A rotaxane is a mechanically interlocked molecular architecture consisting of a "dumbbell shaped molecule", threaded through a "macrocycle". The name is derived from the Latin for axle; the two components of a rotaxane are kinetically trapped since the ends of the dumbbell are larger than the internal diameter of the ring and prevent dissociation of the components since this would require significant distortion of the covalent bonds. Much of the research concerning rotaxanes and other mechanically interlocked molecular architectures, such as catenanes, has been focused on their efficient synthesis or their utilization as artificial molecular machines. However, examples of rotaxane substructure have been found in occurring peptides, including: cystine knot peptides, cyclotides or lasso-peptides such as microcin J25; the earliest reported synthesis of a rotaxane in 1967 relied on the statistical probability that if two halves of a dumbbell-shaped molecule were reacted in the presence of a macrocycle that some small percentage would connect through the ring.
To obtain a reasonable quantity of rotaxane, the macrocycle was attached to a solid-phase support and treated with both halves of the dumbbell 70 times and severed from the support to give a 6% yield. However, the synthesis of rotaxanes has advanced and efficient yields can be obtained by preorganizing the components utilizing hydrogen bonding, metal coordination, hydrophobic forces, covalent bonds, or coulombic interactions; the three most common strategies to synthesize rotaxane are "capping", "clipping", "slipping", though others do exist. Leigh and co-workers described a new pathway to mechanically interlocked architectures involving a transition-metal center that can catalyse a reaction through the cavity of a macrocycle. Synthesis via the capping method relies upon a thermodynamically driven template effect; this dynamic complex or pseudorotaxane is converted to the rotaxane by reacting the ends of the threaded guest with large groups, preventing disassociation. The clipping method is similar to the capping reaction except that in this case the dumbbell shaped molecule is complete and is bound to a partial macrocycle.
The partial macrocycle undergoes a ring closing reaction around the dumbbell-shaped molecule, forming the rotaxane. The method of slipping is one. If the end groups of the dumbbell are an appropriate size it will be able to reversibly thread through the macrocycle at higher temperatures. By cooling the dynamic complex, it becomes kinetically trapped as a rotaxane at the lower temperature. Leigh and co-workers began to explore a strategy in which template ions could play an active role in promoting the crucial final covalent bond forming reaction that captures the interlocked structure. Rotaxane-based molecular machines have been of initial interest for their potential use in molecular electronics as logic molecular switching elements and as molecular shuttles; these molecular machines are based on the movement of the macrocycle on the dumbbell. The macrocycle can rotate around the axis of the dumbbell like a wheel and axle or it can slide along its axis from one site to another. Controlling the position of the macrocycle allows the rotaxane to function as a molecular switch, with each possible location of the macrocycle corresponding to a different state.
These rotaxane machines can be manipulated both by photochemical inputs. Rotaxane based systems have been shown to function as molecular muscles. In 2009, there was a report of a "domino effect" from one extremity to the other in a Glycorotaxane Molecular Machine. In this case, the 4C1 or 1C4 chair-like conformation of the mannopyranoside stopper can be controlled, depending on the localization of the macrocycle. In 2012, unique pseudo-macrocycles consisting of double-lasso molecular machines were reported in Chem. Sci; these structures can be tightened or loosened depending on pH. A controllable jump rope movement was observed in these new molecular machines. Potential application as long-lasting dyes is based on the enhanced stability of the inner portion of the dumbbell-shaped molecule. Studies with cyclodextrin-protected rotaxane azo dyes established this characteristic. More reactive squaraine dyes have been shown to have enhanced stability by preventing nucleophilic attack of the inner squaraine moiety.
The enhanced stability of rotaxane dyes is attributed to the insulating effect of the macrocycle, able to block interactions with other molecules. In a nanorecording application, a certain rotaxane is deposited as a Langmuir–Blodgett film on ITO-coated glass; when a positive voltage is applied with the tip of a scanning tunneling microscope probe, the rotaxane rings in the tip area switch to a different part of the dumbbell and the resulting new conformation makes the molecules stick out 0.3 nanometer from the surface. This height difference is sufficient for a memory dot, it is not yet known. Accepted nomenclature is to designate the number of components of the rotaxane in brackets as a prefix. Therefore, the a rotaxane consisting of a single dumbbell-shaped axial molecule with a single macrocycle around its shaft is called a rotaxane, two cyanostar molecules around the central
Frank Stephens was an American naturalist and the first director of the San Diego Natural History Museum. He was considered the pioneer naturalist of the Southwest, studying the mammals and birds of California and Baja California, his personal specimen collection of 2,000 birds and mammals, donated in 1910, was the foundation of the San Diego Natural History Museum's Birds & Mammals Department, now a major resource on bird and mammal species of western North America, including Baja California. Born on April 2, 1849 near Portage in Livingston County, New York, Frank Stephens was the eldest of the four sons of Nelson and Julia Benson. During his early years, the family moved to the Midwest, farming in Michigan, Illinois and Kansas. An interest in wildlife led him at age 22 to take some lessons in taxidermy. At age 24, he married Elizabeth Fowler, in 1874 the couple moved to Colorado, where he studied taxidermy with ornithologist Charles E. Aiken. Moving to California in 1876, he settled in Witch Creek, San Diego County, where he farmed and continued collecting, working for the U. S.
Biological Survey and the University of California's Museum of Vertebrate Zoology. In the early 1880s, Stephens collected in southwest New Mexico and Arizona for Aikens and for William Brewster of Harvard's Museum of Comparative Zoology, he collected among others. He was a collector for the U. S. Biological Survey's 1891 Death Valley Expedition. Stephens's wife Elizabeth died in January 1898, he married Kate Brown in August 1898, she accompanied him on several collecting trips, including the 1907 expedition to southeastern Alaska sponsored by Annie Montague Alexander. In her own right, Kate Stephens became an authority on shells. Stephens was active both in the study throughout his 60-year career, he participated in Joseph Grinnell's 1910 MVZ expedition on the Colorado River and continued camping out on collecting trips into his 70s. He was a frequent contributor to The Condor, founded the San Diego Society of Natural History's scientific journal, in 1906 self-published his major work, California Mammals.
Stephens was an early member of the San Diego Society of Natural History and the first curator of mammalogy for the San Diego Natural History Museum. He is credited with collecting at least 45 type specimens. Although he had faced difficult conditions on many desert treks, Stephens was felled in the city by modern technology: crossing a street in San Diego, he was struck by a street car on September 25, 1937 and died ten days after the accident on October 5, 1937 at Mercy Hospital in San Diego. American Ornithological Union, 1883. Flickr, San Diego Natural History Museum Research Library. Frank Stephens biography, Islapedia
Earl John Robinson was an American professional baseball outfielder and third baseman who played in Major League Baseball for the Los Angeles Dodgers and Baltimore Orioles. He attended college at the University of California, where he played both baseball and basketball, helping Cal to three straight conference titles in basketball from 1956 to 1958. Born in New Orleans, Robinson attended Berkeley High School in the San Francisco Bay Area before matriculating at Cal. Robinson threw and batted right-handed, stood 6 feet 1 inch tall and weighed 190 pounds, he signed with the Dodgers in their first year in Los Angeles. After spending the minor league season at Class B Green Bay, he received an eight-game audition that September, including five starts at third base, he played errorless ball, handling 14 chances in the field, collected three singles in 15 at bats. Robinson spent both 1959 and 1960 in Triple-A, his contract was sold to the Orioles on December 15, 1960, the last day of the interleague trading period in force.
He platooned with left-handed-hitting Whitey Herzog in 1961, as they shared the Orioles' right field job. Robinson batted.266 with eight home runs in 96 games. But in 1962, he appeared in only 29 games all season. In his final stint with Baltimore, in 1964, Robinson was called up from Triple-A Rochester in July, served as a backup left fielder and center fielder through the end of the season, he hit.273 in 37 games. The 1964 season was Robinson's last in the major leagues, he appeared in 170 games played, collected 113 hits, including 20 doubles, five triples and 12 home runs. He batted.268 with 44 runs batted in. Robinson concluded his pro career after spending 1965 at Triple-A in the Chicago Cubs' organization. Robinson was inducted to the Cal Athletic Hall of Fame in 1988, he was inducted into the Pac-10 Basketball Hall of Honor in 2010. Robinson died July 2014 after suffering from congestive heart failure and two heart attacks. During his years with the Baltimore Orioles, Robinson lived with his wife and two daughters in Castro Valley, California.
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