Theoretical analysis of the smallest carbon cluster containing a planar tetracoordinate carbon

A series of molecules, based on the smallest carbon cluster with one planar tetracoordinate carbon atom, C5(2-), are presented. To gain a better understanding about which electronic factors contribute to their stabilization, several global reactivity indexes, molecular scalar fields, and magnetic responses were calculated. The optimized bond lengths and the topological analysis of the electron density show that the central carbon atom in the parent dianion C5(2-) has a planar local environment, and it is coordinated to four other carbon atoms. The bonding of the parent dianion with the metal cations is highly ionic. The magnetic properties show that the C5(2-) derivatives are strongly diatropic and have a remarkable transferability of structural and electronic features from the anion to the salts. The theoretical analysis suggests that the lithium salt, C5Li2, is the most plausible candidate for experimental detection.     

Characterization of the bis(β-diimino-tetracyano-pyrrolizinido)-metal(II) complexes incorporated in polymeric matrices

The bis(-diimino-tetracyano-pyrrolizinido)-Cu(II) complex (CuL₂) has been incorporated in polystyrene (0.28% w/w), by evaporating tetrahydrofuran solutions either at room temperature (a) or at 100°C (b). From IR and UV-vis measurements and optical microscopy on the resulting films (a orb, thickness 50 m) it is concluded that CuL₂ is present as a concentrated (C10^–1 M) THF solution ina and as small solid particles (diameter <1 m) inb. The difference in colour of the films (dark bluea, light blueb), due to the different physical state of CuL₂ in the matrix, is expected, and has been preliminarily shown using similar films based on NiL₂, to be useful for sensing organic vapours in the atmosphere.     

Ordering of nested square roots of 2 according to the Gray code

In this paper, we discuss some relations between zeros of Lucas–Lehmer polynomials and the Gray code. We study nested square roots of 2 applying a “binary code” that associates bits 0 and 1 to “plus” and “minus” signs in the nested form. This gives the possibility to obtain an ordering for the zeros of Lucas–Lehmer polynomials, which take the form of nested square roots of 2.     

The dependence of 13C-1H coupling constants on CCC bond angles

The relationship between one-bond ¹³C-¹H coupling constants and internuclear CCC bond angles (_n) in hydrocarbons of the type R₂CH₂ is best approximated by a quadratic expression.     

Light‐Driven Charge Separation in Isoxazolidine–Perylene Bisimide Dyads

A series of arrays for light‐driven charge separation is presented, in which perylene tetracarboxylic bisimide is the light‐absorbing chromophore and electron acceptor, whereas isoxazolidines are colourless electron donors, the electron‐releasing properties of which are increased with respect to the amino group by means of the α‐effect. Charge separation (CS) in toluene over a distance ranging from ≈10 to ≈16 Å, with efficiencies of ≈95 to ≈50 % and CS lifetimes from 300 ps to 15 ns, are demonstrated. In dichloromethane the charge recombination reaction is faster than charge separation, preventing accumulation of the CS state. The effects of solvent polarity and molecular structure are discussed in the frame of current theories.     

The emergence of semantic categorization in early visual processing: ERP indices of animal vs. artifact recognition

Background

Neuroimaging and neuropsychological literature show functional dissociations in brain activity during processing of stimuli belonging to different semantic categories (e.g., animals, tools, faces, places), but little information is available about the time course of object perceptual categorization. The aim of the study was to provide information about the timing of processing stimuli from different semantic domains, without using verbal or naming paradigms, in order to observe the emergence of non-linguistic conceptual knowledge in the ventral stream visual pathway. Event related potentials (ERPs) were recorded in 18 healthy right-handed individuals as they performed a perceptual categorization task on 672 pairs of images of animals and man-made objects (i.e., artifacts).

Results

Behavioral responses to animal stimuli were ~50 ms faster and more accurate than those to artifacts. At early processing stages (120–180 ms) the right occipital-temporal cortex was more activated in response to animals than to artifacts as indexed by posterior N1 response, while frontal/central N1 (130–160) showed the opposite pattern. In the next processing stage (200–260) the response was stronger to artifacts and usable items at anterior temporal sites. The P300 component was smaller, and the central/parietal N400 component was larger to artifacts than to animals.

Conclusion

The effect of animal and artifact categorization emerged at ~150 ms over the right occipital-temporal area as a stronger response of the ventral stream to animate, homomorphic, entities with faces and legs. The larger frontal/central N1 and the subsequent temporal activation for inanimate objects might reflect the prevalence of a functional rather than perceptual representation of manipulable tools compared to animals. Late ERP effects might reflect semantic integration and cognitive updating processes. Overall, the data are compatible with a modality-specific semantic memory account, in which sensory and action-related semantic features are represented in modality-specific brain areas.     

Rhenium and technetium tricarbonyl complexes anchored by 5-HT1A receptor-binding ligands containing P,O/N donor atom sets

The (2-methoxyphenyl)piperazine pharmacophore, a part of the WAY 100635 structure, has been functionalized with phosphinoarylbenzylamide or phosphinoarylbenzylamine chelator groups using propylene or hexylene alkyl chains as linkers (L2-L4). These heterofunctionalized phosphines bearing an arylpiperazine moiety have been used to stabilize rhenium tricarbonyl complexes of the type [Re(CO)₃Br(κ²-L)] (4, L = L2; 5, L = L3; 6, L = L4), which have been fully characterized, including by X-ray crystallographic analysis in the case of compounds 4 and 5. These monomeric complexes are six-coordinate, displaying a distorted octahedral coordination geometry with a facial arrangement of the carbonyl groups. The other three remaining positions are occupied by a bromide and by the bidentate heterofunctionalized phosphine, which coordinates through the phosphorus and the oxygen atom or through the phosphorus and the nitrogen atom in 4 and 5, respectively. The ^99mTc complexes (3a-6a) were also prepared and their characterization established by comparative HPLC, using the Re complexes as surrogates. The in vitro binding affinity for the 5HT_1A receptor subtype and the selectivity against the 5HT_2A receptors for the rhenium complexes were determined. Compound 3 is the only one which presents a reasonable affinity and selectively towards 5HT_1A (IC₅₀ = 20 nM) and 5HT_2A (IC₅₀ = 4680 nM) receptors, respectively. When the spacer length between the chelate unit and receptor binding domain increased and/or the amide group in the chelator was replaced by a secondary amine unacceptable affinity values for 5HT_1A receptors (IC₅₀ = 200-1100 nM) and lost of selectivity were observed.     

Quantum treatment of the Ar-HI photodissociation dynamics

A wave packet simulation of the ultraviolet photolysis dynamics of Ar-HI(upsilon = 0) is reported. Cluster photodissociation is started from two different initial states, namely, the ground van der Waals (vdW) and the first excited vdW bending state, associated with the Ar-I-H and Ar-H-I isomeric forms of the system, respectively. Formation of Ar-I radical products is investigated over the energy range of the cluster absorption spectrum. It is found that the yield of bound Ar-I radical complexes is typically 90%-100% and 70%-80% for the initial states associated with the Ar-I-H and Ar-H-I isomers, respectively. This result is in agreement with the experimentally observed time-of-flight spectrum of the hydrogen fragment produced after Ar-HI photodissociation. The high Ar-I yield is explained mainly by the small amount of energy available for the radical that is converted into internal energy in the photofragmentation process, which enhances the Ar-I survival probability. Quantum interference effects manifest themselves in structures in the angular distribution of the hydrogen fragment, and in pronounced rainbow patterns in the rotational distributions of the Ar-I radical.     

Fast Cyclization of a Proline‐Derived Self‐Immolative Spacer Improves the Efficacy of Carbamate Prodrugs

Self‐immolative (SI) spacers are sophisticated chemical constructs designed for molecular delivery or material degradation. We describe herein a (S)‐2‐(aminomethyl)pyrrolidine SI spacer that is able to release different types of anticancer drugs (possessing either a phenolic or secondary and tertiary hydroxyl groups) through a fast cyclization mechanism involving carbamate cleavage. The high efficiency of drug release obtained with this spacer was found to be beneficial for the in vitro cytotoxic activity of protease‐sensitive prodrugs, compared with a commonly used spacer of the same class. These findings expand the repertoire of degradation machineries and are instrumental for the future development of highly efficient delivery platforms.     

Can Raman spectroscopy detect cumulenic structures of linear carbon chains?

The molecular and vibrational structures of cumulenic carbon chains are investigated by density functional theory calculations and compared with that of hydrogen‐capped polyynes. The small value of bond length alternation (BLA) along the CC bonds sequence obtained by geometry optimization of uncapped C_n chains and vinyl‐capped carbon chains confirms their cumulenic structure. It is demonstrated that for finite length chains the structural parameters are determined by end effects as far as the Peierls distortion, expected for very long molecules, does not occur. The Raman spectra of such molecules are calculated to verify the possibility of identifying markers of cumulenic chains by means of vibrational spectroscopy. As expected, the longitudinal mode consisting of the BLA oscillation, which is responsible for the strongest Raman transition of polyynes, becomes very weak for cumulenes; this behaviour is rationalized in terms of local polarizability derivatives. However, other longitudinal modes can be observed in the Raman spectra of C_n chains. The wavenumber behaviour and the optical activity of these modes are interpreted on the basis of the phonon dispersion branch of an ideally infinite cumulenic polymer. Raman intensities computed for chains of different lengths allow to conclude that cumulenic molecules could be detected and identified by means of Raman spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd.