An Internal Damping Model for the Absolute Nodal Coordinate Formulation

Introducing internal damping in multibody system simulations is important as real-life systems usually exhibit this type of energy dissipation mechanism. When using an inertial coordinate method such as the absolute nodal coordinate formulation, damping forces must be carefully formulated in order not to damp rigid body motion, as both this and deformation are described by the same set of absolute nodal coordinates. This paper presents an internal damping model based on linear viscoelasticity for the absolute nodal coordinate formulation. A practical procedure for estimating the parameters that govern the dissipation of energy is proposed. The absence of energy dissipation under rigid body motion is demonstrated both analytically and numerically. Geometric nonlinearity is accounted for as deformations and deformation rates are evaluated by using the Green–Lagrange strain–displacement relationship. In addition, the resulting damping forces are functions of some constant matrices that can be calculated in advance, thereby avoiding the integration over the element volume each time the damping force vector is evaluated.     

Experimental and theoretical studies on the magnetic properties of manganese(II) compounds with mixed isocyanate and carboxylate bridges

Two manganese(II) isocyanate complexes with different flexible zwitterionic dicarboxylate ligands, [Mn(2)(bcpp)(NCO)(4)](n) (1; bcpp=1,3-bis(N-carboxylatomethyl-4-pyridinio)propane) and [Mn(2)(bcp)(NCO)(4)](n) (2; bcp=bis(N-carboxylatomethyl)-4,4'-bipyridinium, have been synthesized and characterized by X-ray crystallography and magnetic measurements. Both compounds consist of two-dimensional coordination layers in which uniform anionic chains with mixed (NCO)(2)(COO) triple bridges are cross-linked by flexible cationic 4,4'-trimethylenedipyridinium spacers. Magnetic studies revealed antiferromagnetic interactions through the triple bridges (J=-8.0 cm(-1) (1) and J=-8.6 cm(-1) (2)), which are stronger than those in the isoelectronic analogue (N(3))(2)(COO). To complement the experimental data, periodic and finite-cluster DFT and CASPT2 calculations were performed on the dimeric units of the (NCO)(2)(COO) and (N(3))(2)(COO) mixed-bridged systems to support the Heisenberg picture and stress the relative efficiency of the magnetic couplers. It was found that the isocyanate ligand plays a greater role in the conveyance of antiferromagnetic behavior than the azide counterpart, and that both pseudohalide bridges function cooperatively with the carboxylate group.     

Unexpected remarkable stability of primary ozonides derived from alkenyl stannanes. One-pot synthesis of 1,2-diols from alkynes

Primary ozonides derived from alkenyl stannanes display an unusual stability and can be transformed into 1,2-diols by treatment with dimethyl sulfide and borane-methyl sulfide complex. This observation has been incorporated into the development of a novel one-pot strategy for the conversion of alkynes into 1,2-diols.     

Optimisation of stir bar sorptive extraction and liquid desorption combined with large volume injection-gas chromatography-quadrupole mass spectrometry for the determination of volatile compounds in wines

Stir bar sorptive extraction and liquid desorption followed by large volume injection coupled to gas chromatography-quadrupole mass spectrometry (SBSE-LD/LVI-GC-qMS) had been applied for the determination of volatiles in wines. The methodology was optimised in terms of extraction time and influence of ethanol in the matrix; LD conditions, and instrumental settings. The optimisation was carried out by using 10 standards representative of the main chemical families of wine, i.e. guaiazulene, E,E-farnesol, β-ionone, geranylacetone, ethyl decanoate, β-citronellol, 2-phenylethanol, linalool, hexyl acetate and hexanol. The methodology shows good linearity over the concentration range tested, with correlation coefficients higher than 0.9821, a good reproducibility was attained (8.9-17.8%), and low detection limits were achieved for nine volatile compounds (0.05-9.09 μg L⁻¹), with the exception of 2-phenylethanol due to low recovery by SBSE. The analytical ability of the SBSE-LD/LVI-GC-qMS methodology was tested in real matrices, such as sparkling and table wines using analytical curves prepared by using the 10 standards where each one was applied to quantify the structurally related compounds. This methodology allowed, in a single run, the quantification of 67 wine volatiles at levels lower than their respective olfactory thresholds. The proposed methodology demonstrated to be easy to work-up, reliable, sensitive and with low sample requirement to monitor the volatile fraction of wine.     

Predicting hydration Gibbs energies of alkyl-aromatics using molecular simulation: a comparison of current force fields and the development of a new parameter set for accurate solvation data

The Gibbs energy of hydration is an important quantity to understand the molecular behavior in aqueous systems at constant temperature and pressure. In this work we review the performance of some popular force fields, namely TraPPE, OPLS-AA and Gromos, in reproducing the experimental Gibbs energies of hydration of several alkyl-aromatic compounds--benzene, mono-, di- and tri-substituted alkylbenzenes--using molecular simulation techniques. In the second part of the paper, we report a new model that is able to improve such hydration energy predictions, based on Lennard Jones parameters from the recent TraPPE-EH force field and atomic partial charges obtained from natural population analysis of density functional theory calculations. We apply a scaling factor determined by fitting the experimental hydration energy of only two solutes, and then present a simple rule to generate atomic partial charges for different substituted alkyl-aromatics. This rule has the added advantages of eliminating the unnecessary assumption of fixed charge on every substituted carbon atom and providing a simple guideline for extrapolating the charge assignment to any multi-substituted alkyl-aromatic molecule. The point charges derived here yield excellent predictions of experimental Gibbs energies of hydration, with an overall absolute average deviation of less than 0.6 kJ mol(-1). This new parameter set can also give good predictive performance for other thermodynamic properties and liquid structural information.     

Novel catalytic effects in ester aminolysis in chlorobenzene

The mechanism of glyme catalyzed ester aminolysis in chlorobenzene should be modified by including a new reaction pathway that shows a first-order dependence on the concentration of the phase transfer catalyst and a second-order dependence on butylamine.     

Synthesis and catalytic applications of new chiral ferrocenyl P,O ligands

A new method to synthesize both enantiomers of 2-diphenylphosphino-ferrocenecarboxaldehyde with the phosphine group protected as a thiophosphine group was developed. These aldehydes react with 1,2 or 1,3 diols to give, in good yields, new chiral phosphine-acetals. For unsymmetrical (R)-1,3-butanediol, the new asymmetrical acetalic carbon is asymmetric and its configuration was completely controlled by the chirality of the diol. These new P,O ligands were tested in the palladium-catalyzed asymmetric allylic substitution of 1,3-diphenylprop-2-enylacetate. Good yields and enantioselectivities up to 77% were observed. The catalytic performances of two diastereoisomeric ligands with opposite configurations in planar chirality only proved to be significantly different, showing a strong influence of both planar and central chiralities.     

Stable and easily available sulfide surrogates allow a stereoselective activation of alcohols

Isothiouronium salts are easily accessible and stable compounds. Herein, we report their use as versatile deoxasulfenylating agents enabling a stereoselective, thiol-free protocol for synthesis of thioethers from alcohols. The method is simple, scalable and tolerates a broad range of functional groups otherwise incompatible with other methods. Late-stage modification of several pharmaceuticals provides access to multiple analogues of biologically relevant molecules. Performed experiments give insight into the reaction mechanism.

A simple and scalable method for stereoselective synthesis of thioethers directly from alcohols using isothiouronium salts is presented. The utility of this thiol-free reaction was exemplified by late-stage modification of complex molecules.     

Formation of pyranoanthocyanins in red wines: a new and diverse class of anthocyanin derivatives

Pyranoanthocyanins constitute one of the most important classes of anthocyanin-derived pigments occurring naturally in red wine. Nonetheless, correct assignment of their structures and pathways of formation in red wine has been relatively recent—less than two decades. Study of these newly discovered pigments is progressively unfolding the chemical pathways that drive the evolution of red wine colour during ageing. The objective of this paper is to review current knowledge regarding the pathway of formation in red wine of a great variety of pyranoanthocyanin structures, namely carboxypyranoanthocyanins, methylpyranoanthocyanins, pyranoanthocyanin-flavanols, pyranoanthocyanin-phenols, portisins, oxovitisins, and pyranoanthocyanin dimers. The chromatic features of some of the compounds, for example their colour expression and acid–base equilibria in aqueous media, are also discussed.