JP4215360B2 - Organic-inorganic composite having spiral structure, metal oxide, and method for producing the same - Google Patents

Description

式（Ｉ）中、ｎは０または１であり、Ｘは下記（II）に示されるいずれかの官能基である。
【０００８】
【化６】

【０００９】
本発明は、さらに、好ましい態様として、以上の方法により得られた有機無機複合体からコレステロール誘導体を除去することを特徴とする中空糸状で螺旋状の金属酸化物の製造方法を提供し（請求項２）、その特に好ましい態様においては、焼成によりコレステロール誘導体を除去する（請求項３）。
【００１０】
さらに、本発明は、別の視点から、上記の方法（請求項１）により製造される有機無機複合体であって、内側が金属を保持した既述の式（Ｉ）で表されるコレステロール誘導体、外側が前記金属とは別異の金属の金属酸化物から成り直径がナノメータのオーダーの円筒構造が螺旋状を呈していることを特徴とする有機無機複合体を提供する。
【００１１】
本発明は、さらに、上記の方法（請求項２，３）により製造されることができ、内径がナノメータのオーダーの円筒状金属酸化物が螺旋状を呈し、その金属酸化物の表面に該金属酸化物を構成する金属とは別異の金属が固着していることを特徴とする中空糸状金属酸化物も提供し、この中空糸状金属酸化物の特に好ましい例はシリカである。
【００１２】
【発明の実施の形態】
上述の式（Ｉ）で表されるアザクラウン環を有するコレステロール誘導体を用いる本発明に従えば、ゲル状態にある該コレステロール誘導体の螺旋（へリックス）構造の向きに応じて螺旋の向きが制御された螺旋構造を有する有機無機複合体または金属酸化物を得ることができる。
【００１３】
以下、本発明の有機無機複合体および金属の製造方法、およびそれらの構成する各要素に沿って本発明の特徴を詳述する。
製造方法
（１）金属を包接したコレステロール誘導体の調製：
本発明に従い有機無機複合体および金属酸化物を製造するには、先ず、上述の式（Ｉ）で表されるアザクラウン環を有するコレステロール誘導体を金属塩溶液に溶解させた後、蒸発乾固することにより、該金属塩由来の金属を包接したアザクラウン環を有するコレステロール誘導体を調製する。この金属塩由来の金属は、それとは別異の金属の金属酸化物（例えば、シリカ）の表面に固着して触媒など所望の機能を発揮するものから選ばれる。
【００１４】
すなわち、式（Ｉ）のｎの値によって定められるアザクラウン環の大きさに応じて該クラウン環に包接され安定な錯体を形成するような金属から選ばれ、好ましい金属としては、周期律表第Ｉａ族の金属（アルカリ金属）、第Ｉｂ族の金属（Ｃｕ、Ａｇなど）などが挙げられる。これらの金属は、コレステロール誘導体を溶解し得る塩化メチレン、ＴＨＦなどの溶媒中で硝酸塩、塩化物、過塩素酸塩、チオシアン塩などの塩として添加される。
【００１５】
（２）ゾルゲル反応溶液を含む混合液の調製：
次に、上記のように調製し金属塩由来の金属を包接したアザクラウン環を有するコレステロール誘導体とゾルゲル反応溶液とを混合して、それらを含有する均一な混合液を調製する。
【００１６】
ここで、ゾルゲル反応溶液は、目的のゾルゲル反応系にもよるが、ゾルゲル反応が進行するような当初のゾルが形成されるように、少なくとも、金属酸化物（無機材料：前述の金属塩由来の金属とは別異の金属の金属酸化物）の前駆体（金属酸化物の出発原料：金属アルコキシド、金属クロリド、金属ジケトネート等）、該金属酸化物の前駆体からゾルゲル反応により金属酸化物を生成するための触媒（酸、アルカリ、アミン等）、および水（金属酸化物の前駆体の加水分解に必要であり、少量でよい）を含まなければならない。但し、これだけではゾルゲル反応系の溶解性が充分でない場合には、それらの前駆体、触媒、水を溶解し得るような溶媒を使用する。さらに、必要により、混合を円滑にするため、コレステロール誘導体とゾルゲル反応溶液とを溶解し得る有機溶媒を用いる。
【００１７】
（３）ゲルの形成：
本発明の方法においては、このようにして得られた混合液中において式（Ｉ）のコレステロール誘導体のゲルを形成させる。ここで、本発明に関連して用いるゲルという語は、一般的には、溶媒を完全に束縛して固まっている状態を指称するが、系を傾け軽い衝撃を与えると流動する程度に有機低分子（コレステロール誘導体）が互いに結合して繊維を形成している状態も含むものとする。このゲル形成の工程は以下のようにして行う。
【００１８】
コレステロール誘導体のゲル形成の生じる温度が室温またはそれ以上である場合には、混合を円滑に行うためにコレステロール誘導体とゾルゲル反応溶液との両者を溶解する有機溶媒を添加して調製した均一混合液から、溶解するために加えた有機溶媒を除去することによりゲルを形成させる。この有機溶媒の除去は、一般に、減圧乾燥により行う。また、コレステロール誘導体が加熱に耐えられる場合は、上記の均一混合液を加熱した後、室温に冷却してゲルを形成する。さらに、ゲル形成温度が室温以下の場合には、コレステロール誘導体とゾルゲル反応溶液とを室温で混合し、系を冷却することによりゲルを形成する。この工程中に、一般に繊維状構造のコレステロール誘導体のゲルが先行して形成され、金属酸化物のゾルゲル反応が一部進行する。
【００１９】
（４）金属酸化物の重合：
本発明に従い有機無機複合体を製造するには、次に、上記のようにゲルが形成した系を、該ゲルが壊れないような条件下に保持しながら、金属酸化物の重合を更に進行させる。すなわち、室温でゲル形成が生じたような系は室温下に、また、冷却によってゲルが形成したような系は、その冷却温度に、適当時間（一般に、数日間以上）保持すれば、金属酸化物のゾルゲル反応により加水分解、重縮合が進行し、金属酸化物の重合度が上がり溶液中に溶解し得なくなった金属酸化物が繊維状構造のコレステロール誘導体表面に付着、析出する。既述の式（Ｉ）で表されるアザクラウン環を有するコレステロール誘導体は、静電力により金属酸化物を付着させるため適度のイオン性を有しているものと推測される。
【００２０】
（５）有機無機複合体および金属酸化物の調製：
以上のような工程の後、乾燥を行い、余分な溶媒を除去し、ゲル構造のコレステロール誘導体分子を残せば、螺旋状で金属塩由来の金属を保持したコレステロール誘導体の表面に、金属酸化物前駆体由来の金属の金属酸化物が付着した有機無機複合体が得られる。さらに、コレステロール誘導体を除去すれば、螺旋状で中空糸状の金属酸化物となる。コレステロール誘導体の除去は、溶媒を用いて溶出させることにより可能な場合もあるが、一般に、本発明の複合体における有機分子は金属酸化物の外壁により強く保護され耐溶剤性を有するので、焼成により行うのが好ましい。
【００２１】
アザクラウン環を有するコレステロール誘導体
上述の式（Ｉ）で表されるアザクラウン環を有するコレステロール誘導体をゲル形成材として用いる本発明に従えば、（金属塩由来の）金属を保持したコレステロール誘導体（Ｉ）のゲルのキラリティ、すなわち、該ゲルが右巻きのヘリックス（螺旋）か左巻きのヘリックス（螺旋）かということに応じて、最終的に得られる有機無機複合体および金属酸化物のキラリティ、すなわち、そのヘリックス（螺旋）構造の向き（右巻きまたは左巻き）を制御することができる。
【００２２】
ゲル状態のキラリティは、ＣＤ（円二色性）スペクトルを測定することにより知ることができる。ＣＤ測定により正の分裂型スペクトル（正の分裂型コットン効果）が見られるときは、ゲルはＲ−キラリティを有し右巻きのヘリックス（螺旋）構造を呈し、逆に、負の分裂型スペクトル（負の分裂型コットン効果）が見られるときは、ゲルはＳ−キラリティを有し左巻きのヘリックス構造を呈する。ゲルのヘリックス構造に影響を与える因子として特に重要なものは、ゲルを形成する際の有機溶媒の種類と冷却方法である。すなわち、一般に、アルコールなどの極性溶媒を用いた場合には正の分裂型スペクトルが見られ、ヘキサン、メチルシクロヘキサンなどの非極性溶媒では負の分裂型スペクトルが見られる。また、高温のゾル溶液を氷水に浸漬させる等急冷してゲルを調製すると、負の分裂型コットン効果（Ｓ−キラリティ）が発現するのに対し、高温のゾル溶液を室温に放置する等のように徐冷してゲルを調製すると正の分裂型コットン効果（Ｒ−キラリティ）が発現する傾向がある。
【００２３】
したがって、式（Ｉ）のコレステロール誘導体を用いる本発明の方法に従えば、予め、これらの因子を調整して該コレステロール誘導体のゲル状態におけるキラリティを確認しておくことにより、ヘリックス（螺旋）構造を有し且つその向き（右巻きか左巻きか）を制御した有機無機複合体および金属酸化物を得ることができる。式（Ｉ）のアザクラウン環を有するコレステロール誘導体から成るゲルを鋳型として用いる本発明の方法により、該コレステロール誘導体ゲルのヘリックス構造に対応した有機無機複合体や金属酸化物が得られる詳細な理由は未だ解明されていないが、式（Ｉ）のコレステロール誘導体から成るゲルは、シリカのような金属酸化物の適量を付着させるとともに、適度の太さの繊維状構造を形成していることに因るのかも知れない。
【００２４】
本発明において用いる式（Ｉ）のコレステロール誘導体は、既知の反応を工夫して図１に例示するような反応スキームに従い、４−（（ブロモブチルオキシフェニル）アゾ）安息香酸とコレステロールを反応させて得られたアゾベンゼン部位を有するコレステロール誘導体に、対応するアザクラウンを反応させることにより合成することができる。
【００２５】
金属酸化物（無機材料）
ゾルゲル反応の進行過程における金属酸化物の表面電荷は金属の種類と溶液のｐＨによって変化するので、コレステロール誘導体ゲルの表面に静電的に付着しやすいように金属の種類とｐＨを選ぶ必要があるが、本発明において用いられ得る金属酸化物の種類に基本的に制限はない。例えば、シリカ、アルミナ、ボレイトの他、チタニア、ジルコニア、ヘマタイト等の遷移金属酸化物が挙げられる。金属酸化物を与えるゾルゲル反応の前駆体（出発物質）としてはこれらの金属のアルコキシドおよびクロリド、ジケトネート等が挙げられる。具体的にはシリカでは、テトラエトキシシラン、メチルトリエトキシシラン、テトラクロロシラン、アルミナではアルミニウムトリ−ｓｅｃ−ブトキシド、アルミニウム（III）２，４−ペンタンジオネート、ボレイトではトリメトキシボラン、チタニアではチタンエトキサイド、ジルコニアではジルコニウムテトラ−ｎ−ブトキサイド等である。
【００２６】
ゾルゲル反応溶液
ゲル状態の繊維状コレステロール誘導体表面への金属酸化物の付着を効率的に進めるために、溶液の組成は金属酸化物重合体が低重合度のうちに析出する組成が望ましい。すなわち、アルコールやＴＨＦ等の金属酸化物に対する溶解度の大きな有機溶媒を多く含まない組成でなければならない。
【００２７】
また金属酸化物の表面電荷はその金属の電気陰性度と溶液のｐＨによって決まるので、鋳型分子を効率的に付着する符号になるｐＨを金属の種類に応じて変化する必要がある。本発明において鋳型となるコレステロール誘導体のゲルはカチオン性となり、これに対して、例えば、酢酸主体のゾルゲル溶液中（ｐＨ≒５）でのシリカ表面はアニオンと考えられ、鋳型分子であるゲルの繊維構造表面に金属酸化物が静電引力的に付着し成長すると考えられる。
【００２８】
金属酸化物（無機材料）の含有量が有機分子（コレステロール誘導体）に比べ多すぎると乾燥時の金属酸化物の収縮によって有機分子が圧縮され中空状構造をとりにくくなるし、金属酸化物同士の融合が生じ独立した繊維状構造にならないので望ましくなく、また少なすぎると金属酸化物の中空状構造が脆弱になる。従って最終的に得られる有機無機複合体に対し金属酸化物の量は重量比で２０〜９０％であることが望ましい。
【００２９】
有機無機複合体と中空糸金属酸化物の特性
本発明の有機無機複合体は、式（Ｉ）で表されるコレステロール誘導体から成る繊維状有機分子の表面に金属酸化物が付着した構造、すなわち、内側が式（Ｉ）のコレステロール誘導体であり、外側が金属酸化物である二重円筒状構造から成る（すなわち、円柱状のコレステロール誘導体の外側に金属酸化物が存在する円環状の横断面を呈する）。該円筒の直径（最外径）はナノメータのオーダー、すなわち、一般的には数ｎｍから数百ｎｍ（例えば、約３０〜２００ｎｍ）である。そして、内側のコレステロール誘導体は、金属塩由来の金属を保持し、鋳型ゲルのヘリックス構造（螺旋構造）に応じた螺旋状を呈するので、有機無機複合体としても全体的に螺旋状を呈する。
【００３０】
このような有機無機複合体から既述のようにコレステロール誘導体を除去すると、コレステロール誘導体の大きさに対応する内径を有する円筒状構造、すなわち、内径がナノメータのオーダー（例えば、約１０〜１００ｎｍ）の中空糸状で且つ螺旋状の金属酸化物であって、その金属酸化物の表面に該金属酸化物を構成する金属とは別異の金属が固着している構造体が得られる。
【００３１】
本発明の有機無機複合体は、中空糸状金属酸化物（例えば、シリカ）の前駆体として有用であるが、それ自身も各種の用途が期待される。例えば、本発明の有機無機複合体は、アゾベンゼンを持つコレステロール誘導体を含むので、アゾベンゼン部分のトランス−シスの構造変化によりフォトクロミックな性質を発現する材料として用いることができる。このとき、中空糸状の構造をとる本発明の有機無機複合体は、芯の部分のコレステロール誘導体を外壁の金属酸化物が外界から遮断するため、耐溶剤性、耐熱性に優れたフォトクロミック材料を与える。
【００３２】
他方、本発明の中空糸状金属酸化物は、中空糸の外表面、内表面のいずれをも利用して触媒、吸着剤等への応用が可能である。特に、ゲル形成剤として触媒活性を有する金属イオンを包接した式（Ｉ）のコレステロール誘導体を用いることにより得られ、該金属の微粒子がシリカのような中空糸状で一定の向きの螺旋構造の金属酸化物の表面に存在する構造体は、キラリティの関与する反応に対する触媒として有用である。また、該コレステロール誘導体に半導体として機能するような金属を包接させることによって得られる本発明の金属酸化物は、量子効果（発光の波長変化）を有する半導体材料等としての用途が期待される。その他、本発明の中空糸状金属酸化物は、繊維状態であるため嵩高く、これに加えて中空構造のため断熱効果が高く、金属酸化物の耐熱性が高いことから断熱材としても優れている。
【００３３】
【実施例】
以下に本発明の特徴をさらに明らかにするため実施例を示すが、本発明はこの実施例によって制限されるものではない。
実施例１：アザクラウン環を有するコレステロール誘導体の合成
図１に示す反応スキームに従って、同図に３として示しているアザクラウン環を有するコレステロール誘導体４−（Ｎ−ベンジルジアザ−１８−クラウン−６−ブトキシ）−４’−（（コレステイルオキシ）カルボニル）アゾベンゼンを合成した。
４−（Ｎ−ベンジルジアザ−１８−クラウン−６−ブトキシ）−４’−（（コレステイルオキシ）カルボニル）アゾベンゼン〔図１の化合物３〕の合成：
４−（（ブロモブチルオキシフェニル）アゾ）安息香酸〔図１に２として示す化合物〕０．７ｇ（１．８ｍｍｏｌ）と、コレステロール０．７１８ｇ（２．２３ｍｍｏｌ）を窒素雰囲気下に２０ｍｌのジクロロメタンに溶解した。得られた溶液を氷浴で０℃に保持し、ジシクロヘキシルカルボジイミド（ＤＣＣ）０．３８３ｇ（１．８６ｍｍｏｌ）とジメチルアミノピリジン（ＤＭＡＰ）０．０２２ｇ（０．１８６ｍｍｏｌ）を添加し、反応混合物を０℃で４時間攪拌した。反応混合物を濾過し、濾液を酸性水溶液および塩基性水溶液で洗浄した（それぞれ５０ｍＬ）。有機層を蒸発乾固し、残留物をＴＨＦ／ｎ−ヘキサン（１：６ｖ／ｖ）を溶出液とするシリカゲルで精製することにより、黄色固体として化合物３を得た。収率２６％。融点１４１．５℃。ＮＭＲ、ＭＳ（質量分析）およびＩＲによる同定データは以下のとおりである。
¹H NMR : (300MHz, CDCl₃) : δ(ppm)=8.17 (2H, d, J=9.0Hz), 7.72(2H, d, J=9.0Ha), 7.90(2H, d, J=9.0Hz), 7.10(2H, d, J=9.0Hz), 5.45(1H, d. J=6.3Hz), 5.02-4.88(1H, m), 41(2H, t, J=6.3Hz), 3.52(2H, t, J=6.2Hz), 2.49(2H, d, J=6.2Hz), 2.28-0.94(35H, m), 0.88(3H, s), ¹³C NMR(75 MHz, CDDl₃) : δ(ppm)=165.1, 161.88, 155.20, 146.98, 139.9, 130.2, 125.18, 122.84, 122.28, 114.72, 67.22, 66,67, 56,67, 56.11, 50.01, 42.30, 39.71, 39.50, 38.20. 37.01, 36.64, 36.17, 35.79, 33.32, 31.92, 31.86, 29.3, 28.32, 28.01, 27.88, 27.78, 24.28, 23.82, 22.83, 22.56, 21.04, 19.38, 19.38, 18.71, 11.86。 MS(SIMS)=745[M+H]⁺。 IR(KBr) : 3005, 1722, 1603, 1579, 1500, 1468, 1284, 1116, 1047cm^-1。
【００３４】
４−（Ｎ−ベンジルジアザ−１８−クラウン−６−ブトキシ）−４’−（（コレステイルオキシ）カルボニル）アゾベンゼン〔図１の化合物３〕の合成：
上記のようにして得られた化合物３の０．１３ｇ（０．１７４ｍｍｏｌ）、モノベンジル−ジアザ−１８−６の０．０６１ｇ（０．１７４ｍｍｏｌ）および炭酸ナトリウムの０．７８４ｇ（１．７４ｍｍｏｌ）から成る混合物を無水ブチロニトリル中で、２４時間還流した。冷却後、濾過し、濾液を真空蒸発させて乾固した。残留物をエタノール／ジクロロメタン（１：３０ｖ／ｖ）を溶出液として酸化アルミニウムにより精製することにより黄色固体として所望の化合物１を得た。収率４３．３％、融点１２８〜１３０℃。ＮＭＲ、ＭＳ、ＩＲおよび元素分析による同定データは以下のとおりである。
¹H NMR : (300MHz, CDCl₃) : δ(ppm)=8.17 (2H, d, J=9.1Hz), 7.93(7H, m), 7.88(2H, d, J=9.0Hz), 7.01(2H, d, J=9.0Hz), 5.45(1H, d. J=6.5Hz), 4.90(1H, m), 4.08(2H, t, J=6.5Hz), 3.73-3.61(26H, m), 2.78(4H, t, J=12.1Hz), 2.75(2H, t, J=6.5Hz), 2.49(2H, d, J=6.3Hz), 2.01-0.69(39H, m), ¹³C NMR(75 MHz, CDDl₃) : δ(ppm)=165.47, 162.13, 155.19, 146.80, 139.54, 134.77, 130.48, 125.13, 122.79, 122.22, 114.72, 74.79, 70,84, 70,73, 70.70, 70.35, 68.14, 56.62, 56.06, 53.94. 49.87, 42,25, 39.66, 39.45, 38.16, 36.97, 36.60, 36.12, 35.75, 31.88, 28.19, 27.96, 27.84, 26.96, 24.24, 23.78, 22.79, 22.53, 21.00, 19.34, 18.67, 11.81。 MS(SIMS)=1019[M+H]⁺。 IR(KBr) : 2943, 2868, 1711, 1599, 1581, 1500, 1468, 1419, 1404, 1275, 1140, 1109cm^-1 元素分析：理論値（Ｃ_６３Ｈ_９２Ｎ_４Ｏ_７として）：Ｃ，74.41；Ｈ，9.1２；Ｎ，5.51 実測値Ｃ，73.70；Ｈ，9.15；Ｎ，5.91。
【００３５】
実施例２：有機無機複合体および金属酸化物の調製
コレステロール誘導体への金属カチオン包接
実施例１で合成したアザクラウン環を有するコレステロール誘導体（図１の化合物１）をＡｇＮＯ_３のＴＨＦ溶液（５．００×１０^-2mol dm^-1）に溶解し、一晩攪拌し透明液とした後、室温で乾燥し溶媒を除去することにより、Ａｇ^＋イオンがコレステロール誘導体に包接されるようにした。
【００３６】
ゲル化およびシリケートのゾルゲル反応
上記のようにＡｇ^＋イオンを包接させたコレステロール誘導体１の残渣を次の組成のゾルゲル反応溶液と混合し、加熱（５０℃）した後、室温に冷却した：１−ブタノール（９８ｍｇ）／ＴＥＯＳ（テトラエトキシシラン）（１６ｍｇ）／水（５．８ｍｇ）／ベンジルアミン（５．６ｍｇ）。比較のために、ＡｇＮＯ_３溶液に添加しないコレステロール誘導体１を用いて同様の条件でゲル化およびゾルゲル反応を実施した。室温に冷却して１日放置すると不透明化してゲルが形成されたことが認められた。図２は、このゲルのＣＤスペクトルを示す。金属を包接していない場合もＣＤ活性であり、正の分裂型スペクトルが示されるが、そのスペクトルは明瞭ではない。これに対して、Ａｇ^＋を包接した場合には明瞭な正の分裂型スペクトル（Ｒ−キラリティ）が認められる。
【００３７】
乾燥および焼成
上記のようなゾルゲル反応後、得られたゲルを室温下に２日間乾燥し、さらに、真空下で５時間乾燥し有機無機複合体を得た。図３は、このようにして得られた有機無機複合体のＳＥＭ（走査電子顕微鏡）写真である。金属イオンを包接したコレステロール誘導体を用いて調製した有機無機複合体は、円筒状で右巻きのヘリックス構造を呈しており、ゲル状態のキラリティを反映していることが理解される。円筒の直径（最外径）は、約３０〜２００ｎｍであることが認められる。
【００３８】
さらに、窒素気流下２００℃で６時間乾燥し、次いで５００℃で２時間、最後に空気気流中で５００℃で４時間焼成し、金属酸化物（シリカ）を得た。図４および図５は、このようにして得られたシリカのそれぞれＳＥＭ写真およびＴＥＭ（透過型電子顕微鏡）写真である。金属イオン（Ａｇ^＋）を包接したコレステロール誘導体１を用いて調製したシリカは、中空糸状で右巻きの螺旋状を呈している。その内径は約２５〜５０ｎｍであり、また、Ａｇ粒子の存在（図５の黒い点状物）が認められる。
【図面の簡単な説明】
【図１】本発明において用いられるアザクラウン環を有するコレステロール誘導体の１例を合成する反応スキームを示す。
【図２】本発明により有機無機複合体および金属酸化物を調製するためのゲルのＣＤスペクトルの例を示す。
【図３】本発明の有機無機複合体の１例の結晶構造を示す走査電子顕微鏡写真（Ｂ）であり、（Ａ）は、参考のためにＡｇＮＯ_３溶液に添加せずに同様に調製した有機無機複合体の結晶構造を示す走査顕微鏡写真である。
【図４】本発明の金属酸化物の１例の結晶構造を示す走査電子顕微鏡写真である。
【図５】本発明の金属酸化物の１例の結晶構造を示す透過電子顕微鏡写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to organic-inorganic composites and metal oxides having novel structures that can be used as catalysts and other functional materials, and methods for producing them.
[0002]
[Prior art and its problems]
Inorganic porous materials typified by silica are widely used as catalysts, supporting materials or adsorbing materials, chromatographic materials, etc., because of their surface area and molecular selectivity due to pore size, and further improvements have been attempted. Yes. For the preparation of these porous materials, a method using some template is used, and for the preparation of microporous materials such as zeolite, organic low molecular weight compounds, surfactants and block copolymers for mesoporous materials, and macroporous materials, There are examples using each emulsion. Among porous materials, fibrous or hollow inorganic materials are synthesized using tartaric acid molecular aggregates, carbon fibers, and carbon nanotubes as templates. On the other hand, in the research on so-called Biomineralization that utilizes the function of biological material, attempts have been made to create various forms of inorganic materials using biological material as a template. Cylindrical organic inorganic using self-organized lipid tubes Complexes and the like have also been obtained. However, there has been no example of preparing an organic-inorganic composite material or an inorganic material using an organic low-molecular gel as a template. Materials reflecting these gel structures exhibiting various forms are expected to have various applications as materials with anisotropy based on unique forms. For example, a new type of functional organic gel-inorganic composite material or porous inorganic material can be obtained by using a fibrous gel, i.e., a linear or helical elongated filamentous gel as a template. Although expected, there is no technology that embodies such materials.
[0003]
[Means for Solving the Problems]
The present inventors previously used a fibrous organic low-molecular gel as a template, and on this gel, a polymer of the metal oxide is produced by a sol-gel reaction from a sol of a metal oxide such as silica. An organic-inorganic composite reflecting the structure of an organic low-molecular gel and a technique capable of obtaining a hollow fiber metal oxide from which an organic substance has been removed have been disclosed (Japanese Patent Application No. 11-108922). Particularly preferred as a small organic molecule as a template is a cholesterol derivative having an azobenzene moiety, for example, by using a cholesterol derivative having an azobenzene moiety and a cationic moiety (ammonium salt) at one end. A hollow fiber silica is obtained (Example 3), and a hollow fiber silica in which a sheet is spirally wound is obtained by using a cholesterol derivative having an azacrown ring at one end (Example 6). .
[0004]
However, when these cholesterol derivatives are used, a structure in which a metal different from the metal constituting the metal oxide is fixed to a helical metal oxide (for example, silica) It has not been obtained yet. A microstructure in which a metal exists on the surface of silica or the like having a helix structure (spiral structure) in a certain direction (right-handed or left-handed) is expected to be useful as a catalyst for reactions involving chirality, for example. The above Japanese Patent Application No. 11-108922 did not disclose such a structure.
[0005]
The present invention relates to an improvement of the technique disclosed in Japanese Patent Application No. 11-108922, which is formed from a cholesterol derivative having an azacrown ring substituted with a specific functional group and holds a metal in advance and has a certain orientation. This is based on the knowledge that a gel having a spiral structure is used as a template to obtain a structure in which a metal different from the metal is fixed to a spiral metal oxide.
[0006]
Thus, the present invention
(1) After a cholesterol derivative having an azacrown ring represented by the following formula (I) is dissolved in a metal salt solution and evaporated to dryness, an azacrown ring in which the metal derived from the metal salt is included Preparing a cholesterol derivative having
(2) a. The cholesterol derivative containing metal,
B. A metal oxide precursor different from a metal derived from the metal salt, a catalyst for forming a metal oxide polymer from the metal oxide precursor by a sol-gel reaction, water, and, if necessary, the A sol-gel reaction solution comprising a metal oxide precursor, a catalyst, a solvent capable of dissolving water, and
C. An organic solvent capable of dissolving the cholesterol derivative and the sol-gel reaction solution if necessary,
A step of preparing a homogeneous mixed solution containing
(3) a. Removing the organic solvent from the homogeneous mixture,
B. The homogeneous mixture is heated and then cooled, or
C. Cooling the homogeneous mixture;
A step of forming a gel of said cholesterol derivative, and
(4) holding the gel-formed system and advancing polymerization of the metal oxide of the metal derived from the metal oxide precursor;
A method for producing an organic-inorganic composite in which a metal oxide of a metal derived from the metal oxide precursor is attached to the surface of the cholesterol derivative that holds the metal derived from the metal salt in a spiral shape (Claim 1).
[0007]
[Chemical formula 5]

In the formula (I), n is 0 or 1, and X is any functional group shown in the following (II).
[0008]
[Chemical 6]

[0009]
The present invention further provides, as a preferred embodiment, a method for producing a hollow fiber-like spiral metal oxide characterized in that a cholesterol derivative is removed from the organic-inorganic composite obtained by the above method (claim). 2) In a particularly preferred embodiment thereof, the cholesterol derivative is removed by calcination (claim 3).
[0010]
Furthermore, the present invention, from another point of view, is an organic-inorganic composite produced by the above method (Claim 1), wherein the inside is a cholesterol derivative represented by the above-mentioned formula (I) holding a metal. The organic-inorganic composite is characterized in that the outer side is made of a metal oxide of a metal different from the metal and the cylindrical structure having a diameter of the order of nanometers has a spiral shape.
[0011]
Further, the present invention can be manufactured by the above method (Claims 2 and 3), and a cylindrical metal oxide having an inner diameter of the order of nanometer has a spiral shape, and the metal oxide is formed on the surface of the metal oxide. Also provided is a hollow fiber metal oxide characterized in that a metal different from the metal constituting the oxide is fixed, and a particularly preferred example of this hollow fiber metal oxide is silica.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention using the cholesterol derivative having an azacrown ring represented by the above formula (I), the direction of the helix is controlled according to the direction of the helix structure of the cholesterol derivative in the gel state. An organic-inorganic composite or metal oxide having a helical structure can be obtained.
[0013]
Hereinafter, the characteristics of the present invention will be described in detail along the organic-inorganic composite and the metal production method of the present invention, and the constituent elements thereof.
Production method
(1) Preparation of cholesterol derivative containing metal:
In order to produce an organic-inorganic composite and a metal oxide according to the present invention, first, a cholesterol derivative having an azacrown ring represented by the above formula (I) is dissolved in a metal salt solution, and then evaporated to dryness. As a result, a cholesterol derivative having an azacrown ring in which the metal derived from the metal salt is included is prepared. The metal derived from the metal salt is selected from those that adhere to the surface of a metal oxide (for example, silica) of a metal different from that and exhibit a desired function such as a catalyst.
[0014]
That is, it is selected from metals that are included in the crown ring and form a stable complex according to the size of the azacrown ring determined by the value of n in formula (I). Preferred metals include the periodic table. Examples include Group Ia metals (alkali metals), Group Ib metals (Cu, Ag, etc.), and the like. These metals are added as salts such as nitrates, chlorides, perchlorates and thiocyanates in solvents such as methylene chloride and THF that can dissolve cholesterol derivatives.
[0015]
(2) Preparation of mixed solution containing sol-gel reaction solution:
Next, a cholesterol derivative having an azacrown ring which is prepared as described above and includes a metal derived from a metal salt is mixed with a sol-gel reaction solution to prepare a uniform mixed solution containing them.
[0016]
Here, the sol-gel reaction solution depends on the target sol-gel reaction system, but at least a metal oxide (inorganic material: derived from the above-mentioned metal salt) is formed so that an initial sol in which the sol-gel reaction proceeds is formed. Metal oxides (metal oxides different from metals) precursors (metal oxide starting materials: metal alkoxides, metal chlorides, metal diketonates, etc.), and metal oxides generated from the metal oxide precursors by sol-gel reaction Catalyst (acid, alkali, amine, etc.) and water (necessary for hydrolysis of the metal oxide precursor and may be in small amounts). However, when the solubility of the sol-gel reaction system is not sufficient by this alone, a solvent capable of dissolving the precursor, catalyst, and water is used. Furthermore, if necessary, an organic solvent capable of dissolving the cholesterol derivative and the sol-gel reaction solution is used in order to facilitate mixing.
[0017]
(3) Formation of gel:
In the method of the present invention, a gel of a cholesterol derivative of the formula (I) is formed in the mixed solution thus obtained. Here, the term gel used in connection with the present invention generally refers to a state in which the solvent is completely constrained and solidified, but the organic low enough to flow when the system is tilted and given a light impact. It also includes a state in which molecules (cholesterol derivatives) are bonded to each other to form a fiber. This gel forming step is performed as follows.
[0018]
When the temperature at which the gel formation of the cholesterol derivative occurs is at room temperature or higher, in order to facilitate mixing, from a homogeneous mixture prepared by adding an organic solvent that dissolves both the cholesterol derivative and the sol-gel reaction solution The gel is formed by removing the organic solvent added to dissolve. This organic solvent is generally removed by drying under reduced pressure. Moreover, when a cholesterol derivative can endure heating, after heating said uniform liquid mixture, it cools to room temperature and forms a gel. Furthermore, when the gel formation temperature is room temperature or lower, the gel is formed by mixing the cholesterol derivative and the sol-gel reaction solution at room temperature and cooling the system. During this process, generally, a gel of a cholesterol derivative having a fibrous structure is formed in advance, and a sol-gel reaction of a metal oxide partially proceeds.
[0019]
(4) Polymerization of metal oxide:
In order to produce the organic-inorganic composite according to the present invention, the polymerization of the metal oxide is further advanced while maintaining the system in which the gel is formed as described above under the condition that the gel is not broken. . That is, a system in which gel formation has occurred at room temperature, and a system in which gel has been formed by cooling will be subjected to metal oxidation if kept at the cooling temperature for an appropriate time (generally several days or more). Hydrolysis and polycondensation proceed due to the sol-gel reaction of the product, the degree of polymerization of the metal oxide increases, and the metal oxide that cannot be dissolved in the solution adheres to and precipitates on the surface of the cholesterol derivative having a fibrous structure. The cholesterol derivative having an azacrown ring represented by the aforementioned formula (I) is presumed to have moderate ionicity because a metal oxide is attached by electrostatic force.
[0020]
(5) Preparation of organic-inorganic composite and metal oxide:
After the above steps, drying is performed to remove the excess solvent, leaving the cholesterol derivative molecule in the gel structure, and the metal oxide precursor is formed on the surface of the cholesterol derivative holding the metal derived from the metal salt in a spiral shape. An organic-inorganic composite having a metal oxide derived from the body attached thereto is obtained. Further, if the cholesterol derivative is removed, a spiral and hollow fiber metal oxide is obtained. Although removal of the cholesterol derivative may be possible by elution using a solvent, in general, the organic molecules in the complex of the present invention are strongly protected by the outer wall of the metal oxide and have solvent resistance. It is preferred to do so.
[0021]
Cholesterol derivatives having an azacrown ring
According to the present invention using a cholesterol derivative having an azacrown ring represented by the above formula (I) as a gel-forming material, the gel chirality of the cholesterol derivative (I) holding a metal (derived from a metal salt), that is, Depending on whether the gel is a right-handed helix or a left-handed helix, the final chirality of the organic-inorganic composite and metal oxide, ie, its helix structure The direction (right-handed or left-handed) can be controlled.
[0022]
The chirality of the gel state can be known by measuring a CD (circular dichroism) spectrum. When a positive splitting spectrum (positive splitting cotton effect) is seen by CD measurement, the gel has a right-handed helix structure with R-chirality, and conversely, a negative splitting spectrum ( When a negative split cotton effect is observed, the gel has S-chirality and a left-handed helical structure. Of particular importance as factors affecting the helical structure of the gel are the type of organic solvent and the cooling method used when forming the gel. That is, generally, when a polar solvent such as alcohol is used, a positive splitting spectrum is seen, and with a nonpolar solvent such as hexane and methylcyclohexane, a negative splitting spectrum is seen. In addition, when a gel is prepared by rapid cooling, such as by immersing a high-temperature sol solution in ice water, a negative split-type cotton effect (S-chirality) appears, whereas a high-temperature sol solution is left at room temperature. When the gel is slowly cooled to prepare a positive split cotton effect (R-chirality) tends to develop.
[0023]
Therefore, according to the method of the present invention using the cholesterol derivative of the formula (I), by adjusting these factors in advance and confirming the chirality in the gel state of the cholesterol derivative, the helix structure is formed. It is possible to obtain an organic-inorganic composite and a metal oxide that have a controlled orientation (right-handed or left-handed). The detailed reason why an organic-inorganic composite or a metal oxide corresponding to the helix structure of the cholesterol derivative gel can be obtained by the method of the present invention using a gel comprising a cholesterol derivative having an azacrown ring of formula (I) as a template is as follows. Although not yet elucidated, the gel composed of the cholesterol derivative of the formula (I) is caused by depositing an appropriate amount of a metal oxide such as silica and forming a fibrous structure having an appropriate thickness. It may be.
[0024]
The cholesterol derivative of formula (I) used in the present invention is prepared by reacting 4-((bromobutyloxyphenyl) azo) benzoic acid and cholesterol according to a reaction scheme as illustrated in FIG. The resulting cholesterol derivative having an azobenzene moiety can be synthesized by reacting the corresponding azacrown.
[0025]
Metal oxide (inorganic material)
Since the surface charge of the metal oxide during the progress of the sol-gel reaction varies depending on the type of metal and the pH of the solution, it is necessary to select the type and pH of the metal so that it easily adheres to the surface of the cholesterol derivative gel. However, there is basically no limitation on the type of metal oxide that can be used in the present invention. Examples thereof include transition metal oxides such as titania, zirconia, and hematite in addition to silica, alumina, and borate. Examples of the precursor (starting material) of the sol-gel reaction that gives a metal oxide include alkoxides and chlorides of these metals, diketonates, and the like. Specifically, silica is tetraethoxysilane, methyltriethoxysilane, tetrachlorosilane, alumina is aluminum tri-sec-butoxide, aluminum (III) 2,4-pentanedionate, borate is trimethoxyborane, and titania is titanium ethoxy. For side and zirconia, zirconium tetra-n-butoxide is used.
[0026]
Sol-gel reaction solution
In order to efficiently promote the adhesion of the metal oxide to the surface of the gel-like fibrous cholesterol derivative, the composition of the solution is preferably a composition in which the metal oxide polymer precipitates with a low degree of polymerization. That is, the composition should not contain a large amount of an organic solvent having high solubility in metal oxides such as alcohol and THF.
[0027]
Further, since the surface charge of the metal oxide is determined by the electronegativity of the metal and the pH of the solution, it is necessary to change the pH, which is a sign for efficiently attaching the template molecule, according to the type of metal. In the present invention, the gel of the cholesterol derivative used as a template becomes cationic. On the other hand, for example, the silica surface in a sol-gel solution mainly composed of acetic acid (pH≈5) is considered to be an anion. It is thought that the metal oxide adheres electrostatically to the structure surface and grows.
[0028]
If the content of metal oxide (inorganic material) is too much compared to organic molecules (cholesterol derivatives), the organic molecules are compressed by the shrinkage of the metal oxide during drying, making it difficult to form a hollow structure. Fusion is not desirable because it does not result in an independent fibrous structure, and if too little, the hollow structure of the metal oxide becomes brittle. Therefore, the amount of the metal oxide is preferably 20 to 90% by weight with respect to the finally obtained organic-inorganic composite.
[0029]
Properties of organic-inorganic composites and hollow fiber metal oxides
The organic-inorganic composite of the present invention has a structure in which a metal oxide is attached to the surface of a fibrous organic molecule composed of a cholesterol derivative represented by the formula (I), that is, the inside is a cholesterol derivative of the formula (I), It consists of a double-cylindrical structure whose outer side is a metal oxide (ie, presents an annular cross section in which the metal oxide is present outside the columnar cholesterol derivative). The diameter (outermost diameter) of the cylinder is on the order of nanometers, that is, generally several nanometers to several hundred nanometers (for example, about 30 to 200 nm). The inner cholesterol derivative retains the metal derived from the metal salt and exhibits a spiral shape corresponding to the helix structure (helical structure) of the template gel, and thus exhibits an overall spiral shape as an organic-inorganic composite.
[0030]
When the cholesterol derivative is removed from the organic-inorganic composite as described above, the cylindrical structure having an inner diameter corresponding to the size of the cholesterol derivative, that is, the inner diameter is on the order of nanometers (for example, about 10 to 100 nm). A structure having a hollow fiber-like and helical metal oxide, and a metal different from the metal constituting the metal oxide is fixed to the surface of the metal oxide.
[0031]
Although the organic-inorganic composite of the present invention is useful as a precursor of a hollow fiber metal oxide (for example, silica), various uses are expected. For example, since the organic-inorganic composite of the present invention contains a cholesterol derivative having azobenzene, it can be used as a material that exhibits photochromic properties due to a trans-cis structural change of the azobenzene moiety. At this time, the organic-inorganic composite of the present invention having a hollow fiber structure provides a photochromic material excellent in solvent resistance and heat resistance because the outer wall metal oxide blocks the cholesterol derivative in the core portion from the outside. .
[0032]
On the other hand, the hollow fiber metal oxide of the present invention can be applied to a catalyst, an adsorbent and the like using both the outer surface and the inner surface of the hollow fiber. In particular, it is obtained by using a cholesterol derivative of the formula (I) in which a metal ion having catalytic activity is included as a gel forming agent, and the metal fine particles are hollow fibers like silica and have a spiral structure in a certain direction. Structures present on the surface of the oxide are useful as catalysts for reactions involving chirality. In addition, the metal oxide of the present invention obtained by including a metal that functions as a semiconductor in the cholesterol derivative is expected to be used as a semiconductor material having a quantum effect (wavelength change of light emission). In addition, the hollow fiber metal oxide of the present invention is bulky because it is in a fiber state, and in addition to this, it has a high heat insulating effect due to its hollow structure, and it is also excellent as a heat insulating material because the metal oxide has high heat resistance. .
[0033]
【Example】
Examples are given below to further clarify the features of the present invention, but the present invention is not limited to these examples.
Example 1: Synthesis of a cholesterol derivative having an azacrown ring
According to the reaction scheme shown in FIG. 1, cholesterol derivative 4- (N-benzyldiaza-18-crown-6-butoxy) -4 ′-((cholesteryloxy) carbonyl) having an azacrown ring shown as 3 in FIG. Azobenzene was synthesized.
Synthesis of 4- (N-benzyldiaza-18-crown-6-butoxy) -4 ′-((cholesteryloxy) carbonyl) azobenzene [Compound 3 of FIG. 1]:
4-((Bromobutyloxyphenyl) azo) benzoic acid [compound shown as 2 in FIG. 1] 0.7 g (1.8 mmol) and cholesterol 0.718 g (2.23 mmol) in 20 ml dichloromethane under nitrogen atmosphere Dissolved. The resulting solution was kept at 0 ° C. in an ice bath, 0.383 g (1.86 mmol) of dicyclohexylcarbodiimide (DCC) and 0.022 g (0.186 mmol) of dimethylaminopyridine (DMAP) were added, and the reaction mixture was cooled to 0 ° C. Stir at 4 ° C. for 4 hours. The reaction mixture was filtered and the filtrate was washed with acidic and basic aqueous solutions (50 mL each). The organic layer was evaporated to dryness, and the residue was purified by silica gel using THF / n-hexane (1: 6 v / v) as an eluent to obtain Compound 3 as a yellow solid. Yield 26%. Melting point 141.5 ° C. Identification data by NMR, MS (mass spectrometry) and IR are as follows.
¹H NMR: (300MHz, CDCl_Three): δ (ppm) = 8.17 (2H, d, J = 9.0Hz), 7.72 (2H, d, J = 9.0Ha), 7.90 (2H, d, J = 9.0Hz), 7.10 (2H, d, J = 9.0Hz), 5.45 (1H, d. J = 6.3Hz), 5.02-4.88 (1H, m), 41 (2H, t, J = 6.3Hz), 3.52 (2H, t, J = 6.2Hz), 2.49 (2H, d, J = 6.2Hz), 2.28-0.94 (35H, m), 0.88 (3H, s),¹³C NMR (75 MHz, CDDl_Three): δ (ppm) = 165.1, 161.88, 155.20, 146.98, 139.9, 130.2, 125.18, 122.84, 122.28, 114.72, 67.22, 66,67, 56,67, 56.11, 50.01, 42.30, 39.71, 39.50, 38.20. 37.01 , 36.64, 36.17, 35.79, 33.32, 31.92, 31.86, 29.3, 28.32, 28.01, 27.88, 27.78, 24.28, 23.82, 22.83, 22.56, 21.04, 19.38, 19.38, 18.71, 11.86. MS (SIMS) = 745 [M + H]⁺. IR (KBr): 3005, 1722, 1603, 1579, 1500, 1468, 1284, 1116, 1047cm^-1.
[0034]
Synthesis of 4- (N-benzyldiaza-18-crown-6-butoxy) -4 '-((cholestyloxy) carbonyl) azobenzene [compound 3 of FIG. 1]:
From 0.13 g (0.174 mmol) of compound 3 obtained as described above, 0.061 g (0.174 mmol) of monobenzyl-diaza-18-6 and 0.784 g (1.74 mmol) of sodium carbonate. The resulting mixture was refluxed in anhydrous butyronitrile for 24 hours. After cooling, it was filtered and the filtrate was evaporated to dryness in vacuo. The residue was purified by aluminum oxide using ethanol / dichloromethane (1:30 v / v) as an eluent to give the desired compound 1 as a yellow solid. Yield 43.3%, melting point 128-130 ° C. Identification data by NMR, MS, IR and elemental analysis are as follows.
¹H NMR: (300MHz, CDCl_Three): δ (ppm) = 8.17 (2H, d, J = 9.1Hz), 7.93 (7H, m), 7.88 (2H, d, J = 9.0Hz), 7.01 (2H, d, J = 9.0Hz), 5.45 (1H, d. J = 6.5Hz), 4.90 (1H, m), 4.08 (2H, t, J = 6.5Hz), 3.73-3.61 (26H, m), 2.78 (4H, t, J = 12.1Hz ), 2.75 (2H, t, J = 6.5Hz), 2.49 (2H, d, J = 6.3Hz), 2.01-0.69 (39H, m),¹³C NMR (75 MHz, CDDl_Three): δ (ppm) = 165.47, 162.13, 155.19, 146.80, 139.54, 134.77, 130.48, 125.13, 122.79, 122.22, 114.72, 74.79, 70,84, 70,73, 70.70, 70.35, 68.14, 56.62, 56.06, 53.94 49.87, 42,25, 39.66, 39.45, 38.16, 36.97, 36.60, 36.12, 35.75, 31.88, 28.19, 27.96, 27.84, 26.96, 24.24, 23.78, 22.79, 22.53, 21.00, 19.34, 18.67, 11.81. MS (SIMS) = 1019 [M + H]⁺. IR (KBr): 2943, 2868, 1711, 1599, 1581, 1500, 1468, 1419, 1404, 1275, 1140, 1109cm^-1  Elemental analysis: theoretical value (C₆₃H₉₂N₄O₇As): C, 74.41; H, 9.12; N, 5.51 Found C, 73.70; H, 9.15; N, 5.91.
[0035]
Example 2: Preparation of organic-inorganic composite and metal oxide
Inclusion of metal cations to cholesterol derivatives
The cholesterol derivative having an azacrown ring synthesized in Example 1 (compound 1 in FIG. 1) was converted to AgNO.₃In THF (5.00 × 10^-2mol dm^-1) And stirred overnight to make a clear liquid, followed by drying at room temperature and removing the solvent to remove Ag.⁺Ions were included in the cholesterol derivative.
[0036]
Gelation and sol-gel reaction of silicate
Ag as above⁺The residue of cholesterol derivative 1 in which ions were included was mixed with a sol-gel reaction solution having the following composition, heated (50 ° C.), and then cooled to room temperature: 1-butanol (98 mg) / TEOS (tetraethoxysilane) ( 16 mg) / water (5.8 mg) / benzylamine (5.6 mg). For comparison, AgNO₃Gelation and sol-gel reaction were carried out under the same conditions using cholesterol derivative 1 not added to the solution. It was observed that when cooled to room temperature and left for 1 day, it became opaque and a gel was formed. FIG. 2 shows the CD spectrum of this gel. CD activity is also present when no metal is included, and a positive splitting spectrum is shown, but the spectrum is not clear. In contrast, Ag⁺A clear positive split-type spectrum (R-chirality) is observed in the case of inclusion.
[0037]
Drying and baking
After the sol-gel reaction as described above, the obtained gel was dried at room temperature for 2 days, and further dried under vacuum for 5 hours to obtain an organic-inorganic composite. FIG. 3 is a SEM (scanning electron microscope) photograph of the organic-inorganic composite thus obtained. It is understood that an organic-inorganic composite prepared using a cholesterol derivative that includes metal ions is cylindrical and has a right-handed helical structure, reflecting the chirality of the gel state. It is recognized that the diameter (outermost diameter) of the cylinder is about 30 to 200 nm.
[0038]
Further, it was dried at 200 ° C. for 6 hours under a nitrogen stream, then calcined at 500 ° C. for 2 hours and finally at 500 ° C. for 4 hours in an air stream to obtain a metal oxide (silica). 4 and 5 are an SEM photograph and a TEM (transmission electron microscope) photograph of the silica thus obtained, respectively. Metal ion (Ag⁺The silica prepared using the cholesterol derivative 1 encapsulating) has a hollow fiber shape and a right-handed spiral shape. The inner diameter is about 25 to 50 nm, and the presence of Ag particles (black dots in FIG. 5) is observed.
[Brief description of the drawings]
FIG. 1 shows a reaction scheme for synthesizing an example of a cholesterol derivative having an azacrown ring used in the present invention.
FIG. 2 shows an example of the CD spectrum of a gel for preparing organic-inorganic composites and metal oxides according to the present invention.
FIG. 3 is a scanning electron micrograph (B) showing the crystal structure of an example of the organic-inorganic composite of the present invention, where (A) is AgNO for reference.₃It is a scanning micrograph which shows the crystal structure of the organic inorganic composite similarly prepared without adding to a solution.
FIG. 4 is a scanning electron micrograph showing the crystal structure of one example of the metal oxide of the present invention.
FIG. 5 is a transmission electron micrograph showing the crystal structure of one example of the metal oxide of the present invention.

Claims (4)

(1) After a cholesterol derivative having an azacrown ring represented by the following formula (I) is dissolved in a metal salt solution and evaporated to dryness, an azacrown ring in which the metal derived from the metal salt is included Preparing a cholesterol derivative having
(2) a. The cholesterol derivative containing metal,
B. A precursor of silica , which is a metal oxide of a metal different from the metal derived from the metal salt, a catalyst for forming a silica polymer from the silica precursor by a sol-gel reaction, water, and, if necessary, the A sol-gel reaction solution comprising a silica precursor, a catalyst, a solvent capable of dissolving water, and
C. An organic solvent capable of dissolving the cholesterol derivative and the sol-gel reaction solution if necessary,
A step of preparing a homogeneous mixed solution containing
(3) a. Removing the organic solvent from the homogeneous mixture,
B. (C) heating or cooling the homogeneous mixture, or c. Cooling the homogeneous mixture;
A step of forming a gel of the cholesterol derivative, and (4) a step of maintaining the gel-formed system and advancing the polymerization of the silica ,
A process for producing an organic-inorganic composite in which silica is attached to the surface of the cholesterol derivative that holds the metal derived from the metal salt in a spiral shape.

[In Formula (I), n is 0 or 1, and X is any functional group shown in the following (II). ]

A method for producing silica , which is a hollow fiber-like spiral metal oxide, comprising removing a cholesterol derivative from an organic-inorganic composite obtained by the method of claim 1. The method for producing silica according to claim 2, wherein the cholesterol derivative is removed by calcination. A cholesterol structure represented by the following formula (I) holding the metal on the inner side and a silica structure made of silica , which is a metal oxide of a metal different from the metal on the outer side, has a cylindrical shape with a diameter of the order of nanometers. An organic-inorganic composite characterized by being exhibited.

[In Formula (I), n is 0 or 1, and X is any functional group shown in the following (II). ]

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