Papers by Andrés Durantini
The Journal of Physical Chemistry B, 2011
In this work we investigate the behavior of the glycerol (GY):N,N-dimethylformamide (DMF) mixture... more In this work we investigate the behavior of the glycerol (GY):N,N-dimethylformamide (DMF) mixture in homogeneous and sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane reversed micelles (RMs) media. To achieve this goal we have used the solvatochromic behavior of 1-methyl-8-oxyquinolinium betaine (QB) as an absorption probe, and dynamic light scattering (DLS). QB shows strong preferential solvation when it is dissolved in the GY:DMF mixture, and, as QB is a good hydrogen bond acceptor molecular probe, it is preferentially solvated by the GY-DMF hydrogen-bonded (H-bonded) species. On the other hand, when the GY:DMF mixture was investigated in AOT RMs, the results show that the mixture is encapsulated in the polar core of the AOT RMs. DLS confirms the formation of the GY:DMF/AOT/n-heptane RMs since an increase in the W(s)=([GY]+[DMF])/[AOT] values causes an increment in the RMs droplets sizes. The solvatochromic behavior of QB, which resides at the AOT RMs interface, shows that QB is mostly solvated by GY molecules, especially at low W(s) values. Thus, it seems that upon encapsulation inside the polar core of the AOT RMs, the GY-DMF interaction diminishes due to the strong AOT-GY interaction. (1)H NMR chemical shifts of GY and DMF measured in the different AOT RMs investigated shows that GY and DMF behave practically as noninteracting solvents inside the RMs.
The Journal of Physical Chemistry B, 2013
In this work, we have investigated the behavior of 4-aminophthalimide (4-AP) in solvent mixtures ... more In this work, we have investigated the behavior of 4-aminophthalimide (4-AP) in solvent mixtures of ethyl lactate (EL)- water and EL-n-heptane and in reversed micelles (RMs) media made of EL-water/sodium 1,4-bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane. We have used dynamics light scattering (DLS) and absorption, steady-state and time-resolved emission (TRES) techniques. 4-AP is a very interesting and unique molecule used to study preferential solvation in water mixtures since its emission profile changes dramatically when its sphere shell is solvated by water molecules. Thus, in homogeneous media 4-AP is strongly solvated by water in the EL-water mixture and by EL in the EL-n-heptane mixture, results that show the importance of the hydrogen bonding in the 4-AP solvation. We were motivated by this feature of 4-AP and have used it to monitor properties in AOT RMs. Thus, we use 4-AP spectroscopic behavior in conjunction with DLS technique to reveal the location of each polar solvent of the mixture encapsulated within the RMs media. We found that in the EL-water/AOT/n-heptane RMs the results strongly depend on the amount of water dissolved. Below W0 = [water]/[AOT] = 5, there are no reversed micelles and EL, water, AOT and n-heptane forms a nonstructured mixture. For W0 values between 5 and 10, the droplet sizes are independent of the EL content because of its strong intermolecular interactions forms an EL polar core and only water is found at the interface. For W0 values higher than 10, the droplets size increase with the EL content and EL molecules are detected at the AOT RMs interface. We inferred that the RMs sizes will change only if the polar solvent encapsulated interacts with the interface changing the surfactant packing parameter. Then, we can assume that it is possible to create RMs with solvents that do not interact with the interface but can be encapsulated in the polar core. These results, give evidence that expand the knowledge about which are the factors that determine when RMs droplet sizes changes with the polar solvent content, giving insights that will help to control the sizes of the AOT RMs. This will open diverse avenues since RMs are interesting nanoreactors for heterogeneous chemistry, templates for nanoparticles and models for electron transfer reaction that happens in membranes.
The Journal of Physical Chemistry B, 2013
ABSTRACT Reply to the comments made by Samanta et al, jp-2013-0217j.
The Journal of Physical Chemistry B, 2013
The behavior of 4-aminophthalimide (4-AP), a common molecular probe utilized in solvation dynamic... more The behavior of 4-aminophthalimide (4-AP), a common molecular probe utilized in solvation dynamics experiments, was revisited in polar aprotic and protic solvents using absorption, steady-state, and timeresolved fluorescence (TRES) techniques. Also, the deuterium isotope effect was investigated using D 2 O as solvent. The absorption spectra of 4-AP consist of two absorption bands with maxima around 300 nm (B2 band) and 370 nm (B1 band) depending on the environment, while the emission feature consists of a single band. In all the solvents investigated (excluding water), the 4-AP photophysics is similar and the emission spectra are independent of the excitation wavelength used. In water the behavior is unique and the emission spectra maximum is different depending on the excitation wavelength used. The emission maximum is 561.7 nm using the excitation wavelength that correspond to the B2 absorption band maximum (λ excB2 = 303.4 nm) but is 545.7 nm when the excitation wavelength that correspond to the B1 absorption maximum (λ excB1 = 370.0 nm) is used. Moreover, while the fluorescence decays of 4-AP in water exhibit no emission wavelength dependence at λ excB2 , the situation is quite different when λ excB1 is used. In this case, we found a time-dependent emission spectrum that shifts to the blue with time. Our results show that the solvent-mediated proton transfer process displays a fundamental role in the 4-AP emission profile and for the first time a mechanism was proposed that fully explains the 4-AP behavior in every solvent including water. The deuterium isotope effect confirms the assumption because the proton-transfer process is dramatically retarded in this solvent. Consequently, we were able to elucidate not only why in water the emission spectra depend on the excitation wavelength but also why the time-dependent emission spectra shift to the blue with time. Thus, our work reveals the importance that the medium has on the behavior of a widespread dye used as chromophore. This is significant since the use of chromophores without understanding its chemistry can induce artifacts into the interpretation of solvation dynamics in heterogeneous environments, in particular, those provided by aqueous biological systems.
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Papers by Andrés Durantini