Detailed Analysis of the Crystal Structures and Magnetic Properties of a Dysprosium(III) Phthalocyaninato Sextuple-Decker Complex: Weak f–f Interactions Suppress Magnetic Relaxation

In the research field of single-molecule magnets (SMMs), lanthanoid–lanthanoid interactions, so-called f–f interactions, are known to affect the SMM properties, although their magnitudes are small. In this article, an SMM with very weak f–f interactions is reported, and the effects of the interactions on the SMM properties are discussed. X-ray structural analysis of the Dy^III-Cd^II-phthalocyaninato sextuple-decker complex (Dy₂Cd₃) reveals that the intramolecular Dy−Dy length in Dy₂Cd₃ is more than 13 Å, which is longer than the intermolecular Dy−Dy length. Even though the two Dy^III ions are far apart, intermolecular ferromagnetic dipole–dipole interactions are observed in Dy₂Cd₃. From detailed analysis of ac magnetic susceptibilities, quantum tunneling of the magnetization (QTM) in Dy₂Cd₃ is partially suppressed owing to the existence of very weak Dy−Dy interactions. Our results show that even very weak Dy−Dy interactions act as a dipolar bias, suppressing QTM.     

LC–high resolution MS in environmental analysis: from target screening to the identification of unknowns

This article provides an overview of the state-of-the-art and future trends of the application of LC–high resolution mass spectrometry to the environmental analysis of polar micropollutants. Highly resolved and accurate hybrid tandem mass spectrometry such as quadrupole/time-of-flight and linear ion trap/orbitrap technology allows for a more reliable target analysis with reference standards, a screening for suspected analytes without reference standards, and a screening for unknowns. A reliable identification requires both high resolving power and high mass spectral accuracy to increase selectivity against the matrix background and for a correct molecular formula assignment to unknown compounds. For the identification and structure elucidation of unknown compounds within a reasonable time frame and with a reasonable soundness, advanced automated software solutions as well as improved prediction systems for theoretical fragmentation patterns, retention times, and ionization behavior are needed.     

Photoinduced Electron Transfer from the Inorganic Core to the Organic Shell of Hybrid Core–Shell Nanoparticles: Impedance Spectroscopy

In hybrid core–shell nanoparticles with inorganic nanocrystals in the core and organic molecules in the shell, photoinduced electron transfer occurs from the core to the shell. This leads to exciton dissociation through an ultrafast electron-transfer process that results in charge separation and finally photocurrent in the external circuit in devices based on such core–shell nanoparticles. In this work, we have fabricated and characterized sandwiched devices based on a series of core–shell systems. From impedance spectroscopy, we have observed that photoinduced charge separation in core–shell systems is associated with a decrease in the device resistance and an increase in the dielectric constant of the active material. In the series of core–shell systems, we have observed a one-to-one correlation between the photoinduced electron-transfer process and the changes in resistive and dielectric parameters upon illumination.     

Assessment of surface heterogeneity of calcite and apatite: from high resolution gas adsorption to the solid–liquid interface

The surface heterogeneity of calcite and apatite was investigated by high resolution adsorption isotherms of argon and nitrogen. The use of the derivative isotherm summation procedure reveals the presence of high energy adsorption sites for nitrogen molecules. These sites are assigned to surface calciums and monohydrogenophosphate groups for calcite and apatite respectively. The comparison of gas adsorption results with experiments at solid–liquid interfaces shows that nitrogen probes the same surface sites as benzoic acid on calcite and decylammonium chloride on apatite.     

Proline–calixarene thiourea host–guest complex catalyzed enantioselective aldol reactions: from nonpolar solvents to the presence of water

A proline–calix[4]arene thiourea host–guest complex catalyzed intermolecular aldol reaction of aromatic aldehydes with cyclohexanone has been developed. The anti-configured products were obtained in good yields and with high enantioselectivities. The reaction is proposed to work via a modified Houk–List model, where the carboxylate part of the proline constitutes as a supramolecular system with the thiourea. The outcome of the study indicates the influence of the calix[4]arene thiourea on both the reactivity and selectivity in a non-polar reaction medium, even in the presence of water at moderate temperatures.     

Application of ATR–FTIR spectroscopy to the analysis of tannins in historic leathers: The case study of the upholstery from the 19th century Portuguese Royal Train

Tanning materials of historic leather samples collected from the 19th century Portuguese Royal train were analyzed by attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy. Studied leathers were visually identified as morocco leathers, one of the most valued types of vegetable tanned leathers. In technical and historic literature, morocco leathers are described as a distinctive type of vegetable tanned leather, with a typical grain surface pattern, made from goat skins and sumac (Rhus coriaria) leaves.ATR–FTIR spectra of the Royal train leathers were investigated and compared with 10 reference tanning materials obtained from different plants in use in the 19th century, here described. Two different types of vegetable tanned leathers were identified. The obtained spectra allowed to confirm the presence of morocco leathers as well as to detect a different type of vegetable tanned leather, probably applied as a restoration material in a past intervention. This study shows the usefulness of ATR–FTIR to distinguish different types of historic leathers based in the spectroscopic characteristic IR bands of vegetable tannins used for leather production, which can be of great assistance for conservation condition assessments.     

Ab Initio Chemical Kinetics for the Thermal Decomposition of SiH4 + Ion and Related Reverse Ion–Molecule Reactions of Interest to PECVD of a-Si:H Films

Plasma Chemistry and Plasma Processing - The thermal unimolecular decomposition of SiH4 + ion and its related reverse reactions, SiH3 + + H and SiH2 + + H2, have...     

Solution Properties of NaHSO4 and Na2SO4: A New Sight from the Water–Ion and Water–Dipole Cooperative Interactions Using Dielectric Relaxation Spectroscopy

The aqueous NaHSO₄ and Na₂SO₄ solutions at concentrations of 0.1–1.0 mol/l in a limited frequency range 0.2–20 GHz are studied by dielectric relaxation spectroscopy with a newly developed fractal concept spectral function. The fractal analysis with α(lnτ) diagrams from dielectric relaxation spectroscopy as functions proposed a new strategy to shed light on the dual nature of ion–water and dipole–water cooperative interactions. A distinct cooperative interaction of ion–water and dipole–water is observed and water molecules perturbed by ions contributing to dielectric constant beyond the first hydration shell is obtained.     

Models of the membrane-bound cytochromes: mössbauer spectra of crystalline low-spin ferriheme complexes having axial ligand plane dihedral angles ranging from 0 degree to 90 degrees

Crystalline samples of four low-spin Fe(III) octaalkyltetraphenylporphyrinate and two low-spin Fe(III) tetramesitylporphyrinate complexes, all of which are models of the bis-histidine-coordinated cytochromes of mitochondrial complexes II, III, and IV and chloroplast complex b(6)f, and whose molecular structures and EPR spectra have been reported previously, have been investigated in detail by M?ssbauer spectroscopy. The six complexes and the dihedral angles between axial ligand planes of each are [(TMP)Fe(1-MeIm)(2)]ClO(4) (0 degree), paral-[(OMTPP)Fe(1-MeIm)(2)]Cl (19.5 degrees), paral-[(TMP)Fe(5-MeHIm)(2)]ClO(4) (26 degrees, 30 degrees for two molecules in the unit cell whose EPR spectra overlap), [(OETPP)Fe(4-Me(2)NPy)(2)]Cl (70 degrees), perp-[(OETPP)Fe(1-MeIm)(2)]Cl (73 degrees), and perp-[(OMTPP)Fe(1-MeIm)(2)]Cl (90 degrees). Of these, the first three have been shown to exhibit normal rhombic EPR spectra, each with three clearly resolved g-values, while the last three have been shown to exhibit "large g(max)" EPR spectra at 4.2 K. It is found that the hyperfine coupling constants of the complexes are consistent with those reported previously for low-spin ferriheme systems, with the largest-magnitude hyperfine coupling constant, A(zz), being considerably smaller for the "parallel" complexes (400-540 kG) than for the strictly perpendicular complex (902 kG), A(xx) being negative for all six complexes, and A(zz) and A(xx) being of similar magnitude for the "parallel" complexes (for example, for [(TMP)Fe(1-MeIm)(2)]Cl, A(zz) = 400 kG, A(xx) = -400 kG). In all cases, A(yy) is small but difficult to estimate with accuracy. With results for six structurally characterized model systems, we find for the first time qualitative correlations of g(zz), A(zz), and DeltaE(Q) with axial ligand plane dihedral angle Deltavarphi.     

Evaluation the synergistic antitumor effect of methotrexate–camptothecin codelivery prodrug from self-assembly process to acid-catalyzed both drugs release: A comprehensive theoretical study

Therapeutic efficiency of amphiphilic methotrexate–camptothecin (MTX-CPT) prodrug compared to free drug mixture (MTX/CPT) has been investigated using all-atom molecular dynamics simulation and first principles density functional theory calculations. This comparison revealed that MTX–CPT prodrug tends to form spherical self-assembled nanoparticle (NP), while free MTX/CPT mixture forms rod-shape NP. These observations are attributed to a structural defect in the MTX–CPT prodrug and solvation free energies of MTX, CPT and MTX-CPT molecules. The results provided evidence that noncovalent interactions (NCIs) among the pharmaceutical drugs play a very important role in anticancer agents aggregation process, leading to enhanced stability of the self-assembled NPs. It is found that the stability of MTX–CPT self-assembled NP is greater than the MTX/CPT NP due to the synergistic effect of hydrogen bonding between monomers and solvent (water). Moreover, the noncatalyzed as well as catalyzed hydrolysis reactions of MTX–CPT prodrug are theoretically studied at the PCM(water)//M06-2X/6−31G(d,p) computational level to shed additional light on the role of acidic condition in tumor tissues. We found that the ester hydrolysis in mild acidic solutions is a concerted reaction. In an agreement between theory and experiment, we also confirmed that the activation energies of the catalyzed-hydrolysis steps are much lower than the activation energies of the corresponding steps in the noncatalyzed reaction. Thus, the MTX–CPT prodrug reveals very promising properties as a pH-controlled drug delivery system.     

Ab Initio Chemical Kinetics for the Thermal Decomposition of SiH2+ and SiH3+ Ions and Related Reverse Ion–Molecule Reactions of Interest to PECVD of α-Si:H Films

Plasma Chemistry and Plasma Processing - The mechanisms and kinetics for the thermal decomposition of SiH2+ and SiH3+ ions, and related reverse reactions involving their ion fragments have been...     

Rational design of core–shell molecularly imprinted polymer based on computational simulation and Doehlert experimental optimization: application to the separation of tanshinone IIA from Salvia miltiorrhiza Bunge

Computational simulation and Doehlert experimental optimization were done for the rational design of a core-shell molecularly imprinted polymer (CS-MIP) for use in the highly selective separation of Tanshinone IIA (TSIIA) from the crude extracts of Salvia miltiorrhiza Bunge (SMB). The functional monomer layer of the polymer shells directed the selective occurrence of imprinting polymerization at the surface of silica through the copolymerization of vinyl end groups with functional monomers and also drove TSIIA templates into the formed polymer shells through the charge-transfer complex interactions between TSIIA and the functional monomer layer. As a result, the maximum rebinding capacity was achieved with the use of optimal grafting ratio by the Doehlert design. The CS-MIP exhibited high recognition selectivity and binding affinity to TSIIA. When the imprinted particles were used as dispersive solid phase extraction sorbents, the recovery yield of TSIIA reached 93% by a one-step extraction from the crude extracts of SMB, and the purity of TSIIA was larger than 98% by HPLC analysis. These results show the possibility of a highly selective separation and enrichment of TSIIA from the SMB using the TSIIA-imprinted core-shell molecularly imprinted polymers.     

Determination of intermolecular copper–copper distances from the EPR half-field transitions and their comparison with distances from X-ray structures: applications to copper(II) complexes with biologically important ligands

An EPR method involving measurement of half-field transitions was applied to determine the intermolecular Cu–Cu distances in copper(II)-carboxylate complexes with biologically important ligands. The experimental powder EPR spectra are composed of allowed (ΔM _S  = ±1) transitions centered at ~3,200 Gauss and of weak intensity, nominally forbidden, half-field (ΔM _S  = ±2) peaks observable at ~1,600 Gauss. Values of the average interspin distance for each complex were determined from the ratios of integrated allowed and forbidden peak areas using each of several methods. The calculated interspin distances were correlated with the copper–copper distances experimentally obtained by X-ray crystallography. The distances determined from the EPR spectra agree well with the X-ray determined values when the crystallographic value for one member of a series is used to calibrate the series. Less satisfactory agreement is found when methods based on Cu-spin-label systems are used.     

Protein–ligand interfaces are polarized: discovery of a strong trend for intermolecular hydrogen bonds to favor donors on the protein side with implications for predicting and designing ligand complexes

Understanding how proteins encode ligand specificity is fascinating and similar in importance to deciphering the genetic code. For protein–ligand recognition, the combination of an almost infinite variety of interfacial shapes and patterns of chemical groups makes the problem especially challenging. Here we analyze data across non-homologous proteins in complex with small biological ligands to address observations made in our inhibitor discovery projects: that proteins favor donating H-bonds to ligands and avoid using groups with both H-bond donor and acceptor capacity. The resulting clear and significant chemical group matching preferences elucidate the code for protein-native ligand binding, similar to the dominant patterns found in nucleic acid base-pairing. On average, 90% of the keto and carboxylate oxygens occurring in the biological ligands formed direct H-bonds to the protein. A two-fold preference was found for protein atoms to act as H-bond donors and ligand atoms to act as acceptors, and 76% of all intermolecular H-bonds involved an amine donor. Together, the tight chemical and geometric constraints associated with satisfying donor groups generate a hydrogen-bonding lock that can be matched only by ligands bearing the right acceptor-rich key. Measuring an index of H-bond preference based on the observed chemical trends proved sufficient to predict other protein–ligand complexes and can be used to guide molecular design. The resulting Hbind and Protein Recognition Index software packages are being made available for rigorously defining intermolecular H-bonds and measuring the extent to which H-bonding patterns in a given complex match the preference key.