Effect of coverage and defects on the adsorption of propanethiol on Au(111) surface: a theoretical study

Periodic density functional calculations have been carried out to investigate both the thiol adsorption on Au(111) surface and the reaction mechanism for the formation of the self-assembled monolayers, taking propanethiol as a representative example. The effect of coverage and surface defects (adatoms and vacancies) has been analyzed. It is found that the most stable physisorption (undissociated) site is an adatom site, whereas the chemisorption site for the thiol is a vacancy site or protrusion consisting of a pair of adatoms, followed by one adatom site. The results point out that the thiolate self-assembled monolayer adsorption process occurs preferentially on step edges.     

Chiral Determination of Salbutamol,Salmeterol and Atenolol by Two-Dimensional LC–LC: Application to Urine Samples

A heart-cut two-dimensional high-performance liquid chromatography method for enantiomeric determination of salbutamol, salmeterol and atenolol in urine is presented. It involves the use of two separations in a liquid chromatography–liquid chromatography achiral–chiral coupling. Target compounds were previously separated in a primary column (Kinetex™ HILIC, 2.6 μm, 150 × 2.1 mm I.D.) with a mixture of MeOH:ACN:ammonium acetate buffer (5 mM, pH 6) 90:5:5 (v/v/v) as mobile phase at a flow rate of 0.40 mL min⁻¹. Enantiomeric separation was carried out by transferring peak of each compound through a switching valve to a vancomycin chiral column (Chirobiotic™ V, 2.6 μm, 150 × 2.1 mm I.D.) using MeOH:ammonium acetate buffer (2 mM, pH 4) 97:3 (v/v) as mobile phase at a flow rate of 0.50 mL min⁻¹. Ultraviolet detection was done at 227 nm. The method was applied to determine target analytes in urine samples after enzymatic hydrolysis with β-glucuronidase from Helix pomatia, followed by a solid-phase extraction procedure using Isolute^® HCX mixed-mode cartridges. Extraction recoveries ranged from 82 to 90 % in urine samples. Detection limits were 0.091–0.095 μg for each enantiomer of atenolol and between 0.058 and 0.076 and 0.18–0.14 μg for enantiomers of salbutamol and salmeterol, respectively (3 mL of urine). Linearity ranges were between 0.5 and 10 μg mL⁻¹. Intraday and interday reproducibilities of enantiomeric ratio and enantiomeric fraction, expressed as relative standard deviation, were between 1.9 and 9.0 %. The optimized method was successfully applied to the analysis of urine samples obtained from excretion studies in volunteers and in freeze-dried urine samples, containing urinary components with MW < 10,000 and components with MW > 10,000, spiked with different amounts of studied drugs.

     

Azetidine iminosugars from the cyclization of 3,5-di-O-triflates of α-furanosides and of 2,4-di-O-triflates of β-pyranosides derived from glucose

Primary amines with either 3,5-di-O-ditriflates of α-furanosides or 2,4-di-O-triflates of β-pyranosides form bicyclic azetidines in high yield.     

Lewis Base Behavior of Bridging Nitrido Ligands of Titanium Polynuclear Complexes

The Lewis base behavior of μ₃‐nitrido ligands of the polynuclear titanium complexes [{Ti(η⁵‐C₅Me₅)(μ‐NH)}₃(μ₃‐N)] ( 1 ) and [{Ti(η⁵‐C₅Me₅)}₄(μ₃‐N)₄] ( 2 ) to MX Lewis acids has been observed for the first time. Complex 1 entraps one equivalent of copper(I ) halide or copper(I ) trifluoromethanesulfonate through the basal NH imido groups to give cube‐type adducts [XCu{(μ₃‐NH)₃Ti₃(η⁵‐C₅Me₅)₃(μ₃‐N)}] (X=Cl ( 3 ), Br ( 4 ), I ( 5 ), OSO₂CF₃ ( 6 )). However, the treatment of 1 with an excess (≥2 equiv) of copper reagents afforded complexes [XCu{(μ₃‐NH)₃Ti₃(η⁵‐C₅Me₅)₃(μ₄‐N)(CuX)}] (X=Cl ( 7 ), Br ( 8 ), I ( 9 ), OSO₂CF₃ ( 10 )) by incorporation of an additional CuX fragment at the μ₃‐N nitrido apical group. Similarly, the tetranuclear cube‐type nitrido derivative 2 is capable of incorporating one, two, or up to three CuX units at the μ₃‐N ligands to give complexes [{Ti(η⁵‐C₅Me₅)}₄(μ₃‐N)_4?n{(μ₄‐N)CuX}_n] (X=Br ( 11 ), n=1; X=Cl ( 12 ), n=2; X=OSO₂CF₃ ( 13 ), n=3). Compound 2 also reacts with silver(I ) trifluoromethanesulfonate (≥1 equiv) to give the adduct [{Ti(η⁵‐C₅Me₅)}₄(μ₃‐N)₃{(μ₄‐N)AgOSO₂CF₃}] ( 14 ). X‐ray crystal structure determinations have been performed for complexes 8 – 13 . Density functional theory calculations have been carried out to understand the nature and strength of the interactions of [{Ti(η⁵‐C₅H₅)(μ‐NH)}₃(μ₃‐N)] ( 1′ ) and [{Ti(η⁵‐C₅H₅)}₄(μ₃‐N)₄] ( 2′ ) model complexes with copper and silver MX fragments. Although coordination through the three basal NH imido groups is thermodynamically preferred in the case of 1′ , in both complexes the μ₃‐nitrido groups act as two‐electron donor Lewis bases to the appropriate Lewis acids.     

Analytical evaluation of a cup-horn sonoreactor used for ultrasound-assisted extraction of trace metals from troublesome matrices

In this work, a sample preparation method based on ultrasound-assisted extraction of trace metals from a variety of biological and environmental matrices using a cup-horn sonoreactor is described. Diluted acids (HNO₃, HCl and HF) and oxidants (H₂O₂) were tried for extraction, the extracts being directly analyzed by electrothermal-atomic absorption spectrometry. The cup-horn sonoreactor combines the advantages of probe and bath sonicators, allowing a variety of conditions to be used for metal extraction from troublesome matrices. This system facilitates the use of HF to destroy the silicate lattice, application of simultaneous treatments of up to six samples and short treatment times. Quantitative metal recoveries are achieved from different matrices (animal and vegetal tissues, soil, sediment, fly ash, sewage sludge) under a set of extraction conditions ranging from the use of 3 min sonication time and 3% volume/volume HNO₃ for some animal tissues to 40 min sonication time along with 5% volume/volume HNO₃ + 20% volume/volume HF for sediment. Vegetal matter required the use of 5% volume/volume HNO₃ + 5% volume/volume HF for extraction of some elements.     

Effect of graphene flake size on functionalisation: quantifying reaction extent and imaging locus with single Pt atom tags

Here, the locus of functionalisation on graphene-related materials and the progress of the reaction is shown to depend strongly on the starting feedstock. Five characteristically different graphite sources were exfoliated and functionalized using a non-destructive chemical reduction method. These archetypical examples were compared via a model reaction, grafting dodecyl addends, evaluated with TGA-MS, XPS and Raman data. A general increase in grafting ratio (ranging from 1.1 wt% up to 25 wt%) and an improvement in grafting stoichiometry (C/R) were observed as flake radius decreased. Raman spectrum imaging of the functionalised natural flake graphite identified that grafting is directed towards flake edges. This behaviour was further corroborated, at atomistic resolution, by functionalising the graphene layers with bipyridine groups able to complex single platinum atoms. The distribution of these groups was then directly imaged using aberration-corrected HAADF-STEM. Platinum atoms were found to be homogeneously distributed across smaller graphenes; in contrast, a more heterogeneous distribution, with a predominance of edge grafting was observed for larger graphites. These observations show that grafting is directed towards flake edges, but not necessary at edge sites; the mechanism is attributed to the relative inaccessibility of the inner basal plane to reactive moieties, resulting in kinetically driven grafting nearer flake edges. This phenomenology may be relevant to a wide range of reactions on graphenes and other 2d materials.

The flake size and morphology of the starting material strongly effect the degree and location of grafting when using reductive functionalisation.     

Selective Michael-aldol reaction by use of sterically hindered aluminum aryloxides as Lewis acids: an easy approach to cyclobutane amino acids

A formal [2 + 2] cycloaddition of 2-amidoacrylates with monosubstituted donor olefins, including its asymmetric version, is described. The stereoselectivity of this reaction can be modulated by the use of sterically hindered aluminum aryloxides or methylaluminoxane as Lewis acids. The reaction was applied to the synthesis of both stereoisomers of 2-benzyloxycyclobutane-alpha-amino acid, which are protected serine analogues c(4)Ser(OBn).     

Ferromagnetism in dinuclear copper(II)-phenolate complexes with exogenous O-donor bridges: a comparative study

The copper(II) complex Cu2L(OAc)(H2O)3.5, 1 x 3.5H2O was obtained and its reactivity in a basic medium investigated. Complex 1 x 3.5H2O shows different reaction patterns in air and in an inert atmosphere. Accordingly, interaction of 1 x 3.5H2O with Me4NOH x 5H2O in methanol-acetonitrile in air yields the hydroxide complex Cu2L(OH)(H2O)1.125, 2 x 1.125H2O while Cu2L(OMe)(MeOH)0.5(H2O), 3 x 0.5MeOH x H2O is isolated under an argon atmosphere. The products 1-3 were fully characterised and single crystals of {[Cu2L(OAc)] x MeCN x 3.5H2O}2, 1 x MeCN x 3.5H2O, {[Cu2L(OH)] x MeCN x 1.125H2O}2, 2 x MeCN x 1.125H2O and [Cu2L(OMe)] x 0.5MeOH x H2O, 3 x 0.5MeOH x H2O solved. The single X-ray study shows that 1-3 are dinuclear complexes with an endogenous phenol oxygen and an exogenous O-bridge. Magnetic characterisation of the three dinuclear complexes was performed, showing an apparent anomalous intramolecular ferromagnetic coupling between the metal atoms in all cases.     

Excess molar properties of ternary system (ethanol + water + 1,3-dimethylimidazolium methylsulphate) and its binary mixtures at several temperatures

The density, dynamic viscosity, and refractive index of the ternary system (ethanol + water + 1,3-dimethylimidazolium methylsulphate) at T = 298.15 K and of its binary systems 1,3-dimethylimidazolium methylsulphate with ethanol and with water at several temperatures T = (298.15, 313.15, and 328.15) K and at 0.1 MPa have been measured over the whole composition range. From these physical properties, excess molar volumes, viscosity deviations, refractive index deviations, and excess free energy of activation for the binary systems at the above mentioned temperatures, were calculated and fitted to the Redlich–Kister equation to determine the fitting parameters and the root-mean-square deviations. For the ternary system, the excess properties were calculated and fitted to Cibulka, Singh et al., and Nagata and Sakura equations. The ternary excess properties were predicted from binary contributions using geometrical solution models.