The ammonia hydrates—model mixed-hydrogen-bonded systems

The three ammonia hydrates (ammonia dihydrate, ADH; ammonia monohydrate, AMH and ammonia hemihydrate, AHH) are amongst the simplest systems to contain mixed nitrogen oxygen–hydrogen bonds. In addition, ADH and AMH are believed to be common in the outer solar system, and their properties are important for modelling bodies such as Uranus, Neptune and Titan. Neutron diffraction studies have provided the first full information on structures at ambient pressure with detailed information on the H-bond geometry and state of hydrogen ordering. High-pressure studies of AMH reveal a rich and complex high-pressure phase diagram. This work reveals that ammonia hydrates are likely to provide a wide variety of geometries for the study of mixed H-bonds. It also provides new experimental information on which to base modelling of Titan.     

The mechanism of amine formation on Si(1 0 0) activated with chlorine atoms

The dissociation of NH₃ on a Si(1 0 0) surface activated with Cl atoms was investigated using X-ray photoelectron spectroscopy. Gas phase UV-Cl₂ (0.1-10 Torr Cl₂ for 10-600 s under 1000 W Xe lamp illumination) completely replaced the H-termination on aqueous-cleaned Si(1 0 0) with 0.82 ± 0.06 ML of Cl at 298 K. A single spin-orbit split Cl 2p doublet indicated that the Cl atoms were bound to Si dimer atoms, forming silicon monochloride (Cl-Si-Si-Cl). Exposing the Cl-terminated surface at 348 K to NH₃ (1-1000 Torr for 5-60 min) replaced one Cl atom with one N atom up to a coverage of 0.33 ± 0.02 ML. Cl atoms lowered the activation energy barrier for reaction to form a primary amine (Si-NH₂). Oxygen was coadsorbed due to competition by H₂O contamination. The presence of Cl on the surface even after high NH₃ exposures is attributed to site blocking and electrostatic interactions among neighboring Cl-Si-Si-NH₂ moieties. The results demonstrate a low temperature reaction pathway for depositing N-bearing molecules on Si surfaces.     

The thermodesorption mechanism of ammonia from Ru(0 0 0 1)

Thermodesorption rates for the desorption of ammonia from Ru(0 0 0 1) are calculated by Transition State Theory including small curvature tunneling corrections. The potential energy surface is derived on a model cluster employing hybrid density functional theory (B3LYP). Two desorption pathways can be identified, just distinguished by the orientation of the leaving ammonia entity. It is found that the rate dominating mechanism comprises an umbrella-like flipping movement of the hydrogen atoms during the desorption. Nevertheless tunneling does not play any significant role in the reaction as the hydrogen movements are shown to occur at the low energy regions of the barrier.     

Molecular theory of phase equilibria in model and real associated mixtures III. Binary solutions of inert gases and n-alkanes in ammonia and methanol

Using new molecular models of ammonia and methanol and thermodynamic perturbation theory, the global phase diagrams of model mixtures of these compounds with a van der Waals fluid, representing a simple nonpolar fluid, have been calculated. The global phase diagram of these mixtures is much richer than that of corresponding aqueous mixtures. More types of critical line behavior are found, including the presence of van Laar points and a small region where the mixtures exhibit a closed liquid-liquid immiscibility loop (Type VI phase behavior). The individual mixture components are characterized by two molecular parameters, which can be adjusted to their critical temperature and critical volume; the mixture model itself contains no adjustable parameters. It is shown that the theory gives qualitatively correct predietions of mixtures with n-alkanes. This includes the prediction of Type III critical line behavior for small and large values of the ratio of the critical temperatures of the components, and Type II over a large range of conditions, including the presence or absence of absolute or limited azeotropy, and temperature and pressure extrema of critical lines and their dependence on the number of carbon atoms.     

1，1’－联－2－萘酚硼烷的辛可宁和麻黄碱衍生物的合成

１，１’－联－２－萘酚硼烷的辛可宁和麻黄碱衍生物的合成单自兴，孙杰，段标，杨洗，赵德杰（武汉大学化学系，武汉，４３００７２）关键词１，１’－联－２－萘酚，硼烷，辛可宁，麻黄碱，硼烷配合物，合成中国法分类号Ｏ６２７·３１ｌ，ｌ’一联一２一条酚在大环化学...     

Measurements of NH3 in the ν2 = 1 state by a solid-state, photomixing, THz spectrometer, and a simultaneous analysis of the microwave, terahertz, and infrared transitions between the ground and ν2 inversion-rotation levels

In this paper, we report 30 THz measurements of ammonia in its excited, ν₂ = 1, inversion state. These measurements include transition frequencies and pressure shifts (where significant enough to be observed). Included in the data are two forbidden and three ro-inversion transitions, as well as 18 transitions never directly measured before. The measurements were made with an all-solid-state, diode-laser, difference-frequency spectrometer. Using an innovative laser-frequency locking scheme, this spectrometer provided accurately determined and continuously tuned THz-frequencies without requiring accurate knowledge of the absolute laser frequencies. The details of the spectrometer’s frequency calibration is discussed. A global analysis of NH₃ based on the available ground state, ν₂ = 1 state, and ν₂-band transitions was carried out, and the resulting set of recommended molecular effective-Hamiltonian parameters for ammonia is presented. In addition, calculated center frequencies and intensities for all possible transitions up to J = 20 between rotation, inversion, and vibration levels in the ground and ν₂ = 1 states are included as supplementary material.     

Synthesis of a boronated amino acid as a potential neutron therapy agent: 1-amino-3-[(dihydroxyboryl)ethyl]cyclobutanecarboxylic acid

A novel boronated aminocyclobutanecarboxylic acid was synthesized in 10 steps for potential use in neutron capture therapy. The molecule was modeled after the unnatural amino acid 1-aminocyclobutanecarboxylic acid, which has shown high uptake in brain tumors.     

二乙胺合三(5-甲基-2-苯并噻唑基)硼烷的晶体结构

标题化合物二乙胺合三（５－甲基－２－苯并噻唑基）硼烷（Ｃ２８Ｈ２９ＢＮ４Ｓ３（Ｍｒ＝５２７．５７）的晶体属于三斜晶系，空间群为Ｐ１，晶胞参数ａ＝０．３９７（８）ｎｍ，ｂ＝１．１７４２（６）ｎｍ，ｃ＝１．３１００（２）ｎｍ，α＝１０４．２９（２）°，β＝９２．９９（３）°，γ＝９８．５８（５）°，Ｖ＝１．３７９０ｎｍ３，Ｚ＝２，Ｄｃ＝１．２７０ｇ／ｃｍ３，μ（ＭｏＫα）＝２．８０４ｃｍ－１．结构的偏离因子Ｒ＝０．０６４８，Ｒｗ＝０．０７３７．结构测定表明，甲基取代基的电子效应导致硼碳键键长的平均化，预示杂环对硼原子的π－电子反馈与胺基氮原子对硼原子的反馈有彼消此长的关系．     

The Role of Free N‐Heterocyclic Carbene (NHC) in the Catalytic Dehydrogenation of Ammonia–Borane in the Nickel NHC System

Enders' N‐heterocyclic carbene (NHC) dehydrogenates ammonia–borane with a relatively low barrier, producing NH₂BH₂ and NHC–(H)₂. The nickel NHC catalyst present in the reaction media can activate the NHC–(H)₂ produced to regenerate the free NHC and release H₂. The release of free NHC enables further dehydrogenation of ammonia–borane.