684 research outputs found
When development meets culture : the contribution of Celso Furtado in the 1970s
No full textThe article assesses the work of Celso Furtado (1920-2004) in the 1970s, when the author promotes an ambitious attempt to redefine the field of development economics. Furtado's works have recently been revisited by several authors, including in the field of history of economic thought. The text is devoted to explore how the author challenges development theory’s perceived failure to explain the reality of underdeveloped nations in the late 1970s by expanding the scope of analysis and giving culture a pivotal role in the dynamics of development and underdevelopment. This theoretical movement happens at the time in which development economics begins to drift out of the mainstream of economic theory. Hence, unlike the concept of underdevelopment introduced in the 1950s, the discussion of creativity and dependence encounters an adverse intellectual landscape, even though it represents one of the author’s most original contributions.Celso Furtado, development, underdevelopment, creativity, culture.
Structural Features of β-Cyclodextrin Solvation in the Deep Eutectic Solvent, Reline
No full textThe inherently amphiphilic nature of native cyclodextrins (CDs) determines their peculiar molecular encapsulation features, enabling applications such as targeted drug nanodelivery, aroma protection, etc. On the contrary, it may also lead to poor solubility in water and other organic solvents and to potentially detrimental flocking in these media, thus posing limitations to more extensive usage. Here we use small angle X-ray scattering to show that deep eutectic solvent reline (1:2 choline chloride:urea) succeeds in dissolving large amounts of β-CD (at least 800 mg/mL, compared with the solubility in water of 18 mg/mL), without aggregation phenomena occurring. At the microscopic level, molecular dynamics simulations highlight the complex interplay of hydrogen bonding-mediated hydrophilic interactions and hydrophobic force mitigation occurring between β-CD and reline components, leading to energetically favorable β-CD solvation. The possibility of achieving very high concentration conditions for unaggregated β-CD in an environmentally responsible media, such as reline, can open the way to new, so far unpredictable applications, addressing multiple societal challenges
Liquid structure of a water-based, hydrophobic and natural deep eutectic solvent: The case of thymol-water. A Molecular Dynamics study
No full textThe structural organization of the first example of a water-based, type V, hydrophobic, natural deep eutectic solvent (DES) is investigated in this work, exploiting the synergy of X-ray scattering and compu- tational techniques. The stoichiometric mixture of thymol:water (4.8:1) has been recently reported to behave as a DES, with a melting point at 6 C, well below the one foreseen for the ideal liquid mixture. Our study provides an atomistic insight into the structural correlations in this system, highlighting the major role played by hydrogen bonding (HB) correlations in affecting morphology as well as the solid– liquid equilibrium. Thymol engages HB-mediated interactions with both thymol and water molecules: evidences of conventional HB interactions involving the hydroxyl group are found, together with indica- tions of p HAO hydrogen bonding correlations with both thymol and water. Overall, in the mixture, thymol is involved in a larger number of HB interactions than in its neat liquid state. Such a strong inter- ference of water into thymol structural organization strongly hinders the development of HB-mediated thymol hexamers that is the structural leitmotif in crystalline thymol. On the other hand, only 30 % of the present water molecule can engage into correlations with at least another water molecule, thus pre- venting the formation of an extended HB network among water molecules that would result incompat- ible with the otherwise hydrophobic environment. Evidences of mesoscopic organization are observed experimentally and confirmed by simulations: these are related to the clustering of thymol hydroxyl groups with water molecules, leading to the formation on polar nano-pools embedded into the apolar matrix. This new solvent extends the range of water based, type V, hydrophobic DES, and represents an additional contribution to the development of sustainable technologies, with appealing properties
Pressure-Induced Formation of Diblock Copolymer "Micelles" in Supercritical Fluids. A Combined Study by Small Angle Scattering Experiments and Mean-Field Theory. I: the Critical Micellization Density Concept
No full textPolymer and diblock copolymer phase separation in supercritical (SC) fluids was analyzed by developing a mean-field theory. A phenomenological hole theory that was extended to consider the polymer/solvent/vacancy pseudoternary mixture was used to describe the highly compressible SC fluid. In high density, the homogeneous phase was was favored while polymer aggregation was triggered by the reduced polymer-solvent contacts at low densities. The critical solvent density required for the onset of phase separation (CMD) decreased linearly with temperature, with its slope being tightly dependent on solvent and polymer properties
Solubility and solvation features of native cyclodextrins in 1-ethyl-3-methylimidazolium acetate
No full textThe comprehension of the mechanism entailing efficient solvation of cyclodextrins (CD) by green solvents is of great relevance to boost environmentally sustainable usages of smart supramolecular systems. Here, 1-ethyl-3-methylimidazolium acetate, an ecofriendly ionic liquid (IL), is considered as an excellent solvent for native CDs. This IL efficiently dissolves up to 40 wt.% β- and γ-CD already at ambient temperature and X-ray scattering indicates that CDs do not tend to detrimental flocculation under these drastic concentration conditions. Simulation techniques reveal the intimate mechanism of CD solvation by the ionic species: while the strong hydrogen bonding acceptor acetate anion interacts with CD's hydroxyl groups, the imidazolium cation efficiently solvates the hydrophobic CD walls via dispersive interactions, thus hampering CD's hydrophobic driven flocking. Overall the amphiphilic nature of the proposed IL provides an excellent solvation environment for CDs, through the synergic action of its components
The chemistry of acetone at extreme conditions by density functional molecular dynamics simulations
No full textDensity functional molecular dynamics simulations have been performed in the NVT ensemble (moles (N), volume (V) and temperature (T)) on a system formed by ten acetone molecules at a temperature of 2000 K and density ρ = 1.322 g cm−3 . These conditions resemble closely those realized at the interface of an acetone vapor bubble in the early stages of supercompression experiments and result in an average pressure of 5 GPa. Two relevant reactive events occur during the simulation:
the condensation of two acetone molecules to give hexane-2,5-dione and dihydrogen and the isomerization to the enolic propen-2-ol form. The mechanisms of these events are discussed in detail
Communication: Anion-specific response of mesoscopic organization in ionic liquids upon pressurization
No full textOne of the outstanding features of ionic liquids is their inherently hierarchical structural organization at mesoscopic spatial scales. Recently experimental and computational studies showed the fading of this feature when pressurising. Here we use simulations to show that this effect is not general: appropriate anion choice leads to an obstinate resistance against pressurization
Time-Resolving Analysis of Cryotropic Gelation of Water/Poly(vinyl alcohol) Solutions via Small-Angle Neutron Scattering
No full textThe structural transformations occurring in initially homogeneous aqueous solutions of poly(vinyl alcohol) (PVA) through application of freezing (-13 degrees C) and thawing (20 degrees C) cycles is investigated by time resolving small-angle neutron scattering (SANS). These measurements indicate that formation of gels of complex hierarchical structure arises from occurrence of different elementary processes, involving different length and time scales. The fastest process that could be detected by our measurements during the first cryotropic treatment consists of the crystallization of the solvent. However, solvent crystallization is incomplete, and an unfrozen liquid microphase more concentrated in PVA than the initial solution is also formed. Crystallization of PVA takes place inside the unfrozen liquid microphase and is slowed down because of formation of a microgel fraction. Water crystallization takes place in the early 10 min of the treatment of the solution at subzero temperatures, and although below 0 degrees C the PVA solutions used for preparation of cryogels should be below the spinodal curve, occurrence of liquid-liquid phase separation could not be detected in our experiments. Upon thawing, ice crystals melt, and transparent gels are obtained that become opaque in approximately 200 min, due to a slow and progressive increase of the size of microheterogeneities (dilute and dense regions) imprinted during the fast freezing by the crystallization of water. During the permanence of these gels at room temperature (for hours), the presence of a high content of water (higher than 85% by mass) prevents further crystallization of PVA. Crystallization of PVA, in turn, is resumed by freezing the gels at subzero temperatures, after water crystallization and consequent formation of an unfrozen microphase. The kinetic parameters of PVA crystallization during the permanence of these gels at subzero temperatures are the same shown by PVA during the first freezing step of the solutions
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