Ironing Out Nitrogen Fixation
Bioinorganic Chemistry: Iron catalyst could aid search for im-proved ammonia process
Ammonia maker
Tris(phosphine)borane-supported Fe-N2 complex catalyzes NH3 formation at low temperature and atmospheric pressure, using an inorganic acid (H+) and electron (e-) source.
Conversion of dinitrogen to ammonia is a process that’s both essential to life on Earth and industrially important in fertilizer production. Researchers have long studied the enzymes that living things use to promote the reaction, but details of their catalytic mechanisms have remained elusive.
Now, Caltech scientists have created an iron complex that catalyzes this conversion in a manner that may help reveal the way nitrogenases do it. The iron catalyst and earlier molybdenum versions could also help lead to improved catalysts for reducing N2 to NH3 industrially.
Bacteria make nitrogenases and use them to convert N2 in air to NH3, a process called nitrogen fixation. The process is a primary source of nitrogen in proteins, nucleic acids, and other biomolecules. The Haber-Bosch process, which was developed in the early-20th century and uses a solid iron catalyst for adding H2 to N2 at high temperatures and pressures to form NH3 for fertilizer production, is now also a primary source of fixed nitrogen.
Most nitrogenases have an active-site cofactor—a molybdenum-iron cluster—but researchers don’t yet know whether it’s Mo or Fe that coordinates and reduces N2. In 2003, Richard R. Schrock’s group at MIT developed the first Mo complex that catalyzes N2 to NH3 conversion under mild conditions. Yoshiaki Nishibayashi of the University of Tokyo and coworkers reported another such Mo complex two years ago. Both Mo complexes are inefficient catalysts and break down quickly, but they work. That could not be said for any Fe-based complex, favoring the idea that nitrogenase’s Mo is the active metal.
John S. Anderson, Jonathan Rittle, and Jonas C. Peters at Caltech have now come up with the first Fe-based complex that directly catalyzes nitrogen fixation to NH3 under mild conditions (Nature 2013, DOI: 10.1038/nature12435).
The tris(phosphine)borane-supported Fe-N2 complex’s catalytic activity is slightly lower than the Mo catalysts’, and it likewise breaks down quickly. But its supporting ligand “can be varied systematically to improve the catalyst, so there are good prospects for future improvement,” notes Patrick L. Holland of Yale University, who specializes in Fe-based cleaving reactions.
The Fe complex tips the balance of evidence back toward the idea that nitrogenase catalysis may be Fe-based. The study “provides favorable information for Fe claimants, but further study is necessary,” Nishibayashi says. One such claimant, Brian M. Hoffman of Northwestern University, says, “You can no longer use the argument that Mo must be it because it’s the only one shown to do the job.”
Peters and coworkers propose that a flexible Fe-boron interaction in their complex may play a key catalytic role and that a carbon-Fe interaction in nitrogenase may work similarly. “Through analogies like this, synthetic compounds can help chemists to gain insight into the mechanisms of enzymes,” Holland says. Nishibayashi also believes the result “provides useful and significant information to elucidate the reaction mechanism of the MoFe cofactor in nitrogenase.” But Schrock says, “It’s a stretch to say it tells us much, if anything, about the mechanism of reduction by various nitrogenases.”
The Fe-based and Mo-based complexes are possible first steps toward developing nitrogen fixation routes that are more economical than the energyintensive Haber-Bosch process. “The work shows that chemistry just has a much wider range of elements and structures to choose from than nature had during evolution and that mechanistically there may be quite a few possibilities for efficient N2-fixing complexes,” says bioinorganic chemist Oliver Einsle of the University of Freiburg, in Germany.
Method Adds Metals To Frameworks Selectively
Atomic layer deposition bypasses pitfalls of other common deposition techniques
A new procedure for tailoring metal-organic framework (MOF) compounds is poised to make this highly popular class of useful solids even more useful (J. Am. Chem. Soc.2013, DOI: 10.1021/ja4050828). MOFs are porous crystals composed of metal ions or clusters connected by organic linkers. The materials’ extreme surface areas and porosities have led to numerous record-breaking demonstrations and some commercialization in gas separation and storage as well as catalysis. Tailoring MOFs’ internal surfaces with chemically active metal ions can enhance the materials’ performance. Yet most methods for adding metals call for solution-phase treatments that can plug the crystals’ pores with unwanted solvents and reagents. Gas-phase deposition could eliminate the need to purify MOFs, but it provides little control over the deposited metals’ distribution. Northwestern University chemists Omar K. Farha and Joseph T. Hupp and coworkers have shown that these problems can be sidestepped by using atomic layer deposition. In this process, sequentially pulsed precursors react to form one atomic layer of products per pulse sequence. The team used diethylzinc and trimethylaluminum to decorate microscopic MOF channels with Zn and Al, respectively. They showed that unlike native MOFs, the metal-decorated versions are active catalysts for modified aldol condensations.
Nanostructures That Heal Themselves
Materials Science: Tiny patterns imprinted on the surface of the polymer Nafion can recover from repeated damage
The iridescence of a butterfly’s wing and the stickiness of a gecko’s foot derive their properties from nanoscale structures on their surfaces. Unlike with those natural materials, nanostructures engineered from synthetic materials often lack the ability to heal themselves when damaged. Now a Singaporean team has imprinted nanopatterns into a shape-memory polymer and found that the patterns can repeatedly recover from damage (Langmuir 2013, DOI: 10.1021/la401621j).
Hong Yee Low, a polymer chemist at the Singapore University of Technology & Design, and her team molded a nanopattern into Nafion, a well-studied fluoropolymer-copolymer. They heated Nafion film at 310 °C for 10 minutes and used a mold to imprint rows of pillars, ranging from 500 nm to 5 μm wide, onto the material. After cooling the polymer to room temperature, the researchers bent the pillars by smudging them with a finger, blasting them with a focused electron beam, or squishing them with a diamond stylus. When the team heated the material to 140 °C, past Nafion’s glass transition temperature, the ruined structures regained their original shape. The structures withstood this damage-and-repair process 25 times. Towards a possible application, Low is now working to mimic the complex nanopatterns on gecko feet with a polyurethane-based polymer that can heal itself. The materials could lead to a new type of dry adhesive.
Polymer revival
Scanning electron micrographs show 5-µm-wide pillars molded into Nafion (left). In the center image, researchers deformed the pillars by rubbing the polymer surface with a finger. At the bottom, the pillars have returned to their original shape after heating. Scale bars are 10 µm for the closeups and 50 µm for the wide views.
Probing Gold’s Catalytic Prowess
The unusually strong Au–C bond in gold alkynyl complexes provides insight on the precious metal’s catalytic activity in cross-coupling reactions
Once thought to be mostly chemically inert, gold has been shown in recent years to display surprising catalytic activity. An international research team studying how gold binds to carbon has now discovered a further surprise behind gold’s catalytic prowessan inverse correlation between bond strength and the multiplicity of Au–C bonds in organogold complexes (Nat. Commun. 2013, DOI: 10.1038/ncomms3223). Gold is a good catalytic activator of alkynes for C–C cross-coupling reactions. To understand why, Brown University’s Lai-Sheng Wang, Tsinghua University’s Jun Li, and coworkers took a close look at Au–C bonding. The researchers used AuI and HC≡CMgCl to create a series of complexes by electrospray ionization in a mass spectrometer and then probed them via photoelectron spectroscopy. They further modeled the complexes and compared the experimental and computational results. The most interesting observation, Wang says, is that the Au–C bond in ClAu–C≡CH–, which one might expect to form during a cross-coupling reaction, is stronger than the double and triple bonds in ClAu=CH2 and ClAu≡C species. The strong Au–C single bond explains gold’s ability to readily form the necessary alkyne intermediates in catalytic cross-couplings, the researchers conclude.
Element 115 Detected Again
Building Blocks: Findings should bolster the case for a spot on the periodic table
Confirmatory evidence for the existence of element 115 has been reported by an international research team that successfully used X-ray detection methods for the first time. The new work should bolster the case for adding the element to the periodic table almost a decade after it was first spotted.
Nuclear physicist Dirk Rudolph of Lund University, in Sweden, led the team. The scientists did the experiment at the GSI heavy ion accelerator center in Darmstadt, Germany. A paper of the work has been accepted by Physical Review Letters.
Element 115 was first observed by physicists at Russia’s Joint Institute for Nuclear Research working with scientists from Lawrence Livermore National Laboratory. An international committee of chemists and physicists will decide whether to add the element to the periodic table.
Rudolph’s team created element 115 by aiming a beam of calcium ions at an americium target. Sifting through the jumble of photons, particles, and atoms that results from such an experiment, the researchers detected particle decay chains consistent with isotopes of element 115 decaying to isotopes of dubnium. They also identified X-ray emissions from the decay chain, a long-sought goal of the nuclear physics community because it can be another piece of supporting evidence.
Interference from other emissions makes the X-rays very hard to detect, says Dawn A. Shaughnessy, an LLNL chemist who was part of the first team to observe element 115.
“The fact that they pulled it off and got these measurements is really phenomenal,” she says of the new report.
Chemistry On Cloth
Catalysis: Modified textiles offer new method for organocatalysis
Organocatalysts have become fashionable in chemistry circles during the past decade. Now, chemists are taking a cue from fashion by immobilizing these small, nonmetallic organic catalysts onto fabric (Science 2013, DOI:10.1126/science.1242196). The new organotextile catalysts offer a general, inexpensive, and practical approach to solid-supported organocatalysis, which aids catalyst recycling and could find use in the manufacture of pharmaceuticals and fine chemicals.
“The difficulty with any catalyst that is not supported on a heterogeneous material is that the recovery from homogenous phase requires an additional operation,” explains Benjamin List, of Germany’s Max Planck Institute for Coal Research, who spearheaded the organotextile research. Heterogeneous catalysts can be easily recovered by filtration, for example.
“One inherent advantage of organocatalysts, as compared to enzymes or metal-based catalysts, is that they can be easily and covalently attached to solid supports,” List adds. Chemists realized this advantage early on, he says, but so far the catalytic activity, selectivity, and recyclability of solidsupported organocatalysts have been inferior to those of homogeneous ones.
Researchers led by Klaus Opwis, of the German Textile Research Center, recently discovered a practical method for modifying textiles, such as nylon, with organic molecules simply by using ultraviolet light.
So List and Opwis teamed up to modify textiles with organocatalysts. To date they’ve made catalyst cloths modified with a Lewis base, a Brønsted acid, and a chiral organocatalyst. The textiles possess excellent stability, activity, and recyclability for various organic transformations. In one example, the researchers noted the high enantioselectivity was maintained for more than 250 cycles of asymmetric catalysis, an unusually high number of catalytic turnovers.
“What excited me most about this work was the incredibly high number of reaction cycles,” comments Franco Cozzi, an organocatalysis expert at the University of Milan, in Italy. “Generally, a supported organocatalyst after a few cycles is totally or at least partially inactivated, but this seems not to be the case in the present work.”
Bioinspired Filter Captures Carbon
ACS Meeting News: Microchannel-filled material based on avian anatomy might one day help remove CO2 from smokestacks
To reduce greenhouse gas emissions, industrial plants filter carbon dioxide from smokestacks by passing flue gas through a column filled with water and nitrogen-containing compounds such as monoethanolamine (MEA). Although it’s widely used, this carbon-capture technique isn’t energy efficient, so researchers have been looking for alternative filtration materials capable of trapping large amounts of CO2.
One research team’s efforts to find such materials has yielded a high-surface-area capture membrane inspired by one of nature’s most efficient gas exchangers: a bird’s lungs. The work, by Aaron P. Esser-Kahn of the University of California, Irvine, and colleagues, was reported at the American Chemical Society national meeting in Indianapolis.
To fly, birds need a lot of energy, so they’ve evolved intricate structures in their lungs to rapidly exchange CO2 for oxygen. “We wanted to be able to match what nature can create,” Esser-Kahn said in a session sponsored by the Division of Polymeric Materials: Science & Engineering.
The chemist and his team produced their birdlung mimics by stretching polylactic acid fibers of two different diameters between a pair of brass plates. They then filled polydimethylsiloxane into a mold around them. After the PDMS set, the team heated the assembly in vacuum to degrade the tightly packed fibers and leave behind microchannels of two sizes.
When the researchers filled the smalldiameter channels with MEA and flowed CO2 through the larger ones, they observed the gas diffuse through the walls of the polymer structure and react with MEA. Surprisingly, Esser-Kahn told the audience, the greenhouse gas transferred most rapidly when the channels were packed into a not-found-in-nature “double square” pattern, rather than a dodecagonal or hexagonal pattern that more closely simulates a bird’s airways.
The Esser-Kahn group’s membrane production method may enable the manufacture of high-surface-area three-dimensional architectures not accessible via standard approaches, says Abraham Dun-can Stroock, a chemical engineer at Cornell University. This “newsworthy” work, he adds, “has taken seriously the challenge of recreating the extraordinary rates of mass transfer that are seen in the vascular systems of animals.”
With these preliminary results in hand, Esser-Kahn’s team will next try to optimize the porosity of its filters and filter material, which can break down over time with exposure to MEA.
Chemical & Engineering News
23 июля исполнилось 60 лет Александру Степановичу Носкову – доктору технических наук, профессору, крупному специалисту в области технологии каталитических процессов и математического моделирования каталитических реакторов. 
по целенаправленному синтезу анодных и катодных электрокатализаторов низкотемпературных топливных элементов (ТЭ), эффективных в окислении водорода и низших спиртов. Был представлен сравнительный анализ методик приготовления высокодисперсных катализаторов с содержанием платины 40–80 мас.%.
Профессор А.А. Хасин из Института катализа СО РАН сделал пленарную лекцию о природе активных мест катализаторов гидрирования. Особое внимание в лекции было уделено катализаторам на основе кобальта для реакции Фишера-Тропша. На ряде примеров был продемонстрирован эффект сильного взаимодействия металл-носитель, оказывающий влияние на активность катализаторов. 
представил результаты тестирования каталитических систем конверсии метана в синтез-газ на основе пористых керамических мембран.
Профессор В.А. Собянин из Института катализа СО РАН рассказал о катализаторах синтеза водорода из диметоксиметана. Доктор А. Тарасов из Института Фрица Хабера в своем докладе подробно рассмотрел проблему зауглероживания катализаторов на основе никеля в условиях каталитической конверсии метана.
В конференции CRS-2 приняли участие около 100 специалистов из 28 стран мира. Научная программа конференции включала 7 пленарных лекций, 5 ключевых презентаций, 38 устных и около 30 стендовых докладов. Пленарную сессию открыл известный специалист в области химической технологии из Швеции, профессор Jan Brandin, Linnaeus University. Он представил обзорную лекцию по современному состоянию развития новых технологий в области производства энергии из возобновляемого сырья, процессов глубокой переработки растительного сырья в Швеции. Традиционно большое внимание было привлечено к лекции одного их ведущих ученых России в области биотехнологии, директора Института биохимической физики им. Н.М. Эмануэля, профессора С.Д. Варфоломеева. Он рассказал о современных подходах и симптоматике в решении технологических проблем переработки отходов в энергию и топливо. Лекция профессора Тапио Салми из Åbo Akademi University, Турку, Финляндия была посвящена применению законов и принципов химического инжиниринга при низкотемпературных превращениях биомассы. Интересные результаты продемонстрировал профессор Жан Карлос Серано-Руиз из компании Abengoa Research, Севилья, Испания. Было показано, что применение каталитических технологий, особенно при производстве энергии из возобновляемого сырья для решения энергетических и экологических проблем, может сыграть ключевую роль в развитии не только биоэнергетики, но также и нефтепереработки. Лекция профессора Владислава Садыкова из Института катализа им. Г.К. Борескова СО РАН (Новосибирск, Россия) была посвящена разработке структурированных нанокомпозитных катализаторов трансформации биотоплива в синтез-газ и водород.
С интересом отнеслась аудитория к лекции профессора Симони Менегетти из Federal University of Alagoas, Бразилия. Материалы ее доклада относились к олео-химии, ориентированной на получение биотоплив. Они касались технологий переработки растительных масел и жиров в биодизель и биокеросин.
Доклад содержал много интересных фактов и привлек внимание слушателей, тем более учитывая, что бразильские ученые и специалисты являются одними из лидеров в области производства биотоплива. Заключительную пленарную лекцию представил профессор Эрик Хеерес из Университета Гронингена, Голландия. Он уделил большое внимание количественной и качественной оценке применения эффективных катализаторов для интенсификации биохимических технологий. 
В результате участники получили исчерпывающую информацию о возможностях экологически чистой утилизации отходов. Из отходов предварительно отделяют металлический мусор.
Бытовые отходы, представляющие собой смесь из органических веществ различного происхождения, являются ничем иным как высококалорийным топливом, не уступающих по энергетике традиционному бурому углю. Особенностью данного завода по утилизации бытовых отходов является глубокая очистка отходящих газов от вредных примесей. Очищенная вода в виде пара подается повторно в печь, способствуя тем самым достижению полного выгорания органической компоненты ТБО. Получаемое тепло используется для отопления жилых домов и производственных зданий. При получении энергии из мусора одновременно решается проблема его утилизации и использования дешевой, практически бесплатной тепловой энергии. 
Основная цель конференции состояла в создании междисциплинарной площадки, обеспечивающей контакт и обмен информацией ученых-нанотехнологов, занимающихся созданием новых наноразмерных материалов, с учеными-нанотоксикологами, являющимися специалистами по вопросам безопасности массового использования этих материалов.
Доктор М.С. Мельгунов в ключевой лекции (Pilling-Bethworth ratio and the Periodic Table) осветил основные тенденции в изменении текстуры при топохимических трансформациях материалов.
Е. Бессуднова (устный доклад Low temperature synthesis and characterization of nanoscale rutile TiO2) описала новый способ приготовления наноразмерного рутила при низких температурах. Г. Чурилов в устном докладе (The nanoparticles with core-shell grain created by plasma of HF discharges) описал физические методы синтеза материалов с морфологией “ядро-оболочка”. 
В ключевых лекциях И.В. Мишакова (Aerogel technology for preparation of nanoscale oxides), О.Б. Бельской (Synthesis of nanostructured mixed oxides M(II)M(III)Ox as supports for platinum catalysts), устных докладах Н.Н. Леонтьевой (Investigation of dehydrated, oxide and hydrated phases derived from Mg-Al and Mg-Ga hydrotalcites by different X-ray diffraction approaches), С. Лазаревой (Synthesis and stabilization of nanosized silicon dioxide) были затронуты вопросы формирования наноразмерных оксидов как катализаторов и носителей катализаторов. Вопрос формования оксидных наноматериалов в макроскопические изделия был освещён в устном докладе Е.А. Мельгуновой (The pathway to the self-supported mesoporous mesophase materials). Т. Диденко в устном докладе (The modified carbon-mineral sorbent for platinum (IV) selective sorption) описала новый углерод-минеральный сорбент для Pt(IV).
Вопросы приготовления и применения магнитоотделяемых наноматериалов были затронуты в пленарной лекции проф. V.I. Parvulescu (Fine tuning the properties of magnetic nanoparticle catalysts for selective transformation of cellulose to value-added chemicals) и ключевой лекции доктора M. Forrester (The dynamics and control of nanomagnet cluster formation in a flow for medical applications). В пленарной лекции проф. F. Kusmartsev (The design of nanomagnets for medical applications) затронуты проблемы синтеза анизотропных наномагнитов для медицинских применений.
Широкое обсуждение получила тема формирования и применения углеродных нановолокон (УНВ) и нанотрубок (УНТ). Так, Д.В. Красников (устный доклад Towards optimization of carbon nanotube properties via in situ studies of growth mechanism) затронул вопросы оптимизации синтеза УНТ применительно к их определённым свойствам на основе детальных исследований механизма их формирования. Особый интерес вызвал устный доклад Ю. Баумана (New catalyst for synthesis of carbon nanofibers from chlorinated hydrocarbons) по синтезу УНВ из хлоросодержащих углеводородов (к которым можно отнести отравляющие вещества и отходы химической промышленности). Такая технология позволила бы перерабатывать трудноутилизируемые отходы в полезные продукты.
В устном докладе И.В. Токаревой (Nanostructuring of carbon microfiber surface) отражены вопросы формирования углерод-углеродных композитов на основе PAN-волокон и УНТ/УНВ, полученных в результате каталитического разложения углеводородов. Это позволяет получать прочные материалы для широкого спектра применений. В пленарной лекции проф. K. Savolainen (Rigid rod-like carbon nanotubes induce signs of allergic asthma) затронуты вопросы применения УНТ для исследования аллергической астмы.
Следует отметить каталитические аспекты применения наноматериалов. Т.В. Чернышова в устном докладе The research of nitrogen compounds effect on the activity of cracking catalysts рассказала о влиянии азотсодержащих компонентов на активность катализаторов крекинга. А.А. Курохтина (Study of selectivity of the Suzuki-Miyaura reaction with aryl bromides using Pd on micro- and mesoporous activated carbons: evidences for nanocatalysis) с соавторами исследовала реакцию Сузуки на палладиевых наночастицах, нанесённых на различные углеродные носители. М.Н. Ефимов (Metal nanoparticles supported by nanodiamonds as novel catalysts for steam ethanol reforming reaction) привёл результаты по использованию металлических наночастиц, нанесённых на наноалмазы в реакции парового риформинга этанола.
Важным аспектом стало применение физических методов для синтеза и исследования наноматериалов: ключевая лекция М.В. Тренихина Electron microscopy investigation of carbon nanomaterials under the influence of high energy beams, устный доклад Н. Торопова Influence of silver nanoparticles on the conformational changes of cyanine dye thin films under laser irradiation, стендовые доклады В. Егорушкина DOS and electrical resistivity in disordered graphene at low temperatures, А.А. Кирсанкина Electron traps in nanostructured oxides of tin and zinc, В.А. Харитонова Organoboron nanoparticles: size, geometry, electronic structure and chemical properties on the example of interaction with ND3.
Токсикологическая характеристика металлических наночастиц была представлена в докладе проф. М.П. Мошкина. На базе Института цитологии и генетики СО РАН и GLP вивария (совместно с сотрудниками Института катализа СО РАН и ряда других институтов) проводится серия исследований по нейрональным эффектам наночастиц марганца при интраназальной экспозиции. Показана возможность прямого транспорта наночастиц марганца из носовой полости в мозг подопытных животных, функциональные и поведенческие нарушения при длительной (3 недели) экспозиции. Исследование поддержано грантом РФФИ и грантом СО РАН.
Исследования транспорта металлических наночастиц в клетки, результаты которых были представлены в докладе проф. Е.И. Рябчиковой (Институт химической биологии и фундаментальной медицины СО РАН), подтвердили, что наночастицы могут воздействовать на клетку химическим путем, т.е. повторять “поведение” макромолекул. Однако наночастицы могут быть более токсичными, т.к. для них не действует барьер эндоцитоза, и частицы могут повреждать внутриклеточные элементы. В физико-химических исследованиях показана высокая активность металлических наночастиц (цинк, никель, алюминий, медь, оксид алюминия, оксид цинка) в физиологических растворах. Исследования поддержаны грантом Минобрнауки РФ.
