Organic photochemistry from 1 to 4 eV
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| Anzahl der Teile | 163 | |
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| Lizenz | CC-Namensnennung - keine Bearbeitung 4.0 International: Sie dürfen das Werk in unveränderter Form zu jedem legalen Zweck nutzen, vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen. | |
| Identifikatoren | 10.5446/50411 (DOI) | |
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00:00
Eau de CologneChemische ReaktionFärbenKohlendioxidMolekülOrganische ChemieRadioaktiver StoffSäureWasserSymptomatologieEau de CologneLammfleischChemische VerbindungenAktivierung <Chemie>AzokupplungFarbenindustrieFluorideFunktionelle GruppeGraphiteinlagerungsverbindungenNatriumRadikalfängerClaus-VerfahrenACEEnhancerFülle <Speise>Biologisches LebensmittelSeifenherstellungQuellgebietElektron <Legierung>Alkoholische LösungChemische ForschungPrimärer SektorPhotochemieOrganisches LösungsmittelWässrige LösungAbsorptionsspektrumAcetonAtomorbitalCarboxylateHydrophobe WechselwirkungCarboxylierungPhenylacetatChemische FormelElektronenakzeptorInduktorBesprechung/Interview
03:55
ExcimereWasserfallGolgi-ApparatChemisches Experiment
04:10
KohlendioxidMischanlageKettenlänge <Makromolekül>Setzen <Verfahrenstechnik>Alkoholische LösungChemisches Experiment
04:18
KohlendioxidSetzen <Verfahrenstechnik>Neutrale LösungChemisches Experiment
04:32
AlterungBiosyntheseChemische StrukturMolekülOrganische ChemiePhotochemieKomplikationKohlenstofffaserChemische VerbindungenAzokupplungMethylgruppeReaktivitätIonenbindungSystemische Therapie <Pharmakologie>QinghaosuNahrungsergänzungsmittelArzneimittelTiermodellCobaltoxideKlinisches ExperimentBiologisches LebensmittelChemisches ExperimentMolekülstruktur
05:54
ArzneimittelChemische ReaktionMolekülOrganische ChemiePharmazieRadioaktiver StoffGesundheitsstörungEnzymkinetikChemische VerbindungenAbsorptionsspektrumAnthrachinonfarbstoffAzokupplungCobaltoxideElektronentransferGraphiteinlagerungsverbindungenInterkristalline KorrosionPhthiseSetzen <Verfahrenstechnik>PulverTransformation <Genetik>IonenbindungSpezies <Chemie>EnhancerOktanzahlDerivateAktivität <Konzentration>EnzymFärbenFleischerFormaldehydZusatzstoffMeereisFlussQuerprofilResistenzTiermodellOptische AktivitätKryptandenChemisches Experiment
08:47
Chemische ReaktionCobaltoxideSubstrat <Chemie>QuerprofilPhthiseReaktionsgleichungSystemische Therapie <Pharmakologie>DruckabhängigkeitHalbedelsteinChemisches Experiment
09:00
Eau de CologneReaktionsgleichungDruckabhängigkeitEnzymkinetikChemischer ProzessCobaltoxidePhthiseIsoliergasChemisches Experiment
09:24
Organisches LösungsmittelDeuteriumChemische ReaktionCobaltoxideDurchflussWasserfallGletscherzungeChemisches Experiment
09:40
Organische ChemieChemische ForschungISO-Komplex-HeilweiseEau de CologneChemische ReaktionPhotochemieGletscherzungeGesundheitsstörungChemische ForschungChemisches ExperimentVorlesung/KonferenzBesprechung/Interview
Transkript: Englisch(automatisch erzeugt)
00:12
Welcome to the Department of Chemistry at the University of Cologne to our research group. We are working on applications of organic photochemistry as you can see here,
00:24
indicated by the symbol of the Sun. So we are using electromagnetic radiation in order to induce chemical reactions. And when you think about organic photochemistry, you always have to think about excitation, energies and excitation wavelength. And one of the well-known wavelengths for excitation of organic molecules,
00:45
which are colored, is 589 nm. This is the wavelength of the very well-known sodium street lamp, which emit yellow light. And this yellow light of 589 nm has the energy appropriately of 2 eV.
01:01
So we have 2 eV energy available for exciting organic molecules. And this is the starting point where we can try to use dye stuffs, which absorb in the visible region for organic reactions. Now we can go into two directions. We can go to the right using lower energy light. We can go to the left using higher energy light.
01:23
For example, we can use 308 nm, which is energy source for photons for electromagnetic radiation, which has about 4 eV energy. And this energy is emitted from a lamp, not a sodium lamp. It's a xenochloride aximal lamp, which we also use in the laboratory to excite organic molecules.
01:44
The question is, what can we do with it? Of course, we can excite electrons. We are not in the region where we excite rotations or vibrations. We excite electrons from the ground state, occupied orbitals into unoccupied orbitals. And in an extreme version, of course, we can detach the electrons. So we can oxidize our molecules to the corresponding radical cations,
02:05
if there is a corresponding electron acceptor. And one of the extremes way or extremist way of exciting electrons, of course, is photodetachment. So we can ionize organic molecules to generate radical anions and radical cations. And one of the applications where we use this xenochloride aximal radiation source
02:24
is the photodetachment of electrons from organic carbonic acids and carboxylic acids. And one of the groups which are important for this kind of application is the group of polyfluorated organic compounds.
02:41
And the abbreviation is PFC. One of the most known compounds is the polyfluoroctanoic acid, which is a highly reluctant, a very stable organic perfluorinated compound. This is the molecular formula of this compound in aqueous solution. It's normally the carboxylic acid anion, which exists because that is about one.
03:04
Now this compound under irradiation with xenochloride in the presence of an appropriate electron acceptor can be oxidized to the corresponding radical, carboxylic radical, which then can be degradated to fluoride and carbon dioxide. And by this way, this highly stable compound can be degradated by a photochemical method.
03:23
And we will show you this in the laboratory by a setup where we can use this kind of excitation in a one-liter aximal radiation falling from the source. Hello, my name is Nestor Nazarov. I would like to show you a photodecarboxylation
03:40
from a three-fluor of material phenyl acetic acid in water and aceton as core solvent in the presence of N-methylimide. I make the reaction on. This is our xenochloride excimer.
04:00
We have very specially apparatus with a falling film. Falling film is very important for constant temperature, for constant light intensity reaching to irradiation solution, and for good mixing.
04:21
For kinetic controlling, I measure a carbon dioxide formation with this carbon dioxide sensor. And for pH value change, I use this pH electrode. A second example of organic photochemistry that I would like to show to you
04:43
is the synthesis of a complex organic molecule and the idea that this organic molecule gave us to make simpler molecules. The structure is a complicated sesquiterpene lactone, and the name of it is artemisinin.
05:03
It has a couple of methyl groups, this position, this position, and this position. But the most important thing about this compound is an oxygen-oxygen bridge over these two carbons. So you can see the special feature of this compound
05:21
is a peroxy bridge as a component of a six-member ring, which I indicated in yellow, a 1, 3, 4, tri-oxane system. So the special feature is the oxygen-oxygen bond, and one can think about how to introduce this bond into organic molecules
05:40
in order to establish the reactivity, the pharmaceutical reactivity of this compound. Now, artemisinin nowadays is something like a lifestyle truck. So you can go into the internet and you can really purchase artemisinin in a very highly pure form, and you can use it for many applications,
06:01
but the most important application, which is known from Chinese folk medicine since more than 2,000 years, is its activity against malaria. So it's one of the highest active malaria pharmaceuticals. Chemists have for a long time now tried to establish the pharmacophore of this compound,
06:22
and the pharmacophore is indicated here by the colors, and they tried to synthesize derivatives of these compounds in order to increase the reactivity, the stability, and to cope with the increasing resistances, which has started in the last years, against other malaria components.
06:42
Now, in order to introduce oxygen-oxygen bonds into organic molecules, we have a series of possibilities, and one of the simplest ways to do this is the activation of normal air oxygen, normal triplet oxygen. Triplet oxygen under most conditions is non-reactive, especially in the absence of enzymes,
07:01
but by a formally easy transformation into an electronically excited state, indicated by this arrow. Now, the difference in energy between the ground state and the excited state corresponds to an excitation wavelength of 1,270 nanometers, which is only about one electron volt. You can generate this near-infrared radiation
07:22
and try to excite triplet oxygen, which is impossible. It doesn't absorb this radiation. So, that's a problem. How to excite triplet oxygen into singlet oxygen? Now, one way which is used in the laboratory is to use a molecule which we call a sensitizer.
07:41
Now, if you use this sensitizer, the sensitizer can transfer its energy to triplet oxygen, and the ground state is reproduced, and the ground state then again can be excited by light to an excited sensitizer molecule. By this way, by a very simple way of dye energy transfer to triplet oxygen, you generate your reactive species,
08:01
which eventually can give rise to product formation like these kind of compounds or simpler derivatives. In the laboratory, we have a couple of different ways to do this, by which we can measure the rate of the singlet oxygen production, by which we can measure also the rate of oxygen consumption. And the more simple ways are just used to transfer organic molecules
08:24
into oxidized species without measuring anything. And we will try to show this to you in the following. Hello, my name is Sarah Silner, and I show you a special apparatus for photo-oxygenation. It's a closed system fulfilled with one millimole of oxygen, and it was designed for monitoring the kinetics of photo-oxygenation reactions.
08:43
The mercury lamp initiates the interaction between the sensitizer and triplet oxygen to generate singlet oxygen, which is needed for the reaction with the substrate. The uptake of oxygen leads to an underpressure in the system, and so this little stone activates the light barrier,
09:02
and the separating funeral balances the pressure in the system, and in this way we can measure the consumption of oxygen and determine the kinetics. Here you see an easier installation we have for our photo-oxygenation process. You cannot measure kinetics here, but the whole installation is very easy.
09:21
You only have to switch on an LED light. The starting material is prepared in a deuterium solvent. As a photosensitizer, we use tetraphenylporphyrin here, and we add a consistent oxygen flow to provide enough oxygen for our reaction.
09:40
The advantage here is that we can always measure an NMR, see if our reaction is completed, and then put it back in front of our light. Photochemistry is much more than only the two examples you just saw. If you want to read more about photochemistry and its applications, I recommend that you read for example this issue of Ballstein JUC.
10:02
Thank you very much for watching our movie.