Visible light photocatalysis in synthesis of pharmaceutically relevant heterocyclic scaffolds

Visible light and photoredox catalysis have emerged as a powerful and long-lasting tool for organic synthesis, demonstrating the importance of a variety of chemical bond formation methods. Natural products, physiologically...

2D-Map of Intermolecular Interactions in Organic Chemistry Reveals Underrepresented Area of Research

The molecular orbital (MO) theory is an indispensable model to describe the interaction between two molecular species, particularly during chemical bond formation. Here we show that by plotting the energy difference (E_DA) of the HOMO of an electron donor and the LUMO of an acceptor against their overlap integral (S_DA), many similar types of bimolecular interactions tend to be clustered near one another on the 2D map. Interestingly, in one of the six arbitrarily divided sections designated as “B2”, the interacting molecular pairs appear to present a type of interaction as a “hybrid” between chemical reaction and radical pair formation, a lesser explored area of research. We propose that such interactions could be crucial for the development of materials with unique optical, magnetic, and catalytic properties from purely organic molecules.<br>

2D-Map of Intermolecular Interactions in Organic Chemistry Reveals Underrepresented Area of Research

The molecular orbital (MO) theory is an indispensable model to describe the interaction between two molecular species, particularly during chemical bond formation. Here we show that by plotting the energy difference (E_DA) of the HOMO of an electron donor and the LUMO of an acceptor against their overlap integral (S_DA), many similar types of bimolecular interactions tend to be clustered near one another on the 2D map. Interestingly, in one of the six arbitrarily divided sections designated as “B2”, the interacting molecular pairs appear to present a type of interaction as a “hybrid” between chemical reaction and radical pair formation, a lesser explored area of research. We propose that such interactions could be crucial for the development of materials with unique optical, magnetic, and catalytic properties from purely organic molecules.<br>

Natural Tannins as New Cross-Linking Materials for Soy-Based Adhesives

Human health problems and formaldehyde emission from wood-based composites are some of the major drawbacks of the traditional synthetic adhesives such as urea formaldehyde resins. There have been many attempts to decrease formaldehyde emission and replace urea formaldehyde resins with bio-based adhesives for wood-based composites. Because of some weakness in soy-based adhesive, chemicals have been used as modifiers. Modified soy-based adhesives without any formaldehyde have been successfully used to prepare wood panels. To achieve this, different synthetic cross-linking chemicals such as phenol formaldehyde resins and polyamidoamine-epichlorohydrin were used. However, in reality, what we need are totally green adhesives that use natural materials. In our previous research work, the use of tannins in combination with soy-based adhesives to make wood composites was investigated. Thus, in this research work, the feasibility of using three types of natural tannins (quebracho, mimosa and chestnut tannins) as cross-linking materials for soy adhesive was studied. The chemical bond formation and adhesion behaviors of tannin-modified soy adhesives were also investigated by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-ToF-MS) and thermo-mechanical analysis (TMA). The results showed that at ambient temperature, both ionic and covalent bonds formed between tannin constituents and amino acids; however, at higher temperature, covalent bonds are largely predominate. Based on the results obtained from the thermo-mechanical analysis, the modulus of elasticity (MOE) of soy adhesive is increased by adding tannins to its formulation. In addition, the chemical bond formation was proved by MALDI-ToF-MS.

Following the microscopic pathway to adsorption through chemisorption and physisorption wells

Adsorption involves molecules colliding at the surface of a solid and losing their incidence energy by traversing a dynamical pathway to equilibrium. The interactions responsible for energy loss generally include both chemical bond formation (chemisorption) and nonbonding interactions (physisorption). In this work, we present experiments that revealed a quantitative energy landscape and the microscopic pathways underlying a molecule’s equilibration with a surface in a prototypical system: CO adsorption on Au(111). Although the minimum energy state was physisorbed, initial capture of the gas-phase molecule, dosed with an energetic molecular beam, was into a metastable chemisorption state. Subsequent thermal decay of the chemisorbed state led molecules to the physisorption minimum. We found, through detailed balance, that thermal adsorption into both binding states was important at all temperatures.

Chemical bond formation showing a transition from physisorption to chemisorption

Surface molecules can transition from physisorption through weak van der Waals forces to a strongly bound chemisorption state by overcoming an energy barrier. We show that a carbon monoxide (CO) molecule adsorbed to the tip of an atomic force microscope enables a controlled observation of bond formation, including its potential transition from physisorption to chemisorption. During imaging of copper (Cu) and iron (Fe) adatoms on a Cu(111) surface, the CO was not chemically inert but transited through a physisorbed local energy minimum into a chemisorbed global minimum, and an energy barrier was seen for the Fe adatom. Density functional theory reveals that the transition occurs through a hybridization of the electronic states of the CO molecule mainly with s-, pz-, and dz2-type states of the Fe and Cu adatoms, leading to chemical bonding.

Evidence of chemical-bond formation at the interface between an epoxy polymer and an isocyanate primer

Sum frequency generation spectroscopy was applied to confirm the presence of a chemical bond at the joining interfaces, suggesting that MDI primers can serve as a chemical bridge for urethane adhesives.

Fabrication of an advanced epoxy based molding compound with high thermal conductivity and outstanding mechanical properties

A novel molding compound was fabricated through surface modification of aluminum particles followed by chemical grafting to an epoxy based resin. The fabricated material demonstrated high thermal conductivity and outstanding mechanical properties. A thin layer of alumina was formed on the surface of aluminum particles (spherical with average 30 μm in diameter) by ultrasonic treatment with hydrogen peroxide followed by functionalization with a hydroxylated long-chain organic acid. The fabricated composite was chemically bonded to epoxy skeleton. The chemical bond formation between the filler and organic matrix was responsible for high thermal conductivity as well as outstanding mechanical properties. As well, the loading capacity of epoxy matrix to surface modified fillers was remarkably higher than non-modified fillers.