Przemysław Szczeciński

13C and 19F NMR study on the structure and conformation of tricarbonylchromium complexes of biphenyl derivatives

Abstract The 13 C and 19 F NMR spectra of 2,2′-difluoro-4,4′-dimethylbiphenyl (BIP), 4,5-difluoro-9,10-dihydrophenanthrene (PHE) and their tricarbonylchromium complexes are reported. The 13 C- 19 F couplings between carbonyl carbons and aromatic fluorine were used to determine the structure and conformation of the investigated complexes. To support the conclusions obtained, the structure of one of the BIP complexes was established by X-ray crystallography.

Application of scalar 13C19F spin—spin couplings between carbonyl carbons and aromatic fluorine to investigation of conformation of tricarbonylchromium complexes of fluorobenzenes

Abstract The 13 C NMR spectra of several meta and para substituted (η 6 -fluorobenzene)tricarbonylchromium complexes have been recorded. An attempt to apply the 13 C 19 F couplings between carbonyl carbons and aromatic fluorine to investigation of the Cr(CO) 3 tripod conformation was undertaken.

A successful DFT calculation of carbon-13 NMR chemical shifts and carbon–fluorine spin–spin coupling constants in (η6-fluoroarene)tricarbonylchromium complexes

Carbon-13 isotropic shielding constants and carbon–fluorine spin–spin coupling constants for fluorobenzene (1), 3-dimethylaminofluorobenzene (2) and 4-dimethylaminofluorobenzene (3) as well as for their tricarbonylchromium complexes (3–6) have been calculated using DFT method with B3LYP and/or BHandH functionals and 6-311++G(2d,p) basis set. In the case of the complexes, the calculations have been performed for two expected orientations of the tricarbonylchromium tripod with respect to the benzene ring. It has been found that, when using B3LYP functional, the experimental 13C NMR chemical shifts for all the investigated compounds can be well reproduced, provided that for the complexes the populations of conformers are adjusted during the experiment/theory correlation. The population parameters determined this way follow perfectly the expectations based on the literature knowledge of the effects of the benzene ring substituents. The calculations with BHandH functional have not been able to reproduce the 13C NMR chemical shifts of carbonyl carbons in tricarbonylchromium complexes. On the other hand, BHandH is a functional of choice in calculations of carbon–fluorine spin–spin coupling constants. All such constants, including the through-space coupling constants between the carbonyl carbons and fluorine, have been reproduced very well. This last coupling constant has been calculated for various relative orientations of carbonyl and C–F bond and a strong angular dependence of this constant has been found.

Scalar 13C19 F spin-spin couplings between carbonyl carbons and aromatic fluorines in tricarbonylchromium complexes of biphenyl derivatives

Abstract The 13 C NMR spectra of the carbonyl carbons region of 2,2′-difluoro-6,6′-dimethylbiphenyl and 4,5-difluoro-9,10-dihydrophenanthrene tricarbonylchromium complexes are reported. The 13 C- 19 F couplings between carbonyl carbons and aromatic fluorines were used to determine the structures of the investigated complexes.

An efficient DFT method of predicting the one-, two- and three-bond indirect spin–spin coupling constants involving a fluorine nucleus in fluoroalkanes

The values of the indirect nuclear spin–spin coupling constants for a series of aliphatic fluorocompounds have been calculated using DFT-based methods and compared with the experimental values of these parameters. The set of the molecular objects contained four fluoromethanes, five fluoroethanes, two fluorocyclopropanes, and eleven fluorocompounds containing either five-membered or six-membered rings. The effectiveness of three hybrid functionals, B3LYP, PBE0 and BHandH and three basis sets, 6-311++G(2d,p) (s), 6-311++G(3df,3pd) (m) and aug-pcJ-3-2006 (l) has been checked. In order to compare the results concerning various types of coupling constants and obtained by various methods, a prediction-quality criterion has been proposed. It has been found that only the BHandH functional ensures calculating the proper values of one-bond fluorine–carbon and two-bond fluorine–fluorine coupling constants. For this functional application of the s basis, the smallest of the bases tested, has already yielded acceptable good results. The DFT BHandH/s PCM method has also provided the proper values of nJ(F,H) (n = 1, 2, 3) and nJ(F,C) (n = 2, 3) parameters. On the other hand, the analysis of the limited number of the results concerning 1J(C,H) coupling constants has pointed out that in this case this method is less effective than the DFT PBE0/l PCM method.

Application of scalar 13C, 19F couplings between carbonyl carbons and aromatic fluorine to investigation of conformation of chelate phosphitodicarbonylchromium and dicarbonyl(phosphine) chromium complexes of fluorobenzenes

Abstract The 13 C NMR spectra of chelate dicarbonyl-(η 6 -2,5-difluorobenzyl)- and −[η 6 -2-(2- or 4-fluorophenyl)ethyl]-diphenylphosphito-chromiums as well as those of dicarbonyl(triphenylphosphine)chromium complexes of fluorobenzene and its meta and para substituted (Me and NMe 2 ) derivatives have been reported. Coupling constants between carbonyl carbons and aromatic fluorine were used for determining the chromium tripod conformation. It was found that in chelate complexes the conformation depends on the length of the arene-metal bridge, on the ability of the arene substituent to stabilize the eclipsed conformation and on the steric interaction between the phosphorus ligand and the ring substituent. The two latter factors appeared also to be of great relevance to conformational equilibrium considerations concerning dicarbonylphosphinechromium complexes.

Evaluation of anti-cancer activity of stilbene and methoxydibenzo[b,f]oxepin derivatives

BACKGROUND Stilbenes, 1,2-diphenylethen derivatives, including resveratrol and combretastatins, show anticancer features especially against tumor angiogenesis. Fosbretabulin, CA-4, in combination with carboplatin, is in the last stages of clinical tests as an inhibitor of thyroid cancer. The mode of action of these compounds involves suppression of angiogenesis through interfering with tubulin (de)polymerization. OBJECTIVE We have previously synthesized five E-2-hydroxystilbenes and seven dibenzo [b,f]oxepins in Z configuration, with methyl or nitro groups at varied positions. The aim of the present work was to evaluate the anticancer activity and molecular mechanism(s) of action of these compounds. RESULTS Two healthy, EUFA30 and HEK293, and two cancerous, HeLa and U87, cell lines were treated with four newly synthetized stilbenes and seven oxepins. Two of these compounds, JJR5 and JJR6, showed the strongest cytotoxic effect against cancerous cells tested and these two were selected for further investigations. They induced apoptosis with sub-G1 or S cell cycle arrest and PARP cleavage, with no visible activation of caspases 3 and 7. Proteomic differential analysis of stilbene-treated cells led to the identification of proteins involved almost exclusively in cell cycle management, apoptosis, DNA repair and stress response, e.g. oxidative stress. CONCLUSION Among the newly synthesized stilbene derivatives, we selected two as potent anticancer compounds triggering late apoptosis/necrosis in cancerous cells through sub-G1 phase cell cycle arrest. They changed cyclin expression, induced DNA repair mechanisms, enzymes involved in apoptosis and oxidative stress response. Compounds JJR5 and JJR6 can be a base for structure modification(s) to obtain even more active derivatives.

An imidazopyrazine-derived anion for lithium conducting electrolyte application

In this work we present a new lithium salt of 4,5-dicyano-2-(trifluoromethyl)imidazopyrazine (LiTDPI) which was designed for use as an electrolyte in lithium-ion cells. It was synthesized and completely characterized by NMR techniques. The salt is thermally stable up to 350 °C and electrochemically stable in carbonate solvents up to +5.1 V vs. Li. Basic electrochemical characterization of this new lithium salt solution shows conductivity of over 2 mS cm−1 at room temperature and a transference number which is higher than the commercial reference salt, LiPF6 (>0.4 in a EC:DMC 1:2 ratio mixture). As a proof of concept, short cycling measurements in a graphite half-cell show good capacity (352 mA h g−1) and capacity retention (96% after 50 cycles). The extremely good stability without compromising the performance parameters shows the next leap in progress for tailoring efficient lithium-conducting electrolytes.