Theoretical Studies on Electronic Spectra and Second-order Nonlinear Optical Properties of Glucosyl Substituted Barbituric Acid Derivatives

AMI semi-empirical method was used to optimize the barbituric acid derivatives substituted with glucosyl B1-5 （series B）, and the thiobarbituric acid derivatives substituted with glucosyl T1-5 （series T）. Based on the optimized structures, INDO/CI method was adopted to calculate the electronic spectra. Meanwhile, the second-order nonlinear optical （NLO） coefficients βμ were calculated with the sum-over-state （SOS） formula. The results show that when the number of glucosyl units was increased, ｜βμ｜ values of the barbituric and thiobarbituric acid derivatives were both enhanced, especially for thiobarbituric acid derivatives. It indicates that non-conjugated substituted group could also improve NLO properties of materials when the number of repeated units was increased. Additionally, the absorption bands appearing in UV area are consistent with the proper change of the number of glucosyl units, and consequently it can be concluded that the high transparencies of all systems were scarcely varied.     

Theoretical study on second‐order nonlinear optical properties of spin crossover Fe(III) phenolate‐pyridyl Schiff base complexes

The density functional and ab initio theory were used to investigate the second‐order nonlinear optical (NLO) properties of Schiff base ligands, open‐shell Fe(III), and closed‐shell Ni(II) complexes. The effect of the metal center in complexes is thus manifold: it templates the formation of acentric structures, imparts high thermal stability to the chelate ring, and display higher second‐order NLO response than their ligands. The second‐order NLO response of metal complexes are intensively sensitive to the exchange donor/acceptor because the differences of the extent of charge separation and the intraligand charge transfer processes. Thus, substituted metal complexes could realize “switches on” the second‐order NLO response by exchange donor/acceptor. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

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.     

Ultrasonic Assisted Synthesis of Naphthalene Substituted Schiff Base Derivatives and Their Antioxidant Activity Studies

New Schiff base derivatives, 2,2′‐[naphthalene‐2,7‐diylbis(oxy)]bis[N′‐substituted acetohydrazide] ( 4a‐m ) were synthesized by the acid catalyzed condensation of aryl/hetero aromatic aldehydes with 2,2′‐ [naphthalene‐2,7‐diylbis(oxy)]diacetohydrazide ( 3 ) under reflux temperature and ultrasonic irradiation. These Schiff base derivatives were confirmed through spectral characterization using IR, ¹H NMR, ¹³C NMR and mass spectra. All the synthesized compounds were screened for their antioxidant activity using DPPH free radical scavenging method.     

含二茂铁双Schiff碱配体及其Ni(Ⅱ)配合物电子光谱和二阶非线性光学性质的密度泛函理论研究

采用密度泛函理论(DFT)B3LYP方法,对含二茂铁双Schiff碱配体及其Ni(Ⅱ)配合物的几何构型进行优化.在得到稳定构型的基础上,采用含时密度泛函理论(TD-DFT)的B3LYP方法计算了配合物的电子光谱,并结合有限场(FF)方法研究了配体和配合物的极化率和二阶非线性光学(NLO)性质.结果表明,配体中引入Ni(...     

Tautomerization Reaction,Experimental and Theoretical Characterizations of the N,N′-Dipyridoxyl(4-Methyl-1,2-Phenylenediamine) Schiff Base and its Cu(II) Complex

Herein, the tetradentate N,N′-dipyridoxyl(4-methyl-1,2-phenylenediamine) [=H²L] Schiff base and its Cu(II) salen complex [Cu(L)] are newly synthesized and characterized by IR, NMR and mass spectroscopies together with the elemental analysis. In addition, their geometrical parameters, assignment of their IR bands and NMR chemical shifts of the Schiff base are calculated using density functional theory (DFT) methods. Natural bond orbital analyses were performed at the same computational level, too. In the optimized geometry of the free ligand the aromatic rings are not in the same plane. The structure of the complex is more planar, where the dianionic Schiff-base acts as a tetradentate ligand in the N,N,O^–,O^–manner. Two phenolic oxygen atoms and two azomethine nitrogen atoms occupy four coordination positions of the square complex. The DFT-calculated results are in good agreement with the experimental values, confirming the suitability of the optimized geometries for the Schiff base and its Cu(II) complex.     

The effect of the protein environment on the structure and charge distribution of the retinal Schiff base in bacteriorhodopsin

The effects of the amino acid side chains of the binding pocket of bacteriorhodopsin (bR) and of a water molecule on the structure of the retinal Schiff base have been studied using Becke3LYP/6-31G* level of density functional theory. A model protonated Schiff base structure including six conjugated double bonds and methyl substituents was optimized in the presence of several amino acid side chains and of a water molecule, separately. The Schiff base structure was also calculated in the form of a neutral species. At each optimized complex geometry the atomic charges of the model Schiff base were calculated using Mulliken population analysis. In agreement with previously proposed counterion(s) of the protonated retinal Schiff base in bR, the results show that Asp₈₅ and Asp₂₁₂, which are present in the form of negatively charged groups, have significantly large effects on the structure and electronic configuration of both unprotonated and protonated model Schiff bases. The presence of a water molecule in the vicinity of the Schiff base demonstrates significant effects which are comparable to those of aspartate groups. Other side chains studied did not show any significant effect in this direction. Apart from the aspartate groups and the water molecule, in none of the other complexes studied are the atomic charges and the bond alternation of the model Schiff base significantly influenced by the presence of the neighboring amino acids. Received: 24 March 1998 / Accepted: 3 September 1998 / Published online: 10 December 1998     

Di‐μ‐acetato‐bis­{[2,4‐dichloro‐6‐(2‐pyridylmethyl­imino­meth­yl)­phenol­ato]zinc(II)} and di‐μ‐thio­cyanato‐bis­{[2,4‐dichloro‐6‐(2‐pyridylmethyl­imino­meth­yl)phenolato]copper(II)}

The two title complexes, [Zn₂(C₁₃H₉Cl₂N₂O)₂(C₂H₃O₂)₂], (I), and [Cu₂(C₁₃H₉Cl₂N₂O)₂(NCS)₂], (II), are dinuclear Schiff base compounds. Both mol­ecules are located on crystallographic centres of inversion. In (I), the Zn^II atom is five‐coordinated in a trigonal–bipyramidal coordination, with one imine N atom of one Schiff base and two acetate O atoms defining the basal plane, and one O atom and one pyridine N atom of the Schiff base occupying the axial positions, while in (II), the Cu^II atom is five‐coordinated in a square‐pyramidal coordination, with one O and two N atoms of one Schiff base and one terminal N atom of a bridging thio­cyanate ligand defining the basal plane, and one terminal S atom of another bridging thio­cyanate ligand occupying the apical position. The different bridging ligands lead to the different coordinations of the complexes.     

Study of solid-state catalytic isotope exchange of hydrogen inl-hydroxyproline under the action of spillover tritium

Reaction of high-temperature solid-state catalytic isotope exchange (HSCIE) of hydrogen in L-hydroxyproline was studied byab initio quantum-chemical calculations. A one-center synchronous mechanism of isotope exchange between the amino acid and the H₃O⁺ model acidic center was considered. The structures of transition states of the reaction and the activation energies were determined. Relative reactivity of the C−H bonds in the hydroxyproline molecule under conditions of HSCIE was studied. The results obtained are in agreement with experimental data on the stereoselectivity and regioselectivity of the HSCIE reaction,viz., the lower the calculated activation energy of isotope exchange, the larger the portion of hydrogen substituted by tritium in a given position of the amino acid molecule. The enhancement of the reactivity under conditions of solid-state isotope exchange can be associated with additional interaction between the exchanging H atoms and the electron-donor O and N atoms of the amino acid molecule in transition state. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1056–1060, June, 1999.     

Chirale Halbsandwich‐Pentamethylcyclopentadienyl‐Rhodium(III)‐ und Iridium(III)‐Komplexe mit Schiff‐Basen aus Salicylaldehyd und α‐Aminosäureestern [1]

Chiral Half‐sandwich Pentamethylcyclopentadienyl Rhodium(III) and Iridium(III) Complexes with Schiff Bases from Salicylaldehyde and α‐Amino Acid Esters [1] A series of diastereoisomeric half‐sandwich complexes with Schiff bases from salicylaldehyde and L‐α‐amino acid esters including chiral metal atoms, [(η⁵‐C₅H₅)(Cl)M(N,O‐Schiff base)], has been obtained from chloro bridged complexes [(η⁵‐C₅Me₅)(Cl)M(μ‐Cl)]₂ (M = Rh, Ir). Abstraction of chloride from these complexes with Ag[BF₄] or Ag[SO₃CF₃] affords the highly sensitive compounds [(η⁵‐C₅Me₅)M(N,O‐Schiff base]⁺X^? (M = Rh, Ir; X = BF₄, CF₃SO₃) to which PPh₃ can be added under formation of [(η⁵‐C₅Me₅)M(PPh₃)(N,O‐Schiff base)]⁺X^?. The diastereoisomeric ratio of the complexes ( 1 ‐ 7 and 11 ‐ 12 ) has been determined from NMR spectra.     

Unprecedented Double aza‐Michael Addition within a Sapphyrin Core

A novel sapphyrin derivative was obtained from the reaction between a free‐base sapphyrin and dimethyl acetylenedicarboxylate (DMAD). The formation of the new compound involved a double aza‐Michael addition of two pyrrolic NH groups to a DMAD molecule, with the formation of a disubstituted ethano bridge. The NMR spectral data reveal a product with an unsymmetrical structure; DFT calculations provided support for a structure in which the ethano bridge links two adjacent pyrrole units. The present study provides a seemingly unprecedented example of an N,N′‐dinucleophile reacting with DMAD to form a heterocyclic compound in which the two N‐atoms are linked to the two sp³ carbon atoms derived from a substituted acetylene.     

二维电荷转移型水杨醛缩乙二胺类双席夫碱及其Zn(Ⅱ)配合物的电子光谱及非线性光学性质的DFT理论研究

用密度泛函理论(DFT)B₃LYP方法,在6-31G(d)基组水平上优化水杨醛缩乙二胺类双席夫碱化合物及其Zn()配合物的几何结构.在稳定构型基础上,引入外电场,运用有限场(FF)方法,计算标题化合物体系的非线性光学(NLO)系数,并与其独立的对称分子片结构进行比较.同时用含时密度泛函理论(TD-DFT)计算各体系的电子光谱.结果表明,两个单席夫碱分子片结合为双席夫碱时,二阶及三阶NLO系数明显增大,且γ比β显著.双键桥连Zn配合物1a的β,γ值均小于相应配体,而单键桥连Zn配合物2a的β和γ值大于相应配体,说明金属Zn在完全共轭和局域共轭体系中所起的作用不同.     

巴比妥酸苯胺取代衍生物二阶非线性光学性质和电子光谱的INDO/CI研究

利用量子化学密度泛函理论（DFT）B3LYP方法，在6-31G~*基组下对巴比妥酸 苯胺取代衍生物体系BA1～BA5进行几何结构优化，以优化后的构型为基础，应用 INDO/CI方法进行电子光谱计算，并结合实验数据进行了分析，同时应用完全态求 和（SOS）公式计算二阶非线性光学（NLO）系数β_μ,设计的系列体系中β_μ最 大值可达到65.47×10~(-30)esu。进一步探讨了体系的共轭性和烷基取代基链的长 度对二者的影响，结果表明，体系的共轭程度越高，烷基取代基的链长度赵长，体 系β_μ值越大，而λ_max红移。     

Preparation of 5,5′‐pyrilidene and 5,5′‐quinolidene bis‐barbituric acid derivatives

NMR reaction following experiments were used to find optimal conditions for the barbituric acid double addition to aromatic and heteroaromatic carboxaldehydes. It was established that aromatic aldehydes with electron‐donating substituents such as hydroxy, methoxy, and dimethylamino produce only the single addition barbituric acid adduct (barbituric acid benzylidenes). If these electron‐donating substituents are transformed into electron‐withdrawing substituents by virtue of protonation (NMe₂ to NHMe₂⁺) then the double barbituric acid adduct becomes the sole product of the reaction. This is also true regardless of the reaction media if strong electron‐withdrawing substituents (such as a nitro group) are present. Considering that the reactive species for nitrogen containing aromatic heterocycles are actually the conjugated acids (electron deficient molecule) only the double barbituric acid adducts are isolated. All synthetic procedures presented are applicable to multi‐gram scale preparations of double barbituric acid adducts.     

Bis­[S‐methyl 3‐(2‐bromo­benzyl­idene)­di­thio­cab­aza­to‐N3,S]­platinum(II)

The Schiff base ligand in the title complex, [Pt(C₉H₈BrN₂S₂)₂], is deprotonated from its tautomeric thiol form and coordinated to Pt^IIvia the mercapto S and β–N atoms. The configuration about Pt^II is a perfect square‐planar, with two equivalent Pt—N [2.023 (3) Å] and Pt—S [2.293 (1) Å] bonds. The phenyl ring is twisted against the coordination moiety Pt1/N1/N1′/S2′/S2 by 31.8 (2)°, due to the steric hindrance induced by ortho‐substituted bulky Br atom.     

Calculations on the Nonlinear Second—Order Optical Polarizabilities for Series of Donor—C60 Molecules

IntroductionThebulkpreparation1ofC6 0 andC70 clusters(fullerenes)hasstimulatedawidevarietyofexperimentalandtheoreticalstudies .2 5Wehavesuccessfullyexaminedthestructures ,UV visiblespectraandthenonlinearthird orderopticalpolarizabilities (γ)ofC6 0 andC70 .6 ,7Byin troductionofsubstituents ,thecentrosymmetriesofC6 0 andC70 arebrokenandthesecond orderopticalnonlinearitiesareinduced .ThechargeseparationinsubstitutedC6 0whichleadstoenhancementofβvaluehasalsobeendis cussed .5Inrecentyears ,a…     

Substituent Effects on the Structural Features and Nonlinear Optical Properties of the Organic Alkalide Li+(calix[4]pyrrole)Li−

The effects of substituents on the structure, character, and nonlinear optical (NLO) properties of the organic alkalide Li⁺(calix[4]pyrrole)Li^? were studied by density functional theory. Natural bond orbital analysis and vertical ionization energies reveal that electron‐donating substituents strengthen the alkalide character of Li⁺(calix[4]pyrrole)Li^? and that they are beneficial for a larger first hyperpolarizability (β₀) value. However, electron‐withdrawing substituents have the opposite effect. The dependence of the NLO properties on the number of substituents and their relative position was detected in multisubstituted Li⁺(calix[4]pyrrole)Li^? compounds. For both the amino‐ and methyl‐substituted derivatives, the polarizabilities and the first hyperpolarizabilities increase as more pyrrole β‐H atoms are substituted. Moreover, distribution of the substituents so that they are as far away from each other as possible resulted in an increase in the β₀ value. The new knowledge obtained in this study may provide an effective approach to enhance the NLO responses of alkalides by employing pyrrole derivatives as complexants.     

Catalytic Oxidative Decarboxylation of Some Benzylcarboxylic Acid Derivatives by a New Iron(III) Schiff Base Complex

A quadridentate Schiff base ligand of N,N’-bis(2-hydroxy-α-methylbenzylidene)ethylenediamine (HMBEDA) and its new iron(III) complex were synthesized and identified by analytical, spectral data (1H NMR, 13C NMR FT-IR and UV-visible) and molar conductance. A rapid and efficient homogeneous oxidative decarboxylation of some benzylcarboxylic acid derivatives was carried out by a catalytic amount of iron(III) Schiff base complex in chloroform, using tetrabutylammonium periodate as a mild oxidant in good to excellent yields at room temperature.     

Synthesis,structural features and biochemical activity assessment of N,N′‐bis‐(2‐mercaptophenylimine)‐2,5‐thiophenedicarboxaldehyde Schiff base and its Co(II), Ni(II), Cu(II) and Zn(II) complexes

The tetradentate Schiff base ligand (SB), N,N′‐bis‐(2‐mercaptophenylimine)‐2,5‐thiophenedicarboxaldehyde was prepared via condensation of 2,5‐thiophene‐dicarboxaldehyde with 2‐aminothiophenol in a 1:2 molar ratio by conventional method. Additionally, its Co(II), Ni(II), Cu(II) and Zn(II) complexes have been synthesized and fully characterized by elemental analysis, FT‐IR, ¹H NMR, ¹³C NMR, UV–Vis, ESR, ESI‐mass, conductivity and magnetic susceptibility measurements. Spectral studies suggested that, the Schiff base coordinate metal ions through the azomethine N‐ and deprotonated thiol S‐ atoms. Based on UV–Vis absorption and magnetic susceptibility data, tetrahedral geometry was assigned for both Co(II) and Zn(II) complexes, whereas on the other hand, square planar geometry for both Ni(II) and Cu(II) complexes. The Schiff base and its metal complexes were screened for their in vitro antimicrobial activity by minimum inhibitory concentration (MIC) method. Free radical scavenging activity of the novel compounds was determined by elimination of 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radicals. In addition, the interactions of the free ligand and its complexes with calf thymus DNA (CT‐DNA) were explored using absorption, emission and viscosity measurements techniques.     

Polymeric Coordination Compounds Derived from Transition Metal(II) with Tetradentate Schiff‐base: Synthetic,Spectroscopic, Magnetic and Thermal Approach

The polymeric coordination compounds have been synthesized using the dipotassium salt of N,N′‐di(carboxymethylene)terephthalaldehydediimine (K₂SB¹) or N,N′‐di(carboxyethylene)terephthalaldehydediimine (K₂SB²) with manganese(II), cobalt(II), nickel(II), copper(II), zinc(II), and cadmium(II). The ligands have been characterized by ¹H‐NMR, and ¹³C‐NMR spectra. The polychelates have been characterized by elemental analyses, magnetic measurements, thermogravimetric analyses, electronic spectra and infrared spectra. The coordination compounds are colored, and the central metal ions are octahedrally coordinated with two water molecules and the Schiff bases. The Schiff bases act as di‐negative tetradentate ligands, in which bonding occurs through two oxygen and two nitrogen atoms. The polymers are insoluble in all common organic solvents such as acetone, methanol, ethanol, N,N‐dimethylformamide and dimethylsulfoxide.