Sonolysis of chlorobenzene in the presence of transition metal salts

Sonolysis of aqueous solution of chlorobenzene at 200 kHz frequency in the presence of transition metals chlorides was investigated. Through analyzing the nature and distribution of the products detected in the reaction mixture, a new mechanism of sonodegradation is advanced. Depending on the metals used and their behavior during sonolysis, we were able to discriminate between inside and outside cavitation bubble mechanisms. Iron and cobalt chlorides, which could undergo redox reactions in the presence of HO radicals generated ultrasonically, give higher amounts of phenolic compounds compared with palladium chloride that undergoes a reduction to metal. Palladium reduction takes place in bulk solution and therefore all organic reactions that compete for hydrogen must occur also in bulk solution. Accordingly, palladium can be a useful tool in determining the reaction site and the decomposition mechanism of organic compounds under ultrasonic irradiation.     

ESR-spin trapping in the presence of cyclodextrins. Detection of PBN-superoxide spin adduct

In phosphate buffer solution the half-life of the PBN-superoxide spin adduct is very short. However, as a result of the formation of inclusion complexes, its ESR signal was easily detected for up to 25 min when the trapping of superoxide anion with PBN was carried out in the presence of different cyclodextrins. Furthermore, the formation of these inclusion complexes results in a significant protection of the PBN-superoxide adduct against l-ascorbate monoanion reduction.     

Intestinal absorption of drugs II. The effect of inclusion in cyclodextrins on the absorption of dantrolene

The inclusion of dantrolene sodium, a muscle relaxant with poor water-solubility, in-,- and-cyclodextrins was determined. Subsequently, the influence of the cyclodextrins on the absorption of the drug from aqueous solutions was investigated in a chronically isolated internal loop in the small intestine of the rat.A good correlation was found between the inclusion of dantrolene in the various cyclodextrins and the decrease in the absorption rate resulting from a reduction of the thermodynamically active dantrolene according to the phase-separation model. It was concluded that the cyclodextrins do not have a significant influence on the passage of dantrolene across the absorption barrier. Furthermore, experimental evidence was collected to support the fact that-cyclodextrin was absorbed to a limited, if not negligible, extent in the small intestine of the rat.     

Complexation behavior of Schiff base toward transition metal ions

Complexes of Iron, Cobalt, Nickel and Zinc ions with the Schiff base derived from p-dimethylaminobenzaldehyde and o-aminobenzoic acid were synthesized and investigated by several techniques using elemental analyse (C,H,N), molar conductance measurements, infrared and electronic spectra. The elemental analysis data suggest the stoichiometry to be 1:1 [M:L] ratio formation. The molar conductance measurements reveal the presence of non-electrolytic nature complexes. Infrared spectral data agreed with the coordination to the central metal ions through both the nitrogen atom of the azomethine and oxygen atom of the carboxyl group of the 2-aminobenzoic acid moiety. The electronic spectral data suggest the existence of octahedral geometry for Fe(III) complex, square planar geometry for Co(II) and Ni(II) complexes and tetrahedral geometry for Zn(II) complex.     

Synthesis of per-6-guanidinylated cyclodextrins

Reaction of per(6-amino-6-deoxy-2,3-di-O-methyl)-α-, β- and γ-cyclodextrins with N,N′-bis(tert-butoxycarbonyl)-N″-triflylguanidine and triethylamine in tetrahydrofuran gave per[6-N,N′-bis(tert-butoxycarbonyl)guanidino-6-deoxy-2,3-di-O-methyl]-α-, β- and γ-cyclodextrins, respectively. Subsequent cleavage of the protective groups with trifluoroacetic acid in dichloromethane afforded per(6-deoxy-6-guanidino-2,3-di-O-methyl)-α-, β- and γ-cyclodextrins in very good overall yields.     

Ring-opening of 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane in the presence of transition metal catalysts

Ring opening of 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane in the presence of various transition metal catalysts has been studied. Pd and Pt compounds are most active. Compounds with bulky ligands [e.g., Pd(PPh₃)₄] lead to the formation of “dimeric” cyclooctasilanes. Compounds with less bulky groups convert monomer to dimers and mixture of oligomers and polymers. Reactions with the all-trans monomer, tttt-(MePhSi)₄, result in the formation of stereoregular dimer, presumably all-trans, tttttttt-(MePhSi)₈, in high yields. Reactions in the presence of oxygen lead to the formation of polymers with inserted oxygen atoms in the main chain. © 1996 John Wiley & Sons, Inc.     

Improvement in protein separation in Barretts esophagus samples using two-dimensional capillary electrophoresis analysis in presence of cyclodextrins as buffer additives

In two-dimensional capillary electrophoresis (2DCE) components are separated based on their size and hydrophobicity. A preliminary run separates analytes in the first capillary based on size (CSE). Following that, fractions are electrokinetically transferred across an interface into a second capillary, where components are further resolved according to hydrophobicity. In order to succeed in this analysis, two orthogonal methods should be selected for the different modes. The transfers from the first to the second capillary must be efficient in order to reduce tailing effects and lost of resolution. We report a new method to improve the resolution with our 2DCE instrumentation using CD doped buffers. When methyl beta cyclodextrin (mβCD) is added to the 2DCE interface buffer a stacking effect is described in the transfers from the first to the second dimension. In addition to that, changes in retention times are observed when proteins form complex with CD's helping in the separation. Protein fingerprints were obtained from BE homogenates using this method in presence of methyl beta cyclodextrin (mβCD). Within-day and between-day precision has been studied in order to establish the reproducibility of the methodology proposed.     

Fluorescence signalling of the transition metal ions: Design strategy based on the choice of the fluorophore component

Transition metal ions are notorious for their fluorescence quenching abilities. In this paper, we discuss the design strategies for the development of efficientoff-on fluorescence signalling systems for the transition metal ions. It is shown that even simplefluorophore-spacer-receptor systems can display excellentoff-on fluorescence signalling towards the quenching metal ions when the fluorophore component is chosen judiciously.     

Development of a Total Organic Carbon method for the quantitative determination of solubility enhancement by cyclodextrins: Application to essential oils

Formation of inclusion complexes with cyclodextrins (CDs) is known to enhance guest solubility in aqueous medium. Different techniques allow determining the evolution in solubility of individual guest compounds. However, examination of mixtures solubility encapsulated in CDs is still a challenge. This is mainly related to the difference in the response of mixture components to the applied technique or to the fact that most of the conventional methods examine the signal of an individual constituent of the mixture. Thus, applying current techniques may not reflect the behavior of the whole mixture. Here, we used for the first time Total Organic Carbon (TOC) analysis to explore and assess the efficiency of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) to enhance the solubility of natural complex mixtures such as essential oils (EOs). Phase solubility studies were performed for eleven EOs with HP-β-CD. The TOC method has provided good validation parameters for linearity, precision and accuracy. For further validation of the method, phase solubility studies were performed with HP-β-CD for eugenol, as a model EO component. The eugenol solubility was determined by UV–Visible and TOC analyses in order to compare the results. Data obtained from both methods were similar (p < 0.05), thereby proving the effectiveness of the developed TOC method. Finally, the phase solubility diagrams of EOs showed that the solubilizing potential of CD increased proportionally with the decrease in EO intrinsic solubility. Results proved that TOC could be successfully applied to investigate CD/guest inclusion complexes and is expected to have a broad range of applications in the field of mixtures encapsulation.     

Effect of transition metal ions on partial ethane oxidation in an electrochemical system

Transition metal ions (Fe²⁺ and Cu²⁺) have been found to enhance the rate of ethane partial oxidation in a gas-liquid electrochemical reactor under mild conditions (363 K, atmospheric pressure). The effect is discussed in terms of a radical-chain mechanism involving OH radicals.     

Changes in the reactivity of the fluorescent reagents carbazole-9-carbonyl chloride and 9-carbazolylacetic acid in the presence of cyclodextrins

Carbazole-9-carbonyl chloride (C9CC) and 9-carbazolylacetic acid (9CAA) were selected as model fluorescent reagents. The effect of different chemically modified cyclodextrins (CDs) added to the aqueous solutions of these reagents was studied in water and in buffered aqueous solutions at pH 4.5 and 8.8. The CDs employed were 2-hydroxypropyl-β-cyclodextrin (HP-βCD), 2,3-di-O-methyl-β-cyclodextrin (DM-βCD) and 2,3,6-tri-O-methyl-β-cyclodextrin (TM-βCD). The inclusion of these reagents inside the cavities of the CDs was verified and this process can affect the derivatization reaction because CDs can modify the reactivity of the guest molecules. The basic conditions necessary for the derivatization reaction between C9CC and amines lead to the formation of carbazole anion through hydrolysis followed by decarboxylation. In the presence of CDs, the hydrolysis-decarboxylation of carbazole-9-carbonyl chloride is faster than in buffered aqueous homogeneous solutions. The behaviour observed for these reagents in aqueous solutions of CDs was compared to the one observed in basic ethanolic solutions. These changes are particularly noticeable in the case of 2,3-di-O-methyl-β-CD and 2-hydroxypropyl-β-CD. The characteristics of the fluorescent reagents are compared to carbazole and 9-methylcarbazole as model compounds. This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May 14–17, 2006.     

Selective detection of phosphaphenanthrenecontaining luminophors with aggregation-induced emission enhancement to transition metal ions

Transition metal ions (Pb²⁺, Zn²⁺, Cd²⁺, Co²⁺, Mn²⁺, Cu²⁺, Ni²⁺, Hg²⁺, Ag⁺, Fe³⁺) in water are used to quench emission of 2-(6-oxido-6H-dibenz 〈c,e〉 〈1,2〉 oxaphosphorin-6-yl)-1,4-phenylene-bis(p-pentyloxylbenzoate)s (MD5) with aggregation-induced emission enhancement (AIEE) in water-acetonitrile (AN) mixture (80:20 by volume). Among all metal ions, Fe³⁺ exhibits the highest quenching efficiency on AIEE of MD5 even when the concentration of Fe³⁺ is lower than 1×10⁻⁶ mol/L. The quenching efficiency of Hg²⁺ is lower than that of Fe³⁺ at the same concentration, though MD5 is used to detect Hg²⁺ efficiently, too. To other metal ions, low quenching efficiency has few relations with a wider concentration range. The UV absorbance spectra show only red shift of absorbance wavelength in the presence of Hg²⁺ and Fe³⁺, which indicates a salt-induced Jaggregation. SEM photos reveal larger aggregation and morphological change of nanoparticles of MD5 in water containing Hg²⁺ and Fe³⁺, which reduce the surface area of MD5 emission for further aggregation. The selective quenching effect of transition metal ions to emission of MD5 has a potential application in chemical sensors of some metal ions.     

Study of interferences by transition metal ions in hydride generation atomic absorption spectrometry of antimony

The mechanism of the interference of metal ions in the hydride generation atomic absorption spectrometry (AAS) of antimony was studied. Experiments on the decomposition rate of sodium tetrahydroborate in acidic media were done in the presence of interfering metals, with and without the addition of masking agents. The results were compared with experiments on the sensitivity of AAS in the presence of the same interfering metals with and without the addition of the same masking agents. AAS experiments are described in which the product of the reaction between sodium tetrahydroborate and one of the interfering metals was present during hydride formation. This reaction product was certainly one of the causes of interference, but the contribution of the catalytic decomposition of sodium tetrahydroborate to interference is not clear.     

Reduction of unsaturated compounds with hydrogen transfer from alcohol in the presence of transition metal salts

Conclusions The reduction of some unsaturated compounds was accomplished in the presence of transition metal salts using alcohol as the hydrogen donor.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5. pp. 1180–1181, May, 1972.     

Nitrosophenol complexes of transition metal salts

Complexes derived from 4-substituted-2-nitrosophenols, 3-Me-2-nitrosophenol, nitrosophyrogallol, nitrososalicylic acid and nitrosogallic acid with cobalt(II), nickel(II) and copper(II) have been prepared and characterized by elemental analysis, electronic and vibrational spectra, together with magnetic susceptibility measurements. The e.s.r. spectra of the copper(II) complexes were investigated, and detailed thermal properties of selected complexes are discussed.     

Modulating the Solubilities of Ionic Liquid Components in Aqueous–Ionic Liquid Biphasic Systems: A Q‐NMR Investigation

Aqueous–ionic liquid (A–IL) biphasic systems have been examined in terms of deuterated water, acid, and IL cation and anion mutual solubilities in the upper (water‐rich, in mole fraction) and lower phase of aqueous/IL biphasic systems at ambient temperature. The biphasic mixtures were composed of deuterated acids of various concentrations (mainly DCl, DNO₃, and DClO₄ from 10^?2 to 10^?4 M ) and five ionic liquids of the imidazolium family with a hydrophobic anion (CF₃SO₂)₂N^?, that is, [C₁C_nim][Tf₂N], (n=2, 4, 6, 8 and 10). The analytical techniques applied were ¹H NMR, ¹⁹F NMR, Karl–Fischer titration, pH potentiometry for IL cations and anions, and water and acid determination. The effects of the ionic strength (μ=0.1 M NaCl and NaNO₃ as well as μ=0.1 M , 0.2 M and 0.4 M NaClO₄, according to the investigated acid), the nature of the IL cation, and the nature of the mineral acid on the solubilities of the (D₂O, D⁺, Tf₂N^?, C₁C_nim⁺) entities in the lower or upper phases were determined. The addition of sodium perchlorate was found to enhance the Tf₂N^? solubility while inhibiting the solubility of the ionic liquid cation. Differences in IL cation and anion solubilities of up to 42 mM were evidenced. The consequences for the characterization of the aqueous biphasic system, the solvent extraction process of the metal ions, and the ecological impact of the ILs are discussed.     

Fluorescence quenching studies on the interaction of a novel deepened cavitand towards some transition metal ions

A novel ‘three-level’ deepened cavitand featuring a significantly sizable portal has been synthesized and its interaction with some transition metal ions has been investigated in THF/H₂O binary solvent using fluorescence quenching technique. The results suggest that among the used transition metal ions including Ag⁺, Cd²⁺, Cu²⁺, Fe³⁺, Cr³⁺, Hg²⁺, La³⁺, Mn²⁺, Ni²⁺, Zn²⁺ and Co²⁺, only Fe³⁺ and Cu²⁺ show good quenching ability. In order to interpret the quenching mechanism, the Stern–Volmer kinetics, and the presence of both the dynamic and static quenching have been discussed. It was found that the simultaneous presence of the sphere-of-action static quenching and dynamic quenching model agrees very well with the experimental results. The limits of detection for Fe³⁺ and Cu²⁺ were found to be 2.1 × 10⁻⁶ mol L⁻¹ (3σ) and 3.6 × 10⁻⁶ mol L⁻¹ (3σ), respectively. Cations with potential interference, such as K⁺, Na⁺, Mg²⁺, Ca²⁺, Co²⁺, La³⁺ and Mn²⁺ do not have significant effects on the determinations of Fe³⁺ and Cu²⁺. This cavitand can be potentially applied as optical sensor for the detection of Fe³⁺ and Cu²⁺.     

Versatility of cyclodextrins in self-assembly systems of amphiphiles

Recently, cyclodextrins (CDs) were found to play important yet complicated (or even apparently opposite sometimes) roles in self-assembly systems of amphiphiles or surfactants. Herein, we try to review and clarify the versatility of CDs in surfactant assembly systems by 1) classifying the roles played by CDs into two groups (modulator and building unit) and four subgroups (destructive and constructive modulators, amphiphilic and unamphiphilic building units), 2) comparing these subgroups, and 3) analyzing mechanisms. As a modulator, although CDs by themselves do not participate into the final surfactant aggregates, they can greatly affect the aggregates in two ways. In most cases CDs will destroy the aggregates by depleting surfactant molecules from the aggregates (destructive), or in certain cases CDs can promote the aggregates to grow by selectively removing the less-aggregatable surfactant molecules from the aggregates (constructive). As an amphiphilic building unit, CDs can be chemically (by chemical bonds) or physically (by host–guest interaction) attached to a hydrophobic moiety, and the resultant compounds act as classic amphiphiles. As an unamphiphilic building unit, CD/surfactant complexes or even CDs on their own can assemble into aggregates in an unconventional, unamphiphilic manner driven by CD–CD H-bonds. Moreover, special emphasis is put on two recently appeared aspects: the constructive modulator and unamphiphilic building unit.