Chemische Synthese des Dodecanucleotids dpT?T?T?T?T?T?C?A?T?C?A?T

Chemical Synthesis of the Dodecanucle otide dpT T T T T T C A T C A T For studies on the specifity of enzymes, the dodecanucleotide dpT T T T T T C A T C A T was required. Its chemical synthesis is reported starting with the mononucleotides dpT, dpC and dpA.     

Chemische Synthese des Dodecanucleotids dC?A?C?A?A?G?C?T?T?G?T?G

Chemical Synthesis of the Dodeecanuceleotide. dC A C A A G C T T G T G For studies of some sequence dependent structural factors the self-complementary dodecanucleotide dC A C A A G C T T G T G was required. Its chemical synthesis is reported according to the diester approach starting with the monomers dC, dpA, dpG, dpC and dpT.     

Calculation of the Detonation Properties of C?H?N?O explosives

On the basis of the steady state model of detonation, using Becker-Kistiakowsky-Wilson equation of state for gaseous products of detonation and Cowan-Fickett equation of state for solid carbon, algorithm and computer program for the calculation of the detonation properties of C H N O type explosives are developed. The program has been tested by the comparison of the calculated data with experimental ones for some high explosives being of different densities and compositions. The calculated data have also been compared with data obtained by program FOR-TRAN BK W. Both comparisons gave satisfactory agreement.     

A New Method for Evaluating the Energy Characteristics of C?H?N?O Energetic Compounds

From the law of conversation of energy, the release energy from the initiation to the Chapman–Jouguet point during the detonation of an energetic compound has been deduced as a function of initial density, detonation velocity, and detonation pressure. For C H N O energetic compounds the relative release energy per unit volume (I_v) approaches the relative specific wall kinetic energy (E_cyl/E_HMX) at 19 mm wall displacement from the cylinder test with HMX as reference. A good linear relationship between I_v and E_cyl/E_HMX has been regressed, implying that E_cyl/E_HMX is also a function of initial density, detonation velocity, and detonation pressure. It has been concluded that I_v can reflect the driving force of detonation products of energetic compounds and is appropriate to be used for the evaluation of energy characteristics. The assessment of the energy for a series of synthesized and theoretically designed high‐energy compounds reveals that the future of C H N O energetic compounds is promising after CL‐20 and ONC.     

Building Functionality through Sequential C?B and C?F Bond Formation

α′‐Fluoro β‐boryl ketones can be efficiently synthesised from a sequential organocatalytic β‐boration pathway and consecutive electrophilic fluorination reaction in an acidic medium. Alternatively, the regioisomers of α‐fluoro β‐boryl ketones can be diastereoselectively obtained from Cu(I)‐mediated β‐boration followed by in situ fluorination of the boron enolate. Enantioenriched mixtures of the major anti‐diastereomer of vicinal C B and C F bonds are found in the presence of the chiral ligand QuinoxP*.     

Zinc‐Catalyzed Organic Synthesis: C?C,C?N,C?O Bond Formation Reactions

Zinc is the 24^th most abundant element in the Earth’s crust. Since the discovery of pure zinc metal in the 18^th century, the main application of zinc metal is as materials. Because zinc salts are abundant, cheap, non‐toxic, and exhibit environmentally benign properties, organic chemists have been interested in using zinc salts as catalysts in organic synthesis during the last three decades. Within this review, we have summarized the progress on applications of zinc salts in organic reactions. Our the target is to emphasize the special properties of zinc catalysts, and further promote the interest of organic chemists.     

Relative Stabilities of M?O and M?S Bonds in some Chelates

Formation constants of the chelates of Ni(II) and Tl(I) with glycollic acid and thioglycollic acid have been determined by Irving-Rossotti technique. The relative stabilities have been interpreted in terms of the possibility of π interaction in the formation of Ni S bond.     

Iron‐Catalyzed C?C Bond Cleavage and C?N Bond Formation

A novel approach for C N bond formation was developed by iron‐catalyzed C C bond cleavage. Anilines and sulfonamides reacted smoothly with 2‐substituted 1,3‐diphenylpropane‐1,3‐diones to afford N‐alkylation products, in which the 1,3‐dicarbonyl group acts as a leaving group in the presence of an iron catalyst. The reversible C C bond cleavage plays a driving force to give the thermodynamically stable products. The method is complementary to the previous methods for C N bond formation.     

C?C Hydrolases for Biocatalysis

Although C C bond hydrolases are distributed widely in Nature, they has as yet have received only limited attention in the area of biocatalysis compared to their counterpart the C‐heteroatom hydrolases, such as lipases and proteases. However, the substrate range of C C hydrolases, and their non‐dependence on cofactors, suggest that these enzymes may have considerable potential for applications in synthesis. In addition, hydrolases such as the β‐diketone hydrolase from Rhodococcus (OCH) are known, that catalyse the formation of interesting chiral intermediates. Further enzymes, such as kynureninase and a meta‐cleavage product hydrolase (MhpC), are able to catalyse carbon‐carbon bond formation, suggesting wider applications in biocatalysis than previously envisaged. In this review, the distribution, catalytic characteristics and applications of C C hydrolases are described, with a view to assessing their potentialfor use in biocatalytic processes in the future.     

Multifunctional Silk?Tropoelastin Biomaterial Systems

New multifunctional, degradable, polymeric biomaterial systems would provide versatile platforms to address cell and tissue needs in both in vitro and in vivo environments. While protein-based composites or alloys are the building blocks of biological organisms, similar systems have not been largely exploited, to date, to generate ad hoc biomaterials able to control and direct biological functions by recapitulating their inherent structural and mechanical complexities. Therefore, we have recently proposed silk tropoelastin material platforms that are able to conjugate a mechanically robust and durable protein, silk, to a highly flexible and biologically active protein, tropoelastin. This review focuses on the elucidation of the interactions between silk and tropoelastin to control the structure of the material its properties, and ultimately functions. In addition, an approach is provided for novel material designs to provide tools to control biological outcomes through surface roughness, elasticity, and net charge for neuronal and mesenchymal stem-cell-based tissue engineering.     

Preceramic polymer for Si?B?N?C fiber via one‐step condensation of silane,BCl3, and silazane

A preceramic polymer for Si? B? N? C fiber, polyborosilazane, has been synthesized by one‐step condensation reaction of dichloromethylsilane, BCl₃, and hexamethyldisilazane with high yield. The reaction mainly involves the condensation of Si? Cl and B? Cl with N? SiMe₃ followed by SiMe₃Cl evaporation and dehydrogenation between N? H and Si? H. The resulted polymer is a soluble colorless transparent solid with melting point of 70°C and molecular weight of 10,800. The backbone of the polymer is mainly composed of ? Si? N? B‐bridge with some borazine rings. The polymer exhibits good processability and flexible polymer fibers with diameter of 15–20 μm were obtained by melt spinning. Pyrolysis of the as‐synthesized polymer to 1000°C under nitrogen atmosphere results in a ceramic yield of 63 wt %, and the obtained Si? B? N? C ceramic remains fully amorphous up to 1700°C, and only small amount of poorly crystallized BN, Si₃N₄, and SiC phases were observed upon heating at 1850°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The Chemistry of Detonations. IX. Some observations regarding a computer based parametric study of detonation characteristics of C?H?N?O explosives

Swaminathan and Rajagopalan (S and R) have recently published a parameter study describing the dependence of important detonation characteristics of C H N O explosives on their densities and enthalpies of formation which is seriously inconsistent with earlier highly reliable calculations by Mader using the same equation of state and presumably the same input information. S and R's computer-based conclusions are also not in accord with parametric relationships established over a decade ago by Johansson and Persson and Kamlet and Jacobs. S and R's calculated detonation pressures are significantly lower at high loading densities and higher at lower loading densities than Mader's corresponding calculations. Also out of line on the high side (compared with Mader's calculations or experimentally observed values) are S and R's calculated detonation velocities. The differences between S and R's parametric relationships and those of the other workers can have important and misleading implications to the planning of future explosives chemistry research. It is suggested to those interested in such parametric studies that the simplified method for detonation property calculation be used, since the input information is explicit and easily checked and the results are at least as reliable as those from complex computer programs.     

Tandem Catalysis: Alcohol Oxidation and C?C Bond Formation via C?H Bond Activation

A tandem process involving oxidation of a benzylic alcohol functionality followed by hydroarylation is described. These two atom‐economic sequences are very convenient to access functionalized aromatic ketones, using simple ruthenium trichloride as catalyst precursor. Moreover they appear to be highly compatible, tolerant, and selective toward various functional groups, and the ease of the protocol should make it very convenient for synthetic purposes.     

Taming Pt 5d state occupancy via Pt?O?Mn electronic linkage for enhanced dehydrogenation activity

The enhancement of catalytic activity is always limited by the dilemma in activation and desorption due to Sabatier principle. Locating the Sabatier optimum by manipulating catalyst electronic structure has been a long-standing challenge in heterogeneous catalysis. Herein, we presented a generic strategy to continuously tailor the Pt 5d state occupancy via tuning the Pt O Mn electronic linkage over Al₂O₃-confined MnO_x islands, aiming at accommodating the C H cleavage and product desorption capabilities in dehydrogenation of liquid organic hydrogen carriers (monocyclic/bicyclic hydrides). Rising Mn valence can decrease the Pt 5d state occupancy through more electron transfer from Pt 5d to O 2p due to the strong π-donation of O 2p to Mn 3d. This will lead to the lower initial C H activation energy barrier while higher product desorption energy barrier. An intermediate Pt 5d filling of ~8.4 in Pt Mn₂O₃/Al₂O₃ enables the balanced level of product desorption and C H activation, thus ensuring a superior dehydrogenation activity. The electron structure-adsorption-performance modulation mechanism described herein provides a benchmark to locate the Sabatier optimum for the metal catalyst design.     

Expedient Synthesis of Functionalized Triarylmethanols through Tandem Formation of Geminal C?C and C?O Bonds

The rearrangement/oxidation of N,N‐disubstituted anilines and the formal dehydrogenative cross‐coupling of diarylmethanols with aniline derivatives have been developed for the preparation of symmetric and unsymmetric functionalized triarylmethanols. Both reactions proceed smoothly in trifluoroacetic acid in the presence of an inexpensive oxidant (manganese dioxide or potassium persulfate) and a catalytic amount of palladium diacetate to give a range of functionalized triarylmethanols in moderate to good yields and with extremely high regioselectivity. The two unprecedented reactions involve tandem formation of geminal C C and C O bonds, and they are synthetically useful, atom‐efficient, and operationally simple.     

Photocatalytic properties of layered hydrous titanium oxide/CdS?ZnS nanocomposites incorporating CdS?ZnS into the interlayer

H₂Ti₄O₉/Cd_0·8Zn_0·2S nanocomposites incorporating Cd_0·8Zn_0·2S particles, less than 1 nm in thickness, were fabricated by the chemical reaction between a Cd²⁺–Zn²⁺ mixture and H₂S in the interlayer of H₂Ti₄O₉. H₂Ti₄O₉/Cd_0·8Zn_0·2S nanocomposites were capable of efficient hydrogen evolution following irradiation with visible light in the presence of Na₂S as a sacrificial donor. The hydrogen production activity of the H₂Ti₄O₉/Cd_0·8Zn_0·2S nanocomposite was superior to those of unsupported Cd_0·8Zn_0·2S and the mixture of H₂Ti₄O₉ and Cd_0·8Zn_0·2S. The hydrogen production was enhanced by doping Pt together with Cd_0·8Zn_0·2S in the interlayer, but was depressed by depositing Pt on the outer surface of the H₂Ti₄O₉/Cd_0·8Zn_0·2S nanocomposite.     

An Efficient Synthesis of Polysubstituted Pyridines via C?H Oxidation and C?S Cleavage of Dimethyl Sulfoxide

An expedient cleavage of the C S bond of dimethyl sulfoxide (DMSO) has been developed for the preparation of substituted pyridines from ketones. In this transformation, the co‐product formic acid was formed from ammonium formate, which acted as an important catalyst for the reaction. Notably, this transformation exhibited a broad substrate scope towards a wide variety of different ketones to give the corresponding substituted pyridines in high yields. Mechanistic studies suggested that dimethyl sulfoxide delivered a methylene fragment, which was subsequently captured in situ to give a pyridine.

     

Direct Trifluoromethylation of the C?H Bond

Trifluoromethylation meets C H activation: after transition metal‐catalyzed trifluoromethylation became more and more popular, trifluoromethylation via C H activation is now emerging as the latest attraction. Several pioneering examples and their mechanisms are discussed in this review.