CN Rotation Research Articles

Magnetic high-order topological insulator in 2D layered CrOCl

High-order topological insulators (HOTIs) have garnered significant interest in recent years due to their unique properties, but their material realization has thus far been limited to those protected by Cn (n = 3,4,6) rotation symmetry and to nonmagnetic crystals. In this study, we propose a HOTI in a recently synthesized two-dimensional (2D) magnetic material, CrOCl. Our findings reveal that the material's ground state, which has ferromagnetic ordering, features corner states carrying a quantized fractional charge. These states are enabled by a twofold rotation symmetry (C2z) and are robust against spin-orbital coupling (SOC). The corner states in CrOCl are distinct from those in nonmagnetic examples and even in magnetic examples, as they can achieve 100% spin polarization in the presence or absence of SOC. Remarkably, the corner states in CrOCl are also robust against layer stacking, symmetry breaking, and even magnetization. Furthermore, under a vertical electric field, the material undergoes a phase transition from HOTI to “hidden high-order topological insulator” phase, with the corner states submerged into edge or bulk states. Our study not only highlights the HOTI properties of 2D CrOCl, but also promotes it as a concrete material platform for exploring the intriguing physics of magnetic HOTIs. We also discuss possible experimental detections and applications of this material, which may pave the way for new advancements in materials sciences and condensed-matter physics.

Development of piperazine conjoined 1,2,3-triazolyl-γ-propyltriethoxysilanes: Fluorometric detection of Cr3+ ions and computational study

Chromium is essential for some biochemical processes, and excess is a big concern that shows adverse effects on human health and the environment. Therefore, it is urgent to design new sensors to detect chromium ions rapidly. The present study discusses the synthesis of piperazine conjoined 1,2,3-triazolyl-γ-propyltriethoxysilanes (4a-4b) and development of 4a as fluorescence turn-on sensor for the detection of Cr3+ ions. The mechanistic insights reveal to the restricted CN rotation and inhibited intramolecular charge transfer (ICT) process. In addition, Job's plot and Benesi-Hildebrand plot justify the 1:1 binding affinity with a binding constant of 9.96 × 105 M−1 for [ligand 4a + Cr3+] complex and the limit of detection for Cr3+ ions is observed as 6.06 × 10-8 M. The fluorescence spectral changes, 1H NMR spectra and DFT studies provide evidences for ligand 4a and Cr3+ ions interactions. Further, the reversibility of the ligand 4a from [ligand 4a + Cr3+] complex on the addition of EDTA can be used in the construction of molecular logic gate where Cr3+ and EDTA are considered as inputs and the fluorescence intensity at 398 nm as output. Further, compounds 4a-4b were then evaluated for their antibacterial activity against bacterial strains (Escherichia coliand Staphylococcus aureus), revealing a modest activity. The binding mode of ligand 4a to Staphylococcus aureus (PDB ID − 3U2K) and Escherichia coli (PDB ID − 5Z4O) was investigated using an in-silico molecular docking technique, which revealed that the triazole ring and silanyl group are involved in hydrogen bonding with proteins and may be the cause of the ligand's antibacterial activity. The ligand 4a demonstrated a high affinity for binding within the active sites of proteins with binding energies of −7.97 kcal/mol (3U2K) and −8.68 kcal/mol (5Z4O).

Bis naphthalene derived dual functional chemosensor: Specific signalling for Al3+ and Fe3+ ions with on-the-spot detection, bio-imaging, and logic gate applications

Bis naphthalene derived Schiff base (R) was achieved as a dual functional chemosensor for highly specific recognition of Al3+ and Fe3+ ions in DMSO-H2O medium. The sensor R acts as a single scavenger to detect dual analytes by colorimetric and fluorimetric techniques through a switch “off–on” process. The probe R detects Al3+ by enhancing the fluorescence emission and Fe3+ by an increase in the absorbance emission respectively, via in restriction of CN rotation, blockage of CN isomerization and inhibition of photoinduced electron transfer (PET) assisted with Excited State Intramolecular Proton Transfer (ESIPT) processes. The binding stoichiometry ratio was determined to be 1:1 complexation by job’s plot method supported by 1H NMR titration, IR studies and DFT analysis. The limit of detection (LOD) was calculated to be 1.7 µM and 23.2 µM for the detection of Fe3+ and Al3+ by probe R through colorimetric and fluorimetric techniques respectively. Further, sensor R was practically applied for the detection of Al3+ and Fe3+ in water samples and bio-imaging of microbial pathogens. Especially, colour change of sensor R on the binding of Al3+ was demonstrated in various applications like paper strip, silica-gel supported analysis and smartphone-colour assist technique.

A lead selective dimeric quinoline based fluorescent chemosensor and its applications in milk and honey samples, smartphone and bio-imaging

Dimeric quinoline-based Schiff base was developed (DQS) for the specific detection of Pb2+ ion via fluorimetry. DQS coordinates with Pb2+, a variation in fluorescence intensity with enhanced radical blue shift was observed due to the restriction of CN rotation, CN isomerization, and photoinduced electron transfer (PET) mechanisms. In addition, the intramolecular charge transfer (ICT) from electron-donating morpholine to phenylene diamine acceptor linked quinoline bridge is responsible for the blue-shifted fluorescence enhancement in the DQS-Pb2+ complex. The binding stoichiometry of DQS: Pb2+ (1:2) was confirmed by host–guest titration and mass spectrometry. The limit of detection (LOD) of the DQS was found to be 1.3 × 10-7 M for Pb2+ ion. The DQS sensing ability of Pb2+ was further applied into milk and honey samples, smartphone, bio-imaging and to construct of an INHIBIT molecular logic gate.

Predissociation spectroscopy of cold CN−H2 and CN−D2

The vibrational predissociation spectra of the CN–H2 and CN–D2 complexes are measured in regions between 450 and 3100 cm in an ion trap at different temperatures at the free electron lasers for infrared experiments (FELIX) Laboratory. Strong differences between the vibrational spectra of the two para and ortho nuclear spin isomers (CN–(p-H2) or CN–(o-H2) and CN–(p-D2) or CN–(o-D2)) are detected. In the case of CN–H2 we could assign the observed bands with the help of an accurate quantum calculation. The spectrum is dominated by the first overtone of the hindered H2 rotation in combination with the hindered CN rotation of the CN–(o-H2) nuclear spin isomer. The energetically higher-lying CN–(p-H2) isomer was not observed due to efficient ortho-para ligand exchange. The C–N stretching mode was recorded at 2040(1) cm. For the CN–D2 system several vibrational modes of both spin isomers overlap in their low-lying intermonomer streching and bending region, but the main observed bands are attributed to the more stable CN–(p-D2) spin isomer. The D–D stretching vibration was found to be at 2898(1) cm.

A bifunctional sensitive fluorescence probe based on pyrene for the detection of pH and viscosity in lysosome

Lysosome is one of the important organelles in intracellular transport. It plays a significant role in the physiological process. The lysosomal microenvironment affects the functions of lysosome. When the original acidic environment of lysozyme is destroyed or the fluid viscosity increases gradually, various diseases are easily induced. However, most fluorescent probes can only locate in cells. The fewer probes of subcellular organelles were found and their functions are often single. So, it is of great importance to design multifunctional fluorescent probes with the capable of localizing in lysosome. In this study, a novel lysosome probe, 4-(4-Pyren-1-yl-but-3-enyl)-morpholine (PIM), was synthesized using pyrene as a fluorescent group and morpholine as a target group. The introduction of morpholine group made PIM localize in lysosome with high selectivity. The fluorescence will be enhanced with the increased viscosity because of restricting the rotation of CC bond and CN in PIM, and the detecting linear range is from 4.05 cP to 393.48 cP, which qualified the requirement of the viscosity monitoring in body. Meanwhile, the fluorescence intensity of PIM declines with the decrease of pH because the Schiff base of PIM is hydrolyzed, which was affirmed by 1H NMR, LC-MS and fluorescence spectra. Moreover, cell imaging and MTT experiments confirmed that PIM as a novel bifunctional probe can be used to detect pH and endogenous viscosity in lysosome.

Chemical Analysis of Zooplankton by Calibration-Free Laser-Induced Breakdown Spectroscopy

Ratios of light metals (Li, Na, K, Mg, and Ca) in zooplankton (Calanus spp.) were determined by laser-induced breakdown spectroscopy without reference samples under the assumption of local thermodynamic equilibrium. The temperature of plasma formed as a result of laser ablation of zooplankton was estimated from the CN rotation–vibration bands, and the electron density was estimated from the Stark broadening of Mg I 383.23 nm, Li I 610.37 nm, and Ca II 396.85 nm lines. These experimentally determined parameters were used for plasma modeling, taking into account the transport of radiation. This made possible a selection of analytical emission lines free from self-absorption. The results are compared with the results of elemental analysis by atomic emission and inductively coupled plasma mass spectrometry. The influence of the ionization equilibrium on the correctness of results is discussed. The described method is proposed to be used for direct semiquantitative determination of Li, Mg, and Ca ratios in zooplankton.

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F1 and F2 spin-rotation levels of the CN products.

One of the most spectacular yet unsolved problems for the ICN -band photodissociation is the non-statistical spin-rotation F1 = N + 1/2 and F2 = N - 1/2 populations for each rotation level N of the CN fragment. The F1 /F2 population difference function f(N) exhibits strong N and λ dependences with an oscillatory behavior. Such details were found to critically depend on the number of open-channel product states, namely, whether both I (2 P3/2 ) and I (2 P1/2 ) are energetically available or not as the dissociation partner. First, in the asymptotic region, the exchange and dipole-quadrupole inter-fragment interactions were studied in detail. Then, as the diabatic basis, we took the appropriate symmetry adapted products of the electronic and rotational wavefunctions for the F1 and F2 levels at the dissociation limits. We found that the adiabatic Hamiltonian exhibits Rosen-Zener-Demkov type nonadiabatic transitions reflecting the switch between the exchange interaction and the small but finite spin-rotation interaction within CN at the asymptotic region. This non-crossing type nonadiabatic transition occurs with the probability 1/2, that is, at the diabatic limit through a sudden switch of the quantization axis for CN spin S from the dissociation axis to the CN rotation axis N. We have derived semiclassical formulae for f(N) and the orientation parameters with a two-state model including the 3A' and 4A' electronic states, and with a four-state model including the 3A' through 6A' electronic states. These two kinds of interfering models explain general features of the F1 and F2 level populations observed by Zare's group and Hall's group, respectively. © 2018 Wiley Periodicals, Inc.

Quadruple-signaling (PET, ICT, ESIPT, [sbnd]C[dbnd]N[sbnd] rotation) mechanism-based dual chemosensor for detection of Cu2+ and Zn2+ ions: TRANSFER, INH and complimentary OR/NOR logic circuits

Herein, we have designed and synthesized o-phenylenediamine-based 4-in-1 dual chemosensor DAU, for simultaneous detection of Cu2+ and Zn2+ through modulation of PET, ICT, ESIPT and CN rotation mechanisms. The binding of first Cu2+ ion with NEt2 group causes red shift of absorption band from 372 nm to 420 nm and fluorescence enhancement due to keto- form at 480 nm (∼20 fold). When concentration of Cu2+ further increased from 1 to 10 equivalents, it results in decrease in absorption intensity at 420 nm and increase in absorption intensity at 300 nm and fluorescence quenching at 480 nm followed by enhancement due to enol- form at 410 nm. In contrary higher concentrations of Zn2+ causes only red shift from 372 to 420 nm however fluorescence remained low due to PET quenching effect. Significantly, when Cu2+ is added to DAU–Zn2+ (1:5) complex, it results in decrease of absorption intensity at 420 nm and increase in fluorescence at 480 nm followed by a 7-fold increase of the emission intensity at 410 nm. The multiple outputs of DAU can be used for fabrication of INHIBIT, TRANSFER logic devices and complementary OR/NOR logic circuit.

Dynamic Mapping of CN Rotation Following Photoexcitation of ICN−

In a spin: the dynamics of photoexcited ICN(-) (Ar)(0-5) are presented. Photodetachment produces quasi-thermal electron emission that leaves ICN with up to 2.85 eV of internal energy. Photodissociation at 2.5 eV leads to one-atom caging and highly solvated anion products. Calculations indicate efficient energy transfer into CN rotation upon excitation to the (2)Π(1/2) excited state. CN rotation is vital to explain the unique dynamics observed.

Dynamic Mapping of CN Rotation Following Photoexcitation of ICN−

Rotationsprinzip: Die Dynamik von angeregtem ICN−(Ar)0–5 wird vorgestellt. Nach der Photoabspaltung eines quasithermischen Elektrons verbleibt ICN mit bis zu 2.85 eV an innerer Energie. Die Photodissoziation bei 2.5 eV führt zu Ein-Atom-Käfigeffekten und hoch solvatisierten anionischen Produkten. Rechnungen sprechen für einen effizienten Energietransfer in die CN-Rotation bei der Anregung in den 2Π1/2-Zustand. Die CN-Rotation ist entscheidend für die Erklärung der beobachteten Dynamik.

A Ag+-selective “off–on” probe based on a naphthalimide derivative

A new naphthalimide-based derivative L bearing an S-benzyldithiocarbazate moiety was synthesized as an “off–on” probe for Ag+. The new probe has high binding selectivity for Ag+ in water media with a detection limit of Ag+ down to 270 nM. Based on the Ag+-induced inhibition of a PET process and restriction of CN rotation, the coordination mode of 1 : 1 between L and Ag+ was proposed.

“Amide Resonance” Correlates with a Breadth of C−N Rotation Barriers

Complete basis set calculations (CBS-QB3) were used to compute the CN rotation barriers for acetamide and eight related compounds, including acetamide enolate and O-protonated acetamide. Natural resonance theory analysis was employed to quantify the "amide resonance" contribution to ground-state electronic structures. A range of rotation barriers, spanning nearly 50 kcal/mol, correlates well to the ground-state resonance weights without the need to account for transition-state effects. Use of appropriate model compounds is crucial to gain an understanding of the structural and electronic changes taking place during rotation of the CN bond in acetamide. The disparate changes in bond length (DeltarCO << DeltarCN) are found to be consonant with the resonance model. Similarly, charge differences are consistent with donation from the nitrogen lone pair electrons into the carbonyl pi* orbital. Despite recent attacks on the resonance model, these findings demonstrate it to be a sophisticated and highly predictive tool in the chemist's arsenal.

The role of water on the acid-promoted E/ Z isomerization of oximes in aqueous solution

Acid-promoted E/ Z isomerization of oximes in water is studied by means of theoretical calculations at the B3LYP/6-31G(d,p) level. We have considered a simple derivative, acetaldoxime, as a model to discuss the isomerization mechanism in more complex systems. The solvent is represented by a continuum or by a discrete-continuum model. Our calculations suggest that E/ Z isomerization in water occurs through the formation of a protonated oxime–water adduct that involves the creation of a C(oxime)–O(water) bond and lies 14.2 kcal/mol above the separated reactants. In this intermediate, there is a single CN bond and rotation around this bond is free. The previously proposed mechanism assumed water addition to the CN double bond of the oxime with formation of a tetrahedral intermediate To. We predict this mechanism to be significantly less favorable than the one proposed in the present work.

Energy disposal in CN(X 2Σ+) produced in the 157 nm photodissociation of acrylonitrile

Photodissociation of acrylonitrile has been studied at 157.6 nm through analysis of laser-induced fluorescence experiments. The CN(X 2Σ+) radicals formed in this dissociation are detected in vibrational levels up to v=6 and rotational population distributions are measured for vibrational levels v=0–3. The average energies found in vibration and rotation of CN are approximately equal and represent about 5% of the available energy if the vinyl radical is the co-fragment. This is close to the 7% expected on the basis of the equipartition theorem which suggests that energy disposal is largely statistical. The vibrational and rotational distributions however are not in good agreement with an energy-conserving prior distribution suggesting that dynamical factors play a significant role in energy disposal.

Three-dimensional time-dependent study of a reaction involving three different heavy atoms and a very deep well: application to the C+NO [formula omitted]CN+O exchange reaction

We present a three-dimensional time-dependent wavepacket study of the C( 3 P)+NO(X 2 Π ) → CN(X 2 Σ + )+O( 3 P) indirect reaction, for total angular momentum J=0. This calculation is the first one which involves three different heavy atoms and a very deep well of about 4.2 eV, corresponding to the linear geometry of the CNO complex. The total reaction probability as well as the percentage of the energy disposal channeled into the vibration and the rotation of CN are obtained for a wide range of scattering energies. These quantities are compared to ones obtained using a quasiclassical approach. A good agreement is observed between these two calculations.

Investigation of multiaxial molecular dynamics by [formula omitted] MAS NMR spectroscopy

The technique of 2 H MAS NMR spectroscopy is presented for the investigation of multiaxial molecular dynamics. To evaluate the effects of discrete random reorientation a Lie algebraic formalism based on the stochastic Liouville–von Neumann equation is developed. The solution to the stochastic Liouville–von Neumann equation is obtained both in the presence and absence of rf irradiation. This allows effects of molecular dynamics to be evaluated during rf pulses and extends the applicability of the formalism to arbitrary multiple pulse experiments. Theoretical methods are presented for the description of multiaxial dynamics with particular emphasis on the application of vector parameters to represent molecular rotations. Numerical time and powder integration algorithms are presented that are both efficient and easy to implement computationally. The applicability of 2 H MAS NMR spectroscopy for investigating molecular dynamics is evaluated from theoretical spectra. To demonstrate the potential of the technique the dynamics of thiourea– 2 H 4 is investigated experimentally. From a series of variable temperature MAS and quadrupole echo spectra it has been found that the dynamics can be described by composite rotation about the CS and CN bonds. Both experiments are sensitive to the fast CS rotation which is shown to be described by the Arrhenius parameters E CS=46.4±2.3 kJ mol −1 and ln( A CS)=32.6±0.9. The MAS experiment represents a significant improvement by simultaneously allowing the dynamics of the slow CN rotation to be fully characterized in terms of E CN=56.3±3.4 kJ mol −1 and ln( A CN)=25.3±1.1.

Energy dependence of the isomerization of HCN+ to HNC+ via ion molecule reactions

The mechanism for isomerization of HCN+ ions to the more stable HNC+ in collision with CO2 at thermal energy has been confirmed to be a double proton transfer in the collision complex. First a proton is transferred from C in HCN+, then, following CN rotation in the complex, the proton is transferred to the N atom, both proton transfers being exothermic. The mechanism has been established by measuring the reaction of HCN+ with CO2 as a function of energy from thermal up to 0.7 eV relative kinetic energy in a selected ion flow drift tube. The isomers are distinguished by the use of monitors that react differently with the two isomers. A similar HCN+ to HNC+ isomerization occurs in thermal collisions with CO.

Quantum dynamics study of H2+CN → HCN+H reaction in full dimensions

Time-dependent (TD) quantum dynamics calculation for the title reaction has been carried out in full mathematical (six) dimensions on a new potential energy surface (denoted TSH3). Our numerical calculation shows that as far as total reaction probabilities and cross sections are concerned, the CN vibration behaves like a spectator bond when both reagents are at ground vibrational state. The vibrational excitation of CN slightly decreases the reaction probability and cross section while vibrational excitation of H2 considerably enhances the reaction probability and cross section. The reaction probability is enhanced by excitations of H2 rotation and more so of CN rotation. Overall, the reaction proceeds by a direct abstraction path without contribution from the insertion process. Comparison of our calculated rate constant with experimental measurements indicates that the effective barrier of the TSH3 PES for the title reaction is perhaps too high by about 0.3 kcal/mol.

Reaction dynamics calculations for the CN+H2→HCN+H reaction: Applications of the rotating-bond approximation

We present quantum dynamics studies of the CN+H2→HCN+H reaction. An extended version of the rotating bond approximation (RBA), in which nonreactive CN stretch motion is taken into account in the dynamics explicitly, has been employed, and we have used a potential energy surface that was recently developed by ter Horst, Schatz, and Harding [J. Chem. Phys. 105, 558 (1996)]. This surface describes the HCN force field quite accurately and has significant coupling between CH and CN stretch vibrations in HCN. We find that neither CN vibration nor rotation affect the reaction cross section for the forward reaction significantly. This result is consistent with the fact that the forward reaction has an early barrier. On the other hand, for the reverse reaction HCN+H, HCN vibrational excitation significantly lowers the reactive threshold and enhances the cross section at energies above threshold. We find for the reverse reaction that all three modes of HCN (CH stretch, CN stretch and bend) reduce the threshold by an amount which equals the energy put into reagent vibration, but the enhancement in the cross section at a fixed energy above threshold is largest for energy put into the CH stretch. We also find that the HCN vibrational state distributions for the CN+H2 reaction show significant population in both CH and CN stretching normal modes. These results indicate that the nonreactive CN bond in the CN+H2 reaction, as well as its reverse, cannot be described totally by a simple spectator model, and that coupling between CH and CN stretch vibrations plays an important role in the dynamics.