Decrypting the critical point of internal rotation of formaldehyde: A rotational study of the acrolein-formaldehyde complex.

The rotational spectrum of an acrolein-formaldehyde complex has been characterized using pulsed jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. One isomer has been observed in pulsed jets, which is stabilized by a dominant O=C⋯O tetrel bond (n → π* interaction) and a secondary C-H⋯O hydrogen bond. Splittings arising from the internal rotation of formaldehyde around its C2v axis were also observed, from which its V2 barrier was evaluated. It seems that when V2 equals or exceeds 4.61 kJ mol-1, no splitting of the spectral lines of the rotational spectrum was observed. The nature of the non-covalent interactions of the target complex is elucidated through natural bond orbital analysis. These findings contribute to a deeper understanding on the non-covalent interactions within the dimeric complex formed by two aldehydes.

Fluorination effects on non-covalent binding forces: A rotational study on the 2-(trifluoromethyl)acrylic acid-water complex.

This study explores the effects of the -CF3 group on non-covalent interactions through a comprehensive rotational investigation of the 2-(trifluoromethyl)acrylic acid-water complex. Employing Fourier transform microwave spectroscopy complemented by quantum chemical calculations, two isomers, i.e., s-cis and s-trans structures, have been observed in the pulsed jet. Based on relative intensity measurements, the s-cis to the s-trans population ratio was experimentally estimated to be âˆ¼ 1:1.2. Subsequently, a comparison of the non-covalent interactions was carried out between the three similar complexes, acrylic acid-water, methacrylic acid-water, and 2-(trifluoromethyl)acrylic acid-water, offering quantitative insights into fluorination affecting the strength of the formed hydrogen bonds important, e.g., in molecular recognition.

C···S Tetrel Bond Favored in the Phenyl Isothiocyanate-CO2 Complex: A Rotational Study.

The rotational spectrum of the phenyl isothiocyanate-CO2 complex was investigated by pulsed-jet Fourier transform microwave spectroscopy complemented by quantum chemical calculations. Only one isomer, with CO2 almost in the plane of phenyl isothiocyanate, has been detected in the pulsed jet, of which the spectrum displays a quadrupole coupling hyperfine structure due to the presence of a 14N nucleus (I = 1). This structure is nearly equal to the lowest energy geometry obtained by B3LYP-D3(BJ)/6-311++G(d,p), which has been dominated by a C···S tetrel bond (n → π* interaction) and one secondary C-H···O hydrogen bond (n → σ* interaction). Molecular electrostatic potential and natural bond orbital analysis were used to characterize the noncovalent interactions of the complex. The results from this study would lay the groundwork for the design and advancement of materials that exhibit high efficiency in capturing CO2.

Conformational equilibria and interaction preference in the complex of isoprene-maleic anhydride.

The rotational spectrum of the isoprene-maleic anhydride complex has been investigated by pulsed jet Fourier transform microwave spectroscopy and interpreted with complementary quantum chemical calculations. Theoretical predictions have yielded four plausible isomers, all residing within an energy window of 12 kJ mol-1. However, two distinct isomers characterized by a π-π stacked configuration have been experimentally observed in pulsed jets, which have differed in the orientation of isoprene over maleic anhydride. The relative population ratio of the two detected isomers has been estimated to be NI/NII ≈ 3/1 from rigorous measurements of the relative intensity on a set of µc-type transitions. Remarkably, this study underscores the pivotal role played by the interaction between the CC bonding orbital (π) of isoprene and the CC antibonding orbital (π*) of maleic anhydride in stabilizing the target complex.

Fluorination effects probed in 4-fluoroacetophenone and its monohydrate.

Rotational spectra of the 4-fluoroacetophenone monomer and its monohydrate were investigated by Fourier transform microwave spectroscopy complemented with quantum chemical calculations. One conformer of 4-fluoroacetophenone and two isomers of 4-fluoroacetophenone-H2O have been observed in the pulsed jets. The observation of all mono-substituted 13C isotopologues in natural abundance allows an accurate structural determination of the 4-fluoroacetophenone monomer. Both detected isomers of 4-fluoroacetophenone-H2O are stabilized by a dominant O-H⋯O and a secondary C-H⋯O hydrogen bond. The fluorination effects on the geometries, intermolecular non-covalent interactions and V3 barrier of the methyl internal rotation were analysed. The relative population ratio of the two observed isomers for 4-fluoroacetophenone-H2O was also estimated to be NI/NII ≈ 7/1.

Laboratory Rotational Spectrum and Radio-Astronomical Search of Acetoin.

The rotational spectrum of acetoin (3-hydroxy-2-butanone) was measured by using Fourier transform microwave spectroscopy with the aid of quantum chemical calculations. Only one conformer of acetoin was detected in the pulsed jet, whose spectrum featured the splittings raised from the internal rotation of the methyl top linking to the C═O group. Based on the spectroscopic result, radio-astronomical searches for acetoin were carried out toward the massive star-forming region Sgr B2(N) using the Shanghai Tianma 65 m and IRAM 30 m radio telescopes. No lines belonging to acetoin were detected toward Sgr B2(N). Its upper limit of column density was calculated.

Scissor-like Face to Face π-π Stacking: A Surprising Preference Induced by the Isocyano Group in the Self-Assembled Dimer of Phenyl Isocyanide.

Phenyl isocyanide has been chosen as a prototype to probe the π-π interaction modulated by the -NC group, which has a chameleonic nature with two main resonance forms showing a triple bond and being carbenoid. The rotational spectroscopic investigation complemented with theoretical analyses indicates that the phenyl isocyanide dimer has a scissor-like configuration controlled by dispersive forces along with the formation of π-π stacking. This is the first rotational spectroscopic evidence, to the best of our knowledge, that the mono-substitution by an -NC group on benzene can activate the meta position in forming noncovalent interactions. This work also provides experimental evidence on the importance of substituent effects in modulating π-π stacked structures, as well as practical proof of a biased interaction behavior of isocyanide-substituted aromatic molecules.

Laboratory Measurements and Astronomical Search for Methoxyacetone and Methyl Methoxyacetate.

High-resolution pure rotational spectra of methoxyacetone and methyl methoxyacetate have been recorded and analyzed by using pulsed jet-expansion Fourier transform microwave spectroscopy with the aid of quantum calculations. The global minima for both target molecules have been detected in pulsed jet, whose spectra are featured with the splittings raised from the methyl internal rotations. On the basis of the spectroscopic results, a radio-astronomical search of methoxyacetone and methyl methoxyacetate was carried out toward the high-mass star-forming region Sgr B2(N) using the Shanghai Tianma 65 m radio telescope. No lines belonging to either of the target molecules were detected, and the upper limits to the column density were derived.

Rotational Spectroscopy Meets Quantum Chemistry for Analyzing Substituent Effects on Non-Covalent Interactions: The Case of the Trifluoroacetophenone-Water Complex.

The most stable isomer of the 1:1 complex formed by 2,2,2-trifluoroacetophenone and water has been characterized by combining rotational spectroscopy in supersonic expansion and state-of-the-art quantum-chemical computations. In the observed isomer, water plays the double role of proton donor and acceptor, thus forming a seven-membered ring with 2,2,2-trifluoroacetophenone. Accurate intermolecular parameters featuring one classical O-H···O hydrogen bond and one weak C-H···O hydrogen bond have been determined by means of a semi-experimental approach for equilibrium structure. Furthermore, insights on the nature of the established non-covalent interactions have been unveiled by means of different bond analyses. The comparison with the analogous complex formed by acetophenone with water points out the remarkable role played by fluorine atoms in tuning non-covalent interactions.

Weak hydrogen bonds between alkyl halides and amides: The microwave spectroscopic and theoretical study of the difluoromethane⋯formamide complex.

The pure rotational spectrum of the complex of difluoromethane with formamide was investigated by means of microwave spectroscopy supplemented with theoretical calculations. The hyperfine structure arising from the 14N nuclear quadrupole coupling effect was completely resolved. The most stable isomer that displays the Cs symmetry with the ∠HCH angle of difluoromethane being bisected by the ab-plane of formamide was detected. The two moieties in the detected isomer are connected via one N-H⋯F and one bifurcated CH2⋯O weak hydrogen bonds confirmed by the non-covalent interaction plot and natural bond orbital analyses. The distances of the NH⋯F and CH2⋯O interactions were determined to be 2.140(14) Å and 2.749(14) Å, respectively. The NH⋯F bond angle was determined to be 150.7°. Symmetry-adapted perturbation theory analysis indicates that the electrostatic component is the largest contributor to the total attractive interaction energy of the difluoromethane⋯formamide complex.

The rotational spectrum of acetophenone-CO2: Preferred non-covalent interactions.

The rotational spectrum of the acetophenone-CO2 complex was investigated by pulsed jet-expansion Fourier transform microwave spectroscopy combined with ab initio calculations. In the supersonically cooled jet, only one isomer has been observed which is characterized by a dominant (CO2)C···O tetrel bond and a secondary (C-H)methyl∙∙∙O weak hydrogen bond. Johnson's non-covalent interaction, Bader's quantum theory of atoms in molecules and Symmetry-Adapted Perturbation Theory analyses have been applied to understand better the nature of non-covalent interactions in the acetophenone-CO2 complex.

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Procambarus clarkii was introduced into China as an important aquatic product in early 20th century. It has characteristics of high fertility, rapid growth, adaptability and digging burrows, which could cause damage of crops, cropland and facilities, decrease local biodiversity and thus threaten local ecosystem. Thus, predicting the potential distribution of P. clarkii in response to climate change was essential for preventing and monitoring this species. Based on the distribution of P. clarkii, the maximum entropy (MaxEnt) and genetic algorithm for rule-set production (GARP) models were used to predict its distribution in China under current climate and four climate scenarios (RCP 2.6, RCP 4.5, RCP 6.0, RCP 8.5) in two periods, 2041-2060 and 2061-2080. Then, the modeling results were tested by ROC curves. The results showed that under current climate, the highly suitable region for distribution predicted by the MaxEnt and GARP models were Shanghai, Jiangsu, Zhejiang and Anhui along the Yangtze River. The main environmental variables affecting its distribution were mean temperature of the coldest quarter, minimum temperature of the warmest month, and temperature seasonality, maximum temperature of the warmest month, precipitation of the driest month. Under the future climate scenarios, the suitable area of P. clarkii distribution varied in 2061-2080. The total suitable area of P. clarkii would increase under RCP2.6 and RCP 4.5, whereas under RCP 8.5 the suitable area of P. clarkii would increase, and then decrease. In RCP 6.0, there was no change. The suitable areas of P. clarkii would disperse to different latitude areas and migrate toward high altitude.

Conformational preference determined by inequivalent n-pairs: rotational studies on acetophenone and its monohydrate.

Acetophenone and its complex with water have been investigated by using pulsed jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. Rotational spectra of the acetophenone monomer comprising nine isotopologues were measured and assigned, enabling the accurate structural description of the carbon skeleton. The most stable isomer of the monohydrate of acetophenone was detected in the supersonic jet expansion. Water serves as a proton donor and acceptor forming an O-HO[double bond, length as m-dash]C hydrogen bond and a secondary C-HO-H weak hydrogen bond with acetophenone through a six-membered ring. The water molecule lies almost in the plane of the aromatic ring. Bader's quantum theory of atoms in molecules, Johnson's non-covalent interaction, electron localization function and natural bond orbital analyses were applied to characterize the nature of the non-covalent interactions in the target complex. All rotational transitions are split into two components arising from the hindered methyl internal rotation. Upon the complexation, the V3 barrier to internal rotation of -CH3 slightly decreases, with 7.50(3) kJ mol-1 for the monomer, and 7.04(5) kJ mol-1 for the acetophenone-H2O dimer, respectively.

Rotational spectrum, internal dynamics, and molecular structure of methylphenylsilane.

The rotational spectra of two isotopologues of methylphenylsilane were measured and assigned by using the supersonic-jet Fourier transform microwave spectroscopic technique in the 2.0-20.5 GHz range. The feature of rotational spectra of methylphenylsilane indicates that the doublets of rotational transitions in methylphenylsilane are contributable to the methyl internal rotation with a V3 barrier of 559 (25) cm-1. No splitting has been observed due to the methyl internal rotation in its carbon analog, ethylbenzene, which indicated that the barrier to such motion should be higher than 700 cm-1. Silicon incorporation of the ethyl group in ethylbenzene leads to a much lower barrier to the methyl internal rotation.

Tetrel bonds and conformational equilibria in the formamide-CO2 complex: a rotational study.

The rotational spectra of the complex formamide-CO2 have been measured and assigned by pulsed jet Fourier transform microwave spectroscopy. Two isomers of the complex have been detected where a CO tetrel bond dominates the interactions, and either N-HO or C-HO forms a secondary linkage. Bader's quantum theory of atoms in molecules and Johnson's non-covalent interaction analyses were applied to unveil the intermolecular binding sites and energetic properties in the complex. Relative intensity measurements on a set of µa-type transitions allowed estimating the relative population of the observed two isomers as NI/NII ≈ 18/1.

Using ensemble forecasting to examine how climate change promotes worldwide invasion of the golden apple snail (Pomacea canaliculata).

The golden apple snail, Pomacea canaliculata, is one of the world's 100 most notorious invasive alien species. Knowledge about the critical climate variables that limit the global distribution range of the snail, as well as predictions of future species distributions under climate change, is very helpful for management of snail. In this study, the climatically suitable habitats for this kind of snail under current climate conditions were modeled by biomod2 and projected to eight future climate scenarios (2 time periods [2050s, 2080s] × 2 Representative Concentration Pathways [RCPs; RCP2.6, RCP8.5] × 2 atmospheric General Circulation Models [GCMs; Canadian Centre for Climate Modelling and Analysis (CCCMA), Commonwealth Scientific and Industrial Research Organisation (CSIRO)]). The results suggest that the lowest temperature of coldest month is the critical climate variable to restrict the global distribution range of P. canaliculata. It is predicted that the climatically suitable habitats for P. canaliculata will increase by an average of 3.3% in 2050s and 3.8% in 2080s for the RCP2.6 scenario, while they increase by an average of 8.7% in 2050s and 10.3% in 2080s for the RCP8.5 scenario. In general, climate change in the future may promote the global invasion of the invasive species. Therefore, it is necessary to take proactive measures to monitor and preclude the invasion of this species.

Disentangling the determinants of species richness of vascular plants and mammals from national to regional scales.

Understanding the spatial patterns in species richness gets new implication for biodiversity conservation in the context of climate change and intensified human intervention. Here, we created a database of the geographical distribution of 30,519 vascular plant species and 565 mammal species from 2,376 counties across China and disentangled the determinants that explain species richness patterns both at national and regional scales using spatial linear models. We found that the determinants of species richness patterns varied among regions: elevational range was the most powerful predictor for the species richness of plants and mammals across China. However, species richness patterns in the Qinghai-Tibetan Plateau Region (QTR) are quite unique, where net primary productivity was the most important predictor. We also detected that elevational range was positively related to plant species richness when it is less than 1,900 m, whereas the relationship was not significant when elevational range is larger than 1,900 m. It indicated that elevational range often emerges as the predominant controlling factor within the regions where energy is sufficient. The effects of land use on mammal species richness should attract special attention. Our study suggests that region-specific conservation policies should be developed based on the regional features of species richness.

Determinants of Mammal and Bird Species Richness in China Based on Habitat Groups.

Understanding the spatial patterns in species richness is a central issue in macroecology and biogeography. Analyses that have traditionally focused on overall species richness limit the generality and depth of inference. Spatial patterns of species richness and the mechanisms that underpin them in China remain poorly documented. We created a database of the distribution of 580 mammal species and 849 resident bird species from 2376 counties in China and established spatial linear models to identify the determinants of species richness and test the roles of five hypotheses for overall mammals and resident birds and the 11 habitat groups among the two taxa. Our result showed that elevation variability was the most important determinant of species richness of overall mammal and bird species. It is indicated that the most prominent predictors of species richness varied among different habitat groups: elevation variability for forest and shrub mammals and birds, temperature annual range for grassland and desert mammals and wetland birds, net primary productivity for farmland mammals, maximum temperature of the warmest month for cave mammals, and precipitation of the driest quarter for grassland and desert birds. Noteworthily, main land cover type was also found to obviously influence mammal and bird species richness in forests, shrubs and wetlands under the disturbance of intensified human activities. Our findings revealed a substantial divergence in the species richness patterns among different habitat groups and highlighted the group-specific and disparate environmental associations that underpin them. As we demonstrate, a focus on overall species richness alone might lead to incomplete or misguided understanding of spatial patterns. Conservation priorities that consider a broad spectrum of habitat groups will be more successful in safeguarding the multiple services of biodiversity.