Basicity and solvent effects on hydrogen bonding in NR3···HCOOH (R=H,CH3) model systems

The effect of the basicity of methyl‐amines on hydrogen bonding (HB) with HCOOH is examined in both gas and solution phases. In the gas phase, the strength of HB may be related to the proton affinity (PA) difference between the carboxylate anion and the methyl‐amine, ΔPA=PA(HCOO⁻)−PA(NR₃). The changes in the driving potential ΔPA are explained on the basis of electronic substituent effects. The electronic substituent effects are rationalized in terms of local reactivity indices such as the Fukui function and the local hardness and softness at the basic center. A simple model is then proposed to explain the enhancement HB in the solution phase. The HB pattern in the solution phase is changed by electrostatic and nonelectrostatic solvation of the zwitterionic and neutral species in equilibrium. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 74: 387–394, 1999     

A study on feasibility of insect—control with γ-ray

Insect-control with Co-γ-ray is a method for conserving archives, books, cotton textiles, historical relics, wood structured houses and furniture, which are called irradiated objects later on. The temporary and residual effects of γ-ray on irradiated objects and the biological effects on insects are presented in this report.

Our study shows that there is no obvious harmful effect on irradiated objects when the ray is below 870 Gy, while there is obvious deterioration on the objects when the ray is above 870 Gy. On the other hand, the ray below 870 Gy is strong enough for the insects. In fact, at the dose of 43.5–130.5 Gy, the irradiated insects could be damaged on reproductive function, even sterilized, or killed.     

The Effect of the Weak Completing Nature of NaF,NaN3, and NaC3H3O3 Supporting Electrolytes on the Electrocatalysis of Nickel(II) Reduction in the Presence of Organic Amines

Abstract

Contrary to the results obtained in essentially noncomplexing supporting electrolyte media (NaClo₄, NaN0₃, NaCl and NaBr), the kinetic limited currents of the catalytic prewaves obtained for the polarographic reduction of Ni(II) in the presence of organic amines (o-phenylenediamine, pyridine, etc.) employing weakly complexing supporting electrolytes (NaF, NaN₃, and NaC₂H₃O₂) do not correlate with ?₂ potentials as predicted by simple double layer theory. However, the limiting current does correlate with the ligand exchange rates for Ni(H₂O)₅X⁺ type complexes (where X = F^?, N₃ ^? and C₂H₃O₂ ^?) with an organic ligand. These results lead to a general mechanism for the electrocatalysis mechanism of Ni(II) reduction.     

Distortions of the π-Electron System in Substituted Benzenes

The factors leading to substituent effects on the electron distribution in aromatic molecules are discussed, particular attention being paid to the π-electron system. IR spectroscopy has proved an extremely useful probe in this field of study. Substituent d-orbital participation and the relevance of the π-inductive effects are also considered.     

The H method: hydrogen atoms with a fictitious nuclear charge. A versatile theoretical tool for study of atom and group properties as substituents: electronegativity and partition of σ and π contributions

We present a preliminary work for a general method of computing the partition of σ and π electronic effects of a given atom A or substituent R on a given substrate. In this aim, the nuclear charge Z^* of a fictitious hydrogen atom H^* is fitted in order that the A–H^* (or R–H^*) bond be purely covalent, i.e. the Mulliken electron population be one electron on H^*. We obtain this way entities of the same electronegativity as A or R, thus having a comparable σ effect, without any π effect.

The values of Z^* obtained for A–H^* diatomic molecules (A=H–Br) exhibit a good linear correlation with the Allred–Rochow scale of electronegativity, as it could be expected on theoretical grounds. The method, applied to R–H^* molecules, allows a determination of the electronegativity of a variety of polyatomic R substituents, and provides H^*(R) having the same inductive effect as R. These results are discussed by comparison with some previous theoretical and experimental data.

As an example of application, the partition of σ and π contributions of R on the ¹³C chemical shifts in a series of monosubstituted benzenes RC₆H₅ has been computed.     

Prominent enhancing effects of substituents on the strength of π···σ‐hole tetrel bond

The potential applications of tetrel bonds involving π‐molecules in crystal materials and biological systems have prompted a theoretical investigation of the strength of π···σ‐hole tetrel bond in the systems with acetylene and its derivatives of CH₃, AuPH₃, Li, and Na as well as benzene as the π electron donors. A weak tetrel bond (ΔE < 15 kJ/mol) is found between acetylene and tetrel donor molecule TH₃F (T = C, Si, Ge, Sn, and Pb). All substituents strengthen the π tetrel bond, but the electron‐donating sodium atoms have the largest enhancing effect and the interaction energy is up to about 24 kJ/mol in C₂Na₂‐CH₃F. The electron‐donating ability of the AuPH₃ fragment is intermediate between the methyl group and alkali metal atom. The origin of the stability of the π tetrel‐bonded complex is dependent on the nature of the tetrel donor and acceptor molecules and can be regulated by the substituents.     

Hydrothermal Synthesis and Crystal Structure of Trioxomolybdate：NaH3OMo3O10

1 INTRODUCTION Polyoxometalates (POM) are of great interest not only for their structural variety but also their unexpected properties[1,2]. These inorganic anions had been widely investigated as divers as catalysis, biology, medicine, magnetochemistry, and materials science[3~5]. The molybdenum in its higher oxidation states is easy to form poly-nuclear anionic metal-oxygen clusters and many giant poly- molybdates with extraordinary variety of the relevant topology and electronic struct…     

Effects of dynamical couplings in hydrogen bond systems in the polarized IR spectra of 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde crystals

This paper presents the investigation results of the polarized IR spectra of 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde crystals measured at 293 and 77 K. Analysis of the results concerned the linear dichroic, H/D isotopic and temperature effects observed in the spectra of the hydrogen and deuterium bond at the frequency ranges of the ν_O–H and the ν_O–D bands, respectively. The main spectral properties of the crystals were interpreted in terms of the “strong-coupling” theory on the basis of the hydrogen bond dimer model. The spectra revealed that the strongest vibrational exciton coupling involved the closely-spaced hydrogen bonds, each belonging to a different chain of associated molecules. The reason for two different crystalline systems, are characterized by almost identical ν_O–H and ν_O–D band shapes, is explained. It was proved that a random distribution of the protons and deuterons took place in the lattices of the isotopically diluted crystals.     

Synergistic Surface Passivation of CH3NH3PbBr3 Perovskite Quantum Dots with Phosphonic Acid and (3-Aminopropyl)triethoxysilane

CH₃NH₃PbBr₃ perovskite quantum dots (PQDs) are synthesized by using four different linear alkyl phosphonic acids (PAs) in conjunction with (3-aminopropyl)triethoxysilane (APTES) as capping ligands. The resultant PQDs are characterized by means of XRD, TEM, Raman spectroscopy, FTIR spectroscopy, UV/Vis, photoluminescence (PL), time-resolved PL, and X-ray photoelectron spectroscopy (XPS). PA chain length is shown to control the PQD size (ca. 2.9–4.2 nm) and excitonic absorption band positions (λ=488–525 nm), with shorter chain lengths corresponding to smaller sizes and bluer absorptions. All samples show a high PL quantum yield (ca. 46–83 %) and high PL stability; this is indicative of a low density of band gap trap states and effective surface passivation. Stability is higher for smaller PQDs; this is attributed to better passivation due to better solubility and less steric hindrance of the shorter PA ligands. Based on the FTIR, Raman, and XPS results, it is proposed that Pb²⁺ and CH₃NH₃⁺ surface defects are passivated by R−PO₃²⁻ or R−PO₂(OH)⁻, whereas Br⁻ surface defects are passivated by R−NH₃⁺ moieties. This study establishes the combination of PA and APTES ligands as a highly effective dual passivation system for the synergistic passivation of multiple surface defects of PQDs through primarily ionic bonding.     

Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac-[Ru(CO)3I3]-

Solvent effects on the 99Ru NMR chemical shift of the complex fac-[Ru(CO)3I3]- are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac-[Ru(CO)3I3]- that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional.     

The Instability of Ni{N(SiMe3)2}2: A Fifty Year Old Transition Metal Silylamide Mystery

The characterization of the unstable Ni^II bis(silylamide) Ni{N(SiMe₃)₂}₂ ( 1 ), its THF complex Ni{N(SiMe₃)₂}₂(THF) ( 2 ), and the stable bis(pyridine) derivative trans‐Ni{N(SiMe₃)₂}₂(py)₂ ( 3 ), is described. Both 1 and 2 decompose at ca. 25 °C to a tetrameric Ni^I species, [Ni{N(SiMe₃)₂}]₄ ( 4 ), also obtainable from LiN(SiMe₃)₂ and NiCl₂(DME). Experimental and computational data indicate that the instability of 1 is likely due to ease of reduction of Ni^II to Ni^I and the stabilization of 4 through dispersion forces.     

Ligand and substrate effects in gas-phase reactions of NiX(+)/RH couples (X=F, Cl, Br, I; R=CH3, C2H5, nC3H7, nC4H9)

The reactions of small saturated hydrocarbons by gaseous nickel cations NiX+ (X=F, Cl, Br, I) are investigated by means of electrospray ionization mass spectrometry. The halide cations are obtained from solutions of the corresponding Ni(II) salts in water or methanol as solvents. NiF+ is the only Ni(II) halide complex that brings about thermal activation of methane. The branching ratios of the observed reactions with C2H6, C3H8, and nC4H10 are shifted systematically by changing the nature of both the ligand X and the substrate RH. In the elimination of HX (X=F, Cl, Br, I), the formal oxidation state of the metal ion appears to be conserved, and the importance of this reaction channel decreases in going from NiF+ to NiI+. A reversed trend is observed in the losses of small closed-shell neutral molecules, that is, H2, CH4 and C2H6, which dominate the gas-phase ion chemistry of NiI+/RH couples. Additionally, inner-sphere electron-transfer reactions take place for a few systems, that is, the delivery of hydride or methanide ions from the hydrocarbon to NiX+ in the course of which the hydrocarbon is converted to a carbenium ion and the cationic metal complex gives rise to a neutral RNiX molecule (R=H, CH3). This process gains importance with decreasing atomic number of the halides and with increasing the size of the alkane. Thus, it constitutes the major pathway in the reactions of NiF+ with propane and n-butane, whereas it is not observed for any of the NiI+/RH couples investigated. Concerning the regioselectivity of the reactions with propane and n-butane, heterolytic cleavage of secondary carbon--hydrogen bonds is clearly preferred compared to that of primary ones, as revealed by deuterium labeling studies. For the NiF+/C3H8 couple, the selectivity of the hydride transfer is as large as 360 in favor of the secondary positions. Though smaller, large preferences for the activation of secondary C--H bonds are also operative in homolytic bond activation of RH (R=nC3H7, nC4H9).     

Synergistic effect of Fe2O3/Ho2O3 Co-modified 2D-titanate heterojunctions on enhanced photocatalytic degradation

TiO₂-based nanosheets (TNSs) co-modified by Fe₂O₃ and Ho₂O₃ were synthesized by one-pot hydrothermal method using Fe(NO₃)₃ and Ho(NO₃)₃ as precursors compositing with TiO₂. The Fe₂O₃/Ho₂O₃-TNSs heterojunctions possessed a thickness of approximately 3–4 nm, large specific surface area of 210–310 cm²/g, with Fe₂O₃ and Ho₂O₃ nanoparticles highly dispersed over the surface of the nanosheets. The crystallization of the samples gradually increased with the amount of Fe₂O₃ nanoparticles, which was confirmed by the XRD, BET and Raman spectra, indicating that Ho₂O₃ and Fe₂O₃ influenced the crystallinity and structure evolution of the TNSs, besides, led to an improved the visible-light absorption. Surface photocurrent and fluorescence spectral studies revealed that the photo-generated charge carrier separation efficiency could be efficiently improved by an appropriate amount of modification. The Fe₂O₃/Ho₂O₃-TNSs exhibited synergistic effect on photocatalytic degradation of RhB as well as MO under visible light. The highest efficiency was obtained by 0.05%-Fe₂O₃/Ho₂O₃-TNSs (Fe:Ho:Ti = 0.05:1:100), which was 8.86 and 6.72 times than that of individual 1.0%-Ho₂O₃-TNSs (Ho:Ti = 1:100) and 0.05%-Fe₂O₃-TNSs (Fe:Ti = 0.05:100), respectively. The possible mechanism for enhanced visible-light-induced photocatalytic activity was proposed. Ho₂O₃ introduced in the photocatalysts may act as the hole capture while Fe₂O₃ may share the same Fermi levels with TNSs and serve as the electron capture center in the n-n-p system, which reduced the recombination rate of photo-induced electron-hole pairs.     

SDS对Na2SeO3-GSH-溶解O2体系的作用研究

围绕GSH－Px和Na2SeO3在清除或催化产生ROS过程中可能共同存在的机理，以Na2SeO3-GSH-溶解O2体系为主要研究对象，引入表面活性剂SDS模拟GSH－Px的笼效应，考察其对Na2SeO3体系的影响。结果表明，表面活性剂可抑制该体系中O2^-的产生，并且具有稳定反应中间体GSSeSG的作用，证明了笼效应在GSH－Px及Na2SeO3与GSH反应体系中的重要作用。     

Direct Catalytic Asymmetric Mannich‐type Reaction of α,β‐Unsaturated γ‐Butyrolactam with Ketimines

We report a direct catalytic asymmetric Mannich‐type addition of α,β‐unsaturated γ‐butyrolactam to α‐ethoxycarbonyl ketimines promoted by a soft Lewis acid/Brønsted base cooperative catalyst. A thiophosphinoyl group on the nitrogen of ketimines was crucial for both electrophilic activation and α‐addition of γ‐butyrolactams. The obtained aza‐Morita–Baylis–Hillman‐type products bear an α‐amino acid architecture with a tetra‐substituted stereogenic center.     

Green chemistry-assisted synthesis of biocompatible Ag,Cu, and Fe2O3 nanoparticles

Green chemistry-assisted biocompatible copper (Cu), silver (Ag), and iron oxide (Fe₂O₃) nanoparticles (NPs) synthesis along with surface modification using Koelreuteria apiculata is demonstrated in this research, for the first time. Appropriate analytical techniques were utilized to confirm the preparation, spherical morphology, and crystalline structure of each of the NPs. The antioxidant nature of synthesized NPs was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging. Besides, the antimicrobial activity was also performed using bacterial strains of Staphylococcus aureus, Escherichia coli, and Salmonella typhi. Aspergillus sp. was designed as marker specie for the antifungal studies. The outcomes of NPs exposure, analyzed with reference to Chlorella sp. of the algal family exhibit the numerical values around 833% for AgNPs, 497% of CuNPs, and 456% for Fe₂O₃NPs. Phytotoxicity assay performed on the seeds of Vigna radiata and Cicer arietinum further validate the accordant nature of NPs towards vivacity. Allium cepa was also used as a test model to ascertain the genotoxic effects of the NPs wherein the mitotic index (MI) was calculated for AgNPs, CuNPs, and Fe₂O₃NPs as 42.1, 51.7, and 54.2% respectively. The outcomes of this research proved the suitability and affordability of our NPs developed using green synthesis for new industrial applications of in-situ reduction of carcinogenic compounds from water and soil.     

Cycloaddition reactions of 3-fluorobutenone

3-Fluorobutenone (8) reacted as a dienophile with several dienes 9, 11, 13, 15, 17 to give cycloaddition products in moderate yields. The regio- and stereoselectivity of the reactions are given. Compound 8 is slightly less reactive than methyl vinyl ketone.