Synthesis of carbaalane halogen derivatives

The carbaalane halogen derivatives [(AlX)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (X = F (9), Cl (7), Br (10), I (11)) were prepared in toluene from [(AlH)(6)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (6) and BF(3).OEt(2), BX(3) (X = Br, I), Me(3)SnF, and Me(3)SiX (X = Cl, Br, I), respectively. A partially halogenated product [(AlH)(2)(AlX)(4)(AlNMe(3))(2)(CCH(2)CH(2)SiMe(3))(6)] (12) (X = Cl (approximately 40%), Br (approximately 60%)) was obtained from 5 and impure BBr(3). [(AlH)(6)(AlNMe(3))(2)(CCH(2)Ph)(6)] (5) was converted to [(AlX)(6)(AlNMe(3))(2)(CCH(2)Ph)(6)] (X = F (13), Cl (14), Br (15), I (16)) using BF(3).OEt(2) and Me(3)SiX (X = Cl, Br, I), respectively. The X-ray single-crystal structures of 11.C(6)H(6), 12.3C(7)H(8), 13.6C(7)H(8), and 15.4C(7)H(8) were determined. Compounds 7 and 9-11 are soluble in benzene/toluene and could be well characterized by NMR spectroscopy and MS (EI) spectrometry. The results demonstrate the facile substitution of the hydridic hydrogen atoms in 5 and 6 by the halides with different reagents.     

Mechanism of formation and decay of the compound nuclei150Gd produced by two entrance channels (16O+134Ba) and (40Ar+110Pd)

Excitation functions have been drawn for evaporation residues issued from¹⁵⁰Gd, a compound nucleus produced either by¹⁶O ions on¹³⁴Ba, or by⁴⁰Ar on¹¹⁰Pd. Absolute cross sections were measured for^145–147Gd,^145–147Eu,^141m Sm,^143m Sm,^140m Pm and^139m Nd. Complete fusion cross sections have been obtained and compared to calculated estimations based, at low energies, on the simple expressionσ _CF=πR _Fuss ² (1?V _Fus/E) whereR _Fus andV _Fus are respectively the distance and the potential for fusion atdV/dr=0. For high energies σ_CF=πR _cr ² (1?V_cr/E) with the model of critical distanceR _cr and critical potentialV _cr. Thresholds energies have been determined with a particular care. The analysis of the shape and the width of excitation functions, particularly for the emission of 4 and 5 neutrons, has been carried out and compared to calculated values. The difference between argon and oxygen induced reactions has been attributed to the difference inl population in the entrance channel.     

Synthesis of 6-(perfluoroalkyl)salicylates by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 3-ethoxy-1-(perfluoroalkyl)prop-2-en-1-ones

6-(Perfluoroalkyl)salicylates were prepared by [3+3] cyclization of 1,3-bis(silyl enol ethers) with 3-ethoxy-1-(perfluoroalkyl)prop-2-en-1-ones.     

Interaction between the antibacterial compound,oleuropein, and model membranes

Oleuropein, a secoiridoid glycoside extracted from the olive tree, Olea europaea L., has been described as showing antibacterial properties. However, the exact mechanism of these antimicrobial properties is not yet well understood. In the present study, we have studied the interaction of oleuropein with phosphatidylglycerol (PG) as a model membrane for Staphylococcus aureus (S. aureus) (Gram-positive bacteria) and phosphatidylethanolamine and Escherichia coli (E. coli) lipid extract as a model membrane for E. coli (Gram-negative bacteria). The study has been carried out using monolayers as model membranes and using kinetics at constant area and compression isotherms with Brewster angle microscopy (BAM) observations. The results show that oleuropein interacts in higher extent with PG monolayers, which is related with its stronger antibacterial effect against Gram-positive bacteria. The effects on the membrane are probably produced at the cell surface because oleuropein did not form stable mixed monolayers with the lipids assayed at the air/water interface.     

Transmetallierung von Zinn(II) in [Sn(μ3‐PSitBu3)]4 durch Barium – von Sn4P4‐Heterocuban‐Strukturen zu heterobinuklearen Käfigverbindungen mit einem zentralen BanSn4−nP4‐Heterocuban‐Polyeder (n = 1, 2 und 3)

Transmetallation of Tin(II) in [Sn(μ₃‐PSitBu₃)]₄ by Barium – from Sn₄P₄ Heterocubane Structures to Heterobinuclear Cage Compounds with a Central Ba_nSn_4?nP₄ Heterocubane Polyhedron (n = 1, 2 and 3) For the preparation of compounds of the type [Ba_nSn_4?n(PSitBu₃)₄] (n = 1 ( 2 ), 2 ( 3 ) and 3 ( 4 )) two synthetic routes are applicable: in the transmetallation reaction homometallic [Sn₄(PSitBu₃)₄] ( 1 ) reacts with barium metal and in a deprotonation reaction (metallation) tri(tert‐butyl)silylphosphane reacts simultaneously with (thf)₂Ba[N(SiMe₃)₂]₂ and Sn[N(SiMe₃)₂]₂. During the transmetallation reaction mixtures of the heterobimetallic cage compounds 2 to 4 are obtained, however, analytically pure compounds 2 and 3 are accessible by the metallation reaction. Compound 4 is formed as a minor product together with 3 . Due to the larger Ba‐P bond lengths compared to the Sn‐P values the substitution of tin by barium leads to strong distortions of the heterocubane moiety. With NMR‐spectroscopic experiments one could show that all the above mentioned compounds form Ba_nSn_4?nP₄ heterocubane cage structures.     

Ring opening of 2-phenylazetidines with allylsilanes

N-Activated 2-phenylazetidines were opened regioselectively at the benzylic carbon with various allylsilanes or propargylsilane in the presence of BF₃·Et₂O, providing amino olefins, precursors of biomolecules such as phenyl-homo-kainoids.     

The dithianyl group as a synthon in porphyrin chemistry: condensation reactions and preparation of formylporphyrins under basic conditions

Vilsmeier formylation is one of the most widely used substitution reactions for the functionalization of porphyrins. However, its utility is limited by the electrophilic/acidic reaction conditions, deactivation of the aromatic system and regiochemical problems, the requirement for metal complexes and necessity for subsequent demetalation under harsh conditions, and low functional group tolerance. To overcome these limitations, the dithianyl group has been utilized as a latent formyl synthon in porphyrin chemistry. 2-Formyl-1,3-dithiane can be used directly in pyrrole condensation reactions to regioselectively yield porphyrins with up to four dithianyl residues. Likewise, 5-dithianyldipyrromethane could be prepared quantitatively as a key building block for various porphyrin condensation reactions yielding the respective free base formylporphyrins after deprotection. Additionally, dithianyllithium can be used as a reagent for the direct aromatic substitution of metallo- and free base porphyrins under nucleophilic conditions.     

Synthetic routes for a new family of chiral tetradentate ligands containing pyridine rings

A series of new tetradentate ligands containing two bipyridine groups or two pyridine moieties carrying amine substituents has been synthesised either from 5'- and 6'-substituted chiral bipyridines, or from chiral pyridine derivatives. These precursors have been prepared from (-)-alpha-pinene or (-)-myrtenal, respectively. The structures of three tetradentate-, and of five chiral bipyridine ligands have been determined by X-ray diffraction.     

通过脱碳控制全球平均温度

Establishing a reliable method to predict the global mean temperature (T_e) is of great importance because CO₂ reduction activities require political and global cooperation and significant financial resources. The current climate models all seem to predict that the earth's temperature will continue to increase, mainly based on the assumption that CO₂ emissions cannot be lowered significantly in the foreseeable future. Given the earth's multifactor climate system, attributing atmospheric CO₂ as the only cause for the observed temperature anomaly is most likely an oversimplification; the presence of water (H₂O) in the atmosphere should at least be considered. As such, T_e is determined by atmospheric water content controlled by solar activity, along with anthropogenic CO₂ activities. It is possible that the anthropogenic CO₂ activities can be reduced in the future. Based on temperature measurements and thermodynamic data, a new model for predicting T_e has been developed. Using this model, past, current, and future CO₂ and H₂O data can be analyzed and the associated T_e calculated. This new, esoteric approach is more accurate than various other models, but has not been reported in the open literature. According to this model, by 2050, T_e may increase to 15.5 ℃ under "business-as-usual" emissions. By applying a reasonable green technology activity scenario, T_e may be reduced to approximately 14.2 ℃. To achieve CO₂ reductions, the scenario described herein predicts a CO₂ reduction potential of 513 gigatons in 30 years. This proposed scenario includes various CO₂ reduction activities, carbon capturing technology, mineralization, and bio-char production; the most important CO₂ reductions by 2050 are expected to be achieved mainly in the electricity, agriculture, and transportation sectors. Other more aggressive and plausible drawdown scenarios have been analyzed as well, yielding CO₂ reduction potentials of 1051 and 1747 gigatons, respectively, in 30 years, but they may reduce global food production. It is emphasized that the causes and predictions of the global warming trend should be regarded as open scientific questions because several details concerning the physical processes associated with global warming remain uncertain. For example, the role of solar activities coupled with Milankovitch cycles are not yet fully understood. In addition, other factors, such as ocean CO₂ uptake and volcanic activity, may not be negligible.