‘Non-Koopmans’ States in Stilbene Cations and a Remarkable Example to the «SDT-Equation»: Indeno [2,1-a]indene

The radical cations of indeno [2, 1-a]indene ( 1 ), stilbene ( 2 ) and 3, 5, 3', 5'-tetramethylstilbene ( 3 ) were prepared by γ-irradiation of the neutral precursors in an electron-scavenging matrix at 77 K . Their electronic spectra were recorded and compared to the photoelectron spectra ( PE .) of the neutral precursors. The results show that either the fourth or the fifth excited doublet state of the cations is of «Non-Koopmans» type, with specific doublet energy (D) D (²B_g)=2.74 eV ( 1 ⁺), =2.59 eV ( 2 ⁺), =2.49 eV ( 3 ⁺). Remarkably, 1 ⁺ possesses two electronic states in the 2.7-2.8 eV energy range: ²A_u («Koopmans»-type) and ²B_g («Non -Koopmans»-type). The «SDT»-equation \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm D} = \sqrt {{\rm S} \cdot {\rm T}} $\end{document} approximately connecting excited singlet (S) and triplet (T) states of a neutral alternant system with the excited doublet (D) states of its radical cation - provided e-promotion occurs For all three excited states between the same (paired) orbitals-is satisfyingly exemplified by 1 : S¹ = 3.92 eV and T¹= 2.06 eV for 1 , D^{4 or 5}=2.74 eV for 1 ⁺.     

Synthesis and properties of 1-(6-methoxy)-2-benzothiazolyl)-2-pyridones

Substituted ]-(6-methoxy-2-benzothiazolyt)-2-pyridones were prepared from 2-amino-6-methoxybenzathiazate through N-(6-methoxy-2-benzothiazotyl) cyanvorearmileaznd-3-aryl-N-(6-methoxy-2-benzothiazolyt)-2-cyano-2-propenamides. The cyclization of the latter with malonodinitrile in the presence of piperidine gave the corresponding pyridones. The structures of the synthesized compounds were confirmed by¹H NMR and mass spectral data.Department of Organic Chemistry, Mass Spectrometry Laboratory, Slovak Technical University, 812 37 Bratislava, Slovakia. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1402–1404, October, 1995. Original article submitted August 24, 1995.     

Non-covalent polyvalent ligands by self-assembly of small glycodendrimers: a novel concept for the inhibition of polyvalent carbohydrate-protein interactions in vitro and in vivo

Polyvalent carbohydrate-protein interactions occur frequently in biology, particularly in recognition events on cellular membranes. Collectively, they can be much stronger than corresponding monovalent interactions, rendering it difficult to control them with individual small molecules. Artificial macromolecules have been used as polyvalent ligands to inhibit polyvalent processes; however, both reproducible synthesis and appropriate characterization of such complex entities is demanding. Herein, we present an alternative concept avoiding conventional macromolecules. Small glycodendrimers which fulfill single molecule entity criteria self-assemble to form non-covalent nanoparticles. These particles-not the individual molecules-function as polyvalent ligands, efficiently inhibiting polyvalent processes both in vitro and in vivo. The synthesis and characterization of these glycodendrimers is described in detail. Furthermore, we report on the characterization of the non-covalent nanoparticles formed and on their biological evaluation.     

Construction of Highly Substituted Nitroaromatic Systems by Cyclocondensation. Part II. Conversion of 4-nitro-3-oxobutyrate to 3-nitrosalicylates

The base-catalyzed reaction of 4-nitro-3-oxobutyrate (6) with acetylacetone ( 8 Scheme 3), formylacetone ( 13 , Scheme 4), formylcyclohexanone ( 31 , Scheme 5), 2,4-dioxopentanoates 39 and 40 (Scheme 6), and 2,4,6-heptanetrione ( 2 , Scheme 7) affords substituted 3-nitrosalicylates, products of a double aldol condensation. With unsymmetrical dicarbonyl compounds both regioisomers are formed. High selectivity was found in the case of β-keto-aldehydes 13 and 31 with preferred addition of the NO₂-substituted carbon to the aldehyde carbonyl. The major products of these cyclocon-densations, which are isolated in yields ranging from 20% to 80%, are all new compounds. Less successful are the conversions with β-alkoxy- and β-chloro-vinyl ketones ( 23, 25 , and 26 ), and with alkinone 24 , where the condensation products are formed in very low yield (Scheme 4).     

New membrane materials for potassium-selective ion-sensitive field-effect transistors

Several polymeric materials were studied as membrane materials for potassium-selective ion-sensitive field-effect transistors (ISFETs) to overcome the problems related with the use of conventional plasticized poly(vinyl chloride) membranes casted on ISFET gate surfaces. Several acrylate materials, such as ACE, Epocryl and derivatives, showed no reproducible results. Three room-temperature vulcanizing (RTV)-type silicone rubbers were tested. The addition-type RTV-2 silicone rubber was not suitable as a membrane material, but the condensation-type RTV-1 and especially the RTV-2 silicone rubber showed good results. ISFETs with a Silopren membrane showed a durability of at least 2 months.     

Regioselective cyclomanganation of Schiff bases. An unexpected effect of chloro substituents

In this paper we describe the synthesis of new metallacycles by the cyclomanganation reaction of benzyl-benzylidene-amines by using [MnMe(CO)₅] as metallating agent. These ligands can undergo metallation on different aromatic carbon atoms but no important differences have been found in the regioselectivity of the process, that can be related to the electronic effect of the substituents, and in all the cases studied the endo-cyclomanganated complexes of para-substituted imines have been obtained. The corresponding exo-metallacycles were obtained by reaction of [MnMe(CO)₅] on the imine 2,6-Cl₂C₆H₃CHNCH₂Ph and 2,4,6-Me₃C₆H₂CHNCH₂Ph, derived from 2,6-dichlorobenzaldehyde and 2,4,6-trimethylbenzaldehyde, respectively.The results described suggest that the mechanism of the cyclomanganation is similar to that of cyclopalladation and it can be proposed that cyclomanganation takes place by the formation of a four-centered transition state, involving the C-H and Mn-C_acetyl bonds, in the acetyl coordination complex formed in the first step of the reaction.     

Recent liquid chromatographic-(tandem) mass spectrometric applications in proteomics

Conventional proteomics makes use of two-dimensional gel electrophoresis followed by mass spectrometric analysis of tryptic fragments derived from in-gel digestion of proteins. Although being a very strong technique capable of separating and visualizing hundreds of proteins, 2D-gel electrophoresis has some well-documented disadvantages as well. More recently, liquid chromatographic-(tandem) mass spectrometric techniques have been developed to overcome some of the shortcomings of 2D-gel electrophoresis. In this review we have described several recent applications of liquid chromatography-(tandem) mass spectrometry in the field of proteomics and especially in the field of membrane proteomics, quantitative proteomics and in the analysis of post-translational modifications.     

A new method for the preparation of 2-thio substituted furans by methylsulfanylation of gamma-dithiane carbonyl compounds

Several related methods for the preparation of differentially substituted 2-thiofurans are described. The general procedure involves the formation of a thionium ion from a gamma-dithianyl substituted carbonyl compound followed by cyclization of this reactive intermediate onto the tethered carbonyl group. Two methods for thionium ion generation were explored. One of these involved an acid-catalyzed reaction of beta-ketenedithioacetals, prepared from the condensation of 2,2-bis(methylsulfanyl)acetaldehyde with a variety of ketones. Cyclization followed by loss of methane thiol gave 2-thiofurans 17, 18 and 23, 24 in 70-90% yield. Attempts to prepare 5-heteroatom substituted 2-thiofurans from the corresponding beta-ketenedithioacetal amides or esters were unsuccessful, leading to 1,2-thio rearranged products. A more successful route involved the reaction of beta-acetoxy-gamma-thianyl carbonyl compounds with dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF). Treatment of the dithiane with this reagent resulted in the smooth generation of a thionium ion. Cyclization followed by loss of acetic acid afforded thiofurans 17, 18, 23, 47-49, 51, and 61-64 in 40-100% yield. The N-butenyl substituted thioamido furan furnished a rearranged hexahydropyrroloquinolin-2-one in high yield when heated at 110 degrees C.