Analysis of a cycloheptenone derivative: an experimental and theoretical approach

A detailed analysis with total assignment of (1)H and (13)C NMR spectral data for a cycloheptenone derivative, a key intermediate for the synthesis of perhydroazulene terpenoids, is related. These assignments are based on 1D (1)H and (13)C NMR and on 2D NMR techniques including gCOSY, gHSQC, gHMBC, J-resolved and NOEDIF experiments. The unequivocal assignments were supported by theoretical chemical shifts and scalar coupling constant calculations at GIAO B3LYP/cc-pVDZ level from optimized structures at the same level of theory.     

Structural assignment of Diels-Alder adducts: an experimental and theoretical approach

A detailed NMR analysis with total assignment of (1)H and (13)C NMR data for the endo and the exo adducts, obtained by Diels-Alder reaction between 2-cyclohexenone and cyclopentadiene, is described. The unequivocal assignment of the endo and exo structures was performed by (1)H and (13)C NMR. These assignments were supported by theoretical chemical shift calculations at GIAO/HF level using 6-311 + g(2d, p) from optimized structures at the B3LYP/6-31g(d) level.     

Retention in overloaded columns, an experimental approach

Employing a micro-bore silica capillary coated with Carbowax 20 M, the dependence of chromatographic retention upon operative variables was studied surpassing the sample capacity of the column. Solution thermodynamics in the non-linear range of the absorption isotherm of n-alkanes on poly(ethylene oxide) were analyzed interpreting the experimental data through a retention equation deduced in a preceding theoretical work. At 120 degrees C, and pressures up to 11 bar abs, deviations from the ideal-gas behavior are found to be negligible, either for the fluid dynamics of the carrier-gas, or the thermodynamics of solution of the n-alkanes. Within the experimental error, for all practical purposes the mobile phase can be treated as an ideal gas. This constraint allows studying a solute molecule placed in an environment ranging from solvent monomers only, to a mixture of varying composition of solvent and solute, avoiding effects from significant interactions in the gas phase. In the experimental conditions explored, the absorption isotherm can be represented by taking only two-terms of its power series development.     

Collision-induced migration of adsorbates on solid surfaces: an experimental approach

Collision-induced migration (CIM) is a process in which energetic gas-phase atoms or molecules at the tail of the Boltzmann distribution enhance surface migration of adsorbates upon collision. It is believed to exist and play an important role in any realistic high pressure-high-temperature heterogeneous catalytic system. Combining supersonic beam-surface collision setup with in-situ optical second harmonic generation diffraction technique from a coverage grating, we have shown, for the first time, that indeed energetic collisions (Kr seeded in He) promote surface mobility of CO-K surface complex on Ru(001) with a threshold total kinetic energy of 3 eV. An average migration distance/collision of more than 30 adsorption sites was estimated from the experimental data at Kr total energy of 3.8 eV. This long-range migration distance per collision is understood in terms of a cascade migration mechanism, where adsorbed CO molecules collide and push their neighbors from high to low coverage areas, in a direction dictated by the collision momentum vector. A similar mechanism has recently been suggested to explain adsorbate mobility at high coverage induced by an STM tip.     

Iodine monochloride-amine complexes: an experimental and computational approach to new chiral electrophiles

Lactonizations are important steps in many synthetic sequences. Substrate-controlled reactions that use chiral auxiliaries or chiral alkenes have already been studied in depth. This study focuses on stereoselective reagent-controlled iodolactonizations, by application of a new method that uses complexes of iodine monochloride and various donor molecules. (R)-1,2,3,4-Tetrahydro-1-naphthylamine and other amines with similar structures were found to be efficient in the iodocyclization of 4-aryl-4-pentenoic acids. Calculations were performed on complexes of (R)-1,2,3,4-tetrahydro-1-naphthylamine with XCl (X = I, H) to identify possible reactive species in these iodocyclizations. Calculations were carried out at various levels of theory, including B3 LYP/6-31+G (d,p) by using a modified SDD basis set for iodine.     

Purification and radioiodination of 2, 4 di-tertiary- butyl phenol extracted from Lactococcus lactis subsp. lactis CAU: 3138-GM2 and its application on myeloma cells

Journal of Radioanalytical and Nuclear Chemistry - Quantitative calculation based on the joint action of anion exclusion and sorption has not been reported. This article studies the diffusion...     

Substituent effect on a family of quinones in aprotic solvents: an experimental and theoretical approach

In this work a comparison between redox potentials, obtained by constructing current-potential plots from chronoamperometric measurements, and the parameter sigma(x), as proposed by Zuman in terms of the Hammett substituent parameters, was performed for several quinone compounds. This study shows the limitations of this approach and proves that methods based on quantum chemistry can be used to study the substituent effect in quinone systems. By using the Density Functional Theory, in the Kohn-Sham context with three exchange-correlation functionals, BLYP, B3LYP, and BHLYP, it was found that the electron affinity is good enough to give a useful relationship with experimental redox potentials of quinone systems. This conclusion is reached when the basis set functions involve diffuse functions, and also when the Hartree-Fock exchange energy is included in the exchange-correlation functional. The Fukui function, to describe preferential sites involved at initial stages of a system that bind an electron, is analyzed when electron donor and electron acceptor groups are present as substituents in quinone systems. The methods applied in this work are valid for any kind of quinone compound and will be used in further analysis of the electron reorganization in semiquinone species.     

Growth kinetic of single and double-walled aluminogermanate imogolite-like nanotubes: an experimental and modeling approach

Atomic Force Microscopy (AFM) and in situ Small Angle X-ray Scattering (SAXS) were used to investigate the evolution of the aluminogermanate imogolite-like nanotubes concentration and morphology during their synthesis. In particular, in situ SAXS allowed quantifying the transformation of protoimogolite into nanotubes. The size distribution of the final nanotubes was also assessed after growth by AFM. A particular attention was focused on the determination of the single and double walled nanotube length distributions. We observed that the two nanotube types do not grow with the same kinetic and that their final length distribution was different. A model of protoimogolites oriented aggregation was constructed to account for the experimental growth kinetic and the length distribution differences.     

QSAR with experimental and predictive distributions: an information theoretic approach for assessing model quality

We propose that quantitative structure–activity relationship (QSAR) predictions should be explicitly represented as predictive (probability) distributions. If both predictions and experimental measurements are treated as probability distributions, the quality of a set of predictive distributions output by a model can be assessed with Kullback–Leibler (KL) divergence: a widely used information theoretic measure of the distance between two probability distributions. We have assessed a range of different machine learning algorithms and error estimation methods for producing predictive distributions with an analysis against three of AstraZeneca’s global DMPK datasets. Using the KL-divergence framework, we have identified a few combinations of algorithms that produce accurate and valid compound-specific predictive distributions. These methods use reliability indices to assign predictive distributions to the predictions output by QSAR models so that reliable predictions have tight distributions and vice versa. Finally we show how valid predictive distributions can be used to estimate the probability that a test compound has properties that hit single- or multi- objective target profiles.     

High resolution scanning optical imaging of a frozen planar polymer light-emitting electrochemical cell: an experimental and modelling study

Light-emitting electrochemical cells(LECs) are organic photonic devices based on a mixed electronic and ionic conductor.The active layer of a polymer-based LEC consists of a luminescent polymer,an ion-solvating/transport polymer,and a compatible salt.The LEC p-n or p-i-n junction is ultimately responsible for the LEC performance.The LEC junction,however,is still poorly understood due to the difficulties of characterizing a dynamic-junction LEC.In this paper,we present an experimental and modeling study of the LEC junction using scanning optical imaging techniques.Planar LECs with an interelectrode spacing of 560μm have been fabricated,activated,frozen and scanned using a focused laser beam.The optical-beam-induced-current(OBIC)and photoluminescence(PL) data have been recorded as a function of beam location.The OBIC profile has been simulated in COMSOL that allowed for the determination of the doping concentration and the depletion width of the LEC junction.     

NMR spectroscopy of intermetallic compounds: an experimental and theoretical approach to local atomic arrangements in binary gallides

The results of the investigation of MGa(2) with M = Ca, Sr, Ba and of MGa(4) with M = Na, Ca, Sr, Ba by a combined application of NMR spectroscopy and quantum mechanical calculations are comprehensively evaluated. The electric-field gradient (EFG) was identified as the most reliable measure to study intermetallic compounds, since it is accessible with high precision by quantum mechanical calculations and, for nuclear spin I>1/2, by NMR spectroscopy. The EFG values obtained by NMR spectroscopy and quantum mechanical calculations agree very well for both series of investigated compounds. A deconvolution of the calculated EFGs into their contributions reveals its sensitivity to the local environment of the atoms. The EFGs of the investigated di- and tetragallides are dominated by the population of the p(x)-, p(y)-, and p(z)-like states of the Ga atoms. A general combined approach for the investigation of disordered intermetallic compounds by application of diffraction methods, NMR spectroscopy, and quantum mechanical calculations is suggested. This scheme can also be applied to other classes of crystalline disordered inorganic materials.     

Molecular aspects of the interaction between plants sterols and DPPC bilayers: an experimental and theoretical approach

The effect of sterols composition in a lipid bilayer was investigated on membranes of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and mixtures with the plant sterols β-sitosterol and stigmasterol. Differential scanning calorimetry, 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence polarization and infrared spectroscopy studies showed that both sterols changed the packing of the membrane and the hydration of the polar headgroup of the phospholipids, disordering the gel phase and, vice versa, ordering the membrane in the liquid crystalline phase. In all cases some differences among β-sitosterol and stigmasterol could be observed, being β-sitosterol slightly more efficient than stigmasterol in ordering a fluid membrane, bringing the membrane to a more packed liquid ordered phase. Molecular dynamic simulations were carried out to better characterize the distinct behavior of both sterols in a DPPC-membrane. The calculated parameters agreed quite well with the experimental results and a molecular model is proposed to explain differences in the sterols molecules and their effect on the DPPC-bilayer.     

Mechanical relaxations in polypropylene: A new experimental and theoretical approach

Accurate dynamic mechanical measurements have been performed on semicrystalline isotactic polypropylene over wide ranges of temperature and frequency. A mechanical model has been used to analyze experimental results in order to separate the behavior of amorphous and crystalline phases. The two main α and β relaxation processes have been analyzed. The β relaxation, related to the glass-rubber transition of the amorphous fraction, has been studied with the help of a physical model. The behavior is similar to that of a wholly amorphous polymer, with two characteristics: a high rubbery plateau, indicating a crosslinking effect by the crystalline phase, and a strong effect of interfaces in shear strain. Experimental data suggest the α relaxation originates within the crystalline phase and that it can be attributed to diffusion of defects. The amorphous phase plays an important role in this process, because it has to adapt itself by cooperative movements to respect the compatibility of deformations of the two phases. The formalism developed here rationalizes experimental results obtained with samples having different thermal histories.     

Making nanometer thick silica glass scaffolds: an experimental approach to learn about size effects in glasses

A convenient method for the synthesis of very well defined porous silica glasses using ionic liquids as templates is presented. Depending on template concentration, these systems form a homologous series of mesoporous systems with diverse shapes, with the pores having constant thickness of about 2.4 nm. These nanostructures allow the analysis of the two-dimensional behavior of glasses, either from a liquid to be embedded in the pore or of the silica glass forming the wall. For the walls, the third reduced dimension can be varied in a systematic fashion. This approach is exemplified by analyzing the static glass structure of 2D-silica by WAXS.     

The ozonation of silanes and germanes: an experimental and theoretical investigation

Ozonation of various silanes and germanes produced the corresponding hydrotrioxides, R3SiOOOH and R3GeOOOH, which were characterized by 1H, 13C, 17O, and 29Si NMR, and by infrared spectroscopy in a two-pronged approach based on measured and calculated data. Ozone reacts with the E-H (E = Si, Ge) bond via a concerted 1,3-dipolar insertion mechanism, where, depending on the substituents and the environment (e.g., acetone-d6 solution), the H atom transfer precedes more and more E-O bond formation. The hydrotrioxides decompose in various solvents into the corresponding silanols/germanols, disiloxanes/digermoxanes, singlet oxygen (O2(1delta(g))), and dihydrogen trioxide (HOOOH), where catalytic amounts of water play an important role as is indicated by quantum chemical calculations. The formation of HOOOH as a decomposition product of organometallic hydrotrioxides in acetone-d6 represents a new and convenient method for the preparation of this simple, biochemically important polyoxide. By solvent variation, singlet oxygen (O2(1delta(g))) can be generated in high yield.