Solvent effects on the three-photon absorption cross-section of a highly conjugated fluorene derivative

Herein, we report the study of the three-photon absorption cross-section dependence on solvents parameters for a highly conjugated organic dye, 2,2'-(4,4'-(1E,1'E)-2,2'-(9,9-didecyl-9H-fluorene-2,7-diyl) bis(ethene-2,1-diyl)bis(4,1-phenylene))dibenzo[d]thiazole (A-pi-pi-pi-A). The three-photon absorption cross-section was measured for this organic dye in solution in four different solvents with polarity function, Deltaf between 0.162 and 0.247. The experiments show how the solvent's reorientation of the electrons and polarity contribute to the 3PA cross-section. Multiphoton-absorption experiments of A-pi-pi-pi-A in all four different solvents were performed with a tunable OPG pumped by a 25 picosecond Nd-YAG laser.     

The impact of the pi-electron conjugation length on the three-photon absorption cross section of fluorene derivatives

The three-photon absorption cross sections of three different fluorene derivatives, with extended pi-electron conjugation lengths was experimentally measured and compared with shorter pi-electron conjugation length analogs. The effect of the conjugation length on the three-photon absorption cross section sigma(3) (') of this family of molecules has been elucidated. It is demonstrated that sigma(3) (') of the asymmetric compound D-pi-pi-pi-A is 6.6 times larger than its shorter configuration D-pi-A, while for the symmetric compounds D-pi-pi-pi-D and A-pi-pi-pi-A a two-fold enhancement was found relative to their shorter conjugation length analogs. Measurements of the three-photon excitation of these compounds in THF solution (10(-3)M) were accomplished with a tunable optical pulse generation pumped by a 25 ps Nd-YAG laser.     

Silver–titanium dioxide nanocomposites as effective antimicrobial and antibiofilm agents

Recent studies have revealed the existence of liver cancer stem cells (CSCs). Therefore, there is an urgent need for new and effective treatment strategies specific to liver CSCs. In this work, the poly(d,l-lactide-coglycolide) nanoparticles containing paclitaxel were prepared by emulsification-solvent evaporation method. The nanoparticles decorated with anti-CD133 antibody, termed targeted nanoparticles, were prepared by carbodiimide chemistry for liver CSCs. The physicochemical characteristics of the nanoparticles (i.e., encapsulation efficiency, particle size distribution, morphology, and in vitro release) were investigated. Cellular uptake and accumulation in tumor tissue of nanoparticles were observed. To assess anti-tumor activity of nanoparticles in vitro and in vivo, cell survival assay and tumor regression study were carried out using liver cancer cell lines (Huh7 and HepG2) and their xenografts. Particle size of targeted nanoparticles was 429.26 ± 41.53 nm with zeta potential of ?11.2 mV. Targeted nanoparticles possessed spherical morphology and high encapsulation efficiency (87.53 ± 5.9 %). The accumulation of targeted nanoparticles depends on dual effects of passive and active targeting. Drug-loaded nanoparticles showed cytotoxicity on the tumor cells in vitro and in vivo. Targeted nanoparticles resulted in significant improvement in therapeutic response through selectively eliminating CD133 positive subpopulation. These results suggested that the novel nanoparticles could be a promising candidate with excellent therapeutic efficacy for targeting liver CSCs.     

Validation of protein structural models using THz spectroscopy: a promising approach to solve three-dimensional structures

Terahertz (THz) spectroscopy is a promising technique for the study of protein structure and internal flexibility. Here, we used THz spectroscopy and molecular modeling for bovine serum albumin (BSA) structure investigation. BSA molecule was built using homology modeling methods and 30 different more relaxed models were obtained by molecular dynamics simulations of the hydrated protein. As the experimental and simulated THz spectra are linear, we compared them by comparing the slopes of the lines that fit them. Six BSA structures had slope values in the range given by the slope of the experimental spectrum $\pm $  0.2 and a total of sixteen BSA structures had slope values in the 0.6 interval near the experimental slope value. BSA average structures were calculated over the six and the sixteen identified BSA molecules. Based on the similarity with the crystal structure of BSA, we validated the average structure calculated over the sixteen BSA conformations. The comparison with the crystal structure showed that the structure validated using THz spectroscopy is a coarse model of BSA, as its root-mean-square deviation relative to the crystal structure is 1.9 Å. The regions from our model that present the highest deviation from the crystal structure are exterior loops. The results presented here show that using THz spectroscopy and molecular modeling is a promising approach to determine the structure of proteins.     

Laser prepared organic heterostructures based on star-shaped arylenevinylene compounds

This paper presents some studies about the preparation by matrix-assisted pulsed laser evaporation (MAPLE) technique of organic bulk heterojunctions made from the mixture of a star-shaped arylenevinylene compound, 4,4′,4″-tris[(4′-diphenylamino)styryl] triphenylamine as donor and fullerene derivative, [6, 6]-phenyl C61 butyric acid butyl ester, as acceptor, in the weight ratio 1:2. The mixed layer has been characterized by spectroscopic (UV–Vis, Fourier transform infrared) and microscopic (AFM) methods, and the effects of the deposition conditions (number of pulses) and of a buffer layer of poly(aniline-co-aniline propane sulfonic acid) or poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) have been analyzed. The study of the electrical properties has revealed a typical solar cell behavior for the heterostructure glass/ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/4,4′,4″-tris[(4′-diphenylamino)styryl] triphenylamine: [6, 6]-phenyl C61 butyric acid butyl ester/Al, confirming that MAPLE could be an adequate method for the preparation of active layer based on bulk heterojunction for solar cells.     

A new ONO3- trianionic pincer-type ligand for generating highly nucleophilic metal-carbon multiple bonds

Appending an amine to a C═C double bond drastically increases the nucleophilicity of the β-carbon atom of the alkene to form an enamine. In this report, we present the synthesis and characterization of a novel CF(3)-ONO(3-) trianionic pincer-type ligand, rationally designed to mimic enamines within a metal coordination sphere. Presented is a synthetic strategy to create enhanced nucleophilic tungsten-alkylidene and -alkylidyne complexes. Specifically, we present the synthesis and characterization of the new CF(3)-ONO(3-) trianionic pincer tungsten-alkylidene [CF(3)-ONO]W═CH(Et)(O(t)Bu) (2) and -alkylidyne {MePPh(3)}{[CF(3)-ONO]W≡C(Et)(O(t)Bu)} (3) complexes. Characterization involves a combination of multinuclear NMR spectroscopy, combustion analysis, DFT computations, and single crystal X-ray analysis for complexes 2 and 3. Exhibiting unique nucleophilic reactivity, 3 reacts with MeOTf to yield [CF(3)-ONO]W═C(Me)(Et)(O(t)Bu) (4), but the bulkier Me(3)SiOTf silylates the tert-butoxide, which subsequently undergoes isobutylene expulsion to form [CF(3)-ONO]W═CH(Et)(OSiMe(3)) (5). A DFT calculation performed on a model complex of 3, namely, [CF(3)-ONO]W≡C(Et)(O(t)Bu) (3'), reveals the amide participates in an enamine-type bonding combination. For complex 2, the Lewis acids MeOTf, Me(3)SiOTf, and B(C(6)F(5))(3) catalyze isobutylene expulsion to yield the tungsten-oxo complex [CF(3)-ONO]W(O)((n)Pr) (6).     

Charge density waves in nanocrystalline thin films of blue bronze K0.3MoO3

Thin granular films of charge density wave (CDW) system K_0.3MoO₃ were prepared by pulsed laser deposition and investigated by various standard characterization methods such as GI-XRD, electric transport, TOF-ERDA, AFM and UV–visible spectroscopy. While all these methods indicate that the thin films consist of nanometer grains of K_0.3MoO₃, it is only the non-destructive femtosecond time-resolved spectroscopy (fsTRS) that demonstrates the charge density wave nature of the ground state and therefore proves directly the presence of K_0.3MoO₃. Furthermore, the comparison of the fsTRS data obtained in thin films and in single crystals shows the reduction of the charge density wave transition temperature and of the photoinduced signal strength in granular thin films with respect to single crystals, which is attributed to the granularity and crystal growth morphology. Our results establish fsTRS technique as the essential tool for the detection and characterization of complex ground states in nano-sized systems.     

Random repeated quantum interactions and random invariant states

We consider a generalized model of repeated quantum interactions, where a system ${\mathcal{H}}$ is interacting in a random way with a sequence of independent quantum systems ${\mathcal{K}_n, n \geq 1}$ . Two types of randomness are studied in detail. One is provided by considering Haar-distributed unitaries to describe each interaction between ${\mathcal{H}}$ and ${\mathcal{K}_n}$ . The other involves random quantum states describing each copy ${\mathcal{K}_n}$ . In the limit of a large number of interactions, we present convergence results for the asymptotic state of ${\mathcal{H}}$ . This is achieved by studying spectral properties of (random) quantum channels which guarantee the existence of unique invariant states. Finally this allows to introduce a new physically motivated ensemble of random density matrices called the asymptotic induced ensemble.     

Palladium(II)-catalyzed enyne cyclization strategies toward the podophyllotoxin ring system

A functionally enriched ABCD ring system of podophyllotoxin was generated through Pd(II)-templated cyclization of an alkynoic alkene, prepared in five steps from commercially available 6-bromopiperonal. This research expands upon the recent carboesterification methodology of Dong et al. (Angew. Chem., Int. Ed. 2009, 48, 9690–9692) by the application of PdCl₂(MeCN)₂, LiCl, and CuCl₂ conditions, which yielded the desired podophyllotoxin scaffold with an embedded vinyl chloride moiety. Likewise, these conditions were successfully applied to a propargylic alkene prepared in three steps from 6-bromopiperonal. The resulting product contains the ABCD ring system of podophyllotoxin, but substitutes a D-ring furan for the D-ring lactone. Application of the recent methodology of Lu et al. (J. Org. Chem. 1995, 60, 1160–1169) on a related 1,6-enyne substrate led to functionalized α-methylene γ-butyrolactones instead (Pd₂(dba)₃·CHCl₃, LiBr, and CuBr₂). The latter conditions applied to an alkynoic alkene afforded the ABCD ring system of podophyllotoxin with a vinyl bromide group. These vinyl halides allow for derivatization at a critical juncture in order to access novel podophyllotoxin analogs.     

Synthesis of dipeptide isosteres by cross-metathesis

This work describes the attachment of two amino acid derivatives by olefin cross-metathesis using Grubbs' second generation catalyst. They were connected at the carboxyl termini. In addition, a cyclic dilactam scaffold was used, which reacted with only a fraction of the amino acid derivatives. The remaining fraction coupled directly coupled with no scaffold. This highly trans-selective double attachment resulted in the cross-metathesis of a variety of amino acids in a single reaction.