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Antibody-mimetic drug conjugate is a novel noncovalent conjugate consisting of an antibody-mimetic recognizing a target molecule on the cancer cell surface and low-molecular-weight payloads that kill the cancer cells. In this study, the efficacy of a photo-activating antibody-mimetic drug conjugate targeting HER2-expressing tumors was evaluated in mice, by using the affibody that recognize HER2 (Z

Visible-light-induced decarboxylative and deboronative reactions using two-molecule organic photoredox catalysts, namely, phenanthrene (Phen) and biphenyl (BP), as electron donors and 9-cyano-10-methoxycarbonylanthracene

We found that N-nitrosoaminoanisole derivatives tethered to dyes work as photocontrollable nitrosonium cation releasers and are converted to potent nitric oxide releasers in the presence of sodium ascorbate.

In the fields of sanitation and medicine, there is an urgent need for the development of convenient methods for imparting antibacterial properties to materials. Polypropylene nonwoven fabrics (PP NWFs) are one of the most common polymer materials; however, it is difficult to impart antibacterial properties to PP NWFs due to their low reactivity and complicated structures. In this study, we discovered that oxidation using photo-activated chlorine dioxide radical (ClO2) gas is a useful method for antibacterial modification of PP NWFs, without the need for any antibacterial agents or multi-step treatments. The as-prepared PP NWFs exhibited excellent antibacterial activity against both Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive). Interestingly, the solvent used to wash the product was analyzed to reveal the formation of nanoparticles around 80 nm in diameter during the oxidation step, particularly at 80 C.

This feature article summarizes the C–H oxygenation reaction involving chlorine radicals generated by light irradiation.

Antibacterial properties were imparted in polypropylene non-woven fabrics (PP NWFs) via a one-step modification using photo-activated ClO2˙. The modified PP NWFs showed 99.9% inhibition of bacterial growth against E. coli and S. aureus.

Chlorine dioxide radical (ClO2˙) under photoirradiation induces the chlorocarboxylation of toluene in a single step to produce 2- and 4-chlorobenzoic acids.

IR700, a silicon phthalocyanine (SiPc) photosensitizer, is an antibody–drug conjugate payload used clinically. It is, however, the sole SiPc payload to date, possibly due to the difficulty of its synthesis, resulting from its asymmetric phthalocyanine skeleton. Here, we report a new axially substituted SiPc payload that is more easily synthesized. Trastuzumab conjugated with the SiPc showed light- and antigen-dependent cytotoxicity in HER2-overexpressing cancer cell lines.

The effects of reaction environments on the radical-scavenging mechanisms of ascorbic acid (AscH(2)) were investigated using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH(•)) as a reactivity model of reactive oxygen species. Water-insoluble DPPH(•) was solubilized by β-cyclodextrin (β-CD) in water. The DPPH(•)-scavenging rate of AscH(2) in methanol (MeOH) was much slower than that in phosphate buffer (0.05 M, pH 7.0). An organic soluble 5,6-isopropylidene-l-ascorbic acid (iAscH(2)) scavenged DPPH(•) much slower in acetonitrile (MeCN) than in MeOH. In MeOH, Mg(ClO(4))(2) significantly decelerated the DPPH(•)-scavenging reaction by AscH(2) and iAscH(2), while no effect of Mg(ClO(4))(2) was observed in MeCN. On the other hand, Mg(ClO(4))(2) significantly accelerated the reaction between AscH(2) and β-CD-solubilized DPPH(•) (DPPH(•)/β-CD) in phosphate buffer (0.05 M, pH 6.5), although the addition of 0.05 M Mg(ClO(4))(2) to the AscH(2)–DPPH(•)/β-CD system in phosphate buffer (0.05 M, pH 7.0) resulted in the change in pH of the phosphate buffer to be 6.5. Thus, the DPPH(•)-scavenging reaction by iAscH(2) in MeCN may proceed via a one-step hydrogen-atom transfer, while an electron-transfer pathway is involved in the reaction between AscH(2) and DPPH(•)/β-CD in phosphate buffer solution. These results demonstrate that the DPPH(•)-scavenging mechanism of AscH(2) are affected by the reaction environments.

The effect of reaction environment on the radical-scavenging mechanism of ascorbic acid (AscH2) was investigated using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) as a reactivity model of reactive oxygen species. Water-insoluble DPPH was solubilized by beta-cyclodextrin (beta-CD) in water to use DPPH in phosphate buffer solutions. The DPPH-scavenging rate of AscH2 in methanol (MeOH) was much slower than that in phosphate buffer (0.05 M, pH 7.0), where AscH2 undergoes deprotonation to produced ascorbate anion (AscH-). An organic soluble 5,6-isopropylidene-L-ascorbic acid (iAscH2) was also used to compare the DPPH-scavenging reactivity in MeOH and acetonitrile (MeCN). iAscH2 scavenged DPPH much slower in MeCN than in MeOH. In MeOH, Mg(ClO4)2 significantly decelerated the DPPH-scavenging reaction by AscH2 and iAscH2, while no effect of Mg(ClO4)2 on the rate of the reaction of iAscH2 with DPPH was observed in MeCN. On the other hand, Mg(ClO4)2 significantly accelerated the reaction between AscH2 and beta-CD-solubilized DPPH (DPPH/beta-CD) in phosphate buffer (0.05 M, pH 6.5), although the addition of 0.05 M Mg(ClO4)2 to the AscH2-DPPH/beta-CD system in phosphate buffer (0.05 M, pH 7.0) resulted in the change in pH of the phosphate buffer to be 6.5. Thus, DPPH-scavenging reaction by iAscH2 in MeCN may proceed via a one-step hydrogen-atom transfer as the rate-determining step, while an electron transfer pathway is partly involved in the reaction between AscH2 and DPPH/beta-CD in phosphate buffer solution, although the detailed mechanism for the deceleration effect of Mg(ClO4)2 in MeOH is under investigation. These results demonstrate that the DPPH-scavenging mechanism by AscH2 are affected by the reaction environments.

Here we report an anionic meso-tetrakis(4-carboxymethylthio-2,3,5,6-tetrafluorophenyl) zinc porphyrin (ZnTF4PPTC4–) to form a supramolecular complex with a cationic lithium endohedral [60]fullerene...

We report the aggregation-induced photosensitizing activity of a cyanine dye in water and the mechanism. In addition, using the supramolecular assembly, visible-light-driven photooxidation of hydrophobic aromatic compounds in water was successfully performed.

A dicationic photoredox catalyst composed of phenylene-bridged bis(benzimidazolium) (BBIm2+) was designed, synthesised and demonstrated to promote the photochemical decarboxylative hydroxylation and dimerisation of carboxylic acids. The catalytic activity of BBIm2+ was higher than that for a monocation analogue, suggesting that the dicationic nature of BBIm2+ plays a key role in these decarboxylative reactions. The rate constant for the decay of the triplet–triplet absorption of the excited BBIm2+ increased with increasing concentration of the carboxylate anion with a saturated dependence, suggesting that photoinduced electron transfer occurs within the ion pair complex composed of the triplet excited state of BBIm2+ and a carboxylate anion., A new organic dication, phenylene-bridged bis(benzimidazolium), catalyses the photochemical decarboxylative hydroxylation and dimerisation of carboxylic acids.

【目的】赤ワインなどに含まれているレスベラトロール(RSV)はスチルベン構造を有し、抗酸化作用をはじめとする種々の生理活性を示すことが知られている。一方、プテロスチルベン(PTS)はRSVの3位と5位のヒドロキシ基がメトキシ基で置換された構造を持ち、RSVよりも生物学的利用能が高いことで注目を集めている。我々は以前に、活性酸素ラジカルのモデルとしてガルビノキシル(GO)ラジカルを用い、アセトニトリル(MeCN)溶媒中、RSVのGOラジカル消去反応について速度論的に検討した。電子移動反応を加速することが知られているマグネシウムイオン(Mg2+)をこの反応系に加えると二次反応速度定数(kH)が大きくなったことから、RSVからGOラジカルへの電子移動を経て反応が進行していることを明らかにした(Chem. Lett. 2007, 36, 1276)。本研究では、PTSによるGOラジカル消去の反応機構を明らかにする目的で、この反応に対するMg2+の影響について検討した。 【方法】反応はユニソクRSP-1000-02NM型ストップトフロー分光測定装置を用いて追跡した。 【結果】MeCN中、25 ℃で、PTSとGOラジカルを混合すると、GOラジカルに由来する428 nmの吸収の現象が観測された。これは、PTSによってGOラジカルが消去されたことを示している。428 nmの吸光度の経時変化を速度論的に解析することにより、この反応の二次反応速度定数(kH)を13 M-1 s-1と決定した。この反応系に過塩素酸マグネシウム(0.1〜0.3 M)を加えても、kH値はほとんど変化しなかった。次に、PTSのフェノール性OH基を重水素で置換した重水素化PTSを合成し、MeCN中、GOラジカルとの反応を行った。その結果、二次反応速度定数(kD)を3.7 M-1 s-1となりkH値よりも顕著に小さくなった。速度論的同位体効果(kH/kD)は3.4となり、PTSによるGOラジカル消去反応において、PTSからGOラジカルへの水素移動が律速段階となっていることが示唆された。 【結論】MeCN中、PTSによるGOラジカル消去反応は、電子移動反応が関与しない水素原子移動機構で進行していることが明らかとなった(Antioxidants 2022, 11, 340)。, 第22回日本抗加齢医学会総会

我々は以前に、活性酸素ラジカルのモデルとして2-フェニル-4,4,5,5-テトラメチルイミダゾリン-1-オキシル 3-オキシド(PTIO)を用い、リン酸緩衝液(0.05 M, pH 7.0)中、25℃で、アスコルビン酸(AscH2)からPTIOへの水素移動反応にトンネル効果が関与していることを明らかにした(Chem Commun 2020; 56: 11505)。本研究では、化合物の構造とトンネル効果との関係を解明する目的で、AscH2またはその類縁体である5,6-イソプロピリデン-L-アスコルビン酸(iAscH2)からPTIOまたはカルボキシPTIOへの水素移動反応を速度論的に検討した。 リン酸緩衝液(0.05 M, pH 7.0)中、25℃で、PTIOにiAscH2を加えると、PTIOに由来する560 nmの吸収が減少した。ユニソクRSP-1000-02NM型ストップトフロー分光測定装置を用いて560 nmの吸光度の経時変化を速度論的に解析し、この反応の二次反応速度定数(kH)を2.7 × 103 M–1 s–1と決定した。水の代わりに重水を用いて調整したリン酸緩衝液(0.05 M, pD 7.0)中ではiAscH2分子中のOH基がOD基に変わり、PTIOとの二次反応速度定数(kD)が顕著に小さくなった(2.2 × 102 M–1 s–1)。速度論的同位体効果(kH/kD)は12.0となり、この反応にもトンネル効果が関与していることが分かった。PTIOの代わりにカルボキシPTIOを用いると、AscH2およびiAscH2のいずれの場合にもkH値およびkD値は顕著に小さくなったが、kH/kD値は大きくなることが明らかとなった。, 第75回日本酸化ストレス学会学術集会

Visible-light-induced oxygenation of chloroform (CHCl3) using chlorine dioxide (ClO2˙) enables the in situ generation of phosgene (COCl2) and the synthesis of carbamoyl chlorides.

Photosensitizers (PSs) are critical substances with considerable potential for use in non-invasive photomedicine. Type I PSs, which generate reactive radical species by electron transfer from the excited state induced via photoirradiation, attracted much attention because of their suitability for photodynamic therapy (PDT) irrespective of the oxygen concentration. However, most organic PSs are type II, which activates only oxygen, generating singlet oxygen (

目的：近年、生命現象における量子効果の役割を解明する研究が注目を集めている。我々は最近、活性酸素ラジカルのモデルとして2-フェニル-4,4,5,5-テトラメチルイミダゾリン-3-オキシド-1-オキシル(PTIO)ラジカルを用い、リン酸緩衝液(0.05 M, pH 7.0)中、25℃で、代表的な水溶性抗酸化物質であるアスコルビン酸(AscH2)からPTIOラジカルへの水素移動反応に量子トンネル効果が関与していることを明らかにした。1) 本研究では、AscH2またはその類縁体である5,6-イソプロピリデン-L-アスコルビン酸(iAscH2)からPTIOラジカルまたはカルボキシPTIOラジカルへの水素移動反応を速度論的に追跡し、化合物の構造と量子トンネル効果との関係について検討した。 方法：反応はユニソクRSP-1000-02NM型ストップトフロー分光測定装置を用いて追跡した。 結果および考察：リン酸緩衝液(0.05 M, pH 7.0)中、25℃で、カルボキシPTIOラジカルにAscH2を加えると、カルボキシPTIOラジカルに由来する560 nmの吸収が減少した。560 nmの吸光度の経時変化を速度論的に解析し、AscH2からカルボキシPTIOラジカルへの水素移動反応の二次反応速度定数(kH)を1100 M-1 s-1と決定した。水の代わりに重水を用いてリン酸緩衝液(0.05 M, pD 7.0)を調製し、これを溶媒として同様の検討を行うと、二次反応速度定数(kD = 77 M-1 s-1)はkH値よりも顕著に小さくなり、速度論的同位体効果(kH/kD)は13.6となった。iAscH2やPTIOラジカルを用いた場合にも同様にkHおよびkD、kH/kD値を決定した。いずれの場合にも大きなkH/kD値が得られ、PTIOラジカルよりもカルボキシPTIOラジカルとの反応の方がkH/kD値が大きくなった。kH/kD値の温度依存性についても検討したので併せて報告する。 1) Nakanishi I., Shoji Y., Ohkubo K., Ozawa T., Matsumoto K., Fukuzumi S., Chem. Commun., 56, 11505-11507 (2020)., 日本薬学会第142年会

Carbamoyl chloride supports modern society as a building block for pharmaceuticals, agrochemicals, and polymers. Although carbamoyl chlorides are generally synthesized via the reaction of amines with phosgene (COCl2), these applications of COCl2 have recently been avoided because of its high toxicity. Herein, we report the visible-light-induced in-situ preparation of COCl2 through the oxygenation of chloroform in the presence of chlorine dioxide, which leads to the safe constructions of carbamoyl chlorides with good-to-high yields and wide substrate scopes. In addition, this method can also be applied to the synthesis of various carbonates that are the starting materials for resins such as polycarbonates and polyurethanes.

Resveratrol (1), 3,5,4'-trihydroxy-trans-stilbene, found in grapes is one of the representative antioxidants that shows a plethora of remarkable biological properties. On the other hand, pterostilbene (2), a methylated analog of 1, has attracted much attention due to its enhanced bioavailability as compared to that of 1. However, little is known about the radical-scavenging mechanism of 2. There are two mechanisms in the radical-scavenging reaction of phenolic antioxidants: a one-step hydrogen-atom transfer from the phenolic OH group; and an electron transfer followed by proton transfer. Redox inactive metal ions, such as magnesium ion (Mg2+), are a powerful tool to distinguish between these two mechanisms, because electron-transfer reactions are known to be accelerated by their presence. In fact, a significant acceleration in the radical-scavenging reaction of 1 was observed in the presence of Mg2+ in acetonitrile (MeCN), suggesting that the reaction may proceed via the electron-transfer mechanism (Chem. Lett. 2007, 36, 1276). We report herein the effect of Mg2+ on the scavenging reaction of galvinoxyl radical (GO) by 2 in MeCN. GO has been frequently used as a reactivity model of reactive oxygen radicals to estimate the activity of antioxidants. Upon mixing of 2 with GO on a UNISOKU RSP-1000-02NM stopped-flow spectrophotometer in MeCN at 298 K, a gradual decrease in the absorption band at 428 nm due to GO was observed, indicating that 2 efficiently scavenged GO. From the time course change in the absorbance at 428 nm, the second-order rate constant (k) for the reaction between 2and GO was determined to be 1.3 × 10 M−1 s−1, which is about 3-fold larger than that of 1 (4.1 M−1 s−1). When Mg(ClO4)2 (0.1−0.3 M) was added to the 2−GO system, no effect of Mg2+ on the k values was observed. Thus, the GO-scavenging reaction by 2 may proceed via the one-step hydrogen-atom transfer rather than the electron transfer followed by proton transfer., PACIFICHEM 2021

The supramolecular photocatalysts in which a Ru(II) complex as a molecular redox photosensitizer unit and a Re(I) complex as a molecular catalyst unit are connected with a various alkyl or ether ch...

We have successfully constructed hydrogen-bonded supramolecular assemblies based on a diprotonated saddle-distorted porphyrin (H4DPP2+) and redox-active molecules bearing a carboxylate group, such ...

A stable radical, 2,2-diphenyl-1-picrylhydrzyl radical (DPPH•), has been frequently used to estimate the activity of antioxidants as a reactivity model of reactive oxygen species for more than six decades [1]. However, the insolubility of DPPH• in water has precluded its use in aqueous media without cosolvents, such as ethanol. On the other hand, we succeeded in solubilizing DPPH• in water by complexation with β-cyclodextrin (β-CD) [2]. We report herein the redox reactivity of β-CD-solubilized DPPH• (DPPH•/β-CD) in aqueous buffer solutions. The cyclic voltammograms of DPPH•/β-CD were recorded in phosphate buffer solutions (0.1 M) under various pH conditions (pH 8.3, 7.2, and 6.1). Quasi-reversible and reversible redox waves were observed for the one-electron oxidation and reduction of DPPH•/β-CD, respectively. The one-electron reduction potentials determined from the reversible redox couples linearly shifted to the positive direction as the pH of the solution decreased, while the quasi-reversible one-electron oxidation waves remained unchanged. Thus, DPPH•/β-CD undergoes one-electron reduction more easily under acidic conditions than under basic conditions. The pH effect on the reactivity of DPPH•/β-CD toward antioxidants was also examined in buffer solutions (0.05 M, pH 6.0–9.1). Ascorbic acid (AscH2), a representative water-soluble antioxidant, efficiently scavenged DPPH•/β-CD in phosphate buffer solution. The second-order rate constants (k) determined for the reaction between AscH2 and DPPH•/β-CD by monitoring the time course change of the absorbance at 527 nm due to DPPH•/β-CD increased with increasing the pH values of the solution [3]. When AscH2 was replaced by Trolox, a water-soluble analog of α-tocopherol (vitamin E), a similar pH dependence on the k values was observed, suggesting that such a pH dependence may be caused by the reactivity of DPPH• in aqueous solutions. The detailed redox mechanism of DPPH• in aqueous media will also be discussed. References: [1] M. S. Blois, Nature, 191, 1199–1200 (1958). [2] I. Nakanishi, K. Ohkubo, K. Imai, M. Kamibayashi, Y. Yoshihashi, K. Matsumoto, K. Fukuhara, K. Terada, S. Itoh, T. Ozawa, S. Fukuzumi, Chem. Commun., 51, 8311–8314 (2015). [3] I. Nakanishi, Y. Shoji, K. Ohkubo, K. Fukuhara, T. Ozawa, K. Matsumoto, S. Fukuzumi, J. Clin. Biochem. Nutr., 68, 115–122 (2021)., ISMAR-APNMR-NMRSJ-SEST 2021

2,2-ジフェニル-1-ピクリルヒドラジル(DPPH)ラジカルは活性酸素ラジカルのモデルとして抗酸化物質の活性評価に頻用されてきた(Blois MS. Nature 1958; 181: 1199)。しかし、DPPHラジカルは水に不溶なため水溶液中で用いるにはアルコールなどの共溶媒が必要となり、pHの制御が困難であった。我々は以前に、β-シクロデキストリンを用いてDPPHラジカルの水溶化に成功した(Chem Commun 2015; 51: 8311)。本研究では、リン酸緩衝液中、水溶性抗酸化物質とDPPHラジカルとの反応に対するpHの影響を速度論的に検討した。 リン酸緩衝液(0.05 M, pH 7.0)中、25℃で、DPPHラジカルにアスコルビン酸を加えると、DPPHラジカルによる527 nmの吸収が減少した。527 nmの吸光度の経時変化をユニソクRSP-1000-02NM型ストップトフロー分光測定装置で追跡し、アスコルビン酸によるDPPHラジカル消去の二次反応速度定数(kH)を決定した(J Clin Biochem Nutr 2021; 68: 116)。kH値はpHの上昇に伴って増大した。アスコルビン酸の代わりに水溶性ビタミンE誘導体Troloxや(+)-カテキン、カフェイン酸を用いた場合にも、kH値に対して同様のpH依存性が観測された。以上の結果から、kH値に対するpHの影響はDPPHラジカルの反応性によるものと考えられる。水溶化DPPHラジカルの酸化還元電位に対するpHの影響についてもALS-630A電気化学アナライザーを用いたサイクリックボルタンメトリーにより検討したので併せて報告する。, 第74回日本酸化ストレス学会・第21回日本NO学会 合同学術集会

目的：赤ワインに含まれているレスベラトロール(Res)はスチルベン骨格を有するフェノール化合物で、抗酸化作用をはじめてとする種々の生理活性を示す。一方、プテロスチルベン(Pte) は、Resの3位と5位のヒドロキシ基がメトキシ基で置換された構造を持ち、Resよりも生物学的利用能が高いことが知られている。しかし、Pteのラジカル消去機構には不明な点が残されている。我々は、電子移動反応がマグネシウムイオンによって加速される性質を利用し、抗酸化物質によるラジカル消去反応に電子移動が関与するかどうかを検討してきた。本研究では、Pteのラジカル消去機構を明らかにする目的で、活性酸素ラジカルのモデルとしてがルビのキシル(GO)ラジカルを用い、PteのGOラジカル消去反応に対するマグネシウムイオンの効果について検討した。 方法：反応はユニソクRSP-1000-02NM型ストップトフロー分光測定装置を用いて追跡した。 結果および考察：アセトニトリル中、25℃で、GOラジカルにPteを加えると、GOラジカルに由来する428 nmの吸収の減少が観測され、GOラジカルは効率良く消去された。428 nmの吸光度の経時変化を速度論的に解析することにより、この反応の二次反応速度定数(k)を13 M-1 s-1と決定した。この反応系に過塩素酸マグネシウム(0.1〜0.3 M)を加えてもk値はほとんど変化しなかった。一方、我々は以前に、アセトニトリル中、ResによるGOラジカル消去反応では、加えた過塩素酸マグネシウムの濃度の増加に伴って、k値が増大することを報告している(Chem. Lett, 36, 1276 (2007))。以上の結果から、アセトニトリル中、ResによるGOラジカル消去反応の律速段階には電子移動が関与しているのに対し、Pteは1段階の水素原子移動機構でGOラジカルを消去することが示唆された。, 日本薬学会第141年会

本研究では、寿命の延伸作用やアルツハイマー病の予防作用で注目されているフィセチンの高機能化を目指して、カテコール構造のオルト位にメチル基を導入したモノメチル体およびジメチル体を合成し、ラジカル消去活性とそのメカニズムを明らかにした。 メチルカテコールを出発原料とし、Alger-Flynn-Oyamada反応を用いてフラボノイド骨格を合成後、脱保護してモノメチル体(2'-メチル体: 1、5'-メチル体: 2)および2',5'-ジメチル体(3)を得た。これらの化合物について、活性酸素のモデル化合物であるガルビノキシルラジカルに対する反応の速度論的解析を行い、ラジカル消去活性を求めた。その結果、フィセチンはメチル基を導入するとラジカル消去活性が増大し、特に2が最も強力な活性を示した。分子軌道計算により最安定化構造を求めたところ、2は分子全体の平面性が保たれているが、1および3は2'-メチル基の立体障害によりAC環に対してB環が大きくねじれた構造を示した。強力なラジカル消去作用を有する2のO-H結合の解離エネルギー(BDE)とイオン化ポテンシャル(IP)は、これらの化合物の中でどちらも最小の値を示した。また、これらの化合物のラジカル消去活性はIPと良好な負の相関を示すことから、ラジカル消去反応は一電子還元反応で進行していることが明らかとなった。 以上、フィセチンのカテコール構造のオルト位にメチル基を導入すると強力なラジカル消去作用を示した。平面性の高い2はラジカル消去反応の過程で一電子移動反応によって生成するラジカルカチオンが分子全体に非局在化するため、最も強力なラジカル消去活性を示すことが考えられる。, 日本農芸化学会2021年度大会

Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant. Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer. Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1. Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media., 20th Biennial Meeting of SFRR International (SFRR-I 2021)

A large kinetic isotope effect (KIE, kH/kD) of 12.8 was observed for the hydrogen-transfer reaction from ascorbic acid to 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO˙) in a phosphate buffer solution (0.05 M, pH/pD 7.0) at 298 K. The isotopic difference in the activation energies (6.8 kJ mol-1) determined from the temperature dependence of the KIE suggests that quantum mechanical tunneling may partly play a role in the reaction, although the isotopic ratio of the Arrhenius prefactor (AH/AD = 0.86) is within the semiclassical limits.

The relationship between radical-scavenging rate constants (k) in an aprotic medium and thermodynamic parameters calculated by density functional theory (DFT) was investigated for 7 flavonols, whic...

Outer-sphere electron transfer from styrene, thioanisole, and toluene derivatives to a triflic acid (HOTf)-bound nonheme Mn(IV)-oxo complex, [(N4Py)MnIV(O)]2+-(HOTf)2 (N4Py = N, N-bis(2-pyridylmethyl)- N-bis(2-pyridyl)methylamine), has been shown to be the rate-determining step of different types of redox reactions such as epoxidation, sulfoxidation, and hydroxylation of styrene, thioanisole, and toluene derivatives, respectively, by [(N4Py)MnIV(O)]2+-(HOTf)2. The rate constants of HOTf-promoted epoxidation of all styrene derivatives with [(N4Py)MnIV(O)]2+ and electron transfer from electron donors to [(N4Py)MnV(O)]2+ exhibit a remarkably unified correlation with the driving force of outer-sphere electron transfer in light of the Marcus theory of electron transfer. The same electron-transfer driving force dependence is observed in the oxygen atom transfer from [(N4Py)MnIV(O)]2+-(HOTf)2 to thioanisole derivatives as well as in the hydrogen atom transfer from toluene derivatives to [(N4Py)MnIV(O)]2+-(HOTf)2. Thus, mechanisms of oxygen atom transfer (epoxidation and sulfoxidation) reactions of styrene and thioanisole derivatives and hydrogen atom transfer (hydroxylation) reactions of toluene derivatives by [(N4Py)MnIV(O)]2+-(HOTf)2 have been unified for the first time as the same reaction pathway via outer-sphere electron transfer, followed by the fast bond-forming step, which exhibits the singly unified electron-transfer driving force dependence of the rate constants as outer-sphere electron-transfer reactions. In the case of the epoxidation of cis-stilbene by [(N4Py)MnIV(O)]2+-(HOTf)2, the isomerization of cis-stilbene radical cation to trans-stilbene radical cation occurs after outer-sphere electron transfer from cis-stilbene to [(N4Py)MnIV(O)]2+-(HOTf)2 to yield trans-stilbene oxide selectively, which is also taken as evidence for the occurrence of electron transfer in the acid-catalyzed epoxidation.

We describe a hybrid system that realizes cooperativity between an organophotoredox acridinium catalyst and a chiral chromium complex catalyst, thereby enabling unprecedented exploitation of unactivated hydrocarbon alkenes as precursors to chiral allylchromium nucleophiles for asymmetric allylation of aldehydes. The reaction proceeds under visible light irradiation at room temperature, affording the corresponding homoallylic alcohols with a diastereomeric ratio >20/1 and up to 99% ee. The addition of Mg(ClO4)2 markedly enhanced both the reactivity and enantioselectivity.

Antibody-drug conjugates (ADCs) are a major therapeutic tool for the treatment of advanced cancer. Malignant cells in advanced cancer often display multiple genetic mutations and become resistant to monotherapy. Therefore, a therapeutic regimen that simultaneously targets multiple molecules with multiple payloads is desirable. However, the development of ADCs is hampered by issues in biopharmaceutical manufacturing and the complexity of the conjugation process of low-molecular-weight payloads to biologicals. Here, we report antibody mimetic-drug conjugates (AMDCs) developed by exploiting the non-covalent binding property of payloads based on high-affinity binding of mutated streptavidin and modified iminobiotin. Miniprotein antibodies were fused to a low immunogenic streptavidin variant, which was then expressed in Escherichia coli inclusion bodies, solubilized, and refolded into functional tetramers. The AMDC developed against human epidermal growth factor receptor 2 (HER2) effectively killed cultured cancer cells using bis-iminobiotin conjugated to photo-activating silicon phthalocyanine. The HER2-targeting AMDC was also effective in vivo against a mouse KPL-4 xenograft model. This AMDC platform provides rapid, stable, and high-yield therapeutics against multiple targets.

We report homogeneous electrocatalytic and photocatalytic H2 evolution using two Ni(II) complexes with S2N2-type tetradentate ligands bearing two different sizes of chelate rings as catalysts. A Ni(II) complex with a five-membered SC2S–Ni chelate ring (1) exhibited higher activity than that with a six-membered SC3S–Ni chelate ring (2) in both electrocatalytic and photocatalytic H2 evolution despite both complexes showing the same reduction potentials. A stepwise reduction of the Ni center from Ni(II) to Ni(0) was observed in the electrochemical measurements; the first reduction is a pure electron transfer reaction to form a Ni(I) complex as confirmed by electron spin resonance measurements, and the second is a 1e–/1H+ proton-coupled electron transfer reaction to afford a putative Ni(II)-hydrido (NiII–H) species. We also clarified that Ni(II) complexes can act as homogeneous catalysts in the electrocatalytic H2 evolution, in which complex 1 exhibited higher reactivity than that of 2. In the photocatalytic ...