István Pálinkó

The C-H...Cl hydrogen bond: Does it exist?

The extensive occurrence of C–H···Cl hydrogen bonds has been established through a systematic statistical analysis of the Cambridge Crystallographic Database; chloride anions are shown to be better hydrogen-bond accepor systems than neutral chloride-containing molecules, and a similar situation pertains for the other halides. As a result of this study, we propose that the conceptual van der Waals cut-off criterion be dropped for establishing the presence of weak intermolecular and intramolecular interactions, and be replaced by a distance/angle criterion determined by the empirical approach outlined here.

Layered double hydroxides and their pillared derivatives – materials for solid base catalysis; synthesis and characterization

Abstract Mg–Al and Zn–Al L(ayered) D(ouble) H(ydroxide)s have been prepared and characterized. Thermal and dehydration/rehydration behaviour was studied by thermoanalytical methods (TG, DTG, DTA) and 27 Al M(agic) A(ngle) S(pinning) NMR spectroscopy, X-ray diffractometry (XRD) and S(canning) E(lectron) M(icroscopy). Acid–base properties of the calcined samples were investigated by T(emperature) P(rogrammed) D(esorption) of preadsorbed CO 2 and the double-bond isomerization reaction of 1-butene. Heat treatment destroyed the layered structure, which could be only partially reconstituted by rehydration. On calcination mixed oxide with the predominance of basic sites were formed. Pillaring of the LDHs with organic (terephtalate, dodecyl sulphate) as well as inorganic (oxometallate, ferrocyanide) anions were also performed. The materials were characterized by infrared (IR) spectroscopy, XRD and BET measurements. Heat stabilities of the pillared substances were investigated too. Pillaring by various methods proved to be successful, however, decreased heat resistance was found in the intercalated materials relative to the host LDHs.

Intercalating amino acid guests into montmorillonite host

Abstract The protonated forms of six amino acids (glycine, l -alanine, l -tryptophane, l -histidine, l -methionine and l -lysine) were ion-exchanged into Na-montmorillonite. A comparison of the FT-IR spectra of the host, the guests and host–guest substances revealed that the guest ions were intercalated successfully. It was verified by X-ray diffractometry and surface measurements as well. The spatial arrangement of the guest ions was modeled by semiempirical quantum chemical method. The intercalated organic ions provide chiral environment within the layers of the host material.

Hydrogen bonding interactions of benzylidene type Schiff bases studied by vibrational spectroscopic and computational methods

The structural features of four benzylidene type Schiff bases [(E)-benzaldehyde-N-phenyl imine, (A) (E)-2-hydroxybenzaldehyde-N-phenyl imine (B) (E)-benzaldehyde-N-2-hydroxyphenyl imine (C) (E)-2-hydroxybenzaldehyde-N-2-hydroxyphenyl imine (D)] were studied by FT-IR spectroscopy in solution, photoacoustic and Raman spectroscopies in the solid state and quantum chemical calculations. It was found that molecule D dimerised in the solid state with concomitant loss of aromaticity in the benzylidene ring. Beside the intermolecular C=O...HO hydrogen bonds, intramolecular N-H...C=O hydrogen bonds could be found experimentally as well as computationally. Spectra taken in solution and ab initio quantum chemical calculation helped to identify hydrogen bonding interactions occurring for compounds B and C. Intramolecular OH...N hydrogen bond predominated in molecule B, while this interaction, although it existed, was weaker.

Sonication assisted gold deposition on multiwall carbon nanotubes

Gold was successfully deposited on multiwall carbon nanotubes (MWNTs). It was achieved by applying a gold colloid stabilised by [tetrakis(hydroxymethyl)phosphonium chloride] (THPC) surfactant and ultrasonic irradiation during preparation. By controlling the quantity of gold and optimising sonication time up to 50 wt% gold could be deposited on MWNTs.

Mixed-metal pillared layer clays and their pillaring precursors

Mixed-metal pillared layer clays (Fe,Al-PILCs and Cr,Al-PILCs) of various compositions and the pillaring precursors have been prepared and characterised with a combination of chemical and instrumental methods. Chemical analysis data, IR, 57 Mossbauer and 27 Al NMR spectroscopic measurements on the precipitated pillaring precursors and comparison of redox behaviour [temperature-programmed reduction (TPR) results and 57 Fe Mossbauer measurements on the heat-treated and the reduced samples] of the ion-exchanged and Al-pillared and mixed-metal pillared clays revealed that isomorphous substitution of Al for Fe or Cr did not occur in either the tetrahedral or the octahedral positions. Heat treatment, however, resulted in mixed-metal pillared clays which were active in both acid-catalysed and redox transformations.

Mechanochemically assisted synthesis of pristine Ca(II)Sn(IV)-layered double hydroxides and their amino acid intercalated nanocomposites

Syntheses of Ca(II)Sn(IV)-layered double hydroxides (LDHs) are attempted by the traditional co-precipitation as well as mechanochemical methods. Both the co-precipitation method and the one-step milling operation proved to be unsuccessful; these methods only produced physical mixtures of hydroxides and carbonates of the two metal ions. However, a two-step milling operation (dry milling followed by milling in the presence of minute amount of water) led to successful synthesis, verified by a range of characterisation methods. Surprisingly, it was found that ball-milling was not even necessary; the reaction proceeded on manual grinding of the components in an agate mortar with a pestle. The preparation of nanocomposites through intercalation of the anions of cystine or valine into Ca(II)Sn(IV)-LDH could also be achieved by the two-step milling method verified again by a range of instrumental methods.

Synthesis of E- and Z-o-Methoxy-Substituted 2,3-Diphenyl Propenoic Acids and Its Methyl Esters

Abstract A series of stereoisomeric o-methoxy-substituted 2,3-diphenyl propenoic acids and their methyl esters have been synthesized. The E isomers were prepared by a modified Perkin condensation (substituted benzaldehyde, phenylacetic acid, Et3N/acetic anhydride). The difficult to access Z isomers were obtained conveniently in good yields when the appropriate coumarin derivatives were allowed to react with KOH and CH3I in DMSO.

Superoxide dismutase activity of a Cu–Zn complex—bare and immobilised

A binuclear, imidazolato-bridged complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(aminoethyl)amine perchlorate) was prepared and immobilised on silica gel or among the layers of montmorillonite. Immobilisation occurred via hydrogen bonding for the silica gel and through electrostatic forces for the montmorillonite. The obtained substances were characterised by EPR and FT-IR spectroscopies and their thermal behaviour was studied by thermogravimetry. The superoxide dismutase (SOD) activity of the complex before and after immobilisation was studied by a SOD assay. It was found that the SOD activity of the host-free complex increased by more than an order of magnitude and approached the efficiency of the real enzyme when silica gel was used as host. The enhanced activity could be assigned to the formation of magnetically isolated centers in the silica pores. On the other hand, the immobilisation with montmorillonite slightly reduced the SOD activity.

Amino acids, precursors for cationic and anionic intercalation synthesis and characterization of amino acid pillared materials

Abstract The preparation and characterization of amino acid pillared materials are reported in this contribution. Host substances were Na-montmorillonite for cationic and hydrotalcite for anionic pillaring. Guest molecules were L -phenylalanine and L -tyrosine. The pillared materials were characterized by powder X-ray diffraction, BET measurements and FT–IR spectroscopy. Pillaring was successful: the layers propped open and the basal distances increased significantly. For hydrotalcite this increase was always significantly larger than for montmorillonite. This fact indicated that the spatial arrangement of the amino acid moieties is widely different. A model for this arrangement is given.