Comparative rotatory power of bent and twisted polyynes.

Linear polyynes of the formula C18 H2 (symmetry D∞h ) were bent in silico by progressively introducing CCC angles less than 180°. The bent structures (symmetry C2v ) were then twisted by introducing torsion angles across the CCCC segments by as much as 60°. The gyration tensors of these 19 structures (linear, bent, and twisted) were computed by linear response methods. Bending is massively generative of optical activity in oriented structures, even achiral structures, whereas twisting in conjunction with bending, serves to linearize the molecules and diminish maximally observable optical activity. This computational exercise is intended to unbind the infelicitous linkage of optical activity and chirality, which is only meaningful in isotropic media. Although bent structures are not optically active in solution-the spatial average of the optical activity is necessarily zero-solution measurements that deliver the spatial averages are a special class of measurements, albeit the overwhelmingly most common chiroptical measurements, that prejudice our common understanding of how π-conjugated structures generate gyration. Bending is far more effective than twisting at generating optical activity along some directions for oriented structures. The respective contributions from the transition electric dipole-magnetic dipole polarizability and the transition electric dipole-electric quadrupole polarizability are compared.

(E)-7-phenyl-2-heptene-4,6-diyn-1-ol from Bidens pilosa as a repellent against isopods.

The development of repellents as alternatives to insecticides has expanded in recent years. However, their use in isopod pest control is limited. To develop an isopod repellent, a plant extract library from wild plants native to the Kochi Prefecture was screened for repellent activity against pillbugs, and 82 samples (87%) exhibited repellent activity. Among them, (E)-7-phenyl-2-heptene-4,6-diyn-1-ol was isolated and identified as a repellent from the root of Bidens pilosa. It had a half-maximal effective concentration of 0.20 µm, with a strong repellency. A study of the structure-activity relationship to (E)-7-phenyl-2-heptene-4,6-diyn-1-ol revealed that the presence of a hydroxyl group and an aromatic at both ends of the length of the seven-carbon chain is important for the expression of repellency. These results can potentially lead to a new repellent of phenylalkyl alcohol.

Macrocyclic Complexes Derived from Four cis-L2 Pt Corners and Four Butadiynediyl Linkers; Syntheses, Electronic Structures, and Square versus Skew Rhombus Geometries.

The dialkyl malonate derived 1,3-diphosphines R2 C(CH2 PPh2 )2 (R=a, Me; b, Et; c, n-Bu; d, n-Dec; e, Bn; f, p-tolCH2 ) are combined with (p-tol3 P)2 PtCl2 or trans-(p-tol3 P)2 Pt((C≡C)2 H)2 to give the chelates cis-(R2 C(CH2 PPh2 )2 )PtCl2 (2 a-f, 94-69 %) or cis-(R2 C(CH2 PPh2 )2 )Pt((C≡C)2 H)2 (3 a-f, 97-54 %). Complexes 3 a-d are also available from 2 a-d and excess 1,3-butadiyne in the presence of CuI (cat.) and excess HNEt2 (87-65 %). Under similar conditions, 2 and 3 react to give the title compounds [(R2 C(CH2 PPh2 )2 )[Pt(C≡C)2 ]4 (4 a-f; 89-14 % (64 % avg)), from which ammonium salts such as the co-product [H2 NEt2 ]+ Cl- are challenging to remove. Crystal structures of 4 a,b show skew rhombus as opposed to square Pt4 geometries. The NMR and IR properties of 4 a-f are similar to those of mono- or diplatinum model compounds. However, cyclic voltammetry gives only irreversible oxidations. As compared to mono-platinum or Pt(C≡C)2 Pt species, the UV-visible spectra show much more intense and red-shifted bands. Time dependent DFT calculations define the transitions and principal orbitals involved. Electrostatic potential surface maps reveal strongly negative Pt4 C16 cores that likely facilitate ammonium cation binding. Analogous electronic properties of Pt3 C12 and Pt5 C20 homologs and selected equilibria are explored computationally.

Trapping of Terminal Platinapolyynes by Copper(I) Catalyzed Click Cycloadditions; Probes of Labile Intermediates in Syntheses of Complexes with Extended sp Carbon Chains, and Crystallographic Studies.

The silylated hexatriynyl complex trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)3 SiEt3 (PtC6 TES) is converted in situ to PtC6 H (wet n-Bu4 N+ F- , THF) and cross coupled with the diyne H(C≡C)2 SiEt3 (HC4 TES; CuCl/TMEDA, O2 ) to give PtC10 TES (71 %). This sequence is repeated twice to afford PtC14 TES (65 %) and then PtC18 TES (27 %). An analogous series of reactions starting with PtC8 TES gives PtC12 TES (60 %), then PtC16 TES (43 %), and then PtC20 TES (17 %). Similar cross couplings with H(C≡C)2 Si(i-Pr)3 (HC4 TIPS) give PtC12 TIPS (68 %), PtC14 TIPS (68 %), and PtC16 TIPS (34 %). The trialkylsilyl species (up to PtC18 TES) are converted to 3+2 "click" cycloadducts or 1,4-disubstituted 1,2,3-triazoles trans-(C6 F5 )(p-tol3 P)2 Pt(C≡C)n-1 C=CHN(CH2 C6 H5 )N=N (29-92 % after workups). The most general procedure involves generating the terminal polyynes PtCx H (wet n-Bu4 N+ F- , THF) in the presence of benzyl azide in DMF and aqueous CuSO4 /ascorbic acid. All of the preceding complexes are crystallographically characterized and the structural and spectroscopic properties analyzed as a function of chain length. Two pseudopolymorphs of PtC20 TES are obtained, both of which feature molecules with parallel sp carbon chains in a pairwise head/tail packing motif with extensive sp/sp van der Waals contacts.

Building from Ga-Porphyrins: Synthesis of Ga-Acetylide Complexes Using Acetylenes and Polyynes.

Multidimensional, conjugated building blocks have been formed through the axial coordination of polyynes to the central Ga atom of tetraarylporphyrins. Electron deficient pentafluorophenyl substituents in the meso-positions provide more stable σ-acetylide complexes to Ga than analogous structures with tert-butylphenyl groups. Mono-, di-, and triynes have been used, including a pyridyl endcapped diyne that allows for formation of porphyrin triads through coordination of the pyridyl ligand to a Ru porphyrin.

On-surface synthesis and characterization of polyynic carbon chains.

Carbyne, an elusive sp-hybridized linear carbon allotrope, has fascinated chemists and physicists for decades. Due to its high chemical reactivity and extreme instability, carbyne was much less explored in contrast to the sp2-hybridized carbon allotropes such as graphene. Herein, we report the on-surface synthesis of polyynic carbon chains by demetallization of organometallic polyynes on the Au(111) surface; the longest one observed consists of ∼60 alkyne units (120 carbon atoms). The polyynic structure of carbon chains with alternating triple and single bonds was unambiguously revealed by bond-resolved atomic force microscopy. Moreover, an atomically precise polyyne, C14, was successfully produced via tip-induced dehalogenation and ring-opening of the decachloroanthracene molecule (C14Cl10) on a bilayer NaCl/Au(111) surface at 4.7 K, and a band gap of 5.8 eV was measured by scanning tunnelling spectroscopy, in a good agreement with the theoretical HOMO-LUMO gap (5.48 eV).

Effects of Structural Variations on Antibacterial Properties for Conjugated Diynes Generated through Glaser Hay Couplings.

Antibiotic resistance is a growing problem facing global societies today. Many new antibiotics are derivatized versions of already existing antibiotics, which allows for antibiotic resistance to arise. To combat this issue, new antibiotics with different core structures need to be elucidated. Asymmetrical polyacetylenes have been isolated from natural products and they have previously been demonstrated to exhibit antimicrobial and antibacterial activity; however, their synthetic preparation has not made them easily amenable to rapid derivatization for SAR studies. Using a combination of solution and solid-supported chemistries, an array of diynes inspired by a known natural product were prepared and assessed for antibacterial activity. Ultimately, several compounds were identified with improved activity in bacterial viability assays. Moreover, some compounds were discovered that displayed a degree of specificity for E. coli over P. fluorescens and vice versa. These new compounds show promise, and further investigation is needed to pinpoint the specific structural components that elicit biological activity.

On-Surface Debromination of C6Br6: C6 Ring versus C6 Chain.

Carbon allotropes comprising sp-hybridized carbon atoms have been investigated for decades for their molecular structure. One of the unsolved mysteries is whether they should take a linear or cyclic configuration in condensed phases due to the lack of atomistic characterizations. Herein, we designed a molecule with a C6 skeleton as a model system to address this issue, which was achieved by eliminating Br atoms from hexabromobenzene (C6Br6) molecule on the Ag(111) substrate via thermal treatment. It is found that the C6 ring intermediate resulting from complete debromination is energetically unstable at room temperature based on theoretical calculations. It subsequently transforms into the C6 polyynic chain via a ring-opening process and ultimately polymerizes into the organometallic polyyne, whose triyne structural unit is revealed by bond-resolved noncontact atomic force microscopy. Theoretical calculations demonstrated an energetically favorable pathway in which the ring-opening process occurs after complete debromination of C6Br6. Our study provides a platform for the synthesis of elusive carbon-rich materials.

Chemo-Preventive Potential of Falcarindiol-Enriched Fraction from Oplopanax elatus on Colorectal Cancer Interfered by Human Gut Microbiota.

Oplopanax elatus (Nakai) Nakai is an oriental herb, the polyyne-enriched fraction of which (PEFO) showed anticolorectal cancer (anti-CRC) effects. Other concomitant components, which are inevitably bio-transformed by gut microbiota after oral administration, might be interfere with the pharmacodynamics of polyynes. However, the influence of human gut microbiota on molecules from O. elatus possessing anticancer activity are yet unknown. In this study, the compounds in PEFO and PEFO incubated with human gut microbiota were analyzed and tentatively identified by HPLC-DAD-QTOF-MS. Two main polyynes ((3S,8S)-falcarindiol and oplopandiol) were not significantly decomposed, but some new unknown molecules were discovered during incubation. However, the antiproliferative effects of PEFO incubated with human gut microbiota for 72 h (PEFO I) were much lower than that of PEFO on HCT-116, SW-480, and HT-29 cells. Furthermore, PEFO possessed better anti-CRC activity in vivo, and significantly induced apoptosis of the CRC cells, which was associated with activation of caspase-3 according to the Western-blot results (P<0.05). These results suggest anticolorectal cancer activity of polyynes might be antagonized by some bio-converted metabolites after incubation with human gut microbiota. Therefore, it might be better for CRC prevention if the polyynes could be orally administrated as purified compounds.

Thermomechanical Stability of Carbyne-Based Nanodevices.

An approach is developed to predict stability of carbyne-based nanodevices. Within this approach, the thermo-fluctuation model of instability and break of contact bond in nanodevices, containing carbyne chains and graphene sheets, is offered. Unlike the conventional models, it does not include empirical constants. The results of DFT calculations are used as initial data for this model. Possibility of synergistic effect of temperature and mechanical load on stability and value of service time of carbyne-based nanodevices is predicted. It is ascertained, that this synergism results in a significant (by many orders of magnitude) decrease in the lifetime of nanodevices containing carbyne chains. The atomic mechanism of this phenomenon is outlined. Conditions of thermo-force loading are predicted at which a service time of these devices is sufficient for applications.