Hazard characterization of carcinogenicity, mutagenicity, and reproductive toxicity for short chain primary nitroalkanes.

Nitroalkanes are organic aliphatic hydrocarbon compounds with a nitro moiety that are commonly used as solvents or intermediates to synthesize a variety of organic compounds due to their inherent reactivity. In June 2020, a harmonized classification and labeling (CLH) proposal was submitted to the European Chemicals Agency (ECHA) for the following harmonized carcinogenicity, mutagenicity, and reproductive toxicity ("CMR") classifications for nitromethane (NM), nitroethane (NE), and 1-nitropropane (1-NP): NM Carc. 1B and Repr. 1B; NE Repr. 1B; and 1-NP Repr. 2. In this assessment, a weight of evidence (WoE) evaluation of studies on animal carcinogenicity and reproductive and developmental toxicity, genotoxicity, and mode of action for these three nitroalkanes was performed to critically assess the relevance of the proposed CMR classifications. Overall, the WoE indicates that NM, NE, and 1-NP are not carcinogenic, genotoxic, nor selective reproductive or developmental toxicants. Based on our analysis, classifying NM, NE, and 1-NP as Category 2 reproductive toxicants is most appropriate. Furthermore, not classifying NE and 1-NP with respect to their carcinogenicity is appropriate based on the available studies for this endpoint coupled with negative results in genotoxicity studies, metabolism data, and in silico predictions. We determined that the classification for NM of Carc. 1B is not appropriate, based on the fact that rat mammary and harderian tumors are likely not relevant to humans and lung and liver tumors reported in mice were equivocal in their dose-response and statistical significance.

Dialkoxybithiazole: a new building block for head-to-head polymer semiconductors.

Polymer semiconductors have received great attention for organic electronics due to the low fabrication cost offered by solution-based printing techniques. To enable the desired solubility/processability and carrier mobility, polymers are functionalized with hydrocarbon chains by strategically manipulating the alkylation patterns. Note that head-to-head (HH) linkages have traditionally been avoided because the induced backbone torsion leads to poor π-π overlap and amorphous film microstructures, and hence to low carrier mobilities. We report here the synthesis of a new building block for HH linkages, 4,4'-dialkoxy-5,5'-bithiazole (BTzOR), and its incorporation into polymers for high performance organic thin-film transistors. The small oxygen van der Waals radius and intramolecular S(thiazolyl)···O(alkoxy) attraction promote HH macromolecular architectures with extensive π-conjugation, low bandgaps (1.40-1.63 eV), and high crystallinity. In comparison to previously reported 3,3'-dialkoxy-2,2'-bithiophene (BTOR), BTzOR is a promising building block in view of thiazole geometric and electronic properties: (a) replacing (thiophene)C-H with (thiazole)N reduces steric encumbrance in -BTzOR-Ar- dyads by eliminating repulsive C-H···H-C interactions with neighboring arene units, thereby enhancing π-π overlap and film crystallinity; and (b) thiazole electron-deficiency compensates alkoxy electron-donating characteristics, thereby lowering the BTzOR polymer HOMO versus that of the BTOR analogues. Thus, the new BTzOR polymers show substantial hole mobilities (0.06-0.25 cm(2)/(V s)) in organic thin-film transistors, as well as enhanced I(on):I(off) ratios and greater ambient stability than the BTOR analogues. These geometric and electronic properties make BTzOR a promising building block for new classes of polymer semiconductors, and the synthetic route to BTzOR reported here should be adaptable to many other bithiazole-based building blocks.

Charge injection engineering of ambipolar field-effect transistors for high-performance organic complementary circuits.

Ambipolar π-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution-processed caesium (Cs) salts, as electron-injection and hole-blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (∼4.1 eV) compared to that of a pristine Au electrode (∼4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility ∼0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility ∼0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated. Most importantly, in these OFETs the counterpart charge carrier currents are highly suppressed for depletion mode operation (I(off) < 70 nA when I(on) > 0.1-0.2 mA). Thus, high-performance, truly complementary inverters (high gain >50 and high noise margin >75% of ideal value) and ring oscillators (oscillation frequency ∼12 kHz) based on a solution-processed ambipolar polymer are demonstrated.

Cross-linked hyperbranched polyglycerols as hosts for selective binding of guest molecules.

The ring-closing metathesis reaction of dendrimers containing allyl ether end groups is known to rigidify them significantly. Herein we report that polyallylated hyperbranched polyglycerol (HPG) 1 complexes the sodium salt of rose Bengal in chloroform solution but releases it readily to water. In contrast, extensively cross-linking 1 with Grubbs catalyst provides 2 which similarly complexes rose Bengal, but does not release it despite 12 h of shaking with water. Both 1 and 2 also complex thymol blue and exhibit the same differential complex stability when extracted with water. Neither 1 nor 2 complex Congo red sodium salt and more weakly solubilize the cesium salt of rose Bengal and thymol blue. Larger loop size cross-linked analogs HPG 5 and 6 also bind rose Bengal (RB) and thymol blue and are able to bind Congo red, but both release the dye more readily when extracted with water. In addition, a bathochromic shift is observed in the UV spectra for complex 6.RB, suggesting a changed microenvironment for the dye due to a tighter binding of the counteranion. Dihydroxylation of the alkene groups in 1, 2, 5, and 6 produced HPGs 3, 4, 7, and 8, respectively. HPGs 3 and 4 are both water-soluble, but 7 and 8 were not and could not be studied further. In water, HPG 4 solubilized less than one nonpolar guest (Nimodipine, pyrene, or Nile red) per polymer at least in part because it forms very large aggregates. Dynamic light scattering (DLS) and size exclusion chromatography (SEC) indicate aggregates with diameters of ca. 100 nm in pure water. The aggregates dissociated in high salt concentrations suggesting applications in stimuli responsive materials.

A high-mobility electron-transporting polymer for printed transistors.

Printed electronics is a revolutionary technology aimed at unconventional electronic device manufacture on plastic foils, and will probably rely on polymeric semiconductors for organic thin-film transistor (OTFT) fabrication. In addition to having excellent charge-transport characteristics in ambient conditions, such materials must meet other key requirements, such as chemical stability, large solubility in common solvents, and inexpensive solution and/or low-temperature processing. Furthermore, compatibility of both p-channel (hole-transporting) and n-channel (electron-transporting) semiconductors with a single combination of gate dielectric and contact materials is highly desirable to enable powerful complementary circuit technologies, where p- and n-channel OTFTs operate in concert. Polymeric complementary circuits operating in ambient conditions are currently difficult to realize: although excellent p-channel polymers are widely available, the achievement of high-performance n-channel polymers is more challenging. Here we report a highly soluble ( approximately 60 g l(-1)) and printable n-channel polymer exhibiting unprecedented OTFT characteristics (electron mobilities up to approximately 0.45-0.85 cm(2) V(-1) s(-1)) under ambient conditions in combination with Au contacts and various polymeric dielectrics. Several top-gate OTFTs on plastic substrates were fabricated with the semiconductor-dielectric layers deposited by spin-coating as well as by gravure, flexographic and inkjet printing, demonstrating great processing versatility. Finally, all-printed polymeric complementary inverters (with gain 25-65) have been demonstrated.

Synthesis and catalytic properties of diverse chiral polyamines.

Chiral polyamines can be utilized for a variety of potential applications, ranging from asymmetric catalysis to nonviral gene delivery systems for DNA and RNA. They can also be utilized to solubilize carbon nanotubes. Thus, methods for the straightforward synthesis of chiral polyamines are needed. We present herein two synthetic strategies for accessing chiral polyamines. The potential of these chiral amines to catalyze two organic reactions with a high degree of chiral induction was also explored.Text: Chiral polyamines have been utilized for a variety of applications. First, polyamines are polycationic at neutral pH; as such, they interact strongly with both DNA and RNA.1 They can therefore be utilized as effective nonviral gene delivery agents.2 Second, chiral polyamines are efficient catalysts for various organic transformations.3 Polyamines have also been used to solubilize carbon nanotubes.4 Finally, chiral polyamines are excellent ligands for many transition metals.5 Due to their numerous applications, high-yielding synthetic strategies for their preparation are in great demand. We present herein two synthetic strategies for accessing chiral polyamines, and the potential of these chiral amines to catalyze two organic reactions.

Does the A.T or G.C base-pair possess enhanced stability? Quantifying the effects of CH...O interactions and secondary interactions on base-pair stability using a phenomenological analysis and ab initio calculations.

An empirically based relationship between overall complex stability (-DeltaG degrees ) and various possible component interactions is developed to probe the question of whether the A.T/U and G.C base-pairs exhibit enhanced stability relative to similarly hydrogen-bonded complexes. This phenomenological approach suggests ca. 2-2.5 kcal mol-1 in additional stability for A.T owing to a group interaction containing a CH...O contact. Pairing geometry and the role of the CH...O interaction in the A.T base-pair were also probed using MP2/6-31+G(d,p) calculations and a double mutant cycle. The ab initio studies indicated that Hoogsteen geometry is preferred over Watson-Crick geometry in A.T by ca. 1 kcal mol-1. Factors that might contribute to the preference for Hoogsteen geometry are a shorter CH...O contact, a favorable alignment of dipoles, and greater distances between secondary repulsive sites. The CH...O interaction was also investigated in model complexes of adenine with ketene and isocyanic acid. The ab initio calculations support the result of the phenomenological approach that the A.T base-pair does have enhanced stability relative to hydrogen-bonded complexes with just N-H...N and N-H...O hydrogen bonds.

Structure-function studies on a synthetic guanosine receptor that simultaneously binds Watson-Crick and Hoogsteen sites.

[structure: see text] A series of receptors (11-16) designed to simultaneously bind the Watson-Crick and Hoogsteen sites of guanosine were synthesized, and their binding of guanosine tri-O-pentanoate (32) was probed via 1H NMR complexation studies in 5% DMSO-d6-chloroform-d. The guanosine receptors were synthesized with aminonaphthalene or aminoquinoline auxiliary groups tethered to N-4 of cytosine via a methylene or carbonyl group. A structure-function relationship was established allowing energetic contributions made by components of nucleoside analogues to be probed and more general design rules formulated that may guide the development of more efficacious DNA bases.

With regard to the hydrogen bonding in complexes of pyridylureas, less is more. a role for shape complementarity and CH...O interactions?

A pyridylurea.tetraazaanthracenedione complex with three hydrogen bonds is more stable than an analogous complex with four hydrogen bonds. An X-ray analysis and modeling suggests a steric mismatch destabilizing the latter and a CH...O contact enhancing the stability of the former.