Aqueous Solution Equilibria and Spectral Features of Copper Complexes with Tripeptides Containing Glycine or Sarcosine and Leucine or Phenylalanine

Copper(II) complexes of glycyl-L-leucyl-L-histidine (GLH), sarcosyl-L-leucyl-L-histidine (Sar-LH), glycyl-L-phenylalanyl-L-histidine (GFH) and sarcosyl-L-phenylalanyl-L-histidine (Sar-FH) have potential anti-inflammatory activity, which can help to alleviate the symptoms associated with rheumatoid arthritis (RA). From pH 2–11, the MLH, ML, MLH-1 and MLH-2 species formed. The combination of species for each ligand was different, except at the physiological pH, where CuLH-2 predominated for all ligands. The prevalence of this species was supported by EPR, ultraviolet-visible spectrophotometry, and mass spectrometry, which suggested a square planar CuN4 coordination. All ligands have the same basicity for the amine and imidazole-N, but the methyl group of sarcosine decreased the stability of MLH and MLH-2 by 0.1–0.34 and 0.46–0.48 log units, respectively. Phenylalanine increased the stability of MLH and MLH-2 by 0.05–0.29 and 1.19–1.21 log units, respectively. For all ligands, 1H NMR identified two coordination modes for MLH, where copper(II) coordinates via the amine-N and neighboring carbonyl-O, as well as via the imidazole-N and carboxyl-O. EPR spectroscopy identified the MLH, ML and MLH-2 species for Cu-Sar-LH and suggested a CuN2O2 chromophore for ML. DFT calculations with water as a solvent confirmed the proposed coordination modes of each species at the B3LYP level combined with 6-31++G**.

DFT STUDIES OF STRUCTURAL PARAMETERS, VIBRATIONAL FREQUENCIES AND NMR SPECTRA OF 3-(1H-BENZO[D]IMIDAZOL-1-YL)-N'-(TOSYLOXY)PROPANIMIDAMIDE

Amidoxime derivatives have practically valuable biological properties. We have previously obtained new spiropyrazolinium compounds by arylsulfo-chlorination of β-aminopropioamidoximes, but in case of β-(benzimidazol-1-yl)pro-pioamidoxime we have obtained O-substitution product – 3-(1H-benzo[d]imidazol-1-yl)-N'-(tosyloxy)pro-panimidamide. The aim of the work is predicting of structural parameters (bond lengths, bond angles), vibrational frequencies and NMR spectra of 3-(1H-benzo-[d]imidazol-1-yl)-N'-(tosyloxy)propanimidamide. The calculations were performed using Gaussian 09 package. Structural parameters and vibrational frequencies was calculated using DFT (B3LYP/B3PW91/WB97XD)/6-31G(d,p). 1H and 13C NMR was predicted using DFT B3LYP/6-31G(d,p)-GIAO in DMSO. All calculated values are in good agreement with experimental data. The calculated bond lengths and bond angles were compared with results of X-ray structural analysis. The best correlation coefficient was 0.981 (calcu-lations with B3LYP level). For bond angles, the best result was obtained with B3LYP level (0.990). For vibrational frequencies correlation coefficients between the calculated and experimental values were 0.997 (B3LYP), 0.996 (B3PW91) and 0.995 (WB97XD). The most accurate method was used for predic-ting NMR spectrum. The correlation coefficients between the experimental and calculated 1H and 13C chemical shifts were 0.949 and 0.999 respectively.

Exploring the Antioxidant Activity of Thiaflavan Compounds: a Quantum Chemical Study

Density functional theory calculations at B3LYP level are performed to theoretically investigate the antioxidant properties of 30 thiaflavan compounds. The main theoretical parameters, such as bond dissociation enthalpy, ionization potential,...

Molecular Structure, Frontier Molecular Orbitals, MESP and UV–Visible Spectroscopy Studies of Ethyl 4-(3,4-dimethoxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate: A Theoretical and Experimental Appraisal

n the current investigation, we wish to report a combined study on the theoretical and experimental investigation of structural, molecular, and spectral properties of ethyl 4-(3,4-dimethoxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (EDMT). The EDMT molecule is synthesized and characterized by UV-Visible, FT-IR, 1H NMR, 13C NMR, DEPT, and mass spectral techniques. The density functional theory (DFT) investigation was performed by using the B3LYP level of theory at 6-311++G (d,p) basis set. Frontier molecular orbital (FMO) analysis is likewise examined. An TD-DFT method was used for the UV-Visible spectral analysis by using the B3LYP level and 6-311++G (d,p) basis set in the DMSO solvent. Experimental and theoretical UV-Visible spectra were compared in the present study. Various reactivity descriptors are discussed. Besides, Mulliken atomic charges, molecular electrostatic surface potential (MESP), and some valuable thermodynamic functions are studied.

Alkylated Sesamol Derivatives as Potent Antioxidants

Sesamol is a phenolic derivative. Its antioxidant activity is low than that of Trolox and depends on benzodioxole moiety. Thus, a molecular modification strategy through alkylation, inspired by natural and synthetic antioxidants, was studied by molecular modeling at the DFT/B3LYP level of theory by comparing the 6-31+G(d,p) and 6-311++G(2d,2p) basis sets. All proposed derivatives were compared to classical related antioxidants such as Trolox, t-butylated hydroxytoluene (BHT) and t-butylated hydroxyanisole (BHA). According to our results, molecular orbitals, single electron or hydrogen-atom transfers, spin density distributions, and alkyl substitutions at the ortho positions related to phenol moiety were found to be more effective than any other positions. The trimethylated derivative was more potent than Trolox. t-Butylated derivatives were stronger than all other alkylated derivatives and may be new alternative forms of modified antioxidants from natural products with applications in the chemical, pharmaceutical, and food industries.

A Computational and Structural Database Study of the Metal-Carbene Bond in Groups IA, IIA, and IIIA Imidazol-2-Ylidene Complexes

Imidazol-2-ylidenes are important N-heterocyclic carbenes which have become universal ligands in organometallic and coordination chemistry. Generally classified as σ-donor ligands, these compounds have been used to stabilize various metal complexes which hitherto were less stable in their catalytic processes. Herein, the number and distribution of group IA, group IIA, and group IIIA metal-imidazol-2-ylidene complexes retrieved from the Cambridge Structural Database (CSD) are assessed. The data showed that the mean M-Ccarbene bond length increases with increasing ionic size but is similar across each diagonal. Dominant factors such as Lewis acidity and electrostatic attractions were found to control the bonding modes of the respective ions. Generally, the metal ions show preference for tetrahedral coordination with larger cations forming complexes with higher coordination numbers. For their high number of entries (101), tetrahedrally coordinated boron complexes with various electron withdrawing and electron donating groups were studied computationally at the DFT/B3LYP level of theory. The strength of the B-Ccarbene bond was found to depend on steric interactions between bulky groups on the borenium atom and substituents on the N-positions of the imidazol-2-ylidene ligand. This observation was further confirmed by estimation of the binding energy, natural charge, and the electron distribution in the B-Ccarbene bond.

Density Functional Calculations on the Molecular, Electronic Structures of Metal-Free, N,N'-Dideuterio and Magnesium Tetra-3,4-Pyridino-Porphyrazines

A theoretical calculation of the fully optimized geometries and electronic structures of the metal-free Tetra-2,3-Pyridino-Porphyrazine (TPdPzH2*), N,N-Dideuterio (TPdPzD2*), and Magnesium (TPdPzMg*) tetra-3,4-pyridino-porphyrazine has been conducted with the density functional B3LYP level using the 6-31G(d) basis set. A comparison among the different Phthalocyanine (Pc) derivatives, including Tetra-2,3-Pyridino-Porphyrazine (TPdPzH2) compounds, for the geometry, molecular orbital, and atomic charge was made. The substitution effect of the N atoms and the isotopic effect of D atoms on the properties of these compounds were discussed. The farther the heterocyclic N atoms in the benzo rings from 16-membered ring are, the smaller it influence the size of the central hole, the bond lengths and bond angles of 16-membered ring, the HOMO-LUMO gaps, and the atomic charges on the core Pz fragment. In other words, the properties of TPdPz* compounds are closer to Pc than TPdPz. With the order of H2Pc<TPdPzH2<TPdPzH2*, the acidity of the inner N-H bonds in the three molecules increased in turn.

Toward of Safer Phenylbutazone Derivatives by Exploration of Toxicity Mechanism

A drug design for safer phenylbutazone was been explored by reactivity and docking studies involving single electron transfer mechanism, as well as toxicological predictions. Several approaches about its structural properties were performed through quantum chemistry calculations at the B3LYP level of theory, together with the 6-31+G(d,p) basis sets. Molecular orbital and ionization potential were associated to electron donation capacity. The spin densities contribution showed a preferential hydroxylation at the para-positions of phenyl ring when compared to other positions. In addition, on electron abstractions the aromatic hydroxylation has more impact than alkyl hydroxylation. Docking studies indicate that six structures 1, 7, 8 and 13–15 have potential for inhibiting human as well as murine COX-2, due to regions showing similar intermolecular interactions to the observed for the control compounds (indomethacin and refecoxib). Toxicity can be related to aromatic hydroxylation. In accordance to our calculations, the derivatives here proposed are potentially more active as well safer than phenylbutazone and only structures 8 and 13–15 were the most promising. Such results can explain the biological properties of phenylbutazone and support the design of potentially safer candidates.

The Hydrogen Passivated Graphene Cluster and its Stability - First Principle DFT (B3LYP) Levels of Approximation with the Basis Set 3-21G

First-principles DFT (B3LYP) levels of calculations with the basis set 3-21G have been carried out in order to study the geometric stability and electronic properties of hydrogen passivated graphene (H-graphene) clusters(CN) (where N = 6, 10, 13, 16, 22, 24, 27, 30, 35, 37, 40, 42, 45, 47, 48, 50, 52, 54, 70 and 96) and perform the DOS spectrum on H-graphene (C16H10, C24H12, C30H14, C48H18, C70H22 and C96H24) using Mulliken population analysis by the Gaussian 03 W set of programs. The variations of ground state energy of graphene clusters are observed on sizes and corresponding number of carbon atoms. The binding energy per carbon atom is the function of carbon atoms for the number of carbon atoms less than 30 and saturated at carbon’s number 30 and more in the DFT (B3LYP) levels of approximation with the basis set 3-21G. The binding energy per carbon atom of a pure graphene sheet C32 is 8.03 eV/atom in the DFT (B3LYP) level of approximation with the choice of the basis set 3-21G, which is acceptable with previous reported data 7.91 eV/atom. The HOMO-LUMO gap in NBO is studied for some H-grapheneclustors C16H10, C24H12, C30H14, C48H18, C70H22 and C96H24.

Mechanistic Investigations of the Organocatalytic Depolymerization of PET Waste with Isosorbide

Glycolysis of PET waste with isosorbide, a biomass derived diol, was catalyzed by commercially available 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) at temperature up to 190�C when low molecular weight oligomer containing at least one equivalent of isosorbide was obtained. The structural assignment of the oligomer product was established by NMR spectroscopy showing predominantly end-chain bonded isosorbide with exo/endo ratio of 55/45. Mechanistic considerations of the transesterification reaction of isosorbide with dimethylterephthalate (DMT) as model reaction revealed that the hydrogen bonding interaction of TBD with this diol is the favored mechanism pathway. This was established by corroborating solution NMR spectroscopy studies with DFT calculations at B3LYP level where it was observed that isosorbide is hydrogen bonded to TBD through both endo and exo hydroxyl groups. On the other hand, the TBD catalyst reacts with dimethylterephthalate at low temperature forming a stable, easy to handle covalently bonded adduct.