Texture changes inside smectic-C droplets in azobenzene Langmuir monolayers

Preparation of Langmuir monolayers of a mixture of trans- and cis-isomers of an azobenzene derivative, 4-[4-[(4-octylphenyl)azo]phenoxy]butanoic acid, results in the segregation of birefringent trans-isomer domains embedded in an isotropic medium of cis-isomers. Brewster angle microscopy observations allow us to identify different textures inside the domains depending on surface pressure, temperature, and domain size. The evolution of the monolayer in the dark, from initial droplets formed after spreading to a stable stripe texture, is described. The dynamics of domain coalescence and some morphological transitions induced by temperature and surface pressure changes are also discussed. A simple theoretical model is included to supplement some of these experimental observations.     

Supramolecular helical mesomorphic polymers. Chiral induction through H-bonding

The work described here concerns a challenge of general interest in supramolecular chemistry: the achievement of chiral helical organizations with controlled structures. This work provides a strategy to obtain supramolecular polymers in which a chiral helical conformation has been induced by a noncovalent association, that is, through hydrogen bonding. Polycatenar 2,4,6-triarylamino-1,3,5-triazines, which organize into columnar mesophases and are susceptible to H-bonding interactions, were chosen as a starting point to build up the chiral supramolecular structure. The stacking of these mesogens has been forced to wind in a helical way by means of H-bond association with (R)-3-methyladipic acid, within the mesophase. The optically active columnar organization has been studied in depth by optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction, and circular dichroism. Formation of stable complexes between the triazine units and (R)-3-methyladipic acid has also been investigated by means of NMR diffusion-ordered spectroscopy (DOSY) experiments in chloroform.     

Poly(2-hydroxyethyl acrylate) hydrogel confined in a hydrophobous porous matrix

A series of interpenetrated polymer networks (IPNs) in which the first component is a porous poly(ethyl methacrylate) (PEMA) hydrophobic network and the second one is a poly(2-hydroxyethyl acrylate) (PHEA) hydrophilic network were synthesized. Equilibrium sorption isotherms can be reduced to a single master curve for all the IPNs when the water absorbed is expressed per gram of PHEA in them. The equilibrium water sorption in immersion is always much smaller than that of pure PHEA. This feature is due to the confining effect of the stiff PEMA matrix. The plasticizing effect of the absorbed water on the PHEA phase was characterized using thermally stimulated depolarization currents, dynamic-mechanical analysis and dielectric relaxation spectroscopy. The results show that the shift of the main relaxation peak towards lower temperatures is unaffected by the presence of the PEMA matrix, and only depends on the water content per gram of PHEA in the IPN.     

5‐Methyl‐N‐[2‐nitro‐4‐(trifluoromethyl)phenyl]‐1H‐pyrazole‐3‐amine: a chain of hydrogen‐bonded R22(6) and R22(16) rings

The molecular skeleton of the title compound, C₁₁H₉F₃N₄O₂, is almost planar and exhibits a polarized (charge‐separated) electronic structure in the nitroaniline portion. Molecules are linked by N—H...N and C—H...O hydrogen bonds to form a chain in which centrosymmetric R₂²(6) and R₂²(16) rings alternate.     

Simple One-Pot Synthesis of New Derivatives of the Macrocyclic Aminal 1,3,7,9,13,15,19,21-Octaazapentacyclo-[19.3.1.13,7.19,13.115,19]octacosane (OAPO)

A series of 2,2′-(dihydropyrimidine-1,3(2H,4H)-diyldimethanediyl)bis(substituted-phenols) was synthesized using a Mannich-type reaction between the macrocyclic aminal 1,3,7,9,13,15,19,21-octaazapentacyclo[19.3.1.1^3,7.1^9,13.1^15,19]octacosane (OAPO) (1) and substituted phenols in basic media. These previously unreported compounds were separated from the reaction mixture by column chromatography in highly pure form with 25–75% yields. The most stable conformer was predicted using AM1-type semiempirical quantum chemical calculations.     

Valence‐to‐Core X‐Ray Emission Spectroscopy of Iron–Carbonyl Complexes: Implications for the Examination of Catalytic Intermediates

Valence‐to‐core X‐ray emission spectroscopy (V2C XES) has been applied to a series of compounds relevant to both homogeneous catalysts and intermediates in heterogeneous reactions, namely [Fe(CO)₅], [Fe₂(CO)₉], [Fe₃(CO)₁₂], [Fe(CO)₃(cod)] (cod=cyclo‐octadienyl), [Fe₂Cp₂(CO)₄] (Cp=cyclo‐pentadienyl), [Fe₂Cp*₂(CO)₄] (Cp*=tetramethylcyclopentadienyl), and [FeCp(CO)₂(thf)][B(ArF)₄] (ArF=pentafluorophenyl). DFT calculations of the V2C XES spectra show very good agreement with experiment, which allows for an in depth analysis of the origins of the observed spectral signatures. It is demonstrated that the observed spectral features can be broken down into specific ligand and metal fragment contributions. The relative intensities of the observed features are further explained through a quantitative investigation of the metal 3p and 4p contributions to the spectra. The ability to use V2C XES to separate carbonyl, hydrocarbon, and solvent contributions is highlighted.     

Application of a new focused microwave technology with species-specific isotope dilution analysis for the quantitative extraction of organometallic contaminants in solid environmental matrices

A new self-tuning single-mode-focused microwave technology has been evaluated in this work to perform the quantitative routine extraction of organometallic species from solid matrices of environmental interest. Species-specific isotope dilution analysis has been employed to better investigate the real influence of the microwave-assisted extractions on the final results. The advantages of such methodology in comparison with other established microwave units for the routine speciation analysis of organomercury and organotin compounds are discussed (such as the capability of using disposable glass vials, a self-tuning mode to provide an accurate control of the temperature and pressure inside of the vials, and the possibility of performing automated sequence of extractions with low sample size). The results obtained in this work demonstrated that such technology provides a fast and reliable quantitative extraction of the organometallic species in a wide range of extraction conditions even when the multi-elemental (Sn and Hg) species-specific determination is carried out.     

Ferromagnetism and chirality in two-dimensional cyanide-bridged bimetallic compounds

The combination of hexacyanoferrate(III) anions, [Fe(CN)(6)](3)(-), with nickel(II) complexes derived from the chiral ligand trans-cyclohexane-1,2-diamine (trans-chxn) affords the enantiopure layered compounds [Ni(trans-(1S,2S)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (1) and [Ni(trans-(1R,2R)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (2). These chiral systems behave as ferromagnets (T(c) = 13.8 K) with a relatively high coercive field (H(c) = 0.17 T) at 2 K. They also exhibit an unusual magnetic behavior at low temperatures that has been attributed to the dynamics of the magnetic domains in the ordered phase.     

Amedeo Avogadro The Man, the Hypothesis, and the Number

Amedeo Avogadro was a multifaceted and prolific scientist active in many areas of physics and chemistry, but most of his results did not make a scientific impact. His hypothesis, equal volumes = equal number of molecules remained in obscurity until Cannizaro rekindled it by making it a stepping-stone in the development of the atomic theory.