In Situ IR Spectroscopic Studies on Molybdenum Nitride Catalysts: Active Sites and Surface Reactions

Recent IR spectroscopic studies on the surface properties of fresh Mo₂N/mg src="/content/r3106273m88h392r/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ catalyst are presented in this paper. The surface sites of fresh Mo₂N/mg src="/content/r3106273m88h392r/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃, both Mo^{mg src="/content/r3106273m88h392r/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">+} (0<mg src="/content/r3106273m88h392r/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0"><2) and N sites, are probed by CO adsorption. Two characteristic IR bands were observed at 2045 and 2200 cm^-1, due to linearly adsorbed CO on Mo and N sites, respectively. The surface N sites are highly reactive and can react with adsorbed CO to form NCO species. Unlike adsorbed CO on reduced passivated one, the adsorbed CO on fresh Mo₂N/mg src="/content/r3106273m88h392r/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ behaves similarly to that of group VIII metals, suggesting that fresh nitride resembles noble metals. It is found that the surface of Mo nitrides slowly transformed into sulfide under hydrotreating conditions, which could be the main reason for the activity drop of molybdenum nitride catalysts in the presence of sulfur-containing species. Some surface reactions, such as selective hydrogenation of 1,3-butadiene, isomerization of 1-butene, and hydrodesulfurization of thiophene, were studied on both fresh and reduced passivated Mo₂N/mg src="/content/r3106273m88h392r/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ catalysts using IR spectroscopy. The mechanisms of these reactions are proposed. The adsorption and reaction behaviors of these molecules on fresh molybdenum nitride also resemble those on noble metals, manifesting the unique properties of fresh molybdenum nitride catalysts. Mo and N sites are found to play different roles in the adsorption and catalytic reactions on the fresh Mo₂N/mg src="/content/r3106273m88h392r/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Al₂O₃ catalyst. Generally, Mo sites are the main active sites for the adsorption and reactions of adsorbates; N sites are not directly involved in catalytic reactions but they modify the electronic properties of Mo sites.     

Highly conformationally constrained halogenated 6-spiroepoxypenicillins as probes for the bioactive side-chain conformation of benzylpenicillin

Summary The halogenated 6-spiroepoxypenicillins are a series of novel semisyntheticmg src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-lactam compounds with highly conformationally restricted side chains incorporating an epoxide. Their biological activity profiles depend crucially on the configuration at position C-3 of that epoxide. In derivatives with aromatic-containing side chains, e.g., anilide, the 3R-compounds possess notable Gram-positive antibacterial activity and potentmg src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-lactamase inhibitory properties. The comparable 3S-compounds are antibacterially inactive, but retainmg src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-lactamase inhibitory activity.Using the molecular simulation programs COSMIC and ASTRAL, we attempted to map a putative, lipophilic accessory binding site on the PBPs that must interact with the side-chain aromatic residue. Comparative computer-assisted modelling of the 3R, and 3S-anilides, along with benzylpenicillin, indicated that the available conformational space at room temperature for the side chains of the 3R and the 3S-anilides was mutually exclusive. The conformational space for the more flexible benzylpenicillin could accommodate the side chains ofboth the constrained penicillin derivatives. By a combination of van der Waals surface calculations and a pharmacophoric distance approach, closely coincident conformers of the 3R-anilide and benzylpenicillin were identified. These conformers must be related to the antibacterial, mg src="/content/m85x27l4758x6745/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">bioactivemg src="/content/m85x27l4758x6745/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> conformer for the classicalmg src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-lactam antibiotics. From these proposed bioactive conformations, a model for the binding of benzylpenicillin to the PBPs relating the three-dimensional arrangement of a putative lipophilic S₂-subsite, specific for the side-chain aromatic moiety, and the 3mg src="/content/m85x27l4758x6745/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-carboxylate functionality is presented.This work has been reported in preliminary form at the 4th Royal Society of Chemistry International Symposium on Recent Advances in the Chemistry ofmg src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-lactam Antibiotics, Churchill College, Cambridge, U.K., 3&amp;#x2013;6 July 1988.     

RNA Methylation m6A: A New Code and Drug Target?

The m⁶A‐RNA modification is a dynamic and reversible process, which has emerged as a new RNA code for the regulation of gene expression. The functional network of methyltransferases (writers), demethylases (erasers), and binding proteins (readers) modulate the level of m⁶A modification. Dysfunction of RNA methylation has been associated with various fundamental biological processes and human diseases. Herein, we briefly introduce an understanding‐enabled manipulation on m⁶A‐RNA modification with an emphasis on the use of small‐molecule intervention. mg alt="image" class="section_image" src="/cms/asset/78669a23-1265-42a2-befe-65bb28293d15/cjoc201900490-gra-0001.png">     

Reaction of 4,4′-dimethyldiphenyl ether with phosphorus trichloride in the presence of anhydrous aluminum chloride

The reaction of 4,4mg src="/content/x2m7215863766042/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">-dimethyldiphenyl ether with phosphorus trichloride in the presence of anhydrous aluminum chloride was studied. This reaction affords 2,8-dimethyl-10H-10mg src="/content/x2m7215863766042/xxlarge955.gif" alt="lambda" align="BASELINE" BORDER="0">⁵-phenoxaphosphine 10-oxide as virtually the only product. In air, the latter in an alkaline solution is quantitatively transformed into 10-hydroxy-2,8-dimethyl-10H-10mg src="/content/x2m7215863766042/xxlarge955.gif" alt="lambda" align="BASELINE" BORDER="0">⁵-phenoxaphosphine 10-oxide.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2762&amp;#x2013;2765, December, 2004.     

All-Solid-State PVC Membrane Ag+-Selective Electrodes Based on Diaza-18-Crown-6 Compounds

Two diaza-crown ether compounds were synthesized and evaluated as Ag⁺-selective carriers in polyvinylchloride (PVC) membrane electrodes of solid-state type. The all-solid-state PVC membrane electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 exhibited a super-Nernstian response (75&amp;plusmn;10mg src="/content/m6d5ltjf7br53l8v/xxlarge8201.gif" alt="thinsp" align="MIDDLE" BORDER="0">mV per decade) over the concentration range of 1&amp;times;10^{&amp;#x2013;1} to 7&amp;times;10^{&amp;#x2013;6}mg src="/content/m6d5ltjf7br53l8v/xxlarge8201.gif" alt="thinsp" align="MIDDLE" BORDER="0">M of Ag⁺ ion and a detection limit of 3&amp;times;10^{&amp;#x2013;6}mg src="/content/m6d5ltjf7br53l8v/xxlarge8201.gif" alt="thinsp" align="MIDDLE" BORDER="0">M, at a wide range of pH (pH 4&amp;#x2013;7). The response time of the electrode was fast (less than mg src="/content/m6d5ltjf7br53l8v/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">10s), and it can be used for three months without any significant deviation in potential. The proposed all-solid-state PVC membrane electrodes revealed high selectivity toward Ag⁺ ion with respect to alkali, alkaline earth, heavy and transition metal ions. A flow-through cell of all-solid-state PVC membrane Ag⁺-selective electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 has also been prepared and applied for flow-injection analysis of Ag⁺ ion in solution.     

双峰倍增配平法用于同步、导数-同步荧光法同时测定邻羟基苯甲酸和间羟基苯甲酸

邻羟基苯甲酸（ｏＨＢＡ）和间羟基苯甲酸（ｍＨＢＡ）荧光光谱严重重叠，同步及导数技术虽使选择性有所改善，但仍不能完全分辨开重叠谱。用双峰倍增配平计算法结合同步、一阶导数－同步荧光法对双组分体系（邻羟基苯甲酸／间羟基苯甲酸，ｐＨ１２介质）同时测定。结合计算的两种测定方法精密度、回收率和不同组分间浓度比范围均优于一阶导数－同步荧光法。     

Isomerisierung bei der Komplexbildung von 3-Acetyl-tetramsäure: Struktur und magnetische Eigenschaften des CuII- und NiII-Komplexes von 2,7-Bis(1′, 5′, 5′-trimethylpyrrolidin-2′, 4′-dion-3′ -yl)-3, 6-diazaocta-2, 6-dien

Isomerization at the Complexation of 3-Acetyltetramic Acid: Structure and Magnetic Properties of the Cu^II- and Ni^II-Complex of 2,7-Bis (1′, 5′, 5′ -trimethylpyrrolidin-2′,4′ -dion-3′ -yl)-3,6-diazaocta-2,6-dien 2,7-Bis(1′, 5′, 5′ -trimethylpyrrolidin-2′, 4′ -dion-3′ -yl)-3,6-diazaoctadien formes Cu^II and Ni^II complexes with different constitutions (because of the Z/E isomerization). Results of X-ray analysis of N,N′ -ethylenbis(1′, 5′, 5′ -trimethylpyrrolidin-2′, 4′ -dion-3′ -acetiminato)nickel(II) 1 respectively -copper(II) 2 shows, that the complexing agent in 1 occurs in the E-form, whereas the ligand of the Cu^II complex forms the Z-form. Magnetic susceptibility and shift effects of the ¹³C-NMR signals point to a weak paramagnetism of the Ni^II complex. ESR-spectra are obtained from 2 only. Furthermore, the Cu^II complex reduces the relaxation times T₁ and T₂ of ¹H and ¹⁷O nuclei spins from water. From the temperature dependence of the shortening of the relaxation times an activation energy is calculated which describes the reorientation of the copper complex in the “water matrix”.     

Organoruthenaborane Chemistry. X. The SM2-catalysed formation of [ l-(η6-C6Me6)-isocloso-RuB9H9], and some B-phenylamino derivatives. NMR and X-ray diffraction studies

The action of SMe₂ on the ten-vertex nido-ruthenaborane [6-(η⁶-C₆Me₆)RuB₉H_l3] ( 1 ) provides a high-yield route to the unsubstituted isocloso-ruthenaborane [1-(η⁶-C₆Me₆)RuB₉H₉] (2). The benzene analogue [1-(η⁶-C₆Me₆)RuB₉H₉] is prepared similarly. By contrast, reaction of (1) with PhNH₂ gives a variety of B-phenylamino isocloso derivatives, including orange crystals of [1-(η⁶-C₆Me₆)-2-(PhNH)-isocloso-1-RuB 9 H₈] ( 3 ), red-orange [1-(η⁶-C₆Me₆)-2,3-(PhNH)₂-isocloso-1-RuB₉H₇] ( 4 ) and dark-red [1-(η⁶-C₆Me₆)-5,6,7-(PhNH)₃-isocloso-1-RuB₉H₆] ( 5 ). Detailed ¹H and ¹¹B nmr properties of these various compounds are described. The structure of ( 3 ) has been established by a single-crystal X-ray diffraction study of the solvate [1-(η⁶-C₆Me₆)-2-(PhNH)-isocloso-1-RuB₉H₈] · 1/2 CH₂Cl₂; the crystals were monoclinic, space group C2/c, with a = 1895.1(3), b = 1556.6(3), c = 1716.4(3) pm, β = 104.37(1)° and z = 8.     

An investigation of microbore reverse-phase columns containing 3 μm packing materials

A procedure for packing 15 cm × 1 mm id reverse-phase microbore columns with 3 μm silicas obtained from different manufacturers is described. The speed of analysis and detection limits are compared to those obtained with a 50 cm × 1 mm id column packed with 10 μm ODS. The effect of detector time constant on the system, and flow rates on column efficiency are also examined.