In this report, we designed and synthesized ten N-(R-phenyl)-3-carboxamide-coumarin derivatives (2a-2j), exploring the coumarin nucleus, and an R-phenyl group as a structural scaffold and a peptide bond as a linker between them. The structure-activity relationships were investigated with different R-substituents (H, Br, NO2, Cl) in ortho, meta, or para positions from the phenyl group. Coumarins were obtained in good yields (72-95%), and in vitro screening against Canavalia ensiformis urease showed potential inhibitory percentages ranging from 42 to 65%. Half-maximal inhibitory concentration (IC50) values were determined for the best compounds 2b (R = 2-Br) and 2d (R = 4-Br). After conducting molecular docking and molecular dynamics on urease from C. ensiformis and Helicobacter pylori, potential binding modes for the most effective compounds 2b and 2d showed that these derivatives are able to interact with the crucial residue Cys592, thereby blocking the access of the urea substrate to the active site. According to density functional theory (DFT) calculations, 4-Br substitution on H. pylori urease was necessary for interacting with catalytic amino acids on the active site. report NRphenyl3carboxamidecoumarin NRphenylcarboxamidecoumarin N R 3 carboxamide 2a2j, 2a2j aj 2a 2j , j (2a-2j) nucleus Rphenyl them structureactivity structure activity Rsubstituents substituents H, H (H Br NO2 NO Cl ortho meta 7295%, 7295 72 95% 95 (72-95%) 4 65 65% Halfmaximal Half maximal IC50 IC (IC50 b 2Br 2 2-Br d 4Br. 4Br . 4-Br) C Cys592 Cys site DFT (DFT calculations NRphenyl carboxamidecoumarin (2a-2j 7295% 729 7 9 (72-95% 6 IC5 (IC5 Cys59 (72-95 (IC Cys5 (72-9 (72- (72 (7 (

Developing new non-noble metal electrocatalysts for oxygen reduction reaction (ORR) is an essential challenge in electrochemical device research. Among these, we highlight the metal Schiff-base complexes, which can be used as modified carbon paste electrodes (CPE). Herein, we present a facile one-pot method for preparing a new family of cobalt(II) complexes with Schiffbase ligands obtained from glycine and para-substituted aldehydes. Complexes were characterized by different techniques, and the effects of para-substituents on the electronic properties of the complexes were confirmed by ultraviolet-visible spectroscopy and cyclic voltammetry (CV). The CV was also used to evaluate the ORR behavior of metal complex-modified CPE in an alkaline medium. The three complex-modified CPE were found to be highly effective for ORR, and the electron-withdrawing character of para-substituent affects the electrochemical reactivity. Density functional theory (DFT) calculations were used to complement the study and correlate the electrochemical activity, the redox potentials, and the Hammett parameter (σp) with the singly occupied molecular orbital (SOMO) energy of the complexes. DFT data were also able to shed light on the likely ORR mechanism. In summary, electronic tuning of the ligand affects the electronic properties of the metal center and allows for systematic oxygen reduction-catalytic control. nonnoble non noble (ORR research these Schiff base CPE. . (CPE) Herein onepot one pot cobaltII cobalt II cobalt(II parasubstituted para substituted aldehydes techniques parasubstituents substituents ultravioletvisible ultraviolet visible CV. (CV) complexmodified complex medium electronwithdrawing electron withdrawing parasubstituent substituent reactivity (DFT activity potentials σp (σp SOMO (SOMO mechanism summary reductioncatalytic catalytic control (CPE (CV

The built of qualitative energy-level molecular diagrams for different geometries of simple molecules allow to explain the preferred geometry. The diagrams are built using simple symmetry principles and explain, on basis of the number of nonbonding electrons, for example, why the molecule of water is bent and not linear and ammonia is pyramidal and not planar. This simple energy principle does not need to consider the Valence Shell Electron-Pair Repulsion theory (VSEPR theory) neither hybrid orbitals to explain the geometry of simple molecules. This discussion is more appropriate to inorganic chemistry courses where symmetry is a common topic.

Dois ligantes tridentados, HL1, [(2-hidroxibenzil)(2-(imidazol-2-il)etil)]amina, e HL2, [(2-hidroxibenzil)(2-(piridil-2-il)etil]amina, foram usados na síntese dos complexos binucleares [Cu2(L1)2]Cl2•2H2O, complexo 1, e [Cu2(L2)2](ClO4)2•1.5H2O, complexo 2,para serem empregados como catalisadores em processos de oxidação. Os complexos foram caracterizados por análise elementar e espectroscopias na região do infravermelho, ultravioleta-visível e ressonância paramagnética eletrônica. Foram também estudados por voltametria cíclica e titulação potenciométrica, a fim de caracterizar seus comportamentos em solução. A resolução da estrutura cristalina do complexo 1 mostrou um cátion binuclear contendo dois grupos fenóxido em ponte. Este arranjo possui uma distância Cu...Cu de 3.043(10) Å, similar à observada na catecol oxidase (2.90 Å). Os comportamentos catalíticos destes complexos foram investigados nas oxidações de cicloexano e de catecol. Na oxidação de cicloexano observou-se baixa atividade para ambos os complexos, que pode ser atribuída ao estereoimpedimento produzido pela falta de coplanaridade entre os anéis aromáticos do arcabouço dos ligantes, sugerindo que a aproximação entre o substrato e o centro ativo binuclear é uma etapa determinante no mecanismo da reação. Com relação à atividade de catecolase, foram observadas altas eficiências, com o complexo 2 sendo mais ativo que o complexo 1. Isto indica que o ligante piridina é capaz de estabilizar melhor o intermediário proposto para esse processo, que contém o centro CuI CuI. Isto é corroborado pela grande participação da piridina no LUMO (lowest unoccupied molecular orbital) do complexo 2, que pode ajudar a acomodar a carga negativa adicional quando o complexo é reduzido da forma CuII CuII para CuI CuI.

The tridentate ligands HL1, [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine, and HL2, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine, were used to synthesize binuclear CuII complexes, [Cu2(L1)2]Cl2•2H2O, complex 1, and [Cu2(L2)2](ClO4)2•1.5H2O, complex 2, in order to obtain catalysts for oxidative processes. Both complexes were characterized by elemental analysis, IR, UV-Vis and EPR spectroscopies. In addition, they were studied by cyclic voltammetry and potentiometric titration in order to investigate their behavior in solution. The crystal structure of complex 1 revealed a binuclear cation where the metal centers are bridged by two phenoxo groups. This arrangement provides a Cu...Cu distance of 3.043(10) Å, which is similar to the observed for catechol oxidase (2.90 Å). The catalytic reactivities of both complexes were investigated for hydrocarbon and catechol oxidations. Complexes 1 and 2 led to low overall hydrocarbon oxidation conversion values of 6.34 % and 7.15 %, respectively. However, for complex 1, only cyclohexanol (Cy-OH) and cyclohexanone (Cy=O) were isolated as reaction products, with selectivities of 68.1% for Cy-OH. This low overall conversion is tentatively attributed to steric hindrance effects produced by the non-coplanar aromatic rings of the ligand scaffolds, which suggest that the access of the hydrocarbon molecule to the binuclear active center is a determinant step in the reaction mechanism. Investigation of catecholase activities has shown high efficiencies, with complex 2 being more active than complex 1. It indicates that the pyridine-containing ligand is able to stabilize the intermediate CuI CuI center which is proposed to be formed in this process. This is corroborated by the strong participation of pyridine in the LUMO (lowest unoccupied molecular orbital) of complex 2, which can help to accommodate the additional negative charge when the complex is reduced from CuII CuII to CuI CuI.

Este trabalho relata a síntese e a caracterização dos complexos de manganês(II) [MnII(Hbpeten)] e [MnII(Hbnbpeten)], respectivamente [N,N'-bis-(2-hidroxibenzil)-N-(2-piridilmetil)-N'-(2-hidroxietil)etano-1,2-diamine]manganês(II) e [N,N'-bis-(5-nitro-2-hidroxibenzil)-N'-(2-hidroxietil)etano-1,2-diamin]manganês(II), por análise elementar, voltametria cíclica, espectroscopias eletrônica (UV-Vis) e vibracional (FTIR), ressonância magnética nuclear de hidrogênio (¹H NMR) e espectroeletroquímica de ressonância paramagnética eletrônica (EPR). Os dados de espectroeletroquímica de EPR foram consistentes com a redução de um grupo nitro, tanto no H3bnbpeten livre quanto no complexo de manganês. Além disso, os cálculos teóricos foram consistentes com os resultados experimentais, mostrando que somente um grupo nitro contribui para a formação dos orbitais LUMO e sugerindo que os resultados teóricos são adequados para explicar as propriedades eletrônicas dos complexos.

The synthesis and characterization of the manganese(II) complexes [MnII(Hbpeten)] and [MnII(Hbnbpeten)], where H3bpeten and H3bnbpeten are respectively [N,N'-bis-(2-hydroxybenzyl)-N-(2-pyridylmethyl)-N'-(2-hydroxyethyl)ethane-1,2-diamine] and [N,N'-bis-(5-nitro-2-hydroxybenzyl)-N'-(2-hydroxyethyl)ethane-1,2-diamine], are reported. The characterization was carried out by elemental analyses, cyclic voltammetry, spectroscopic methods (UV-Vis, FTIR, ¹H NMR), electronic paramagnetic resonance spectroelectrochemistry (EPR) and theoretical DFT calculations. The electrochemistry and EPR espectroelectrochemistry data were consistent with the reduction of one of the nitro groups in free H3bnbpeten and in the respective manganese(II) complex. These results were supported by DFT calculations, which showed that only one nitro group contributes to the LUMO. The theoretical data appear to be suitable to describe the electronic properties of the compounds.

A reação entre Fe(ClO4)3.nH2O e N,N'-bis[(2-hidroxibenzil)-N,N' -bis(1-metilimidazol-2-il-metil)]etilenodiamina (H2bbimen) resulta na formação de dois isômeros geométricos, A e B, do cátion complexo [Fe(bbimen)]+, os quais foram isolados e caracterizados por espectroscopia na região do infravermelho e UV-visível, espectrometria de massas, medidas de condutividade molar, voltametria cíclica, espectroeletroquímica e espectroscopia de ressonância paramagnética eletrônica (RPE). A geometria de um desses isômeros foi claramente demonstrada por análise cristalográfica de raios X de monocristal. O composto cristaliza no sistema monoclínico, grupo espacial P2(1)/c, a = 14,104 (3), b = 15,626 (3), c = 13,291 (3) Å, beta = 98,07 (3)º, Z = 4, R1 = 6,35% e wR2 = 20,57%. As propriedades eletroquímicas do cátion [Fe(bbimen)]+ (-0,58 V versus NHE) são bastante similares às das transferrinas (-0,52 V versus NHE), indicando que o complexo é um bom modelo para as propriedades redox daquelas metaloenzimas. A espectroscopia de RPE foi a única técnica espectroscópica capaz de diferenciar os dois isômeros isolados (A e B). Os estudos de RPE revelaram que o isômero A trata-se de um complexo de FeIII spin alto distorcido rombicamente (E/D <FONT FACE=Symbol>@</FONT> 0,33) e apresenta um espectro caracterizado por uma linha estreita em g1 <FONT FACE=Symbol>@</FONT> 4,1 e outra larga em g2 <FONT FACE=Symbol>@</FONT> 9,0. O espectro de RPE do isômero B apresenta, além das linhas em g1 <FONT FACE=Symbol>@</FONT> 4,2 e em g2 <FONT FACE=Symbol>@</FONT> 9,0, um conjunto de linhas em g1 <FONT FACE=Symbol>@</FONT> 3,0, g2 <FONT FACE=Symbol>@</FONT> 3,6 e g3 <FONT FACE=Symbol>@</FONT> 5,1, que têm sido atribuídas a complexos de FeIII com simetria tendendo à axial (E/D <FONT FACE=Symbol>@</FONT> 0,22). Estudos teóricos empregando cálculos semi-empíricos, combinados com os dados de RPE, foram essenciais para a atribuição das estruturas geométricas dos isômeros A e B.

The reaction of Fe(ClO4)3.nH2O with N,N'-bis[(2-hydroxybenzyl)-N,N' -bis(1-methylimidazole-2-yl-methyl)]ethylenediamine (H2bbimen) affords two geometric isomers, A and B, of the complex cation [Fe(bbimen)]+, which were fully characterized by IR and UV-visible spectroscopies, ESI mass spectrometry, molar conductivity measurements, cyclic voltammetry, spectroelectrochemistry and EPR spectroscopy. The geometry of one of these isomers has been clearly demonstrated through X-ray crystallographic analysis. It crystallizes in the monoclinic system, space group P2(1)/c, a = 14.104 (3), b = 15.626 (3), c = 13.291 (3) Å, beta = 98.07 (3)º, Z = 4, R1 = 6.35% and wR2 = 20.57%. The electrochemical properties of [Fe(bbimen)]+ (-0.58 V versus NHE) are quite similar to those of transferrins (-0.52 V versus NHE) and indicate that it is a good model for the redox potential of these metalloenzymes. EPR spectroscopy was the only spectroscopic technique able to differentiate the isolated isomers A and B. EPR studies revealed that isomer A is better described as a rhombically distorted (E/D <FONT FACE=Symbol>@</FONT> 0.33) high-spin FeIII complex (g1 <FONT FACE=Symbol>@</FONT> 4.1 with a shoulder at g2 <FONT FACE=Symbol>@</FONT> 9.0), while the spectrum of B has a set of lines at g1 <FONT FACE=Symbol>@</FONT> 3.0, g2 <FONT FACE=Symbol>@</FONT> 3.6 and g3 <FONT FACE=Symbol>@</FONT> 5.1, in addition to the line at g1 <FONT FACE=Symbol>@</FONT> 4.2 and a shoulder at g2 <FONT FACE=Symbol>@</FONT> 9.0, which have been ascribed to FeIII complexes in axial symmetry (E/D <FONT FACE=Symbol>@</FONT> 0.22). Semi-empirical theoretical studies, combined with EPR data, were essential to the proposition of the geometric structures of A and B.

In this work we present a new parametrization in molecular mechanics for studying iron complexes. This force field was implemented in the FORCES 2000 program, developed in our group for studying in coordination compounds of interest in bioinorganic chemistry. Mononuclear and dinuclear iron complexes were studied using this program with good success.

Apresentamos neste trabalho a síntese, estrutura cristalina e as propriedades espectrais de ¹H NMR do complexo mononuclear [ZnII(L-Br)].2H2O o qual contém em sua primeira esfera de coordenação, o ligante hexadentado H2L-Br (H2L-Br = N,N'-bis-(5- bromo-2-hidróxibenzil)- N,N'-bis-(piridin-2-ilmetil)-1,2-etanodiamina). Cálculos teóricos utilizando DFT mostram boa correlação entre os parâmetros calculados e aqueles obtidos através de cristalografia de raios X em monocristais e revelam que somente os grupos fenolatos do ligante H2L-Br participam na formação do HOMO, enquanto somente os anéis piridínicos contribuem para a formação do LUMO.

We describe herein the synthesis, crystal structure and ¹H NMR properties of the mononuclear [ZnII(L-Br)].2H2O complex containing the hexadentate H2L-Br ligand (H2L-Br = N,N'-bis-(5-bromo-2-hydroxybenzyl)-N,N '-bis-(pyridin-2-ylmethyl)-ethane-1,2-diamine). DFT calculations demonstrate very good agreement between parameters calculated and those determined by X-ray crystallography, and reveal that only the phenolate groups of the H2L-Br ligand participate in the formation of the HOMO, while only one of the pyridine rings contributes to the LUMO formation.

The problem of the dropping out of the graduate chemistry courses is not new in the Brazilian University. What are the principal factors for this dropping out? Are there rules to measure this dropping out? In this work we present our experience in the Chemistry Institute of the Federal University of Rio de Janeiro to deal with this problem.