Rhodamine B-Containing Chitosan-Based Films: Preparation, Luminescent, Antibacterial, and Antioxidant Properties.

In this study, Rhodamine B-containing chitosan-based films were prepared and characterized using their mechanical, photophysical, and antibacterial properties. The films were synthesized using the casting method and their mechanical properties, such as tensile strength and elongation at break, were found to be dependent on the chemical composition and drying process. Infrared spectroscopy and X-ray diffraction analysis were used to examine the chemical structure and degree of structural perfection of the films. The photophysical properties of the films, including absorption spectra, fluorescence detection, emission quantum yields, and lifetimes of excited states, were studied in detail. Rhodamine B-containing films exhibited higher temperature sensitivity and showed potential as fluorescent temperature sensors in the physiological range. The antibacterial activity of the films was tested against Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli, with Rhodamine B-containing films demonstrating more pronounced antibacterial activity compared to blank films. The findings suggest that the elaborated chitosan-based films, particularly those containing Rhodamine B can be of interest for further research regarding their application in various fields such as clinical practice, the food industry, and agriculture due to their mechanical, photophysical, and antibacterial properties.

Fe(III)-Based Phenylsilsesquioxane/Acetylacetonate Complexes: Synthesis, Cage-like Structure, and High Catalytic Activity.

Unprecedented iron-based silsesquioxane/acetylacetonate complexes were synthesized. The intriguing cage-like structure of compounds is alkaline metal-dependent: the Fe2Li2 complex includes condensed Si6-silsesquioxane and four acetylacetonate ligands; the Fe4Na4 complex exhibits two cyclic Si4-silsesquioxane and eight acetylacetonate ligands, while the Fe3K3 complex features two cyclic Si3-silsesquioxane and six acetylacetonate ligands. The latter case is the very first observation of small trimeric silsesquioxane ligands in the composition of cage-like metallasilsesquioxanes. The Fe4Na4-based complex exhibits a record high activity in the oxidation of inert alkanes with peroxides (55% yield of oxygenates in cyclohexane oxidation). It also acts as a catalyst in the cycloaddition of CO2 with epoxides, leading to cyclic carbonates in good yields (58-96%).

Novel Highly Efficient Antibacterial Chitosan-Based Films.

In this study, we elaborated new chitosan-based films reinforced by iron(III)-containing chitosan nanoparticles Fe(III)-CS-NPs at different concentrations. We found that the optimum concentration of Fe(III)-CS-NPs for the improvement of antibacterial and mechanical properties of the films was 10% (σb = ca. 8.8 N/mm2, εb = ca. 41%, inhibition zone for S. aureus = ca. 16.8 mm and for E. coli = ca. 11.2 mm). Also, using the click-chemistry approach (thiol-ene reaction), we have synthesized a novel water-soluble cationic derivative of chitin. The addition of this derivative of chitin to the chitosan polymer matrix of the elaborated film significantly improved its mechanical (σb = ca. 11.6 N/mm2, εb = ca. 75%) and antimicrobial (inhibition zone for S. aureus = ca. 19.6 mm and for E. coli = ca. 14.2 mm) properties. The key mechanism of the antibacterial action of the obtained films is the disruption of the membranes of bacterial cells. The elaborated antibacterial films are of interest for potential biomedical and food applications.

Chitosan-Based Ciprofloxacin Extended Release Systems: Combined Synthetic and Pharmacological (In Vitro and In Vivo) Studies.

Ciprofloxacin is one of the most effective antibiotics, but it is characterized by a range of side effects. Elaboration of drug-releasing systems which allow to diminish toxicity of ciprofloxacin is a challenging task in medicinal chemistry. The current study is focused on development of new ciprofloxacin releasing systems (CRS). We found that ultrasound efficiently promotes N,N'-dicyclohexyl carbodiimide-mediated coupling between COOH and NH2 functionalities in water. This was used for conjugation of ciprofloxacin to chitosan. The obtained ciprofloxacin/chitosan conjugates are capable of forming their self-assembled nanoparticles (SANPs) in aqueous medium. The SANPs can be additionally loaded by ciprofloxacin to form new CRS. The CRS demonstrated high loading and encapsulation efficiency and they are characterized by extended release profile (20 h). The elaborated CRS were tested in vivo in rats. The in vivo antibacterial effect of the CRS exceeded that of the starting ciprofloxacin. Moreover, the in vivo acute and subacute toxicity of the nanoparticles was almost identical to that of the chitosan, which is considered as the non-toxic biopolymer.

The first selenium containing chitin and chitosan derivatives: Combined synthetic, catalytic and biological studies.

Ultrasonic approach to the synthesis of the first selenium-containing derivatives of chitin and chitosan has been developed. The synthetic procedure is simple, provides high yields, does not require harsh conditions, and uses water as the reaction medium. The elaborated chitin and chitosan derivatives and their based nanoparticles are non-toxic and possess high antibacterial and antifungal activity. Their antimicrobial activity exceeds the effect of the classic antibiotics (Ampicillin and Gentamicin) and the antifungal drug Amphotericin B. The obtained selenium-containing cationic chitin and chitosan derivatives exhibit a high transfection activity and are promising gene delivery vectors. Nanoparticles of the synthesized polymers are highly efficient catalysts for the oxidation of 1-phenylethyl alcohol to acetophenone by bromine at room temperature.

Chitosan derivatives and their based nanoparticles: ultrasonic approach to the synthesis, antimicrobial and transfection properties.

In the present work, we demonstrate that alkylation of chitosan by alkyl halides, aza-Michael reaction with chitosan, and AdN-E reaction of chitosan with aldehydes can be efficiently mediated by ultrasound. An optimization of ultrasonic irradiation parameters allowed us to (i) accelerate the rate of the reactions dramatically, (ii) achieve high selectivity, and (iii) preserve integrity of the polysaccharide backbone avoiding its depolymerization. We evaluated antibacterial/antifungal and transfection activity of 8 different derivatives of chitosan and their based nanoparticles in vitro. Moreover, we studied antibacterial activity of the most efficient polymer and their based nanoparticles in vivo. The tested polymer proved to be superior to reference commercial antibiotics ampicillin and gentamicin.

Design of new anti-Alzheimer drugs: ring-expansion synthesis and synchrotron X-ray diffraction study of dimethyl 4-ethyl-11-fluoro-1,4,5,6,7,8-hexa-hydro-azonino[5,6-b]indole-2,3-di-carboxyl-ate.

The title compound, C20H23FN2O4, is the product of a ring-expansion reaction from a seven-membered fluorinated hexa-hydro-azepine to a nine-membered azonine. The nine-membered azonine ring of the mol-ecule adopts a chair-boat conformation. The C=C and C-N bond lengths [1.366 (3) and 1.407 (3) Å, respectively] indicate the presence of conjugation within the enamine CH2-C=C-N-CH2 fragment. The substituent planes at the C=C double bond of this fragment are twisted by 16.0 (3)° as a result of steric effects. The amine N(Et) N atom has a trigonal-pyramidal configuration (sum of the bond angles = 346.3°). The inter-planar angle between the two carboxyl-ate substituents is 60.39 (8)°. In the crystal, mol-ecules form zigzag chains along [010] by inter-molecular N-H⋯O hydrogen-bonding inter-actions, which are further packed in stacks toward [100]. The title azonino-indole might be considered as a candidate for the design of new Alzheimer drugs.

Ring-expansion synthesis and crystal structure of dimethyl 4-ethyl-1,4,5,6,7,8-hexa-hydro-azonino[5,6-b]indole-2,3-di-carboxyl-ate.

The title compound, C20H24N2O4, is the product of a ring-expansion reaction from a seven-membered hexa-hydro-azepine to a nine-membered azonine. The azonine ring of the mol-ecule adopts a chair-boat conformation. In the crystal, mol-ecules are linked by bifurcated N-H⋯(O,O) hydrogen bonds, generating [010] zigzag chains. The title compound shows inhibitory activity against acetyl-cholinesterase and butyrylcholinesterase, and might be considered as a candidate for the design of new types of anti-Alzheimer's drugs.

Crystal structures of N-[(4-phenyl-thia-zol-2-yl)carbamo-thio-yl]benzamide and N-{[4-(4-bromo-phen-yl)thia-zol-2-yl]carbamo-thio-yl}benzamide from synchrotron X-ray diffraction.

The title compounds, C17H13N3OS2, (I), and C17H12BrN3OS2, (II), are potential active pharmaceutical ingredients. Compound (I) comprises two almost planar fragments. The first is the central (carbamo-thio-yl)amide (r.m.s. deviation = 0.038 Å), and the second consists of the thia-zole and two phenyl rings (r.m.s. deviation = 0.053 Å). The dihedral angle between these planes is 15.17 (5)°. Unlike (I), compound (II) comprises three almost planar fragments. The first is the central N-(thia-zol-2-ylcarbamo-thio-yl)amide (r.m.s. deviation = 0.084 Å), and the two others comprise the bromo-phenyl and phenyl substituents, respectively. The dihedral angles between the central and two terminal planar fragments are 21.58 (7) and 17.90 (9)°, respectively. Both (I) and (II) feature an intra-molecular N-H⋯O hydrogen bond, which closes an S(6) ring. In the crystal of (I), mol-ecules form hydrogen-bonded layers parallel to (100) mediated by N-H⋯S and C-H⋯O hydrogen bonds. In the crystal of (II), mol-ecules form a three-dimensional framework mediated by N-H⋯Br and C-H⋯O hydrogen bonds, as well as secondary S⋯Br [3.3507 (11) Å] and S⋯S [3.4343 (14) Å] inter-actions.