Carbon-bound diazeniumdiolates from the reaction of nitric oxide with amidines

[reaction: see text] The enediamine tautomer of a variety of substituted amidine free bases reacts with nitric oxide (NO) to produce compounds containing a carbon-bound diazeniumdiolate [R1R2R3C-N(O)=NO-] functional group (previously called "nitrosohydroxylamines"). The new reaction has been shown to be quite general, although the nature of the products does vary. Amidines containing more than one replaceable hydrogen produce polydiazeniumdiolates as intermolecular salts, while those in which only one diazeniumdiolation can occur provide zwitterionic salts. These diazeniumdiolated amidines are shown to be useful NO donor compounds which undergo very slow spontaneous dissociation on dissolution in pH 7.4 phosphate buffer to produce mixtures of NO and nitrous oxide containing mostly NO. The most advantageous manifestation of the new discovery is the preparation of the monodiazeniumdiolated amidine zwitterions. Reaction of the medically relevant alpha-adrenergic agonists tetrahydrozoline and idazoxan produced monodiazeniumdiolated amidine zwitterions from which NO release was observed for up to 28 days and showed little sign of ending. The reaction should be applicable to a variety of pharmaceutical agents, including NO synthase inhibitors, antitumor agents, and antibacterials.     

Structural and rate studies of the 1,2-additions of lithium phenylacetylide to lithiated quinazolinones: influence of mixed aggregates on the reaction mechanism

The 1,2-addition of lithium phenylacetylide (PhCCLi) to quinazolinones was investigated using a combination of structural and rate studies. (6)Li, (13)C, and (19)F NMR spectroscopies show that deprotonation of quinazolinones and phenylacetylene in THF/pentane solutions with lithium hexamethyldisilazide affords a mixture of lithium quinazolinide/PhCCLi mixed dimer and mixed tetramer along with PhCCLi dimer. Although the mixed tetramer dominates at high mixed aggregate concentrations and low temperatures used for the structural studies, the mixed dimer is the dominant form at the low total mixed aggregate concentrations, high THF concentrations, and ambient temperatures used to investigate the 1,2-addition. Monitoring the reaction rates using (19)F NMR spectroscopy revealed a first-order dependence on mixed dimer, a zeroth-order dependence on THF, and a half-order dependence on the PhCCLi concentration. The rate law is consistent with the addition of a disolvated PhCCLi monomer to the mixed dimer. Investigation of the 1,2-addition of PhCCLi to an O-protected quinazolinone implicates reaction via trisolvated PhCCLi monomers.     

Predissociation spectroscopy of the argon-solvated H5O2+ "zundel" cation in the 1000-1900 cm(-1) region

Predissociation spectra of the H5O2+.Ar(1,2) cluster ions are reported in the 1000-1900 cm(-1) region. The weakly bound argon atoms enable investigation of the complex in a linear action mode, and the resulting spectra are much simpler than those reported previously in this region [Asmis et al., Science 299, 1375 (2003) and Fridgen et al., J. Phys. Chem. A 108, 9008 (2004)], which were obtained using infrared multiphoton dissociation of the bare complex. The observed spectrum consists of two relatively narrow bands at 1080 and 1770 cm(-1) that are likely due to excitation of the shared proton and intramolecular bending vibrations of the two water molecules, respectively. The narrow linewidths and relatively small (60 cm(-1)) perturbation introduced by the addition of a second argon atom indicate that the basic "zundel" character of the H5O2+ ion survives upon complexation.     

Large-scale resonance amplification of optical sensing of volatile compounds with chemoresponsive visible-region diffraction gratings

Micropatterning of the vapochromic charge-transfer salt, [Pt(CNC6H4C10H21)4][Pd(CN)4], on transparent platforms yields transmissive chemoresponsive diffraction gratings. Exposure of the gratings to volatile organic compounds (VOCs) such as chloroform and methanol leads to VOC uptake by the porous material comprising the grating lattice or framework, and a change in the material's complex refractive index, ?. The index change is accompanied by a change in the degree of index contrast between the lattice and the surrounding medium (in this case, air), and a change in the diffraction efficiency of the grating. When a monochromatic light source that is not absorbed by the lattice material is employed as a probe beam, only changes in the real component of ? are sensed. Under these conditions, the grating behaves as a nonselective, but moderately sensitive, sensor for those VOCs capable of permeating the porous lattice material. When a probe color is shifted to a wavelength coincident with the vapochromic charge-transfer transition of the lattice material, the sensor response is selectively amplified by up to 3.5 orders of magnitude, resulting in greatly enhanced sensitivity and some degree of chemical specificity. On the basis of studies at four probe wavelengths, the amplification effect is dominated by resonant changes in the imaginary component of the refractive index. The observed wavelength- and analyte-dependent amplification effects are quantitatively well described by a model that combines a Kramers-Kronig analysis with an effective-medium treatment of dielectric effects.     

On the choice of active space orbitals in MCSCF calculations

We describe a procedure which may be used to aid selection of the active space in multiconfigurational self-consistent field (MCSCF) calculations for general chemical systems. Starting from a restricted Hartree-Fock calculation, we define a hierarchy of interacting virtual orbitals for every occupied orbital. The most strongly interacting orbitals are then taken to constitute the active space in a configuration interaction (CI) calculation. The natural orbital occupation numbers obtained from the CI calculation are then used to choose the active space to be used in a subsequent MCSCF calculation. We illustrate our method on a number of systems (Li₂, B₂, C₂, carbonyl oxide and the transition state for oxidation of H₂S by dioxirane). In all these cases, ‘intuitive’ active spaces are inadequate, as are active spaces derived from the natural orbitals of unrestricted Hartree-Fock calculations.     

New synthetic approaches to 3-carhoxamides of 4-hydroxy-2H-1,2-benzothiazine 1,1-dioxide

Two new synthetic approaches to the title compounds are reported. In the first of these, starting with N-carbobenzyloxysarcosine, four synthetic steps are employed to finally assemble the C³? C⁴ bond of the 1,2-benzothiazine ring. In the second approach, an enol ether is employed as a protecting group to allow formation of the 3-carboxamide function, which is followed by cleavage of the ether function to yield the desired 4-hydroxy-1,2-benzothiazine-3-carboxamide 1,1-dioxide.     

Synthesis of enzyme-inhibitory phospholipid analogs II. Preparation of chiral 1-acyl-2-acylamido-2-deoxyglycerophosphorycholines from serine

A facile and efficient stereospecific route to the enzyme-inhibitory 2-amide analogs of phosphatidycholine is reported.     

Vesicle adsorption and lipid bilayer formation on glass studied by atomic force microscopy

The adsorption of phosphatidylcholine (PC) vesicles (30, 50, and 100 nm nominal diameters) and of dye-labeled PC vesicles (labeled with 6% Texas Red fluorophore (TR) and encapsulated carboxy fluorescein (CF)) to glass surfaces was studied by contact mode atomic force microscopy in aqueous buffer. These studies were performed in part to unravel details of the previously observed isolated rupture of dye-labeled PC vesicles on glass (Johnson, J. M.; Ha, T.; Chu, S.; Boxer, S. G. Biophys. J. 2002, 83, 3371-3379), specifically to differentiate partial rupture, that is, pore formation and leakage of entrapped dye, from full rupture to form bilayer disks. In addition, the adhesion potential of PC vesicles on glass was calculated based upon the adhesion-driven flattening of adsorbed vesicles and a newly developed theoretical model. The vesicles were found to flatten considerably upon adsorption to glass (width-to-height ratio of approximately 5), which leads to an estimate for the adhesion potential and for the critical rupture radius of 1.5 x 10(-4) J/m2 and 250 nm, respectively. Independent of vesicle size and loading with dye molecules, the adsorption of intact vesicles was observed at all concentrations below a threshold concentration, above which the formation of smooth lipid bilayers occurred. In conjunction with previous work (Johnson, J. M.; Ha, T.; Chu, S.; Boxer, S. G. Biophys. J. 2002, 83, 3371-3379), these data show that 6% TR 20 mM CF vesicles adsorb to the surface intact but undergo partial rupture in which they exchange content with the external buffer.     

The chemistry of fluorine containing phosphaalkenes, arsaalkenes and selenocarbonyls

This review covers our extensive research activities in the area of fluorine containing phospha- and arsaalkenes as well as selenocarbonyls, which differ considerably in their properties and reactivities from their alkyl and aryl counterparts and thus contribute in a gratifying manner to the still growing field of unsaturated element-carbon compounds of 3rd and 4th row main group elements E. Of particular interest is the influence of the fluorine substituents and other small groups (OR, NR₂) with either inductive and/or mesomeric effects on the polarity and reactivity of the EC bond. Addition reactions of proton acidic and hydridic polar HX reactants as well as [2+2], [3+2] and [4+2] cycloadditions have been thoroughly studied. The results obtained allow a classification of the EC systems within five different types, A to E, and prove a change from “normal” to “inverse” heteroalkenes in this sequence. The ligand properties of some derivatives have also been investigated in some detail.