1,721,031 research outputs found
Proprietà psicometriche della versione italiana del Questionario di Buss e Durkee per la Valutazione dell'Ostilità e della Colpa in soggetti non clinici.
No full textA 2H and 13C NMR multifield relaxation study of some nonaqueous systems of sodium dodecyl sulfate
No full textAlkylation of Complementary Ribonucleotides in Nanoreactors
No full textThe aim of the present study was to provide experimental evidence that base pairing, commonly
occurring between nucleic bases in more complex supramolecular arrangements, may affect the
reaction pathways associated with the alkylation of bases themselves. In pursuit of this aim, dilute
aqueous solutions of Cytidine- (CMP) and Guanosine-Mono-Phosphate (GMP) as single
reactants or in an equimolar mixture were treated with the electrophilic alkylating agent 1,2-
Dodecyl-Epoxide (DE), which was preventively dispersed into micellar solutions prepared with
the cationic surfactant hexadecyltrimethylammonium bromide (CTAB). In the early stage of the
reaction, CTAB micelles acted as micro-heterogeneous nanoreactors, but as the reaction
progresses the systems evolved toward the formation of polydisperse aggregates, whose size and
surface-charge properties were monitored as a function of reaction time. From mass spectrometry
analyses, it was found that the deamination of cytosine, a side reaction related to the alkylation
of the amino group of CMP, was reduced when both the complementary ribonucleotides were
present in the same reaction mixture. The involvement of specific sites able to establish C:G
interactions (possibly via H-bonding or p–p stacking) could explain the reduced reactivity
occurring at the level of some of the nucleophilic centers responsible for molecular recognition
Size distribution in emulsions
No full textEmulsions are generally opaque and scatter light widely. This characteristic is a considerable obstacle to the use of optical techniques such as dynamic light scattering and optical microscopy.
However, the optical appearance of a sample is totally irrelevant for nuclear magnetic resonance (NMR) measurements. In this paper we use general methods to calculate the size distribution of a collection of droplets in dilute emulsion systems using NMR pulse gradient spin-echo measurements. We show that such methods are also successful in describing a bimodal distribution of droplets
Cytosine to uracil conversion through hydrolytic deamination of cytidine monophosphate hydroxy-alkylated on the amino group: a liquid chromatography – electrospray ionization – mass spectrometry investigation.
No full textA novel pathway for cytosine to uracil conversion performed in a micellar environment, leading to the generation of uridine
monophosphate (UMP), was evidenced during the alkylation reaction of cytidine monophosphate (CMP) by dodecyl epoxide.
Liquid chromatography-electrospray ionization – ion trap - mass spectrometry was used to separate and identify the reaction
products and to follow their formation over time. The detection of hydroxy-amino-dodecane, concurrently with free UMP, in
the reaction mixture suggested that, among the various alkyl-derivatives formed, CMP alkylated on the amino group of
cytosine could undergo tautomerization to an imine and hydrolytic deamination, generating UMP. Interestingly, no evidence
for this peculiar conversion pathway was obtained when guanosine monophosphate (GMP), the complementary ribonucleotide
of CMP, was also present in the reaction mixture, due to the fact that NH2-alkylated CMP was not formed in this case. The last
finding emphasized the role played by CMP–GMP molecular interactions, mediated by a micellar environment, in hindering the
alkylation reaction at the level of the cytosine amino group
Phase Diagram And Phase Properties Of The System Lecithin-water-cyclohexane
No full textThe isothermal quasi-ternary-phase diagram of the lecithin - cyclohexane - water system was determined at 25 degrees C using a combination of polarizing microscopy, small-angle X-ray diffraction, and NMR techniques. The system contains four lyotropic liquid-crystalline phases and two isotropic liquid phases. Apart from the lamellar (L-alpha) phase, there are only reverse-type aggregates with a water interior, in addition to an essentially pure water phase, whose relative locations in the phase diagram follow the sequence (from the oil corner to the surfactant corner): reverse micellar solution (L-2), reverse anisotropic nematic (N-2), reverse micellar cubic (I-2), reverse hexagonal (H-2), and finally, the lamellar phase. The aggregates have a finite swelling with water, and coexistence with excess water is found at higher water contents. The area per lecithin molecule was determined in the H-2 and L-alpha phases,This area varies with the mole ratio [H2O]/[Lec] = W-0 at lower W-0 values, but saturates at an area of 90 Angstrom(2)/ molecule for W-0 greater than or equal to 15. The phase diagram is discussed in relation to the known formation of giant wormlike reverse micelles in the Liquid L-2 phase. Of particular interest here is the transition from liquid (L-2) to nematic (N-2) as the wormlike aggregate concentration is increased
Use of Rhodotorula minuta live cells hosted in water-in-oil macroemulsion for biotransformation reaction
No full textA lecithin/water/isooctane water-in-oil macroemulsion was used as a host system for biotransformation reactions. In particular, the hydrolytic activity of the yeast Rhodotorula minuta towards (±)-succinic acid bis-2-isopropyl-5-methylcyclohexyl ester and p-nithrophenylbutirate is reported. Evidence that R. minuta entrapped in w/o macroemulsion is able to hydrolyze the p-nithrophenylbutirate ester is presented. By performing the yeast-catalyzed hydrolysis of (±)-succinic acid bis-2-isopropyl-5-methylcyclohexyl ester, the synthesis of (-)-menthol was obtained, indicating that R. minuta retains its high stereoselectivity in the macroemulsion system. In addition, no significant differences were observed among the hydrolysis rates and yields obtained using yeast cells hosted into w/o macroemulsions containing different amounts of water.
Optical microscopy studies on the distribution of diameters of the dispersed phase indicate that the macroemulsion system is stable in terms of polidispersity. The diameter of the w/o macroemulsion droplets is indeed constant irrespective of the addition of water and/or chemicals (involved in the biotransformation reaction) to the system hosting yeast cells.
The reactor devised here might be applied to other interesting bioconversion processes
SURFACTANT SELF-ASSOCIATION IN SOME NON-AQUEOUS SYSTEMS. A PRELIMINARY REPORT ON SELF-DIFFUSION AND NMR RELAXATION STUDIES
No full textA 2H and 13C NMR multifield relaxation study of aqueous aggregate systems of sodium dodecyl sulfate
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