Fluorescence study of the fluidity and cooperativity of the phase transitions of zwitterionic and anionic liposomes confined in sol-gel glasses

The current work makes use of different fluorescent reporter molecules and fluorescent spectroscopic techniques to characterize the thermotropic, physical, and dynamical properties of large unilamellar liposomes formed from either 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-glycerol] (DMPG) encapsulated in sol-gel matrixes. In particular, cooperativity of the phase transition is analyzed from steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), the interfacial properties are studied by measuring the spectral shift of Laurdan, and the structural organization (heterogeneity) of the lipid bilayer is determined from the fluorescence lifetime of trans-parinaric acid (t-PnA). In addition, information regarding order and dynamical properties in the bulk hydrophobic core is obtained from time-resolved fluorescence anisotropy of t-PnA and 3-(4-(6-phenyl)-1,3,5-hexatrienyl)-phenylpropionic acid (PA-DPH). The spectroscopic study reveals that upon encapsulation, the basic thermodynamic properties as well as the fluidity of the lipid bilayer practically remain intact for DMPG liposomes but not for DMPC liposomes, whose lipid bilayer exhibits large gel-fluid heterogeneity. On the basis of these experimental results, electrostatic interactions between phospholipid polar heads and the porous surface of the host matrix seem to play a capital role for the preservation of the structural integrity of encapsulated bilayer.     

Multi-capillary column-ion mobility spectrometry: a potential screening system to differentiate virgin olive oils

The potential of a headspace device coupled to multi-capillary column-ion mobility spectrometry has been studied as a screening system to differentiate virgin olive oils (“lampante,” “virgin,” and “extra virgin” olive oil). The last two types are virgin olive oil samples of very similar characteristics, which were very difficult to distinguish with the existing analytical method. The procedure involves the direct introduction of the virgin olive oil sample into a vial, headspace generation, and automatic injection of the volatiles into a gas chromatograph-ion mobility spectrometer. The data obtained after the analysis by duplicate of 98 samples of three different categories of virgin olive oils, were preprocessed and submitted to a detailed chemometric treatment to classify the virgin olive oil samples according to their sensory quality. The same virgin olive oil samples were also analyzed by an expert’s panel to establish their category and use these data as reference values to check the potential of this new screening system. This comparison confirms the potential of the results presented here. The model was able to classify 97% of virgin olive oil samples in their corresponding group. Finally, the chemometric method was validated obtaining a percentage of prediction of 87%. These results provide promising perspectives for the use of ion mobility spectrometry to differentiate virgin olive oil samples according to their quality instead of using the classical analytical procedure.     

Concerted aminolysis of diaryl carbonates: Kinetic sensitivity on the basicity of the nucleophile,nonleaving group,and nucleofuge

The kinetics of the reactions of 4‐methylphenyl, phenyl, and 4‐chlorophenyl 2,4,6‐trinitrophenyl carbonates ( 1 , 2 , and 3 , respectively) with a series of anilines and secondary alicyclic (SA) amines has been carried out spectrophotometrically in 44 wt% ethanol–water, at 25.0°C, ionic strength 0.2 M. The Brønsted plots (statistically corrected) for the reactions of carbonates 1 – 3 with anilines and SA amines were linear with slopes (β_N) in the range of 0.69–0.78 and 0.45–0.48, respectively, attributed to a concerted mechanism. The negative values found for the sensitivity of log k_N to the basicity of the nonleaving (β_nlg) and leaving (β_lg) groups are discussed. Anilines are more reactive than isobasic SA amines, probably because of the greater steric hindrance offered by the latter. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 604–611, 2012     

Coumarin derivatives for dye sensitized solar cells: a TD-DFT study

Time dependent density functional theory (TD-DFT) calculations have been carried out to study the electronic structure and the optical properties of five coumarin based dyes: C343, NKX-2311, NKX-2586, NKX-2753 and NKX-2593. We have found out that the position and width of the first band in the electronic absorption spectra, the absorption threshold and the LUMO energy with respect to the conduction band edge are key parameters in order to establish some criteria that allow evaluating the efficiency of coumarin derivatives as sensitizers in Dye Sensitized Solar Cells (DSSC). Those criteria predict the efficiency ordering for the coumarin series in good agreement with the experimental evidence. Presumably, they might be used in the design of new efficient organic based DSSC.     

Monochromatic Paths and at Most 2-Coloured Arc Sets in Edge-Coloured Tournaments

We call the tournament T an m-coloured tournament if the arcs of T are coloured with m-colours. If v is a vertex of an m-coloured tournament T, we denote by ξ(v) the set of colours assigned to the arcs with v as an endpoint. In this paper is proved that if T is an m-coloured tournament with |ξ(v)|≤2 for each vertex v of T, and T satisfies at least one of the two following properties (1) m≠3 or (2) m=3 and T contains no C₃ (the directed cycle of length 3 whose arcs are coloured with three distinct colours). Then there is a vertex v of T such that for every other vertex x of T, there is a monochromatic directed path from x to v. Received: April, 2003     

Richardson’s Theorem in <Emphasis Type="Italic">H</Emphasis>-coloured Digraphs

Let H be a digraph possibly with loops and D a finite digraph without loops whose arcs are coloured with the vertices of H (D is an H-coloured digraph). The sets V(D) and A(D) will denote the sets of vertices and arcs of D respectively. A directed path W in D is an H-path if and only if the consecutive colors encountered on W form a directed walk in H. A set \(N\subseteq \hbox {V}(D)\) is an H-kernel if for every pair of different vertices in N there is no H-path between them, and for every vertex \(u\in \hbox {V}(D){\setminus }N\) there exists an H-path in D from u to N. Let D be an m-coloured digraph. The color-class digraph of D, denoted by \({\mathscr {C}}_C(D\)), is the digraph such that: the vertices of the color-class digraph are the colors represented in the arcs of D, and \((i,j) \in A({\mathscr {C}}_C(D\))) if and only if there exist two arcs namely (u, v) and (v, w) in D such that (u, v) has color i and (v, w) has color j. Let \(W=(v_0, \ldots , v_n\)) be a directed walk in \({\mathscr {C}}_C(D)\), with D an H-coloured digraph, and \(e_i = (v_{i},v_{i+1})\) for each \(i \in \{0, \ldots ,n-1\}\). Let \(I = \{i_1, \ldots , i_k\}\) a subset of \(\{0, \ldots , n-1\}\) such that for 0 \(\le s \le n-1\), \(e_s \in \hbox { A}(H^c)\) if and only if \(s \in I\) (where \(H^c\) is the complement of H), then we will say that k is the \(H^c\)-length of W. Since V(\({\mathscr {C}}_C(D)) \subseteq \hbox {V}(H)\), the main question is: What structural properties of \({\mathscr {C}}_C(D)\), with respect to H, imply that D has an H-kernel? In this paper we will prove the following: If \({\mathscr {C}}_C(D)\) does not have directed cycles of odd \(H^c\)-length, then D has an H-kernel. Finally we will prove Richardson’s theorem as a direct consequence of the previous result.