A triptych is a work of art, divided into three sections, or three carved panels that are hinged together and can be folded shut or displayed open. It is therefore a type of the term for all multi-panel works; the middle panel is the largest and it is flanked by two smaller related works, although there are triptychs of equal-sized panels. The form can be used for pendant jewelry. Despite its connection to an art format, the term is sometimes used more to connote anything with three parts if they are integrated into a single unit; the triptych form arises from early Christian art, was a popular standard format for altar paintings from the Middle Ages onwards. Its geographical range was from the eastern Byzantine churches to the Celtic churches in the west. During the Byzantine period, triptychs were used for private devotional use, along with other relics such as icons. Renaissance painters such as Hans Memling and Hieronymus Bosch used the form. Sculptors used it. Triptych forms allow ease of transport.
From the Gothic period onward, both in Europe and elsewhere, altarpieces in churches and cathedrals were in triptych form. One such cathedral with an altarpiece triptych is Llandaff Cathedral; the Cathedral of Our Lady in Antwerp, contains two examples by Rubens, Notre Dame de Paris is another example of the use of triptych in architecture. One can see the form echoed by the structure of many ecclesiastical stained glass windows. Although identified as an altarpiece form, triptychs outside that context have been created, some of the best-known examples being works by Hieronymus Bosch, Max Beckmann, Francis Bacon; the highest price paid for an artwork at auction was $142.4 million for a 1969 triptych, Three Studies of Lucian Freud, by Francis Bacon in November 2012. The record was broken in May 2015 by $179.4 million for Pablo Picasso's 1955 painting Les Femmes d’Alger. The format has been used in other religions, including Islam and Buddhism. For example: the triptych Hilje-j-Sherif displayed at the National Museum of Oriental Art, Italy, a page of the Qur'an at the Museum of Turkish and Islamic Arts in Istanbul, exemplify Ottoman religious art adapting the motif.
Tibetan Buddhists have used it in traditional altars. A photographic triptych is a common style used in modern commercial artwork; the photographs are arranged with a plain border between them. The work may consist of separate images that are variants on a theme, or may be one larger image split into three. Annunciation with St. Margaret and St. Ansanus by Simone Martini Stefaneschi Triptych by Giotto The Mérode Altarpiece by Robert Campin The Garden of Earthly Delights, Triptych of the Temptation of St. Anthony and The Haywain Triptych by Hieronymus Bosch The Portinari Altarpiece by Hugo van der Goes The Buhl Altarpiece, 7 m wide The Raising of the Cross by Peter Paul Rubens Departure by Max Beckmann Three Studies for Figures at the Base of a Crucifixion by Francis Bacon The Pioneer by Frederick McCubbin Diptych Polyptych Polyvision Three hares The Institution of the Eucharist at the Last Supper with St. Peter and St. Paul, Metropolitan Museum of Art On the triptych as a writing instrument Example of triptych features and restoration
Paul Doughty Bartlett
Paul Doughty Bartlett was an American chemist. Bartlett was born in Ann Arbor and grew up in Indianapolis, he received his B. A. from Amherst College in 1928. After his graduation from Harvard with James Bryant Conant, Bartlett worked at the Rockefeller Institute and the University of Minnesota. Most of his career was spent at Harvard. Among other achievements, Bartlett was co-author with Lawrence H. Knox of a classic paper on organic reaction mechanisms. After his retirement in 1972, he started his second career at Texas Christian University, he was elected a Fellow of the American Academy of Arts and Sciences in 1946. He was awarded the Willard Gibbs Award in 1963, National Medal of Science in 1968, the John Price Wetherill Medal in 1970. In 1969, Paul Doughty Bartlett was elected as member of the German Academy of Sciences Leopoldina. F. H. Westheimer. "Paul Doughty Bartlett". Proceedings of the American Philosophical Society. 142: 446–456. Oral History interview transcript with Paul Bartlett 18 July 1978, American Institute of Physics, Niels Bohr Library and Archives National Academy of Sciences Biographical Memoir
The Jmol applet, among other abilities, offers an alternative to the Chime plug-in, no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, the Sculpt mode. Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS 9. Jmol operates on a wide variety of platforms. For example, Jmol is functional in Mozilla Firefox, Internet Explorer, Google Chrome, Safari. Chemistry Development Kit Comparison of software for molecular mechanics modeling Jmol extension for MediaWiki List of molecular graphics systems Molecular graphics Molecule editor Proteopedia PyMOL SAMSON Official website Wiki with listings of websites and moodles Willighagen, Egon. "Fast and Scriptable Molecular Graphics in Web Browsers without Java3D". Doi:10.1038/npre.2007.50.1
Phosphine ligands are phosphines, compound of the formula PRR'R" that are used as ligands in metal complexes related to organometallic chemistry and homogeneous catalysis. These compounds are used in other areas of chemistry; the most common phosphine ligands are of the type PR3. They are three-fold symmetric with equivalent substituents; some routine phosphine ligands are trimethylphosphine. The triarylphosphines are white shelf-stable solids, whereas the trialkylphosphines are colorless liquids that tend to air-oxidize to the corresponding phosphine oxides; such ligands can be classified according to steric bulk. These properties can be quantified by the Tolman electronic parameter and ligand cone angle, respectively. Alkyl phosphines are stronger bases and σ-donors. Common bidentate chelating phosphine ligands include dppe and dmpe, R2PCH2CH2PR2. Tridentate triphosphines come in two classes and tripodal; these ligands are both called triphos. The phenyl-substituted versions have the formula CH3C3 and PhP2.
Examples of tetradentate tripodal phosphines include trisphosphine. Two basic types of chiral phosphine ligands exist; these are of interest for e.g. asymmetric hydrogenation. Chiral diphosphines have been popularized. P-chiral phosphines such as DIPAMP have three different phosphorus substituents. BINAP is a well known example of a C2-symmetric diphosphine which forms chiral complexes due to atropisomerism
A paddle wheel is a form of waterwheel or impeller in which a number of paddles are set around the periphery of the wheel. It has several uses, some of which are: Very low-lift water pumping, such as flooding paddy fields at no more than about 0.5 m height above the water source. To move and mix algae culture in the raceway ponds used for algaculture. Propulsion of boats Low head hydro power Flow sensors AeratorsThe paddle wheel is an ancient invention but is still used today in a wide range of industrial and agriculture applications; the paddle wheel is a device for converting between rotary motion of a shaft and linear motion of a fluid. In the linear-to-rotary direction, it is placed in a fluid stream to convert the linear motion of the fluid into rotation of the wheel; this rotation can be used as an indication of the speed of flow. In the rotary-to-linear direction, it is driven by a prime mover such as an electric motor or steam engine and used to pump a fluid or propel a vehicle such as a paddle-wheel steamer or a steamship
Synthetic molecular motor
Synthetic molecular motors are molecular machines capable of continuous directional rotation under an energy input. Although the term "molecular motor" has traditionally referred to a occurring protein that induces motion, some groups use the term when referring to non-biological, non-peptide synthetic motors. Many chemists are pursuing the synthesis of such molecular motors; the basic requirements for a synthetic motor are repetitive 360° motion, the consumption of energy and unidirectional rotation. The first two efforts in this direction, the chemically driven motor by Dr. T. Ross Kelly of Boston College with co-workers and the light-driven motor by Feringa and co-workers, were published in 1999 in the same issue of Nature. An example of a prototype for a synthetic chemically driven rotary molecular motor was reported by Kelly and co-workers in 1999, their system is made up from a three-bladed triptycene rotor and a helicene, is capable of performing a unidirectional 120° rotation. This rotation takes place in five steps.
The amine group present on the triptycene moiety is converted to an isocyanate group by condensation with phosgene. Thermal or spontaneous rotation around the central bond brings the isocyanate group in proximity of the hydroxyl group located on the helicene moiety, thereby allowing these two groups to react with each other; this reaction irreversibly traps the system as a strained cyclic urethane, higher in energy and thus energetically closer to the rotational energy barrier than the original state. Further rotation of the triptycene moiety therefore requires only a small amount of thermal activation in order to overcome this barrier, thereby releasing the strain. Cleavage of the urethane group restores the amine and alcohol functionalities of the molecule; the result of this sequence of events is a unidirectional 120° rotation of the triptycene moiety with respect to the helicene moiety. Additional forward or backward rotation of the triptycene rotor is inhibited by the helicene moiety, which serves a function similar to that of the pawl of a ratchet.
The unidirectionality of the system is a result from both the asymmetric skew of the helicene moiety as well as the strain of the cyclic urethane, formed in c. This strain can be only be lowered by the clockwise rotation of the triptycene rotor in d, as both counterclockwise rotation as well as the inverse process of d are energetically unfavorable. In this respect the preference for the rotation direction is determined by both the positions of the functional groups and the shape of the helicene and is thus built into the design of the molecule instead of dictated by external factors; the motor by Kelly and co-workers is an elegant example of how chemical energy can be used to induce controlled, unidirectional rotational motion, a process which resembles the consumption of ATP in organisms in order to fuel numerous processes. However, it does suffer from a serious drawback: the sequence of events that leads to 120° rotation is not repeatable. Kelly and co-workers have therefore searched for ways to extend the system so that this sequence can be carried out repeatedly.
Their attempts to accomplish this objective have not been successful and the project has been abandoned. In 2016 David Leigh's group invented the first autonomous chemically-fuelled synthetic molecular motor; some other examples of synthetic chemically driven rotary molecular motors that all operate by sequential addition of reagents have been reported, including the use of the stereoselective ring opening of a racemic biaryl lactone by the use of chiral reagents, which results in a directed 90° rotation of one aryl with respect to the other aryl. Branchaud and co-workers have reported that this approach, followed by an additional ring closing step, can be used to accomplish a non-repeatable 180° rotation. Feringa and co-workers used this approach in their design of a molecule that can repeatably perform 360° rotation; the full rotation of this molecular motor takes place in four stages. In stages A and C rotation of the aryl moiety is restricted. In stages B and D the aryl can rotate with respect to the naphthalene with steric interactions preventing the aryl from passing the naphthalene.
The rotary cycle consists of four chemically induced steps which realize the conversion of one stage into the next. Steps 1 and 3 are asymmetric ring opening reactions which make use of a chiral reagent in order to control the direction of the rotation of the aryl. Steps 2 and 4 consist of the deprotection of the phenol, followed by regioselective ring formation. In 1999 the laboratory of Prof. Dr. Ben L. Feringa at the University of Groningen, The Netherlands reported the creation of a unidirectional molecular rotor, their 360° molecular motor system consists of a bis-helicene connected by an alkene double bond displaying axial chirality and having two stereocenters. One cycle of unidirectional rotation takes 4 reaction steps; the first step is a low temperature endothermic photoisomerization of the trans isomer 1 to the cis 2 where P stands for the right-handed helix and M for the left-handed helix. In this process, the two axial methyl groups are converted into two less sterically favorable equatorial methyl groups.
By increasing the temperature to 20 °C these methyl groups convert back exothermally to the cis axial groups in a helix inversion. Because the axial isomer is more stable than the equatorial isomer, reverse rotation is blocked. A second photoisomerization converts cis 3 into trans 4, again with accompanying formation of sterically unfavorable equatorial methyl groups. A thermal isomerization process at 60 °C closes the 360° cycle back to the axial positions
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is hard and ductile. Pure nickel, powdered to maximize the reactive surface area, shows a significant chemical activity, but larger pieces are slow to react with air under standard conditions because an oxide layer forms on the surface and prevents further corrosion. So, pure native nickel is found in Earth's crust only in tiny amounts in ultramafic rocks, in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere. Meteoric nickel is found in combination with iron, a reflection of the origin of those elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth's outer and inner cores. Use of nickel has been traced as far back as 3500 BCE. Nickel was first isolated and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who mistook the ore for a copper mineral, in the cobalt mines of Los, Hälsingland, Sweden.
The element's name comes from a mischievous sprite of German miner mythology, who personified the fact that copper-nickel ores resisted refinement into copper. An economically important source of nickel is the iron ore limonite, which contains 1–2% nickel. Nickel's other important ore minerals include pentlandite and a mixture of Ni-rich natural silicates known as garnierite. Major production sites include the Sudbury region in Canada, New Caledonia in the Pacific, Norilsk in Russia. Nickel is oxidized by air at room temperature and is considered corrosion-resistant, it has been used for plating iron and brass, coating chemistry equipment, manufacturing certain alloys that retain a high silvery polish, such as German silver. About 9% of world nickel production is still used for corrosion-resistant nickel plating. Nickel-plated objects sometimes provoke nickel allergy. Nickel has been used in coins, though its rising price has led to some replacement with cheaper metals in recent years. Nickel is one of four elements that are ferromagnetic at room temperature.
Alnico permanent magnets based on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is valuable in modern times chiefly in alloys. A further 10% is used for nickel-based and copper-based alloys, 7% for alloy steels, 3% in foundries, 9% in plating and 4% in other applications, including the fast-growing battery sector; as a compound, nickel has a number of niche chemical manufacturing uses, such as a catalyst for hydrogenation, cathodes for batteries and metal surface treatments. Nickel is an essential nutrient for some microorganisms and plants that have enzymes with nickel as an active site. Nickel is a silvery-white metal with a slight golden tinge, it is one of only four elements that are magnetic at or near room temperature, the others being iron and gadolinium. Its Curie temperature is 355 °C; the unit cell of nickel is a face-centered cube with the lattice parameter of 0.352 nm, giving an atomic radius of 0.124 nm. This crystal structure is stable to pressures of at least 70 GPa.
Nickel belongs to the transition metals. It is hard and ductile, has a high for transition metals electrical and thermal conductivity; the high compressive strength of 34 GPa, predicted for ideal crystals, is never obtained in the real bulk material due to the formation and movement of dislocations. The nickel atom has two electron configurations, 3d8 4s2 and 3d9 4s1, which are close in energy – the symbol refers to the argon-like core structure. There is some disagreement. Chemistry textbooks quote the electron configuration of nickel as 4s2 3d8, which can be written 3d8 4s2; this configuration agrees with the Madelung energy ordering rule, which predicts that 4s is filled before 3d. It is supported by the experimental fact that the lowest energy state of the nickel atom is a 3d8 4s2 energy level the 3d8 4s2 3F, J = 4 level. However, each of these two configurations splits into several energy levels due to fine structure, the two sets of energy levels overlap; the average energy of states with configuration 3d9 4s1 is lower than the average energy of states with configuration 3d8 4s2.
For this reason, the research literature on atomic calculations quotes the ground state configuration of nickel as 3d9 4s1. The isotopes of nickel range in atomic weight from 48 u to 78 u. Occurring nickel is composed of five stable isotopes. Isotopes heavier than 62Ni cannot be formed by nuclear fusion without losing energy. Nickel-62 has the highest mean nuclear binding energy per nucleon of any nuclide, at 8.7946 MeV/nucleon. Its binding energy is greater than both 56Fe and 58Fe, more abundant elements incorrectly cited as having the most tightly-bound nuclides. Although this would seem to predict nickel-62 as the most abundant heavy element in the universe, the high rate of photodisintegration of nickel in stellar interiors causes iron to be by far the most abundant. Stable isotope nickel-60 is the daughter product of the extinct radionuclide 60Fe, whi