Synthesis, spectroscopic, and in vitro photosensitizing efficacy of ketobacteriochlorins derived from ring-B and ring-D reduced chlorins via pinacol-pinacolone rearrangement

In this report, we present a regioselective oxidation of a series bacteriochlorins, which on reacting with either ferric chloride (FeCl(3)) or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) yielded the corresponding ring-B or ring-D reduced chlorins. The effect of the number of electron-withdrawing groups present at the peripheral position, with or without a fused isocyclic ring (ring-E), did not make any significant difference in regioselective oxidation of the pyrrole rings. However, depending on the nature of substituents, the intermediate bis-dihydroxy bacteriochlorins on subjecting to pinacol-pinacolone reaction conditions gave various ketochlorins. The introduction of the keto-group at a particular position in the molecule possibly depends on the stability of the intermediate carbocation species. The newly synthesized bacteriochlorins show strong long-wavelength absorption and produced significant in vitro (Colon26 cells) photosensitizing ability. Among the compounds tested, the bacteriochlorins containing a keto-group at position 7 of ring-B with cleaved five-member isocyclic ring showed the best efficacy.     

Diastereoselectivity control in formal nucleophilic substitution of bromocyclopropanes with oxygen- and sulfur-based nucleophiles

A diastereoconvergent formal nucleophilic substitution of bromocyclopropanes with oxygen- and sulfur-based nucleophiles is described. The reaction proceeds via in situ formation of a highly reactive cyclopropene intermediate and subsequent diastereoselective addition of a nucleophile across the strained C═C bond. Three alternative means of controlling the diastereoselectivity of addition have been demonstrated: (1) thermodynamically driven epimerization of enolizable carboxamides, (2) steric control by bulky substituents, and (3) directing effect of carboxamide or carboxylate functions.     

Structure, thermodynamics, and energy content of aluminum-cyclopentadienyl clusters

We present quantum chemistry simulations of aluminum clusters surrounded by a surface layer of cyclopentadiene-type ligands to evaluate the potential of such complexes as novel fuels or energetic materials. Density functional theory simulations are used to examine the aluminum-ligand bonding and its variation as the size of the aluminum cluster increases. The organometallic bond at the surface layer arises mainly from ligand charge donation into the Al p orbitals balanced with repulsive polarization effects. Functionalization of the ligand and changes in Al cluster size are found to alter the relative balance of these effects, but the surface organometallic bond generally remains stronger than Al-Al bonds elsewhere in the cluster. In large clusters, such as the experimentally observed Al(50)Cp(12)*, this suggests that unimolecular thermal decomposition likely proceeds through loss of surface AlCp* units, exposing the strained interior aluminum core. The calculated heats of combustion per unit volume for these systems are high, approaching 60% that of pure aluminum. We discuss the possibility of using organometallic aluminum clusters as a means of achieving rapid combustion in propellants and fuels.     

Inhibition of Acinetobacter baumannii biofilm formation on a methacrylate polymer containing a 2-aminoimidazole subunit

A polymeric composite containing a 2-aminoimidazole derivative was synthesized. It was found that this polymer was resistant to biofilm colonization by Acinetobacter baumannii, no leaching of the 2-aminoimidazole derivative was observed after 2 weeks of treatment with deionized water, and the resulting polymer was not hemolytic.     

Group 4 initiators for the stereoselective ROP of rac-β-butyrolactone and its copolymerization with rac-lactide

In this paper we demonstrate the utility of Group 4 metals for the well-controlled and stereoselective (syndiotactic) ring opening polymerization (ROP) of rac-β-butyrolactone (BBL) and their ability to form copolymers.     

C-N bond formation via ligand-induced nucleophilicity at a coordinated triamidoamine ligand

Reaction of (N(3)N)ZrX complexes (X = amido, Cl(-), CH(3)(-)) with carbodiimide substrates results in insertion into an Zr-N bond of the triamidoamine ligand rather than the Zr-X bond as has been observed for related (N(3)N)ZrX complexes (X = PR(2)(-), AsR(2)(-)).     

Natural bond orbital analysis, electronic structure, non-linear properties and vibrational spectral analysis of L-histidinium bromide monohydrate: a density functional theory

The spectroscopic properties of the crystallized nonlinear optical molecule L-histidinium bromide monohydrate (abbreviated as L-HBr-mh) have been recorded and analyzed by FT-IR, FT-Raman and UV techniques. The equilibrium geometry, vibrational wavenumbers and the first order hyperpolarizability of the crystal were calculated with the help of density functional theory computations. The optimized geometric bond lengths and bond angles obtained by using DFT (B3LYP/6-311++G(d,p)) show good agreement with the experimental data. The complete assignments of fundamental vibrations were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The natural bond orbital (NBO) analysis confirms the occurrence of strong intra and intermolecular N-H?O hydrogen bonding.     

Enabling electrochemical studies of chemically-modified carbon nanotubes in non-aqueous electrolytes using superparamagnetic nanoparticle-nanotube composites co-modified by diazirine molecular “tethers”

Multiwalled carbon nanotubes (MWCNTs) were covalently modified with polymer-coated superparamagnetic Fe₃O₄ nanoparticles via amide bond formation to surface oxo-groups located predominantly at the ends of the nanotubes to form “magnetic MWCNTs”. The sidewalls of the magnetic MWCNTs were then selectively covalently modified with ferrocenyl groups via the photolysis of 3-[3-(trifluoromethyl) diazirin-3-yl] phenyl ferrocene monocarboxylate, which uses an aryldiazirine moiety as a molecular “tether”. We demonstrate that the assembly of the chemically-modified magnetic MWCNTs onto the surface of a magnetic carbon electrode enables one to obtain stable voltammetric signals of chemically-modified carbon nanotubes in non-aqueous electrolytes even under vigorous hydrodynamic conditions of stirring at 3000 rpm for up to twenty minutes. In contrast, non-magnetic chemically modified MWCNTs are removed from the electrode surface within the first two minutes of stirring.     

Top-Down Mass Spectrometry of Supercharged Native Protein-Ligand Complexes

Tandem mass spectrometry (MS/MS) of intact, noncovalently-bound protein-ligand complexes can yield structural information on the site of ligand binding. Fourier transform ion cyclotron resonance (FT-ICR) top-down MS of the 29 kDa carbonic anhydrase-zinc complex and adenylate kinase bound to adenosine triphosphate (ATP) with collisionally activated dissociation (CAD) and/or electron capture dissociation (ECD) generates product ions that retain the ligand and their identities are consistent with the solution phase structure. Increasing gas phase protein charging from electrospray ionization (ESI) by the addition of supercharging reagents, such as m-nitrobenzyl alcohol and sulfolane, to the protein analyte solution improves the capability of MS/MS to generate holo-product ions. Top-down proteomics for protein sequencing can be enhanced by increasing analyte charging.