Investigation of degradation mechanisms by portable Raman spectroscopy and thermodynamic speciation: the wall painting of Santa María de Lemoniz (Basque Country, North of Spain)

To characterise the polymeric properties of processed lignins, a new method has been developed using hydrophobic interaction chromatography (HIC). This method separates the lignin polymers into fractions based on differences in hydrophobicity using low pressure liquid chromatography (LPLC). The hydrophobic column material consists of monodisperse polystyrene/divinylbenzene beads. An elution gradient was prepared monitoring the electrolyte concentration and pH. Citric acid buffer, containing ammonium sulphate that promotes adsorption to the column material, was used as mobile phase in a step-wise gradient together with ethanol (20/80% (v/v) ethanol/water, pH 12) and isopropanol (40/60% (v/v) isopropanol/water, pH 12). Depending on eluent composition, the degree of elution was 94% or higher. With the HIC method developed, lignosulphonates and kraft lignins were separated into seven distinctive peaks according to hydrophobicity.     

In situ Raman spectroscopy reveals the mechanism of titanium substitution in P2–Na2/3Ni1/3Mn2/3O2: Cathode materials for sodium batteries

Layered P2–Na_2/3Ni_1/3Mn_2/3O_2 is a promising cathode material. It exhibits a high capacity and suitable operating voltage and undergoes a phase transition from P2 to O2 during charge/discharge.Researchers have used Ti substitution to improve the cathode, yet the chemical principles that underpin elemental substitution and functional improvement remain unclear. To clarify these principles, we used in situ Raman spectroscopy to monitor chemical changes in P2–Na2/3 Ni1/3 Mn1/3 Ti1/3 O2 and P2–Na_2/3Ni_1/3Mn_2/3O_2 during charge/discharge. Based on the change in the A_1g and E_g peaks during charge/discharge, we concluded that Ti substitution compressed the transition metal layer and expanded the planar oxygen layer in the unit cell. Titanium stabilized the P2 phase structure, which improved the cycling stability of P2–NaNMT. Our results provide clear theoretical support for future research on modifying electrodes by elemental substitution.     

PMA/SiO2: An Efficient and Reusable Heterogeneous Catalyst for the Synthesis of β-Acetamidocarbonyl Compounds by Multicomponent Reaction

Phosphomolybdic acid supported on silica (PMA/SiO₂) has been used as an efficient heterogeneous catalyst for the preparation of β-acetamidoketones and esters in good yields. The reaction conditions are mild, and the catalyst can be recycled.     

Cationic palladium(II)-allyl-complexes containing 2-pyridyldiphenylphosphine: X-ray crystal structure of the binuclear complex [Pd(η-2-Me-allyl)(μ-Ph2PPy)]2(BF4)2. Detection of an intramolecular C(allyl)-H?phenyl ring π-interaction

Reaction of [PdCl(η³-2-Me-allyl)(Ph₂PPy)] (1) with AgBF₄ affords the new dinuclear cationic complex [Pd(η³-2-Me-allyl)(μ-Ph₂PPy)]₂(BF₄)₂ (2). The X-ray structural analysis of 2 shows that the 2-pyridyldiphenylphosphine ligands adopt a binucleating role through the P and N atoms bridging two independent palladium centres to form an eight-membered metallocyclic ring. One of the anti hydrogen atoms of the allyl moiety was located very close to a phenyl ring of Ph₂PPy indicating the occurrence of a CH/π interaction. Addition of one equivalent of Ph₂PPy to complex (2) affords the mononuclear cationic complex [Pd(η³-2-Me-allyl)(Ph₂PPy)₂](BF₄) (3).     

Towards understanding monomer coordination in atom transfer radical polymerization: synthesis of [Cu(PMDETA)(π-M)][BPh4] (M = methyl acrylate, styrene, 1-octene, and methyl methacrylate) and structural studies by FT-IR and H NMR spectroscopy and X-ray crystallography

Cu^I complexes of the form [Cu^I(PMDETA)(π-M)][BPh₄] (where PMDETA = N,N,N′,N″,N″-pentamethyldiethylenetriamine, and M = vinyl monomer) were synthesized and isolated from solution as crystals with methyl acrylate (MA), styrene (Sty), and 1-octene (Oct). The interaction of the CC double bond of the vinyl monomer with Cu^I was characterized via FT-IR and ¹H NMR spectroscopy and single crystal X-ray crystallography. A fourth complex with methyl methacrylate (MMA) was synthesized and characterized spectroscopically, but no crystals suitable for X-ray structure analysis could be obtained. In all complexes, PMDETA acts as a tridentate ligand, while the pseudotetrahedral coordination geometry around Cu^I is completed by a π-interaction with the CC double bond of M in the presence of a non-coordinating counter-ion. A decrease in CC IR stretching frequencies of Δν(CC) = −110, −80, −109, and −127 cm⁻¹ for complexes with MA, Sty, Oct, and MMA, respectively, was observed upon coordination. No significant change in CC bond length was seen in the crystal structure for complexes with MA and Oct while a slight lengthening was observed for the Sty complex. The upfield shift of the vinyl proton resonances indicated the presence of significant π-back-bonding.