New hybrid method for reactive systems from integrating molecular orbital or molecular mechanics methods with analytical potential energy surfaces Potential energy surface for the CH 3 + HBr → CH 4 + Br hydrogen abstraction reaction: Thermal and stateselected rate constants, and kinetic isotope effects Ab initio molecular orbital and density functional characterization of the potential energy surface of the N 2 O+Br reaction J. Chem. Phys. 109, 9410 (1998); 10.1063/1.477602An ab initio molecular orbital study of the potential energy surface of the HO 2 +NO reaction We present an efficient algorithm for generating semiglobal potential energy surfaces of reactive systems. The method takes as input molecular mechanics force fields for reactants and products and a quadratic expansion of the potential energy surface around a small number of geometries whose locations are determined by an iterative process. These Hessian expansions might come, for example, from ab initio electronic structure calculations, density functional theory, or semiempirical molecular orbital theory. A 2ϫ2 electronic diabatic Hamiltonian matrix is constructed from these data such that, by construction, the lowest eigenvalue of this matrix provides a semiglobal approximation to the lowest electronically adiabatic potential energy surface. The theory is illustrated and tested by applications to rate constant calculations for three gas-phase test reactions, namely, the isomerization of 1,3-cis-pentadiene, OHϩCH

The dynamics of the double proton transfer in formic acid dimer (FAD) complex has been studied by the direct dynamics approach with variational transition state theory using multidimensional semiclassical tunneling approximations. High-level ab initio quantum mechanical calculations were performed to estimate the energetics of the double proton transfer. Dimerization energies and the barrier height have been calculated at the G2* level of theory, which yields -14.2 and 8.94 kcal mol -1 , respectively. A quantum mechanical potential energy surface has been constructed using the AM1 Hamiltonian with specific reaction parameters (AM1-SRP) which are obtained by adjusting the standard AM1 parameters to reproduce the energetics by high-level ab initio quantum mechanical calculation. The minimum energy path has been calculated on this potential energy surface and other characteristics of the surface were calculated as needed. The two protons are transferred synchronously, so the transition state possesses D 2h symmetry. The reaction path curvature is very large, so the tunneling coefficient is also very large as calculated by the large-curvature ground-state tunneling approximation (LCG3). The distance which the proton hops during tunneling is about 0.429 Å. This is a very long distance compared with the normal single proton transfer. Before the tunneling the hydrogenic motion is minimal. Mostly the heavy atoms move to bring the two formic acid molecules closer. The kinetic isotope effect (KIE) was also calculated. The tunneling contribution to the KIE is not extremely large since not only two protons but two deuterium atoms tunnel well. The quasiclassical contribution to the KIE is quite large due to the synchronous motion of the two protons.

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Gibberella zeae, a major cause of cereal scab, may be divided into two chemotypes based on production of the trichothecenes deoxynivalenol (DON) and nivalenol (NIV). We cloned and sequenced the gene cluster for trichothecene biosynthesis from each chemotype. G. zeae H-11 is a DON producer isolated from corn, and G. zeae 88-1 is a NIV producer from barley. We sequenced a 23-kb gene cluster from H-11 and a 26-kb cluster from 88-1, along with the unlinked Tri101 genes. Each gene cluster contained 10 Tri gene homologues in the same order and transcriptional directions as those of Fusarium sporotrichioides. Between H-11 and 88-1 all of the Tri homologues except Tri7 were conserved, with identities ranging from 88 to 98% and 82 to 99% at the nucleotide and amino acid levels, respectively. The Tri7 sequences were only 80% identical at the nucleotide level. We aligned the Tri7 genes and found that the Tri7 open reading frame of H-11 carried several mutations and an insertion containing 10 copies of an 11-bp tandem repeat. The Tri7 gene from 88-1 carried neither the repeat nor the mutations. We assayed 100 G. zeae isolates of both chemotypes by PCR amplification with a primer pair derived from the Tri7 gene and could differentiate the chemotypes by polyacrylamide gel electrophoresis. The PCR-based method developed in this study should provide a simple and reliable diagnostic tool for differentiating the two chemotypes of G. zeae.

Double-stranded RNA (dsRNA) viruses in some fungi are associated with hypovirulence and have been used or proposed as biological control agents. We isolated 7.5-kb dsRNAs from 13 of 286 field strains of Fusarium graminearum isolated from maize in Korea. One of these strains, DK21, was examined in more detail. This strain had pronounced morphological changes, including reduction in mycelial growth, increased pigmentation, reduced virulence towards wheat, and decreased (60-fold) production of trichothecene mycotoxins. The presence or absence of the 7.5-kb dsRNA was correlated with the changes in pathogenicity and morphology. The dsRNA could be transferred to virus-free strains by hyphal fusion, and the recipient strain acquired the virus-associated phenotype of the donor strain. The dsRNA was transmitted to approximately 50% of the conidia, and only colonies resulting from conidia carrying the mycovirus had the virus-associated phenotype. Partial nucleotide sequences of the purified dsRNA identify an RNA-dependent RNA polymerase sequence and an ATP-dependent helicase that are closely related to those of Cryphonectria hypovirus and Barley yellow mosaic virus. Collectively, these results suggest that this dsRNA isolated from F. graminearum encodes traits for hypovirulence.Double-stranded RNA (dsRNA) mycoviruses have been described for a wide variety of fungi and plant-pathogenic fungi (7,9,27,42,44,55,58). These dsRNA mycoviruses are classified into three families based on number of genome segments, capsid structure, and nucleotide sequences, with some dsRNA mycoviruses remaining unclassified (8,20,24,31,39,45). The isometric dsRNA mycoviruses are classified into two families, Totiviridae and Partitiviridae, consisting of viruses that are enclosed in nonenveloped isometric particles of 25 to 50 nm in diameter and typically cause latent infections in their host fungi (20). Totiviruses have a nonsegmented genome, while partitiviruses have segmented genomes. Hypoviruses (family Hypoviridae) are the unusual exception in that they can result in considerable morphological and physiological changes, including cytological alterations, changes in colony morphology and growth rate, and persistently attenuate novel virulence-related phenotypes (hypovirulence) (2,7,13,25,28,34,42). Hypoviruses lack conventional virions, and their dsRNAs are enclosed in host-encoded vesicles (17).Among Fusarium species, dsRNA mycoviruses have been reported to be present in F. poae and F. solani f. sp. robiniae (14,39,40). dsRNA elements of the same electrophoretic mobility isolated from vegetatively compatible strains of F. poae were similar or identical in many cases. Similar-sized dsRNA elements of vegetatively incompatible strains of the fungus could contain both homologous and nonhomologous dsRNAs (14). Morphological alterations or signs of degeneration of F. poae, however, were not observed in any of the dsRNA-containing isolates.We have isolated Fusarium graminearum Schwabe [telemorph: Gibberella zeae (Schwein.) Petch] and occasionally fou...

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Triboelectric charging involves frictional contact of two different materials, and their contact electrification usually relies on polarity difference in the triboelectric series. This limits the choices of materials for triboelectric contact pairs, hindering research and development of energy harvest devices utilizing triboelectric effect. A progressive approach to resolve this issue involves modification of chemical structures of materials for effectively engineering their triboelectric properties. Here, we describe a facile method to change triboelectric property of a polymeric surface via atomic-level chemical functionalizations using a series of halogens and amines, which allows a wide spectrum of triboelectric series over single material. Using this method, tunable triboelectric output power density is demonstrated in triboelectric generators. Furthermore, molecular-scale calculation using density functional theory unveils that electrons transferred through electrification are occupying the PET group rather than the surface functional group. The work introduced here would open the ability to tune triboelectric property of materials by chemical modification of surface and facilitate the development of energy harvesting devices and sensors exploiting triboelectric effect.

We show by experiments that nonheme Fe(IV)O species react with cyclohexene to yield selective hydrogen atom transfer (HAT) reactions with virtually no C═C epoxidation. Straightforward DFT calculations reveal, however, that C═C epoxidation on the S = 2 state possesses a low-energy barrier and should contribute substantially to the oxidation of cyclohexene by the nonheme Fe(IV)O species. By modeling the selectivity of this two-site reactivity, we show that an interplay of tunneling and spin inversion probability (SIP) reverses the apparent barriers and prefers exclusive S = 1 HAT over mixed HAT and C═C epoxidation on S = 2. The model enables us to derive a SIP value by combining experimental and theoretical results.