Rational chemical design of the next generation of molecular imaging probes based on physics and biology: mixing modalities, colors and signals

In recent years, numerous in vivo molecular imaging probes have been developed. As a consequence, much has been published on the design and synthesis of molecular imaging probes focusing on each modality, each type of material, or each target disease. More recently, second generation molecular imaging probes with unique, multi-functional, or multiplexed characteristics have been designed. This critical review focuses on (i) molecular imaging using combinations of modalities and signals that employ the full range of the electromagnetic spectra, (ii) optimized chemical design of molecular imaging probes for in vivo kinetics based on biology and physiology across a range of physical sizes, (iii) practical examples of second generation molecular imaging probes designed to extract complementary data from targets using multiple modalities, color, and comprehensive signals (277 references).     

Bottom-up synthesis of gold octahedra with tailorable hollow features

Gold octahedra with hollow features have been synthesized in high yield via the controlled overgrowth of preformed concave cube seeds. This Ag(+)-assisted, seed-mediated synthesis allows for the average edge length of the octahedra and the size of the hollow features to be independently controlled. We propose that a high concentration of Ag(+) stabilizes the {111} facets of the octahedra through underpotential deposition while the rate of Au(+) reduction controls the dimensions of the hollow features. This synthesis represents a highly controllable bottom-up approach for the preparation of hollow gold nanostructures.     

Highly aminated mesoporous silica nanoparticles with cubic pore structure

Mesoporous silica with cubic symmetry has attracted interest from researchers for some time. Here, we present the room temperature synthesis of mesoporous silica nanoparticles possessing cubic Pm3?n symmetry with very high molar ratios (>50%) of 3-aminopropyl triethoxysilane. The synthesis is robust allowing, for example, co-condensation of organic dyes without loss of structure. By means of pore expander molecules, the pore size can be enlarged from 2.7 to 5 nm, while particle size decreases. Adding pore expander and co-condensing fluorescent dyes in the same synthesis reduces average particle size further down to 100 nm. After PEGylation, such fluorescent aminated mesoporous silica nanoparticles are spontaneously taken up by cells as demonstrated by fluorescence microscopy.     

Sortin1-hypersensitive mutants link vacuolar-trafficking defects and flavonoid metabolism in Arabidopsis vegetative tissues

Sortin1 is a chemical genetic-hit molecule that causes specific mislocalization of plant and yeast-soluble and membrane vacuolar markers. To better understand its mode of action, we designed a Sortin1-hypersensitive screen and identified several Sortin1-hypersensitive and flavonoid-defective mutants. Mechanistically, Sortin1 mimics the effect of the glutathione inhibitor buthionine sulfoximine and alters the vacuolar accumulation of flavonoids, likely blocking their transport through vacuole-localized ABC transporters. Structure-activity relationship studies conducted in Arabidopsis revealed the structural requirements for Sortin1 bioactivity and demonstrated that overlapping Sortin1 substructures can be used to discriminate between vacuolar-flavonoid accumulations and vacuolar-biogenesis defects. We conclude that Sortin1 is a valuable probe for dissecting novel links among flavonoid transport, vacuolar integrity, and the trafficking of vacuolar targeted cargoes in Arabidopsis.     

Formation of gallaoxetanes: C-O activation of 1,2-epoxybutane by ground-state Ga atoms

(69/71)Ga atoms were reacted with 1,2-epoxybutane and its isotopomers, 1,2-epoxybutane-1,1-d(2) (CH(3)CH(2)CHOCD(2)) and 1,2-epoxybutane-2-d(1) (CH(3)CH(2)CDOCH(2)), under matrix-isolation conditions. The novel gallaoxetanes CH(3)CH(2)CHCH(2)GaO and CH(3)CH(2)CHCH(2)OGa, resulting from the insertion of the metal atom in the C(1)-O and C(2)-O bonds, respectively, of the 1,2-epoxybutane, were detected by EPR spectroscopy. The Ga and H hyperfine interaction (hfi) values of the gallaoxetanes, calculated using a DFT method, were used to help assign the EPR spectra. A third Ga-centered species, detected at 190 K, underwent spectral changes similar to those of the C(2)-O insertion product upon isotopic substitution of the 1,2-epoxybutane. Although the Ga hfi for this species was 36% smaller than that of the C(2)-O insertion product, the values for the H hfi were similar, suggesting that the carrier of the spectrum was the C(2)-O insertion product where Ga was perturbed by the matrix constraints. The alkyl radical CH(3)CH(2)(?CH)CH(2)OGa, resulting from ring-opening at the C(2)-O bond of 1,2-epoxybutane, was observed at temperatures below 150 K. This radical has been implicated in the formation of the C(2)-O insertion product. The unusually small value found for two of the β-hydrogens of the alkyl radical is discussed.     

Oxidation of a guanine derivative coordinated to a Pt(IV) complex initiated by intermolecular nucleophilic attacks

In this study we report that fac-[Pt(IV)(dach)(9-EtG)Cl(3)](+) (dach = d,l-1,2-diaminocyclohexane, 9-EtG = 9-ethylguanine) in high pH (pH 12) or phosphate solution (pH 7.4) produces 8-oxo-9-EtG and Pt(II) species. The reaction in H(2)(18)O revealed that the oxygen atom in hydroxide or phosphate ends up at the C8 position of 8-oxo-G. The kinetics of the redox reaction was first order with respect to both Pt(IV)-G and free nucleophiles (OH(-) and phosphate). The oxidation of G initiated by hydroxide was approximately 30～50 times faster than by phosphate in 100 mM NaCl solutions. The large entropy of activation of OH(-1) (ΔS(?) = 26.6 ± 4.3 J mol(-1) K(-1)) due to the smaller size of OH(-) is interpreted to be responsible for the faster kinetics compared to phosphate (ΔS(?) = -195.5 ± 11.1 J mol(-1) K(-1)). The enthalpy of activation for phosphate reaction is more favorable relative to the OH(-) reaction (ΔH(?) = 35.4 ± 3.5 kJ mol(-1) for phosphate vs. 96.6 ± 11.4 kJ mol(-1) for OH(-1)). The kinetic isotope effect of H8 was determined to be 7.2 ± 0.2. The rate law, kinetic isotope effect, and isotopic labeling are consistent with a mechanism involving proton ionization at the C8 position as the rate determining step followed by two-electron transfer from G to Pt(IV).     

One-pot synthesis of Cu1.94S-CdS and Cu1.94S-Zn(x)Cd(1-x)S nanodisk heterostructures

Nanodisk heterostructures consisting of monoclinic Cu(1.94)S and wurtzite CdS have been colloidally synthesized for the first time. Initially, hexagonal-shaped nanodisks of Cu(1.94)S were produced upon thermolysis of a copper complex in a solvent mixture of HDA and TOA at 250 °C. Rapid addition of Cd precursor to the reaction mixture resulted in the partial conversion of Cu(1.94)S into CdS, yielding Cu(1.94)S-CdS nanoheterostructures. The original morphology of the Cu(1.94)S nanodisks was conserved during the transformation. When Zn precursor was added together with the Cd precursor, Cu(1.94)S-Zn(x)Cd(1-x)S nanodisks were generated. These two-component nanostructures are potentially useful in the fabrication of heterojunction solar cells.     

The design of a new concept chromatography column

Active Flow Management is a new separation technique whereby the flow of mobile phase and the injection of sample are introduced to the column in a manner that allows migration according to the principles of the infinite diameter column. A segmented flow outlet fitting allows for the separation of solvent or solute that elutes along the central radial section of the column from that of the sample or solvent that elutes along the wall region of the column. Separation efficiency on the analytical scale is increased by 25% with an increase in sensitivity by as much as 52% compared to conventional separations.     

Ligand-free copper-catalyzed arylation of amidines

Copper-catalyzed cross-coupling reactions of amidine salts were utilized to synthesize monoarylated amidines in moderate to high yields with ligand-free conditions. DMF was the superior solvent for the N-arylation of benzamidines, while MeCN was used in the formation of N-aryl amidines in moderate to high yield.     

Hammett correlations in the chemistry of 3-phenylpropyl radicals

The energetics and kinetics of the reaction of variously substituted benzyl radicals with a model alkene were calculated at the G3(MP2)-RAD//B3-LYP/6-31G(d) level of theory to determine whether such reactions are amenable to Hammett analysis. The reactions were studied both in the gas phase and in toluene solution in the temperature range 298-353 K; calculations include 1D-hindered rotor corrections for low frequency torsional modes, and the solvation energies were calculated using COSMO-RS at the BP/TZP level of theory. The addition reaction was found to be dominated by radical stabilization effects, but under circumstances where olefin substituent effects were decoupled from aryl substituent effects, a modest polar effect comes into play, which is enhanced by solvation. Reasonable correlations with empirical substituent parameters such as Hammett σ and σ(?) are observed for the enthalpy of activation, but additional entropic factors act to decrease the degree of correlation with respect to free energies and rate coefficients, confirming hypotheses from earlier experimental work. Substituent effects on the reverse β-fragmentation reaction, and potential cyclization of the 3-phenylpropyl radicals formed by addition are also discussed.