Impact of Halogen Termination and Chain Length on π-Electron Conjugation and Vibrational Properties of Halogen-Terminated Polyynes

We explored the optoelectronic and vibrational properties of a new class of halogen-terminated carbon atomic wires in the form of polyynes using UV-vis, infrared absorption, Raman spectroscopy, X-ray single-crystal diffraction, and DFT calculations. These polyynes terminate on one side with a cyanophenyl group and on the other side, with a halogen atom X (X = Cl, Br, I). We focus on the effect of different halogen terminations and increasing lengths (i.e., 4, 6, and 8 sp-carbon atoms) on the π-electron conjugation and the electronic structure of these systems. The variation in the sp-carbon chain length is more effective in tuning these features than changing the halogen end group, which instead leads to a variety of solid-state architectures. Shifts between the vibrational frequencies of samples in crystalline powders and in solution reflect intermolecular interactions. In particular, the presence of head-to-tail dimers in the crystals is responsible for the modulation of the charge density associated with the π-electron system, and this phenomenon is particularly important when strong I··· N halogen bonds occur.

Cycloaddition-Retro-Electrocyclization Click Reaction of Amine End-Capped Oligoynes with Tetracyanoethylene

This study shows the first example of cycloaddition-retro-electrocyclization (CA-RE) click reaction involving nitrogen end-capped push-pull oligoynes. The reported CA-RE reaction with TCNE (tetracyanoethylene) is fully regioselective and leads exclusively to the unprecedented TCBD (tetracyanobuta-1,3-diene-2,3-diyl) end-capped carbon rods. The molecular structure of the products was unambiguously confirmed using X-ray single crystal diffraction and their optical and electronic properties were investigated experimentally and rationalized using DFT (density functional theory) calculations.

Homogeneous Gold Catalysis for Regioselective Carbocyclization of Alkynyl Precursors

π-Activation of alkynyl precursors possessing an endogenous carbon nucleophile is one of the imperative topics in homogeneous gold catalysis as it offers Csp3-Csp2 and Csp2-Csp2 linked carbocycles. However, the exo-dig and endo-dig cyclization modes unlocks the possibility of both small and large rings respectively, thereby losing regioselectivity. Nevertheless, several gold-catalyzed carbocyclizations which permits one isomer by controlling or avoiding the formation of other went largely unnoticed. Hence, this review is an attempt to summarize such approaches reported from early 2000's to till date along with our viewpoint on contributing parameters for regioselectivity. This review covers only unimolecular reactions with classifications primarily based on the type of endogenous nucleophiles such as silyloxyenols, enamides/enamines, benzenoids, heteroaromatics and alkyls/alkenyls. From an application perspective, these reactions are significant in total synthesis and materials science. Therefore, those reactions that finds application in natural product synthesis and π-functional materials are highlighted in appropriate places.

Characterization of Octa-aminopropyl polyhedral oligomeric silsesquioxanes (OA-POSS) nanoparticles and their effect on sweet basil (Ocimum basilicum L.) response to salinity stress

Salt stress is of the most detrimental abiotic stress factors on either crop or non-crop species. Of the strategies employed to boost the performance of the plants against harmful impacts of salt stress; application of novel nano-engineered particles have recently gained great attention as a promising tool. Octa-aminopropyl polyhedral oligomeric silsesquioxanes nanoparticles (OA-POSS NPs) were synthesized and then a foliar-application of OA-POSS NPs were carried out on sweet basil plants subjected to the salt stress. In that context, interactive effects of OA-POSS NPs (25, 50 and 100 mg L^-1) and salinity stress (50 and 100 mM NaCl) were assayed by estimating a series of agronomic, physiological, biochemical and analytical parameters. OA-POSS NPs decreased the harmful effects of salinity by increasing photosynthetic pigment content, adjusting chlorophyll fluorescence, and triggering non-enzymatic (phenolic content) and enzymatic antioxidant components. The findings suggested that 25 mg L^-1 OA-POSS NPs is the optimum concentration for sweet basil grown under salt stress. Considering the essential oil profile, estragole was the predominant compound with a percentage higher than 50% depending on the treatment. In comparison to the control group, 50 mM NaCl did not significantly affect estragole content, whilst 100 mM NaCl caused a substantial increase in estragole content. Regarding OA-POSS NPs treatments, increments by 16.8%, 11.8% and 17.5% were observed following application with 25, 50 and 100 mg L^-1, respectively. Taken together, the current study provides evidence that POSS NPs can be employed as novel, 'green' growth promoting agents in combating salt stress in sweet basil.

Analysis of dead-core formation in catalytic reaction and diffusion processes with generalized diffusion flux

Dead-core and non-dead-core solutions to the nonlinear diffusion-reaction equation based on the generalized diffusion flux with gradient-dependent diffusivity and the power-law reaction kinetics in catalyst slabs are established. The formation of dead zones where the reactant concentration vanishes is characterized by the critical Thiele modulus that is derived as a function of reaction order and diffusion exponent in the generalized diffusion flux. The effects of reaction order and diffusion exponent on the reactant concentration distribution in the slab and dead-zone length are analyzed. It is particularly demonstrated that by contrast to the model based on the standard Fick's diffusion, dead-core solutions exist in the case of first-order reactions. Also, the relationship between critical Thiele moduli for models based on the generalized and standard Fick's diffusion fluxes is established.

Direct Preparation of N-Substituted Pyrazoles from Primary Aliphatic or Aromatic Amines

Despite a large number of synthesis procedures for pyrazoles known today, those directly employing primary amines as substrates are rare. Herein, we report an original method for the preparation of N-alkyl and N-aryl pyrazoles from primary aliphatic or aromatic amines as a limiting reagent of the reaction. The protocol utilizes no inorganic reagents and requires a short reaction time, mild conditions, and the use of structurally simple and commercially available starting reagents. During this study, pyrazoles containing a wide variety of N-substituents were obtained using the same procedure for both aliphatic and aromatic amines.

Serendipitous Formation of Various Selenium Heterocycles Hidden in the Classical Synthesis of Selenophene

Synthesis of complex di(selenophen-3-yl)diselenides and 3-methylene-3H-1,2-diselenoles directly from 1-bromobutadiynes is described. The transformation is performed under conditions used before for the synthesis of simple selenophenes from butadiynes. The reaction is operationally straightforward, and complex products were obtained in high yields. Structures of the final products were unambiguously confirmed by the means of 77Se NMR and single-crystal X-ray diffraction.

Solvent-free C–H alkynylation of azulenes

Simple grinding of azulenes with 1-haloalkynes and solid Al2O3 in a mortar leads to alkynylated azulenes without the use of solvents or precious metal catalysts. Such a method was used for the synthesis of azulene end-capped carbon molecular wires.

Zinc Imine Polyhedral Oligomeric Silsesquioxane as a Quattro-Site Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Low-Pressure CO2

In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique Zn^II complex of imine-functionalized polyhedral oligomeric silsesquioxane (POSS) is designed, and hereby described, as a catalyst for the synthesis of cyclic carbonates from epoxides and CO₂. The uncommon features of the designed catalytic system is the elimination of the need for a high pressure of CO₂ and the significant shortening of reaction times commonly associated with such difficult transformations like that of styrene oxide to styrene carbonate. Our studies have shown that imine-POSS is able to chelate metal ions like Zn^II to form a unique coordination complex. The silsesquioxane core and the hindrance of the side arms (their steric effect) influence the construction process of the homoleptic Zn₄@POSS-1 complex. The compound was characterized in solution by NMR (¹H, ¹³C, ²⁹Si), ESI-MS, UV/Vis spectroscopy and in the solid state by thermogravimetric/differential thermal analysis (TG-DTA), elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), cross-polarization magic angle spinning (CP MAS) NMR (¹³C, ²⁹Si) spectroscopy, and X-ray crystallography.

Free and hydrogel encapsulated exosome-based therapies in regenerative medicine

Over the last few decades, mesenchymal stem cells-derived exosomes (MSCs-Ex) have attracted a lot of attention as a therapeutic tool in regenerative medicine. Exosomes are extracellular vehicles (EVs) that play important roles in cell-cell communication through various processes such as stress response, senescence, angiogenesis, and cell differentiation. Success in the field of regenerative medicine sparked exploration of the potential use of exosomes as key therapeutic effectors of MSCs to promote tissue regeneration. Various approaches including direct injection, intravenous injection, intraperitoneal injection, oral administration, and hydrogel-based encapsulation have been exploited to deliver exosomes to target tissues in different disease models. Despite significant advances in exosome therapy, it is unclear which approach is more effective for administering exosomes. Herein, we critically review the emerging progress in the applications of exosomes in the form of free or association with hydrogels as therapeutic agents for applications in regenerative medicine.

Design and functionalization of bioactive benzoxazines. An unexpected ortho-substitution effect

A family of o, p- and N-functionalized dihydro-2H-benzo-1,3-oxazines was synthesized and characterized.

Selective synthesis of iridium(iii) end-capped polyynes by oxidative addition of 1-iodopolyynes to Vaska's complex

The reaction of bis(triphenylphosphine)iridium(i) carbonyl chloride (Vaska's complex) with a series of 1-iodopolyynes (1-C_nI and 2-C_nI) gave σ-polyynyl iridium(iii) complexes with general formula R(C[triple bond, length as m-dash]C)_nIr(PPh₃)₂(Cl)(I)(CO). The use of acetonitrile as a solvent appeared crucial and allowed selectively obtaining only one from a few possible isomers. The X-ray single crystal diffraction experiment for 2-C₄[Ir]I allowed the determination of the exact structure of this complex. Further spectroscopic measurements, especially ³¹P NMR, confirmed the formation of the same type of isomers with trans coordinated phosphines in each case. All complexes were fully characterized with the use of NMR (¹H, ¹³C and ³¹P), IR, UV/Vis, cyclic voltammetry and (ESI)HRMS techniques. Moreover, DFT calculations were performed for all the resulting species. The complexes with a linear carbon chain from butadiyne to decapentayne are the longest iridium end-capped polyynes known to date since only compounds with a (C[triple bond, length as m-dash]C)₂ structural motif have been reported so far. Moreover, we confirmed that the synthetic approach, first used for palladium(ii) end-capped polyynes, may be also applied for the synthesis of other structurally new organometallic polyynes.

Porous Silsesquioxane-Imine Frameworks as Highly Efficient Adsorbents for Cooperative Iodine Capture

The efficient capture and storage of radioactive iodine (¹²⁹I or ¹³¹I), which can be formed during nuclear energy generation or nuclear waste storage, is of paramount importance. Herein, we present highly efficient aerogels for reversible iodine capture, namely, porous silsesquioxane-imine frameworks (PSIFs), constructed by condensation of octa(3-aminopropyl)silsesquioxane cage compound and selected multitopic aldehydes. The resulting PSIFs are permanently porous (Brunauer-Emmet-Teller surface areas up to 574 m²/g), thermally stable, and present a combination of micro-, meso-, and macropores in their structures. The presence of a large number of imine functional groups in combination with silsesquioxane cores results in extremely high I₂ affinity with uptake capacities up to 485 wt %, which is the highest reported to date. Porous properties can be controlled by the strut length and rigidity of linkers. In addition, PSIF-1a could be recycled at least four times while maintaining 94% I₂ uptake capacity. Kinetic studies of I₂ desorption show two strong binding sites with apparent activation energies of 77.0 and 89.0 kJ/mol. These energies are considerably higher than the enthalpy of sublimation of bulk I₂.

Synthesis of cubic spherosilicates for self-assembled organic–inorganic biohybrids based on functionalized methacrylates

Covalent hybrid networks created by fully substituted cubic spherosilicates containing functionalized methacrylates as side chains were synthesized.

DFT calculations as a ligand toolbox for the synthesis of active initiators for ROP of cyclic esters

New heteroleptic zinc dimeric complexes bearing an aminophenolate ligand of a single-site initiator framework were synthesized and characterized by spectroscopic methods, X-ray analysis, and DFT calculations. The theoretical study, verified by the experimental data, explains the catalytic behaviour in the ROP of lactide in the examined zinc complexes. The presented simple DFT protocol constitutes a valuable method for the qualification of the ancillary ligand to rationally design new complexes to improve their catalytic activity.

First step towards a model system of the drug delivery network based on amide-POSS nanocarriers

We present the synthetic and release aspects of a novel drug delivery system (DDS) based on amido-functionalized POSS. DDS after drug release hydrolyses at pH = 7.40 to non-toxic products such as carboxylic acid salts and aminopropyl-POSS.

Transition-Metal Free Mechanochemical Approach to Polyyne Substituted Pyrroles

In this contribution, the synthesis of long chain hexatriynyl- and octatetraynyl-substituted pyrroles in one step from 1-halopolyyne precursors is reported. The products were obtained via a mechanochemical approach by simple grinding of 1-haloalkynes with N-substituted pyrroles and potassium carbonate which played a role of heterogeneous catalyst and this solvent- and transition metal-free approach is unprecedent in the synthesis of new, organic, long chain polyynes. Additionally, an extensive X-ray single crystal study of pyrrole end-capped polyynes is presented. Such compounds are possible substrates for different oligoheterocycles and have a significant application potential such as for instance molecular wires.

Zebra reaction or the recipe for the synthesis of heterodimeric zinc complexes

A series of asymmetric heterodimeric zinc complexes have been synthesized in a direct reaction between conformationally flexible chiral/achiral homodimers. The cooperative activity of steric factors and coordination codes resulted in an intriguing chiral self-sorting process. Herein, we are reporting our recent exploration of the first example of such a type of reaction.

Synthesis and microstructural properties of the scaffold based on a 3-(trimethoxysilyl)propyl methacrylate–POSS hybrid towards potential tissue engineering applications

The biomimetic organic–inorganic scaffold with the chemical composition, structural dimensions, topography, and microstructural properties that fulfills the requirements for hard-tissue engineering was developed.

Multifunctional imine-POSS as uncommon 3D nanobuilding blocks for supramolecular hybrid materials: synthesis, structural characterization, and properties

Imino-functionalized cage-like octasilsesquioxanes provide unique examples of the 3D supramolecular network and their relationship to the assembly of tunable materials from nanobuilding blocks.

Synthesis of Long, Palladium End-Capped Polyynes through the Use of Asymmetric 1-Iodopolyynes

The synthesis of a unique series of long, asymmetric 1-iodopolyynes (1-Cn I and 2-Cn I) with the sp-hybridized carbon chain up to a decapentayne is reported. These compounds were then used as substrates in reactions with Pd(PPh3 )4 leading to another series of palladium end-capped polyynes, which were unstable in solution. Organometallic octatetraynes 1-C8 [Pd]I, 2-C8 [Pd]I, and decapentayne 1-C10 [Pd]I are palladium end-capped polyyne compounds with the longest carbon chains reported so far. All the complexes as well as their organic precursors were fully characterized by NMR, HRMS(ESI), IR, TGA-DTA, and UV/Vis techniques, and the X-ray crystal structures of two silyl-protected precursors and one palladium complex are presented. The synthetic approach for palladium species is envisioned as a general route for the synthesis of labile organometallic polyynes.

Spectral dependence of nonlinear optical properties of symmetrical octatetraynes with p-substituted phenyl end-groups

Organic compounds containing conjugated carbon chains have been extensively investigated due to their interesting properties including nonlinear optical response.

Designing ancillary ligands for heteroleptic/homoleptic zinc complex formation: synthesis, structures and application in ROP of lactides

Synthesis and characterization of a series of new amino-phenol/naphthol ligands (L1,2-H) have been developed and their respective zinc complexes (1 and 2-Zn) have been synthesized.

Direct synthesis of butadiynyl-substituted pyrroles under solvent- and transition metal-free conditions

The work describes a convenient and highly efficient C–H butadiynylation of substituted pyrroles under mild and solvent-free conditions.

Novel organic–inorganic hybrids based on T8 and T10 silsesquioxanes: synthesis, cage-rearrangement and properties

A simple approach for the synthesis of well-defined macromolecules based on isolated amino- and amido-functionalized octa T₈ and deca T₁₀ silsesquioxanes is presented. Here we show how the reorganization of the siloxane cage-like core (cage rearrangement) can be performed.

A versatile and highly efficient method for 1-chlorination of terminal and trialkylsilyl-protected alkynes

A highly efficient one-pot procedure for the preparation of 1-chloroalkynes and 1-chlorobutadiynes from terminal and trialkylsilyl-protected precursors is reported. This convenient reaction, proceeding under mild conditions, utilizes N-chlorosuccinimide as the chlorinating agent and tolerates a range of functional groups.