Synthesis,Properties, and Dispersion of Few‐Layer Graphene Fluoride

We have fluorinated few‐layer graphene (FLG) by using a low‐temperature fluorination route with gaseous ClF₃. The treatment process resulted in a new graphene derivative with a finite approximate composition of C₂F. TEM studies showed that the product consisted of thin transparent sheets with no more than 10 fluorographene layers stacked together. Spectroscopic methods revealed a predominantly covalent nature of the C? F bonds in the as‐synthesized product and we found no evidence for the existence of so‐called “semi‐ionic” C? F bonds, as observed in bulk C_xF. In contrast to the case of graphite and typical (thick) expanded graphites, fluorination of FLG did not lead to the intercalation of ClF₃ molecules, owing to the lack of a 3D layered structure. The approximate “critical” number of graphene layers that were necessary to form a phase of intercalated compound was estimated to be more than 12, thus providing a “chemical proof” of the difference between the properties of few‐layered graphenes and bulk graphites. Fluorographene C₂F was successfully delaminated into thinner layers in organic solvents, which is an important property for its integration into electronic devices, nanohybrids, etc.     

The Nature of One‐Dimensional Carbon: Polyynic versus Cumulenic

A question of both fundamental as well as practical importance is the nature of one‐dimensional carbon, in particular whether a one‐dimensional carbon allotrope is polyynic or cumulenic, that is, whether bond‐length alternation occurs or not. By combining the concept of aromaticity and antiaromaticity with the rule of Peierls distortion, the occurrence and magnitude of bond‐length alternation in carbon chains with periodic boundary conditions and corresponding carbon rings as a function of the chain or ring length can be explained. The electronic properties of one‐dimensional carbon depend crucially on the bond‐length alternation. Whereas it is generally accepted that carbon chains in the limit of infinite length have a polyynic structure at the minimum of the potential energy surface with bond‐length alternation, we show here that zero‐point vibrations lead to an effective equalization of all carbon–carbon bond lengths and thus to a cumulenic structure.     

Noneikonal approach to the scattering of hadrons from nuclei. II. Proton and pion scattering from D, 3He and 4He (kL ≳ 1 GeV/c)

A previously formulated noneikonal theory for hadron-nucleus scattering valid for all angles is applied to p and π scattering on the lightest targets (k_L ? 1 GeV/c). When the required input is known, calculated differential cross sections agree well with experiments out to medium angles, far beyond the region of previous analyses. In the case of pA scattering at k_L = 1.2 GeV/c at which momentum some parameters in the elementary amplitudes F_xN are badly known, limits on their values have been obtained by demanding simultaneous agreement between theory and data for several targets. Generally speaking the agreement evidences the existence of some major corrections to the eikonal amplitude, namely, propagator off-shell and nucleon recoil effects. Inclusion of the latter primarily affects the single scattering amplitude, which may dominate the large-q² cross section if F_xN (like F_pp) itself rises with q². The calculation of pD and p⁴He cross sections requires knowledge of body form factors S_A often unknown for large q². Consistency requirements for angular distributions at several k_L lead to a conjectured large-q² behavior of S_A(q). In the case of the D the conjecture has been largely confirmed by a recent measurement of the electric form factor. The agreement leaves little room for $\text{NN}{}^1$ components in the D as heretofore derived from pD scattering. We speculate that in general, reasonable estimates for nuclear form factors out to very large q² may be obtained from hadron-nucleus scattering data with existing facilities. Since higher q² values can be reached in hadron-nucleus than in eA scattering, the former may well provide the first tests for predicted scaling of nuclear form factors.     

Some Properties of Essential Spectra of a Positive Operator

Let E be a Banach lattice, T be a bounded operator on E. The Weyl essential spectrum σ_ew(T) of the operator T is a set , where is a set of all compact operators on E. In particular for a positive operator T next subsets of the spectrum

Chiroptical study and absolute configuration of securinine oxidation products

Time-dependant density functional theory–electronic circular dichroism spectra prediction was carried out to study the absolute configuration of phyllanthidine-type derivatives 5 and 6, derived from securinine (1) and its enantiomer virosecurinine (2), respectively. This method demonstrated to be very reliable in this alkaloid series. Thus, 5 and 6 shared the same stereochemistry as their parent precursors, confirming the retentive nature of the oxidation sequence. In addition, this study highlighted the key role of the methylene bridge (BC ring) in the chiroptical activity of these compounds. These results fully clarified the stereochemical relationships between the phyllanthidine and the securinine subgroups.     

Photochemical Strain-Release-Driven Cyclobutylation of C(sp3)-Centered Radicals

A new photoredox-catalyzed decarboxylative radical addition approach to functionalized cyclobutanes is described. The reaction involves an unprecedented formal Giese-type addition of C(sp³)-centered radicals to highly strained bicyclo[1.1.0]butanes. The mild photoredox conditions, which make use of a readily available and bench stable phenyl sulfonyl bicyclo[1.1.0]butane, proved to be amenable to a diverse range of α-amino and α-oxy carboxylic acids, providing a concise route to 1,3-disubstituted cyclobutanes. Furthermore, kinetic studies and DFT calculations unveiled mechanistic details on bicyclo[1.1.0]butane reactivity relative to the corresponding olefin system.     

Novel Cysteine Tags for the Sequencing of Non-Tryptic Disulfide Peptides of Anurans: ESI-MS Study of Fragmentation Efficiency

Mass spectrometry faces considerable difficulties in de novo sequencing of long non-tryptic peptides with S–S bonds. Long disulfide-containing peptides brevinins 1E and 2Ec from frog Rana ridibunda were reduced and alkylated with nine novel and three known derivatizing agents. Eight of the novel reagents are maleimide derivatives. Modified samples were subjected to MS/MS studies on FT-ICR and Orbitrap mass spectrometers using CAD/HCD or ECD/ETD techniques. Procedures, fragmentation patterns, and sequence coverage for two peptides modified with 12 tags are described. ECD/ETD and CAD fragmentation revealed complementary sequence information. Higher-energy collisionally activated dissociation (HCD) sufficiently enhanced y-ions formation for brevinin 1E, but not for brevinin 2Ec. Some novel tags [N-benzylmaleimide, N-(2,6-dimethylphenyl)maleimide] along with known N-phenylmaleimide and iodoacetic acid showed high total sequence coverage taking into account combined ETD and HCD fragmentation. Moreover, modification of long (34 residues) brevinin 2Ec with N-benzylmaleimide or N-(2,6-dimethylphenyl)maleimide yielded high sequence coverage and full C-terminal sequence determination with ECD alone.