A Comparison between the Experimental and Theoretical Investigations on Carbon‐13 Isotropic Shielding Constants of Some Tripodal Tetraamine Ligands

The direct implementation of GIAO and CSGT methods for calculation of ¹³C isotropic shielding constants of fully protonated forms of six tripodal tetraamine ligands tren, pee, ppe, tpt, epb and ppb at the Hartree‐Fock level of theory are presented. The shielding constants were determined using hybrid methods (including a mixture of Hartree‐Fock exchange and DFT exchange‐correlation) and are close to the experimental data. A splayed‐like conformation was considered for fully protonated forms of all ligands, and it was confirmed that this is the most stable conformation for the latter form of such ligands. A good linear correlation between the calculated chemical shielding at gas‐phase and experimental shift values in D₂O solution was obtained.     

Selection of possible marker peptides for the detection of major ruminant milk proteins in food by liquid chromatography-tandem mass spectrometry

The aim of this work was the determination of peptides, which can function as markers for identification of milk allergens in food samples. Emphasis was placed on two casein proteins (α- and β-casein) and two whey proteins (α-lactalbumin and β-lactoglobulin). In silico tryptic digestion provided preliminary information about the expected peptides. After tryptic digestion of four milk allergens, the analytical data obtained by combination of reversed-phase high performance liquid chromatography and quadrupole tandem mass spectrometry (LC-MS/MS) led to the identification of 26 peptides. Seven of these peptides were synthesized and used for calibration of the LC-MS/MS system. Species specificity of the selected peptides was sought by BLAST search. Among the selected peptides, only LIVTQTMK from β-lactoglobulin (m/z 467.6, charge 2+) was found to be cow milk specific and could function as a marker. Two other peptides, FFVAPFPEVFGK from α-casein (m/z 693.3, charge 2+) and GPFPIIV from β-casein (m/z 742.5, charge 1+), occur in water buffalo milk too. The other four peptides appear in the milk of other species also and can be used as markers for ruminant species milk. Using these seven peptides, a multianalyte MS-based method was developed. For the establishment of the method, it was applied at first to different dairy samples, and then to chocolate and blank samples, and the peptides could be determined down to 1 ng/mL in food samples. At the end, spiked samples were measured, where the target peptides could be detected with a high recovery (over 50%).     

A Mild Procedure for the Preparation of o‐Nitrophenols by Nitro Urea or Ammonium Nitrate in the Presence of Silica Sulfuric Acid (SiO2‐OSO3H)

A mixture of ammonium nitrate or nitro urea and silica sulfuric acid was found to be efficient and environmentally friendly nitrating media for the preparation of orto‐nitro phenols in dichloromethane at room temperature.     

Experimental Investigation on Upgrading of Lignin‐Derived Bio‐Oils: Kinetic Analysis of Anisole Conversion on Sulfided CoMo/Al2O3 Catalyst

Kinetics of the hydroprocessing of anisole, a compound representative of lignin‐derived bio‐oils, catalyzed by a commercial sulfided CoMo/Al₂O₃, was determined at 8–20 bar pressure and 573–673 K with a once‐through flow reactor. The catalyst was sulfided in an atmosphere of H₂ + H₂S prior to the measurement of its performance. Selectivity‐conversion data were used as a basis for determining an approximate, partially quantified reaction network showing that hydrodeoxygenation (HDO), hydrogenolysis, and alkylation reactions take place simultaneously. The data indicate that these reactions can be stopped at the point where HDO is virtually completed and hydrogenation reactions (and thus H₂ consumption) are minimized. Phenol was the major product of the reactions, with direct deoxygenation of anisole to give benzene being kinetically almost insignificant under our conditions. We infer that the scission of the C_methyl–O bond is more facile than the scission of the C_aromatic–O bond, so that the HDO of anisole likely proceeds substantially through the reactive intermediate phenol to give transalkylation products such as 2‐methylphenol. The data determine rates of formation of the major primary products. The data show that if oxygen removal is the main processing goal, higher temperatures and lower pressures are favored.     

Gram-Scale Synthesis of the 1,1,n,n-Tetramethyl[n](2,11)teropyrenophanes

A gram-scale synthesis of a series of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n=7–9) has been accomplished as well as the first synthesis of the next higher homologue 1,1,10,10-tetramethyl[10](2,11)teropyrenophane. The scale-up of the original small-scale synthesis required the development of several heavily modified synthetic methods, including a chlorination/Friedel–Crafts alkylation protocol and an iodination/Wurtz coupling protocol, which were performed on 25–30 g and 30–60 g scales, respectively. Two separate sets of conditions for the key teropyrene-forming cyclodehydrogenation reaction at the end of the synthetic pathway were developed, an acid-promoted one for the two less strained congeners and an acid-free method for the two more strained homologues.     

Substituent Effect on the Thermodynamics and Kinetics of Carbyne Complex [(η5-C5H5)(CO)(COMe)Re≡CC6H4X] Isomerization to Carbene Complex [(η5-C5H5)(CO)2Re=C(Me)(para-C6H4X]: A Theoretical Study

Russian Journal of Physical Chemistry A - This study investigates the effect of different substituents on the isomerization reaction of the [(η5‑C5H5)(CO)(Me)Re≡CC6H5] carbyne...