Regioselective Sequential Additions of Nucleophiles and Electrophiles to Perfluoroalkylfullerenes: Which Cage C Atoms Are the Most Reactive and Why?

The sequential addition of CN^? or CH₃^? and electrophiles to three perfluoroalkylfullerenes (PFAFs), C_s‐C₇₀(CF₃)₈, C₁‐C₇₀(CF₃)₁₀, and C_s‐p‐C₆₀(CF₃)₂, was carried out to determine the most reactive individual fullerene C atoms (as opposed to the most reactive C?C bonds, which has previously been studied). Each PFAF reacted with CH₃^? or CN^? to generate metastable PFAF(CN)^? or PFAF(CH₃)₂^2? species with high regioselectivity (i.e., one or two predominant isomers). They were treated with electrophiles E⁺ to generate PFAF(CN)(E) or PFAF(CH₃)₂(E)₂ derivatives, also with high regioselectivity (E⁺=CN⁺, CH₃⁺, or H⁺). All of the predominant products, characterized by mass spectrometry and ¹⁹F NMR spectroscopy, are new compounds. Some could be purified by HPLC to give single isomers. Two of them, C₇₀(CF₃)₈(CN)₂ and C₇₀(CF₃)₁₀(CH₃)₂(CN)₂, were characterized by single‐crystal X‐ray diffraction. DFT calculations were used to propose whether a particular reaction is under kinetic or thermodynamic control.     

Harnessing the Flexibility of Peptidic Scaffolds to Control their Copper(II)‐Coordination Properties: A Potentiometric and Spectroscopic Study

Designing small peptides that are capable of binding Cu²⁺ ions mainly through the side‐chain functionalities is a hard task because the amide nitrogen atoms strongly compete for Cu²⁺ ion coordination. However, the design of such peptides is important for obtaining biomimetic small systems of metalloenyzmes as well as for the development of artificial systems. With this in mind, a cyclic decapeptide, C‐Asp, which contained three His residues and one Asp residue, and its linear derivative, O‐Asp, were synthesized. The C‐Asp peptide has two Pro? Gly β‐turn‐inducer units and, as a result of cyclization, and as shown by CD spectroscopy, its backbone is constrained into a more defined conformation than O‐Asp, which is linear and contains a single Pro? Gly unit. A detailed potentiometric, mass spectrometric, and spectroscopic study (UV/Vis, CD, and EPR spectroscopy) showed that at a 1:1 Cu²⁺/peptide ratio, both peptides formed a major [CuHL]²⁺ species in the pH range 5.0–7.5 (C‐Asp) and 5.5–7.0 (O‐Asp). The corrected stability constants of the protonated species (log K*_CuH(O?Asp)=9.28 and log K*_CuH(C?Asp)=10.79) indicate that the cyclic peptide binds Cu²⁺ ions with higher affinity. In addition, the calculated value of K_eff shows that this higher affinity for Cu²⁺ ions prevails at all pH values, not only for a 1:1 ratio but even for a 2:1 ratio. The spectroscopic data of both [CuHL]²⁺ species are consistent with the exclusive coordination of Cu²⁺ ions by the side‐chain functionalities of the three His residues and the Asp residue in a square‐planar or square‐pyramidal geometry. Nonetheless, although these data show that, upon metal coordination, both peptides adopt a similar fold, the larger conformational constraints that are present in the cyclic scaffold results in different behaviour for both [CuHL]²⁺ species. CD and NMR analysis revealed the formation of a more rigid structure and a slower Cu²⁺‐exchange rate for [CuH(C‐Asp)]²⁺ compared to [CuH(O‐Asp]²⁺. This detailed comparative study shows that cyclization has a remarkable effect on the Cu²⁺‐coordination properties of the C‐Asp peptide, which binds Cu²⁺ ions with higher affinity at all pH values, stabilizes the [CuHL]²⁺ species in a wider pH range, and has a slower Cu²⁺‐exchange rate compared to O‐Asp.     

A Combined Kinetic and Thermodynamic Approach for the Interpretation of Continuous‐Flow Heterogeneous Catalytic Processes

The heterogeneous proline‐catalyzed aldol reaction was investigated under continuous‐flow conditions by means of a packed‐bed microreactor. Reaction‐progress kinetic analysis (RPKA) was used in combination with nonlinear chromatography for the interpretation, under synthetically relevant conditions, of important mechanistic aspects of the heterogeneous catalytic process at a molecular level. The information gathered by RPKA and nonlinear chromatography proved to be highly complementary and allowed for the assessment of optimal operating variables. In particular, the determination of the rate‐determining step was pivotal for optimizing the feed composition. On the other hand, the competitive product inhibition was responsible for the unexpected decrease in the reaction yield following an apparently obvious variation in the feed composition. The study was facilitated by a suitable 2D instrumental arrangement for simultaneous flow reaction and online flow‐injection analysis.     

A synthetic strategy toward branched oligomesogenic phosphonic acids: comparison of alternative pathways

This work is devoted to the elaboration of a practical scheme for the synthesis of dendritic derivatives of gallic acid containing a carboxylate-ω-alkylphosphonic acid group and three terminal promesogenic substituents. Two synthetic strategies toward the target compounds were examined that differ in the sequence of the introduction of the promesogenic units and ω-alkylphosphonic group.     

Polymerization of Ethylene by Silica‐Supported Dinuclear CrIII Sites through an Initiation Step Involving C?H Bond Activation

The insertion of an olefin into a preformed metal–carbon bond is a common mechanism for transition‐metal‐catalyzed olefin polymerization. However, in one important industrial catalyst, the Phillips catalyst, a metal–carbon bond is not present in the precatalyst. The Phillips catalyst, CrO₃ dispersed on silica, polymerizes ethylene without an activator. Despite 60 years of intensive research, the active sites and the way the first Cr C bond is formed remain unknown. We synthesized well‐defined dinuclear Cr^II and Cr^III sites on silica. Whereas the Cr^II material was a poor polymerization catalyst, the Cr^III material was active. Poisoning studies showed that about 65 % of the Cr^III sites were active, a far higher proportion than typically observed for the Phillips catalyst. Examination of the spent catalyst and isotope labeling experiments showed the formation of a Si–(μ‐OH)–Cr^III species, consistent with an initiation mechanism involving the heterolytic activation of ethylene at Cr^III O bonds.     

xMAP-based analysis of three most prevalent staphylococcal toxins in Staphylococcus aureus cultures

Detection of staphylococcal toxins presents a great interest for medical diagnostics. Screening of clinical samples for the presence of several types of staphylococcal toxins using traditional methods—biological tests on animals or cell cultures as well as ELISA—is laborious. Multiplex detection methods would simplify testing. We have designed an xMAP-based assay to detect three staphylococcal toxins—enterotoxins A and B (SEA and SEB) and toxic shock syndrome toxin (TSST)—in cultural supernatants obtained from different strains of Staphylococcus aureus. The limits of detection of SEA, SEB, and TSST multiplex detection in S. aureus growth medium were 10, 1,000, and 5 pg/mL, respectively. Fifty-nine samples of S. aureus cultural supernatants were tested with the xMAP assay. The developed assay has proved highly effective detection of the natural toxins in the samples obtained due to bacterial cells cultivation. In prospect, the developed test system can be used in clinical diagnostics and in monitoring of foodstuffs and environmental objects.     

Callitriche cophocarpa — a new rich source of active phenolic compounds

This study was focused on the analysis of the contents (by HPLC-DAD) and antioxidant activity of phenolic compounds of aquatic higher plant Callitriche cophocarpa. The novelty of the work was: 1) the study of the species which is almost unknown in the context of investigations of bio-active compounds and, 2) the application of a unique L-band electron resonance spectroscopy (L-band EPR) to measure antioxidant activity of samples. The results were compared with those obtained for microalgae Chlorella and Spirulina which are widely distributed as the diet supplements. The obtained results are very promising with respect to the freeze-dried material of Callitriche, which revealed both high level of phenolic compounds (33 mg g^?1 dry weight) and antioxidant activity (0.14 g of reduced DPPH· g^?1 dry weight). An isoform of sinapic acid appeared to be the main fraction in this sample. The average content of the total phenolic compounds in Callitriche freeze-dried samples was ca. 43 or 25 times higher than in the case of the Chlorella or Spirulina samples, respectively. These samples showed also 16 times lower scavenging activity in relation to freeze-dried Callitriche material.      

Optical constants of organic insulators in the UV range extracted from reflection electron energy loss spectra

Reflection electron energy loss spectroscopy (REELS) spectra were measured for seven insulating organic compounds (DNA, Irganox 1010, Kapton, polyethylene [PE], poly(methyl methacrylate) [PMMA], polystyrene [PS] and polytetrafluoroethylene [PTFE]). Optical constants and energy band gaps were extracted from the measured REELS spectra after elimination of multiple electron scattering via a deconvolution and fitting the normalised single scattering energy loss spectra to Drude and Drude–Lindhard model dielectric functions, constrained by the Kramers–Kronig sum and f-sum rules. Satisfactory agreement is found for those optical constants for which literature data exists. For PTFE, the observed features in the optical data correspond to its electronic structure.