Infra-Red Study of Tautomerism in Some Schiff Bases.

Infra-Red spectra of a series of substituted salicylaldehyde and 2-hydroxy-naphthaldehyde Schiff bases were used to investigate enol-keto tautomeric equilibrium. Two model compounds, namely, salicylidinaniline and naphthylidinequinolineamine Schiff bases were used to represent the enol and keto forms, respectively. From the IR spectra of the model compounds it was possible to assign the IR absorption for the C=O and the C=N groups in both the keto and the enol form. It was also possible to assign other absorptions which were either specific to the keto or the enol forms. Specific pattern were observed for all the studied compounds.     

三种Schiff碱的Raman振动特性及其归属

本文研究了三种反对称Schiff碱的Raman振动特性,分析了三种Schiff碱的拉曼振动模式,给出了所观察到的Raman振动的归属。     

Mass Spectral Study of Tauotomerism in Some Schiff Bases

Mass spectra of a series of substituted salicylaldehyde and 2-hydroxy-naphthaldehyde Schiff bases were used to investigate enol-keto tautoraeric equilibrium. Two model compounds, namely, salicylidinaniline and naphthylidinequinolineamine Schiff bases were used to represent the enol and keto forms, respectively. Mass spectral measurements reveal the fragmentation pattern in all compounds studied. Only naphthylidinequinoline amine Schiff base show a different fragmentation pattern compared to the other Schiff bases in the series which give an evidence for its suggested keto structure.     

Synthesis and Spectral Properties of the Europiumciiid Chelates with Schiff Bases

The complexes of Eu(III) and the Schiff bases were obtained and the structure, nature of chemical bonds, and symmetry of the compounds were eluciaded on the basis of spectroscopic and elemental analysis data. Two of the compounds were the monomers with 8-coordinated europium and one of them was a dimer with 6-coordinated europium.     

水杨醛氨基酸席夫碱水溶液的电子光谱研究

通过电子光谱研究了7种水杨醛氨基酸席夫碱配体Sal-aa在水溶液中的生成情况。Sal-tyr的生成浓度下限为10-5 mol·L-1,其余6种Sal-aa的生成浓度下限均为10-4 mol·L-1。除Sal-his的生成pH为9～10外,其余6种Sal-aa都是pH值增大有利于席夫碱生成。Sal-gly和Sal-tyr的生成pH下限为8,其余4种Sal-aa的pH下限为9。Sal-cys水溶液放置36 h后席夫碱浓度比新生成溶液的大,其余6种Sal-aa都是自生成后就开始缓慢分解。Sal-gly和Sal-glu水溶液的相对稳定存在时间为24 h,其余4种Sal-aa的相对稳定存在时间为48 h。本工作为探索用于放射性药物研究的水杨醛氨基酸席夫碱水溶液标记放射性核素提供了实验基础。     

FT-Far Infrared Study of Complexes Involving Schiff Bases and Phenols

Abstract

Long range inter—ring “zig—zag” coupling between C-4 and H-8 (J₄₈ ?1.5 to ?1.8 Hz) has been observed in some 2,4? and 2,3,4? haloquinolines at 75 MHz. The coupling is influenced by the 4-halo substituent.     

Infrared Spectra and Transmission of Substituent Effects Through the Arylazomethine Group in Aromatic Schiff Bases

The IR frequencies and integrated intensities of the nitrile group of two series of aromatic Schiff bases have been measured. The data obtained are compared with the Hammett σ constants as well as with the calculated dipole moment derivatives of the nitrile group. An evaluation of the transmission coefficient Π of the arylazomethine group is reported.     

基于低聚壳聚糖的希夫碱化合物与BSA的相互作用

窄分子量分布低聚壳聚糖CS_<i>n(n表示壳聚糖的聚合度,n=6, 8, 11)和对二甲氨基苯甲醛(DMABA)通过缩合反应得到了新型的基于壳聚糖的希夫碱化合物DMABA-CS_n。利用荧光光谱法,同步荧光光谱法,圆二色谱法(CD)和等温滴定微量热法(ITC)研究了DMABA-CS_n与牛血清白蛋白 (BSA)之间的相互作用。通过荧光光谱法探讨了DMABA-CS_n对BSA的荧光猝灭机制。结果表明,DMABA-CS_<i>n(n=6, 8, 11) 均能使BSA的荧光猝灭,猝灭机制是形成DMABA-CS_n/BSA复合物的静态猝灭。利用同步荧光光谱法和圆二色谱法考察了DMABA-CS_n对BSA构象的影响。研究结果表明,BSA的构象在DMABA-CS_n的溶液微环境中发生了变化。另外,ITC热力学测定结果(ΔH<0, ΔS<0, ΔG<0)表明,BSA与DMABA-CS_n的作用过程是自发进行的放热过程,二者之间的作用力类型主要是氢键和疏水作用。同时,研究结果也说明在一定的分子量范围内,随着CS_n聚合度的增加,DMABA-CS_n更容易与BSA结合。研究结果为DMABA-CS_<i>n(n=6, 8, 11)作为潜在药物的药理作用机制研究提供了一定的理论参考。     

Substitution and Solvent Effect of Some Substituted Hydroxy Schiff Bases

Abstract

The uv-vis spectra of eight ortho-hydroxy- andpara-hydroxy schiff bases were recorded in different solvents. Inductive and resonance effect of the substituents affect the electronic spectra of those molecules, while, intra-molecular hydrogen bond formation or breakage have little effect on the uv-visible spectra.     

Synthesis,Spectroscopic and Antimicrobial Studies of Lead (II) Complexes of Schiff Bases Derived From Amino Acids and Isatins

A new series of lead (II) complexes have been synthesized with Schiff bases derived from isatins and amino acids. These ligands act as bidentate species and coordinate to the metal atom through the azomethine nitrogen and carboxylate oxygen atom via deprotonation. The synthesized complexes have been characterized by elemental analysis, conductance measurements, and molecular weight determinations. The mode of bonding of the complexes has been suggested on the basis of infrared, UV-visible, and ¹H- and ¹³C-NMR spectroscopy, and probable structures have been assigned to these complexes. Few representative ligands and metal complexes have also been screened for their antifungal and antibacterial activities. Molecular modeling and analysis for bond lengths and bond angles have also been carried out for one of the representative compound, [Pb(L³)₂], to substantiate the proposed structures.     

Synthesis and two-photon optical characterization of D-π-D type Schiff bases

The title compounds, several Schiff bases with D-π-D type have been successfully synthesized from reaction of 4-(N-dialkylamino) benzaldehyde and hydrazine or p-phenylenediamine in ethanol. These compounds were characterized by IR, ¹H NMR, elemental analysis and electronspray mass spectrometry. One-photon fluorescence and two-photon fluorescence properties have been investigated. The two-photon absorption (TPA) cross section (σ) of these compounds was obtained by using the open-aperture Z-scan technique. Based on theoretical calculations and factual test, the influence that a series of substituted groups and the conjugated frame imposed on TPA cross section were systematically discussed.     

Synthesis and Spectroscopic Studies of Some New Polyether Ligands of the Schiff Base Type

Abstract

New polyether ligands of Schiff base type (3–13) were synthesized from the reaction of diethylene glycol bis(2‐aminophenyl)ether and triethylene glycol bis(2‐aminophenyl)ether with salicylaldehyde, 5‐methoxysalicylaldehyde, 5‐bromosalicylaldehyde, 5‐nitro salicylaldehyde, and 2‐hydroxy‐1‐naphthaldehyde. The products were characterized by elemental analysis, IR, ¹H, ¹³C NMR, and UV‐VIS techniques. The UV‐VIS spectra of those Schiff bases with an OH group in the ortho position to the imino group were studied in polar and nonpolar solvents in acidic and basic media. The compounds are in tautomeric equilibrium (enol‐imine, O–H · N?keto‐amine, O · H–N forms) in solvents, acidic chloroform, and benzene solutions and basic DMSO, chloroform, and benzene solutions. These tautomers were not observed in polar and non‐polar solvents and in basic solutions of DMSO, chloroform, and benzene for the Schiff bases 5–10. Tautomer proportions, which were obtained from ¹H NMR and UV‐VIS data in DMSO, were compared for compounds 3, 4, 11, and 12.     

高氯酸锂在有机溶剂中离子溶剂化和离子缔合的红外光谱研究

利用红外光谱技术研究了LiClO4在碳酸丙烯酸,γ－丁内酯和碳酸二乙酯中的离子缔合和离子溶剂化。溶剂分子谱带的变化证明,锂离子与溶剂分子的相互作用主要是通过羰基氧原子进行的,醚氧也可能参与了相互作用,高氯酸锂的v1和v4谱带变化则证明了溶液中离子对的存在,而离子对的种类与溶剂分子的特性有关。     

Fluorescence Characteristics of Schiff Bases Derived from Amino- and Aminoalkylpyridines

The fluorescence characteristics of the Schiff bases 2-(3-pyridylmethyliminornethyl)phenol (1), 2-(2 pyridyliminomethyl)phenol (2), N.N-bis(salicylidene)-2,3-pyridinediamine (3), N,N'-bis(salicylidene)-2,6-pyridinediamine (4) and 2-(2-amino-4-methoxymethyl-6-methyl-3-pyridylmethyliminomethyl)phenol (5) were studied in various solvents at different pH values. Corresponding quantum efficiencies were determined. Compound 1, which showed a tendency towards tautomeric mterconversion to ketoamine in polar protic solvents, was not fluorescent at pH < 8. The fluorescence of other compounds was very sensitive to solvent polarity and the pH of the medium. Compounds 2-4, preferably present as enolimines in all solvents, were not fluorescent in non-polar and moderately polar solvents, whereas weak emission was observed in polar solvents, like methanol, dimethylformamide and dioxane/water 1/1 (0.001 < Q < 0.072). A significant increase in Stokes shifts and in quantum efficiencies was noted as a result of increasing polarity of dioxane/water mixtures, indicating specific interactions with polar water molecules. The emission was promoted at acidic pH values where a pyridinium cation was formed (0.061 < Q < 0.519, in dioxane/water 1/1 at pH 3.4). Compound 5, which was a tautomeric mixture of enoiimine and cyclic diamine in all solvents, was fluorescent in polar as well as in non-polar media. The quantum efficiency varied dependent on the solvent and pH (0.023 <Q< 0.435). The cyclic diamine, i. e. the more rigid structure was supposed to be responsible for the fluorescence in non-polar and aprotic solvents as well as at neutral, and weakly basic pH values.     

Theoretical analysis of the experimental UV-Vis absorption spectra of some phenolic Schiff bases

The time-dependent density functional theory (TDDFT) was applied in conjunction with the natural bond orbital analysis to examine the UV-Vis properties of 10 phenolic Schiff bases. The calculations were performed with different functionals, but main discussion refers to results obtained at the B3LYP/6-311+G(d,p) level of theory. The approach based on the natural localised molecular orbital clusters indicates similar behaviour for majority of examined compounds. The HOMO (“highest occupied molecular orbital”) cluster is delocalised over the ring which is electron richer, the HOMO-1 cluster is spread over the other ring, whereas the LUMO (“lowest unoccupied molecular orbital”) cluster is situated on the imino group. The two bands at long wavelengths correspond to the HOMO → LUMO and HOMO-1 → LUMO transitions, i.e. from both A and B rings to the imino group. The next band originates from a transition from the imino group to the imino group. The band at the smallest wavelengths originates from a transition from the A ring to the A ring, or from the B ring to the B ring. Our findings are in very good agreement with the existing literature data.     

有机溶剂中水的分光光度法测定

在有机溶剂中有水存在时 ,氯醌酸发生离解 ,其最大吸收波长发生红移 ,且吸收强度显著增加。详细地研究了氯醌酸变色机理及其用于测定水的最佳条件 ,建立了一种新的测定有机溶剂中水含量的分光光度分析方法。测定了白酒、食用酒精与试剂无水酒精中的水含量 ,得到满意测定结果。测定线性范围为φ(H2 O) 0 0 2 %～ 10 % ,方法简单、灵敏度高、重现性好。对甲醇、异丙醇、丁酮、丙酮、乙腈、四氢呋喃中水的测定进行了实验 ,得到了相应的吸光度与浓度校准曲线     

不同溶剂中取代基对芳香胺红外吸收光谱的影响

对２１种芳香胺在不同极性的溶剂中测定了红外光谱,并对不同取代基对氨基的对称伸缩动和非对称伸缩振动吸收峰峰位的影响进行了讨论。甲基在不同极性的溶剂中表现不同的电子效应;甲氧基处于氨基的邻位的电子效应和处于间位时不同,氯和硝基取代基使氨基的两吸收峰均向蓝移,氨基取代基使氨基的两吸收峰向红移。     

Comparison of the ht Ultraviolet-Visible Spectra of the Copper(Ii) Complexes of Bidentate Schiff Base Ligands

Abstract

The bis(salicylaldiminato)copper(II) complexes of the ligand series of salicylaldimines derived from the condensation of n-alkyl or n-alkyloxy substituted aromatic amines with 2,4-dihydroxybenzaldehyde were synthesized. a series of Schiff base ligands with the general formula 4-X-N-(2,4-dihydroxybenzylidene)-aniline and differing only in substituents were synthesized. Some of these compounds have already been reported in literature. X=OCH₃[1],OC₂H₅[2],C₄H₉[1]. the copper(II) complexes of these ligands having the general formula, copper, bis[o-[N-(p-X-phenyl) formimidoyl]-4-hydroxyphenolato] were also synthesized. the ligands and their complexes, a total of 24 in number, are studied systematically with ultraviolet-visible spectroscopy to examine the effect of various n-alkyl- and n-alkyloxy substituents on the ligands and on their complexes. in the electronic spectrum of these compounds, the bands observed in the 200-450 run region which involve charge transfer π-π? transition were interpreted.     

A multinuclear magnetic resonance study of intramolecular hydrogen bonding in some Schiff and Schiff-Mannich bases in solution and in the solid state

Two Schiff bases; N, N′-bis(5-bromosalicylidene)-1,2-diaminoethane, BS, and 7-[(1-{5-bromo-2-hydroxyphenyl} methylidene)amino]-4-methylcoumarin, Sc, and two appropriate Schiff–Mannich bases, N, N′-bis{5-bromo-3-[(diethylamino)methyl]salicylidene}-1,2-diaminoethane, BSM, and 7-[(1-{5-bromo-3-[(diethylamino)methyl]-2-hydroxyphenyl} methylidene)amino]-4-methylcoumarin, SMc, capable of intramolecular hydrogen bonding have been investigated by multinuclear magnetic resonance methods in both solid and liquid phases. In all of the compounds under investigation tautomeric equilibrium involving an intramolecular hydrogen bond has been found. The Schiff–Mannich bases, which can form two different kinds of H bonds at room temperature, form relatively weak H bonds with the imino nitrogen atoms. At low temperatures the tautomeric proton exchange becomes slow on the NMR time scale and both hydrogen-bonded forms can be observed by ¹H, ¹³C, and ¹⁵N NMR methods. In the solid state the tautomeric process is frozen and only one H-bonded form is present. On the basis of 13C and ¹⁵N CPMAS NMR spectra this is identified as the form with hydrogen bonds involving the imino groups. This conclusion is in good agreement with previous results obtained by X-ray diffraction methods.

The investigated Schiff bases (BS and Sc) form relatively weak H bonds. The proton position in the hydrogen bridge, estimated from ¹⁵N and ¹³C chemical shifts, is very similar in both the solution and solid phases. In chloroform solution the observed tautomeric equilibria are almost insensitive to a temperature change within the range 223 to 303 K.     

Electronic Studies of Copper(II) Complexes of Amino Acids. III. EPR Spectra of Some Vitamin B6 Schiff Base Analogs

Schiff base coordination compounds of amino acids are good models to study the transamination reaction^2,3 of vitamin B₆. Several studies^4-6 have focused on the preparation, characterization and spectra study of these Schiff base coordination compounds, represented schematically in Figure 1, where R has been varied. In our continued studies of Cu(II) coordination compounds of amino acids, we have prepared a series of compounds with alanine (R=CH₃) and either a 4 or 5 substituent on the ring (X=H, OH, NO₂, Cl). In order to obtain as many of the EPR magnetic parameters as possible⁷, we prepared solid solutions in Zn(II) matrices with a Zn(II) to Cu(II) ratio of about 95:5. In this fashion we were able to reduce the dipole coupling and to calculate the [sgrave] molecular orbital coefficients for this important new series of compounds.