Ternary mixed-ligand complexes of copper(II) with α-aminoalkylphosphonic acids and amino acids

Formation of ternary mixed-ligand complexes of copper (II) with 16 -amino acids and -aminophosphonic acids (APA) with a 111 ratio of initial concentrations has been studied by potentiometric titration at 25C and 0.1 M KC1 in aqueous solution. The complexes Cu_pA_nB_sH_q are formed in solution, where A and B are the deprotonated ligands. The stability of the mixed-ligand complexes (log ) increases and the equilibrium is displaced more towards their formation (log K) as the hydrophobic nature of the ligands increases.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 570–575, March, 1991.     

Thermal Analysis of Poly(AN—co—St) and Poly(AN—St—MMA)

Poly(AN—co—St) (PAS) and poly(AN—St—MMA)(PASM) were synthetized by emulsion polymerisation. The glass transition temperatures (T_g) of the copolymers and the relationship between T_g and the components of the copolymers were investigated by differential scanning calorimetry. The results show that T_g for the AN—St bipolymers has apeak value in the range 115–118°C at a content of 50 mass% St. When methyl methacrylate was added, the T_g of the terpolymer was decreased by about 2–6°C.The thermostability and the activation energy E of degradation were determined by thermogravimetric analysis.This revised version was published online in November 2005 with corrections to the Cover Date.     

Poly(vinyl methyl ether) hydrogels at temperatures below the freezing point of water—molecular interactions and states of water

Water interacting with a polymer reveals a number of properties very different to bulk water. These interactions lead to the redistribution of hydrogen bonds in water. It results in modification of thermodynamic properties of water and the molecular dynamics of water. That kind of water is particularly well observable at temperatures below the freezing point of water, when the bulk water crystallizes. In this work, we determine the amount of water bound to the polymer and of the so-called pre-melting water in poly(vinyl methyl ether) hydrogels with the use of Raman spectroscopy, dielectric spectroscopy, and calorimetry. This analysis allows us to compare various physical properties of the bulk and the pre-melting water. We also postulate the molecular mechanism responsible for the pre-melting of part of water in poly(vinyl methyl ether) hydrogels. We suggest that above ?60 °C, the first segmental motions of the polymer chain are activated, which trigger the process of the pre-melting.     

Copper(II)salen catalysed, asymmetric synthesis of α,α-disubstituted amino acids

Cu(salen) complex 1 was found to be a versatile catalyst for the asymmetric alkylation of a range of enolates derived from α-amino acids, leading to α,α-disubstituted amino acids. The enantioselectivity of the process decreases as the size of the amino acid sidechain increases, but functionalized amino acids such as allylglycine and aspartic acid are substrates for the process. Benzylic bromides are found to be more enantioselective alkylating agents than propargylic bromides. As an example of the utility of this chemistry, an α-propargylic allylglycine derivative is prepared and subjected to ene-yne metathesis using Grubbs' catalyst to give a non-racemic cyclopentenyl amino acid.     

Microgels at droplet interfaces of water-in-oil emulsions—challenges and progress

Most of the commonly used microgels (MGs) are hydrophilic and tend to form oil-in-water emulsions. In this review, we discuss the function of MGs at the droplet interface in order to stabilize water-in-oil (w/o) emulsions. This topic addresses both interesting questions in fundamental research and a significant impact for applications, where the w/o emulsion type is of essential importance. Promising approaches to stabilize w/o emulsions with MGs are highlighted from different perspectives, ranging from novel MG modifications to assisted co-stabilization by adding soft or hard particles. We summarize the accumulated knowledge, evaluate the challenges and solutions, and highlight future research trends.     

Enamines of 3-acyltetramic acids from β-enamino amides and amino acids

A novel approach for the synthesis of enamine derivatives of N-protected 3-acyltetramic acids is described. The synthetic procedure relies on α-C-acylation of β-enamino amides with N-protected α-amino acids and subsequent cyclisation of the obtained intermediates in refluxing TFA. The tetramic derivatives are obtained with very good enantiopurity (e.r. ≥95:5). Ring-enlarged analogues (piperidine-2,4-diones) can also be obtained from β-amino acids.     

Raman Spectroscopic Study of the Conformation and Melting of Poly(dG) · Poly(dC) and Poly(dG-dC) · Poly(dG-dC) in Aqueous Solution

Raman spectroscopic measurements on aqueous solutions of poly(dG) · poly(dC)indicate that the conformation of the polynucleotides in this double helicalcomplex are distributed between the A and B types at room temperature, the Aform being predominant at –15°C and decreasing progressively upon raising thetemperature to 65°C. A reversible pretransition has been found in this complexnear 70°C. Modifications in the spectra at this temperature indicate no majorconformational changes, but rather suggest altered base pairing and hydration ofthe carbonyl groups, accompanied by a slight distortion of the double helix,resulting in a slightly reduced stacking of the cytosine bases. Measurements inself-pressurized solutions of the complex at high temperature show that it meltsat 103°C in 0.1M NaCl solution (107°C in 0.5M NaCl). These values are somewhatlower than those we have determined in the same manner for the complexpoly(dG-dC) · poly(dG-dC): 117°C in 0.1M MgCl₂ and 113°C or higher in 0.1MNaCl solution.     

9-α-Nitro(hydroxy,amino)benzylidene- and 9-Hydroxy(amino)methylene-4-azafluorenes

Nitration of 9-benzylidene-4-azafluorene with acetyl nitrate leads to the formation of its 9--nitrobenzylidene derivative; reduction of the latter gives the corresponding enamine and oxime. Reaction of 4-azafluorene with ethyl benzoate and ethyl formate gives the hydroxybenzylidene and hydroxymethylene derivatives, which upon condensation with amines generate the corresponding enamines. Reduction of 9-formylazafluorene oxime gives 9-aminomethyleneazafluorene. All of the newly synthesized compounds were isolated in the form of mixtures of their Z- and E-isomers, and their structures were established using PMR spectroscopy.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 212–217, February, 1991.     

Poly(4-vinylpyridine-co-aniline)-modified electrode—synthesis, characterization, and application as cadmium(II) ion sensor

A poly(4-vinylpyridine-co-aniline) (poly(4VP-co-Ani))-based solid-state ion sensor for cadmium (Cd) was developed. This was obtained from studies done on a number of selected monomers electropolymerized onto a poly(4vinylpyridine) (P4VP)-modified graphite pencil rod, surface characterizing them and then analyzing their performances as a Cd(II) ion sensor. Among them, the membrane of poly(4VP-co-Ani) at a mole ratio of 0.05:0.15 was found to be the best. The fabricated poly(4VP-co-Ani) solid-state electrode had a linear response of 1?×?10^?6 to 1?×?10^?2?M Cd²⁺, slope of 29.4?±?0.5 mV decade^?1, detection limit of 7.94?×?10^?7?M Cd²⁺, and response time of 15 s at pH 4.5–8.5 with excellent selectivity. The sensor was operationally stable within a period of 3 months. The proposed sensor was tested for determination of Cd²⁺ in environmental, plant, and pharmaceutical samples. The analyses were comparable to the standard atomic absorption spectrophotometric method.     

Heterogeneous interaction between zwitterions of amino acids and glycerol in aqueous solutions at 298.15 K

The enthalpies of mixing of six kinds of amino acid (glycine, L-alanine, L-valine, L-serine, L-threonine, and L-proline) with glycerol in aqueous solutions and the enthalpies of diluting of amino acid and glycerol aqueous solutions have been determined by flow microcalorimetry at 298.15 K. Employing McMillan–Mayer theory, the enthalpies of mixing and diluting have been used to calculate heterogeneous enthalpic pairwise interaction coefficients (h _xy ) between amino acids and glycerol in aqueous solutions. Combining h _xy values of amino acids with glycol in the previous study, the variations of the h _xy values between amino acids and glycerol have been interpreted from the point of view of solute–solute interactions.     

Structural Characterization of Poly(α-Fluoroacrylonitrile) and Poly(Ethyl α-Fluoroacrylate)

Abstract

Monomers α-fluoroacrylonitrile (FAN) and ethyl α-fluoroacrylate (EFA) and homopolymers poly(α-fluoroacrylonitrile) (PFAN) and poly-(ethyl α-fluoroacrylate) (PEFA) have been synthesized and spectroscopi-cally characterized in detail for the first time. The ¹³C- and ¹⁹F-NMR spectroscopic results are reported, and the results are correlated to the tacticity and microstructure of both homopolymers. The major portion of the polymers is atactic. TGA analysis of PFAN indicates that the polymer is stable to about 200°C with subsequent loss of HF. PEFA is stable to 300 °C. Molecular weights determined by intrinsic viscosity (M_v ) are found to be about 130,000 for PFAN, and GPC analysis of PEFA indicates a molecular weight (M_n ) of about 36,000. Dielectric permittivities (ε) for PFAN and PEFA were determined to be 8.9 and 4.0, respectively, at 50 Hz.     

Oxovanadium(IV) and amino acids—I. The system L-alanine+VO2+ ; a potentiometric and spectroscopic study

The equilibria in aqueous solution in the system L-alanine+VO²⁺ have been studied by a combination of pH-potentiometric and spectroscopic methods (EPR, visible absorption and circular dichroism) in the pH range 1.5–13. For pH > 4, high ligand to metal ratios were used. The results of the various methods are made self-consistent, then rationalized assuming an equilibrium model including the species MAH, MA, MAH₋₂, MA₂H₂, MA₂H, MA₂, MA₂H₋₁, M₂A₂H₋₂, M₂A₂H₋₃ (where HA denotes L-alanine) and several hydrolysis products; their formation constants and individual electronic spectra (isotropic and circular dichroism) are given. The isomerism arising from the combination of the lop-sided oxovanadium ion with the asymmetric carbon ligand is analysed.     

Probing eudesmane cation-π interactions in catalysis by aristolochene synthase with non-canonical amino acids

Stabilization of the reaction intermediate eudesmane cation (3) through interaction with Trp 334 during catalysis by aristolochene synthase from Penicillium roqueforti was investigated by site-directed incorporation of proteinogenic and non-canonical aromatic amino acids. The amount of germacrene A (2) generated by the mutant enzymes served as a measure of the stabilization of 3. 2 is a neutral intermediate, from which 3 is formed during PR-AS catalysis by protonation of the C6,C7 double bond. The replacement of Trp 334 with para-substituted phenylalanines of increasing electron-withdrawing properties led to a progressive accumulation of 2 that showed a good correlation with the interaction energies of simple cations such as Na(+) with substituted benzenes. These results provide compelling evidence for the stabilizing role played by Trp 334 in aristolochene synthase catalysis for the energetically demanding transformation of 2 to 3.     

Polylactones. 13. Transesterification of Poly(L-Lactide) with Poly(Glycoude), Poly(β-Propio-Lactone), and Poly[ε -Caprolactone)

Homogeneous blends of poly(L-lactide) (M _n = 30 000 to 40 000) and poly(β-propiolactone) or poly(ε-caprolactone) were prepared in solution. The solvent-free blends were subjected to transesterification catalyzed by means of methyl triflate, triflic acid, boron trifluoride, or tributyltin methoxide at 100 or 150°C. At 100°C, transesterification was barely detectable even after 96 h. When poly(β-propiolactone) was used as the reactant at 150°C, degradation was faster than transesterification regardless of the catalyst. The same negative result was obtained for heterogeneous blends of poly(L-lactide) and poly(glycolide). In the case of poly(ε-caprolactone), copolyesters with slightly blocky sequences were obtained with tributyltin methoxide as catalyst, whereas the acidic catalysts caused rapid degradation. The copolyesters were characterized by means of ¹H-NMR spectroscopy with regard to their molar composition, by means of ¹³C-NMR spectroscopy with regard to their sequences, and by means of differential scanning calorimetry with regard to crystallinity.     

Synthesis,Thermal Properties,and Radiolysis of Poly(Cyclohexyl α-Chloroacrylate)

Cyclohexyl α-chloroacrylate (CCA) was polymerized by radical anionic and γ-radiation initiation. The anionic polymerization of cyclohexyl α-chloroacrylate gave moderately isotactic polymer in toluene and syndiotactic-rich polymer in THF. Poly(cyclohexyl α-chloroacrylate) (PCCA) was found to undergo two-stage weight loss in thermogravimetric analysis, and the first-stage weight loss was attributed to the lactonization reaction. PCCA degraded under γ-radiation, and the radiation yields of crosslinking and scission, G _x and G _s, were 0.6 and 3.8, respectively.     

Recognition of amino acids and anions by a Zn(Ⅱ)-methylazacalix[4]pyridine complex

As a powerful macrocyclic host molecule with unique conformation and cavity structure that are fine-tuned by the bridging nitrogen atoms, methylazacalix[4]pyridine (MACP-4) has been shown to selectively recognize Zn2+ and form stable Zn(Ⅱ)-MACP-4 complexes both in solid state and solution with an association constant up to 5.97 (logKs). The molecular recognition of Zn(Ⅱ)-MACP-4 complexes towards various amino acids and anions with different geometry was investigated by using the spectral titration methods a...     

Poly(ethylene glycol)-supported Piperazine——Synthesis and Application in Knoevenagel Condensation

A soluble,poly(ethylene glycol)-supported piperazine catalyst was prepared.This soluble catalyst efficiently catalyzes the Knoevenagel condensation of various aromatic aldehydes with diethyl malonate or ethyl acetoacetate in a homogeneous phase to afford the desired alkenes in good purity and yield with a facile work-up process.It was found that the polymer reagent could be repeatedly used at least four times without the too much loss of activity.The catalyst has shown a good activity,stability,and recyclin...