Carbosilane dendrimers NN8 and NN16 form a stable complex with siGAG1

A new mechanism of gene expression inhibition has been discovered as RNA interference, in which the ability of double-stranded RNA to stimulate specific degradation of an mRNA target with a complementary sequence to one of the double-stranded RNA strands. Water-soluble carbosilane dendrimers containing ammonium or amine groups at their periphery are biocompatible molecules that may be good candidates as non-viral carriers of small interfering RNA. In studying the formation of complex between anti-HIV siRNA siGAG1 and carbosilane dendrimers NN8 and NN16 by circular dichroism, fluorescence, and zeta-potential, the size of nanoparticles formed has been estimated by dynamic light scattering. At a charge ratio of 1:3-4 (siGAG1:dendrimer), the dendriplexes formed were in the size range of 250-350 nm.     

Complete classification of surfaces with a canonical principal direction in the Euclidean space \mathbb{E} 3

In the present paper we classify all surfaces in $ \mathbb{E} $ \mathbb{E} ³ with a canonical principal direction. Examples of this type of surfaces are constructed. We prove that the only minimal surface with a canonical principal direction in the Euclidean space $ \mathbb{E} $ \mathbb{E} ³ is the catenoid.     

Time-resolved studies on the photoisomerization of a phenylene-silylene-vinylene type compound in its first singlet excited state

In femtosecond laser-flash photolysis experiments, the first singlet excited state of trans-ST, ((E,E)-{1,4-bis(2-dimethylphenylsilyl)ethenyl}benzene) showed a strong S1(π,π^?)-Sn absorption band at 540 nm in acetonitrile and at 550 nm in hexane. The lifetime of this state was determined to be 13.2±2.0 and 11.1±1.5 ps, respectively. Intersystem crossing was shown not to be a principal route for the deactivation of this S1 state of trans-ST. Evidence for this conclusion involved two complementary nanosecond laser-flash photolysis experiments. In one experiment involving direct excitation, no transient absorption spectrum was detected in the 350-650 nm spectral range. Yet, in the second experiment, on triplet sensitization, using xanthone, a transient absorption at 400 nm was tentatively assigned to the triplet state absorption of trans-ST. Photoisomerization was monitored in nanosecond time-resolved bleaching experiments. From these experiments the trans-cis photoisomerization quantum yield was determined to be 0.23 on direct trans-ST excitation. In a xanthone-sensitized stationary-state excitation experiment, the trans-cis isomerization quantum yield was determined to be 0.32. The main deactivation route of trans-ST in its S1 state is repopulation of the ground state directly through internal conversion or with the intermediacy of conformers with twisted geometry.     

A mathematical model for the dynamics and synchronization of cows

We formulate a mathematical model for the daily activities of a cow (eating, lying down, and standing) in terms of a piecewise linear dynamical system. We analyze the properties of this bovine dynamical system representing the single animal and develop an exact integrative form as a discrete-time mapping. We then couple multiple cow “oscillators” together to study synchrony and cooperation in cattle herds. We comment on the relevant biology and discuss extensions of our model. With this abstract approach, we not only investigate equations with interesting dynamics but also develop biological predictions. In particular, our model illustrates that it is possible for cows to synchronize less when the coupling is increased.     

Characterization,optical and thermal properties of new azomethines based on heptadecafluoroundecyloxy benzaldehyde

New thermotropic liquid crystals containing a long alkoxysemiperfluorinated chain (-O-(CH₂)₃-(CF₂)₇-CF₃), one linking unit in mesogenic cores (HC=N-) and different functional end-groups such as 4-hexadecyl-, 4-n-hexadecyloxy- chain, or biphenyl-4-carbonitrile, 4-diazenyl-N,N-dimethylbenzene or pyren were synthesized via a one-step route. The methods of nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), ultraviolet–visual (UV-vis) and photoluminescence (PL) spectroscopy as well as differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) were used. The absorption (UV-vis) and PL features of all compounds are documented. The amine had an effect on the mesomorphic properties of the azomethines. An enantiotropic smectic phase was observed for all of the systems studied. As a result of DSC and POM investigations, it is shown that liquid crystalline properties of the azomethines exhibit a strong dependence of the end-groups. The mesomorphic behaviour of the compounds was investigated also by FTIR(T) and UV-vis(T) spectroscopy. Current–voltage measurements were performed on an ITO/compound/Alq₃/Al device.     

Application of normal-phase high-performance liquid chromatography followed by gas chromatography for analytics of diesel fuel additives

The paper presents the results of investigations on new procedures of determination of selected cleaning additives in diesel fuel. Two procedures: one-step analysis using gas chromatography with flame ionization detection (GC-FID) or mass spectrometry (GC-MS) and a two-step procedure in which normal-phase high-performance liquid chromatography (NP-HPLC) was used for preliminary separation of the additives, were compared. The additive fraction was collected using either simple elution or eluent backflush. Final determinations were performed by GC-FID and GC-MS. The studies revealed that it was impossible to determine the investigated analytes by one-step procedures, i.e. by using solely HPLC or GC. On the other hand, the use of a two-step procedure ensures reproducible results of determinations, and the limits of quantitation are, depending on the method of fraction collection by HPLC, from 1.4–2.2 ppm (GC-MS in SIM mode) to 9.6–24.0 ppm (GC-FID). Precision and accuracy of the developed procedures are compared, and possible determination errors and shortcomings discussed.

Phosphonate-Mediated Synthesis of Biologically Active Cyclopentanones and Cyclopentenones

The synthesis and reactivity of 3-(phosphorylmethyl)cyclopent-2-enones as well as a complete desymmetrization of meso -tartaric acid are discussed as a platform for developing the synthesis of racemic rosaprostol and enantiomeric forms of prostaglandin B 1 methyl ester, isoterrein, and neplanocin A.     

New Free Radical Syntheses and Reactions of Functionalized Phosphonates

Abstract

Reactions of α,β and β-phosphonyl radicals with alkenes leading to the formation of the P(C)_n-C bonds (n=1 ÷ 3) and illustrated by a synthesis of Methylenomycin B are described. Desulfenylation and deselenylation reactions of α-heterosubstituted α-phosphoryl sulfides and selenides are also presented.     

A New Asymmetric Synthesis of β-Aminophosphonic Acids

Addition of α-phosphonate carbanions to (S)-sulfinimines 2 gives N-sulfinyl-β-aminophosphonates 3 with a high diastereoselectivity (up to 10:1). The major diastereomer of 3 (R=Ph) was converted into (+)-(R)-β-amino-β-phenylethanephosphonic acid 5.     

Studies on hydrogen diffusivity in iron aluminides using the Devanathan–Stachurski method

An electrolytic method for cathodic hydrogen saturation developed by Devanathan and Stachurski was successfully used to study hydrogen diffusivity in iron aluminides. Both an appropriate electrolyte and a saturating current density are required for this method. A proper form of the saturation curve was only obtained with 35% NaCl electrolyte, which removed the oxide film blocking hydrogen penetration without further corrosive destruction of the iron aluminide. The optimum saturation current density for determining the most reliable diffusivity was 1.91 A/cm², yielding D_eff,H = 4.81 × 10⁻⁶ cm²/s for Fe–40 at.% Al.