Giorgio Cerichelli

Sequential alkylation/transition metal catalysed annulation reactions of 1,3-dicarbonyl compounds with propargyl bromide

Abstract β-Diketones, β-ketoesters and β-ketonitriles in the presence of propargyl bromide, DBU and a catalytic amount of CuI in toluene give 2,3,5-trisubstituted furans through sequential alkylation/cyclisation/isomerisation reactions.

Cyclization of 2-(3-halopropyloxy)phenoxide ions in functionalized surfactants

Abstract Observed rate constants (kobs) of cyclization of 2-(3-halopropyloxy)phenoxide (halo = bromo, iodo; PhBr7 and Ph17, respectively) in aqueous micelles of N-hexadecyl-N-(2-hydroxyethyl)-N,N-dimethylammonium bromide (1) depend on [1] and [NaOH]. The rate profiles go through a maximum and, at high [1], the catalytic effect is modest. By contrast, kobs in aqueous micelles of N-hexadecyl-N-(2-hydroxyethyl)-N,N-dimethylammonium sulfate (2) increases monotonically with increasing surfactant concentration and becomes constant at high [2]. 1H, 13C, and 14N NMR spectra of 1 and 2 show that micelles of 1 and 2 do not differ in dimension and shape and that the average conformations of 1 and 2 are similar.

Synthesis and aggregation behaviour of a new sultaine surfactant

The aggregation properties of a new sultaine surfactant have been studied in buffered aqueous solution at pH 7.4 under controlled condition of osmolarity. Spontaneously formed sultaine vesicles with a mean diameter of about 1 μm can be observed by optical microscopy. The phase behaviour of the surfactant has been investigated by differential scanning calorimetry (DSC) and Nile Red fluorescence. Two critical vesicular concentrations (CVC(1) and CVC(2)) have been fluorimetrically measured, by using pyrene and Nile Red as the fluorescent probes. The two populations of vesicles behave differently as a consequence of their size. The stability of extruded large unilamellar vesicles (LUV) formed slightly above the CVC(1) has been evaluated in the temperature range 25-75°C by following the rate of spontaneous release of entrapped 5(6)-carboxyfluorescein (CF). The stability of the same vesicles at 70°C has also been investigated under osmotic stress obtained by adding NaCl or sucrose to the bulk solution. At a sultaine concentration above the CVC(2) LUV tend to associate and form stable larger closely packed aggregates as suggested by Dynamic Laser Light Scattering and rheological measurements.

Alkylation of Carbonyl Compounds in Water: Formation of CC and CO Bonds in the Presence of Surfactants

The formation of C-C and C-O bonds by the reaction of enolate intermediates with electrophilic substrates commonly requires strong bases, aprotic solvents and very low temperatures. A way of performing the same reactions with sodium hydroxide at moderate temperatures in aqueous surfactant solutions is presented. Different halides, ketones and surfactants (cationic, zwitterionic and anionic) have been used. The results obtained show that the amount of ketone alkylation is much higher and that the reactions are faster in the presence than in the absence of surfactant aggregates. The hydrolysis of the halide is minimised in the presence of cationic or zwitterionic surfactants.

Structure and solvation properties of aqueous sulfobetaine micelles in the presence of organic spin probes: a Molecular Dynamics simulation study

Structural and mechanical-dynamical information on a micelle formed by 72 monomers of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB 3–12) in water solution have been obtained through Molecular Dynamics simulations. Additional simulations have been carried out to evaluate whether and to what extent the structural features of the micelle are affected by the presence of a spin probe, typically utilized for the experimental characterization of these, rather complex, systems. Results indicate that the micelle shows a spherical shape not heavily influenced by the presence of the probe which only produces a slight volume increase. Further analysis also indicates that the probe, although inducing scarce alterations at the micelle-solvent interface, heavily influences the micelle core which appears less stable (more fluctuating) and less hydrated. Finally, analysis of residence times of water indicate—in line with many previous studies—the presence of a dual population characterized by different interactions with micelle interior.

Synthesis and physicochemical characterization of new twin-tailed N-oxide based gemini surfactants

New gemini surfactants (GSs) constituted by two double alkyl chain (from 7 to 17 methylenic units) N-oxide monovalent surfactants joined by a PEG spacer of different length (from 3 to 21 ethylene glycol units), thus combining the properties of both N-oxide and GS surfactants, were synthetized and characterized. The different hydrophilic/hydrophobic balance of the molecular structure strongly influences the morphology and the electrical features of the aggregates. Despite the zwitterionic nature of the polar head groups, all the aggregates are characterized by positive potential thus suggesting protonation at the interface; however, the extent of protonation was shown to strongly depend on the length of the alkyl chain and of the spacer.

Solvent and micellar effects upon the cyclisation of o-3-halopropyloxyphenoxide ions

Rates of intramolecular cyclisations of o-(3-halopropyloxy)phenoxide ion [(1a, b), halogen = Br or I, respectively] increase with decreasing solvent polarity in the order H2O < MeOH < EtOH < PriOH < MeCN, except that reaction of (1a) is faster in H2O than in MeOH, and in H2O (1a) is more reactive than (1b). These effects depend upon the solvation of the oxide ion and the leaving halide ion in the transition state, and relative reactivities kI/kBr indicate the relative importance of these interactions. Micelles of CTAX [C16H33NMe3X, X = Br, Cl, NO3, OH, OTs, or (SO4)0.5] increase the rates by factors of ca. 2 for (1a) and by 4 for (1b), with little effect by the counter-ion. Rate enhancements and kI/kBr increase sharply in the sequence of surfactant head groups N+Me3 < N+ Et3 < N+Pr3 < N+Bu3. Increasing the size of the n-alkyl group apparently decreases hydration of the aryloxide without destabilising the transition state. These micellar medium effects can be related to medium effects in intermolecular reactions in micelles.

Inclusion of cybotactic effect in the theoretical modeling of absorption spectra of liquid-state systems with perturbed matrix method and molecular dynamics simulations: the UV-Vis absorption spectrum of para-nitroaniline as a case study

In this study, we present an extension of the theoretical–computational approach developed in our group and based on molecular dynamics simulations, quantum chemical calculations, perturbed matrix method, and essential dynamics analysis for taking into account the cybotactic effect in the computational modeling of absorption spectra of molecular systems in condensed phase. The low-energy UV–Vis spectra of para-nitroaniline in water, methanol, and in the presence of a zwitterionic micelle have been computationally addressed and compared to the experimental data. The approach, considering all the systematic errors deriving from the intrinsic limitations of the computational setup (force field, quantum chemical calculations, and the approximations of the method), satisfactorily reproduces the experimental spectral shifts and peaks shapes and provides a promising tool of investigation for reproducing spectral observables of very complex systems.

Cyclisation and decarboxylation in zwitterionic micelles: effects of head group structure

The spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion is strongly catalysed by micelles of zwitterionic surfactants, viz., sulfobetaines [C14H29N+R2(CH2)3SO3–, R = Me, Pr and C16H33N+Me2(CH2)3SO3–] and amine oxides (C14H29N+R2O–, R = Me, Pr), with rates enhanced by factors of up to 1800. These micelles and those of the corresponding carboxybetaines are more effective catalysts than those of the corresponding cationic surfactants. In all cases a change from Me to Pr at the head group speeds reaction by factors of ca. 5–8 for the sulfobetaines and amine oxides and ca. 14 for the cationic surfactants. Cyclizations of the o-3-halopropyloxyphenoxide ions (halogen = Br, I), which are intramolecular SN2 reactions, are modestly micellar catalysed, but structural effects on the micellar catalysis by cationic and betaine surfactants are in the same sequence, as for decarboxylation.

Structural and conformational analysis of 2-triphenylphosphoranylidene succinic acid derivatives by 1H, 13C and 31P one and two dimensional NMR spectroscopy and molecular modelling

The structure and conformation of 2-triphenylphosphoranylidenesuccinic acid derivatives have been studied by 1H, 13C and 31P NMR spectroscopy, in various solvents and at variable temperatures. In 2-triphenylphosphoranylidenesuccinic anhydride (1) the conformation is constrained but in the corresponding monoethyl (2) and the diethyl (3) esters there is an anticlinal relationship between the phosphorus and hydrogens on C-3 and signals of Z and E isomers were observed with the diethyl ester 3 in solvent-dependent ratios based on 1H, 13C and 31P resonances. Similar results were obtained with the diethyl ester of the 3-methyl derivative 4. Protonation (deuteronation) of 2 and 3 changes their conformation and P–H couplings. The NMR evidence on conformations of the phosphoranylidenesuccinic acid esters is consistent with T1 relaxation times and results of molecular modelling.