No abstract

Both the arrest and thecreationofmovement are fundamental aspects of dynamics on macroscopic as well as microscopic levels. Brakes and motors dominate the operation of machines, be they those of daily life, such as vehicles and appliances, or those of living systems. like muscles and Ilagellae. On the molecular level motion is thenorm;spontanwus freerotationaroundsinglebonds is thus the rule, not the exception. In machines of ordinary experience, such as automobiles, the brake is often as important as the accelerator. We now report the first molecular analog: a reversible molecular brake. Figure I presents theconcept inbothgeneral andspecific terms. 1 (biako ofl) 3 (brako on) -"W 2 (brake ott) 4 (brake on) Figure 1. Conceptualandaetualdepictionoftheoperationofa molecular brake. With the brakedisengaged. the wheel-(a) representedasa threetoothed gear ( I ) and (b) constructed as a triptycene (2)' -spins rapidly. Engagement ofthe brake (3and4) slowsorstopsrotation. With the actual system, the brake is activated remotely (2 -4) by addition of Hg2+ ion. In the absence of Hgz+ (or other metal ions), the triptycene wheel spins rapidly a t 30 OC, as evidenced by the simplicity of the 'H NMR spectrum of 2 (Figure 2b). wherein by virtue of C, symmetry arising from relatively rapid rotation, the 12 triptycene aromatic protons give rise to only four sets (asterisked) of resonances. Addition of Hg(OzCCF3)z to 2 results in profound changes in the 30 OC (and other) 'H NMR spectrum (Figure 3a). Most noteworthy are the change in the extraordinarychemicalshiftoftheB-ringmethoxyin 2 (6 2.1 to a normal 6 4. I 3 value (not shown) and the obvious broadening of the four resonances attributable to the hydrogens in the three benzo rings of the triptycene. Variable-temperature 'H NMR experiments3 (see Figure 3) document the engagement of the brake. In particular, a t -30 OC (contrast Figure 2),thethreearomaticringsofthetriptyceneare nolongerequivalent becauseofthearrest ofrotation on theNMR . . ( I ) For the use of triptycenaas gean see, inter alia (a) Guenzi. A,: Johnson. C.(2) The 9-ring mcthary group is evidently (see models) in the shielding zone of the lriplycene knzo rings; the B-ring melhory group in 9 is similarly shielded (6 2.W).'(3) See supplementary material for specifis.

No abstract

Theanine is a non-protein amino acid that occurs naturally in the tea plant (Camellia sinensis) and contributes to the favourable taste of tea. It is also associated with effects such as the enhancement of relaxation and the improvement of concentration and learning ability. It is also linked with health benefits including the prevention of certain cancers and cardiovascular disease, the promotion of weight loss and enhanced performance of the immune system. Thus, there has been a significant rise in the demand for theanine. While theanine has been chemically and biologically synthesised, techniques to isolate theanine from natural sources remain an important area of research. In this review article, the properties and health benefits of theanine are summarised and the synthesis and isolation of theanine are reviewed and discussed. Future perspectives for the isolation of theanine from natural sources are also outlined.

No abstract

This study aimed to study the impact of selected common organic solvents on extractable solids, phytochemical composition, and antioxidant capacity of S. chinensis. The results showed that the tested solvents played an important role in extraction of total solid and phytochemical composition as well as antioxidant capacity of S. chinensis. Acetone (50% v/v) was found to be the optimal extraction solvent for extractable solids (12.2%), phenolic compounds (60 mg GAE/g DW), flavonoids (100 mg CE/g DW), proanthocyanidins (47.4 mg CE/g DW), and saponins (754 mg EE/g DW) as well as antioxidant capacity (ABTS 334 mM TE/g DW, DPPH 470 mM TE/g DW, FRAP 347 mM TE/g DW, and CUPRAC 310 mM TE/g DW). The extract prepared from 50% acetone had high levels of bioactive compounds (TPC 555 mg GAE/g CRE, flavonoids 819 mg CE/g CRE, proanthocyanidins 392 mg CE/g CRE, and saponins 1,880 mg EE/g CRE) as well as antioxidant capacity (ABTS 414 mM TE/g, DPPH 407 mM TE/g, FRAP 320 mg TE/g, and CUPRAC 623 mM TE/g), thus further confirming that 50% acetone is the solvent of choice. Therefore, 50% acetone is recommended for extraction of phenolic compounds, their secondary metabolites, saponins, and antioxidant capacity from the root of S. chinensis for further isolation and utilisation.

The main aim of this study was to develop rice starch (RS), ι-carrageenan (ι-car) based film. Different formulations of RS (1-4%, w/w), ι-car (0.5-2%, w/w) was blended with stearic acid (SA; 0.3-0.9%, w/w) and glycerol (1%, w/w) as a plasticizer. The effect of film ingredients on the thickness, water vapour permeability (WVP), film solubility (FS), moisture content (MC), colour, film opacity (FO), tensile strength (TS), elongation-at-break (EAB) of film was examined. Interactions and miscibility of partaking components was studied by using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Hydrocolloid suspension solution of mix polysaccharides imparted a significant impact (p<0.05) on the important attributes of resulting edible film. TS and EAB of film were improved significantly (p<0.05) when ι-car was increased in the film matrix. Formulation F1 comprising 2% ι-car, 2% RS, 0.3% SA, Gly 30% w/w and 0.2% surfactant (tween20) provided film with good physical, mechanical and barrier properties. FT-IR and XRD results reveal that molecular interactions between RS-ι-car have a great impact on the film properties confining the compatibility and miscibility of mixed polysaccharide. Results of the study offers new biodegradable formulation for application on fruit and vegetables.

Summary The aim of this study was to investigate the effect of freeze‐drying, hot air‐drying and vacuum‐drying at 70, 90 and 110 °C, on dried lemon pomace polyphenols and antioxidant capacity. The total phenolic content and antioxidant capacity were higher in lemon pomace dried by hot air or under vacuum than those dried by freeze‐drying and increased as the temperature increased. The highest total flavonoid content was recorded in the pomace dried under vacuum at 70 and 90 °C. Lemon pomace dried by freeze‐drying had the highest neohesperidin content, whereas pomace dried under vacuum at 70 °C had the highest rutin and p‐coumaric acid content. The highest gallic acid content was recorded in the pomace dried by hot air at 110 °C. The results of this study indicate that drying technique should be carefully selected according to the bioactive compounds aimed to be extracted.