One electron less or one proton more: how do they differ?

From the NIST website and the literature, we have collected the Ionisation Energies (IE) of 3,052 and the Proton Affinities (PA) of 1,670 compounds. For 614 of these, both the IE and PA are known; this enables a study of the relationships between these quantities for a wide variety of molecules. From the IE and PA values, the hydrogen atom affinities (HA) of molecular ions M^?+ may also be assessed. The PA may be equated to the heterolytic bond energy of [MH]⁺ and HA to the homolytic bond energy. Plots of PA versus IE for these substances show (in agreement with earlier studies) that, for many families of molecules, the slope of the ensuing line is less negative than ?1, i.e. changes in the PA are significantly less than the concomitant opposite changes in IE. At one extreme (high PA, low IE) are the metals, their oxides and hydroxides, which show a slope of close to ?1, at the other extreme (low PA, high IE) are the hydrogen halides, methyl halides and noble gases, which show a slope of ca. ?0.3; other molecular categories show intermediate behaviour. One consequence of a slope less negative than ?1 is that the changes in ionic enthalpies of the protonated species more closely follow the changes in the enthalpies of the neutral molecules compared with changes in the ion enthalpies of the corresponding radical cations. This is consistent with findings from ab initio calculations from the literature that the incoming proton, once attached to the molecule, may retain a significant amount of its charge. These collected data allow a comparison of the thermodynamic stability of protonated molecules in terms of their homolytic or heterolytic bond cleavages. Protonated nitriles are particularly stable by virtue of the very large hydrogen atom affinities of their radical cations.     

Chemical Synthesis and Immunological Evaluation of a Pentasaccharide Bearing Multiple Rare Sugars as a Potential Anti‐pertussis Vaccine

With the infection rate of Bordetella pertussis at a 60‐year high, there is an urgent need for new anti‐pertussis vaccines. The lipopolysaccharide (LPS) of B. pertussis is an attractive antigen for vaccine development. With the presence of multiple rare sugars and unusual glycosyl linkages, the B. pertussis LPS is a highly challenging synthetic target. In this work, aided by molecular dynamics simulation and modeling, a pertussis‐LPS‐like pentasaccharide was chemically synthesized for the first time. The pentasaccharide was conjugated with a powerful carrier, bacteriophage Qβ, as a vaccine candidate. Immunization of mice with the conjugate induced robust anti‐glycan IgG responses with IgG titers reaching several million enzyme‐linked immunosorbent assay (ELISA) units. The antibodies generated were long lasting and boostable and could recognize multiple clinical strains of B. pertussis, highlighting the potential of Qβ‐glycan as a new anti‐pertussis vaccine.     

Reactivity studies on Fe(III)-(O2(2-))-Cu(II) compounds: influence of the ligand architecture and copper ligand denticity

Heme-Cu/O2 adducts are of interest in the elucidation of the fundamental metal-O2 chemistry occurring in heme-Cu enzymes which effect reductive O-O cleavage of dioxygen to water. In this report, the chemistry of four heme-peroxo-copper [FeIII-(O22-)-CuII]+ complexes (1-4), varying in their ligand architecture, copper-ligand denticity, or both and thus their structures and physical properties are compared in their reactivity toward CO, PPh3, acids, cobaltocene, and phenols. In 1 and 2, the copper(II) ligand is N4-tetradentate, and the peroxo unit is bound side-on to iron(III) and end-on to the copper(II). In contrast, 3 and 4 contain a N3-tridentate copper(II) ligand, and the peroxo unit is bound side-on to both metal ions. CO "displaces" the peroxo ligand from 2-4 to form reduced CO-FeII and CO-CuI species. PPh3 reacts with 3 and 4 displacing the peroxide ligand from copper, forming (porphyrinate)FeIII-superoxide plus CuI-PPh3 species. Complex 2 does not react with PPh3, and surprisingly, 1 reacts neither with PPh3 nor CO, exhibiting remarkable stability toward these reagents. The behavior of 1 and 2 compared to that of 3 and 4 correlates with the different denticity of the copper ligand (tetra vs tridentate). Complexes 1-4 react with HCl releasing H2O2, demonstrating the basic character of the peroxide ligand. Cobaltocene causes the two-electron reduction of 1-4 giving the corresponding micro-oxo [FeIII-(O2-)-CuII]+ complexes, in contrast to the findings for other heme-peroxo-copper species of different design. With t-butyl-substituted phenols, no reaction occurs with 1-4. The results described here emphasize how ligand design and variations influence and control not only the structure and physical properties but also the reactivity patterns for heme-Cu/O2 adducts. Implications for future investigations of protonated heme/Cu-peroxo complexes, low-spin analogues, and ultimately O-O cleavage chemistry are discussed.     

Nanoscale protein pores modified with PAMAM dendrimers

We describe nanoscale protein pores modified with a single hyperbranched dendrimer molecule inside the channel lumen. Sulfhydryl-reactive polyamido amine (PAMAM) dendrimers of generations 2, 3 and 5 were synthesized, chemically characterized, and reacted with engineered cysteine residues in the transmembrane pore alpha-hemolysin. Successful coupling was monitored using an electrophoretic mobility shift assay. The results indicate that G2 and G3 but not G5 dendrimers permeated through the 2.9 nm cis entrance to couple inside the pore. The defined molecular weight cutoff for the passage of hyperbranched PAMAM polymers is in contrast to the less restricted accessibility of flexible linear poly(ethylene glycol) polymers of comparable hydrodynamic volume. Their higher compactness makes sulfhydryl-reactive PAMAM dendrimers promising research reagents to probe the structure of porous membrane proteins with wide internal diameters. The conductance properties of PAMAM-modified proteins pores were characterized with single-channel current recordings. A G3 dendrimer molecule in the channel lumen reduced the ionic current by 45%, indicating that the hyperbranched and positively charged polymer blocked the passage of ions through the pore. In line with expectations, a smaller and less dense G2 dendrimer led to a less pronounced current reduction of 25%. Comparisons to recordings of PEG-modified pores revealed striking dissimilarities, suggesting that differences in the structural dynamics of flexible linear polymers vs compact dendrimers can be observed at the single-molecule level. Current recordings also revealed that dendrimers functioned as ion-selectivity filters and molecular sieves for the controlled passage of molecules. The alteration of pore properties with charged and hyperbranched dendrimers is a new approach and might be extended to inorganic nanopores with applications in sensing and separation technology.     

An acoustically enhanced gold film Raman sensor on a lithium niobate substrate

The surface enhanced Raman scattering effect has shown immense potential for detecting trace amounts of explosive vapor molecules. To date, efforts to produce a commercially available, reliable SERS sensor have been impeded by an inability to separate the electromagnetic enhancement produced by the metallic nanostructure from other signal enhancing effects. Here, we show a new Raman sensor that uses surface acoustic waves (SAWs) to produce controllable surface structures on gold films deposited on LiNbO₃ substrates that modulate the Raman signal of a target compound (thiophenol) adsorbed on the films. We demonstrate that this sensor can dynamically control the Raman signal simply by changing the SAW's amplitude, allowing the Raman signal enhancement factor to be directly measured with no variation in the concentration of the target compound. The physically adsorbed molecules can be removed from the sensor without physical cleaning or damage, making it possible to reuse it for real‐time Raman detection. Copyright © 2014 John Wiley & Sons, Ltd.     

Phase diagram of the D3/D5 system in a magnetic field and a BKT transition

We study the full temperature and chemical potential dependence of the D3/D5 2+1$2+1$-dimensional theory in the presence of a magnetic field. The theory displays separate transitions associated with chiral symmetry breaking and melting of the bound states. We display the phase diagram which has areas with first and second order transitions meeting at two critical points similar to that of the D3/D7 system. In addition there is the recently reported BKT transition at zero temperature leading to distinct structure at low temperatures.     

Liquid electrolytes for dye-sensitized solar cells

The present review offers a survey of liquid electrolytes used in dye-sensitized solar cells from the beginning of photoelectrochemical cell research. It handles both the solvents employed, and the prerequisites identified for an ideal liquid solvent, as well as the various effects of electrolyte solutes in terms of redox systems and additives. The conclusions of the present review call for more detailed molecular insight into the electrolyte-electrode interface reactions and structures.     

Synthesis of substituted isoquinolines via Pd-catalyzed cross-coupling approaches

Palladium complexes incorporating ligands based on a 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantanyl scaffold were used to catalyze the arylation of ethyl cyanoacetate, malononitrile, and various ketones. The products from these reactions can be elaborated to substituted β-arylethylamines and used in microwave-assisted Pictet-Spengler reactions. The protocol developed is suitable for the synthesis of libraries of substituted isoquinolines.     

Affinity‐Based Drug Delivery

Affinity‐based drug delivery systems utilize interactions between the therapeutic drug and the delivery system to manipulate drug loading and to control drug release. In this paper, affinity‐based drug delivery system syntheses, types of therapeutic factors delivered, and delivery system loading and release are discussed in detail. The paper is divided into three subsections, based on the type of delivery system: molecular imprinting systems, growth‐factor delivery, and cyclodextrin‐based delivery. The objective of this paper is to examine the current state of research, highlight the breakthroughs and challenges, point out potential impacts of this relatively new technology, and explore future developmental areas.

     

Protein side chain modeling with orientation-dependent atomic force fields derived by series expansions

We describe the development of new force fields for protein side chain modeling called optimized side chain atomic energy (OSCAR). The distance‐dependent energy functions (OSCAR‐d) and side‐chain dihedral angle potential energy functions were represented as power and Fourier series, respectively. The resulting 802 adjustable parameters were optimized by discriminating the native side chain conformations from non‐native conformations, using a training set of 12,000 side chains for each residue type. In the course of optimization, for every residue, its side chain was replaced by varying rotamers, whereas conformations for all other residues were kept as they appeared in the crystal structure. Then, the OSCAR‐d were multiplied by an orientation‐dependent function to yield OSCAR‐o. A total of 1087 parameters of the orientation‐dependent energy functions (OSCAR‐o) were optimized by maximizing the energy gap between the native conformation and subrotamers calculated as low energy by OSCAR‐d. When OSCAR‐o with optimized parameters were used to model side chain conformations simultaneously for 218 recently released protein structures, the prediction accuracies were 88.8% for χ₁, 79.7% for χ_{1 + 2}, 1.24 Å overall root mean square deviation (RMSD), and 0.62 Å RMSD for core residues, respectively, compared with the next‐best performing side‐chain modeling program which achieved 86.6% for χ₁, 75.7% for χ_{1 + 2}, 1.40 Å overall RMSD, and 0.86 Å RMSD for core residues, respectively. The continuous energy functions obtained in this study are suitable for gradient‐based optimization techniques for protein structure refinement. A program with built‐in OSCAR for protein side chain prediction is available for download at http://sysimm.ifrec.osaka‐u.ac.jp/OSCAR/ . © 2011 Wiley Periodicals, Inc. J Comput Chem 2011