Synthesis of a conformationally locked version of puromycin amino nucleoside

[reaction: see text] A conformationally locked carbocyclic version of puromycin amino nucleoside was synthesized via Mitsunobu coupling of a 3-azido-substituted carbocyclic moiety with 6-chloropurine without interference from the azido group reacting with triphenylphosphine. The requisite 3-azido-substituted carbocyclic pseudosugar was prepared by a double inversion of configuration at C3' (nucleoside numbering) involving a nucleophilic displacement with azide.     

Using molecular dynamics simulations to identify the key factors responsible for chiral recognition by an amino acid-based molecular micelle

Molecular dynamics (MD) simulations were used to investigate the binding of six chiral compounds to the amino acid-based molecular micelle (MM) poly-(sodium undecyl-(L)-leucine-leucine) or poly(SULL). The MM investigated is used as a chiral selector in capillary electrophoresis. The project goal was to characterize the chiral recognition mechanism in these separations and to move toward predictive models to identify the best amino acid-based MM for a given separation. Poly(SULL) was found to contain six binding sites into which chiral compounds could insert. Four sites had similar sizes, shapes, and electrostatic properties. Enantiomers of alprenolol, propranolol, 1,1′-bi-2-naphthyl-2,2′-diyl hydrogen phosphate, 1,1′-bi-2-naphthol, chlorthalidone, or lorazepam were separately docked into each binding pocket and MD simulations with the resulting intermolecular complexes were performed. Solvent-accessible surface area calculations showed the compounds preferentially associated with binding sites where they penetrated into the MM core and shielded their non-polar atoms from solvent. Furthermore, with five of the six compounds the enantiomer with the most favorable free energy of MM association also experienced the most favorable intermolecular hydrogen bonding interactions with the MM. This result suggests that stereoselective intermolecular hydrogen bonds play an important role in chiral discrimination in separations using amino acid-based MMs.GRAPHICAL ABSTRACT     

One-pot synthesis of new iso-DPP derivatives from terminal alkynes and isocyanates

The reaction of phenyl acetylide anion with aryl isocyanates followed by quenching with water is shown to produce pyrrolopyrrole (iso-DPP) derivatives in addition to the isomeric cyclopentadienone imines previously reported. If the reaction is quenched with dilute HCl, 5-ylidenepyrrol-2(5H)-ones, formed by a Meyer-Schuster rearrangement, can be isolated instead. A possible mechanism for this reaction is suggested.     

1,2,4,5‐Tetrakis(2‐vinyl­pyridyl)­benzene–di­chloro­methane (1/2)

The title compound, C₃₄H₂₆N₄·2CH₂Cl₂, lies about an inversion center. The solvent mol­ecules interact with the benzene mol­ecule both through C—H⃛N hydrogen bonding to span pyridine N atoms of adjacent vinyl groups, possibly stabilizing the rotational conformation observed, and through a π interaction between a dichloromethane Cl atom and a pyridyl ring C—C bond of a c‐glide‐related mol­ecule. The benzene mol­ecules form stacks along the a axis such that two of the four olefin groups are properly oriented for photoreactivity (2+2 cyclo­dimerization).     

Dithiolene transfer from nickel to a dimolybdenum centre: the first dithiolene alkyne complex

Transfer of dithiolene ligands from [Ni(S₂C₂Ph₂)₂] to the dimolybdenum complex [Mo₂(μ-C₂R₂)(CO)₄Cp₂] (R=CO₂Me, Cp=η-C₅H₅) affords the first example of a dithiolene alkyne complex, [Mo₂(μ-C₂R₂)(μ-S₂C₂Ph₂)₂Cp₂], together with [Mo₂(μ-SCRCR)(μ-SCPhCPh)Cp₂] in which sulfur transfer from dithiolene to alkyne has occurred.     

Site-directed coordination chemistry with P22 virus-like particles

Protein cage nanoparticles (PCNs) are attractive platforms for developing functional nanomaterials using biomimetic approaches for functionalization and cargo encapsulation. Many strategies have been employed to direct the loading of molecular cargos inside a wide range of PCN architectures. Here we demonstrate the exploitation of a metal-ligand coordination bond with respect to the direct packing of guest molecules on the interior interface of a virus-like PCN derived from Salmonella typhimurium bacteriophage P22. The incorporation of these guest species was assessed using mass spectrometry, multiangle laser light scattering, and analytical ultracentrifugation. In addition to small-molecule encapsulation, this approach was also effective for the directed synthesis of a large macromolecular coordination polymer packed inside of the P22 capsid and initiated on the interior surface. A wide range of metals and ligands with different thermodynamic affinities and kinetic stabilities are potentially available for this approach, highlighting the potential for metal-ligand coordination chemistry to direct the site-specific incorporation of cargo molecules for a variety of applications.     

Coordination versatility of tridentate pyridyl aroylhydrazones towards iron: tracking down the elusive aroylhydrazono-based ferric spin-crossover molecular materials

The two potentially tridentate and monoprotic Schiff bases acetylpyridine benzoylhydrazone (HL(1)) and acetylpyridine 4-tert-butylbenzoylhydrazone (HL(2)) demonstrate remarkable coordination versatility towards iron on account of their propensity to undergo tautomeric transformations as imposed by the metal centre. Each of the pyridyl aroylhydrazone ligands complexes with the ferrous or ferric ion under strictly controlled reaction conditions to afford three six-coordinate mononuclear compounds [Fe(II)(HL)(2)](ClO(4))(2), [Fe(II)L(2)] and [Fe(III)L(2)]ClO(4) (HL = HL(1) or HL(2)) displaying distinct colours congruent with their intense CT visible absorptions. The synthetic manoeuvres rely crucially on the stoichiometry of the reactants, the basicities of the reaction mixtures and the choice of solvent. Electrochemically, each of these iron compounds exhibits a reversible metal-centred redox process. By all appearances, [Fe(III)(L(1))(2)]ClO(4) is one of only two examples of a crystallographically elucidated iron(III) bis-chelate compound of a pyridyl aroylhydrazone. Several pertinent physical measurements have established that each of the Schiff bases stabilises multiple spin states of iron; the enolate form of these ligands exhibits greater field strength than does the corresponding neutral keto tautomer. To the best of our knowledge, [Fe(III)(L(1))(2)]ClO(4) and [Fe(III)(L(2))(2)]ClO(4) are the first examples of ferric spin crossovers of aroylhydrazones. Whereas in the former the spin crossover (SCO) is an intricate gradual process, in the latter the (6)A(1)?(2)T(2) transition curve is sigmoidal with T(?)～280 K and the SCO is virtually complete. As regards [Fe(III)(L(1))(2)]ClO(4), M?ssbauer and EPR spectroscopic techniques have revealed remarkable dependence of the spin transition on sample type and extent of solvation. In frozen MeOH solution at liquid nitrogen temperature, both iron(III) compounds exist wholly in the doublet ground state.     

Summary of ISO/TC 201 Standard: ISO 22415—Surface chemical analysis—Secondary ion mass spectrometry—Method for determining yield volume in argon cluster sputter depth profiling of organic materials

The International Standard ISO 22415 provides methods to measure sputtering yield volumes of organic test materials using argon cluster ions. The test materials should consist of thin films of known thicknesses between 50 and 1000 nm. The format of the test materials, the measurement of sputtering ion dose, sputtered depth, and reporting requirements for sputtering yield volumes are described.     

Effect of UV-A irradiance on lipid accumulation in Nannochloropsis oculata

Lipids produced by microalgae can be grouped into two categories, storage lipids and structural lipids. Storage lipids are mainly triglycerides (TGs) made up of saturated fatty acids; TGs can be transesterified to produce biodiesel. Structural lipids are made of polyunsaturated fatty acids (PUFAs), which are essential nutrients for aquatic animals and humans. The objectives of this study were: (1) to determine the effect of UV-A at different levels of exposure on total lipid accumulation in Nannochloropsis oculata and check for reciprocity and (2) to study the interactive effect of UV-A and nutrient concentration on lipid accumulation in N. oculata. Objective 1 was accomplished by testing the effects of a range of UV-A irradiance (I), duration of exposure (T) and UV-A doses (I × T) on lipid production by N. oculata. If the same doses have a similar effect, irrespective of I and T, reciprocity holds. UV-A treatments significantly increased the chlorophyll-specific lipid concentration of N. oculata cells, and we were unable to falsify that reciprocity holds. Objective 2 was addressed by a factorial bioassay experiment with manipulated nutrient and UV-A levels. UV-A and decreased nutrients had a synergistic effect on chlorophyll-specific lipid concentration of N. oculata, resulting in higher lipid:chl ratios.