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.

Temperature-Controlled Selective Mono- vs. Di-ortho-Arylation for the Synthesis of Arylhydrazine Derivatives.

A method of palladium-catalyzed C-H arylation assisted with a 3,4,4-trimethylpyrazol-5-on directing group, selectively providing mono- and di-ortho-arylated products is reported. Steric hindrance appearing between the directing group and the already introduced aryl substituent enables control of mono- vs. diarylation selectivity by the temperature of the reaction. Taking advantage of this, a series of monosubstituted and disubstituted derivatives were obtained in good yields. Moreover, unsymmetrical double-arylation in a one-pot procedure was developed to give corresponding products in reasonable yields. Additionally, synthesis and X-ray study of intermediate palladium metallacycles of both, the first and second arylation reactions, were conducted. X-ray structure comparison emphasizes the geometrical differences that were consistent with the observed reactivity. Finally, decarboxylative cleavage of the pyrazolone directing group under mild conditions gave synthetically useful hydrazones. The presented solution opens the alternative synthetic way to such ortho arylated derivatives of arylhydrazines.

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.

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 ZnII 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 ZnII 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.

Is It Conjugated or Not? The Theoretical and Experimental Electron Density Map of Bonding in p-CH3CH2COC6H4-C≡C-C≡C-p-C6H4COCH3CH2.

The electron density of p-CH3CH2COC6H4-C≡CC≡C-p-C6H4COCH3CH2 has been investigated on the basis of single-crystal X-ray diffraction data collected to high resolution at 100 K and from theoretical calculations. An analysis of the X-ray data of the diyne showed interesting "liquidity" of electron distribution along the carbon chain compared to 1,2-diphenylacetylene. These findings are compatible with the results of topological analysis of Electron Localization Function (ELF), which has also revealed a larger (than expected) concentration of the electron density at the single bonds. Both methods indicate a clear π-type or "banana" character of a single bond and a significant distortion from the typical conjugated structure of the bonding in the diyne with a small contribution of cumulenic structures.

Use of Stable Amine-Capped Polyynes in the Regioselective Synthesis of Push-Pull Thiophenes.

The reactions of a series of 1-halopolyynes with secondary amines led to novel amine end-capped polyynes exhibiting surprisingly high stability toward moisture. The new compounds were characterized by NMR spectroscopy, ESI-MS spectrometry, and X-ray single-crystal diffractometry. The use of amine end-capped polyynes as precursors to substituted push-pull thiophenes was next presented. The results show the first-to the best of our knowledge-transformation of ynamine to thiophene and the first regioselective transformation of a longer polyynes to butadiyne-substituted thiophene. Photophysical studies of the resulting compounds show that some of the substituted thiophenes have high quantum yield photoluminescence upon UV light irradiation.

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.

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. Polyynes are a group of compounds where the conjugation can be modified by appropriate selection of end-groups, enabling "control" and improvement of nonlinear effects. In this work, we investigate three newly synthesized aryl end-capped octatetraynes, exhibiting strong nonlinear absorption and nonlinear refraction properties, which can be attributed to the presence of aryl end-groups with electron-withdrawing functional groups suitable for further extending the conjugation. Nonlinear optical measurements were performed using a f-scan (modified Z-scan) technique with a femtosecond laser system at various wavelengths in the visible and near-infrared range (540-1600 nm), revealing strong negative third-order nonlinear refraction (3NR) and two-photon absorption (2PA) below 600 nm and a noticeable three-photon absorption (3PA) at longer wavelengths. The results of spectroscopic characterization and the crystallographic data for the investigated compounds are also presented.

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.

High-yield synthesis of amido-functionalized polyoctahedral oligomeric silsesquioxanes by using acyl chlorides.

Homosubstituted amido-functionalized polyoctahedral oligomeric silsesquioxanes (POSS) have been synthesized by using acyl chlorides in high yields (ca. 95%). The method proved to be superior over "conventional" syntheses applying carboxylic acids or acid anhydrides, which are much less efficient (ca. 60% yield). A palette of aryl and alkyl groups has been used as side-chains. The structures of the resulting amide-POSS are supported by multinuclear (1)H, (13)C, (29)Si NMR and FTIR spectroscopy and their full conversion into octasubstituted derivatives was confirmed using mass spectrometry. We also demonstrate that the functionalized silsesquioxanes with bulky organic side-chains attached to cubic siloxane core form spherical-like, well-separated nanoparticles with a size of approximately 5 nm.

Gyroscope-like molecules consisting of PdX2/PtX2 rotators within three-spoke dibridgehead diphosphine stators: syntheses, substitution reactions, structures, and dynamic properties.

Threefold intramolecular ring-closing metatheses of trans-[MCl2(P{(CH2)(m)CH=CH2}3)2] are effected with Grubbs' catalyst. Following hydrogenation catalyzed by [RhCl(PPh3)3], the title complexes trans-[MCl2(P((CH2)n)3P)] (n=2m+2; M/n=Pt/14, 4 c; Pt/16, 4 d; Pt/18, 4 e; Pd/14, 5 c; Pd/18, 5 e) and sometimes isomers partly derived from intraligand metathesis, trans-[MCl2{P(CH2)n(CH2)n}P(CH2)n)] (4'c-e, 5'e), are isolated. These react with LiBr, NaI, and KCN to give the corresponding MBr2, MI2, and M(CN)2 species (58-99%). (13)C NMR data show that the MX2 moieties rapidly rotate within the diphosphine cage on the NMR timescale, even at -120 °C. The reaction of 4 c and KSCN gives separable Pt(NCS)2 and Pt(NCS)(SCN) adducts (13 c, 28%; 14 c, 20%), and those of 4 c,e and Ph2Zn give PtPh2 species (15 c, 61%; 15 e, 90%). (13)C NMR spectra of 13 c-15 c show two sets of CH2 signals (ca. 2:1 intensity ratios), indicating that MX2 rotation is no longer rapid. Reactions of 4 c or 4'c and excess NaC≡CH afford the free diphosphines P{(CH2)14}3P (91%) and (CH2)14P(CH2)14P(CH2)14 (90%). The latter has been crystallographically characterized as a bis(BH3) adduct. The crystal structures of eight complexes with P(CH2)14P linkages (PtCl2, PtBr2, PtI2, Pt(NCS)2, PtPh2, PdCl2, PdBr2, PdI2) and 15 e have been determined, and intramolecular distances analyzed with respect to MX2 rotation. The conformations of the (CH2)14 moieties and features of the crystal lattices are also discussed.

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.

Novel hybrid-glass-based material for infiltration of early caries lesions.

OBJECTIVES: To assess the effectiveness of two experimental, hybrid-glass-based infiltrants in arresting artificial white spot lesions (WSLs) in vitro, and to compare it with resin-based infiltrant Icon. METHODS: Artificial WSLs were formed on bovine enamel specimens (n = 68). Specimens were divided into four groups according to WSLs treatment: 1) no-treatment control (NTC), 2) infiltration with Icon (Icon), 3) infiltration with experimental hybrid-glass material (EXP), and 4) infiltration with experimental hybrid-glass material containing hydroxyapatite (HAp) nanoparticles (1%) (EXP-HAp). Half of the specimens from each group were subjected to cariogenic challenge using pH-cycling, consisting of a 7-day alternate incubation (37°C) in demineralization (4 h/day, pH=4.6) and remineralization solutions (20 h/day, pH=7.2). Another half of the specimens was incubated in distilled water (control). Caries progression was assessed by measuring surface micro-hardness (SMH), roughness (Ra) and average surface level, and by analyzing WSLs morphology. Non-cycled and pH-cycled specimens were compared with Man-Whitney U test, while different treatment groups were compared with Kruskal-Wallis test with pairwise comparisons (p < 0.05). RESULTS: In all groups (NTC, Icon and EXP-HAp) except EXP, SMH decreased significantly after pH cycling. In addition, SMH increased in EXP upon pH cycling and was significantly higher than in other pH-cycled groups (<0.001). Ra increased considerably, while surface level decreased after pH cycling in all groups except in EXP. Signs of demineralization and roughness increase in NTC, Icon and EXP-HAp were also observed with the SEM. SIGNIFICANCE: Experimental hybrid-glass-based material without HAp-nanoparticles could completely arrest the progression of WSLs, unlike its version with HAp-nanoparticles and resin-based infiltrant Icon.

Cytotoxicity and anti-biofilm properties of novel hybrid-glass-based caries infiltrant.

OBJECTIVES: To assess the cytotoxicity of an experimental hybrid-glass-based infiltrant and its effect on biofilm attachment, growth and metabolic activity, and to compare it to the resin-based infiltrant Icon. METHODS: Cytotoxicity of hybrid-glass-based material (EXP) and resin-based infiltrant Icon (Icon) was tested in direct contact tests on freshly cured (direct_mat) and on materials kept for 24 h in cell culture medium (direct_exmat), and extract test with materials 24-h extracts (extract). Cell viability of L929 mouse fibroblast cell line was measured with MTT assay, according to ISO10993-5:2009. Biofilm attachment (5 h), growth (24 h and 48 h) and lactic-acid production (24 h and 48 h) on glass-disk specimens coated with EXP or Icon, or uncoated (control), were assessed using a microcosm biofilm model and Amsterdam Active Attachment system. At indicated time points, biofilms were harvested, plated, and CFU counts were determined, while lactic-acid production was measured colorimetrically. RESULTS: Cell viability reduction by EXP was below 30%-threshold in direct contact tests, while in extract test an increased cell viability was observed. Icon reduced cell viability substantially in all three tests. Significantly less bacteria attached to the surface of EXP after 5 h compared to Icon and control. Biofilm growth was significantly lower on EXP than on Icon and control after 24 h, but this difference was smaller and statistically insignificant after 48 h. There was no difference in lactic-acid production among groups. SIGNIFICANCE: Novel hybrid-glass-based infiltrant seems to have a better biocompatibility and accumulates on its surface less bacteria than resin-based infiltrant, which makes it an attractive resin-free alternative.

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.

Synergies in exosomes and autophagy pathways for cellular homeostasis and metastasis of tumor cells.

BACKGROUND: Eukaryotic cells demonstrate two tightly linked vesicular transport systems, comprising intracellular vesicle transport and extracellular vesicle transport system. Intracellular transport vesicles can translocate biomolecules between compartments inside the cell, for example, proteins from the rough endoplasmic reticulum to the Golgi apparatus. Whereas, the secreted vesicles so-called extracellular vesicles facilitate the transport of biomolecules, for example, nucleic acids, proteins and lipids between cells. Vesicles can be formed during the process of endocytosis or/and autophagy and not only act as mediators of intra- and inter-cellular communication but also represent pathological conditions of cells or tissues. METHODS: In this review, we searched articles in PubMed, published between 2000 and 2020, with following terms: autophagy, autophagocytosis, transport vesicles, lysosomes, endosomes, exocytosis, exosomes, alone or in different combinations. The biological functions that were selected based on relevancy to our topic include cellular homeostasis and tumorigenesis. RESULTS: The searched literature shows that there is a high degree of synergies between exosome biogenesis and autophagy, which encompass endocytosis and endosomes, lysosomes, exocytosis and exosomes, autophagocytosis, autophagosomes and amphisomes. These transport systems not only maintain cellular homeostasis but also operate synergically against fluctuations in the external and internal environment such as during tumorigenesis and metastasis. Additionally, exosomal and autophagic proteins may serve as cancer diagnosis approaches. CONCLUSION: Exosomal and autophagy pathways play pivotal roles in homeostasis and metastasis of tumor cells. Understanding the crosstalk between endomembrane organelles and vesicular trafficking may expand our insight into cooperative functions of exosomal and autophagy pathways during disease progression and may help to develop effective therapies against lysosomal diseases including cancers and beyond.