Perry J. Pellechia

Tailoring Microporosity in Covalent Organic Frameworks

The microporosity of covalent organic frameworks (COFs) is tailored using a facile synthetic approach that introduces alkyl functionalities into the pore and generates networks with pore diameters between 1-2 nm. The added substituents significantly alter the host-guest properties of the resulting materials.

Influence of reaction time and temperature on product formation and characteristics associated with the hydrothermal carbonization of cellulose

Studies have demonstrated that hydrothermal carbonization of biomass and waste streams results in the formation of beneficial materials/resources with minimal greenhouse gas production. Data necessary to understand how critical process conditions influence carbonization mechanisms, product formation, and associated environmental implications are currently lacking. The purpose of this work is to hydrothermally carbonize cellulose at different temperatures and to systematically sample over a 96-h period to determine how changes in reaction temperature influence product evolution. Understanding cellulose carbonization will provide insight to carbonization of cellulosic biomass and waste materials. Results from batch experiments indicate that the majority of cellulose conversion occurs between the first 0.5-4h, and faster conversion occurs at higher temperatures. Data collected over time suggest cellulose solubilization occurs prior to conversion. The composition of solids recovered after 96h is similar at all temperatures, consisting primarily of sp(2) carbons (furanic and aromatic groups) and alkyl groups.

Self-Assembled Phenylethynylene Bis-urea Macrocycles Facilitate the Selective Photodimerization of Coumarin

There is much interest in designing molecular sized containers that influence and facilitate chemical reactions within their nanocavities. On top of the advantages of improved yield and selectivity, the studies of reactions in confinement also give important clues that extend our basic understanding of chemical processes. We report here, the synthesis and self-assembly of an expanded bis-urea macrocycle to give crystals with columnar channels. Constructed from two C-shaped phenylethynylene units and two urea groups, the macrocycle affords a large pore with a diameter of ∼9 Å. Despite its increased size, the macrocycles assemble into columns with high fidelity to afford porous crystals. The porosity and accessibility of these channels have been demonstrated by gas adsorption studies and by the uptake of coumarin to afford solid inclusion complexes. Upon UV-irradiation, these inclusion complexes facilitate the conversion of coumarin to its anti-head-to-head (HH) photodimer with high selectivity. This is contrary to what is observed upon the solid-state irradiation of coumarin, which affords photodimers with low selectivity and conversion.

A rigid molecular balance for measuring face-to-face arene-arene interactions.

A new molecular balance was developed to measure face-to-face arene-arene interactions. The balance adopts distinct folded and unfolded conformations due to restricted rotation about a C aryl-N imide bond. In the folded conformer, the rigid bicyclic framework enforces an offset face-to-face geometry to the exclusion of edge-to-face geometries, which was verified by X-ray crystallography. Measurement of the folded to unfolded ratio yields accurate values for the arene-arene interaction in a range of different solvents.

Thermal Reaction of a Columnar Assembled Diacetylene Macrocycle

Reported is a macrocyclic diacetylene that assembled into columns to afford porous crystals. Heating this assembly initiated a topochemical polymerization of the preorganized diacetylene units to give covalent conjugated polydiacetylenes. These stable conjugated materials maintained permanent porosity as evidenced by their type I gas adsorption isotherms with CO(2) (g). Such conjugated polymeric nanotubes could possess unusual properties for sensing and electronics.

Additivity of Substituent Effects in Aromatic Stacking Interactions

The goal of this study was to experimentally test the additivity of the electrostatic substituent effects (SEs) for the aromatic stacking interaction. The additivity of the SEs was assessed using a small molecule model system that could adopt an offset face-to-face aromatic stacking geometry. The intramolecular interactions of these molecular torsional balances were quantitatively measured via the changes in a folded/unfolded conformational equilibrium. Five different types of substituents were examined (CH3, OCH3, Cl, CN, and NO2) that ranged from electron-donating to electron-withdrawing. The strength of the intramolecular stacking interactions was measured for 21 substituted aromatic stacking balances and 21 control balances in chloroform solution. The observed stability trends were consistent with additive SEs. Specifically, additive SE models could predict SEs with an accuracy from ±0.01 to ±0.02 kcal/mol. The additive SEs were consistent with Wheeler and Houks direct SE model. However, the indirect or polarization SE model cannot be ruled out as it shows similar levels of additivity for two to three substituent systems, which were the number of substituents in our model system. SE additivity also has practical utility as the SEs can be accurately predicted. This should aid in the rational design and optimization of systems that utilize aromatic stacking interactions.

Do deuteriums form stronger CH-π interactions?

The D/H isotope effect for the CH-π interaction was studied experimentally and computationally. First, a series of molecular balances that are very sensitive to changes in the strength of the CH-π interactions in solution were designed. Balances with deuterated and non-deuterated alkyl groups were synthesized, and their intramolecular CH-π interactions were compared. The geometries of their intramolecular CH-π and CD-π interactions were characterized in the solid state by X-ray analysis, and the strength of each interaction was characterized in solution by the folded/unfolded ratio as measured by (1)H NMR spectra. Second, the relative strengths of the CH-π and CD-π interactions were also assessed computationally using dispersion-corrected DFT (PDE-D2/6-31+G*). No significant differencee was observed in either the experimental or theoretical studies, indicating that the D/H isotope effect for the CH-π interaction is either very small or nonexistent.

A Molecular Balance for Measuring Aliphatic CH−π Interactions

A series of conformationally flexible bicyclic N-arylimides were employed as molecular balances to study the weak aliphatic CH-π interaction between alkyl and arene groups. The formation of intramolecular CH-π interactions in the folded conformers was characterized by X-ray crystallography. The strengths of the interactions were characterized in CDCl(3) by the changes in the folded/unfolded ratios, as measured by (1)H NMR. The CH-π interaction between a methyl group and an aromatic surface was ∼1.0 kcal/mol and was easily disrupted or masked by conformational entropy and repulsive steric interactions.

Phosphorus forms in conventional and organic dairy manure identified by solution and solid state p-31 NMR spectroscopy.

Organic dairy production has increased rapidly in recent years. Organic dairy cows (Bos taurus) generally eat different diets than their conventional counterparts. Although these differences could impact availability, utilization, and cycling of manure nutrients, little such information is available to aid organic dairy farmers in making nutrient and manure management decisions. In this study, we comparatively characterized P in organic and conventional dairy manure using solution and solid state (31)P NMR spectroscopic techniques. Phosphorus in both types of dairy manure was extracted with water, Na acetate buffer (100 mmol L(-1), pH 5.0) plus 20 mg Na dithionite mL(-1), or 0.025 mol L(-1) NaOH with 50 mmolL(-1) EDTA. Solution NMR analysis revealed that organic dairy manure contained about 10% more inorganic phosphate than conventional dairy manure. Whereas organic dairy manure did contain slightly more phytate P, it contained 30 to 50% less monoester P than conventional dairy manure. Solid state NMR spectroscopy revealed that mono-, di-, and trivalent metal P species with different stabilities were present in the two dairy manures. Conventional dairy manure contained relatively higher contents of soluble inorganic P species and stable metal phytate species. In contrast, organic dairy manure contained more Ca and Mg species of P. These results indicate that P transformation rates and quantities should be expected to differ between organic and conventional dairy manures.

Proton grease: an acid accelerated molecular rotor.

A molecular rotor was designed that rotates 7 orders of magnitude faster upon protonation. The quinoline rotor is based on a rigid N-arylimide framework that displays restricted rotation due to steric interaction between the quinoline nitrogen and imide carbonyls. At rt (23 °C), the rotor rotates slowly (t(1/2) = 26 min, ΔG(‡) = 22.2 kcal/mol). However, upon addition of 3.5 equiv of acid the rotor rotates rapidly (t(1/2) = 2.0 × 10(-4) s, ΔG(‡) = 12.9 kcal/mol). Mechanistic studies show that this dramatic acid catalyzed change is due to stabilization of the planar transition state by the formation of an intramolecular hydrogen bond between the protonated quinoline nitrogen (N(+)-H) and an imide carbonyl (O═C). The acid catalyzed acceleration is reversible and can be stopped by addition of base.