Porphyrin-based photocatalytic lithography

Photocatalytic lithography couples light with photoreactive coated mask materials to pattern surface chemistry. We excite porphyrins to create radical species that photocatalytically oxidize, and thereby pattern, chemistries in the local vicinity. The technique advantageously is suited for use with a wide variety of substrates. It is fast and robust, and the wavelength of light does not limit the resolution of patterned features. We have patterned proteins and cells to demonstrate the utility of photocatalytic lithography in life science applications.     

Cu-ATSM: a radiopharmaceutical for the PET imaging of hypoxia

Copper(II)-diacetyl-bis(N(4)-methylthiosemicarbazone), Cu-ATSM, labeled with a positron emitting isotope of copper ((60)Cu, (61)Cu, (62)Cu or (64)Cu) has been shown, in vitro and in vivo, to be selective for hypoxic tissue. In silico studies have explored the mechanism of its hypoxia selectivity, and clinical studies with this agent have shown non-invasive imaging data that is predictive of a cancer patients' response to conventional therapy. This Perspective discusses the evolution of Cu-ATSM, how its selectivity can be improved upon, and where this metal-ligand platform could be taken in the future.     

Reaction of a copper-dioxygen complex with nitrogen monoxide (*NO) leads to a copper(II)-peroxynitrite species

A discrete peroxynitrite-copper(II) complex, [(TMG3tren)CuII(-OONO)]+ (3), has been generated in solution (ESI-MS, m/z = 565.15; tetragonal EPR) by reacting *NO(g) with superoxo complex [(TMG3tren)CuII(O2*-)]+ (2). Complex 3 undergoes a thermal transformation to give CuII-nitrite complex [(TMG3tren)CuII(-ONO)]+ (4) (X-ray) along with ca. 0.5 molar equiv dioxygen. A DFT calculation derived structure with cyclic bidentate k2-O,O'-OONO bound peroxynitrite moiety and dx2-y2 ground state is proposed. Experiments using 18O2 suggest that the adjacent peroxo oxygen atoms in 3 are derived from molecular oxygen. Further, 18O2 containing 3 undergoes O-O bond cleavage to form singly 18-O-labeled 4. The results suggest the viability of biological CuI/O2/(*NO) peroxynitrite formation and chemistry, that is, not coming from free superoxide plus *NO reaction.     

Mechanism of OMP decarboxylation in orotidine 5'-monophosphate decarboxylase

Despite extensive experimental and theoretical studies, the detailed catalytic mechanism of orotidine 5'-monophosphate decarboxylase (ODCase) remains controversial. In particular simulation studies using high level quantum mechanics have failed to reproduce experimental activation free energy. One common feature of many previous simulations is that there is a water molecule in the vicinity of the leaving CO2 group whose presence was only observed in the inhibitor bound complex of ODCase/BMP. Various roles have even been proposed for this water molecule from the perspective of stabilizing the transition state and/or intermediate state. We hypothesize that this water molecule is not present in the active ODCase/OMP complex. Based on QM/MM minimum free energy path simulations with accurate density functional methods, we show here that in the absence of this water molecule the enzyme functions through a simple direct decarboxylation mechanism. Analysis of the interactions in the active site indicates multiple factors contributing to the catalysis, including the fine-tuned electrostatic environment of the active site and multiple hydrogen-bonding interactions. To understand better the interactions between the enzyme and the inhibitor BMP molecule, simulations were also carried out to determine the binding free energy of this special water molecule in the ODCase/BMP complex. The results indicate that the water molecule in the active site plays a significant role in the binding of BMP by contributing approximately -3 kcal/mol to the binding free energy of the complex. Therefore, the complex of BMP plus a water molecule, instead of the BMP molecule alone, better represents the tight binding transition state analogue of ODCase. Our simulation results support the direct decarboxylation mechanism and highlight the importance of proper recognition of protein bound water molecules in the protein-ligand binding and the enzyme catalysis.     

Modulation of the ligand-field anisotropy in a series of ferric low-spin cytochrome c mutants derived from Pseudomonas aeruginosa cytochrome c-551 and Nitrosomonas europaea cytochrome c-552: a nuclear magnetic resonance and electron paramagnetic resonance study

Cytochromes of the c type with histidine-methionine (His-Met) heme axial ligation play important roles in electron-transfer reactions and in enzymes. In this work, two series of cytochrome c mutants derived from Pseudomonas aeruginosa (Pa c-551) and from the ammonia-oxidizing bacterium Nitrosomonas europaea (Ne c-552) were engineered and overexpressed. In these proteins, point mutations were induced in a key residue (Asn64) near the Met axial ligand; these mutations have a considerable impact both on heme ligand-field strength and on the Met orientation and dynamics (fluxionality), as judged by low-temperature electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectra. Ne c-552 has a ferric low-spin (S = 1/2) EPR signal characterized by large g anisotropy with g(max) resonance at 3.34; a similar large g(max) value EPR signal is found in the mitochondrial complex III cytochrome c1. In Ne c-552, deletion of Asn64 (NeN64Delta) changes the heme ligand field from more axial to rhombic (small g anisotropy and g(max) at 3.13) and furthermore hinders the Met fluxionality present in the wild-type protein. In Pa c-551 (g(max) at 3.20), replacement of Asn64 with valine (PaN64V) induces a decrease in the axial strain (g(max) at 3.05) and changes the Met configuration. Another set of mutants prepared by insertion (ins) and/or deletion (Delta) of a valine residue adjacent to Asn64, resulting in modifications in the length of the axial Met-donating loop (NeV65Delta, NeG50N/V65Delta, PaN50G/V65ins), did not result in appreciable alterations of the originally weak (Ne c-552) or very weak (Pa c-551) axial field but had an impact on Met orientation, fluxionality, and relaxation dynamics. Comparison of the electronic fingerprints in the overexpressed proteins and their mutants reveals a linear relationship between axial strain and average paramagnetic heme methyl shifts, irrespective of Met orientation or dynamics. Thus, for these His-Met axially coordinated Fe(III), the large g(max) value EPR signal does not represent a special case as is observed for bis-His axially coordinated Fe(III) with the two His planes perpendicular to each other.     

Rapid and quantitative DNA analysis of genetic mutations for polycystic kidney disease (PKD) using magnetic/luminescent nanoparticles

Rapid and accurate detection of genetic mutations based on nanotechnology would provide substantial advances in detection of polycystic kidney disease (PKD), a disease whose current methods of detection are cumbersome due to the large size and duplication of the mutated gene. In this study, a nanotechnology-based DNA assay was developed for detection of SNPs (single nucleotide polymorphisms) in a feline autosomal dominant PKD (ADPKD) model which can readily be adapted to diagnosis of human ADPKD type 1. Europium and terbium phosphors were doped into gadolinium crystal hosts with a magnetic core, providing stable luminescence and the possibility of magnetic manipulations in a solution-based assay. A hybridization-in-solution DNA assay was optimized for feline PKD gene SNP detection using genomic DNA extracted from feline kidney tissue and blood. This assay showed a substantial differentiation between PKD and control specimens. The nanotechnology-based DNA assay is attractive from the viewpoint of rapid availability, simple methodology, and cost reduction for clinical use to detect mutations involved in human ADPKD and other genetic diseases. Figure Schematic diagram of PKD (Polycystic Kidney Disease) SNPs detection assay using feline genomic DNA in magnetic/luminescent nanoparticle-based DNA hybridization     

Enhanced surface photochemistry in chloride-nitrate ion mixtures

Heterogeneous reactions of sea salt aerosol with various oxides of nitrogen lead to replacement of chloride ion by nitrate ion. Studies of the photochemistry of a model system were carried out using deliquesced mixtures of NaCl and NaNO3 on a Teflon substrate. Varying molar ratios of NaCl to NaNO3 (1 : 9 Cl- : NO3-, 1 : 1 Cl- : NO3-, 3 : 1 Cl- : NO3-, 9 : 1 Cl- : NO3-) and NaNO3 at the same total concentration were irradiated in air at 299 +/- 3 K and at a relative humidity of 75 +/- 8% using broadband UVB light (270-380 nm). Gaseous NO2 production was measured as a function of time using a chemiluminescence NO(y) detector. Surprisingly, an enhanced yield of NO2 was observed as the chloride to nitrate ratio increased. Molecular dynamics (MD) simulations show that as the Cl- : NO3- ratio increases, the nitrate ions are drawn closer to the interface due to the existence of a double layer of interfacial Cl- and subsurface Na+. This leads to a decreased solvent cage effect when the nitrate ion photodissociates to NO2+O*-, increasing the effective quantum yield and hence the production of gaseous NO2. The implications of enhanced NO2 and likely OH production as sea salt aerosols become processed in the atmosphere are discussed.     

Synthesis of gem-difluorinated nucleoside analogues of the liposidomycins and evaluation as MraY inhibitors

Two gem-difluoromethylenated nucleoside moieties of liposidomycins, 3 and 4, were designed and synthesized. Compound 3 was assembled from lactol 5 and gem-difluoromethylenated nucleoside 6. In the synthesis of target molecule 4, the coupling of the trichloroacetimidate derivative of gem-difluoromethylenated furanose 7 with nucleoside 8 in the presence of TMSOTf gave the unexpected compound 16 when CH3CN was used as solvent. This results from acetonitrile acting as a nucleophile and participating in the glycosylation reaction. This unusual process may be correlated with the presence of the electron-withdrawing gem-difluoro substituents at the C-2 position of furanose. Compound 3 demonstrated 29% inhibition of MraY at 11.4 mM.     

Early discovery of individual firm insolvency

Email: wxding{at}uic.edu Received on 11 January 2006. Accepted on 21 November 2006. This paper proposes a new methodology for the early discoveryof individual firm insolvency without employing any other firm'sdata. The proposed individual-level model can be applied todifferent firms, regardless of industry type or asset size,and thereby overcomes the sample selection problem commonlyfound in aggregate-level prediction models. Unlike many previousstudies, which assume that the distributions of variables involveddo not change over time and that the variables follow a singleknown distribution, the proposed model can capture each individualfirm's potential multiple data-generating processes and determinethe actual distributions exhibited in its own data. Thus, itcaptures each individual firm's intrinsic heterogeneity. Anempirical study illustrates the greater predictive power ofthis model compared with the current conventional methods. Specifically,the predictive accuracy of the proposed model is 92.65% and77.45% for 2 and 5 years prior to actual bankruptcy, respectively.Moreover, the proposed model is adaptive and simple to implement.