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Crystal field theory (CFT) is a model that describes the breaking of degeneracies of electronic orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution (anion neighbors). This theory has been used to describe various spectroscopies of transition metal coordination complexes, in particular optical spectra (colours). CFT successfully accounts for some magnetic properties, colours, hydration enthalpies, and spinel structures of transition metal complexes, but it does not attempt to describe bonding. CFT was developed by physicists Hans Bethe and John Hasbrouck van Vleck in the 1930s. CFT was subsequently combined with molecular orbital theory to form the more realistic and complex ligand field theory (LFT), which delivers insight into the process of chemical bonding in transition metal complexes.
At almost exactly the same time that chemists were developing the valence-bond model for coordination complexes, physicists such as Hans Bethe, John Van Vleck, and Leslie Orgel were developing an alternative known as crystal field theory. This theory tried to describe the effect of the electrical field of neighboring ions on the energies of the valence orbitals of an ion in a crystal. Crystal field theory was developed by considering two compounds: manganese(II) oxide, MnO, and copper(I) chloride, CuCl.
Octahedral Crystal Field
Each Mn2+ ion in manganese(II) oxide is surrounded by six O2- ions arranged toward the corners of an octahedron, as shown in the figure below. MnO is therefore a model for an octahedral complex in which a transition-metal ion is coordinated to six ligands.
What happens to the energies of the 4s and 4p orbitals on an Mn2+ ion when this ion is buried in an MnO crystal? Repulsion between electrons that might be added to these orbitals and the electrons on the six O2- ions that surround the metal ion in MnO increase the energies of these orbitals. The three 4p orbitals are still degenerate, however. These orbitals still have the same energy because each 4p orbital points toward two O2- ions at the corners of the octahedron.
The d-block elements are commonly known as transition metals or transition elements
The transition metals are also known as the transition elements or the d-block elements. As the name implies, the chemistry of this group is determined by the extent to which the d electron suborbital levels are filled. Chemical similarities and periodicities can be easily seen horizontally across the d-block of the Periodic Table The chemistry is far from simple, however, and there are many exceptions to the orderly filling of the electron shells,
As previously stated, the chemical properties in the Periodic Table are grouped in two ways: vertically, by group, for similar chemical and some physical properties. Horizontally, by row or period, for consistent periodic changes in the chemical and physical properties. For example, the metals in group 11 have similar characteristics of electrical conductivity, luster, crystal structure, ductility, and tensile strength. Characteristic Properties of Transition Metals Transition metals can be said to possess the following characteristics generally not found in the main grouping of the Periodic Table. They can be mostly attributed to incomplete filling of the electron d-levels.
· The formation of compounds whose color is due to d – d electronic transitions.
· The formation of compounds in many oxidation states, due to the relatively low reactivity of unpaired d electrons.
· The formation of many paramagnetic compounds due to the presence of unpairedd electrons. A few compounds of main group elements are also paramagnetic (e.g. nitric oxide, oxygen).
Color in transition-series metal compounds is generally due to the electronic transitions of two principal types of charge transfer transitions. An electron may jump from a predominantly ligand orbital to a predominantly metal orbital, giving rise to a ligand-to-metal charge-transfer (LMCT) transition. These can most easily occur when the metal is in a high oxidation state. For example, the color of chromate, dichromate and permanganate ions is due to LMCT transitions. Another example is that mercuric iodide, HgI2, is red because of a LMCT transition.
A metal-to ligand charge transfer (MLCT) transition will be most likely when the metal is in a low oxidation state and the ligand is an easily reduced d-d transition. An electron jumps from one d-orbital to another. In complexes of the transition metals, the dorbitals do not all have the same energy.
Transition metal compounds are paramagnetic when they have one or more unpaired delectrons. Some compounds are diamagnetic. These include octahedral, low-spin, d6and square-planar d8 complexes. In these cases, crystal field splitting is such that all the electrons are paired up. Ferromagnetism occurs when individual atoms are paramagnetic and the spin vectors are aligned parallel to each other in a crystalline material. Metallic iron and the alloy alnico are examples of ferromagnetic materials involving transition metals. Anti-ferromagnetism is another example of a magnetic property arising from a particular alignment of individual spins in the solid state.
The transition metals and their compounds are known for their homogeneous andheterogeneous catalytic activity. This activity is attributed to their ability to adoptmultiple oxidation states and to form complexes.
An electron may jump from a predominantly ligand orbital to a predominantly metal orbital, giving rise to a ligand-to-metal charge-transfer (LMCT) transition. These can most easily occur when the metal is in a high oxidation state. For example, the color of chromate, dichromate and permanganate ions is due to LMCT transitions. Another example is that mercuric iodide, HgI2, is red because of a LMCT transition.
A metal-to ligand charge transfer (MLCT) transition will be most likely when the metal is in a low oxidation state and the ligand is easily reduced.
An electron jumps from one d-orbital to another. In complexes of the transition metals, the d orbitals do not all have the same energy. The pattern of splitting of the d orbitals can be calculated using crystal field theory. The extent of the splitting depends on the particular metal, its oxidation state and the nature of the ligands.
In centrosymmetric complexes, such as octahedral complexes, d-d transitions are forbidden by the Laporte rule and only occur because of vibronic coupling, in which a molecular vibration occurs together with a d-d transition. Tetrahedral complexes have a somewhat more intense color because mixing d and p orbitals is possible when there is no center of symmetry, so transitions are not pure d-d transitions. The molar absorptivity (ε) of bands caused by d-d transitions are relatively low, roughly in the range 5-500 M−1cm−1 (where M = mol dm−3). Some d-d transitions are spin forbidden. An example occurs in octahedral, high-spin complexes of manganese(II), which has a d5 configuration in which all five electrons have parallel spins. The color of such complexes is much weaker than in complexes with spin-allowed transitions. In fact, many compounds of manganese(II) appear almost colourless. The spectrum of [Mn(H2O)6]2+ shows a maximum molar absorptivity of about 0.04 M−1cm−1 in the visible spectrum. Transition metal compounds are paramagnetic when they have one or more unpaired d electrons. In octahedral complexes with between four and seven d electrons, both high spin and low spin states are possible. Tetrahedral transition metal complexes, such as [FeCl4]2−, are high-spin because the crystal field splitting is small. This means that the energy to be gained by virtue of the electrons being in lower energy orbitals is always less than the energy needed to pair up the spins.
Some compounds are diamagnetic. These include octahedral, low-spin, d6 and square-planar d8 complexes. In these cases, crystal field splitting is such that all the electrons are paired up. Ferromagnetism occurs when individual atoms are paramagnetic and the spin vectors are aligned parallel to each other in a crystalline material. Metallic iron and the alloy alnico are examples of ferromagnetic materials involving transition metals. Anti-ferromagnetism is another example of a magnetic property arising from a particular alignment of individual spins in the solid state. As implied by the name, all transition metals are metals and conductors of electricity. In general transition metals possess a high density and high melting points and boiling points. These properties are due to metallic bonding by delocalized d electrons, leading to cohesion which increases with the number of shared electrons. However, the group 12 metals have much lower melting and boiling points since their full d subshells prevent d–d bonding. In fact, mercury has a melting point of −38.83 °C (−37.89 °F) and is a liquid at room temperature. Many transition metals can be bound to a variety of ligands. In regards to atomic size of transition metals, there is variation Typically, when moving left to right across the table, there is a trend of decreasing atomic radius. However, in the transition metals, moving left to right, there is a trend of increasing atomic radius which levels off and becomes constant. In the transition elements, the number of electrons are increasing but in a particular way. The number of electrons increase going across a period, thus, there is more pull of these electrons towards the nucleus. However, with the d−electrons, there is some added electron-electronrepulsion. For example, in chromium, there is a promotion of one of the 4s electrons to half fill the 3d sublevel, the electron-electron repulsions are less and the atomic size is smaller. The opposite holds true for the latter part of the row.
The government has failed to auction spectrum for third generation (3G) and fourth generation (4G) services based on the spectrum policy implemented last year. This has resulted in delays in making new services available in the market and left the telecom sector hard hit. In November 4 last year the Ministry of Information and Communications (MoIC) had introduced the “Telecommuni-cation Service Radio Frequency (Distribution and Pricing) Policy 2012”, fixing new pricing for frequencies and plan for effective distribution of the scarce resource. However, officials at the Nepal Telecommunications Authority (NTA) admit that the policy has become just a guideline to collect a spectrum fee rather than pushing for development in the sector. Two major telecom companies, Ncell and Nepal Telecom (NT), have been planning to roll out 4G service for the last three years and had sought spectrum required for the this technology. Based on the policy, the MoIC was supposed to form a committee to study the international practice, pricing and auctioning procedure, however this has not made any headway to date. The spectrum policy was devised with a focus on the auctioning of high value spectrum such as 3G and 4G, re-framing these resources, and carrying out regulatory monitoring by the MoIC and NTA on use of airwaves by the telecom companies. It had also talked about taking back the frequencies from companies that are using more than government set limit, and fixing frequency for emergency telecommunication management. The policy has not been implemented effectively due to the controversies regarding the appointment of NTA Chairman Digambar Jha and unified telecom licence, according to the Nepal Telecommunications Authority (NTA) which is responsible for implementing the policy. The authority only collected fees based on the policy from the telecom companies and assigned 2 Mhz spectrum to Smart Telecom that received the unified licence or Basic Telephone Service amid the controversy. Ananda Raj Khanal, acting chief of the NTA, said that they were focusing on frequency fee collection in the absence of a Chairman to make policy level decisions. “We are just waiting for the court’s decision regarding the NTA Chairman and the unified licence,” he added. Currently, a case against the appointment of NTA Chairman Digambar Jha is under consideration of the Supreme Court. Similarly, cases regarding the unified licence are also subjected in the court. The existing Telecommunications Act holds NTA Chairman as the key person on making any policy decisions. Based on the policy, the NTA collected around Rs 3 billion spectrum fees from telecom companies and this is considered as one of the best results of the policy impact. The amount collected includes: charges for 3G spectrum assigned to Ncell and NT, fees for additional and maximum spectrums being used by companies and limited mobility service. Previously, there was no specific provision regarding charges on 3G frequency.
Microsoft has agreed a deal to buy Nokia's mobile phonebusiness for 5.4bn euros ($7.2bn; £4.6bn).
Microsoft Corp. struck a $7 billion deal to acquire Nokia Corp.'s core cellphone business, a bold move to try to catch up in a fast-growing mobile business that is now dominated by Samsung and Apple.
The deal comes on the heels of announcing the planned retirement of Microsoft Chief Executive Steve Ballmer. As part of the deal for the devices-and-services business, Microsoft will bring aboard several executives who could be contenders for Mr. Ballmer's job. Nokia will also license its patents and mapping services to Microsoft. Nokia shares jumped 35% on the news, whereas Microsoft's fell more than 5%. The purchase is set to be completed in early 2014, when about 32,000 Nokia employees will transfer to Microsoft. Nokia has fallen behind rivals Samsung and Apple, while critics say Microsoft has been slow into the mobile market. Describing the deal as a "big, bold step forward", Microsoft chief executive Steve Ballmer told the BBC that his company was in the process of transforming itself from one that "was known for software and PCs, to a company that focuses on devices and services". "We've done a lot of great work in the two-and-a-half years that we've been in partnership with Nokia, going literally from no phones to 7.4 million smart Windows phones in the last quarter that was reported," he said. But he admitted: "We have more work to do to expand the range of applications on our product."
The findings were published recently in the early online edition of ACS Nano.
The human body operates under a constant state of martial law. Chief among the enforcers charged with maintaining order is the immune system, a complex network that seeks out and destroys the hordes of invading bacteria and viruses that threaten the organic society as it goes about its work.
The immune system is good at its job, but it's not perfect. Most cancerous cells, for example, are able to avoid detection by the immune system because they so closely resemble normal cells, leaving the cancerous cells free to multiply and grow into life-threatening tumors while the body's only protectors remain unaware.
Shanta Dhar and her colleagues are giving the immune system a boost through their research.
"What we are working on is specifically geared toward breast cancer," said Dhar, the study's co-author and an assistant professor of chemistry in the UGA Franklin College of Arts and Sciences. "Our paper reports for the first time that we can stimulate the immune system against breast cancer cells using mitochondria-targeted nanoparticles and light using a novel pathway."
In their experiments, Dhar and her colleagues exposed cancer cells in a petri dish to specially designed nanoparticles 1,000 times finer than the width of a human hair. The nanoparticles invade the cell and penetrate the mitochondria -- the organelles responsible for producing the energy a cell needs to grow and replicate.
They then activated the nanoparticles inside the cancer cells by exposing them to a tissue-penetrating long wavelength laser light. Once activated, the nanoparticles disrupt the cancer cell's normal processes, eventually leading to its death.
The dead cancer cells were collected and exposed to dendritic cells, one of the core components of the human immune system. What the researchers saw was remarkable.
"We are able to potentially overcome some of the traditional drawbacks to today's dendritic cell immunotherapy," said Sean Marrache, a graduate student in Dhar's lab. "By targeting nanoparticles to the mitochondria of cancer cells and exposing dendritic cells to these activated cancer cells, we found that the dendritic cells produced a high concentration of chemical signals that they normally don't produce, and these signals have traditionally been integral to producing effective immune stimulation."
Dhar added that the "dendritic cells recognized the cancer as something foreign and began to produce high levels of interferon-gamma, which alerts the rest of the immune system to a foreign presence and signals it to attack. We basically used the cancer against itself."
She cautions that the results are preliminary, and the approach works only with certain forms of breast cancer. But if researchers can refine the process, this technology may one day serve as the foundation for a new cancer vaccine used to both prevent and treat disease.
"We particularly hope this technique could help patients with advanced metastatic disease that has spread to other parts of the body," said Dhar, who also is a member of the UGA Nanoscale Science and Engineering Center, Cancer Center and Center for Drug Discovery.
If the process were to become a treatment, doctors could biopsy a tumor from the patient and kill the cancerous cells with nanoparticles. They could then produce activated dendritic cells in bulk quantities in the lab under controlled conditions before the cells were injected into the patient.
Once in the bloodstream, the newly activated cells would alert the immune system to the cancer's presence and destroy it.
"These are the things we can now do with nanotechnology," Dhar said. "If we can refine the process further, we may be able to use similar techniques against other forms of cancer as well."
Fight! Google and Microsoft are locked in a war of words after the Big G banned the YouTube app for Windows Phone a second time.
Google has blocked the new version of the app, for purported violations of its rules, after barring a previous version. But Microsoft has blasted Google's "excuses".
"Google's reasons for blocking our app are manufactured so that we can't give our users the same experience Android and iPhone users are getting," claims Microsoft lawyer David Howard.
"The roadblocks Google has set up are impossible to overcome, and they know it."
Microsoft's first attempt at a YouTube app was blocked by Google for not showing ads. Google then demanded the new app be built in HTML5 rather than as a proprietary Windows Phone app -- despite the fact neither Apple or Android versions of the video app are built in HTML5.
Google also cites problems with the app's branding, and problems with ads. Microsoft says the branding has never been a problem in previous years, and the ad issue is dependent on information from Google that the search company has yet to provide.
Google responds, "Unfortunately, Microsoft has not made the browser upgrades necessary to enable a fully featured YouTube experience, and has instead re-released a YouTube app that violates our terms of service. It has been disabled."
Is Google unfairly penalising Windows Phone over Apple and Android -- or is Microsoft trying to get away with peddling a substandard app?
Sources of this news : http://crave.cnet.co.uk/mobiles/google-and-microsoft-in-war-of-words-over-youtube-app-50012012/
A sandwich-structured composite is a special class of composite materials that is fabricated by attaching two thin but stiff skins to a lightweight but thick core. The core material is normally low strength material, but its higher thickness provides the sandwich composite with high bending stiffness with overall low density. Open- and closed-cell-structured foams like polyvinylchloride, polyurethane, polyethylene or polystyrene foams, balsa wood, syntactic foams, and honeycombs are commonly used core materials. Open- and closed-cell metal foam can also be used as core materials. Laminates of glass or carbon fiber-reinforced thermoplastics or mainly thermoset polymers (unsaturated polyesters, epoxies...) are widely used as skin materials. Sheet metal is also used as skin material in some cases. The core is bonded to the skins with an adhesive or with metal components by brazing together Types of sandwich structures
Metal composite material (MCM) is a type of sandwich formed from two thin skins of metal bonded to a plastic core in a continuous process under controlled pressure, heat, and tension. Recycled paper is also now being used over a closed-cell recycled kraft honeycomb core, creating a lightweight, strong, and fully repulpable composite board. This material is being used for applications including point-of-purchase displays, bulkheads, recyclable office furniture, exhibition stands, and wall dividers. To fix different panels, among other solutions, a transition zone is normally used, which is a gradual reduction of the core height, until the two fiber skins are in touch. In this place, the fixation can be made by means of bolts, rivets, or adhesive. Properties of sandwich structures
The strength of the composite material is dependent largely on two factors: The outer skins: If the sandwich is supported on both sides, and then stressed by means of a force in the middle of the beam, then the bending moment will introduce shear forces in the material. The shear forces result in the bottom skin in tension and the top skin in compression. The core material spaces these two skins apart. The thicker the core material the stronger the composite. This principle works in much the same way as an I-beam does. The interface between the core and the skin: Because the shear stresses in the composite material change rapidly between the core and the skin, the adhesive layer also sees some degree of shear force. If the adhesive bond between the two layers is too weak, the most probable result will be delamination. Application of sandwich structures
Sandwich structures can be widely used in sandwich panels, this kinds of panels can be in different types such as FRP sandwich panel, aluminum composite panel etc. FRP polyester reinforced composite honeycomb panel (sandwich panel) is made of polyester reinforced plastic, multi-axial high-strength glass fiber and PP honeycomb panel in special antiskid tread pattern mold through the process of constant temperature vacuum adsorption & agglutination and solidification.
References , copy from http://en.wikipedia.org/wiki/Sandwich-structured_composite
A duo of British designers' passion for cycling and life-long dreams of flight has spawned one of the world's first flying bicycles -- a conventional bike that converts to an easy-to-operate aircraft that they say can soar to 4,000 feet and cover 75 miles-plus after liftoff.
Yannick Read, 42, and John Foden, 37, who met while living on the same road in Kingston upon Thames, England, quickly learned that aside from both being designers and avid cyclists, they always wanted to fly. The two decided to partner on what they saw as the next step in cycling: aviation.
"Growing up we wanted to be pilots," Read told ABCNews.com. "But training and maintenance and cost are real barriers. We wanted to create an aircraft that was as accessible, relatively speaking, as could be."
Read said he sent a long-shot email to Jim Edmondson with British paramotor manufacturer Parajet in March 2011, in which he outlined the duo's design and concept for their flying bike. To his surprise, he was quickly greeted with an enthusiastic response.
Read and Folden were encouraged to widen their concept and told they could have the Jim Edmondson's assistance and support.
A different kind of flying bicycle recently achieved liftoff in Prague. Read more here.
The duo began to pen out ideas and concepts for what eventually became the Paravelo, a combination of a para-wing and a conventional bike, which tows a trailer carrying a powerful fan. Once in an open clearing, the cyclist can unfurl the para-wing, start the fan with an electric-start motor and, within a matter of yards, be airborne.
Read and Foden began a Kickstarter campaign this week with a goal of reaching £50,000 (about $78,000) to launch what he they're calling "safe, practical and affordable personal flight."
"We built a series of prototypes, and the current one is fairly polished," he said. "The next version, with funding, would be to develop, to ruggedize it, make it more robust, the way we envision it being used -- as a bicycle Monday to Friday. You will be able to commute on the bike. Then, make use of the flying capability."
Read says the latest prototype, which he describes as the size of a flight suitcase, can fit in the trunk of a car. "It's a niche product. We're not going to see cities with these swarming through the skies," Read said. "It's an unusual and adventurous evolution for the bicycle."
But is the flying bicycle, which in the U.K. doesn't require a special license to operate and is unregulated, totally safe for the average user? Read says it is.
"It's safe because of low air speeds. You're flying about 25 miles per hour, that low speed makes it so safe," he said. "In terms of controlling, it's like controlling a little Vespa scooter."
Training for flight in the Paravelo, Read says, can be completed in as little as seven days and, he adds, the vehicle could be useful for a number of professions, including park rangers and border patrol, as well as being a great addition for the adventurous weekender.
The prototype even features a built-in tent for what read calls "flamping," or flying and camping.
As for his and Foden's crowd-funding campaign, Read sees it not just as a way to help his dream take flight, but as exploratory means to gauge reaction and interest.
"Were being up front and saying that it looks pretty, and it works," he said. "We want to show it's a robust, practical, usable machine, that won't work just the day you buy it, but for many, many years.
Samsung's Galaxy S4 line gets another family member in the Samsung Galaxy S4 Active, a hardened, ruggedized spin off of the company's flagship model.
Waterproof to a meter below the surface and for up to 30 minutes, the Active carries on computing with Android 4.2 Jelly Bean, Samsung's TouchWiz interface, and a 1.9GHz quad-core processor, the same as its more delicate Galaxy S4 sibling.
Many of its other specs are also similar, but one that stands out is the camera, whose 8-megapixel module can take this bad boy under the waves with its brand-new aqua mode.
I love that Samsung has finally made waterproofing a feature rather than a fail-safe against damage. A lot of other rugged handsets that make the same waterproof claims stop short of turning the capability into a real benefit.
The handset's lower-caffeinated camera compared with the original GS4's may seem like a downgrade for some, but for the S4 Active's price of $199.99 on AT&T, its rugged features are a pretty fair compromise. We'll know a lot more when the phone launches on June 21 (see the teaser video above). Our team will also plan to get our hands on the Galaxy S4 Active on June 20 in London.
Since the Galaxy S4 Active arrives this summer, I have a feeling we're going to have a heck of a time testing out its aqua camera mode firsthand. Pool party, anyone?
This news is copy from http://reviews.cnet.com/smartphones/samsung-galaxy-s4-active/4505-6452_7-35783536.html
A new study confirms directly what scientists previously knew only indirectly: The poisonous "rotten egg" gas hydrogen sulfide is generated by our body's growing cells.
Hydrogen sulfide, or H2S, is normally toxic, but in small amounts it plays a role in cardiovascular health.
In the new study, chemists developed a chemical probe that reacts and lights up when live human cells generate hydrogen sulfide, says chemist Alexander R. Lippert, Southern Methodist University, Dallas. The discovery allows researchers to observe the process through a microscope.
The researchers captured on video the successful chemical probe at work, said Lippert, an assistant professor in the SMU Department of Chemistry.
"We made a molecular probe that, when it reacts with hydrogen sulfide, forms a fluorescent compound that can be visualized using fluorescence microscopy," Lippert said. "This is the first time that endogenously generated hydrogen sulfide has been directly visualized in a living system. This confirms a lot of hypotheses that scientists have, but no one had the tools to directly detect it in real time."
H2S is one of several small gaseous molecules increasingly recognized as key signaling molecules in the body. For example, H2S helps reduce high blood pressure. Scientists discovered in the past decade that cells in the human body generate small quantities of H2S molecules, which in turn deliver information to proteins. The proteins act on the information to perform critical functions in the body.
Previously, scientists couldn't observe H2S being generated in live cells. As a result, researchers faced challenges when studying hydrogen sulfide in living systems, Lippert said. The new discovery now provides a tool to view directly how and when hydrogen sulfide is generated, he said. Lippert and study co-author chemist Vivian S. Lin made the discovery.
Discovery provides research tool for scientists to observe H2S in live cells
"Having the tools to do this in living systems is going to open up a lot of possibilities and experiments for scientists," Lippert said. "As a tool, this will allow researchers to ask questions that weren't possible before."
Lippert's real-time video features live human cells, taken from the lining of blood vessels and treated with the chemical probe and with a protein known to promote cell growth. Once the cells start generating H2S, they behave like squiggly fluorescent green worms.
The researchers' scientific article, "Cell-trappable fluorescent probes for endogenous hydrogen sulfide signaling and imaging H2O2-dependent H2S production," was published online in theProceedings of the National Academy of Sciences.
Lippert and Lin authored the research with Christopher J. Chang, principal investigator. Lin is a PhD candidate at the University of California at Berkeley. Chang is with the Howard Hughes Medical Institute, University of California at Berkeley. Lippert and Lin carried out the research in Chang's UC Berkeley laboratory.
H2S -- along with nitric oxide, carbon monoxide and others in this emerging class of gaseous signaling molecules -- assists the body's large proteins.
Large proteins do much of the functional work in the body, such as digesting the food we eat and harnessing the energy in the oxygen we breathe. Their size, however, forces them to move slowly inside the cell. In contrast, H2S and other small gaseous molecules diffuse quickly and easily across cellular membranes, enabling them to travel much faster and rapidly deliver information that mediates critical functions, such as blood pressure regulation, Lippert said.
For their experiments, Lippert and Lin placed living endothelial cells cultured from the internal lining of a blood vessel into a petri dish under a microscope.
Lippert and Lin then added a chemical solution containing an azide-functionalized organic molecule that they'd synthesized to act as a molecular probe. They gave the cells time to absorb the probe, then added a protein solution known to stimulate blood vessel formation. As the cells initiated blood vessel formation, H2S was generated. In reaction, the scientists observed a steady increase in the probe's fluorescence.
"Essentially we're observing the initial events that lead to the building of new blood vessels, a process that's active in babies as they develop, or in women during their menstruation cycles," Lippert said. "We see the cells get really bright as they start moving around and ruffling their membranes. That's the H2S being formed. In the control group, which weren't stimulated with the growth protein, they don't get any brighter and they don't move around."
The discovery provides new insights that can help scientists attack diseases, such as cancer, by starving the nutrient supply to a tumor, Lippert said.
"When tumors grow they need a lot of blood support because they need the nutrients to support their rapid growth," he said. "If you can stop blood vessel formation you could starve the tumor and the tumor will die. So inhibiting H2S formation might be a way to treat cancer using this method."
This news is copy originally from : http://www.sciencedaily.com/releases/2013/06/130618131854.htm
