Effect of protonation state and N-acetylation of chitosan on its interaction with xanthan gum: a molecular dynamics simulation study

Hydrophilic matrices composed of chitosan (CS) and xanthan gum (XG) complexes are of pharmaceutical interest in relation to drug delivery due to their ability to control the release of active ingredients. Molecular dynamics simulations (MDs) have been performed in order to obtain information pertaining to the effect of the state of protonation and degree of N-acetylation (DA) on the molecular conformation of chitosan and its ability to interact with xanthan gum in aqueous solutions. The conformational flexibility of CS was found to be highly dependent on its state of protonation. Upon complexation with XG, a substantial restriction in free rotation around the glycosidic bond was noticed in protonated CS dimers regardless of their DA, whereas deprotonated molecules preserved their free mobility. Calculated values for the free energy of binding between CS and XG revealed the dominant contribution of electrostatic forces on the formation of complexes and that the most stable complexes were formed when CS was at least half-protonated and the DA was ≤50%. The results obtained provide an insight into the main factors governing the interaction between CS and XG, such that they can be manipulated accordingly to produce complexes with the desired controlled-release effect

Evaluation of Three Chitin Metal Silicate Co-Precipitates as a Potential Multifunctional Single Excipient in Tablet Formulations

The performance of the novel chitin metal silicate (CMS) co-precipitates as a single multifunctional excipient in tablet formulation using direct compression and wet granulation methods is evaluated. The neutral, acidic, and basic drugs Spironolactone (SPL), ibuprofen (IBU) and metronidazole (MET), respectively, were used as model drugs. Commercial Aldactone®, Fleximex® and Dumazole® tablets containing SPL, IBU and MET, respectively, and tablets made using Avicel® 200, were used in the study for comparison purposes. Tablets of acceptable crushing strength (>40 N) were obtained using CMS. The friability values for all tablets were well below the maximum 1% USP tolerance limit. CMS produced superdisintegrating tablets (disintegration time < 1 min) with the three model drugs. Regarding the dissolution rate, the sequence was as follow: CMS > Fleximex® > Avicel® 200, CMS > Avicel® 200 > Dumazole® and Aldactone® > Avicel® 200 > CMS for IBU, MET and SPL, respectively. Compressional properties of formulations were analyzed using density measurements and the compression Kawakita equation as assessment parameters. On the basis of DSC results, CMS co precipitates were found to be compatible with the tested drugs. Conclusively, the CMS co-precipitates have the potential to be used as filler, binder, and superdisintegrant, all-in-one, in the design of tablets by the direct compression as well as wet granulation methods

Comparative analysis of co-processed starches prepared by three different methods

Co-processing is currently of interest in the generation of high-functionality excipients for tablet formulation. In the present study, comparative analysis of the powder and tableting properties of three co-processed starches prepared by three different methods was carried out. The co-processed excipients consisting of maize starch (90%), acacia gum (7.5%) and colloidal silicon dioxide (2.5%) were prepared by co-dispersion (SAS-CD), co-fusion (SAS-CF) and co-granulation (SAS-CG). Powder properties of each co-processed excipient were characterized by measuring particle size, flow indices, particle density, dilution potential and lubricant sensitivity ratio. Heckel and Walker models were used to evaluate the compaction behaviour of the three co-processed starches. Tablets were produced with paracetamol as the model drug by direct compression on an eccentric Tablet Press fitted with 12 mm flat-faced punches and compressed at 216 MPa. The tablets were stored at room temperature for 24 h prior to evaluation. The results revealed that co-granulated co-processed excipient (SAS-CG) gave relatively better properties in terms of flow, compressibility, dilution potential, deformation, disintegration, crushing strength and friability. This study has shown that the method of co-processing influences the powder and tableting properties of the co-processed excipient

Comparative analysis of co-processed starches prepared by three different methods

Co-processing is currently of interest in the generation of high-functionality excipients for tablet formulation. In the present study, comparative analysis of the powder and tableting properties of three co-processed starches prepared by three different methods was carried out. The co-processed excipients consisting of maize starch (90%), acacia gum (7.5%) and colloidal silicon dioxide (2.5%) were prepared by co-dispersion (SAS-CD), co-fusion (SAS-CF) and co-granulation (SAS-CG). Powder properties of each co-processed excipient were characterized by measuring particle size, flow indices, particle density, dilution potential and lubricant sensitivity ratio. Heckel and Walker models were used to evaluate the compaction behaviour of the three co-processed starches. Tablets were produced with paracetamol as the model drug by direct compression on an eccentric Tablet Press fitted with 12 mm flat-faced punches and compressed at 216 MPa. The tablets were stored at room temperature for 24 h prior to evaluation. The results revealed that co-granulated co-processed excipient (SAS-CG) gave relatively better properties in terms of flow, compressibility, dilution potential, deformation, disintegration, crushing strength and friability. This study has shown that the method of co-processing influences the powder and tableting properties of the co-processed excipient

The efficiency of Amman Financial Market : an empirical study

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Selective colorimetric molecular probe for cyanide ion detection in aqueous solution

5-Nitro-2-hydroxybenzaldehyde (1) demonstrated to be a sensitive, and a selective molecular probe for cyanide ion (CN-) in aqueous media. In acetonitrile, compound 1 shows sensitivity and selectivity for cyanide, acetate and fluoride, in comparison to other investigated anions using both visual and spectroscopic means. In aqueous solution, the color becomes intense yellow upon addition of cyanide, while acetate showed this effect to a much lower extent. Significant spectral changes were also detected with the appearance of two new absorption bands at 358 and 387 nm. This was accompanied by concomitant intensity decrease for the band at 314 nm. Fluoride, dihydrogen phosphate, chloride, bromide, perchlorate, and azide showed negligible color and spectral changes for the probe in aqueous solutions. On the other hand, hydrogen sulfate caused fainting of the yellow color and gave a spectrum similar to that of the sensor in polar aprotic solvents. The cyanide ion was detected at micro molar levels in aqueous solutions with a stoichiometry of 1:1 for CN: probe in acetonitrile as the solvent. Cyanide, hydroxide, acetate, fluoride and dihydrogen phosphate showed identical changes to color and spectra, indicating a hydrogen bonding and a deprotonation mechanism

Computational study on the encapsulation of glucosamine anomers by cucurbit[6]uril and cucurbit[8]uril in aqueous solution

Recently, we have investigated the cucurbit[7]uril (CB7) recognition of the α- and β-anomers of neutral, protonated, and acetylated forms of glucosamine in water. In the present work, we employed molecular dynamics (MD) and thermodynamic integration methods (TI) to investigate the recognition of these molecules by cucurbit[6]uril (CB6) and cucurbit[8]uril (CB8). MD revealed the formation of stable 1:1 inclusion complexes by all studied molecules with cucurbit[n]urils (CBn), and 2:1 complex by the α-anomer of the acetylated form of glucosamine with the large homologue CB8. CB6 forms roughly twice as many hydrogen bonds with the guest molecules as CB8. MM-PBSA results indicated that the electrostatic contribution to the binding free energy of each guest:CB complex was larger for CB6 than for CB8, and that CB6 and CB8 have lower affinity toward the different forms of glucosamine compared to CB7. Furthermore, TI was used to estimate the relative affinities of CB6 and CB8 toward the α- and β-anomers for each form of the studied glucosamine and compare with CB7

Molecular recognition of tripeptides containing tryptophan by cucurbit[8]uril: A computational study

In this work, molecular dynamics (MD) simulations and time-dependent density functional theory (TD-DFT) calculations were applied to study the formation of binary and ternary complexes between cucurbit[8]uril (CB8) and three tryptophan-containing tripeptides (WGG, GWG, and GGW), as well as heteroternary complexes of the tripeptides in the presence of methyl viologen (MV) as an auxiliary ligand. All complexes were stable in water, and exhibited encapsulation of the indole moiety of W. Analysis of the MD trajectories of the homoternary complexes revealed π-π stacking within the CB8 cavity between the indole rings. MM-PBSA analysis indicated higher binding energy for tripeptides containing W residue at the N-terminus. The heteroternary complexes showed two binding modes, one with MV fully included (and π-π stacked with the indole ring) and the other with MV mostly excluded. The computed UV–Visible spectra of the free guests and their heteroternary complexes exhibited new bands emerged in the spectra of the complexes, which resulted from the transitions from HOMO and HOMO–1 to LUMO related to W–MV charge transfer (CT) complexes