Photocontrol of micellar catalysis

A photoresponsive surfactant with a cationic azobenzene head group (I) was synthesized. It was demonstrated that by mixing (I) with a conventional cationic micelle the rate of the micelle-catalyzed reaction (base-catalyzed proton abstraction from benzoin) can be controlled by light. The origin of the photocontrol was accounted for by the difference in the partitioning of trans-(I) and cis-(I) in the micelle phase.     

Photocontrol of the collagen triple helix: synthesis and conformational characterization of bis-cysteinyl collagenous peptides with an azobenzene clamp

For the photomodulation of the collagen triple helix with an azobenzene clamp, we investigated various collagenous peptides consisting of ideal (Gly-Pro-Hyp) repeats and containing cysteine residues in various positions for a side chain-to-side chain crosslink with a suitable chromophore derivative. Comparative conformational analysis of these cysteine peptides indicated an undecarepeat peptide with two cysteine residues located in the central portion in i and i+7 positions and flanked by (Gly-Pro-Hyp) repeat sequences as the most promising for the cross-bridging experiments. In aqueous alcoholic solution the azobenzene-undecarepeat peptide formed a stable triple helix in equilibrium with the monomeric species as a trans-azobenzene isomer, whereas photoisomerization to the cis isomer leads to unfolding of at least part of the triple helix. Furthermore, the residual supercoiled structure acts like an intermolecular knot, thus making refolding upon cis-to-trans isomerization a concentration-independent fast event. Consequently, these photoswitchable collagenous systems should be well suited for time-resolved studies of folding/unfolding of the collagen triple helix under variable thermodynamic equilibria.     

乳酸氧化酶共价交联于蛋膜上制备乳酸传感器

以牛血清白蛋白 戊二醛为交联剂 ,将乳酸氧化酶固定于鸡蛋膜上 ,氧电极作电化学敏感元件 ,制成乳酸氧化酶电极。传感器的线性响应范围为 5 .0×1 0 - 5～ 2 .5× 1 0 - 2 mol/L ,检测限为 2 .0× 1 0 - 5mol/L ,RSD为 1 .4% (n =1 1 ) ,回收率为 97.5 %～ 1 0 4 .0 %。该传感器可用于临床乳酸的测定。     

Photoswitchable Chiral Organocatalysts: Photocontrol of Enantioselective Reactions

This study presents recent advances in photoswitchable chiral organocatalysts and their applications in the photomodulation of enantioselective reactions. Under irradiation with an appropriate wavelength of light, the E/Z-photoisomerization of the photoresponsive units on the catalysts leads to the control of the catalytic activity and/or selectivity of the enantioselective reactions. Additionally, this study elucidates the design, synthesis, and catalytic application of the fabricated azobenzene BINOL-based photoswitchable chiral phase-transfer catalysts. This account will provide insights into the appropriate design of a photoswitchable chiral organocatalyst that can achieve both good enantioselectivity and photocontrol.     

Photocontrol of peptide secondary structure through non-azobenzene photoswitches

The rapidly expanding field of photoswitchable biomolecules is a major frontier in scientific research and provides unparalleled opportunities for studying biological pathways and disease progression. In particular, the development of photochromic peptides has delivered both scientific tools and candidates for photopharmaceuticals. The action and function of the peptide can be remotely altered using light, allowing detection of its biological role in complex biological settings, while also enabling folding studies that provide greater understanding of protein structure dynamics. In this review we provide a key, comprehensive overview of the different types of photoswitches that have been used to control peptide structure, excluding the already extensively reviewed azobenzene. This will help address the question as to which synthetic photoswitch to use in a given study.     

Cationic Polymerization: From Photoinitiation to Photocontrol

During the last 40 years, researchers investigating photoinitiated cationic polymerizations have delivered tremendous success in both industrial and academic settings. A myriad of photoinitiating systems have been developed, thus allowing polymerization of a broad array of monomers (e.g., epoxides, vinyl ethers, alkenes, cyclic ethers, and lactones) under practical, inexpensive, and environmentally benign conditions. More recently, owing to progress in photoredox catalysis, photocontrolled cationic polymerization has emerged as a means to precisely regulate polymer chain growth. This Minireview provides a concise historical perspective on cationic polymerization induced by light and discusses the latest advances in both photoinitiated and photocontrolled processes. The latter are exciting new directions for the field that will likely impact industries ranging from micropatterning to the synthesis of complex biomaterials and sequence‐controlled polymers.     

Photocontrol of DNA binding specificity of a miniature engrailed homeodomain

Control of DNA binding of HDH-3, a 18-residue polypeptide based on the recognition helix of the Q50K engrailed homeodomain, has been achieved. HDH-3 was linked to an azobenzene cross-linker through two cysteine residues in an i, i + 11 spacing. For the thermodynamically stable trans configuration of the cross-linker, the dark-adapted peptide (dad-HDH-3) adopted a mainly alpha-helical structure as judged by circular dichroism (CD) spectroscopy. After irradiation with light of 360 nm, the helical content of the peptide (irrad-HDH-3) was reduced significantly and the CD spectrum of the irradiated peptide resembled that of the largely unstructured, unalkylated peptide. Despite lacking helices-1 and -2 and the N-terminal arm of Q50K engrailed, dad-HDH-3 bound to its natural DNA target sequence TAATCC (QRE) with high affinity (K(D) = 7.5 +/- 1.3 nM). The binding affinity for the mutant DNA sequence, TAATTA (ERE), was reduced significantly (K(D) = 140 +/- 11 nM). Unlike irrad-HDH-3, which like the unalkylated parent peptide displayed only marginal DNA binding specificity, dad-HDH-3 specified base pairs 5 and 6 of QRE with an accuracy rivaling that of the intact wild-type Q50K engrailed homeodomain, making dad-HDH-3 the most specific designed DNA binding miniature homeodomain reported to date. Moreover, DNA binding affinity and specificity of HDH-3 could be controlled externally by irradiation with light.     

两种医用胶原膜 60Co辐照改性的比较

胶原作为一种新型生物材料,具有无毒,良好的生物相容性,生物可降解性及可吸收性,广泛用于皮肤创伤的治疗、骨缺损的修复、药物缓释的载体、止血敷料、组织工程支架材料等。但胶原在体内降解太快,不能与组织再生速度相匹配。有必要探讨胶原生物材料的改性方法,便于其更好     

Mineralization of biomimetically carboxymethylated collagen fibrils in a model dual membrane diffusion system

In the present work, we show for the first time, that N^?-carboxymethyllysine is the major product of the in vitro non-enzymatic glycation reaction between fibrillar collagen and glucuronic acid. Dual diffusion membrane system was effectively used for oriented crystal growth of octacalcium phosphate/hydroxyapatite on the biomimetically carboxymethylated collagen fibrils. We hypothesize that the function of biomimetically carboxymethylated collagen is to increase the local concentration of corresponding ions in such a way that a critical nucleus of ions can be formed, leading to the formation of the mineral under specific micro-environment conditions achieved by using diffusion membrane system.     

Photocontrol of supramolecular architecture in azopolymers: Achiral and chiral aggregation

The absorption spectra and circular dichroism responses upon irradiation with 488 nm circularly polarized light (CPL) have been studied on polymeric films processed from two nematic copolymers containing azobenzene chromophores. Influence of the aggregation and orientation of azobenzenes on the photoinduced chiroptical properties has been analyzed. Moreover, polymeric films and 4 μm planar cells filled with the copolymers were studied by polarized optical microscopy (POM) with the aim of investigating the change of macroscopic optical properties and textures of azopolymers upon irradiation with CPL.     

由乳酸铵直接合成乳酸乙酯的研究

乳酸乙酯在传统的消费领域中多用于香精、香料、食品及酿酒行业,是良好的添加剂;此外在制药工业中用做压制药片的润滑剂,药物心得静的中间体;饲料工业中用做香味剂。乳酸乙酯最具发展前景的用途是：利用其具有无毒、溶解性好、不易挥发等特点作为“绿色溶剂”,它可以取代目前使用的许多对人和环境有毒的溶剂,如：卤代类、醚类以及破坏臭氧层的氟氯碳溶剂等,同时乳酸乙酯又具有可生物降解性,因此乳酸乙酯是极具开发价值和应用前景的“绿色产品”。     

Fluorimetric determination of lactate with immobilized lactate dehydrogenase

In measuring inter-phase distribution coefficients (k_{$\text{1}\text{11}$})it is often convenient, and sometimes necessary, to obtain all of the analytical data from one phase. A rigorous formula, applicable to both low and high k_{$\text{1}\text{11}$} values has been derived; measurements of the distribution of mercury, methylmercury and ⁶⁷Cu²⁺ between various pairs of phases with this formula gave k_{$\text{1}\text{11}$} values similar to those obtained from other approaches.     

Study of the morphological and adhesion properties of collagen fibers in the Bruch's membrane

The Bruch's membrane is located beneath the retina in vertebrate eyes. We have used atomic force microscopy to examine the morphological and adhesion properties of collagen fibers located in different portions of the membrane. The D-periodicity of the fibers was 62.54 +/- 4.25 nm and 63.78 +/- 4.14 nm for regions away from the optic nerve and close to it, respectively. The adhesion properties of the collagen fibers were evaluated using force volume imaging on a number of different eye samples. The adhesion force we recorded in regions away from the optic nerve was different compared to regions close to the optic nerve. The reported results allow us to understand the nanoscopic properties of connective tissues in the eye and are important for the design of new and improved biomaterials.     

Photocontrol of tyrosine phosphorylation in mammalian cells via genetic encoding of photocaged tyrosine

We report the first site-specific genetic encoding of photocaged tyrosine into proteins in mammalian cells. By photocaging Tyr701 of STAT1 we demonstrate that it is possible to photocontrol tyrosine phosphorylation and signal transduction in mammalian cells.     

Photocontrol of cell adhesion and proliferation by a photoinduced cationic polymer surface

In this study photoinduced cation generation, based on the photochemical properties of malachite green (MG), was used for the surface design and in vitro photochemical control of cell adhesion and proliferation. The MG-derivatized surface was prepared by coating a photoreactive polymer as a substrate onto a poly(ethylene terephthalate) (PET) sheet. The photoreactive polymer was radical copolymer of styrene with the MG-derivatized monomer diphenyl(4-vinylphenyl)methane leucohydroxide (degree of substitution of MG unit: 12.4 mol%). Water contact angle measurements and X-ray photoelectron spectroscopy revealed high hydrophobicity and homogeneous distribution of the MG groups on the outermost surface of the coated film, respectively. When the coated film was exposed to ultraviolet light (UV) irradiation at wavelengths of 290-410 nm, a time-dependent color change of the film was observed from pale yellow, before irradiation, to green. These results indicated generation of cations on the film surface by photochemical cation generation of the MG groups, which was quantitatively characterized by force versus distance curves measurements in atomic force microscopic (AFM) observation using a carboxylated AFM tip. The seeding and culture of endothelial cells showed a marked reduction in adhesion on the nonirradiated coated film surface, whereas the UV-irradiated surface promoted cell adhesion and proliferation except for incubation in serum-free medium, which was similar to commercial tissue culture PET sheet. These observations may be due to adsorption of cell adhesive proteins, typified by fibronectin, in serum-containing medium onto the cationized photoreactive copolymer surface by electrostatic interactions.