Real-time observation of single-molecule fluorescence in microdroplet streams

We report real-time observation of fluorescence bursts from individual Rhodamine 6G molecules in streams of microdroplets (peak signal-to-noise ratios, approximately 30) whose trajectories are constrained with a linear electric quadrupole. This approach offers a reasonable dynamic range in droplet size (3- 12-microm diameter) with <1% shot-to-shot size fluctuations and sensitivity comparable with that of droplet levitation techniques with at least 10(3) higher analysis rates. Applications to the study of single-molecule microcavity effects and stimulated emission are discussed.     

COMPARISON OF PHOTOTRAP COMPLEXES FROM CHROMATOPHORES OF RHODOSPIRILLUM RUBRUM, RHODOPSEUDOMONAS SPHEROIDES, AND THE R-26 MUTANT OF RHODOPSEUDOMONAS SPHEROIDES*

Abstract— After dissolution of the membrane structure of chromatophores from Rhodospirillum rubrum, Rhodopseudomonas spheroides , and the R-26 mutant of Rhodopseudomonas spheroides , active phototrap complexes from each have been purified by a column electrophoresis procedure. Phospholipids and transition metals were well separated from the phototrap complex in all three systems. The purified R. rubrum phototrap complex retained a full complement of antenna bacteriochlorophyll and carotenoid pigments which had nearly the same absorbance spectra as in the intact cell, and which delivered absorbed light energy to the phototrap with just as high efficiency as in the intact cell. Sodium dodecyl sulfate (SDS) disc gel electrophoresis using Tris buffer showed that these preparations often contained only two prominent polypeptides of 30,000 ± 2000 and 12,000 ± 4000 mol. wt., and a lesser amount of a third polypeptide of 21,000 ± 2000 mol. wt.
The phototrap complexes prepared from the wild type and the R-26 mutant of R. spheroides were similar, in that a partial separation from antenna pigments occurred during column electrophoresis. Both complexes had prominent polypeptides of 24,000 ± 2000 and 21,000 ± 2000 mol. wt., but no polypeptide of 30,000 mol. wt remained after electrophoresis. A third major polypeptide occurred with a mol. wt. of about 12,000 but seemed identifiable with an incompletely separated antenna pigment fraction. The phototrap complex prepared from the R-26 mutant had a typical reaction center spectrum.
In the case of wild type R. spheroides purification, two distinct protein-pigment complexes separated. Although the absorbance of the bacteriochlorophyll and carotenoid pigments were little changed from those of the in vivo system, different polypeptides in the two fractions were observed by SDS disc gel electrophoresis; only one fraction seemed to be intimately related with the phototrap complex.     

Photogenerated N-methyl-N-1-naphthylnitrenium ion: laser flash photolysis, trapping rates, and product study

N-Methyl-N-1-naphthylnitrenium ion (2) was generated through photolysis of 1-(N-methyl-N-(1-naphthyl)amino)-2,4,6-trimethylpyridinium tetrafluoroborate (1). Laser flash photolysis (LFP) with time-resolved UV-vis (TRUV) detection as well as photoproduct analysis verified that the expected nitrenium ion was formed cleanly and rapidly following photolysis. Consistent with an earlier study, which used competitive trapping methods (Novak, M. et al. J. Org. Chem. 1999, 64, 6023-6031), it is found that 2 reacts rapidly with a variety of nucleophiles. The high reactivity of 2 relative to other arylnitrenium ions is discussed in terms of steric and electronic effects.     

Asymptotic behavior of the solutions of an integrodifferential system

Summary We consider the system(L): , t ⩾ p, y(t)=f(t), t⩽0, where y is an n-vector and each A_i, B(t) are n × n matrices. System(L) generates a semigroup by means of T_tf(s)=y (t+s, f), f(s) ∈ BC_l(− ∞, 0]. Under some hypotheses concerning the roots ofdet where is the Laplace transform of B(t), the asymptotic behavior of y(t) is discussed. Two typical results are: Theorem 3.1: suppose ∥B(t)∥ ɛ L₁[0, ∞), thendet forRe λ>0 iff for every ɛ>0 there is an M_ɛ>0 such that ∥T_tf∥_l ⩽ ⩽ M_ɛ exp [ɛt]∥f∥_l for t ⩾ 0. Corollary 3.1.1: suppose exp [at]B(t) ∈ ∈ L₁[0, ∞) for some a>0 anddet forRe λ>−a. Then the solution of(L) is exponentially asymptotically stable. Entrata in Redazione il 21 marzo 1975. The author is grateful to ProfessorC. Corduneanu for suggesting this problem and for many helpful discussions during the preparation of the paper.     

Synthetic and Spectral Studies of Some Nickel Complexes Involving the Iminoquinolinone-Type Ligand

In this study we prepared N,O-bidentate ligands, sodium salt of 5-(4′-hydroxyphenylimino)quinolin-8-one, and sodium salt of 5,8-quinolinequinone-5-(8-hydroxy-5-quinolylimide) [indoöxine]. According to experimental results, formation of nickel complexes causes a large bathochromic shift of the absorption bands; in addition, these absorption bands appear in the near-infrared region at 678-812 nm. Also, EA, ¹³C NMR, UV, and IR were performed to characterize these complexes. The above results suggest that coordination occurs via the oxygen atom of the quinoneimine moiety and the nitrogen atom of the pyridine moiety.     

Efficient synthesis of immolative carbamate dendrimer with olefinic periphery

An efficient synthetic strategy for immolative carbamate dendrons and dendrimers is described that requires no protection/deprotection in the convergent growth step. 1,3-Diamino-2-propanol was used as AB₂ building block and 4-nitrophenyl chloroformate as carbamate forming reagent. The method was demonstrated with a G3-dendron. A combination of convergent and divergent growth method was used to couple G2-dendrons to a G2-core or G3-dendrons to a tetrahedral G1-core with amine functional groups to form a spherical carbamate dendrimer (G4) possessing an olefinic periphery.     

One-step construction of the pentacyclic skeleton of saframycin A from a "Trimer" of alpha-amino aldehydes

The entire skeleton of the saframycin antitumor antibiotics is assembled in one remarkable transformation (8 --> 9) from an N-linked oligomer of three alpha-amino aldehyde components, a reaction pathway that may parallel the biosynthetic route to the saframycins.