Isolation of Fluorescent 2π-Aromatic 1,3-Disiladiboretenes.

Herein, we reported the isolation of 2π-aromatic disiladiboretenes (L2Si2B2Ph2) [L = ArC(NtBu)2, Ar = Ph (1), Mes (2)], which have been synthesized from the straightforward reduction of silylene-borane adducts (LSiX → BX2Ph) [X = Cl, Br] with potassium graphite (KC8). X-ray diffraction analysis of 1 and 2 revealed that the Si2B2 units are completely planar, and DFT calculations suggested delocalization of 2π-electrons over the Si2B2 rings. Moreover, their photophysical properties and reactivity toward sulfur were also investigated in detail.

Burkholderia semiarida as Cause of Recurrent Pulmonary Infection in Immunocompetent Patient, China.

Burkholderia semiarida was previously identified solely as a plant pathogen within the Burkholderia cepacia complex. We present a case in China involving recurrent pneumonia attributed to B. semiarida infection. Of note, the infection manifested in an immunocompetent patient with no associated primary diseases and endured for >3 years.

Non-IRC Mechanism of Bimolecular Reactions with Submerged Barriers: A Case Study of Si+ + H2O Reaction.

Chemical reactions with submerged barriers may feature interesting dynamic behaviors that are distinct from those with substantial barriers or those entirely dominated by capture. The Si+ + H2O reaction is a prototypical example, involving even two submerged saddle points along the reaction path: one for the direct dissociation of H (H-dissociation SP) and another for H migration from the O-side to the Si-side (H-migration SP). We investigated the intricacies of this process by employing quasi-classical trajectory calculations on an accurate, full-dimensional ab initio potential energy surface. Through careful trajectory analysis, an interesting nonintrinsic reaction coordinate mechanism was found to play an important role in producing SiOH+ and H. This new pathway is featured as that the H atoms do not form HSiOH+ complexes along the minimum-energy path but directly dissociate into the products after passing through the H-migration SP. Furthermore, based on artificially scaled potential energy surfaces (PESs), the impact of barrier height on the reaction is also explored. This work provides new insights into the dynamics of the Si+ + H2O reaction and enriches our understanding of reactions with submerged barriers.

Role of keystone drives polycyclic aromatic hydrocarbons degradation and humification especially combined with aged contaminated soil in co-composting.

Accumulation of persistent organic pollutants polycyclic aromatic hydrocarbons (PAHs) in soil has become a global problem. Composting is considered one of the more economical methods of soil remediation and is important for the resourceful use of wastes. Agroforestry waste is produced in huge amounts and is utilized at low rates, hence there is an urgent need to manage it. Here, leaf (LVS) or rice straw (SVS) was co-composting with aged contaminated soil to investigate bacteria interaction to PAHs degradation and humus formation. The degradation rate of high molecular weight PAHs (HMW-PAHs) in LVS and SVS reached 58.9% and 52.5%, and the low molecular weight PAHs (LMW-PAHs) were 77.5% and 65%. Meanwhile, the humus increased by 44.8% and 60.5% in LVS and SVS at the end of co-composting. The topological characteristics and community assembly of the bacterial community showed that LVS had higher complexity and more keystones than SVS, suggesting that LVS might more beneficial for the degradation of PAHs. The stability of the co-occurrence network and stochastic processes (dispersal limitation) dominated community assembly made SVS beneficial for humus formation. Mantel test and structural equation models indicated that the transformation of organic matter was important for PAHs degradation and humus formation. Degradation of HMW-PAHs led to bacterial succession, which affected the formation of precursors and ultimately increased the humus content. This study provided potential technology support for improving the quality of agroforestry organic waste composting and degrading PAHs in aged contaminated soil.

Guest-Facilitated Heteroleptic Assembly of Helical Anionocages Enables Reversible Chirality Modulation.

We report a novel strategy for reversible modulation of the supramolecular chirality based on guest-facilitated heteroleptic assembly of helical anionocages. Two triple-stranded helical anionocages including a chiral cage 1 (A2 L1 3 ) and a crown ether functionalized achiral cage 2 (A2 L2 3 ) were synthesized by anion coordination of bis-monourea-based ligands and PhPO3 2- . Both cages exhibited favorable binding with tetraethylammonium TEA+ and cobaltocenium Cob+ (endo-guest, bound in the cavity). Additionally, cage 2 could reversibly release and recapture the guests through binding the exo-guest potassium ions (K+ ) in the crown ethers and subsequent removal of the K+ by [2,2,2]-cryptand. The circular dichroism (CD) spectrum of cage 1 was not significantly affected by guest encapsulation or mixing with the "empty" cage 2. However, in the presence of both cage 2 and an endo-guest/exo-guest, the Cotton effects were reversed at 391 nm and significantly enhanced at 310 nm. This observation was attributed to the guest-facilitated formation of heteroleptic cages that enabled effective chirality transfer from the chiral to the achiral ligands. The CD changes induced by K+ could be fully reversed by removing it with [2,2,2]-cryptand. Sequential addition and removal of K+ allowed reversible modulation of the chirality for at least 10 cycles without significant attenuation.

ON-OFF Fluorescent Cyanine Dye Based on a Benzothiophenyl Rotor Enables Selective Illumination of G-Quadruplexes in Mitochondria.

Conventional cyanine dyes exist as "always-on" fluorescent probes leading to inevitable background signals which often limit their performance and scope of applications. To develop specific fluorescent probes with high sensitivity and robust OFF/ON switching for targeting G4s, we introduced aromatic heterocycles through conjugation with polymethine chains to construct a rotor-π system. Here, a universal strategy is presented to synthesize pentamethine cyanines with different aromatic heterocycle substituents on the meso-polymethine chain. In these probes, SN-Cy5-S is self-quenched in aqueous solution due to H-aggregation. The structure indicates that SN-Cy5-S with a flexible meso-benzothiophenyl rotor conjugated to the cyanine backbone matches adaptively with G-tetrad planes, enhancing π-π stacking and resulting in triggered fluorescence. This allows recognition of G-quadruplexes due to the synergy of disaggregation-induced emission (DIE) and inhibited twisted intramolecular charge-transfer effects. This combination leads to a robust lighting-up fluorescence response for c-myc G4 with superior fluorescence enhancement (98-fold), allowing for a low detection limit of 1.51 nM, which is much more sensitive than the previously reported DIE-based G4 probes (22-83.5 nM). In addition, the superior imaging properties and rapid internalization time (5 min) in mitochondria allow SN-Cy5-S to also have a high potential for mitochondrially targeting anti-cancer therapy.

Stereoselective Assembly of Hydrogen-Bonded Anionic Cages Dictated by Organophosphate-Based Chiral Nodes.

Inspired by the signal transduction function of organophosphates in biological systems, bioactive organophosphates were utilized for the first time as chiral nodes to dictate the stereoselective assembly of hydrogen-bonded anionic cages. Phosphonomycin (antibiotics), tenofovir (antivirals), adenosine monophosphate (natural product, AMP) and clindamycin phosphate (antibiotics) were assembled with an achiral bis-monourea ligand, thereby leading to the stereoselective formation of quadruple or triple helicates. The extent of the stereoselectivity could be enhanced by either lowering the temperature or adding stronger-binding cations as templates. With the chiral anionic cages as the host, some enantioselectivity was achieved when binding chiral quaternary ammonium cations.

Less is More: A Shortcut for Anionocages Design Based on (RPO3 2- )-Monourea Coordination.

Anionocages have been developed as a unique family of hydrogen bonded cages. However, strategies for constructing anionocages are mainly limited to that based on (PO4 3- )-bisurea coordination, neither the ligands nor the anions lack the simplicity and diversity of the maturely developed analogues based on metal coordination (i.e. metallocage). We report herein a more simple strategy for anionocages design based on (RPO3 2- )-monourea coordination, utilizing monourea rather than bisurea as the hydrogen binding donor, and RPO3 2- rather than PO4 3- as the acceptor. Two fluorescent, quadruple helicate anionocages were constructed by a bis-monourea ligand, and dianions PhOPO3 2- (H1 ) or HOPO3 2- (H1A ), respectively, which were capable of encapsulating a series of cation guests. As revealed by molecular modeling, H1 features remarkable guest-adaptive cavity breathing without change of the quadruple helicate topology, which allowed the encapsulation of different sized guests in an "induced fit" manner.

Mode-specific dynamics in multichannel reaction NH+ + H2.

The vibrational- and rotational-mode specificity of the multichannel NH+ + H2 reaction is studied on a recently constructed ab initio-based global potential energy surface using an initial state selected quasi-classical trajectory method, and the trajectories are analyzed using an isometric feature mapping and k-means approach. All excitation modes promote two reactions (R1: NH'+ + H2 → NH+ + HH' and R4: NH'+ + H2 → NH2+ + H') where both NH and HH bonds are broken, but reduce the reactivity of the proton-transfer reaction R2 (NH'+ + H2 → N + H'H2+) at low collision energies. For the hydrogen-transfer reaction R3 (NH'+ + H2 → HNH'+ + H), the rotational excitation of NH+ enhances the reactivity remarkably, while its vibrational excitation has an inhibiting effect on the reaction. The trajectory analyses show that the vibrational and rotational excitations of NH+ make R3 tend to go over a submerged saddle point instead of extracting hydrogen atoms directly. On the other hand, the motions of the H2 reactant facilitate the enhancement of the reactivity but they do not affect the mechanism of R3. In addition, the results suggest that the coupling of the isometric feature mapping and the k-means approach in the trajectory analysis is an appropriate tool for reaction-dynamics studies.

Fine-Tuning the Spring-Like Motion of an Anion-Based Triple Helicate by Tetraalkylammonium Guests.

Supramolecular springs are a class of molecular devices that may provide implications to the macroscopic spring behavior from the molecular level. Helical structures are suitable molecular springs because the specific twisting of the helical strands can cause spring-like (extension-contraction) movement along the axis upon external stimuli. Herein we report an anion-based triple-helicate spring, which can undergo reversible contraction-extension motion through introduction and removal of tetraalkylammonium cations, including TMA+ and analogous irregular tetrahedral cations bearing different alkyl chains, while the relative orientation of the two phosphate ions changes to facilitate guest inclusion. Notably, the degree of contraction (shortening of the helical pitch) can be fine-tuned by varying the shape and size of guest cation. However, with the larger cations (TEA+ , TPA+ and TBA+ ), the meso-helicate configuration is obtained, which interconverts with the helicate by addition/removal of TMA+ ion.

Crown Ether Functionalized Potassium-Responsive Anionocages for Cascaded Guest Delivery.

In many critical biological processes, host-guest chemistry of protein receptors is regulated by effector molecules to realize cascaded delivery of messenger molecules between different targets. Mimicking these natural processes with artificial receptors remains a challenge. Herein, we report a cascaded guest delivery between two anionocages (anion-coordination-driven cages), in a reversible manner, wherein binding of K+ ions by a crown ether functionalized, heteroleptic A2 L3 (A=anion, L=ligand) anionocage triggers the release and delivery of a TEA+ (tetraethylammonium) guest to another A2 L3 anionocage that is a weaker and less K+ -sensitive receptor. Elimination of the K+ with [2,2,2]-cryptand enables recapture of the TEA+ by the crown ether functionalized anionocage and thus realizes a reversed guest delivery. Moreover, integrative self-sorting of anionocages is firstly reported, leading to heteroleptic cages with enhanced guest binding affinities.

Multiple Transformations among Anion-based A2nL3n Assemblies: Bicapped Trigonal Antiprism A8L12, Tetrahedron A4L6, and Triple Helicate A2L3 (A = Anion).

The construction of sophisticated, high-nuclearity polyhedral cages is an attractive yet challenging task in supramolecular chemistry. Herein we report the anion-coordination-driven assembly (ACDA) of a series of A2nL3n architectures ("A" denotes anion, L is ligand, n = 1, 2, 4) with a biphenylene-spaced bis-bis(urea) ligand including triple helicate A2L3 (H), tetrahedron A4L6 (T), and the octanuclear, bicapped trigonal antiprism (or parallelepiped) A8L12 (P). Among them, P is held by 96 hydrogen bonds, the largest number ever reported in a discrete polyhedron, and encapsulates multiple guests (three tetramethylammonium cations) in three compartments. Remarkably, multiple reversible transformations of these dynamic assemblies have been realized by alternation of the template guest, solvent, and concentration. Furthermore, a chiral ligand (L2S) with carbon stereocenters at both termini of the bis-bis(urea) backbone was designed and assembled with phosphate to form the enantio-pure triple helicate or tetrahedron. The chiral amplification effect in the tetrahedral complex is significantly larger than that in the triple helicate as a function of the point chirality.

A Silylene-Germylene Molecule Containing a SiI -GeI Single Bond.

The first isolable silylene-germylene complex 5 was assembled by a salt metathesis reaction between the germylene anion 3 and the N-heterocyclic chlorosilylene 4, and structurally characterized. The central structure of 5 demonstrates a remarkable gauche-bent geometry with the silylene and germylene units, which are interconnected by a Si-Ge bond with a length of 2.4498(9) Å. This value is not only perceptibly longer than the distances known in doubly bonded germasilenes, and also slightly longer than those in germylsilanes. The DFT calculations on 5 confirmed a nearly nonpolar SiI -GeI single-bond nature and its bonding orbital, as well as the aromaticity of the C3 NGe-rings in 3 and 5. The latter increases the molecular stability of 3 and 5, and makes the preparation of silylene-germylene complex 5 a reality.

Quasi-classical trajectory analysis with isometric feature mapping and locally linear embedding: deep insights into the multichannel reaction on an NH3+(4A) potential energy surface.

From the perspective of data analysis, finding and determining reaction paths from the quasi-classical trajectories of a polyatomic reaction system are equivalent to finding low-dimensional manifolds embedded in a high-dimensional space. Two manifold learning methods, isometric feature mapping and locally linear embedding, are applied to the analysis of reaction trajectories, which are calculated by the quasi-classical trajectory approach on a newly developed accurate quartet state NH3+(4A) potential energy surface for a multichannel reaction NH+ + H2→ N + H3+/NH2+ + H. The results show that isometric feature mapping can clearly identify different reaction paths from the reactive trajectories, and the locally linear embedding is better for the classification of non-reactive trajectories, and both of them facilitate quantitative analysis. With the help of trajectory analysis, the competition between the two H-atom abstraction reactions can be attributed to two different capture paths.

Unexpected Indirect Dynamics in Base-Induced Elimination.

Base-induced elimination (E2) and bimolecular nucleophilic substitution (SN2) are two of the most versatile reactions that are important in preparative organic chemistry. These stereospecific reactions are often found in direct competition with each other. Elimination can proceed via two distinct transition states, referred to as anti and syn, of which anti is commonly energetically favored. To investigate the intrinsic dynamics of base-induced elimination, reactions under single-collision conditions are required. Here, we present reactive scattering results on the prototype reaction of the fluoride anion with tert-butyl halides. The observed mechanistic fingerprints are associated with the E2 reaction, because steric hindrance at the α-carbon suppresses the SN2 reaction [Carrascosa, E.; Meyer, J.; Zhang, J.; Stei, M.; Michaelsen, T.; Hase, W. L.; Yang, L.; Wester, R. Nat. Commun. 2017, 8, 25]. The reaction coordinate shows energetically submerged transition states, with anti favored over syn, and we found a very shallow prereaction well for anti. We predominantly found indirect dynamics for a range of collision energies, which can be separated into three remarkably different mechanisms. At low collision energies, the first is a large impact parameter indirect mechanism which leads to a forward-backward symmetric scattering signature. The second mechanism is attributed to low-impact parameter reactions with a near-statistical partitioning of the total available energy. The majority of events are associated with widespread isotropic scattering. Unexpectedly, the product ion kinetic energy distributions are independent of collision energy. We associate this with dynamic trapping in a prereaction well supported by a large centrifugal potential. These measured fingerprints support that atomistic reaction dynamics cannot be predicted based on stationary arguments alone.

A Tetra-amido-Protected Ge5-Spiropentadiene.

The first isolable Ge5-spiropentadiene 1 was synthesized via the reduction of (iPr3Si)2NGeCl (3) with potassium. The crystal structure of 1 reveals a spirocyclic Ge5 skeleton containing two Ge-Ge double bonds (avg. 2.34 Å), which are fettered in two Ge3 rings with a dihedral angle of 70.193°. The DFT calculations and orbital analysis show that the σ-delocalization of the Ge5 skeleton and the 2π-delocalized aromatic Ge3 rings enhance the stability of molecule 1.

Types of Six-Membered N-Heterocyclic Germanium Radicals: A Combined Computational and Experimental Study.

A new stable six-membered cyclic germylene radical C (•L3Ge:; •L3 = •[CH3C(PhCN-Dip)2]2-, where Dip = 2,6- iPr2C6H3) has been synthesized and structurally characterized. Unlike the germanium-centered radical A (L1•Ge:, L1 = [HC( tBuCN-Dip)2]-), C is a π-type radical with spin density mainly distributed on the NC3N backbone, similar to that in the germylene radical B (•L2Ge:; •L2 = •[PhC(PhCN-Dip)2]2-). The electronic effects in six-membered N-heterocyclic germanium radicals were systematically investigated using density functional theory calculations. The type of radical, which basically depends on the strong inductive effect of substituents on the side C atoms of the NC3N backbone, is confirmed by monitoring the change in the ordering of the frontier molecular orbitals during radical formation. However, the radical with moderately electronegative substituents or two substituents with comparable electron pushing and pulling abilities could not be isolated in experiments, probably because of the kinetic instability during the reduction process from the germylene chloride precursor to radical.

Isotope-selective chemistry in the Be+(2S1/2) + HOD → BeOD+/BeOH+ + H/D reaction.

Low temperature reactions between laser-cooled Be+(2S1/2) ions and partially deuterated water (HOD) molecules have been investigated using an ion trap and interpreted with zero-point corrected quasi-classical trajectory calculations on a highly accurate global potential energy surface for the ground electronic state. Both product channels have been observed for the first time, and the branching to BeOD+ + H is found to be 0.58 ± 0.14. The experimental observation is reproduced by both quasi-classical trajectory and statistical calculations. Theoretical analyses reveal that the branching to the two product channels is largely due to the availability of open states in each channel.

GeI-GeI Coupling Reaction Induced by a Mixture of CoBr2 and a Seven-Membered N-Heterocyclic Carbene.

A new digermylene has been synthesized through the reaction of a six-membered cyclic radical germylene precursor with a mixture of CoBr2 and a seven-membered N-heterocyclic carbene. The density functional theory simulation on the geometry of the digermylene agrees well with the experimental X-ray diffraction result. The digermylene possesses the shortest GeI-GeI bond [2.4853(6) Å] compared to the known singly bonded analogues, which can be attributed to σ → π* conjugation. In addition, it is revealed that a stable dative bond cannot form for the reductive radical germylene with the oxidative metal centers.

Dynamics and kinetics of the reaction OH + H2S → H2O + SH on an accurate potential energy surface.

The dynamics and kinetics of the prototypical hydrogen abstraction reaction OH + H2S → H2O + SH were studied using the quasi-classical trajectory approach on a new accurate ab initio potential energy surface (PES) for the ground electronic state. The PES was developed by fitting 82 680 ab initio points at the level of UCCSD(T)-F12a/aug-cc-pVTZ using the fundamental invariant-neural network method. On one hand, excitation of either the symmetric stretching mode or the asymmetric stretching mode of the reactant H2S almost equivalently enhances the reaction. The promotional effect of exciting the bending mode of H2S is not as strong as exciting the stretching modes while it increases with the collision energy. On the other hand, the calculated vibrational state distribution of the product H2O based on the normal mode analysis method agrees reasonably well with the earlier experimental result, which was rationalized by the underlying reaction mechanisms. In addition, the rate constants of the reaction have a non-Arrhenius temperature dependence.