Hydrogen desorption exceeding ten weight percent from the new quaternary hydride Li3BN2H8

Mobile applications of hydrogen power have long demanded new solid hydride materials with large hydrogen storage capacities. We report synthesis of a new quaternary hydride having the approximate composition Li(3)BN(2)H(8) with 11.9 wt % theoretical hydrogen capacity. It forms by reacting LiNH(2) and LiBH(4) powders in a 2:1 molar ratio either by ball milling or by heating the mixed powders above 95 degrees C. This new quaternary hydride melts at approximately 190 degrees C and releases > or =10 wt % hydrogen above approximately 250 degrees C. A small amount of ammonia (2-3 mol % of the generated gas) is released simultaneously. Preliminary calorimetric measurements suggest that hydrogen release is exothermic and, hence, not easily reversible.     

Meta nitration of thiacalixarenes

Nitration of thiacalix[4]arene, immobilized in the 1,3-alternate conformation, leads regioselectively to meta-substituted products. Depending on the reaction conditions, mono- and dinitro-derivatives can be isolated in acceptable yields. This unique substitution pattern is inaccessible in classical calixarene chemistry, and yields inherently chiral compounds, which makes thiacalixarenes very attractive as building blocks or molecular scaffolds.     

Introducing an amine group to calix[5]arene: comparison of several methods

Abstract

Chemists often use an amine group as an intermediate in syntheses of imines, amides and ureas; however, in the case of syntheses of p-aminophenol type compounds, several problems might occur. In this article, we prepared p-aminocalix[5]arene-pentaol by reduction of both nitro and azo derivatives, and compared four methods of the amine preparation, focusing mainly on its gramme scale and time-consuming issues.     

Calculation of circular dichroism spectra from optical rotatory dispersion, and vice versa, as complementary tools for theoretical studies of optical activity using time-dependent density functional theory

A comparison of two theoretical methods based on time-dependent density functional theory for the calculation of the linear dispersive and absorptive properties of chiral molecules has been made. For this purpose, a recently proposed computational method for the calculation of circular dichroism (CD) spectra from the imaginary part of the optical rotation parameter has been applied to six rigid organic molecules. The results have been compared to the CD spectra obtained from the rotatory strengths and from the Kramers-Kronig transformation of optical rotatory dispersion (ORD) curves. We have also investigated a criterion based on the Kramers-Kronig integration formula to determine a number of excitations in truncated CD spectra which may yield a reasonable low frequency resonant ORD. It has been tested by calculating the ORD from the sum-over-states formula both in the nonresonant and resonant regions. Finally, we have applied these methods to model the resonant optical activity of proline at low pH.     

On the Initial Development of the Slip Band Near an Inclusion in the Interface

A problem is solved for a slip band near a rigid inclusion located in the interface between dissimilar half-spaces. The length of the slip band, the stress intensity near the inclusion apex, and the angle of band development depending on the loading and composition parameters are determined.     

S-alkylation of thiacalixarenes: how the regio- and stereoselectivities depend on the starting conformation

S-alkylation of all four thiacalix[4]arene conformations was accomplished using alkyl triflates. The corresponding sulfonium salts are formed in a highly regio- and stereoselective manner depending on the conformation used. Interestingly, only mono- or disubstituted sulfonium salts can be prepared. Although many regio- and stereoisomers are theoretically possible, only one dialkylated cone and 1,2-alternate derivatives were formed, while only a single isomer of monoalkylated partial cone and 1,3-alternate were isolated. The combination of experimental results with the quantum-chemical approach using the B3LYP/6-311G(d,p) method resulted in the elucidation of the rules governing the regio- and stereochemical outcomes of the alkylation reactions. All S-alkylated compounds represent a novel type of substitution pattern in calixarene chemistry showing the wide-ranging possibility of thiacalixarene skeleton modifications.     

Time dependent density functional theory modeling of chiroptical properties of small amino acids in solution

Time dependent density functional theory (TDDFT) and the conductor-like screening model (COSMO) of solvation were used to model the specific rotation and optical rotatory dispersion (ORD) of alanine, proline and serine solutions. Zwitterionic, cationic and anionic forms of amino acids were investigated and the results compared with experimental literature data obtained in neutral, acidic and basic conditions, respectively. It was found that TDDFT consistently underestimated the electronic excitation energies of the molecules, leading to calculated optical rotations that are of the correct sign but somewhat larger in magnitude than those of experiment. An additional challenge was encountered in the modeling of serine, an amino acid with a strong tendency to form intramolecular hydrogen bonds. The model used overestimated the extent of such hydrogen bonding for the zwitterions while possibly underestimating such bonding for the cationic form. This effect on the calculated mole fractions of the different conformers had an impact on the specific rotation.