Synthesis of a new photoactive nanovehicle: a nanoworm

A nanovehicle with a new photoactive moiety has been synthesized. The incorporation of the azobenzene chassis allows for potential wormlike movement accompanying the rolling behavior of the wheels. Two versions, the fullerene-wheeled and carborane-wheeled nanoworms, were synthesized to examine the solution-based photoisomerization yields of the chassis.     

Inverse-phosphocholine lipids: a remix of a common phospholipid

Zwitterionic inverse-phosphocholine (iPC) lipids contain headgroups with an inverted charge orientation relative to phosphocholine (PC) lipids. The iPC lipid headgroup has a quaternary amine adjacent to the bilayer interface and a phosphate that extends into the aqueous phase. Neutral iPC lipids with ethylated phosphate groups (CPe) and anionic iPC lipids nonethylated phosphate groups (CP) were synthesized. The surface potential of CPe liposomes remains negative across a broad pH range and in the presence of up to 10 mM Ca(2+). CP liposomes aggregate in the presence of Ca(2+), but at a slower rate than other anionic lipids. Hydrolysis of CP lipids by alkaline phosphatases generates a cationic lipid. CPe liposomes release encapsulated anionic carboxyfluorescein (CF) 20 times faster than PC liposomes and release uncharged glucose twice as fast as PC liposomes. As such, iPC lipids afford a unique opportunity to investigate the biophysical and bioactivity-related ramifications of a charge inversion at the bilayer surface.     

Architecture of a validated microRNA::target interaction

MicroRNAs are small approximately 22 nucleotide regulators of numerous biological processes and bind target gene messenger RNAs to control gene expression. The C. elegans microRNA let-7 and its target lin-41 were the first microRNA::target interaction to be validated in vivo. let-7 molecules form imperfect duplexes with two required let-7 complementary sites in the lin-41 3' UTR. Here, we show that base pairing at both the 5' and 3' ends of the let-7 binding site, as well as the presence of unpaired RNA residues in the predicted duplexes, are required for lin-41 downregulation. In this study, our model for microRNA::target interactions also demonstrates that the context of a microRNA binding can be critical for function, revealing an unforeseen complexity in microRNA::target interactions.     

Thermal properties of a disc-like compound benzene-hexa-n-pentanoate: a precursor of a discotic mesogen

The heat capacity of a disk-like compound, benzene-hexa-n-pentanoate (BH5), a precursor of a discotic mesogen, has been measured by adiabatic calorimetry between 13 and 390 K. BH5 showed four different crystalline phases, but no liquid crystalline phase. Molar entropy and transition entropies were determined and compared with those of other homologues (BH6, BH7, and BH8). An odd-even effect with respect to the number of carbon atoms in the alkyl chain was observed for the cumulative entropies of the phase transitions occurring in the solid state. This effect is discussed by comparing with data for the n-alkanes. The molar entropies of the crystalline state, especially below 250 K, exhibited a peculiar 'pairing effect' between BH(2m- 1) and BH(2m), where m is an integer.     

Thermal properties of a disc-like compound benzene-hexa-n-pentanoate: a precursor of a discotic mesogen

The heat capacity of a disk-like compound, benzene-hexa-n-pentanoate (BH5), a precursor of a discotic mesogen, has been measured by adiabatic calorimetry between 13 and 390 K. BH5 showed four different crystalline phases, but no liquid crystalline phase. Molar entropy and transition entropies were determined and compared with those of other homologues (BH6, BH7, and BH8). An odd-even effect with respect to the number of carbon atoms in the alkyl chain was observed for the cumulative entropies of the phase transitions occurring in the solid state. This effect is discussed by comparing with data for the n-alkanes. The molar entropies of the crystalline state, especially below 250 K, exhibited a peculiar 'pairing effect' between BH(2m- 1) and BH(2m), where m is an integer.     

Serendipitous synthesis of a ditwistane: a one-step access!

4-tert-Butyl-2-cyclohexen-1-one dimerizes in THF solution via its kinetic enolate, leading to di-tert-butylditwistane 8 in up to 36% yield (−78 °C → room temp., protonolysis, flash chromatography). X-ray crystallography shows that 8 incorporates one R and one S enantiomer of the starting ketone; none of the diastereomeric ditwistanes epi-8, epi’-8 or iso-8 was isolated. This means that the formation of 8 proceeds with mutual kinetic resolution and 100% induced diastereoselectivity.     

The birth of a bubble: a molecular simulation study

We study the nucleation of a bubble in a metastable Lennard-Jones (LJ) fluid, confined to a spherical pore with wetting walls, by a combination of grand canonical, canonical ensemble, and gauge cell Monte Carlo simulation methods complemented by the Voronoi-Delaunay tessellation analysis of statistical geometry of intermolecular cavities. We construct the isotherm of confined fluid in the form of a continuous van der Waals' loop, in which the unstable backward trajectory between the spinodals corresponds to bubble states. We show that as the degree of metastability increases and the fluid becomes progressively stretched, the decrease of fluid density is associated with the evolution of a population of interstitial intermolecular cavities. At the spinodal, the fluid becomes mechanically unstable: Interstitial cavities partly coalesce into a larger cavity located due to the system symmetry around the pore center. This cavity represents a bubble embryo, which grows at the expense of interstitial cavities. The nucleation barrier is calculated by direct thermodynamic integration along the isotherm. We compare our simulation results to the predictions of the classical nucleation theory and experiments on capillary condensation-evaporation of nitrogen in pores of hybrid organic-inorganic mesoporous molecular sieve HMM-3.     

Bond-stretch isomerism: a case study of a quiet controversy

The phenomenon of bond-stretch isomerism in transition metal coordination chemistry – two isomers of a complex differing only in one bond length – was first suggested in the early 1970s and remained controversial until the early 1990s, when it was generally agreed to be illusory. The course of this controversy is considered from two points of view, as a straightforward narrative in chemical history, and in the context of several concepts promulgated by studies of science from the outside.     

Syntheses of cyanines: a review

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Synthesis of (+)-uniflorine a: a structural reassignment and a configurational assignment

The total synthesis of (+)-uniflorine A has allowed for the structural reassignment and the configurational assignment of the alkaloid (-)-uniflorine A from a 1,2,6,7,8-pentahydroxyindolizidine structure to (-)-(1 R,2 R,3 R,6 R,7 S,7a R)-1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine (6- epi-casuarine).     

Exploring a solvated dimer of Gefitinib: a quantitative analysis

Gefitinib or Iressa is an orally administered anilinoquinazoline used in cancer chemotherapy for the treatment of lung and breast cancer. It is reported to exist in two polymorphic forms, a stable form I and a metastable form II. Both of the forms belong to the triclinic P space group. In this work, we report the crystallization of Gefitinib to form a methanol solvate [systematic name: N‐(3‐chloro‐4‐fluorophenyl)‐7‐methoxy‐6‐[3‐(morpholin‐4‐yl)propoxy]quinazolin‐4‐amine methanol hemisolvate, C₂₂H₂₄ClFN₄O₃·0.5CH₃OH] that was theoretically and experimentally investigated. The unit cell is composed of two independent Gefitinib molecules (A and B) that form a stable molecular complex with methanol in the crystal lattice. To understand the crystal lattice stabilization, a combination of techniques, namely X‐ray diffraction, IR spectroscopy, thermogravimetric/differential scanning calorimetry (TG‐DSC), Hirshfeld surface analysis and CLP‐PIXEL methods were used. The analysis of the crystal structure of this dimer revealed a three‐dimensional isostructurality with the already reported form II. The A and B molecules are connected via trifurcated C—H…O and N—H…O hydrogen bonding. In addition, the presence of the methanol molecule stabilizes the crystal structure via C—H…O, N—H…O and C—H…Cl interactions between the two monomers. The IR analysis of the dimer has shown characteristic fingerprint values when compared to the commercial form. The TG‐DSC analysis of the solvated dimer is in good agreement with the patent reporting cocrystals of Gefitinib. Finally, theoretical calculations by the CLP‐PIXEL method and Hirshfeld surface and two‐dimensional (2D) fingerprint plot analysis were carried out in order to quantify the different intermolecular interactions and their energies in the crystal packing.     

Low-temperature-induced swelling of a hydrophobic polymer: a lattice approach

The authors investigate equilibrium properties of a simple model of hydrophobic polymer in aqueous solution by means of dynamic Monte Carlo simulations. The solvent is described by a simplified two-dimensional model, defined on a triangular lattice, which has been previously shown to account for most thermodynamic anomalies of pure water and of hydrophobic solvation for monomeric solutes. The polymer is modeled as a self-avoiding walk on the same lattice. In this framework, the degrees of freedom of water are taken into account explicitly, and in principle there is no need to introduce effective self-contact interactions for the polymer in order to mimic the hydrophobic effect. In certain conditions, the authors observe low-temperature-induced swelling, i.e., expansion of the polymer globule upon decreasing temperature. The authors discuss the relationship between this phenomenon and the anomalous properties of the solvent.     

Complex formation of a calcium-dependent antibody: a thermodynamical consideration

The elution of FLAG-fusions (an octapeptide with the sequence DYKDDDDK) from immobilized anti-FLAG antibody M1 cannot be explained by a switch of the equilibrium binding constant to a lower value. To get a further insight into thermodynamics, the binding of anti-FLAG antibody M1 to the FLAG peptide was studied by real-time biosensor technology at seven different temperatures in the range from 5 to 35 degrees C. Binding studies were performed in the presence and absence of calcium. Thermodynamic parameters such as change in Gibbs free energy (deltaG), enthalpy (deltaH) and entropy (deltaS) were evaluated from the corresponding equilibrium data applying the integrated Van't Hoff equation. In contrast to similar kinetic data obtained, the contribution of deltaH and deltaS to deltaG in the presence or absence of calcium results in a different conformation of the antibody-antigen complex under binding and non-binding conditions. Therefore, complex dissociation with EDTA must be effected during a transition state of complex formation and dissociation.     

Manganese as a template: a new synthesis of corrole

The reaction of 2,2'-bisdipyrrins 1, 2, and 3 with manganese(II) acetate tetrahydrate and molecular dioxygen yields the manganese(III)corroles 4, 5 and 6, which are readily demetalated to the respective free-base corroles.     

Taming Mars with a tent and a tunnel: creation of a biosphere-city

An unconventional site-specific outdoor utility sculpture, used as a Strait of Gibraltar stopper, may soon store unwanted Earth-atmosphere derived wastes (mineralized CO2 and CFCs) for hundreds of years. Such a Land Art processing facility, an anti-global warming/cooling antidote, is an appropriate macro-engineering response to allegedly impending human survival macro-problems.