The recently developed high-accuracy extrapolated ab initio thermochemistry method for theoretical thermochemistry, which is intimately related to other high-precision protocols such as the Weizmann-3 and focal-point approaches, is revisited. Some minor improvements in theoretical rigor are introduced which do not lead to any significant additional computational overhead, but are shown to have a negligible overall effect on the accuracy. In addition, the method is extended to completely treat electron correlation effects up to pentuple excitations. The use of an approximate treatment of quadruple and pentuple excitations is suggested; the former as a pragmatic approximation for standard cases and the latter when extremely high accuracy is required. For a test suite of molecules that have rather precisely known enthalpies of formation {as taken from the active thermochemical tables of Ruscic and co-workers [Lecture Notes in Computer Science, edited by M. Parashar (Springer, Berlin, 2002), Vol. 2536, pp. 25-38; J. Phys. Chem. A 108, 9979 (2004)]}, the largest deviations between theory and experiment are 0.52, -0.70, and 0.51 kJ mol(-1) for the latter three methods, respectively. Some perspective is provided on this level of accuracy, and sources of remaining systematic deficiencies in the approaches are discussed.

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 10% post consumer waste. Cellulase C. bescii CelA, a highly active and stable enzyme, exhibits a new cellulose digestion paradigm promoting inter-cellulase synergy. C. bescii CelA, a hydrolytic enzyme with multiple functional domains, may have several advantages over other fungal and bacterial cellulases for use in biofuels production: very high specific activity, stability at elevated temperatures , and a novel digestion mechanism.

A new method is presented for treating the effects of quadruple excitations in coupled-cluster theory. In the approach, quadruple excitation contributions are computed from a formula based on a non-Hermitian perturbation theory analogous to that used previously to justify the usual noniterative triples correction used in the coupled cluster singles and doubles method with a perturbative treatment of the triple excitations (CCSD(T)). The method discussed in this paper plays a parallel role in improving energies obtained with the full coupled-cluster singles, doubles, and triples method (CCSDT) by adding a perturbative treatment of the quadruple excitations (CCSDT(Q)). The method is tested for an extensive set of examples, and is shown to provide total energies that compare favorably with those obtained with the full singles, doubles, triples, and quadruples (CCSDTQ) method.

Lignin is a major component of plant cell walls that is typically underutilized in selective conversion strategies for renewable fuels and chemicals. The mechanisms by which thermal and catalytic treatments deconstruct lignin remain elusive, which is where quantum mechanical calculations can offer fundamental insights. Here, we compute homolytic bond dissociation enthalpies (BDEs) for four prevalent linkages in 69 lignin model compounds, including β-O-4, α-O-4, β-5, and biphenyl bonds, with a large range of natural and oxidized substituents. These calculations include ab initio benchmark values extrapolated to the complete basis set limit and full conformational searches for each compound. The results quantify both the relative BDEs among common lignin bonds and the effect of native and oxidized substituents on the functional groups in lignin. These data yield insights into thermal lignin deconstruction for a large range of prevalent linkages and aid in the identification of targets for catalytic cleavage.

Cellulose is a crystalline polymer of β1,4-D-glucose that is difficult to deconstruct to sugars by enzymes. The recalcitrance of cellulose microfibrils is a function of both the shape of cellulose microfibrils and the intrinsic work required to decrystallize individual chains, the latter of which is calculated here from the surfaces of four crystalline cellulose polymorphs: cellulose Iβ, cellulose Iα, cellulose II, and cellulose III(I). For edge chains, the order of decrystallization work is as follows (from highest to lowest): Iβ, Iα, ΙΙΙ(Ι), and II. For cellulose Iβ, we compare chains from three different locations on the surface and find that an increasing number of intralayer hydrogen bonds (from 0 to 2) increases the intrinsic decrystallization work. From these results, we propose a microkinetic model for the deconstruction of cellulose (and chitin) by processive enzymes, which when taken with a previous study [Horn et al. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 18089] identifies the thermodynamic and kinetic attributes of enzyme and substrate engineering for enhanced cellulose (or chitin) conversion. Overall, this study provides new insights into the molecular interactions that form the structural basis of cellulose, which is the primary building block of plant cell walls, and highlights the need for experimentally determining microfibril shape at the nanometer length scale when comparing conversion rates of cellulose polymorphs by enzymes.

Intermediates of bacterial aromatic catabolism contain chemical functionality that could enable them to serve as precursors to environmentally compatible materials with similar or superior properties relative to petroleum-derived incumbents. Here, Pseudomonas putida was engineered to convert aromatic molecules and glucose into 16 of these metabolic intermediates including muconic acid, which was produced at a 41% yield from glucose. Several of these molecules were then polymerized to generate performance-advantaged materials.

Background: Aromatic residues line glycoside hydrolase active sites mediating ligand binding. Results: Binding affinity is significantly altered upon tryptophan to alanine mutation, although relative to the location in the active site. Conclusion: Aromatic-carbohydrate interactions are employed in a variety of functionalities within the purview of ligand binding. Significance: Understanding the functional role of aromatic residues in the active site is necessary for the rational design of new carbohydrate-active enzymes.

Background:Lignin is a plant cell wall polymer that inhibits enzymatic saccharification of polysaccharides for the production of biofuel. Results: The adsorption of enzymes to lignin surfaces correlates to solvent-exposed hydrophobic clusters. Conclusion: Hydrophobicity, not surface charge, identifies proteins that preferentially adsorb to lignin. Significance: The method could be used to design improved cellulase cocktails to lower the cost of biofuel production.