Steven J. Geib

High and Selective CO2 Uptake in a Cobalt Adeninate Metal−Organic Framework Exhibiting Pyrimidine- and Amino-Decorated Pores

The synthesis and structure of Co(2)(ad)(2)(CO(2)CH(3))(2) x 2 DMF x 0.5 H(2)O (bio-MOF-11) is described. Pyrimidine and amino groups of adeninate (ad) decorate the pores of the framework. The porosity of this material was studied, and its CO(2) and H(2) adsorption properties were evaluated. bio-MOF-11 exhibits a high heat of adsorption for CO(2) (approximately 45 kJ/mol), a high CO(2) capacity (approximately 6 mmol/g, 273 K), and exceptional selectivity for CO(2) over N(2) at 273 K (81:1) and 298 K (75:1).

Cation-Triggered Drug Release from a Porous Zinc−Adeninate Metal−Organic Framework

A porous anionic metal-organic framework, bio-MOF-1, constructed using adenine as a biomolecular building block is described. The porosity of this material is evaluated, its stability in biological buffers is studied, and its potential as a material for controlled drug release is investigated. Specifically, procainamide HCl is loaded into the pores of bio-MOF-1 using a simple cation exchange process. Exogenous cations from biological buffers are shown to affect the release of the adsorbed drug molecules.

N-heterocyclic carbene boryl radicals: a new class of boron-centered radical.

Reduction of xanthates by N-heterocyclic carbene boranes (NHC-boranes) has been suggested to occur by a radical chain mechanism involving heretofore unknown NHC-boryl radicals. In support of this suggestion, both the expected borane dithiocarbonate product and an unexpected borane xanthate product have now been isolated. These are the first NHC-boranes with boron-sulfur bonds, and their structures have been secured by spectroscopic and crystallographic means. The first rate constants for H-atom transfer from an NHC borane complex were determined by using the ring opening of a substituted cyclobutylcarbinyl radical as a clock reaction. The rate constant for reaction of the NHC-borane with a secondary alkyl radical at ambient temperature is 4 x 10(4) M(-1) s(-1), and the Arrhenius function displayed an entropic term (log A term) that was typical for a bimolecular reaction. The B-H bond dissociation energy of an NHC-borane complex has been estimated at 88 kcal/mol. The putative NHC-boryl radical in these transformations has been detected by EPR spectroscopy. Spectral analysis suggests that it is a pi-radical, analogous to the benzyl radical.

Synthesis, structure, assembly, and modulation of the CO2 adsorption properties of a zinc-adeninate macrocycle.

The preparation and self-assembly of zinc adeninate macrocycles [Zn(6)(adeninate)(6)(pyridine)(6)(dimethylcarbamate)(6)] is described. The macrocycles self-assemble through adenine-adenine hydrogen bonding interactions into a 3-D porous crystalline material that maintains its structural integrity after removal of guest molecules and coordinated pyridine molecules. By adjusting the activation temperature prior to gas adsorption measurements, the size of the pore aperture can be modulated to afford unique gas sorption properties including selective gas adsorption and CO(2) sequestration.

Lanthanide near infrared imaging in living cells with Yb3+ nano metal organic frameworks.

We have created unique near-infrared (NIR)–emitting nanoscale metal-organic frameworks (nano-MOFs) incorporating a high density of Yb3+ lanthanide cations and sensitizers derived from phenylene. We establish here that these nano-MOFs can be incorporated into living cells for NIR imaging. Specifically, we introduce bulk and nano-Yb-phenylenevinylenedicarboxylate-3 (nano-Yb-PVDC-3), a unique MOF based on a PVDC sensitizer-ligand and Yb3+ NIR-emitting lanthanide cations. This material has been structurally characterized, its stability in various media has been assessed, and its luminescent properties have been studied. We demonstrate that it is stable in certain specific biological media, does not photobleach, and has an IC50 of 100 μg/mL, which is sufficient to allow live cell imaging. Confocal microscopy and inductively coupled plasma measurements reveal that nano-Yb-PVDC-3 can be internalized by cells with a cytoplasmic localization. Despite its relatively low quantum yield, nano-Yb-PVDC-3 emits a sufficient number of photons per unit volume to serve as a NIR-emitting reporter for imaging living HeLa and NIH 3T3 cells. NIR microscopy allows for highly efficient discrimination between the nano-MOF emission signal and the cellular autofluorescence arising from biological material. This work represents a demonstration of the possibility of using NIR lanthanide emission for biological imaging applications in living cells with single-photon excitation.

Near-infrared emitting ytterbium metal–organic frameworks with tunable excitation properties

The design of metal-organic frameworks (MOFs) incorporating near-infrared emitting ytterbium cations and organic sensitizers allows for the preparation of new materials with tunable and enhanced photophysical properties.

Hydrogen bonding control of self-assembly: Simple isophthalic acid derivatives form cyclic hexameric aggregates

In this paper we demonstrate that six molecules of a functionalized isophthalic acid derivative form a cyclic aggregate stabilized by a network of 12 hydrogen bonds. The structure and stability of the aggregate were studied by X-ray crystallography, vapor phase osmometry and 1H NMR.

Substitution Reactions at Tetracoordinate Boron: Synthesis of N-Heterocyclic Carbene Boranes with Boron-Heteroatom Bonds

Boryl halide, carboxylate and sulfonate complexes of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (dipp-Imd-BH(2)X, X = halide or sulfonate) have been prepared from the parent borane dipp-Imd-BH(3) by (1) substitution reactions with R-X (X = halide or sulfonate), (2) reactions with electrophiles (like I(2) or NIS), or (3) acid/base reactions with HX (provided that HX has a pK(a) of about 2 or less). Dipp-Imd-BH(2)I is most conveniently prepared by reaction with diiodine while dipp-Imd-BH(2)OTf is best prepared by reaction with triflic acid. These and other less reactive complexes behave as electrophiles and can be substituted by a wide range of heteroatom nucleophiles including halides, thiolates and other sulfur-based nucleophiles, isocyanate, azide, nitrite, and cyanide. The resulting products are remarkably stable, and many have been characterized by X-ray crystallography. Several are members of very rare classes of functionalized boron compounds (boron azide, nitro compound, nitrous ester, etc.).

Synthesis and biological evaluation of the first pentafluorosulfanyl analogs of mefloquine.

Two novel SF5 analogs of the antimalarial agent mefloquine were synthesized in 5 steps and 10-23% overall yields and found to have improved activity and selectivity against malaria parasites. This work also represents the first report of SF5-substituted quinolines.

Rotational features of carbon-nitrogen bonds in axially chiral o-tert-butyl anilides and related molecules. Potential substrates for the ‘prochiral auxiliary’ approach to asymmetric synthesis

Abstract A new strategy for asymmetric induction termed the ‘prochiral auxiliary’ approach is introduced. Reactions of acylating agents with prochiral N -methyl- o - tert -butyl aniline provide anilides that are axially chiral by virtue of restricted rotation about the NAr bond. Rotamer populations about the amide bond (E/Z) were studied by 1 H NMR. Several pairs of enantiomeric o - tert -butyl anilides were separated by chiral chromatography and barriers about the NAr bond were measured by thermal racemization. Related o -(1-(trialkylsilyloxy)-1-methylethyl) anilides were also studied.