The effect of enriched versus depleted housing on eucalyptus smoke-induced cardiovascular dysfunction in mice.

Objectives: Living conditions play a major role in health and well-being, particularly for the cardiovascular and pulmonary systems. Depleted housing contributes to impairment and development of disease, but how it impacts body resiliency during exposure to environmental stressors is unknown. This study examined the effect of depleted (DH) versus enriched housing (EH) on cardiopulmonary function and subsequent responses to wildfire smoke. Materials and Methods: Two cohorts of healthy female mice, one of them surgically implanted with radiotelemeters for the measurement of electrocardiogram, body temperature (Tco) and activity, were housed in either DH or EH for 7 weeks. Telemetered mice were exposed for 1 h to filtered air (FA) and then flaming eucalyptus wildfire smoke (WS) while untelemetered mice, which were used for ventilatory assessment and tissue collection, were exposed to either FA or WS. Animals were continuously monitored for 5-7 days after exposure. Results: EH prevented a decrease in Tco after radiotelemetry surgery. EH mice also had significantly higher activity levels and lower heart rate during and after FA and WS. Moreover, EH caused a decreased number of cardiac arrhythmias during WS. WS caused ventilatory depression in DH mice but not EH mice. Housing enrichment also upregulated the expression of cardioprotective genes in the heart. Conclusions: The results of this study indicate that housing conditions impact overall health and cardiopulmonary function. More importantly, depleted housing appears to worsen the response to air pollution. Thus, non-chemical factors should be considered when assessing the susceptibility of populations, especially when it comes to extreme environmental events.

First Report of Anthracnose on Euonymus japonicus Thunb. Caused by a Provisionally Novel Species of Colletotrichum in the Magnum Complex in South Korea.

Euonymus japonicus Thunb., also known as the evergreen spindle tree, is an evergreen tree, which is widely planted as a hedge plant along streets in South Korea. In April 2022, severe anthracnose symptoms were observed on the leaves of this tree in Jangsu in the Jeonbuk Province of the country (35°43'49.44″N, 127°34'53.7″E). About 80% of the leaves of each affected tree within a 0.03-ha area showed incidence of the disease on approximately 30 trees were planted along the roadside (~30 m). These symptoms typically included circular or irregularly shaped whitish-gray lesions with a diameter of 2.0 to 3.0 cm. In cases where some leaves were severely affected, larger blotches formed. To isolate the pathogen, about ten leaves showing anthracnose symptoms on each tree were randomly selected and brought to the laboratory. Fungal isolations were made from acervuli filled with conidial masses on infected evergreen tissues, followed by plating onto 2% potato dextrose agar (PDA) as well as incubated at 25℃. On the PDA, colonies were circular, raised, green-grey or dark grey, and had a distinct white margin. The conidia were single-celled, transparent, cylindrical with rounded ends, had smooth walls, with a length ranging from 12 µm to 16.7 µm and a width raging from 4 µm to 6.5 µm (av. = 14.1 X 5.0 µm, n=40). Of those that were successfully recovered with approximately 90% frequency, two monoconidial isolates were deposited to the culture collection at Chungnam National University in South Korea (Accession number: CDH059-060). To ensure the identity of the fungus, genomic DNAs were extracted from the selected isolates, CDH059-060, and were sequenced. This was achieved based on partial sequences of the internal transcribed spacer (ITS), actin and beta-tubulin (TUB2) gene regions which were amplified using ITS1F / ITS4 (Gardes and Bruns 1993; White et al. 1990), ACT-512F / ACT-783R (Carbone and Kohn 1999), and T1 / Bt2b (O'Donnell and Cigelnik 1997; Glass and Donaldson 1995) primer pairs, respectively. The resulting sequences were deposited to GenBank (OR984424-425) for ITS, (OR996289-290) for actin, and (OR996291-292) for TUB2. For a phylogenetic analysis, sequences from different gene regions (ITS, actin and TUB2) retrieved from GenBank were aligned, concatenated, and analyzed as a single dataset based on a maximum likelihood analysis. The phylogenetic result revealed that the fungus isolated in this study was positioned in a clearly distinct lineage, provisionally representing an undetermined species of Colletotrichum, which is most closely related to Colletotrichum liaoningense (Y.Z. Diao, C. Zhang, L. Cai & X.L. Liu, CGMCC3.17616 (KP890104 for ITS, KP890097 for actin, and KP890111 for TUB, Diao et al. 2017). Sequence comparisons revealed that this pathogen differed from C. liaoningense at 20 of 494 characters (∼4.0%) in the ITS and 2 of 251 (∼1.0%) in the actin sequences. For pathogenicity tests, three seedlings of E. japonicus were used. The leaves for each tree were treated with 10 ml of a conidial suspension by spraying (1x106 conidia ml-1 of the isolate, CDH059), while the three seedlings were treated with distilled water as control. After sprayed, the treated areas were sealed with plastic bags for a day to maintain humidity. Anthracnose symptoms identical to those observed in the field appeared seven days after inoculations, while no symptoms were observed in the control. Re-isolations were successfully achieved from the treatments, fulfilling Koch's postulates. Anthracnose associated with the provisionally novel species of Colletotrichum sp. on E. japonicus has not been recorded elsewhere, and in this regard, this is the first report of anthracnose caused by Colletotrichum sp. on E. japonicus in Korea. To effectively control the disease, more attention should be paid to the host range of the pathogen and other regions where the disease caused by the pathogen might occur in the country.

First Report of Anthracnose Caused by Colletotrichum siamense on Machilus thunbergii Siebold & Zucc. in South Korea.

Machilus thunbergii Siebold & Zucc., known as Japanese bay tree, is an evergreen tree distributed widely in East Asia, including South Korea, where the species is of ecological importance. Machilus thunbergii provides habitat for wildlife species and is a common urban tree. In September 2022, anthracnose symptoms on leaves were observed in Jeju (33°26'02.4"N, 126°19'48.8"E) and Tongyeong (34°49'27.1"N, 128°24'01.8"E) in South Korea. Disease incidence on leaves of each affected tree, naturally growing in an urban forest area covering approximately 0.5 ha was approximately ~ 70 % in each study area. Anthracnose symptoms that were observed on 70 to 80% leaves per tree in each study area included orbicular or irregular, whitish-grey spots on leaves that were 1.5 to 3.0 cm in diam. In some cases where leaves were severely affected, larger blotches were formed, leading to bleaching symptoms and eventually defoliation. For pathogen isolation, two or three leaves showing anthracnose symptoms from each of the 15 trees were randomly selected and brought to the laboratory. Fungal isolations were then directly made by transferring spores from acervuli that developed on diseased leaves onto potato dextrose agar (PDA) media. Cushion shaped acervuli filled with salmon to orange-colored conidial masses were produced on media approximately two weeks after the incubation at 25 ± 1°C with a photoperiod of 12 h. Conidia were single celled, hyaline, cylindrical with rounded ends, smooth walls, 13.7 to 18.1 µm long and 3.1 to 4.5 µm wide (n=30). Among 15 cultures that were successfully isolated, 10 isolates were retained based on culture characteristics, and two randomly selected monoconidial cultures were deposited in the culture collection (CDH) of the Chungnam National University, Republic of Korea (Accession No. CDH057-58). Two isolates selected, CDH057 and CDH058, were subjected to identification, and this was achieved based on multiplesequence comparisons using on internal transcribed spacer regions of rDNA (ITS1 and ITS2), partial sequences of actin (ACT) and ß-tubulin (TUB2) gene regions amplified using ITS1F / ITS4, ACT-512F / ACT-783R and T1 / Bt2b, respectively (Weir et al. 2012). The representative sequence data were deposited in GenBank under the accession numbers OR473277 and OR473278 for the ITS, OR480772 and OR480773 for ACT, and OR480774 and OR480775 for TUB2. The resulting sequences were further used for a phylogenetic analysis based on the maximum likelihood method using a concatenated dataset of the ITS, ACT and TUB2 gene sequences for Colletotrichum species in the C. gloeosporioides clade. The results showed that the pathogen isolated in this study clustered with Colletotrichum siamense (Vouchered specimens: MFLU 090230, COUFPI291, and COUFPI294) (Prihastuti et al. 2009). Sequence comparisons revealed that the isolates obtained in this study differed from the type species of C. siamense (MFLU 090230; FJ972613 for ITS, FJ 907423 for ACT, FJ907438 for TUB2) at 2 of 258 bp (∼0.8%) and 6 of 387 bp (∼1.6%) in the ACT and TUB2 sequences, respectively, while the ITS was identical to the type species. For pathogenicity tests, a total of ten three-year-old seedlings of M. thunbergii were used. The leaves of each tree were sprayed with 5 ml of conidial suspension (105 conidia/ml, isolate CDH057). Three control plants were sprayed with sterile water. After being sprayed, treated areas were sealed with a plastic bag for 24 hours to preserve humidity. Anthracnose symptoms, identical to those observed in the field, appeared five to seven days after the inoculations, while no symptoms were observed on control plants. The isolates used in the pathogenicity test were reisolated from 90% of lesions, and their identity was confirmed based on sequence comparisons, thus fulfilling Koch's postulates. Species of the C. gloeosporioides species complex include important plant pathogens, particularly C. siamense, which cause significant losses of economic and ecological relevance on a wide range of hosts (~ 100 hosts) (Talhinhas and Baroncelli 2021). Although C. fioriniae in the C. acutatum species complex, was found on M. thunbergii in South Korea (Thao et al. 2023), anthracnose associated with C. siamense on M. thunbergii has not been reported in the country. In this regard, this is the first report of anthracnose caused by C. siamense on M. thunbergii in South Korea. To effectively control the disease, more attention should be paid on the host range of the pathogen and other regions where the disease caused by the pathogen might occur in the country.

Venom Peptide Toxins Targeting the Outer Pore Region of Transient Receptor Potential Vanilloid 1 in Pain: Implications for Analgesic Drug Development.

The transient receptor potential vanilloid 1 (TRPV1) ion channel plays an important role in the peripheral nociceptive pathway. TRPV1 is a polymodal receptor that can be activated by multiple types of ligands and painful stimuli, such as noxious heat and protons, and contributes to various acute and chronic pain conditions. Therefore, TRPV1 is emerging as a novel therapeutic target for the treatment of various pain conditions. Notably, various peptides isolated from venomous animals potently and selectively control the activation and inhibition of TRPV1 by binding to its outer pore region. This review will focus on the mechanisms by which venom-derived peptides interact with this portion of TRPV1 to control receptor functions and how these mechanisms can drive the development of new types of analgesics.

Stem Cell Therapy for Modulating Neuroinflammation in Neuropathic Pain.

Neuropathic pain (NP) is a complex, debilitating, chronic pain state, heterogeneous in nature and caused by a lesion or disease affecting the somatosensory system. Its pathogenesis involves a wide range of molecular pathways. NP treatment is extremely challenging, due to its complex underlying disease mechanisms. Current pharmacological and nonpharmacological approaches can provide long-lasting pain relief to a limited percentage of patients and lack safe and effective treatment options. Therefore, scientists are focusing on the introduction of novel treatment approaches, such as stem cell therapy. A growing number of reports have highlighted the potential of stem cells for treating NP. In this review, we briefly introduce NP, current pharmacological and nonpharmacological treatments, and preclinical studies of stem cells to treat NP. In addition, we summarize stem cell mechanisms-including neuromodulation in treating NP. Literature searches were conducted using PubMed to provide an overview of the neuroprotective effects of stem cells with particular emphasis on recent translational research regarding stem cell-based treatment of NP, highlighting its potential as a novel therapeutic approach.

Experimental and Theoretical Studies on the Mechanism of DDQ-Mediated Oxidative Cyclization of N-Aroylhydrazones.

The controversial single-electron-transfer process, frequently proposed in many 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-mediated reactions, was investigated experimentally and theoretically using the oxidative cyclization of aroylhydrazone with DDQ. DDQ-mediated oxadiazole formation involves several processes, including cyclization to form an oxadiazole ring and N-H bond cleavage, either by proton, hydride, or hydrogen atom transfer. The detailed mechanistic study using the M06-2X density functional theory, and the 6-31+G(d,p) basis set, suggests that the pathways involving radical ion pair (RIP) intermediates, which resulted from single-electron transfer (SET), were found to be energetically nearly identical to the pathway without the SET. The substituent-dependent reactivity of oxadiazole formation was consistent with the free energy profiles of both pathways, with or without the SET. This result indicates that in addition to the electron-transfer pathway, the nucleophilic addition/elimination pathway for DDQ should be considered as a possible mechanism of the oxidative transformation reaction using DDQ.

Accessible Real-Time Surveillance Radar System for Object Detection.

As unmanned ground and aerial vehicles become more accessible and their usage covers a wider area of application, including for threatening purposes which can cause connected catastrophe, a surveillance system for the public places is being considered more essential to respond to those possible threats. We propose an inexpensive, lighter, safer, and smaller radar system than military-grade radar systems while keeping reasonable capability for use in monitoring public places. The paper details the iterative process on the system design and improvements with experiments to realize the system used for surveillance. The experiments show the practical use of the system and configuration for a better understanding of using the system. Cyber-physical systems for outdoor environments can benefit from the system as a sensor for sensing objects as well as monitoring.

Microstructure and Texture of P-Type Bi-Sb-Te Alloy by Using Gas-Atomization and Extrusion Processes.

Microstructure and texture of P-type 75%Sb2Te3-25%Bi2Te3 alloy fabricated by using gas-atomization and extrusion processes was investigated. The microstructure of the gas-atomized powders exhibited fine grains with needle shape. After hot extrusion, grain size was characterized by fine and equiaxed grains due to dynamic recrystallization by severe deformation. (0001) basal planes of the extruded specimens were preferentially orientated parallel to extrusion direction. As extrusion temperature, fraction of the basal planes was increased.

Microstructure and Mechanical Properties of Al-Si-Fe-Cu-Mn-x Zn Alloys Processed by Extrusion.

In this work, Al-0.15Si-0.2Fe-0.3Cu-0.9Mn alloys with different Zn addition (0, 0.15 and 0.3 wt%) were melted and extruded at 200 °C. The effect of Zn on the microstructure, texture evolution and mechanical properties of Al-0.15Si-0.2Fe-0.3Cu-0.9Mn alloys was investigated using scanning electron microscope (SEM), equipped with energy-dispersive X-ray spectrometry (EDS) and electron backscatter diffraction (EBSD) and in the present study. In order to evaluate the mechanical properties, we implemented the tensile tests by a universal material test machine. Al-0.15Si-0.2Fe- 0.3Cu-0.9Mn-xZ resulted in the formation of Al-(Fe, Mn)-Si and Al-(Fe, Mn) intermetallic compounds. The formation of the intermetallic compound and this phase was broken in to small particles during extrusion. The ultimate strength and elongation of the as-extruded Al-0.15Si-0.2Fe-0.3Cu- 0.9Mn alloy were 96.51 MPa and 34.01%, while those of the Al-0.15Si-0.2Fe-0.3Cu-0.9Mn-0.3Zn alloy were 99.08 MPa and 36.21%, respectively. Al-0.15Si-0.2Fe-0.3Cu-0.9Mn alloys with Zn addition resulted in improving the strength with no reduction in elongation.

Study on Microstructure of Nb-Ti Based Alloy by Groove Rolling Process.

Niobium-titanium alloy is attractive materials for industrials as a superconducting magnets to high critical magnetic field and supercurrent density at -283 °C. The Nb-Ti alloy has been shown in earlier work to exhibit Van Gosh Sky microstructures. They may also be accentuated by plastic deformation due to work and temperature exposure during deformation. In order to miniaturize the magnet generating the same magnetic field, it is necessary to increase the critical current density of the superconducting wire. When fabricating superconducting wires, it is important to increase critical current density by optimizing processing and annealing conditions. When the α-phase of the Ti rich phase is uniformly precipitated by the heat treatment, the non-superconducting α-phase is dispersed in the superconducting Nb-Ti matrix. It becomes a pinning point that serves to fix the magnetic flux, which improves the critical current density. Also, if the shape of the precipitate is changed by machining, the superconducting and non-superconducting characteristics are further improved. In the present study, we studied the fraction of α-Ti phase of strain amount through groove rolling and heat treatment. The specimens were processed by groove rolling at room temperature and strain of 2.0, 3.16, 4.28 and 5.57. A microstructural analysis of the Nb-Ti alloys was performed by field emission scanning electron microscopy (FESEM).

Effects of Heat-Treatment Conditions on Densification, Microstructure, and Magnetic Properties of Fe Powder.

In this study, the effects of heat-treatment conditions on the densification, microstructure, and magnetic properties of Fe powder were investigated. The oxygen content of the Fe powders heat-treated in Ar and Ar-H2 atmosphere was much lower than that of the Fe powder heat-treated in air atmosphere. The density of the compacts of the Fe powder heat-treated in Ar and Ar + H2 atmosphere was higher than that of the compacts of Fe powders heat-treated in air. Oxygen content in the heat-treatment conditions played a significant role in the improvement of the densification and magnetic properties.

The Effects of Dy Addition on Microstructure and Mechanical Properties of the As-Cast Mg-5Al-3Ca-2Nd Alloys.

The microstructure of the as-cast Mg-5Al-3Ca-2Nd-xDy alloys consists of α-Mg matrix, (Mg, Al)2Ca eutectic phase, Al-Nd and Al-Dy intermetallic compounds. α-Mg matrix morphology was changed from dendritic to equiaxed with the increase Dy addition. And grain size was remarkably refined. As Dy content was increased, yield strength was improved due to the refined grains and the homogeneous distribution of Al-Dy phase.

Microstructure and Mechanical Properties of Mg-11Li-6Zn-0.6Zr-0.4Ag-0.2Ca-x Y Alloys.

Magnesium and its alloys are potential candidates for many automotive and aerospace applications due to their low density and high specific strength. However, the use of magnesium as wrought products is limited because of its poor workability at ambient temperatures. Mg-Li alloys containing 5-11 wt.% Li exhibit a two-phase structure consisting of a α (hcp) Mg-rich phase and a ß (bcc) Li-rich phase. Mg-Li alloys with Li content greater than 11 wt.% exhibit a single-phase structure consisting of only the ß phase. In the present study, we studied the effects of Y addition on the microstructure and mechanical properties of Mg-11Li-6Zn-0.6Zr-0.4Ag-0.2Ca based alloys. The melt was maintained at 720 °C for 20 min and poured into a mold. Then, the as-cast Mg alloys were homogenized at 350 °C for 4 h and were hot-extruded onto a 4-mm-thick plate with a reduction ratio of 14:1. The as-cast Mg-11Li-6Zn-0.6Zr-0.4Ag-0.2Ca-xY (x 0, 1, 3, and 5 wt.%) alloys were composed of α-Mg, ß-Li, γ-Mg2Zn3Li, I-Mg3YZn6, W-Mg3Y2Zn3, and X-Mg12YZn phases. By increasing the Y content from 0 to 5 wt.%, the composition of the W-Mg3Y2Zn3 phase increased. With increasing Y content, from 0 to 1, 3, and 5 wt.%, the average grain size and ultimate tensile of the as-extruded Mg alloys decreased slightly, from 8.4, to 3.62, 3.56, and 3.44 µm and from 228.92 to 215.57, 187.47, and 161.04 MPa, respectively, at room temperature.

Study on Microstructure and Mechanical Properties of Al-Li Based Alloys Processed by Extrusion.

Aluminum and its alloys, due to their low density, high specific strength and high corrosion resistance amongst various structural materials, are used in a wide range of industrial applications for different aqueous solutions. In the present study, we studied effects of Ce addition on microstructure and mechanical properties of Al-2Li-1Cu-0.8Mg-0.1Zr alloys. The melt was held at 780 °C for 20 min and poured into a mold. And as-cast Al alloys were hot-extruded into a plate that was 4 mm in thickness with a reduction ratio of 14:1. The extruded plates were held at 540 °C for 4 hr in water quenching to solution treatment them. As-extruded Al-2Li-1Cu-0.8Mg-0.1Zr-xCe (x = 0.3, 0.6, 0.9 and 1.2 wt.%) alloys are composed of Al, AlLi, AlCuLi and Al11Ce3 phases. By increasing the Ce content from 0 to 1.2 wt.%, the Al11Ce3 phase is increased, after solution treatment the AlLi and AlCuLi phases are decreased. With increasing Ce addition from 0 to 1.2 wt.%, the average grain size of the as-extruded Al alloys were decreased slightly from 100.7, 113.74, 84.3, 74.7 and 61.7 µm and ultimate tensile strength was decreased slightly from 267.59, 264.92, 237.40, 220.93 and 207.83 MPa at room temperature. After solution treatment, ultimate tensile strength was measured with 205.13, 198.12, 195.50, 198.27 and 208.01 MPa at room temperature.

Effect of Mn and AlTiB Addition and Heattreatment on the Microstructures and Mechanical Properties of Al-Si-Fe-Cu-Zr Alloy.

The microstructure and mechanical properties of as-extruded Al-0.1 wt%Si-0.2 wt%Fe- 0.4 wt%Cu-0.04 wt%Zr-xMn-xAlTiB (x = 1.0 wt%) alloys under various annealing processes were investigated and compared. After the as-cast billets were kept at 400 °C for 1 hr, hot extrusion was carried out with a reduction ratio of 38:1. In the case of the as-extruded Al-Si-Fe-Cu-Zr alloy at annealed at 620 °C, large equiaxed grain was observed. When the Mn content is 1.0 wt%, the phase exhibits a skeleton morphology, the phase formation in which Mn participated. Also, the volume fraction of the intermetallic compounds increased with Mn and AlTiB addition. For the Al-0.1Si-0.2Fe-0.4Cu-0.04Zr alloy with Mn and AlTiB addition from 1.0 wt%, the ultimate tensile strength increased from 100.47 to 119.41 to 110.49 MPa. The tensile strength of the as-extruded alloys improved with the addition of Mn and AlTiB due to the formation of Mn and AlTiB-containing intermetallic compounds.

Grain Refinement of Al-Si-Fe-Cu-Zn-Mn Based Alloy by Al-Ti-B Alloy and Its Effect on Mechanical Properties.

We investigated the effects of Al-5.0wt%Ti-1.0wt%B addition on the microstructure and mechanical properties of the as-extruded Al-0.15wt%Si-0.2wt%Fe-0.3wt%Cu-0.15wt%Zn-0.9wt%Mn based alloys. The Aluminum alloy melt was held at 800 °C and then poured into a mould at 200 °C. Aluminum alloys were hot-extruded into a rod that was 12 mm in thickness with a reduction ratio of 38:1. AlTiB addition to Al-0.15Si-0.2Fe-0.3Cu-0.15Zn-0.9Mn based alloys resulted in the formation of Al3Ti and TiB2 intermetallic compounds and grain refinement. With increasing of addition AlTiB, ultimate tensile strength increased from 93.38 to 99.02 to 100.01 MPa. The tensile strength of the as-extruded alloys was improved due to the formation of intermetallic compounds and grain refinement.

VTST/MT studies of the catalytic mechanism of C-H activation by transition metal complexes with [Cu2(µ-O2)], [Fe2(µ-O2)] and Fe(IV)-O cores based on DFT potential energy surfaces.

High-valent Cu and Fe species, which are generated from dioxygen activation in metalloenzymes, carry out the functionalization of strong C-H bonds. Understanding the atomic details of the catalytic mechanism has long been one of the main objectives of bioinorganic chemistry. Large H/D kinetic isotope effects (KIEs) were observed in the C-H activation by high-valent non-heme Cu or Fe complexes in enzymes and their synthetic models. The H/D KIE depends significantly on the transition state properties, such as structure, energies, frequencies, and shape of the potential energy surface, when the tunneling effect is large. Therefore, theoretical predictions of kinetic parameters such as rate constants and KIEs can provide a reliable link between atomic-level quantum mechanical mechanisms and experiments. The accurate prediction of the tunneling effect is essential to reproduce the kinetic parameters. The rate constants and HD/KIE have been calculated using the variational transition-state theory including multidimensional tunneling based on DFT potential energy surfaces along the reaction coordinate. Excellent agreement was observed between the predicted and experimental results, which assures the validity of the DFT potential energy surfaces and, therefore, the proposed atomic-level mechanisms. The [Cu2(µ-O)2], [Fe2(µ-O)2], and Fe(IV)-oxo species were employed for C-H activation, and their role as catalysts was discussed at an atomic level.

Is It Fe(III)-Oxyl Radical That Abstracts Hydrogen in the C-H Activation of TauD? A Theoretical Study Based on the DFT Potential Energy Surfaces.

Taurine:α-ketoglutarate dioxygenase (TauD) is one of the most important enzymes in the α-ketoglutarate dioxygenase family, which are involved in many important biochemical processes. TauD converts taurine into amino acetaldehyde and sulfite at its nonheme iron center, and a large H/D kinetic isotope effect (KIE) has been found in the hydrogen atom transfer (HAT) of taurine suggesting a large tunneling effect. Recently, highly electrophilic Fe(III)-oxyl radicals have been proposed as a key species for HAT in the catalytic mechanism of C­H activation, which might be prepared prior to the actual HAT. In order to investigate this hypothesis and large tunneling effect, DFT potential energy surfaces along the intrinsic reaction path were generated. The predicted rate constants and H/D KIEs using variational transition-state theory including multidimensional tunneling, based on these potential surfaces, have excellent agreement with experimental data. This study revealed that the reactive processes of C­H activation consisted of two distinguishable parts: (1) the substrate approaching the Fe(IV)-oxo center without C­H bond cleavage, which triggers the catalytic process by inducing metal-to-ligand charge transfer to form the Fe(III)-oxyl species, and (2) the actual HAT from the substrate to the Fe(III)-oxyl species. Most of the activation energy was used in the first part, and the actual HAT required only a small amount of energy to overcome the TS with a very large tunneling effect. The donor­acceptor interaction between σC­H and σ*Fe­O orbitals reduced the activation energy significantly to make C­H activation feasible.

Kinetic Isotope Effects as a Probe for the Protonolysis Mechanism of Alkylmetal Complexes: VTST/MT Calculations Based on DFT Potential Energy Surfaces.

Protonolysis by platinum or palladium complexes has been extensively studied because it is the microscopic reverse of the C-H bond activation reaction. The protonolysis of (COD)PtIIMe2, which exhibits abnormally large kinetic isotope effects (KIEs), is proposed to occur via a concerted pathway (SE2 mechanism) with large tunneling. However, further investigation of KIEs for the protonolysis of ZnMe2 and others led to a conclusion that there is no noticeable correlation between the mechanism and magnitude of KIE. In this study, we demonstrated that variational transition state theory including multidimensional tunneling (VTST/MT) could accurately predict KIEs and Arrhenius parameters of the protonolysis of alkylmetal complexes based on the potential energy surfaces generated by density functional theory. The predicted KIEs, EaD - EaH values, and AH/AD ratios for the protonolysis of (COD)PtIIMe2 and ZnIIMe2 by TFA agreed very well with experimental values. The protonolysis of ZnMe2 with the concerted pathway has a very flat potential energy surface, which produces a very small tunneling effect and therefore a small KIE. The predicted KIE for the stepwise protonolysis (SE(ox) mechanism) of (COD)PtIIMe2 was much smaller than that of the concerted pathway, but greater than the KIE of the concerted protonolysis of ZnMe2. A large KIE, which entails a significant tunneling effect, could be used as an experimental probe of the concerted pathway. However, a normal or small KIE should not be used as an indicator of the stepwise mechanism, and the interplay between experiments and reliable theory including tunneling would be essential to uncover the mechanism correctly.

Mechanical Properties and Fracture Behaviors of the As-Extruded Mg-5Al-3Ca Alloys Containing Yttrium at Elevated Temperature.

Effects of yttrium (Y) addition on mechanical properties and fracture behaviors of the as-extruded Mg-Al-Ca based alloys at elevated temperature were investigated by a tensile test. After hot extrusion, the average grain size was refined by Y addition and eutectic phases were broken down into fine particles. Y addition to Mg-5Al-3Ca based alloy resulted in the improvement of strength and ductility at elevated temperature due to fine grain and suppression of grain growth by formation of thermally stable Al2Y intermetallic compound.