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 CH₃ 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

Manifesting Direction-Specific Complexation in [HFIP_–H·H₂O₂]⁻: 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

Cl-Loss Dynamics of Vinyl Chloride Cations in the B²A″ State: Role of the C²A′ State

The dissociative photoionization of vinyl chloride (C₂H₃Cl) 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, A²A′, B²A″, and C²A′, of the C₂H₃Cl⁺ cation were prepared, and their dissociation dynamics were investigated. A unique fragment ion, C₂H₃⁺, was observed within the excitation energy range. TPEPICO three-dimensional time-sliced velocity map images of C₂H₃⁺ provided the kinetic energy release distributions (KERD) and anisotropy parameters in dissociation of internal-energy-selected C₂H₃Cl⁺ 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 C₂H₃Cl⁺ in the B²A″ and C²A′ 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 C₂H₃Cl⁺

Identification of Alcohol Conformers by Raman Spectra in the C–H Stretching Region

The spontaneous polarized Raman spectra of normal and deuterated alcohols (C₂–C₅) have been recorded in the C–H stretching region. In the isotropic Raman spectra, a doublet of −C_αH stretching vibration is found for all alcohols at below 2900 cm^–1 and above 2950 cm^–1. By comparing the experimental and calculated spectra of various deuterated alcohols, the doublets are attributed to the −C_αH stretching vibration of different conformers. For ethanol, the band observed at 2970 cm^–1 is assigned as the stretching vibration of −C_αH in the C_α–O–H plane of the <i>gauche-</i>conformer, while the band at 2895 cm^–1 is contributed from both the −C_αH₂ symmetrical stretching vibration of the <i>trans-</i>conformer and the −C_αH stretching vibration out of the C_α–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