13C- and 1H-NMR. Assignments for colchicine derivatives

The ¹³C-NMR. spectra of a number of colchicine derivatives are given comprising examples of the normal series ( 4→10 ), iso series ( 11→16 ) and colchicine series ( 17 ), which were either reported in the literature or obtained by partial synthesis or degradation reactions. The ¹³C-NMR. assignments were made by comparisons with known compounds and selective single-frequency offresonance decoupling experiments. Selective proton decoupling experiments have also allowed assignments of the H —C(11) and H —C(12) protons of the iso and colchicine series.     

Micelle formation of N-decanoylglycine and N-decanoyl-L-alanine oligomer potassium-salts and the micellar structure. A small-angle neutron scattering study

 Potassium salts of N-decanoylglycine and N-decanoyl-L-alanine oligopeptides (monomer, dimer and trimer) were synthesized. For these oligomer salts in aqueous solutions, the microstructures of micelles have been investigated by small-angle neutron-scattering (SANS). In the calculation of SANS intensity data, the thickness of the hydrophilic layer was altered by changing the conformation of the oligomer moiety (helical and β-sheet structures). For micelles of the trimer salts, the helical structure models provide the best fit to the observed SANS intensity data. For micelles of the monomer-and dimer-salts, the β-sheet model provides the best fit to the observed data. For the monomer-and dimer-micelles, the aggregation number (n) is not dependent on the species of amino acid residue, imply-ing that the decanoyl group plays a critical role in micelle formation. However, for the trimer micelles, the n value is dependent on the species of amino acid residue. Received: 11 July 1996 Accepted: 11 September 1996     

Thermodynamic and spectroscopic properties of mixtures of β-lactoglobulin and dioleylphosphatidylcholine

 The behavior of the single spreading monolayers of β-lacto-globulin (β-LG) and dioleyl-phosphatidylcholine (DOPC), as well as their mixtures, has been studied on subphases containing Na⁺ or Ca⁺⁺ ions. The results show an influence of temperature and subphase on the studied systems. The behavior of the areas as a function of the weight fraction of the two components shows significative and prevalently positive deviations from the additivity and their bidimensional miscibility. The variation of ΔG ^ex, ΔH ^ex and ΔS ^ex calculated for the DOPC–β-LG mixture having maximum deviation on two different supports allows to deduce that the interactions are prevalently repulsive. FTIR–ATR spectra of transferred plurilayers show that DOPC has a surface orientation which can originate the miscibility between the protein and DOPC. Received: 3 February 1997 Accepted: 3 June 1997     

Cobalt nanoparticles in block copolymer micelles: Preparation and properties

 The preparation and properties of Co nanoparticles in polystyrene(PS)-poly-4-vinyl-py-ridine(PVP) micelles were studied. Elementary Co was generated by two methods: (i) by reduction of micelles loaded with CoCl₂, and (ii) by thermal decomposition of Co₂(CO)₈ in micel-lar solutions of such block copolymers. Co particles formed by both processes are effectively stabilized by the block copolymer matrix and do not aggregate. For CoCl₂ as a Co-source, the formed particles have a size less than 1 nm. Thermal treatment of such dried polymers at 200 ^°C for 2 h leads to spherical particles of 3–5 nm in size. The polymeric hybrid materials prepared in this way display remarkably high values of magnetization at rather low Co contents in the polymer, i.e., we obtain a tenfold increase of the specific magnetization density. Co₂(CO)₈ as a Co source, results in a more complex behavior. Co₂(CO)₈ dissolves in the solvent as well as in the micelle core where it is converted to an cationic–anionic complex involving the 4-VP units. The shape and size of the Co nanoparticles formed by thermolysis can be controlled by the balance of 4-VP/Co and can be varied from spherical particles in the limit of lower Co loads being mainly attached to the micelle core to a star-like and cubic morphology in case of excess of Co₂(CO)₈. Both superparamagnetic and ferromagnetic materials can be prepared. For ferromagnetic samples coercive force varies from 250 to 475 Oe depending on Co content and polymer sample. Received : 27 September 1996 Accepted: 22 November 1996     

13C- and 1H-NMR. Spectra of ortho-benzoquinones. On the assignment problem in 13C spectra

¹³C- and ¹H-NMR. spectra of ortho-benzoquinone 1 and its methyl derivatives have been analysed. By means of heteronuclear double resonance experiments it is shown that assignments given in the literature for the olefinic carbon resonances of 1 and of a series of substituted ortho-benzoquinones have to be inverted. ¹³C-carbonyl frequencies of various six-membered cyclic ketones are presented.     

Influence of alkoxyethanols on the mixed micelle formation by hexadecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide surfactant mixtures

 The conductances of hexadecyltrimethylammonium bromide (HTAB) and tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of HTAB were measured in aqueous binary mixtures of ethylene glycol monomethyl ether, monoethyl ether, and monobutyl ether, and of diethylene glycol monomethyl ether and monoethyl ether containing 10–30 wt% additive in their respective binary mixtures at 30 °C. Each conductivity curve showed a single break over the whole mole fraction range of HTAB–TTAB mixtures. From the break in the conductivity curve, various micellar parameters were calculated and the results were discussed with respect to the alkoxyethanol's additive effect on the mixed micelle formation. The micellar parameters of HTAB, TTAB, and of their mixtures showed a strong dependence both on the amount as well as on the number of repeating units in the presence of ethylene glycol derivatives, whereas a significant dependence only on the amount of additive was observed in aqueous diethylene glycol derivatives. The results in the former case were attributed to the hydrophobic hydration of the mixed micelles by the ethylene glycol derivatives, which showed a large dependence on the increase in the alkyl chain length of the additive. The hydrophobic hydration was considerably reduced in the case of diethylene glycol derivatives owing to the presence of an extra ether oxygen. An evaluation of the nonideality in the HTAB–TTAB mixtures revealed that in spite of the strong hydrophobic hydration of the HTAB–TTAB mixtures by the alkoxyethanols, the mixed micelles remain almost free from the additive molecules. Received: 11 January 2000/Accepted: 14 April 2000     

Living polymers and polymer solutions: a misleading analogy

 Experimental results from colloidal suspensions of worm-like micelles are currently interpreted in terms of close analogies between this kind of systems and polymeric solutions. In particular, it was hypothesized that the viscoelastic properties of dense systems of giant flexible cylindrical micelles can be rationalized in terms of an entangled network of worm-like aggregates, very similar to a neutral random polymeric network. Such an idea is strongly supported by theoretical results that, in a mean-field appro ximation, suggests for an unlimited growth process of the micellar contour length with concentration. The mean-field theory indicates for an exponentially shaped length distribution function, with mean <L> depending on concentration, φ, in agreement with a scaling law <L>∝φ^α (α=0.5 in the simpler approach). A number of experimental results seem to be successfully interpretable within this framework. Aim of this work is to show that the agreement between theory and experiment is just an accident, being the mean-field approach, in principle, inadequate in describing systems dense enough to show a concen tration dependence of the mean micellar size. It will be unambiguously shown that there is no way to describe semi-diluted micellar solutions through a mean-field approximation and that there does not exist any scaling law of the kind <L>∝φ^α. Furthermore, it will be shown that the shape of the size distribution function is markedly different from the exponential one. The basis for a more realistic approach for the growth process of micellar aggregates is also presented and some pre liminary indications are success fully compared with experimental results. Received: 24 February 1997 Accepted: 22 April 1997     

Calorimetric investigation of the formation of ZnS nanoparticles in w/o microemulsions

The enthalpies of precipitation of ZnS nanoparticles within water containing reversed micelles of sodium bis(2-ethylhexyl) solfosuccinate, L-α phosphatidylcholine, tetraethyleneglycol-mono-n-dodecyl ether and didodecyldimethylammonium bromide as a function of the molar concentration ratioR (R=[water]/[surfactant]) were measured by calorimetric technique. The results indicate that the energetic state of ZnS nanoparticles confined in the aqueous core of the reversed micelles is different from that in bulk water. Effects due to nanoparticle size, adsorption of HS⁻ ions on the nanoparticle surface and interactions between nanoparticles and water/surfactant interfaces are discussed. This work has been supported by MURST.     

Surface structure of silica gel reacted with 3-mercaptopropyltriethoxysilane and 3-aminopropyltriethoxysilane: formation of the S–S bridge structure and its characterization by Raman scattering and diffuse reflectance Fourier transform spectroscopic studies

 Silica gel samples, modified with 3-mercaptopropyltriethoxysilane, and their S–S-bridged samples have been prepared. In order to characterize the microstructure of the surface of these silica gel samples, Raman scattering and diffuse reflectance Fourier transform IR spectra of these samples have been examined by comparison with Raman spectra of various n-alkyl disulfides and their related silane polymers. The S–S and C–S stretch modes characteristic of the CH₂SSCH₂ segment, in addition to the SH and C–S stretch modes of the CH₂SH segment, have been assigned for these silica gel samples. It has been found that, even on the surface of the silica gel, a specific conformer is stabilized about the CH₂SSCH₂ segment. Received: 1 May 2001 Accepted: 16 June 2001     

Asymmetric diblock copolymers-phase behaviour and kinetics of structure formation

 The structure of a series of three molecular weights of diblock copolymers polystyrene/b-isoprene with 11% volume fraction of polystyrene and low polydispersity has been investigated using small angle X-ray scattering (SAXS). In between the disordered and the BCC ordered state a micellar state with liquid-like order was found. The transition between these states was investigated in a temperature-driven experiment. Whereas the micelles appear gradually with lowering temperature the formation of the BCC ordered state occurs discontinuously at a well-defined temperature. Detailed analysis of the scattering profiles provides access to the micellar size and distance in the liquid-like as well as in the BCC state. The kinetics of the ordering transition was studied using time-resolved SAXS after temperature jumps from the liquid-like to the BCC state. The growth of the micelles and their ordering on the periodic lattice were found to occur on clearly separated time scales. Received: 12 September 1996 Accepted: 2 December 1996     

Time-resolved near-infrared and two-dimensional near-infrared correlation spectroscopic studies of the polymerization process of silane coupling agents. Dynamic behavior of water molecules in the 3-aminopropyltriethoxysilane–ethanol–water system

The polymerization behavior of 3-aminopropyltriethoxysilane, a process initiated by water molecules, has been examined using time-resolved near-IR and 2D near-IR correlation spectra. By deconvolution of the time-resolved near-IR spectra, the existence of the component bands at 5189, 5265 and 5300 cm⁻¹, whose intensities decrease markedly as the reaction proceeds, has been confirmed in the 5000–5400 cm⁻¹ region. The band at 5189 cm⁻¹ has been assigned to water molecules, while those at 5265 and 5300 cm⁻¹ have been assigned to the strongly and weakly associated silanol groups, respectively. The kinetics of the hydrolysis of the ethoxy groups and of the formation of a siloxane bond have been analyzed using the time-dependent integral intensities of these three bands and the mechanisms of the reactions have been discussed. Evidence for this polymerization process is also clearly evident in the 2D near-IR correlation spectra. Received: 14 March 2000/Accepted: 15 May 2000     

Percolative phenomena in lecithin reverse micelles: the role of water

 The role played by the solvation water molecules on the macroscopically observed sol–gel transition in lecithin/cyclohexane/water reverse micelles is investigated by quasielastic neutron scattering, dielectric relaxation and conductivity measurements. The experimental results are juxtaposed to those from spherical Aerosol OT reverse micelles. It is shown how the results from lecithin-based system can be interpreted only assuming that, in contrast to Aerosol OT systems, the water molecules are entrapped at the interfaces without coalescing into an inner water pool. It is suggested that, in the case of lecithin, the solvation water can induce a change in the surface curvature, in such a way promoting the formation of branch points. Such a hypothesis is supported by the temperature dependence of the conductivity which agrees with the hypothesis of an intermicellar bond percolation. The investigation of the structures imposed by an external electric field is also studied. The observed electrorheological behaviour seems to confirm the existence of a percolated transient network in the gel phase. Received: 21 March 2001 Accepted: 24 August 2001     

Anion Selectivity of Tetravalent Tin Compounds in Membranes Studied by 119Sn-, 13C- and 1H-NMR

The fundamental molecular aspects of trialkyltin compounds of the type R₃SnY have been investigated in view of their applicability as ion-selective components in solvent polymeric membranes. The interaction between these compounds and anions has been studied using ¹¹⁹Sn- and ¹³C-NMR. Neutral tetracoordinated trialkyltin compounds form a negatively charged pentacoordinated complex upon interaction with Cl-ions in homogeneous organic phases as well as in membranes in contact with aqueous solutions. Although in a homogeneous phase, the electronegative substituent Y determines the complex-formation constant, it has no influence on the potentiometric anion selectivity in liquid membranes containing trialkyltin carriers R₃SnY with different Y. The observed selectivity pattern is not given by the magnitude of the stability constants in a homogeneous phase but is dictated by the prevailing association-dissociation process leading to tetracoordinated compounds which change in constitution due to varying sample composition, The results obtained from equilibrium studies of tetravalent mono tin compounds with anions in both homogeneous phase and in two-phase systems confirm the earlier hypothesis that trialkyltin compounds incorporated in solvent polymeric membranes act as electrically neutral carriers for anions.     

Partial molar volume of dodecyltrimethylammonium hydroxide in water and NaOH aqueous solutions

 The partial molar volume of dodecyltrimethylammonium hydroxide in water and aqueous NaOH solutions was measured. The addition of NaOH did not affect either the micellized or the unmicellized molecules. The expansion on micellization is much larger than in dodecyltrimethylammonium bromide systems, which reflects the stronger ionization of the hydroxide surfactant micelles, when compared with that of the bromide amphiphile. Received: 27 October 1997 Accepted: 4 March 1998     

Action of HCl on 3-hydroxypyrazolo(iso)quinolines to give 1-chloropyrazoles: evidence for an addition–elimination mechanism by ab initio calculations in gas phase and water

 Addition–elimination reactions involving a nucleophile and a remote leaving group [S^H _N(AE)^tele] are well-known under basic conditions, especially amongst electron-poor six-membered heterocycles, but are less commonly encountered for five-membered heterocycles and are rare under acidic conditions. Concentrated HCl converts 1-hydroxy-1H-pyrazolo[3,4-c] isoquinoline and 1-hydroxy-1H-pyrazolo[3,4-c]quinoline into 3-chloro-1H-pyrazolo[3,4-c]isoquinoline and 3-chloro-1H-pyrazolo[3,4-c]quinoline, respectively. However, apparently neither the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)-quinolines nor the parent 1-hydroxypyrazole undergo this reaction. Additionally, all these systems are refractory under basic conditions. We present a plausible mechanism for the reaction, involving the 3-addition of Cl^- to the diprotonated heterocycle, followed by the elimination of water. Calculations of the initial transition states and intermediates, using optimisation at B3LYP/6-311+G(d,p), including thermochemistry [HF/6-31+G(d)], and single-point Poisson–Boltzmann self-consistent reaction field determination of the free energy of solvation (Jaguar Poisson–Boltzmann self-consistent reaction field), support this mechanism and reproduce the observed order of reactivity, the addition step being 2–4 kcal less favourable for the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)quinolines and provide a rationalisation for the role of strong acid. Received: 27 June 2002 / Accepted: 6 September 2002 / Published online: 14 February 2003     

Styrène solubilization in micelles of dodecyltrimethylammonium hydroxide

 The solubilization of styrene molecules in aqueous dodeciltrimethylammonium Hydroxide (DTAOH) solution was studied by UV-Vis spectroscopy. In short, fully ionized DTAOH aggregates the styrene molecules in the micelle double layer, oriented with their vinyl group to the micelle core and the aryl ring to the intermicellar solution. At increased surfactant concentration, when the aggregates incorporate counterions in their Stern layer, the orientation is maintained, but styrene molecules gradually penetrate into the micelle core as the micelle size and degree of counterion union increased, until they were completely immersed in the hydrocarbon core of rod-like micelles. Received: 6 November 1996 Accepted: 10 February 1997     

Enzymic activity of whole cells entrapped in reversed micelles

Studies have been conducted on the enzymic activity of Baker’s yeast and also of Brewer’s yeast entrapped into the reversed micelles formed by cetyl pyridinium chloride (CPC1) in n-hexane. The activities of α-amylase and invertase enzymes in the entrapped cells have been estimated and compared with those in the control experiments where there was no entrapment. The following significant observations have been made: 1. except for invertase, enzymes in Brewer’s yeast, the entrapped yeast cells showed enhanced enzymic activities; 2. when the yeast cells were entrapped inside the reversed micelles along with substrates of the two enzymes, α-amylase, and invertase, the activity of each of these enzymes showed a further enhancement in comparison to that showed in the experiments in which substrates of the individual enzymes alone were entrapped-the phenomenon of synergism; 3. when the yeast cells and the respective substrates were entrapped inside separate reversed micelles and the solutions containing entrapped cells and entrapped substrates were mixed, the activities of the individual enzymes, α-amylase and invertase, showed further enhancement in comparison to the case in which the cells and the substrates were entrapped inside the same reversed micelle (in this case also the phenomenon of synergism was observed); and (4) In the case of experiments in which there was no entrapment, it was observed that the presence of substrates induced more release of enzymes from the yeast cells. These observations on yeast cells, which to the best of our knowledge have not been reported before, should be biotechnologically relevant.     

Study of the required HLB for the solubilization of cholesterol in aqueous solution

 The solubilization of cholesterol by anionic surfactant mixtures was studied as a function of their HLB values. The relationship between the logarithm of the critical micelle concentration and the HLB value of the mixtures was not linear, which was attributed to a lack of strict additivity of the HLB values. The solubilized cholesterol/surfactant ratio was determined and it was found to be higher than that in bile salts in all the studied surfactant mixtures. Below HLB=24, emulsions were obtained, and the remaining cholesterol was solid. Above that value, limpid solutions were obtained, giving a solubility maximum at HLB≈35. The non-solubilized cholesterol was mainly in the form of lamellar mesophase. Received: 23 June 1997 Accepted: 12 August 1997     

Aqueous biphase formation by mixtures of dextran and hydrophobically modified dextran

 A series of modified dextrans was prepared by condensation of straight chain saturated C3, C4 and C6 fatty acids and the phase behavior of aqueous solutions of these materials with unmodified dextran was measured as a function of temperature, concentration and degree of substitution. At a constant degree of substitution the tendency towards aqueous biphase formation increased with the length of the hydrophobic substituent, the temperature and the molecular weight. Fluorescence studies of the modified dextrans with pyrene as a probe indicated the presence of hydrophobic micro-domains. Rheological study showed that there was no large-scale association for C3 and C4 substituted dextran, mainly intramolecular association, however some intermolecular association existed for C6 substituted dextran. The results are compared with the behavior of the classical PEG/dextran biphase systems, and mechanisms driving phase separation are discussed. Received: 7 October 1997 Accepted: 20 January 1998