Functionalized polymer colloids bearing primary amino groups

Polymer colloids are prepared via radicalic emulsion polymerisation of butylacrylate. Functionalization with amino groups is achieved by copolymerisation of 2-amino-ethylmethacrylates. In order to over-compensate the positive surface charges resulting from the amino groups additionally vinylbenzenesulfonic acid is copolymerized. The size of the resulting particles is controlled by the molar ratio of amino to sulfonic acid groups. The suitability of amino groups for coupling reactions is demonstrated by electrophilic addition of fluorescein-5-isothiocyanate. The resulting particles are characterized by dynamic light scattering and zeta potential measurements as well as by optical spectroscopy. The suitability of labelled particles for optical tracer experiments is demonstrated by fluorescence correlation spectroscopy.     

Novel non-aggregated soluble metallophthalocyanines bearing carboxylic acid groups

Synthesis and characterization of zinc and cobalt phthalocyanines substituted with biphenylmethylpropionic acids, methyl-o-tolylpropionic acids, and methyl-p-tolylpropionic acids are described in this study. The new compounds have been characterized by elemental analyses, FT-IR, UV-Vis, MALDI-TOF, and ¹H NMR spectroscopy. All new compounds are soluble in THF, DMF, DMSO, and dilute sodium hydroxide solution. The influence of the carboxylic acid and bulky biphenyl, ortho-methylbenzyl and para-methylbenzyl groups on the spectroscopic properties has been investigated. UV-Vis experiments suggest that the tendency of phthalocyanines to aggregate in polar solvents is significantly reduced owing to the carboxylic acid groups and bulky peripheral substituents.     

Procedure for activating polymers with primary and/or secondary hydroxyl groups

A new facile method using 2-fluoro-1-methylpyridinium toluene-4-sulfonate (FMP) for activating polymeric hydroxyl groups has recently been developed (Refs. 1–2). Such activated polymers are useful for immobilization of enzymes, antibodies and other biomolecules and for affinity matrix development. The activation method involves reacting, at room temperature, the polymer with FMP in the presence of a tertiary amine for 0.5 to 1 hour. The activated hydroxyls react readily with nucleophiles, such as amino or thiol ligands at pH 5–10. The resulting linkages between the ligand and the polymer are respectively stable secondary amine and thioether bonds. The activated polymer remains active and usable for several months when stored at 4°C in either an acidic aqueous solution or an inert anhydrous organic solvent. The “half-life” of the activated groups in non-nucleophilic buffer solution varies from 10 to 300 hours in the pH range of 10 to 6, being most stable at low pH. Both primary and secondary hydroxyl groups of different polymers were facilely activated and shown to react readily with nucleophilic groups of biomolecules. Furthermore, FMP provides a convenient handle for the synthesis of unique conjugates consisting of FMP and a guiding molecule. These conjugates function as an activator of the hydroxyl group of a solid support as well as a molecular guide which orients the position of the ligand to be immobilized. The conjugates make it possible to immobilize ligands in an affinity-directed way.     

Novel C2-symmetric macrocycles bearing diamide-diester groups: synthesis and enantiomeric recognition for primary alkyl ammonium salts

We synthesized a series of novel macrocycles with diamide-diester groups (S,S)-1, (S,S)-2, (S,S)-3, and (R,R)-1, derived from dimethyloxalate and amino alcohols by high dilution technique, and evaluated enantiomeric recognition properties of these macrocycles toward primary alkyl ammonium salts by 1H NMR titration. Taking into account the host employed, important differences were observed in the Ka values of (R)-Am and (S)-Am for (S,S)-1 and (R,R)-1 hosts, KS/KR = 5.55 and KR/KS = 3.65, Delta Delta Go = 0.43 and -0.32 kJ mol-1, respectively. There seems a general tendency for the host to include the guests with the same absolute configuration.     

Synthesis and properties of alkylruthenium complexes bearing primary and secondary amine ligands

A series of 18-electron alkylruthenium complexes, RuR[κ²(N,N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) (Ph = C₆H₅, R′ = p-CH₃C₆H₄ and CH₃), bearing a N-sulfonylated diamine ligand was synthesized from the reaction of RuCl[κ²(N, N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) with alkylzinc reagents, in which transmetalation proceeded smoothly to give the desired alkyl complexes in good yield and selectivity. Although the isolable amine Ru complexes bearing functionalized alkyl ligands were thermally stable, the simple methyl and ethyl Ru complexes underwent intramolecular deprotonation from NH protons to give the amido Ru complexes with release of the alkanes. The reactivity of the alkyl Ru complexes is highly affected by the structures of the arene ligands.     

Metal-organic coordination architectures of azole heterocycle ligands bearing acetic acid groups: Synthesis, structure and magnetic properties

Four new coordination complexes with azole heterocycle ligands bearing acetic acid groups, [Co(L¹)₂]_n (1), [CuL¹N₃]_n (2), [Cu(L²)₂·0.5C₂H₅OH·H₂O]_n (3) and [Co(L²)₂]_n (4) (here, HL¹=1H-imidazole-1-yl-acetic acid, HL²=1H-benzimidazole-1-yl-acetic acid) have been synthesized and structurally characterized. Single-crystal structure analysis shows that 3 and 4 are 2D complexes with 4⁴-sql topologies, while another 2D complex 1 has a (4³)₂(4⁶)-kgd topology. And 2 is a 3D complex composed dinuclear μ_1,1-bridging azido Cu^II entities with distorted rutile topology. The magnetic properties of 1 and 2 have been studied.     

Liquid crystalline polyaniline and phthalocyanine-based polysiloxanes bearing lateral fluoro-substituted benzoic acid groups

A series of novel liquid crystalline polymers (PI, PII, PIII and PIV) containing lateral fluoro-substituted benzoic acid groups was synthesised using cholesteryl 4-(2-propenyloxy)-benzoate, 4-(allyloxy)-3-fluorobenzoic acid and poly(methylhydrogeno)siloxane. PI and PII showed smectic phase, but PIII and PIV showed chiral nematic phase due to more lateral fluoro-substituted benzoic acid groups in the polymer systems. Liquid crystalline polyaniline (PAN) and phthalocyanine (Pc)-based polysiloxanes showing chiral nematic phase were prepared by use of Pc, PAN and these liquid-crystalline polymers via hydrogen bond. PAN-based polysiloxanes showed different liquid crystalline behaviours from Pc-based polysiloxanes due to the difference of molecular structure. PAN-based polysiloxanes showed greater d-spacings between the side mesogenic groups than Pc-based polysiloxanes due to long rod-like geometrical shapes. Hydrogen bond based on lateral fluoro-substituted benzoic acid groups was formed to different geometrical shapes (strip or roundness) between PAN and Pc-based polysiloxanes.     

2-Cyano-2-indolylpropanoic acid as a chiral derivatizing agent for the absolute configuration assignment of secondary alcohols and primary amines by 1H NMR and VCD

A convenient approach for the absolute configuration assignment of secondary alcohols in the (8R,1′R,2′S,5′R)-15,25, (8S,1′R,2′S,5′R)-15,25, (8R,1′R)-21–24, and (8S,1′R)-21–24 ester series, and of primary amines in the (8R,1′R)-32–37 and (8S,1′R)-32–37 amide series, by means of ¹H NMR and VCD spectroscopy, using 2-cyano-2-indolylpropanoic acid as a chiral derivatizing agent is presented. DFT calculations were carried out to demonstrate the anisotropic effect of the indole skeleton on the chiral alcohol or the amine fragment. Vibrational circular dichroism (VCD) measurements of the above series indicated a VCD bisignated couplet resulting from the interaction of the ester carbonyl group and the CN group. The absolute configuration assignments were further tested by X-ray diffraction analysis.     

Synthesis, structure, and reactivity of novel 3,4-diphosphacyclobutenes bearing silyl groups

[reaction: see text] Copper-mediated homocoupling of sterically hindered 2-(2,4,6-tri-tert-butylphenyl)-1-trialkylsilyl-2-phosphaethenyllithiums afforded 1,2-bis(trialkylsilyl)-3,4-diphosphacyclobutenes (1,2-dihydrodiphosphetenes) through a formal electrocyclic [2+2] cyclization in the P=C-C=P skeleton as well as 2-trimethylsilyl-1,4-diphosphabuta-1,3-diene. Reduction of 1,2-bis(trimethylsilyl)-3,4-diphosphacyclobutenes followed by quenching with electrophiles afforded ring-opened products, (E)-1,2-bis(phosphino)-1,2-bis(trimethylsilyl)ethene and (Z)-2,3-bis(trimethylsilyl)-1,4-diphosphabut-1-ene. The structures of the ring-opened products indicated E/Z isomerization around the C=C bond after P-P bond cleavage of 5, and the isomerization of the P-C=C skeleton. Ring opening of 1,2-bis(trimethylsilyl)-3,4-diphosphacyclobutenes affording (E,E)- and (Z,Z)-1,4-diphosphabuta-1,3-dienes was observed upon desilylation.     

An in silico analysis of primary and secondary structure specificity determinants for human peptidylarginine deiminase types 2 and 4

Human peptidylarginine deiminases (hPADs) are a family of five calcium-dependent enzymes that facilitate citrullination, which is the post-translational modification of peptidyl arginine to peptidyl citrulline. The isozymes hPAD2 and hPAD4 have been implicated in the development and progression of several autoimmune diseases, including rheumatoid arthritis and multiple sclerosis. To better characterize the primary and secondary structure determinants of citrullination specificity, we mined the literature for protein sequences susceptible to citrullination by hPAD2 or hPAD4. First, protein secondary structure classification (α-helix, β-sheet, or coil) was predicted using the PSIPRED software. Next, we used motif-x and pLogo to extract and visualize statistically significant motifs within each data set. Within the data sets of peptides predicted to lie in coil regions, both hPAD2 and hPAD4 appear to favor citrullination of glycine-containing motifs, while distinct hydrophobic motifs were identified for hPAD2 citrullination sites predicted to reside within α-helical and β-sheet regions. Additionally, we identified potential substrate overlap between coil region citrullination and arginine methylation. Together, these results confirm the importance and offer some insight into the role of secondary structure elements for citrullination specificity, and provide biological context for the existing hPAD specificity and arginine post-translational modification literature.     

Synthesis and properties of polyimides bearing acid groups on long pendant aliphatic chains

A series of novel polyimide electrolytes having long pendant sulfo‐ or phosphoalkoxy groups were synthesized for fuel‐cell applications. Sulfodecyloxy‐, phosphodecyloxy‐, and sulfophenoxydodecyloxy‐substituted benzidine monomers were synthesized from dihydroxybenzidine. These monomers were copolymerized with naphthalene tetracarboxylic dianhydride and fluorenylidene dianiline to give the corresponding polyimides. A flexible, ductile, and self‐standing membrane was obtained via casting from the polyimide solution. Because the acid groups were on long pendant side chains and away from the main chains, the polyimide membrane showed improved oxidative and hydrolytic stability in comparison with the polyimides with sulfonic acid groups on the main chains or on the short side chains. High thermal stability (no glass‐transition temperature and a decomposition temperature > 200 °C) was also obtained. The polyimide membrane displayed high proton conductivity of 10^?1 S cm^?1 at 120 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3995–4005, 2006     

A partition function algorithm for nucleic acid secondary structure including pseudoknots

Nucleic acid secondary structure models usually exclude pseudoknots due to the difficulty of treating these nonnested structures efficiently in structure prediction and partition function algorithms. Here, the standard secondary structure energy model is extended to include the most physically relevant pseudoknots. We describe an O(N(5)) dynamic programming algorithm, where N is the length of the strand, for computing the partition function and minimum energy structure over this class of secondary structures. Hence, it is possible to determine the probability of sampling the lowest energy structure, or any other structure of particular interest. This capability motivates the use of the partition function for the design of DNA or RNA molecules for bioengineering applications.     

Synthesis and characterization of proton‐conducting copolyimides bearing pendant sulfonic acid groups

A series of sulfonated copolyimides (co‐SPIs) bearing pendant sulfonic acid groups were synthesized from 1,4,5,8‐naphthalenetetracarboxylic dianhydride (NTDA), bis(3‐sulfopropoxy) benzidines (BSPBs), and common nonsulfonated diamines via statistical or sequenced polycondensation reactions. Membranes were prepared by casting their m‐cresol solutions. The co‐SPI membrane had a microphase‐separated structure composed of hydrophilic and hydrophobic domains, but the connecting behavior of hydrophilic domains was different from that of the homo‐SPIs. The co‐SPI membranes displayed clear anisotropic membrane swelling in water with negligibly small dimensional changes in the plane direction of the membrane. With water uptake values of 39–94 wt %, they showed dimensional changes in membrane thickness of about 0.11–0.58, which were much lower than those of homo‐SPIs. The proton conductivity σ values of co‐SPI membranes with ion exchange capacity values ranging from 1.95–2.32 meq/g increased sigmoidally with increasing relative humidity. They displayed σ values of 0.05–0.16 S/cm at 50 °C in liquid water. Increasing temperature up to 120 °C resulted in further increase in proton conductivity. The co‐SPI membranes showed relatively good conductivity stability during the aging treatment in water at 100 °C for 300 h. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1545–1553, 2005     

Crystal structure of 2-selenobenzyl-1-benzoic acid.

C14H12O2Se is monoclinic, P2(1)/c. Unit-cell dimensions at 293 K are a = 8.1055(7), b = 5.8403(11), c = 26.0302(17)A, beta = 94.560(5) degrees, V = 1228.3(3)A3, Dx = 1.575 g/cm3, and Z = 4. The R value is 0.048 for 2144 observed reflections. The dihedral angle between the phenyl rings is 74.9(2)degrees. There is an intermolecular hydrogen bond between two symmetry related carboxyl groups with an O1-O2 distance of 2.668(6)A. The molecules in the crystal are packed at normal van der Waals distances.     

Electrophilic amination of enolates with oxaziridines: effects of oxaziridine structure and reaction conditions

A range of N-alkoxycarbonyl- and N-carboxamido-oxaziridines has been prepared to test the effects of oxaziridine structure on yields of enolate amination product. Side-products arising from reaction of aldehyde-derived oxaziridines with base were identified, while a ketone-derived oxaziridine afforded moderate yields of amination product with stabilised carbanions.     

Regioselective conversion of the secondary hydroxyl groups of D-glucuronic acid without the requirement of O-protecting groups

Trifluoromethanesulfonic acid anhydride (triflic acid anhydride) transforms the bicyclic thiazolidinlactam 1 a into the crystalline elimination product 2, in which all four secondary hydroxyl groups of 1 a are differently functionalized. Compound 2 can then add nucleophiles with high chemo- and stereoselectivity. Altogether, the four secondary hydroxyl groups of D-glucuronic acid are selectively transformed without the need for any O-protecting groups. Minimizing the number of O-protecting groups is a prerequisite for the use of sugar scaffolds in molecular libraries. The hapalosin analogues 15, 16, 19, and 22 outline the strategy towards O-diversified glucose derivatives.     

Direct preparation and structure determination of tertiary and secondary amine boranes from primary or secondary amine boranes

New secondary and tertiary amine borane derivatives were prepared in a one-pot reaction starting from primary amine boranes. The reaction involves treatment of an amine borane with 2 equivalents of s-BuLi at −78 °C. In general, mixtures of mono and di metallated products were obtained. Alkyl iodides and benzyl chloride reacted with the lithiated amine, but aldehydes and ketones were reduced. Conversion was high as determined by NMR, but moderate to low yields were obtained after chromatography, possibly due to decomposition on silica. Crystal structures were obtained for the compounds 3a, 3b and 3c.