August A. Gallo

Cu(I)-catalyzed allylic amination of olefins

Abstract The copper(I) complex [Cu(CH3CN)4]PF6 catalyzes the allylic amination of alkenes by aryl hydroxylamine in fair to moderate yields. Unsymmetrical alkenes react with high regioselectivity with N-functionalization occuring at the less substituted vinylic carbon. Trapping experiments indicate that free PhNO is not an intermediate in these reactions.

Cell wall components affect mechanical properties: studies with thistle flowers

Pollen presentation of Cirsium horridulum depends partially on the thigmonastic contraction of staminal filaments. Although the elastic cuticle is a major component in filament elasticity, it is not clear how the cell wall copes with the shape change. Based on mechanical studies, FT-IR spectroscopy and biochemical analyses we investigated the relationship between cell wall composition and elastic properties using thistle floral tissues as a model. EDTA-extractable pectin correlated with the increased elasticity of the filament and the basal style, suggesting that pectin plays a major role in the elastic behavior of soft tissues. In contrast, covalently linked pectin contributes to the stiffness of the upper style and corolla. Mechanical tests contrasting the soft basal and rigid apical parts of the style after incubation in solutions designed to alter the pectin network confirmed these results. The rigid corolla contained more cellulose than the softer style and filaments. The cellulose-associated xyloglucan of the style and filament cell walls increase the flexibility of cell walls.

QM/MM (ONIOM) study of glycerol binding and hydrogen abstraction by the coenzyme B12-independent dehydratase.

Glycerol binding and the radical-initiated hydrogen transfer by the coenzyme B(12)-independent glycerol dehydratase from Clostridium butyricum were investigated by using quantum mechanical/molecular mechanical (QM/MM) calculations based on the high-resolution crystal structure (PDB code: 1r9d). Our QM/MM calculations of enzyme catalysis considered the electrostatic coupling between the quantum-mechanical and molecular-mechanical subsystems and two alternative mechanisms. In addition to performing QM/MM calculations in the enzyme, we evaluated energetics along the same reaction pathway in aqueous solution modeled by the polarized dielectric and in the virtual enzyme site that included full steric component from the enzyme residues described by molecular mechanics but lacked the electrostatic contribution of these residues. In this way, we established significant enzyme catalytic effect with respect to reference reactions in both an aqueous solution and a nonpolar cavity. Structurally, four hydrogen bonds formed between glycerol and H164, S282, E435, and D447 anchor glycerol for hydrogen abstraction by thiyl radical on C433. These hydrogen-bond partners orient glycerol molecule to facilitate the formation of the transition state for hydrogen abstraction from carbon C1. This reaction then proceeds with the activation free energy of 6.3 kcal/mol and the reaction free energy of 6.1 kcal/mol. The polarization effects imposed by these hydrogen bonds represent a predominant contribution to a 7.5 kcal/mol enzyme catalytic effect. These results demonstrate the importance of electrostatic catalysis and hydrogen-bonding in enzyme-catalyzed radical reactions and advance our understanding of the catalytic mechanism of B(12)-independent glycerol dehydratases.

Direct Synthesis of β-Alkyl N-Aryl Aza Baylis–Hillman Adducts via Nitroso-Ene Reaction

A new approach for the direct Fe-catalyzed synthesis of β-alkyl N-aryl aza Baylis-Hillman (ABH) adducts is reported. This approach involves the formation of a C-N bond via a nitroso-ene reaction. This is a simple, fast, and best alternate method to overcome the substrate scope limitations of the ABH reaction, which converts allyl esters and carbonyl compounds to novel ABH adducts. A variety of arylhydroxylamines reacted with esters, aldehydes, ketone, and nitriles to yield the corresponding products in moderate to excellent yields.

CH···π Interactions Do Not Contribute to Hydrogen Transfer Catalysis by Glycerol Dehydratase

The role of the nonbonded CH···π interaction in the hydrogen abstraction from glycerol by the coenzyme B(12)-independent glycerol dehydratase (GDH) was examined using the QM/MM (ONIOM), MP2, and CCSD(T) methods. The studied CH···π interaction included the hydrogen atom of the -C(2)H(OH)- group of the glycerol substrate and the tyrosine-339 residue of the dehydratase. A contribution of this interaction to the stabilization of the transition state for the transfer of a hydrogen atom from the adjacent terminal C(1)H(2)(OH) group to cysteine 433 was determined by ab initio HF, MP2, and CCSD(T) calculations with the aug-cc-pvDZ basis set for the corresponding methane/benzene, methanol/phenol, and glycerol radical/phenol subsystems. The calculated CH···π distance, defined as the distance between the H atom and the center of the phenol ring, shortened from 2.62 to 2.52 Å upon going from the ground- to the transition-state of the GDH-catalyzed reaction. However, this shortening was not accompanied by the expected lowering of the CH···π interaction free energy. Instead, this interaction remained weak (about -1 kcal/mol) along the entire reaction coordinate. Additionally, the mutual orientation of the CH group and the phenol ring did not change significantly during the reaction. These results suggest that the phenol group of the tyrosine-339 does not contribute to lowering the activation barrier in the enzyme, but do not exclude the possibility that tyrosine 339 facilitates proper orientation of glycerol for the electrostatic catalysis, or inhibits side-reactions of the reactive glycerol radical intermediate.

The diversity and molecular modelling analysis of B 12-dependent and B 12-independent glycerol dehydratases

To broaden our knowledge on the diversity of glycerol dehydratases, comprehensive sequence and molecular modelling analyses of these enzymes were performed. Our sequence analysis showed that B 12-dependent and B 12-independent glycerol dehydratases are not related, suggesting that they evolved from different ancestors. Second, our study demonstrated that a gene fusion event occurred between α and β subunits of B 12-dependent glycerol dehydratases in several bacteria during enzyme evolution. In addition, our sequence and molecular modelling analyses revealed more B 12-independent glycerol dehydratases including hypothetical proteins. Furthermore, we found that some microorganisms contain both B 12-dependent and B 12-independent glycerol dehydratases in their genomes.

Cobalt(III) complexes of tripod amines. Kinetics of aquation of dichloro(N-(2-aminoethyl)-N,N-bis- (3-aminopropyl)amine)cobalt(III) ion

A new series of six-coordinate cobalt(III) complexes containing tripod tetradentate-N donors (N4), [Co(abap)Cl2]ClO4 · H2O, [Co(abap)(H2O)Cl]Cl(ClO4) and [Co(N4)X2]ClO4 (N4 = abap, X = N3, NO2; N4 = TPA, X = Cl, NO2) where abap = N-(2-aminoethyl)-N,N-bis(3-aminopropyl)amine and TPA = tris(2-pyridylmethyl)amine were synthesized and characterized by elemental analyses, UV–Vis, and IR. The kinetics of the primary aquation of the complex ion [Co(abap)Cl2]+ to [Co(abap)(H2O)Cl]2+ was followed spectrophotometrically in 50/50 (v/v) CH3CN/aqueous HClO4 (16–37°C and I = 0.50 M NaClO4). Rate constants (k 1) evaluated under pseudo first-order conditions, were found to be independent of the [H3O+] over the range of 0.10–0.50 M HClO4 and of the initial complex concentration. At 25°C, the k 1 value was found to be 1.65 × 10−3 s−1 indicating that this process is, unexpectedly, slightly slower than the corresponding reaction in [Co(tren)Cl2]+ (k 1 = 2.96 × 10−3 s−1). The activation parameters were calculated (  = 61.9 ± 1.8 kJ mol−1 and  = −91.0 ± 6.1 J K−1mol−1), and the results are discussed in relation to other closely related systems with a dissociative I d mechanism.

Bone Glue Modified Asphalt: A Step towards Energy Conservation and Environment Friendly Modified Asphalts

Asphalt has been modified for the past several decades using various additives, including synthetic polymers. Polymer modification improves structural and engineering characteristics of the binder, which is a result of improvement in rheological characteristics of binder as well as its adhesion capability with the aggregate. Such enhancement inevitably enhances the performance characteristics of hot mix asphalts (HMA) such as fatigue life, resistance to rutting, and thermal cracking. Even though polymer-modified HMA is popular in North America and European countries, its use is still limited in developing countries of Southeast Asia due to high costs associated with its manufacturing, processing, and energy consumption. In this study, a new kind of asphalt modifier derived from animal wastes, such as bones, hides, and flesh commonly known as Bone Glue, is studied. This biomaterial which is a by-product of food and cattle industries is cheap, conveniently available, and produced locally in developing countries. The results of the research study showed that the bone glue can easily be mixed with asphalt without significantly altering the asphalt binders viscosity and mixing and compaction temperatures of HMA. Additionally, improvements in complex shear modulus for a range of temperatures were also determined and it was found that complex shear modulus was improved by bone glue modification.