Sum frequency generation spectroscopic study of the condensation effect of cholesterol on a lipid monolayer

Sum frequency generation (SFG) spectra and surface pressure–molecular area (π–A) isotherms have been obtained for mixed cholesterol–DPPC monolayers with cholesterol mole fractions, x(chol.), from 0 to 1.0, at the air–water interface, under same conditions, at 22 °C. Analysis of the spectra indicated that incorporation of cholesterol into the monolayers at 3 mN m⁻¹ greatly increases the conformational and orientational order of the alkyl chains of DPPC, maximizing these properties at x(chol.)=0.4. Analysis also indicated that order in the mixed monolayers at 15 and 35 mN m⁻¹ is not affected by incorporation of cholesterol. The π–A isotherms measured at 3 mN m⁻¹ for the mixed monolayer with x(chol.)=0.4 have the largest negative deviation of the molecular area relative to those of ideal mixtures (the so-called “condensation effect” of cholesterol), indicating the most thermodynamically stable state. Comparison of results from SFG spectra and π–A isotherms explicitly proved that the condensation effect can be interpreted in terms of conformational and orientational ordering of the alkyl chains of DPPC.     

Simultaneous determination of polyamines and acetylpolyamines in human urine by capillary electrophoresis with fluorescence detection

There has been evidence linking elevated polyamines (PAs) and acetylpolamines (AcPAs) level and cancer. So the simultaneous analysis of these compounds has become important task for cancer diagnosis and antitumor drug monitoring. A simple, fast and inexpensive CZE‐LIF method has been developed for the determination of cadaverine (CAD), putrescine (PUT), spermine (SPM), spermidine (SPD), acetylspermine (ASPM), and acetylspermidine (ASPD) in human urine using 4‐chloro‐7‐nitro‐2,1,3‐benzooxadiazole as a fluorescent reagent. Labeling reaction conditions were systematically investigated and were found to be 20 mM borate buffer at pH 7.4, labeling reaction time, and temperature were 10 min and 70°C, respectively. Under these optimized conditions the four PAs, two AcPAs and the internal standard were separated in 6 min. An Exactive‐MS with an ESI source was used for identification of the bis‐derivative of the ASPM. The method was validated in term of linearity, LODs, repeatability, intra‐ and interday assays, recovery, and selectivity. The LODs for CAD, PUT, SPM, SPD, ASPM, and ASPD were found to be 7.6, 10.0, 9.0, 8.8,7.8, and 3.3 nM, respectively. The method was successfully applied for the analysis of PAs and AcPAs in healthy human urine samples.     

Photochemical reactions of surfactant molecules in condensed monolayer assemblies--environmental control and modification of reactivity.

An investigation of the effects of a controlled microenvironment on reactivity has been carried out by the synthesis and study in organized monolayers of surfactant molecules containing photochemically reactive chromophores. Reactions where substantial environmental effects have been observed include the cis-trans isomerization of olefins, ketone photoeliminations, ligand substitution processes, excimer and photodimer formation, and photoredox reactions. Both reactions occurring within the organized assemblies as well as interfacial phenomena have been investigated. Results obtained in these studies suggest possible extensions and applications for the development of new catalyst systems, biological models and controlled syntheses.     

In situ UV-Vis and ex situ IR spectroelectrochemical investigations of amorphous and crystalline electrochromic Nb2O5 films in charged/discharged states

Niobium oxide (Nb₂O₅) films and powders have been obtained via the sol-gel route from an NbCl₅ precursor. XRD spectra revealed that films with pseudohexagonal (TT-phase) and orthorhombic (T-phase) structure were formed at 500  °C and 800  °C, respectively, while at 300  °C films were amorphous. Infrared (IR) and Raman spectra of powders and films of Nb₂O₅ in different polymorphic forms were detected, and vibrational band assignments were made. Electrochromic properties of amorphous films and films with the TT-phase were established from in situ ultraviolet visible (UV-Vis) spectroelectrochemical measurements and correlated with ex situ IR transmission spectra of charged films. Ex situ IR spectra revealed that charging of amorphous films is accompanied by variations of the Nb-O stretching mode intensity, while, for films with the TT- and T-phase, splitting of the Nb₃-O stretching modes and the appearance of polaron absorption were noted with Li⁺ ion insertion. Ex situ X-ray diffraction (XRD) spectra of charged films with the TT-phase showed changes of the unit cell dimensions with charging. The influence of the polaron absorption on the ex situ near-grazing incidence angle (NGIA) IR reflection-absorption spectra of charged/discharged films is discussed in detail. Received: 21 August 1997 / Accepted: 9 October 1997     

First evidence for the use of polyamines as nucleophiles in a regioselective palladium-catalyzed allylic amination reaction

Palladium-catalyzed reaction of unsymmetrical allylic electrophiles with polyamines gives rise to regioisomeric allylic polyamines. An original catalytic procedure providing an efficient method for the regioselective synthesis of new classes of polyamino derivatives of biological interest is reported. Based on experimental considerations, a mechanistic rationale involving a thermodynamically controlled isomerization of the initially formed branched product is proposed to account for the total regioselectivity observed.     

Dehydration of synthetic and natural vivianite

Thermal analyses of synthetic and natural vivianite (Fe²⁺)₃(PO₄)₂·8H₂O) were determined using a high-resolution thermal analyser coupled to a mass spectrometer.Five dehydration weight loss steps were observed for the natural vivianite at 105, 138, 203, 272 and 437 °C. The first weight loss step involves the reaction (Fe²⁺)₃(PO₄)₂·8H₂O→(Fe²⁺)₃(PO₄)₂·3H₂O+5H₂O. The TGA/MS for the synthetic vivianite gave similar results to that of the natural sample. Mass spectrometry shows that water is lost up to 450 °C and after this temperature oxygen is lost. Changes in the structure of vivianite were followed using infrared emission spectroscopy. A model is proposed for the dehydration of vivianite.     

Improvement of alternariol monomethyl ether detection at gold electrodes modified with a dodecanethiol self-assembled monolayer

The electro-oxidation of alternariol monomethyl ether (AME), one of the main metabolites of the Alternaria genus mycotoxins, is studied at 1-dodecanethiol (DDT)-modified gold electrodes, in acetonitrile (ACN) – aqueous phosphate buffer solutions of different pH values, by using cyclic (CV) and square-wave (SWV) voltammetries. The AME voltammetric response at the bare electrode suffers from two drawbacks: it appears at potentials close to the onset of gold oxide formation, and it is hampered by a fouling of the electrode surface due to the accumulation of oxidized products. These shortcomings are circumvented by the use of DDT-coated electrodes, since the intervening monolayer inhibits gold oxide formation and surface passivation by the electrochemical products, without affecting the oxidation kinetics of AME significantly. Diagnostic criteria based on the voltammetric peak parameters show that the electrochemical behavior of AME at the modified electrode is mainly controlled by reactant diffusion from solution, with a weak adsorption of both the mycotoxin and its oxidation products at monolayer defects. Calibration curves were constructed from the AME square-wave voltammetric response and a detection limit of 9.1 × 10⁻⁸ mol dm⁻³ was determined, which is about three times smaller than a previous estimate at platinum and glassy carbon electrodes, and about fifty times smaller than the limit derived from measurements carried out at a polyphenol oxidase-modified carbon paste electrode.     

Studies of polyamines transport through liquid membranes with D2EHPA as a carrier

The transport of polyamines through the liquid membranes with di-2-ethylhexyl phosphoric acid (D2EHPA) was investigated. The study was performed in three main steps: liquid-liquid extraction (LLE), bulk liquid membrane (BLM) extraction, and supported liquid membrane (SLM) extraction. Equilibrium distribution experiments allowed determining the extraction constants and stoichiometric coefficients for each polyamine. It turned out that one amino group binds two molecules of carrier (one D2EHPA dimer) and the extractability of polyamine rises with the increase in number of function groups in the molecule. The BLM and SLM experiments showed that despite considerable differences in distribution ratio between various polyamines the extraction efficiencies for all of them are very approximate. The smaller diamines compensate the lowest affinity to membrane phase with faster interface reaction kinetics and higher diffusivity. Finally, the SLM extraction conditions were optimized. The main parameters that influence the transport are the pH of the donor and acceptor phases. The extraction efficiencies obtained for polyamines are high (80-90%) and give hope for an application in bioanalytical chemistry.     

Miscibility of an acylated hepatitis A synthetic antigen derivative [palmitoyl VP3(110-121)] with lipids: a monolayer study

Mixed monolayers of an acylated derivative of hepatitis A synthetic peptide VP3(110-121) with neutral, cationic or anionic lipids were spread at the air/water interface. Deviations from ideality as well as thermodynamic values were calculated at different surface pressures using the free-excess energy, the interaction parameter and the enthalpy. The miscibility at the collapse point was also checked. Maximum deviations from ideality were found for mixtures containing the anionic lipid phosphatidylglycerol (PG), and it seems that the monolayer composition is not stable through compression, as the peptide is ejected from the film. Films containing neutral [dipalmitoylphosphatidylcholine (DPPC)] or cationic [stearylamine (SA)] lipids showed more regular behaviour. As the peptide has a net negative charge it is probable that electrostatic interactions are in part responsible of the good miscibility of palmitoyl VP3(110-121) with SA. In order to prepare liposomes containing palmitoyl VP3(110–121), lipids such as SA or DPPC/SA will be a more suitable choice than anionic lipids such as PG. Received: 26 May 2000 Accepted: 22 September 2000     

Structure and properties of hydrophobically end-capped poly(ethylene oxide) solutions in the presence of monovalent and divalent cations

Hydrophobically modified poly(ethylene oxide), HMPEO, was studied in concentrated salt solutions. The influence of salts was compared to the effect of temperature on poly(ethylene oxide), PEO. As expected, the addition of monovalent cations (Na(+), K(+)) has the same effect as an increase in temperature in agreement with the thermodynamic properties of PEO: a decrease in solubility, micelle size, and viscosity was observed. Moreover, the intensity of neutron scattering peaks (characteristic of the semi-dilute solutions of these associative polymers) increases due to the collapse of PEO coronae in micelles. Very peculiar behavior was observed in the presence of divalent cations (Ca(2+), Mg(2+)): larger micelle aggregates and higher viscosities, relaxation times, and activation energies were observed by dynamic rheology. This behavior is attributed to interactions between divalent cations and oxygen in PEO backbones close to the micelle core, which may reinforce intermicellar bridges.     

Thermal decomposition of natural and synthetic plumbojarosites: Importance in ‘archeochemistry’

Plumbojarosite and argentoplumbojarosite were sources of lead and silver in ancient and medieval times. The understanding of the chemistry of the thermal decomposition of these minerals is of vital importance in ‘archeochemistry’. The thermal decomposition of plumbojarosite was studied using a combination of thermogravimetric analysis coupled to a mass spectrometer. Three mass loss steps are observed at 376, 420 and 502 °C. These are attributed to dehydroxylation, loss of sulphate occurs at 599 °C, and loss of oxygen and formation of lead occurs at 844 and 953 °C. The temperatures of the thermal decomposition of the natural jarosite were found to be less than that for the synthetic jarosite. This is attributed to a depression of freezing point effect induced by impurities in the natural jarosite. Raman spectroscopy was used to study the structure of plumbojarosite. Plumbojarosites are characterised by stretching bands at 1176, 1108, 1019 and 1003 cm⁻¹ and bending modes at 623 and 582 cm⁻¹. Changes in the molecular structure during thermal decomposition were followed by infrared emission spectroscopy. The technique shows the loss of intensity in the hydroxyl stretching region attributed to dehydroxylation. Loss of sulphate only occurs after dehydroxylation. Lead is formed at higher temperatures through oxygen evolution.     

Cation removal and lattice alteration of a biotite by a resin charged with different cations

Summary A suspension of a biotite was shaken with a synthetic cation exchanger. Alteration of the mineral lattice and amounts of cations taken up by the resin as a function of time and species of the cations with which the resin was originally saturated, was studied.A H⁺–charged resin first caused an expansion, then a contraction, but later the lattice seemed to have been completely broken down.When the resin was originally saturated with NH₄ ⁺ or Ca⁺⁺ no evident change of the basal spacing was observed.Both Na⁺– and Mg⁺⁺–charged resin caused expansions of the lattice with the consequent formation of a vermiculite-like mineral.

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Zusammenfassung Eine Biotitsuspension wurde mit einem synthetischen Kationenaustauscher behandelt. Der Einfluß auf das Gitter und die vom Austauscher gebundenen Kationen wurde in Abhängigkeit von der Zeit und von der Art der ursprünglich am Austauscher gebundenen Kationen untersucht. Ein mit einem H+beladener Austauscher verursacht zunächst eine Schichtaufweitung, dann eine Kontraktion, bevor das Gitter vollständig zerstört wird. Wenn der Austauscher mit NH⁺ ₄ oder Ca⁺⁺ beladen war, wurde keine merkliche Anderung des Schichtabstandes beobachtet. Mit Na+ und Mg⁺⁺-Austauschern trat eine Gitteraufweitung auf unter Bildung vermikulitähnlicher Minerale.

     

Infrared spectroscopic study of natural hydrotalcites carrboydite and hydrohonessite

Infrared spectroscopy has proven most useful for the study of anions in the interlayer of natural hydrotalcites. A suite of naturally occurring hydrotalcites including carrboydite, hydrohonessite, reevesite, motukoreaite and takovite were analysed. Variation in the hydroxyl stretching region was observed and the band profile is a continuum of states resulting from the OH stretching of the hydroxyl and water units. Infrared spectroscopy identifies some isomorphic substitution of sulphate for carbonate through an anion exchange mechanism for the minerals carrboydite and hydrohonessite. The infrared spectra of the CO3 and SO4 stretching region of takovite is complex because of band overlap. For this mineral some sulphate has replaced the carbonate in the structure. In the spectra of takovites, a band is observed at 1346 cm(-1) and is attributed to the carbonate anion hydrogen bonded to water in the interlayer. Infrared spectroscopy has proven most useful for the study of the interlayer structure of these natural hydrotalcites.     

Determination of polyamines in human urine by precolumn derivatization with benzoyl chloride and high-performance liquid chromatography coupled with Q-time-of-flight mass spectrometry

A simple and sensitive HPLC/Q-TOF MS method for simultaneous determination of 1,3-diaminopropane, putrescine, cadaverine, spermidine, spermine and acetyl-spermine in human urine was developed in electrospray-ionization source by positive ion mode. The samples were firstly pretreated by 10% HClO₄ and then derivatized by benzoyl chloride with 1,6-diaminohexane as internal standard. The derived polyamines were separated on a C₁₈ column by a gradient elution with methanol-water, and then sensitively detected with Q-TOF MS. The limits of detection for polyamines ranged from 0.02 to 1.0 ng ml⁻¹ with excellent linearity within the range from 1 to 1000 ng ml⁻¹ except acetyl-spermine from 5 to 1000 ng ml⁻¹. The intra- and inter-day R.S.D. for all polyamines were 2.0-14.7% and 3.9-12.9%, respectively. The method was applied to determine the polyamines in human urine from 10 cancer patients and 15 healthy volunteers. Results showed that the mean levels of polyamines in urine of patients were all higher than those in healthy volunteers. The cluster analysis was used to establish the distinction mode between cancer sufferers and healthy individuals.     

Synthesis of triarylphosphines having para -SH and -SMe groups: Preparation of their complexes and formation of a monolayer on a gold surface

The phosphines P(C₆H₄-4-SR)₃ (R = H, Me, 2-C₅H₉O) and (C₆H₄-4-SR)₂PCH₂CH₂P(C₆H₄-4-SR)₂ (R = H, Me) have been synthesized. The phosphines with -SMe groups can be prepared by reaction of 4-BrC₆H₄SMe with either BuLi or magnesium (to generate the corresponding Grignard compound) followed by reaction with PCl₃ or Cl₂PCH₂CH₂PCl₂, respectively. The methyl group can be eliminated by reaction with sodium in liquid NH₃. Other methods of protection/deprotection of the thiol group failed to afford the desired compounds. Reaction of 4-BrC₆H₄SH with dihydropyrane afforded the protected thiol 4-BrC₆H₄S-2-C₅H₉O from which the corresponding phosphine was successfully synthesized. However, attempts to remove the tetrahydropyranyl group by reaction with AgNO₃-HCl, gave an insoluble polymer as product. Reaction of P(C₆H₄SR)₃ (R = H, Me) with Ni(CO)₄ affords the corresponding mono phosphine complex quantitatively. The complex with the unprotected thiol group can be absorbed on a gold surface and the corresponding ν_CO bands were detected by grazing angle Fourier transform infrared reflection absorption spectroscopy (grazing angle FTIR-RAS). Reaction of Rh(acac)(CO)₂ with P(C₆H₄SR)₃ (R = Me) affords the complex Rh(acac)(CO)(P(C₆H₄SR)₃) (R = Me), but if R = H a polymer insoluble in any solvent was obtained. The same occurs in the case of PtCl₂(CO)(DMSO). Apparently, once P(C₆H₄SH)₃ is coordinated to a metal not in the zero oxidation state, oxidation of the thiol group to disulphide becomes very easy even in a dinitrogen atmosphere.     

Molecular modelling of amphipathic basic model peptides: Interactions in aqueous solutions and in the presence of lipids

Molecular modelling calculations based on experimental data obtained in solution and in small unilamellar vesicles are used to study interactions between amphiphilic basic peptides and membranes. The behaviour of such peptides during the initial and final stages of the adsorption process is our primary interest. Primary sequences of 20 amino acid residues were designed with equal numbers of basic lysines and hydrophobic leucines in order to get an amphipathic α helix. First, in solution, aggregates with an increasing number (up to nine) of helical monomers were built up and the hydrophobic solvent accessible surface per monomer was analysed on energy minimised structures. This showed that aggregates with 5–8 of monomers should be equally probable, in reasonable accordance with experimental data. In addition, models of membranes with 21 dimyristoyl-phosphatidylcholine lipids were constructed; amphiphilic peptides were merged into these assemblies with their axes parallel to the monolayer surface and the whole lipid/peptide complex was submitted to a few steps of simulated annealing and further energy minimisation techniques in order to equilibrate alkyl chains in the vicinity of the peptide. These simulations yield an estimation of the penetration depth for the peptide in the monolayer of ∼3.2 ?, whereas experimental approaches to this question were not productive. The modification in the peptide net electrical charge by interchanging Leu in Lys residues in such systems is also examined: for low-charged peptides the penetration depth increases. Received: 20 May 1998 / Accepted : 3 September 1998 / Published online: 7 December 1998     

An efficient and mild carboxylation of multiwall carbon nanotubes using H2O2 in the presence of heteropolyacid

A clean,fast,and facile oxidation of multiwalled carbon nanotubes（MWCNTs） by H₂O₂/heteropolyacid(H₃PW₁₂O₄₀) gave highly carboxylated MWCNTs under mild conditions,at a conveniently accessible temperature.After an easy workup,the product was characterized by SEM,XRD,and FT-IR.     

An infrared and Raman spectroscopic study of polyanilines co-doped with metal ions and H+

Polyanilines doped with (HCl+KCl) and (HCl+CoCl2) were prepared by co-doping method, respectively. For comparison, polyaniline emeraldine salt (ES) by doping with HCl and its emeraldine base (EB) form were also synthesized. The co-doped polyanilines, ES and EB samples were all characterized by Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy aiming to understand the transformations in the different doping status. The results show that the doping degree of K+ ions is considerably higher than that of Co2+ ions under the same co-doping conditions possibly due to different pseudoprotonation constants of EB with K+ ions and Co2+ ions. Moreover, morphology difference of polyaniline co-doped with alkaline metal ions or transition meal ions may arise from different coordination geometry of metal ions. Nevertheless, there are similar chemical transformations of quinoid units to benzenoid ones on polyaniline backbones for the ES and both co-doped samples. And the polyaniline backbones co-doped with H+ and metal cations are found to attain weaker charge delocalization than the ES which is doped solely with H+.