Pentamidine Analogs: Syntheses, Structures in Solid State by 13C CP/MAS NMR Spectroscopy, and X-Ray Crystallography and their Preliminary Biological Screening Against Human Cancer

Summary. The synthesis of four new 1,5-bis(4-amidinophenoxy)-3-oxapentane analogs is described. The structures of the obtained bis-amidines and bis-nitriles in the solid state are evaluated on the basis of ¹³C CP/MAS NMR spectra and theoretical calculations at DFT level. A single crystal X-ray diffraction structure is presented for 1,5-bis(4-amidinophenoxy)-3-oxapentane. A preliminary anticancer assay against three cell lines is also given.     

Synthesis,Characterization and Electronic Properties of a Symmetric Bidentate Schiff-Base Ligand and Its Complex with CadmIum(II)

A symmetric bidentate Schiff-base ligand and its complex with Cd(II) is described. The ligand and its complex were characterized by microanalysis, UV-Vis, GC-Mass and FT-IR spectroscopic methods. The present work also studied the structures and electronic properties of the bidentate Schiff-base ligand by using ab initio and AM1 molecular orbital methods. Ab initio and AM1 geometrical predictions have been compared. The analysis of molecular orbitals (MOs) indicates that the N(3) and N(6) atoms could be the coordination sites in this ligand.     

Experimental and Computational Studies on Cobalt(I)-Catalyzed Regioselective Allylic Alkylation Reactions

Here, we report the development of cobalt(I)-catalyzed regioselective allylic alkylation reactions of tertiary allyl carbonates with 1,3-dicarbonyl compounds. A family of well-defined tetrahedral cobalt(I) complexes bearing commercially available bidentate bis(phosphine) ligands [(P,P)Co(PPh₃)Cl] are synthesized and explored as catalysts in allylic alkylation reactions. The catalyst [(dppp)Co(PPh₃)Cl] (dppp=1,3-Bis(diphenylphosphino)propane) enables the alkylation of a large variety of tertiary allyl carbonates with high yields and excellent regioselectivity for the branched product. Remarkably, this methodology is selective for the activation of tertiary allyl carbonates even in the presence of secondary allyl carbonates. This contrasts with the selectivity observed in cobalt-catalyzed allylic alkylations enabled by visible light photocatalysis. Mechanistic insights by means of experimental and computational investigations support a Co(I)/Co(III) catalytic cycle.     

Electrochemical and computational studies of an expired vilazodone Drug as environmentally safe corrosion inhibitor for aluminum in chloride medium

Through using chemical and electrochemical methods, the theoretical and experimental investigation of the expired vilazodone drug's ability to prevent corrosion on aluminium (Al) in a corrosive medium of HCl (1 M) has been examined. Weighing tests (WL), electrochemical (impedance spectroscopy (EIS), potentiodynamic polarization (PDP)), atomic force microscopy (AFM), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) tests at 25 °C have all been used to investigate Vilazodone's capability to prevent corrosion of Al in 1 M HCl in the concentration in the range of 25–150 ppm. The corrosion inhibition effect of the investigate Vilazodone's against Al in acid environment was investigated weight loss and electrochemical methods. The highest % inhibition efficiency (%IE) was 95% resulted from weight loss technique at the highest concentration for inhibitor. According to the PDP data, this examined vilazodone function as a mixed-type inhibitor, impacting both the anodic and cathodic reactions. The inhibitors covered the active points of the metal surface, according to electrochemical impedance spectroscopy (EIS), to prevent corrosion. It was discovered that the inhibitor adsorption on the Al surface obeyed the Langmuir adsorption isothermal model. AFM, SEM, and FTIR surface examinations proved the inhibitor had a significant protective effect against Al dissolution in 1 M HCl. The outcomes from chemical and electrochemical methods are relatively consistent. Vilazodone acted as an effective corrosion inhibitor, according to all of the experimental data.     

Spectroscopy of Ru(II) polypyridyl complexes used as intercalators in DNA: Towards a theoretical study of the light switch effect

The absorption spectroscopy of [Ru(phen)₂dppz]²⁺ and [Ru(tap)₂dppz]²⁺ (phen = 1,10-phenanthroline, tap = 1,4,5,8-tetraazaphenanthrene; dppz = dipyridophenazine) complexes used as molecular light switches by intercalation in DNA has been analysed by means of Time-Dependent Density Functional Theory (TD-DFT). The electronic ground state structures have been optimized at the DFT (B3LYP) level of theory. The absorption spectra are characterized by a high density of excited states between 500 nm and 250 nm. The absorption spectroscopy of [Ru (phen)₂dppz]²⁺ in vacuum is characterized by metal-to-ligand-charge-transfer (MLCT) transitions corresponding to charge transfer from Ru(II) either to the phen ligands or to the dppz ligand with a strong MLCT () absorption at 411 nm. In contrast, the main feature of the lowest part of the vacuum theoretical spectrum of [Ru(tap)₂dppz]²⁺ between 522 nm and 400 nm is the presence of various excited states such as MLCT (), ligand-to-ligand-charge-transfer LLCT () or intra-ligand IL () states. When taking into account solvent corrections within the polarizable continuum model (PCM) approach (H₂O, CH₃CN) the absorption spectrum of [Ru(tap)₂dppz]²⁺ is dominated by a strong absorption at 388 nm (CH₃CN) or 390 nm (H₂O) assigned to a ¹IL () corresponding to a charge transfer from the outside end of the dppz ligand to the site of coordination to Ru(II). These differences in the absorption spectra of the two Ru(II) complexes have dramatic effects on the mechanism of deactivation of these molecules after irradiation at about 400 nm. In particular, the electronic deficiency at the outside end of the dppz ligand created by absorption to the ¹IL state will favour electron transfer from the guanine to the Ru(II) complex when it is intercalated in DNA.     

A theoretical approach for designing fluorescent reagentless biosensors: The optical model

In this paper a mathematical model describing the analytical signal obtained in fluorescence sensors is presented and compared with other commonly used models. The model starts from the Kubelka-Munk theory for solid surfaces but incorporates new theoretical improvements, being principally: (a) the increase in the effective optical pathlength due to the Scattering Induced Path Variation (SIPV), the incorporation of this parameter allows us to deduce that the fluorescence intensity from solid surfaces does not linearly change with the fluorophore concentrations; (b) the influence of the inner filter effect and how the error can be rectified and (c) the calculation of the scattering coefficients in sensor films for this kind of sensor. From this model it is possible to predict the effect of the fluorophore concentration, the sensor film scattering coefficient and the sample inner filter effect on the fluorescence signal. The conclusions obtained can be extended to other types of fluorescence measurements from solid surfaces.     

The subtle electronic effects of alkyl groups on the conformational equilibria and intramolecular hydrogen-bond strength in cis-3-alkoxycyclohexanols

(1)H NMR data for cis-3-n-propoxycyclohexanol (cis-3-PCH) and cis-3-isopropoxy-cyclohexanol (cis-3-ICH) show that a concentration increase shifts the conformational equilibrium from the diaxial (aa) conformer, stabilized by an intramolecular hydrogen bond (IAHB), to the diequatorial (ee) conformer [X(ee)=42% and 21% (at 0.01molL(-1)) to 58% and 56% (at 0.40molL(-1)), in CCl(4,) respectively] due to intermolecular hydrogen bonds (IEHB), as confirmed by IR data. The Deltanu values, obtained by IR spectra, indicated that increasing the size of the OR group [R=CH(3), CH(2)CH(2)CH(3) and CH(CH(3))(2)], increases the IAHB strength, due to an increase in the inductive effect of R group, which makes the oxygen lone pairs more available for an IAHB with OH group, in opposition to the steric effect. The percentage of ee conformer increases with the solvent basicity for cis-3-PCH and cis-3-ICH, from 48% and 36% in CCl(4) to 97% and 96% in DMSO, respectively. Values of 4.58, 6.06 and 6.33kcalmol(-1) for the IAHB strength in cis-3-PCH, cis-3-ICH and cis-3-TCH (cis-3-tert-butoxycyclohexanol), respectively, were obtained, from the theoretical data through the CBS-4M method, confirming the experimental results and indicating that the IAHB strength increases with the increasing bulk of OR substituent in this series of compounds.     

Theoretical calculations of the molecular properties of maleimide and its dimer

B3LYP theoretical calculations with 6-31++G(d,p) basis set have been performed to study the infrared spectrum of maleimide and its dimer. Our calculations have shown that the dimer formation leads to a binding energy of 44.0kJmol(-1) involving two intermolecular hydrogen bonds between the amide hydrogen and a carbonyl group of two neighboring maleimides. This value is essentially due to the electrostatic interaction term. Our calculations have also revealed the vibrational changes, in terms of frequencies and IR intensities, after dimer formation. The most affected modes are associated with the NH stretching and in-plane bending bands. This behavior can be adequately interpreted by the hydrogen atomic charge and NH charge-flux based on the modified charge-charge flux-overlap model for infrared intensities. The B3LYP frequency shifts are in very good agreement with the experimental ones.     

Theoretical calculations and vibrational spectra of 1,4-benzodioxan in its S(1)(pi, pi*) electronic excited state

The structure and vibrational frequencies of 1,4-benzodioxan in its S₁(π, π^*) electronic state have been calculated using the GAUSSIAN 03 and TURBOMOLE programs. The results have been compared to experimental data and also to the ground state. Structural data for the T₁(π, π^*) state have also been calculated. The theoretical frequencies agree very well with the experimental values for the S₀ electronic ground state but are less accurate for the S₁ excited state. Nonetheless, they provide valuable guidance for excited state calculations.