Alkaline Hydrolysis (alkaline + hydrolysis)

Distribution by Scientific Domains
Distribution within Chemistry

Selected Abstracts

Analysis of Linear Free-Energy Relationships Combined with Activation Parameters Assigns a Concerted Mechanism to Alkaline Hydrolysis of X-Substituted Phenyl Diphenylphosphinates

Ik-Hwan Um Prof.
Abstract A kinetic study is reported for alkaline hydrolysis of X-substituted phenyl diphenylphosphinates (1,a,i). The Brønsted-type plot for the reactions of 1,a,i is linear over 4.5 pKa units with ,lg=,0.49, a typical ,lg value for reactions which proceed through a concerted mechanism. The Hammett plots correlated with ,o and ,, constants are linear but exhibit many scattered points, while the corresponding Yukawa,Tsuno plot results in excellent linear correlation with ,=1.42 and r=0.35. The r value of 0.35 implies that leaving-group departure is partially advanced at the rate-determining step (RDS). A stepwise mechanism, in which departure of the leaving group from an addition intermediate occurs in the RDS, is excluded since the incoming HO, ion is much more basic and a poorer nucleofuge than the leaving aryloxide. A dissociative (DN + AN) mechanism is also ruled out on the basis of the small ,lg value. As the substituent X in the leaving group changes from H to 4-NO2 and 3,4-(NO2)2, ,H,, decreases from 11.3,kcal,mol,1 to 9.7 and 8.7,kcal,mol,1, respectively, while ,S,, varies from ,22.6,cal,mol,1,K,1 to ,21.4 and ,20.2,cal,mol,1,K,1, respectively. Analysis of LFERs combined with the activation parameters assigns a concerted mechanism to the current alkaline hydrolysis of 1,a,i. [source]

Hydrolysis of an isolable selenoseleninate under acidic and alkaline conditions

Akihiko Ishii
Acid-catalyzed hydrolysis of a selenoseleninate [TripSe(O)SeTrip](Trip = 9-triptycyl) in 2 M HClO4 -1,4-dioxane at room temperature yielded the selenenic acid (TripSeOH). Alkaline hydrolysis of TripSe(O)SeTrip gave the diselenide (TripSeSeTrip) and the seleninic acid (TripSeO2H), where air oxidations of the resulting selenol (TripSeH) and TripSeOH occur at a considerable rate. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:198,203, 2001 [source]

Alkaline hydrolysis of cinnamaldehyde to benzaldehyde in the presence of ,-cyclodextrin

AICHE JOURNAL, Issue 2 2010
Hongyan Chen
Abstract A facile, novel, and cost-effective alkaline hydrolysis process of cinnamaldehyde to benzaldehyde under rather mild conditions has been investigated systematically in the presence of ,-cyclodextrin (,-CD), with water as the only solvent. ,-CD could form inclusion complex with cinnamaldehyde in water, with molar ratio of 1:1, so as to promote the reaction selectivity. The complex has been investigated experimentally and with computational methods. 1H-NMR, ROESY, UV,Vis, and FTIR have been utilized to analyze the inclusion complex. It shows that the equilibrium constant for inclusion (Ka) is 363 M,1, and the standard Gibbs function for the reaction, ,,G (298 K), is ,14.6 kJ mol,1. In addition, the structures of the proposed inclusion compounds were optimized with hybrid ONIOM theory. Benzaldehyde could be obtained at an yield of 42% under optimum conditions [50°C, 18 h, 2% NaOH (w/v), cinnamaldehyde:,-CD (molar ratio) = 1:1]. To explain the experimental data, NMR, FTIR, and elemental analysis results were used to determine the main reaction by-product 1-naphthalenemethanol. A feasible reaction mechanism including the retro-Aldol condensation of cinnamaldehyde and the Aldol condensation of acetaldehyde and cinnamaldehyde in basic aqueous ,-CD solution has been proposed. The calculated activation energy for the reaction was 45.27 kJ mol,1 by initial concentrations method. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Hydrolysis of oxaliplatin,evaluation of the acid dissociation constant for the oxalato monodentate complex

Elin Jerremalm
Abstract Alkaline hydrolysis of the platinum anticancer drug oxaliplatin gives the oxalato monodentate complex and the dihydrated oxaliplatin complex in two consecutive steps. The acid dissociation constant for the oxalato monodentate intermediate was determined by a kinetic approach. The pKa value was estimated as 7.23. The monodentate intermediate is assumed to rapidly react with endogenous compounds, resulting in a continuous conversion of oxaliplatin via the monodentate form. © 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 92:436,438, 2003 [source]

Synthesis of rhombohedral strontium carbonate aggregates at the water/hexamethylene interface with cetyltrimethylammonium bromide

Long Chen
Abstract Unusual rhombohedral strontium carbonate (SrCO3) aggregates have been synthesized in situ from strontium nitrate by the slow release of carbon dioxide by alkaline hydrolysis of diethyl carbonate at the water/hexamethylene interface in the presence of cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray powder diffractometry were used to characterize the products. The results indicate that rhombohedral SrCO3 aggregates are obtained with weaker crystallinity and sizes of several micrometers. The possible formation mechanism of the SrCO3 aggregates at the interface is discussed, which can be interpreted by particle-aggregation based non-classical crystallization laws. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Synthesis of Phenyl Arylsulfonyl-alkyl-dithiocarbamates and Their Hydrolytic Reactivity in Hydroxide and Hydroperoxide Media

Fátima Norberto
Abstract Eight previously unreported phenyl arylsulfonyl-alkyl-dithiocarbamates were synthesized by treatment of arylsulfonamides with phenyl chlorodithioformate in an adaptation of a general amine acylation method. A kinetic investigation of their alkaline hydrolysis was performed and the experimental data are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

tmRNA from Thermus thermophilus

FEBS JOURNAL, Issue 3 2003
Interaction with alanyl-tRNA synthetase, elongation factor Tu
The interaction of a Thermus thermophilus tmRNA transcript with alanyl-tRNA synthetase and elongation factor Tu has been studied. The synthetic tmRNA was found to be stable up to 70 °C. The thermal optimum of tmRNA alanylation was determined to be around 50 °C. At 50 °C, tmRNA transcript was aminoacylated by alanyl-tRNA synthetase with 5.9 times lower efficiency (kcat/Km) than tRNAAla, primarily because of the difference in turnover numbers (kcat). Studies on EF-Tu protection of Ala,tmRNA against alkaline hydrolysis revealed the existence of at least two different binding sites for EF-Tu on charged tmRNA. The possible nature of these binding sites is discussed. [source]

Determination of enalapril and enalaprilat by enzyme linked immunosorbent assays: application to pharmacokinetic and pharmacodynamic analysis

Khalid Matalka
We have developed two enzyme linked immunosorbent assay (ELISA) methods for determining enalapril and enalaprilat in plasma. In this study, 48 healthy subjects received an oral dose of either 10 or 20 mg of enalapril and plasma concentrations of enalapril and enalaprilat were determined by their specific ELISA methods. These plasma concentrations and blood pressure measurements were applied to evaluate the pharmacokinetic (PK) and pharmacodynamic (PD) parameters of both enalapril and enalaprilat. The enalapril values for the area under the curve (AUC0,,) were 480 ± 216 and 832 ± 325 ngh/mL, maximum plasma concentrations (Cmax) were 310 ± 187 and 481 ± 185 ng/mL, and times required to reach the maximum concentration (tmax) were 1.13 ± 0.22 and 1.09 ± 0.33 h for 10 and 20 mg doses, respectively. The enalaprilat values for AUC0,, were 256 ± 122 and 383 ± 158 ngh/mL, Cmax values were 57 ± 29 and 72.9 ± 33.6 ng/mL and tmax values were 4.28 ± 1.45 and 4.05 ± 01.22 h for 10 and 20 mg doses, respectively. The Cmax values of enalapril were ,10 times higher than those in the literature, which were determined by angiotensin converting enzyme (ACE) inhibition assays following alkaline hydrolysis, but similar to those of enalaprilat. The PD profiles revealed a significant correlation between enalaprilat concentrations in plasma and the decrease in systolic and diastolic blood pressures (r=,0.95 with P < 0.001 and r=,0.95 with P < 0.001), respectively, following a single oral dose of enalapril. These ELISA methods have the advantage of being simple, accurate, sensitive, and do not depend on enalaprilat binding to ACE. Such methods can be used for analysis and kinetic testing of enalapril and enalaprilat in biological fluids. [source]

Kinetics and mechanism of alkaline hydrolysis of 4-nitrophthalimide in the absence and presence of cationic micelles

M. Niyaz Khan
Pseudo-first-order rate constants (kobs) for alkaline hydrolysis of 4-nitrophthalimide (NPTH) decreased by nearly 8- and 6-fold with the increase in the total concentration of cetyltrimethyl-ammonium bromide ([CTABr]T) from 0 to 0.02 M at 0.01 and 0.05 M NaOH, respectively. These observations are explained in terms of the pseudophase model and pseudophase ion-exchange model of micelle. The increase in the contents of CH3CN from 1 to 70% v/v and CH3OH from 0 to 80% v/v in mixed aqueous solvents decreases kobs by nearly 12- and 11-fold, respectively. The values of kobs increase by nearly 27% with the increase in the ionic strength from 0.03 to 3.0 M. The mechanism of alkaline hydrolysis of NPTH involves the reactions between HO, and nonionized NPTH as well as between HO, and ionized NPTH. The micellar inhibition of the rate of alkaline hydrolysis of NPTH is attributed to medium polarity effect. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 407,414, 2001 [source]

Poly(ethylene terephthalate) recycling and recovery of pure terephthalic acid by alkaline hydrolysis

G. P. Karayannidis
Abstract Poly(ethylene terephthalate) (PET) taken from postconsumer soft-drink bottles was subjected to alkaline hydrolysis after cutting it into small pieces (flakes). The reaction took place in an autoclave at 120,200°C with aqueous NaOH solutions and at 110,120°C with a nonaqueous solution of KOH in methyl Cellosolve. The disodium or dipotassium terephthalate received was treated with sulfuric acid and terephthalic acid (TPA) of high purity was separated. The 1H NMR spectrum of the TPA revealed an about 2% admixture of isophthalic acid together with the pure 98% TPA. The purity of the TPA obtained was tested by determining its acidity and by polymerizing it with ethylene glycol by using tetrabutyl titanate as catalyst. A simple theoretical model was developed to describe the hydrolysis rate. The activation energy calculated was 99 kJ/mol. This method is very useful in recycling of PET bottles and other containers because nowadays TPA is replacing dimethyl terephthalate (the traditional monomer) as the main monomer in the industrial production of PET. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 250,259, 2002; Published online in Wiley InterScience ( DOI 10.1002/adv.10029 [source]

Direct hydroxide attack is a plausible mechanism for amidase antibody 43C9,

Lillian T. Chong
Abstract Direct hydroxide attack on the scissile carbonyl of the substrate has been suggested as a likely mechanism for esterase antibodies elicited by phosphonate haptens, which mimic the transition states for the alkaline hydrolysis of esters.1 The unique amidase activity of esterase antibody 43C9 has been attributed to nucleophilic attack by an active-site histidine residue.2 Yet, the active site of 43C9 is strikingly similar to those of other esterase antibodies, particularly 17E8. We have carried out quantum mechanical calculations, molecular dynamics simulations, and free energy calculations to assess the mechanism involving direct hydroxide attack for 43C9. Results support this mechanism and suggest that the mechanism is plausible for other antiphosphonate antibodies that catalyze the hydrolysis of (p -nitro)phenyl esters. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1371,1377, 2003 [source]


ABSTRACT A large amount of waste permeates generated from the processing of yellow mustard protein was concentrated fivefold using a nanofilter with a molecular weight cut off of 1,000 Da, while approximately 74% of sinapic acid was retained. Sinapic acid was then released from sinapine, its esterified form, by an alkaline hydrolysis. The hydrolyzed solution was acidified to prevent oxidation of the sinapic acid and to precipitate the remaining proteins. Subsequently, sinapic acid and other phenolics were extracted by a two-stage extraction using a mixture of diethyl ether and ethyl acetate (1:1), 165-min extraction time and permeate-to-solvent ratio of 1:2. Approximately 95% of the sinapic acid in the acidified permeate was finally concentrated in the solvent phase. PRACTICAL APPLICATIONS This development has led to an economical process to recover phenolics and to treat effluent from a process of oilseed protein while reducing the use of water during the extraction of protein. A reduction of water usage makes the processing of oilseed protein isolate more economically attractive, and the recovered phenolics may find a use as a nutraceutical. The developed process is not only limited to the recovery of phenolics from mustard, but also applied for recovering phenolic acids, specifically sinapic acid, from waste water from membrane processing of protein from mustard and similar polyphenol-containing oilseeds. [source]

Synthesis, structure, and some chemical properties of diferrocenyl-1,2,3-triazines

Elena I. Klimova
The reactions of 1-amino-2,3-diferrocenylcyclopropenylium tetrafluoroborate (5a,c) or 2,3-diferrocenyl-1-methylthiocyclopropenylium iodide with sodium azide afford 5-amino-4,6-diferrocenyl-1,2,3-triazines (7a,c) or 5-methylthio-4,6-diferrocenyl- and 4-methylthio-5,6-diferrocenyl-1,2,3-triazines (8a and 8b), respectively. Their structures were established using spectroscopic methods and that of compound 8a was confirmed using X-ray diffraction analysis. Triazines 5a,c react with alkyl iodides to yield N(2)- and N-alkyl-C(5)-derivatives. Their alkaline hydrolysis results in 2-methyl-4,6-diferrocenyl-2,5-dihydro-1,2,3-triazin-5-one (16) and 4,6-diferrocenyl-5-hydroxy-1,2,3-triazine (17). J. Heterocyclic Chem., 46, 477 (2009). [source]

Synthesis and properties of novel macrocyclic compounds bearing thiourea moieties by use of chemical feature of hypervalent sulfur

Noboru Matsumura
Macrocyclic compounds 5a-i bearing two tetraazathiapentalene frameworks were synthesized by the reaction of 10-S-3 tetraazathiapentalene derivatives 3a-f with compounds having various diisothiocyanate functions 4a-e. The reduction of the macrocyclic compounds with NaBH4 afforded the ring-opened macrocyclic compounds 11a-b and 11e-h by elimination of the hypervalent sulfur. The structures of these compounds were established by their spectral data and also by the X-ray crystallographic analysis of lla. The other ring-opened macrocyclic compounds 14a and 14e-h that bear four thiourea groups were synthesized by alkaline hydrolysis of 5a and 5e-h in that elimination of the C=SIV moiety in the tetraazathiapentalene rings occurred. [source]

The mechanism of alkaline hydrolysis of amides: a comparative computational and experimental study of the hydrolysis of N -methylacetamide, N -methylbenzamide, and acetanilide

Diana Cheshmedzhieva
Abstract Theoretical computations and experimental kinetic measurements were applied in studying the mechanistic pathways for the alkaline hydrolysis of three secondary amides: N -methylbenzamide, N -methylacetamide, and acetanilide. Electronic structure methods at the HF/6-31+G(d,p) and B3LYP/6-31+G(d,p) levels of theory are employed. The energies of the stationary points along the reaction coordinate were further refined via single point computations at the MP2/6-31+G(d,p) and MP2/6-311++G(2d,2p) levels of theory. The role of water in the reaction mechanisms is examined. The theoretical results show that in the cases of N -methylbenzamide and N -methylacetamide the process is catalyzed by an ancillary water molecule. The influence of water is further assessed by predicting its role as bulk solvent. The alkaline hydrolysis process in aqueous solution is characterized by two distinct free energy barriers: the formation of a tetrahedral adduct and its breaking to products. The results show that the rate-determining stage of the process is associated with the second transition state. The entropy terms evaluated from theoretical computations referring to gas-phase processes are significantly overestimated. The activation barriers for the alkaline hydrolysis of N -methylbenzamide and acetanilide were experimentally determined. Quite satisfactory agreement between experimental values and computed activation enthalpies was obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Effects of non-ionic and mixed cationic,non-ionic micelles on the rate of alkaline hydrolysis of phthalimide

M. Niyaz Khan
Abstract Pseudo-first-order rate constants (kobs) for the alkaline hydrolysis of phthalimide (PTH) show a monotonic decrease with the increase in [C16E20]T (total concentration of Brij 58) at constant [CH3CN] and [NaOH]. This micellar effect is explained in terms of the pseudophase model of micelles. The rate of hydrolysis of PTH in C16E20 micellar pseudophase appears to be negligible compared with that in the aqueous pseudophase. The values of kobs for C12E23 (Brij 35) show a sharp decrease at very low values of [C12E23]T followed by a very slow decrease with increase in [C12E23]T at relatively higher values of the latter. The rate of hydrolysis becomes too slow to monitor at [C12E23]T ,0.04,M in the absence of cetyltrimethylammonium bromide (CTABr) and at [C12E23]T ,0.05,M in the presence of 0.006,0.02,M CTABr at 0.02,M NaOH whereas such characteristic behavior is kinetically absent with C16E20. The values of kobs, obtained at different [NIS]T (where NIS represents C16E20 and C12E23) in the presence of a constant amount of CTABr, follow the empirical relationship kobs,=,(k0,+,kK[NIS]T)/(1,+,K[NIS]T) where k and K are empirical parameters. The values of k are only slightly affected whereas the values of K decrease with increase in [CTABr]T for the mixed C16E20,CTABr micellar system. The rate of hydrolysis of PTH at ,0.01,M C12E23 and ,0.01,M CTABr reveals the formation of phthalic anhydride whereas this was not observed in the mixed C16E20,CTABr micellar system under similar experimental conditions. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Synthesis and properties of novel soluble polyamides having ether linkages and laterally attached p -terphenyl units

Sheng-Huei Hsiao
Abstract A new ether-bridged aromatic dicarboxylic acid, 2,,5,-bis(4-carboxyphenoxy)- p -terphenyl (3), was synthesized by the aromatic fluoro-displacement reaction of p -fluorobenzonitrile with 2,,5,-dihydroxy- p -terphenyl in the presence of potassium carbonate, followed by alkaline hydrolysis. A set of new aromatic polyamides containing ether and laterally attached p -terphenyl units was synthesized by the direct phosphorylation polycondensation of diacid 3 with various aromatic diamines. The polymers were produced with high yields and moderately high inherent viscosities (0.44,0.79 dL/g). The polyamides derived from 3 and rigid diamines, such as p -phenylenediamine and benzidine, and a structurally analogous diamine, 2,,5,-bis(4-aminophenoxy)- p -terphenyl, were semicrystalline and insoluble in organic solvents. The other polyamides were amorphous and organosoluble and could afford flexible and tough films via solution casting. These films exhibited good mechanical properties, with tensile strengths of 91,108 MPa, elongations to break of 6,17%, and initial moduli of 1.95,2.43 GPa. These polyamides showed glass-transition temperatures between 193 and 252 °C. Most of the polymers did not show significant weight loss before 450 °C, as revealed by thermogravimetric analysis in nitrogen or in air. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4056,4062, 2004 [source]

Synthesis, characterization, and in vitro degradation of thermotropic polyesters and copolyesters based on terephthalic acid, 3-(4-hydroxyphenyl)propionic acid, and glycols

Minoru Nagata
Abstract A new series of thermotropic liquid-crystalline (LC) polyesters were prepared from a diacyl chloride derivative of 4,4,-(terephthaloyldioxy)-di-4-phenylpropionic acid (PTP) and glycols with a different number of methylene groups (n) [HO(CH2)n OH, n = 6,10, 12] by high-temperature solution polycondensation in diphenyl oxide. PTP6/10 and PTP6/hydroquinone (H) LC copolyesters were also prepared according to a similar procedure. The chemical structure, LC, phase-transition behaviors, thermal stability, and solubility were characterized by elemental analysis, Fourier transform infrared spectroscopy, 1H and 13C NMR spectra, differential scanning calorimetry (DSC), thermogravimetric analysis, and a polarizing light microscope. The melting and isotropization temperatures decreased in a zigzag manner as the number of n increased. All of the polyesters formed a nematic phase with the exception of PTP8. The temperature ranges of the mesophase (,T) were much wider for the polyesters with an odd number of n's than those with an even number. ,T increased markedly for the PTP6/10 and PTP6/H copolyesters. The in vitro degradations of the polymers were ascertained by enzymatic hydrolysis and alkaline hydrolysis. The model compound, PTP dihexylester, was synthesized and found to be degraded into terephthalic acid, 3-(4-hydroxyphenyl)propionic acid, and 1-hexanol by Rhizopus delemar lipase, but PTPn homopolyesters and PTP6/10 and PTP6/H copolyesters were resistant to Rhizopus delemar hydrolysis. They were degradable in a sodium hydroxide buffer solution of pH 12 at 60 °C, depending on the number of n's and the copolymer composition. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3043,3051, 2001 [source]

Phenols in spikelets and leaves of field-grown oats (Avena sativa) with different inherent resistance to crown rust (Puccinia coronata f. sp. avenae)

Lena H Dimberg
Abstract BACKGROUND: Avenanthramides, health-beneficial phenols in oats, are produced in response to incompatible races of the crown rust fungus, Puccinia coronata, in seedlings of greenhouse-grown oats. This study aimed to elucidate whether avenanthramides and/or other phenolic compounds, together with the activities of phenylalanine ammonia lyase (PAL), phenoloxidase (PO) and the avenanthramide biosynthetic enzyme hydroxycinnamoyl-CoA:hydroxyanthranilate- N -hydroxycinnamoyl transferase (HHT), are associated with crown rust infection in mature field-grown oats. Nine oat (Avena sativa L.) genotypes with wide variation in crown rust resistance were exposed to naturally occurring fungal spores during the growth period. RESULTS: In the spikelets avenanthramides as well as HHT activities were more abundant in the crown rust resistant genotypes, whereas p -coumaric and caffeic acids were more abundant in the susceptible ones. In the leaves avenanthramides were not associated with resistance. Instead two unknown compounds correlated negatively with the rust score. Phenols released by alkaline hydrolysis and PAL and PO activities were not related to rust infection, either in spikelets or in the leaves. CONCLUSION: Because grains of crown rust-resistant oat genotypes seemed to have higher endogenous levels of health-promoting avenanthramides, use of resistant oats may contribute to a food raw material with health-beneficial effects. Copyright © 2009 Society of Chemical Industry [source]

Evaluation of lignans and free and linked hydroxy-tyrosol and tyrosol in extra virgin olive oil after hydrolysis processes

Nadia Mulinacci
Abstract We describe chemical hydrolytic procedures to evaluate the total amount of tyrosol and hydroxy-tyrosol free and/or linked to secoiridoidic molecules (acid hydrolysis). At the same time a rapid determination of the lignans in complex minor polar compound (MPC) extracts is proposed (alkaline hydrolysis). High-performance liquid chromatography/diode array detection (HPLC/DAD) and HPLC/MS were applied as reference methods to evaluate the quantitative results from the hydrolysis experiments. The optimized acid hydrolysis procedures were first applied to an oleuropein standard and then to MPC fractions extracted from several commercial extra virgin olive oils. The results confirm the applicability of the method, consisting in the acid hydrolysis of complex mixtures of secoiridoidic derivatives, to determine the antioxidant potential in terms of MPC. These data can contribute to forecasting the potential ageing resistance of an extra virgin olive oil in terms of antioxidant potency. Finally, alkaline hydrolysis allows confirmation and easy determination of the amount of lignans, especially in those MPC fractions which are particularly complex. Copyright © 2006 Society of Chemical Industry [source]

Preparation of Water-Absorbing Polyacrylonitrile Nanofibrous Membrane

Haiqing Liu
Abstract Summary: Hydrophilic acrylic nanofibers were prepared from alkaline hydrolysis of hydrophobic polyacrylonitrile (PAN) nanofibers. Water contact angle, pore volume, and liquid retention capacity of PAN nanofibrous membranes were measured to determine their dependence on hydrolysis parameters such as base concentration, temperature, and time. Vertical water retention capacity of hydrolyzed PAN nanofibrous membrane could reach as large as 200 times of that of original membrane. Fiber twinning in post-hydrolyzed PAN nanofibrous membrane. [source]

Molar Mass and Structural Characteristics of Poly[(lactide- co -(aspartic acid)] Block Copolymers

Ida Poljan
Abstract Summary: We report on various synthetic procedures for the preparation of biodegradable and biocompatible poly(lactide- co -aspartic acid) block copolymers based on natural monomeric units , lactic acid and aspartic acid. Multiblock poly(lactide- co -aspartic acid) copolymers of different comonomer composition were synthesized by heating a mixture of L-aspartic acid and L,L-lactide in melt without the addition of any catalyst or solvent and with further alkaline hydrolysis of the cyclic succinimide rings to aspartic acid units. Diblock poly(lactide- co -aspartic acid) copolymers with different block lengths were prepared by copolymerization of amino terminated poly(, -benzyl-L-aspartate) homopolymer and L,L-lactide with subsequent deprotection of the benzyl protected carboxyl group by hydrogenolysis. The differences in the structure, composition, molar mass characteristics, and water-solubility of the synthesized multiblock and diblock poly(lactide- co -aspartic acid) copolymers are discussed. [source]

Partially hydrolyzed kappa carrageenan,polyacrylonitrile as a novel biopolymer-based superabsorbent hydrogel: Synthesis, characterization, and swelling behaviors

M. T. Savoji
In this paper, synthesis and swelling behavior of a novel superabsorbent hydrogel based on kappa carrageenan (,C) and polyacrylonitrile (PAN) was investigated. To achieve partially hydrolyzed ,C-PAN hydrogel, physical mixture of ,C and PAN was hydrolyzed by NaOH solution. During alkaline hydrolysis, the nitrile groups of PAN are converted to a mixture of hydrophilic carboxamide and carboxylate groups follow by in situ crosslinking of the grafted PAN chains. The reaction variables affecting on the swelling capacity of the hydrogel were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Under the optimized conditions concluded, super swelling hydrogel with the ability of water absorption up to 3260 g/g (water/dry hydrogel powder) has been prepared. Swelling measurements of the synthesized hydrogels was carried out in various salt solutions and solutions with different pH. The results indicate that the hydrogels have good pH sensitivity and pH-reversible property between pH 2 and pH 8. POLYM. ENG. SCI. 46:1778,1786, 2006. © 2006 Society of Plastics Engineers. [source]

Structure determination of oligomeric alkannin and shikonin derivatives

Apostolos Spyros
Abstract Monomeric alkannin and shikonin (A/S) are potent pharmaceutical substances with a wide spectrum of biological activity and comprise the active ingredients for several pharmaceutical preparations. Therefore, the determination of the impurities, degradation products or byproducts in alkannin and shikonin samples is of great importance. Oligomeric alkannin and shikonin are formed during biosynthesis of these bioactive secondary metabolites in Boraginaceaous root plants, during tissue culture production of A/S, during alkaline hydrolysis of A/S esters and also thermal treatment of A/S. In the present study, a dimeric alkannin/shikonin compound was isolated by size exclusion chromatography from alkannin and shikonin commercial samples and its structure was determined by one- and two-dimensional NMR spectroscopy. The structure of the most abundant oligomeric species in these samples, a dimeric naphthoquinone, was established for the ,rst time, indicating that coupling of the side chain of one naphthoquinone unit with the aromatic ring of a second naphthoquinone leads to dimer formation. This type of coupling allows further oligomerization by leaving one isohexenyl side chain available at the second monomer unit. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Conformations and properties of the L -tryptophyl-containing peptides in solution, depending on the pH,Theoretical study vs. experiments

BIOPOLYMERS, Issue 8 2010
Bojidarka B. Ivanova
Abstract The conformational preference and electronic properties of three L -tryptophyl-containing dipeptides, i.e., glycyl- L -tryptophane (H-Gly-Trp-OH), L -alanyl- L -tryptophane (H-Ala-Trp-OH), and L -methionyl- L -tryptophane (L -Met-Trp-OH) in solution depending on the pH of the media are studied both theoretically and experimentally. The effect of the protonation of the COO, and deprotonation of the NH as well as the alkaline hydrolysis of the amide fragment in a strong basic media on the electronic spectra are discussed. Ab initio and density functional theory (DFT) methods as well as the time-dependent DFT (TD-DFT) method as a function of the basis set are performed with a view to obtain the geometry and electronic properties of all of the species as well as the intermediate, obtained in the alkaline hydrolysis mechanism. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 727,734, 2010. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at [source]

Analysis of Linear Free-Energy Relationships Combined with Activation Parameters Assigns a Concerted Mechanism to Alkaline Hydrolysis of X-Substituted Phenyl Diphenylphosphinates

Ik-Hwan Um Prof.
Abstract A kinetic study is reported for alkaline hydrolysis of X-substituted phenyl diphenylphosphinates (1,a,i). The Brønsted-type plot for the reactions of 1,a,i is linear over 4.5 pKa units with ,lg=,0.49, a typical ,lg value for reactions which proceed through a concerted mechanism. The Hammett plots correlated with ,o and ,, constants are linear but exhibit many scattered points, while the corresponding Yukawa,Tsuno plot results in excellent linear correlation with ,=1.42 and r=0.35. The r value of 0.35 implies that leaving-group departure is partially advanced at the rate-determining step (RDS). A stepwise mechanism, in which departure of the leaving group from an addition intermediate occurs in the RDS, is excluded since the incoming HO, ion is much more basic and a poorer nucleofuge than the leaving aryloxide. A dissociative (DN + AN) mechanism is also ruled out on the basis of the small ,lg value. As the substituent X in the leaving group changes from H to 4-NO2 and 3,4-(NO2)2, ,H,, decreases from 11.3,kcal,mol,1 to 9.7 and 8.7,kcal,mol,1, respectively, while ,S,, varies from ,22.6,cal,mol,1,K,1 to ,21.4 and ,20.2,cal,mol,1,K,1, respectively. Analysis of LFERs combined with the activation parameters assigns a concerted mechanism to the current alkaline hydrolysis of 1,a,i. [source]