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

Despite various applications of alkylzinc complexes supported by N,N-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 N,N'-diphenylformamidinate ligands as model N,N'-unsubstituted and N,N'-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). The results indicate that [RZnL]x-type amidinate moieties are essentially unstable and tend to undergo Schlenk equilibria-mediated ligand scrambling leading to more thermodynamically stable non-stoichiometric [R2Zn3L4]- and [R3Zn4L5]-type complexes. This process is significantly influenced by the secondary coordination sphere noncovalent interactions as well as the steric hindrance provided by both zinc-bounded alkyl groups and the N-substituents.

Molecular Oscillator Affects Susceptibility of Caterpillars to Insecticides: Studies on the Egyptian Cotton Leaf Worm-Spodoptera littoralis (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., rhythmic metabolism of xenobiotics, including insecticides). We disrupted the clock operation in S. littoralis larvae by injecting the dsRNA of clock genes into their body cavity and culturing the larvae under continuous light. As a result, the daily susceptibility of larvae to insecticides was abolished and the susceptibility itself increased (in most cases). In the fat body, midgut, and Malpighian tubules (the main organs metabolizing xenobiotics) of the larvae treated with injected-dsRNA, the daily activity profiles of enzymes involved in detoxification-cytochrome P450 monooxygenases, Glutathione-S-transferase, and esterase-have changed significantly. The presented results prove the role of the molecular oscillator in the regulation of larvae responses to insecticides and provide grounds for rational use of these compounds (at suitable times of the day), and may indicate clock genes as potential targets of molecular manipulation to produce plant protection compounds based on the RNAi method.

Mechanochemical vs Wet Approach for Directing CO2 Capture toward Various Carbonate and Bicarbonate Networks.

The distinct research areas related to CO2 capture and mechanochemistry are both highly attractive in the context of green chemistry. However, merger of these two areas, i.e., mechanochemical CO2 capture, is still in an early stage of development. Here, the application of biguanidine as an active species for CO2 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. We demonstrate that in solution, the formation of the carbonate vs bicarbonate networks can be directed by the organic solvent, while, remarkably, in the liquid-assisted mechanochemical synthesis employing the same solvents as additives, the selectivity in network formation is inversed. In general, our findings support the view of mechanochemistry not only as a sustainable alternative but rather as a complementary strategy to solution-based synthesis.

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. The electronic properties are estimated in the liquid state; for example, via the 77 Se liquid state NMR of Se-NHC adducts. We demonstrate that 77 Se NMR crystallography can contribute to the characterization of the structural and electronic properties of NHC in solid and liquid states. Selected Se-NHC adducts are investigated via 77 Se solid state NMR and X-ray crystallography, supported by quantum chemical calculations. This investigation reveals a correlation between the molecular structure of adducts and NMR parameters, including not only isotropic chemical shifts but also the other chemical shift tensor components. Afterwards, the liquid state 77 Se NMR data is presented and interpreted in terms of the quantum chemistry modelling. The discrepancy between the structural and electronic properties, and in particular the π-accepting abilities of adducts in the solid and liquid states is discussed. Finally, the 13 C isotropic chemical shift from the liquid state NMR and the 13 C tensor components are also discussed, and compared with their 77 Se counterparts. 77 Se NMR crystallography can deliver valuable information about NHC ligands, and together with liquid state 77 Se NMR can provide an in-depth outlook on the properties of NHC ligands.

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)3 (µ-OC(H)Ph2 )2 (µ3 -OC(H)Ph2 )] and a ladder-type tetramer [(PhZn)4 (µ-OC(H)Ph2 )2 (µ3 -OC(H)Ph2 )2 ], incorporating diphenylmethanolate as a model alkoxide ligand, are reported. Both novel aggregates are robust in the solid state and resistant towards mechanical force. By using 1 H NMR and diffusion-order spectroscopy, it is demonstrated that new RZnOR' alkoxides are kinetically labile in solution and readily undergo ligand scrambling, such as in the case of Schlenk equilibrium. The elucidated key structural issues, which have remained undiscovered for decades, significantly advance the chemistry of RZnOR' alkoxides and should support the rational design of zinc alkoxide-based applications.

C60 in a peptidic cage: a case of symmetry mismatch studied by crystallography and solid-state NMR.

A supramolecular complex, formed by encapsulation of C60 fullerene in a molecular container built from two resorcin[4]arene rims zipped together by peptidic arms hydrogen bonded into a cylindrical ß-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. Solid-state NMR measurements at 184-333 K indicate that the thermal motion of C60 in this temperature range is fast but has different activation energies at different temperatures, which was attributed to a phase transition, which was confirmed by DSC. Intriguingly, the activation energy for reorientations of C60 in the solid state is very similar for the free and encaged molecules. Also, the rotational diffusion coefficients seem to be very similar or even slightly higher for the encaged fullerene compared to the free molecule. We also found that chemical shift anisotropy (CSA) is not the main relaxation mechanism for the 13C spins of C60 in the studied complex.

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

Amyloid ß, Aß(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 Aß activity toward a brain-like model membrane and demonstrate that this activity strongly depends on the Aß oligomer size. PeakForce quantitative nanomechanical mapping mode of atomic force microscopy imaging revealed that the interaction of large-size (LS) Aß oligomers, corresponding to high-molecular-weight Aß oligomers, with the brain total lipid extract (BTLE) membrane resulted in accelerated Aß fibrillogenesis on the membrane surface. Importantly, the fibrillogenesis did not affect integrity of the membrane. In contrast, small-size (SS) Aß oligomers, corresponding to low-molecular-weight Aß oligomers, created pores and then disintegrated the BTLE membrane. Both forms of the Aß oligomers changed nanomechanical properties of the membrane by decreasing its Young's modulus by ∼45%. Our results demonstrated that both forms of Aß oligomers induce the neurotoxic effect on the brain cells but their action toward the membrane differs significantly.

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. At a constant level of available resources, uninterrupted development was the superior life strategy. Once population fluctuations appeared (generated by the stochastic variability of available resources), temporal developmental arrest became more advantageous than continuous development. We did not observe the selection of the optimum length of dormancy, but rather the evolution of a diversified period of developmental arrest. The fittest organisms employed bet-hedging strategy and produced diversified dormant forms postponing development for a different number of generations (from 0 to several generations, in decreasing or equal proportions). The maximum length of suspended development increased asymptotically with increasing environmental variability and was inversely related to the mortality of dormant forms. The prolonged dormancy may appear beneficial not only in erratic habitats but also in seasonal ones that are exposed to long-term variability of environmental conditions during the growing seasons. In light of our simulations the phenomenon of very long diapause (VLD), lasting tens to thousands of generations, which is occasionally observed in ontogenesis of some living creatures, may not be explained by the benefits of bet-hedging revival strategies. We propose an alternative reasoning for the expression of VLD.

Nonclassical dynamics of the methyl group in 1,1,1-triphenylethane. Evidence from powder 1H 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. The values of their ratio, or the nonclassicallity coefficient, determined hitherto from NMR spectra of single crystals and solutions range from about 1.20 to 1.30 in the latter case to above 5.0 in the former, with the value of 1 corresponding to the jump model. Presently, first systematic investigations of the DQR effects in wide-line NMR spectra of a powder sample are reported. For 1,1,1-triphenylethane deuterated in the aromatic positions, the relevant line-shape effects were monitored in the range 99-121 K. The values of the nonclassicality coefficient dropping from 2.7 to 1.7 were evaluated in line shape fits to the experimental powder spectra from the range 99-108 K. At these temperatures, the fits with the conventional line-shape model are visibly inferior to the DQR fits. Using a theoretical model reported earlier, a semiquantitative interpretation of the DQR parameters evaluated from the spectra is given. It is shown that the DQR effects as such can be detected in wide-line NMR spectra of powdered samples, which are relatively facile to measure. However, a fully quantitative picture of these effects can only be obtained from the much more demanding experiments on single crystals.

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

Hindered rotation of the -NH3+ 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 HBF4. 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. Because of these additional effects, an effective rate constant of the hindered rotation could be evaluated at only one temperature for the neutral solution of the salt. For one of the acidified samples, which was prepared with special precautions against moisture, these complications are practically nonexistent at low and intermediate temperatures. For the latter sample, the Arrhenius parameters of the hindered rotation could be determined from the rotation rates evaluated in the range 194-226 K.

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. We analyzed the abundance of 20 gene transcripts throughout the day in the whole bodies of D. pulex (single clone); we found that 15 of these genes were transcriptionally active, and most had daily expression level changes. According to the functional classification of their homologues in insects, these genes may represent elements of the Daphnia molecular oscillator core and its input and output pathways. Studies of PERIOD (PER) protein, one of the main clock components, revealed its rhythmic expression pattern in the epidermis, gut, and ovaries. Finally, the cycling levels of many of these clock components observed in animals reared in continuous light led to the conclusion that the Daphnia oscillator, even if it is structurally similar to the oscillators of other arthropods, can be considered a particularly important adaptive mechanism for living in environments with extreme photoperiods.

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. The entire variety of relaxation effects in protonated methyl groups have recently been given a consistent quantum mechanical explanation not invoking the jump model regardless of the temperature range. It exploits the damped quantum rotation (DQR) theory originally developed to describe NMR line shape effects for hindered methyl groups. In the DQR model, the incoherent dynamics of the methyl group include two quantum rate (i.e., coherence-damping) processes. For proton relaxation only one of these processes is relevant. In this paper, temperature-dependent proton spin-lattice relaxation data for the methyl groups in polycrystalline methyltriphenyl silane and methyltriphenyl germanium, both deuterated in aromatic positions, are reported and interpreted in terms of the DQR model. A comparison with the conventional approach exploiting the phenomenological Arrhenius equation is made. The present observations provide further indications that incoherent motions of molecular moieties in the condensed phase can retain quantum character over much broader temperature range than is commonly thought.

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. For the first time, a highly SABRE-active pyridine-based biocompatible molecular framework is incorporated into synthetic oligopeptides. The SABRE activity is preserved, demonstrating the importance of such earmarking. Finally, a crucial exchange process responsible for SABRE activity is identified and discussed.

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. At the same time the rotational diffusion parameters describing the reorientation of the C-Br vectors have been determined for the investigated molecules on the basis of the dipolar relaxation of protonated carbons. These diffusion parameters are crucial for interpretation of the bromine relaxation rates. The values of the indirect (1)J((13)C,(79)Br) coupling constants, magnetic shielding of carbon nuclei and quadrupole coupling constants of bromines, determined for the investigated compounds, have been compared with the results of the theoretical calculations which take into account relativistic effects. The origin of some divergences between the results obtained by different methods has been discussed.

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. Here, we demonstrate the temporal (restricted to the evening and early night hours) accumulation of membranous vesicles containing proteins in the SV lumen of D. melanogaster. When SV vesicles were isolated from the semen and co-incubated with testis-derived spermatozoa in vitro, their contents bound to the spermatozoa along their tails. The proteins of the SV vesicles were then characterized using 2-D electrophoresis. We identified a prominent protein spot of around 45-47 kDa, which disappears from the SV vesicles in the night, i.e. shortly after they appear in the SV lumen. Sequencing of peptides derived from this spot by mass spectrometry revealed identity with three yolk proteins (YP1-3). This unexpected result was confirmed by western blotting, which demonstrated that SV vesicles contain proteins that are immunoreactive with an antibody against D. melanogaster YP1-3. The expression of all yp genes was shown to be a unique feature of testis tissues. Using RNA probes we found that their transcripts localize exclusively to the cc that cover fully developed spermatozoa in the distal part of each testis. Temporally, the expression of yp genes was found to be restricted to a short period during the day and is followed by the evening accumulation of YP proteins in the cc. Immunohistochemical staining confirmed that cc are the source of SV vesicles containing YPs that are released into the SV lumen. These vesicles interact with spermatozoa and as a result, YPs become extrinsic proteins of the sperm membrane. Thus, we describe for the first time the expression of yolk proteins in the male reproductive system of D. melanogaster under physiological conditions, and show that somatic cells of the testes are the source of these proteins.

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. Despite this striking similarity, they use entirely different molecules for this purpose. The necessity to keep the master oscillator intact for the survival of every cell/organism allows evolutionary changes in only the secondary mechanisms and processes of the cell cycle. This is especially clear in oocytes and embryos, which have a direct impact on the reproductive success of an adult organism. Here, we present examples of cues driving such mild evolutionary changes of certain aspects of cell cycle progression in oocytes and early embryos. We suggest that weak linkages between core processes that rely on randomness (stochasticity) have led to the evolution of strategies increasing fitness similar to bet-hedging, a stochastic-based survival strategy of risk minimization widely implemented by populations of bacteria, yeast, arthropods, and birds. Stochastic diversification of phenotypes by isogenic cells increases their fitness in unpredictable environments and improves their survival rate upon exposure to stress, a trait beneficial in evading antibiotic treatment by bacteria or withstanding chemotherapy by cancer cells. The evolution of bet-hedging has been observed experimentally for bacteria and attributed to specific molecular mechanisms involved in this strategy. In this chapter, we set out to answer whether similar strategies could have evolved at the level of oocytes and embryos. We indicate possible evolutionary cues capable of realizing bet-hedging-like mechanisms.

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. Correlated with this behavior, males reduce their molecular defenses against stress, such as the production of heat shock proteins (HSPs), and do not maintain the physiological machinery that triggers an increase in HSP levels in response to stress. In contrast, female D. magna actively select habitats that offer optimal conditions for growth and production of offspring. Consequently, females are exposed to variable environmental conditions that may be associated with increased stress. To permit survival in these different habitats, D. magna females require molecular mechanisms to protect their cells from rapid changes in stress levels. Thus, they maintain high constitutive levels of the heat shock proteins from HSP 60, 70, and 90 families, and they have the potential to further enhance the production of the majority of these proteins under stress conditions. The results of this study indicate that the separate habitats selected by male and female D. magna result in different patterns of HSP production, leading us to hypothesize that that male and female Daphnia magna adopt different strategies to maximize the fitness of the species.