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71.
72.
Piotr Król Bożena Król Lech Subocz Paweł Andruszkiewicz 《Colloid and polymer science》2006,285(2):177-183
The following electrical properties were found for polymer coatings obtained from polyurethane anionomers synthesised with the use of various diisocyanates: volume resistivity, permittivity and dielectric dissipation factor. The effects were discussed from the molecular structures and phase structures of those anionomers on the value of their ionic conductivity and polarizability. The anionomer prepared from the aliphatic diisocyanate was found to offer ionic conductivity; hence, that material can be considered to be a solid electrolyte, which exhibits a considerable susceptibility to structural modifications in the alternating electric field. 相似文献
73.
It has been shown that1H,13C,14N,15N,17O, and77Se NMR are very successful techniques for the identification and investigation of potential valence tautomerism in all types of mesoionic compounds. Especially the combined use of14N and15N NMR studies has been shown to be very effective in solving structural problems. From15N NMR it is possible to obtain accurate chemical shifts and spin-spin couplings, whereas the14N NMR spectra provide us with nuclear relaxation and some chemical shift data. In particular14N NMR is very useful for the identification of charged nitrogen atoms in molecules containing non equivalent nitrogen positions. This information is available from the relative14N signal widths, which depend upon the rates of14N relaxation, positively charged nitrogen atoms usually have relatively slow14N relaxation rates thus giving rather sharp NMR signals. Some solid state, CP MAS,13C and15N NMR results are available for comparison with the solution NMR data.Published in Khimiya Geterotsiklischeskikh Soedinenii, No. 9, pp. 1180–1199. September 1995. 相似文献
74.
Kozerski L Kamieński B Kawecki R Urbanczyk-Lipkowska Z Bocian W Bednarek E Sitkowski J Zakrzewska K Nielsen KT Hansen PE 《Organic & biomolecular chemistry》2003,1(20):3578-3585
Parent genistein and its new amine complexes with morpholine and piperazine were studied comparatively in the solid and liquid states by X-ray crystallography and 13C and 15N NMR spectroscopy. Biochanine A and its complexes were used as reference. Secondary deuterium isotope effects on 13C chemical shifts in solution were studied in parent isoflavones and their morpholine and piperazine complexes to aid in evaluation of the electronic distribution in both systems. In addition, to quantify the extent of proton transfer as well as to establish strong hydrogen bonding of the 7-OH group in a morpholine complex, proton transfer from the 7-OH group to the piperazine nitrogen atom was also confirmed by 13C NMR in the solid state and by X-ray studies. The effect of 7-OH deprotonation yields a high frequency shift of 7-8 ppm on the C-7 carbon atom of the piperazine complex whereas it is as large as 12 ppm in the morpholine complex in the solid. The former trend is confirmed from solution state concentration studies which also show that the isoflavones have a strong tendency to form complexes with bases. Depending on the pKa difference between the isoflavones and the base this leads either to proton transfer and ion-pair formation or, in the case of a larger pKa difference, to a hydrogen bonded ion pair. The concentration studies show formation of a 1:1 genistein-piperazine complex in DMSO. Addition of water leads to formation of solvent separated ions. The C-5 OH group is involved in strong intramolecular hydrogen bonding leading to a pseudo aromatic ring extending the aromatic part of the drug pharmacophore. The analysis also suggests the way that both the C-7 and C-4' hydroxyl group of genistein may participate in stabilising the ternary inhibitor complexes of tyrosine-specific kinases or DNA topoisomerase II. 相似文献
75.
Lech Wilczek Joseph P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》1987,25(12):3255-3265
Essentially quantitative allylation of linear and three-arm star tert-chloro capped polyisobutylenes [tCl–PIB–Clt and PIB(Clt)3] has been achieved by the use of allyltrimethylsilane (AllylSiMe3) and Friedel–Crafts acids. Quantitative allylation occurs under suitable conditions, e.g., slight molar excess of TiCl4 and AllySiMe3 polar media, ?70°C. These conditions have been developed from quantitative model allylation experiments using 2,4,4-trimethyl-2-chloropentane. Essentially quantitative allylation occurs with long-chain or “once fired” tert-chloro-end groups. Complete allylation can also be effected in a “one-pot two-step” synthesis, i.e., by first preparing the tert-chloro-ended PIB by the inifer method and without isolating the product, completing the synthesis by allylation in the same reactor. Extensive but not quantitative allylation can also be obtained in situ, i. e., during polymerization, by the use of the AllylSiMe3/cumyl chloride/BCI3/isobutylene combination. While allylation proceeds with great ease under the mildest conditions, e.g., ?70°C, vinylation with vinyltrimethylsilane could not be achieved even under more forcing conditions. 相似文献
76.
In the framework of our studies on acid=nbase equilibria in systems comprisingsubstituted pyridines and nonaqueous solvents, acid dissociation constants havebeen determined potentiometrically for a variety of cationic acids conjugatedwith pyridine and its derivatives in the polar protophobic aprotic solvent nitromethane. The potentiometric method enabled a check as to whether and to whatextent cationic homoconjugation equilibria of the BH+/B type, as well as cationicheteroconjugation equilibria in BH+/B1 systems without proton transfer, are setup in nitromethane. The equilibrium constants were compared with thosedetermined in water and two other polar protophobic aprotic solvents, propylenecarbonate and acetonitrile. The pK
a values of acids conjugate to the N-bases innitromethane fall in the pK
a range of 5.84 to 17.67, i.e., 6 to 7 pK
a units, onaverage, higher than in water, 1 to 2 units higher than in propylene carbonate,and less than 1 unit lower than in acetonitrile. This means that the basicity ofthe pyridine derivatives increases on going from propylene carbonate throughnitromethane to acetonitrile. Further, it was found that the sequence of the pK
achanges of the protonated amines was consistent in all three media, thus providingthe basis for establishing linear correlations among these values. In the majorityof the BH+/B systems in nitromethane, cationic homoconjugation equilibria havebeen established. The cationic homoconjugation constants, log K
BHB+, arerelatively low, falling in the range 1.60–2.89. A comparison of the homoconjugationconstants in nitromethane with those in propylene carbonate and acetonitrile showsthat nitromethane is a more favorable solvent for the cationic homoconjugationequilibria than the other two solvents. Moreover, results of the potentiometricmeasurements revealed that cationic heteroconjugation equilibria were not presentin the majority of the BH+/B1 systems in nitromethane. The heteroconjugationconstant could be determined in one system only, with logdiK
BHB1
+ = 2.56. 相似文献
77.
The nucleobase 5-methylcytosine (I) is a minor component of eukaryotic DNA thought to be important in regulation of gene expression. The photochemical reactions of this nucleobase and its 2'-deoxyribonucleoside, 5-methyl-2'-deoxycytidine (II), in water have been studied. These reactions lead, respectively, to 3-amino-2-methylacrylamidine (Ib) and 3-(2-erythro-D-pentopyranos-1-yl)amino-2-methylacrylamidine (IIb) as the main photoproducts. The structure of the photoproducts was established by spectroscopic methods (1H and 13C NMR, UV spectroscopy, electron impact and liquid secondary ion mass spectrometry); in the case of Ib, confirmatory evidence was obtained by chemical methods (photolysis of 5-methyl[2-13C]cytosine, hydrolysis of N-carbomethoxy-3-amino-2-methylacrylamidine and reaction of Ib with 1,1'-carbonyldiimidazole to give I). The quantum yield for formation of Ib was determined to be 1.8 x 10(-3) at pH 7.5 while the quantum yield for formation of IIb has a lower value of 0.2 x 10(-3) at pH 7.5. These quantum yields depend strongly on pH and reach maximum values of 2.0 x 10(-3) at pH 7.0 (Ib) and 0.6 x 10(-3) at pH 5.0 (IIb). The mechanism of formation of Ib (or IIb) is proposed to involve nucleophilic attack of water on the C-2 position of photoexcited I (or II), followed by ring opening and decarboxylation of an intermediate carbamic acid. 相似文献
78.
?ukasz Gurzyński Mariusz Makowski Lech Chmurzyński 《The Journal of chemical thermodynamics》2006,38(12):1584-1591
By using the potentiometric method, acidity constants have been determined in systems of tri- and tetra-substituted pyridine N-oxides. The potentiometric measurements in systems of four 4-chloropyridine N-oxide derivatives containing the chlorine atom at position 4 to the NO2 group and four bromine counterparts were carried out in polar non-aqueous solvents, viz. amphiprotic methanol (MeOH) and aprotic protophilic dimethyl sulfoxide (DMSO). It was found that in all the systems studied the pKa values were readily determinable (as indicated by small standard deviations) in MeOH, whereas in DMSO large standard deviations were obtained making the pKa values either hardly determinable or indeterminable from potentiometric measurements. Furthermore, it was demonstrated that the acidity constants of protonated N-oxides studied in MeOH changed according to the sequence of their acidity constants in water. It was also found that in the polar solvents studied, i.e. in the amphiprotic methanol and the highly basic aprotic dimethyl sulfoxide, the cationic homo-conjugation equlibrium constants could not be determined using potentiometric method. Also, by using ab initio methods at the RHF and MP2 levels and the PCM model, utilizing the Gaussian 6-31++G∗∗ basis set, energies and Gibbs free energies of the protonation reactions of the N-oxides have been determined. The energy parameters have been compared with acidity constants of the protonated N-oxides determined by potentiometric titration in methanol to establish a correlation between these approaches. 相似文献
79.
Roman Luboradzki Janusz Lipkowski Wikor Koźmiński Lech Stefaniak 《Journal of chemical crystallography》1995,25(1):29-35
An X-ray diffraction study is reported for three molecules of salts containing a cation with a positive charged 2,3-diphenyltetrazolium ring. The results confirm aromatic structure of the tetrazole ring and the delocalization of charge on the whole molecules of the cations. The molecular geometry obtained is compared with that for free mesoionic 2,3-diphenyltetrazoles which have already been studied and the ring parameters do not reveal significant differences. But is shows that the geometry of the (NNO)– exocyclic group is changed as a result of alkylation. Compound I C13H12N5Cl, P21/a,a=16.934(4),b=6.575(1),c=26.121(4) Å, =108.15(2)°, II C14H13N6OI, P312,a=10.774(3),c=12.821(4) Å, IV C26H20N8Cl2, C2/c,a=22.316(4),b=6.6903(7),c=20.437(3) Å, =92.51(1)°. 相似文献
80.
New dichloride platinum(II) complexes with 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO) have been synthesized and characterized by thermal analysis, infrared and 1H, 13C, 15N, 195Pt NMR spectroscopy. X-ray crystal structures of cis-PtCl2(NH3)(HmtpO) (1) and cis-PtCl2(HmtpO)2 · 4H2O (2b) were determined to R = 0.0332 and R = 0.0802, respectively. In both complexes the Pt(II) ions have a square-planar geometry with two adjacent corners being occupied by two nitrogens of HmtpO molecules for 2b or NH3 and HmtpO molecules for 1, whereas the remaining adjacent corners are occupied by two chloride anions. Spectroscopic data confirm the square planar geometry with N(3) bonded HmtpO, S-bonded dimethylsulfoxide and two trans chloride anions for trans-PtCl2(dmso) · 4H2O (3). 相似文献