Controlled hydrolysis of AlMe to tetramethylalumoxane and a new look at incipient adducts with water.

We present an efficient route to tetramethylalumoxane by the controlled hydrolysis of AlMe in the presence of pyridine. The AlMe(pyr) hydrolysis by 0.5 and 1 equiv.

Factors controlling the structure of alkylzinc amidinates: on the role of -substituents.

Despite various applications of alkylzinc complexes supported by ,-bidentate ligands in chemistry and materials science, the corresponding organozinc amidinates still represent an insufficiently explored area. To gain a more in-depth understanding of factors controlling the structure and stability of alkylzinc amidinates, we selected benzamidinate and ,'-diphenylformamidinate ligands as model ,'-unsubstituted and ,'-diaryl substituted ligands, respectively, to systematically modify the secondary coordination sphere of the Zn center. A series of new alkylzinc amidinates has been synthesized and their molecular structures identified in both the solid state (single-crystal X-ray crystallography) and solution (NMR and FTIR spectroscopy).

Molecular Oscillator Affects Susceptibility of Caterpillars to Insecticides: Studies on the Egyptian Cotton Leaf Worm- (Lepidoptera: Noctuidae).

The molecular oscillator is the core of the biological clock and is formed by genes and proteins whose cyclic expression is regulated in the transcriptional-translational feedback loops (TTFLs). Proteins of the TTFLs are regulators of both their own and executive genes involved in the control of many processes in insects (e.g.

Mechanochemical vs Wet Approach for Directing CO Capture toward Various Carbonate and Bicarbonate Networks.

The distinct research areas related to CO capture and mechanochemistry are both highly attractive in the context of green chemistry. However, merger of these two areas, , mechanochemical CO capture, is still in an early stage of development. Here, the application of biguanidine as an active species for CO capture is investigated using both solution-based and liquid-assisted mechanochemical approaches, which lead to a variety of biguanidinium carbonate and bicarbonate hydrogen-bonded networks.

NMR Crystallography Enhanced by Quantum Chemical Calculations and Liquid State NMR Spectroscopy for the Investigation of Se-NHC Adducts*.

N-heterocyclic carbene ligands (NHC) are widely utilized in catalysis and material science. They are characterized by their steric and electronic properties. Steric properties are usually quantified on the basis of their static structure, which can be determined by X-ray diffraction.

Unravelling Structural Mysteries of Simple Organozinc Alkoxides.

Simple RZnOR' alkoxides are among the first known organozinc compounds, and widespread interest in their multifaced chemistry has been driven by their fundamental significance and potential applications including various catalytic reactions. Nevertheless, their chemistry in solution and in the solid state remains both relatively poorly understood and a subject of constant debate. Herein, the synthesis and structural characterization of long-sought structural forms, a roof-like trimer [(tBuZn) (μ-OC(H)Ph ) (μ -OC(H)Ph )] and a ladder-type tetramer [(PhZn) (μ-OC(H)Ph ) (μ -OC(H)Ph ) ], incorporating diphenylmethanolate as a model alkoxide ligand, are reported.

C in a peptidic cage: a case of symmetry mismatch studied by crystallography and solid-state NMR.

A supramolecular complex, formed by encapsulation of C fullerene in a molecular container built from two resorcin[4]arene rims zipped together by peptidic arms hydrogen bonded into a cylindrical β-sheet, was studied by X-ray crystallography, solid-state and solution NMR, EPR spectroscopy and differential scanning calorimetry (DSC). The crystal structure, determined at 100 K, reveals that the complex occupies 422 site symmetry, which is compatible with the molecular symmetry of the container but not of the fullerene molecule, which has only 222 symmetry. The additional crystallographic symmetry leads to a complicated but discrete disorder, which could be resolved and modelled using advanced features of the existing refinement software.

Size-Dependent Interaction of Amyloid β Oligomers with Brain Total Lipid Extract Bilayer-Fibrillation Versus Membrane Destruction.

Amyloid β, Aβ(1-42), is a component of senile plaques present in the brain of Alzheimer's disease patients and one of the main suspects responsible for pathological consequences of the disease. Herein, we directly visualize the Aβ activity toward a brain-like model membrane and demonstrate that this activity strongly depends on the Aβ oligomer size. PeakForce quantitative nanomechanical mapping mode of atomic force microscopy imaging revealed that the interaction of large-size (LS) Aβ oligomers, corresponding to high-molecular-weight Aβ oligomers, with the brain total lipid extract (BTLE) membrane resulted in accelerated Aβ fibrillogenesis on the membrane surface.

How long to rest in unpredictably changing habitats?

In the present study, we investigated the optimum length of prolonged dormancy (developmental arrest extending over favourable periods) of organisms under uncertain environmental conditions. We used an artificial life model to simulate the evolution of suspended development in the ontogenesis of organisms inhabiting unpredictably changing habitats. A virtual population of semelparous parthenogenetic individuals that varied in a duration of developmental arrest competed for limited resources.

Nonclassical dynamics of the methyl group in 1,1,1-triphenylethane. Evidence from powder H NMR spectra.

According to the damped quantum rotation (DQR) theory, hindered rotation of methyl groups, evidenced in nuclear magnetic resonance (NMR) line shapes, is a nonclassical process. It comprises a number of quantum-rate processes measured by two different quantum-rate constants. The classical jump model employing only one rate constant is reproduced if these quantum constants happen to be equal.

Frozen Rotation of the Ammonium Group Observed for the First Time in Liquid-Phase NMR Spectra.

Hindered rotation of the -NH group in a sterically crowded molecular environment was frozen on the NMR time scale. These effects were observed for solutions of 1,2,3,4-tetrabromotriptycyl-9-ammonium tetrafluoroborate in tetrahydrofuran with and without excess of HBF. In the absence of acid, the hindered rotation is accompanied by a number of other effects originating in part from practically nonremovable traces of water in the solvent.

Temporal Expression of the Clock Genes in the Water Flea Daphnia pulex (Crustacea: Cladocera).

The timekeeping mechanisms that operate at the core of circadian clocks (oscillators) are based on interacting molecular feedback loops consisting of clock and clock-associated genes. However, there is a lack of comprehensive studies on the expression of clock genes (particularly those forming its core) in single crustacean species at the mRNA and protein levels, and these studies could serve as a basis for constructing a model of the crustacean molecular oscillator. Studies on Daphnia pulex are well suited to fill this gap because this species is the only representative crustacean whose genome has been sequenced.

A quantum mechanical alternative to the Arrhenius equation in the interpretation of proton spin-lattice relaxation data for the methyl groups in solids.

The theory of nuclear spin-lattice relaxation in methyl groups in solids has been a recurring problem in nuclear magnetic resonance (NMR) spectroscopy. The current view is that, except for extreme cases of low torsional barriers where special quantum effects are at stake, the relaxation behaviour of the nuclear spins in methyl groups is controlled by thermally activated classical jumps of the methyl group between its three orientations. The temperature effects on the relaxation rates can be modelled by Arrhenius behaviour of the correlation time of the jump process.

NMR signal enhancement by effective SABRE labeling of oligopeptides.

Signal amplification by reversible exchange (SABRE) can enhance nuclear magnetic resonance signals by several orders of magnitude. However, until now this was limited to a small number of model target molecules. Here, a new convenient method for SABRE activation applicable to a variety of synthetic model oligopeptides is demonstrated.

Scalar relaxation of the second kind. A potential source of information on the dynamics of molecular movements. 4. Molecules with collinear C-H and C-Br bonds.

Continuing studies based on measurements of the nuclear spin relaxation rates running via the SC2 mechanism (scalar relaxation of the second kind), we present in this work the results obtained for three molecules: 9-bromotriptycene, 1,3,5-tribromobenzene, and 1-(2-bromoethynyl)-4-ethynylbenzene in which C-Br bond and one of C-H bonds are collinear. Separation of saturation-recovery or inversion-recovery curves of (13)C NMR signals of bromine-bonded carbons in the investigated compounds on two components has provided the longitudinal SC2 relaxation rates of these carbons in (79)Br- and (81)Br-containing isotopomers. These data have enabled experimental determination of the bromine-carbon spin-spin coupling constants and relaxation rates of quadrupole bromine nuclei, hardly accessible by direct measurements.

Yolk proteins in the male reproductive system of the fruit fly Drosophila melanogaster: spatial and temporal patterns of expression.

In insects, spermatozoa develop in the testes as clones of single spermatogonia covered by specialized somatic cyst cells (cc). Upon completion of spermatogenesis, spermatozoa are released to the vas deferens, while the cc remain in the testes and die. In the fruit fly Drosophila melanogaster, the released spermatozoa first reach the seminal vesicles (SV), the organ where post-testicular maturation begins.

Accurate determination of the ultrafast proton transfer rate in porphycene using nuclear spin relaxation.

The longitudinal (15)N relaxation rate and (15)N{(1)H} NOE enhancement were determined for porphycene in a CD2Cl2 solution. By invoking the rotational diffusion tensor of porphycene as previously determined, these data could be used to evaluate the tautomerization rate of protons in the NHN bridges. The proton transfer rate compares well to the results obtained by other authors by means of optical spectroscopy.

Determination of the rotational diffusion tensor of porphycene by 13C and 1H spin relaxation methods.

The longitudinal (13)C and (1)H relaxation rates were determined in porphycene in CD(2)Cl(2) solution. These data, augmented by (13)C{(1)H} NOE enhancements were numerically analyzed to evaluate the rotational diffusion tensor of the molecule and the vibrational correction for the one-bond (13)C-(1)H dipolar couplings. The (13)C and (1)H relaxation data seem to be consistent with each other, and the emerging picture of the rotational dynamics of porphycene compares well with the results that can be found in the literature.

Evolution of bet-hedging mechanisms in cell cycle and embryo development stimulated by weak linkage of stochastic processes.

Our current understanding of the origin and evolution of the cell cycle is largely filled with gaps and unresolved questions. Numerous similarities between the processes comprising the cell cycle in distant organisms from the Pro- and Eukaryota kingdoms provide some clues about the course that evolution has taken. Contemporary Prokaryotes and Eukaryotes regulate their cell cycles in a quite similar way, using a master oscillator that regulates cell division.

Differential levels of stress proteins (HSPs) in male and female Daphnia magna in response to thermal stress: a consequence of sex-related behavioral differences?

In two independent experiments, we compared: (1) water depth selection (and accompanying temperature selection) by male and female Daphnia magna under different kinds of environmental stress, including the presence of filamentous cyanobacteria, the risk of predation from fish, and the presence of toxic compounds; and (2) sex-dependent production of heat shock proteins (HSP60, 70, and 90) in response to a sudden change in temperature. Male D. magna selected deep water strata, which offer a relatively stable environment, and thereby avoided the threat of predation and the presence of toxic compounds in surface waters.

Daphnia response to biotic stress is modified by PCBs.

The aim of this study was to examine the influence of xenobiotics (PCBs) on the responses of Daphnia to biotic factors such as the presence of a predator (fish kairomone) or filamentous cyanobacteria. Both behaviour (depth selection) and life history (body size at first reproduction and fecundity) were affected by these stressors. Though there was no direct effect of PCBs, their influence resulted in disruption of the "natural" reaction to the presence of fish or cyanobacteria, leading to inadequate responses of Daphnia to these biotic threats.

A simple one-dimensional method of chemical shift anisotropy determination under MAS conditions.

A method of determination of chemical shift anisotropy (CSA) tensor principal components under MAS condition is presented. It is a simple, one-dimensional, and robust alternative to the commonly exploited, but more complicated 2D-PASS. The required CSA components are delivered by simultaneous numerical analysis of a few regular MAS spectra acquired under different spinning rates.

Carbon-13 NMR relaxation study of the internal dynamics in cyclodextrins in isotropic solution.

(13)C nuclear spin relaxation processes in seven cyclodextrins (from six-membered alpha to twelve-membered eta) were investigated in (2)H(2)O solution at multiple magnetic fields. Detailed analysis of (13)C longitudinal relaxation in laboratory and rotating frames and (13)C{(1)H} nuclear Overhauser enhancement in these molecules yielded their rotational diffusion tensors and a semiquantitative picture of their internal dynamics.

Structural studies on aryl-substituted enaminoketones and their thio analogues. Part I. Analysis of high-resolution (1)H, (13)C NMR and (13)C CP MAS spectra combined with GIAO-DFT calculations.

A series of aryl-substituted enaminoketones and their thio analogues in CDCl(3) solution and in the solid state were studied by the use of high-resolution (1)H and (13)C as well as (13)C cross polarization magic angle spinning (CP MAS) NMR spectra in combination with gauge including atomic orbitals-density functional theory (GIAO-DFT) calculations performed at the B3PW91/6-311 + + G(d,p) level of theory using the B3PW91/6-311 + + G(d,p)-optimized geometries. The analysis of the (13)C NMR spectra in solution was done by using the Incredible Natural Abundance DoublE QUAntum Transfer Experiment (INADEQUATE) technique, whereas trends observed in the (13)C shielding constants, calculated for the compounds studied, were a great help in assigning most of the signals in the (13)C CP MAS NMR spectra. It was established on the basis of the experimental and theoretical NMR data that both groups of compounds exist in the form of Z-s-Z-s-E isomers in CDCl(3) solution as well as in the solid state, with the NH hydrogen atom involved in intramolecular hydrogen bonding.