Nadia A. Mohamed

Preparation and antimicrobial activity of some carboxymethyl chitosan acyl thiourea derivatives

Acetyl, chloroacetyl and benzoyl thiourea derivatives of carboxymethyl chitosan (ATUCMCS, CATUCMCS, and BZTUCMCS) with comparable grafting degree were synthesized and their structures were characterized by FTIR spectroscopy and elemental analyses. The antimicrobial behaviors of CMCS and its derivatives against three types of bacteria [Bacillis subtilis (B. subtilis), Staphylococous aureus (S. aureus) and Escherichia coli (E. coli)] and three crop-threatening pathogenic fungi [Aspergillus fumigate (A. fumigate), Geotrichum candidum (G. candidum) and Candida albicans (C. albicans)] were investigated. The results indicated that the antibacterial and the antifungal activities of the acyl thiourea derivatives are much higher than that of the parent CMCS. The acyl thiourea derivatives were more potent in case of Gram-positive bacteria than Gram-negative bacteria. This is illustrated for example by the values of minimum inhibitory concentration (MIC) of the ATUCMCS, CATUCMCS and BZTUCMCS against B. subtilis were 3.9, 15.6 and 62.5, respectively, while the MIC values of these derivatives against E. coli were 62.5, 125 and 500. Moreover, the antifungal activity of the CATUCMCS is higher than that of the acetyl and benzoyl thiourea derivatives. This may be due to the presence of chlorine atom.

Organic thermal stabilizers for rigid poly(vinyl chloride) I. Barbituric and thiobarbituric acids

Abstract Barbituric acid (BA) and thiobarbituric acid (TBA) have been investigated as thermal stabilizers for rigid poly(vinyl chloride) (PVC) at 180°C, in air. The efficiency of these compounds as thermal stabilizers was evaluated by measuring the length of the induction period ( T s ), during which no detectable amount of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric titration on one hand, and the extent of discoloration of the degraded polymer on the other. The stabilizing efficiencies were compared with that of dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), barium–cadmium–zinc stearate (Ba–Cd–Zn stearate), n -octyl tin mercaptide ( n -OTM) and dibutyl tin maleate (DBTM). With the exception of DBTM reference stabilizer which shows a comparable stabilizing efficiency with BA and TBA, the investigated organic stabilizers exhibit a greater efficiency than those of all other reference stabilizers. Moreover, they impart better color stability to the degraded samples. A radical mechanism for the stabilizing action is suggested. The stabilizing efficiency is attributed to the replacement of the labile chlorine atoms on the PVC chains by a relatively more stable moiety of the stabilizer. This disrupts the formation of conjugated double bonds, which are responsible for the discoloration.

Quaternized N-substituted carboxymethyl chitosan derivatives as antimicrobial agents

Introduction of quaternary ammonium moieties into N-substituted carboxymethyl chitosan (N-substituted CMCh) derivatives enhances their biological activity. Several derivatives of CMCh having a variety of N-aryl substituents bearing either electron-donating or electron withdrawing groups have been synthesized by the reaction between amino group of CMCh with various aromatic aldehydes under acidic conditions, followed by reduction of the produced Schiff base derivatives with sodium cyanoborohydride. Each of the reduced derivatives was further quaternized using N-(3-chloro-2-hydroxy-propyl)trimethylammonium chloride (Quat-188). The resulting quaternized materials were characterized by FTIR and (1)H NMR spectroscopy. Their antibacterial activities against Streptococcus pneumoniae (S. pneumonia, RCMB 010010), Bacillis subtilis (B. subtilis, RCMB 010067), as Gram positive bacteria and against Escherichia coli (E. coli, RCMB 010052) as Gram negative bacteria and their antifungal activities against Aspergillus fumigatus (A. fumigates, RCMB 02568), Geotricum candidum (G. candidum, RCMB 05097), and Candida albicans (C. albicans, RCMB 05031) were examined using agar disk diffusion method. The results indicated that all the quaternized derivatives showed better antimicrobial activities than that of CMCh. These derivatives are highly potent against Gram positive bacteria compared to Gram negative bacteria. This is illustrated for example as the values of minimum inhibitory concentration (MIC) of Q4NO2-BzCMCh against B. subtilis and S. pneumonia were 6.25 and 12.5 μg/mL, respectively corresponded to 20.0 μg/mL against E. coli. The antimicrobial activity of quaternized N-aryl CMCh derivatives affected by not only the nature of the microorganisms but also by the nature, position and number of the substituent groups on the phenyl ring. Thus while the derivatives with groups of electron withdrawing nature show higher inhibition zone diameter and lower MIC values relative to that of those having electron-donating nature, the non-substituted derivative lies between these two extremes. Antibacterial activities of Q4NO2-BzCMCh, Q3Cl-BzCMCh and Q3Br-BzCMCh against E. coli are nearly equivalent to that of the standard drug Gentamycin. Q3Br-BzCMCh emerged almost equivalent antibacterial activity to Ampicillin against S. pneumonia.

Synthesis and Antimicrobial Activity of Some Novel Cross-Linked Chitosan Hydrogels

Four novel hydrogels based on chitosan were synthesized via a cross-linking reaction of chitosan with different concentrations of oxalyl bis 4-(2,5-dioxo-2H-pyrrol- 1(5H)-yl)benzamide. Their structures were confirmed by fourier transform infrared X-ray (FTIR), scanning electron microscopy (SEM) and X-ray diffraction. The antimicrobial activities of the hydrogels against two crop-threatening pathogenic fungi namely: Aspergillus fumigatus (A. fumigatus, RCMBA 06002), and Aspergillus niger (A. niger, RCMBA 06106), and five bacterial species namely: Bacillis subtilis (B. subtilis, RCMBA 6005), Staphylococcus aureus (S. aureus, RCMBA 2004), Streptococcus pneumoniae (S. pneumonia, RCMB 000101) as Gram positive bacteria, and Salmonella typhimurium (S. typhimurium, RCMB 000104), and Escherichia coli (E. coli, RCMBA 5003) as Gram negative bacteria have been investigated. The prepared hydrogels showed much higher antimicrobial activities than that of the parent chitosan. The hydrogels were more potent in case of Gram-positive bacteria than Gram-negative bacteria. Increasing the degree of cross-linking in the hydrogels resulted in a weaker antimicrobial activity.

N-(Substituted phenyl)itaconimides as organic stabilizers for rigid poly(vinyl chloride) against photo-degradation

Abstract N -(Substituted phenyl)itaconimide derivatives, N -(RPh)II, (R: –NO 2 , –COOH, –H, –OH, –OMe, –Me, –Cl or –Br) have been investigated as organic photo-stabilizers for rigid poly(vinyl chloride) (PVC). Their stabilizing efficiencies were evaluated by measuring the length of the induction period ( T s ), the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination, the extent of discoloration and the change in the mechanical properties of the degraded polymer on the other. The efficiencies were also evaluated by determining the amount of gel formation as well as the intrinsic viscosity of the insoluble and of the soluble fractions of the degraded polymer, respectively. Their stabilizing efficiencies were compared with that of phenyl salicylate UV absorber which is a commonly used industrial stabilizer. The results have proved the higher stabilizing efficiency of almost all the investigated materials as compared with phenyl salicylate. This is well illustrated not only by the greater T s values, but also by the lower rates of dehydrochlorination at later stages of degradation. The results also reveal that the type and position of the substituent plays a major role in determining the stabilizing potency of these materials. It was found that the stabilizing efficiency increases with the increase in the ability of the substituent to increase the electron density around the carbon–carbon double bond of the itaconimide. The stabilizing efficiency of the itaconimides is attributed to their radical trapping potency which intervenes with the radical degradation of PVC. This most probably occurs not only through trapping the radical species in the degradation process, but also by blocking the newly formed radical sites on the polymer chains. The radical attack seems to occur firstly on the ethylenic carbon–carbon double bond of the itaconimide then by the imide linkages at later stages of degradation. Moreover, it was found that these materials lower the extent of discoloration of the polymer during degradation as compared with phenyl salicylate. This improvement in the colour stability is most probably attributable to the ability of the itaconimides to react by a Diels–Alder reaction with the conjugated double bonds created on the polymeric chains as a result of degradation, and responsible for the coloration of the polymer. Furthermore, the extent of cross-linking of the polymer in the presence of the investigated derivatives has been proved to be lower than that in the presence of phenyl salicylate, which implies a greater extent for preserving the mechanical properties of the polymer from being drastically changed. Finally, the results illustrate that blending of the itaconimide derivatives with phenyl salicylate improves both the T s values and the degree of discoloration, and this improvement attains its maximum when both the investigated stabilizers and phenyl salicylate are taken in equimolar ratios. The observed synergistic effect is most probably attributed to the combination of the mechanisms by which the itaconimide and phenyl salicylate work.

Aromatic hydrazides as stabilizers for rigid PVC against thermo-oxidative degradation

Aromatic hydrazides and their derivatives have been investigated as thermal stabilizers for rigid polyvinyl chloride (PVC) at 180 °C in air by measuring the rate of dehydrochlorination and the extent of discoloration of the degraded polymer. The results reveal the greater stabilizing efficiency of the investigated compounds as shown by their longer induction periods (Ts) and lower dehydrochlorination rates in relation to n-octyltin mercaptide, dibasic lead carbonate and cadmium-barium-zinc stearate stabilizers commonly used in industry. The stabilizing induction periods at the early stages of the degradation process increase with increasing number of hydrazide linkages as well as with the introduction of electron donating substituents in the phenyl ring of the stabilizer molecule. The stabilizer efficiency is attributed to the replacement of the labile chlorine on the PVC chains by a relatively more thermally stable aromatic hydrazide moiety. An ionic mechanism for the stabilizing action of the investigated aromatic hydrazide derivatives is offered. Moreover, the investigated stabilizers impart better color stability for the degraded samples as compared with the reference stabilizers. This may be attributed to the ability of these compounds to disrupt the formation of conjugated double bonds which are responsible for discoloration. A synergistic effect is achieved when the materials under investigation were blended in various molar ratios with either cadmium-barium-zinc stearate or dibasic lead carbonate, reaching its maximum at a 3:1 molar ratio of hydrazide compound to reference stabilizer. This synergism may be due to the ability of the hydrazide linkages to form stable complexes with the metal chlorides formed as a reference stabilizer by-product, thus protecting the polymer from their auto catalytic deleterious accelerating degradative effect.

Organic thermal stabilizers for rigid poly(vinyl chloride) II. Benzal thiobarbituric acid and some of its derivatives

Abstract Benzal thiobarbituric acid (BTBA) and two of its derivatives: para -methoxy benzal thiobarbituric acid ( p -MeO-BTBA) and para -chloro benzal thiobarbituric acid ( p -Cl-BTBA) have been investigated as thermal stabilizers for rigid PVC at 180°C, in air. Their stabilizing efficiency is based on measuring the rate of dehydrochlorination and the extent of discoloration of the degraded polymer. The results reveal the higher stabilizing efficiency of the investigated materials as thermal stabilizers for rigid PVC as compared with the industrially used thermal stabilizers: dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), n -octyl tin mercaptide ( n -OTM), dibulyl tin maleate (DBTM) and barium–cadmium–zinc stearate (Ba–Cd–Zn stearate). This is well illustrated by the longer induction period ( T s ) values and by the lower rate of dehydrochlorination. The stabilization efficiency is affected by the nature of the substituent found in the phenyl ring of the BTBA derivatives. Moreover, it was found that these materials lower the extent of discoloration of the polymer during degradation as compared with the reference stabilizers. A radical mechanism for the stabilizing effect of BTBA and its derivatives is proposed. The effect of blending p -Cl-BTBA with either of the reference stabilizers on the stabilizing efficiency of the thermally degraded rigid PVC has been also investigated. The results reveal that mixing of the stabilizers improves both the T s values, the rate of dehydrochloration and the extent of discoloration. This improvement attains its maximum when both the investigated and the reference stabilizers are taken in equivalent weight ratio.

N-substituted maleimides as thermal stabilizers for plasticized poly(vinyl chloride)

Abstract N -Substituted maleimides have been investigated as thermal stabilizers for plasticized PVC at 180°C in air by measuring the rate of dehydrochlorination and the extent of discoloration of the degraded polymer. The results reveal a higher stabilizing efficiency of the products investigated compared with basic lead carbonate, dibutyl tin maleate, and barium-cadmium stearate stabilizers which are commonly used industrially. The induction period (Ts) is influenced by the nature and position of substituents in the aryl ring together with the nature of the plasticizer used. Moreover, it has been found that the stabilizers investigated impart better color stability to the degraded samples compared with the stearate stabilizer. A synergistic effect was achieved when the products investigated were used as mixtures with the reference stabilizer in equimolar ratios. A radical mechanism is proposed which illustrates the stabilizing action of the products investigated.

Novel wholly aromatic polyamide-hydrazides: 6. Dependence of membrane reverse osmosis performance on processing parameters and polymer structural variations

Integrally skinned phase inversion membranes were successfully cast from dimethylacetamide solutions of a series of novel wholly aromatic polyamide-hydrazides for reverse osmosis performance. All the membranes were characterized for their salt rejection (percentage) and water permeability (cm3 cm−2 day−1) of 0.5 N aqueous sodium chloride feed solution at 3924 kPa operating pressure. The effect of polymer structural variations together with several processing parameters to achieve the best combination of high selectivity and permeability were discussed. The polymers structural variations were obtained by varying their para- and meta-oriented phenylene rings content. The latter was changed from 0 to 50 mol%. The processing variables included temperature and period of the solvent evaporation of the cast membranes, coagulation temperature of the thermally treated membranes and annealing of the coagulated membranes, casting solution composition, membrane thickness and the operating pressure. During the thermal treatment step the asymmetric structure of the membranes with a thin dense skin surface layer supported on a more porous layer was established. The former layer seems to be responsible for the separation performance. The results revealed that the membrane performance depended strongly on the conditions of its processing as well as the structure of the polymer from which it is cast. Under identical preparation condition, substitution of p-phenylene rings for m-phenylene ones within the polymer series resulted in an increase in salt rejection capability of the membranes. This may be attributed to an increase in their chain symmetry associated with increased molecular packing and rigidity through enhanced intermolecular hydrogen bonding. This produces a barrier with much smaller pores that would efficiently prevent the solute particles from penetration. For a given membrane, the higher the temperature and the longer the period of the solvent evaporation would result in a membrane of lower solvent content and with a thicker skin layer and consequently led to higher salt rejection at lower water permeability. Further, annealing in deionized water at 100°C produced membranes with optimum salt rejection. Upon annealing, the membrane shrinks resulting in decreasing its pore size particularly in the skin layer. This membrane morphology change improved the salt rejection. Addition of lithium chloride to the casting solution produced a membrane with increased porosity and improved its water permeability. The effects of coagulation temperature and thickness of the membrane on the separation efficiency were also discussed. The optimum salt separation of the membranes was attained at nearly 4000 kPa operating pressure. Membranes showed rejection up to 99.5% at water permeability 13 cm3 cm−2 day−1.

Synthesis, characterization and application of biodegradable crosslinked carboxymethyl chitosan/poly(vinyl alcohol) clay nanocomposites

Crosslinked poly(vinyl alcohol) (PVA)/carboxymethyl chitosan (CMCh) nanocomposites were synthesized using terephthaloyl diisothiocyanate crosslinker, in the presence of montmorillonite (MMT), in different ratios of the two matrices. Characterization of nanocomposites was performed using different analyses. Swelling behavior was studied in different buffered solutions. It was found that formation of crosslinked CMCh/PVA hydrogels increased the swellability. Metal ion adsorption has also been investigated. The results indicated that crosslinked CMCh adsorbs various metal ions much more than non crosslinked CMCh. Antimicrobial activity was examined against Gram positive bacteria, against Gram negative bacteria, and also against fungi. Results indicated that most of these nanocomposites exhibited good antimicrobial potency. Degradation study was carried out in Simulated Body Fluid (SBF) for different time periods in order to find out degradation index (Di). Results showed that weight loss of most of the nanocomposites increased as a function of incubation time.