Flax (Linum usitatissimum L.) phloem fibers elongate considerably during their development and intrude between existing cells. We questioned whether fiber elongation is caused by cell tip growth or ...intercalary growth. Cells with tip growth are characterized by having two specific zones of cytoplasm in the cell tip, one with vesicles and no large organelles at the very tip and one with various organelles amongst others longitudinally arranged cortical microtubules in the subapex. Such zones were not observed in elongating flax fibers. Instead, organelles moved into the very tip region, and cortical microtubules showed transversal and helical configurations as known for cells growing in intercalary way. In addition, pulse-chase experiments with Calcofluor White resulted in a spotted fluorescence in the cell wall all over the length of the fiber. Therefore, it is concluded that fiber elongation is not achieved by tip growth but by intercalary growth. The intrusively growing fiber is a coenocytic cell that has no plasmodesmata, making the fibers a symplastically isolated domain within the stem.
Recently, Marina Bennati and coworkers (M. Bennati
,
, 2020,
, 373-379., M. Bennati
,
, 2021,
, 107091) proposed to use electron nuclear double resonance (ENDOR) spectroscopy in the W-band for a pair ...of labels, nitroxide and
F, for measurements of short (0.5-1.0 nm) distances in biomolecules. In our paper, we investigated the suitability of high-field ENDOR spectroscopy in the W-band for pairs of triarylmethyl and fluorine labels using five newly synthesized model compounds. It is shown that the application of strong magnetic fields allows distinguishing nuclear frequencies of
F and protons with sufficient resolution. On the one hand, in contrast to nitroxides, for triarylmethyl radicals, it is not necessary to obtain spectra in different orientations owing to low
-factor anisotropic and long electron spin relaxation times of triarylmethyls. On the other hand, the size of the triarylmethyl radical is substantially larger than that of nitroxide and comparable with measured distances. We theoretically analyzed the suitability of the dipole-dipole approach for triarylmethyl to be used in a
F ENDOR experiment and determined limitations of this approach. Finally, for comparison, we performed paramagnetic relaxation enhancement (PRE) NMR on the same compounds. In addition, we applied this approach to study the process of a thiol exchange between molecules of triarylmethyl-labeled and
F-labeled human serum albumin (HSA).
According to the NMR data, long-lived 10,10-dimethyl-9-phenylethynyl-9,10-dihydrophenanthren-9-ylium in acid medium undergoes cyclization whose direction is determined by the acidity of the medium. ...The cyclization in HSO
3
F-SbF
5
superacid involves the aromatic ring in the phenanthrene core as nucleophilic component and yields 5a,6-dimethyl-4-phenyl-4,5,5a,6-tetrahydroacephenantrylene-4,6-bis(ylium). In trifluoroacetic acid the nucleophilic component is the side-chain phenyl group, and the cyclization product is neutral 8b,14b-dimethyl-8b,14b-dihydrobenzo
g
chrysen-10-yl trifluoroacetate. Both cyclization directions are observed in moderate-strength trifluoromethanesulfonic acid.
According to the NMR data, 9-(R-ethynyl)-9-hydroxy-10,10-dimethyl-9,10-dihydrophenanthrenes (R = H, Me, Ph) in superacid medium (HSO
3
F-SO
2
ClF) at low temperature undergo dehydroxylation with ...formation of the corresponding long-lived 10,10-dimethyl-9-(R-ethynyl)-9,10-dihydrophenanthren-9-yl cations which do not isomerize to 10-(R-ethynyl)-9,10-dimethyl-9,10-dihydrophenanthren-9-ylium. In contrast, longlived 10,10-dimethyl-9-(3,3,3-trifluoroprop-1-yn-1-yl)-9,10-dihydrophenanthren-9-yl cation derived from 9-(3,3,3-trifluoroprop-1-yn-1-yl)-10,10-dimethyl-9,10-dihydrophenanthren-9-ol undergoes partial isomerization to 10-(3,3,3-trifluoroprop-1-yn-1-yl)-9,10-dimethyl-9,10-dihydrophenanthren-9-yl cation.
Dynamic NMR study showed that long-lived 9-cyclopropyl-9,10-dimethyl-9,10-dihydrophenanthren-9-yl cation generated from 9-cyclopropyl-9,10-dimethyl-9,10-dihydrophenanthren-9-ol in HSO₃F-SO₂ClF-CD₂Cl₂ ...at −100 to −75°C undergoes fast degenerate 1,2-shift of the cyclopropyl group. The Arrhenius parameters for this process were determined: E a = 33.7 kJ/mol, log A = 13.0.
DFT quantum-chemical calculations predicted structural nonrigidity of 9,9,10-trimethyl- and 4,5,9,9,10-pentamethylphenanthrenylium ions. The cross section of the potential energy surface at the ...nonrigidity coordinate for the first of these ions is symmetric, and for the second, asymmetric. These results were confirmed experimentally: the ¹³C NMR spectra of 4,5,9,9,10-pentamethylphenanthrenylium showed considerable temperature dependence of chemical shifts which is not typical of 9,9,10-trimethylphenanthrenylium.
The Semmler-Wolff aromatization of 4-hydroxyimino-4,5,6,7-tetrahydro2,1,3benzoxadiazole and its 1-oxide derivative in sulfuric acid and in acetic anhydride gave 4-amino2,1,3benzoxadiazole and ...4-acetamido2,1,3benzoxadiazole 1-oxide. Some reactions of the resultant amines were studied.
Long-lived 9-cyano-9,10-dimethylphenanthrenyl cation was generated in superacidic medium, and its structure was determined by
1
H and
13
C NMR spectroscopy. The energy barrier to 1,2-shift of the ...cyano group in 9-cyano-9,10-dimethylphenanthrenyl cation was estimated by NMR and DFT calculations.
Rearrangements of 6b,7,8,8a-tetramethyl-6b,8a-dihydrocyclobutaacenaphthylene in acids were investigated by NMR spectroscopy. The initially formed ...3b,4-exo,4a,5-tetramethyl-3b,4,4a,5-tetrahydro-4H-cyclopropaaphenalen-5-yl cation and its endo-epimer rearranged into carbocations of phenalenyl type. Therewith the direction and the rate of rearrangement sharply changed at relatively small variations in the medium acidity.
The behavior of 10,10-dimethyl-9-trimethylsiloxy-9,10-dihydrophenanthrene-9-carbonitrile in trifluoromethanesulfonic acid and acid systems CF
3
SO
3
H-CD
2
Cl
2
, HSO
3
F-SO
2
ClF-CD
2
Cl
3
, and CF
...3
COOH-CD
2
Cl
2
were studied by NMR spectroscopy. Principal reaction schemes were determined; the first step in these schemes is protonation of the initial compound at the oxygen or nitrogen atom.
