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51.
Laura Gagliardi Giorgio Orlandi Fernando Bernardi Alessandro Cembran Marco Garavelli 《Theoretical chemistry accounts》2004,111(2-6):363-372
In the present paper we report the results of a multiconfigurational computational study on potential-energy curves of azobenzene along the NN twisting to clarify the role of this coordinate in the decay of the S2(*) and S1(n*) states. We have found that there is a singlet state, S3 at the trans geometry, on the basis of the doubly excited configuration n2*2, that has a deep minimum at about 90° of twisting, where it is the lowest excited singlet state. The existence of this state provides an explanation for the short lifetime of S2(*) and for the wavelength-dependence of azobenzene photochemistry. We have characterized the S1(n*) state by calculating its vibrational frequencies, which are found to correspond to the recently observed transient Raman spectrum. We have also computed the potential-energy curve for the triplet T1(n*) at the density functional theory B3LYP level, which indicates that in this state the isomerization occurs along the twisting coordinate.Acknowledgement The financial support from MIUR (project Modellistica delle proprietà spettroscopiche di sistemi molecolari complessi funds ex 60% and project Dinamiche molecolari in sistemi di interesse chimico funds ex 40%), from the University of Bologna (Funds for Selected Research Topics) is gratefully acknowledged.Contribution to the Jacopo Tomasi Honorary Issue 相似文献
52.
Transmembrane anion transport mediated by halogen bonding and hydrogen bonding triazole anionophores
Laura E. Bickerton Alistair J. Sterling Paul D. Beer Fernanda Duarte Matthew J. Langton 《Chemical science》2020,11(18):4722
Transmembrane ion transport by synthetic anionophores is typically achieved using polar hydrogen bonding anion receptors. Here we show that readily accessible halogen and hydrogen bonding 1,2,3-triazole derivatives can efficiently mediate anion transport across lipid bilayer membranes with unusual anti-Hofmeister selectivity. Importantly, the results demonstrate that the iodo-triazole systems exhibit the highest reported activity to date for halogen bonding anionophores, and enhanced transport efficiency relative to the hydrogen bonding analogues. In contrast, the analogous fluoro-triazole systems, which are unable to form intermolecular interactions with anions, are inactive. The halogen bonding anionophores also exhibit a remarkable intrinsic chloride over hydroxide selectivity, which is usually observed only in more complex anionophore designs, in contrast to the readily accessible acyclic systems reported here. This highlights the potential of iodo-triazoles as synthetically accessible and versatile motifs for developing more efficient anion transport systems. Computational studies provide further insight into the nature of the anion-triazole intermolecular interactions, examining the origins of the observed transport activity and selectivity of the systems, and revealing the role of enhanced charge delocalisation in the halogen bonding anion complexes.Halogen and hydrogen bonding 1,2,3-triazole derivatives efficiently mediate anion transport across lipid bilayer membranes with unusual anion selectivity profiles. 相似文献
53.
New poly(d-glucaramidoamine)s induce DNA nanoparticle formation and efficient gene delivery into mammalian cells 总被引:1,自引:0,他引:1
In this report, four new poly(d-glucaramidoamine)s (1-4) have been designed to lower the toxicity of conventional polymeric nucleic acid delivery vehicles by incorporating a carbohydrate comonomer within a polyethylenimine (PEI)-like backbone. Polymers 1-4 were synthesized via polycondensation of esterified d-glucaric acid and four different amine-containing comonomers [diethylenetriamine (1), triethylenetetramine (2), tetraethylenepentamine (3), and pentaethylenehexamine (4)] in methanol. Viscometry and NMR studies suggest that the polymers are mostly linear (for 1-4, the alpha value in the Mark-Houwink-Sakurada equation = 0.6-0.7), thus indicating that polymerization occurs predominantly through the primary amines with a low degree of branching off the secondary amines. Results of gel electrophoresis shift assays show that polymers 1-4 bind pDNA at N/P ratios of 5, 3, 2, and 2, respectively. Also, dynamic light scattering and TEM experiments indicate that 1-4 compact DNA into nanoparticles (polyplexes) between 140 and 440 nm at an N/P ratio of 30. Furthermore, polyplexes formed with 1-4 deliver pDNA (plasmid DNA) containing the firefly luciferase reporter gene to BHK-21 cells in a nontoxic and highly efficient manner (as determined by luciferase gene expression). In particular, polymer 4 reveals very high delivery efficiency (equivalent to linear PEI). This result may be due in part to the "proton sponge" hypothesis proposed by Behr et al. Polymers containing amines that are protonated in the endosomal pH range (between about 7.4-5.0) reveal enhanced gene delivery profiles. 相似文献
54.
Maria Cristina Righetti Maria Laura Di Lorenzo Elpidio Tombari 《European Polymer Journal》2007,43(11):4726-4738
The isothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) (PBT) in binary blends with poly(ε-caprolactone) (PCL) was investigated as a function of PCL molecular mass by differential scanning calorimetry and optical microscopy. The components are miscible in the melt when oligomeric PCL (Mw = 1250) is blended with PBT, whereas only partial miscibility was found in mixtures with higher molecular mass (Mw = 10,000 and 50,000). The equilibrium melting point of PBT in the homopolymer and in blends with PCL was determined through a non-linear extrapolation of the Tm = f(Tc) curve. The PBT spherulitic growth rate and bulk crystallization rate were found to increase with respect to plain PBT in blends with PCL1250 and PCL10000, whereas addition of PCL50000 causes a reduction of PBT solidification rate. The crystallization induction times were determined by differential scanning calorimetry for all the mixtures through a blank subtraction procedure that allows precise estimation of the crystallization kinetics of fast crystallizing polymers. The results have been discussed on the basis of the Hoffman-Lauritzen crystallization theory and considerations on both the transport of chains towards the crystalline growth front and the energy barrier for the formation of critical nuclei in miscible and partially miscible PBT/PCL mixtures are widely debated. 相似文献
55.
Dupont A Eastoe J Martin L Steytler DC Heenan RK Guittard F Taffin de Givenchy E 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):9960-9967
Hybrid fluorocarbon-hydrocarbon (F-H) sulfate surfactants are shown to be efficient stabilizers in water-in-CO2 (w/c) microemulsions. The chain structure and F-H ratio affect the regions of P-T phase stability and aggregation structure in these w/c phases. High-pressure near-infrared spectroscopy and small-angle neutron scattering measurements of microemulsified water provide evidence for the stabilization of w/c microemulsion droplets. The relative lengths of the two chains were found to influence the favored aggregation structure: for symmetric chain surfactants (F8H8, F7H7) spherical reverse micelles are present, but for asymmetric chain surfactants (F7H4, F8H4) extended cylinder aggregates form. These changes in aggregation are consistent with different surfactant packing parameters owing to the controlled variations in molecular structure. Furthermore, the general order of w/c phase transition pressures (F8H8 < F7H7 and F8H4 < F7H4) is in line with estimations of surfactant fractional free volume, as proposed by Johnston et al. (J. Phys. Chem. B 2004, 108, 1962-1966). Studies of adsorption at the poly(dimethylsiloxane)-water interface are shown to be valuable for assessing the CO2-philicity of new surfactants. All in all, the symmetric F8H8 and F7H7 analogues are seen to be the most efficient compounds from this class for applications in CO2. 相似文献
56.
Capillary sodium dodecyl sulfate (SDS)-DALT electrophoresis (SDS-DALT-CE) refers to CE separation of proteins based on their size; DALT is the abbreviation for Dalton, the unit used to describe molecular weight. In this work, seven proteins from 18 to 116 kDa were denatured by SDS, labeled by 3-(2-furoyl) quinoline-2-carboxaldehyde, separated by SDS-DALT-CE in polyethylene oxide sieving matrix, and detected by laser-induced fluorescence (LIF) in a sheath flow cuvette. This method was combined with detergent differential fractionation, which is a protein fractionation method using a series of detergent-containing buffers to sequentially extract protein fractions from cells, to analyze the proteins in HT29 human colon adenocarcinoma cells. In addition, on-column labeling was demonstrated for protein analysis by SDS-DALT-CE with LIF, and applied to analysis of proteins in a single HT29 cancer cell. Most proteins had molecular masses from 10 to 120 kDa. Similar protein profiles were obtained for single cells and protein extract of a large cell population. 相似文献
57.
Darío Gmez Marina Dos Santos Fabin Fujiwara Griselda Polla Julieta Marrero Laura Dawidowski Patricia Smichowski 《Microchemical Journal》2007,85(2):276-284
A study was undertaken to evaluate the distribution of Al, As, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn in fly ashes collected in the electrostatic precipitator of a thermal power plant in San Nicolás (Argentina). Five samples were collected during one week of operation. For the fractionation, the scheme applied consisted in extracting the elements in four fractions namely (i) soluble and exchangeable elements; (ii) carbonates, oxides and reducible elements; (iii) bound to sulfidic metals; and (iv) residual elements. Metals and metalloids at μg g− 1 level were determined in each fraction by inductively coupled plasma optical emission spectrometry (ICP OES). For validation, a standard reference material (SRM 1633 coal fly ash) from NIST was subjected to the same chemical sequential extraction procedure that the samples. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the major minerals present in the matrix. Total analyte concentration (in μg g− 1) varied from 10.6 for Pb to 17,622 for Al. Minimum and maximum concentrations (in μg g− 1) found in individual samples in the four fractions were: Al, 92.7–9668; As, < 0.3–143; Cr, 2.0–10.4; Cu, < 0.2–35.6; Fe, < 0.3–4992; Mn, < 0.1–128; Ni, < 0.3–139; Pb, < 0.5–9.1; Ti, < 0.3–2243; V, 17.0–112.9; and Zn, < 0.1–68.2. The leachability of the 11 elements under study proved to be different. Low percentages of Al (1%), V (7%) and Cr (8%) were detected in the most bioavailable fraction. Arsenic was found to be most abundant in the non-silicate phase, represented by the second and third fractions, while Cr, Fe, Ni, Pb and Zn were mostly associated to the residual fraction. 相似文献
58.
Laura Bertani 《Journal of Geometry》1980,15(2):158-169
In this paper,suggested by André's papers ([2), [3]), we construct geometrical structures (X,?,//}) where X is a finite set of points, ? is a set of lines, and // is an equivalence relation on ?. These constructions are made starting with a finite and not empty set X and a permutation group G which is 2-transitive on X and such that the stabilizer of two distinct points of X is different from the identical subgroup. We look for conditions such that the structure (X, ?) is a (3,q)-Steiner system. We remember that a (3,q)-Steiner system is a pair (X,B), where X is a set of elements (called points), B is a system of subsets of X (called blocks), such that:
- every block contains q points exactly;
- given three distinct points x,y,z of X, there is exactly one subset of X belonging to B and containing x,y,z.
59.
60.
Roitershtein D Domingos A Pereira LC Ascenso JR Marques N 《Inorganic chemistry》2003,42(23):7666-7673
Reaction of yttrium and lanthanum trichloride with 1 equiv of sodium or potassium hydrotris(3,5-dimethylpyrazolyl)borate and 1 equiv of 2,2'-bipyridine gives good yields of the complexes [MCl(2)(Tp(Me2))(C(10)H(8)N(2))] (M = Y (1), La (2)). The analogous compounds with 1,10-phenanthroline, [MCl(2)(Tp(Me2))(C(12)H(8)N(2))] (M = Y (3), La (4)), have been obtained by a similar procedure. The solid-state structures of 2-4 were determined by single-crystal X-ray diffraction and revealed that the compounds are all seven-coordinate with capped octahedral geometry. In contrast, reaction of yttrium trichloride with 1 equiv of sodium hydrotris(3,5-dimethylpyrazolyl)borate in the presence of 1 equiv of neocuproine affords [YCl(3)(Tp(Me2))][Na(neoc)(3))] (5). Compounds 1 and 2 provide an entry for the synthesis of complexes containing the bipyridyl ligand in a radical anionic form or in a dianionic form. Reaction of 1 and 2 with an excess of sodium amalgam gives [Y(Tp(Me2))(bipy)(THF)(2)] (6) and [La(Tp(Me2))(2)(bipy)] (7), respectively. The structures of both compounds have been determined by X-ray crystallography. Compound 7 can be oxidized with iodine to give [La(Tp(Me2))(2)(bipy)]I (8). 相似文献