Kinetic chain

Inertial effects caused by perturbations of dynamical equilibrium during the flow of soft matter constitute a hallmark of turbulence. Such perturbations are attributable to an imbalance between energy storage and energy dissipation. During the flow of Newtonian fluids, kinetic energy can be both stored and dissipated, while the flow of viscoelastic soft matter systems, such as polymer fluids, induces the accumulation of both kinetic and elastic energies. The accumulation of elastic energy causes local stiffening of stretched polymer chains, which can destabilise the flow...

Stenotrophomonas spp. intrinsically resistant to many β-lactam antibiotics are found throughout the environment. CESS-1 identified in Stenotrophomonas sp. KCTC 12332 is an uncharacterized class A β-lactamase. Here, CESS-1 was revealed to display hydrolytic activities toward penicillins (penicillin G and ampicillin) and cephalosporins (cephalexin, cefaclor, and cefotaxime), while its activity toward carbapenems (imipenem and meropenem) was negligible. Although cefaclor, cephalexin, and ampicillin have similar structures with identical R1 side chains, the catalytic parameters of CESS-1 toward the three β-lactam antibiotics were distinct...

ConspectusAluminum is the most abundant metal in the earth's crust at 8%, and it is also widely available domestically in many countries worldwide, which ensures a stable supply chain. To further the applications of aluminum (Al), such as in catalysis and electronic and energy storage materials, there has been significant interest in the synthesis and characterization of new Al coordination compounds that can support electron transfer (ET) and proton transfer (PT) chemistry. This has been achieved using redox and chemically noninnocent ligands (NILs) combined with the highly stable M(III) oxidation state of Al and in some cases the heavier group 13 ions, Ga and In...

Solution-state self-assemblies of block copolymers to form nanostructures are tremendously attractive for their tailorable morphologies and functionalities. While incorporating moieties with strong ordering effects may introduce highly orientational control over the molecular packing and dictate assembly behaviors, subtle and delicate driving forces can yield slower kinetics to reveal manifold metastable morphologies. Herein, we report the unusually convoluted self-assembly behaviors of a liquid crystalline block copolymer bearing triphenylene discotic mesogens...

Due to the putative role of butyrylcholinesterase (BChE) in regulation of acetylcholine levels and functions in the late stages of the Alzheimer's disease (AD), the potential of selective inhibitors (BChEIs) has been envisaged as an alternative to administration of acetylcholinesterase inhibitors (AChEIs). Starting from our recent findings, herein the synthesis and in vitro evaluation of cholinesterase (ChE) inhibition of a novel series of some twenty 3,4,5,6-tetrahydroazepino[4,3-b]indol-1(2H)-one derivatives, bearing at the indole nitrogen diverse alkyl-bridged 4-arylalkylpiperazin-1-yl chains, are reported...

We study the nonequilibrium dynamics of the Floquet quantum East model (a Trotterized version of the kinetically constrained quantum East spin chain) at its "deterministic point," where evolution is defined in terms of CNOT permutation gates. We solve exactly the thermalization dynamics for a broad class of initial product states by means of "space evolution." We prove: (i) the entanglement of a block of spins grows at most at one-half the maximal speed allowed by locality (i.e., half the speed of dual-unitary circuits); (ii) if the block of spins is initially prepared in a classical configuration, speed of entanglement is a quarter of the maximum; (iii) thermalization to the infinite temperature state is reached exactly in a time that scales with the size of the block...

An amphiphilic aza-BODIPY dye (S)-1 bearing two chiral hydrophilic side chains with S-stereogenic centers was synthesized. This dye exhibited kinetic-controlled self-assembly pathways and supramolecular chiral polymorphism properties in MeOH/H2O (9/1, v/v) mixed solvent. The (S)-1 monomers first aggregated into a kinetic controlled, off-pathway species Agg. A, which was spontaneously transformed into an on-pathway metastable aggregate (Agg. B) and subsequently into the thermodynamic Agg. C. The three aggregate polymorphs of dye (S)-1 displayed distinct optical properties and nanomorphologies...

Per- and polyfluoroalkyl substances (PFAS) are widely used synthetic chemicals that persist in the environment and bioaccumulate in animals and humans. There is growing evidence that PFAS exposure adversely impacts neurodevelopment and neurological health. Steroid 5α-reductase 1 (SRD5A1) plays a key role in neurosteroidogenesis by catalyzing the conversion of testosterone or pregnenolone to neuroactive steroids, which influence neural development, cognition, mood, and behavior. This study investigated the inhibitory strength and binding interactions of 18 PFAS on human and rat SRD5A1 activity using enzyme assays, molecular docking, and structure-activity relationship analysis...

In capsaicin biosynthesis, vanillin aminotransferase (VAMT; EC 2.6.1.119) catalyzes the conversion of vanillin (V) to vanillylamine (VA). In vitro analysis of the recombinant VAMT enzyme has been reported; however, this enzyme catalyzed only the V-forming reaction and not the VA-forming reaction, which is inconsistent with the postulated pathway for capsaicin biosynthesis. In this study, we expressed, purified, and characterized functional recombinant VAMT of Capsicum chinense cv. Habanero from an Escherichia coli strain...

Lytic polysaccharides monooxygenases (LPMOs) catalyze a reaction that is crucial for the biological decomposition of various biopolymers and for the industrial conversion of plant biomass. Despite the importance of LPMOs, the exact molecular-level nature of the reaction mechanism is still debated today. Here, we investigated the pH dependent conformation of a second sphere histidine (His) that we call the "stacking histidine", which is conserved in fungal AA9 LPMOs, and is speculated to assist catalysis in several of the LPMO reaction pathways...

The concept of a 'microbiota-gut-brain axis' has recently emerged as an important player in the pathophysiology of Parkinson disease (PD), not least because of the reciprocal interaction between gut bacteria and medications. The gut microbiota can influence levodopa kinetics, and conversely, drugs administered for PD can influence gut microbiota composition. Through a two-step enzymatic pathway, gut microbes can decarboxylate levodopa to dopamine in the small intestine and then dehydroxylate it to m-tyramine, thus reducing availability...

Sulfur-coordinated coordination polymers (S-CPs) have unique optoelectrical properties that originate from infinite M-S bond networks. In this study, we synthesized and characterized two polymorphs of a two-dimensional Pb(II) S-CP with a formula of [Pb(tzdt)(OAc)] (Htzdt = 1,3-thiazolidine-2-thione, OAc = acetate). Our findings revealed that the thermodynamic product (KGF-26) possesses (-Pb-O-)n chains only, whereas the kinetic product (KGF-27) has both one-dimensional (-Pb-O-)n chains and two-dimensional (-Pb-S-)n layers...

Loop formation in complex environments is crucially important to many biological processes in life. In the present work, we adopt three-dimensional Langevin dynamics simulations to investigate passive and active polymer looping kinetics in crowded media featuring polymer-crowder attraction. We find polymers undergo a remarkable coil-globule-coil transition, highlighted by a marked change in the Flory scaling exponent of the gyration radius. Meanwhile, looping time as a function of the crowder's volume fraction demonstrates an apparent non-monotonic alteration...

Electroactive polymer materials are known to play important roles in a vast spectrum of modern applications such as in supercapacitors, fuel cells, batteries, medicine, and smart materials, etc. They are usually divided into two main groups: first, conducting π-conjugated organic polymers, which conduct electricity by cation-radicals delocalized over a polymer chain; second, redox polymers, which conduct electricity via an electron-hopping mechanism. Polymer materials belonging to these two main groups have been thoroughly studied and their thermodynamic and kinetic models have been built...

The majority of known peptides with high bioactivity (BAPs) such as antihypertensive, antidiabetic, antioxidant, hypocholesterolemic, anti-inflammatory and antimicrobial actions, are short-chain sequences of less than ten amino acids. These short-chain BAPs of varying natural and synthetic origin must be bioaccessible to be capable of being adsorbed systemically upon oral administration to show their full range of bioactivity. However, in general, in vitro and in vivo studies have shown that gastrointestinal digestion reduces BAPs bioactivity unless they are protected from degradation by encapsulation...

The kinetics of the chlorination of leucine, isoleucine, and valine (BCAAs) was studied in excess HOCl by stopped-flow and spectrophotometric methods (25 ◦ C, I = 1.0 M NaClO4 ). The intermediates and products were identified and monitored by 1 H NMR spectroscopy. It was established that these reactions are fully analogous and proceed according to distinct mechanisms under alkaline and neutral conditions. At high pH, the formation and subsequent rate determining decomposition of N-monochloroamino acid control the process...

A general theory is developed to explain the expansion kinetics of a polymer released from a confining cavity in a d -dimensional space. At beginning, the decompressed chain undergoes an explosive expansion while keeping the structure resembling a sphere. As the process continues, the chain transitions to a coil conformation, and the expansion significantly slows down. The kinetics are derived by applying Onsager's variational principle. Computer simulations are then conducted in a quasi-two-dimensional space to verify the theory...

Winery effluents containing high ethanol concentrations and diverse organic matter are ideal substrates for producing medium-chain carboxylic acids via fermentation and chain elongation. However, the process needs to be better understood. This study presents novel insights into the bioconversion mechanisms of medium-chain carboxylic acids by correlating fermentation and chain elongation kinetic profiles with the study of microbial communities at different pH (5 to 7) conditions and temperatures (30 to 40 °C)...

Phenoxyimine (FI)-nickel(II)(2-tolyl)(DMAP) compounds were synthesized and evaluated as precatalysts for the C(sp2 )-C(sp3 ) Suzuki-Miyaura cross coupling of (hetero)arylboronic acids with alkyl bromides. With 5 mol % of the optimal (MeOMe FI)Ni(Aryl)(DMAP) precatalyst, the scope of the cross-coupling reaction was established and included a variety of (hetero)arylboronic acids and alkyl bromides (>50 examples, 33-97% yield). A β-hydride elimination-reductive elimination sequence from reaction with potassium isopropoxide base, yielding a potassium (FI)nickel(0)ate, was identified as a catalyst activation pathway that is responsible for halogen atom abstraction from the alkyl bromide...

Physicochemical investigations on the inclusion of anionic polyamidoaminesuccinamic acid dendrimer, generation 5 (PAMAM-SA, G5) with positively charged hybrid vesicles (HCV), prepared using soylecithin, ion pair amphiphile (IPA), cholesterol and dihexadecyldimethylammonium bromide, were investigated by dynamic light scattering, transmission electron/atomic force microscopy (TEM/AFM), differential scanning calorimetry, fluorescence spectroscopy and surface pressure-time isotherm studies. Adsorption of dendrimer onto vesicle surface and subsequent bilayer disruption strongly depends on the bilayer composition and dendrimer concentration...