Preparation and Structure of Magnesium Bis(hydrogen β‐glutamate) Hexahydrate

The dissociation equilibria of aqueous solutions of β‐glutamic acid were studied by potentiometric titration and the three pK values determined under standard conditions. The hydrogen β‐glutamate anion β‐GluH⁻ was found to be the dominating species in the physiologically relevant pH range 4.0–9.4. Neutralization of β‐glutamic acid by magnesium oxide affords magnesium bis(hydrogen β‐glutamate) Mg (β‐GluH)₂, which crystallizes as the hexahydrate from dilute aqueous solution. A single‐crystal X‐ray study showed that the β‐GluH⁻ anions are not part of the coordination sphere of the magnesium ion. Instead hexahydrated dications [Mg(H₂O)₆]²⁺ are intimately associated with free β‐GluH⁻ anions through a three‐dimensional network of H‐bonds. This study provides the first structural and conformational reference data for the β‐GluH⁻ anion.     

Depyrimidination of synthetic poly(uridylic acid) analogue

A poly(uridylic acid) analogue, poly{[1′‐(β‐uracil‐1‐yl)‐5′‐deoxy‐D‐erythro‐pent‐4′‐enofuranose]‐alt‐[maleic acid]} (3), was synthesized by the alternating copolymerization of nucleoside derivative 1 and maleic anhydride and subsequent hydrolysis. N‐glycosidic bonds of the polymer were hydrolyzed spontaneously to liberate uracil from the polymer backbone in a buffer solution (pH 7.4) at room temperature. The depyrimidination rate constant of the polymer at pH 7.4 at 80 °C was 8.2 × 10⁻⁵ s⁻¹, which was 10⁴ times higher than that of the depyrimidination of DNA (1.2 × 10⁻⁹ s⁻¹) under the same condition. The activation energy for the depyrimidination was 16 kcal/mol, which was about half of that for the relevant nucleoside reactions. The increase in the depyrimidination rate was attributable to the high potential energy of the polymer caused by the crowded environment around the bases, so that the polymer was more susceptible to the hydrolysis. Because natural nucleic acids often have compact structures with a crowded environment around the bases by an intricate chain folding, the pyrimidination also may have been accelerated in a similar manner in the biological system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 423–429, 2000     

Controlled helical orientation of carbazole in amino acid derived poly(N‐propargylamide)s

Novel L ‐alanine and L ‐glutamic acid derivatized, carbazole‐containing N‐propargylamides [N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐alanine N′‐propargylamide and N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐glutamic acid‐γ‐benzyl ester N′‐propargylamide] were synthesized and polymerized with (nbd)Rh⁺[η⁶‐C₆H₅B^?(C₆H₅)₃] (nbd = norbornadiene) as a catalyst to obtain the corresponding polymers with moderate molecular weights in high yields. Polarimetry, circular dichroism, and ultraviolet–visible spectroscopy studies revealed that both poly[N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐alanine N′‐propargylamide] and poly[N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐glutamic acid‐γ‐benzyl ester N′‐propargylamide] took a helical structure with a predominantly one‐handed screw sense in tetrahydrofuran, CHCl₃, and CH₂Cl₂. The helix content of poly[N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐alanine N′‐propargylamide] could be tuned by heat or the addition of a protic solvent, and the helical sense of poly[N‐(9‐carbazolyl) ethyloxycarbonyl‐L ‐glutamic acid‐γ‐benzyl ester N′‐propargylamide] was inverted by heat in CHCl₃ or in mixtures of tetrahydrofuran and CH₂Cl₂. Poly[N‐(9‐carbazolyl) ethyloxycarbonyl‐L ‐alanine N′‐propargylamide] and poly[N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐glutamic acid‐γ‐benzyl ester N′‐propargylamide] also took a helical structure in film states. They showed small fluorescence in comparison with the monomers and redox activity based on carbazole. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 253–261, 2007     

Chemical synthesis of poly‐γ‐glutamic acid by polycondensation of γ‐glutamic acid dimer: Synthesis and reaction of poly‐γ‐glutamic acid methyl ester

α‐Methyl glutamic acid (L ‐L )‐, (L ‐D )‐, (D ‐L )‐, and (D ‐D )‐γ‐dimers were synthesized from L ‐ and D ‐glutamic acids, and the obtained dimers were subjected to polycondensation with 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride and 1‐hydroxybenzotriazole hydrate as condensation reagents. Poly‐γ‐glutamic acid (γ‐PGA) methyl ester with the number‐average molecular weights of 5000∼20,000 were obtained by polycondensation in N,N‐dimethylformamide in 44∼91% yields. The polycondensation of (L ‐L )‐ and (D ‐D )‐dimers afforded the polymers with much larger |[α]_D | compared with the corresponding dimers. The polymer could be transformed into γ‐PGA by alkaline hydrolysis or transesterification into α‐benzyl ester followed by hydrogenation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 732–741, 2001     

Novel temperature‐ and pH‐responsive graft copolymers composed of poly(L‐glutamic acid) and poly(N‐isopropylacrylamide)

A series of novel temperature‐ and pH‐responsive graft copolymers, poly(L ‐glutamic acid)‐g‐poly(N‐isopropylacrylamide), were synthesized by coupling amino‐semitelechelic poly(N‐isopropylacrylamide) with N‐hydroxysuccinimide‐activated poly(L ‐glutamic acid). The graft copolymers and their precursors were characterized, by ESI‐FTICR Mass Spectrum, intrinsic viscosity measurements and proton nuclear magnetic resonance (¹H NMR). The phase‐transition and aggregation behaviors of the graft copolymers in aqueous solutions were investigated by the turbidity measurements and dynamic laser scattering. The solution behavior of the copolymers showed dependence on both temperature and pH. The cloud point (CP) of the copolymer solution at pH 5.0–7.4 was slightly higher than that of the solution of the PNIPAM homopolymer because of the hydrophilic nature of the poly(glutamic acid) (PGA) backbone. The CP markedly decreased when the pH was lowered from 5 to 4.2, caused by the decrease in hydrophilicity of the PGA backbone. At a temperature above the lower critical solution temperature of the PNIPAM chain, the copolymers formed amphiphilic core‐shell aggregates at pH 4.5–7.4 and the particle size was reduced with decreasing pH. In contrast, larger hydrophobic aggregates were formed at pH 4.2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4140–4150, 2008     

Photochemical Behavior of Folic Acid in Alkaline Aqueous Solutions and Evolution of Its Photoproducts

The photolysis of folic acid (=N‐(4‐{[(2‐amino‐1,4‐dihydro‐4‐oxopteridin‐6‐yl)methyl]amino}benzoyl)‐L ‐glutamic acid) in alkaline aqueous solution (pH 10.0–11.0) was carried out at 350 nm at room temperature and monitored by UV/VIS spectrophotometry, anal. and prep. thin‐layer chromatography (TLC), and high‐performance liquid chromatography (HPLC, HPLC/MS). The folate species underwent at least two independent photo‐oxidation pathways, which were not observed when the acid form was photolyzed at pH<7. The presence of O₂ was essential in these oxidation pathways. Evidence for the role of singlet oxygen was established. In one of the pathways, the folate underwent cleavage, yielding 6‐formylpterin (=2‐amino‐1,4‐dihydro‐4‐oxopteridine‐6‐carboxaldehyde) and (4‐aminobenzoyl)glutamic acid as photoproducts. The other pathway yielded a new photostable product A of molecular mass 455, which could be isolated and stored in acidic or neutral aqueous solution. However, A was rather unstable in alkaline media undergoing a thermal reaction to a product B of lower molecular mass (427). The kinetics of this thermal reaction was analyzed with a stopped‐flow spectrophotometer. A linear dependence of the first‐order rate constant with the OH⁻ concentration was observed. The corresponding bimolecular rate constant was 1.1 M ⁻¹ s⁻¹. The quantum yields of substrate consumption and of photoproduct formation were determined. The here‐reported photochemical behavior of folate solutions departs from results in acid media, where phototransformation proceeded via the cleavage of the acid form into 6‐formylpterin and (4‐aminobenzoyl)glutamic acid as the first major photoproducts, and where no thermal reactions were observed.     

Establishment of a kinetic model for the intramolecular catalyzed hydrolysis of [18F]‐benzylfluoride containing amino acid analogues by linking experimental and DFT studies

In an earlier publication, we suggested that the faster radiodefluorination kinetics of no‐carrier‐added (S)‐3‐(2‐[¹⁸F]fluoromethyl‐phenyl)‐2‐amino‐propionic acid (2‐[¹⁸F]FMLP), as compared to 4‐[¹⁸F]‐fluoromethyl‐l ‐phenylalanine (4‐[¹⁸F]FMLP), was caused by an intramolecular interaction between the CH₂F group on the 2‐position of the phenyl ring and the ammonium group of the amino acid. As the presence of nonradioactive (S)‐3‐(2‐fluoromethyl‐phenyl)‐2‐amino‐propionic acid (2FMLP) in a concentration up from 10^?6 mol/L reduces considerably the defluorination rate due to the formation of dimers, conventional experimental methods, like spectroscopy, cannot be performed for the study of the hydrolysis in no‐carrier‐added conditions occurring at a concentration range of about 5.0 10^?10 mol/L. In the present study, we aim to provide a proof that supports aforementioned hypothesis as well as to establish a kinetic model and to put forward accompanying rate equations for this hydrolysis reaction by combining ab initio quantum chemical calculations and kinetic data. The calculations of the optimized geometries and the corresponding energies of the reactants involved in the hydrolysis of 2‐[¹⁸F]FMLP and 4‐[¹⁸F]FMLP were performed at the DFT[B3LYP/6‐31⁺⁺G**] level of theory. Interpretation of these data reveals that in 2‐[¹⁸F]FMLP three intramolecular hydrogen bond interactions can be identified that are not present in 4‐[¹⁸F]FMLP. The most important interaction is the one between the amino acid ammonium group and the benzylic fluorine atom, rendering the rupture of the C? F bond much more favorable. These findings align with the experimental data and enabled us to put forward the rate expressions that define the unexpected pseudo–zero‐order defluorination reaction of 2‐[¹⁸F]FMLP at neutral pH. This study also proves that in the development of [¹⁸F]‐benzylfluoride containing tracers present‐day quantum chemical calculations are capable of predicting intramolecular interactions, affecting their reactivity toward hydrolysis at the no‐carrier‐added level. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 705–711, 2012     

Ester Hydrolysis by a Cyclodextrin Dimer Catalyst with a Tridentate N,N′,N′′‐Zinc Linking Group

A new β‐cyclodextrin dimer, 2,6‐dimethylpyridine‐bridged‐bis(6‐monoammonio‐β‐cyclodextrin) (pyridyl BisCD, L), is synthesized. Its zinc complex (ZnL) is prepared, characterized, and applied as a catalyst for diester hydrolysis. The formation constant (log K_ML=7.31±0.04) of the complex and deprotonation constant (pK_a1=8.14±0.03, pK_a2=9.24±0.01) of the coordinated water molecule were determined by a potentiometric pH titration at (25±0.1)°C, indicating a tridentate N,N′,N′′‐zinc coordination. Hydrolysis kinetics of carboxylic acid esters were determined with bis(4‐nitrophenyl)carbonate (BNPC) and 4‐nitrophenyl acetate (NA) as the substrates. The resulting hydrolysis rate constants show that ZnL has a very high rate of catalysis for BNPC hydrolysis, yielding an 8.98×10³‐fold rate enhancement over uncatalyzed hydrolysis at pH 7.00, compared to only a 71.76‐fold rate enhancement for NA hydrolysis. Hydrolysis kinetics of phosphate esters catalyzed by ZnL are also investigated using bis(4‐nitrophenyl)phosphate (BNPP) and disodium 4‐nitrophenyl phosphate (NPP) as the substrates. The initial first‐order rate constant of catalytic hydrolysis for BNPP was 1.29×10^?7 s^?1 at pH 8.5, 35 °C and 0.1 mM catalyst concentration, about 1600‐fold acceleration over uncatalyzed hydrolysis. The pH dependence of the BNPP cleavage in aqueous buffer was shown as a sigmoidal curve with an inflection point around pH 8.25, which is nearly identical to the pK_a value of the catalyst from the potentiometric titration. The k_BNPP of BNPP hydrolysis promoted by ZnL is found to be 1.68×10^?3 M ^?1 s^?1, higher than that of NPP, and comparatively higher than those promoted by its other tridentate N,N′,N′′‐zinc analogues.     

Synthesis and Characterization of Diastereoisomerically Pure Tetracyclo[6.2.1.13,6.02,7]dodec‐9‐ene‐4‐carboxylic Acid Derivatives

The synthesis and detailed NMR analysis of diastereoisomerically pure samples of 4‐methyltetracyclo[6.2.1.1^3,6.0^2,7]dodec‐9‐ene‐4‐carboxylic acid ( 2 ), tetracyclo[6.2.1.1^3,6.0^2,7]dodec‐9‐ene‐4‐carboxylic acid ( 6 ) and their tert‐butyl esters are reported. Mixtures containing two isomers of the methyl esters of these compounds were obtained by a twofold, sequential Diels‐Alder reaction between cyclopentadiene, and methyl methacrylate or methyl acrylate, respectively. Pure diastereoisomers of the acids were prepared by selective hydrolysis of their methyl esters.     

Fast and Stable N‐Terminal Cysteine Modification through Thiazolidino Boronate Mediated Acyl Transfer

We report a novel conjugation of N‐terminal cysteines (NCys) that proceeds with fast kinetics and exquisite selectivity, thereby enabling facile modification of NCys‐bearing proteins in complex biological milieu. This new NCys conjugation proceeds via a thiazolidine boronate (TzB) intermediate that results from fast (k₂: ≈5000 m ^?1 s^?1) and reversible conjugation of NCys with 2‐formylphenylboronic acid (FPBA). We designed a FPBA derivative that upon TzB formation elicits intramolecular acyl transfer to give N‐acyl thiazolidines. In contrast to the quick hydrolysis of TzB, the N‐acylated thiazolidines exhibit robust stability under physiologic conditions. The utility of the TzB‐mediated NCys conjugation is demonstrated by rapid and non‐disruptive labeling of two enzymes. Furthermore, applying this chemistry to bacteriophage allows facile chemical modification of phage libraries, which greatly expands the chemical space amenable to phage display.     

Synthesis and evaluation of new dental monomers with both phosphonic and carboxylic acid functional groups

Novel dental monomers containing both phosphonic and carboxylic acid functional groups were prepared. The monomers were based on t‐butyl α‐bromomethacrylate (t‐BuBMA) and synthesized in three steps: The reaction of o‐hydroxyaryl phosphonates [diethyl (2‐hydroxyphenyl) phosphonate, tetraethyl (2,5‐dihydroxy‐1,4‐phenylene) diphosphonate and tetraethyl 5,5′‐(propane‐2,2‐diyl)bis(2‐hydroxy‐5,1‐ phenylene) diphosphonate] with t‐BuBMA, the hydrolysis of phosphonate groups to phosphonic acid using trimethyl silylbromide, and the hydrolysis of the t‐butyl groups to carboxylic acid with trifluoroacetic acid. The monomers were solids and soluble in water and ethanol. The structures of the monomers were determined by Fourier transform infrared (FTIR), ¹H, ¹³C, and ³¹P nuclear magnetic resonance (NMR) spectroscopy. The copolymerization behaviors of the synthesized monomers with glycerol dimethacrylate were first investigated in bulk using photodifferential scanning calorimetry at 40 °C with 2,2′‐dimethoxy‐2‐phenyl acetophenone as photoinitiator. Then, the solution copolymerization of the monomers with acrylamide in ethanol and water was studied, indicating that the synthesized monomers are incorporated into the copolymers. The acidic nature of the aqueous solutions of these monomers (pH values 1.72–1.87) is expected to give them etching properties important for dental applications. The interaction of the monomers with hydroxyapatite was investigated using ¹³C NMR and FTIR techniques. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1953–1965, 2009     

Characterization of novel hydrolysis products of carbapenems by electrospray ionization mass spectrometry

Carbapenems, including meropenem and imipenem, exhibit low stability against acid or base reagents. The fragmentation behavior of meropenem and its acid hydrolysis products was investigated by Fourier transform ion cyclotron resonance electrospray ionization tandem mass spectrometry and ion trap tandem multi‐stage mass spectrometry in both positive and negative ion mode. Only one neutral loss of CO₂ was observed from the precursor ion to the MS⁴ product ions for the acid hydrolysis product and this behavior did not correspond to that expected for the previously accepted 1‐pyrroline or 2‐pyrroline structure with two carbonyl acid units. The unknown product was then proposed to be 2‐(4‐(5‐(dimethylcarbamoyl)pyrrolidin‐3‐ylthio)‐5‐imino‐3‐methyl‐6‐oxotetrahydro‐2H‐pyran‐2‐yl)‐3‐hydroxybutanoic acid on the basis of the multi‐stage mass spectrometric and accurate mass data. A similar acid hydrolysis product of imipenem was also identified by mass spectrometry, confirming that these carbapenems had the same acid hydrolysis behavior. The proposed structures were further confirmed by NMR experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

Near‐Infrared Luminescence Sensing of Glutamic Acid,Aspartic Acid,and Their Dipeptides with Tris(β‐diketonato)lanthanide Probes

A series of tris(β‐diketonato)lanthanides with Yb³⁺, Eu³⁺, and Nd³⁺ centers were characterized as luminescent sensing probes specific to glutamic acid, aspartic acid, and their dipeptides, which are important substrates involved in nervous systems, taste receptors, and other biological systems. In particular, tris(6,6,7,7,8,8,8‐heptafluoro‐2,2‐dimethyloctane‐3,5‐dionato)ytterbium(III) exhibited a near‐infrared emission around 980 nm in response to these biological substrates. Near‐infrared‐emissive complexes have several advantages over common luminescent probes; therefore, the proposed lanthanide complexes have potential analytical applications in proteomics, metabolics, food science, astrobiology, and related technologies.     

Novel 3D Neuron Regeneration Scaffolds Based on Synthetic Polypeptide Containing Neuron Cue

Neural tissue engineering has become a potential technology to restore the functionality of damaged neural tissue with the hope to cure the patients with neural disorder and to improve their quality of life. This paper reports the design and synthesis of polypeptides containing neuron stimulate, glutamic acid, for the fabrication of biomimetic 3D scaffold in neural tissue engineering application. The polypeptides are synthesized by efficient chemical reactions. Monomer γ‐benzyl glutamate‐N‐carboxyanhydride undergoes ring‐opening polymerization to form poly(γ‐benzyl‐l ‐glutamate), then hydrolyzes into poly(γ‐benzyl‐l ‐glutamate)‐r‐poly(glutamic acid) random copolymer. The glutamic acid amount is controlled by hydrolysis time. The obtained polymer molecular weight is in the range of 200 kDa for good quality of fibers. The fibrous 3D scaffolds of polypeptides are fabricated using electrospinning techniques. The scaffolds are biodegradable and biocompatible. The biocompatibility and length of neurite growth are improved with increasing amount of glutamic acid in scaffold. The 3D scaffold fabricated from aligned fibers can guide anisotropic growth of neurite along the fiber and into 3D domain. Furthermore, the length of neurite outgrowth is longer for scaffold made from aligned fibers as compared with that of isotropic fibers. This new polypeptide has potential for the application in the tissue engineering for neural regeneration.     

Acid‐labile,thermoresponsive (meth)acrylamide polymers with pendant cyclic acetal moieties

Acid‐labile, thermoresponsive polymers with pendant six‐membered cyclic acetal groups were prepared by radical polymerization of two monomers, N‐(2,2‐dimethyl‐1,3‐dioxan‐5‐yl) methacrylamide (NDMM) and N‐(2,2‐dimethyl‐1,3‐dioxan‐5‐yl) acrylamide (NDMA). The aqueous solution properties of the polymers, PNDMM and PNDMA, were studied by turbidimetry, ¹H NMR, fluorescence, and DSC measurements. It is found that both polymers show sensitive and reversible phase transitions with distinct lower critical solution temperatures (LCST). Below their LCSTs, there are still some polymer aggregates as evidenced by measurements of pyrene excitation spectra and urea effects on the cloud points (CP) of polymers. The salting effect of six inorganic sodium salts on the phase transition behavior of PNDMM was investigated by turbidimetric approach. The salting‐out to salting‐in effect is in the order of SO₄^2? > F^? > Cl^? > Br^? > I^? > SCN^?, following the Hofmeister's series. pH‐dependent hydrolysis of PNDMM and PNDMA was studied by turbidimetric and ¹H NMR methods. They are both pH‐sensitive and their hydrolysis rates significantly increase with decreasing pH value. The CP of PNDMM gradually increases with the acid‐triggered hydrolysis of the acetal groups and the hydrolyzed polymer with ～ 30% hydrolysis degree does not show thermally induced phase transition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4332–4343, 2008     

High‐performance liquid chromatography/mass spectrometric and proton nuclear magnetic resonance spectroscopic studies of the transacylation and hydrolysis of the acyl glucuronides of a series of phenylacetic acids in buffer and human plasma

The use of high‐performance liquid chromatography/mass spectrometry (HPLC/MS) and proton nuclear magnetic resonance (¹H NMR) spectroscopy for the kinetic analysis of acyl glucuronide (AG) isomerisation and hydrolysis of the 1‐β‐O‐acyl glucuronides (1‐β‐O‐AG) of phenylacetic acid, (R)‐ and (S)‐α‐methylphenylacetic acid and α,α‐dimethylphenylacetic acid is described and compared. Each AG was incubated in both aqueous buffer, at pH 7.4, and control human plasma at 37°C. Aliquots of these incubations, taken throughout the reaction time‐course, were analysed by HPLC/MS and ¹H NMR spectroscopy. In buffer, transacylation reactions predominated, with relatively little hydrolysis to the free aglycone observed. In human plasma incubations the calculated rates of reaction were much faster than for buffer and, in contrast to the observations in buffer, hydrolysis to the free aglycone was a significant contributor to the overall reaction. A diagnostic analytical methodology based on differential mass spectrometric fragmentation of 1‐β‐O‐AGs compared to the 2‐, 3‐ and 4‐positional isomers, which enables selective determination of the former, was confirmed and applied. These findings show that HPLC/MS offers a viable alternative to the more commonly used NMR spectroscopic approach for the determination of the transacylation and hydrolysis reactions of these AGs, with the major advantage of having the capability to do so in a complex biological matrix such as plasma. Copyright © 2010 John Wiley & Sons, Ltd.     

Liquid Crystalline Period Variations in Self‐Assembled Block Copolypeptides–Surfactant Ionic Complexes

We investigate the complexation of ampholytic poly(N‐isopropylacylamide)‐block‐poly‐ (L ‐glutamic acid)‐block‐poly(L ‐lysine) (PNiPAM‐b‐PLG‐b‐PLLys) triblock copolymers and PNiPAM‐block‐(PLG‐co‐PLLys) diblock copolymers with counter charged anionic and cationic surfactants. Both triblock and diblock copolymers are able to selectively form complexes through either L ‐glutamic acid–cationic surfactant or L ‐lysine–anionic surfactant ionic pairs, depending on the protonated or deprotonated states of the ampholytic peptide units. The complexes show ordering at multiple length scales: i) the block copolymer length scale (10¹ nm), ii) the liquid crystalline length scale (10⁰ nm), and, iii) the peptidic secondary structures length scale (10⁰ nm). We show that the liquid crystalline period can be tuned by varying the random/block copolypeptide architectures and the composition of the ampholytic amino acid species.

     

Nucleation and growth kinetics of silver nanoparticles prepared by glutamic acid in micellar media

The title reaction in the presence of cetyltrimethylammonium bromide (CTAB) has been followed spectrophotometrically at 325 nm. In the process of reduction, characteristic surface resonance plasmon absorption peaks appear for the silver nanoparticles (NP) and the intensities increase with reaction time. UV–visible spectra suggest that [CTAB] and glutamic acid influence the morphology of the silver NP and act as shape‐directing agents, whereas [Ag⁺] has no effect. The effects of the total [glutamic acid], [CTAB], and [Ag⁺] on the apparent rate constants of silver NP formation are determined. The sigmoidal curve of absorbance versus reaction time indicates an autocatalytic path involved in the growth process. The α‐amino and ? COOH groups undergo chemical transformation (oxidative deamination and decarboxylation). The particles are spherical in shape with average diameters ranging between 12 and 25 nm, and their size distribution is wide. A plausible mechanism has been proposed with the following rate law: (d[silver sol])/dt = k[Ag⁺][Glutamic acid]_T. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 680–691, 2012     

Influence of Montmorillonite's Concentration on the Thixotropy of Hydrotalcite-like Compounds/Montmorillonite Suspensions

In this paper, we found that the change of sodium montmorillonite's (MT) concentration in the magnesium‐aluminum‐ferrum hydrotalcite‐like compounds (Mg‐Al‐Fe‐HTlc)/MT suspensions would greatly influence the thixotropic type of the suspensions. Specifically, the increase in the MT's concentration increases the viscosities (η) of the HTlc/MT suspensions with the same R value (the mass ratio of HTlc to MT was signed as R, e.g., R=m_HTlc/m_MT), meaning that the structure strength of the HTlc/MT suspensions increases. With the variation of MT's concentration, the thixotropic type of the HTlc/MT suspensions changed accordingly, and the mechanism has been discussed in this paper.     

Novel block ionomers. I. Synthesis and characterization of polyisobutylene‐based block anionomers

A series of novel block anionomers consisting of polyisobutylene (PIB) and poly(methacrylic acid) (PMAA) segments were prepared and characterized. The specific targets were various molecular weight diblocks (PIB‐b‐PMAA^?), triblocks (PMAA^?‐b‐PIB‐b‐PMAA^?), and three‐arm star blocks [Φ(PIB‐b‐PMAA^?)₃] consisting of rubbery PIB blocks with a number‐average degree of polymerization of 50–1000 (number‐average molecular weight = 3000–54,000 g/mol) connected to blocks of PMAA^? anions with a number‐average degree of polymerization of 5–20. The overall strategy for the synthesis of these constructs consisted of four steps: (1) synthesis by living cationic polymerization of t‐chloro‐monotelechelic, t‐chloro‐ditelechelic, and t‐chloro‐tritelechelic PIBs; (2) site transformation to obtain PIBs fitted with termini capable of mediating the atom transfer radical polymerization (ATRP) of tert‐butyl methacrylate (tBMA); (3) ATRP of tBMA, and (4) hydrolysis of poly(tert‐butyl methacrylate) to PMAA^?. The architectures created and the synthesis steps employed are summarized. Kinetic and model experiments greatly assisted in the development of convenient synthesis methods. The microarchitectures of the various block anionomers were confirmed by spectroscopy and other techniques. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3662–3678, 2002