Enhanced biosynthesis of coated silver nanoparticles using isolated bacteria from heavy metal soils and their photothermal-based antibacterial activity: integrating Response Surface Methodology (RSM) Hybrid Artificial Neural Network (ANN)-Genetic Algorithm (GA) strategies.

This study explores the biosynthesis of silver nanoparticles (AgNPs) using the Streptomyces tuirus S16 strain, presenting an eco-friendly alternative to mitigate the environmental and health risks of chemical synthesis methods. It focuses on optimizing medium culture conditions, understanding their physicochemical properties, and investigating their potential photothermal-based antibacterial application. The S16 strain was selected from soils contaminated with heavy metals to exploit its ability to produce diverse bioactive compounds. By employing the combination of Response Surface Methodology (RSM) and Artificial Neural Network (ANN)-Genetic Algorithm (GA) strategies, we optimized AgNPs synthesis, achieving an improvement of nearly 2.45 times the initial yield under specific conditions (Bennet's medium supplemented with glycerol [5 g/L] and casamino-acid [3 g/L] at 30 °C for 72 h). A detailed physicochemical characterization was conducted. Notably, the AgNPs were well dispersed, and a carbonaceous coating layer on their surface was confirmed using energy-dispersive X-ray spectroscopy. Furthermore, functional groups were identified using Fourier-transform infrared spectroscopy, which helped enhance the AgNPs' stability and biocompatibility. AgNPs also demonstrated efficient photothermal conversion under light irradiation (0.2 W/cm2), with temperatures increasing to 41.7 °C, after 30 min. In addition, treatment with light irradiation of E. coli K-12 model effectively reduced the concentration of AgNPs from 105 to 52.5 µg/mL, thereby enhancing the efficacy of silver nanoparticles in contact with the E. coli K-12.

Synthesis of Imidazolium Cations Linked to Para-t-Butylcalix[4]arene Frameworks and Their Use as Synthons for Nickel-NHC Complexes Tethered to Calix[4]arenes.

A series of cationic p-tert-butylcalix[4]arenes, with side-arms that are functionalized with imidazolium groups, have been synthesized in good yields. The parent tetrahydroxy para-t-butyl-calix[4]arene was dialkylated at the phenolic hydrogen atoms using α,ω-dibromo-alkanes to yield bis(mono-brominated) alkoxy-chains of variable length. The brominated side-arms in these compounds were then further alkylated with substituted imidazoles (N-methylimidazole, N-(2,4,6-trimethyl-phenyl)imidazole, or N-(2,6-di-isopropylphenyl)imidazole) to yield a series of dicationic calixarenes with two imidazolium groups tethered, via different numbers of methylene spacers (n = 2-4), to the calixarene moiety. Related tetracationic compounds, which contain four imidazolium units linked to the calix[4]arene backbone, were also prepared. In all of these compounds, the NMR data show that the calixarenes adopted a cone configuration. All molecules were characterized by NMR spectroscopy and by MS studies. Single crystal X-ray diffraction studies were attempted on many mono-crystals of these cations, but significant disorder problems, partly caused by occluded solvent in the lattice, and lack of crystallinity resulting from partial solvent loss, precluded the good resolution of most X-ray structures. Eventually, good structural data were obtained from an unusually disordered single crystal of 5a, (1,3)-Cone-5,11,17,23-tetra-t-butyl-25,27-di-hydroxy-26,28-di-[2-(N-2,6-diisopropylphenyl-imidazolium)ethoxy]calix[4]arene dibromide and its presumed structure was confirmed. The structure revealed the presence of H-bonded interactions and some evidence of π-stacking. Some of these imidazolium salts were reacted with nickelocene to form the nickel N-heterocyclic carbene (NHC) complexes 7a-7d. A bis-carbene nickel complex 8 was also isolated and its structure was established by single crystal X-ray diffraction studies. The structure was disordered and not of high quality, but the structural data corroborated the spectroscopic data.

Electrophilic Si-H Activation by Acetonitrilo Benzo[h]quinoline Iridacycles: Influence of Electronic Effects in Catalysis.

The performance of six newly synthesized benzo[h]quinoline-derived acetonitrilo pentamethylcyclopentadienyl iridium(III) tetrakis(3,5-bis-trifluoromethylphenyl)borate salts bearing different substituents -X (-OMe, -H, -Cl, -Br, -NO2 and -(NO2 )2 ) on the heterochelating ligand were evaluated in the dehydro-O-silylation of benzyl alcohol and the monohydrosilylation of 4-methoxybenzonitrile by Et3 SiH, two reactions involving the electrophilic activation of the Si-H bond. The benchmark shows a direct dependence of the catalytic efficiency with the electronic effect of -X, which is confirmed by theoretical assessment of the intrinsic silylicities Π of hydridoiridium(III)-silylium adducts and by the theoretical evaluation of the propensity of hydridospecies to transfer the hydrido ligand to the activated substrate. The revisited analysis of the Ir-Si-H interactions shows that the most cohesive bond in hydridoiridium(III)-silylium adducts is the Ir-H one, while the Ir-Si is a weak donor-acceptor dative bond. The Si…H interaction in all the cases is noncovalent in nature and dominated by electrostatics confirming the heterolytic cleavage of the hydrosilane's Si-H bond in this key catalytically relevant species.

Transient self-assembly of metal-organic complexes.

Implementing transient processes in networks of dynamic molecules holds great promise for developing new functional behaviours. Here we report that trichloroacetic acid can be used to temporarily rearrange networks of dynamic imine-based metal complexes towards new equilibrium states, forcing them to express complexes otherwise unfavourable in their initial equilibrium states. Basic design principles were determined for the creation of such networks. Where a complex distribution of products was obtained in the initial equilibrium state of the system, the transient rearrangement temporarily yielded a simplified output, forcing a more structured distribution of products. Where a single complex was obtained in the initial equilibrium state of the system, the transient rearrangement temporarily modified the properties of this complex. By doing so, the mechanical properties of an helical macrocyclic complex could be temporarily altered by rearranging it into a [2]catenane.

Modulation of the structural information in shape-defined heterocyclic strands: the case of a (pyridine-hydrazone)2pyrazine ligand.

Metal ions (Ag+, Cd2+, Eu3+, Sm3+) and protons can, through coordination and protonation, modulate in three specific ways the structural information contained in the pyrazine-based heterocyclic strand L (obtained from 2,5-bis(methylhydrazino)pyrazine and 2 equivalents of 2-pyridinecarboxaldehyde), thus generating two linear rod-like conformations and a bent one. This conformational diversity is associated with a structural one that consists of two diprotonated forms (H2L(PF6)2 and H2L(CF3SO3)2), a polymeric architecture [AgL]n(CF3SO3)n, two rack-like complexes ([Eu2H2L3(CF3SO3)6](PF6)2 and [Sm2H2L3(CF3SO3)6](PF6)2) and a grid-like structure ([Cd4L4](CF3SO3)8).

A Single Bioinspired Hexameric Nickel Catechol-Alloxazine Catalyst Combines Metal and Radical Mechanisms for Alkene Hydrosilylation.

Mechanisms combining organic radicals and metallic intermediates hold strong potential in homogeneous catalysis. Such activation modes require careful optimization of two interconnected processes: one for the generation of radicals and one for their productive integration towards the final product. We report that a bioinspired polymetallic nickel complex can combine ligand- and metal-centered reactivities to perform fast hydrosilylation of alkenes under mild conditions through an unusual dual radical- and metal-based mechanism. This earth-abundant polymetallic complex incorporating a catechol-alloxazine motif as redox-active ligand operates at low catalyst loading (0.25 mol%) and generates silyl radicals and a nickel-hydride intermediate through a hydrogen atom transfer (HAT) step. Evidence of an isomerization sequence enabling terminal hydrosilylation of internal alkenes points towards the involvement of the nickel-hydride species in chain walking. This single catalyst promotes a hybrid pathway by combining synergistically ligand and metal participation in both inner- and outer- sphere processes.

Cross-metathesis of Allenes. Mechanistic Analysis and Identification of a Ru-CAAC as the Most Effective Catalyst.

The first examples of cross-metathesis between two different allenes is disclosed. First- and second-generation Ru complexes were found to be ineffective, at most affording only oligomeric products. The exception was a first-generation complex bearing a bidentate phenyl isopropoxy ligand (i.e., PCy3 is not released upon initiation), reactions with which afforded a 1,3-disubstituted allenyl boronate in 22% yield. On the basis of mechanistic studies designed to gain deeper understanding of the reasons for the ineffectiveness of different Ru catalysts, it was discovered that phosphine-free Ru-CAAC complexes have the steric and electronic attributes to be highly effective. The results of these investigations pave the way for development of additional olefin metathesis reactions that generate allenes.

Optical spin-state polarization in a binuclear europium complex towards molecule-based coherent light-spin interfaces.

The success of the emerging field of solid-state optical quantum information processing (QIP) critically depends on the access to resonant optical materials. Rare-earth ion (REI)-based molecular systems, whose quantum properties could be tuned taking advantage of molecular engineering strategies, are one of the systems actively pursued for the implementation of QIP schemes. Herein, we demonstrate the efficient polarization of ground-state nuclear spins-a fundamental requirement for all-optical spin initialization and addressing-in a binuclear Eu(III) complex, featuring inhomogeneously broadened 5D0 → 7F0 optical transition. At 1.4 K, long-lived spectral holes have been burnt in the transition: homogeneous linewidth (Γh) = 22 ± 1 MHz, which translates as optical coherence lifetime (T2opt) = 14.5 ± 0.7 ns, and ground-state spin population lifetime (T1spin) = 1.6 ± 0.4 s have been obtained. The results presented in this study could be a progressive step towards the realization of molecule-based coherent light-spin QIP interfaces.

Simultaneous Generation of a [2 × 2] Grid-Like Complex and a Linear Double Helicate: a Three-Level Self-Sorting Process.

Two constitutional dynamic libraries (CDLs)-each containing two amines, two dialdehydes, and two metal salts-have been found to self-sort, generating two pairs of imine-based metallosupramolecular architectures (sharing no component) each with a [2 × 2] grid-like complex and a linear double helicate. These CDLs provided unique examples of a three-level self-sorting process, as only two imine-based ligand constituents, two metal complexes, and two architectures were selected during their assembly out of all the possible combinations of their initial components. The metallosupramolecular architectures assembled were characterized by NMR, mass spectroscopy, and X-ray crystallography.

Bi-stable spin-crossover in charge-neutral [Fe(R-ptp)2] (ptp = 2-(1H-pyrazol-1-yl)-6-(1H-tetrazol-5-yl)pyridine) complexes.

Bi-stable charge-neutral iron(ii) spin-crossover (SCO) complexes are a class of switchable molecular materials proposed for molecule-based switching and memory applications. In this study, we report on the SCO behavior of a series of iron(ii) complexes composed of rationally designed 2-(1H-pyrazol-1-yl)-6-(1H-tetrazol-5-yl)pyridine (ptp) ligands. The powder forms of [Fe2+(R-ptp-)2]0 complexes tethered with less-bulky substituents-R = H (1), R = CH2OH (2), and R = COOCH3 (3; previously reported)-at the 4-position of the pyridine ring of the ptp skeleton showed abrupt and hysteretic SCO at or above room temperature (RT), whereas complex 5 featuring a bulky pyrene substituent showed incomplete and gradual SCO behavior. The role of intermolecular interactions, lattice solvent, and electronic nature of the chemical substituents (R) in tuning the SCO of the complexes is elucidated.

Entrapment of THF-Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination.

The reaction of H3 SiR (R=Ph, nBu) with cationic η5 -C5 Me5 - (Cp*) and benzo[h]quinolinyl-based iridacycle [1 b]+ gives rise to new [(IrH)→SiRH2 ]+ adducts. In the presence of THF these adducts readily undergo elimination of H2 gas at subambient temperature to form THF-stabilized metallacyclic IrIII silylene complexes, which were characterized in situ by NMR spectroscopy, trapped in minute amounts by reactive crystallization, and structurally characterized by XRD. Theoretical investigations (static DFT-D reaction-energy profiling, ETS-NOCV) support the promoting role of THF in the H2 elimination step and the consolidation of the Ir-to-Si interaction in the spontaneous (ΔG<0) formation of Ir silylenes in the presence of THF. Mechanistic insights indicate that the Ir silylene species arising from the [1 b]+ /phenylsilane system are relevant catalytic species in the hydrodefluorination of fluoroalkanes.

Low valent Al(ii)-Al(ii) catalysts as highly active ε-caprolactone polymerization catalysts: indication of metal cooperativity through DFT studies.

The present study first describes the reactivity of low valent Al(ii) and Ga(ii) complexes of the type (dpp-bian)M-M(dpp-bian) (1, M = Al; 2, Ga; dpp-bian2- = 1,2-bis-(2,6-iPr2-C6H3)-acenaphthenequinonediamido) with cyclic esters/carbonates such as ε-caprolactone (CL) and trimethylene carbonate (TMC). CL and TMC both readily coordinate to the Al(ii) species 1 to form the corresponding bis-adducts (dpp-bian)Al(L)-(L)Al(dpp-bian) (3, L = CL; 4, L = TMC), which were structurally characterized confirming that the Al(ii)-Al(ii) dimetallic backbone retains its integrity in the presence of such cyclic polar substrates. In contrast, the less Lewis acidic Ga(ii) analogue 2 shows no reaction in the presence of stoichiometric amounts of CL and TMC at room temperature. In combination with BnOH, the dinuclear Al(ii) species 1 revealed to be an extremely active Al(ii) initiator for the controlled ROP of CL at room temperature, outperforming all its Al(iii) congeners reported thus far. Detailed DFT studies on the ROP mechanism are consistent with a process occurring thanks to the metallic cooperativity between the two Al(ii) proximal (since directly bonded) metal centers in 1, which undoubtedly favors the ROP process through bimetallic activation and thus rationalizes the unusually high CL ROP activity at room temperature.

Synthesis and Study at a Solid/Liquid Interface of Porphyrin Dimers Linked by Metal Ions.

Several porphyrin dimers linked by metal ions were prepared. One trimeric compound was also isolated and one porphyrin dimer linked by palladium(II) could be structurally characterized. In solution, the size of the new compounds was estimated by DOSY NMR techniques. These compounds all contained long aliphatic chains (O-C12H25), which were used to assemble them at a highly oriented pyrolytic graphite (HOPG)/liquid interface. The highly ordered arrays were visualized by scanning tunneling microscopy (STM).

Mononuclear salen-gallium complexes for iso-selective ring-opening polymerization (ROP) of rac-lactide.

A series of mononuclear salen-supported gallium amido/alkoxide derivatives were prepared and structurally characterized and subsequently used as initiators in rac-lactide ring-opening polymerisation (ROP). The reaction of variously substituted salen ligands (1a-1f) with 0.5 equiv. of Ga2(NMe2)6 allowed the isolation of the corresponding (salen)Ga-NMe2 chelates (2b-2d, 2f) via an amine elimination route, as poorly soluble compounds in common solvents. The (salen)Ga-OBn derivatives (3a-3e) may be readily accessed by an amine-elimination/alcoholysis sequence and the molecular structures of 3a, 3d and 3e were confirmed through X-ray crystallography diffraction analysis. The present (salen)Ga-X species may effectively mediate the iso-selective ROP of rac-LA in a controlled manner (Pm up to 0.77 using a 1/1 2f/BnOH mixture as ROP initiator), with a ROP activity greatly dependent upon steric hindrance and geometrical constraints imposed by the variously substituted salen ligands. Based on the present study, salen ligands with limited steric hindrance and a certain degree of flexibility appear best suited for iso-selective ROP by (salen)Ga chelates. The salen-gallium complex 3a is also effective for the controlled ROP of ε-caprolactone (CL) and the production of PCL-b-PLA copolymers.

trans-cis C-Pd-C rearrangement in hemichelates.

Kinetically unstable heteroleptic trans-bispalladacycles were isolated by using hemichelation. Three structures of trans isomers and five of cis isomers were characterized by X-ray diffraction analysis. The ready trans-to-cis isomerization of such hemichelates that was monitored by variable temperature NMR experiments is facilitated dynamically because the Pd(ii) center can preserve its square planar coordination in a rather low lying transition state, which was localized by methods of the density functional theory. This process is not achievable in the isomerization of conventional homoleptic trans-bispalladacycles since it involves the preliminary partial chelate decoordination and an unfavorable high-lying planar trigonal coordinated - or Y-shaped-Pd(ii) transition state according to DFT investigations.

Comparative Study of the Synthesis and Structural and Physicochemical Properties of Diketopiperazines vs Aza-diketopiperazines.

Aza-diketopiperazines (aza-DKPs) represent an underprivileged motif obtained by scaffold hopping of 2,5-diketopiperazines (2,5-DKPs). Herein, we compare the synthesis and the structural and physicochemical properties of aza-DKP 4 vs 2,5-DKP 7. Thus, X-ray and 1H NMR studies show that aza-DKP 4 is a rigid and nonflat scaffold like the 2,5-DKP 7. Moreover, the replacement of one Cα-stereogenic center by a nitrogen atom results in a significant improvement of both the water solubility and the microsomal stability.

New Pd(II) hemichelates devoid of incipient bridging COPd interactions.

In organometallic chemistry the commonly known Sidgwick-Langmuir 18 electron rule is constantly being probed for further discovery of molecular compounds that arise as exceptions. The present study examines the formation and the structure of three novel hemichelates of Pd(ii) derived from the reaction of in situ-formed indene and hydrophenanthrene-based organometallic anions with three different µ-chloro-bridged palladacycles. Electronic structure and interaction behavior have been calculated with methods of the density functional theory at the (ZORA) MetaGGA-D TPSS-D3(BJ), GGA-D PBE-D3(BJ), and hybrid PBE0-dDsC dispersion corrected levels, all with the implementation of all electron triple zeta single polarization basis set. A particular focus of the theoretical investigation was made on the nature of the interaction between the [Cr(CO)3] moiety and the Pd(ii) centers, which according to X-ray diffraction analyses lack significant incipient bridging COPd character. Structures were further assessed - Natural Bonding Orbitals (NBO), Quantum Theory of Atoms in Molecules (QTAIM), and Extended Transition State with Natural Orbitals for Chemical Valence (ETS-NOCV) analysis methods. As a result, intramolecular interactions of interest, primarily around the Pd atom, were analyzed as a measure of natural atomic orbital (NAO) contributions to the natural bonding orbital (NBO) formation, QTAIM analysis with special attention to the bonding critical points (BCPs), as well as energetic analysis of intramolecular interaction forces by Energy Decomposition Analysis (EDA). Theoretical analyses confirm that attractive electrostatics dominate the stabilization of Pd(ii) hemichelates. In the case of complexes , and we expand the known amount of 14 electron transition metal complexes that can be synthesized via reliable synthetic methods. However, complex presented some means of stability but was more reactive to moisture and air under laboratory conditions and escaped thorough analytical characterization.

Normal-to-Abnormal NHC Rearrangement of Al(III) , Ga(III) , and In(III) Trialkyl Complexes: Scope, Mechanism, Reactivity Studies, and H2 Activation.

The present contribution reports experimental and theoretical mechanistic investigations on a normal-to-abnormal (C2-to-C4-bonded) NHC rearrangement processes occurring with bulky group 13 metal NHC adducts, including the scope of such a reactivity for Al compounds. The sterically congested adducts (nItBu)MMe3 (nItBu=1,3-di-tert-butylimidazol-2-ylidene; M=Al, Ga, In; 1 a-c) readily rearrange to quantitatively afford the corresponding C4-bonded complexes (aItBu)MMe3 (4 a-c), a reaction that may be promoted by THF. Thorough experimental data and DFT calculations were performed on the nNHC-to-aNHC process converting the Al-nNHC (1 a) to its aNHC analogue 4 a. A nItBu/aItBu isomerization is proposed to account for the formation of the thermodynamic product 4 a through reaction of transient aItBu with THF-AlMe3 . The reaction of benzophenone with (nItBu)AlMe3 afforded the zwitterionic species (aItBu)(CPh2 -O-AlMe3 ) (6), reflecting the unusual reactivity that such bulky adducts may display. Interestingly, the nItBu/Al(iBu)3 Lewis pair behaves like a frustrated Lewis pair (FLP) since it readily reacts with H2 under mild conditions. This may open the way to future reactivity developments involving commonly used trialkylaluminum precursors.

A Ca(2+)-, Mg(2+)-, and Zn(2+)-Based Dendritic Contractile Nanodevice with Two pH-Dependent Motional Functions.

A contractile dendritic motional device is reported where metal ions with biological importance--Ca(2+) (the main regulatory and signaling species of the natural muscles), Mg(2+), and Zn(2+)--initiate two kinds of motional functions. The first motional function is the metal-ion-induced contraction of a linear strand into a Z-shaped dinuclear complex, and the second one is the change of the height of Z-shaped complexes via transmetalation. By means of the pH-dependent counterligand tren, the two motional features of the machine can depend on alternate additions of acid and base. An optical response is associated with the conversion of the linear form (which is yellow) into the metalated Z-shaped one (which is red).

Crystal structure of 1,1'-{(pentane-1,5-di-yl)bis[(aza-niumylyl-idene)methanylyl-idene]}bis(naphthalen-2-olate).

The whole mol-ecule of the title compound, C27H26N2O2, is generated by twofold rotational symmetry, with the central C atom of the pentyl chain located on the twofold rotation axis. The compound crystallizes as a bis-zwitterion, and there are two intra-molecular N-H⋯O hydrogen bonds generating S(6) ring motifs. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, forming ribbons propagating along [001], and enclosing R 2 (2)(22) ring motifs.