Efficient parametric estimation for a signal-plus-noise Gaussian model from discrete time observations

Statistical Inference for Stochastic Processes - This paper deals with the parametric inference for integrated continuous time signals embedded in an additive Gaussian noise and observed at...     

Ferrocenyl-Pyrenes,Ferrocenyl-9,10-Phenanthrenediones,and Ferrocenyl-9,10-Dimethoxyphenanthrenes: Charge-Transfer Studies and SWCNT Functionalization

The synthesis of 1-Fc- ( 3 ), 1-Br-6-Fc- ( 5 a ), 2-Br-7-Fc- ( 7 a ), 1,6-Fc₂- ( 5 b ), 2,7-Fc₂-pyrene ( 7 b ), 3,6-Fc₂-9,10-phenanthrenedione ( 10 ), and 3,6-Fc₂-9,10-dimethoxyphenanthrene ( 12 ; Fc=Fe(η⁵-C₅H₄)(η⁵-C₅H₅)) is discussed. Of these compounds, 10 and 12 form 1D or 2D coordination polymers in the solid state. (Spectro)Electrochemical studies confirmed reversible Fc/Fc⁺ redox events between −130 and 160 mV. 1,6- and 2,7-Substitution in 5 a (E°′=−130 mV) and 7 a (E°′=50 mV) influences the redox potentials, whereas the ones of 5 b and 7 b (E°′=20 mV) are independent. Compounds 5 b , 7 b , 10 , and 12 show single Fc oxidation processes with redox splittings between 70 and 100 mV. UV/Vis/NIR spectroelectrochemistry confirmed a weak electron transfer between Fe^II/Fe^III in mixed-valent [ 5 b ]⁺ and [ 12 ]⁺. DFT calculations showed that 5 b non-covalently interacts with the single-walled carbon nanotube (SWCNT) sidewalls as proven by, for example, disentangling experiments. In addition, CV studies of the as-obtained dispersions confirmed exohedral attachment of 5 b at the SWCNTs.     

Huisgen click cycloadditions from a copper(II)-tren precatalyst without external sacrificial reductant

The copper(II) complex [Cu(C18₆tren)](Br)₂, 2, is an efficient precatalyst for the Huisgen ‘click’ cycloaddtion which can be used at low loading without the requirement of an external sacrificial reductant such as sodium ascorbate. EPR studies support the in situ reduction of 2 by the alkyne to generate a reactive copper(I) catalyst.     

Insight of the Metal–Ligand Interaction in f-Element Complexes by Paramagnetic NMR Spectroscopy

The magnetic properties of Ln^III and An^III complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single-crystal X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal–ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher-order terms of the dipolar and contact contributions are required, especially for the lightest Ln^III and almost all the studied An^III. Bleaney's parameters <S_z>_a and relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of <S_z>_a and . However, the values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for Ln^III. Other parameters, such as the crystal field parameter and the hyperfine constants F_i obtained from the experimental data of the [An(ethyl-dpa)₃]³⁻ complexes (ethyl-dpa=4-ethyl-2,6-dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory.     

On the behavior of spray combustion in a turbulent spatially-evolving jet investigated by direct numerical simulation

Detailed investigations of turbulent spray combustion are very challenging due to the complexity of the underlying physicochemical processes. Experimentally, laboratory-scale burners are increasingly used to investigate these processes and support model development. One ultimate objective of these studies would be to deliver suitable benchmark data. In the present paper, the focus is similar but relying exclusively on direct numerical simulations. Conditions close that found in lab-scale burners are considered in the simulations, so that direct comparisons will ultimately become possible. The current analysis concentrates on the temporal evolution of temperature and concentrations of OH, CH₂O, and CH₄. The profiles of these variables show very complex features, therefore separate zones corresponding to characteristic physicochemical regimes have been tracked in time and space. It is found that, based on the temperature profile, four different zones coexist in the domain, associated to different degrees of competition between evaporation and reaction. It is observed that high concentrations of CH₂O and CH₄ can be used to delineate between three characteristic locations: 1) the evaporation zone; 2) close to the jet tip, at high temperatures; and 3) regions where evaporated droplets are entrained by mixing. This study demonstrates that direct numerical simulation of small spray burners can be used to deliver important information and to contribute useful benchmark data.     

Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene

Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio‐calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT‐calculated spectra of the eclipsed (D_5h) and staggered (D_5d) forms of ferrocene (Fc), and its deuterated analogue, within RCM explain the IR spectra of Fc in gas (350 K), solution (300 K), solid solution (7–300 K), and solid (7–300 K) states. In each case the D_5h rotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution‐phase samples (ca. 6 kJ mol^?1) than for the gas‐phase species (1–3 kJ mol^?1). The generality of the approach is demonstrated with application to tricarbonyl(η⁴‐norbornadiene)iron(0), Fe(NBD)(CO)₃. The temperature‐dependent coalescence of the ν(CO) bands of Fe(NBD)(CO)₃ is well explained by the RCM without recourse to NMR‐like rapid exchange. The RCM establishes a clear link between the calculated ground and transition states of dynamic molecules and the temperature‐dependence of their vibrational spectra.     

Synthesis and characterization of photosensitive cinnamate-modified cellulose acetate butyrate spin-coated or network derivatives

The photochemical behavior of photosensitive materials obtained by spin-coating or network synthesis of a cellulosic polymer bearing photo-cross-linkable cinnamate groups was investigated. First, cinnamate groups were grafted on a cellulose acetate butyrate polymer, with different grafting densities. The photochemical properties of the polymers were studied in solution by UV–visible and ¹H NMR spectroscopy. Then spin-coated films and networks were prepared and characterized as a function of the number of cinnamate groups per cellulosic unit. The water-wetting properties of both surfaces were studied by dynamic contact angle measurements, before and after photoirradiation, and subsequent heating. The surfaces obtained by the two methods have significantly different behaviors that can be assigned to the distinct photochemical pathways of the cinnamate groups upon irradiation depending on the sample preparation. Indeed, dimerization reaction is evidenced as the main process in the spin-coated films while the expected isomerization is predominant at the surface of the polymer networks.     

Chiral single-molecule magnet with a 35 K energy barrier for relaxation of the magnetization

The reaction of [Mn^II(S-mandelato)₂] complexes with 5-Methyl-salicylaldoxim (5-Me-saloxH₂) leads to the chiral hexanuclear manganese(III) complex [Mn₆(μ₃-O)₂(5-Me-salox)₆(S-mandelato)₂(EtOH)₆]. The structure can be viewed as two neutral stacked {Mn₃(μ₃-O)(5-Me-salox)₃(S-mandelato)(EtOH)₃} triangular subunits linked together in a head-to-tail manner by two phenoxo and two oximato μ₃-oxygen atoms of the deprotonated oxime groups of the ligands. The magnetic study of this chiral hexanuclear manganese(III) complex reveals a SMM behaviour with an energy barrier of the slow relaxation of the magnetisation equal to 35 K. Considering the structural features, the fitting of the temperature dependence of the magnetic susceptibility gives a good agreement with the experimental data considering two sets of interactions: J₁ = +0.37 cm⁻¹ and J₂ = −0.70 cm⁻¹ within (ferromagnetic) and between (antiferromagnetic), respectively, the {Mn₃(μ₃-O)(5-Me-salox)₃(S-mandelato)(EtOH)₃} triangular subunits.     

Magnetic ordering of Ni4 Cubane complexes through hydrogen bonds

The serendipity synthesis of the 2-hydroxy-3-methoxy-benzaldehyde or o-vanillin nickel(II) cubane complex, obtained by ourselves and other workers, can be rationalized to give the cubane in a high yield by direct use of 2-hydroxy-3-methoxy-benzaldehyde (H-ovan). The structural determinations of crystals obtained according to the two experimental processes show that the complex formulated [(MeOH)Ni(μ₃-OMe)(ovan)]₄ (ovan = deprotonated form of o-vanillin) is characterized in the two cases. Ni-Ni ferromagnetic interactions (J_NiNi = 5.8 cm⁻¹) giving an S = 4 ground state are active in the Ni₄ cubane. Replacement of methanol molecules coordinated to the Ni ions by a diol, an amino-alcohol or an amino-ether allows self-association of these Ni₄ units according to two different ways: by direct coordination bonds through the diol ligand or by hydrogen bonds involving the OMe groups of o-vanillin located at the periphery of the cubane and the hydrogen atoms of the primary amine functions. This association is suggested in the two cases by the presence of out-of-phase signals (χ”) when ac susceptibility measurements are performed at different frequencies. These molecules do not behave as SMM for these χ” signals, that are not frequency-dependent, correspond to the establishment of a three-dimensional ordering.     

New serinolic amino-<Emphasis Type="Italic">s</Emphasis>-triazines by chemoselective amination of cyanuric chloride and their (pro)diastereomerism in restricted rotational phenomena

The highly chemoselective preparation of new elaborated N-unsymmetrically substituted chlorodiamino-s-triazines and melamines, seen as building-blocks for iterative synthesis, is reported. It consisted of amination of cyanuric chloride with commercial C-2-substituted 2-aminopropane-1,3-diols (“serinols”), playing the role as “open-chain” unit and enantiopure (1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diols (“p-nitrophenylserinols”) based amino-1,3-dioxanes (“closed-chain” unit). Issued from the restricted rotation about C(s-triazine)-N(exocyclic) partial double bonds, seen as axes of (pro)diastereomerism, a global four-component rotational equilibrium involving the title compounds is discussed based on DFT computation and (VT) NMR data. Depending on π-deficiency of the s-triazine core, an (un)synchronised deblocking of the generated rotational diastereomers was observed. They are discussed as influence of intra-vs. intermolecular NH...OH (dynamic) interactions occurring in the “open-chain” unit and the anancomeric, axial vs. equatorial, amino-anchorage of the “closed-chain” unit.