The electronic structures of the first-row transition-metal metallocenes, MCp 2 (M ) V, Cr, Mn, Fe, Co, and Ni), have been studied using a broad range of density functional methods with flexible double-ζ plus polarization (DZP) basis sets. Geometrical parameters of the D 5h and D 5d conformations (and structures of lower symmetry for CrCp 2 and CoCp 2 ) were fully optimized. For the ferrocene system, best characterized experimentally, the B3LYP, BLYP, and BP86 methods give structures in good agreement with experiment. For the D 5h -D 5d energy difference, the same three methods predict 0.75 kcal/mol (B3LYP), 0.99 kcal/mol (BLYP), and 1.13 kcal/mol (BP86). The cyclopentadienyl rings are very nearly planar; the angles of the C-H bond out of the Cp ring are less than 1°for all metallocenes except ferrocene. The C-H bonds are bent slightly away from the metal for V and Mn, slightly toward the metal for Fe and Ni, and virtually not at all from chromocene. According to the energetic and vibrational analyses, the D 5h conformations are found to be the global minima, leaving open the possibility that the D 5d conformations may exist under certain conditions. However, MnCp 2 probably exists as a mixture of both D 5h and D 5d conformations, because both are genuine minima with only a small energy difference. The predicted B3LYP energy differences (D 5h -D 5d ) for the six metallocenes are 0.29 (V), 0.28 (Cr), 0.13 (Mn), 0.75 (Fe), 0.38 (Co), and 0.23 kcal/mol (Ni). A number of reassignments of experimental vibrational bands are suggested. The molecular orbital energy level diagrams and the electron configurations for the metallocenes are compared. This information, obtained in a consistent manner across the first transition metal series, is helpful for discussion of the bonding characters and the chemical reactivities of these metallocenes.

Despite the perceived importance of exudation to forest ecosystem function, few studies have attempted to examine the effects of elevated temperature and nutrition availability on the rates of root exudation and associated microbial processes. In this study, we performed an experiment in which in situ exudates were collected from Picea asperata seedlings that were transplanted in disturbed soils exposed to two levels of temperature (ambient temperature and infrared heater warming) and two nitrogen levels (unfertilized and 25 g N m À2 a À1). Here, we show that the trees exposed to an elevated temperature increased their exudation rates I (lg C g À1 root biomass h) in the unfertilized plots. The altered morphological and physiological traits of the roots exposed to experimental warming could be responsible for this variation in root exudation. Moreover, these increases in root-derived C were positively correlated with the microbial release of extracellular enzymes involved in the breakdown of organic N (R 2 = 0.790; P = 0.038), which was coupled with stimulated microbial activity and accelerated N transformations in the unfertilized soils. In contrast, the trees exposed to both experimental warming and N fertilization did not show increased exudation rates or soil enzyme activity, indicating that the stimulatory effects of experimental warming on root exudation depend on soil fertility. Collectively, our results provide preliminary evidence that an increase in the release of root exudates into the soil may be an important physiological adjustment by which the sustained growth responses of plants to experimental warming may be maintained via enhanced soil microbial activity and soil N transformation. Accordingly, the underlying mechanisms by which plant root-microbe interactions influence soil organic matter decomposition and N cycling should be incorporated into climate-carbon cycle models to determine reliable estimates of long-term C storage in forests.

Alpine ecosystems are harsh environments where low temperatures are generally a limiting factor. Predicted global warming is thus expected to have a profound impact on alpine ecosystems in the future. This study was conducted to compare the effect of experimental warming on soils in two contrasting forest ecosystems (a dragon spruce plantation and a natural forest) using the open top chamber (OTC) method in the Eastern Tibetan Plateau of China. The OTC enhanced average daily mean soil temperatures by 0.61°C (plantation) and 0.55°C (natural forest), respectively, throughout the growing season. Conversely, soil volumetric moisture declined by 4.10% in the plantation and by 2.55% in the natural forest. Across all measuring dates, warming increased average soil CO 2 efflux by 10.6% in the plantation and by 15.4% in the natural forest. However, elevated temperatures did not affect the respiration quotient in either forest. Two-stage sulfuric acid hydrolysis was used to quantify labile and recalcitrant C and N fractions in the two contrasting soils. Warming significantly reduced labile C and N fractions in both ecosystems but did not influence the total, recalcitrant and microbial biomass C and N pools. Labile C, N and microbial biomass C showed significant interactions in warming × forest type × season. Irrespective of warming treatments, all measured pools were significantly larger in the natural forest compared to the plantation. Taken together, our results indicate that the lowered soil labile C and N pools may be induced by the increased soil CO 2 efflux. The responses of the natural forest soil were more sensitive to experimental warming than those of the plantation. We conclude that reforestation dramatically lowers soil C and N pools, further affecting the responses of forest soils to future global warming.

No abstract

In the present work the adsorption of doxorubicin (DOX) on the surface of single-walled carbon nanotube (SWCNT) as well as its encapsulation in SWCNT, and their dependence on the protonation of NH2 group of DOX, solvent, and the diameter of armchair (n,n) SWCNT were systematically investigated using theoretical methods such as PM6-DH2 and M06-2X in the scheme of OMIOM. It was found that the two loadings, adsorption on the sidewall of CNT and the encapsulation in CNT, have distinct solvent, protonation and diameter dependences. The encapsulation is much stronger than the adsorption of DOX on the sidewall of CNT, and the former also has significantly higher solvent and protonation effects than the latter. The adsorption primarily occurs through π-π stacking and just becomes slightly stronger as the diameter of CNT increases, while besides π-π stacking the additional C-H/N-H/O-H…π and C=O…π also contribute to the encapsulation of DOX in CNT. It seems that (8,8) CNT (diameter ~ 11Å) energetically is an onset for the encapsulation since the encapsulation turns from endothermic to exothermic as the diameter is larger than approximately 11 Å, and the optimal diameter for the encapsulation is 14Å corresponding to (10,10) CNT. Thus for the thick CNT the encapsulation may also play an important role in the loading and releasing for the CNT-based drug delivery system of the DOX.

Nitrogen (N) deposition has increased globally and has profoundly influenced the structure and function of grasslands. Previous studies have discussed how N addition affects aboveground biomass (AGB), but the effects of N addition on the AGB of different functional groups in grasslands remain unclear. We conducted a meta-analysis to identify the responses of AGB and the AGB of grasses (AGB grass ) and forbs (AGB forb ) to N addition across global grasslands. Our results showed that N addition significantly increased AGB and AGB grass by 31 and 79%, respectively, but had no significant effect on AGB forb . The effects of N addition on AGB and AGB grass increased with increasing N addition rates, but which on AGB forb decreased. Although study durations did not regulate the response ratio of N addition for AGB, which for AGB grass increased and for AGB forb decreased with increasing study durations. Furthermore, the N addition response ratios for AGB and AGB grass increased more strongly when the mean annual precipitation (MAP) was 300-600 mm but decreased with an increase in the mean annual temperature (MAT). AGB forb was only slightly affected by MAP and MAT. Our findings suggest that an acceleration of N deposition will increase grassland AGB by altering species composition.Nitrogen (N) deposition in terrestrial ecosystems is estimated to increase to 200 Tg N yr −1 by 2050 due to industrial and agricultural N fertilizer use 1 . Nitrogen enrichment will potentially influence species diversity, biomass production and soil conditions 2-6 . The effects of N addition on forest ecosystem biomass have been summarized and analysed in previous studies 7-9 . However, because grasslands are mainly controlled by water, the effects of changes in precipitation patterns on aboveground biomass (AGB) were emphasized in previous studies [10][11][12] , and the effects of N addition on grassland biomass remain unknown. Grasslands are a type of terrestrial ecosystem and cover approximately 25% of the land surface on Earth 13 . AGB is an important contributor to soil organic matter, which significantly impacts the global carbon cycle under the background of N deposition 14,15 . Therefore, analysing and summarizing the effects of N addition on grassland AGB are particularly important for estimating and predicting the carbon budget under climate change.Many case studies that have been conducted to understand how N addition (N deposition) affects grassland AGB have yielded significantly different results 2, 16-18 . For example, several studies have reported significant increases 2,18,19 and decreases 17 or insignificant changes in AGB 16,20 following N addition. The differences between these results may be attributed to the use of different N addition rates, study durations, plant functional types and climatic conditions (such as the mean annual precipitation (MAP) or the mean annual temperature (MAT)). For instance, some previous studies have demonstrated a threshold value for the positive effects of N addition on AGB 2,21 . If N appl...

In order to asses performance of the LDA in describing physisorption on graphene, adsorptions of TCNE, TCNQ, TNF, TTF, and DMPD as well as four benzene derivatives on C54H18 and C110H30 were explored with a variety of DFTs such as MPWB1K, M06-2X, PBE-D and LSDA. Although it is well known that the LDA considerably overestimate non-covalent interaction, the LSDA predicted adsorption energies except for TCNE on C110H30 are systematically lower than those from the M06-2X by 0.4–3.2 kcal/mol, and they are more significantly lower than those from the PBE-D for all the molecules by 3–6 kcal/mol. However, the LSDA adsorption energy sequence is consistent with that from the PBE-D, TNF~TCNQ>TCNE~DMPD>TTF. Moreover, the domain interaction between the electron donor and acceptor molecules with graphene through cooperative π···π, C-H···π and N-H···π were visualized with sign(λ2)×ρ, and the relationships between the binding energy with London force, molecular electronegativity, and frontier orbital level were extensively discussed.

Aim We sought to understand how the individual and combined effects of multiple environmental change drivers differentially influence terrestrial nitrogen (N) concentrations and N pools and whether the interactive effects of these drivers are mainly antagonistic, synergistic or additive. Location Worldwide. Time period Contemporary. Major taxa studied Plants, soil, and soil microbes in terrestrial ecosystems. Methods We synthesized data from manipulative field studies from 758 published articles to estimate the individual, combined and interactive effects of key environmental change drivers (elevated CO2, warming, N addition, phosphorus addition, increased rainfall and drought) on plant, soil, and soil microbe N concentrations and pools using meta‐analyses. We assessed the influences of moderator variables on these effects through structural equation modelling. Results We found that (a) N concentrations and N pools were significantly affected by the individual and combined effects of multiple drivers, with N addition (either alone or in combination with another driver) showing the strongest positive effects; (b) the individual and combined effects of these drivers differed significantly between N concentrations and N pools in plants, but seldom in soils and microbes; (c) additive effects of driver pairs on N concentrations and pools were much more common than synergistic or antagonistic effects across plants, soils and microbes; and (d) environmental and experimental factors were important moderators of the individual, combined and interactive effects of these drivers on terrestrial N. Main conclusions Our results indicate that terrestrial N concentrations and N pools, especially those of plants, can be significantly affected by the individual and combined effects of environmental change drivers, with the interactive effects of these drivers being mostly additive. Our findings are important because they contribute to the development of models to better predict how altered N availability affects ecosystem carbon cycling under future environmental changes.