Friday, November 4, 2011

New knowledge about 'flawed' diamonds could speed the development of diamond-based quantum computers

 A University at Buffalo-led research team has established the presence of a dynamic Jahn-Teller effect in defective diamonds, a finding that will help advance the development of diamond-based systems in applications such as quantum information processing.

"We normally want things to be perfect, but defects are actually very important in terms of electronic applications," said Peihong Zhang, the UB associate professor of physics who led the study. "There are many proposals for the application of defective diamonds, ranging from quantum computing to biological imaging, and our research is one step toward a better understanding of these defect systems."

The research was published online Sept. 30 in Physical Review Letters.

The findings deal with diamonds whose crystal structure contains a particular defect: a nitrogen atom that sits alongside a vacant space in an otherwise perfect lattice made only of carbon.

At the point of the imperfection -- the so-called "nitrogen-vacancy center" -- a single electron can jump between different energy states. (The electron rises to a higher, "excited" energy state when it absorbs a photon and falls back to a lower energy state when it emits a photon).

Understanding how the diamond system behaves when the electron rises to an excited state called a "3E" state is critical to the success of such proposed applications as quantum computing.

The problem is that at the nitrogen-vacancy center, the 3E state has two orbital components with exactly the same energy -- a configuration that is inherently unstable.

In response, the lattice "stabilizes" by rearranging itself. Atoms near the nitrogen-vacancy center move slightly, resulting in a new geometry that has a lower energy and is more stable.

This morphing is known as the Jahn-Teller effect, and until recently, the effect's precise parameters in defective diamonds remained unknown.

Zhang and colleagues from the Rensselaer Polytechnic Institute in Troy, N.Y., are the first to crack that mystery. Using UB's supercomputing facility, the Center for Computational Research, the team conducted calculations that reveal how, exactly, the diamond lattice distorts.

Their findings align with experimental results from other research studies, and shed light on important topics such as how long an excited electron at the nitrogen-vacancy center will stay coherently at a higher energy state.

The UB-Rensselaer study was funded by the Department of Energy.

The above story is reprinted (with editorial adaptations ) from materials provided by University at Buffalo.

Journal Reference:

Tesfaye Abtew, Y. Sun, Bi-Ching Shih, Pratibha Dev, S. Zhang, Peihong Zhang. Dynamic Jahn-Teller Effect in the NV- Center in Diamond. Physical Review Letters, 2011; 107 (14) DOI: 10.1103/PhysRevLett.107.146403

Self-replication process holds promise for production of new materials

 New York University scientists have developed artificial structures that can self-replicate, a process that has the potential to yield new types of materials. In the natural world, self-replication is ubiquitous in all living entities, but artificial self-replication has been elusive. The new discovery is the first steps toward a general process for self-replication of a wide variety of arbitrarily designed seeds. The seeds are made from DNA tile motifs that serve as letters arranged to spell out a particular word. The replication process preserves the letter sequence and the shape of the seed and hence the information required to produce further generations.

The work, conducted by researchers in NYU's Departments of Chemistry and Physics and its Center for Soft Matter Research, appears in the latest issue of the journal Nature.

This process holds much promise for the creation of new materials. DNA is a robust functional entity that can organize itself and other molecules into complex structures. More recently DNA has been used to organize inorganic matter, such as metallic particles, as well. The re-creation by the NYU scientists of this type of assembly in a laboratory raises the prospect for the eventual development of self-replicating materials that possess a wide range of patterns and that can perform a variety of functions. The breakthrough the NYU researchers have achieved is the replication of a system that contains complex information. Thus, the replication of this material, like that of DNA in the cell, is not limited to repeating patterns.

To demonstrate this self-replication process, the NYU scientists created artificial DNA tile motifs -- short, nanometer-scale arrangements of DNA. Each tile serves as a letter -- A or B -- that recognizes and binds to complementary letters A' or B'. In the natural world, the DNA replication process involves complementary matches between bases -- adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C) -- to form its familiar double helix. By contrast, the NYU researchers developed an artificial tile or motif, called BTX (bent triple helix molecules containing three DNA double helices), with each BTX molecule composed of 10 DNA strands. Unlike DNA, the BTX code is not limited to four letters -- in principle, it can contain quadrillions of different letters and tiles that pair using the complementarity of four DNA single strands, or "sticky ends," on each tile, to form a six-helix bundle.

In order to achieve self-replication of the BTX tile arrays, a seed word is needed to catalyze multiple generations of identical arrays. BTX's seed consists of a sequence of seven tiles -- a seven-letter word. To bring about the self-replication process, the seed is placed in a chemical solution, where it assembles complementary tiles to form a "daughter BTX array" -- a complementary word. The daughter array is then separated from the seed by heating the solution to ~ 40 oC. The process is then repeated. The daughter array binds with its complementary tiles to form a "granddaughter array," thus achieving self-replication of the material and of the information in the seed -- and hence reproducing the sequence within the original seed word. Significantly, this process is distinct from the replication processes that occur within the cell, because no biological components, particularly enzymes, are used in its execution -- even the DNA is synthetic.

"This is the first step in the process of creating artificial self-replicating materials of an arbitrary composition," said Paul Chaikin, a professor in NYU's Department of Physics and one of the study's co-authors. "The next challenge is to create a process in which self-replication occurs not only for a few generations, but long enough to show exponential growth."

"While our replication method requires multiple chemical and thermal processing cycles, we have demonstrated that it is possible to replicate not just molecules like cellular DNA or RNA, but discrete structures that could in principle assume many different shapes, have many different functional features, and be associated with many different types of chemical species," added Nadrian Seeman, a professor in NYU's Department of Chemistry and a co-author of the study.

The research was supported by grants from the W.M. Keck Foundation, the MRSEC Program of the National Science Foundation, the National Institute of General Medical Sciences, the Army Research Office, NASA, and the Office of Naval Research.

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by New York University.

Journal Reference:

Tong Wang, Ruojie Sha, Rémi Dreyfus, Mirjam E. Leunissen, Corinna Maass, David J. Pine, Paul M. Chaikin, Nadrian C. Seeman. Self-replication of information-bearing nanoscale patterns. Nature, 2011; 478 (7368): 225 DOI: 10.1038/nature10500

Tests to catch the makers of dangerous 'legal high' designer drugs

Urgently needed tests which could help identify the manufacturers of designer 'legal high' drugs are being developed in research led at the University of Strathclyde in Glasgow.

The drugs, known by names such as 'ivory wave' and NRG-1" and sold labelled as , and incense, mimic the effects of illegal drugs such as , cocaine and ecstasy. Although these so-called 'designer drugs' can be dangerous, many have not yet been made illegal and are difficult to detect with current drug tests.

A means of potentially tracing the source of the raw materials, and consequently providing information as to who is making the 'bath salts,' is being developed by scientists at Strathclyde and The James Hutton Institute.

The bath salts drug can cause euphoria, paranoia, anxiety and . It often contains mephedrone, a structurally related to methcathinone, which is found in Khat - a plant which, like mephedrone itself, is illegal in many countries.

The bath salts drug is labelled as being not for human consumption and is not illegal in the UK but its import has been banned. The term 'bath salts' is used by those who sell the drug as a way of circumventing legislation when supplying it.

The researchers developing tests for the drug are using a technique known as isotope ratio mass spectrometry (IRMS) to reveal the course of a drug's manufacture.

The research is being carried out by Dr Oliver Sutcliffe, at the Strathclyde Institute of Pharmacy and Biomedical Sciences, and Professor Niamh Nic Daeid and Dr Katy Savage at the Centre for in the Department of Pure and Applied Chemistry, in collaboration with Dr Wolfram Meier-Augenstein at The James Hutton Institute.

Dr Sutcliffe said: "The legal status of varies around the world but they present many dangers to users and these are borne out by the Home Office's decision to ban the import of 'bath salts.'

"The new method we have used has enabled us to work backwards and trace the substances back to their starting materials. IRMS measures the relative amounts of an element's different forms- it is successful because these relative amounts are transferred like a fingerprint through the synthesis of the drug."

Provided by University of Strathclyde

First practical scientific test to date and authenticate priceless silk masterpieces

 Scientists are reporting development of the first fast and reliable scientific method to determine the age and authenticity of priceless silk tapestries and other treasures -- such as Civil War General Phillip Sheridan's famous red-and-white battle flag -- in museums and other collections around the world. A report on their work appears in Analytical Chemistry.

Mehdi Moini and colleagues at the Smithsonian Institution point out that for thousands of years, , consisting of unwound from the cocoons of the silkworm, have been woven into not just garments, but wall hangings, tapestries, carpets and painted silk artworks. Until now, however, there has been no practical scientific way to tell whether a silk tapestry is a well-preserved example from the Fontainebleu series from the 1540s or a copy made just last week. In many cases, scientists could not use the familiar carbon-14 dating process, because it involves taking samples of material large enough to cause visible damage to the silk object.

Their solution is a new test that tracks time-related deterioration the amino acid building blocks in . As silk ages, the so-called L-amino acids in its protein changed into so-called D-amino acids. The D/L ratio provides a highly accurate measure of a silk object's age, age to within 50-100 years and whether it is deteriorating and needs conservation work. Archaeologists had used the D/L approach to date ancient teeth and bone, but Moini's team simplified it and adapted it for silk. The researchers demonstrated the test, called "CE-MS," on Sheridan's flag, a Fontainebleu tapestry, ancient silks from China and other old samples from masterpieces in museums around the world. The method only takes 20 minutes and requires only microscopic samples of silk -- a major improvement over the familiar carbon-14 dating method, which requires large samples that may cause visible damage to the object.

More information: Dating Silk By Capillary Electrophoresis Mass Spectrometry, Anal. Chem., 2011, 83 (19), pp 7577–7581. DOI: 10.1021/ac201746u

A new capillary electrophoresis mass spectrometry (CE-MS) technique is introduced for age estimation of silk textiles based on amino acid racemization rates. With an l to d conversion half-life of 2500 years for silk (B. mori) aspartic acid, the technique is capable of dating silk textiles ranging in age from several decades to a few-thousand-years-old. Analysis required only 100 µg or less of silk fiber. Except for a 2 h acid hydrolysis at 110 °C, no other sample preparation is required. The CE-MS analysis takes 20 min, consumes only nanoliters of the amino acid mixture, and provides both amino acid composition profiles and d/l ratios for 11 amino acids.

Provided by American Chemical Society (news : web)