Ion-exchange selectivity and chromatographic separation of trivalent metals on titanium antimonate

Summary The ion exchange selectivity of trivalent metal ions has been determined on titanium antimonate cation exchanger prepared by coprecipitation of antimony to titanium at different mole ratios. The selectivity sequence Al³⁺<Cr³⁺<Ga³⁺<In³⁺<Fe³⁺ was found for trivalent metal ions at an initial concentration of 10^–4 mol dm^–3 in nitric acid media. A high separation factor ^Ga/Al = Kd^Ga/Kd^Al, 4.8×10³, was observed for the Ga³⁺–Al³⁺ pair on titanium antimonate with an antimony to titanium ratio of 0.34. The effective separation of Ga³⁺ and In³⁺ from Al³⁺ was achieved using a 3 cm×0.5 cm i.d. column containing titanium antimonate with an antimony to titanium ratio of 0.34.     

Transformations of 3,4-bisindolylmaleimides with differently bonded indole and maleimide moieties under the action of protic acids: A quantum chemical study

Intramolecular cyclization reactions of 3,4-bis(indol-3-yl)maleimides 1, 3-(indol-1-yl)-4-(indol-3-yl)maleimides 2, and 3,4-bis(indol-1-yl)maleimides 3 under the action of protic acids were studied in order to estimate the parameters of the interaction between protonated and unprotonated indole moieties. Geometric parameters, charge distributions, energy characteristics, and information concerning the frontier orbitals of bisindolylmaleimides 1–3 were obtained from density functional B3LYP/6-31G(d) quantum chemical calculations. Alternative pathways of protonation of bisindolylmaleimides with differently bonded indole and maleimide moieties were studied and pathways of cyclization of corresponding conjugated acids leading to polyannelated compounds were analyzed. All the key intermediates of the cyclization reactions correspond to stationary points on the potential energy surfaces (minima and transition states). Analysis of the potential energy surfaces revealed almost linear dependences of the activation energies of the cyclization reactions under study on the distances between the reaction centers, on the angle of approach of intramolecular electrophile, and on the energy gap (energy difference between frontier orbitals). The key role in the cyclization reactions is played by structural similarity between the starting indoleninium cations and the activated complexes of the reactions under study. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 754–760, May, 2006.     

Polarization Dependent Photoinduced Supramolecular Chirality in High-Performance Azo Materials

Here, we will show photo-induced supramolecular chirality in thin films of achiral amorphous polymers with azo groups in their side-chain. A matter of particular interest is the effect of various film thicknesses on azimuthal rotation and ellipticity of incident/transmitted polarized light. Furthermore, we investigated the temporal stability of inscribed chirality. By polarimetric measurements, we found out that the azimuthal rotation gets higher with layer thickness. In this scope, we were able to measure a very high azimuthal rotation of Δψ/d=112.5∘/μm. The inscribed chirality was stable for several days. Furthermore, we investigated the time-resolved behavior of incident and transmitted polarization ellipticities for various thicknesses. The time dependency may be explained by a two-step process: (1) fast trans-cis-isomerization resulting in photo-orientation and (2) slow photo-induced mass flow.     

Molecular recognition: comparative study of a tunable host-guest system by using a fluorescent model system and collision-induced dissociation mass spectrometry on dendrimers

Host-guest interactions between the periphery of adamantylurea-functionalized dendrimers (host) and ureido acetic acid derivatives (guest) were shown to be specific, strong and spatially well-defined. The binding becomes stronger when using phosphonic or sulfonic acid derivatives. In the present work we have quantified the binding constants for the host-guest interactions between two different host motifs and six different guest molecules. The host molecules, which resemble the periphery of a poly(propylene imine) dendrimer, have been fitted with an anthracene-based fluorescent probe. The two host motifs differ in terms of the length of the spacer between a tertiary amine and two ureido functionalities. The guest molecules all contain an acidic moiety (either a carboxylic acid, a phosphonic acid, or a sulfonic acid) and three of them also contain an ureido moiety capable of forming multiple hydrogen bonds to the hosts. The binding constants for all 12 host-guest complexes have been determined by using fluorescence titrations by monitoring the increase in fluorescence of the host upon protonation by the addition of the guest. The binding constants could be tuned by changing the design of the acidic part of the guest. The formation of hydrogen bonds gives, in all cases, higher association constants, demonstrating that the host is more than a proton sensor. The host with the longer spacer (propyl) shows higher association constants than the host with the shorter spacer (ethyl). The gain in association constants are higher when the urea function is added to the guests for the host with the longer spacer, indicating a better fit. Collision-induced dissociation mass spectrometry (CID-MS) is used to study the stability of the six motifs using the corresponding third generation dendrimer. A similar trend is found when the six different guests are compared.     

Metathesis of hex-1-ene in ionic liquids catalyzed by WCl6

Metathesis of hex-1-ene in ionic liquids catalyzed by WCl₆ was studied. The metathesis is preceded by isomerization of hex-1-ene to hex-2-ene, from which the main reaction product, viz., oct-4-ene, is derived. The WCl₆-1-butyl-3-methylimidazolium tetrafluoroborate (BMIM·BF₄) system efficiently catalyzes metathesis of linear olefin, the ionic liquid serving as the reaction medium by forming a stable homogeneous catalytic system with WCl₆. The yields of the metathesis products increase with increasing reaction temperature. The addition of tin-containing promoters leads to a substantial increase in the reaction rate. In the WCl₆-BMIM·BF₄-SnBu₄ system, the selectivity of the formation of oct-4-ene is significantly enhanced.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2094–2097, October, 2004.     

Electrochemical Amination in the System Ti(IV)–NH2OH–C6H6: The Efficiency of the Process in a Sulfuric Acid Solution Containing an Organic Solvent

Electrolysis of the system Ti(IV)–NH₂OH–C₆H₆ in an 11 M H₂SO₄ solution shows that using an organic solvent (acetic acid, acetonitrile) during cathodically initiated amination of aromatic substrates permits the production of aromatic amines with the overall yield by hydroxylamine reaching 91%. Due to a chain mechanism of radical substitution, the benzene amination in electrolytes containing 5 M CH₃COOH and 5.5 M CH₃CN terminates largely upon consuming 70–75 and 50–55% of the charge required theoretically for a one-electron process. The maximum efficiency of electrochemical amination is observed at low hydroxylamine conversions and the overall current efficiency for mono- and disubstituted products of the benzene amination may exceed in these conditions 750%.     

Determination of trace rhodium by supramolecular catalytic kinetic spectrofluorimetry of β-CD-rhodium-KBrO3-vanillin salicylhydrazone

A sensitive catalytic kinetic spectrofluorimetric approach for determining ng mL⁻¹ levels of rhodium is presented, and the possible mechanism of the catalytic reaction was investigated. The determination is based on the catalytic property of rhodium to enhance the reaction of o-vanillin salicylhydrazone (OVSH) with potassium bromate in a water-ethanol medium at pH 4.80 and 45 °C. The presence of β-cyclodextrin (β-CD) obviously sensitized the assay due to its high inclusion ability towards OVSH. Under optimized experimental conditions, fluorescence measurements of the β-CD-rhodium-KBrO₃-OVSH catalytic kinetic reaction system were carried out in its fluorescent band centered at λ_ex = 333 nm and λ_em = 476 nm, respectively. The calibration graph was linear over the concentration range of 0.47–100 ng mL⁻¹ with a detection limit of 0.14 ng mL⁻¹. The effect of interferences was discussed, and the results show that the extraction method can be used to separate rhodium from interference species such as iridium. The proposed method, applied to several synthetic mixtures containing rhodium mixed with varying amounts of metal salts, produced satisfactory results.     

Synthesis, structure, and dynamics of six-membered metallacoronands and metallodendrimers of iron and indium

In the reaction of the N-substituted diethanolamines (H(2)L(1-3)) (1-3) with calcium hydride followed by addition of iron(III) or indium(III) chloride, the iron wheels [Fe(6)Cl(6)(L(1))(6)] (4) and [Fe(6)Cl(6)(L(2))(6)] (6) or indium wheels [In(6)Cl(6)(L(1))(6)] (5), [In(6)Cl(6)(L(2))(6)] (8) and [In(6)Cl(6)(L(3))(6)] (9) were formed in excellent yields. Exchange of the chloride ions of 6 by thiocyanate ions afforded [Fe(6)(SCN)(6)(L(2))(6)] (7). Whereas the structures of 4, 5 and 7 were determined unequivocally by single-crystal X-ray analyses, complexes 8 and 9 were characterised by NMR spectroscopy. Contrary to what is normally presumed, the scaffolds of six-membered metallic wheels are not generally rigid, but rather undergo nondissociative topomerisation processes. This was shown by variable temperature (VT) (1)H NMR spectroscopy for the indium wheel [In(6)Cl(6)(L(1))(6)] (5) and is highlighted for the enantiotopomerisation of one indium centre [ 1/6[S(6)-5]<==>[1/6[S(6)-5']]. The self-assembly of metallic wheels, starting from diethanolamine dendrons, is an efficient strategy for the convergent synthesis of metallodendrimers.     

Two-component dendritic gel: effect of stereochemistry on the supramolecular chiral assembly

The self-assembly of diaminododecane solubilised by four different stereoisomeric dendritic peptides to form gel-phase materials in toluene was investigated. The second generation dendritic peptides were based on D- and L-lysine building blocks, and each contained three chiral centres. By designing dendritic peptides in which the configurations of the chiral centres were modified, and applying them as gelator units, the assembly of stereoisomers could be investigated. In all cases, the self-assembly of gelator units resulted in macroscopic gelation. However, the degree of structuring was modulated by the stereoisomers employed, an effect which changed the morphology and macroscopic behavior of the self-assembled state. Enantiomeric (L,L,L or D,D,D) gelator units formed fibrous molecular assemblies, whilst the racemic gel (50 % L,L,L : 50 % D,D,D) formed a flat structure with a "woven" appearance. Gelator units based on L,D,D or D,L,L dendritic peptides also formed fibrous assemblies, but small-angle X-ray scattering indicated significant morphological differences were caused by the switch in chirality. Furthermore, the macroscopic stability of the gel was diminished when these peptides were compared with their L,L,L or D,D,D analogues. In this paper it is clearly shown that individual stereocentres, on the molecular level, are directly related to the helicity within the fibre. It is argued that the chirality controls the pattern of hydrogen bonding within the assembly, and hence determines the extent of fibre formation and the macroscopic gel strength.     

Synthesis and solid-state organization of coil-ring-coil block copolymers

Shape-persistent macrocycles based on the phenyl-ethynyl-butadienyl backbone containing two extraannular hydroxyl groups were prepared by the oxidative coupling of the appropriate phenylethynyl oligomers. Carbodiimide-directed coupling with independently synthesized polystyrene carboxylic acid oligomers led to ABA coil-ring-coil block copolymers in which the central macrocycle serves as rigid and the polystyrene oligomers as flexible elements. Depending on the size of the coil blocks, these structures aggregate in cyclohexane into supramolecular hollow cylindrical brushes in which the rigid core is surrounded by the flexible matrix. However, in the solid state it is not possible to identify a morphology in which isolated channels based on aggregated macrocycles are embedded in a matrix of polystyrene. Detailed X-ray and electron diffraction studies on samples prepared from a solution in cyclohexane under equilibrium conditions show that the material adopts a lamellar morphology in the solid state in which columns of macrocycles are aggregated into layers which are separated by polystyrene.