Long-chain alkanoylcholines, a new category of soft antimicrobial agents that are enzymatically degradable

Enhancing the Antimicrobial Properties of Experimental Resin-Based Dental Composites through the Addition of Quaternary Ammonium Salts

Secondary caries is one of the main reasons for dental filling replacement. There is a need to obtain dental restorative material that is able to act against caries-inducing microorganisms. This study explores the antimicrobial properties of cetyltrimethylammonium bromide (CTAB) or dimethyldioctadecylammonium bromide (DODAB)-modified photo-cured experimental dental composites against Escherichia coli, Streptococcus mutans, and Candida albicans. The antimicrobial activity against Escherichia coli, Streptococcus mutans, and Candida albicans was assessed by using an Accuri C6 flow cytofluorimeter, and then analyzed using BD CSampler software (1.0.264). Bacterial/yeast surface colonization was carried out by using an GX71 inverted-optics fluorescence microscope equipped with a DP 73 digital camera. For bactericidal surface analysis of each sample type, simultaneous standardization was performed using a positive control (live cells) and a negative control (dead cells). A positive correlation between the increasing concentration of CTAB or DODAB and the dead cell ratio of Escherichia coli, Streptococcus mutans, and Candida albicans was revealed. In particular, CTAB at a 2.0 wt% concentration exhibits superior efficiency against pathogens (65.0% dead cells of Escherichia coli, 73.9% dead cells of Streptococcus mutans, and 23.9% dead cells of Candida albicans after 60 min). However, Candida albicans is more resistant to used salts than bacteria. A CTAB- or DODAB-modified experimental dental composite exhibits antimicrobial potential against Escherichia coli, Streptococcus mutans, and Candida albicans after 10 and 60 min of incubation, and the antimicrobial efficiency increases with the wt% of QAS in the tested material.

Double BAC and Triple BAC: A Systematic Analysis of the Disinfectant Properties of Multicationic Derivatives of Benzalkonium Chloride (BAC)

Over the past decades, the shortcomings of established quaternary ammonium disinfectants have become increasingly clear. Although benzalkonium chloride (BAC) has enjoyed nearly a century of significantly protecting human health through surgical preparation, home use, and industrial applications, increasing levels of bacterial resistance have rendered it decreasingly effective. In light of more recent efforts that have informed us that multicationic amphiphilic disinfectants show both higher activity as well as diminished susceptibility to resistance, we embarked on the preparation of 27 multicationic QACs in an attempt to clearly document structure-activity relationships of next-generation BAC structures. Select biscationic BAC derivatives demonstrate single-digit micromolar activity against all seven bacteria tested and MIC values of 2- to 32-fold better than BAC. Particularly notable is the improvement against the more concerning bacteria like Acinetobacter baumannii and Pseudomonas aeruginosa, which pose a modern threat to legacy disinfectants like BAC. With simple synthetic paths, consistently high yields (averaging ∼80 %), and strong biological activity, potent structures with clear SAR trends and strong therapeutic indices have been established.

Soft QPCs: Biscationic Quaternary Phosphonium Compounds as Soft Antimicrobial Agents

Quaternary ammonium compounds (QACs) serve as a first line of defense against infectious pathogens. As resistance to QACs emerges in the environment, the development of next-generation disinfectants is of utmost priority for human health. Balancing antibacterial potency with environmental considerations is required to effectively counter the development of bacterial resistance. To address this challenge, a series of 14 novel biscationic quaternary phosphonium compounds (bisQPCs) have been prepared as amphiphilic disinfectants through straightforward, high-yielding alkylation reactions. These compounds feature decomposable or "soft" amide moieties in their side chains, anticipated to promote decomposition under environmental conditions. Strong bioactivity against a panel of seven bacterial pathogens was observed, highlighted by single-digit micromolar activity for compounds P6P-12A,12A and P3P-12A,12A. Hydrolysis experiments in pure water and in buffers of varying pH revealed surprising decomposition of the soft QPCs under basic conditions at the phosphonium center, leading to inactive phosphine oxide products; QPC stability (>24 h) was maintained in neutral solutions. The results of this work unveil soft QPCs as a potent and environmentally conscious new class of bisQPC disinfectants.

Biodegradable Cationic and Ionizable Cationic Lipids: A Roadmap for Safer Pharmaceutical Excipients

Cationic and ionizable cationic lipids are broadly applied as auxiliary agents, but their use is associated with adverse effects. If these excipients are rapidly degraded to endogenously occurring metabolites such as amino acids and fatty acids, their toxic potential can be minimized. So far, synthesized and evaluated biodegradable cationic and ionizable cationic lipids already showed promising results in terms of functionality and safety. Within this review, an overview about the different types of such biodegradable lipids, the available building blocks, their synthesis and cleavage by endogenous enzymes is provided. Moreover, the relationship between the structure of the lipids and their toxicity is described. Their application in drug delivery systems is critically discussed and placed in context with the lead compounds used in mRNA vaccines. Moreover, their use as preservatives is reviewed, guidance for their design is provided, and an outlook on future developments is given.

N-Benzylethanolammonium Ionic Liquids and Molten Salts in the Synthesis of 68Ga- and Al18F-Labeled Radiopharmaceuticals

Ionic liquids (ILs), due to their structural features, have unique physical and chemical properties and are environmentally friendly. Every year, the number of studies devoted to the use of ILs in medicine and pharmaceutics is growing. In nuclear medicine, the use of ILs with self-buffering capacity in the synthesis of radiopharmaceuticals is extremely important. This research is devoted to obtaining new ionic buffer agents containing N-benzylethanolammonium (BEA) cations and anions of carboxylic acids. A series of new BEA salts was synthesized and identified by NMR (¹H, ¹³C), IR spectroscopy and elemental and thermal analysis. The crystal structures of BEA hydrogen succinate, hydrogen oxalate and oxalate were determined by x-ray diffraction. Newly synthesized compounds were tested as buffer solutions in ⁶⁸Ga- and Al¹⁸F-radiolabeling reactions with a series of bifunctional chelating agents and clinically relevant peptides used for visualization of malignancies by positron emission tomography. The results obtained confirm the promise of using new buffers in the synthesis of ⁶⁸Ga- and Al¹⁸F-labeled radiopharmaceuticals.

Review of the toxic effects of ionic liquids

Interest in ionic liquids (ILs), called green or designer solvents, has been increasing because of their excellent properties such as thermal stability and low vapor pressure; thus, they can replace harmful organic chemicals and help several industrial fields e.g., energy-storage materials production and biomaterial pretreatment. However, the claim that ILs are green solvents should be carefully considered from an environmental perspective. ILs, given their minimal vapor pressure, may not directly cause atmospheric pollution. However, they have the potential to cause adverse effects if leaked into the environment, for instance if they are spilled due to human mistakes or technical errors. To estimate the risks of ILs, numerous ILs have had their toxicity assessed toward several micro- and macro-organisms over the past few decades. Since the toxic effects of ILs depend on the method of estimating toxicity, it is necessary to briefly summarize and comprehensively discuss the biological effects of ILs according to their structure and toxicity testing levels. This can help simplify our understanding of the toxicity of ILs. Therefore, in this review, we discuss the key findings of toxicological information of ILs, collect some toxicity data of ILs to different species, and explain the influence of IL structure on their toxic properties. In the discussion, we estimated two different sensitivity values of toxicity testing levels depending on the experiment condition, which are theoretical magnitudes of the inherent sensitivity of toxicity testing levels in various conditions and their changes in biological response according to the change in IL structure. Finally, some perspectives, future research directions, and limitations to toxicological research of ILs, presented so far, are discussed.

Innovative Textiles Used in Face Masks: Filtration Efficiency and Self-Disinfecting Properties against Coronaviruses

Within the current SARS-CoV-2 pandemic, personal protective equipment, including face masks, is one important tool to interrupt virus transmission chains within the community. In this context, the quality of different face masks is frequently discussed and should, therefore, be evaluated. In this study, nanofleece textiles with a particle filtering effect and textiles with a self-disinfecting treatment were examined, which may be combined in face masks. Firstly, newly developed nanofleece textiles were tested regarding their filtration efficiency against airborne coronavirus, using feline coronavirus (FCoV) as a surrogate for SARS-CoV-2. The tested nanofleece textiles showed filtration efficiencies of over 95% against FCoV when used as a double layer and were, therefore, almost on par with the FFP-2 mask material, which was used as a reference. Secondly, eight treated, self-disinfecting textiles, which may increase the safety in the handling of potentially contaminated masks, were tested against SARS-CoV-2. Three out of eight treated textiles showed significant activity against SARS-CoV-2 and achieved about three LOG10 (99.9%) of virus titer reduction after twelve hours of incubation. Since all possible transmission paths of SARS-CoV-2, as well as the minimal infection doses, remain unknown, both investigated approaches seem to be useful tools to lower the virus spread within the community.

Advancements in the Development of Non-Nitrogen-Based Amphiphilic Antiseptics to Overcome Pathogenic Bacterial Resistance

The prevalence of quaternary ammonium compounds (QACs) as common disinfecting agents for the past century has led bacteria to develop resistance to such compounds. Given the alarming increase in resistant strains, new strategies are required to combat this rise in resistance. Recent efforts to probe and combat bacterial resistance have focused on studies of multiQACs. Relatively unexplored, however, have been changes to the primary atom bearing positive charge in these antiseptics. Here we review the current state of the field of both phosphonium and sulfonium amphiphilic antiseptics, both of which hold promise as novel means to address bacterial resistance.

Synthesis, antibacterial activity, and biocompatibility of new antibacterial dental monomers

PURPOSE

To synthesize a small library of antibacterial dental monomers based on quaternary ammonium salts and to test their antibacterial activity against cariogenic bacteria.

METHODS

Five new antibacterial monomers were synthesized and characterized by NMR, IR and HRMS.

RESULTS

Cytotoxicity assays using human gingival fibroblast cells showed that these new antibacterial monomers were biocompatible at concentrations of 10⁻⁵ M and displayed less cytotoxicity than BisGMA, a common dental monomer. When analyzed in vitro, all new monomers demonstrated strong inhibitory activity against biofilm formation by cariogenic Streptococcus mutans and Lactobacillus casei. Results indicated that antibacterial monomers containing a long alkyl (i.e. hexadecyl) chain are superior to their shorter-chain counterparts. The cross-linking monomers based on glycerol dimethacrylate also consistently outperformed their monomethacrylate analogs. Finally, the ammonium salts containing the dimethylbenzyl moiety were superior to the similar structures containing 1,4-diazabicyclo[2.2.2]octane (DABCO) in some cases.

CLINICAL SIGNIFICANCE

All five new monomers were deemed biocompatible at concentrations of 10⁻⁵ M or less, and most had better biocompatibility than BisGMA. Dimethacrylate monomers 5 and 6 generally demonstrated high antibacterial activities, with the highest activity shown for the most lipophilic monomer 6, and these new antibacterial monomers have potential future application in dental composites and bonding agents.

Silane coatings of metallic biomaterials for biomedical implants: A preliminary review

In response to increased attention in literature, this work provides a qualitative review surrounding the application of silane-based coatings of metallic biomaterials for biomedical implants. Included herein is both a brief summary of existing knowledge and concepts regarding silane-based thin films, along with an analysis of recent peer-reviewed publications and advances towards their practical application for biomedical coatings. Specifically, the review identifies innovative silane-based coatings according to their molecular identity and film structure and analyses their impact on the biocorrosion resistance, protein adsorption, cell viability, and antimicrobial properties of the overall coated implant. It is shown that a range of common silanes clearly exhibit promising properties for biomedical implant coatings, but further work is needed, particularly on mechanisms of physiological interaction and characteristic effects of silane functional groups, before seeing clinical use. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2901-2918, 2018.

Ester- and amide-containing multiQACs: Exploring multicationic soft antimicrobial agents

Quaternary ammonium compounds (QACs) are ubiquitous antiseptics whose chemical stability is both an aid to prolonged antibacterial activity and a liability to the environment. Soft antimicrobials, such as QACs designed to decompose in relatively short times, show the promise to kill bacteria effectively but not leave a lasting footprint. We have designed and prepared 40 soft QAC compounds based on both ester and amide linkages, in a systematic study of mono-, bis-, and tris-cationic QAC species. Antimicrobial activity, red blood cell lysis, and chemical stability were assessed. Antiseptic activity was strong against a panel of six bacteria including two MRSA strains, with low micromolar activity seen in many compounds; amide analogs showed superior activity over ester analogs, with one bisQAC displaying average MIC activity of ∼1μM. For a small subset of highly bioactive compounds, hydrolysis rates in pure water as well as buffers of pH =4, 7, and 10 were tracked by LCMS, and indicated good stability for amides while rapid hydrolysis was observed for all compounds in acidic conditions.

Quaternary Ammonium Compounds: An Antimicrobial Mainstay and Platform for Innovation to Address Bacterial Resistance

Quaternary ammonium compounds (QACs) have represented one of the most visible and effective classes of disinfectants for nearly a century. With simple preparation, wide structural variety, and versatile incorporation into consumer products, there have been manifold developments and applications of these structures. Generally operating via disruption of one of the most fundamental structures in bacteria-the cell membrane-leading to cell lysis and bacterial death, the QACs were once thought to be impervious to resistance. Developments over the past decades, however, have shown this to be far from the truth. It is now known that a large family of bacterial genes (generally termed qac genes) encode efflux pumps capable of expelling many QAC structures from bacterial cells, leading to a decrease in susceptibility to QACs; methods of regulation of qac transcription are also understood. Importantly, qac genes can be horizontally transferred via plasmids to other bacteria and are often transmitted alongside other antibiotic-resistant genes; this dual threat represents a significant danger to human health. In this review, both QAC development and QAC resistance are documented, and possible strategies for addressing and overcoming QAC-resistant bacteria are discussed.

Inhibition of biofouling by modification of forward osmosis membrane using quaternary ammonium cation

In the operation of the forward osmosis (FO) process, biofouling of the membrane is a potentially serious problem. Development of an FO membrane with antibacterial properties could contribute to a reduction in biofouling. In this study, quaternary ammonium cation (QAC), a widely used biocidal material, was conjugated with a silane coupling agent (3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride) and used to modify an FO membrane to confer antibacterial properties. Fourier transform infrared spectroscopy (FT-IR) demonstrated that the conjugated QAC was successfully immobilized on the FO membrane via covalent bonding. Bacterial viability on the QAC-modified membrane was confirmed via colony count method and visualized via bacterial viability assay. The QAC membrane decreased the viability of Escherichia coli to 62% and Staphylococcus aureus to 77% versus the control membrane. Inhibition of biofilm formation on the QAC modified membrane was confirmed via anti-biofilm tests using the drip-flow reactor and FO unit, resulting in 64% and 68% inhibition in the QAC-modified membrane against the control membrane, respectively. The results demonstrate the effectiveness of the modified membrane in reducing bacterial viability and inhibiting biofilm formation, indicating the potential of QAC-modified membranes to decrease operation costs incurred by biofouling.

Thermal behavior of long-chain alkanoylcholine soaps

Long-chain alkanoylcholines prepared from fatty acids adopt a diversity of thermally interconvertible phases made of a bilayered structure with alkanoyl chains crystallized or interdigitated in a more or less extent depending on temperature and alkanoyl chain length.

Structure and properties of cholesterol-based hydrogelators with varying hydrophilic terminals: biocompatibility and development of antibacterial soft nanocomposites

The present work demonstrates a rational designing and synthesis of cholesterol-based amino acid containing hydrogelators with the aim to improve the biocompatibility of these amphiphilic molecules. A thorough structure-property correlation of these hydrogelators was carried out by varying the hydrophilic terminal from a neutral amine to a quaternized ammonium chloride. The amphiphiles having a cationic polar head as the hydrophilic domain and cholesterol as the hydrophobic unit showed better water gelation efficiency (minimum gelation concentration (MGC) ∼0.9-3.1%, w/v) than the analogous free amines. Presumably, the additional ionic interactions for the quaternized amphiphiles might have played the crucial role in gelation as counterions also got involved in hydrogen bonding with solvent molecules. Hence, the attainment of desired hydrophilic-lipophilic balance (HLB) of hydrophobic cholesterol in combination with the appropriate hydrophilic terminal led to the development of efficient hydrogels. Microscopic investigations revealed the formation of various supramolecular morphologies of hydrogels due to the variation in the molecular structure of the amphiphile. Spectroscopic investigations showed the involvement of hydrogen-bonding, hydrophobic, and π-π interactions in the self-assembled gelation. Importantly, biocompatibility of all the cholesterol-based hydrogelators tested against human hepatic cancer derived HepG2 cells showed increased cell viability than the previously reported alkyl-chain-based amphiphilic hydrogelators. In order to incorporate broad spectrum antibacterial properties, silver nanoparticles (AgNPs) were synthesized in situ within the hydrogels using sunlight. The amphiphile-AgNP soft nanocomposite exhibited notable bactericidal property against both gram-positive and gram-negative bacteria.

Cleavable cationic antibacterial amphiphiles: synthesis, mechanism of action, and cytotoxicities

The development of novel antimicrobial agents having high selectivity toward bacterial cells over mammalian cells is urgently required to curb the widespread emergence of infectious diseases caused by pathogenic bacteria. Toward this end, we have developed a set of cationic dimeric amphiphiles (bearing cleavable amide linkages between the headgroup and the hydrocarbon tail with different methylene spacers) that showed high antibacterial activity against human pathogenic bacteria (Escherichia coli and Staphylococcus aureus) and low cytotoxicity. The Minimum Inhibitory Concentrations (MIC) were found to be very low for the dimeric amphiphiles and were lower or comparable to the monomeric counterpart. In the case of dimeric amphiphiles, MIC was found to decrease with the increase in the spacer chain length (n = 2 to 6) and again to increase at higher spacer length (n > 6). It was found that the compound with six methylene spacers was the most active among all of the amphiphiles (MICs = 10-13 μM). By fluorescence spectroscopy, fluorescence microscopy, and field-emission scanning electron microscopy (FESEM), it was revealed that these cationic amphiphiles interact with the negatively charged bacterial cell membrane and disrupt the membrane integrity, thus killing the bacteria. All of the cationic amphiphiles showed low hemolytic activity (HC(50)) and high selectivity against both gram-positive and gram-negative bacteria. The most active amphiphile (n = 6) had a 10-13-fold higher HC(50) than did the MIC. Also, this amphiphile did not show any cytotoxicity against mammalian cells (HeLa cells) even at a concentration above the MIC (20 μM). The critical micellar concentration (CMC) values of gemini surfactants were found to be very low (CMC = 0.30-0.11 mM) and were 10-27 times smaller than the corresponding monomeric analogue (CMC = 2.9 mM). Chemical hydrolysis and thermogravimetric analysis (TGA) proved that these amphiphiles are quite stable under both acidic and thermal conditions. Collectively, these properties make the newly synthesized amphiphiles potentially superior disinfectants and antiseptics for various biomedical and biotechnological applications.

Biotransformation of alkanoylcholines under methanogenic conditions

Ester quaternary ammonium compounds (esterquats), which are mainly used as active ingredients in fabric softeners and personal care products, are beginning to replace traditional quaternary ammonium compounds. As a result of hydrophobicity and increasing use, esterquats reach anaerobic treatment systems. However, little is known about the fate of esterquats under anaerobic conditions. In the present study, the potential inhibitory effect and biotransformation of two alkanoylcholines - acetylcholine chloride (ACh-Cl) and lauroylcholine chloride (LCh-Cl) - which are simple esterquats, under methanogenic conditions were investigated. ACh-Cl up to 300 mg/L was not inhibitory to a mixed methanogenic culture. In contrast, methanogenesis was inhibited by LCh-Cl above 50 mg/L, primarily caused by the accumulation of lauric acid which resulted from the abiotic hydrolysis of LCh. Below inhibitory concentrations, both ACh and LCh were transformed to methane by the mixed methanogenic culture. Mass spectrometric analysis confirmed that both alkanoylcholines were first abiotically hydrolyzed to choline and the corresponding alkanoic acid, which were then biotically transformed to methane, carbon dioxide, and ammonia. Thus, alkanoylcholine-containing waste streams can be bioprocessed to form methane, but hydrolysis products such as long-chain alkanoic acids may adversely impact the anaerobic bioconversion of alkanoylcholines.

Effects of a dental adhesive incorporating antibacterial monomer on the growth, adherence and membrane integrity of Streptococcus mutans

OBJECTIVES

This study was attempted to incorporate an antibacterial monomer, methacryloxylethyl cetyl dimethyl ammonium chloride (DMAE-CB), into a commercial dental adhesive and to evaluate the antibacterial activity of the DMAE-CB-incorporated adhesive after being cured against Streptococcus mutans.

METHODS

DMAE-CB was incorporated at 3% (w/v) into a clinically used dental adhesive, Single Bond 2. Single Bond 2 without DMAE-CB was served as a negative control; Clearfil Protect Bond, containing an intensively researched antibacterial monomer MDPB, was enrolled as a positive control. The effects of the cured adhesives and their eluents on the growth of S. mutans were determined by film contact test and absorbance measurement, respectively. The effects of the cured adhesives on the adherence and membrane integrity of S. mutans were investigated using confocal laser scanning microscopy (CLSM) in conjunction with fluorescent indicators.

RESULTS

Compared with negative control, the cured DMAE-CB-incorporated dental adhesive and positive control were found to exhibit inhibitory effect on the growth of S. mutans (P<0.05), whereas their eluents did not show detectable antibacterial activity. Moreover, the fluorescence analysis of CLSM images demonstrated that the cured DMAE-CB-incorporated adhesive and positive control could hamper the adherence of S. mutans and exert detrimental effect on bacterial membrane integrity (P<0.05).

CONCLUSIONS

The incorporation of DMAE-CB can render dental adhesive with contact antibacterial activity after polymerization via influencing the growth, adherence and membrane integrity of S. mutans.

Ester Quats: The Novel Class of Cationic Fabric Softeners

Esterquats, which are quaternary ammonium compounds having two long (C(16)-C(18)) fatty acid chains with 2 weak ester linkages, represent a new generation of fabric softening agents, having replaced the dialkyldimethylammonium salts (e.g. DTDMAC and DSDMAC). The inclusion of ester linkages into the aliphatic chains has significantly improved the kinetics of biodegradation of the cationic surfactants, lowering the environmental exposure levels. This new generation of fabric softening agents combines a good environmental profile with the structural features required for an effective fabric conditioner. The present paper reviews the synthesis, types, actives combines a good environmental profile with the structural features required for a properties and applications of esterquats.

Ultrashort antibacterial and antifungal lipopeptides

Host-defense cationic antimicrobial peptides ( approximately 12-50 aa long) play an essential protective role in the innate immune system of all organisms. Lipopeptides, however, are produced only in bacteria and fungi during cultivation, and they are composed of specific lipophilic moieties attached to anionic peptides (six to seven amino acids). Here we report the following. (i) The attachment of an aliphatic chain to otherwise inert, cationic D,L tetrapeptides endows them with potent activity against various microorganisms including antibiotic resistance strains. (ii) Cell specificity is determined by the sequence of the short peptidic chain and the length of the aliphatic moiety. (iii) Despite the fact that the peptidic chains are very short, their mode of action involves permeation and disintegration of membranes, similar to that of many long antimicrobial peptides. Besides adding important information on the parameters necessary for host-defense lipopeptides to kill microorganisms, the simple composition of these lipopeptides and their diverse specificities should make them economically available, innate immunity-mimicking antimicrobial and antifungal compounds for various applications.

Synthesis and Antibacterial Properties of Novel Hydrolyzable Cationic Amphiphiles. Incorporation of Multiple Head Groups Leads to Impressive Antibacterial Activity

Two sets of novel multiheaded cationic amphiphiles bearing one, two, and three trimethylammonium headgroups (T1, T2, and T3) and pyridinium headgroups (P1, P2, and P3), have been synthesized and tested for antimicrobial activities against both Gram-positive and Gram-negative bacteria. The multicationic headgroups in these amphiphiles were attached covalently via scissile ester-type linkages. The results were compared with those for known surface-active, nonhydrolyzable compounds cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB). The killing effects of the new single-headed amphiphiles (T1 and P1) were lower than those of CTAB and CPB, but with an increase in the number of headgroups in the amphiphiles, the killing effects increased for both sets of compounds. It was found that amphiphiles with triple headgroups (T3 and P3) were most active among all the amphiphiles, whereas amphiphile P1 had a very poor killing effect on both types of bacteria. The multiheaded pyridinium amphiphiles were more active compared to their trimethylammonium counterparts. The time needed to kill bacteria with multiheaded amphiphiles was significantly less than that of single-headed amphiphiles. Owing to the presence of a cleavable ester moiety, these new amphiphiles are hydrolyzed spontaneously at physiological conditions. This property enables them to be readily metabolized and therefore have the potential to be superior disinfectants and antiseptics for food and body surfaces.

Ester synthesis from trimethylammonium alcohols in dry organic media catalyzed by immobilized Candida antarctica lipase B

Twenty-one different organic solvents were assayed as possible reaction media for the synthesis of butyryl esters from trimethylammonium alcohols in dry conditions catalyzed by immobilized Candida antarctica lipase B. The reactions were carried out following a transesterification kinetic approach, using choline and L-carnitine as primary and secondary trimethylammonium alcohols, respectively, and vinyl butyrate as acyl donor. The synthetic activity of the enzyme was strictly dependent on the water content, the position of the hydroxyl group in the trimethylammonium molecule, and the Log P parameter of the assayed solvent. Anhydrous conditions and a high excess of vinyl butyrate over L-carnitine were necessary to synthesize butyryl-L-carnitine. The synthetic reaction rates of butyryl choline were practically 100-fold those of butyryl-L-carnitine with all the assayed solvents. In both cases, the synthetic activity of the enzyme was dependent on the hydrophobicity of the solvent, with the optimal reaction media showing a Log P parameter of between -0.5 and 0.5. In all cases, 2-methyl-2-propanol and 2-methyl-2-butanol were shown to be the best solvents for both their high synthetic activity and negligible loss of enzyme activity after 6 days.

In vitro and in vivo antimicrobial activity of covalently coupled quaternary ammonium silane coatings on silicone rubber

Biomaterial-centered infection is a dreaded complication associated with the use of biomedical implants. In this paper, the antimicrobial activity of silicone rubber with a covalently coupled 3-(trimethoxysilyl)-propyldimethyloctadecylammonium chloride (QAS) coating was studied in vitro and in vivo. Gram-positive Staphylococcus aureus ATCC 12600, Staphylococcus epidermidis HBH, 102, and Gram-negative Esherichia coli O2K2 and Pseudomonas aeruginos AK1 were seeded on silicone rubber with and without QAS-coating, in the absence or presence of adsorbed human plasma proteins. The viability of the adherent bacteria was determined using a live/dead fluorescent stain and a confocal laser scanning microscope. The coating reduced the viability of adherent staphylococci from 90% to 0%), and of Gram-negative bacteria from 90% to 25% while the presencc of adsorbed plasma proteins had little influence. The biomaterials were also subcutaneously implanted in rats for 3 or 7 days, while pre- or postoperatively seeded with S. aureus ATCC 12600. Preoperative seeding resulted in infection of 7 out of 8 silicone rubber implants against 1 out of 8 QAS-coated silicone rubber implants. Postoperative seeding resulted in similar infection incidences on both implant types, but the numbers of adhering bacteria were 70% lower on QAS-coated silicone rubber. In conclusion, QAS-coated silicone rubber shows antimicrobial properties against adhering bacteria, both in vitro and in vivo.

Nonionic Cellulose Ethers as Potential Drug Delivery Systems for Periodontal Anesthesia

Nonionic cellulose ethers displaying a lower consolute temperature, or cloud-point, close to body temperature were investigated as potential carrier systems for the delivery of local anesthetic agents to the periodontal pocket. The interaction between the polymers, i.e., ethyl(hydroxyethyl)cellulose (EHEC) and hydrophobically modified EHEC (HM-EHEC), and ionic surfactants was determined in the absence and in the presence of the local anesthetic agents lidocaine and prilocaine. The cloud-point and rheology data indicate interactions between the polymer and both anionic and cationic surfactants. More precisely, a number of ionic surfactants were found to result in an increase in cloud-point at higher surfactant concentrations, a surfactant-concentration-dependent thickening, and a temperature-induced gelation upon heating. Upon addition of the local anesthetic agents lidocaine and prilocaine in their uncharged form to EHEC and HM-EHEC, in the absence of surfactants, only minor interaction with the polymer could be inferred. However, these substances were found to affect the polymer-surfactant interaction. In particular, the drug release rate in vitro as well as the stability and temperature-dependent viscosity were followed for an EHEC/SDS system and EHEC/myristoylcholine bromide system upon addition of lidocaine and prilocaine. The data indicate a possibility of formulating a local anesthetic drug delivery system suitable for administration into the periodontal pocket where at least small amounts of active ingredients can be incorporated into the system without severely affecting the gelation behavior. The results found for the cationic myristoylcholine bromide system are particularly interesting for the application in focus here since this surfactant is antibacterial and readily biodegradable. Copyright 2000 Academic Press.

Physicochemical and solubilization properties of N, N-dimethyl-N-(3-dodecylcarbonyloxypropyl)amineoxide: a biodegradable nonionic surfactant

The physicochemical characteristics of N,N-dimethyl-N-(3-dodecylcar- bonyloxypropyl)amineoxide (DDCPNO), a biodegradable analogue of a N, N-dimethylalkylamine-N-oxide, are compared with those of N, N-dimethyldodecylamine-N-oxide (DDNO) to establish the effect on the properties of DDNO of inserting a propoxy linker between the hydrophobic tail and hydrophilic head region. Surface tension measurements gave a critical micelle concentration of 0.33 mM for DDCPNO compared with a value of 1.57 mM for DDNO, suggesting that the former was the more hydrophobic surfactant. This result was confirmed by laser light scattering studies in which total intensity light scattering indicated the presence of DDCPNO micelles of aggregation number 85.0. Photon correlation spectroscopy studies yielded a limiting hydrodynamic diameter of 4.0 nm in comparison with values of 57.5 and 3.3 nm obtained for the aggregation number and the limiting hydrodynamic size, respectively, of DDNO micelles. Studies demonstrated that neither a dilute aqueous solution of DDCPNO or DDNO exhibited a cloud point within the temperature range 293-373 K. Solubilization studies showed that the capacity of DDCPNO micelles for a range of drugs of varying size and polarity was less than that observed with DDNO micelles at an equivalent surfactant concentration. As a further measure of solubilization, the ability of DDCPNO to form oil-in-water microemulsions with a range of ethyl ester oils was investigated and found to be slightly higher than that achieved with DDNO. Together these studies suggest that the presence of the semipolar linker significantly alters the properties of this low molecular weight surfactant.

Bacterial colonization of functionalized polyurethanes

A protocol was developed for studying the growth of bacteria upon polyurethanes subsequent to the establishment of an adherent bacterial population. An inocula of approximately 10(5) cfu S. aureus were spread on functionalized polyurethanes which included Pellethane, sulfonated Pellethane, phosphonated Pellethane, quaternized amine polyurethanes, and a zwitterionic phosphonated polyurethane. After 24 h incubation, Pellethane, sulfonated Pellethane, and phosphonated Pellethane showed bacterial growth by at least a factor of 10. In contrast, the zwitterionic phosphonated polyurethane showed a factor of 10 decrease in bacteria after 24 h and the quaternized amine polyurethanes reduced the bacteria to only a few hundred after only 1 h. When treated with bovine serum albumin, Pellethane, sulfonated Pellethane, and phosphonated Pellethane again showed bacterial growth by as much as a factor of 10 over 24 h. The quaternized amine polyurethanes and the zwitterionic phosphonated polyurethane still exhibited bactericidal abilities even when coated with bovine serum albumin, with the zwitterionic material reducing bacteria by more than a factor of 10 over 24 h and the quaternized amine polyurethane reducing the bacteria to only a few hundred after only 1 h. A zone of inhibition study suggested that the bactericidal activity of the zwitterionic phosphonated polyurethane was due to the leaching of cadmium ions. A quaternized amine polyurethane which contained chloride instead of iodide as the counterion to the amine moiety was less bactericidal than the iodide-containing polymer when treated with albumin. Thus, bacteria were able to colonize Pellethane, phosphonated sulfonated Pellethane, and phosphonated Pellethane, but the iodide-containing quaternized amine polyurethane and the zwitterionic polyurethane prevented colonization.

Loss of bactericidal capacity of long-chain quaternary ammonium compounds with protein at lowered temperature

Amphiphilic betaine esters are quaternary ammonium compounds (QACs) with rapid microbicidal effect, which spontaneously hydrolyze into nontoxic products. thus being referred to as soft antimicrobial agents. The bactericidal effect of 1-decyl (B10), 1-dodecyl (B12), and 1-tetradecyl (B14) betaine esters on Salmonella typhimurium was strongly influenced by temperature, pH and length of hydrocarbon chain. At pH 6.0, presence of 1.5 mM (10% w/v) BSA raised the concentration of B14 for 99% killing (BC2) from 0.006 mM to 1.8 mM. There was a stoichiometric relationship between concentration of BSA and BC2 of B14, indicating that one molecule of B14 was bound per BSA molecule when 99% killing was achieved. When the temperature was lowered to 0 degrees C only minor killing was seen in 1.5 mM BSA at the highest concentration of B14 tested, 57 mM. With B10 at 30 degrees C and pH 6.0, the presence of 1.5 mM BSA raised the bactericidal concentration (BC2) from 0.69 mM to 4.1 mM, and at 0 degrees C and 1.5 mM BSA the BC2 was 11 mM. Thus, the impairment caused of the bactericidal effect of B10 by BSA and lower temperature was less than for B14, since B14 is much more active than B10 at 30 degrees C in the absence of BSA, somewhat more active than B10 at 30 degrees C in the presence of 1.5 mM BSA, and much less active than B10 at 0 degrees C in the presence of BSA. B12 showed properties intermediate between B10 and B14. Lowered pH reduced the bactericidal effect particularly when reduced from pH 5.0 to 4.0 with B10. In the presence of 1.5 mM BSA, the bactericidal effect of 1-dodecyl (DTAB) and 1-hexadecyl (CTAB) trimethylammonium bromide decreased in the same manner as for B10 and B14, respectively. Increasing the time of incubation at 0 degrees C to 50 min, a 99% killing effect was seen with 17 mM CTAB, whereas the same killing effect was reached in 8 min with 17 mM DTAB. Binding of [3H]CTAB to S. typhimurium was also reduced at 0 degrees C in the presence of BSA. Thus, in the presence of 1.5 mM BSA, QACs with the longer hydrocarbon chain were most efficient at 30 degrees C, whereas at 0 degrees C those with the shorter hydrocarbon chain were most active. Consequently, QACs with shorter tails should be used for disinfection in the presence of proteins at lower temperatures.

Submicellar complexes may initiate the fungicidal effects of cationic amphiphilic compounds on Candida albicans

The killing of Candida albicans by a series of amphiphilic quaternary ammonium compounds (QACs) with different hydrocarbon chain lengths was closely related to the binding of the compounds to the cells and damage of the cell membranes. The membrane damage was measured as the level of release of the UV-absorbing material into the medium in which the cells were suspended and as the level of uptake of propidium iodide in individual cells by flow cytometry. It was shown that of the compounds tested, hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide [CTAB]) bound most efficiently. Tetradecyl betainate chloride (B14), tetradecanoylcholine bromide (C14), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB) followed and had declining degrees of binding efficiency. The proportion of CTAB bound was almost total at concentrations up to the critical micelle concentration (CMC) of the compound, whereas that of B14 was somewhat smaller. For the two remaining tetradecyl compounds (C14 and TTAB), still smaller proportions were bound at low concentrations, but the proportions rose disproportionally at increasing concentrations to a distinct maximum at concentrations of 0.2 to 0.5 times the CMC. We propose that interfacial micelle-like aggregates are formed at the cell surface as a step in the binding process. An analogous, but less conspicuous, maximum was seen for DTAB. Thus, great differences in the binding affinity of QACs with different hydrocarbon chains at different concentrations to C. albicans were observed. These differences were related to the CMC of the compound. In contrast, the binding of TTAB to Salmonella typhimurium 395 MS was almost total at low as well as high concentrations until saturation was attained, indicating fundamental differences between binding to the yeast and binding to gram-negative bacteria. The importance of lipid-type complexes or aggregates to the antifungal effect of membrane-active substances are discussed.