Collision-Induced Dissociation Fragmentation Inside Disulfide C-Terminal Loops of Natural Non-Tryptic Peptides

Collision-induced dissociation (CID) spectra of long non-tryptic peptides are usually quite complicated and rather difficult to interpret. Disulfide bond formed by two cysteine residues at C-terminus of frog skin peptides precludes one to determine sequence inside the forming loop. Thereby, chemical modification of S–S bonds is often used in “bottom up” sequencing approach. However, low-energy CID spectra of natural non-tryptic peptides with C-terminal disulfide cycle demonstrate an unusual fragmentation route, which may be used to elucidate the “hidden” C-terminal sequence. Low charge state protonated molecules experience peptide bond cleavage at the N-terminus of C-terminal cysteine. The forming isomeric acyclic ions serve as precursors for a series of b-type ions revealing sequence inside former disulfide cycle. The reaction is preferable for peptides with basic lysine residues inside the cycle. It may also be activated by acidic protons of Asp and Glu residues neighboring the loop. The observed cleavages may be quite competitive, revealing the sequence inside disulfide cycle, although S–S bond rupture does not occur in this case.

Superposition operator on the space of sequences almost converging to zero

We study the superposition operator f on on the space ac ₀ of sequences almost converging to zero. Conditions are derived for which f has a representation of the form f x = a+bx +g x, for all x ∈ ac ₀ with a = f 0, b ∈ D(ac ₀), g a superposition operator from ℓ_∞ into I(ac ₀), D(ac ₀) = {z: zx ∈ ac ₀ for all x ∈ ac ₀}, and I(ac ₀) the maximal ideal in ac ₀. If f is generated by a function f of a real variable, then f is linear. We consider the conditions for which a bounded function f generates f acting on ac ₀ and the conditions for which there exists a sequence y ∈ ac ₀ such that y − f y ∈ ac ₀. In terms of f, criteria for the boundedness, continuity, and sequential σ(ac ₀ℓ₁)-continuity of f on ac ₀ are given. It is shown that the continuity of f is equivalent to the weak sequential continuity. Finally, properties of spaces D(ac ₀) and I(ac ₀) are studied, and in particular it is established that the inclusion I(ac ₀) ⊕ {λe: λ ∈ ℝ} ⊂ D(ac ₀) is proper, where e = (1, 1, …). By means of D(ac ₀), a number of Banach-Mazur limit properties are derived.     

Re(I) Complexes as Backbone Substituents and Cross-Linking Agents for Hybrid Luminescent Polysiloxanes and Silicone Rubbers

This study focuses on the synthesis of hybrid luminescent polysiloxanes and silicone rubbers grafted by organometallic rhenium(I) complexes using Cu(I)-catalyzed azido-alkyne cycloaddition (CuAAC). The design of the rhenium(I) complexes includes using a diimine ligand to create an MLCT luminescent center and the introduction of a triple C≡C bond on the periphery of the ligand environment to provide click-reaction capability. Poly(3-azidopropylmethylsiloxane-co-dimethylsiloxane) (N₃-PDMS) was synthesized for incorporation of azide function in polysiloxane chain. [Re(CO)₃(MeCN)(5-(4-ethynylphenyl)-2,2′-bipyridine)]OTf (Re1) luminescent complex was used to prepare a luminescent copolymer with N₃-PDMS (Re1-PDMS), while [Re(CO)₃Cl(5,5′-diethynyl-2,2′-bipyridine)] (Re2) was used as a luminescent cross-linking agent of N₃-PDMS to obtain luminescent silicone rubber (Re2-PDMS). The examination of photophysical properties of the hybrid polymer materials obtained show that emission profile of Re(I) moiety remains unchanged and metallocenter allows to control the creation of polysiloxane-based materials with specified properties.