Charge separation in a molecule consisting of two identical atoms: Size matters

Physicists from the University of Stuttgart show the first experimental proof of a molecule consisting of two identical atoms that exhibits a permanent electric dipole moment. This observation contradicts the classical opinion described in many physics and chemistry textbooks.

The work was recently published in the journal Science.

A dipolar molecule forms as a result of a charge separation between the negative charged electron cloud and the positive core, creating a permanent electric dipole moment. Usually this charge separation originates in different attraction of the cores of different elements onto the negative charged electrons. Due to symmetry reasons homonuclear molecules, consisting only of atoms of the same element, therefore could not possess dipole moments.

However, the dipolar molecules that were discovered by the group of Prof. Tilman Pfau at the 5th Institute of Physics at the University of Stuttgart do consist of two atoms of the element rubidium. The necessary asymmetry arises as a result of different electronically excited states of the two alike atoms. Generally this excitation will be exchanged between the atoms and the asymmetry will be lifted. Here this exchange is suppressed by the huge size of the molecule, which is about 1000 times larger than an oxygen molecule and reaches sizes of viruses. Therefore the probability to exchange the excitation between the two atoms is so small that it would statistically only happen once in the lifetime of the universe. Consequently, these homonuclear molecules possess a dipole moment. A permanent dipole moment additionally requires an orientation of the molecular axis. Due to their size the molecules rotate so slowly that the dipole moment does not average out from the viewpoint of an observer.

Physicists from the University of Stuttgart succeeded in experimentally detecting the dipole moment. They measured the energy shift of the molecule in an electric field by laser spectroscopy in an ultra cold atomic cloud. The same group caused worldwide a stir when they created these weakly bound Rydberg molecules for the first time in 2009. The molecules consist of two identical atoms whereof one is excited to a highly excited state, a so-called Rydberg state. The unusual binding mechanism relies on scattering of the highly excited Rydberg electron of the second atom. So far theoretical descriptions of this binding mechanism did not predict a dipole moment. However, the scattering of the Rydberg electron of the bound atom changes the probability distribution of the electron. This breaks the otherwise spherical symmetry and creates a dipole moment. In collaboration with theoretical physicists from the Max-Plank-Institute for the Physics of Complex Systems in Dresden and from the Harvard-Smithonian Center for Astrophysics in Cambridge, USA, a new theoretical treatment was developed that confirms the observation of a dipole moment.

The proof of a permanent dipole moment in a homonuclear molecule not only improves the understanding of polar molecules. Ultra cold polar molecules are also promising to study and control chemical reactions of single molecules.

Story Source:

The above story is reprinted from materials provided by University of Stuttgart.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

W. Li, T. Pohl, J. M. Rost, S. T. Rittenhouse, H. R. Sadeghpour, J. Nipper, B. Butscher, J. B. Balewski, V. Bendkowsky, R. Low, T. Pfau. A Homonuclear Molecule with a Permanent Electric Dipole Moment. Science, 2011; 334 (6059): 1110 DOI: 10.1126/science.1211255

Human skin yields stem cell-like cells

These skin cells, called keratinocytes, form the outermost layer of skin and can be cultured from discarded skin tissues or biopsy specimens.

The findings, published in the Nov. 4 edition of the peer-reviewed Journal of Biological Chemistry, may be beneficial for individuals with limited sources of endogenous stem cells.

The gene known as ?Np63? is highly synthesized in regenerating cells of various tissues. The UCLA researchers found that introducing ?Np63? into skin keratinocytes makes them lose their skin-cell characteristics and de-differentiate to resemble mesenchymal stem cells (MSCs), undifferentiated cells that can self-renew and differentiate to yield specialized cells of various tissue types.

MSCs may serve as an internal repair system by replenishing cells needed for tissue regeneration and homeostasis and are currently being investigated for a number of regenerative therapeutics.

The conversion of keratinocytes into mesenchymal-like cells involves a process known as epithelial-mesenchymal transition. This is the first study to show that the gene ?Np63? triggers this process in human skin keratinocytes and that the transformed cells acquire multipotent stem cell characteristics.

Since the skin cells transformed by ?Np63? are induced to acquire the mesenchymal and stem cell characteristics, the research team named them "induced mesenchymal stem cells," or iMSCs. Specifically, the researchers demonstrated that iMSCs can be triggered to form bone-like tissues or become fat tissues in a laboratory setting.

Dr. Mo K. Kang, the Jack A. Weichman Chair of Endodontics at the UCLA School of Dentistry and a member of the research team, said the finding had great significance for human health.

"Since iMSCs may be obtained by taking a small punch-biopsy of skin tissues from patients, these cells are an easily accessible, patient-specific source of stem cells, which can be used for regenerative purposes," Kang said.

Stem cell-based therapies are currently being developed to treat degenerative conditions such as heart disease, diabetes, neuronal disorders and liver diseases. Many of these diseases are strongly associated with aging. Endogeneous MSCs found in various tissues, such as bone marrow, fat tissues and, in certain cases, dental tissues such as dental pulp, lose their regenerative potential during the aging process.

"It is possible that iMSCs retain their stem-cell characteristics even when derived from aged patients," Kang said. "In such cases, this new approach may be useful, especially for geriatric patients or individuals with limited therapeutic value of their endogenous stem cells."

"The UCLA School of Dentistry is very proud to be at the forefront of this research inquiry, which may facilitate future advances in regenerative dentistry and medicine," said Dr. No-Hee Park, dean of the UCLA School of Dentistry and one of the study's co-authors. "While the focus of this study was on the use of adult stem cells to regenerate dental tissue, including dental pulp and periodontal ligament, these findings could lead to further development of a variety of cell-based therapies."

Provided by University of California

Stabilizing entangled spaghetti-like materials: Controling forces between oppositely charged polymers opens new route for gene therapy vectors

Gene therapy can only be effective if delivered by a stable complex molecule. Now, scientists have determined the conditions that would stabilise complex molecular structures that are subject to inherent attractions and repulsions triggered by electric charges at the surfaces of the molecules, in a study about to be published in the European Physical Journal E, by Valentina Mengarelli and her colleagues from the Solid State Physics Laboratory at the Paris-Sud University in Orsay, France, in collaboration with Paris 7 and Évry Universities scientists.

The authors studied soluble complexes made of negatively charged DNA or another negatively charged polymer -- polystyrene-sulfonate (PSSNa) -- and a so-called condensation agent, which is a negatively charged polymer, known as linear polyethyleneimine (PEI). PEI participates in the condensation process by tying onto a molecule such as DNA, like tangled hair, to form an overall positively charged DNA/polymer complex structure. Previous research focused mainly on non-soluble complexes, while the few attempts at focusing on soluble complexes dealt either with smaller polymers or those with a weaker electric charge, which may therefore be easier to stabilise.

The French team thus confirmed experimentally that the complexation process does not depend on the rigidity of the original molecule, be it DNA or PSSNa, but on the positive/negative electric charge ratio and on the polymer concentrations. It is the interactions between electrically charged parts within the complex that govern its properties. When the condensation agent is in excess, the positively charged complex is then attracted to negatively charged biological cell membranes. This could be used to deliver the DNA into a targeted cell nucleus as part of gene therapy treatment.Future work will focus on using long DNA molecules and novel polymers to form complexes of controlled size and electric charge for gene therapy.

Story Source:

The above story is reprinted from materials provided by Springer.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Mengarelli V, Auvray L, Pastré D, and Zeghal M,. Charge inversion, condensation and decondensation of DNA and Polystyrene sulfonate by polyethylenimine. European Physical Journal E (EPJE), 2011; 34, 127 DOI: 10.1140/epje/i2011/11127-3

Engineered botulism toxins could have broader role in medicine

Edwin Chapman and colleagues explain that toxins, or poisons, produced by Clostridium botulinum bacteria, cause of a rare but severe form of food poisoning, are the most powerful toxins known to science. Doctors can inject small doses, however, to block the release of the neurotransmitters, or chemical messengers, that transmit signals from one nerve cell to another. The toxins break down a protein in nerve cells that mediates the release of neurotransmitters, disrupting nerve signals that cause pain, muscle spasms and other symptoms in certain diseases. That protein exists not just in nerve cells, but in other cells in the human body. However, these non-nerve cells lack the receptors needed for the botulinum toxins to enter and work. Chapman's group sought to expand the potential use of the botulinum toxins by hooking it to a molecule that can attach to receptors on other cells.

Their laboratory experiments showed that these engineered botulinum toxins do work in non-nerve cells, blocking the release of a protein from immune cells linked to inflammation, which is the underlying driving force behind a range of diseases. Such botulinum toxin therapy holds potential in a range of chronic inflammatory diseases and perhaps other conditions, which could expand the role of these materials in medicine.

More information: “Retargeted Clostridial Neurotoxins as Novel Agents for Treating Chronic Diseases” Biochemistry, 2011, 50 (48), pp 10419–10421. DOI: 10.1021/bi201490t

Provided by American Chemical Society (news : web)

'Left-handed iron corkscrews' point the way to new weapon in battle against superbugs like MRSA

Researchers have created a new synthetic class of helix-shaped molecules which they believe could be a key tool in the worldwide battle against antibiotic resistance.

By twisting molecules around iron atoms they have created what they term 'flexicates' which are active against MRSA and E-coli - but which also appear to have low toxicity, reducing the potential for side effects if used in treatment.

The work is published in Nature Chemistry.

The new structures harness the phenomenon of 'chirality' or 'handedness' whereby the corkscrew molecules could be left-handed or right-handed.

By making the most effective 'hand' to attack a specific disease, the University of Warwick research paves the way towards a more targeted approach to killing pathogens.

In the case of E-coli and MRSA, it is the left 'hand' which is most effective.

Professor Peter Scott of the University of Warwick's chemistry department said although this particular study concentrated on flexicates' activity against MRSA and E-coli, the new method of assembly could also result in new treatments for other diseases.

"It's a whole new area of chemistry that really opens up the landscape to other practical uses.

"These new molecules are synthetically flexible, which means that with a bit of tweaking they can be put to use against a whole host of different diseases, not just bugs like MRSA which are rapidly developing resistance to traditional antibiotics.

"Flexicates are also easier to make and produce less waste than many current antibiotics."

Scientists have long been able to copy nature's corkscrew-shaped molecules in man-made structures known as helicates – but they have thus far not been able to use them in fighting diseases.

One of the key issues is the problem of handedness.

Sometimes 'left-handed' molecules in drugs are the most effective at combating some disease, while sometimes the 'right-handed' version works best.

Until now, scientists working with helicates have found it difficult to make samples containing just one type of corkscrew; either the right- or left-handed twist.

But with flexicates, the University of Warwick scientists have succeeded in making samples containing just one type of twist – resulting in a more targeted approach which would allow the drug dosage to be halved.

And flexicates solve other problems encountered by helicates, as they are easier to optimise for specific purposes, are better absorbed by the body and are also easier to mass-produce synthetically.

Professor Scott said: "Drugs often have this property of handedness - their molecules can exist in both right and left handed versions but the body prefers to use only one of them."

"For this reason, drug companies have to go to the trouble of making many traditional molecules as one hand only.

"What we have done is solve the 'handedness' problem for this new type of drug molecule.

"By getting the correct hand we can halve the drug dose, which has the benefits of minimising side effects and reducing waste.

"For patients, it's safer to swallow half the amount of a drug.

"Our work means that we can now make whichever hand of the corkscrew we want, depending on the job we require it to do."

More information: The study, entitled Optically pure, water-stable metallo-helical 'flexicate' assemblies with antibiotic activity, is published in Nature Chemistry. http://dx.doi.org/ … 8/NCHEM.1206

Provided by University of Warwick (news : web)