Statistical copolymer metal organic nanotubes.

Metal-organic nanotubes (MONTs) are 1-dimensional crystalline porous materials that are formed from ligands and metals in a manner identical to more typical 3-dimensional metal-organic frameworks (MOFs). MONTs form anisotropically in one dimension making them excellent candidates for linker engineering for control of chemical composition and spacing. A novel series of MONTs was synthesized utilizing a mixture of 1,2,4-ditriazole ligands containing both a fully protonated aryl moiety and its tetrafluorinated analog in ratios of, 0 : 1, 1 : 4, 1 : 1, 4 : 1, and 1 : 0, respectively. All MONTs were characterized by both bulk and nanoscale measurements, including SCXRD, PXRD, ssNMR and TEM, to determine the resulting co-polymer architecture (alternating, block, or statistical) and the ligand ratios in the solid materials. All characterization methods point towards statistical copolymerization of the materials in a manner analogous to 3D MOFs, all of which notably could be achieved without destructive analytical methods.

Atomic View of Aqueous Cyclosporine A: Unpacking a Decades-Old Mystery.

An atomic view of a main aqueous conformation of cyclosporine A (CycA), an important 11-amino-acid macrocyclic immunosuppressant, is reported. For decades, it has been a grand challenge to determine the conformation of free CycA in an aqueous-like solution given its poor water solubility. Using a combination of X-ray and single-crystal neutron diffraction, we unambiguously resolve a unique conformer (A1) with a novel cis-amide between residues 11 and 1 and two water ligands that stabilize hydrogen bond networks. NMR spectroscopy and titration experiments indicate that the novel conformer is as abundant as the closed conformer in 90/10 (v/v) methanol/water and is the main conformer at 10/90 methanol/water. Five other conformers were also detected in 90/10 methanol/water, one in slow exchange with A1, another one in slow exchange with the closed form and three minor ones, one of which contains two cis amides Abu2-Sar3 and MeBmt1-MeVal11. These conformers help better understand the wide spectrum of membrane permeability observed for CycA analogues and, to some extent, the binding of CycA to protein targets.

Design, development, synthesis, and crystal structure of the prototype of a new class of deep blue-fluorescing boron heterocycle estrogen mimics.

To further the development of boron heterocyclic compounds that are useful to medicinal chemistry, we demonstrate how the class of compounds known as the diazaborines can be elaborated to produce an exceptionally close structural mimic of a natural estrogen. After building progressively closer models, a benzyloxy-substituted formylphenylboronic acid was ultimately condensed with a hydroxymethylated ß-hydrazinocyclopentenone to give, after debenzylation, an isosteric mimic (diazaborine 1) of the naturally-occurring estrogen equilenin and the prototype of a new class of boron heterocycle estrogen mimics. X-ray crystallography revealed the prototype to be planar, with a transmolecular interoxygen distance virtually identical to that found in equilenin and with a strong hydrogen-bond-donating hydroxyl group. From this it can be anticipated that members of this unique class of boron heterocycle estrogen mimics will be found to possess useful biological properties. Furthermore, the prototype was found to fluoresce in the deep blue region of the visible spectrum, and so the development of members serving as light-emitting probes in biochemical and biological studies can also be anticipated.

Late Lanthanide Macrocyclic Tetra-NHC Complexes.

An isostructural set of macrocyclic tetra-N-heterocyclic carbene (NHC) complexes were synthesized on late lanthanides including Lu, Yb, Ho, Dy, and Gd. They were characterized by single-crystal X-ray diffraction, multinuclear NMR, electrochemistry, and SQUID magnetometry. Solid-state structures show that all complexes are in a highly distorted square-pyramidal geometry with an axial HMDS ligand. 1H NMR for Lu, Yb, and Dy demonstrates that these geometries are maintained in solution. Electrochemical measurements on the Yb complex show that the NHCs are very strong σ-donors compared to other organometallic Yb complexes. Magnetic measurements of the Yb and Dy complexes reveal slow relaxation of the magnetization in both complexes. The highly anisotropic Dy complex possesses an energy barrier to spin reversal of 52.42 K/36.43 cm-1 and waist-restricted hysteresis up to 2.8 K. Finally, an 18-atom macrocycle variant of the Lu complex was synthesized for comparison in reactivity and stability. These complexes are the first lanthanides prepared with macrocyclic NHCs and suggest that NHCs may be a promising ligand for developing single-molecule magnets.

Actinide tetra-N-heterocyclic carbene 'sandwiches'.

Highly-symmetrical, thorium and uranium octakis-carbene 'sandwich' complexes have been prepared by 'sandwiching' the An(iv) cations between two anionic macrocyclic tetra-NHC ligands, one with sixteen atoms and the other with eighteen atoms. The complexes were characterized by a range of experimental methods and DFT calculations. X-ray crystallography confirms the geometry at the metal centre can be set by the size of the macrocyclic ring, leading to either square prismatic or square anti-prismatic shapes; the geometry of the latter is retained in solution, which also undergoes reversible, electrochemical one-electron oxidation or reduction for the uranium variant. DFT calculations reveal a frontier orbital picture that is similar to thorocene and uranocene, in which the NHC ligands show almost exclusively σ-donation to the metal without π-backbonding.

Chemically driven superstructural ordering leading to giant unit cells in unconventional clathrates Cs8Zn18Sb28 and Cs8Cd18Sb28.

The unconventional clathrates, Cs8Zn18Sb28 and Cs8Cd18Sb28, were synthesized and reinvestigated. These clathrates exhibit unique and extensive superstructural ordering of the clathrate-I structure that was not initially reported. Cs8Cd18Sb28 orders in the Ia3̄d space group (no. 230) with 8 times larger volume of the unit cell in which most framework atoms segregate into distinct Cd and Sb sites. The structure of Cs8Zn18Sb28 is much more complicated, with an 18-fold increase of unit cell volume accompanied by significant reduction of symmetry down to P2 (no. 3) monoclinic space group. This structure was revealed by a combination of synchrotron X-ray diffraction and electron microscopy techniques. A full solid solution, Cs8Zn18-x Cd x Sb28, was also synthesized and characterized. These compounds follow Vegard's law in regard to their primitive unit cell sizes and melting points. Variable temperature in situ synchrotron powder X-ray diffraction was used to study the formation and melting of Cs8Zn18Sb28. Due to the heavy elements comprising clathrate framework and the complex structural ordering, the synthesized clathrates exhibit ultralow thermal conductivities, all under 0.8 W m-1 K-1 at room temperature. Cs8Zn9Cd9Sb28 and Cs8Zn4.5Cd13.5Sb28 both have total thermal conductivities of 0.49 W m-1 K-1 at room temperature, among the lowest reported for any clathrate. Cs8Zn18Sb28 has typical p-type semiconducting charge transport properties, while the remaining clathrates show unusual n-p transitions or sharp increases of thermopower at low temperatures. Estimations of the bandgaps as activation energy for resistivity dependences show an anomalous widening and then shrinking of the bandgap with increasing Cd-content.

One macrocyclic ligand, four oxidation states: A 16-atom ringed dianionic tetra-NHC macrocycle and its Cr(II) through Cr(V) complexes.

Despite chromium being among the first transition metals ever reported to bind to an NHC, chromium NHC complexes, especially in mid and high oxidation states, have received scant attention. Herein, the synthesis, characterization, and reactivity of a series of Cr(II) to Cr(V) complexes bearing a 16-atom ringed dianionic tetra-NHC macrocycle are reported. The Cr(II) dimer is diamagnetic and displays a very short Cr-Cr quadruple bond, unprecedented for Cr-NHC complexes to date. Oxidative cleavage of the Cr-Cr bond leads to the formation of a highly stable diamagnetic Cr(IV) oxo complex. Similar reactions with organic azides lead to paramagnetic Cr(IV) imide complexes. Notably, the Cr(IV) oxo can be oxidized in a reversible reaction to yield a Cr(V) cationic oxo complex, which is a very rare high oxidation state Cr-NHC-compound. This Cr(V) oxo undergoes stoichiometric oxygen atom transfer. Similar reactions were attempted with molybdenum and tungsten to form macrocyclic NHC complexes, but only a molybdenum dimer could be isolated.

Isolation and Crystallographic Characterization of Two, Nonisolated Pentagon Endohedral Fullerenes: Ho3 N@C2 (22010)-C78 and Tb3 N@C2 (22010)-C78.

Purified samples of Ho3 N@C2 (22010)-C78 and Tb3 N@C2 (22010)-C78 have been isolated by two distinct processes from the rich array of fullerenes and endohedral fullerenes present in carbon soot from graphite rods doped with Ho2 O3 or Tb4 O7 . Crystallographic analysis of the endohedral fullerenes as cocrystals with Ni(OEP) (in which OEP is the dianion of octaethylporphyrin) shows that both molecules contain the chiral C2 (22010)-C78 cage. This cage does not obey the isolated pentagon rule (IPR) but has two sites where two pentagons share a common C-C bond. These pentalene units bind two of the metal ions, whereas the third metal resides near a hexagon of the cage. Inside the cages, the Ho3 N or Tb3 N unit is planar. Ho3 N@C2 (22010)-C78 and Tb3 N@C2 (22010)-C78 use the same cage previously found for Gd3 N@C2 (22010)-C78 rather than the IPR-obeying cage found in Sc3 N@D3h -C78 .

Elucidating the Growth of Metal-Organic Nanotubes Combining Isoreticular Synthesis with Liquid-Cell Transmission Electron Microscopy.

Metal-organic nanotubes (MONTs) are tunable porous 1D materials that are envisioned to be complementary to carbon nanotubes for anisotropic applications. To date, characterization of MONTs relies on single crystal X-ray diffraction (SCXRD) to determine structure and composition. This requires crystals on the micrometer regime, effectively rendering bulk 3D materials. By tracking the growth of a MONT as a function of time with liquid-cell transmission electron microscopy (LCTEM), TEM, and SCXRD, it was possible to ascertain that the material in the bulk phase matches the nanomaterial in terms of molecular structure. This result allowed for the first measurements of finite bundles of MONTs on the nanometer scale. By employing in situ LCTEM, a time course of the formation of small bundles of MONTs could be acquired which provided mechanistic information on MONT formation which is of utility in reaction optimization and applications development.

Unprecedented Five-Coordinate Iron(IV) Imides Generate Divergent Spin States Based on the Imide R-Groups.

Three five-coordinate iron(IV) imide complexes have been synthesized and characterized. These novel structures have disparate spin states on the iron as a function of the R-group attached to the imide, with alkyl groups leading to low-spin diamagnetic (S=0) complexes and an aryl group leading to an intermediate-spin (S=1) complex. The different spin states lead to significant differences in the bonding about the iron center as well as the spectroscopic properties of these complexes. Mössbauer spectroscopy confirmed that all three imide complexes are in the iron(IV) oxidation state. The combination of diamagnetism and 15 N labeling allowed for the first 15 N NMR resonance recorded on an iron imide. Multi-reference calculations corroborate the experimental structural findings and suggest how the bonding is distinctly different on the imide ligand between the two spin states.

Genotypic diversity and antifungal susceptibility of Cryptococcus neoformans isolates from paediatric patients in China.

Cryptococcosis is a life-threatening mycosis primarily occurring in adult patients particularly those with immunosuppression such as HIV infection/AIDS. The number of reported cases of paediatric cryptococcosis has increased in the last decade around the world, including China. However, current information on the characteristics of cryptococcosis in children, particularly the genotypic diversity and antifungal susceptibility of the isolates, is limited. In the present study, a total of 25 paediatric isolates of Cryptococcus neoformans were genotyped using the ISHAM-MLST scheme. In vitro susceptibility to antifungal agents of the 22 isolates was tested using the CLSI M27-A3 method. Our analyses revealed that the genotypic diversity of C. neoformans isolates from Chinese paediatric patients was low, with ST 5 (80%) and ST 31 (12%) being the two major sequence types. Reduced susceptibility to fluconazole (FLU), 5-flucytosine (5-FC) and itraconazole (ITR) was observed among C. neoformans isolates from Chinese paediatric patients, particularly among the ST5 isolates, which was similar to observations made on C. neoformans isolates from Chinese adult patients. In addition, the majority of isolates (3/4, 75%) obtained from deceased patients showed decreased antifungal susceptibility, which indicates that further monitoring of antifungal susceptibility of Cryptococcus isolates is warranted in management of paediatric cryptococcosis.

The Preparation of Luminescent, Mechanochromic Molecular Containers from Non-Emissive Components: The Box Cations, [Au6 (Triphos)4 Br]5+ and [Au6 (Triphos)4 Br2 ]4.

Two new molecular boxes, the mono-bromo box [Au6 (Triphos)4 Br](SbF6 )5 ⋅6(CH2 Cl2 ), 4 mB, and the dibromo box, [Au6 (Triphos)4 Br2 ⋅H2 O](SbF6 )4 ⋅4(CH2 Cl2 ), 5 dB, have been prepared in crystalline form. Although constructed from non-luminescent components, both are strongly luminescent. Like its chloro counterpart, the mono-bromo box [Au6 (Triphos)4 Br](SbF6 )5 ⋅6(CH2 Cl2 ), 4 mB, is mechanochromic. Under grinding, it loses its luminescence. The bromo-bridged helicate, [(µ-Br){Au3 (Triphos)2 }2 ](CF3 SO3 )5 ⋅2(CH2 Cl2 ), 3µ-H, with a cation that is isomeric with the box [Au6 (Triphos)4 Br]5+ , has also been prepared and crystallographically characterized. Unlike its chloro analogue, [(µ-Br){Au3 (Triphos)2 }2 ](CF3 SO3 )5 ⋅2(CH2 Cl2 ) is not luminescent. Thus, the cation produced upon grinding may be the cation present in the bromo-bridged helicate, [(µ-Br){Au3 (Triphos)2 }2 ](CF3 SO3 )5 ⋅2(CH2 Cl2 ), 3µ-H. The dibromo box, [Au6 (Triphos)4 Br2 ⋅H2 O](SbF6 )4 ⋅4(CH2 Cl2 ), 5 dB, is not significantly mechanochromic.

Cleavage of Carbon Disulfide by n-Propyldiphenylphosphine and Nickel(II) Bromide.

Carbon disulfide is cleaved by n-propyldiphenylphosphine and nickel(II) bromide in a one-step process, to form two unprecedented complexes: orange, [Ni(S2 C2 (Pn PrPh2 )2 )Br(Pn PrPh2 )]Br⋅CS2 (1) and purple [Ni{η2 -SC(Pn PrPh2 )2 }Br(Pn PrPh2 )]Br⋅0.5CS2 (2). Orange (1) contains a dithiolene-related ligand that results from carbon-carbon bond formation, while purple (2) contains a remarkable ligand in which two n-propyldiphenylphosphine molecules have added to a carbon atom of a CS unit that is coordinated to nickel.

Identification and molecular analysis of a lncRNA-HOTAIR transcript from secondary hair follicle of cashmere goat reveal integrated regulatory network with the expression regulated potentially by its promoter methylation.

The HOTAIR transcript is transcribed from the antisense strand within the HOXC gene cluster, and it is thought to play a role in regulating the inductive capacity of dermal papilla cells during the reconstruction of hair-follicle. In the current investigation, we firstly isolated and characterized a lncRNA-HOTAIR transcript from the secondary hair follicle of cashmere goat. Also, we analyzed its transcriptional pattern and methylation level of HOTAIR gene promoter in secondary hair follicle of cashmere goat during anagen and telogen stages. Nucleotide composition analysis indicated that the contents of Adenine (A) and Thymine (T) are higher than that of Guanine (G) and Cytosine (C) in lncRNA-HOTAIR transcript of cashmere goat with the highest frequency distribution of AG nucleotide pair (8.06%). The regulatory network analysis showed a directly or indirectly complex regulatory relationships between lncRNA-HOTAIR of cashmere goat and its potential target molecules: miRNAs, mRNAs and proteins. Also, we showed that lncRNA-HOTAIR was properly transcribed at both anagen and telogen stages of secondary hair follicle of cashmere goat with the anagen being significantly higher than telogen in its expression, which suggest that lncRNA-HOTAIR transcript might be involved in the reconstruction of secondary hair follicle with the formation and growth of cashmere fiber. Taken together with methylation analysis of HOTAIR gene promoter, our data suggest that the promoter methylation of HOTAIR gene most likely is involved in its transcriptional suppression in secondary hair follicle of cashmere goat.

Identifying a Needle in a Haystack: Isolation and Structural Characterization of Er2 C94 as the Carbide Er2 C2 @D3 (85)-C92.

A method has been developed for isolating a pure sample of Er2 C94 from the myriad of fullerenes and endohedral fullerenes that are formed in the electric arc process. Crystallographic analysis of Er2 C94 in a cocrystal formed with Ni(OEP) reveals that the molecule is the carbide Er2 C2 @D3 (85)-C92 . Crystals of Er2 C2 @D3 (85)-C92 ⋅Ni(octaethylporphyrin)⋅2 C7 H8 are isostructural with those of Sm2 @D3 (85)-C92 ⋅Ni(octaethylporphyrin)⋅2 (chlorobenzene). Comparisons are made between the four crystallographically characterized endohedrals (Er2 C2 @D3 (85)-C92 , Gd2 C2 @D3 (85)-C92 , La2 C2 @D3 (85)-C92 , and Sm2 @D3 (85)-C92 ) that utilize the chiral D3 (85)-C92 cage.

Utilization of a Nonemissive Triphosphine Ligand to Construct a Luminescent Gold(I)-Box That Undergoes Mechanochromic Collapse into a Helical Complex.

Luminescent gold(I) complexes ([Au6(Triphos)4Cl](PF6)5·2(CH3C6H5), [Au6(Triphos)4Cl](AsF6)5·8(CH3C6H5), and [Au6(Triphos)4Cl](SbF6)5·7(CH3C6H5) where Triphos = bis(2-diphenylphosphinoethyl)phenylphosphine) with a boxlike architecture have been prepared and crystallographically characterized. A chloride ion resides at the center of the box with two of the six gold(I) ions nearby. Mechanical grinding of blue luminescent crystals containing the cation, [Au6(Triphos)4Cl]5+, results in their conversion into amorphous solids with green emission that contain the bridged helicate cation, [µ-Cl{Au3(Triphos)2}2]5+. A mechanism of the mechanochromic transformation is proposed. The structures of the blue-emitting helicate, [Au3(Triphos)2](CF3SO3)3·4(CH3C6H5)·H2O, and the green-emitting bridged-helicate, [µ-Cl{Au3(Triphos)2}2](PF6)5·3CH3OH have been determined by single crystal X-ray diffraction.

An ordering phase transition, short hydrogen bonds and high Z' in the structure of Ni(Hpydc)2·3H2O.

The structure of Ni(Hpydc)2·3H2O (H2pydc = pyridine-2,6-dicarboxylic acid, also known as dipicolinic acid) has been reinvestigated at variable temperatures. At room temperature, it matches the known structure in the space group P21/c, but at 180 K it undergoes a phase transformation to a twinned structure in Cc. By 120 K, the structure is ordered and twinned with Z' = 4, and shows interesting short hydrogen-bonding interactions that include the formation of hydroxonium species.

Zigzag Sc2C2 Carbide Cluster inside a [88]Fullerene Cage with One Heptagon, Sc2C2@Cs(hept)-C88: A Kinetically Trapped Fullerene Formed by C2 Insertion?

A non-isolated pentagon rule metallic carbide clusterfullerene containing a heptagonal ring, Sc2C2@Cs(hept)-C88, was isolated from the raw soot obtained by electric arc vaporization of graphite rods packed with Sc2O3 and graphite powder under a helium atmosphere. The Sc2C2@Cs(hept)-C88 was purified by multistage high-performance liquid chromatography (HPLC), cocrystallized with Ni-(octaethylporphyrin), and characterized by single-crystal X-ray diffraction. The diffraction data revealed a zigzag Sc2C2 unit inside an unprecedented Cs(hept)-C88 carbon cage containing 13 pentagons, 32 hexagons, and 1 heptagon. Calculations suggest that the observed nonclassical fullerene could be a kinetically trapped species derived from the recently reported Sc2C2@C2v(9)-C86 via a direct C2 insertion.

Postmating Reproductive isolation between strains of Drosophila willistoni.

Speciation can occur through the presence of reproductive isolation barriers that impede mating, restrict cross-fertilization, or render inviable/sterile hybrid progeny. The D. willistoni subgroup is ideally suited for studies of speciation, with examples of both allopatry and sympatry, a range of isolation barriers, and the availability of one species complete genome sequence to facilitate genetic studies of divergence. D. w. willistoni has the largest geographic distribution among members of the Drosophila willistoni subgroup, spanning from Argentina to the southern United States, including the Caribbean islands. A subspecies of D. w. willistoni, D. w. quechua, is geographically separated by the Andes mountain range and has evolved unidirectional sterility, in that only male offspring of D. w. quechua females × D. w. willistoni males are sterile. Whether D. w. willistoni flies residing east of the Andes belong to one or more D. willistoni subspecies remains unresolved. Here we perform fecundity assays and show that F1 hybrid males produced from crosses between different strains found in Central America, North America, and northern Caribbean islands are reproductively isolated from South American and southern Caribbean island strains as a result of unidirectional hybrid male sterility. Our results show the existence of a reproductive isolation barrier between the northern and southern strains and suggest a subdivision of the previously identified D. willistoni willistoni species into 2 new subspecies.

Experimental demonstration of an actuated exercise machine.

Experimental results are obtained for a single degree of freedom prototype next generation exercise machine that aims to maximize the user's power output and ensure passivity with the user. In an effort to optimize the user's power expenditure, the desired velocity trajectory is developed that seeks the unknown user-dependent optimal velocity setpoint. A numerical extremum-seeking algorithm is utilized to seek the optimal velocity setpoint while ensuring the trajectory is sufficiently differentiable. To track the reference trajectory and to ensure passivity, a nonlinear controller is utilized.