Molecular Ions of Transient Species: Vinylamine-Cation

Vinylamine 1 was prepared by thermolysis of cyclobutylamine and its photoelectron spectrum was measured. I = 8.20 eV and I = 8.65 eV were found, the dominant vibrational progression (? = 725 cm^?1) indicating that in the course of 1(X)→1 ⁺( X? ) flattening around the N-atom occurs. The Franck-Condon profile of this band, however, suggests that a skeletal mode of ? ≈ 1400 cm^?1 (observed also in the iso-π-electronic systems vinyl-alcohol-cation and allyl radical) may also be excited. Comparison with the data for the isomer acetaldehyde-imine 2 and its cation s ⁺ shows that the isomer couple 1/2 constitutes a further notable example for a relative thermochemical stability inversion on going from the neutrals to the cations.     

Molecular Machines: Stimulation of Cation Motion in Molecular Switches

The theoretical aspects of the mechanism of the motion of cations and ligands in molecular machines referred to as redox switches are presented. The interrelated properties of cations—the energetic, electrochemical, spectral, and magnetic properties; their propensity to form either covalent or ionic bonds; and the relative softness and hardness of cations and ligands—stimulate molecular motion. These properties determine the thermal stability and stability to destruction caused by electrochemical processes and, eventually, the maximal number of transformation cycles. The maximal efficiency of redox switches is attained when the redox reaction involves a cation with a half-filled (d ⁵, f ⁷) or complete (d ¹⁰, f ¹⁴) electronic shell. The role of the Jahn-Teller effect is considered: it is responsible for geometry distortion, which stimulates cation motion. The properties of nd and 4f cations are compared from the standpoint of their use for designing redox switches. In switches constructed on the basis of supramolecular compounds containing hard and soft moieties, softer cations (Fe²⁺, Co²⁺, Cu⁺, etc.) prefer to coordinate to soft ligands and harder cations (Fe³⁺, Co³⁺, Cu²⁺, etc.) prefer to coordinate to hard ligands. A cation moves due to the soft-hard change of its coordination sphere in the course of the redox reaction. Design of redox switches based on solid compounds with a cation in mixed oxidation state is shown to be promising. Cations can change their oxidation state with a change in temperature or pressure. The possibility of designing “magnetic switches” is considered.     

Transient Phosphenium and Arsenium Ions versus Stable Stibenium and Bismuthenium Ions

Fluoride abstraction from bis-m-terphenylelement fluorides (2,6-Mes₂C₆H₃)₂EF (E=P, As) generated the highly reactive phosphenium ion [(2,6-Mes₂C₆H₃)₂P]⁺ and the arsenium ion [(2,6-Mes₂C₆H₃)₂As]⁺, which immediately underwent intramolecular electrophilic substitution and formation of an 1,2,4-trimethyl-6-mesityl-5-m-terphenyl-benzo[b]phospholium ion and an 1,2,4-trimethyl-6-mesityl-5-m-terphenyl-benzo[b]arsolium ion, respectively. The formation of the latter involved a methyl group migration from the ortho-position of a flanking mesityl group to the meta-position. This reactivity of [(2,6-Mes₂C₆H₃)₂E]⁺ (E=P, As) is in sharp contrast to the related stibenium ion [(2,6-Mes₂C₆H₃)₂Sb]⁺ and bismuthenium ion [(2,6-Mes₂C₆H₃)₂Bi]⁺, which have been recently isolated and fully characterized (Angew. Chem. Int. Ed. 2018, 57 , 10080–10084). On the basis of DFT calculations, a mechanism for the rearrangement of the phosphenium and arsenium ions into the phospholium and arsolium ions is proposed, which is not feasible for the stibenium and bismuthenium ions.     

Molecular Identification of the Transient Species Mediating the Deactivation Dynamics of Solvated Guanosine and Deazaguanosine

Small structural alterations of the purine/pyrimidine core have been related to important photophysical changes, such as the loss of photostability. Similarly to canonical nucleobases, solute-solvent interactions can lead to a change in the excited state lifetimes and/or to the interplay of different states in the photophysics of these modified nucleobases. To shed light on both effects, we here report a complete picture of the absorption spectra and excited state deactivation of deoxyguanosine and its closely related derivative, deoxydeazaguanosine, in water and methanol through the mapping of the excited state potential energy surfaces and molecular dynamics simulations at the TD-DFT level of theory. We show that the N by CH exchange in the imidazole ring of deoxyguanosine translates into a small red-shift of the bright states and slightly faster dynamics. In contrast, changing solvent from water to methanol implies the opposite, i.e., that the deactivation of both systems to the ground state is significantly hindered.     

弱酸根离子与铜离子双水解反应的实验探究

从理论分析和实验探究的角度，对反应温度及浓度对Cu2+与弱酸根离子双水解反应的影响进行了讨论。实验结果表明：Cu2+能与CO32-、HCO3-、AlO2-等弱酸根离子发生双水解反应，但同时还可能伴随着其他反应的发生；HCO3-、AlO2-浓度的变化与双水解反应的速率以及生成物无太大关系，而随着CO32-浓度的减小，双水解反应会更加剧烈并倾向于生成Cu（OH）2沉淀。     

Photodestruction of Diatomic Molecular Ions: Laboratory and Astrophysical Application

In this work, the processes of photodissociation of some diatomic molecular ions are investigated. The partial photodissociation cross-sections for the individual rovibrational states of the diatomic molecular ions, which involves alkali metals, as well as corresponding data on molecular species and molecular state characterizations, are calculated. Also, the average cross-section and the corresponding spectral absorption rate coefficients for those small molecules are presented in tabulated form as a function of wavelengths and temperatures. The presented results can be of interest for laboratory plasmas as well as for the research of chemistry of different stellar objects with various astrophysical plasmas.     

Electrochemistry and Spectroelectrochemistry of Polynuclear Zinc Phthalocyanines: Formation of Mixed Valence Cation Radical Species

The electrochemistry and spectroelectrochemistry of mononuclear, binuclear and tetranuclear zinc neopentoxy-substituted phthalocyanines are presented. The binuclear and tetranuclear species show two oxidation waves to the radical cation indicating the existence of stable mixed-valence, half-oxidized species. The electronic spectra of the half? and fully-oxidized species are presented and discussed. Nernstian analysis shows that pairs of phthalocyanine rings are oxidized simultaneously in the tetranuclear species, via a one-electron oxidation pathway.     

阳离子交换树脂分离-铝试剂分光光度法测定土壤中铝形态

研究了铝试剂光度法测定土壤溶液中铝的最佳条件,着重探讨了共存离子,特别是土壤溶液中的无机离子和有机阴离子对测定铝的影响。采用阳离子交换树脂分离,建立了测定土壤溶液及天然水中铝形态方法。用该法可测定总反应性铝、总单核铝和稳定性单核铝。由总反应性铝减去总单核铝求得酸溶性铝。由总单核铝减去稳定单核铝求得不稳定单核铝。与阳离子树脂交换分离-邻苯二酚紫光度法进行了比较。结果表明：邻苯二酚紫光度法灵敏度较高,但铁的干扰较大。铝试剂光度法灵敏度略低,但铁的干扰较少。阳离子树脂交换分离-铝试剂光度法更适合于测定含铁量比较高的土壤溶液中的铝形态。     

Transient ITP in Nonaqueous CE by Introducing Ions with a Long Hydrophobic Chain as Terminating Ions

Transient isotachophoresis (tITP) is an efficient sample-preconcentration procedure for improving detection limits. An isotachophoretic state exists at the beginning of the procedure as a result of the introduction of both leading and terminating ions into the system. tITP has usually been applied in aqueous media, and hydrophilic compounds have been used as leading and terminating ions; this study, however, focused on nonaqueous capillary electrophoresis (NACE) and use of ions with long hydrophobic chains as terminating ions for tITP. Because the long alkyl or aryl structures of these compounds can lead to low mobility in capillary electrophoresis, use of such ions as terminating ions in tITP can broaden the applicable range of the tITP procedure and achieve the ITP effect under more flexible running conditions.     

阳离子修饰纳米Pt的合成及其在Nafion膜上的自组装行为研究

以季铵阳离子聚合物为修饰离子、乙醇为还原剂,在水溶液中合成了具有稳定电位的阳离子修饰纳米Pt颗粒,还原过程采用UV-vis光谱监控,粒子形貌采用TEM表征.结果表明,合成体系在45 min左右还原完毕,颗粒粒径约为4.5 nm,呈多晶态结构,粒径分布狭窄,具有良好的分散性.采用Zeta电位测定仪分析了不同pH条件下粒子的电位,选择了合适的组装pH值并运用静电自组装的方法把Pt颗粒成功地组装到Nafion膜表面.同时对该自组装体系的影响因素进行了一些理论分析,并以此对组装过程的动力学性质和组装膜电化学特性进行了解释.     

Carbamate Ions as Propagating Species in N-Carboxy Anhydride Polymerizations

Polymerizations of N-carboxy anhydrides of L-phenylalanine, γ-benzyl-L-glutamate, O-carbobenzoxy-L-tyrosine, L-leucine, and sarcosine, as initiated by primary, secondary, and tertiary amines in N₂ or CO₂ atmospheres and in the presence or absence of NaH, indicate that they proceed via carbamate salt intermediates. This conclusion is supported by radiotracer studies as well as by NMR studies of the initial products of NCA-amine reaction mixtures.

The “activated monomer” mechanism of strong-base initiated polymerizations is discounted on the bases that polypeptides are not formed in aprotic tertiary amine-initiated systems (hydantoins and diketopiperazines are obtained instead) and that methoxyl end groups are detected in polypeptides initiated with ¹⁴C-labeled NaOCH₃.     

On the Structure of Oxirane Molecular Cation. Preliminary Communication

A recent controversy on the interpretation of the ESR spectrum of ionized oxirane is clarified on the basis of the electronic absorption spectra of ionized tetramethyloxirane and 9,10-octalineoxide. The results favour a ring-opened structure for oxirane molecular cation, resulting from C? C bond cleavage and being iso-π-electronic to allyl radical.     

脂肪胺分子离子及质子化脂肪胺分子的碎裂反应

应用碰撞诱导解离(CID)技术研究了电子轰击方法产生的脂肪胺分子离子和化学电离方法产生的质子化脂肪胺分子的碎裂反应。质子化脂肪胺碰撞活化后的主要碎裂通道包括丢失C_XH_(2X)、C_XH_(2X 1)、C_XH_(2X 2)单元及NH_3和生成[C_yH_(2y 1)]及CH_3CH=NH_2~ 离子。脂肪胺分子离子碰撞活化后的主要碎裂通道是丢失C_XH_(2X)、C_XH_(2X 1)及NH_3和生成[C_mH_(2m-1)]~ 、CH_2NH_2~ 及CH_3CHNH_2~ 离子。随着碰撞能的增加,远电荷碎裂反应和电荷诱导碎裂反应之间竞争引起产物离子的的分布发生变化,如[C_mH_(2m-1)]~ 和[C_yH_(2y 1)]~ 离子。自由基机理可以解释质子化脂肪胺分子的远电荷反应。分子内氢抽取可以解释脂肪胺分子离子的碎裂反应。     

The Kinetics of Uptake of Cu++ Ions in Ionac SR-5 Cation Exchange Resin

The kinetics of sorption of Cu⁺⁺ ions in a typical cation exchange resin (IONAC SR-5) have been studied by two methods; the traditional batch method which involves following the change in Cu⁺⁺ concentration in a solution of finite volume in contact with the resin, and by removing and sectioning individual resin particles to follow the progress of the adsorption front. The results obtained by both methods are consistent. The equilibrium isotherm for this system is of highly favorable (Langmuir) form and the uptake kinetics show a clear transition from linear Fickian behavior at low concentrations to irreversible (shrinking core) behavior at high concentrations. The addition of ammonia to the system has little effect on the equilibrium isotherm but the intraparticle diffusivity is increased by a factor of about four. This may be due to reduction in the degree of hydration of the cuprammonium ion in comparison with uncomplexed Cu⁺⁺.     

Novel Transient Species of DNA Bases From Laser Photolysis

The laser photochemistry and photosensitization of DNA bases were carried out by using a nanosecond kinetic spectroscopy. A novel triplet state of thymine and its OH adduct were observed in N_2 and N_2O saturated aqueous solution respectively. The transient absorption spectra of triplet cytosine, cytidine and deoxycytidine monophosphoric acid were observed for the first time. Triplet guanosine was confirmed and its pK, value, 8.7, was obtained. Kinetic studies of the growth-decay of the above transient species were performed and their reaction mechanisms were elucidated in detail.     

Regioselective Hydrosilylation of Olefins Catalyzed by a Molecular Calcium Hydride Cation

Chemo‐ and regioselectivity are often difficult to control during olefin hydrosilylation catalyzed by d‐ and f‐block metal complexes. The cationic hydride of calcium [CaH]⁺ stabilized by an NNNN macrocycle was found to catalyze the regioselective hydrosilylation of aliphatic olefins to give anti‐Markovnikov products, while aryl‐substituted olefins were hydrosilyated with Markovnikov regioselectivity. Ethylene was efficiently hydrosilylated by primary and secondary hydrosilanes to give di‐ and monoethylated silanes. Aliphatic hydrosilanes were preferred over other commonly employed hydrosilanes: Arylsilanes such as PhSiH₃ underwent scrambling reactions promoted by the nucleophilic hydride, while alkoxy‐ and siloxy‐substituted hydrosilanes gave isolable alkoxy and siloxy calcium derivatives.