The Enzyme Source Effect on the Performance of a Catalase Organic Phase Enzyme Electrode

The role of the enzyme source was studied in the reaction of hydrogen peroxide decomposition by immobilised catalase in acetonitrile. Enzymes isolated from bacterial and mammalian sources were conveniently immobilised on a spectroscopic graphite to obtain an organic-phase enzyme electrode (OPEE). Amperometry at constant potential was employed as basic analytical approach in this study.     

Functionalisation of the template-free and template-structured silica films synthesised on glass substrates by sol–gel technique

Possibility of the post-synthesis functionalisation of the template-free and template-structured silica films of ca. 200 nm thickness on glass slides was evaluated. The films were prepared by dip-coating from TEOS sol–gel precursor in the absence or presence of CTAB template. It has been found out that the template-structured silica films can be functionalised with Ag nanoparticles via [Ag(NH₃)₂]NO₃ ion-exchange or with adsorbed Methylene Blue (MB) cationic dye due to the presence of the well-organised mesopores after template removal. In contrast, only the external geometric surface of the template-free silica films appeared to be accessible for modifier molecules. Possibility of functionalisation of the multi-layered template-structured silica film depends on the sequence of dip-coating and calcination steps upon their preparation. When preparation includes reiteration of dip-coating and calcination steps, only the latest top silica film appears to be accessible to modifier molecules. When preparation includes successive dip-coating cycles accomplished by calcination of the final multi-layered film, all pores appear to be accessible since their formation occurs via simultaneous removal of the template molecules over the whole thickness of the multi-layered template-structured silica film.     

Study of the chemistry of ortho- and para-biphenylnitrenes by laser flash photolysis and time-resolved IR experiments and by B3LYP and CASPT2 calculations

The photochemistry of ortho-biphenyl azide (1a) has been studied by laser flash photolysis (LFP), with UV-vis and IR detection of the transient intermediates formed. LFP (266 nm) of 1a in glassy 3-methylpentane at 77 K releases singlet ortho-biphenylnitrene (1b) (lambda(max) = 410 nm, tau = 59 +/- 6 ns), which under these conditions decays cleanly to the lower energy triplet state. In fluid solution at 298 K, 1b rapidly (tau < 10 ns) partitions between formation of isocarbazole (4) (lambda(max) = 430 nm, tau = 70 ns) and benzazirine (1e) (lambda(max) = 305 nm, tau = 12 ns). Isocarbazole 4 undergoes a 1,5-hydrogen shift, with k(H)/k(D) = 3.4 at 298 K to form carbazole 9 and smaller amounts of two other isocarbazoles (7 and 8). Benzazirine 1e ring-opens reversibly to azacycloheptatetraene (1f), which serves as a reservoir for singlet nitrene 1b. Azacycloheptatetraene 1f ultimately forms carbazole 9 on the millisecond time scale by the pathway 1f --> 1e --> 1b --> 4 --> 9. The energies of the transient intermediates and of the transition structures connecting them were successfully predicted by CASPT2/6-31G calculations. The electronic and vibrational spectra of the intermediates, computed by density functional theory, support the assignment of the transient spectra, observed in the formation of 9 from 1a.     

Chiral resolution of diastereomeric di- and tripeptides on a teicoplanin aglycone phase by capillary electrochromatography

The chiral separation ability of a capillary packed with teicoplanin aglycone as a chiral stationary phase was investigated. This stationary phase was used successfully for chiral resolution of both diastereomeric dipeptides and tripeptides possessing one or two chiral centers. The composition of the mobile phase was shown to be crucial for separation. The use of reversed-phase mode was clearly superior to the polar-organic mode. The nature of the organic modifier was found to have a marked influence on separation. After optimizing conditions, all diasteromeric dipeptides and tripeptides investigated were baseline-resolved, however, it was not possible to find a uniform mobile phase showing optimal results for all peptides investigated.     

Molecular structure and conformations of 2,2-di-tert-butyl-1,3-diaza-2-silacyclopentane: gas electron diffraction and quantum chemical calculations

The geometric structure and conformational properties of the saturated five-membered-ring compound 2,2-di-tert-butyl-1,3-diaza-2-silacyclopentane, (t-Bu)(2)Si(NH)(2)(CH(2))(2), was investigated by gas electron diffraction and quantum chemical methods (B3LYP and MP2 with 6-31G basis sets). The compound exists as a mixture of two conformers, both possessing a twist conformation and C(2) symmetry. In the prevailing form (76(6) % at 305 K) the N-H bonds stagger the adjacent CH(2) groups, and in the minor form the N-H bonds eclipse the CH(2) groups. This conformational mixture corresponds to a free energy difference of DeltaG degrees = 0.69(19) kcal/mol. The B3LYP method predicts a preference for the eclipsed conformer. The largest torsion occurs around the C-C bond with tau(NCCN) = 29.2(24) degrees. The degree of puckering in the title compound is considerably smaller than that in silacyclopentane with tau(CCCC) = 49.7(14) degrees. This has been rationalized by larger angle strain in the title compound.     

1,2‐Diaza‐3‐silacyclopent‐5‐ene – Synthese und Reaktionen

1,2‐Diaza‐3‐silacyclopent‐5‐ene – Synthesis and Reactions The dilithium salt of bis(tert‐butyl‐trimethylsilylmethylen)ketazine ( 1 ) forms an imine‐enamine salt. 1 reacts with halosilanes in a molar ratio of 1:1 to give 1,2‐diaza‐3‐silacyclopent‐5‐enes. Me₃SiCH=CCMe₃ [N(SiR,R′)‐N=C‐C]HSiMe₃ ( 2 ‐ 7 ). ( 2 : R,R′ = Cl; 3 : R = CH₃, R′ = Ph; 4 : R = F, R′ = CMe₃; 5 : R = F, R′ = Ph; 6 : R = F, R′ = N(SiMe₃)₂; 7 : R = F, R′ = N(CMe₃)SiMe₃). In the reaction of 1 with tetrafluorosilane the spirocyclus 8 is isolated. The five‐membered ring compounds 2 ‐ 7 and compound 9 substituted on the silicon‐fluoro‐ and (tert‐butyltrimethylsilyl) are acid at the C(4)‐atom and therefore can be lithiated. Experiments to prepare lithium salts of 4 with MeLi, n‐BuLi and PhLi gave LiF and the substitution‐products 10 ‐ 12 . 9 forms a lithium salt which reacts with ClSiMe₃ to give LiCl and the SiMe₃ ring system ( 13 ) substituted at the C(4)‐atom. The ring compounds 3 ‐ 7 and 10 ‐ 12 form isomers, the formation is discussed. Results of the crystal structure and analyses of 8 , 10 , 12 , and 13 are presented.     

Ab initio study of charge transfer between lithium and para-disubstituted benzenes

The present work examines how substituents affect the interaction of lithium with the benzene ring and considers whether two configurations, “loose” and “tight,” can be found for the investigated set of complexes as in the lithium complexes with polyaromatic hydrocarbons. The two conformations were actually found for the electron-donating substituents, whereas for the electron-withdrawing substituents, CF₃ and NO₂, only tight conformation could be optimized. For complexes in the loose conformation [with the N(CH₃)₂, NH₂, OH, H, Cl, and CH₃ substituents], the transfer of electron density was directed from the region occupied by a disubstituted benzene to that occupied by Li. The amount of transferred density was very similar for all the complexes (0.21–0.25 a.u.). By contrast, in the tight complexes, the density transfer direction was opposite and the amount of the transferred density depended on the electronegativity of the substituents on benzene ring, being ?0.09, ?0.09, ?0.13, ?0.15, ?0.15, ?0.20, and ?0.30 a.u. for N(CH₃)₂, NH₂, OH, H, Cl, CF₃, and NO₂, respectively. Geometries of the loose and tight conformations differed notably. The six-membered ring was significantly more warped in the tight conformation than in the loose one: In the latter, the ring was nearly planar, whereas in the former, the ring had the boat structure.     

New Method for the Synthesis and Reactivity of (5‐R‐1,3,4‐Oxadiazol‐2‐yl)furoxans

A new, simple and general one‐pot method for the preparation of (5‐R‐1,3,4‐oxadiazol‐2‐yl)furoxans has been developed on the basis of the interaction between accessible 3‐methylfuroxan‐4‐carboxylic acid hydrazide and aliphatic, aromatic and heterocyclic carboxylic acids or their chlorides in the presence of POCl₃. The synthesis and study of (5‐R‐1,3,4‐oxadiazol‐2‐yl)furoxans reactivity resulted in new polyheterocyclic ensembles incorporating furoxan, 1,3,4‐oxadiazole, pyrrole, triazole, furan, thiophene, pyrimidine, and other heterocycles in different combinations.     

Impact of Deuteration on the Assembly Kinetics of Transthyretin Monitored by Native Mass Spectrometry and Implications for Amyloidoses

It is well established that the formation of transthyretin (TTR) amyloid fibrils is linked to the destabilization and dissociation of its tetrameric structure into insoluble aggregates. Isotope labeling is used for the study of TTR by NMR, neutron diffraction, and mass spectrometry (MS). Here MS, thioflavin T fluorescence, and crystallographic data demonstrate that while the X‐ray structures of unlabeled and deuterium‐labeled TTR are essentially identical, subunit exchange kinetics and amyloid formation are accelerated for the deuterated protein. However, a slower subunit exchange is noted in deuterated solvent, reflecting the poorer solubility of non‐polar protein side chains in such an environment. These observations are important for the interpretation of kinetic studies involving deuteration. The destabilizing effects of TTR deuteration are rather similar in character to those observed for aggressive mutations of TTR such as L55P (associated with familial amyloid polyneuropathy).     

Length‐Independent Charge Transport in Chimeric Molecular Wires

Advanced molecular electronic components remain vital for the next generation of miniaturized integrated circuits. Thus, much research effort has been devoted to the discovery of lossless molecular wires, for which the charge transport rate or conductivity is not attenuated with length in the tunneling regime. Herein, we report the synthesis and electrochemical interrogation of DNA‐like molecular wires. We determine that the rate of electron transfer through these constructs is independent of their length and propose a plausible mechanism to explain our findings. The reported approach holds relevance for the development of high‐performance molecular electronic components and the fundamental study of charge transport phenomena in organic semiconductors.