The Synthesis and STM/AFM Imaging of ‘Olympicene’ Benzo[cd]pyrenes

H‐Benzo[cd]pyrene (‘Olympicene′) is a polyaromatic hydrocarbon and non‐Kekulé fragment of graphene. A new synthetic method has been developed for the formation of 6H‐benzo[cd]pyrene and related ketones including the first time isolation of the unstable alcohol 6H‐benzo[cd]pyren‐6‐ol. Molecular imaging of the reaction products with scanning tunnelling microscopy (STM) and non‐contact atomic force microscopy (NC‐AFM) characterised the 6H‐benzo[cd]pyrene as well as the previously intangible and significantly less stable 5H‐benzo[cd]pyrene, the fully conjugated benzo[cd]pyrenyl radical and the ketones as oxidation products.     

Structural and Dynamic Properties of Monoclonal Antibodies Immobilized on CNTs: A Computational Study

Due to the widespread application of carbon nanotube (CNT)‐based materials in nanomedicine, it is nowadays of paramount importance to unravel at the atomistic level of detail the structural properties of such bioconjugates in order to rationalize and predict the effect exerted by the graphitic framework on the bio‐active counterpart. In this paper, we report for the first time all‐atom explicit solvent molecular dynamics (MD) simulations investigating the structural and dynamic properties of a noncovalent bioconjugate in which the monoclonal Cetuximab antibody (Ctx) is adsorbed on a CNT surface. Upon selection of the three most representative adsorption modes as obtained by docking studies, force‐field MD and DFT simulations unambiguously showed that hydrophobic interactions mainly govern the adsorption of the protein on the graphitic surface. Two main adsorption poses have been predicted: a pose‐fab (p‐fab) and pose‐fc (p‐fc) (fab = fragment antigen binding region; fc = fragment crystallizable region), the former being favored with small‐diameter tubes (≤40 Å). In all the predicted poses, the secondary structure of Ctx is largely unaffected by the presence of the graphitic surface and, consistently with previous literature studies, our simulations reveal that positively charged amino acidic residues, such as Lys and Arg, predominantly contribute to the stabilization of the CNT?Ctx complex acting like surfactants. The predicted structural models are consistent with the experimental data, for which the immobilization of the antibody on CNTs does not disrupt the structural and recognition properties of the Ctx, consequently supporting the reliability of the used bioconjugation strategy for engineering stable and responsive hybrid nanomaterials for therapeutic applications. Moreover, a remarkable structural similarity of Ctx with antibodies of different isotypes suggests that in principle the CNT framework can interact in the same manner with all antibodies currently used in clinical applications.     

Photochemistry of trans-Cr(cyclam)(ONO)2+, a nitric oxide precursor

Experimental and density functional theory (DFT) studies are described that are focused on outlining the reactivity of the known photochemical nitric oxide precursor trans-Cr(cyclam)(ONO)(2)(+) ("CrONO", cyclam = 1,4,8,11-tetrazacycltetradecane). Studies in both aerated and deaerated aqueous media are described as are the roles of both the oxidant O(2) and a reductant such as glutathione in trapping the apparent Cr(IV) photoreaction intermediate trans-Cr(cyclam)(O)(ONO)(+). Also reported and characterized structurally is the Cr(V) product of long-term photolysis in the absence of reducing agents, the trans-dioxo species [trans-Cr(cyclam)(O)(2)](ClO(4)). Photosensitization experiments indicate that at least a significant fraction of the reaction occurs from the lowest energy doublet excited state(s). Lastly, cell culture experiments demonstrate that CrONO has little or no acute toxicity either before or after photolysis.     

Nuclear magnetic resonance study of alkane conformational statistics

NMR spectra of ethane, propane, and n-butane as solutes in the nematic liquid crystals 4-n-pentyl-4(')-cyanobiphenyl (5CB) and Merck ZLI 1132 (1132) are investigated over a wide temperature range. The ratios of dipolar couplings of ethane to propane are constant over the entire temperature range. Assuming that this constancy applies to the butane conformers facilitates the separation of probability from order parameter. This separation allows the investigation of conformational distribution without the need of invoking any model for the anisotropic intermolecular potential. The results give an order matrix that is consistent with that predicted from model potentials that describe the orientational potential in terms of short-range size and shape effects. The isotropic intermolecular potential contribution to the trans-gauche energy difference E(tg) is found to be temperature dependent with the values and variation in agreement with that found when the same results are analyzed using the chord model for anisotropic interactions [A. C. J. Weber and E. E. Burnell, Chem. Phys. Lett. 506, 196 (2011)]. The fit obtained for 9 spectra in 5CB (63 dipolar couplings) has an RMS difference between experimental and calculated dipolar couplings of 2.7 Hz, while that for the 16 spectra in 1132 (112 couplings) is 6.2 Hz; this excellent fit with nine adjustable parameters suggests that the assumption of equal temperature dependencies of the order parameters for ethane, propane, and each conformer of butane is correct. Also the fit parameters (E(tg) and the methyl angle increase) obtained for 1132 and 5CB agree. The results indicate that the chord model, which was designed to treat hydrocarbon chains, is indeed the model of choice for these chains. The temperature variation of E(tg) provides a challenge for theoreticians. Finally, even better fits to the experimental dipolar couplings are obtained when the energy in the Boltzmann factor is used for scaling ethane to butane results. However, in this case the values obtained for E(tg) differ between 1132 and 5CB.     

Strategies for the intracellular delivery of nanoparticles

The ability to target contrast agents and therapeutics inside cells is becoming important as we strive to decipher the complex network of events that occur within living cells and design therapies that can modulate these processes. Nanotechnology researchers have generated a growing list of nanoparticles designed for such applications. These particles can be assembled from a variety of materials into desirable geometries and configurations and possess useful properties and functionalities. Undoubtedly, the effective delivery of these nanomaterials into cells will be critical to their applications. In this tutorial review, we discuss the fundamental challenges of delivering nanoparticles into cells and to the targeted organelles, and summarize strategies that have been developed to-date.     

Effect of substituents on the stabilities of multiply-substituted carbon-centered radicals

The bond dissociation energies (BDEs) and radical stabilization energies (RSEs) which result from 166 reactions that lead to carbon-centered radicals of the type ˙CH(2)X, ˙CHXY and ˙CXYZ, where X, Y and Z are any of the fourteen substituents H, F, Cl, NH(2), OH, SH, CH[double bond, length as m-dash]CH(2), C[triple bond, length as m-dash]CH, BH(2), CHO, COOH, CN, CH(3), and CF(3), were calculated using spin-restricted and -unrestricted variants of the double-hybrid B2-PLYP method with the 6-311+G(3df,2p) basis set. The interactions of substituents X, Y, and Z in both the radicals (˙CXYZ) and in the precursor closed-shell molecules (CHXYZ), as well as the extent of additivity of such interactions, were investigated by calculating radical interaction energies (RIEs), molecule interaction energies (MIEs), and deviations from additivity of RSEs (DARSEs) for a set of 152 reactions that lead to di- (˙CHXY) and tri- (˙CXYZ) substituted carbon-centered radicals. The pairwise quantities describing the effects of pairs of substituents in trisubstituted systems, namely pairwise MIEs (PMIEs), pairwise RIEs (PRIEs) and deviations from pairwise additivity of RSEs (DPARSEs), were also calculated for the set of 61 reactions that lead to trisubstituted radicals (˙CXYZ). Both ROB2-PLYP and UB2-PLYP were found to perform quite well in predicting the quantities related to the stabilities of carbon-centered radicals when compared with available experimental data and with the results obtained from the high-level composite method G3X(MP2)-RAD. Particular selections of substituents or combinations of substituents from the current test set were found to lead to specially stable radicals, increasing the RSEs to a maximum of +68.2 kJ mol(-1) for monosubstituted radicals ˙CH(2)X (X = CH[double bond, length as m-dash]CH(2)), +131.7 kJ mol(-1) for disubstituted radicals ˙CHXY (X = NH(2), Y = CHO), and +177.1 kJ mol(-1) for trisubstituted radicals ˙CXYZ (X = NH2, Y = Z = CHO).     

Synthesis of Metastable Inorganic Solids with Extended Structures

The number of known inorganic compounds is dramatically less than predicted due to synthetic challenges, which often constrains products to only the thermodynamically most stable compounds. Consequently, a mechanism-based approach to inorganic solids with designed structures is the holy grail of solid state synthesis. This article discusses a number of synthetic approaches using the concept of an energy landscape, which describes the complex relationship between the energy of different atomic configurations as a function of a variety of parameters such as initial structure, temperature, pressure, and composition. Nucleation limited synthesis approaches with high diffusion rates are contrasted with diffusion limited synthesis approaches. One challenge to the synthesis of new compounds is the inability to accurately predict what structures might be local free energy minima in the free energy landscape. Approaches to this challenge include predicting potentially stable compounds thorough the use of structural homologies and/or theoretical calculations. A second challenge to the synthesis of metastable inorganic solids is developing approaches to move across the energy landscape to a desired local free energy minimum while avoiding deeper free energy minima, such as stable binary compounds, as reaction intermediates. An approach using amorphous intermediates is presented, where local composition can be used to prepare metastable compounds. Designed nanoarchitecture built into a precursor can be preserved at low reaction temperatures and used to direct the reaction to specific structural homologs.