Heparan sulfate and heparin, two sulfated glycosaminoglycans (GAGs), extracted collagen-tailed acetylcholinesterase (ACHE) from the extracellular matrix (ECM) of the electric organ of Discopyge tschudii. The effect of heparan sulfate and heparin was abolished by protamine; other GAGs could not extract the esterase. The solubilization of the asymmetric AChE apparently occurs through the formation of a soluble AChE-GAG complex of 30S. Heparitinase treatment but not chondroitinase ABC treatment of the ECM released asymmetric AChE forms. This provides direct evidence for the in vivo interaction between asymmetric AChE and heparan sulfate residues of the ECM. Biochemical analysis of the electric organ ECM showed that sulfated GAGs bound to proteoglycans account for 5% of the total basal lamina. Approximately 20% of the total GAGs were susceptible to heparitinase or nitrous acid oxidation which degrades specifically heparan sulfates, and ~80% were susceptible to digestion with chondroitinase ABC, which degrades chondroitin-4 and -6 sulfates and dermatan sulfate. Our experiments provide evidence that asymmetric AChE and carbohydrate components of proteoglycans are associated in the ECM; they also indicate that a heparan sulfate proteoglycan is involved in the anchorage of the collagen-tailed AChE to the synaptic basal lamina.Acetylcholinesterase (ACHE) ~ is one of the major functional components of the neuromuscular junction of both muscle and the electric organ, and is responsible at least in part for terminating the actions of the neurotransmitter acetylcholine released from the presynaptic nerve terminals (1). AChE occurs in several molecular forms that can be separated by velocity sedimentation. These molecules have been shown to belong to two distinct structural classes: the asymmetric and the globular forms (2). The asymmetric forms are composed of tetramers of the globular subunits attached to a long, collagen-like tail (3, 4).We are interested in the study of the interactions involved ~Abbreviations used in this paper: ACHE, acetylcholinesterase; ECM, extracellular matrix; GAGs, glycosaminoglycans. in the attachment of asymmetric AChE to the synaptic extracellular matrix (ECM). AChE occupies <0.1% of the total area of the basal lamina at the nerve-muscle synapse, which suggests a high degree of specificity in its distribution. The factors involved in the AChE-ECM interaction are unknown. We have previously reported on the association of collagentailed AChE with ECM of cultured mouse muscle cells (5) and of the electric organ of Electrophorus and Torpedinidae fishes (6). The three most prevalent classes of molecules in the ECM are collagen type IV; glycoproteins, including laminin, entactin, nidogen, and fibronectin; and proteoglycans formed by complex sugars called glycosaminoglycans (GAGs) (7-11). Multiple interactions of ECM components could play a role in the deposition of asymmetric ACHE. Accordingly,

No abstract

Since the early studies of William J. McCormick in the 1950s, vitamin C has been proposed as a candidate for the treatment of cancer. A number of reports have shown that pharmacological concentrations of vitamin C selectively kill cancer cells in vitro and decrease the growth rates of a number of human tumor xenografts in immunodeficient mice. However, up to the date there is still doubt regarding this possible therapeutic role of vitamin C in cancer, mainly because high dose administration in cancer patients has not showed a clear antitumor activity. These apparent controversial findings highlight the fact that we lack information on the interactions that occurs between cancer cells and vitamin C, and if these transformed cells can uptake, metabolize and compartmentalize vitamin C like normal human cells do. The role of SVCTs and GLUTs transporters, which uptake the reduced form and the oxidized form of vitamin C, respectively, has been recently highlighted in the context of cancer showing that the relationship between vitamin C and cancer might be more complex than previously thought. In this review, we analyze the state of art of the effect of vitamin C on cancer cells in vitro and in vivo, and relate it to the capacity of cancer cells in acquiring, metabolize and compartmentalize this nutrient, with its implications on the potential therapeutic role of vitamin C in cancer.

A concept of interlayer-sensitized photoluminescence (PL) of quasi-2D hybrid perovskite (PVK) with a π-conjugated optically interacting organic cation layer is introduced and demonstrated. A rod-shaped aggregation-induced enhanced emission (AIEE) organic cation (BPCSA+), well fitted into the lattice size of 2D PVK layers, is designed and synthesized to prolong the exciton lifetime in a condensed layer assembly in the PVK. The BPCSA+ promotes the PL of this hybrid PVK up to 10-folds from that of a non-π-conjugated organic cation (OA) 2D PVK. Notably, different from PL of OA 2D PVK, the increased PL intensity of BPCSA 2D PVKs with an increase of the BPCSA ratio in the PVK indicates a critical photon-harvesting contribution of BPCSA. The films of BPCSA 2D PVKs are incredibly stable in ambient environments for more than 4 months and even upon direct contact with water. Additionally, due to the strong two-photon absorption property of BPCSA, the BPCSA 2D PVK displays superior emission properties upon two-photon excitation with a short wavelength IR laser. Thus, the AIEE sensitization system for quasi-2D PVK hybrid system can make a drastic improvement in performance as well as in the stability of the PVK emitter and PVK based nonlinear optical devices.

Atomically thin 2D materials, currently being at the forefront of scientific and technological interest, can be categorized as metallic, semimetallic, semiconducting, insulating, or superconducting, depending on their chemical composition and structural configuration. They also exhibit, in some cases, a transition from an indirect to a direct bandgap alignment when bulk materials are scaled down to monolayers. An important class of 2D materials is layered transition metal dichalcogenides (TMDs) with a tunable bandgap, because photogenerated optical excitations and subsequent excitation dynamics, which produce energy migration and photogenerated charge carrier transport, make them promising candidates for a variety of optoelectronic devices, including solar cells, photodetectors, light-emitting diodes, and phototransistors. In this work, we probe the excitation dynamics following nonlinear optical absorption/scattering in two unexplored TMDs, metallic NbS 2 and semimetallic ZrTe 2 , using a combination of the standard optical Z-scan and photoacoustic Z-scan techniques, and compare them with semiconducting MoS 2 . The comparison of optical Z-scan (OZ-scan), which depends on the contributions of both nonlinear scattering and nonlinear absorption, with photoacoustic Z-scan (PAZ-scan), which depends only on nonlinear absorption due to local heating from nonradiative relaxation, allows us to separate these contributions from the total nonlinear response. In addition, these studies also allow us to look at the nature of nonlinear absorption as to whether it is due to saturable absorption (SA) of a onephoton transition, reverse saturable absorption (RSA) derived from two-photon excitation processes, or any combination thereof. In MoS 2 , NbS 2 , and ZrTe 2 , we observed both SA and RSA. The relevant nonlinear absorption coefficient parameters were obtained. Density functional theory modeling provides an insight onto possible underlying physical processes.

No abstract

No abstract

The understanding of the nonlinear optical (NLO) properties of photonic materials is relevant and necessary for basic studies and technological developments. Among the materials with high optical nonlinearities, layered transition-metal dichalcogenides (LTMDs) have attracted considerable attention from the viewpoint of both synthesis as well as characterization and applications. We report here the third-order NLO properties of one LTMDthe metallic NbS2that was prepared by a modified redox exfoliated method, suspended in acetonitrile. The LTMD was morphologically and compositionally characterized using transmission electron microscopy, atomic force microscopy, X-ray diffraction, Raman scattering, and linear absorption. The Z-scan technique was employed to characterize the nonlinear refraction (NLR) and nonlinear absorption (NLA) behavior in the femtosecond regime. Metallic NbS2 presented a sign inversion of the nonlinear refractive index from negative (self-defocusing) to positive (self-focusing) with the increase of intensity up to 100 GW/cm2. Two distinct features characteristic of NLA, two-photon absorption and saturated absorption, were also observed for different intensity ranges, with the former evolving into the latter as the intensity increased in the same range as for the NLR measurements. The material’s band structure of NbS2 was calculated using the density functional theory, and the origin of the nonlinearities is discussed by comparison with the experimental data.