Synthesis of a peptide nucleic acid with a novel 1‐methyl‐6‐mercaptopurine base

A novel peptide nucleic acid (PNA) monomer 16 containing a novel 1‐methyl‐6‐mercaptopurine base was synthesized by coupling the in situ generated acid chloride of (1‐methyl‐6‐mercaptopurin‐9‐yl)acetic acid ( 6 ) into an L‐lysine backbone ( 13 ) using 10% CCl₄ in pyridine and Ph₃P. Compound 6 was synthesized from 6‐mercapto‐1‐methylpurine and ethylbromoacetate in the presence of NaH followed by alkaline hydrolysis and subsequent neutralization with a cation exchange resin. The L‐lysine backbone ( 13 ) was obtained by the reaction of N?‐CBZ‐L‐lysine allyl ester with Boc‐aminoactaldehyde in the presence of NaBH₃CN under reductive amination conditions. Oligomerization of the monomer 16 to PNA analogues was achieved using BOC‐BHA‐PEG‐PS resin as a solid support and the in situ generated acid chloride of 16 by 10% CCl₄ in DCM in the presence of Ph₃P.     

Advanced High‐Voltage Aqueous Lithium‐Ion Battery Enabled by “Water‐in‐Bisalt” Electrolyte

A new super‐concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra‐high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO₂ as the anode material, and a 2.5 V aqueous Li‐ion cell based on LiMn₂O₄ and carbon‐coated TiO₂ delivered the unprecedented energy density of 100 Wh kg^?1 for rechargeable aqueous Li‐ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the “water‐in‐salt” electrolyte further pushed the energy densities of aqueous Li‐ion cells closer to those of the state‐of‐the‐art Li‐ion batteries.     

Molecular-thermodynamic theory of micellization of multicomponent surfactant mixtures: 1. Conventional (pH-Insensitive) surfactants

A molecular-thermodynamic (MT) theory was developed to model the micellization of mixtures containing an arbitrary number of conventional (pH-insensitive) surfactants. The theory was validated by comparing predicted and experimental cmc's of ternary surfactant mixtures, yielding results that were comparable to, and sometimes better than, the cmc's determined using regular solution theory. The theory was also used to model a commercial nonionic surfactant (Genapol UD-079), which was modeled as a mixture of 16 surfactant components. The predicted cmc agreed well with the experimental cmc, and the monomer concentration was predicted to increase significantly above the cmc. In addition, the monomer and the micelle compositions were predicted to vary significantly with surfactant concentration. These composition variations were rationalized in terms of competing steric and entropic effects and a micelle shape transition near the cmc. To understand the packing constraints imposed on ternary surfactant mixtures better, the maximum micelle radius was also examined theoretically. The MT theory presented here represents the first molecular-based theory of the micellization behavior of mixtures of three or more conventional surfactants. In article 2 of this series, the MT theory will be extended to model the micellization of mixtures of conventional and pH-sensitive surfactants.     

Superatom compounds, clusters, and assemblies: ultra alkali motifs and architectures

It has recently been demonstrated that chosen clusters of specific size and composition can exhibit behaviors reminiscent of atoms in the periodic table and hence can be regarded as superatoms forming a third dimension. An Al(13) cluster has been shown to mimic the behavior of halogen atoms. Here, we demonstrate that superatom compounds formed by combining superhalogens (Al(13)) with superalkalis (K(3)O and Na(3)O) can exhibit novel chemical and tunable electronic features. For example, Al(13)(K(3)O)3 is shown to have low first and second ionization potentials of 2.49 and 4.64 eV, respectively, which are lower than alkali atoms and can be regarded as ultra alkali motifs. Al(13)K(3)O is shown to be a strongly bound molecule that can be assembled into stable superatom assemblies (Al(13)K(3)O)n with Al(13) and K(3)O as the superatom building blocks. The studies illustrate the potential of creating new materials with an unprecedented control on physical and electronic properties.     

On the role of water in intermolecular proton-transfer reactions

We study the mechanism of proton transfer (PT) between the photoacid (8-hydroxy-1,3,6-pyrenetrisulfonic acid (HPTS)) and the base acetate in aqueous solution using femtosecond vibrational spectroscopy. By probing the vibrational resonances of the photoacid, the accepting base, and the hydrated proton we find that intermolecular PT in this model system involves the transfer of the proton across several water molecules linking the donor-acceptor pair by hydrogen bonds (H-bonds). We find that at high base concentration the rate of PT is not determined by the mutual diffusion of acid and base but rather by the rate of Grotthuss-like conduction of the proton between molecules. This long-range PT requires an activated solvent configuration to facilitate the charge transfer.     

Selectivity enhancement of anion-responsive electrodes by pulsed chronopotentiometry

A large and robust selectivity improvement of ion-selective electrodes is presented for the measurement of abundant ions. An improvement in selectivity by more than two orders of magnitude has been attained for the hydrophilic chloride ions measured in a dilute background of the lipophilic ions perchlorate and salicylate in a pulsed chronopotentiometric measurement mode. This is attributed to a robust kinetic discrimination of the dilute lipophilic ions in this measuring mode, which is not possible to achieve in classical potentiometry. Maximum tolerable concentrations of the interfering ions are found to be on the order of 30 μM before causing substantial changes in potential. As an example of practical relevance, the robust detection of chloride in 72 μM salicylate (reflecting 1:10 diluted blood) with a detection limit of 0.5 mM chloride is demonstrated. Corresponding potentiometric sensors did not give a useful chloride response under these conditions.