Core-modified, meso-alkylidenyl porphyrins and their expanded analogues: a new family of nonplanar porphyrinoids

New core-modified, meso-alkylidenyl porphyrinoids bearing multiple exocyclic double bonds were synthesized and characterized. The synthesis was accomplished using a typical "3 + 1"-type condensation approach. Stable exocyclic tautomers bearing double bonds at the meso positions, as well the corresponding endocyclic tautomers, were isolated in the case of both thiabenziporphyrin and thiapyriporphyrin products prepared in the course of this study. On the other hand, only the exocyclic tautomer was isolated in the case of the congeneric oxapyriporphyrin and oxabenziporphyrin. Expanded analogues of the exocyclic forms of oxabenziporphyrin and thiabenziporphyrin were also isolated as minor products. A single-crystal X-ray diffraction analysis of the expanded thiabenziporphyrin (20) revealed that all four pyrrole rings displayed an inverted geometry, presumably reflecting the strong hydrogen-bonding extant between the pyrrole N-H proton and the carbonyl group of the malonate moiety in the solid state. On the other hand, the expanded oxabenziporphyrin (14) was found to possess a severely distorted geometry with only one pyrrole ring being inverted. Careful analysis of the structure revealed that the solid-state geometry of the expanded macrocycles correlates well with the internal angle defined by the 2- and 5 substituents and the centers of the furan (14) or thiophene (20) subunits.     

Synthesis, structure of [H3dien]·(MF6)·H2O (M=Cr, Fe) and Fe Mössbauer study of [H3dien]·(FeF6)·H2O

Single crystals of [H₃dien]·(FeF₆)·H₂O (I) and [H₃dien]·(CrF₆)·H₂O (II) are obtained by solvothermal synthesis under microwave heating. I is orthorhombic (Pna2₁) with a=11.530(2) Å, b=6.6446(8) Å, c=13.787(3) Å, V=1056.3(2) Å³ and Z=4. II is monoclinic (P2₁/c) with a=13.706(1) Å, b=6.7606(6) Å, c=11.3181(9) Å, β=99.38(1)°, V=1034.7(1) Å³ and Z=4. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R₁/wR₂ reliability factors 0.028/0.066 for I and 0.035/0.102 for II. The structures of I and II are built up from isolated FeF₆ or CrF₆ octahedra, water molecules and triprotonated amines. In both structures, each octahedron is connected by hydrogen bonds to six organic cations and two water molecules. The iron-based compound is also characterized by ⁵⁷Fe Mössbauer spectrometry: the hyperfine structure confirms the presence of Fe³⁺ in octahedral coordination and reveals the existence of paramagnetic spin fluctuations.     

The molecular structure of N-fluorobis(trifluoromethanesulfonyl)imide, NF(SO(2)CF(3))(2), as studied in the gas phase by electron diffraction restrained by ab initio calculations

The structure of N-fluorobis(trifluoromethylsulfonyl)imide, prepared by a relatively safe and easy method, has been determined by gas-phase electron diffraction (GED), employing the SARACEN method, with flexible restraints based on the MP2/6-311G* structure, and by X-ray crystallography at 150 K. The strongly electron-withdrawing CF(3) and SO(2)CF(3) groups make the C-S and N-S distances long, averaging 187.7(3) and 171.7(3) pm, respectively, in the gas phase. The gas consists of two conformers, one (75%) with a CF(3) group on each side of the SNS plane, one anti-periplanar and one syn-periplanar to the further N-S bond (ap, sp), and the other with both CF(3) groups on the same side, i.e. denoted ap, ap. These conformers have very different SNS angles, 126.9(9) degrees and 117.1(17) degrees respectively. In the crystal all molecules have the ap, sp conformation, with parameters similar to those found for this conformer in the gas phase.     

Versatile synthesis of rare nucleotide furanoses

Direct activation of unprotected thioimidoyl furanosides yielded in only one step and few minutes a panel of rare uridine 5'-diphospho-furanoses. Diastereoselectivity of the reaction was tightly connected with reaction time, temperature, and nature of the furanosyl donor. This approach was totally selective since no ring expansion from the initial five-membered ring to the more stable pyranose form was observed.     

Discrete Periodic Sampling with Jitter and Almost Periodically Correlated Processes

The zero-mean process is said to be almost periodically correlated whenever its shifted covariance kernel is almost periodic in t uniformly with respect to . Then it admits a Fourier–Bohr decomposition: . This paper deals with the estimation of the spectral covariance a(λ,τ) from a discrete time observation of the process , when jitter and delay phenomena are present in conjunction with periodic sampling. Under mixing conditions, we establish the consistency and the asymptotic normality of empirical estimators as the sampling time step tends to 0 and the sampling period tends to infinity.      

Movement in an axial symmetric wave propagating in the solid state plasma in external fields

It is shown that an analog of Thomson waves, existing in an ideal fluid, is possible in metals and semiconductors. Possibility of observation of such waves is discussed.     

Hydrodynamics of modulated finite-amplitude waves in dispersive media

Analytic approaches are developed for integrating the nondiagonalizable Whitham equations for the generation and propagation of nonlinear modulated finite-amplitude waves in dissipationless dispersive media. Natural matching conditions for these equations are stated in a general form analogous to the Gurevich-Pitaevskii conditions for the averaged Korteweg-de Vries equations. Exact relationships between the hydrodynamic quantities on different sides of a dissipationless shock wave, an analog of the shock adiabat in ordinary dissipative hydrodynamics and first proposed on the basis of physical considerations by Gurevich and Meshcherkin, are obtained. The boundaries of a self similar, dissipationless shock wave are determined analytically as a function of the density jump. Some specific examples are considered. Zh. éksp. Teor. Fiz. 115, 1116–1136 (March 1999)     

Germes de d\'etermination infinie dans des classes lisses

We give sufficient conditions of infinite determinacy (in the sense of Mather) with respect to right equivalence, in subrings of C ^∞ (ℝ ⁿ ,0) defined by estimates on successive derivatives, such as rings of Gevrey germs. In this quantitative setting, a defect (hidden in the classical C ^∞ case) appears between the regularity of equivalent germs and the regularity of local diffeomorphisms of (ℝⁿ,0) giving the equivalence. Our conditions yield precise estimates of this defect, related to some suitable Łojasiewicz exponents of critical loci. We also show that the result is sharp in general. Received: Received: 27 May 1998     

Synthesis of certain 5-substituted thieno[2,3-b]thiophene-2-sulfonamides and thieno[2,3-b]thiophene-2-sulfonamide 6,6-dioxides

A series of the title compounds were prepared for evaluation as inhibitors of carbonic anhydrase II. Oxidation of 5-substituted thieno[2,3-b]thiophene-2-sulfonamides provided the first examples of thiophene[2,3-b]thiophene-2-sulfonarnide 6,6-dioxides. These cyclic vinyl sulfones readily underwent addi tion to give predominately that 4,5-cis addition product.     

Photoprotective Effect of Black Tea Extracts Against UVB-induced Phototoxicity in Skin

In previous studies, we showed that green tea and black tea extracts and their major polyphenolic constituents protect against UVB light-induced carcinogenesis in murine skin. All of these studies required chronic administration of tea extracts or specific constituents either topically or orally. However, it is not known whether acute or subchronic administration of black tea extracts or constituents can ameliorate UVB-induced early effects in skin. In the present study, cultured keratinocytes and mouse and human skin were employed to assess the effect of both oral and topical administration of standardized black tea extract (SBTE) and its two major polyphenolic subfractions namely BTF1 and BTF2 against UVB-induced photodamage. In SKH-1 hairless mice, topical application of SBTE (0.2 mg/cm2) prior to UVB exposure (180 mJ/cm2) resulted in 40% reduced incidence and 64% reduced severity of erythema and 50% reduction in skinfold thickness by day 6 when compared to nontreated UVB-exposed animals. The SBTE was also effective in protecting against UVB-induced erythema in human volunteers. Administration of SBTE 5 min after UVB irradiation was similarly effective in reducing UVB-induced inflammation in both murine and human skin. The major polyphenolic subfractions, BTF1 and BTF2, were also effective in protecting in mouse skin. The SBTE subfractions inhibited UVB-induced tyrosine phosphorylation of epidermal growth factor receptor (EGFR). The UVB irradiation of human epidermoid carcinoma cells resulted in 3.3-fold induction of tyrosine phosphorylation of EGFR. Pretreatment with BTF1 and BTF2 reduced tyrosine phosphorylation of EGFR by 53% and 31%, respectively. The UVB-mediated enhanced expression of the early response genes, c-fos and c-jun in human epidermal keratinocytes was reduced in a dose-dependent manner by SBTE. Topical application of SBTE was also effective in reducing accumulation of c-fos and p53 proteins by 82% and 78%, respectively, in UVB-exposed mouse skin. These data provide evidence that constituents of black tea can abrogate UVB-induced erythema and associated early events in murine and human skin.