Poly(ʟ-lactide)s with Tetraphenylethylene: Role of Polymer Chain Packing on Aggregation-Induced Emission Behavior of Tetraphenylethylene

Development of biocompatible and biodegradable fluorescent polymers and understanding their fluorescent characteristics are highly desirable. In this work, we synthesized one-armed, two-armed and four-armed poly(ʟ-lactide)s by ring-opening polymerization of ʟ-lactide...

Molecular and Crystal Structure of a Chitosan−Zinc Chloride Complex

We determined the molecular and packing structure of a chitosan–ZnCl2 complex by X-ray diffraction and linked-atom least-squares. Eight D-glucosamine residues—composed of four chitosan chains with two-fold helical symmetry, and four ZnCl2 molecules—were packed in a rectangular unit cell with dimensions a = 1.1677 nm, b = 1.7991 nm, and c = 1.0307 nm (where c is the fiber axis). We performed exhaustive structure searches by examining all of the possible chain packing modes. We also comprehensively searched the positions and spatial orientations of the ZnCl2 molecules. Chitosan chains of antiparallel polarity formed zigzag-shaped chain sheets, where N2···O6, N2···N2, and O6···O6 intermolecular hydrogen bonds connected the neighboring chains. We further refined the packing positions of the ZnCl2 molecules by theoretical calculations of the crystal models, which suggested a possible coordination scheme of Zn(II) with an O6 atom.

Innovative Preservation Technology for the Fresh Fruit and Vegetables

The preservation of the freshness of fruits and vegetables until their consumption is the aim of many research activities. Quality losses of fresh fruit and vegetables during cold chain are frequently attributable to an inappropriate use of postharvest technologies. Moreover, especially when fresh produce is transported to distant markets, it is necessary to adopt proper postharvest preservation technologies in order to preserve the initial quality and limit microbial decay. Nowadays, for each step of supply chain (packing house, cold storage rooms, precooling center, refrigerate transport and distribution), are available innovative preservation technologies that, alone or in combination, could improve the fresh products in order to maintain the principal quality and nutritional characteristics. The issue groups five original studies and two comprehensive reviews within the topic of preservation technologies related to innovative packaging and postharvest operation and treatments, highlighting their effect on quality keeping.

The spirobichroman-based polyimides with different side groups: from structure–property relationships to chain packing and gas transport performance

Effect of substituents on the dihedral angle and chain packing plays a critical role in the enhancement in the gas separation performance of polymer membranes.

Cadherin-11 dimerization multi-site kinetics: combined partial unfolding and strand-swapping

Cadherin extracellular domain 1 (EC1) mediates dimerization of type II cadherins between opposing cell surfaces to facilitate cell-cell adhesion. EC1 forms domain-swapped dimers, with residues Trp2 and Trp4 crucial to anchor the EC1 A-strand in the strand-swapped conformation. In the present work, the specific roles of Trp2 and Trp4 in the dimerization mechanism of Cadherin-11 have been elucidated using NMR spectroscopy of wild-type and designed mutant EC1 domains. The results show that the dominant monomeric state, with the A strand and Trp side chains packed intramolecularly, is in equilibrium with a sparsely populated (1.6%) partially strand-exposed state, in which the Trp2 side chain packing is disrupted and with a sparsely populated (1.6%) fully strand-exposed state, in which the A strand, Trp2 and Trp4 side chain packing are fully disrupted. The exchange kinetics between the major state and the partially strand-exposed state are slow-intermediate (kex = 700 – 734 s-1) and the exchange kinetics between the major state and the fully strand-exposed state are intermediate-fast (kex = 3470 - 3591 s-1,) on the NMR chemical shift time scale. These three conformations, varying in the degree of A-strand exposure, also are coupled to additional conformational states on very fast and very slow timescales. The very fast exchange process arises from interconversion between ordered and random coil conformations of the BC loop in proximity to the Trp2 binding pocket, with relative populations that depend on the extent of A-strand exposure and dimerization status. The very slow exchange processes link the folded partially and fully strand-exposed conformations with partially unfolded conformational states, which have been recognized as crucial intermediates for domain-swapping in proteins other than cadherins. This framework reveals the dimerization mechanism of type II Cadherins as coupled folding and strand-swapping.

Low-flux scanning electron diffraction reveals substructures inside the ordered membrane domain

Ordered/disordered phase separation occurring in bio-membranes has piqued researchers’ interest because these ordered domains, called lipid rafts, regulate important biological functions. The structure of the ordered domain has been examined with artificial membranes, which undergo macroscopic ordered/disordered phase separation. However, owing to technical difficulties, the local structure inside ordered domains remains unknown. In this study, we employed electron diffraction to examine the packing structure of the lipid carbon chains in the ordered domain. First, we prepared dehydrated monolayer samples using a rapid-freezing and sublimation protocol, which attenuates the shrinkage of the chain-packing lattice in the dehydration process. Then, we optimised the electron flux to minimise beam damage to the monolayer sample. Finally, we developed low-flux scanning electron diffraction and assessed the chain packing structure inside the ordered domain formed in a distearoylphosphatidylcholine/dioleoylphosphatidylcholine binary monolayer. Consequently, we discovered that the ordered domain contains multiple subdomains with different crystallographic axes. Moreover, the size of the subdomain is larger in the domain centre than that near the phase boundary. To our knowledge, this is the first study to reveal the chain packing structures inside an ordered domain.