Modulating the Photochemistry of Bipyridylic Compounds by Symmetric Substitutions

A quantum electronic study of the effect of substituents on (2,2′‐bipyridyl)‐3,3′‐diol and (2,2′‐bipyridyl)‐3,3′‐diamine is presented. A large difference in the photochemical behavior between the original and the substituted selected systems is expected. For the sake of simplicity, the study is restricted to the symmetrically bi‐substituted compounds: fluorine, the more electronegative atom and thus a strong σ‐acceptor but also a weak π‐donor group, and NO₂, a strong π‐acceptor substituent. Among the large set of compounds studied, two receive special attention: 5,5′‐dinitro‐(2,2′‐bipyridyl)‐3,3′‐diamine and 6,6′‐difluoro‐(2,2′‐bipyridyl)‐3,3′‐diol. While in the former case the nitro substitution transforms (2,2′‐bipyridyl)‐3,3′‐diamine, previously suggested to behave as a photomemory material, into a simple fluorescent species, the latter substitution turns (2,2′‐bipyridyl)‐3,3′‐diol into a fresh new candidate for a photomemory device.     

Luminescent Complexes of Europium (III) with 2-(Phenylethynyl)-1,10-phenanthroline: The Role of the Counterions

New antenna ligand, 2-(phenylethynyl)-1,10-phenanthroline (PEP), and its luminescent Eu (III) complexes, Eu(PEP)₂Cl₃ and Eu(PEP)₂(NO₃)₃, are synthesized and characterized. The synthetic procedure applied is based on reacting of europium salts with ligand in hot acetonitrile solutions in molar ratio 1 to 2. The structure of the complexes is refined by X-ray diffraction based on the single crystals obtained. The compounds [Eu(PEP)₂Cl₃]·2CH₃CN and [Eu(PEP)₂(NO₃)₃]∙2CH₃CN crystalize in monoclinic space group P2_1/n and P2_1/c, respectively, with two acetonitrile solvent molecules. Intra- and inter-ligand π-π stacking interactions are present in solid stat and are realized between the phenanthroline moieties, as well as between the substituents and the phenanthroline units. The optical properties of the complexes are investigated in solid state, acetonitrile and dichloromethane solution. Both compounds exhibit bright red luminescence caused by the organic ligand acting as antenna for sensitization of Eu (III) emission. The newly designed complexes differ in counter ions in the inner coordination sphere, which allows exploring their influence on the stability, molecular and supramolecular structure, fluorescent properties and symmetry of the Eu (III) ion. In addition, molecular simulations are performed in order to explain the observed experimental behavior of the complexes. The discovered structure-properties relationships give insight on the role of the counter ions in the molecular design of new Eu (III) based luminescent materials.     

Dynamic properties of soy globulin adsorbed films at the air-water interface

In this paper we present surface dilatational properties of soy globulins (beta-conglycinin, glycinin, and reduced glycinin with 10 mM of dithiothreitol (DTT)) adsorbed onto the air-water interface, as a function of adsorption time. The experiments were performed at constant temperature (20 degrees C), pH (8.0), and ionic strength (0.05 M). The surface rheological parameters were measured as a function of protein concentration (ranging from 1 to 1x10(-3)% wt/wt). We found that the surface dilatational modulus, E, increases, and the phase angle, phi, decreases with time, theta, which may be associated with protein adsorption. These phenomena have been related to protein adsorption, unfolding, and/or protein-protein interactions (at long-term adsorption) as a function of protein concentration in solution. From a rheological point of view, the surface viscoelastic characteristics of soy globulin films adsorbed at the air-water interface are practically elastic. The main conclusion is that the dilatational properties of the adsorbed films depend on the molecular structure of the protein.     

CYP119 plus a Sulfolobus tokodaii strain 7 ferredoxin and 2-oxoacid:ferredoxin oxidoreductase constitute a high-temperature cytochrome P450 catalytic system

The cytochrome P450 superfamily of enzymes catalyzes a broad range of oxidative processes involved in the metabolism of fatty acids, biosynthesis of sterols, and elimination of drugs and xenobiotics. Application of the unique properties of P450 enzymes as fine biocatalysts in biotechnology is limited due to their thermal instability and the requirement for auxiliary electron-donor proteins and cofactors. CYP119, a thermophilic P450 enzyme from Sulfolobus solfataricus, was characterized some time ago, but no high-temperature redox partners have been available for it. Here we report reconstitution of CYP119 with a novel high-temperature electron-donor system consisting of a ferredoxin and 2-oxoacid:ferredoxin oxidoreductase from Sulfolobus tokodaii strain 7 that, unlike all other known P450 electron-donor partners, utilizes coenzyme-A and pyruvic acid rather than NADH or NADPH as the source of electrons. The oxidation of lauric acid by the reconstituted system increased 16-fold as the temperature increased from 25 to 70 degrees C and was functional for more than 30 min at the higher temperature. This first in vitro high-temperature P450 catalytic system is a key step in the development of practical high-temperature monooxygenase systems.     

Application of the Kohonen artificial neural network in the identification of proteinaceous binders in samples of panel painting using gas chromatography-mass spectrometry

Historically, three types of proteinaceous matter--casein, egg and animal glue--were used as binders for pigments or as adhesives in easel and wall painting. The relative percentage content of alanine, glycine, valine, leucine, isoleucine, serine, tyrosine, phenylalanine, aspartic acid, glutamic acid, lysine, methionine, proline and hydroxyproline, as determined by GC-MS, is used for binder identification. In this paper we analyse the viability of a multivariate modelling using Kohonen's neural network to characterise the wood adhesive in 16 old samples from Italian panel paintings of the 12-16th centuries. As a training set we use the amino acid composition of 141 samples contributed by the Opificio delle Pietre Dure of Florence (Cultural Heritage Ministry, Italy). Of the 141 samples, 113 were used to train the Kohonen neural network and the remaining 28 as the evaluation set. A specificity and sensitivity of 100% was achieved in training and 92-100% in prediction depending on the assignation criteria employed. The neural network thus trained and evaluated was applied to the old samples, achieving identification of all of them. In addition, the map obtained for each amino acid provides relevant information as to its importance in the characterisation of the sample.     

Guest‐Assisted Proton Conduction in the Sulfonic Mesoporous MIL‐101 MOF

Post‐synthesis modification of MIL‐101(Cr)‐NO₂ was explored in order to decorate the organic backbone by propyl‐sulfonic groups, with the aim to incorporate mobile and acidic protons for solid‐state proton electrolyte applications. The resulting solid switched from insulating towards proton superconductive behavior under humidity, while the conductivity recorded at 363 K and 95 % relative humidity reached 4.8×10^?3 S cm^?1. Propitiously, the impregnation of the material by strong acidic molecules (H₂SO₄) further boosted the proton conductivity performances up to the remarkable σ value of 1.3×10^?1 S cm^?1 at 363 K/95 % RH, which reaches the performances of the best proton conductive MOF reported so far.     

Study of the Photochemical Properties and Conical Intersections of [2,2′‐Bipyridyl]‐3‐amine‐3′‐ol

The two isoelectronic bipyridyl derivatives [2,2′‐bipyridyl]‐3,3′‐diamine and [2,2′‐bipyridyl]‐3,3′‐diol are experimentally known to undergo very different excited‐state double‐proton‐transfer processes, which result in fluorescence quantum yields that differ by four orders of magnitude. In a previous study, these differences were explained from a theoretical point of view, because of topographical features in the potential energy surface and the presence of conical intersections (CIs). Here, we analyze the photochemical properties of a new molecule, [2,2′‐bipyridyl]‐3‐amine‐3′‐ol [BP(OH)(NH₂)], which is, in fact, a hybrid of the former two. Our density functional theory (DFT), time‐dependent DFT (TDDFT), and complete active space self‐consistent field (CASSCF) calculations indicate that the double‐proton‐transfer process in the ground and first singlet π→π* excited state in BP(OH)(NH₂) presents features that are between those of their “parents”. The presence of two CIs and the role they may play in the actual photochemistry of BP(OH)(NH₂) and other bipyridyl derivatives are also discussed.     

Influence of assembling pH on the stability of poly(L-glutamic acid) and poly(L-lysine) multilayers against urea treatment

Polyelectrolyte multilayers of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) were built up using the layer-by-layer (LbL) technique in low pH (3.6, PM3.6) and in neutral pH (7.4, PM7.4) solutions. The multilayers were then treated with a concentrated urea (one kind of denaturant for proteins and polypeptides) solution (8M) and rinsed with corresponding buffer. The buildup and treatment processes were investigated by ultraviolet visible spectroscopy and ellipsometry. The surface morphology was observed by scanning force microscopy (SFM). The inner structures were determined by X-ray reflectometry and circular dichroism spectroscopy (CD). An exponential growth of the optical mass and the layer thickness was observed for both PM3.6 and PM7.4. After urea treatment, a significant mass loss for PM3.6 was found, while no mass change was recorded for PM7.4. The dominant driving force for PM7.4 is electrostatic interaction, resulting in multilayers with an abundant beta-sheet structure, which has higher stability against urea treatment. By contrast, the dominant driving force for PM3.6 is hydrogen bonding and hydrophobic interaction, which are sensitive to the urea treatment. The mechanism is substantiated by molecular mechanics calculation. This has offered a convenient pathway to mediate the multilayer properties, which is of great importance for potential applications.     

A new algorithm to evaluate bielectronic integrals with 1s Slater‐type orbitals obtained by the integral transforms

This article presents a variation of the integral transform method to evaluate multicenter bielectronic integrals (12|34), with 1s Slater‐type orbitals. It is proved that it is possible to define, out of the expression of (12|34) given by the integral transform method, a function F(q) that has the property of having a unique Q, such that F(Q) = (12|34). Therefore, F(q) may be used to calculate (12|34). It is shown that the evaluation of F(Q) turns out to be simpler than the three‐dimensional integral involved in the calculation of (12|34), and an algorithm is presented to calculate Q. The results show that relative errors on the order of 10^?3 or lower are obtained very efficiently. In addition, it is shown that the proposed algorithm is very stable. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004