Solvatochromic rotaxane molecular shuttles

A strongly fluorescent bistable rotaxane is described in which the relative position of the macrocyclic ring with respect to a solvatochromic fluorophore gives a strong response in the spectral domain.     

Quantitative and sensitive detection of rare mutations using droplet-based microfluidics

Somatic mutations within tumoral DNA can be used as highly specific biomarkers to distinguish cancer cells from their normal counterparts. These DNA biomarkers are potentially useful for the diagnosis, prognosis, treatment and follow-up of patients. In order to have the required sensitivity and specificity to detect rare tumoral DNA in stool, blood, lymph and other patient samples, a simple, sensitive and quantitative procedure to measure the ratio of mutant to wild-type genes is required. However, techniques such as dual probe TaqMan(?) assays and pyrosequencing, while quantitative, cannot detect less than ～1% mutant genes in a background of non-mutated DNA from normal cells. Here we describe a procedure allowing the highly sensitive detection of mutated DNA in a quantitative manner within complex mixtures of DNA. The method is based on using a droplet-based microfluidic system to perform digital PCR in millions of picolitre droplets. Genomic DNA (gDNA) is compartmentalized in droplets at a concentration of less than one genome equivalent per droplet together with two TaqMan(?) probes, one specific for the mutant and the other for the wild-type DNA, which generate green and red fluorescent signals, respectively. After thermocycling, the ratio of mutant to wild-type genes is determined by counting the ratio of green to red droplets. We demonstrate the accurate and sensitive quantification of mutated KRAS oncogene in gDNA. The technique enabled the determination of mutant allelic specific imbalance (MASI) in several cancer cell-lines and the precise quantification of a mutated KRAS gene in the presence of a 200,000-fold excess of unmutated KRAS genes. The sensitivity is only limited by the number of droplets analyzed. Furthermore, by one-to-one fusion of drops containing gDNA with any one of seven different types of droplets, each containing a TaqMan(?) probe specific for a different KRAS mutation, or wild-type KRAS, and an optical code, it was possible to screen the six common mutations in KRAS codon 12 in parallel in a single experiment.     

In vitro antiprotozoal activity of extracts of five Turkish Lamiaceae species

The in vitro antiprotozoal activities of crude methanolic extracts from the aerial parts of five Lamiaceae plants (Salvia tomentosa, S. sclarea, S. dichroantha, Nepeta nuda subsp. nuda and Marrubium astracanicum subsp. macrodon) were evaluated against four parasitic protozoa, i.e. Trypanosoma brucei rhodesiense, T. cruzi, Leishmania donovani and Plasmodium falciparum. The cytotoxic potentials of the extracts on L6 cells were also evaluated. Melarsoprol, benznidazole, miltefosine, chloroquine and podophyllotoxin were used as reference drugs. All crude MeOH extracts showed antiprotozoal potential against at least three parasites, so they were dispersed in water and partitioned against n-hexane and chloroform to yield three subextracts that were screened in the same test systems. The n-hexane extract of N. nuda was the most active against T. brucei rhodesiense while the CHCl3 extracts of S. tomentosa and S. dichroantha showed significant activity against L. donovani. All organic extracts displayed in vitro antimalarial and moderate trypanocidal activities against T. cruzi with the n-hexane extract of S. sclarea being the most active against the latter. The extracts displayed low or no cytotoxicity towards mammalian L6 cells.     

An unsolvable hypoelliptic differential operator

It is proved that the differential operatorD ₁ +ix ₁ D ₂ ² is hypoelliptic everywhere, but is not locally solvable in any open set which intersects the linex ₁=0. Thus, this operator is not contained in the usual classes of hypoelliptic differential operators. The proofs involve certain properties of the characteristic Cauchy problem for the backward heat operator.     

DSC and X-ray diffraction studies of HxBPA

A detailed DSC study has been done for the substance HxBPA in the temperature range 170 to 380 K and the scheme of transitions in this compound has been deduced. From X-ray work, values for the smectic layer thickness and inplane intermolecular distance have been found in two of the liquid crystalline phases, P₂ and S_H.     

Existence of a utility in infinite dimensional partially ordered spaces

An example is given of a preference order on a space of denumerable algebraic dimension that has no utility, and necessary and sufficient conditions for the existence of utilities in various linear spaces are given. Research partially supported by the U.S. Office of Naval Research under contract No. N 62558-3586.     

Optimal iterative perturbation technique for solving Jeffery--Hamel flow with high magnetic field and nanoparticle

In this research paper, a different semi-analytical analysis of modified magnetohydrodynamic Jeffery--Hamel flow is conducted via the newly developed technique. We use the optimal iterative perturbation method with multiple parameters to see the effects of the magnetic field and nanoparticle on the Jeffery--Hamel flow. Comparing our new approximate solutions with some earlier works proved the excellent accuracy of the newly proposed technique. Convergence analysis of the proposed method is also discussed and error estimation is given to anticipate the accuracy of higher-order approximate solutions.     

Ion specific surface forces between membrane surfaces

Entities such as ion distributions and forces between lipid membranes depend on effects due to the intervening salt solution that have not been recognized previously. These specific ion or Hofmeister effects influence membrane fusion. A typical illustrative example is this: measurements of forces between double-chained cationic bilayers adsorbed onto molecularly smooth mica surfaces across different 0.6-2 mM salt solutions have revealed a large degree of ion specificity [Pashley et al. J. Phys. Chem. 1986, 90, 1637]. This has been interpreted in terms of very specific anion "binding" to the adsorbed bilayers, as it would too for micelles and other self-assembled systems. However, we show here that inclusion of nonelectrostatic (NES) or ionic dispersion potentials acting between ions and the two surfaces explains such "ion binding". The observed Hofmeister sequence for the calculated pressure without any direct ion binding is given correctly. This demonstrates the importance of a source of ion specificity that has been ignored. It is due to ionic physisorption caused by attractive NES ionic dispersion potentials. There appear to be some far reaching consequences for interpretations of membrane intermolecular interactions in salt solutions.     

Light harvesting and efficient energy transfer in a boron-dipyrrin (BODIPY) functionalized perylenediimide derivative

[reaction: see text] Click chemistry has been successfully applied in the synthesis of a bay region tetraboron-dipyrrin (BODIPY) appended perylenediimide (PDI). This light-harvesting molecule presents a large cross section for the absorption of light in the visible region. Excitation energy is efficiently channeled to the perylenediimide core. This novel antenna system is the first demonstration of the efficiency of energy transfer in a BODIPY-PDI bichromophoric system and appears to be highly promising for the design and synthesis of similar dendritic structures.     

Ionic conductivity of PVdF-co-HFP/LiClO4 in terms of free volume defects probed by positron annihilation lifetime spectroscopy

ABSTRACT

Polymers based on ionic conducting materials have important interest because of their potential applications in polymer electrolytes and membranes for fuel cell application. PVdF-co-HFP poly(viniliden-co-hexafluoropropylene) was chosen as a polymer matrix because of its high ionic conductivity and better mechanical properties. Polymer matrix composites were prepared with various amounts of LiClO₄ salt by a solution casting method. The sample-ionic conductivity measurements were recorded by AC impedance analyzer at different frequencies from 0.1?Hz to 20?MHz and at different temperatures from 273 to 373?K.

The changes of nanoscopic free volume and free volume fraction in these materials were investigated in terms of temperature from 273 to 373?K using Positron Annihilation Lifetime Spectroscopy (PALS) and Simha-Somcynsky (SS) Hole Theory. The free volume had a bump at about 3% in weight percentage of the salt and there is a slight increase after 10%. The effects of weight percentages of LiClO₄ and temperature were investigated. The mechanism of the ac ionic conductivity was presented in terms of the free volume models, however thermo-occupancy function justifies the best accurate representation of the data.