Native Chromophore Research Articles

Modulating the pH dependent photophysical properties of green fluorescent protein.

The photophysical properties of the β-barrel superfolder green fluorescent protein (sfGFP) arise from the chromophore that forms post-translationally in the interior of the protein. Specifically, the protonation state of the side chain of tyrosine 66 in the chromophore, in addition to the network of hydrogen bonds between the chromophore and surrounding residues, is directly related to the electronic absorbance and emission properties of the protein. The pH dependence of the photophysical properties of this protein were modulated by the genetic, site-specific incorporation of 3-nitro-l-tyrosine (mNO2Y) at site 66 in sfGFP. The altered photophysical properties of this noncanonical amino acid (ncAA) sfGFP construct were assessed by absorbance and fluorescence spectroscopies. Notably, a comparison of the pK a of the 3-nitrophenol side chain of mNO2Y incorporated in the protein relative to the phenol side chain of the tyrosine at site 66 in the native chromophore as well as the pK a of the 3-nitrophenol side chain of the free ncAA were measured and are compared. A structural analysis of the ncAA containing sfGFP construct is presented to yield molecular insight into the origin of the altered absorbance and fluorescence properties of the protein.

Tuning Two-Photon Absorption in Rhodopsin Chromophore via Backbone Modification: The Story Told by CC2 and TD-DFT.

We investigate here a systematic way to tune two-photon transition strengths (δ2PA) and two-photon absorption (2PA) cross sections (σ2PA) of the rhodopsin's chromophore 11-cis-retinal protonated Schiff base (RPSB) via the modulation of the methyl groups pattern along its polyene chain. Our team employed the resolution of identity, coupled cluster approximate second order (RI-CC2) method with Dunning's aug-cc-pVDZ basis set, to determine the structural impact on δ2PA, as well as its correlation to both transition dipole moments and permanent electric dipole moments. Seven structures were probed in vacuo, including five-double-bond-conjugated model of the native chromophore, shortened by the β-ionone ring (RPSB5), and its de/methylated analogues: 9-methyl, 13-methyl, planar and twisted models of 9,10-dimethyl and 9,10,13-trimethyl. Our results demonstrate that the magnitude of δ2PA is dictated by both the position and number of methylated groups attached to its polyene chain as well as the degree of dihedral twist that is introduced due to the de/methylation. In fact, a strong correlation between δ2PA enhancement and the presence of a C13-methyl group in the planar RPSB5 species is found. Trends in δ2PA values follow the trends observed in their corresponding changes in the permanent dipole moment upon the S0-S1 excitation nearly exactly. The assessment of four DFT functionals, i.e., M11, MN15, CAM-B3LYP, and BHandHLYP, previously found most successful in predicting 2PA properties in biological chromophores, points to a long-range-corrected hybrid meta-GGA M11 as the top-performing functional, albeit still delivering underestimated δ2PA and σ2PA values by a factor of 3.3-5.3 with respect to the CC2 results. In the case of global-hybrid meta-NGA (MN15), as well as CAM-B3LYP and BHandHLYP functionals, this factor deteriorates significantly to 6.7-20.9 and is mostly related to significantly lower quality of the ground- and excited-state dipole moments.

A Visible-Light Regulated ATP Transport in Retinal-Modified Pillar[6]arene Layer-by-Layer Self-Assembled Sub-Nanochannel.

Natural light-responsive rhodopsins play a critical role in visual conversion, signal transduction, energy transmission, etc., which has aroused extensive interest in the past decade. Inspired by these gorgeous works of living beings, scientists have constructed various biomimetic light-responsive nanochannels to mimic the behaviors of rhodopsins. However, it is still challenging to build stimuli-responsive sub-nanochannels only regulated by visible light as the rhodopsins are always at the sub-nanometer level and regulated by visible light. Pillar[6]arenes have an open cavity of 6.7 Å, which can selectively recognize small organic molecules. They can be connected to ions of ammonium or carboxylate groups on the rims. Therefore, we designed and synthesized the amino and carboxyl-derived side chains of pillar[6]arenes with opposite charges. The sub-nanochannels were constructed through the electrostatic interaction of layer-by-layer self-assembled amino and carboxyl-derived pillar[6]arenes. Then, the natural chromophore of the retinal with visible light-responsive performance was modified on the upper edge of the sub-nanochannel to realize the visible light switched on and off. Finally, we successfully constructed a visible light-responsive sub-nanochannel, providing a novel method for regulating the selective transport of energy-donating molecules of ATP.

Rational Design of Key Enzymes to Efficiently Synthesize Phycocyanobilin in Escherichia coli.

Phycocyanobilin (PCB) is a natural blue tetrapyrrole chromophore that is found in phycocyanin and plays an essential role in photosynthesis. Due to PCB's antioxidation, anti-inflammatory and anti-cancer properties, it has been utilized in the food, pharmaceutical and cosmetic industries. Currently, the extraction of PCB from Spirulina involves complex processes, which has led to increasing interest in the biosynthesis of PCB in Escherichia coli. However, the PCB titer remains low because of the poor activity of key enzymes and the insufficient precursor supply. Here, the synthesis of PCB was firstly improved by screening the optimal heme oxygenase (HO) from Thermosynechococcus elongatus BP-1(HOT) and PCB: ferredoxin oxidoreductase from Synechocystis sp. PCC6803 (PcyAS). In addition, based on a rational design and the infrared fluorescence method for high-throughput screening, the mutants of HOT(F29W/K166D) and PcyAS(D220G/H74M) with significantly higher activities were obtained. Furthermore, a DNA scaffold was applied in the assembly of HOT and PcyAS mutants to reduce the spatial barriers, and the heme supply was enhanced via the moderate overexpression of hemB and hemH, resulting in the highest PCB titer (184.20 mg/L) obtained in a 5 L fermenter. The strategies applied in this study lay the foundation for the industrial production of PCB and its heme derivatives.

Expanding the toolbox for phycobiliprotein assembly: phycoerythrobilin biosynthesis in Synechocystis

AbstractPhycobiliproteins (PBPs) play a vital role in light harvesting by cyanobacteria, which enables efficient utilization of photon energy for oxygenic photosynthesis. The PBPs carry phycobilins, open‐chain tetrapyrrole chromophores derived from heme. The structure and chromophore composition of PBPs is dependent on the organism's ecological niche. In cyanobacteria, these holo‐proteins typically form large, macromolecular antenna complexes called phycobilisomes (PBSs). The PBS of Synechocystis sp. PCC 6803 (hereafter Synechocystis) consists of allophycocyanin (APC) and phycocyanin (PC), which exclusively harbor phycocyanobilin (PCB) as a chromophore. Investigations into heterologous PBP biosynthesis in E. coli have proven limiting with respect to PBP assembly and their functional characterization. Consequently, we wanted to engineer a platform for the investigation of heterologously produced PBPs, focusing on unusual, phycoerythrobilin (PEB)‐containing light‐harvesting proteins called phycoerythrins (PEs) in Synechocystis. As a first step, a gene encoding for the synthesis of the natural cyanobacterial chromophore, PEB, was introduced into Synechocystis. We provide spectroscopic evidence for heterologous PEB formation and show covalent attachment of PEB to the α‐subunit of PC, CpcA, by HPLC and LC–MS/MS analyses. Fluorescence microscopy and PBS isolation demonstrate a cellular dispersal of PBPs with modified phycobilin content. However, these modifications have minor effects on physiological responses, as demonstrated by growth rates, oxygen evolution, nutrient accumulation, and PBP content analyses. As a result, Synechocystis demonstrates the capacity to efficiently manage PEB biosynthesis and therefore reflects a promising platform for both biochemical and physiological investigations of foreign and unusual PEs.

Two-photon fluorescent chemosensors based on the GFP-chromophore for the detection of Zn2+ in biological samples – From design to application

A library of twelve novel fluorescent GFP chromophore based chemosensors (GFZnPs) was prepared for the detection of Zn2+ in biological samples with two-photon microscopy. The presented compounds are the hybrids of the Zn2+ chelator 8-aminoquinoline motif and the GFP chromophore, exploiting and enhancing the properties of the natural chromophore. In the presented probes, the quenching rotation around the benzylidene carbon of the GFP chromophore is conditionally blocked upon Zn2+ binding, resulting in a fluorescent response to the ion. GFZnPs have an efficient and simple synthesis making them one of the most easily accessible two-photon (2P) Zn2+ sensors. We present the comprehensive spectroscopical characterization of the probe family highlighting their bright fluorescent emission (ε × Φ > 200) at λem∼520 nm upon excitation by λex∼450 nm light. The sensors feature high selectivity for Zn2+ with an affinity in the nanomolar range, excellent water solubility, and usability at a wide pH-range (pH > 6). The relationship between the structure of compounds and their properties was studied and rationalized by theoretical considerations. The 2P-action cross section of the probes reaches δ × Φcomp > 5 GM at λex,2P= 900 nm, with an increase up to 200-fold, which makes them one of the best two-photon probes for Zn2+. The applicability of selected probes was demonstrated by epifluorescent and 2P microscopy on cultured cells and brain slices. This work expands the toolbox of efficient two-photon zinc sensors with a valuable new family.

Characteristic Photoprotective Molecules from the Sphagnum World: A Solution-Phase Ultrafast Study of Sphagnic Acid.

A natural UV-absorbing chromophore extracted from sphagnum mosses, sphagnic acid, is proposed as a new natural support to chemical UV filters for use in cosmetic applications. Sphagnic acid is structurally related to the cinnamate family of molecules, known for their strong UV absorption, efficient non-radiative decay, and antioxidant properties. In this study, transient electronic absorption spectroscopy is used, in conjunction with steady-state techniques, to model the photodynamics following photoexcitation of sphagnic acid in different solvent systems. Sphagnic acid was found in each system to relax with lifetimes of ~200 fs and ~1.5 ps before generating a cis-isomer photoproduct. This study helps to elucidate the photoprotective mechanism of a new potential natural support to sunscreens, from a unique plant source.

Nanomaterial-decorated micromotors for enhanced photoacoustic imaging

Micro-and nanorobots have the potential to perform non-invasive drug delivery, sensing, and surgery in living organisms, with the aid of diverse medical imaging techniques. To perform such actions, microrobots require high spatiotemporal resolution tracking with real-time closed-loop feedback. To that end, photoacoustic imaging has appeared as a promising technique for imaging microrobots in deep tissue with higher molecular specificity and contrast. Here, we present different strategies to track magnetically-driven micromotors with improved contrast and specificity using dedicated contrast agents (Au nanorods and nanostars). Furthermore, we discuss the possibility of improving the light absorption properties of the employed nanomaterials considering possible light scattering and coupling to the underlying metal-oxide layers on the micromotor’s surface. For that, 2D COMSOL simulation and experimental results were correlated, confirming that an increased spacing between the Au-nanostructures and the increase of thickness of the underlying oxide layer lead to enhanced light absorption and preservation of the characteristic absorption peak. These characteristics are important when visualizing the micromotors in a complex in vivo environment, to distinguish them from the light absorption properties of the surrounding natural chromophores.

Interaction of the Fluorophenyl Analog of Retinal with Proteorhodopsin from Exiguobacterium sibiricum

—We have developed an alternative method for the synthesis of an analog of natural retinal, which contains the p-fluorophenyl fragment instead of the trimethylcyclohexene ring. The proposed scheme for the synthesis of the target all-E-isomer of the target retinoid consists of using C5-phosphonate that contains the terminal nitrile group under Horner–Emmons reaction conditions. It has been shown that this scheme is more efficient and provides a higher total yield of the target product than the previously described variant. The procedure has been developed for the preparation of an analog of microbial proteorhodopsin ESRh from Exiguobacterium sibiricum, which contains a modified chromophore. It has been found that, as in the case of bacterioopsin from Halobacterium salinarum, the replacement of the trimethylcyclohexene ring in the natural chromophore by the p-fluorophenyl fragment does not prevent the formation of the artificial pigment F-Phe-ESRh from proteorhodopsin ESRh, which preserves the cycle of photochemical reactions. Certain differences have been found between the properties of native recombinant ESRh and its analog F-Phe-ESRh including a shift in the absorption maximum to the short-wavelength region, the formation of M intermediate at lower pH values, the presence of “long-lived M,” and a general slowdown in the photocycle. The reduced stability of the resulting proteorhodopsin analog F-Phe-ESRh to prolonged exposure to visible light has been also demonstrated.

Harnessing Biobased Materials in Photosynaptic Transistors with Multibit Data Storage and Panchromatic Photoresponses Extended to Near‐Infrared Band

AbstractOwing to ever‐increasing environmental impact, nature‐inspired biomimetic electronics are key to unlock the potential of developing environmentally friendly brain‐like computing and biomimetic artificial‐intelligence systems. Thus far, the development of photosynaptic devices via green processing using biobased materials has become a major challenge, owing to restrictions in complex architecture, material design, and stimulation wavelength. This article reports on the first bioinspired phototransistor using biocomposites comprising semiconducting block copolymers, poly(3‐hexylthiophene)‐block‐maltoheptaose, and bacteriochlorophyll (BCHL), which extend the photoresponse from visible to UV to near‐infrared light, to exhibit fundamental sensing, computing, and memory functions. The superior ultrafast (50 ms) and multilevel (>9 bits) photoresponses of a single cell of the synaptic devices are attributed to hydrogen‐bonding interaction (i) between the block copolymers to facilitate the self‐assembled microstructure, and (ii) within the block copolymer and BCHL to homogeneously disperse the natural chromophore. Notably, a two‐terminal flexible synaptic device comprising biocomposites and a biobased poly(ethylene furanoate) substrate with high mechanical endurance is demonstrated to exhibit synaptic functionality and environmentally benign properties without using a gate impetus and hazardous ingredients. Collectively, the photosynaptic transistor comprising a biocomposite successfully provides an effective guide for applications in artificial visual perception, sensing, and memory in neuromorphic computing and intelligent systems.

LIF spectroscopy of epithelial tissues: Assay of structural changeover due to the cancer progression.

Most of the human cancers occur in epithelial tissues containing basic cells with different shapes, and not only do the spectral properties of the tissue pigments alter due to cancer, but the cellular architecture also change. However, in optical diagnosis of the cancerous tissues, attention has been paid to the spectral changeover of native chromophores as bio-markers. Here, we have attempted to assay the structural alterations of the epithelial tissues during the cancer progression utilizing Laser induced fluorescence (LIF) spectroscopy as a fast, sensitive and easy-to-use method. In this regard, angular dependence of the LIF spectral features of the healthy and cancerous epithelial tissues (soaked in Rhodamine 6G solution) from three different human organs i. e. uterus, colon and kidney with distinct microstructures have been examined. In general, both wavelength and intensity at the peak of the LIF spectra depend on the tissue orientation and the angle of detection respect to the laser beam direction. Those optical parameters also demonstrate distinctive alterations in different tissues that is explicated based on the morphological alteration of the epithelial cells in each carcinoma type provided by pathology data.

Optoaccoustic Tomography – good news for microcirculatory research

Tomographic imaging is a well established technology in preventive medicine and biomedical research, although not without limitations and concerns. Optoacoustic tomography (OAT) is a recent development that bridges optical and sonographic techniques to solve spatial resolution in deep-tissue imaging. In addition to safety advantages, OAT allows multiple wavelength readings for natural thermoelastic chromophores. In this study, we explore Multi Spectral Optoacoustic Tomography (MSOT) capacities to simultaneously acquire three independent chromophores – deoxygenated haemoglobin (Hb), oxygenated haemoglobin (HbO2), and melanin, from healthy human volunteers, with maximal molar extinction of HbO2 at 950 nm, Hb at 750 nm and melanin at 680 nm. Later we demonstrate how image stability during acquisition is fundamental for optimal resolution, precision and consistency of high throughout MSOT data collection. From recorded scans, a workflow is layered for data evaluation. With the MSOT dedicated software results were extracted from 3D image analysis of deep (15 mm3) vessels. The possibilities offered by this new system, specially in vascular pathophysiology, are immense and can be extended beyond current knowledge.

Optoaccoustic Tomography – good news for microcirculatory research

Tomographic imaging is a well established technology in preventive medicine and biomedical research, although not without limitations and concerns. Optoacoustic tomography (OAT) is a recent development that bridges optical and sonographic techniques to solve spatial resolution in deep-tissue imaging. In addition to safety advantages, OAT allows multiple wavelength readings for natural thermoelastic chromophores. In this study, we explore Multi Spectral Optoacoustic Tomography (MSOT) capacities to simultaneously acquire three independent chromophores – deoxygenated haemoglobin (Hb), oxygenated haemoglobin (HbO2), and melanin, from healthy human volunteers, with maximal molar extinction of HbO2 at 950 nm, Hb at 750 nm and melanin at 680 nm. Later we demonstrate how image stability during acquisition is fundamental for optimal resolution, precision and consistency of high throughout MSOT data collection. From recorded scans, a workflow is layered for data evaluation. With the MSOT dedicated software results were extracted from 3D image analysis of deep (15 mm3) vessels. The possibilities offered by this new system, specially in vascular pathophysiology, are immense and can be extended beyond current knowledge.

New natural organic–inorganic pH indicators: Synthesis and characterization of pro-ecological hybrid pigments based on anthraquinone dyes and mineral supports

We present a strategy that leads to the formation of high-performance hybrid pigments made from natural anthraquinone chromophores (alizarin, purpurin) and mineral supports (palygorskite (PAL), sepiolite (SEP), and hydroxyapatite (HAP)). Thanks to the mineral filler form features and the synergy between the organic and inorganic components, the as-prepared hybrid pigments showed excellent thermal and chemical stability. The natural pigments exhibited strong pH-sensing activity, changing their color upon exposure to HCl and/or NH3 vapors. The PAL-based pigments were found to be the most effective pH indicators, showing pronounced color changes after 10 min of exposure to HCl (ΔE for PAL/A was 7.4). ToF-SIMS, 13C NMR and XPS techniques revealed interactions between the organic dyes and metal ions present in the minerals. XPS spectroscopy was also used to examine the alterations in the structure of the hybrid colorants following exposure to acid vapors. The proposed pH sensors were successfully applied to elastomer and thermoplastic elastomer matrices. The purpurin-based hybrid pigments exhibited significantly reduced migration from the polymer (about six times lower concentration in ethanol after 14 days). The results of this study pave a new way for the design, development, and application of advanced hybrid colorants with pH-sensing activity and improved stability.

Bidispersed Colloidal Assemblies Containing Xanthommatin Produce Angle‐Independent Photonic Structures

AbstractThe biological chromophore xanthommatin (Xa) contributes to the yellow, red, and brown colors and hues in cephalopods and arthropods. In many cases, Xa is also present as part of or coupled to supramolecular nanostructures, whose function has yet to be fully explored. To investigate how such structural elements impact the perceived color of these natural chromophores, amorphous photonic assemblies containing Xa chemically coupled to 100 nm polystyrene nanoparticles (PS100‐XA) are fabricated, and blended with pure polystyrene (PS) nanoparticles of varying sizes. Structural colors are observed comprising these bidispersed colloidal assemblies that are tuned by the particle size of PS nanoparticles, the concentration of PS100‐XA, the local environment, and the method of assembly. In all cases, the addition of PS100‐XA regulates the color hue and contrast of the resultant assemblies by increasing light absorption while minimizing incoherent light scattering. Taken together, the results demonstrate how biochromes like Xa can enhance the color intensity and the diversity in colors present in common photonic assemblies.

Plant tannin and chitosan-templated cellulose for improved absorption of UV protective natural chromophores

This study reported a facile and sustainable modification of cellulose by plant tannins and chitosan polymer for higher impregnation of UV protective natural chromophores (UVPNCs) derived from the banana floral stem (BFS). The phytochemical screening demonstrated that BFS extracts have different UVPNCs including condensed tannin, flavonoids, anthocyanin, betacyanin and anthraquinone. The optimized impregnation temperature and time for UVPNCs entrapping were found at 80°C with a time interval of 60 min and the overall inherent fixation rate of UVPNCs was ranging from 53 to 63%. The cellulose substrate templated with plant tannins (extracted from Terminalia chebula and Phyllanthus emblica) and chitosan improved the UVPNCs absorption amount almost 2 and 1.8 folds, respectively, which was expressed in terms of color strength (K/S). Interestingly, the UVPNCs entrapping ability of bio-crosslinked cellulose was also higher than typical metallic salts treated cellulose. The higher absorption mechanism of UVPNCs for tannins (-OH and –COOH) and chitosan (-NH2) templating have been discussed in terms of molecular orientation (TCI, LOI), inter and intra-molecular hydrogen bonding configuration (HBI, EH, R), and the total amount of anchored-UVPNCs which was expressed by the asymmetric factor (AF). The UV shielding property of the UVPNCs impregnated modified cellulose was compared and a maximum of two folds higher UPF value was found in bio-templated cellulose substrate (UPF range = 223 to 459) than metal treated cellulose substrates (UPF range = 163 to 175). Furthermore, the functional durability of UVPNCs impregnated substrates was evaluated in terms of several colorfastness and found very good to excellent grading.

Promoting photocatalytic CO2 reduction with a molecular copper purpurin chromophore

CO2 reduction through artificial photosynthesis represents a prominent strategy toward the conversion of solar energy into fuels or useful chemical feedstocks. In such configuration, designing highly efficient chromophores comprising earth-abundant elements is essential for both light harvesting and electron transfer. Herein, we report that a copper purpurin complex bearing an additional redox-active center in natural organic chromophores is capable to shift the reduction potential 540 mV more negative than its organic dye component. When this copper photosensitizer is employed with an iron porphyrin as the catalyst and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the sacrificial reductant, the system achieves over 16100 turnover number of CO from CO2 with a 95% selectivity (CO vs H2) under visible-light irradiation, which is among the highest reported for a homogeneous noble metal-free system. This work may open up an effective approach for the rational design of highly efficient chromophores in artificial photosynthesis.

Comparative dyeing behavior and UV protective characteristics of cotton fabric treated with polyphenols enriched banana and watermelon biowaste

This study reported a facile structural modification of cellulosic fabric (cotton) by applying two different polyphenol enriched extracts derived from the banana floral stem (BFS) and watermelon rind (WR) for imparting UV protective functionality. The dye extracts are comprised of various UV protective natural chromophores (UVPNCs) such as tannin, flavonoids, anthraquinone, anthocyanin, betacyanine. The concentrations and absorbance intensities of UVPNCs were confirmed by phytochemical screening and UV spectroscopy. Better absorption behavior for BFS and WR chromophores into cellulose was found at 80°C and 60°C temperature with a constant runtime of 60 minutes. At this conditions, the fixation rate of BFS and WR was 53-63% and 25–85%, respectively. Furthermore, cellulose substrates were chelated with different types of metals (Al3+, Sn2+, Fe2+, and Cu2+) to promote the chromophore fixation. The effect of metal chelation with cellulose chain was estimated in terms of crystallinity indices, hydrogen bonding configurations and asymmetric factor, which were correlated with the enhanced UVPNCs fixation. The higher amount of BFS and WR chromophores were absorbed for Fe2+ and Cu2+, demonstrating ~61% and ~ 26% improvement in color strength (K/S), respectively. The formation of UVPNCs-metal-cellulose complex, decreased the UV transmission rate of the BFS and WR dyed fabrics. Interestingly, BFS dyed substrate exhibited higher (UPF = 50+) UV shielding ability compared to WR dyed substrate (UPF = 4.20) due to higher UVPNCs absorbance intensities and bonding capacity of BFS extract. Finally, the durability of functionality of BFS and WR dyed substrates was confirmed in terms of various colorfastness.

Functional modification of cellulose by chitosan and gamma radiation for higher grafting of UV protective natural chromophores

This study demonstrated a green functionalization process of a cellulose substrate by combining the chitosan treatment and gamma radiation. To impart the UV protection characteristics in the cellulosic structure, natural chromophores derived from Banana floral stem (BFS) was grafted in the functionalized cellulose surface. Phytochemical screening was performed to confirm the types of UV protective natural chromophores (UVPNCs) presented in BFS. The result exhibited the presence of condensed tannin, flavonoids, anthocyanin, betacyanin, and anthraquinone as the major UVPNC components in BFS. The optimum conditions for maximum sorption of UVPNCs into the functionalized cellulose matrix were recorded at 80°C for 60 min. The cationic biopolymer chitosan (2 g/L), different gamma absorbs doses (2, 4, and 6 kGy), and combined chitosan and gamma treatment into cellulose resulted around 15–23%, 44%, and 41–64% improved absorption of UVPNCs, respectively, as demonstrated by the change in color strength (K/S) compared to unmodified cellulose matrix. The concurrent treatments greatly improved the total crystallinity index (TCI), hydrogen bond intensity (HBI), hydrogen bonding energy (EH), hydrogen bonding distance (R) and asymmetric factor (AF) from 1.358 to 1.363, 0.971 to 0.988, 27.15 kJ–27.40 kJ (at 3274 cm−1), 2.766 Å to 2.764 Å (at 3274 cm−1) and 0.47 to 0.10, respectively. For gamma treatment, 6 kGy irradiation dose provided the best result for improved molecular orientation of cellulose and in combination of chitosan the substrate attained a maximum K/S of 1.98 after UVPNCs grafting. It was found that the UV protection factor (UPF) rating has a linear relationship with the UVPNCs absorption (K/S) and a maximum four-fold increase in UPF (165–506) was evident. The excellent bonding durability of the UVPNCs grafted samples was further ensured in terms of several colorfastness properties. This sustainable functionalization of cellulose with high UPF offers a great promise for applications in health care and photodegradation protection.

A Visible-Light-Regulated Chloride Transport Channel Inspired by Rhodopsin.

Inspired by the light-regulating capabilities of naturally occurring rhodopsin, we have constructed a visible-light-regulated Cl- -transport membrane channel based on a supramolecular host-guest interaction. A natural retinal chromophore, capable of a visible-light response, is used as the guest and grafted into the artificial channel. Upon introduction of an ethyl-urea-derived pillar[6]arene (Urea-P6) host, threading or de-threading of the retinal and selective bonding of Cl- can be utilized to regulate ion transport. Based on the visible-light responsiveness of the host-guest interaction, Cl- transport can be regulated by visible light between ON and OFF states. Visible-light-regulated Cl- transport as a chemical model permits to understand comparable biological ion-selective transport behaviors. Furthermore, this result also supplies a smart visible-light-responsive Cl- transporter, which may have applications in natural photoelectric conversion and photo-controlled delivery systems.