William N. Lipscomb Jr.
|Born|| December 9, 1919 |
|Died||April 14, 2011 91) (aged|
|Alma mater|| University of Kentucky |
California Institute of Technology
|Awards|| Peter Debye Award (1973)|
Nobel Prize in Chemistry (1976)
|Fields|| Nuclear magnetic resonance |
|Institutions|| University of Minnesota |
|Doctoral advisor||Linus Pauling|
|Doctoral students|| Richard E. Dickerson |
Russell M. Pitzer
Thomas A. Steitz
Don C. Wiley
|Other notable students|| Martha L. Ludwig |
Raymond C. Stevens
William Nunn Lipscomb Jr. (December 9, 1919 –April 14, 2011) was a Nobel Prize-winning American inorganic and organic chemist working in nuclear magnetic resonance, theoretical chemistry, boron chemistry, and biochemistry.
Inorganic chemistry deals with the synthesis and behavior of inorganic and organometallic compounds. This field covers all chemical compounds except the myriad organic compounds, which are the subjects of organic chemistry. The distinction between the two disciplines is far from absolute, as there is much overlap in the subdiscipline of organometallic chemistry. It has applications in every aspect of the chemical industry, including catalysis, materials science, pigments, surfactants, coatings, medications, fuels, and agriculture.
Organic chemistry is a subdiscipline of chemistry that studies the structure, properties and reactions of organic compounds, which contain carbon in covalent bonding. Study of structure determines their chemical composition and formula. Study of properties includes physical and chemical properties, and evaluation of chemical reactivity to understand their behavior. The study of organic reactions includes the chemical synthesis of natural products, drugs, and polymers, and study of individual organic molecules in the laboratory and via theoretical study.
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong static magnetic field are perturbed by a weak oscillating magnetic field and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca. 20 tesla, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR results from specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is widely used to determine the structure of organic molecules in solution and study molecular physics, crystals as well as non-crystalline materials. NMR is also routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging (MRI).
Lipscomb was born in Cleveland, Ohio. His family moved to Lexington, Kentucky in 1920,and he lived there until he received his Bachelor of Science degree in Chemistry at the University of Kentucky in 1941. He went on to earn his Doctor of Philosophy degree in Chemistry from the California Institute of Technology (Caltech) in 1946.
Cleveland is a major city in the U.S. state of Ohio, and the county seat of Cuyahoga County. The city proper has a population of 385,525, making it the 51st-largest city in the United States, and the second-largest city in Ohio. Greater Cleveland is ranked as the 32nd-largest metropolitan area in the U.S., with 2,055,612 people in 2016. The city anchors the Cleveland–Akron–Canton Combined Statistical Area, which had a population of 3,515,646 in 2010 and is ranked 15th in the United States.
Ohio is a Midwestern state in the Great Lakes region of the United States. Of the fifty states, it is the 34th largest by area, the seventh most populous, and the tenth most densely populated. The state's capital and largest city is Columbus.
Lexington, consolidated with Fayette County and often denoted as Lexington-Fayette, is the second-largest city in Kentucky and the 60th-largest city in the United States. By land area, Lexington is the 28th largest city in the United States. Known as the "Horse Capital of the World," it is the heart of the state's Bluegrass region. It has a nonpartisan mayor-council form of government, with 12 council districts and three members elected at large, with the highest vote-getter designated vice mayor. In the 2018 U.S. Census Estimate, the city's population was 323,780 anchoring a metropolitan area of 516,697 people and a combined statistical area of 746,330 people.
From 1946 to 1959 he taught at the University of Minnesota. From 1959 to 1990 he was a professor of chemistry at Harvard University, where he was a professor emeritus since 1990.
The University of Minnesota, Twin Cities is a public research university in Minneapolis and Saint Paul, Minnesota. The Minneapolis and St. Paul campuses are approximately 3 miles (4.8 km) apart, and the St. Paul campus is actually in neighboring Falcon Heights. It is the oldest and largest campus within the University of Minnesota system and has the sixth-largest main campus student body in the United States, with 50,943 students in 2018-19. The university is the flagship institution of the University of Minnesota system, and is organized into 19 colleges and schools, with sister campuses in Crookston, Duluth, Morris, and Rochester.
Chemistry is the scientific discipline involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.
Harvard University is a private Ivy League research university in Cambridge, Massachusetts, with about 6,700 undergraduate students and about 15,250 postgraduate students. Established in 1636 and named for its first benefactor, clergyman John Harvard, Harvard is the United States' oldest institution of higher learning, and its history, influence, and wealth have made it one of the world's most prestigious universities.
Lipscomb was married to the former Mary Adele Sargent from 1944 to 1983.They had three children, one of whom lived only a few hours. He married Jean Evans in 1983. They had one adopted daughter.
Lipscomb resided in Cambridge, Massachusetts until his death in 2011 from pneumonia.
Cambridge is a city in Middlesex County, Massachusetts, and part of the Boston metropolitan area.
Pneumonia is an inflammatory condition of the lung affecting primarily the small air sacs known as alveoli. Typically symptoms include some combination of productive or dry cough, chest pain, fever, and trouble breathing. Severity is variable.
"My early home environment ... stressed personal responsibility and self reliance. Independence was encouraged especially in the early years when my mother taught music and when my father's medical practice occupied most of his time."
In grade school Lipscomb collected animals, insects, pets, rocks, and minerals.
Interest in astronomy led him to visitor nights at the Observatory of the University of Kentucky, where Prof. H. H. Downing gave him a copy of Baker's Astronomy. Lipscomb credits gaining many intuitive physics concepts from this book and from his conversations with Downing, who became Lipscomb's lifelong friend.
The young Lipscomb participated in other projects, such as Morse-coded messages over wires and crystal radio sets, with five nearby friends who became physicists, physicians, and an engineer.
Morse code is a character encoding scheme used in telecommunication that encodes text characters as standardized sequences of two different signal durations called dots and dashes or dits and dahs. Morse code is named for Samuel F. B. Morse, an inventor of the telegraph.
A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most important component, a crystal detector, originally made from a piece of crystalline mineral such as galena. This component is now called a diode.
At age of 12, Lipscomb was given a small Gilbert chemistry set, He expanded it by ordering apparatus and chemicals from suppliers and by using his father's privilege as a physician to purchase chemicals at the local drugstore at a discount. Lipscomb made his own fireworks and entertained visitors with color changes, odors, and explosions. His mother questioned his home chemistry hobby only once, when he attempted to isolate a large amount of urea from urine.
Lipscomb credits perusing the large medical texts in his physician father's library and the influence of Linus Pauling years later to his undertaking biochemical studies in his later years. Had Lipscomb become a physician like his father, he would have been the fourth physician in a row along the Lipscomb male line.
The source for this subsection, except as noted, is Lipscomb's autobiographical sketch.
Lipscomb's high-school chemistry teacher, Frederick Jones, gave Lipscomb his college books on organic, analytical, and general chemistry, and asked only that Lipscomb take the examinations. During the class lectures, Lipscomb in the back of the classroom did research that he thought was original (but he later found was not): the preparation of hydrogen from sodium formate (or sodium oxalate) and sodium hydroxide.He took care to include gas analyses and to search for probable side reactions.
Lipscomb later had a high-school physics course and took first prize in the state contest on that subject. He also became very interested in special relativity.
In college at the University of Kentucky Lipscomb had a music scholarship. He pursued independent study there, reading Dushman' s Elements of Quantum Mechanics, the University of Pittsburgh Physics Staff's An Outline of Atomic Physics, and Pauling's The Nature of the Chemical Bond and the Structure of Molecules and Crystals. Prof. Robert H. Baker suggested that Lipscomb research the direct preparation of derivatives of alcohols from dilute aqueous solution without first separating the alcohol and water, which led to Lipscomb's first publication.
For graduate school Lipscomb chose Caltech, which offered him a teaching assistantship in Physics at $20/month. He turned down more money from Northwestern University, which offered a research assistantship at $150/month. Columbia University rejected Lipscomb's application in a letter written by Nobel prizewinner Prof. Harold Urey.
At Caltech Lipscomb intended to study theoretical quantum mechanics with Prof. W. V. Houston in the Physics Department, but after one semester switched to the Chemistry Department under the influence of Prof. Linus Pauling. World War II work divided Lipscomb's time in graduate school beyond his other thesis work, as he partly analyzed smoke particle size, but mostly worked with nitroglycerin–nitrocellulose propellants, which involved handling vials of pure nitroglycerin on many occasions. Brief audio clips by Lipscomb about his war work may be found from the External Links section at the bottom of this page, past the References.
The source for this subsection, except as noted, is Lipscomb's autobiographical sketch.
The Colonel is how Lipscomb's students referred to him, directly addressing him as Colonel. "His first doctoral student, Murray Vernon King, pinned the label on him, and it was quickly adopted by other students, who wanted to use an appellation that showed informal respect. ... Lipscomb's Kentucky origins as the rationale for the designation."Some years later in 1973 Lipscomb was made a member of the Honorable Order of Kentucky Colonels.
Lipscomb, along with several other Nobel laureates, was a regular presenter at the annual Ig Nobel Awards Ceremony, last doing so on September 30, 2010.
Lipscomb has worked in three main areas, nuclear magnetic resonance and the chemical shift, boron chemistry and the nature of the chemical bond, and large biochemical molecules. These areas overlap in time and share some scientific techniques. In at least the first two of these areas Lipscomb gave himself a big challenge likely to fail, and then plotted a course of intermediate goals.
In this area Lipscomb proposed that: "... progress in structure determination, for new polyborane species and for substituted boranes and carboranes, would be greatly accelerated if the [boron-11] nuclear magnetic resonance spectra, rather than X-ray diffraction, could be used."This goal was partially achieved, although X-ray diffraction is still necessary to determine many such atomic structures. The diagram at right shows a typical nuclear magnetic resonance (NMR) spectrum of a borane molecule.
Lipscomb investigated, "... the carboranes, C2B10H12, and the sites of electrophilic attack on these compoundsusing nuclear magnetic resonance (NMR) spectroscopy. This work led to [Lipscomb's publication of a comprehensive] theory of chemical shifts. The calculations provided the first accurate values for the constants that describe the behavior of several types of molecules in magnetic or electric fields."
Much of this work is summarized in a book by Gareth Eaton and William Lipscomb, NMR Studies of Boron Hydrides and Related Compounds,one of Lipscomb's two books.
In this area Lipscomb originally intended a more ambitious project: "My original intention in the late 1940s was to spend a few years understanding the boranes, and then to discover a systematic valence description of the vast numbers of electron deficient intermetallic compounds. I have made little progress toward this latter objective. Instead, the field of boron chemistry has grown enormously, and a systematic understanding of some of its complexities has now begun."Examples of these intermetallic compounds are KHg13 and Cu5Zn7. Of perhaps 24,000 of such compounds the structures of only 4,000 are known (in 2005) and we cannot predict structures for the others, because we do not sufficiently understand the nature of the chemical bond. This study was not successful, in part because the calculation time required for intermetallic compounds was out of reach in the 1960s, but intermediate goals involving boron bonding were achieved, sufficient to be awarded a Nobel Prize.
Lipscomb confirmed the molecular structure of boranes (compounds of boron and hydrogen) using X-ray crystallography in the 1950s and developed theories to explain their bonds. Later he applied the same methods to related problems, including the structure of carboranes (compounds of carbon, boron, and hydrogen).
The three-center two-electron bond is illustrated in diborane (diagrams at right). In an ordinary covalent bond a pair of electrons bonds two atoms together, one at either end of the bond, the diboare B-H bonds for example at the left and right in the illustrations. In three-center two-electron bond a pair of electrons bonds three atoms (a boron atom at either end and a hydrogen atom in the middle), the diborane B-H-B bonds for example at the top and bottom of the illustrations.
Lipscomb's group did not propose or discover the three-center two-electron bond, nor did they develop formulas that give the proposed mechanism. In 1943, Longuet-Higgins, while still an undergraduate at Oxford, was the first to explain the structure and bonding of the boron hydrides. The paper reporting the work, written with his tutor R. P. Bell,also reviews the history of the subject beginning with the work of Dilthey. Shortly after, experimental spectroscopic work was performed by Price that confirmed Longuet-Higgins' structure for diborane. Longuet-Higgins and Roberts discussed the electronic structure of an icosahedron of boron atoms and of the borides MB6. The mechanism of the three-center two-electron bond was also discussed in a later paper by Longuet-Higgins, and an essentially equivalent mechanism was proposed by Eberhardt, Crawford, and Lipscomb. Lipscomb's group also achieved an understanding of it through electron orbital calculations using formulas by Edmiston and Ruedenberg and by Boys.
The Eberhardt, Crawford, and Lipscomb paperdiscussed above also devised the "styx number" method to catalog certain kinds of boron-hydride bonding configurations.
Wandering atoms was a puzzle solved by Lipscombin one of his few papers with no co-authors. Compounds of boron and hydrogen tend to form closed cage structures. Sometimes the atoms at the vertices of these cages move substantial distances with respect to each other. The diamond-square-diamond mechanism (diagram at left) was suggested by Lipscomb to explain this rearrangement of vertices. Following along in the diagram at left for example in the faces shaded in blue, a pair of triangular faces has a left-right diamond shape. First, the bond common to these adjacent triangles breaks, forming a square, and then the square collapses back to an up-down diamond shape by bonding the atoms that were not bonded before. Other researchers have discovered more about these rearrangements.
The B10H16 structure (diagram at right) determined by Grimes, Wang, Lewin, and Lipscomb found a bond directly between two boron atoms without terminal hydrogens, a feature not previously seen in other boron hydrides.
Lipscomb's group developed calculation methods, both empiricaland from quantum mechanical theory. Calculations by these methods produced accurate Hartree–Fock self-consistent field (SCF) molecular orbitals and were used to study boranes and carboranes.
The ethane barrier to rotation (diagram at left) was first calculated accurately by Pitzer and Lipscombusing the Hartree–Fock (SCF) method.
Lipscomb's calculations continued to a detailed examination of partial bonding through "... theoretical studies of multicentered chemical bonds including both delocalized and localized molecular orbitals."This included "... proposed molecular orbital descriptions in which the bonding electrons are delocalized over the whole molecule."
"Lipscomb and his coworkers developed the idea of transferability of atomic properties, by which approximate theories for complex molecules are developed from more exact calculations for simpler but chemically related molecules,..."
Subsequent Nobel Prize winner Roald Hoffmann was a doctoral studentin Lipscomb's laboratory. Under Lipscomb's direction the Extended Hückel method of molecular orbital calculation was developed by Lawrence Lohr and by Roald Hoffmann. This method was later extended by Hoffman. In Lipscomb's laboratory this method was reconciled with self-consistent field (SCF) theory by Newton and by Boer.
Noted boron chemist M. Frederick Hawthorne conducted earlyand continuing research with Lipscomb.
Much of this work is summarized in a book by Lipscomb, Boron Hydrides,one of Lipscomb's two books.
The 1976 Nobel Prize in Chemistry was awarded to Lipscomb "for his studies on the structure of boranes illuminating problems of chemical bonding".In a way this continued work on the nature of the chemical bond by his Doctoral Advisor at the California Institute of Technology, Linus Pauling, who was awarded the 1954 Nobel Prize in Chemistry "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances."
The source for about half of this section is Lipscomb's Nobel Lecture.
Lipscomb's later research focused on the atomic structure of proteins, particularly how enzymes work. His group used x-ray diffraction to solve the three-dimensional structure of these proteins to atomic resolution, and then to analyze the atomic detail of how the molecules work.
The images below are of Lipscomb's structures from the Protein Data Bankdisplayed in simplified form with atomic detail suppressed. Proteins are chains of amino acids, and the continuous ribbon shows the trace of the chain with, for example, several amino acids for each turn of a helix.
Carboxypeptidase A(left) was the first protein structure from Lipscomb's group. Carboxypeptidase A is a digestive enzyme, a protein that digests other proteins. It is made in the pancreas and transported in inactive form to the intestines where it is activated. Carboxypeptidase A digests by chopping off certain amino acids one-by-one from one end of a protein. The size of this structure was ambitious. Carboxypeptidase A was a much larger molecule than anything solved previously.
Aspartate carbamoyltransferase.(right) was the second protein structure from Lipscomb's group. For a copy of DNA to be made, a duplicate set of its nucleotides is required. Aspartate carbamoyltransferase performs a step in building the pyrimidine nucleotides (cytosine and thymidine). Aspartate carbamoyltransferase also ensures that just the right amount of pyrimidine nucleotides is available, as activator and inhibitor molecules attach to aspartate carbamoyltransferase to speed it up and to slow it down. Aspartate carbamoyltransferase is a complex of twelve molecules. Six large catalytic molecules in the interior do the work, and six small regulatory molecules on the outside control how fast the catalytic units work. The size of this structure was ambitious. Aspartate carbamoyltransferase was a much larger molecule than anything solved previously.
Leucine aminopeptidase,(left) a little like carboxypeptidase A, chops off certain amino acids one-by-one from one end of a protein or peptide.
HaeIII methyltransferase(right) binds to DNA where it methylates (adds a methy group to) it.
Human interferon beta(left) is released by lymphocytes in response to pathogens to trigger the immune system.
Chorismate mutase(right) catalyzes (speeds up) the production of the amino acids phenylalanine and tyrosine.
Fructose-1,6-bisphosphatase(left) and its inhibitor MB06322 (CS-917) were studied by Lipscomb's group in a collaboration, which included Metabasis Therapeutics, Inc., acquired by Ligand Pharmaceuticals in 2010, exploring the possibility of finding a treatment for type 2 diabetes, as the MB06322 inhibitor slows the production of sugar by fructose-1,6-bisphosphatase.
Lipscomb's group also contributed to an understanding of concanavalin A(low resolution structure), glucagon, and carbonic anhydrase (theoretical studies).
Subsequent Nobel Prize winner Thomas A. Steitz was a doctoral student in Lipscomb's laboratory. Under Lipscomb's direction, after the training task of determining the structure of the small molecule methyl ethylene phosphate,Steitz made contributions to determining the atomic structures of carboxypeptidase A and aspartate carbamoyltransferase. Steitz was awarded the 2009 Nobel Prize in Chemistry for determining the even larger structure of the large 50S ribosomal subunit, leading to an understanding of possible medical treatments.
Subsequent Nobel Prize winner Ada Yonath, who shared the 2009 Nobel Prize in Chemistry with Thomas A. Steitz and Venkatraman Ramakrishnan, spent some time in Lipscomb's lab where both she and Steitz were inspired to pursue later their own very large structures.This was while she was a postdoctoral student at MIT in 1970.
The mineral lipscombite (picture at right) was named after Professor Lipscomb by the mineralogist John Gruner who first made it artificially.
Low-temperature x-ray diffraction was pioneered in Lipscomb's laboratoryat about the same time as parallel work in Isadore Fankuchen's laboratory at the then Polytechnic Institute of Brooklyn. Lipscomb began by studying compounds of nitrogen, oxygen, fluorine, and other substances that are solid only below liquid nitrogen temperatures, but other advantages eventually made low-temperatures a normal procedure. Keeping the crystal cold during data collection produces a less-blurry 3-D electron-density map because the atoms have less thermal motion. Crystals may yield good data in the x-ray beam longer because x-ray damage may be reduced during data collection and because the solvent may evaporate more slowly, which for example may be important for large biochemical molecules whose crystals often have a high percentage of water.
Other important compounds were studied by Lipscomb and his students. Among these are hydrazine,nitric oxide, metal-dithiolene complexes, methyl ethylene phosphate, mercury amides, (NO)2, crystalline hydrogen fluoride, Roussin's black salt, (PCF3)5, complexes of cyclo-octatetraene with iron tricarbonyl, and leurocristine (Vincristine), which is used in several cancer therapies.
Five books and published symposia are dedicated to Lipscomb.
A complete list of Lipscomb's awards and honors is in his Curriculum Vitae.
Roald Hoffmann is a Polish-American theoretical chemist who won the 1981 Nobel Prize in Chemistry. He has also published plays and poetry. He is the Frank H. T. Rhodes Professor of Humane Letters, Emeritus, at Cornell University, in Ithaca, New York.
Erich Armand Arthur Joseph Hückel was a German physicist and physical chemist. He is known for two major contributions:
Boranes is the name given to the class of synthetic hydrides of boron with generic formula BxHy. In the past, borane molecules were often labeled "electron-deficient" because of their multicenter bonding (in which a pair of bonding electrons links more than two atoms, as in 3-center-2-electron bonds); this was done in order to distinguish such molecules from hydrocarbons and other classically bonded compounds. However, this usage is incorrect, as most boranes and related clusters such as carboranes are actually electron-precise, not electron-deficient. For example, the extremely stable icosahedral B12H122- dianion, whose 26 cluster valence electrons exactly fill the 13 bonding molecular orbitals, is in no actual sense deficient in electrons; indeed it is thermodynamically far more stable than benzene.
Dilithium, Li2, is a strongly electrophilic, diatomic molecule comprising two lithium atoms covalently bonded together. Li2 is known in the gas phase. It has a bond order of 1, an internuclear separation of 267.3 pm and a bond energy of 102 kJ mol−1 or 1.06eV in each bond. The electron configuration of Li2 may be written as σ2.
Diborane(6), generally known as diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless, pyrophoric gas with a repulsively sweet odor. Synonyms include boroethane, boron hydride, and diboron hexahydride. Diborane is a key boron compound with a variety of applications. It has attracted wide attention for its electronic structure. Its derivatives are useful reagents.
Electron deficiency is a term describing atoms or molecules having fewer than the number of electrons required for maximum stability. At the atomic level, main group atoms having less than 8 electrons or transition metal atoms having less than 18 electrons are described as electron-deficient. At the molecular level, molecules which have an incompletely filled set of bonding molecular orbitals are considered to be electron-deficient. Thus, CH3 and BH3 are electron-deficient, while methane (CH4) and diborane (B2H6) are not. Not surprisingly, electron-deficient molecules are typically strongly electron-attracting (electrophilic). As the most extreme form of electron deficiency one can consider the metallic bond.
Carboranes are electron-delocalized clusters composed of boron, carbon and hydrogen atoms that may also contain other metallic and nonmetallic elements in the cluster framework. Like many of the related boron hydrides, these clusters are polyhedra or fragments of polyhedra, and are similarly classified as closo-, nido-, arachno-, hypho-, etc. based on whether they represent a complete (closo-) polyhedron, or a polyhedron that is missing one (nido-), two (arachno-), three (hypho-), or more vertices. Carboranes are a notable example of heteroboranes.
Tetraborane was the first boron hydride compound to be classified by Stock and Messenez in 1912 and was first isolated by Alfred Stock. It has a relatively low boiling point at 18 °C and is a gas at room temperature. Tetraborane gas is foul smelling and toxic.
The extended Hückel method is a semiempirical quantum chemistry method, developed by Roald Hoffmann since 1963. It is based on the Hückel method but, while the original Hückel method only considers pi orbitals, the extended method also includes the sigma orbitals.
Organoborane or organoboron compounds are chemical compounds of boron and carbon that are organic derivatives of BH3, for example trialkyl boranes. Organoboron chemistry or organoborane chemistry is the chemistry of these compounds. Organoboron compounds are important reagents in organic chemistry enabling many chemical transformations, the most important one called hydroboration.
In chemistry the polyhedral skeletal electron pair theory (PSEPT) provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by Kenneth Wade and were further developed by Michael Mingos and others; they are sometimes known as Wade's rules or the Wade–Mingos rules. The rules are based on a molecular orbital treatment of the bonding. These rules have been extended and unified in the form of the Jemmis mno rules.
Octadecaborane is an inorganic compound, a borane with chemical formula B18H22. It is a colorless flammable solid, like many higher boron hydrides. Although the compound has no practical applications, its structure is of theoretical and pedagogical interest.
Ascalaph Designer is a computer program for general purpose molecular modelling for molecular design and simulations. It provides a graphical environment for the common programs of quantum and classical molecular modelling ORCA, NWChem, Firefly, CP2K and MDynaMix . The molecular mechanics calculations cover model building, energy optimizations and molecular dynamics. Firefly covers a wide range of quantum chemistry methods. Ascalaph Designer is free and open-source software, released under the GNU General Public License, version 2 (GPLv2).
Thomas Arthur Steitz was an American biochemist, a Sterling Professor of Molecular Biophysics and Biochemistry at Yale University, and investigator at the Howard Hughes Medical Institute, best known for his pioneering work on the ribosome.
Eluvathingal Devassy Jemmis or E. D. Jemmis is a Professor of theoretical chemistry at the Indian Institute of Science, Bangalore, India. He was the founding Director of Indian Institute of Science Education and Research, Thiruvananthapuram (IISER-TVM). His primary area of research is applied theoretical chemistry with emphasis on structure, bonding and reactivity, across the periodic table of the elements. Apart from many of his contributions to applied theoretical chemistry, an equivalent of the structural chemistry of carbon, as exemplified by the Huckel 4n+2 Rule, benzenoid aromatics and graphite, and tetrahedral carbon and diamond, is brought in the structural chemistry of boron by the Jemmis mno rules which relates polyhedral and macropolyhedral boranes to allotropes of boron and boron-rich solids. He has been awarded Padma Shri in Science and Engineering category by the Government of India.
Trihydridoboron, also known as borane or borine, is an unstable and highly reactive molecule with the chemical formula BH
3. The preparation of borane carbonyl, BH3(CO), played an important role in exploring the chemistry of boranes, as it indicated the likely existence of the borane molecule. However, the molecular species BH3 is a very strong Lewis acid. Consequently it is highly reactive and can only be observed directly as a continuously produced, transitory, product in a flow system or from the reaction of laser ablated atomic boron with hydrogen.
1,2-Dimethyldiborane is an organoboron compound with the formula [(CH3)BH2]2. Structurally, it is related to diborane, but with methyl groups replacing terminal hydrides on each boron. It is the dimer of methylborane, CH3BH2, the simplest alkylborane. 1,2-Dimethyldiborane can exist in a cis- and a trans arrangement. 1,2-Dimethyldiborane is an easily condensed, colorless gas that ignites spontaneously in air.
Dimethylborane, (CH3)2BH is the simplest dialkylborane, consisting of a methyl group substituted for a hydrogen in borane. As for other boranes it normally exists in the form of a dimer called tetramethyldiborane or TMDB (CH3)2BH)2. Other combinations of methylation occur on diborane, including monomethyldiborane, trimethyldiborane, 1,2-dimethylborane, 1,1-dimethylborane and trimethylborane. At room temperature the substance is at equilibrium between these forms. The methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s.
Trimethyldiborane, (CH3)3B2H3 is a molecule containing boron carbon and hydrogen. It is an alkylborane, consisting of three methyl group substituted for a hydrogen in diborane. It can be considered a mixed dimer: (CH3)2BH2BH(CH3) or dimethylborane and methylborane. called 1,2-dimethyldiborane. Other combinations of methylation occur on diborane, including monomethyldiborane, 1,2-dimethyldiborane, tetramethyldiborane, 1,1-dimethylborane and trimethylborane. At room temperature the substance is at equilibrium between these forms, so it is difficult to keep it pure. The methylboranes were first prepared by H. I. Schlesinger and A. O. Walker in the 1930s.
Methyldiborane, CH3B2H5, or monomethyldiborane is the simplest alkyldiborane, consisting of a methyl group substituted for a hydrogen in diborane. As with other boranes it exists in the form of a dimer with a twin hydrogen bridge that uses three-center two-electron bonding between the two boron atoms, and can be imagined as methyl borane (CH3BH2) bound to borane (BH3). Other combinations of methylation occur on diborane, including 1,1-dimethylborane, 1,2-dimethyldiborane, trimethyldiborane, tetramethyldiborane, and trimethylborane (which is not a dimer). At room temperature the substance is at equilibrium between these molecules.