetra- and hexacatenar compounds in series 2a–f display an enantiotropic hexagonal columnar phase. Whereas, in the case of the series 3, only the tetracatenar Schiff bases (3a, 3c and 3e) display enantiotropic hexagonal columnar mesomorphism, hexacatenar Schiff bases (3b, 3d and 3f) do not show mesomorphic properties. Photophysical studies were realised in solution and in solid state. Also, a thermogravimetric analysis was performed. A fibre obtained from compound 3b was analysed by POM showing that the mesophase is maintained in the fibre.     

Novel chiral liquid crystals based on amides and azo compounds derived from 2-amino-1,3,4-thiadiazoles: synthesis and mesomorphic properties

Novel chiral amides (Ia-Ie, II) and azo compounds (III, IV) with a 1,3,4-thiadiazole unit in the rigid core were synthesized and their liquid crystalline properties investigated by polarizing optical microscopy and differential scanning calorimetry. The amides Ia-Ie contain a chiral alkoxy chain derived from (R)-2-octanol and an achiral chain varying from 6 to 10 carbon atoms at the end of the rigid core. In amide II one of the terminal group is a chiral alkoxy chain derived from (S)-isoleucine and the other terminal substituent is an achiral n-decyloxy chain. Azo compounds III and IV contain an achiral n-decyloxy chain and a chiral alkoxy chain derived from (R)-2-octanol and (S)-isoleucine, respectively, at the end of the rigid core. The first homologue in the series of amides (Ia) exhibits enantiotropic smectic X (SmX)-chiral nematic (N*) dimorphism and the homologues Ib-Ie display enantiotropic SmX-chiral smectic C (SmC*)-N* mesomorphism. Amide II displays an enantiotropic smectic A phase. The azo compounds III and IV do not show smectic order and only an enantiotropic N* phase was observed. Thus, the mesomorphic behaviour depends on the nature of the central linkage and on the nature of the chiral alkoxy chain.     

Copper(II) complexes of 2-amino-1,3,4-thiadiazole and 2-ethylamino-1,3,4-thiadiazole

Summary Some copper(II) complexes of 2-amino-1,3,4-thiadiazole (atz) and 2-ethylamino-1,3,4-thiadiazole (eatz) have been prepared and studied by electronic, i.r. and e.p.r. spectra and by magnetochemical and conductometric methods. The CuX₂ · atz (X=Cl, Br) and CuCl₂ · eatz complexes are presumably six-coordinate with bridging ligand molecules and asymmetrically bridging halide ions, while the CuX₂ · 2 atz (X=Cl, Br) complexes probably have a flattened tetrahedral N₂X₂ moiety with apical interactions. The CuBr₂ · 5/3 eatz · 2/3 MeOH and Cu(OAc)₂ · L (L=atz or eatz) complexes have subnormal magnetic moments (1.53-1.40 B.M.). The acetato-complexes have a dimeric structure with bridging acetato-groups, copper-copper interactions and apical ligand molecules. The ligands bond principally through the amine nitrogen atom and, when bridging, also through one ring-nitrogen.     

Spectroscopic and biological properties of platinum complexes derived from 2-pyridyl Schiff bases

The reactions of a range of aromatic primary amines with pyridine-2-carboxaldehyde were reported, highlighting the effect of the substituents of the amine on the outcomes of the Schiff base reactions. The variant products of the Schiff base reactions were reacted with cis-[PtCl₂(DMSO)₂], generating platinum(II) complexes with PtCl₂(N^N) general formula. The ligands and platinum(II) complexes were identified and characterized by IR and NMR spectroscopic methods. Single crystal XRD offered structural confirmation for three of the organic compounds and two platinum complexes. The spectral, antimicrobial, DNA-binding and molecular docking of the platinum complexes were studied, highlighting the effect of the different functional group in the Schiff base ligands on their properties. In general, introducing the electron-withdrawing group nitro or acetyl in the 2-pyridyl Schiff base ligands, results in a red-shift in the absorption maxima of the platinum complex. In addition, the enhancement in the antimicrobial activities and the increase in the ct-DNA-binding affinity were also observed when the nitro or acetyl functional group is introduced to the Schiff base ligand in the platinum(II) complex.     

2-氨基-5-(4-吡啶基)-1, 3, 4-噻二唑Schiff碱的合成及其生物活性

2-氨基-5-(4-吡啶基)-1;3;4-噻二唑Schiff碱的合成及其生物活性;噻二唑;Schiff碱;合成;生长素;细胞分裂素     

2-氨基-5-对羟基苯基-1,3,4-噻二唑及其席夫碱的合成

POCl3催化对羟基苯甲酸(1)和氨基硫脲(2)反应合成了5-(对羟基苯基)-2-氨基-1,3,4-噻二唑(3);3与水杨醛缩合制得对应的席夫碱,其结构经1H NMR和IR确征.合成3的较适宜反应条件为:150 mmol,250mmol,POCl3 30 mL,第一步于80℃反应80 min,第二步于110℃反应4 h,混合溶剂[V(DMF):V(水)=1∶2]的重结晶效果最好.在此条件下,3的收率达80.3%.     

Copper(I) and silver(I) complexes of 2-amino-1,3,4-thiadiazole and 2-ethylamino-1,3,4-thiadiazole

The following copper(I) and silver(I) complexes of 2-amino-1,3,4-thiadiazole (atz) and 2-ethylamino-1,3,4-thiadiazole (eatz) have been prepared and studied by conductometric, IR and Raman methods: CuXL(X = Cl, Br, I; L = atz, eatz), CuXL₃(X = ClO₄, NO₃; L = atz, eatz), AgClO₄·1.5atz·1/3 EtOH, AgNO₃·2.5atz, AgClO₄·3eatz, AgNO₃·eatz. The ligands are bonded through the amine nitrogen atoms with ν(MN) bands in the 520–410 cm^?1 region. The CuXL complexes have a trigonal (N, 2X_b) coordination with a probable weaker axial interaction. The CuXL₃ and AgCIO₄·3eatz complexes probably have a trigonal pyramidal (3N,O) coordination. In the atz complexes of silver perchlorate and nitrate some ligand molecules are bridging. The AgNO₃·2.5atz complex is likely to have a dimeric structure with tetrahedral coordination of the silver ion.     

Novel amides and Schiff's bases derived from 1,3,4-oxadiazole derivatives: synthesis and mesomorphic behaviour

The synthesis and liquid crystalline properties of novel achiral amides (Ia–g, IIa–g and IVa,b), achiral Schiff's bases (IIIa–g and Va–g), chiral amides (VI, VII) and chiral Schiff's bases (VIII–XI) incorporating a 1,3,4-oxadiazole ring are reported. All amides of the series I and II display an enantiotropic smectic A phase. The amide IVa,b did not show mesomorphic properties. Amides of the series Ia–g and IIa–g contain a flexible n-tetradecylthio chain, the other terminal substituent is an n-alkoxy chain and n-alkyl chain, respectively (n?=?4–10) and the 1,3,4-oxadiazole is in the terminal rigid core. Amides Ia–g have broader mesomorphic range and higher thermal stability than the corresponding amides IIa–g. Amides IVa,d contain the 1,3,4-oxadiazole ring in the centre of the rigid core and two flexible alkoxy chains as flexible terminal substituents. Thus, the mesomorphic properties are favoured if 1,3,4-oxadiazole is shifted to a terminal position of the rigid core. Schiff's bases IIIa–g display an enantiotropic dimorphism smectic C–smectic A. Schiff's bases IIIa–g have a broader mesomorphic range than the analogous amides Ia–g. Schiff's bases Va–g exhibit a dimorphism smectic A–nematic, and in contrast to this the analogous amide IVa,b did not show mesomorphism. The chiral amides VI and VII and chiral Schiff's bases X and XI did not show mesomorphic properties and only the chiral Schiff's bases VIII and IX display a chiral smectic C phase in a short mesomorphic range. A density functional theory theoretical study at the B3LYP/6–311++G(d,p) level was performed in order to analyse the structural features that must be related with the mesomorphic behaviour of the reported compounds.     

Oxovanadium(IV) complexes of tetradentate unsymmetrical Schiff bases derived from 7-amino-4-methyl-5-aza-3-hepten-2-one

Summary Vanadyl complexes of tetradentate unsymmetrical Schiff bases have been obtained. They present different arrangements of the donor atoms around the vanadyl ion: N₂O₂, N₃O, N₂OS, affording a fivefold coordination for the metal centre. Other complexes with sixfold coordination have also been synthesized and isolated. The whole set of complexes has been characterized by elemental analysis, i.r., electronic spectroscopy, e.p.r. and magnetic susceptibility measurements.