Functionalized Hydroperoxide Formation from the Reaction of Methacrolein-Oxide,an Isoprene-Derived Criegee Intermediate,with Formic Acid: Experiment and Theory

Methacrolein oxide (MACR-oxide) is a four-carbon, resonance-stabilized Criegee intermediate produced from isoprene ozonolysis, yet its reactivity is not well understood. This study identifies the functionalized hydroperoxide species, 1-hydroperoxy-2-methylallyl formate (HPMAF), generated from the reaction of MACR-oxide with formic acid using multiplexed photoionization mass spectrometry (MPIMS, 298 K = 25 °C, 10 torr = 13.3 hPa). Electronic structure calculations indicate the reaction proceeds via an energetically favorable 1,4-addition mechanism. The formation of HPMAF is observed by the rapid appearance of a fragment ion at m/z 99, consistent with the proposed mechanism and characteristic loss of HO₂ upon photoionization of functional hydroperoxides. The identification of HPMAF is confirmed by comparison of the appearance energy of the fragment ion with theoretical predictions of its photoionization threshold. The results are compared to analogous studies on the reaction of formic acid with methyl vinyl ketone oxide (MVK-oxide), the other four-carbon Criegee intermediate in isoprene ozonolysis.     

Diazo compounds for the bioreversible esterification of proteins

A diazo compound is shown to convert carboxylic acids to esters efficiently in an aqueous environment. The basicity of the diazo compound is critical: low basicity does not lead to a reaction but high basicity leads to hydrolysis. This reactivity extends to carboxylic acid groups in a protein. The ensuing esters are hydrolyzed by human cellular esterases to regenerate protein carboxyl groups. This new mode of chemical modification could enable the key advantages of prodrugs to be translated from small-molecules to proteins.     

Aromatic molecules in anion recognition: electrostatics versus H-bonding

Mass-selected complexes A-.C6FnH(6-n) (A = Cl, I, SF6; n = 0-5) were studied by infrared photodissociation spectroscopy and computational chemistry methods to investigate the interaction of negative ions and aromatic molecules, in which the charge distribution can be tuned by fluorination. Surprisingly, we find that, despite positive partial charges on the carbon atoms at high levels of fluorination, all anions under study prefer hydrogen bonding to the remaining H atoms in the ligand rather than binding to the positively charged ring. Moreover, bifurcated hydrogen bonds to two neighboring CH groups are energetically favored over linear hydrogen bonds to a single CH group.     

Systematic investigation of trigonal-bipyramidal cyanide-bridged clusters of the first-row transition metals

Reactions between [M'(III)(CN)(6)](3-) anions (M' = Co, Cr, or Fe) and mononuclear complexes of M(II) ions (M = Cr, Mn, Co, Ni, or Zn) produce a family of pentanuclear clusters {[M(tmphen)(2)](3)[M'(CN)(6)](2)]}. The core of the clusters is formed by five metal ions that are bridged through six CN- linkers into a trigonal bipyramid, with M and M' ions occupying equatorial and axial positions of the bipyramid, respectively. Three of the CN- ligands from each M' center remain terminal and point toward the outside of the cluster, along the trigonal axes. Studies of magnetic coupling in the {[M(tmphen)(2)](3)[M'(CN)(6)](2)]} family of clusters revealed a similarity between the observed magnetic exchange constants and the values estimated for the molecule-based magnets of the Prussian blue family. The type of the magnetic exchange varies across the series, changing from antiferromagnetic for M = Cr and Mn to ferromagnetic for M = Co and Ni. Complexes {[M(tmphen)(2)](3)[M'(CN)(6)](2)]}, which contain diamagnetic Co(III) ions in the axial positions, serve as convenient model compounds for an accurate assessment of the magnetic parameters for the equatorial M ions in the absence of magnetic interactions. The {[Co(tmphen)(2)](3)[Cr(CN)(6)](2)]} cluster exhibits cyanide linkage isomerism, the relative amount of which depends on the synthetic conditions.     

Economic analysis of ethanol production in California using traditional and innovative feedstock supplies

In this article, we estimate the costs of using alternative feedstocks to produce ethanol in a 40 million-gal facility in California’s San Joaquin Valley. Feedstocks include corn imported from Midwestern states and locally grown agricultural products such as corn, grapes, raisins, oranges, and other tree fruits. The estimated feedstock costs per gallon of ethanol include $0.92 for Midwestern corn, $1.21 for locally grown corn, $6.79 for grapes, $3.36 for raisins, $3.92 for citrus, and $1.42 for other tree fruit. Adjusting for coproduct values lowers the estimated net feedstock costs to $0.67/gal of ethanol for Midwestern corn, $0.96 for locally grown corn, $6.53 for grapes, and $3.30 for raisins. We also examine the potential increases in net revenue to raisin producers, made possible by having an alternative outlet available for selling surplus raisins.     

Analysis of commercial beverage products by size exclusion chromatography coupled with UV-vis absorbance detection and dynamic surface tension detection

Multidimensional analysis of instant coffee and barley beverage samples using size exclusion chromatography (SEC) combined with a dynamic surface tension detector (DSTD) and a UV-vis absorbance detector (UV) is reported. A unique finding of this study was the action of the tetrabutylammonium (TBA) cation as a modifying agent (with bromide as the counter anion) that substantially increased the surface pressure signal and sensitivity of many of the proteins in the chromatographically separated samples. The tetrabutylammonium bromide (TBAB) enhancement of the surface pressure signal was further investigated by studying the response of 12 commercial standard proteins (α-lactalbumin, β-lactoglobulin, human serum albumin (HSA), albumin from chicken egg white (OVA), bovine serum albumin (BSA), hemoglobin, α-chymotrypsinogen A, cytochrome C, myoglobin, RNase A, carbonic anhydrase, and lysozyme) in buffer performed using flow injection analysis (FIA) coupled with the DSTD with and without various concentrations of TBAB. The FIA-DSTD data show that 1 mM TBAB enhances sensitivity of HSA detection, by lowering the limit of detection (LOD) from 2 mg/mL to 0.1 mg/mL. Similarly, the LOD for BSA was reduced from 1 mg/mL to 0.2 mg/mL. These FIA-DSTD experiments allowed the detection conditions to be optimized for further SEC-UV/DSTD experiments. Thus, the SEC-UV/DSTD system has been optimized and successfully applied to the selective analysis of surface-active protein fractions in a commercial instant coffee sample and in a soluble barley sample. The complementary selectivity of using the DSTD relative to an absorbance detector is also demonstrated.     

A third mode of DNA binding: Phosphate clamps by a polynuclear platinum complex

We describe a 1.2 A X-ray structure of a double-stranded B-DNA dodecamer (the Dickerson Dodecamer, DDD, [d(CGCGAATTCGCG)]2) associated with a cytotoxic platinum(II) complex, [{trans-Pt(NH3)2(NH2(CH2)6(NH3+)}2-mu-{trans-Pt(NH3)2(NH2(CH2)6NH2)2}] (TriplatinNC). TriplatinNC is a multifunctional DNA ligand, with three cationic Pt(II) centers, and directional hydrogen bonding functionalities, linked by flexible hydrophobic segments, but without the potential for covalent interaction. TriplatinNC does not intercalate nor does it bind in either groove. Instead, it binds to phosphate oxygen atoms and thus associates with the backbone. The three square-planar tetra-am(m)ine Pt(II) coordination units form bidentate N...O...N complexes with OP atoms, in a motif we call the Phosphate Clamp. The geometry is conserved among the 8 observed phosphate clamps in this structure. The interaction appears to prefer O2P over O1P atoms (frequency of interaction is O2P > O1P, base and sugar oxygens > N). The high repetition and geometric regularity of the motif suggests that this type of Pt(II) center can be developed as a modular nucleic acid binding device with general utility. TriplatinNC extends along the phosphate backbone, in a mode of binding we call "Backbone Tracking" and spans the minor groove in a mode of binding we call "Groove Spanning". Electrostatic forces appear to induce modest DNA bending into the major groove. This bending may be related to the direct coordination of a sodium cation by a DNA base, with unprecedented inner-shell (direct) coordination of penta-hydrated sodium at the O6 atom of a guanine.     

New cuprates featuring ladderlike periodic arrays of [Cu3O8]10- trimeric magnetic nanostructures

A new family of cuprates, Li2Cu3(SiO3)4 (1) and Na2Cu3(GeO3)4 (2), was isolated in molten salt media. The extended lattices contain ladderlike periodic arrays of [Cu3O8]10- magnetic nanostructures. Magnetic properties of the Na2Cu3Ge(4-x)SixO12 series, where x = 0, 0.86, and 1.72, were systematically studied. The geometrically induced magnetic couplings are tunable upon cation substitution.