Twist-bend nematics,liquid crystal dimers,structure–property relations

ABSTRACT

One of the current challenges in liquid crystal science is to understand the molecular factors leading to the formation of the intriguing twist-bend nematic phase (N_TB) and determine its properties. During our earlier hunt for the N_TB phase created on cooling directly from the isotropic phase and not the nematic phase, we had prepared 30 symmetric liquid crystal dimers. These had odd spacers and methylene links to the two mesogenic groups; desirable but clearly not essential features for the formation of the N_TB. Here, we report the phases that the dimers exhibit and their transition temperatures as functions of both the lengths of the spacer and the terminal chains. In addition we describe the transitional entropies, their optical textures, the X-ray scattering patterns and the ²H NMR spectra employed in characterising the phases. All of which may lead to important properties of the twist-bend nematic phase.     

Spectroscopic and morphological study of laser ablated Titanium

The optical characteristics of biological tissues sampled from the anterior abdominal wall of laboratory rats are for the first time experimentally studied in a wide wavelength range (350-2500 nm). The experiments have been performed in vitro using a LAMBDA 950 (PerkinElmer, United States) spectrophotometer. Inverse Monte Carlo simulation is used to restore the spectral dependences for scattering and absorption coefficients, as well as the scattering anisotropy factor for biological tissue based on the recorded spectra of diffuse reflection and total and collimated transmissions.     

Synthesis and antiviral screening of 2-(propylthio)-7-substituted-thiazolo[5,4-d]pyrimidines as anti-bovine viral diarrhea virus agents

7-Chloro-2-(propylthio)thiazolo[5,4-d]pyrimidine 4 was prepared and used as a precursor for synthesizing new derivatives of thiazolo[5,4-d]pyrimidine through the nucleophilic displacement of the chlorine atom by different types of amino derivatives. Reaction of compound 4 with primary and secondary amines produced the corresponding substituted amino derivatives. Reaction of 4 with hydrazine hydrate then followed by condensation with aromatic aldehydes afforded hydrazone derivatives. Reaction of 4 with hydrazine hydrate then followed by reaction with isothiocyanates gave the disubstituted thiosemicarbazides. Finally, treatment of 4 with hydrazine derivatives afforded the novel disubstituted hydrazine derivatives. Preliminary antiviral screening on the bovine viral diarrhea virus (BVDV) was carried out, which was classified as a member of the same family of Hepatitis C virus. The results indicated that some of the tested compounds exhibited anti-BVDV activity which may be suitable for a new lead molecule to design more potent anti-BVDV agents.     

On Some Inequalities Concerning Rate of Growth of Polynomials

In this paper we consider a class of polynomials P(z) = a0+∑n v=t a v z v, t ≥ 1not vanishing in |z|k, k≥1 and investigate the dependence of max|z|=1|P(Rz)-P(rz)on max|z|=1|P(z)|, where 1 ≤ r R. Our result generalizes and refines some know polynomial inequalities.     

Fused polyaza‐heterocycles and 1,3,4‐thiadiazoles via a tricyano synthon

Treatment of 2‐cyano‐3‐phenyl‐2‐pentenedinitrile with some heterocyclic diazonium salts afforded the corresponding heterocyclic hydrazones. Some of the latter hydrazones were converted into fused polyaza‐heterocycles upon boiling in pyridine. Reaction of 2‐cyano‐3‐phenyl‐2‐pentenedinitrile with phenylisothiocyanate gave a tricyano‐thiole derivative which on treatment with hydrazonoyl chlorides and 1‐(benzothiazol‐2‐yl)‐2‐bromoethanone furnished 1,3,4‐thiadiazole and thiazole derivatives, respectively.     

Antioxidants and Bioactive Compounds in Licorice Root Extract Potentially Contribute to Improving Growth,Bulb Quality and Yield of Onion (Allium cepa)

The increasing culinary use of onion (Alium cepa) raises pressure on the current production rate, demanding sustainable approaches for increasing its productivity worldwide. Here, we aimed to investigate the beneficial effects of licorice (Glycyrrhiza glabra) root extract (LRE) in improving growth, yield, nutritional status, and antioxidant properties of two high-yielding onion cultivars, Shandaweel and Giza 20, growing under field conditions in two consecutive years. Our results revealed that pretreatments of both onion cultivars with LRE exhibited improved growth indices (plant height and number of leaves) and yield-related features (bulb length, bulb diameter, and bulb weight) in comparison with the corresponding LRE-devoid control plants. Pretreatments with LRE also improved the nutritional and antioxidant properties of bulbs of both cultivars, which was linked to improved mineral (e.g., K⁺ and Ca²⁺) acquisition, and heightened activities of enzymatic antioxidants (e.g., superoxide dismutase, catalase, ascorbate peroxidase, glutathione peroxidase, and glutathione S-transferase) and increased levels of non-enzymatic antioxidants (e.g., ascorbic acid, reduced glutathione, phenolics, and flavonoids). LRE also elevated the contents of proline, total free amino acids, total soluble carbohydrates, and water-soluble proteins in both onion bulbs. In general, both cultivars displayed positive responses to LRE pretreatments; however, the Shandaweel cultivar performed better than the Giza 20 cultivar in terms of yield and, to some extent, bulb quality. Collectively, our findings suggest that the application of LRE as biostimulant might be an effective strategy to enhance bulb quality and ultimately the productivity of onion cultivars under field conditions.     

Combining enabling techniques in organic synthesis: solid-phase-assisted catalysis under microwave conditions using a stable Pd(II)-precatalyst

The catalytic activity of a 2-pyridinealdoxime-based Pd(II)-complex covalently anchored via the oxime moiety to a glass/polymer composite material was evaluated in Suzuki-Miyaura cross-coupling reactions of aryl and heteroaryl halides, including arylchlorides, with aryl and heteroaryl boronic acids both under thermal as well as microwave irradiating conditions in water. The stability and reusability of this Pd-precatalyst is part of the present study.     

Synthesis of spiro‐pyrazole‐3,3′‐thiopyrano[2,3‐b]pyridines and azolo[a]pyrido[2′,3′:5,6]thiopyrano[3,4‐d]pyrimidines as new ring systems with antifungal and antibacterial activities

Reactions of 2,3‐dihydro‐4‐oxo‐thiopyrano[2,3‐b]pyridine with aldehydes and with DMF‐DMA furnished the 3‐benzylidene and 3‐(N,N‐dimethylamino)‐methylene derivatives. The latter products afforded spiro‐pyrazolo‐3,3′‐thiopyrano[2,3‐b]pyridines and new tetra‐ and penta‐heterocyclic ring systems when treated with nitrilimines and aminoazoles, respectively. A number of the products showed high antifungal and antibacterial activities.