Oxygen binding of water-soluble cobalt porphyrins in aqueous solution

Water-soluble cobalt porphyrin 1Co and imidazole ligand 2 were synthesized. 1Co binds dioxygen in the presence of imidazole ligand 2 in aqueous solution. The formation of the oxygen adduct 2-1Co(O(2)) was studied using UV-vis and EPR spectroscopy. The impact of pH on the kinetic stability of the oxygen adduct was examined.     

Competitive decay at two- and three-state conical intersections in excited-state intramolecular proton transfer

We demonstrate the existence of a simultaneous degeneracy (not required by symmetry) of three electronic states in malonaldehyde. This is one of the first reports of such a triple degeneracy involving S0, S1, and S2 in a molecule with a closed-shell ground state. We further report on a two-state S2/S1 conical intersection which is higher in energy than the three-state intersection, but closer to the Franck-Condon point. First-principles quantum dynamics calculations of the photochemistry after excitation to S2 show that there is a competition between these intersections, with more than half of the population decaying to S1 through the higher energy S2/S1 intersection. Surprisingly, much of the population which makes it to the triple degeneracy point is not funneled directly to S0, but rather remains trapped on S1. We attribute this to the large dimensionality of the branching plane at a three-state intersection (the degeneracy is lifted along at least five distinct molecular displacements).     

PEG- and peptide-grafted aliphatic polyesters by click chemistry

Novel aliphatic polyesters with pendent acetylene groups were prepared by controlled ring-opening polymerization and subsequently used for grafting poly(ethylene glycol) and oligopeptide moieties by the Cu(I)-catalyzed addition of azides and alkynes, a type of "click" chemistry. These aliphatic polyesters possess an acetylene graft density that can be tailored by ring-opening copolymerization of alpha-propargyl-delta-valerolactone (1) with epsilon-caprolactone. Since the mild conditions associated with the click reaction are shown to be compatible with the polyester backbone, this method is a generally useful means for grafting numerous types of functionality onto aliphatic polyesters. The amphiphilic graft polyesters prepared in this study are shown to be biocompatible by in vitro cytotoxicity evaluation, suggesting their suitability for a range of biomaterial applications.     

Chiral imides as potential chiroptical switches: synthesis and optical properties

A series of chiral aromatic imides and diimides were synthesized and their electrochemical, absorption, fluorescent, and chiroptical properties were examined for their potential application as molecular chiroptical switches. These compounds exhibit strong UV-vis absorptions, and can be electrochemically reduced to radical anions that absorb in the near infrared (NIR) region. Further reduction to the dianionic states results in new absorptions in the visible region. The changes in circular dichroism upon redox switching were apparent in the UV-vis region but were absent in the NIR region.     

Syntheses and conformations of some cyclic hydroxamates. X-Ray crystal structure of 2-(p-nitrobenzoyl)tetrahydro-2H-1,2-oxazine

Alkylation of potassium p-nitrobenzohydroxamate with 1,4-dibromobutane gave 2-(p-nitrobenzoyl)tetrahydro-2H-1,2-oxazine (3). The X-ray crystal structure of 3 has been determined. The crystals are monoclinic, space group P2₁/n with a = 6.749(1), b = 7.644(1), c = 21.557(2)Å, β = 98.89(1), V = 1098.8(2)ų and Z = 4. The structure, which was refined to R = 0.039 using 1340 observed reflections, shows the oxazine and carbonyl oxygen atoms trans to each other. Alkylation of potassium benzohydroxamate with 1,3-dibromobutane gave a mixture of 3-methyl-2-benzoyloxazolidine (4) and 5-methyl-2-benzoyloxazolidine (5). The ¹H and ¹³C nmr spectra of the mixture of 4 and 5 indicates that these cyclic hydroxamates exist predominantly in the s-trans conformation.     

The Radical Anion,Dianion and Electron Transport Properties of Tetraiodotetraazapentacene

Tetraiodotetraazapentacene I₄TAP , the last missing derivative in the series of halogenated silylated tetraazapentacenes, was synthesized via condensation chemistry from a TIPS-ethynylated diaminobenzothiadiazol in three steps. Single and double reduction furnished its air-stable monoanion and relatively air-stable dianion, both of which were characterized by crystallography. All three species are structurally and spectroscopically compared to non-halogenated TAP and Br₄TAP . I₄TAP is an n-channel material in thin-film transistors with average electron mobilities exceeding 1 cm² (Vs)⁻¹.     

Selective,Transition Metal-free 1,2-Diboration of Alkyl Halides,Tosylates, and Alcohols

Defunctionalization of readily available feedstocks to provide alkenes for the synthesis of multifunctional molecules represents an extremely useful process in organic synthesis. Herein, we describe a transition metal-free, simple and efficient strategy to access alkyl 1,2-bis(boronate esters) via regio- and diastereoselective diboration of secondary and tertiary alkyl halides (Br, Cl, I), tosylates, and alcohols. Control experiments demonstrated that the key to this high reactivity and selectivity is the addition of a combination of potassium iodide and N,N-dimethylacetamide (DMA). The practicality and industrial potential of this transformation are demonstrated by its operational simplicity, wide functional group tolerance, and the late-stage modification of complex molecules. From a drug discovery perspective, this synthetic method offers control of the position of diversification and diastereoselectivity in complex ring scaffolds, which would be especially useful in a lead optimization program.