Germanium-oxygen interactions in acyl-substituted germyleneazines L2GeNNC(COX)(COY)

MNDO calculations have been carried out on the reactions of the electron-rich germylene L₂Ge [L=(H₃Si)₂N] with diazo compounds, as models for the experimentally observed reactions of L₂Ge [L=(Me₃Si)₂N]. The most stable form of the 11 adduct of L₂Ge with N₂C(COOMe)₂ is found to have a cyclic configuration resulting from a strong intramolecular interaction between the oxygen of one of the carbonyl groups and the germanium atom. Protonation of this cyclic adduct occurs at nitrogen, giving an intermediate, addition to which of nucleophiles X^– provides acyclic L₂Ge(X)NHN(COOMe)₂, as observed experimentally. Two similar cyclic adducts are formed between L₂Ge and N₂C(COCH₃)(COOCH₃), the most stable of which provides, after a proton shift, the observed 1,3,4,2-oxadiazagermine system . Adduct formation between Me₂Si=NSiMe₃ and simple Lewis bases (H₂O, NH₃, THF, H₂CO) is calculated to be strong, but the corresponding adducts of Me₂Ge=NSiMe₃ are very weak: much stronger adducts are predicted for L₂GeNNC(COOMe)₂.     

Bis(trimethylsilyl)diimine: Preparation,Structure, and Reactivity

The highly reactive compound bis(trimethylsilyl)diimine (BSD), which was first prepared by oxidation of lithium tris(trimethylsilyl)hydrazide, is light blue, sensitive to thermolysis and hydrolysis, and ignites spontaneously in air. On the basis of electron transfer, acid-base, or free-radical reactions, it acts in particular as a (preparatively useful) redox system and as an agent for the introduction of azo groups. Redox reactions lead by oxidation or reduction of the other reactant through two oxidation stages to hydrazine derivatives or molecular nitrogen, and in the case of electrochemical reduction, to BSD radical-anions. Azo-group transfers, on the other hand, yield new inorganic azo compounds with no change in the oxidation state of the diimine group.     

Thermal rearrangements of spiro[2.4]hepta-1,4,6-trienes

Thermolysis of spiro[2.4]hepta-1,4,6-triene (1a) at 50 degrees C yielded bicyclo[3.2.0]hepta-1,3,6-triene (5), which dimerized in two different fashions to form cyclobutanes. The 1,2-dimethyl and 1-propyl derivatives of 1a also rearranged at 50 degrees C, but at a faster rate, each yielding a pair of cyclobutane dimers. The structures of these symmetrical dimers were investigated by 1D and 2D NMR and NOE difference spectroscopy. Ab initio calculations indicated that the two strained olefins 1a and 5 had comparable energies about 50 kcal/mol lower than norborna-1(7),2,5-triene, which was thus excluded as a reaction intermediate.     

Simultaneous determination of albumin and immunoglobulin G with fluorescence spectroscopy and multivariate calibration

A method is proposed for the simultaneous determination of albumin and immunoglobulin G (IgG1) with fluorescence spectroscopy and multivariate calibration with partial least squares regression (PLS). The influence of some instrumental parameters were investigated with two experimental designs comprising 19 and 11 experiments, respectively. The investigated parameters were excitation and emission slit, detection voltage and scan rate. When a suitable instrumental setting had been found, a minor calibration and test set were analysed and evaluated. Thereafter, a larger calibration of albumin and IgG1 was made out of 26 samples (0-42 μg ml⁻¹ albumin and 0-12.7 μg ml⁻¹ IgG1). This calibration was validated with a test set consisting of 14 samples in the same concentration range. The precision of the method was estimated by analysing two test set samples for six times each. The scan modes tested were emission scan and synchronous scan Δ60 nm. The results showed that the method could be used for determination of albumin and IgG1 (albumin, root mean square error of prediction (RMSEP) <2, relative standard error of prediction (RSEP) <6% and IgG1, RMSEP <1, RSEP <8%) in spite of the overlapping fluorescence of the two compounds. The estimated precision was relative standard deviation (R.S.D.) <1.7%. The method was finally applied for the analysis of some sample fractions from an albumin standard used in affinity chromatography.     

Comparative study of anionic and radical cyclization for the preparation of 1,3-dimethylindans: highly stereoselective preparation of cis-1,3-disubstituted indans via intramolecular carbolithiation

[reaction: see text] The preparation of 1,3-dimethylindans from 4-(2-bromophenyl)-1-pentene (1) and 2-(2-iodo-1-methylethyl)styrene (2) substrates via radical-mediated cyclization and intramolecular carbolithiation has been investigated. Although cyclization of the radical derived from either substrate proceeds with modest selectivity for the cis-isomer, as does cycloisomerization of the aryllithium derived from substrate 1 (cis/trans approximately 2), intramolecular cyclization of the alkyllithium derived from substrate 2 is a highly cis-selective process (cis/trans = 12).     

Das chlorsilylsubstituierte Silanimin Bu2SiNSiClBu2

In the thermolysis of the silaterazolines silatetrazoline ^tBu₂SiNSiCl^tBu₂ · ^tBu₃SiN₃ the silanimine ^tBu₂SiNSiCl^tBu₂ and the silyl azide ^tBu₃SiN₃ are formed quantitatively. The silanimine ^tBu₂SiNSiCl^tBu₂ has been trapped with Et₃NHF, Me₃NHCl, water, 1-butene, 2,3-dimethyl-1,3-butadiene, isobutene, methylvinyl ether, and ^tBu₂SiClN₃. The structure of the disiloxane (^tBu₂SiCl-NH-Si^tBu₂)₂O and of the bis(di-tert-butylchlorsilyl)-substituted silatetrazoline ^tBu₂SiNSiCl^tBu₂ · ^tBu₂SiClN₃ has been determined by X-ray structure analysis.     

The C7-C10 cycloalkanes revisited

The conformers of cycloheptane through cyclodecane have been examined at the B3LYP/6-311+G* and MP2/6-311+G* theoretical levels, with some additional calculations at the CCD/6-311+G* and CCSD(T)/6-311++G** levels. With cyclooctane, B3LYP predicts that the boat-chair and crown conformers have similar energies, whereas MP2 and CCSD(T) predict that the crown conformer is 2 kcal/mol higher in energy. The latter is in agreement with the electron diffraction data. With cyclononane, B3LYP predicts that two of the higher-energy conformers found in molecular mechanics calculations should convert to one of the lower-energy conformers. However, MP2/6-311+G* optimizations find them to be true minima on the potential energy surface. B3LYP systematically predicts larger C-C-C bond angles for these compounds than either MP2 or CCD. The results of molecular mechanics MM4 calculations are generally in good agreement with those obtained using MP2.     

A Memristive Element Based on an Electrically Controlled Single-Molecule Reaction

The exponential proliferation of data during the information age has required the continuous exploration of novel storage paradigms, materials, and devices with increasing data density. As a step toward the ultimate limits in data density, the development of an electrically controllable single-molecule memristive element is reported. In this device, digital information is encoded through switching between two isomer states by applying a voltage signal to the molecular junction, and the information is read out by monitoring the electrical conductance of each isomer. The two states are cycled using an electrically controllable local-heating mechanism for the forward reaction and catalyzed by a single charge-transfer process for the reverse switching. This single-molecule device can be modulated in situ, is fully reversible, and does not display stochastic switching. The I–V curves of this single-molecule system also exhibit memristive character. These features suggest a new approach for the development of molecular switching systems and storage-class memories.