Investigation of the initial fragmentation of oligodeoxynucleotides in a quadrupole ion trap: Charge level-related base loss

The charge state distribution and CID fragmentation of two series of deprotonated oligodeoxynucleotide (ODN) 9-mers (5'-GGTTXTTGG-3' and 5'-CCAAYAACC-3', X/Y = G, C, A, or T) have been studied in detail in an ion trap in an effort to understand the intrinsic properties of DNA in vacuo. The distribution of charge states (-2 to -6) is similar for both the X- and Y-series, with the most abundant being the -4 charge state. The T-rich X-series prefers higher charge states (-6 and -5) than does the Y-series. Calculations show that phosphate groups located nearest a thymine are more acidic than those near an adenine, cytosine, or guanine, thus explaining why the X-series prefers higher charge states. We use the term "charge level" to define the ratio of the charge state to the total number of phosphate groups present in the ODN. We find, consistent with previous studies, that the initial step of fragmentation is loss of nucleobase either as an anion or as a neutral. We observe the former for ODNs with charge levels greater than 50% and the latter for ODNs with charge levels below 50%. The overall anionic base loss follows the trend A(-) > G(-) approximately T(-) > C(-); electrostatic potential calculations indicate that this trend follows delocalization of electron density for each anion, with A(-) being the most stabilized through delocalization. For neutral base loss, thymine (TH) is rarely cleaved, while the preferences for AH, GH, and CH loss vary. Proton affinity (PA) calculations show that a nearby negatively charged phosphate enhances the PA of proximally located nucleobases; this PA enhancement probably plays a role in promoting neutral base loss. The trends differ by charge level. At a charge level of 37.5% (-3 charge state), AH loss is preferred over CH and GH loss, regardless of sequence. However, at a charge level of 25% (-2 charge state), the terminal bases are preferentially lost over the internal bases, regardless of identity. By reconstructing the ODN sequences from structurally informative (a-BH) and w ions, we are able to identify the charge locations for the -3 and -2 charge states. For the -3 charge state, one charge resides on each "most terminal" phosphate, with the third being in the middle. For the -2 charge state, each charge resides on the penultimate phosphate groups. We compare our data to earlier experiments in an effort to generalize trends.     

Measurement of electrostatic interactions in protein folding with the use of protein charge ladders

This paper describes a new method for the measurement of the role of interactions between charged groups on the energetics of protein folding. This method uses capillary electrophoresis (CE) and protein charge ladders (mixtures of protein derivatives that differ incrementally in number of charged groups) to measure, in a single set of electrophoresis experiments, the free energy of unfolding (DeltaG(D-N)) of alpha-lactalbumin (alpha-LA) as a function of net charge. These same data also yield the hydrodynamic radius, R(H), and net charge measured by CE, Z(CE), of the folded and denatured proteins. Alpha-LA unfolds to a compact denatured state under mildly alkaline conditions; a small increase in R(H) (11%, 2 A) coincides with a large increase in Z(CE) (71%, -4 charge units), relative to the folded state. The increase in Z(CE), in turn, predicts a large pH dependence of free energy of unfolding (-22 kJ/mol per unit increase in pH), due to differences in proton binding in the folded and denatured states. The free energy of unfolding correlates with the square of net charge of the members of the charge ladder. The differential dependence of DeltaG(D-N) on net charge for holo-alpha-LA, (partial differential) DeltaG(D-N)/(partial differential)Z = -0.14Z kJ/mol per unit of charge. This dependence of DeltaG(D-N) on net charge is a result of a net electrostatic repulsion among charge groups on the protein. These results, together with data from pH titrations, show that both the effects of electrostatic repulsion and differences in proton binding in the folded and denatured states can play an important role in the pH dependence of this protein; the relative magnitude of these effects varies with pH. The combination of charge ladders and CE is a rapid and efficient tool that measures the contributions of electrostatics to the energetics of protein folding, and the size and charge of proteins as they unfold. All this information is obtained from a single set of electrophoresis experiments.     

Effects of charge and size on condensation of supersaturated water vapor on nanoparticles of SiO2

The effects of size and charge on the condensation of a supersaturated water vapor on monodisperse nanoparticles of SiO(2) were investigated in a flow cloud chamber. The dependences of the critical supersaturation S(cr) on particle size at diameters of 10, 12, and 15 nm as well as on charge and charge polarity are determined experimentally. A novel electrospray aerosol generator was developed to generate a high concentration of SiO(2) nanoparticles of less than 10 nm by electrospraying silicon tetraethoxide (STE) ethanol solution followed by the thermal decomposition of STE. The effects of liquid flow rate, liquid concentration, flow rate of carrier gas, and liquid conductivity on the particle size distribution and concentration were examined. For charged particles, the nucleation occurs at a critical supersaturation S(cr) lower than that on neutral particles, and the charge effect fades away as particle size increases. The charge effect is stronger than the theoretical predictions. In addition, a sign preference is detected, i.e., water vapor condenses more readily on negatively charged particle, a trend consistent with those observed on ions. However, both effects of charge and charge polarity on S(cr) are stronger than that predicted by Volmer's theory for ion-induced nucleation.     

The fiber charge measurement depending on the poly-DADMAC accessibility to cellulose fibers

Cellulose fiber charge is a significant parameter for porous cellulose fibers, and strongly affects the swelling ability of cellulose fibers and the properties of cellulose-based materials as well. Actually, it includes surface charge and inner charge. The surface charge is mentioned often in papermaking wet-end chemistry, however, the inner charge or the total charge is paid less attention to. In this study, the cationic polydiallyldimethyl ammonium chloride (poly-DADMAC) with different molecular weight (Mw) was applied for the accessibility evaluation to the cellulose fiber charges by using polyelectrolyte adsorption technique. Results showed that higher fiber charge was detected by lower Mw poly-DADMAC (7.5–15 kDa) due to its highly efficient penetration into the fiber cell walls and neutralization with inner charges, while lower fiber charge was obtained by using higher Mw poly-DADMAC (higher than 100 kDa) because of its adsorption onto fiber surface. As a consequence, high-Mw poly-DADMAC was used to determine the surface charge of cellulose fibers, and low-Mw poly-DADMAC could be used to measure the total charge under the saturated adsorption and low ionic strength (or salts concentration). This was confirmed by SEM–EDS analysis. The low-Mw poly-DADMAC adsorption had a good agreement with conventional conductometric titration, and a linear regression equation with slope of 1.03 and regression coefficient of 0.99 was obtained.     

Surface charge density/surface potential relationship for a spherical colloidal particle in a salt-free medium

On the basis of a theory of Imai and Oosawa (Busseiron Kenkyu52, 42 (1952); 59, 99 (1953)), approximate analytic expressions for the surface charge density/surface potential relationship for a spherical colloidal particle in a salt-free (aqueous or nonaqueous) medium containing only counterions are derived. There is a certain critical value of the surface charge density (or the total surface charge) separating two distinct cases: low surface charge density case and high surface charge density case. In the latter case counterion condensation occurs in the vicinity of the particle surface. The results are in excellent agreement with numerical calculations for the case of dilute suspensions.     

Dependence of (35)Cl NQR on hydrogen bonding and temperature in dichlorophenol-aniline charge transfer complexes

The hydrogen-bonded charge transfer complexes of aniline with pi-acceptors (or proton donors) such as 2,5-, 2,6-, 3,4- and 3,5-dichlorophenol were prepared. The (35)Cl nuclear quadrupole resonance (NQR) frequencies of these charge transfer complexes in the temperature range 77-300 K were measured to ascertain the existence or otherwise of a phase transition upon complex formation. Further, the NQR frequency and asymmetry parameter of the electric field gradient at the site of quadrupole nucleus were used to estimate the chemical bond parameters, namely ionic bond, double bond character of the carbon-chlorine(C--Cl) bond and the percentage charge transfer between the donor-acceptor components in charge transfer complexes. The effect of hydrogen bonding and temperature on the charge transfer process is analysed.     

Charge separation from the bursting of bubbles on water

Film droplets formed from the bursting of 2.4 mm diameter bubbles on the surface of pure water are predominantly negatively charged. The charge generated per bubble varies chaotically; a few bubbles generate more than -3 × 10(6) elementary charges (e) but the vast majority generate much less. The average is -5 × 10(4)e/bubble, and it is not significantly affected by bubbling rate or temperature. The charge diminishes with increasing salt concentration and vanishes for concentrations above 10(-3) M. We propose a mechanism consistent with the observed charge separation. The model relies on the assumption that the surface of pure water has a slight excess of hydroxide ions. The charge separation results when water with entrained counterions (H(3)O(+)) flows out of the thinning film of the bubble cap, leaving behind the excess OH(-) on the surface. Addition of salt reduces the Debye length, and the charge separation mechanism becomes less effective as the Debye length becomes small compared with the film thickness. The excess charge near the surface of pure water is very small, around -4 nC/m(2).     

Charge transfer excitations in cofacial fullerene-porphyrin complexes

Porphyrin and fullerene donor-acceptor complexes have been extensively studied for their photo-induced charge transfer characteristics. We present the electronic structure of ground states and a few charge transfer excited states of four cofacial porphyrin-fullerene molecular constructs studied using density functional theory at the all-electron level using large polarized basis sets. The donors are base and Zn-tetraphenyl porphyrins and the acceptor molecules are C(60) and C(70). The complexes reported here are non-bonded with a face-to-face distance between the porphyrin and the fullerene of 2.7 to 3.0 A?. The energies of the low lying excited states including charge transfer states calculated using our recent excited state method are in good agreement with available experimental values. We find that replacing C(60) by C(70) in a given dyad may increase the lowest charge transfer excitation energy by about 0.27 eV. Variation of donor in these complexes has marginal effect on the lowest charge transfer excitation energy. The interfacial dipole moments and lowest charge transfer states are studied as a function of face-to-face distance.     

Efficient charge transport along phenylene-vinylene molecular wires

We have studied the motion of charge carriers along isolated phenylene-vinylene (PV) chains using a combination of experimental and theoretical methods. The conductive properties of positive charges along PV chains in dilute solution were studied by using the pulse-radiolysis time-resolved microwave conductivity (TRMC) technique. This technique enables the measurement of high-frequency (tens of GHz) charge carrier mobilities along isolated PV chains without the use of electrodes. The charge carrier mobility along PV chains with finite and infinite length was studied theoretically by charge transport simulations with parameters from density functional theory (DFT) calculations. The high-frequency charge carrier mobility is found to depend strongly on the conjugation length of the PV chains and is found to increase both with increasing length of the PV chain and with increasing conjugation fraction. The experimental results are in good agreement with the calculated results. On the basis of this combined experimental and theoretical study an intrachain charge carrier mobility of a few tens of cm2/Vs is expected for an infinitely long PV chain without conjugation breaks.     

Differences in the conformational state of a zinc-finger DNA-binding protein domain occupied by zinc and copper revealed by electrospray ionization mass spectrometry.

Transition metal ions are important in biological regulation partly because they can bind to and stabilize protein surface domain structures in specific conformations that are involved in key molecular recognition events. There are two C2-C2 type zinc-finger sequences within the highly conserved DNA-binding domain of the estrogen receptor protein (ERDBD). Electrospray ionization (ESI) mass spectrometry has been used to demonstrate that the metal-binding sites within the 71-residue ERDBD can bind either Zn (up to 2) or Cu (up to 4). Evidence for the induction and/or stabilization of a different conformational state with bound Cu is revealed by a characteristic shift in the ESI charge envelope. The 10+ charge state is most abundant for the fully reduced ERDBD apopeptide and the ERDBD-Zn holopeptide (bound Zn does not alter the charge envelope). In contrast, the 8+ charge state is typically the optimum charge state observed for the ERDBD-Cu holopeptide; indeed, the entire charge envelope is frame-shifted to lower charge states with bound Cu. Interpretation of the altered charge states is simplified because (i) a single type of metal-binding ligand (sulfur) is involved in the case of both Zn and Cu binding, and (ii) the two different metal cations are both divalent. Thus, it is likely that the dissimilar charge envelopes represent different peptide conformers, each of which is stabilized by a different type of bound metal ion.(ABSTRACT TRUNCATED AT 250 WORDS)     

利用充电曲线数据计算钝态金属的腐蚀速度

对 钝态金 属腐蚀体 系推导了 不含近 似处 理的 充电 曲线 方程 式．提 出 了使 用数 值 微分和线性 回归求 解体系电 化学参数 的计算 机方法．     

Method of measuring charge distribution of nanosized aerosols

In this paper, we present the development of a method to accurately measure the positive and negative charge distribution of nanosized aerosols using a tandem differential mobility analyzer (TDMA) system. From the series of TDMA measurements, the charge fraction of nanosized aerosol particles was obtained as a function of equivalent mobility particle diameter ranging from 50 to 200 nm. The capability of this new approach was implemented by sampling from a laminar diffusion flame which provides a source of highly charged particles due to naturally occurring flame ionization process. The results from the TDMA measurement provide the charge distribution of nanosized aerosols which we found to be in reasonable agreement with Boltzmann equilibrium charge distribution theory and a theory based upon charge population balance equation (PBE) combined with Fuchs theory (N.A. Fuchs, Geofis. Pura Appl. 56 (1963) 185). The theoretically estimated charge distribution of aerosol particles based on the PBE provides insight into the charging processes of nanosized aerosols surrounded by bipolar ions and electrons, and agree well with the TDMA results.     

Photoinduced charge carrier generation in a poly(3-hexylthiophene) and methanofullerene bulk heterojunction investigated by time-resolved terahertz spectroscopy

We report on the ultrafast photoinduced charge separation processes in varying compositions of poly(3-hexylthiophene) (P3HT) blended with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Through the use of time-resolved terahertz spectroscopy, the time- and frequency-dependent complex photoconductivity is measured for samples with PCBM weight fractions (WPCBM) of 0, 0.2, 0.5, and 0.8. By analysis of the frequency-dependent complex conductivity, both the charge carrier yield and the average charge carrier mobility have been determined analytically and indicate a short (<0.2 nm) carrier mean free path and a suppressed long-range transport that is characteristic of carrier localization. Studies on pure films of P3HT demonstrate that charge carrier generation is an intrinsic feature of the polymer that occurs on the time scale of the excitation light, and this is attributed to the dissociation of bound polaron pairs that reside on adjacent polymer chains due to interchain charge transfer. Both interchain and interfacial charge transfer contribute to the measured photoconductivity from the blended samples; interfacial charge transfer increases as a function of increasing PCBM. The addition of PCBM to the polymer films surprisingly does not dramatically increase the production of charge carriers within the first 2 ps. However, charge carriers in the 0.2 and 0.5 blended films survive to much longer times than those in the P3HT and 0.8 films.     

Effect of surface-active substances on the surface charge density of purple membrane fragments

The surface charge density of purple membrane fragments and its alteration upon treatment of purple membranes with several surface-active substances [sodium dodecyl sulphate (SDS), cetylpyridinium chloride (CPC) and 3-[(3-cholamidopropyl) dimethylammonio]-1-propane-sulphonate (CHAPS) were examined by use of 9-amino-acridine fluorescence.The value of the surface charge density of native purple membrane fragments (0.8 electric charges/nm²) obtained by this method is comparable to previously reported values and in agreement with the structural model of the purple membrane.An increase followed by a decrease in the negative surface charge density was observed after treatment of purple membranes with the negatively charged surfactant SDS within the concentration range 0–5 mM, whereas treatment with the positively charged surfactant CPC and zwitterionic derivative of cholic acid (CHAPS) led to a decrease in the surface charge density. The large reduction of the surface charge density after treatment of purple membranes with CHAPS (i.e. partial delipidation of purple membranes) proves the significant contribution of the negative charges of the lipid polar head groups to the negative surface charge of purple membranes.     

Sequential hydration of small protonated peptides

The sequential addition of water molecules to a series of small protonated peptides was studied by equilibrium experiments using electrospray ionization combined with drift cell techniques. The experimental data were compared to theoretical structures of selected hydrated species obtained by molecular mechanics simulations. The sequential water binding energies were measured to be of the order of 7-15 kcal/mol, with the largest values for the first water molecule adding to either a small nonarginine containing peptide (e.g., protonated dialanine) or to a larger peptide in a high charge state (e.g., triply protonated neurotensin). General trends are (a) that the first water molecules are more strongly bound than the following water molecules, (b) that very small peptides (2-3 residues) bind the first few water molecules more strongly than larger peptides, (c) that the first few water molecules bind more strongly to higher charge states than to lower charge states, and (d) that water binds less strongly to a protonated guanidino group (arginine containing peptides) than to a protonated amino group. Experimental differential entropies of hydration were found to be of the order of -20 cal/mol/K although values vary from system to system. At constant experimental conditions the number of water molecules adding to any peptide ion is strongly dependent on the peptide charge state (with higher charge states adding proportionally more water molecules) and only weakly dependent on the choice of peptide. For small peptides molecular mechanics calculations indicate that the first few water molecules add preferentially to the site of protonation until a complete solvation shell is formed around the charge. Subsequent water molecules add either to water molecules of the first solvation shell or add to charge remote functional groups of the peptide. In larger peptides, charge remote sites generally compete more effectively with charge proximate sites even for the first few water molecules.     

A Direct Mapping Approach to Understand Carrier Relaxation Dynamics in Varied Regions of a Polycrystalline Perovskite Film

We developed a direct mapping approach to overlay the image of a polycrystalline perovskite film obtained from the transient absorption microscope (TAM) with that from the scanning electron microscope (SEM). By mapping these imaging data pixel by pixel, we are able to observe the relaxation dynamics of the photo-generated charge carriers on varied regions of the film. The carrier relaxation dynamics contain a dominated single-exponential decay component owing to the recombination of charge carriers. The lifetime distribution of charge recombination shows a bimodal feature, for which the rapid and slow distributions are assigned as free and trapped carriers, respectively. The charge recombination was slower in the grain boundary (GB) region than in the grain interior (GI) region. The small grains have longer lifetimes than the large grains for the crystal size smaller than 500 nm. Therefore, GB with retarded charge recombination might play a positive role in a perovskite solar cell.     

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.     

含酯基和酰胺基支链的苯并菲液晶电荷传输性质的量子化学研究

根据Marcus半经典模型,计算了支链中含酰胺基和含酯基的苯并菲盘状液晶化合物C18H6(OC2H5)3(OCH2CONHCH3)3和C18H6(OC2H5)3(OCH2COOCH3)3的电荷转移反应的速率常数。这两种化合物的支链都可以对称性分布,也可以非对称性分布。计算表明,支链排列的对称性对电荷转移矩阵元和电荷传输速率常数的影响很大,非对称性分子的正电荷传输速率常数和负电荷传输速率常数均大于对称性分子。所以,取代基非对称性排列对增加电荷传输速率常数有利。其原因是支链非对称排列的分子的质量中心与几何中心不重合,当液晶分子绕质量中心旋转的同时形成了分子间的相对平移,从而增大了电荷转移矩阵元。本文为设计、改善液晶分子的电荷传输性能提供了一条新的思路。     

Synthetic high-charge organomica: effect of the layer charge and alkyl chain length on the structure of the adsorbed surfactants

A family of organomicas was synthesized using synthetic swelling micas with high layer charge (Na(n)Si(8-n)Al(n)Mg(6)F(4)O(20)·XH(2)O, where n = 2, 3, and 4) exchanged with dodecylammonium and octadecylammonium cations. The molecular arrangement of the surfactant was elucidated on the basis on XRD patterns and DTA. The ordering conformation of the surfactant molecules into the interlayer space of micas was investigated by (13)C, (27)Al, and (29)Si MAS NMR. The arrangement of alkylammonium ions in these high-charge synthetic micas depends on the combined effects of the layer charge of the mica and the chain length of the cation. In the organomicas with dodecylammonium, a transition from a parallel layer to a bilayer-paraffin arrangement is observed when the layer charge of the mica increases. However, when octadecylammonium is the interlayer cation, the molecular arrangement of the surfactant was found to follow the bilayer-paraffin model for all values of layer charge. The amount of ordered conformation all-trans is directly proportional of layer charge.     

双向脉冲充电法对锂枝晶生成的抑制

采用双向脉冲电流充电方法取代传统的直流电充电方法, 研究了金属锂电极在有机电解液1 mol•L−1 LiPF6/碳酸乙烯酯(EC):二甲基碳酸脂(DMC)(1:1, V/V)中的充电过程. 锂电极的表面变化通过原位显微镜观测和交流阻抗谱进行检测. 原位显微镜观测结果显示, 在直流充电时锂电极上明显地出现了枝晶, 而在双向脉冲充电时, 枝晶的产生和生长受到了抑制. 交流阻抗谱结果显示在双向脉冲充电下, 锂电极的表面积增长较直流充电时缓慢. 这种抑制枝晶生长, 稳定锂沉积的新充电方法有望用于锂阳极二次电池.