Nitrophenyl Esters Research Articles

Enantioselective Hydrolysis of Amino Acid Esters Promoted by Bis(β-cyclodextrin) Copper Complexes

It is challenging to create artificial catalysts that approach enzymes with regard to catalytic efficiency and selectivity. The enantioselective catalysis ranks the privileged characteristic of enzymatic transformations. Here, we report two pyridine-linked bis(β-cyclodextrin) (bisCD) copper(II) complexes that enantioselectively hydrolyse chiral esters. Hydrolytic kinetic resolution of three pairs of amino acid ester enantiomers (S1–S3) at neutral pH indicated that the “back-to-back” bisCD complex CuL1 favoured higher catalytic efficiency and more pronounced enantioselectivity than the “face-to-face” complex CuL2. The best enantioselectivity was observed for N-Boc-phenylalanine 4-nitrophenyl ester (S2) enantiomers promoted by CuL1, which exhibited an enantiomer selectivity of 15.7. We observed preferential hydrolysis of L-S2 by CuL1, even in racemic S2, through chiral high-performance liquid chromatography (HPLC). We demonstrated that the enantioselective hydrolysis was related to the cooperative roles of the intramolecular flanking chiral CD cavities with the coordinated copper ion, according to the results of electrospray ionization mass spectrometry (ESI-MS), inhibition experiments, rotating-frame nuclear Overhauser effect spectroscopy (ROESY), and theoretical calculations. Although the catalytic parameters lag behind the level of enzymatic transformation, this study confirms the cooperative effect of the first and second coordination spheres of artificial catalysts in enantioselectivity and provides hints that may guide future explorations of enzyme mimics.

Supernucleophilic systems based on functionalized surfactants in the decomposition of 4-nitrophenyl esters derived from phosphorus and sulfur acids. III. Reactivity of mixed micellar systems based on tetraalkylammonium and imidazolium surfactants

Reactivity of mixed micellar systems based on the functionalized imidazolium and tetraalkylammonium surfactanats in the reaction of cleavage of 4-nitrophenyl ethyl ethylphosphonate was studied. Replacing of an imidazolium fragment in the detergent structure with a tetraalkylammonium one reveals decreasing the substrate solubilization efficiency. In the case of dimeric surfactants, the nucleophilicity of the oximate fragment is considerably (ca. 2 times) decreased thus additionally decreasing the rate of cleavage of the organophosphorus substarte. Therefore the nature of the cationic center in the head group may affect the extent of the observed micellar effects of functionalized surfactants.

Phosphatase models: Synthesis, structure and catalytic activity of zinc complexes derived from a phenolic Mannich-base ligand

A series of dinuclear [Zn2(L1)2X2] (1–3) and mononuclear [Zn(HL2)X2] complexes (4–6), (X=Cl, Br, I) were synthesised from two Mannich-base compartmental ligands, namely [bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL1) and 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL2), respectively. They were characterised by routine physicochemical techniques (CHN, UV, IR, ESI-MS and NMR) and complex 2–5 was further structurally characterised by single crystal X-ray analysis where the Zn…Zn bond-distance is 3.10–3.12Å. All the quintessential complexes exhibit excellent phosphatase activity and the experimental first order rate constant values (kcat) for the hydrolysis of 4-nitrophenyl phosphate ester (PNPP) reaction in methanol are in the range from 1.05 to 214s−1 at 25°C evaluated by monitoring spectrophotometrically the gradual release of p-nitrophenolate (λmax=427nm, ε=18500M−1cm−1). The coordinated X halides affect the phosphatase activity in the order Br>Cl>I (in dinuclear complexes) and Cl>Br>I (in mononuclear) and the trend in the two cases has been well recognised to be due to a different rate determining step. Moreover the influence of chloro atom in para-position of the phenol ring and the role of solvent have been rationalised by comparing the kinetic parameters with those obtained for the corresponding methyl analogues having reasonably close structural resemblance as reported by Sanyal et al. (2014).

Ligand binding to the FA3-FA4 cleft inhibits the esterase-like activity of human serum albumin.

The hydrolysis of 4-nitrophenyl esters of hexanoate (NphOHe) and decanoate (NphODe) by human serum albumin (HSA) at Tyr411, located at the FA3-FA4 site, has been investigated between pH 5.8 and 9.5, at 22.0°C. Values of K s, k +2, and k +2/K s obtained at [HSA] ≥ 5×[NphOXx] and [NphOXx] ≥ 5×[HSA] (Xx is NphOHe or NphODe) match very well each other; moreover, the deacylation step turns out to be the rate limiting step in catalysis (i.e., k +3 << k +2). The pH dependence of the kinetic parameters for the hydrolysis of NphOHe and NphODe can be described by the acidic pK a-shift of a single amino acid residue, which varies from 8.9 in the free HSA to 7.6 and 7.0 in the HSA:NphOHe and HSA:NphODe complex, respectively; the pK>a-shift appears to be correlated to the length of the fatty acid tail of the substrate. The inhibition of the HSA-Tyr411-catalyzed hydrolysis of NphOHe, NphODe, and 4-nitrophenyl myristate (NphOMy) by five inhibitors (i.e., diazepam, diflunisal, ibuprofen, 3-indoxyl-sulfate, and propofol) has been investigated at pH 7.5 and 22.0°C, resulting competitive. The affinity of diazepam, diflunisal, ibuprofen, 3-indoxyl-sulfate, and propofol for HSA reflects the selectivity of the FA3-FA4 cleft. Under conditions where Tyr411 is not acylated, the molar fraction of diazepam, diflunisal, ibuprofen, and 3-indoxyl-sulfate bound to HSA is higher than 0.9 whereas the molar fraction of propofol bound to HSA is ca. 0.5.

Study of Extraction Equilibria in the Reaction of Alkaline Hydrolysis of Activated Amino Acid Esters / Badanie Równowag Ekstrakcji W Reakcji Zasadowej Hydrolizy Aktywowanych Estrów Aminokwasów

Abstract Correlation between observed kinetic effects of phase-transfer catalytic reaction of the alkaline hydrolysis of 4-nitrophenyl ester of N-benzyloxycarbonylglycine-4 in the two-phase system chloroform-borate buffer pH = 10 and a content of ionic forms of catalyst was investigated. The phosphonium salts QX (X = Cl¯, Br¯, I¯) shows high catalytic reactivity. Dependence of the reaction kinetics discussed in the framework of the extraction mechanism with a competitive extraction of a nucleophile ОН¯, nucleofuge 4-NO2C6H4O¯ and anion X¯ of the phase-transfer catalyst.

Dual-responsive polymer–drug nanoparticles for drug delivery

A well-defined, dual temperature- and pH-responsive drug carrier was synthesized through the radical copolymerization of methacrylic acid, N-isopropylacrylamide, and an N-(methacryloyl)glycylglycine 4-nitrophenyl ester. When the anticancer agent gemcitabine or antibiotic sulfamethoxazole was conjugated with a polymer and heated beyond its low critical solution temperature (40°C), a dual temperature- and pH-induced phase transition was observed. This temperature was considered ideal for activating drug aggregation under hyperthermic and acidic conditions. The structure and properties of polymer drugs were investigated using nuclear magnetic resonance, Fourier transform infrared spectrometry, ultraviolet–visible absorption, transmission electron microscopy, and gel permeation chromatography. At a critical micelle concentration of 1mg/mL, both polymer drugs formed micellar structures with diameters ranging from 50nm to 150nm, based on TEM image. These micelles exhibited higher pharmacological efficacy than the free drug alone did, and the cytotoxicity at the target site was substantially enhanced compared with that of the polymer–drug conjugate formed under normal physiological conditions.

Δ9-tetrahydrocannabinol and endocannabinoid degradative enzyme inhibitors attenuate intracranial self-stimulation in mice.

A growing body of evidence implicates endogenous cannabinoids as modulators of the mesolimbic dopamine system and motivated behavior. Paradoxically, the reinforcing effects of Δ(9)-tetrahydrocannabinol (THC), the primary psychoactive constituent of cannabis, have been difficult to detect in preclinical rodent models. In this study, we investigated the impact of THC and inhibitors of the endocannabinoid hydrolytic enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) on operant responding for electrical stimulation of the medial forebrain bundle [intracranial self-stimulation (ICSS)], which is known to activate the mesolimbic dopamine system. These drugs were also tested in assays of operant responding for food reinforcement and spontaneous locomotor activity. THC and the MAGL inhibitor JZL184 (4-[bis(1,3-benzodioxol-5-yl)hydroxymethyl]-1-piperidinecarboxylic acid 4-nitrophenyl ester) attenuated operant responding for ICSS and food, and also reduced spontaneous locomotor activity. In contrast, the FAAH inhibitor PF-3845 (N-3-pyridinyl-4-[[3-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenyl]methyl]-1-piperidinecarboxamide) was largely without effect in these assays. Consistent with previous studies showing that combined inhibition of FAAH and MAGL produces a substantially greater cannabimimetic profile than single enzyme inhibition, the dual FAAH-MAGL inhibitor SA-57 (4-[2-(4-chlorophenyl)ethyl]-1-piperidinecarboxylic acid 2-(methylamino)-2-oxoethyl ester) produced a similar magnitude of ICSS depression as that produced by THC. ICSS attenuation by JZL184 was associated with increased brain levels of 2-arachidonoylglycerol (2-AG), whereas peak effects of SA-57 were associated with increased levels of both N-arachidonoylethanolamine (anandamide) and 2-AG. The cannabinoid receptor type 1 receptor antagonist rimonabant, but not the cannabinoid receptor type 2 receptor antagonist SR144528, blocked the attenuating effects of THC, JZL184, and SA-57 on ICSS. Thus, THC, MAGL inhibition, and dual FAAH-MAGL inhibition not only reduce ICSS, but also decrease other reinforced and nonreinforced behaviors.

Liquid chromatography–mass spectrometry structural characterization of neo glycoproteins aiding the rational design and synthesis of a novel glycovaccine for protection against tuberculosis

Hereby we describe a pilot study for the rational design and synthesis of a glycoconjugate vaccine against Tuberculosis (TB) by site-specific coupling of well-defined glycans to non-antigenic amino acids in a selected protein carrier. A combination of ESI-MS and LC–MS analytical methods was applied for the systematic characterization of the reactivity of the surface amino acids in the glycosylation reaction with monosaccharides towards 2-iminomethoxyethyl or homobifunctional (4-nitrophenyl ester) linkers, both on the model protein, ribonuclease A (RNase A) and on TB10.4, the simplest antigenic protein isolated from Mycobacterium tuberculosis (MTB). Intact protein analysis was carried out to quantify the glycosylation degree and profile the glycoform composition of all the prepared neo glycoconjugates, while pronase and chymotriptic digests were analyzed to map and rank the reactivity of protein residues. Neo glycopeptides were purified by on-line porous graphitized carbon solid-phase extraction, separated by hydrophilic interaction liquid chromatography and analyzed by electrospray mass spectrometry (ESI-MSn). Significantly, different site specificity and glycosylation efficiency were demonstrated for the two linkers, resulting in structurally diverse glycoconjugates. A computational analysis of the amino acids involved in the epitope formation in TB10.4 addressed the choice to 2-iminomethoxyethyl-saccharide activation, that resulted in a more targeted and selective conjugation preserving the protein antigenicity. Additionally, a rational design of experiments lead to the identification of suitable experimental conditions for the preparation of highly pure and homogeneous neo glycoconjugates.

Feruloyl esterase from the edible mushroom Panus giganteus: a potential dietary supplement.

A novel 61 kDa feruloyl esterase (FAE) was purified to homogeneity from freshly collected fruiting bodies of Panus giganteus. The isolation procedure involved chromatography on the ion exchangers DEAE-cellulose and Q-Sepharose, followed by size exclusion chromatography on Superdex 75, which produced a purified enzyme with a high specific activity (170.0 U/mg) which was 130-fold higher than that of crude extract. The purified FAE exhibited activity toward synthetic methyl esters and short-chain fatty acid nitrophenyl esters. The Km and Vmax for this enzyme on methyl ferulate were 0.36 mM and 18.97 U/mg proteins, respectively. FAE activity was attained at a maximum at pH 4 and 40 °C, respectively. The FAE activity was inhibited by metal ions to various degrees. The purified FAE could bring about the release of ferulic acid from wheat bran and corn bran under the action of the single purified FAE, and the amount released from wheat bran rose to 51.9% (of the total amount) by the synergistic action of xylanase.

An extracellular solvent stable alkaline lipase from Pseudomonas sp. DMVR46: Partial purification, characterization and application in non-aqueous environment

The biosynthesis of esters is currently of much commercial interest because of the increasing popularity and demand for natural products among consumers. Biotransformation and enzymatic methods of ester synthesis are more effective when performed in non-aqueous media. In present study, an organic solvent stable Pseudomonas sp. DMVR46 lipase was partially purified by acetone precipitation and ion exchange chromatography with 28.95-fold purification. The molecular mass of the lipase was found to be ∼32kDa. The partially purified lipase was optimally active at 37°C and pH 8.5. The enzyme showed greater stability toward organic solvents such as isooctane, cyclohexane and n-hexane retaining more than 70% of its initial activity. The metal ions such as Ca2+, Ba2+ and Mg2+ had stimulatory effects on lipase activity, whereas Co2+ and Zn2+ strongly inhibited the activity. Also lipase exhibited variable specificity/hydrolytic activity toward different 4-nitrophenyl esters. DMVR46 lipase was further immobilized into AOT-based organogels used for the synthesis of flavor ester pentyl valerate in presence of organic solvents. The organogels showed repeated use of enzyme with meager loss of activity even upto 10 cycles. The solvent-stable lipase DMVR46 thus proved to be an efficient catalyst showing an attractive potency for application in biocatalysis under non-aqueous environment.

Supernucleophilic systems based on functionalized surfactants in the decomposition of 4-nitrophenyl esters derived from phosphorus and sulfur acids: II. Influence of the length of hydrophobic alkyl substituents on micellar effects of functionalized monomeric and dimeric imidazolium surfactants

New dimeric functionalized surfactants, 3,3′-[2-(hydroxyimino)propan-1,3-diyl]bis(1-alkyl-1H-imidazol-3-ium) dichlorides (Alk = C12H25, C14H29, C16H33), underlie the supernucleophilic microorganized systems capable of abnormally fast cleavage of acyl-containing substrates. Micellar effects both of monomeric and dimeric imidazolium surfactants in the cleavage processes of 4-nitrophenyl esters of diethylphosphonic, diethylphosphoric, and 4-toluenesulfonic acids are governed mostly by the hydrophobicity of the reaction components (acceleration ∼102–103 times). The unquestionable advantage of dimeric surfactants is their especially low critical micelle concentrations (≤10−5 mol L−1), providing a possibility to attain the same micellar effects at the surfactant concentration lower by an order of magnitude (and yet even lower) than in the case of monomeric analogs.

A multisubstrate assay for lipases/esterases: Assessing acyl chain length selectivity by reverse-phase high-performance liquid chromatography

Lipases and esterases are hydrolytic enzymes and are known to hydrolyze esters with unique substrate specificity and acyl chain length selectivity. We have developed a simple competitive multiple substrate assay for determination of acyl chain length selectivity of lipases/esterases using RP-HPLC with UV detection. A method for separation and quantification of 4-nitrophenyl fatty acid esters (C4–C18) was developed and validated. The chain length selectivity of five lipases and two esterases was determined in a multisubstrate reaction system containing equimolar concentrations of 4-nitrophenyl esters (C4–C18). This assay is simple, reproducible, and a useful tool for determining chain length selectivity of lipases/esterases.

Synthesis, characterisation and some chemistry of C- and B-substituted carboxylic acids of cobalt bis(dicarbollide)

Low temperature reactions of lithiated cobalt bis(1,2-dicarbollide)(1-) (1⁻) in DME with carbon dioxide leads to the substitution of 1⁻ at the C-atoms by carboxy function(s). This results in a good yield formation of monosubstituted and disubstituted products of formulations [(1-HOOC-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co)](-) (2⁻) and [(HOOC)2-(1,2-C2B9H10)2-3,3'-Co](-) (3a,b⁻), respectively. Indeed, the latter compound is in fact a mixture of two diastereoisomers, denoted here as 1,1'-anti (3a⁻) and 1,2'-syn-isomer (3b⁻), from which only the former major species (3a⁻) could be isolated in pure form. Considerations about stereochemistry of these species are supported by geometry optimizations and calculations of (11)B NMR shifts at the GIAO-DFT level. In addition, three monocarboxylic acids with three different linear spacers between the carboxy groups and the cage are reported. The first one of the formula [(1-HOOC-CH2-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co](-) (5⁻) results in a lithiation followed by reaction with BrCH2COOEt and hydrolysis of the respective ethyl ester (4⁻). Another one with ethylene chain [(1-HOOC-(CH2)2-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co](-) (6⁻) was prepared by the oxidation of a hydroxypropyl derivative of the ion 1⁻. The sole representative of B-substituted species of the formulation [8-(HOOC-CH2-O-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co](-) (7⁻) is prepared by alkylation of the known 8-hydroxy derivatives of the ion 1⁻ by BrCH2COOEt and alkaline hydrolysis. A synthetic route to active nitrofenyl esters (8⁻, 9⁻ and 10⁻) is described here based on the respective acids 5⁻ to 7⁻. As verified, the nitrophenyl esters provide easy access to the formation of amidic bonds between the boron cage and organic primary amino functions. Examples of compounds containing butylamide or benzylamide [(1-RNHOC-(CH2)n-1,2-C2B9H10)(1',2'-C2B9H11)-3,3'-Co](-) (n = 1,2; R = Bu 11a,b⁻, R = Bn: 12a,b⁻) end group are described. Also the possibility of inter-connecting two clusters of the anion 1⁻ via the amidic bond is shown in derivative (13⁻). These methods are applicable in the synthesis of a variety of functional molecules, particularly those applicable in drug design, surface modifications, and material science.

Cloning, expression and characterization of a new enantioselective esterase from a marine bacterium Pelagibacterium halotolerans B2T

• An esterase was cloned from a marine bacterium and overexpressed in Escherichia coli . • The enzyme was alkalitolerance and halotolerance. • The enzyme preferred short chain p -nitrophenyl esters, and was not a metalloenzyme. • The enzyme was useful in the synthesis of methyl ( R )-3-(4-fluorophenyl)glutarate. • ( R )-3-MFG was obtained in 71.6% ee and 73.2% yield after 36 h reaction. An esterase, designated as PE8 (219 aa, 23.19 kDa), was cloned from a marine bacterium Pelagibacterium halotolerans B2 T and overexpressed in Escherichia coli Rosetta, resulting an active, soluble protein which constituted 23.1% of the total cell protein content. Phylogenetic analysis of the protein showed it was a new member of family VI lipolytic enzymes. Biochemical characterization analysis showed that PE8 preferred short chain p -nitrophenyl esters (C2–C6), exhibited maximum activity toward p -nitrophenyl acetate, and was not a metalloenzyme. PE8 was an alkaline esterase with an optimal pH of 9.5 and an optimal temperature of 45 °C toward p -nitrophenyl acetate. Furthermore, it was found that PE8 exhibited activity and enantioselectivity in the synthesis of methyl ( R )-3-(4-fluorophenyl)glutarate (( R )-3-MFG) from the prochiral dimethyl 3-(4-fluorophenyl)glutarate (3-DFG). ( R )-3-MFG was obtained in 71.6% ee and 73.2% yield after 36 h reaction under optimized conditions (0.6 M phosphate buffer (pH 8.0) containing 17.5% 1,4-dioxane under 30 °C). In addition, PE8 was tolerant to extremely strong basic and high ionic strength solutions as it exhibited high activity even at pH 11.0 in 1 M phosphate buffer. Given its highly soluble expression, alkalitolerance, halotolerance and enantioselectivity, PE8 could be a promising candidate for the production of ( R )-3-MFG in industry. The results also demonstrate the potential of the marine environment as a source of useful biocatalysts.

Supernucleophilic systems based on functionalized surfactants in the decomposition of 4-nitrophenyl esters derived from phosphorus and sulfur acids: I. Reactivity of a hydroxyimino derivative of gemini imidazolium surfactant

A new functionalized gemini surfactant, 3,3′-[2-(hydroxyimino)propane-1,3-diyl]bis(1-dodecyl-1H-imidazol-3-ium) dichloride, and its non-micelle-forming methyl analog, were synthesized. Nucleophilicity of the oximate group in these compounds in the decomposition of 4-nitrophenyl esters derived from phosphorus and sulfur acids follows Bronsted relations for monomeric functionalized surfactants and non-micelle-forming oximes. As compared to the single-chained analog, the gemini surfactant ensured the same observed rate of substrate decomposition at lower concentration and lower pH. Micellar effects of the gemini surfactant in these reactions attain a value of ∼103 and are determined mainly by substrate concentration in the micellar pseudophase.

Cell surface display of Staphylococcus haemolyticus L62 lipase in Escherichia coli and its application as a whole cell biocatalyst for biodiesel production

• Plasmid pPELB-Tu::L62 was constructed to display SHL62 lipase on the surface of Escherichia coli using EstAβ8 domain as an anchoring motif. • SHL62 lipase was successfully displayed on the cell surface of E. coli . • The displayed SHL62 lipase was used as a whole cell biocatalyst for biodiesel production. Staphylococcus haemolyticus L62 (SHL62) lipase was displayed on the cell surface of Escherichia coli using an autotransporter protein of Pseudomonas putida EstAβ8 as an anchoring motif. Localization of the SHL62 lipase on the cell surface of E. coli was confirmed by immunofluorescence microscopy, flow cytometry analysis, Western blot, protease accessibility, and whole-cell enzyme activity assays. SHL62 lipase activity of whole cells reached 168 U/g dry cell weight toward p -nitrophenyl caprylate after being induced by 0.1 mM IPTG for 24 h. The optimum temperature and pH of the displayed SHL62 lipase was 40–45 °C and pH 10, respectively. The displayed SHL62 was stable up to 45 °C, at which it had >80% of maximum activity. The displayed SHL62 lipase showed a preference for medium chain fatty acids of p -nitrophenyl esters. Moreover, the displayed SHL62 lipase was used as a whole cell catalyst to produce biodiesel that was obtained at a yield of nearly 89.4% after a 96 h reaction at 30 °C. These results suggest that the displayed SHL62 lipase on the cell surface of E. coli using an EstAβ8 anchoring motif can be used for biocatalytic applications.

Study of the Kulinkovich Synthesis of 1-Methylcyclopropanol and Its Conversion into 1-Methylcyclopropyl 4-Nitrophenyl Carbonate

A detailed investigation of the preparation of 1-methylcyclopropanol via the Kulinkovich reaction is presented. Reaction and workup parameters were optimized to provide a reproducible procedure for the synthesis of multigram quantities of 1-methylcyclopropanol. Key improvements were the use of titanium tetra(2-ethyl)hexyloxide as catalyst, reduction in the volume of reaction solvent, addition of the methyl acetate starting material in portions, and azeotropic distillation to remove by-products. The preparation of the 4-nitrophenyl carbonate ester was likewise studied and optimized.

Influence of ammonium salts on the lipase/esterase activity assay using p‐nitrophenyl esters as substrates

p-Nitrophenyl esters with a short-chain carboxylic group, such as p-nitrophenyl acetate (p-NPA) and p-nitrophenyl butyrate (p-NPB), could be effectively hydrolyzed by ammonium salts. p-Nitrophenyl esters were usually used as substrates to assay the lipase/esterase activity. Ammonium sulfate precipitation was often used to purify proteins, and some ammonium salts were usually used as nitrogen sources or inorganic salts for the lipase/esterase production. To study the effect of ammonium salts on the assay of the lipase/esterase activity, the contributing factors of hydrolysis of p-NPA/p-NPB catalyzed by ammonium salts were investigated. The lipase activities were compared in the presence and absence of ammonium sulfate. The hydrolysis reaction could be catalyzed under neutral and alkaline circumstances. The hydrolysis rate increased with the increase in the reaction temperature or the concentration of ammonium ion. When p-NPA was employed as the substrate for the analysis of the lipase/esterase activity, the effect of ammonium sulfate on the analysis could be neutralized by setting a control when the concentration of ammonium sulfate was less than 40% saturation. However, when the concentration of ammonium sulfate increased from 40% to 100% saturation, the enzyme activities decreased about 13-40%, which could not be ignored for accurate analysis of the enzyme activity.

Reactivity of the H2O2/B(OH)3/HO- system in the decomposition of 4-nitrophenyl esters of diethylphosphonic and diethylphosphoric acids

The kinetics of the decomposition of 4-nitrophenyl diethylphosphonate and 4-nitrophenyl diethyl phosphate by the H2O2/B(OH)3/HO– system with wide variation of the pH and the initial concentrations of H2O2 and B(OH)3 (water, 25°C) was studied. Additions of boric acid either weakly accelerate the reaction or retard it, depending on the ratio of the initial concentrations of hydrogen peroxide and boric acid and on the nature of the substrate. The peroxoborate anions (HO)3BOOH–, (HO)2B(OOH) 2 – , and (HO)3BOOB(OH) 3 2– anions generated by this system do not affect the decomposition rate of the substrates. In both substrates linear relationships were found between the observed rate constants k and the concentrations of peroxide anion.

Synthesis and characterization of a new polymer–drug conjugate with pH-induced activity

A well-defined, stimuli-responsive tetrapolymer with pH-responsive characteristics and targeting specificity has been synthesized by radical copolymerization of methacrylic acid, N-(2-hydroxypropyl)methacrylamide, methacryloyl glycylglycyl sulfamethoxazole, and N-(methacryloyl)glycylglycine 4-nitrophenyl ester. The structure and properties of tetrapolymer were investigated by NMR, FT-IR, UV–visible absorption, TEM and gel permeation chromatography. Incorporation of maleimide linker into tetrapolymer facilitates its conjugation with antibody fragments, as demonstrated by the solid-phase immunoassay experiments. The TEM image shows that tetrapolymer had self-assembled a spherical micelle with a diameter ranging from 50 to 150 nm. Altering the pH of the solution leads to a different extent of aggregation at pH 6.5–3.5, responding in accordance with the properties associated with the extracellular environment of solid tumors and endocytosis. Furthermore, fluorescence spectroscopy indicated a critical micelle concentration (CMC) of 1 mg/mL. Because of the solvation and ionization effects, the tetrapolymer showed considerably enhanced antibacterial activities against Escherichia coli in the presence of DMSO and the antibacterial activity increased with decreasing pH value.