Femtosecond time-resolved absorption spectroscopy of astaxanthin in solution and in alpha-crustacyanin

Steady-state absorption and femtosecond time-resolved spectroscopic studies have been carried out on astaxanthin dissolved in CS2, methanol, and acetonitrile, and in purified alpha-crustacyanin. The spectra of the S0 --> S2 and S1 --> S(n) transitions were found to be similarly dependent on solvent environment. The dynamics of the excited-state decay processes were analyzed with both single wavelength and global fitting procedures. In solution, the S1 lifetime of astaxanthin was found to be approximately 5 ps and independent of solvent. In alpha-crustacyanin, the lifetime was noticeably shorter at approximately 1.8 ps. Both fitting procedures led to the conclusion that the lifetime of the S2 state was either comparable to or shorter than the instrument response time. The data support the idea that dimerization of astaxanthin in alpha-crustacyanin is the primary molecular basis for the bathochromic shift of the S0 --> S2 and S1 --> S(n) transitions. Planarization of the astaxanthin molecule, which leads to a longer effective pi-electron conjugated chain and a lower S1 energy, accounts for the shorter tau1 in the protein.     

Jahn‐Teller‐Ordnung in pipzH2[Mn2F8], einem Fluoromanganat(III) mit neuer Schichtstruktur

Jahn‐Teller Ordering in pipzH₂[Mn₂F₈], a Fluoromanganate(III) with a New Layer Structure From a solution of (pipzH₂)[MnF₂(HPO₄)(H₂O)]·(H₂PO₄) in concentrated hydrofluoric acid the title compound could be crystallized and was characterized by X‐ray crystallography: monoclinic, space group P2₁/n, Z = 8, a = 13.275(1), 10.400(1), c = 14.928(1) Å, β = 112.337(8), R = 0.0265. The structure shows a new type of anionic layers [Mn₂F₈] built of dimers of edge‐sharing [MnF₆] octahedra linked via common vertices, alternating with layers of piperazinium(2+) cations. A dense network of hydrogen bonds N–H···F achieves a strong 3D interconnection. Strong elongation of the [MnF₆] octahedra is observed due to the Jahn‐Teller effect.The long axes show parallel (ferrodistortive) orientation within the dimers, but the ordering between the dimers is antiferrodistorive. A possible mechanism of formation is discussed on the basis of precursor structures.     

Catalytic osmylation and oxypalladation of khellin. Two useful methods for furan ring degradation. Replacement of the furan ring by an isoxazole ring.

Two oxidation reactions are described which result in the selective degradation of the furan ring in khellin. Conversion of these products to previously inaccessible analogues is described.     

Correlation of ring nitrogen substituents with carbon-13 nuclear magnetic resonance data in azoloazines

Carbon–13 nuclear magnetic resonance data have been acquired on 22 azoloazines. Chemical shifts have been correlated by a step–wise linear multiple regression with nitrogen substituents in both the 5- and 6-membered rings using pyrrolo[1,2-α]pyridine as the reference for chemical shift correlation. The data demonstrate that a highly correlated set of chemical shift parameters exist. Nitrogen substitution in the five–membered ring produces larger cross–ring effects than are oberved in the five–membered ring when substitution occurs in the six–membered ring. Within the six–membered ring a constant para- substituent parameter is noted. The meta- and para- parameters are more complex and fall into two groups for each parameter. Within the five–membered ring, a highly regular chemical shift pattern is observed which reflects an attenuated perturbation from nitrogen substitution in the six–membered ring.     

Fluoro-olefin chemistry Part 20 [1]. Reaction of hexafluoropropene with alcohols

Reaction of hexafluoropropene (HFP) with a series of alcohols under thermal, photochemical or peroxide-initiated conditions affords the 1:1 adducts CF₃CHFCF₂CR¹R²OH (R¹ = H, R² = H, Me, Prⁿ or CF₃; R¹ = Me, R² = Me or Et) in high yield via a radical chain mechanism. Adduct are not formed with the alcohols (CF₃)₂CHOH and CF₃CHFCF₂CH₂OH. Other 1:1 adducts of structure CHF₂CF(CF₃)CH₂OH and CH₃(C₂H₃CF₂CHFCF₃)CH₂OH are formed as minor products in the methanol and $\text{n}$-butanol reactions, respectively.     

Synthesis of substituted 2-amino-3-cyano-4-methylpyrroles

A facile route for the synthesis of substituted 2-amino-3-cyano-4-methylpyrroles from N-acetyl-α-amino ketones and malononitrile is reported.     

Synthesis of the o-quinones and other oxidized metabolites of polycyclic aromatic hydrocarbons implicated in carcinogenesis

Efficient new syntheses of the o-quinone derivatives of benzo[a]pyrene (BPQ), 7,12-dimethylbenz[a]anthracene (DMBAQ), and benz[a]anthracene (BAQ), implicated as active carcinogenic metabolites of the parent polycyclic aromatic hydrocarbons (PAHs), are reported. These PAH quinones also serve as starting compounds for the synthesis of the other active metabolites of these PAHs thought to be involved in their mechanism(s) of carcinogenesis. The latter include the corresponding o-catechols, trans-dihydrodiols, and the corresponding anti- and syn-diol epoxides.     

Distribution of single DNA molecule electrophoretic mobilities in semidilute and dilute hydroxyethylcellulose solutions

The distribution of center of mass electrophoretic mobility mobilities and normalized migration time of up to 1080 lambda DNA molecules per experiment were measured in both semidilute hydroxyethylcellulose HEC/0.5 x Tris-borate-EDTA (TBE) solutions and dilute HEC/0.5 x TBE solution by high-speed video microscopy. Measurements were made microscopically over a short migration distance in homogeneous DNA HEC/0.5 x TBE solution and after electrophoretic migration of a plug of DNA through 7 cm. Video at 120 frames/s (semidilute HEC solution) and 236 frames/s (dilute HEC solution) allowed visualization with adequate resolution for single molecule mobility measurements. The electrophoretic migration times and band shapes predicted from the measurements corresponded well with those measured by conventional capillary electrophoresis (CE) in both semidilute and dilute HEC. In semidilute solution, the band width predicted by a square root of time scaling is in good agreement with the results of conventional CE. However, in dilute solution the precision of the measurements was not good enough to allow scaled estimates of band widths.     

K-region oxides and imines of benzo[b]phenanthro[2,3-d]thiophene and benzo[b]phenanthro[3,2-d]thiophene

The syntheses of the K-oxides and K-imine derivatives of benzo[b]phenanthro[2,3-d]thiophene and benzo-[b]phenanthro[3,2-d]thiophene are described. The parent hydrocarbons 1 and 2 were oxidized with osmium tetroxide and sodium metaperiodate, and the dialdehydes 12 and 18 so formed, cyclized to the corresponding epoxides 1a,12b-dihydrobenz[b]oxireno[9,10]phenanthro[2,3-d]thiophene ( 7 ) and 1a,12b-dihydrobenz-[b]oxireno[9,10]phenanthro[3,2-d]thiophene ( 13 ). Reaction of the oxiranes with sodium azide gave mixtures of azido-alcohols that, in turn, were transformed to the thiaarene imines 1a,12b-dihydro-1H-benz[b]azirino-[9,10]phenanthro[2,3-d]thiophene ( 8 ) and 1a,12b-dihydro-1H-benz[b]azirino[9,10]phenanthro[3,2-d]thiophene ( 14 ), respectively, with the aid of tri-n-butylphosphine.