The quantitative molecular weight-antimicrobial activity relationship for chitosan polymers, oligomers, and derivatives

Chitosan and chitosan derivatives can kill pathogenic microorganisms including bacteria and fungi. The antimicrobial activity is dependent on the degree of acetylation, substituent structure, and molecular weight. Over the past four decades, numerous studies have endeavored to elucidate the relationship between molecular weight and the activity against microorganisms. However, investigators have reported divergent and, at times, conflicting conclusions. Here a bilinear equation is proposed, delineating the relationship between antimicrobial activity, defined as log (1/MIC), and the molecular weight of chitosan and chitosan derivatives. Three constants AMin, AMax, and CMW govern the shape of the curve determined by the equation. The constant AMin denotes the minimal activity expected as the molecular weight tends towards zero while AMax represents the maximal activity observed for molecular weights exceeding CMW, the critical molecular weight required for max activity. This equation was applied to analyze data from seven studies conducted between 1984 and 2019, which reported MIC (Minimum Inhibitory Concentration) values against bacteria and fungi for various molecular weights of chitosan and its derivatives. All the 29 datasets exhibited a good fit (R2 ≥ 0.5) and half excellent (R2 ≥ 0.95) fit to the equation. The CMW generally ranged from 4 to 10 KD for datasets with an excellent fit to the equation.

Optimizing N,N,N-trimethyl chitosan synthesis: A design of experiments (DoE) approach

This study aimed to optimize the synthesis of trimethyl chitosan (TMC) with a high degree of N,N,N-trimethylation (DTM) through a one-step procedure, minimizing reagent use, reaction time, and avoiding O-methylation, using the Design of Experiments (DoE) approach. Initially, sequential designs were done. Following the determination of the initial conditions a Fractional Factorial Design was used, investigating methyl iodide (MeI) and NaHCO3 molar ratios, temperature, and reaction time on DTM. MeI and NaHCO3 molar ratios were found to be significant (p-values equal to 0.02 and 0.02, respectively), the reaction temperature (p = 0.04) displayed a non-linear effect, while the reaction time was found to be non-significant (p = 0.93). Finally, a Full Factorial Design was done to optimize temperature and base addition methods. Incremental addition of the base was determined to be feasible without affecting the DTM, thereby preventing any viscosity-related problems. DTM was achieved up to 72 % in a one-step procedure, with no O-methylation. These optimized conditions offer a cost-effective, one-step synthesis method for TMC production, holding significant promise for industrial applications by avoiding multistep reactions, ensuring minimal reagent use, and preventing O-methylation. The findings mark a substantial advancement in TMC synthesis, presenting a streamlined and efficient approach with substantial practical implications for process development.

The European Polysaccharide Network of Excellence (EPNOE) research roadmap 2040: Advanced strategies for exploiting the vast potential of polysaccharides as renewable bioresources

Polysaccharides are among the most abundant bioresources on earth and consequently need to play a pivotal role when addressing existential scientific challenges like climate change and the shift from fossil-based to sustainable biobased materials. The Research Roadmap 2040 of the European Polysaccharide Network of Excellence (EPNOE) provides an expert's view on how future research and development strategies need to evolve to fully exploit the vast potential of polysaccharides as renewable bioresources. It is addressed to academic researchers, companies, as well as policymakers and covers five strategic areas that are of great importance in the context of polysaccharide related research: (I) Materials & Engineering, (II) Food & Nutrition, (III) Biomedical Applications, (IV) Chemistry, Biology & Physics, and (V) Skills & Education. Each section summarizes the state of research, identifies challenges that are currently faced, project achievements and developments that are expected in the upcoming 20 years, and finally provides outlines on how future research activities need to evolve.

Chitosan-hydroxycinnamic acid conjugates: Optimization of the synthesis and investigation of the structure activity relationship

A new synthesis method was developed and optimized by a full factorial design for conjugating hydroxycinnamic acids (HCA-s) to chitosan. Cinnamic acid and tert-butyldimethylsilyl protected HCA-s were converted to their corresponding acyl chlorides and reacted with 3,6-di-O-tert-butyldimethylsilyl-chitosan to selectively form amide linkages, resulting in water-soluble conjugates after deprotection. Nineteen conjugates were obtained with various degrees of substitution (DS) ranging from 3% to 60%. The conjugates were found to be bactericidal against Staphylococcus aureus and Escherichia coli, with their activities equal to chitosan at low DS but an increase in the DS correlated with reduced activity. DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging assay was performed to determine the EC₅₀ values. Chitosan only exhibited low antioxidant activity, whereas the HCA-chitosan conjugates exhibited higher antioxidant activities correlating with the DS. One caffeic acid conjugate (21%) was 4000 times more active than chitosan and more active than free caffeic acid.

Antibacterial properties of poly (N,N-dimethylaminoethyl methacrylate) obtained at different initiator concentrations in solution polymerization

The samples of poly(N,N-dimethylaminoethyl methacrylate) were synthesized by radical polymerization. The amount of monomer and solvent was constant as opposed to an amount of initiator which was changing. No clear relationship between polymerization conditions and the molecular weight of the polymer was found, probably due to the branched configuration of produced polymer. Bactericidal interactions in all samples against Gram-positive and Gram-negative bacteria have been demonstrated. However, the observed effect has various intensities, depending on the type of bacteria and the type of sample.

Chitotriazolan (poly(β(1-4)-2-(1H-1,2,3-triazol-1-yl)-2-deoxy-d-glucose)) derivatives: Synthesis, characterization, and evaluation of antibacterial activity

Here we describe the first synthesis of a new type of polysaccharides derived from chitosan. In these structures, the 2-amino group on the pyranose ring was quantitively replaced by an aromatic 1,2,3-triazole moiety. The 2-amino group of chitosan and di-TBDMS chitosan was converted into an azide by diazo transfer reaction. The chitosan azide and TBDMS-chitosan azide were poorly soluble but could be fully converted to triazoles by "copper-catalysed Huisgen cycloaddition" in DMF or DMSO. The reaction could be done with different alkynes but derivatives lacking cationic or anionic groups were poorly soluble or insoluble in tested aqueous and organic solvents. Derivatives with N,N-dimethylaminomethyl, N,N,N-trimethylammoniummethyl, sulfonmethyl, and phosphomethyl groups linked to the 4-position of the triazole moiety were soluble in water at neutral or basic conditions and could be analyzed by ¹H, ¹³C APT, COSY, and HSQC NMR. The quaternized cationic chitotriazolan's had high activity against S. aureus and E. coli, whereas the anionic chitotriazolan's lacked activity.

In vitro biological response of human osteoblasts in 3D chitosan sponges with controlled degree of deacetylation and molecular weight

We have studied the effect of chitosan sponges, produced from chitosan batches with distinct degree of deacetylation (DDA) and molecular weight (Mw), on the adhesion, growth and differentiation of primary human osteoblasts with an aim to offer a suitable tool for guided bone regeneration. All the chitosan sponges revealed similar microstructure, irrespective of the DDA (58, 73, 82, 88, and 91 %) and Mw (749, 547, 263, 215, and 170 kDa, respectively). Cell spreading was higher on sponges having a higher DDA. Higher DDA induced a more pronounced increase in alkaline phosphatase activity, osteopontin (OPN), vascular endothelial growth factor-A (VEGF), interleukin-6 (IL-6), and reduction in monocyte chemoattractant protein-1 (MCP-1), sclerostin (SOST) and dickkopf related protein-1 as compared to lower DDA. Lower DDA induced the increased secretion of osteoprotegerin and SOST as compared to higher DDA. The combination of higher DDA and Mw induced an increased secretion of VEGF and IL-6, however reduced the secretion of OPN as compared to chitosan with similar DDA but with lower Mw. In summary, the variations in cellular responses to the different chitosan sponges indicate a potential for individual tailoring of desired responses in guided bone regeneration.

The Effect of Molecular Weight on the Antibacterial Activity of N,N,N-Trimethyl Chitosan (TMC)

N,N,N-trimethyl chitosan (TMC) with 93% degree of trimethylation was synthesized. TMC and the chitosan starting material were subjected to acidic hydrolysis to produce 49 different samples with a reduced average molecular weight (Mw) ranging from 2 to 144 kDa. This was done to allow the investigation of the relationship between antibacterial activity and Mw over a wide Mw range. NMR investigation showed that hydrolysis did not affect the degree of trimethylation (DSTRI) or the structure of the polymer backbone. The activity of TMC against Staphylococcus aureus (S. aureus) increased sharply with Mw until a certain Mw value (critical Mw for high activity, CMW) was reached. After the CMW, the activity was not affected by a further increase in the Mw. A similar pattern of activity was observed for chitosan. The CMW was determined to be 20 kDa for TMC and 50 kDa for chitosan.

Endosome Targeting meso-Tetraphenylchlorin-Chitosan Nanoconjugates for Photochemical Internalization

Four amphiphilic covalently linked meso-tetraphenylchlorin-chitosan nanoconjugates were synthesized and evaluated for use in photochemical internalization (PCI) in vitro and in vivo. The synthetic protocol for the preparation of two different hydrophobic chlorin photosensitizers, 5-(4-aminophenyl)-10,15,20-triphenylchlorin and 5-(4-carboxyphenyl)-10,15,20-triphenylchlorin, was optimized. These monofunctional photosensitizers were covalently attached to carrier chitosan via silyl-protected 3,6-di-O-tert-butyldimethylsilyl-chitosan (Di-TBDMS-chitosan) with 0.10 degree of substitution per glucosamine (DS). Hydrophilic moieties such as trimethylamine and/or 1-methylpiperazine were incorporated with 0.9 DS to give fully water-soluble conjugates after removal of the TBDMS groups. A dynamic light scattering (DLS) study confirmed the formation of nanoparticles with a 140-200 nm diameter. These nanoconjugates could be activated at 650 nm (red region) light, with a fluorescence quantum yield (Φ_F) of 0.43-0.45, and are thus suitable candidates for use in PCI. These nanoconjugates were taken up and localized in the endocytic vesicles of HCT116/LUC human colon carcinoma cells, and upon illumination they substantially enhanced plasmid DNA transfection. The nanoconjugates were also evaluated in preliminary in vivo experiments in tumor-bearing mice, showing that the nanoconjugates could induce a strong photodynamic therapy (PDT) and also PCI effects in treatment with bleomycin.

Experimental design for determining quantitative structure activity relationship for antibacterial chitosan derivatives

Experimental design was utilized for synthesis and optimization of antimicrobial chitosan derivatives and for the development of their structure–activity relationship.

Antimicrobial peptide shows enhanced activity and reduced toxicity upon grafting to chitosan polymers

Here we report that grafting of a short antimicrobial peptide, anoplin, to chitosan polymers is a strategy for abolishing the hemolytic propensity, and at the same time increasing the activity of the parent peptide. Anoplin-chitosan conjugates were synthesized by CuAAC reaction of multiple peptides through 2-azidoacetyl groups on chitosan.

Antibacterial phototoxic effects of synthetic asymmetric and glycosylated curcuminoids in aqueous formulations: studies on curcumin and curcuminoids. LIV

The aim of this study was to evaluate the in vitro phototoxic potential of synthetic asymmetric and glycosylated curcuminoids on planktonic model bacteria by counting the colony forming units. The Gram-positive Enterococcus faecalis and the Gram-negative Escherichia coli were exposed to aqueous solutions of the curcuminoids (⩽2.5 μM) in the presence or absence of selected pharmaceutical excipients (Pluronic F127, PEG 400 and HPγCD) in combination with a low irradiation dose (5 J/cm(2); λmax: 450 nm) of constant irradiance and time. All the asymmetric curcuminoids, but only one of the glycosylated curcuminoids demonstrated substantial phototoxic effect on E.faecalis (⩾4.7 log reduction). Only two of the asymmetric curcuminoids showed a moderate to low phototoxic effect on the more persistent E.coli. This study emphasized that aromatic hydroxyl substituents in the para-position are important to maintain the phototoxic potential of curcuminoids independent of molecular symmetry. Glycosylation of the aromatic substituents resulted in a substantial loss in phototoxicity towards planktonic bacteria, an apparent change in the non-radiative S₁-decay process and a weaker interaction with Pluronic F127 compared to the non-glycosylated curcuminoids. The selected excipients Pluronic F127, PEG 400 and HPγCD strongly influenced the phototoxic potential of the unsymmetrical, non-glycosylated compounds.

Numerical modelling of transdermal delivery from matrix systems: parametric study and experimental validation with silicone matrices

A model is presented for transdermal drug delivery from single-layered silicone matrix systems. The work is based on our previous results that, in particular, extend the well-known Higuchi model. Recently, we have introduced a numerical transient model describing matrix systems where the drug dissolution can be non-instantaneous. Furthermore, our model can describe complex interactions within a multi-layered matrix and the matrix to skin boundary. The power of the modelling approach presented here is further illustrated by allowing the possibility of a donor solution. The model is validated by a comparison with experimental data, as well as validating the parameter values against each other, using various configurations with donor solution, silicone matrix and skin. Our results show that the model is a good approximation to real multi-layered delivery systems. The model offers the ability of comparing drug release for ibuprofen and diclofenac, which cannot be analysed by the Higuchi model because the dissolution in the latter case turns out to be limited. The experiments and numerical model outlined in this study could also be adjusted to more general formulations, which enhances the utility of the numerical model as a design tool for the development of drug-loaded matrices for trans-membrane and transdermal delivery.

Challenges in evaluation of chitosan and trimethylated chitosan (TMC) as mucosal permeation enhancers: From synthesis to in vitro application

The polysaccharide chitosan and the water soluble chitosan derivative N,N,N-trimethyl chitosan (TMC) have been widely investigated as permeation enhancers of mucosal surfaces with numerous papers published over the last two decades. Although both chitosan and TMC increase permeation of markers through mucosal membranes, such as the intestinal and airway epithelium as well as in in vivo models, these investigations have not led to their use in marketed drug formulations. In this review, the reported extent of the permeation enhancement and cell viability after chitosan or TMC treatment in intestinal and airway models is critically evaluated and concluded that the apparent discrepancies can be explained by differences in polymer structure, experimental conditions and in vitro models. Additionally, aspects regarding the synthesis of TMC and its structural characterization are described, focusing on new synthetic strategies implemented to reduce O-methylation. Finally recommendations are provided on how studies can be conducted to improve understanding of the structure–activity relationship and elucidate possible mechanism of action.

Numerical modelling and experimental investigation of drug release from layered silicone matrix systems

Medical devices and polymeric matrix systems that release drugs or other bioactive compounds are of interest for a variety of applications. The release of the drug can be dependent on a number of factors such as the solubility, diffusivity, dissolution rate and distribution of the solid drug in the matrix. Achieving the goal of an optimal release profile can be challenging when relying solely on traditional experimental work. Accurate modelling complementing experimentation is therefore desirable. Numerical modelling is increasingly becoming an integral part of research and development due to the significant advances in computer simulation technology. This work focuses on numerical modelling and investigation of multi-layered silicone matrix systems. A numerical model that can be used to model multi-layered systems was constructed and validated by comparison with experimental data. The model could account for the limited dissolution rate and effect of the drug distribution on the release profiles. Parametric study showed how different factors affect the characteristics of drug release. Multi-layered medical silicone matrices were prepared in special moulds, where the quantity of drug in each layer could be varied, and release was investigated with Franz-diffusion cell setup. Data for long-term release was fitted to the model and the full depletion of the system predicted. The numerical model constructed for this study, whose input parameters are the diffusion, effective dissolution rate and dimensional solubility coefficients, does not require any type of steady-state approximation. These results indicate that numerical model can be used as a design tool for development of controlled release systems such as drug-loaded medical devices.

Hydrolysis kinetics and QSAR investigation of soft antimicrobial agents

Quaternary ammonium surfactants, such as benzalkonium chloride and cetylpyridinium chloride, are commonly used as antibacterial agents for disinfectants and for general environmental sanitation, as well as in surfactants, penetration enhancers and preservatives in pharmaceutical and cosmetic formulations. However, these agents are known to cause various side-effects and toxic reactions that are believed to be associated with their chemical stability. Soft analogues of the long-chain quaternary ammonium compounds were synthesized according to the soft drug approach and their physicochemical properties investigated, such as their hydrolytic rate constant, surface activity and lipophilicity. Structure-activity studies showed that the antimicrobial activity of the compounds was strongly influenced by their lipophilicity and chemical stability, the activity increasing with increasing lipophilicity and stability. However, in soft drug design structure-activity relationships are combined with structure-inactivation relationships during the lead optimization. The safety index (SI) of compounds was defined as the hydrolytic rate constant divided by the minimum inhibitory concentration. The SI of the soft antibacterial agents was found to increase with increasing lipophilicity but optimum SI was obtained when their hydrolytic t1/2, at pH 6 and 60°C, was about 11 h. Optimization of the soft antibacterial agents through SI optimization resulted in potent but chemically unstable quaternary ammonium antibacterial agents.

Investigation of curcumin-cyclodextrin inclusion complexation in aqueous solutions containing various alcoholic co-solvents and alginates using an UV-VIS titration method. Studies of curcumin and curcuminoides, XXXV

The effect of pharmaceutical excipients like alcoholic co-solvents and water-soluble polymers on the inclusion complexation of curcumin in hydroxypropyl-beta-cyclodextrin and hydroxypropyl-gamma-cyclodextrin was investigated with a UV-VIS titration method. The association constants and the stoichiometries of the inclusion complexes in buffered media containing various amounts dl of alcoholic co-solvents and alginates were determined. The results showed a 1 : 1 stoichiometry between curcumin and both the cyclodextrins investigated in buffered media containing 10% (v/v) alcoholic co-solvents, although some 1 : 2 (host:guest) complexation was suspected between curcumin and hydroxypropyl-beta-cyclodextrin. The presence of 0.1% (w/v) sodium alginate or propylene glycol alginate did apparently not change the stoichiometry of the complexes formed. Curcumin was found to have a more than 30-fold higher association constant with hydroxypropyl-gamma-cyclodextrin compared to hydroxypropyl-beta-cyclodextrin in buffer containing 0.5% ethanol. Large variation in the association constants between curcumin and the cyclodextrins as a result of different co-solvents in the aqueous complexing media were found. A decrease in the association constant was seen as the chain lenght of the added co-solvent increased. Further, a decrease in the association constants was observed by addition of alginates in the case of hydroxypropyl-gamma-cyclodextrin at 0.5 or 5% (v/v) ethanol. The trend was opposite in the case of hydroxypropyl-beta-cyclodextrin, where a 30-90% increase in the association constant was observed in the presence of alginates. The results in the current study showed the large variations in the complexation between curcumin and hydroxypropyl-beta-cyclodextrin and hydroxypropyl-gamma-cyclodextrin, resepctively, as a result of various alcoholic co-solvents and alginates in the complexing media. The results also illustrated the importance of optimizing the solvent systems when utilizing cyclodextrins as drug carriers.

Release of anti-inflammatory drugs from a silicone elastomer matrix system

The focus of the current study was to overcome the obstacles to incorporating non-steroidal anti-inflammatory drugs (NSAIDs) into a medical silicone elastomer and to investigate how the physicochemical properties of the drugs affect the curing process and drug release. Five representative NSAIDs were selected with different molecular weights and physicochemical properties. Silicone blends with 1% (w/w) drug in the sodium salt form could be obtained in a fully cured medical elastomer matrix whereas drugs in various other salt forms or the free acid form interfered with the curing process. The release rate was mainly dependent on the solubility in the drug-salt elastomer matrix, with ibuprofen sodium showing the fastest rate. These results indicate that inclusion of the NSAID salts in the silicone matrix does not change the microstructure or the permeability of the silicone matrix, and channel formation is minimal. The properties of NSAID-containing silicone blends are compatible with processes used for the manufacture of medical devices from silicone such as silicone stents or catheters, and could therefore be considered for such devices to reduce inflammation at the site of an implant and also for local delivery.

Studies on curcumin and curcuminoids

A series of curcuminoids, including curcumin, were studied with the main focus on their solubility, phase-distribution, hydrolytic stability and photochemical stability in cyclodextrin (CD) solutions. Their radical scavenging properties were also briefly studied. All the investigated derivatives were more stable towards hydrolytic degradation in CD solutions than curcumin, and the general order of the stabilising effect was HPbetaCD>MbetaCD>>HPgammaCD. In contrast, the photochemical studies showed that curcumin is generally more stable than its derivatives. Solubility and phase-distribution studies showed that curcuminoids with side groups on the phenyl moiety have higher affinity for the HPgammaCD than for the betaCDs and that the relative affinity of the larger HPgammaCD cavity increases with the curcuminoid molecule size. The radical scavenging studies showed that curcumin is more active than the derivatives investigated and that the free phenolic hydroxyl group may be essential for the scavenging properties. This study also indicates that the two halves of the symmetric curcumin molecule act as two separate units and scavenge one radical each.

Development and evaluation of an artificial membrane for determination of drug availability

Various artificial membranes (e.g. PAMPA) and cellular-based membranes (e.g. Caco-2) are used for screening during early stages of drug discovery. However, these methods are not well suited for evaluation of pharmaceutical formulations and the effects of various excipients on drug availability. When drug molecules permeate biological membranes they encounter two types of permeation resistance, a membrane resistance in the lipophilic membrane and diffusion resistance in the unstirred water layers adjacent to both surfaces of the lipophilic membrane. We have developed an artificial membrane that is cheap and simple to prepare. The unstirred water layer consists of a hydrated semi-permeable cellophane membrane with a molecular weight cutoff (MWCO) of 12,000-14,000 Da and a lipophilic membrane of pure n-octanol in a nitrocellulose matrix. In the diffusion cell the hydrated cellophane membrane (thickness 210-230 microm) is on the donor side and the lipophilic octanol membrane (thickness about 120 microm) on the receptor side. Permeation of ionizable lipophilic drug molecules was diffusion-controlled when the drug was unionized but lipophilic membrane controlled when the drug was ionized. Drug permeation patterns from cyclodextrin containing formulations through the membrane were similar to those previously observed for biological membranes such as hairless mouse skin and the eye cornea.

Investigation of soft long chain quaternary ammonium compounds as co-factors to enhance in vitro gene delivery

The effect of soft long chain quaternary ammonium antibacterial agents on the in vitro gene delivery of a luciferase plasmid to COS-1 cell lines was investigated. Low concentrations of these compounds could be used to enhance gene delivery with Lipofectamine Plus.

Evaluation of cyclodextrin solubilization of drugs

The most common stoichiometry of drug/cyclodextrin complexes is 1:1, i.e. one drug molecule forms a complex with one cyclodextrin molecule, and the most common method for stoichiometric determination during formulation studies is the phase-solubility method. However, in recent years it has becoming increasingly clear that solubilizing effects of cyclodextrins are frequently due to the formation of multiple inclusion and non-inclusion complexes. The aqueous solubility of 38 different drugs was determined in pure aqueous solution, aqueous buffer solutions and aqueous cyclodextrin solutions, and the apparent stability constant (K1:1) of the 1:1 drug/cyclodextrin complexes calculated by the phase-solubility method. For poorly soluble drugs (aqueous solubility <0.1mM) the intrinsic solubility (S0) is in general much larger than the intercept of the phase-solubility diagram (Sint) resulting in non-linearity of otherwise linear (AL-type) phase-solubility diagram. This can lead to erroneous K(1:1)-values. A more accurate method for determination of the solubilizing efficiency of cyclodextrins is to determine their complexation efficiency (CE), i.e. the concentration ratio between cyclodextrin in a complex and free cyclodextrin. CE is calculated from the slope of the phase-solubility diagrams, it is independent of both S0 and Sint, and more reliable when the influences of different pharmaceutical excipients on the solubilization are being investigated.

Novel Water-Soluble Quaternary Piperazine Derivatives of Chitosan: Synthesis and Characterization

Novel synthesis methods for the preparation of quaternary piperazine derivatives of chitosan were developed. Quaternary ammonium moiety can be selectively inserted into either one or both of the piperazine nitrogens, yielding structurally uniform chitosan derivative structures. Water-soluble end products were thoroughly characterized with FT-IR, 1H NMR, 13C NMR and 2D 1H-13C HSQC NMR. The molecular weights of the end products were determined by GPC with triple detection.

Influence of aqueous diffusion layer on passive drug diffusion from aqueous cyclodextrin solutions through biological membranes

Most drugs permeate biological membranes via passive diffusion and it is generally assumed that the main barrier is the lipophilic structure of the membrane. However, we have observed that the unstirred water layer adjacent to the membrane surface can in some cases be a barrier just as effective as the lipophilic membrane itself. Hydrophilic cyclodextrins can enhance drug delivery through biological membranes by increasing the availability of dissolved drug molecules immediate to the membrane surface, i.e. by increasing drug delivery through the unstirred water layer. Cyclodextrins and drug/ cyclodextrin complexes are, in most cases, unable to permeate lipophilic membranes. Thus, excess cyclodextrin, more than is needed to solubilize the drug in the aqueous exterior, will hamper drug delivery through biological membranes.

Synthesis of Novel Quaternary Chitosan Derivatives via N-Chloroacyl-6-O-triphenylmethylchitosans

Various quaternary chitosan derivative structures were synthesized by reacting N-chloroacyl-6-O-triphenylmethylchitosans with tertiary amines. Full substitutions were obtained from the quaternization reactions and the obtained water-soluble quaternary chitosan derivatives were thoroughly characterized with (1)H NMR, (13)C NMR, (1)H-(13)C HSQC NMR, and FT-IR.

Investigation of drug-cyclodextrin complexes by a phase-distribution method: some theoretical and practical considerations

The purpose of the study was to evaluate an octanol-water phase distribution method for investigation of drug/cyclodextrin (D/CD) complexes and to compare stability constant values obtained by this method to values obtained by the phase solubility method. A general equation for determination of 1 : 1 D/CD complex stability constant (K1 : 1) from the slope of a phase-distribution diagram (a diagram of the reciprocal of the apparent partition coefficient vs. the total CD concentration) was derived. The equation accounted for the possible inclusion of the organic solvent in the CD cavity and the gradual saturation of the CD binding with increasing concentration of the guest compound. This method was used to determine K1 : 1 for 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD) complexes of hydrocortisone, prednisolone, diazepam, beta-estradiol and diethylstilbestrol. These values were comparable to K1 : 1 values determined by the phase-solubility method. The phase-distribution method could also be applied to determine stability constants for the neutral and ionic forms of the weakly acidic drugs, naproxen and triclosan and the weakly basic drug lidocaine. The phase-distribution method is a very versatile and fast method and has the advantage, compared to the phase-solubility method, that it only requires very small drug samples. Thus, this method would be suitable for screening of new drug candidates.

Cyclodextrins in drug delivery

Cyclodextrins are a family of cyclic oligosaccharides with a hydrophilic outer surface and a lipophilic central cavity. Cyclodextrin molecules are relatively large with a number of hydrogen donors and acceptors and, thus, in general they do not permeate lipophilic membranes. In the pharmaceutical industry cyclodextrins have mainly been used as complexing agents to increase aqueous solubility of poorly soluble drugs, and to increase their bioavailability and stability. Studies in both humans and animals have shown that cyclodextrins can be used to improve drug delivery from almost any type of drug formulation. However, the addition of cyclodextrins to existing formulations without further optimisation will seldom result in acceptable outcome. Currently there are approximately 30 different pharmaceutical products worldwide containing drug/cyclodextrin complexes on the market.

N-Chloroacyl-6-O-triphenylmethylchitosans: Useful Intermediates for Synthetic Modifications of Chitosan

An efficient synthetic route was developed for the mild chloroacylation of chitosan with different chloroacyl chlorides. Full N-chloroacylation was obtained with this procedure without any O-acylation, and products having lower degrees of substitution can also be produced. Organo-soluble 6-O-triphenylmethylchitosan was used as a starting material for the acylation reactions. The resulting N-chloroacyl-6-O-triphenylmethylchitosan intermediates were also organo-soluble and characterized by FT-IR. N-Methylpiperazine moieties were attached to make end products that were sufficiently soluble for characterization by NMR and also to prove that the present intermediates could be used for further modifications. The end products were fully characterized by 1H NMR, 13C NMR, and 2D 1H-13C heteronuclear single-quantum correlation NMR spectroscopy. The degrees of substitution were determined by 1H NMR. Molecular weight determination by GPC-LS displayed a significant degradation of the polymer. The weight-average molar masses (M(w)) of the end products ranged from 29.6 to 49.4 kDa, when the M(w) of the starting material was 144.2 kDa.

Self-Association of Cyclodextrins and Cyclodextrin Complexes

Cyclodextrins are useful functional excipients, which are being used in an ever-increasing way to camouflage undesirable pharmaceutical characteristics, especially poor aqueous solubility. It has generally been assumed that the mechanism whereby cyclodextrins exert their effects, especially their augmentation of solubility, is via the formation of noncovalent, dynamic inclusion complexes. This is a model, which regards drug-cyclodextrin interactions as a discrete phenomenon and ignores the possible interaction of these complexes with one another. It is becoming increasingly apparent that such assumptions may not be universally applicable or all encompassing. Specifically, there is a growing body of evidence that supports the important contribution of non-inclusion-based aspects for drug solubilization by cyclodextrins including surfactant-like effects and molecular aggregation. This short review attempts to assess the available literature for areas in which such non-inclusion mechanisms are apparent and tries to interpret these in the context of a broader working theory as to how cyclodextrins exert their beneficial effects.

Marine lipids as building blocks for soft quaternary ammonium compounds and their antibacterial activity

Environmental friendly antibacterial agents have to degrade relatively rapid to non-toxic and inactive products after they have had their desired effect. Environmental friendly quaternary ammonium agents were designed according to Bodor's soft drug approach and evaluated in vitro. Structure-activity relationship (SAR) studies showed that the antibacterial activity of a given soft agent will only be acceptable if its chemical stability is adequate to allow the agent to express its activity for sufficient duration of time. However, the studies also showed that increasing the lipophilicity of a chemically labile antibacterial agent could increase its potency. Two of the lipophilic quaternary ammonium antibacterial agents evaluated had minimum inhibitory concentration (MIC) against Staphylococcus aureus as low as 2 microg/ml and estimated degradation half-life less than 4 to 6 days at room temperature. Decreased MIC could only be obtained by increasing the degradation half-life of the agents.

Preparation of solid drug/cyclodextrin complexes of acidic and basic drugs

One of the main obstacles in pharmaceutical applications of cyclodextrins is their increase of the formulation bulk. Even at maximum incorporation 500 mg of a solid drug/cyclodextrin complex will only contain between 50 and 125 mg of the drug, assuming a low molecular weight drug (MW 200 to 400 Dalton) and an average molecular weight cyclodextrin (MW about 1500 Dalton). In general, the complexation efficiency is low and consequently the complex powder contains a significant amount of empty cyclodextrin molecules. In the present study the complexation efficiency is increased by ionization of the drug molecule through addition of volatile acid (i.e. acetic acid) or base (i.e. ammonia) to the aqueous complexation media of basic or acidic drugs, respectively. The volatile acid or base was then removed during lyophilization and heating in a vacuum oven resulting in formation of solid cyclodextrin complexes of the unionized drug. Thus, the complexation efficiency was temporary increased by the ionization but then again decreased leading to formation of the thermodynamically unstable solid drug/cyclodextrin complexes. When dissolved the energy of the system was lowered by expelling the drug molecules from the cyclodextrin cavities resulting in formation of supersaturated drug solutions and ultimately precipitation of the drug.

Soft antimicrobial agents: synthesis and activity of labile environmentally friendly long chain quaternary ammonium compounds

A series of soft quaternary ammonium antimicrobial agents, which are analogues to currently used quaternary ammonium preservatives such as cetyl pyridinium chloride and benzalkonium chloride, were synthesized. These soft analogues consist of long alkyl chain connected to a polar headgroup via chemically labile spacer group. They are characterized by facile nonenzymatic and enzymatic degradation to form their original nontoxic building blocks. However, their chemical stability has to be adequate in order for them to have antimicrobial effects. Stability studies and antibacterial and antiviral activity measurements revealed relationship between activity, lipophilicity, and stability. Their minimum inhibitory concentration (MIC) was as low as 1 microg/mL, and their viral reduction was in some cases greater than 6.7 log. The structure-activity studies demonstrate that the bioactive compounds (i.e., MIC for Gram-positive bacteria of <10 microg/mL) have an alkyl chain length between 12 and 18 carbon atoms, with a polar headgroup preferably of a small quaternary ammonium group, and their acquired inactivation half-life must be greater than 3 h at 60 degrees C.

The effects of organic salts on the cyclodextrin solubilization of drugs

Previous studies have indicated that conventional description of drug/cyclodextrin complexes in aqueous solutions as inclusion complexes are not as unambiguous as one might think. It has been shown that in some cases drug/cyclodextrin complexes consist of a mixture of inclusion and non-inclusion complexes. Furthermore it has been shown that drug/cyclodextrin complexes can form aggregates containing up to couple of hundred complexes. In this present study beta-cyclodextrin (betaCD) solubilization of hydrocortisone is enhanced by including short-chain anionic and cationic species in the aqueous complexation medium. For example, maximum hydrocortisone solubility in pure aqueous betaCD solutions or suspensions is 2.2 mg/ml. Addition of 1% (w/v) sodium acetate to the complexation medium increases this value to 7.1 mg/ml (or over 220%). Further addition of 0.25% (w/v) hydroxypropyl methylcellulose to the medium increased the hydrocortisone solubility to over 9 mg/ml. Similar results were obtained when sodium salicylate or benzalkonium chloride were added to the complexation medium. It is also shown that cyclodextrin complexes of lipophilic compounds that have good affinity for the cyclodextrin cavity can be used to enhance cyclodextrin solubilization of drugs that have low affinity for the cavity. All these observations can be explained by formation of drug/cyclodextrin complex aggregates.