Adsorption of<Emphasis Type="Italic"> N</Emphasis>-dodecyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl-3-ammonio-1-propanesulfonate (DDAPS), a model zwitterionic surfactant,on the Au(111) electrode surface

Electrochemical measurements including cyclic voltammetry, differential capacity, and chronocoulometry have been used to characterize the adsorption behaviors of the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) on the Au(111) electrode surface. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DDAPS has a multistate character. The first two states are observed at potentials close to zero charge. At low bulk DDAPS concentrations, it corresponds to the formation of a film of nearly flat adsorbed molecules. At higher concentrations it is converted into a hemimicellar state. The second state is formed at negative potentials and charge densities close to 0 C cm^–2. It corresponds to a film of tilted molecules oriented with the hydrocarbon tail towards the metal and the polar head toward the solution.Dedicated to Professor Zbigniew Galus on the occasion of his 70^th birthday and in recognition of his many contributions to electrochemistry.     

Effects of ionization on the phase behavior of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-acrylic acid) and poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethylacrylamide-co-acrylic acid) in water

Phase transitions of poly(N-isopropylacrylamide-co-acrylic acid) (PiPA-AA) and poly(N,N- diethylacrylamide-co-acrylic acid) (PdEA-AA) in water have been investigated by means of turbidimetry, Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The phase transition temperatures (T_p) of these copolymers increase with the degree of ionization () of the acrylic acid (AA) units, which in turn is dependent on the pH of the solutions. Apparent values of pK_a for the AA units, determined from the pH dependencies of T_p, are 4.7 and 5.4 for PiPA-AA and PdEA-AA, respectively. Differences between T_p for PiPA-AA and T_p for PiPA homopolymer (T_p) are +1.5 and –0.2 °C/mol% of AA at =1 and 0, respectively. The values of T_p for PdEA-AA are +2.6 (ionic) and –0.5 (nonionic)°C/mol%, indicating that the incorporated AA units have a larger effect on PdEA than on PiPA. DSC measurements performed with each of these copolymers at different pH values show a linear relationship between T_p and the enthalpy of transition (H). IR measurements of PiPA-AA show that the profiles of IR bands from both iPA and AA units exhibit critical changes at T_p of the copolymer. Heating the solution above T_p leads to shifts of the amide II, C–H stretch, and C–H bend bands from the iPA units toward lower wavenumbers, as well as a shift of the amide I band from the iPA units toward higher wavenumbers. A decrease in the intensity of the symmetric C=O stretch IR band from carboxylate anions (1560 cm^–1), and an increase in the intensity of the C=O stretch band from COOH groups (1705 cm^–1) suggest that a partial protonation of the carboxylate groups (COO^–+H⁺COOH) takes place upon the phase transition.     

Hexafluoroacetone as Protecting and Activating Reagent. A New Approach to <Emphasis Type="Italic">N</Emphasis>-Glycosides

Summary. N-Glycosides of Asn and homologues have been synthesized starting from hexafluoroacetone-protected -activated Asp, Glu, and Aad derivatives and glycosylamines. The synthetic value of the new building blocks was demonstrated by the concise incorporation of N-glycosylated Asn, Gln, and Aad -amides into glycopeptides.     

Determination of epoxides by high-performance liquid chromatography following derivatization with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethyldithiocarbamate

A reversed-phase, high-performance liquid chromatography (RP-HPLC) method that allows quantitation of low levels of epoxides has been described. The method involved derivatization of epoxides using 100- to 1,000-fold excess N,N-diethyldithiocarbamate (DTC) at 60 °C for 20 min at neutral pH. The unreacted DTC was then decomposed to CS₂ and diethyl amine by acidification of the reaction mixture to pH 2 using orthophosphoric acid. The first two steps could be performed in the same reaction vessel by sequential addition of reagents. In the final step, an aliquot (20 μL) of the derivatized sample was analyzed for the presence of stable esters of DTC by RP-HPLC using a Supelcosil LC-18-S (150 × 4.6-mm) column and a mobile phase consisting of 40% (v/v) acetonitrile in water at a flow of 1 mL min⁻¹. Using UV detection at 278 nm, the epoxides gave linear responses in the concentration range of 0.25 to 50 μM. The method is robust, and as low as 5 pmol of the analyte could be successfully detected and quantified with recoveries of ≥94%. Following a minimal pretreatment such as ultrafiltration (molecular weight cutoff 5,000 Da), the method is suitable for analysis of epoxides in complex physiological fluids (e.g., fetal bovine serum). The method has been rigorously evaluated and adapted in our laboratory for routine analysis and determination of stability of epoxides of 1,3-butadiene and other alkenes added to cell cultures.     

Synthesis and characterization of thermoresponsive poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-<Emphasis Type="Italic">N</Emphasis>-hydroxymethylacrylamide-co-2-hydroxyethyl methacrylate) hydrogels

Thermoresponsive hydrogels based on N-isopropylacrylamide, N-hydroxymethylacrylamide, and 2-hydroxyethyl methacrylate, poly(NIPAM–co-NHMAAm–co-HEMA), have been synthesized and their swelling—deswelling behavior studied as a function of NIPAM concentration, NIPAM/NHMAAm and NIPAM/HEMA mole ratio, and total monomer concentration. Copolymers varying in composition have been obtained by redox copolymerization of these three monomers. Temperature has been changed in the ranges from 4 to 70 °C at fixed pH and total ionic strength. Equilibrium swelling ratio, dynamic swelling ratio, and dynamic deswelling ratio were evaluated for all hydrogel systems. The equilibrium swelling ratios of the copolymeric gels decrease with increasing NHMAAm and HEMA content. The formation of the intermolecular hydrogen bonding between hydroxyl and amido groups decreases the hydrophilic group numbers of the gel and the affinity of the gel towards water decreases. The copolymer gels also showed rapid volume transitions with time. The time required for equilibrium shrinking increased with increasing NHMAAm and HEMA content in the gel.     

New acyl derivatives of <Emphasis Type="Italic">N</Emphasis>-deacetyllappaconitine

New N-acylates of the norditerpenoid alkaloid N-deacetyllappaconitine that were modified in the aromatic ring and are interesting as potential pharmacologically valuable compounds were prepared. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 275–279, May–June, 2008.     

Effect of Cu(II) on the electrochemically initiated reaction of thiols with<Emphasis Type="Italic"> N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethyl-<Emphasis Type="Italic">p</Emphasis>-phenylenediamine: methodology for the indirect voltammetric determination of Cu(II)

The effect of Cu(II) on the determination of homocysteine via its electrochemically initiated reaction with N,N-diethyl-p-phenylenediamine is examined. The presence of copper inhibited the detection process for homocysteine owing to a complexation reaction occurring. This provided an indirect route for the sensitive and selective determination of Cu(II), which produced a linear response over the range from 2.5 to 500 M and a limit of detection of 2.5 M. The detection pathway was examined in the presence of metallic and inorganic ions, with negligible interference observed.     

Convenient synthesis and NMR spectral studies of variously substituted <Emphasis Type="Italic">N</Emphasis>-methylpiperidin-4-one-<Emphasis Type="Italic">O</Emphasis>-benzyloximes

Abstract  A series of variously substituted N-methylpiperidin-4-one-O-benzyloximes were synthesized by three different methods. Among them, the direct conversion of 2,6-diarylpiperidin-4-ones into the corresponding oxime ethers (method A) was proved to be better than the other two methods in the sense of good yield, convenience, easy work-up and quick reaction time. All the synthesized compounds are characterized by IR, Mass and NMR (¹H NMR, ¹³C NMR, ¹H-¹H COSY, ¹H-¹³C COSY and HMBC) spectral studies. The conformational preference of the synthesized oxime ethers with/without alkyl and aryl substituents at C-3/C-5 and C-2/C-6 is discussed using the spectral data. The observed chemical shifts and coupling constants suggest that the synthesized oxime ethers adopt chair conformation with equatorial orientation of all the substituents, whereas 1-methyl-3-isopropyl-2,6-diphenylpiperidin-4-one-O-benzyloxime also exists in boat conformation. Based on the NMR data, the effects of oximination on ring carbons and their associated protons and alkyl substituents are discussed. In addition, the effect of NMe group on the 2,6-diarylpiperidin-4-one-O-benzyloximes was also studied. Graphical abstract        

Synthesis of graft copolymers of wood and <Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone

Lignocellulose copolymers with grafted lactam rings were prepared by graft copolymerization of wood with N-vinylpyrrolidone initiated by Fe²⁺-H₂O₂. The principal features of their formation were investigated as functions of reactant concentrations, temperature, and polymerization time. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 174–176, March–April, 2008.     

Synthesis of amphiphilic diblock copolymers poly[2-(<Emphasis Type="Italic">N</Emphasis>, <Emphasis Type="Italic">N</Emphasis>-dimethylamino)ethyl methacrylate]-<Emphasis Type="Italic">b</Emphasis>-poly(stearyl methacrylate) and their self-assembly in mixed solvent

Amphiphilic diblock copolymers consisting of 2-(N, N-dimethylamino)ethyl methacrylate (DMAEMA, abbreviated as DMA) and stearyl methacrylate (SMA) with different degrees of polymerization and compositions were prepared by reversible addition–fragmentation chain transfer (RAFT) copolymerization. The composition and chemical structures of (co)polymers were confirmed by the measurements of ¹H NMR spectroscopy and gel permeation chromatography (GPC). The self-aggregating structures of amphiphilic diblock copolymers with the concentration of 0.1~0.3 wt.% in THF/water mixed solvent was investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS). It was found that both the morphologies and aggregating particle size resulted from the amphiphilic diblock copolymers depended on the variation of pH values, the lengths of the hydrophobic PSMA chains, and the weight ratio of THF/water mixed solvent.     

Synthesis and characterization of <Emphasis Type="Italic">N</Emphasis>-tolyglycosylamines

N-Tolylglycosylamines were synthesized from o-, m-, and p-toluidines and aldoses (D-glucose, D-galactose, D-mannose, L-rhamnose, D-xylose, and L-arabinose). The anomeric and isomeric compositions of the synthesized products were established using ¹³C NMR methods. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 333–335, July–August, 2008.     

Study of the mechanism of redox transformations of sterically hindered <Emphasis Type="Italic">N</Emphasis>-aryl-<Emphasis Type="Italic">o</Emphasis>-iminoquinones

The mechanisms of redox transformations of sterically hindered [¹IBQ]-[³IBQ], 9,10-iminophenanthraquinone [⁴IFQ], and o-aminophenol [⁵AP] have been studied by cyclic voltammetry. It has been shown that the reduction process in tetrahydrofuran consists of two consecutive reversible steps leading to the formation of a radical anion and a dianion. In the case of acetonitrile, only the first redox process is detected, which involves the steps of protonation and electron addition resulting in the formation of a monoanion. Quantum-chemical calculations indicate a lower degree of participation of the six-membered nonaromatic carbon ring in the spin density delocalization in the o-iminosemiquinonate radical anions as compared to o-benzosemiquinonate radical anions. The oxidation of iminoquinones results in the formation of an unstable radical cation, which undergoes further chemical transformations. An increase in the acidity of a medium leads to the formation of protonated forms with the reduction potential being shifted anodically. The introduction of screening groups makes it possible to suppress side reactions of hydrolysis and cyclization of oxidized o-aminophenol [⁵AP] forms. Therefore, the major product of complete electrolysis is o-iminobenzoquinone [²IBQ].     

Starch Derivatives of High Degree of Functionalization 11: Studies on Alternative Acylation of Starch with Long-chain Fatty Acids Homogeneously in <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethyl acetamide/LiCl

Starch materials of different amylose content were allowed to react with saturated and unsaturated fatty acids of varying chain length from C₁₄ to C₁₈ under homogeneous conditions applying the solvent N,N-dimethyl acetamide in combination with LiCl. As reagent the corresponding acid chlorides and, alternatively, carboxylic acids in situ activated with toluene-4-sulfonyl chloride and N,N′-carbonyldiimidazole (CDI) were studied. Using fatty acid chlorides (FACl) and toluene-4-sulfonyl chloride-activated acids an almost complete substitution of the starch occurs. By in situ activation of the fatty acids with CDI, products with a degree of substitution up to 2 were obtained, which, in particular, represents a simple and very mild procedure.     

Detection of <Emphasis Type="Italic">N</Emphasis>-monomethyl-lysine generated by metabolic transmethylation

Administration of radiolabelled deprenyl to rats resulted in the urinary elimination of a ¹⁴C-labelled N-monomethyl-lysine. An increased level of N-monomethyl-lysine was found following an oral dose of another drug, also containing an N-methyl group. The urine sample was treated with 9-fluorenylmethoxycarbonyl chloride and then subjected to high-performance liquid chromatography (HPLC); the radioactive fraction was identified as N-monomethyl-lysine by using HPLC-MS in electrospray mode. Identification of N-monomethyl-lysine in the radioactive fraction gives experimental proof of transmethylation from a well-known drug to an endogenous compound.     

Splitting of the <Emphasis Type="Italic">d</Emphasis><Superscript><Emphasis Type="Italic">N</Emphasis></Superscript> atomic states in icosahedral 3<Emphasis Type="Italic">d</Emphasis> metal endofullerenes M@C<Subscript>60</Subscript>

Group-theoretical and quantum-chemical investigations of the spectrum of low-lying excited states have been performed by the ROHF and FCI-RAS (Full CI in Restricted Active Space) methods for 3d metal endofullerenes (MEFs) M@C₆₀ (M =Mn, Cr, and Fe) in different charged states. The major purpose of this study is quantum-chemical verification of the anomalous (“non-Bethe’s”) character of splitting of the d ^N atomic states in an electrostatic field with icosahedral symmetry, predicted previously within the theory of integral invariants theory. The interrelation between the integral invariants theory and the quantumchemical methods applied in this work is considered in detail. Our calculations suggest that the d ^N atomic states in the icosahedral field generated by fullerene C60 (I _h ) on a metal atom (ion) remain non-split for different charged states of the metal and C₆₀. Reasons for this phenomenon and other possible approaches to verification of the prediction are discussed. It is demonstrated that the d ^N states of the encapsulated metal are split in icosahedral 3d MEFs only under very strong compression of these structures.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-(2-chloroethyl)glycine and -<Emphasis Type="SmallCaps">DL</Emphasis>-alanine esters

Two methods for the synthesis of N-(2-chloroethyl)glycine and-DL-alanine esters are proposed: 1) reductive amination of the C=O group of glyoxilic or pyruvic acids upon treatment with 2-chloroethylamine and sodium cyanoborohydride in methanol and 2) alkylation of 2-chloroethylamine with α-haloalkanoic acid esters in K₂CO₃-MeCN two-phase system. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2372–2374, December, 2007.     

Electrooxidation of undiluted organic liquids swelling<Emphasis Type="Italic"> N</Emphasis>-isopropylacrylamide-based copolymers

Polyacrylate gels such as: N-isopropylacrylamide (NIPA), ionic copolymer NIPA-co-sodium acrylate (NIPA-co-SA) and ionic copolymer NIPA-co-[2-(acryloyloxy)ethyl]trimethylammonium chloride (NIPA-co-XCl) were swollen by methanol, ethanol and N,N-dimethylformamide. These solvents were oxidized voltammetrically in the gels at platinum microelectrodes. The blocking coefficients, defined as the ratio of the currents observed in the presence and absence of the polymeric chains, were different for the solvents in the charged and uncharged polymers and did not differ for the electroactive probe, ferrocene, present in the solvents at millimolar level. This may mean that the micro ionic layer that is formed at microelectrodes at the plateau of the voltammetric solvent waves leads to a kind of collapse/phase transition of the polymer in the depletion layer. For methanol, the gel structure was found to prevent occasionally the formation of large gas bubbles at the potentials positive versus the first wave and then three one-electron waves could be obtained. Experiments done with a capillary cell and an optical microscope indicated that before formation of large bubbles at the Pt microelectrode a very dynamic, dense stream of microbubbles leaves the electrode surface.Dedicated to Zbigniew Galus on the occasion of his 70th birthday     

Comparison of planar SDS-PAGE,CGE-on-a-chip,and MALDI-TOF mass spectrometry for analysis of the enzymatic de-<Emphasis Type="Italic">N</Emphasis>-glycosylation of antithrombin III and coagulation factor IX with PNGase F

Three different analytical techniques (planar SDS-PAGE, CGE-on-a-chip and MALDI-TOF-MS) applied for determination of the molecular weight of intact and partly and completely de-N-glycosylated human serum glycoproteins (antithrombin III and coagulation factor IX) have been compared. N-Glycans were removed from the protein backbone of both complex glycoproteins using PNGase F, which cleaves all types of asparagine-attached N-glycan provided the oligosaccharide has at least the length of a chitobiose core unit. Two of the applied techniques were based on gel electrophoretic separation in the liquid phase while the third technique was the gas-phase technique mass spectrometry. It was demonstrated that the enzymatic de-N-glycosylation generally worked well (completely or partially) with both glycoproteins (one containing only N-glycans and the second N- and O-glycans). All three methods were suitable for monitoring the de-N-glycosylation progress. While the molecular weights determined with MALDI-TOF-MS were most accurate, both gel electrophoretic methods provided molecular weights that were too high because of the attached glycan structures. Figure CGE-on-a-chip, SDS-PAGE and MALDI mass spectrometric pattern obtained from therapeutic glycoprotein     

Quorum sensing in <Emphasis Type="Italic">Erwinia</Emphasis> species

The term quorum sensing (QS) refers to the ability of bacteria to regulate gene expression according to the accumulation of signalling molecules that are made by every cell in the population. The erwiniae group of bacteria are often phytopathogens and the expression of a number of their important virulence determinants and secondary metabolites is under QS control. The erwiniae utilise two types of QS signalling molecules: N-acyl homoserine lactones and AI-2-type signalling molecules. Here, we review the regulatory networks involving QS in the soft rot erwiniae.     

A circular dichroism study of the interaction between<Emphasis Type="Italic"> n</Emphasis>-decanoyl-<Emphasis Type="Italic">N</Emphasis>-methylglucamide and surface active agents in mixed micelles

The interaction between MEGA-10 and surface active agents was studied by means of circular dichroism. The molecular ellipticity of MEGA-10 varied with the addition of surface active agents, but its peak wavelength did not. The carbonyl group of MEGA-10 did not interact with the nonionic surface active agents nor the catanionic surfactant (of which the anionic and cationic portions were decanesulfonate and decyltrimethylammonium, respectively). It did, however, interact with the ionic surfactants, and also strongly with the ammonium group and the benzene ring. The interaction between MEGA-10 and ionic surfactant charges did not differ according to the sign of the charge. Circular dichroism spectra are a useful tool for performing research into the interaction between an optically active carbonyl group and an additive.