Visible-Light Photoswitching by Azobenzazoles

Three visible-light responsive photoswitches are reported, azobis(1-methyl-benzimidazole) ( 1 ), azobis(benzoxazole) ( 2 ) and azobis(benzothiazole) ( 3 ). Photostationary distributions are obtained upon irradiation with visible light comprising approximately 80 % of the thermally unstable isomer, with thermal half-lives up to 8 min and are mostly invariant to solvent. On protonation, compound 1 H⁺ has absorption extending beyond 600 nm, allowing switching with yellow light, and a thermal half-life just under 5 minutes. The two isomers have significantly different pK_a values, offering potential as a pH switch. The absorption spectra of 2 and 3 are insensitive to acid, although changes in the thermal half-life of 3 indicate more basic intermediates that significantly influence the thermal barrier to isomerization. These findings are supported by high-level ab initio calculations, which validate that protonation occurs on the ring nitrogen and that the Z isomer is more basic in all cases.     

Half-life of <Superscript>97</Superscript>Zr,re-measured

Summary The half-life of ⁹⁷Zr, used for the calculation of thermal/epithermal neutron flux ratio in k₀-NAA, is re-determined using three measurement systems with different pulse processing principles. The result of 16.755±0.013 hours clarifies the discrepancy between two widely used literature values, 16.744±0.011 and 16.90±0.05 hours. Different dead-time correction methods used on various measurement systems are evaluated. Factors influencing precise measurement of relative peak counting rates are discussed in time-series measurements over a dynamic range of 1000-fold radioactive intensities (10 half-lives).     

A Dissipative Reaction Network Drives Transient Solid–Liquid and Liquid–Liquid Phase Cycling of Nanoparticles

Transient states maintained by energy dissipation are an essential feature of dynamic systems where structures and functions are regulated by fluxes of energy and matter through chemical reaction networks. Perfected in biology, chemically fueled dissipative networks incorporating nanoscale components allow the unique properties of nanomaterials to be bestowed with spatiotemporal adaptability and chemical responsiveness. We report the transient dispersion of gold nanoparticles in water, powered by dissipation of a chemical fuel. A dispersed state that is generated under non-equilibrium conditions permits fully reversible solid–liquid or liquid–liquid phase transfer. The molecular basis of the out-of-equilibrium process is reversible covalent modification of nanoparticle-bound ligands by a simple inorganic activator. Activator consumption by a coupled dissipative reaction network leads to autonomous cycling between phases. The out-of-equilibrium lifetime is tunable by adjusting the pH value, and reversible phase cycling is reproducible over several cycles.     

Characterization of Sol-gel bioencapsulates for ester hydrolysis and synthesis

Candida rugosa lipase was entrapped in silica sol-gel particles prepared by hydrolysis of methyltrimethoxysilane and assayed by p-nitrophenyl palmitate hydrolysis, as a function of pH and temperature, giving pH optima of 7.8 (free enzyme) and 5.0–8.0 (immobilized enzyme). The optimum temperature for the immobilized enzyme (50–55°C) was 19°C higher than for the free enzyme. Thermal, operational, and storage stability were determined with n-butanol and bytyric acid, giving at 45°C a half-life 2.7 times greater for the immobilized enzyme; storage time was 21 d at room temperature. For ester synthesis, the optimum temperature was 47°C, and high esterification conversions were obtained under repeated batch cycles (half-life of 138 h).     

Synthesis,characterization and computational evaluation of bicyclooctadienes towards molecular solar thermal energy storage

Molecular solar-thermal energy storage (MOST) systems are based on photoswitches that reversibly convert solar energy into chemical energy. In this context, bicyclooctadienes (BODs) undergo a photoinduced transformation to the corresponding higher energy tetracyclooctanes (TCOs), but the photoswitch system has not until now been evaluated for MOST application, due to the short half-life of the TCO form and limited available synthetic methods. The BOD system degrades at higher temperature via a retro-Diels–Alder reaction, which complicates the synthesis of the compounds. We here report a cross-coupling reaction strategy that enables an efficient synthesis of a series of 4 new BOD compounds. We show that the BODs were able to switch to the corresponding tetracyclooctanes (TCOs) in a reversible way and can be cycled 645 times with only 0.01% degradation. Half-lives of the TCOs were measured, and we illustrate how the half-life could be engineered from seconds to minutes by molecular structure design. A density functional theory (DFT) based modelling framework was developed to access absorption spectra, thermal half-lives, and storage energies which were calculated to be 143–153 kJ mol⁻¹ (0.47–0.51 MJ kg⁻¹), up to 76% higher than for the corresponding norbornadiene. The combined computational and experimental findings provide a reliable way of designing future BOD/TCO systems with tailored properties.

Molecular solar-thermal energy storage (MOST) systems are based on photoswitches that reversibly convert solar energy into chemical energy.     

Acid-Cleavable Poly(ethylene glycol) Hydrogels Displaying Protein Release at pH 5

PEG is the gold standard polymer for pharmaceutical applications, however it lacks degradability. Degradation under physiologically relevant pH as present in endolysosomes, cancerous and inflammatory tissues is crucial for many areas. The authors present anionic ring-opening copolymerization of ethylene oxide with 3,4-epoxy-1-butene (EPB) and subsequent modification to introduce acid-degradable vinyl ether groups as well as methacrylate (MA) units, enabling radical cross-linking. Copolymers with different molar ratios of EPB, molecular weights (M_n) up to 10 000 g mol⁻¹ and narrow dispersities (Đ<1.05) were prepared. Both the P(EG-co-isoEPB)MA copolymer and the hydrogels showed pH-dependent, rapid hydrolysis at pH 5–6 and long-term storage stability at neutral pH (pH 7.4). By designing the degree of polymerization and content of degradable vinyl ether groups, the release time of an entrapped protein OVA-Alexa488 can be tailored from a few hours to several days (hydrolysis half-life time t_1/2 at pH 5: 13 h to 51 h).     

Light-fueled dissipative self-assembly at molecular and macro-scale enabled by a visible-light-responsive transient hetero-complementary quadruple hydrogen bond

The development of out-of-equilibrium self-assembly systems using light as input fuel is highly desirable and promising for the fabrication of smart supramolecular materials. Herein, we report the construction of new artificial light-fueled dissipative molecular and macroscopic self-assembly systems based on a visible-light-responsive transient quadruple H-bonding array, which consists of an azobenzene-modified ureidopyrimidinone (UPy) module (Azo-O-UPy) and a nonphotoactive diamidonaphthyridine (DAN) derived competitive binder (Napy-1). The visible light (410 nm) irradiation can induce the E to Z isomerization of the azobenzene unit of E-Azo-O-UPy to produce Z-Azo-O-UPy with an opened UPy binding site, which can complex with Napy-1 to form a quadruply H-bonded heterodimer. The heterodimer is metastable and can be quickly disassembled in dark, owing to the fast thermal relaxation of Z-Azo-O-UPy to E-Azo-O-UPy. While introducing such transient quadruple H-bonding interaction into a linear polymer system or a polymeric gel system, light-fueled out-of-equilibrium polymeric assembly both at molecular and macro-scale can be achieved.     

ortho-Substituted 2-Phenyldihydroazulene Photoswitches: Enhancing the Lifetime of the Photoisomer by ortho-Aryl Interactions

Photochromic molecules are systems that undergo a photoisomerization to high-energy isomers and are attractive for the storage of solar energy in a closed-energy cycle, for example, in molecular solar thermal energy storage systems. One challenge is to control the discharge time of the high-energy isomer. Here, we show that different substituents in the ortho position of a phenyl ring at C-2 of dihydroazulene (DHA-Ph) significantly increase the half-life of the metastable vinylheptafulvene (VHF-Ph) photoisomer; thus, the energy-releasing VHF-to-DHA back-reaction rises from minutes to days in comparison to the corresponding para- and meta-substituted systems. Systems with two photochromic DHA-Ph units connected by a diacetylene bridge either at the para, meta and ortho positions and corresponding to a linear or to a cross-conjugated pathway between the two photochromes are also presented. Here, the ortho substitution was found to compromise the switching properties. Thus, irradiation of ortho-bridged DHA-DHA resulted in degradation, probably due to the proximity of the different functional groups that can give rise to side-reactions.     

Dual‐responsive copolymer poly(2,2,3,4,4,4‐hexafluorobutyl methacrylate)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] synthesized via photoATRP for surface with tunable wettability

In this work, a series of block copolymers of poly(2,2,3,4,4,4‐hexafluorobutyl methacrylate)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] (PHFBMA‐b‐PDMAEMA) were synthesized via photo‐induced atom transfer radical polymerization (photoATRP) at room temperature. By the introduction of PDMAEMA segment, the hydrophilicity of the silicon wafer surface spin‐coated with PHFBMA homopolymer was improved. Furthermore, the study of tunable surface wettability showed that the surface wettability was pH‐dependent and thermal‐independent at pH 2 and 10. The as‐fabricated surface coated with PHFBMA₁₁₀‐b‐PDMAEMA₁₈₇ showed switchable water contact angle from 85.4° at pH > 4 to 55.0° at pH 2 due to the protonation and deprotonation of tertiary amine groups of PDMAEMA. However, because of the ascendancy of protonated PDMAEMA at pH 2 and the decreased LCST at pH 10, the wettability of the as‐prepared surfaces was thermal‐insensitive. Finally, surface morphology and composition investigation showed that the property of wettability‐controllable surface was not only influenced by surface composition, but also affected by chain conformation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3868–3877     

Dual Responsive Regulation of Host–Guest Complexation in Aqueous Media to Control Partial Release of the Host

The regulation of the concentration of a wide range of small molecules is ubiquitous in biological systems because it enables them to adapt to the continuous changes in the environmental conditions. Herein, we report an aqueous synthetic system that provides an orchestrated, temperature and pH controlled regulation of the complexation between the cyclobis(paraquat-p-phenylene) host ( BBox ) and a 1,5-dialkyloxynaphthalene ( DNP ) guest attached to a well-defined dual responsive copolymer composed of N-isopropylacrylamide as thermoresponsive monomer and acrylic acid as pH-responsive monomer. Controlled, partial release of the BBox , enabling control over its concentration, is based on the tunable partial collapse of the copolymer. This colored supramolecular assembly is one of the first synthetic systems providing control over the concentration of a small molecule, providing great potential as both T and pH chromic materials and as a basis to develop more complex systems with molecular communication.     

On the use of catalysis to bias reaction pathways in out-of-equilibrium systems

Catalysis is an essential function in living systems and provides a way to control complex reaction networks. In natural out-of-equilibrium chemical reaction networks (CRNs) driven by the consumption of chemical fuels, enzymes provide catalytic control over pathway kinetics, giving rise to complex functions. Catalytic regulation of man-made fuel-driven systems is far less common and mostly deals with enzyme catalysis instead of synthetic catalysts. Here, we show via simulations, illustrated by literature examples, how any catalyst can be incorporated in a non-equilibrium CRN and what their effect is on the behavior of the system. Alteration of the catalysts'' concentrations in batch and flow gives rise to responses in maximum conversion, lifetime (i.e. product half-lives and t90 – time to recover 90% of the reactant) and steady states. In situ up or downregulation of catalysts'' levels temporarily changes the product steady state, whereas feedback elements can give unusual concentration profiles as a function of time and self-regulation in a CRN. We show that simulations can be highly effective in predicting CRN behavior. In the future, shifting the focus from enzyme catalysis towards small molecule and metal catalysis in out-of-equilibrium systems can provide us with new reaction networks and enhance their application potential in synthetic materials, overall advancing the design of man-made responsive and interactive systems.

We show, via simulations, how catalytic control over individual paths in a fuel-driven non-equilibrium chemical reaction network in batch or flow gives rise to responses in maximum conversion, lifetime and steady states.     

Elaboration of ZnO Thin Films with Preferential Orientation by a Soft Chemistry Route

Microcrystalline ZnO films presenting well-defined and tunable orientation were obtained by spin coating of alcoholic sols by two different approaches, based on controlled hydrolysis-condensation of Zn-ethanolamine complexes. As-deposited films are formed by amorphous zinc oxide-acetate submicronic particles, which are transformed into oriented ZnO after thermal treatment. The orientation of ZnO depends on the synthesis method, and the solvent. While in ethanol and [Zn] = 0.05 mol·L^–1, films consist of rectangular platelets oriented with the (100) planes parallel to the substrate (a//n), the orientation of the particles changes to (c//n) for systems in 2-methoxyethanol (2-ME) and [Zn] = 0.75 mol·L^–1. A study of chemical factors that influence the orientation (precursor, solvent, MEA/Zn ratio, concentration, coating parameters, heat treatment) is presented.     

Preparation and Characterization of Pepsin Immobilized on Polymeric Supports

Abstract

Immobilization of pepsin on crosslinked resinous materials SRF (salicylic acid-resorcinol-formaldehyde), Amberlite IRA-400, and poly-(vinyl alcohol) is reported. Enzyme concentration, pH of the coupling medium, and nature and concentration of crosslinking agents were optimized for the better retention of activity of immobilized pepsin. The immobilized systems were characterized through pH, thermal, and storage stabilities. Michaelis constant (K _m) and maximum reaction velocity (V _m) for the free and immobilized enzymes were calculated from Lineweaver-Burk plots. Effect of temperature on enzyme activity was studied, and the thermoinactivation constant (K _ti) and energy of activation (E _a) for free and immobilized enzymes were also calculated. The immobilized pepsin was used in a continuous fluidized bed reactor for the study of clotting of skimmed milk. Rate of coagulation was considerably high for the treated milk sample at 50°C and pH 6–6.2.     

六、七、八元瓜环与苯胺系列衍生物的相互作用

利用紫外吸收光谱、荧光光谱以及¹H NMR方法详细考察了六、七、八元瓜环(Q[6], Q[7], Q[8])与苯胺系列衍生物客体的相互作用和体系pH对其作用的影响. 实验结果表明, 3种瓜环与苯胺系列衍生物客体的相互作用强弱、作用比例以及作用模式与体系的酸度密切相关: 在“高”或“低”pH条件下, 未观察到瓜环与这些客体的明显作用; 在介于“高”与“较高”或“低”与“较低”的pH范围, 瓜环与这些客体发生相互作用, 形成1∶1的包结配合物; 而在介于“较高”与“较低”的pH范围, 瓜环与这些客体发生相互作用, 可形成1∶2的包结配合物. 对于不同的瓜环-客体作用体系, 相应的pH范围各不相同. 本文利用简便的实验方法, 测试了这些pH值及其范围. 根据测定的结果, 结合瓜环以及客体的结构特征, 对体系主客体在不同的酸度区域表现出的不同作用模式进行了探讨.     

Ionic and pH effects on the osmotic properties and structure of polyelectrolyte gels

We investigate the effects of salt concentration and pH on neutralized poly(acrylic acid) (PAA) gels in near physiological salt solutions. Either adding calcium ions or decreasing the pH is found to induce reversible volume transitions but the nature of these transitions seems to be different. For example, the osmotic pressure exhibits a simple power law dependence on the concentration as the transition is approached in both systems, but the power law exponent n is substantially different in the two cases. On decreasing the pH the value of n gradually increases from 2.1 (at pH = 7) to 3.2 (at pH = 1). By contrast, n decreases with increasing calcium ion concentration from 2.1 (in 100 mM NaCl solution) to 1.6 (0.8 mM CaCl₂ in 100 mM NaCl solution). In both systems, a strong increase of the small-angle neutron scattering intensity (SANS) is observed near the volume transition. The SANS results reveal that calcium ions favor the formation of linearly aligned regions in PAA gels. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2803–2810, 2008     

Synthesis and characterization of pH‐sensitive and thermosensitive double hydrophilic graft copolymers

A series of poly(N‐isopropylacrylamide)‐co‐poly(N^ε‐benzyloxycarbonyl‐L ‐lysine) graft copolymers (PNIPAm‐co‐PZLLys) with different side chains (degree of polymerization, DP = 5～40) and unit ratios (from 30 to 70 mol %) were prepared via free radical polymerization, followed by cleaving benzyloxycarbonyl groups (Z groups) to obtain the double hydrophilic graft copolymer, poly(N‐isopropylacrylamide)‐co‐poly(L ‐lysine) (PNIPAm‐co‐PLLys). The pH‐ and temperature‐response properties of the graft copolymers in aqueous solution were studied. The experimental results indicate L15‐N30 and L15N‐70, that is, the PNIPAm‐co‐PLLys having the poly(L ‐lysine) of DP = 15 as side chains as well as 30 and 70 mol %, respectively, of PNIPAm as backbone, have coil‐to‐helix transitions from pH 6 to pH 12 at room temperature and form uniform nanoscale micelle‐like dispersions in aqueous solution at pH 12. The graft copolymers also could form uniform and nanoscale micelle‐like structures at 50 °C in pH 6 buffer solution due to slightly polymer aggregation. With temperature and pH increased, both the deprotonated PLLys side chains and PNIPAm backbone become hydrophobic, leading to polymer precipitation. These results illustrate that a double tunable hydrophilic graft copolymer had been successfully synthesized via a simple radical polymerization, and could form micelles without serious polymer aggregation at a lower pH and a higher temperature. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Mechanistic Insights into the Photoisomerization of N,N′-Disubstituted Indigos

N,N′-disubstituted indigos are photoswitchable molecules that have recently caught the attention due to their addressability by red-light. When alkyl and aryl groups are utilized as the N-substituents, the thermal half-lives of Z isomers can be tuned independently while maintaining the advantageous red-shifted absorption spectra. To utilize these molecules in real-world applications, it is of immense importance to understand how their molecular structures as well as the environment influence their switching properties. To this end, we probed their photoisomerization mechanism by carrying out photophysical and computational studies in solvents of different polarities. The fluorescence and transient absorption experiments suggest for more polar excited and transition states, which explains the bathochromic shifts of absorption spectra and shorter thermal half-lives. On the other hand, the quantum chemical calculations reveal that in contrast to N-carbonyl groups, N-alkyl and N-aryl substituents are not strongly conjugated with the indigo chromophore and can thus serve as a tool for tuning the thermal stability of Z isomers. Both approaches are combined to provide in-depth understandings of how indigos undergo photoswitching as well as how they are influenced by N-substituent and the chemical surroundings. These mechanistic insights will serve as guiding principles for designing molecules eyeing broader applications.     

Fused Bis(hemi-indigo): Broad-Range Wavelength-Independent Photoswitches

Wavelength-independent conversion of organic photoswitches in the photostationary state is a rare phenomenon that opens up a way for many practical applications. In this work, three fused bis(hemi-indigo) derivatives with different substitution patterns were synthesized and their photoswitching was investigated by optical spectroscopy, real-time NMR spectroscopy and TD-DFT calculations. We disclosed that the Z-E photoisomerization of the meta-bis(hemi-indigo) derivative was remarkably independent of the irradiation wavelength from UV up to yellow light. The wavelength-independent forward photoswitching together with the inhibited backward photoisomerization, high thermal stability of the photoinduced isomers as well as significant overlap between the photoswitch absorption and the solar spectrum allows to suggest bis(hemi-indigo) derivatives as promising candidates for molecular solar thermal energy storage (MOST) systems.     

Controllable Macroscopic Chirality of Coordination Polymers through pH and Anion-Mediated Weak Interactions

Helical architectures with controllable helical sense bias have recently attracted considerable interest for mimicking biological helices and developing novel chiral materials. Coordination polymers (CPs), composed of metal ion nodes and organic linkers, are intriguing systems showing tunable structures and functions. However, CPs with helical morphologies have rarely been explored so far. Particularly, chirality inversion through external stimulus has not been achieved in helical CPs. In this work, we carried out an in-depth investigation on the self-assembly of 1D gadolinium(III) phosphonate CPs using GdX₃ (X=Cl, Br, I) and Gd(RSO₃) (R=CH₃, C₆H₅, CF₃) as metal sources and R-(1-phenylethylamino)methyl phosphonic acid (R-pempH₂) as ligand. Superhelices were formed by precise control of the interchain interactions through different intercalated anions. Furthermore, the twisting direction of superhelices could be controlled by synergistic effect of anions and pH. This study may provide a new route to fabricate helical nanostructures of CPs with a desirable chiral sense and help understand the inner mechanism of the self-assembly process of macroscopic helical structures of molecular systems.     

<Superscript>234</Superscript>U/<Superscript>235</Superscript>U activity ratios as a probe for the <Superscript>238</Superscript>U/<Superscript>235</Superscript>U half-life ratio

High-resolution alpha-particle spectrometry was performed on three uranium materials enriched in ²³⁵U. Besides the ²³⁵U peaks, separate peaks belonging to impurity traces of ²³⁴U could be quantified. Relying on the isotopic composition of the uranium, as determined by mass spectrometry, the ratio of the half-lives of ²³⁸U and ²³⁵U was determined via the activity ratio of ²³⁴U and ²³⁵U in the materials. As an intermediate link, the ²³⁴U/²³⁸U half-life ratio was taken from published mass spectrometric analyses of ‘secular equilibrium’ uranium material. The resulting half-life ratio T _1/2(²³⁸U)/T _1/2(²³⁵U) = 6.351±0.031 is in agreement with the commonly adopted half-life values determined by Jaffey et al.