Blue and red light-induced germination of resting spores in the red-tide diatom Leptocylindrus danicus

Photophysiological and pharmacological approaches were used to examine light-induced germination of resting spores in the red-tide diatom Leptocylindrus danicus. The equal-quantum action spectrum for photogermination had peaks at about 440 nm (blue light) and 680 nm (red light), which matched the absorption spectrum of the resting spore chloroplast, as well as photosynthetic action spectra reported for other diatoms. DCMU, an inhibitor of photosynthetic electron flow near photosystem II, completely blocked photogermination. These results suggest that the photosynthetic system is involved in the photoreception process of light-induced germination. Results of pharmacological studies of the downstream signal transduction pathway suggested that Ca(2+) influx is the closest downstream neighbor, followed by steps involving calmodulin, nitric oxide synthase, guanylyl cyclase, protein-tyrosine-phosphatase, protein kinase C and actin polymerization and translation.     

Synthesis and biological evaluation of triazole analogues of antillatoxin

Antillatoxin 1, a cyclic lipopeptide, is known as an activator of voltage-gated sodium channels and exhibits potent neurotoxicity toward Neuro 2a mouse neuroblastoma cells. To investigate the biological effects of the side-chain structures at C5 and C5′ in detail, we planned SAR studies of C5- and C5′-modified antillatoxin analogues. To diversify the structures at the last step of the synthesis, two key intermediates 4 and 6 possessing terminal alkynes at the C5- and C5′-positions were designed and synthesized using two distinct strategies. Sixteen side-chain derivatives were then prepared from 4 and 6 by coupling with a wide variety of azides via click chemistry, and subjected to the cytotoxicity assay. Although almost all of the C5-substituted analogues exhibited no cytotoxicity, the C5′-substituted analogues showed modest cytotoxicity. These results showed that C5′ is more tolerant than C5 to structural modifications. The present SAR study will provide valuable information for designing new antillatoxin-based molecular probes for neuroscience research.     

Syntheses of Tetrasubstituted [10]Cycloparaphenylenes by a Pd‐catalyzed Coupling Reaction. Remarkable Effect of Strain on the Oxidative Addition and Reductive Elimination

A small library of tetrasubstituted [10]cycloparaphenylene ([10]CPP) derivatives bearing alkyl, alkenyl, alkynyl and aryl substituents was constructed by a Pd‐catalyzed cross‐coupling reaction starting from tetratriflate [10]CPP 5 e , which was readily available in high yields on a >2 g scale. The CPP skeleton increases the reactivity of aryl triflate for oxidative addition to the Pd species, and 5 e is 10 times more reactive than its linear paraphenylene analogue, as determined by competition experiments. Theoretical calculations suggest that the accumulation of the small strain relief from each paraphenylene unit not involved in the reaction is responsible for the observed enhanced reactivity.     

Ultrafast Exciton Self-Trapping and Delocalization in Cycloparaphenylenes: The Role of Excited-State Symmetry in Electron-Vibrational Coupling

Upon photon absorption, π-conjugated organics are apt to undergo ultrafast structural reorganization via electron-vibrational coupling during non-adiabatic transitions. Ultrafast nuclear motions modulate local planarity and quinoid/benzenoid characters within conjugated backbones, which control primary events in the excited states, such as localization, energy transfer, and so on. Femtosecond broadband fluorescence upconversion measurements were conducted to investigate exciton self-trapping and delocalization in cycloparaphenylenes as ultrafast structural reorganizations are achieved via excited-state symmetry-dependent electron-vibrational coupling. By accessing two high-lying excited states, one-photon and two-photon allowed states, a clear discrepancy in the initial time-resolved fluorescence spectra and the temporal dynamics/spectral evolution of fluorescence spectra were monitored. Combined with quantum chemical calculations, a novel insight into the effect of the excited-state symmetry on ultrafast structural reorganization and exciton self-trapping in the emerging class of π-conjugated materials is provided.     

SYNTHESES AND SOME PROPERTIES OF SULFOXIDES,SULFILIMINES, AMINOSULFONIUM SALTS AND SULFOXIMINES CONTAINING PYRIDINE NUCLEI

Abstract

Several 2-pyridyl sulfides (1) (e.g., methyl (1a), ethyl (1b), isopropyl (1c), benzyl (1d), 1-phenylethyl (1e), l-menthyl (If) 2-pyridyl sulfides; and bis(2-pyridylthio)methane (1g), and methyl 2-(N-oxy-pyridyl) sulfide (1h) were prepared by the usual method. Sulfoxides (2) were prepared by oxidation of the corresponding sulfides with m-chloroperbenzoic acid in good yields. A few sulfoxides were found to work as phase-transfer catalysts for some typical nucleophilic reactions in nonpolar solvents such as benzene, and in two-phase systems such as benzene-water. S-2-Pyridyl-N-(p-toluenesulfonyl) sulfilimines (3) were prepared upon treatment of sulfides with Chloramine-T. Hydrolysis of N-(p-toluenesulfonyl)-2-pyridyl-o-tolylsulfilimine (3i) with conc. sulfuric acid gave the corresponding free sulfilimine in a moderate yield. S-2-Pyridyl sulfoximines (4) were not obtained by the general method from the sulfoxides and hydrazoic acid. Alkyl-2-pyridyl sulfoximines, however, were obtained by oxidation of the free sulfilimines derived from the corresponding aminosulfonium salts (5) prepared by reaction of the sulfides with mesitylene-sulfonylhydroxylamine (MSH). These free sulfilimines and sulfoximines thus prepared were found to give adducts with a few copper salts.     

KINETICS OF THE REACTION OF SULFIMIDES WITH POTASSIUM HYDROXIDE IN METHANOL

Abstract

The reaction of sulfimides with hydroxide ion in methanol gave the corresponding sulfoxide (the solvolysis product) and/or the corresponding α-methoxysulfide (the Pummerer type product). The pseudo first order rates for the solvolysis reaction and the Pummerer type reaction were determined using a large excess of potassium hydroxide. The rates of the solvolyses are correlated with [sgrave] values and the values of ρ _X = +1.2 and ρ _Y = +0.8 were obtained for aryl methyl N-aryl-sulfonylsulfimides (p-XC₆H₄S(NSO₂C₆H₄Y-p)CH₃), and both the activation enthalpy and entropy calculated are δH≠ = 18.8 kcal mol^?1 and δS≠ = –23.9 e.u. (PhS(NSO₂C₆H₄CH₃-p)CH₃), respectively. Hammett correlation with [sgrave] values for the Pummerer type reaction gave ρz = +2.0 for N-aryl-sulfonyltetramethylenesulfimides ((CH₂)₄SNSO₂C₆H₄Z-p), and the activation enthalpy and entropy are δH≠ = 27.9 kcal mol^?1 and δS≠ = +13.3 eu ((CH₂)₄SNSO₂C₆H₄CH₃-p), respectively. All these observations suggest that the solvolysis reaction proceeds via the initial nucleophilic attack of hydroxide ion on the sulfur atom of the sulfimide namely via an S _N 2 process at the sulfur atom whereas the Pummerer type reaction proceeds by way of the E 1cb mechanism.     

STUDY OF THE MECHANISM FOR THE REARRANGEMENT OF THIOLSULFINATE WITH ACETIC ANHYDRIDE BY 13C AND 18O-TRACER EXPERIMENTS

Abstract

Recently, we found that benzyl phenylmethanethiolsulfinate (I) reacts with acetic anhydride at 60°C to afford the rearranged sulfoxide, i.e., an almost 1:1 mixture of both erythro and threo-1-(acetoxylthio)benzyl benzyl sulfoxides(II) in a substantial yield.     

A Two Phase Model for the Binding of Cations To Long-Chain Polyphosphate Anions

Abstract

Binding of uni- and divalent cations to long-chain polyphosphate anions was investigated in the presence of excess uni-univalent salt. It was concluded that the binding occurs mainly in a “territorial binding” mode, i.e., most of the bound cations move freely within a specified volume around the polymer. Intrinsic complex formation (site binding) should be expressed as an equilibrium in the polymer phase.     

Synthesis and Reactions of Phosphorus Substituted Acetylenes

Abstract

To construct phosphorus-functional group substituted Ir-electron systems, synthesis of acetylenes possessing phosphorus substituents and the reactions with CpCo(CO)₂ were investigated.     

Sodium ion sensors based on dibenzo-16-crown-5 compounds with amide side arms

Abstract

Lipophilic dibenzo-16-crown-5 compounds with amide-containing side arms attached to the central carbon atom of the three-carbon bridge in the polyether ring have been applied as neutral carriers for sodium ion-selective field-effect transistors (Na⁺-ISFET′s). ISFET′s based on these lariat ether amides exhibit excellent Na⁺/K⁺ selectivities (K_Na′K ^Pot = 7 × 10^?3) and Na⁺/H⁺ selectivities (K_Na′H ^Pot = 3 × 10^?3) with good selectivities for Na⁺ over other alkali metal cations and alkaline-earth metal cations. High sensor durability was obtained for these ISFET′s.