Complex Pore Structure of Mesoporous Zeolites: Unambiguous TEM Imaging Using Platinum Tracking

The article proposes a new way for visualization of mesopores and quantitative evaluation of the pore structure in zeolite crystals. The approach is based on platinum tracking inside the zeolite material after its incorporation from a gaseous precursor using an electron beam prior to preparing a TEM specimen by the focused ion beam technique. The pores in mesoporous silica and purely microporous zeolite Y were visualized in TEM images in a demonstration of the capabilities of the approach. Finally, platinum tracking was used for studying the pore structure of zeolite Y (CBV 720) containing mesopores both inside the crystal and those emerging at its surface, which were unambiguously distinguished from each other. The obtained sizes of the mesopores and the calculated material porosity are in good agreement with the results obtained by the low-temperature argon sorption isotherms method.     

From Specific γ-CD/[Nb6Cl12(H2O)6]2+ Recognition to Biological Activity Tuning

Specific molecular recognition of γ-cyclodextrin (γ-CD) by the cationic hexanuclear niobium [Nb₆Cl₁₂(H₂O)₆]²⁺ cluster complex in aqueous solutions results in a 1:1 supramolecular assembly {[Nb₆Cl₁₂(H₂O)₆]@γ-CD}²⁺. NMR spectroscopy, isothermal titration calorimetry (ITC), and ESI-MS were used to study the interaction between the inorganic cluster and the organic macrocycle. Such molecular association affects the biological activity of [Nb₆Cl₁₂(H₂O)₆]²⁺, decreasing its cytotoxicity despite enhanced cellular uptake. The 1:1 stoichiometry is maintained in solution over a large window of the reagents’ ratio, but crystallization by slow evaporation produces a 1:2 host–guest complex [Nb₆Cl₁₂(H₂O)₆@(γ-CD)₂]Cl₂ ⋅ 20 H₂O featuring the cluster encapsulated between two molecules of γ-CD. The 1:2 complex was characterized by XRD, elemental analysis, IR spectroscopy, and thermogravimetric analysis (TGA). Quantum chemical calculations were performed to model host–guest interaction.     

Structure of Supramers Formed by the Amphiphile Biotin-CMG-DOPE

The synthetic function-spacer-lipid (FSL) amphiphile biotin-CMG-DOPE is widely used for delicate ligation of living cells with biotin residues under physiological conditions. Since this molecule has an “apolar-polar-hydrophobic” gemini structure, the supramolecular organization is expected to differ significantly from the classical micelle. Its organization is investigated with experimental methods and molecular dynamics simulations (MDS). Although the linear length of a single biotin-CMG-DOPE molecule is 9.5 nm, the size of the dominant supramer globule is only 14.6 nm. Investigations found that while the DOPE tails form a hydrophobic core, the polar CMG spacer folds back upon itself and predominantly places the biotin reside inside the globule or planar layer. MDS demonstrates that <10 % of biotin residues on the highly water dispersible globules and only 1 % of biotin residues in layer coatings are in an linear conformation and exposing biotin into the aqueous medium. This explains why in biotin-CMG-DOPE apolar biotin residues both in water dispersible globules and coatings on solid surfaces are still capable of interacting with streptavidin.     

Effective manipulation of the electronic effects and its influence on the emission of 5-substituted tris(8-quinolinolate) aluminum(III) complexes

The unique electron-transport and emissive properties of tris(8-quinolinolate) aluminum(III) (Alq(3)) have resulted in extensive use of this material for small molecular organic light-emitting diode (OLED) fabrication. So far, efforts to prepare stable and easy-to-process red/green/blue (RGB)-emitting Alq(3) derivatives have met with only a limited success. In this paper, we describe how the electronic nature of various substituents, projected via an arylethynyl or aryl spacer to the position of the highest HOMO density (C5), may be used for effective emission tuning to obtain blue-, green-, and red-emitting materials. The synthetic strategy consists of four different pathways for the attachment of electron-donating and electron-withdrawing aryl or arylethynyl substituents to the 5-position of the quinolinolate ring. Successful tuning of the emission color covering the whole visible spectrum (lambda=450-800 nm) was achieved. In addition, the photophysical properties of the luminophores were found to correlate with the Hammett constant of the respective substituents, providing a powerful strategy with which to predict the optical properties of new materials. We also demonstrate that the electronic nature of the substituent affects the emission properties of the resulting complex through effective modification of the HOMO levels of the quinolinolate ligand.     

Structural transitions and melting in LJ(74-78) Lennard-Jones clusters from adaptive exchange Monte Carlo simulations

Phase changes in Lennard-Jones (LJ) clusters containing between 74 and 78 atoms are investigated by means of exchange Monte Carlo simulations in the canonical ensemble. The replica temperatures are self-adapted to facilitate the convergence. Although the 74- and 78-atom clusters have icosahedral global minima, the clusters with 75-77 atoms have decahedral ground-state structures and they undergo a structural transition to icosahedral minima before melting. The structural transitions are characterized by quenching and by looking at the Q4 and Q6 orientational bond order parameters. The transition temperatures are estimated to be 0.114, 0.065, and 0.074 reduced units for LJ75, LJ76, and LJ77, respectively. These values, their ordering and the associated latent heats are compared with other estimates based on the harmonic superposition approach.     

Characterization of anacardic acids by micellar electrokinetic chromatography and mass spectrometry

A possibility of using capillary electrophoresis for separation of anacardic acids (6-alkylsalicylic acids) has been studied. Conventional micellar electrokinetic chromatography (MEKC) in non-coated fused silica capillaries and reversed-flow micellar electrokinetic chromatography (RF-MEKC) in capillaries coated with polydimethylacrylamide was applied for separation of anacardic acids extracted from cashew nuts. Influence of the composition of background electrolyte on the resolution of anacardic acid isomers was evaluated. Separations were performed using sodium dodecyl sulphate (SDS) micelles and mixed micelles of SDS and polyoxyethylene lauryl ether as a pseudostationary phase. To further improve the separation in RF-MEKC, beta-cyclodextrin and a dual cyclodextrin system of beta-cyclodextrin with heptakis-6-sulphato-beta-cyclodextrin was added to the working electrolyte. Best separation of anacardic acids were achieved in the polydimethylacrylamide-coated capillary using 10 mM phosphate background electrolyte pH 6.5 with addition of 1 M urea, 20% acetonitrile, 10 mM of beta-cyclodextrin and 1 mM of heptakis-6-sulfo-beta-cyclodextrin. Mass spectrometry was used for the identification of anacardic acids in the extract from cashew nuts in single and tandem mode using Q-TOF instrument. Nine anacardic acids were identified in the extract form the cashew nuts.     

Can the theory of gradient liquid chromatography be useful in solving practical problems?

Advances in the theory of gradient liquid chromatography and their practical impacts are reviewed. Theoretical models describing retention in reversed-phase, normal-phase and ion-exchange modes are compared. Main attention is focused on practically useful models described by two- or three-parameter equations fitting the experimental data in the range of mobile phase composition utilized for sample migration during gradient elution. The applications of theory for gradient method development, optimization and transfer are addressed. The origins and possibilities for overcoming possible pitfalls are discussed, including the effects of the instrumental dwell volume, uptake of mobile phase components on the column and size of the sample molecules. Special attention is focused on gradient separations of large molecules.     

Water-Soluble Non-Classical Benzene Mimetics

A new generation of saturated benzene mimetics, 2-oxabicyclo[2.1.1]hexanes, was developed. These compounds were designed as analogues of bicyclo[1.1.1]pentane with an improved water solubility. Crystallographic analysis of 2-oxabicyclo[2.1.1]hexanes revealed that they occupy a novel chemical space, but, at the same time, resemble the motif of meta-disubstituted benzenes.     

The extraction of europium and americium by the nitrobenzene solution of dicarbollylcobaltate in the presence of some commercially available dioxadiamides

Journal of Radioanalytical and Nuclear Chemistry - We investigated the extraction of microamounts of Eu3+ and Am3+ from aqueous nitric acid solutions using nitrobenzene solutions of hydrogen...     

Probing Transient Conformational States of Proteins by Solid‐State R1ρ Relaxation‐Dispersion NMR Spectroscopy

The function of proteins depends on their ability to sample a variety of states differing in structure and free energy. Deciphering how the various thermally accessible conformations are connected, and understanding their structures and relative energies is crucial in rationalizing protein function. Many biomolecular reactions take place within microseconds to milliseconds, and this timescale is therefore of central functional importance. Here we show that R_1ρ relaxation dispersion experiments in magic‐angle‐spinning solid‐state NMR spectroscopy make it possible to investigate the thermodynamics and kinetics of such exchange process, and gain insight into structural features of short‐lived states.