Structural Investigation of (5-Amino-1,3,4-thiadiazolyl-2-thionato)trimethyltin(IV): 1D Chains Generated by Hydrogen Bonding

ABSTRACT

The geometry of the four-coordinated Sn atom in the title compound, (CH₃)₃Sn(C₂H₂N₃S₂), is distorted tetrahedral with three Sn–C bonds and one Sn–S bond. Two crystallographically distinct molecules a and b within the asymmetric unit are hydrogen bonded. Intermolecular “N–H?N” hydrogen bond interactions generate infinite 1D chains consisting of alternating, centrosymmetric R2,2(8) and R4,2(10) rings.     

Conformational Analysis of Baclofen Analogues by 1H and 13C NMR: Phaclofen,Saclofen, and Hydroxy-Saclofen. Influence of the Anionic Moiety

The conformations of three analogues of baclofen 1: phaclofen, saclofen, and hydroxy-saclofen 2–4, potent GABA_B antagonists, in solution (D₂O) are estimated from high-resolution (300 MHz) H NMR coupling data. Conformations and populations of conformers are calculated by means of a modified Karplus-like relationship for the vicinal coupling constants. H NMR spectral analysis evidences how 1–3 keep in solution the preferred a conformation around C3-C4 bond. A partial rotation is set up around C2–C3 bond (the conformations about C2–C3 are all highly populated in solution) particularly for 2 and 3 while 1 shows a relative preferred a conformation. This evidences the influence of the anionic moiety.     

Structural Assignment of Stilbenethiols and Chalconethiols and Differentiation of Their Isomeric Derivatives by Means of 1H‐ and 13C‐NMR Spectroscopy

Abstract

The ¹H‐ and ¹³C‐NMR spectra of some substituted stilbenes and chalcones were assigned unambiguously on the basis of a combination of homo‐ (COSY) and heteronuclear (HETCOR) two‐dimensional methods, the chemical shifts, as well as spin‐coupling constants. The A_ik empirical parameters of the –O–C(S)–N(CH₃)₂, –S–C(O)–N(CH₃)₂, and –SH group were calculated to help predict the chemical shifts of substituted stilbenes, 4′‐nitrostilbenes, and chalcones. The ¹H‐ and ¹³C‐NMR spectra have been shown to be able to differentiate between the isomers of O‐stilbenyl (4, 5) and S‐stilbenyl N,N‐dimethylthiocarbamates (7, 8) as well as O‐chalconyl (6) and S‐chalconyl N,N‐dimethylthiocarbamates (9).     

NMR Studies of Crowded Diels–Alder Adducts of Phencyclone with N‐(2,6‐Dialkylphenyl)maleimides. Hindered Rotations and Magnetic Anisotropy

Abstract

Phencyclone, 1, reacted with N‐(2,6‐dimethylphenyl)maleimide, 2a; with N‐(2,6‐diethylphenyl)maleimide, 2b; and with N‐(2,6‐diisopropylphenyl)maleimide, 2c, respectively, to yield the corresponding Diels–Alder adducts, 3a–c. The adducts were extensively characterized by NMR (7 T) at ambient temperatures using one‐ and two‐dimensional (1D and 2D) proton and carbon‐13 techniques for assignments. Slow exchange limit (SEL) spectra were observed, demonstrating slow rotations on the NMR timescales, for the unsubstituted bridgehead phenyl groups [C(sp³)–C(aryl sp²) bond rotations] and for the 2,6‐dialkylphenyl groups [N(sp²)–C(aryl sp²) bond rotations]. Substantial magnetic anisotropic shifts were seen in the adducts. For example, in the N‐(2,6‐dialkylphenyl) moieties of the adducts, one of the alkyl groups is directed “into” the adduct cavity, toward the phenanthrenoid portion, and these “inner” alkyl proton NMR signals were shifted upfield. Thus, in CDCl₃, the “inner” methyl of adduct 3a exhibits a proton resonance at ?0.13 ppm, upfield of tetramethylsilane (TMS); the “inner” ethyl group signals from 3b appear at 0.026 ppm (CH₂, quartet), and ?0.21 ppm (CH₃, triplet); and the “inner” isopropyl group from 3c is seen at ?0.06 ppm (methine, approx. septet) and ?0.39 ppm (CH₃, doublet). Proton NMR of the crude N‐(2,6‐dialkylphenyl)maleamic acids (used as precursors of the maleimides, 2a–c) exhibited two sets of AB quartet signals, suggesting possible conformers from hindered rotation in the amide groups about the HN–C?O bonds.     

Probe the accumulation modes of the Au–C22H14 dimer on the structure and NLO properties

In 2006, the Au–C₂₂H₁₄ with a covalent bond between an individual pentacene (C₂₂H₁₄) and a gold (Au) atom was synthesised and characterised, and its nonlinear optical (NLO) properties were explored. To further investigate the NLO properties from molecules to materials, three kinds of different dimers (Au–C₂₂H₁₄)₂ (2, 3 and 4) were designed to probe the monomer accumulation modes on the structures and NLO properties. The results indicate that Au atoms doping breaks the conjugate structures of the two pentacenes to different extent. On the other hand, their NLO properties investigated by three density functional theory methods Becke-Half-and-Half-LYP (BHandHLYP), Coulomb-attenuating method Becke-3-Lee–Yang–Parr (CAM-B3LYP) and Minnesota 2005 double the amount of nonlocal exchange (M05-2X) show the same order, and 2 has the largest first hyperpolarisability (β_tot) than the other molecules. At the same time, natural bond orbital analysis shows the Au atoms play a crucial role in pushing electron density. Meanwhile, the frontier molecular orbital analysis shows that charge transfer has occurred between the two pentacene molecules and Au atoms. As a result, the order of transition energy is opposite to the order of β_tot values. Because the pentacene is taken as a simplified fragment of the graphene, our present work may be beneficial to the development of high-performance NLO materials.     

Transport and relaxation properties of isotopomeric hydrogen–helium binary mixtures. II. HD,D2, T2–He mixtures

The comprehensive comparison between calculated bulk non-equilibrium properties of hydrogen–helium isotopomeric mixtures and experiment that has previously been carried out for H₂–helium mixtures [2004, Molec. Phys., submitted] has been extended to mixtures of HD, D₂ and T₂ with ³He and ⁴He. For HD–⁴He mixtures, comparison is also made, where possible, with previous calculations of Köhler and Schaefer [1983, Physica A, 120, 185]. The phenomena examined herein include low temperature interaction second virial coefficients, binary diffusion and thermal conductivity coefficients, rotational relaxation, transport property field effects and flow birefringence. Scattering calculations have been carried out for the HD–He PES of Schaefer and Köhler [1985, Physica A, 129, 469], and for both the Köhler–Schaefer and Tao [1994, J. chem. Phys., 100, 4947] potential surfaces for the D₂–He and T₂–He interactions. Comparisons between calculated and experimental results for HD, D₂, T₂–He mixtures confirm the conclusion, reached earlier from the H₂–He comparisons, that these potential surfaces are very close to the correct one for the hydrogen–helium interaction, and that the small differences between them cannot be distinguished readily by measurements of bulk gas phenomena unless the attendant experimental uncertainties are better than ±0.3%.     

A theoretical study of the structures and stabilities of N4O2 isomers

Five N₄O₂ isomers and their possible decomposition pathways were investigated with Møller–Plesset perturbation theory (MP2) and density functional theory (DFT). The most stable isomer is the open-chain C_2v structure, which has not been reported before. For all five N₄O₂ isomers, dissociation energies and eight transition states were studied in the present paper. The open-chain isomer 1 and the planar (C_2h) isomer 3 could be potential candidates for high energy density materials (HEDM) due to their large dissociation energy and moderate dissociation barrier.     

A Ketene Intermediate in 3-Cyclopentenone Photolysis : Matrix-Isolation and Gas Phase Experiments

Abstract

Photolysis experiments are performed at λ  230 nm on argon matrix-isolated and on gas phase 3-cyclopentenone ( 1 ); in both cases, a ketene intermediate (KE) is detected (FT-IR spectra : 2121–2126 cm^?1 in argon matrix; 2066–2210 cm^?1 in gas phase). 1,3-butadiene ( 2 ) and carbon monoxide are the reaction products. Two first-order consecutive photochemical processes occur 1 ^k1 > KE ^k2 > 2 + CO with k₁ = 1.7 10–2 s^?1 and k₂ = 2.4 10–2 s^?1.     

Is the Pauli exclusion principle the origin of electron localisation?

ABSTRACT

In this work, we inquire into the origins of the electron localisation as obtained from the information content of the same-spin pair density, γ^{σ, σ}(r₂∣r₁). To this end, we consider systems of non-interacting and interacting identical Fermions contained in two simple 1D potential models: (1) an infinite potential well and (2) the Kronig–Penney periodic potential. The interparticle interaction is considered through the Hartree–Fock approximation as well as the configuration interaction expansion. Morover, the electron localisation is described through the Kullback–Leibler divergence between γ^{σ, σ}(r₂∣r₁) and its associated marginal probability. The results show that, as long as the adopted method properly includes the Pauli principle, the electronic localisation depends only modestly on the interparticle interaction. In view of the latter, one may conclude that the Pauli principle is the main responsible for the electron localisation.     

Infrared diode laser spectroscopy of the Kr–N2O van der Waals complex: the v 1 symmetric stretch region of N2O

The rovibrational spectra of four isotopomers of the Kr–N₂O van der Waals complex, namely ⁸²Kr–N₂O, ⁸³Kr–N₂O, ⁸⁴Kr–N₂O and ⁸⁶Kr–N₂O, were measured in the v ₁ vibrational band region of the N₂O monomer (～1285?cm^?1) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. Rotational constants for both ground and excited vibrational states of these four isotopomers were accurately determined. The band-origin of Kr–N₂O was observed to shift by +0.1065?cm^?1 from that of the monomer. The band-origin shifts of Rg–N₂O (Rg?=?Ne, Ar, Kr) in the v ₁ vibrational band region could also be well explained by the model based on a Buckingham intermolecular potential [W.A. Herrebout, H.-B. Qian, H. Yamaguchi and B.J. Howard, J. Mol. Spectrosc. 189, 235 (1998)]. But the band-origin shift of He–N₂O was found to deviate significantly from this model. The possible reason is discussed and the band-origin shift of Xe–N₂O predicted.     

The Schiff Base Probe With J-aggregation Induced Emission for Selective Detection of Cu2+

Here, three Schiff bases 3a-c, differing by the substitutions (–H, –Cl, and –N(CH₃)₂) on the phenyl ring, have been designed and synthesized via the reaction of ortho-aminophenol with benzaldehyde, 2,4-dichlorobenzaldehyde and para-dimethylamine benzaldehyde in 1:1 molar ratio with favourable yields of 89–92%, respectively. Their structural characterizations were studied by FT-IR, NMR, MALDI-MS and elemental analysis. The fluorescence behaviours of compounds 3a and 3b exhibited a severe aggregation caused quenching (ACQ) effect in EtOH/water system. On the contrary, compound 3c had an obvious J-aggregation induced emission (AIE) feature in EtOH/water mixture (v/v?=?1:1), and exhibited excellent sensitivity and anti-interference towards Cu²⁺ with the limit of detection (LOD) of 1.35?×?10^–8 M. Job’s plot analysis and MS spectroscopic study revealed the 2:1 complexation of probe 3c and Cu²⁺. In addition, probe 3c was successfully applied to the determination of Cu²⁺ in real aqueous samples.

     

The structure,dynamics and solvation mechanisms of ions in water from long time molecular dynamics simulations: a case study of CaCl2 (aq) aqueous solutions

Systematic long time (5–20 ns) molecular dynamics (MD) simulations have been carried out to study the structural and dynamical properties of CaCl₂ aqueous solutions over a wide range of concentrations (≤9.26 m) in this study. Our simulations reveal totally different structural characteristics of those yielded from short time (≤1 ns) MD simulations [A.A. Chialvo and J.M. Simonson, J. Chem. Phys. 119, 8052 (2003); T. Megyes, I. Bako, S. Balint, T. Grosz, and T. Radnai, J. Mol. Liq. 129, 63 (2006)]. An apparent discontinuity was found at 4–5 m of CaCl₂ in various properties including ion–water coordination number and self-diffusion coefficient of ions, which were first noticed by Phutela and Pitzer in their thermodynamic modelling [R.C. Phutela and K.S. Pitzer, J. Sol. Chem. 12, 201 (1983)]. In this study, residence time was first taken into consideration in the study of Ca²⁺–Cl^? ion pairing, and it was found that contact ion pair and solvent-sharing ion pair start to form at the CaCl₂(aq) concentrations of about 4.5 and 4 m, respectively, which may be responsible for the apparent discontinuity. In addition, the residence time of water molecules around Ca²⁺ or Cl^? showed that the hydration structures of Ca²⁺ and Cl^? are flexible with short residence time (<1 ns). It needs to be pointed out that it takes much longer simulation time for the CaCl₂–H₂O system to reach equilibrium than what was assumed in previous studies.     

Normal appearing brain white matter changes in relapsing multiple sclerosis: Texture image and classification analysis in serial MRI scans

ObjectiveThere is a clinical interest in identifying normal appearing white matter (NAWM) areas in brain T2-weighted (T₂W) MRI scans in multiple sclerosis (MS) subjects. These areas are susceptible to disease development and areas need to be studied in order to find potential associations between texture feature changes and disease progression.MethodsThe subjects investigated had a first demyelinating event (Clinically Isolated Syndrome-CIS) at baseline (Time₀), and the NAWM₀ (i.e. NAWM at Time₀) of the brain tissue was subsequently converted to demyelinating plaques (as evaluated in a follow up MRI at Time_6–12). 38 untreated subjects that had developed a CIS, had brain MRI scans within an interval of 6–12 months (Time_6–12 at follow-up). An experienced MS neurologist manually delineated the demyelinating lesions at Time₀ (L₀) and at Time_6–12 (L_6–12). Areas in the Time_6–12 MRI scans, where new lesions had been developed, were mapped back to their corresponding NAWM areas on the Time₀ MR scans (ROIS₀). In addition, contralateral ROIs of similar size and shape were segmented on the same images at Time₀ (ROIS_C0) to form an intra-subject control group. Following that, texture features were extracted from all prescribed areas and MS lesions.ResultsTexture features were used as input into Support Vector Machine (SVM) models to differentiate between the following: NAWM₀ vs ROIS_C0, NAWM₀ vs NAWM_6–12, NAWM₀ vs L₀, NAWM_6–12 vs L_6–12, ROIS₀ vs L₀, ROIS₀ vs L_6–12 and ROIS₀ vs ROIS_C0, where the corresponding % correct classifications scores were 89%, 95%, 98%, 92%, 85%, 90% and 65% respectively.ConclusionsTexture features may provide complementary information for following up the development and progression of MS disease. Future work will investigate the proposed method on more subjects.     

13C Nuclear Magnetic Resonance Studies of the Conformations of Serine‐3′‐ and 5′‐Thymidine Monophosphate Conjugates

The differences in the backbone conformation between O‐thymidine‐3′‐(1) and 5′‐yl O‐alkyl N‐phosphoryl serine methyl esters (2) have been investigated by solution ¹³C NMR spectroscopy. The stereo‐sensitive vicinal ³¹P–¹³C coupling constants were measured and used in the conformational analysis for the P–O5′–C5′, P–O3′–C3′, and P–N–C_α bonds. Three‐dimensional structural characteristics of dephosphorylation reactions of Compounds are also discussed.     

Influence of Y2Cu2O5 nanoparticles doping on superconducting properties of YBa2Cu3O7-δ

ABSTRACT

The blue phase of YBa₂Cu₃O_{7- δ} (YBCO) family, Y₂Cu₂O₅ (Y202) nanoparticles were prepared and doped into (YBCO) superconductor and the effect of doping on critical current density and critical temperature was investigated. Y202 nanoparticles with particle sizes of 47, 107 and 206?nm were prepared by a sol–gel combustion method and added into the YBCO superconductor by 0.5–2?wt.%. XRD and scanning electron microscope measurements were used to characterize the samples. The measurement of critical current density at 77?K revealed that the doped superconductors had larger critical current density compared to the undoped superconductors. For a fixed dopant concentration, by increasing the size of nanoparticles, the J_c was increased. For the samples including 0.5?wt.% of nanoadditives, J_c was higher. The highest critical current density of 137?A/cm² was measured for the superconductors containing 0.5?wt.% of 206?nm Y202 nanoparticles. Also, by increasing the nanoparticles concentration, the T_c was reduced.     

New thiourea and urea derivatives containing trifluoromethyl- and bis-triflouromethyl-4H-chromen-3-yl substituents

Two new thiourea (1) and urea (2) derivatives, substituted with 2-trifluoromethyl-4H-chromen-3-yl moieties at defined positions, were obtained by convenient synthetic methodologies. The pure compounds were studied in solid state by vibrational spectroscopy (FT-IR and Raman) and in solution by NMR and UV–Vis spectroscopy. The crystal structure of the urea derivative (compound 2) was also determined by X-ray diffraction. The crystal packing is governed by N–H···O intramolecular interactions of moderate strength in a self-assembled dimer of the terminal amide fragment (C(=O)–NH₂). Hirshfeld surface and 2D-fingerprint plots were also performed to characterise the role in the packing stabilisation of all contacts, including weak C–H···F hydrogen bonds and π–π stacking interactions. For both compounds, the tentative assignment of vibrational and electronic spectra was assisted by theoretical calculations. Besides, to evaluate the influence on the pharmacokinetic and pharmacodynamic properties of molecules with –CF₃ groups, the anti-microbial activity of the title compounds was tested against the standard strains of various Gram-positive and Gram-negative organisms with noteworthy antimicrobial effect over Staphylococcus aureus, Klebsiella pneumoniae and Salmonella typhi.     

Theoretical study on the influence of different NˆN ligands on the electronic structures and optoelectronic properties of heteroleptic Iridium(III) complexes

DFT/TDDFT calculations were carried out to investigate the electronic structures, absorption and phosphorescence properties of a series of heteroleptic Ir(III) complexes consisting of two N-heterocyclic carbene ligands and a conjugated bicyclic N,N′-heteroaromatic (N?N) ligand. On the basis of the results reported herein, we attempt to explain the experimental observations according to which complex (mpmi)₂Ir(pybi) (1) [Hmpmi = 1-(4-tolyl)-3-methyl-imidazole; Hpybi = 2-(pyridin-2-yl)-1H-benzo[d]imidazole] emits green light with an extremely high-quantum phosphorescence efficiency (Φ _PL ) of 79.3%, while a relatively lower Φ _PL (only 11%) was measured for (fpmi)₂Ir(tfpypz) (2) [fpmi = 1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C, C^2′; tfpypz = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato] emitting blue light by tuning the N?N ligands. Besides, we also designed (fpmi)₂Ir(pyN3) (3) [pyN3H = 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine] and (fpmi)₂Ir(pyN4) (4) [pyN4H = 2-(1H-tetrazol-5-yl)pyridine] to explore the influence of electron-withdrawing substituents on N?N ligands on the electronic and optical properties of these Ir(III) complexes. The results revealed that electron-withdrawing substituents can stabilise both HOMOs and LUMOs and induce HOMO–LUMO energy gap change. Moreover, the emission properties can be significantly tuned by introducing different N?N ligands. While new insights were gained on structural and electronic properties, the extremely high Φ _PL of 1 was found to be not inherent to spin-orbital coupling effects, but determined by its large transition dipole moment (μ_{S 1}) upon S ₀–S ₁ transition compared with that of 2. On the basis of these results, the designed complexes 3 and 4 are considered to be the promising candidates for blue-emitting phosphorescence materials with higher Φ _PL than the complex 2.     

Optimization of Pretreatment Method for Alkylmercuries Speciation in Coal by High‐Performance Liquid Chromatography Coupled with UV‐Digestion Cold Vapor Atomic Fluorescence Spectrometry

Abstract

Exhaustive extraction of analytes in their original chemical forms from samples with complex matrices is a pivotal step for speciation analysis. Herein we propose a pretreatment method for extracting and preconcentrating methylmercury and ethylmercury from coal samples by using KBr–H₂SO₄/CuSO₄–C₆H₅CH₃–Na₂S₂O₃ system. The extraction conditions, including the volume of the organic phase and the extraction time, were optimized in detail. Speciation analysis of alkylmercuries was carried out by high‐performance liquid chromatography online coupled with UV‐digestion and cold vapor atomic fluorescence spectrometry. The detection limits were 0.6 ng mL^?1 for methylmercury and 1 ng mL^?1 for ethylmercury, respectively. The recoveries of methylmercury and ethylmercury spiked in a sample were 84% and 82%, respectively. The method was applied successfully to analysis of alkylmercuries in four coal samples collected from northeast China.     

Crystal Structures of Tetrakis‐(4‐chlorophenylthio)‐butatriene and Tetrakis‐(tert‐butylthio)‐butatriene

Tetrakis‐(4‐chlorophenylthio)‐butatriene (3a) and tetrakis‐(tert‐butylthio)‐butatriene (3b) were synthesized, and their crystal structures were determined. The compound 3a is monoclinic, space group P2₁/c, a=6.9785(8), b=8.6803(9), c=22.884(2) Å, β=93.887(6)^o, V=1383.0(3) ų, Z=2. The compound 3b is monoclinic, space group P2₁/n, a=11.0615(6), b=10.8507(4), c=11.2717(6) Å, β =116.427(2)^o, V=1211.5(1) ų, Z=4. The title compounds 3a and 3b reside on an inversion center so that only half of the molecule is crystallographically unique. Both compounds are not planar. The crystal structures of 3a and 3b have cumulated double bonds. The C7–C8–C8ⁱ and C5–C6–C6ⁱ angles that show the linearity in both structures, respectively, are 176.4(3)° in 3a and 175.6(2)° in 3b.     

Crystalline structures as an approximant of quasicrystal and distortion of B12 icosahedron in boron-rich solids: Search for semiconducting quasicrystal

Analyzing the crystalline structure of α- and β-rhombohedral boron as an approximant structure of a quasicrystal, atomic structures of two unit cells (prolate and oblate rhombohedra) of icosahedral quasicrystal are constructed. According to molecular orbital calculation, a neutral B ₁₂ H ₁₂ icosahedral cluster is distorted to a cubic or rhombohedral type by the Jahn–Teller effect. The distortion of B ₁₂ in the β-rhombohedral boron and K₂B₁₂H₁₂ has the same sign as the lowest energy distortion in the calculation. Among the α-rhombohedral type structures, the distortion of B₁₂ is correlated with the rhombohedral axis angle, and the angle is the closest to the icosahedral angle for B₆O and the distortion is the smallest for B–C. A meta-stable phase has been found on the way towards crystallization of amorphous B–C films.