1-Alkyl-4-dialkylaminopyridinium Halides as Phase-Transfer Catalysts in Dichlorocarbene Reactions

 A series of 1-alkyl-4-dialkylaminopyridinium halides derived from 4-dimethylamino- and 4-morpholinopyridines were synthesized and tested as phase-transfer catalysts in three typical reactions of dichlorocarbene: dehydration of benzamide, N-formylation of diphenylamine, and dichlorocyclopropanation of styrene. The catalytic performance of the above compounds was found comparable or higher than that of conventional quaternary ammonium catalysts. The influence of catalyst structure on the reactivity was evaluated.     

Synthesis and properties of new biotin compounds containing hexyltriethylene glycol chain

The synthesis of a new halogenide containing hexyltriethylene glycol chain functionalized with biotin is reported. The general possibility of this linker to use as the building block for biotinylated compounds syntheses is demonstrated. Two biotinylated esters with different properties for useful surface modification and as fluorescence probes for proteins marking were synthesized. The properties of mentioned compounds were investigated by using surface plazmon resonance ellypsometry and fluorescence spectroscopy.     

Raman spectroelectrochemical study of Meldola blue, adsorbed and electropolymerized at a gold electrode

Surface-enhanced Raman spectroscopy (SERS) was used to probe the structure of adsorbed and electropolymerized Meldola blue (MB) films on roughened gold surfaces in solutions with pH 1.0 and 7.0 by using 785 nm excitation wavelength. Spectral bands were assigned based on density functional theory (DFT) calculations at B3LYP/6-311+G(2d, p) level. The most characteristic band of the oxidized MB form was found to be the breathing vibration of the central ring containing heteroatoms at 596 cm(-1). Based on a red shift of bands assigned to vibrations of double C=N(C(2)H(6)) bonds and adjacent ring C=C bonds in surface spectra as compared with solution 1 it was suggested that polymerization and interaction with an electrode surface proceed through these moieties. The presence of out-of-plane bands in SERS spectra was attributed to "flat" or slightly "tilted" orientation of aromatic rings at the interface. Potential-dependent spectral changes were followed by SERS spectroscopy. Raman spectra of the reduced MB form were obtained in both pH 1.0 and pH 7.0 solutions by analysis of the potential-difference SERS spectra. Reduced MB form can be recognized by characteristic bands near 1620, 1574, 1374, and 1234 cm(-1). By comparing the intensities of 1637 cm(-1) (oxidized MB form) and 1374 cm(-1) (reduced MB form) bands in experimental spectra of polymerized MB in pH 1.0 solution, a reduction-induced decrease by factor of 7 was estimated. A similar tendency in intensity changes showed calculations indicating that this effect is associated with reduction-induced changes in the molecular structure of the dye.     

Reflection Absorption Infrared Spectroscopy Characterization of SAM Formation from 8-Mercapto-N-(phenethyl)octanamide Thiols with Phe Ring and Amide Groups

Multifunctional amide-containing self-assembled monolayers (SAMs) provide prospects for the construction of interfaces with required physicochemical properties and distinctive stability. In this study, we report the synthesis of amide-containing thiols with terminal phenylalanine (Phe) ring functionality (HS(CH₂)₇CONH(CH₂)₂C₆H₅) and the characterization of the formation of SAMs from these thiols on gold by reflection absorption infrared spectroscopy (RAIRS). For reliable assignments of vibrational bands, ring deuterated analogs were synthesized and studied as well. Adsorption time induced changes in Amide-II band frequency and relative intensity of Amide-II/Amide-I bands revealed two-state sigmoidal form dependence with a transition inflection points at 2.2 ± 0.5 and 4.7 ± 0.5 min, respectively. The transition from initial (disordered) to final (hydrogen-bonded, ordered) structure resulted in increased Amide-II frequency from 1548 to 1557 cm⁻¹, which is diagnostic for a strongly hydrogen-bonded amide network in trans conformation. However, the lateral interactions between the alkyl chains were found to be somewhat reduced when compared with well-ordered alkane thiol monolayers.     

A study of cysteamine ionization in solution by Raman spectroscopy and theoretical modeling

Different cysteamine (H2N-CH2-CH2-SH) ionization forms have been studied by polarized Raman spectroscopy in solutions prepared with H2O and D2O and by DFT calculations at the B3LYP/6-31++G(d,p) level. To account for solvation effects, we employed the integral equation formalism polarizable continuum model (IEFPCM) option and explicit water molecules. Calculated relative energies and Raman spectra revealed that gauche rotamers around the C-C bond are the most stable conformers in solution. The experimental pKa values and Raman spectra of various ionization forms were best predicted by using a model with three explicit water molecules and the IEFPCM option. In general, the use of IEFPCM tends to lower the calculated frequencies for a few bands, but in some cases (S-H stretching mode) this effect is expressed very strongly. Potential energy distribution (PED) analysis of gauche conformers of various cysteamine ionization forms provided the possibility of discriminating spectroscopically methylene groups adjacent to sulfur, (CH2)S, and nitrogen, (CH2)N, sites. In general, stretching and scissoring modes as well as wagging and twisting vibrations of the (CH2)N group were found to be at higher frequencies. The influence of ionization of SH and NH2 groups on the vibrational spectrum is discussed, and Raman markers for further amine group ionization studies are suggested.     

Synthesis and intramolecular cyclization of 2‐methylsulfany‐4‐oxo‐3(4H)‐quinazolinyl)acetohydrazide

Treatment of ambident sodium salt of 2‐methylsulfanyl‐4(3H)‐quinazolinone with methyl bromoacetate resulted in N₍₃₎‐alkyl ester formation. Reaction of the resulted ester with hydrazine hydrate gave 2‐methylsulfanyl‐4‐oxo‐3(4H)‐quinazolinyl)acetohydrazide, which underwent intramolecular cyclization under heating in dimethylformamide to give 1‐aminoimidazo[2,1‐b]quinazoline‐2,5(1H,3H)‐dione. The latter took place in acylation reaction and in condensation with aromatic aldehydes.     

Synthesis and isomerism of hydrazones of 2-(5-thioxo-4,5-dihydro-1,3,4-thiadiazol-2-ylthio)acetohydrazide

New hydrazones of 2-(5-thioxo-4,5-dihydro-1,3,4-thiadiazol-2-ylthio)acetohydrazide have been obtained and the percentages of anti/syn - conformers were determined. Based on the analyses of ¹H NMR spectra, it was concluded that for hydrazones obtained from the 2- hydroxybenzaldehydes and 2’-hydroxycetophenones the ratio between the anti-and syn-conformers depends on the strength of intramolecular hydrogen bond (IMHB) between the nitrogen atom of the imino group and the proton of the 2-hydroxy group. It was shown that increase in IMHB strength results in stabilization of the anti-conformer in solution.      

1-Alkyl-4-dialkylaminopyridinium Halides as Phase-Transfer Catalysts in Dichlorocarbene Reactions

Summary.  A series of 1-alkyl-4-dialkylaminopyridinium halides derived from 4-dimethylamino- and 4-morpholinopyridines were synthesized and tested as phase-transfer catalysts in three typical reactions of dichlorocarbene: dehydration of benzamide, N-formylation of diphenylamine, and dichlorocyclopropanation of styrene. The catalytic performance of the above compounds was found comparable or higher than that of conventional quaternary ammonium catalysts. The influence of catalyst structure on the reactivity was evaluated. Received June 27, 2001. Accepted (revised) September 25, 2001     

Infrared and Raman bands of phytantriol as markers of hydrogen bonding and interchain interaction

Hydrogen bonding and interchain interactions in phytantriol, 3,7,11,15-tetramethyl-1,2,3-hexadecanetriol, have been studied by Fourier transform infrared (FT-IR) and Raman spectroscopies. Assignments of the bands were performed based on the OH/OD isotopic substitution, molecular modeling, and measurements of polarized Raman spectra. Marker bands were evaluated from the temperature-dependent spectral changes. It is shown that Raman spectroscopy provides sensitive markers, namely I(delta(CH2))/I(deltas(CH3)), tau(CH)2, I(nus(CH3)(FR))/I(nus(CH2)), and nus(CH2) for probing the interactions between the hydrocarbon chains. Hydrogen bonding interaction might be studied through the difference Raman spectroscopy by the analysis of polarized band at 811 cm-1. Relationship is found between the frequencies of IR bands at 883-873 and 1097-1086 cm-1, associated with the vibrations localized at the primary COH site, and the frequencies of OH stretching mode, making these bands specific markers in the analysis of hydrogen bonding. Evaluated marker bands may be of utility to probe the interchain and hydrogen bonding interaction of phytantriol with guest molecules in the practically important aqueous liquid-crystalline phases of this lipid.