Charge Detection Mass Spectrometry with Resolved Charge States

Charge detection mass spectrometry (CDMS) measurements have been performed for cytochrome c and alcohol dehydrogenase (ADH) monomer using a modified cone trap incorporating a cryogenically cooled JFET. Cooling the JFET increases its transconductance and lowers thermal noise, improving the signal to noise (S/N) ratio. Single ions with as few as 9 elementary charges (e) have been detected. According to simulations, the detection efficiency for ions with a charge of 13 e is 75 %, and for charges above 13 e the detection efficiency rapidly approaches 95 %. With the low limit of detection achieved here, adjacent charge states are easily resolved in the m/z spectrum, so the accuracy and precision of the image charge measurements can be directly evaluated by comparing the measured image charge to the charge deduced from the m/z spectrum. For ADH monomer ions with 32 to 43 charges, the root mean square deviation of the measured image charge is around 2.2 e. Ions were trapped for over 1500 cycles. The number of cycles detected appears to be limited mainly by collisions with the background gas.

Charge stripping C

Measurements of the translational energy loss accompanying the charge-stripping reactions M⁺+N→M²⁺+N+e⁻ and M²⁺+N→M³⁺+N+e⁻ have been performed for C, C and C, C respectively. The energy nesessary to remove the second electron from Buckminsterfullerene was determined, Q=IE(C→C=12.25±0.5 eV.     

Successive Charge Transitions of Unusually High‐Valence Fe3.5+: Charge Disproportionation and Intermetallic Charge Transfer

A perovskite‐structure oxide containing unusually high‐valence Fe^3.5+ was obtained by high‐pressure synthesis. Instability of the Fe^3.5+ in Ca_0.5Bi_0.5FeO₃ is relieved first by charge disproportionation at 250 K and then by intermetallic charge transfer between A‐site Bi and B‐site Fe at 200 K. These previously unobserved successive charge transitions are due to competing intermetallic and disproportionation charge instabilities. Both transitions change magnetic and structural properties significantly, indicating strong coupling of charge, spin, and lattice in the present system.     

有机电荷传输材料

光导体是一种重要的信息功能材料,可广泛应用于静电复印,全息照相,计算机终端仪器的激光打印,轻印刷制版等。自1938年美国人Calson^[1]等发明了利用感光导电现象的复写方式——电子照相以来,用于光导体的材料开发非常活跃。近年来,有机光导体(OPC)的实用化研究工作非常活跃,受到世人的瞩目.     

Charge carrier photogeneration in polymers

The charge carrier photogeneration in polymers can be depicted as a multistage process that involves i) photoexcitation to a neutral molecular electronic state, ii) autoionization of the excited state, iii) thermalization of the hot electron, leading to the formation of a Coulomb field-bound geminate electron-hole pair, and iv) thermal dissociation of the electron-hole pair into free carriers. This model is proposed for all types of polymers with a large ocnjugated pendant group and both the saturated and non-saturated main chain. The separation distance of the electron-hole pairs ranges from 2 to 3 nm, and the primary quantum efficiency of the electron-hole pairs formation assumes values of several tenths of charge per photon. In intrinsic materials like substituted polyacetylenes both the interchain and intrachain charge transfer excitons can be formed. Onsager's theory can provide a satisfactory explanation of the dissociation step. In polymers with the saturated main chain and large conjugated pendant groups the charge-transfer excitons are very often stabilized by self-trapping in dimer deep traps. Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

Studies on Zero Point of Charge and Permanent Charge Density of Mg-Fe Hydrotalcite-like Compounds

The theoretical analysis on the zero point of charge (ZPC) and charge density of colloidal particle possessing permanent charges indicates that ZPC determined directly by means of potentiometric titration (PT) should be zero point of net charge (ZPNC) and the permanent charge density (σ_P) can be obtained from the adsorption amount of H⁺ and OH^-(Γ_OH--Γ_H+) at ZPNC. ZPNC does not change with the electrolyte concentration while the zero point of variable charge (ZPVC) changes with the electrolyte concentration. When σ_P is zero, ZPNC equals to ZPVC, and only under this condition is ZPC measured directly by PT equal to ZPVC. The relationship between ZPNC, ZNVC, σ_P, the variable charge density (σ_V)5 or the total net surface charge density (σ_T) with pH or electrolyte concentration is derived.     

电荷转移分光光度法测定阿莫西林

阿莫西林与对苯醌在pH 5.8～6.2的乙酸-乙酸钠缓冲溶液中形成1:1荷移络合物,其最大吸收波长为476 nm,表观摩尔吸光率为2.0×103L·mol-1·cm-1,阿莫西林质量浓度在200 mg·L-1以内服从比耳定律.用此方法测定药物制剂中阿莫西林的含量,结果与药典方法一致.相对标准偏差(n=6)均小于1.5%.     

Charge transfer between quasi-zero-dimensional nanostructures

In the present paper, we show the main features of the theoretical formula allowing us to understand the irreversible transfer of electrons or holes, as it may be observed in some electrically conducting (conjugated) polymers. The formula reported here is derived with the use of the nonequilibrium quantum transport theory. The key role in the formula is played by the electron–phonon interaction which is included in an approximation going beyond the limits of the finite order of the perturbation calculation. The transfer formula is developed for a simple model of the stacked conjugated polymer, which is represented here by two interacting quantum dots. The numerical calculations show the dependence of the charge carrier mobility on the charge carrier concentration and on the lattice temperature. A comparison with organic field-effect transistor experiments and with molecular-scale modeling on conjugated polymers is promising.     

Charge separation in mesoporous aluminosilicates

EPR spectroscopy has been used to investigate spontaneous and/or photo-induced electron transfer between adsorbed organic molecules and the mesoporous aluminosilicate MCM-41 host. Spontaneous electron transfer occurs from the host to electron acceptor molecules with sufficiently favourable reduction potentials (TCNE, TCNQ, 1,4-benzoquinone, 1,4-naphthaquinone and 1,4-anthraquinone), provided the MCM-41 contains aluminium and the radical anion yield correlates with the aluminium content of the host. The semiquinone radical anions are interacting strongly with exposed Al³⁺ sites, whereas the TCNE and TCNQ radical anions are loosely bound and can be washed from the host. Radical cation formation is observed when electron donor molecules with favourable oxidation potentials are adsorbed in MCM-41 containing aluminium, and the radical cations formed interact with exposed Al³⁺ sites. This work shows that aluminium-containing MCM-41 contains both electron donating and electron accepting sites which may intervene in intra-molecular charge separation processes in adsorbed organic molecules.     

Photodissociation of Charge Tagged Peptides

Tris(2,4,6-trimethoxyphenyl) phosphonium acetyl (TMPP-Ac) was previously introduced to improve the mass spectrometric sequence analysis of peptides by fixing a permanent charge at the N-termini. However, peptides containing arginine residues did not fragment efficiently after TMPP-Ac modification. In this work, we combine charge derivatization with photodissociation. The fragmentation of TMPP-derivatized peptides is greatly improved and a series of N-terminal fragments is generated with complete sequence information. Arginine has a special effect on the fragmentation of the TMPP tagged peptides when it is the N-terminal peptide residue. Theoretical and experimental results suggest that this is due to hydrogen transfer from the charged N-terminus to the hydrogen-deficient peptide sequence.     

Charge distributions in polyatomic ions

The determination of charge distributions in polyatomic ions through both energetic and quantum mechanical (CNDO/2) methods is discussed. Results from both methods are shown to be in good agreement.The author is grateful to Dr. R. Grinter of the University of East Anglia for assistance with the quantum mechanical calculations.     

Charge hopping in DNA.

The efficiency of charge migration through stacked Watson-Crick base pairs is analyzed for coherent hole motion interrupted by localization on guanine (G) bases. Our analysis rests on recent experiments, which demonstrate the competition of hole hopping transitions between nearest neighbor G bases and a chemical reaction of the cation G(+) with water. In addition, it has been assumed that the presence of units with several adjacent stacked G bases on the same strand leads to the additional vibronic relaxation process (G(+)G...G) --> (GG...G)(+). The latter may also compete with the hole transfer from (G(+)G...G) to a single G site, depending on the relative positions of energy levels for G(+) and (G(+)G...G). A hopping model is proposed to take the competition of these three rate steps into account. It is shown that the model includes two important limits. One corresponds to the situation where the charge relaxation inside a multiple guanine unit is faster than hopping. In this case hopping is terminated by several adjacent G bases located on the same strand, as has been observed for the GGG triple. In the opposite, slow relaxation limit the GG...G unit allows a hole to migrate further in accord with experiments on strand cleavage exploiting GG pairs. We demonstrate that for base pair sequences with only the GGG triple, the fast relaxation limit of our model yields practically the same sequence- and distance dependencies as measurements, without invoking adjustable parameters. For sequences with a certain number of repeating adenine:thymine pairs between neighboring G bases, our analysis predicts that the hole transfer efficiency varies in inverse proportion to the sequence length for short sequences, with change to slow exponential decay for longer sequences. Calculations performed within the slow relaxation limit enable us to specify parameters that provide a reasonable fit of our numerical results to the hole migration efficiency deduced from experiments with sequences containing GG pairs. The relation of the results obtained to other theoretical and experimental studies of charge transfer in DNA is discussed. We propose experiments to gain a deeper insight into complicated kinetics of charge-transfer hopping in DNA.     

Charge distribution in BEDT-TTF cation

Using the INDO method we obtained the equilibrium structure of bis(ethylenedithiol) tetrathiafulvalene (BEDT-TTF), studied the properties of its electronic distribution, and determined the ionization potential of the BEDT-TTF molecule.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 357–360, May–June, 1987.The author is grateful to I. I. Ukrainskii for initiating the quantum chemical calculations of molecular components of organic metals.