Search

The grain boundary (GB) plays a critical role in a material’s properties and device performance. Therefore, the characterization of a GB’s atomic structure and electrostatic characteristics is a matter of great importance for materials science. Here, we report on the atomic structure and electrostatic analysis of a GB in a SrTiO3 bicrystal by four-dimensional scanning transmission electron microscopy (4D-STEM). We demonstrate that the Σ5 GB is Ti-rich and poor in Sr. We investigate possible effects on the variation in the atomic electrostatic field, including oxygen vacancies, Ti-valence change, and accumulation of cations. A negative charge resulting from a space-charge zone in SrTiO3 compensates a positive charge accumulated at the GB, which is in agreement with the double-Schottky-barrier model. It demonstrates the feasibility of characterizing the electrostatic properties at the nanometer scale by 4D-STEM, which provides comprehensive insights to understanding the GB structure and its concomitant effects on the electrostatic properties.

A mild condition via PPh3/I2/imidazole for the deoxygenation of substituted methanol derivatives has been identified. This metal-free process was found to proceed well on secondary or tertiary alcohols substituted with one or two heteroaryl groups, and it tolerates acid-sensitive heterocycles. This condition works for methanol derivatives substituted with 2-pyridyl, 4-pyridyl, or other heterocyclic groups, allowing the negative charge formed during the reaction to resonate to a nitrogen atom. Methanol derivatives substituted with 3-pyridyl or heterocyclic groups that do not allow the negative charge formed during the reaction to resonate to a nitrogen atom will not undergo deoxygenation under this condition.

Light-induced cell harvest shows much potential in in vitro cell culture. In this work, a light-responsive monolayer graphene (Gr)/titanium dioxide nanodot (TN) film is designed and used for light-induced cell harvest. It is found that after 20 min of 365 nm UV or 450 nm visible light illumination, different types of cells could be detached from the surface effectively. The highest cell detachment ratio reaches about 95%. The mechanism of such a cell detachment is contributed to light illumination generates charge accumulation, which, in turn, changes the conformation of the extracellular matrix protein molecules adsorbed to a more disordered state, and eventually leads to the cells detachment. Such UV and visible light responsive Gr/TiO2 film could be a good candidate for a surface with light-induced cell detachment property.

In this work, for the first time it is demonstrated that supported single Au in either a positive or a negative charge state can catalyze acetylene hydrochlorination competitively with regard to ot...

Cationic frameworks are an emerging class of exceptional solid adsorbents capable of encapsulating highly toxic and persistent anionic pollutants. The controlled generation of cationic frameworks, however, lags behind the abundant design strategies devised to control the structures and topologies of neutral frameworks. In this regard, we report a rational approach that allows the conversion of the synthetic approach toward constructing a neutral framework into one allowing for the synthesis of a cationic one without incurring any changes to the overall topology or the selected metal ion. We demonstrate that the replacement of a functional group on an organic linker that promotes a similar coordination mode, but bearing one less negative charge, can yield the systematic generation of cationic frameworks. Moreover, we confirm the cationic nature of the metal-organic frameworks through preliminary anion-exchange experiments and propose a method to retain permanent porosity in cationic frameworks through the use of strongly binding anions. Altogether, these results show great promise for the construction of tunable nanoporous frameworks capable of carrying out anion-exchange processes.

Radical anions of electrochemically reduced compounds (anolytes) have been suggested for storage of negative charge in nonaqueous redox flow batteries. The lower the redox potential of the anolyte molecule, the higher is the stored energy density. However, the stability of the radical ions frequently suffers as their redox potentials become extreme, and there is a compromise between the energy density and the chemical stability in the active form. In this study, we scrutinize this trade-off using one such “extreme,” the heterocyclic anolyte 2,1,3-benzothiadiazole, BzNSN, by adjusting the redox potential of BzNSN via installed electron-donating and electron-withdrawing groups. We show that the stability of the radical anion strongly depends on the degree of ion pairing in solution, with the worst being for the contact lithium ion pairs. For BzNSN derivatives, there is a strong correlation between the lifetime of the radical anion and the redox potential. The root cause appears to be the proton transfer fro...

The stability of small Aum (m = 4–7) clusters is investigated by analyzing their energetic, geometric, vibrational, magnetic, and electron density properties. Gold clusters can be constructed from stable cyclic 3-center-2-electron (3c-2e) Au3+ units (3-rings) with σ-aromaticity. The stabilization requires a flow of negative charge from internal 3-rings with electron-deficient bonding to peripheral 3-ring units with stronger Au–Au bonds. The valence-isoelectronic clusters Au6 and Au5Zn+ have similar electronic properties: Au5Zn+ is a strongly σ-aromatic molecule. An understanding of the structure of Aum clusters is obtained by deriving a Clar’s Rule equivalent for polycyclic gold clusters: The structure with the larger number of rings with dominant 3c-2e character and a smaller degree of 3c-3e character occupies the global minimum of the Aum potential energy surface.

GH-18 chitinases are chitinolytic enzymes, primarily responsible for the recycling of insoluble chitin biomaterials. These enzymes contain three invariant acidic active-site residues within a DXDXE motif, which play a synergistic role in the catalytic cycle of chitin degradation. We employed a pKa calculation approach to approximate the protonation states of residues D1, D2, and E in the DXDXE motif of 75 GH-18 chitinases. Theoretical pH-activity profiles of these enzymes were subsequently constructed and compared with the experimentally determined pH-activity profiles. Theoretical pKa data indicate that in the majority of chitinases the D1 side-chain is in the “up” and the E side-chain in the “down” position, while the position of the D2 side-chain is versatile and depends on the state of the enzyme. The pKa values in 75 GH-18 chitinases were predicted to be

The novel ruthenaphosphaalkenyls [Ru{P═C(H)SiMe2R}Cl- (CO)(PPh3)2] (R = p-C6H4CF3, nBu) have been prepared for the first time, and studied alongside precedent analogues (R = Me, Ph, p-tol) for their reactions with HCl. In contrast to chemistry defined for the tert-butyl congener [Ru{P═C(H)tBu}Cl(CO)(PPh3)2], which initially adds a single equivalent of HCl across the Ru−P linkage, all five silyl derivatives undergo spontaneous addition of a second equivalent to afford [Ru{η1-PHCl−CH2SiMe2R}Cl(CO)(PPh3)2], extremely rare examples of coordinated “PHXR” type ligands. Where R = SiMe3, a distorted octahedral geometry with a conformationally restricted “PHXR” ligand is observed crystallographically; this structure is appreciably retained in solution, as determined from multinuclear NMR spectroscopic features, which include a Karplus-like PPh3−Ru−P−H spin−spin coupling dependence. Computational data suggest a silyl-induced increase in negative charge density at the phosphaalkenic carbon, rather than an intrinsic thermodynamic driver, as the likely origin of the disparate reactivity.

Hagfish slime, a remarkable soft and elastic hydrogel, is formed by hagfish as a defense mechanism against predation. The extremely fast slime formation, the high water content, and protein threads up to 30 cm in length make it a promising material for the development of hydrogels with embedded fibers. However, under environmental conditions, i.e., in agitation in seawater, the slime collapses. To address the limited structural stability but use the potential of the protein threads as a backbone in fiber enforced materials, we generated composite structures of hagfish slime with biopolymers. Hagfish slime mixed with chitosan reveals that the slime's mucin fraction has a negative charge due to strong aggregation of both components. The gels formed by κ-carrageenan and starch show synergistic effects by exhibiting high values of water content, elasticity, and viscosity. We demonstrated that in combination with negatively charged biopolymers, fiber enforced hydrogels can be formed. This fiber enforced material has a pronounced cohesiveness and stability, thus combining both properties of biopolymers and hagfish slime.

We studied the adsorption and reaction of nitrogen dioxide gas on the surface of an ice film at temperatures of 100–170 K under ultrahigh vacuum (UHV) conditions. Cs+ reactive ion scattering (RIS) and low-energy sputtering (LES) techniques were used to identify and quantify the reactants and products on the surface of the ice film, in conjunction with the use of temperature-programmed desorption (TPD) to monitor the species desorbed. Temperature-ramping experiments were performed to examine the changes in the populations of these species as a function of temperature. Adsorption of NO2 gas on the ice film at

The pH-low insertion peptide (pHLIP) targets acidic diseases such as cancer. The acidity of the environment causes key aspartic acids in pHLIP to become protonated, causing the peptide to insert into membranes. Here we investigate how the negative charge of the membrane influences how pHLIP enters and exits the lipid bilayer. We found that electrostatic repulsion affected differently the membrane entry and exit of pHLIP for negatively charged membranes. As a consequence, a large hysteresis was observed. We propose this is not a consequence of structural changes but results from local changes in the environment of aspartic acids, shifting their pK values.

The structures of various para-substituted biphenyls (Bp-X; X = -OH, -OCH3, -CH3, -H, -CONH2, -COOH, and -CN) and their radical anions (Bp-X(•-)) were investigated by time-resolved resonance Raman spectroscopy combined with pulse radiolysis. The inter-ring C1-C1' stretching modes (ν6) of Bp-X were observed at ∼1285 cm(-1), whereas the ν6 modes of Bp-X(•-) with an electron-donating or -withdrawing substituent were significantly up-shifted. The difference (Δf) between the ν6 frequencies of Bp-X and Bp-X(•-) showed a significant dependence on the electron affinity of the substituent and exhibited a correlation with the Hammett substituent constants (σp). In contrast to Bp-H(•-) with a planar geometry, the theoretical and experimental results reveal that all Bp-X(•-) with an electron-donating or -withdrawing substituent have a slightly twisted structure. The twisted structure of Bp-X(•-) is due to the localization of the unpaired electron and negative charge density on one phenyl moiety in Bp-X(•-).

In this submission, two independent sets of microgels were synthesized that exhibit pH responsivity over different solution pH ranges. The microgels were synthesized by copolymerizing two different comonomers with poly(N-isopropylacrylamide) (pNIPAm). The microgels copolymerized with acrylic acid exhibit a negative charge above pH 4.25, while the microgels copolymerized with N-[3-(dimethylamino)propyl]methacrylamide exhibit a positive charge below pH 8.4; these microgels are neutral outside of these pH ranges. We show that aggregates form when the two independent sets of microgels are exposed to one another in a solution that renders them both charged. Furthermore, in solutions of pH outside of this range, the microgels disaggregate because one of the microgels becomes neutralized. This behavior was exploited to load (aggregation) and release (disaggregation) a small-molecule model drug, methylene blue. This aggregate-based system is one example of how pNIPAm-based microgels can be used for controlled/triggered drug delivery, which can have implications for therapeutics.

A dramatic "ortho effect" was observed during gas-phase dissociation of ortho-, meta-, and para-methoxybenzoate anions. Upon activation under mass spectrometric collisional activation conditions, anions generated from all three isomers undergo a CO2 loss. Of the m/z 107 ions generated in this way, only the 1-dehydro-2-methoxybenzene anion from the ortho isomer underwent an exclusive formaldehyde loss. A peak for a formaldehyde loss in the spectra of 2,4-, 2,5-, and 2,6-dimethoxybenzoates and the absence of an analogous peak from 3,4- and 3,5-dimethoxy derivatives confirmed that this is a diagnostically useful ortho-isomer-specific phenomenon. Moreover, the spectrum from 2,3-dimethoxybenzoic acid showed peaks for two consecutive formaldehyde losses. The 1-dehydro-2,3,4-trimethoxybenzene anion (m/z 167) generated from 2,3,4-trimethoxybenzoate in this way endures three consecutive eliminations of formaldehyde units. For this, the negative charge, initially located on position 1, circumambulates to position 2, then to position 3, and finally to position 4 to form the final phenyl anion. The proposed stepwise fragmentation pathway, which resembles the well-known E1cB-elimination mechanism, is supported by tandem mass spectrometric observations made with 2-[(13)C(2)H3]methoxy-3-[(13)C]methoxy-4-methoxybenzoic acid, and ab initio calculations. In addition, the spectra of ions such as 1-dehydro-3,4-dimethoxybenzene anion show peaks for consecutive methyl radical losses, a feature that establishes the 1,2-relationship between the two methoxy groups.

The targets of β-lactam antibiotics are bacterial DD-peptidases (penicillin-binding proteins). β-Lactam SAR studies over many years have demonstrated the importance of a specifically placed negative charge, usually carboxylate, on these molecules. We show here that neutral analogues of classical β-lactam antibiotics are of comparable activity to the originals against β-lactam-resistant high molecular mass DD-peptidases of the B1 class, a group that includes PBP2a of methicillin-resistant Staphylococcus aureus. These neutral β-lactams may direct new development of antibiotics against certain penicillin-resistant bacteria. These molecules do have antibiotic activity against Gram-positive bacteria.

We prepared hybrid halloysite nanotubes (HNT/sodium alkanoates) in which the inner cavity of the nanoclay was selectively modified. Physicochemical studies evidenced the interactions between HNT and sodium alkanoates, ruled out clay exfoliation, quantified the amount of the loaded substance, and showed an increase of the total net negative charge, allowing us to obtain rather stable aqueous nanoclay dispersions. These dispersions were exploited as inorganic micelles to capture hydrocarbon and aromatic oils in the vapor and liquid states and were revealed to be nonfoaming but very efficient in encapsulating oils. Here, we have fabricated biocompatibile and low-cost inorganic micelles that can be exploited for industrial applications on a large scale.

The para-OMe functional group, usually regarded as a conjugative p-donor, acts as an efficient hyperconjugative σ-acceptor in reductive cycloaromatization reactions. This apparent reversal of electronic properties is associated with a conformational change that aligns the σ*(O-C) orbital with the adjacent aromatic system and provides stabilization to the developing negative charge in the TS of the dianionic cyclization of enediynes. The chameleonic character of the OMe group illustrates the important role of negative hyperconjugation in anionic processes.

The reaction of [CH2(PPh2S)2] (1) with 2 equiv of MeLi in Et2O followed by addition of 0.5 equiv of SiCl4 afforded the base-stabilized 2-silaallene [(PPh2S)2CSiC(PPh2S)2] (2). It has been characterized by X-ray crystallography, NMR spectroscopy, and theoretical studies. The results show that compound 2 comprises a C¯–Si2+–C¯ ylidic skeleton with a negative charge at the Cmethanediide atoms and two positive charges at the Si atom. The reaction of 2 with excess PriN═C═NPri in refluxing toluene gave the thiophosphinoyl-stabilized silene [(PPh2S)2C–—Si+(NPri)2C═C(PPh2S)2] (3).

The perturbation of salt ions on the solubility of a monoclonal antibody was systematically studied at various pHs in Na(2)SO(4), NaNO(3), NaCl, NaF, MgSO(4), Mg(NO(3))(2) and MgCl(2) solutions below 350 mM. At pH 7.1, close to the pI, all of the salts increased the solubility of the antibody, following the order of SO(4)(2-)NO(3)(-)Cl(-)F(-) for anions and Mg(2+)Na(+) for cations. At pH 5.3 where the antibody had a net positive charge, the anions initially followed the order of SO(4)(2-)NO(3)(-)Cl(-)F(-) for effectiveness in reducing the solubility and then switched to increasing the solubility retaining the same order. Furthermore, the antibody was more soluble in the Mg(2+) salt solutions than in the corresponding Na(+) salt solutions with the same anion. At pH 9.0 where the antibody had a net negative charge, an initial decrease in the protein solubility was observed in the solutions of the Mg(2+) salts and NaF, but not in the rest of the Na(+) salt solutions. Then, the solubility of the antibody was increased by the anions in the order of SO(4)(2-)NO(3)(-)Cl(-)F(-). The above complex behavior is explained based on the ability of both cation and anion from a salt to modulate protein-protein interactions through their specific binding to the protein surface.

The properties of radical anions and dianions of three related spatial ketones, 9-triptindanone (T1), 9,10-triptindanedione (T2), and 9, 10,11-triptindanetrione (T3), in DMF solutions containing tetraalkylammonium and lithium cations were investigated by electrochemical methods and compared with the properties of radical anions of planar 1-indanone (I1), 1,3-indanedione (I2), and 1,2,3-indanetrione (I3). Electronic communication between carbonyl groups in T2 in the presence of tetraethyl and tetrabutyl cations was found to be two times smaller than for I3, but communication decreases substantially in the presence of Li+. Radical anions T1(center dot-) and T2(center dot-) and dianion T2(2-) that form ion pairs with Li+ cations and corresponding association constants K-ass are equal to 493 +/- 38, 418 +/- 32 and (2.6 +/- 0.9) x 10(7) dm(3) mol(-1), respectively. The chelating structure of the last ion pair is supported by theoretical calculations of the distribution of the negative charge. A linear relationship between log K-ass and maximum values of the surface charge was observed. For T2, the highest equilibrium constant (log K-disp(l) = -2.387 +/- 0.064) was found for the disproportionation of the T2(center dot-) radical anion and its ion pair.

This paper reports on the preparation of a water-soluble nanoemulsion of the highly lipid-soluble drug tamoxifen (TAM). In addition, relative to a suspension of TAM, the nanoemulsion preparation demonstrated a greater zeta potential (increased negative charge) which has previously been associated with increasing drug/membrane permeability. This study also reports that relative to suspensions of TAM with particle sizes greater than 6000 nm, nanoemulsions of TAM, having mean particle sizes of 47 nm, inhibited cell proliferation 20-fold greater and increased cell apoptosis 4-fold greater in the HTB-20 breast cancer cell line. Thus, this work suggests that a nanoemulsion compared to a suspension preparation of TAM increases its anticancer properties relative to breast cancer.

Possible mechanisms for degrading chloromethylmercury (CH3HgCl) and dimethylmercury [(CH3)2Hg] involving thiol and ammonium residues were investigated by DFT and atoms-in-molecules (QTAIM) calculations. Using H2S and HS- as models for thiol and thiolate groups RSH and RS-, respectively, we obtained transition states and energy barriers for possible decomposition routes to Hg(SH)2 based on a model proposed by Moore and Pitts (Moore, M. J.; Distefano, M. D.; Zydowsky, L. D.; Cummings, R. T.; Walsh, C. T. Acc. Chem. Res. 1990, 23, 301. Pitts, K. E.; Summers, A. O. Biochemistry 2002, 41, 10287). Demethylation was found to be a multistep process that involved initial substitution of Cl- by RS-. We found that successive coordination of Hg with thiolates leads to increased negative charge on the methyl group and facilitates the protonolysis of the Hg−C bond by H−SH. This was also found to be the case for (CH3)2Hg. We found that NH4+ readily protonolyzes the Hg−C bond of these thiolate complexes, suggesting that ...

Photoemission from sodium deposited on ice films is described. Deposition of 0.02 ML of sodium is found to dramatically reduce the threshold for photoemission from the ice film to (2.3+/-0.2) eV. Thus, the cross-section for photoemission reaches10(-18) cm2 in the visible region of the spectrum. It is proposed that the initial state is a solvated electron on the ice surface, which is supported by optical transmission spectroscopy. The potential significance of these results in understanding unexplained charging phenomena in the mesosphere is discussed.

The mobility of one of two types of fast moving negative charge carriers was measured by a time-of-flight method over a wide range of the solvent density ρ in gaseous, supercritical, and liquid car...

The gas-phase acidities of meta- and para-substituted phenols have been calculated at the B3LYP/6-311+G, MP2/6-311+G, MP2/6-311++G, and MP2/6-311+G(2df,2pd) theoretical levels. The larger basis sets give the more satisfactory DeltaHacid values that are correlated with the observed acidities with a slope close to unity. They are systematically about 2 kcal/mol too small. The acidities of most substituted phenols are linearly related to those of the corresponding substituted benzoic acids and benzyl alcohols. Here, the substituent effect is a Coulombic interaction (field effect) of the distributed charge in the benzene ring with the negative charge of the anionic center. The exceptions are strong para-substituted pi-acceptors such as NO(2) and CHO, and to a smaller extent, CN and CF(3). Here there is direct charge transfer from the phenoxide oxygen to the substituent.

The carboxylic acid dianions, CO2(CH2)pCO22-, are the simplest model for two deprotonated acidic side chains, such as Glu or Asp, which are on opposite sides of a nondenatured globular protein. Rat...

9,10-Dimethylacridinium chloride (1: X = Cl) exhibited strong acidity of pH 3.90 (3.4 x 10(-3) M, 20 degrees C) in an aqueous solution. H-D exchange reaction of 1 in D2O indicated that protons in the 9-methyl group dissociated to generated H+ ions. This is a unique example of a methyl proton functioning as an acid. The acidity derives from the wider pi face in acridinium capable of delocalizing the newly formed negative charge upon proton dissociation. PM3 calculations provided stabilization factors (deltaDeltaH(f)o) between proton dissociated and undissociated forms of several N-heterocycles and also confirmed the acidity observed in acridinium.

Direct force measurements, surface plasmon resonance spectroscopy, and genetic manipulations were used to investigate the impact of the orientation of immobilized cytochrome b5 (cyt b5) on its interactions with cytochrome c (cyt c). In this work, we used two cyt b5 orientational variants that present different regions of the protein surface when immobilized. Direct force measurements demonstrated that the two orientations generate a small difference in the electrostatic surface potential of the protein monolayers, in agreement with the calculated electrostatic potential distribution across the protein surface. This difference did not result in any differences in the electrostatic force between cyt c and the cyt b5 variants, however. The measured equilibrium binding constant for the cyt c interaction with cyt b5 also did not depend on the orientation of the latter. These results suggest that, at large separations, cyt c initially interacts relatively nonspecifically with a large patch of negative charge on...

The effects of Ni and Zn on the electronic and chemical properties of MoS2 clusters have been investigated using INDO/S and ab initio SCF calculations. The deposition of Ni or Zn atoms on a series of clusters (Mo5S10, Mo6S12, Mo8S18, Mo9S18, Mo12S24, and Mo18S36) that resemble the MoS2(0002)-S and MoS2(1010)-Mo surfaces produces a substantial reduction (0.5−2 eV) in the stability of the HOMOs of these systems. In all the cases examined, there was an admetal→MoS2 charge transfer that increased the negative charge on S and reduced the positive charge on Mo. The electronic and chemical perturbations induced by Ni were much larger than those induced by Zn. Ab initio SCF results for Ni-promoted MoS2(1010)-Mo clusters showed a simultaneous increase in the electron density on Mo and in the reactivity of this metal toward H2 and thiophene. On the (1010)-Mo surface, Ni facilitated the dissociation of H2 by largely increasing the stability of the transition state and products for this reaction. The bonding inter...

The first isolable gold(I) fluoride complex, stabilized by an N-heterocyclic carbene (NHC) ligand, has been isolated in two-coordinate monomeric form. DFT calculations show significant pπ/dπ interactions between fluoride and gold(I) and indicate a substantial negative charge on fluorine.

The reaction of closo derivatives of 1,2-dithio- 1,2-dicarba-closo-dodecaborane with [MCl(PPh 3 ) 2 ] (M=Cu, Ag) in ethanol, produces complexes of the corresponding nido derivatives of 7,8-dithio-7,8-dicarba-nido-undecaborate-(1-). These nido ligands form via formal B + elimination in the closo precursors, becoming anionic, i.e., they have a negative charge which greatly enhances their coordinating capabilities

The study was undertaken to investigate the effect of reduction of negative charge by nonspecific chemical modification of carboxyl groups on the physicochemical properties, milk-clotting activity and structure of M. miehei proteinase

The thermodynamics of disproportionation of 1,4-benzosemiquinone (BQ{sup {sm bullet}{minus}}) and 1,4-naphthosemiquinone (NQ{sup {sm bullet}{minus}}) in cacodylic-cacodylate buffer at pH 7.1 was studied by electron spin resonance (ESR) spectroscopy and solution calorimetry. The disproportionation of BQ{sup {sm bullet}{minus}} was found to be more exergonic and exothermic than that corresponding to NQ{sup {sm bullet}{minus}} in both aqueous and gas phases. These semiquinones disproportionate about 40 times more exothermically in the gaseous than in the aqueous phase. The differences between the enthalpies of disproportionation corresponding to BQ{sup {sm bullet}{minus}} and NQ{sup {sm bullet}{minus}} are 51 and 14 kJ/mol in the gaseous and aqueous phases, respectively. The heats of hydration of BQ{sup {sm bullet}{minus}} and NQ{sup {sm bullet}{minus}} were determined with a convenient thermochemical cycle based on the enthalpies of disproportionation. The single-ion heats of hydration of BQ{sup {sm bullet}{minus}} and NQ{sup {sm bullet}{minus}} were found to be {minus}360 and {minus}377 kJ/mol, respectively. The heats of hydration of the net negative charge in BQ{sup {sm bullet}{minus}} and NQ{sup {sm bullet}{minus}} were found to be the same.

Progressive isomorphous incorporation of TiIV (or BIII) heteroatoms into the MFI structure of as-synthesized silicalite-1 caused a decrease in the amount of siloxy groups (anions), requisite for counter-balancing the structural directing agent (cation), as determined using 1H MAS NMR to quantify the silanol protons H-bonded to the siloxy oxygen. This revealed the negative charge on the incorporated heteroatoms, identifying them as TiO5 (or BO4) sites.

We report here the synthesis and binding studies of oligo-2'-deoxyribonucleotides (ODNs) containing 2'-deoxyuridines, modified at the 5-position by linkers ending with either one or two guanidinium groups. Comparison was made with ODNs containing 2'-deoxyuridines modified at the 5-position with linkers ending with either two or one amino groups. One or two modified 2'-deoxyuridines were incorporated into pyrimidine strands, and their influence on the stability of duplex (with both DNA and RNA targets) and triplex structures was studied. The strongest stabilization was obtained with modified ODNs containing guanidinium groups. This result confirms that the reduction of the global negative charge number on one strand is an important parameter in the stability of duplex and triplex structures.

Reconformation/reorientation of tethers on particles to minimize the energy of interaction, proposed as the mechanism for their deposition on similarly charged surfaces, has been confirmed using direct force measurements using atomic force microscopy. The force experienced by latex particles of net negative charge on negative glass surfaces, in the presence of the apparent energy barrier based on their ζ potential, is measured to monitor possible rearrangement of surface hairs to enable deposition of zwitterionic latexes while preventing that of the anionic ones.

The present report details the results of a high-level theoretical investigation of benzene−AlX3 and ethene−AlX3 (X = H, F, Cl) interactions. The binding energies, preferred modes of interaction of AlX3 with benzene and ethene, and vibrational frequencies for these complexes have been evaluated at the MP2 level using basis sets ranging from the 6-31+G* to the much larger (6-311++G(2df,p) + diffuse(d,p)). In the lowest energy conformers of the benzene complexes, the Al atom is directly placed over one of the benzene carbons, while in the ethene complexes, the Al atom lies above the center of the π bond. The binding energies of both the benzene and ethene complexes of AlX3 are dominated by electrostatic contributions, which is in contrast to the dominance of the electron correlation energy in the benzene−BX3 complexes. A very sharp increase in the negative charge of the benzene carbon closest to the Al atom in the lowest energy conformers of the benzene complexes from −0.2 to −0.4 au points to an important ...

In an attempt to ascertain whether acidity can be correlated with some molecular parameter, the charge distribution within 24 oxoacid molecules and their conjugate base anions were examined by calculating the partial positive or negative charge on each atom.

Entropy changes associated with the two half-reactions [Ni III L 2 ] 3+ +e − =[Ni II L 2 ] 2+ and [Ni III Y] 0 +e − =[Ni II Y] − (L=1,4,7-triazacyclononane, Y 3− =1,4,7-triazacyclononane-N,N',N″-triacetate have been determined through the investigation of the temperature dependence of the E 1/2 (Ni III /Ni II ) parameter over the 0.1-3.5 M concentration range of the background electrolyte (NaCl)

In connection with our studies on the nature of the forces operating in the combination of haptens with hapten-homologous antisera it became apparent that a study should be made of an antiserum prepared against a haptenic group containing two or more discrete negative charges, in order to determine the difference in combining power with this antibody of substances containing a single negative charge and substances containing two charges. Great specificity for the charged group has been observed for singly charged haptenic groups: thus benzenesulfonate ion and benzenearsonate ion were found not to combine with antibodies homologous to the benzoate ion group, and benzenesulfonate ion and benzoate ion were found not to combine with antibodies to the benzenearsonate ion group; but when the ions are very closely related, as are benzenephosphonate ion and benzenearsonate ion, there is appreciable cross reaction. We were interested to discover whether antibodies homologous to haptenic groups containing two charges would show greater or less specificity than was shown by these antibodies.

Oxygen in water is negative because a negative charge, unlike a positive, can be stabilized using ground state ionic resonance structures.