The Role of the Amino Acid Molecular Characteristics on the Formation of Fluorescent Gold- and Silver-Based Nanoclusters

Role of amino acids like L-phenylalanine (Phe), L-glutamine (Gln) and L-arginine (Arg) is described and interpreted in terms of their potential for preparation of fluorescent molecular-like gold and silver nanostructures. We are among the first to demonstrate the effect of syntheses conditions as well as the molecular characteristics of Phe, Gln and Arg amino acids on the structure of the formed products. Comprehensive optical characterizations (lifetime, quantum yield (QY%)) of the blue-emitting products were also carried out. It was confirmed that for all Au-containing samples and for Gln-Ag system the characteristic fluorescence originates from few-atomic metallic nanoclusters (NCs) where the reduction of metal ions was promoted by citrate in some cases. Relatively high QY% (∼18 %) was obtained for Arg-stabilized Au NCs due to the existence of an electrostatic interaction between the electron rich, positively charged guanidium side chain of Arg and the negatively charged carboxylate group of citrate on the metallic surface. Size and structural analysis of the products were evaluated by infrared measurements and dynamic light scattering techniques.

Key Parameters on the Antibacterial Activity of Silver Camphor Complexes

Nine new complexes with camphor imine or camphor sulfonimine ligands were synthesized and analytically and spectroscopically characterized, aiming to identify the key parameters that drive the antibacterial activity of the complexes with metal cores and imine substituents with distinct electronic and steric characteristics. The antimicrobial activity of all complexes was evaluated by determining their minimum inhibitory concentrations (MIC) against the Gram-negative Escherichia coli ATCC25922, Pseudomonas aeruginosa 477, and Burkholderia contaminans IST408, and the Gram-positive Staphylococcus aureus Newman. Camphor imine complexes based on the hydroxyl silver center ({Ag(OH)}) typically perform better than those based on the nitrate silver center ({Ag(NO₃)}), while ligands prone to establish hydrogen bonding facilitate interactions with the bacterial cell surface structures. A different trend is observed for the silver camphor sulfonimine complexes that are almost non-sensitive to the nature of the metal cores {Ag(OH)} or {Ag(NO₃)} and display low sensitivity to the Y substituent. The antibacterial activities of the Ag(I) camphor sulfonimine complexes are higher than those of the camphor imine analogues. All the complexes display higher activity towards Gram-negative strains than towards the Gram-positive strain.

Synthesis of sandwich type acyclic tetra-nuclear silver(I)-N-heterocyclic carbene complexes for wound healing applications

Two meta-xylyl linked tetrakis-benzimidazolium salts (L1-L2) as multidentate ligands and two respective silver complexes (C1 and C2) were synthesized. A multistep reaction was done at room temperature, starting with simple benzimidazole and alkyl halides, going through precursors and salt formation by reflux and finally in situ deprotonation of tetrabenzimidazolium salts with Ag2O to yield respective tetra-nuclear Ag(I)-N-heterocyclic Carbene (NHC) complexes. Propyl and butyl groups were bonded at the terminal positions of tetra-azolium open chain salts. Characterization of compounds was done by analytical and spectroscopic techniques. On the basis of spectroscopic data, a chemical structure with open chains having four Ag(I) ions sandwiched between NHC layers was established. Potential of synthesized complexes (C1 & C2) for wound contraction was evaluated and compared with standard wound contraction gel. Percentage wound contraction of both complexes was found very close to that of standard drug used in parallel.

Template-Controlled Synthesis of Polyimidazolium Salts by Multiple [2+2] Cycloaddition Reactions

The tetrakisimidazolium salt H4 -2(Br)4 , featuring a central benzene linker and 1,2,4,5-(nBu-imidazolium-Ph-CH=CH-) substituents reacts with Ag2 O in the presence of AgBF4 to yield the tetranuclear, oktakis-NHC assembly [3](BF4 )4 . Cation [3]4+ features four pairs of olefins from the two tetrakis-NHC ligands perfectly arranged for a subsequent [2+2] cycloaddition. Irradiation of [3](BF4 )4 with a high pressure Hg lamp connects the two tetra-NHC ligands through four cyclobutane linkers to give compound [4](BF4 )4 . Removal of the template metals yields the novel oktakisimidazolium salt H8 -5(BF4 )8 . The tetrakisimidazolium salt H4 -2(BF4 )4 and the oktakisimidazolium salt H8 -5(BF4 )8 have been used as multivalent anion receptors and their anion binding properties towards six different anions have been compared.

Antiviral, Antibacterial, Antifungal, and Cytotoxic Silver(I) BioMOF Assembled from 1,3,5-Triaza-7-Phoshaadamantane and Pyromellitic Acid

The present study reports the synthesis, characterization, and crystal structure of a novel bioactive metal-organic framework, [Ag4(µ-PTA)2(µ3-PTA)2(µ4-pma)(H2O)2]n·6nH2O (bioMOF 1), which was assembled from silver(I) oxide, 1,3,5-triaza-7-phosphaadamantane (PTA), and pyromellitic acid (H4pma). This product was isolated as a stable microcrystalline solid and characterized by standard methods, including elemental analysis, 1H and 31P{1H} NMR and FTIR spectroscopy, and single crystal X-ray diffraction. The crystal structure of 1 disclosed a very complex ribbon-pillared 3D metal-organic framework driven by three different types of bridging ligands (µ-PTA, µ3-PTA, and µ4-pma4-). Various bioactivity characteristics of bioMOF 1 were investigated, revealing that this compound acts as a potent antimicrobial against pathogenic strains of standard Gram-negative (Escherichia coli, Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria, as well as a yeast (Candida albicans). Further, 1 showed significant antiviral activity against human adenovirus 36 (HAdV-36). Finally, bioMOF 1 revealed high cytotoxicity toward an abnormal epithelioid cervix carcinoma (HeLa) cell line with low toxicity toward a normal human dermal fibroblast (NHDF) cell line. This study not only broadens the family of PTA-based coordination polymers but also highlights their promising multifaceted bioactivity.

Preparation and Characterization of Silver(I) Ethylcellulose Thin Films as Potential Food Packaging Materials

Ag(I)-containing ethylcellulose (EC) films suitable as antbacterial packaging materials have been prepared and fully characterized. Different preparation methods, including the use of green casting solvents, are proposed. The Ag(I) acylpyrazolonato complexes, [Ag(Q^py,CF3 )(L)], L=benzylimidazole (Bzim) and L=ethylimidazole (EtimH), used as active additives, display different modes of interactions with EC, depending on their structural features. A thorough investigation of the EC liquid-crystalline lyotropic phase and its changes with the introduction of silver additives, has been conducted, revealing either the inclusion of complex molecules into the inner structure of the EC matrix or their dispersion on its surface. Moreover, the bactericidal activity of the prepared Ag(I) films seems to be related to the interaction between silver additives and the polymeric EC matrix. Indeed, the EC-2b films show a particularly good performance even with a low silver content, with a relative bacterial killing of about 100 %. Tests for Ag(I) migration have been performed by using three food stimulants under two assay conditions. Low values of silver release are recorded, particularly at low concentration of silver content, in the case of all new prepared Ag(I) films.

Antimicrobial Activity of Silver Camphorimine Complexes against Candida Strains

Hydroxide [Ag(OH)L] (L = ^IVL, ^VL, ^VIL, ^VIIL), oxide [{AgL}₂}(μ-O)] (L = ^IL, ^IIL, ^IIIL, ^VL, ^VIL) or chloride [Ag^IIL]Cl, [Ag(^VIL)₂]Cl complexes were obtained from reactions of mono- or bicamphorimine derivatives with Ag(OAc) or AgCl. The new complexes were characterized by spectroscopic (NMR, FTIR) and elemental analysis. X-ray photoelectron spectroscopy (XPS), ESI mass spectra and conductivity measurements were undertaken to corroborate formulations. The antimicrobial activity of complexes and some ligands were evaluated towards Candida albicans and Candida glabrata, and strains of the bacterial species Escherichia coli, Burkholderia contaminans, Pseudomonas aeruginosa and Staphylococcus aureus based on the Minimum Inhibitory Concentrations (MIC). Complexes displayed very high activity against the Candida species studied with the lowest MIC values (3.9 µg/mL) being observed for complexes 9 and 10A against C. albicans. A significant feature of these redesigned complexes is their ability to sensitize C. albicans, a trait that was not found for the previously investigated [Ag(NO₃)L] complexes. The MIC values of the complexes towards bacteria were in the range of those of [Ag(NO₃)L] and well above those of the precursors Ag(OAc) or AgCl. The activity of the complexes towards normal fibroblasts V79 was evaluated by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay. Results showed that the complexes have a significant cytotoxicity.

Mesomorphic Behavior in Silver(I) N-(4-Pyridyl) Benzamide with Aromatic π⁻π Stacking Counterions

Organic semiconductor materials composed of π–π stacking aromatic compounds have been under intense investigation for their potential uses in flexible electronics and other advanced technologies. Herein we report a new family of seven π–π stacking compounds of silver(I) bis-N-(4-pyridyl) benzamide with varying counterions, namely [Ag(NPBA)2]X, where NPBA is N-(4-pyridyl) benzamine, X = NO₃⁻ (1), ClO₄⁻ (2), CF₃SO₃⁻ (3), PF₆⁻ (4), BF₄⁻ (5), CH₃PhSO₃⁻ (6), and PhSO₃⁻ (7), which form extended π−π stacking networks in one-dimensional (1D), 2D and 3D directions in the crystalline solid-state via the phenyl moiety, with average inter-ring distances of 3.823 Å. Interestingly, the counterions that contain π–π stacking-capable groups, such as in 6 and 7, can induce the formation of mesomorphic phases at 130 °C in dimethylformamide (DMF), and can generate highly branched networks at the mesoscale. Atomic force microscopy studies showed that 2D interconnected fibers form right after nucleation, and they extend from ~30 nm in diameter grow to reach the micron scale, which suggests that it may be possible to stop the process in order to obtain nanofibers. Differential scanning calorimetry studies showed no remarkable thermal behavior in the complexes in the solid state, which suggests that the mesomorphic phases originate from the mechanisms that occur in the DMF solution at high temperatures. An all-electron level simulation of the band gaps using NRLMOL (Naval Research Laboratory Molecular Research Library) on the crystals gave 3.25 eV for (1), 3.68 eV for (2), 1.48 eV for (3), 5.08 eV for (4), 1.53 eV for (5), and 3.55 eV for (6). Mesomorphic behavior in materials containing π–π stacking aromatic interactions that also exhibit low-band gap properties may pave the way to a new generation of highly branched organic semiconductors.

Synthesis and antimicrobial activity of novel Ag-N-hetero-cyclic carbene complexes

A series of imidazolidinium ligand precursors are metallated with Ag2O to give silver(I) N-heterocyclic carbene complexes. All compounds were fully characterized by elemental analyses, 1H-NMR, 13C-NMR and IR spectroscopy techniques. All compounds studied in this work were screened for their in vitro antimicrobial activities against the standard strains: Enterococcus faecalis (ATCC 29212), Staphylococcus aureus (ATCC 29213), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853) and the fungi Candida albicans and Candida tropicalis. The new imidazolidin-2-ylidene silver complexes have been found to display effective antimicrobial activity against a series of bacteria and fungi.