5 research outputs found
Characteristics of soil microbial biomass and community composition in <i>Pinus yunnanensis</i> var. <i>Tenuifolia</i> secondary forests
<p><i>Pinus yunnanensis</i> var. <i>Tenuifolia</i> is an important species of timber and grease in southern China, but the characteristics of the soil microbial community in <i>P. yunnanensis</i> var. natural secondary forests are still poorly understood. Using a fumigation-extraction method and phospholipid fatty acid (PLFA) analysis, we study microbial biomass and community composition in the topsoil (0–10 cm) of three types of secondary forests (PYI, PYII, PYIII) dominated by <i>P. yunnanensis</i> var. to varing degrees. Microbial biomass carbon and nitrogen, total PLFA, and PLFA contents of bacterial, fungal, and arbuscular mycorrhizal fungi were significantly lower in PYI than PYII or PYIII, and there were significant differences in the monounsaturated/saturated fatty acid ratio among the tested forests. Principal component analysis indicated that the soil microbial community structure of the tested forests differed significantly. The changes in soil microbial biomass and community composition were positively correlated with soil water content, pH, organic matter (SOM), total nitrogen (TN), and total phosphorus. Season did not significantly affect the soil microbial community structure, but significantly affected soil microbial biomass, SOM, and TN, which were higher in the dry season than in the wet season.</p
C–H···O Interaction in Methanol–Water Solution Revealed from Raman Spectroscopy and Theoretical Calculations
A combination
of temperature-dependent Raman spectroscopy and quantum chemistry
calculation was employed to investigate the blue shift of CH<sub>3</sub> stretching vibration in methanol–water mixtures. It shows
that the conventional O–H···O hydrogen bonds
do not fully dominate the origin of the C–H blue shift and
the weak C–H···O interactions also contribute
to it. This is consistent with the temperature-dependent results,
which reveal that the C–H···O interaction is
enhanced upon increasing the temperature, leading to further C–H
blue shift in observed spectra at high temperature. This behavior
is in contrast with the general trend that the conventional O–H···O
hydrogen bond is destroyed by the temperature. The results will shed
new light onto the nature of the C–H···O interaction
and be helpful to understand hydrophilic and hydrophobic interactions
of amphiphilic molecules in different environments
Cl-Loss Dynamics of Vinyl Chloride Cations in the B<sup>2</sup>A″ State: Role of the C<sup>2</sup>A′ State
The
dissociative photoionization of vinyl chloride (C<sub>2</sub>H<sub>3</sub>Cl) in the 11.0–14.2 eV photon energy range was
investigated using threshold photoelectron photoion coincidence (TPEPICO)
velocity map imaging. Three electronic states, namely, A<sup>2</sup>A′, B<sup>2</sup>A″, and C<sup>2</sup>A′, of
the C<sub>2</sub>H<sub>3</sub>Cl<sup>+</sup> cation were prepared,
and their dissociation dynamics were investigated. A unique fragment
ion, C<sub>2</sub>H<sub>3</sub><sup>+</sup>, was observed within the
excitation energy range. TPEPICO three-dimensional time-sliced velocity
map images of C<sub>2</sub>H<sub>3</sub><sup>+</sup> provided the
kinetic energy release distributions (KERD) and anisotropy parameters
in dissociation of internal-energy-selected C<sub>2</sub>H<sub>3</sub>Cl<sup>+</sup> cations. At 13.14 eV, the total KERD showed a bimodal
distribution consisting of Boltzmann- and Gaussian-type components,
indicating a competition between statistical and non-statistical dissociation
mechanisms. An additional Gaussian-type component was found in the
KERD at 13.65 eV, a center of which was located at a lower kinetic
energy. The overall dissociative photoionization mechanisms of C<sub>2</sub>H<sub>3</sub>Cl<sup>+</sup> in the B<sup>2</sup>A″
and C<sup>2</sup>A′ states are proposed based on time-dependent
density functional theory calculations of the Cl-loss potential energy
curves. Our results highlight the inconsistency of previous conclusions
on the dissociation mechanism of C<sub>2</sub>H<sub>3</sub>Cl<sup>+</sup>
Manifesting Direction-Specific Complexation in [HFIP<sub>–H</sub>·H<sub>2</sub>O<sub>2</sub>]<sup>−</sup>: Exclusive Formation of a High-Lying Conformation
Size-selective, negative ion photoelectron spectroscopy
in conjunction
with quantum chemical calculations is employed to investigate the
geometric and electronic structures of a protype system in catalytic
olefin epoxidation research, that is, deprotonated hexafluoroisopropanol
([HFIP–H]−) complexed with hydrogen
peroxide (H2O2). Spectral assignments and molecular
electrostatic surface analyses unveil a surprising prevalent existence
of a high-lying isomer with asymmetric dual hydrogen-bonding configuration
that is preferably formed driven by influential direction-specific
electrostatic interactions upon H2O2 approaching
[HFIP–H]− anion. Subsequent inspections
of molecular orbitals, charge, and spin density distributions indicate
the occurrence of partial charge transfer from [HFIP–H]− to H2O2 upon hydrogen-bonding
interactions. Accompanied with electron detachment, a proton transfer
occurs to form the neutral complex of [HFIP·HOO•] structure. This work conspicuously illustrates the importance of
directionality encoded in intermolecular interactions involving asymmetric
and complex molecules, while the produced hydroperoxyl radical HOO• offers a possible new pathway in olefin epoxidation
chemistry
Identification of Alcohol Conformers by Raman Spectra in the C–H Stretching Region
The
spontaneous polarized Raman spectra of normal and deuterated
alcohols (C<sub>2</sub>–C<sub>5</sub>) have been recorded in
the C–H stretching region. In the isotropic Raman spectra,
a doublet of −C<sub>α</sub>H stretching vibration is
found for all alcohols at below 2900 cm<sup>–1</sup> and above
2950 cm<sup>–1</sup>. By comparing the experimental and calculated
spectra of various deuterated alcohols, the doublets are attributed
to the −C<sub>α</sub>H stretching vibration of different
conformers. For ethanol, the band observed at 2970 cm<sup>–1</sup> is assigned as the stretching vibration of −C<sub>α</sub>H in the C<sub>α</sub>–O–H plane of the <i>gauche-</i>conformer, while the band at 2895 cm<sup>–1</sup> is contributed from both the −C<sub>α</sub>H<sub>2</sub> symmetrical stretching vibration of the <i>trans-</i>conformer
and the −C<sub>α</sub>H stretching vibration out of the
C<sub>α</sub>–O–H plane of the <i>gauche-</i>conformer. The population of <i>gauche</i>-conformer is
estimated to be 54% in liquid ethanol. For the larger alcohols, the
same assignments for the doublet are obtained, and the populations
of <i>gauche</i>-conformers with plane carbon skeleton are
found to be slightly larger than that of ethanol, which is consistent
with results from molecular dynamics simulations