Subdiffraction resolution in total internal reflection fluorescence microscopy with a grating substrate

We propose a fluorescence surface imaging system that presents a power of resolution beyond that of the diffraction limit without resorting to saturation effects or probe scanning. This is achieved by depositing the sample on an optimized periodically nanostructured substrate in a standard total internal reflection fluorescence microscope. The grating generates a high-spatial-frequency light grid that can be moved throughout the sample by changing the incident angle. An appropriate reconstruction procedure permits one to recover the fluorescence amplitude from the images obtained for various incidences. Simulations of this imaging system show that the resolution is not limited by diffraction but by the period of the grating.     

Über Umlagerungen bei der Cyclialkylierung von Arylpentanolen zu 2,3‐Dihydro‐1H‐inden‐Derivaten, 1. Mitteilung

On Rearrangements by Cyclialkylations of Arylpentanols to 2,3‐Dihydro‐1 H ‐indene Derivatives. Part 1. An Unexpected Rearrangement by the Acid‐Catalyzed Cyclialkylation of 4‐(2‐Chlorophenyl)‐2,4‐dimethyl pentan‐2‐ol under Formation of trans ‐4‐Chloro‐2,3‐dihydro‐1,1,2,3‐tetramethyl‐1 H ‐indene The acid‐catalyzed cyclialkylation of 2,4‐dimethyl‐4‐phenylpentan‐2‐ol led exclusively to the expected product, 2,3‐dihydro‐1,1,3,3‐tetramethyl‐1H‐indene. However, analogous cyclialkylation of 4‐(2‐chlorophenyl)‐2,4‐dimethylpentan‐2‐ol ( 1 ) gave a ca. 1 : 1 mixture of 4‐chloro‐2,3‐dihydro‐1,1,3,3‐tetramethyl‐1H‐indene ( 2 ) and of trans‐4‐chloro‐2,3‐dihydro‐1,1,2,3‐tetramethyl‐1H‐indene ( 3 ; Scheme 1). The specific action of the Cl substituent is investigated and a mechanism for this unexpected frame‐work transposition proposed.     

Clan structure analysis and rapidity gap probability

Clan structure analysis in rapidity intervals is generalized from negative binomial multiplicity distribution to the wide class of compound Poisson distributions. The link of generalized clan structure analysis with correlation functions is also established. These theoretical results are then applied to minimum bias events and evidentiate new interesting features, which can be inspiring and useful in order to discuss data on rapidity gap probability atTevatron andHera.     

Increasing the angular tolerance of resonant grating filters with doubly periodic structures

One can increase the angular tolerance of resonant grating filters without modifying the spectral bandwidth by adding a second grating component parallel to the first one. The angular tolerance and the filter linewidth can be controlled by the designer in an independent way. Numerical results show that this property permits the use of waveguide-grating filters with standard collimated beams.     

Über Umlagerungen bei der Cyclialkylierung von Arylpentanolen zu 2,3‐Dihydro‐1H‐inden‐Derivaten, 3. Mitteilung

On Rearrangements by Cyclialkylations of Arylpentanols to 2,3‐Dihydro‐1 H ‐indene Derivatives. Part 3. The Acid‐Catalyzed Cyclialkylation of 3,4‐Dimethyl‐ and 3‐([ ² H ₃ ]Methyl)‐4‐methyl‐3‐phenylpentan‐2‐ol The cyclialkylation of 2‐([²H₃]methyl)‐4‐methyl‐4‐phenyl[1,1,1‐²H₃]pentan‐3‐ol ( 4 ) yielded a 1 : 1 mixture of 1,1‐di([²H₃]methyl)‐2,3‐dimethyl‐1H‐indene ( 5 ) and of 2,3‐dihydro‐2,3‐di([²H₃]methyl)‐1,1‐dimethyl‐1H‐indene ( 6 ) (Scheme 1) [1]. However, it was not clear whether the transposition takes place through the successive migration of a Ph, a Me and again the Ph group (Scheme 2, Path A: shift IV → VII → VIIa ) or through Ph‐, Me‐, and then i‐Pr‐group (Scheme 2, Path B: IV → VII → VIIb ). The cyclialkylation of 3‐([²H₃]methyl)‐4‐methyl‐3‐phenylpentan‐2‐ol ( 7 ) yielded only one product, the 2,3‐dihydro‐2‐([²H₃]methyl)‐1,1,3‐trimethyl‐1H‐indene ( 8 ), in accordance with the migrations according to Path A. This result is also a support for the total mechanism proposed for the cyclialkylation of 4 (Scheme 2). The transition of a tertiary to a secondary carbenium ion is not definitely ensured (see [1]).     

New 9,10‐Secosteroids from Biotransformations of Bile Acids with Rhodococcus ruber

The biotransformations of cholic, deoxycholic, and hyocholic acids with Rhodococcus ruber are reported. In all biotransformations, the C₁₇‐side chain is partially degraded, and the new 9,10‐secosteroids 4a (54%) and 4b (55%) are obtained from cholic and deoxycholic acids, respectively. The loss of H₂O from C(11)? C(12) of secosteroids 4a and 4b affords the compounds 5a (5%) and 5b (20%), respectively. On the other hand, in the biotransformation of hyocholic acid with R. ruber the 9,10‐secosteroid 4c is not detected, but, rearranging to an intramolecular hemiacetal form, it evolves to the final furan derivative 6c (35%) by easy elimination of two molecules of H₂O. The new secosteroids were characterized by IR, NMR, and 2D‐NMR spectroscopy, and mass spectroscopy.     

Enzymatic diastereo- and enantioselective synthesis of α-alkyl-α,β-dihydroxyketones

An enzymatic strategy for the preparation of optically pure α-alkyl-α,β-dihydroxyketones is reported. Homo- and cross-coupling reactions of α-diketones catalyzed by acetylacetoin synthase (AAS) produce a set of α-alkyl-α-hydroxy-β-diketones (30-60%, ee 67-90%), which in turn are reduced regio-, diastereo-, and enantioselectively to the corresponding chiral α-alkyl-α,β-dihydroxyketones (60-70%, ee >95%) using acetylacetoin reductase (AAR) as catalyst. Both enzymes are obtained from Bacillus licheniformis and used in a crude form. The relative syn stereochemistry of the enantiopure α,β-dihydroxy products is assigned by NOE experiments, whereas their absolute configuration is determined by conversion of the selected 3,4-dihydroxy-3-methyl-pentan-2-one to the natural product (+)-citreodiol.     

Polymorph formation from solvate desolvation

Spironolactone (C₂₄H₃₂O₄S) usually crystallizes into an orthorhombic phase, named Form II. Another orthorhombic phase, named Form I, is also known but seems difficult to obtain. Studies of the kinetics of desolvation of the ethanol solvate at room temperature showed that these two forms can be obtained through different mechanisms of desolvation.