Molecular sieve catalysts for the regioselective and shape- selective oxyfunctionalization of alkanes in air

Discrete Water Hexamers and Template-Assisted Molecular Recognition in an Elastic Zincophosphate Lattice

Water molecules and terephthalic acid, respectively, exist as a self-assembled monolayer of cyclic (H2O)6 clusters and (TA)infinity chiral chains between the zincophosphate sheets (in blue wires); the irremovable template H3tren3+ ions (in purple wires) are dynamic and could translate back and forth on the sheets during the conversion of the supramolecule contained in one another.

Fine-Tuning the Electronic Properties of Highly Stable Organometallic CuIII Complexes Containing Monoanionic Macrocyclic Ligands

A family of highly stable organometallic Cu(III) complexes with monoanionic triazamacrocyclic ligands (L(i)) with general formula [CuL(i)]+ have been prepared and isolated, and their structural, spectroscopic, and redox properties thoroughly investigated. The HL(i) ligands have been designed in order to understand and quantify the electronic effects exerted by electron donor and electron-withdrawing groups on either the aromatic ring or the central secondary amine or on both. In the solid state the Cu(III) complexes were mainly characterized by single-crystal X-ray diffraction analysis, whereas in solution their structural characterization was mainly based on 1H NMR spectroscopy given the diamagnetic nature of the d(8) square-planar Cu(III) complexes. Cyclic voltammetry together with 1H NMR and UV/Vis spectroscopy have allowed us to quantify the electronic effects exerted by the ligands on the Cu(III) metal center. A theoretical analysis of this family of Cu(III) complexes has also been undertaken by DFT calculations to gain a deeper insight into the electronic structure of these complexes, which has in turn allowed a greater understanding of the nature of the UV/Vis transitions as well as the molecular orbitals involved.

Assembly of Helical Hydrogen Bonds in a New Layered Aluminophosphate [C6N3H17][Al2(HPO4)(PO4)2]

A new layered aluminophosphate, [C6N3H17][Al2(HPO4)(PO4)2] (denoted AlPO-CJ21), has been prepared in an alcoholic system by the use of N-(2-aminoethyl)-piperazine (AEPP) as the template. Its inorganic layer containing a series of bridged six-membered rings (MRs) is a new type of 4.6-net sheet built up from AlO4, PO2(OH)(=O), and PO3(=O) tetrahedra. Interestingly, inorganic helical chains of right- or left-handedness are presented in the aluminophosphate layers, and fascinating hydrogen-bonded helices are self-assembled under solvothermal conditions between organic templates and inorganic sheets via strong hydrogen bondings of O...N atoms. Crystal data: monoclinic, P2(1) (No. 4), a = 10.069(2) A, b = 8.0875(16) A, c = 10.598(2) A, beta = 94.71(3) degrees, z = 2, R(1) = 0.0325 [I > 2sigma(I)], and wR(2) = 0.0807 (all data); Flack parameter: 0.03.

A sol-gel method using acetic anhydride in the presence of cholesterol in organic solution media: preparation of silicas that recognize steroid hormones

Silicas were prepared by a sol-gel method from tetraethoxysilane and acetic anhydride in the presence of cholesterol in organic solution media. Some silicas had higher pore volumes than silicas obtained in the absence of cholesterol. The adsorption abilities by these silicas were compared using various compounds in benzene solution. Although no clear difference among their adsorptions of cholesterol was observed, progesterone and other analogous steroid hormones were well adsorbed by silicas prepared in the presence of cholesterol, especially, prepared with n-heptane as an additional solvent. This silica adsorbed steroid hormones more selectively than other analogous compounds such as bisphenol A and hexestrol. On the other hand, a silica prepared by the usual aqueous sol-gel method with cholesterol had no clear adsorption selectivity to steroid hormones. Furthermore, no selective adsorption of steroid hormones was observed in the case of a common silica gel for column chromatography. This unique property of adsorption observed in silicas prepared using acetic anhydride in the presence of cholesterol is likely to be induced by the imprinting effect of the steroid skeleton part of cholesterol in silica matrix.

Isomorphous Substitution of Transition-Metal Ions in the Nanoporous Nickel Phosphate VSB-5

The transition-metal-incorporated nickel phosphate molecular sieves (TMI-VSB-5) have been hydrothermally synthesized at 453 K in weak basic conditions under microwave irradiation. By means of X-ray diffraction, inductively coupled plasma (ICP), ultraviolet-visible (UV-vis) diffuse reflectance, and Mössbauer spectroscopies, successful isomorphous (at least partial) substitution of transition-metal ions in the VSB-5 framework has been verified. Characterization results show that the framework structure of nanoporous VSB-5 can accommodate a substantial level of isomorphous substitution of transition-metal ions up to about 10, 5, and 3 atom % for Fe, Mn, and V, respectively, in both octahedral nickel sites (Mn and Fe) and tetrahedral phosphorus sites (V). The isomorphous substitution including the replacement mechanism was studied by not only the change of unit cell parameters but also spectroscopic analysis. The unit cell parameters of TMI-VSB-5 including a unit cell volume and a-axis length relied on the ionic radii difference between the incorporated ion and the original framework ions such as Ni or P (RTMI - RNi or RTMI - RP).

Process implementation aspects for biocatalytic hydrocarbon oxyfunctionalization

Oxidoreductases catalyze a large variety of regio-, stereo-, and chemoselective hydrocarbon oxyfunctionalizations, reactions, which are important in industrial organic synthesis but difficult to achieve by chemical means. This review summarizes process implementation aspects for the in vivo application of the especially versatile enzyme class of oxygenases, capable of specifically introducing oxygen from molecular oxygen into a large range of organic molecules. Critical issues such as reaching high enzyme activity and specificity, product degradation, cofactor recycling, reactant toxicity, and substrate and oxygen mass transfer can be overcome by biochemical process engineering and biocatalyst engineering. Both strategies provide a growing toolset to facilitate process implementation, optimization, and scale-up. Major advances were achieved via heterologous overexpression of oxygenase genes, directed evolution, metabolic engineering, and in situ product removal. Process examples from industry and academia show that the combined use of different concepts enables efficient oxygenase-based whole-cell catalysis of various commercially interesting reactions such as the biosynthesis of chiral compounds, the specific oxyfunctionalization of complex molecules, and also the synthesis of medium-priced chemicals. Better understanding of the cell metabolism and future developments in both biocatalyst and bioprocess engineering are expected to promote the implementation of many and various industrial biooxidation processes.

Synthesis of a Single Four-Ring (S4R) Molecular Zinc Phosphate and Its Assembly to an Extended Polymeric Structure: A Single-Crystal and in-Situ MAS NMR Investigation

A reaction of ZnO, HCl, H(3)PO(4), and 2-pyridylpiperazine in THF/H(2)O mixture at 75 degrees C for 72 h produces a new zinc phosphate, [(C(5)NH(5))(C(4)N(2)H(10))][Zn(H(2)PO(4))(2)(HPO(4))], I. Zinc phosphate I consists of single four-ring (S4R) units with terminal phosphoryl groups hanging from the Zn center. On reaction with zinc acetate dihydrate in the presence of water at 100 degrees C, I gave another new zinc phosphate, [(C(5)NH(5))(C(4)N(2)H(10))][Zn(2)(H(2)PO(4))(HPO(4))(PO(4))] x 2H(2)O, II. II has a layer structure with apertures formed by 4- and 8-T atoms (T = Zn, P). An examination of the two structures reveals that I and II are related, II being formed by the direct addition of Zn(2+) ions to I. Room-temperature (31)P MAS NMR studies show the presence of different phosphorus species in both compounds. An in-situ (31)P MAS NMR investigation on the formation of II from I in the presence of Zn(2+) ions and water reveals the transformation to be facile. What is noteworthy in this study is that the structural integrity of the S4Rs has been maintained during the formation of II. Donor-acceptor hydrogen bond interactions and pi-pi interactions involving the pyridyl groups also appear to play subtle roles in both phosphates. This study, the first attempt of its kind, combines the principles of supramolecular organic chemistry with inorganic building units and contributes to our understanding of the formation of framework solids.

Laboratory evolution of a soluble, self-sufficient, highly active alkane hydroxylase

We have converted cytochrome P450 BM-3 from Bacillus megaterium (P450 BM-3), a medium-chain (C12-C18) fatty acid monooxygenase, into a highly efficient catalyst for the conversion of alkanes to alcohols. The evolved P450 BM-3 exhibits higher turnover rates than any reported biocatalyst for the selective oxidation of hydrocarbons of small to medium chain length (C3-C8). Unlike naturally occurring alkane hydroxylases, the best known of which are the large complexes of methane monooxygenase (MMO) and membrane-associated non-heme iron alkane monooxygenase (AlkB), the evolved enzyme is monomeric, soluble, and requires no additional proteins for catalysis. The evolved alkane hydroxylase was found to be even more active on fatty acids than wild-type BM-3, which was already one of the most efficient fatty acid monooxgenases known. A broad range of substrates including the gaseous alkane propane induces the low to high spin shift that activates the enzyme. This catalyst for alkane hydroxylation at room temperature opens new opportunities for clean, selective hydrocarbon activation for chemical synthesis and bioremediation.

Three-dimensional open-framework neodymium oxalates with organic functional groups protruding in 12-member channels

Two open-framework neodymium oxalates, [NH(3)CH(2)CH(NH(3))CH(3)][Nd(C(2)O(4))(2)(HCOO)].H(2)O (I) and [OC(CH(3))NCH(2)CH(CH(3))NH(3)][Nd(C(2)O(4))(2)].H(2)O (II), have been synthesized hydrothermally in the presence of 1,2-diaminopropane (1,2-DAP) and formic (I) and acetic (II) acids. The Nd atoms in both these oxalates have 9-fold coordination with respect to the oxygens, with the Nd atom in a distorted monocapped square antiprism coordination in I and in an idealized D(3)(h) triply capped trigonal prism coordination in II. The three-dimensional framework structures of I and II are built up by in-plane linkages between the Nd and the oxalate moieties, forming layers with 12-membered honeycomb-like apertures, pillared by an out-of-plane oxalate unit. The 12-memberd channel in I contains a dangling formate group in addition to the disordered amine molecule, while in II, the channel has N-(2-aminopropyl acetimide) molecules formed by the in situ reaction of 1,2-DAP and acetic acid. The accessibility of the formate and N-(2-aminopropyl acetimide) functional groups in I and II, respectively, uniformly distributed within the channels enables chemical manipulation. Crystal data: I, monoclinic, space group P2(1)/c (no. 14), M = 459.5, a = 9.0279(4) A, b = 18.1362(8) A, c = 8.5631(4) A, beta = 102.735(10) degrees, V = 1367.56(11) A(3), Z = 4, R(1) = 0.0229, wR(2) = 0.0599 [1782 observed reflections with I > 2sigma(I)]; II, triclinic, space group P(-)1 (no. 2), M = 454.5, a = 8.6222(9) A, b = 9.5683(10) A, c = 9.5712(10) A, alpha = 109.388(2) degrees, beta = 98.508(10) degrees, gamma = 102.361(12) degrees, V = 706.73(13) A(3), Z = 2, R(1) = 0.0446, wR(2) = 0.115 [1730 observed reflections with I > 2sigma(I)].

Nanopore and nanoparticle catalysts

The design, atomic characterization, performance, and relevance to clean technology of two distinct categories of new nanocatalysts are described and interpreted. Exceptional molecular selectivity and high activity are exhibited by these catalysts. The first category consists of extended, crystallographically ordered inorganic solids possessing nanopores (apertures, cages, and channels), the diameters of which fall in the range of about 0.4 to about 1.5 nm, and the second of discrete bimetallic nanoparticles of diameter 1 to 2 nm, distributed more or less uniformly along the inner walls of mesoporous (ca. 3 to 10 nm diameter) silica supports. Using the principles and practices of solid-state and organometallic chemistry and advanced physico-chemical techniques for in situ and ex situ characterization, a variety of powerful new catalysts has been evolved. Apart from those that, inter alia, simulate the behavior of enzymes in their specificity, shape selectivity, regio-selectivity, and ability to function under ambient conditions, many of these new nanocatalysts are also viable as agents for effecting commercially significant processes in a clean, benign, solvent-free, single-step fashion. In particular, a bifunctional, molecular sieve nanopore catalyst is described that converts cyclohexanone in air and ammonia to its oxime and caprolactam, and a bimetallic nanoparticle catalyst that selectively converts cyclic polyenes into desirable intermediates. Nanocatalysts in the first category are especially effective in facilitating highly selective oxidations in air, and those in the second are well suited to effecting rapid and selective hydrogenations of a range of organic compounds.

Solvent-free routes to clean technology

A major aim for the chemical technology of the future is the avoidance of noxious and environmentally unacceptable organic solvents. In this concept article we discuss more environmentally friendly and highly selective alternatives which we have evolved for carrying out a number of important chemical conversions. These entail the use of porous heterogeneous catalysts in which the active sites have been atomically engineered and fully characterized. Such solid catalysts operate under solvent-free conditions and usually entail one-step processes.