An assessment of theoretical procedures for π-conjugation stabilisation energies in enones

We introduce a representative database of 22 α,β- to β,γ-enecarbonyl isomerisation energies (to be known as the EIE22 data-set). Accurate reaction energies are obtained at the complete basis-set limit CCSD(T) level by means of the high-level W1-F12 thermochemical protocol. The isomerisation reactions involve a migration of one double bond that breaks the conjugated π-system. The considered enecarbonyls involve a range of common functional groups (e.g., Me, NH₂, OMe, F, and CN). Apart from π-conjugation effects, the chemical environments are largely conserved on the two sides of the reactions and therefore the EIE22 data-set allows us to assess the performance of a variety of density functional theory (DFT) procedures for the calculation of π-conjugation stabilisation energies in enecarbonyls. We find that, with few exceptions (M05-2X, M06-2X, BMK, and BH&;HLYP), all the conventional DFT procedures attain root mean square deviations (RMSDs) between 5.0 and 11.7 kJ mol^?1. The range-separated and double-hybrid DFT procedures, on the other hand, show good performance with RMSDs below the ‘chemical accuracy’ threshold. We also examine the performance of composite and standard ab initio procedures. Of these, SCS-MP2 offers the best performance-to-computational cost ratio with an RMSD of 0.8 kJ mol^?1.     

Optical properties of microphytobenthic biofilms (MPBOM): Biomass retrieval implication

Microphytobenthos Optical Model (MPBOM) provides the optical properties, absorption coefficient and refractive index, of a laboratory simulated microphytobenthic biofilm using the reflectance measurements derived from HySpex laboratory images, with the final aim of estimating photosynthetically active biomass. The high correlation between this biomass, expressed in chlorophyll a (mg Chl a m⁻²) and the absorption coefficient at the corresponding absorption wavelength of Chl a (673 nm) made possible the estimation of biomass for any absorption coefficient calculated from reflectance measurements of any other data set. The latter was validated for an independent data set which performed an acceptable estimation of biomass in comparison with the biomass measured by HPLC (R²=0.93). Finally, this model is designed to be applied to hyperspectral images, like airborne or satellite, in order to map biomass in the field.     

Synthesis of Benzoxazoles Catalyzed by MCM-41, a Green and Reusable Catalyst

Benzoxazoles can be rapidly and efficiently synthesized from acyl chloride with 2-aminophenols in one simple step, which provided a practical and efficient method for high-throughput synthesis of this important class of heterocyclic compounds.     

Tuning the Size and Geometry of Heteroleptic Coordination Cages by Varying the Ligand Bent Angle

Spherical assemblies of the type [Pd_nL_2n]²ⁿ⁺ can be obtained from Pd^II salts and curved N-donor ligands, L. It is well established that the bent angle, α, of the ligand is a decisive factor in the self-assembly process, with larger angles leading to complexes with a higher nuclearity, n. Herein, we report heteroleptic coordination cages of the type [Pd_nL_nL′_n]²ⁿ⁺, for which a similar correlation between the ligand bent angle and the nuclearity is observed. Tetranuclear cages were obtained by combining [Pd(CH₃CN)₄](BF₄)₂ with 1,3-di(pyridin-3-yl)benzene and ligands featuring a bent angle of α=120°. The use of a dipyridyl ligand with α=149° led to the formation of a hexanuclear complex with a trigonal prismatic geometry; for linear ligands, octanuclear assemblies of the type [Pd₈L₈L′₈]¹⁶⁺ were obtained. The predictable formation of heteroleptic Pd^II cages from 1,3-di(pyridin-3-yl)benzene and different dipyridyl ligands is evidence that there are entire classes of heteroleptic cage structures that are privileged from a thermodynamic point of view.     

Radiochromic Hydrogen-Bonded Organic Frameworks for X-ray Detection

Porous materials have been investigated as efficient photochromic platforms for detecting hazardous radiation, while the utilization of hydrogen bonded organic frameworks (HOFs) in this field has remained intact. Herein, two HOFs were synthesized through self-assembly of tetratopic viologen ligand and formic acid (PFC-25, PFC-26), as a new class of “all-organic” radiochromic smart material, opening a gate for HOFs in this field. PFC-26 is active upon both X-ray and UV irradiation, while PFC-25 is only active upon X-ray irradiation. The same building block yet different radiochromic behaviors of PFC-25 and PFC-26 allow us to gain a deep mechanistic understanding of the factors that control the detection specificity. Theoretical and experimental studies reveal that the degree of π-conjugation of viologen ligand is highly related to the threshold energy of triggering a charge transfer, therefore being a vital factor for the particularity of radiochromic materials. Thanks to its convenient processibility, nanoparticle size, and UV silence, PFC-25 can be further fabricated into a portable naked-eye sensor for X-ray detection, which shows obvious color change with the merits of high transmittance contrast, good sensitivity (reproducible dose threshold of 3.5 Gy), and excellent stability. The work exhibits the promising practical potentials of HOF materials in photochromic technology.     

Hydrophobic properties of surfaces coated with fluoroalkylsiloxane and alkylsiloxane monolayers

A comparative analysis of hydrophobicity of fluoroalkylsiloxane and alkylsiloxane monolayers is presented. In order to compare wetting behavior on smooth and rough substrates, a simple model considering various self-assembly degrees of organic molecules and various area fractions of air inclusion is used. Sliding behavior for water on rough silanized needle-like surfaces is also evaluated. On smooth surfaces, regardless of assembly degree of coatings, contact angles of fluoroalkylsiloxane monolayers are always ∼10° larger. The difference, however, decreases when rough substrates with air inclusion are used. It is shown that assembly order of silane molecules and reduced water-solid contact area are the key factors leading to both high contact angles and low sliding angles. Such coatings are expected to be potential snow- and ice-repellent materials.     

Electrochemical synthesis of 6-amino-5-(3,4-dihydroxyphenyl) pyrimidine

Electrochemical oxidation of several catechols is studied in the presence of 4(6)-aminouracil (3a) and 6-amino-1,3-dimethyl uracil (3b) as nucleophiles in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results reveal that quinones derived from catechols participate in Michael additions with 3a and 3b to give the corresponding catecholamine derivatives via an electron transfer followed by chemical reaction (EC) mechanistic pathway in good yields and purities.     

Fabrication of Fe3O4@graphene oxide core-shell nanospheres for ferrofluid-based dispersive solid phase extraction as exemplified for Cd(II) as a model analyte

Microchimica Acta - The authors describe the synthesis of core-shell structured Fe3O4@graphene oxide nanospheres (denoted as Fe3O4@GO NSs) via a chemical (covalent) bonding method. A chemical...     

Determination of amine and aldehyde surface densities: application to the study of aged plasma treated polyethylene films

The aim of this work was to test and to compare different methods reported in the literature to quantify amine and aldehyde functions on the surface of polyethylene (PE) films treated by ammonia plasma and to specify their stability against time. A low pressure ammonia plasma reactor was used to functionalize PE films with amine groups, which could be subsequently used for further immobilization of biomolecules. In order to determine the density of amine groups on the surface of treated films, various molecule probes and spectrophotometric analytical methods have been investigated. Two methods using (i) sulfosuccinimidyl 6-[3'-(2-pyridyldithio)-propionamido] hexanoate (sulfo-LC-SPDP) and (ii) 2-iminothiolane (ITL) associated with bicinchoninic acid (BCA) have been proved to be reliable and sensitive enough to estimate the surface concentration of primary amine functions. The amount of primary amino groups on the functionalized polyethylene films was found to be between 1.2 and 1.4 molecules/nm2. In a second step, the surface concentration of glutaraldehyde (GA), which is currently used as a spacer arm before immobilization of biomolecules, has been assessed: two methods were used to determine the surface density of available aldehyde functions, after the reaction of GA with the aminated polyethylene film. The concentration of GA was found to be in the same range as primary amine concentration. The influence of aging time on the density of available amino and aldehyde groups on the surfaces were evaluated under different storage conditions. The results showed that 50% of the initial density of primary amine functions remained available after storage during 6 days of the PE samples in PBS (pH 7.6) at 4 degrees C. In the case of aldehyde groups, the same percentage of the initial density (50%) remained active after storage in air at RT over a longer period, i.e., 15 days.