Name: coulomb explosion imaging as a tool to distinguish between stereoisomers
Uploaded: 2017-08-18T15:00:00.000+00:00
Duration: 8 min 51 s
Description: Watch this Scientific Journal Video about Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers at JoVE.com

Biz Robert Berger (Philipps-Universität Marburg, Almanya) için teşekkür ederiz bizim veri ve moleküler sembolik yorumu hakkında tartışmalar genel olarak ilham verici. Örnek sağlamak için ZHAW Wädenswil (İsviçre) Julia Kiedrowski, Alexander Schießer ve Michael Reggelin TU Darmstadt (Almanya), gelen yanı sıra Benjamin Spenger, Manuel Mazenauer ve Jürgen Stohner için minnettarız.
Proje Hessen devlet girişimi tarafından bilimsel ve ekonomik mükemmellik için odak ELCH (kiral sistemlerinin Electron dynamics) ve Federal Bakanlığı Eğitim ve araştırma (BMBF) altında desteklenmiştir. MS finansal destek Adolf Messer Vakfı tarafından kabul eder.

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H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+the+Absolute+Configuration+of+a+Chiral+Epoxide+in+the+Gas+Phase.">Imaging the Absolute Configuration of a Chiral Epoxide in the Gas Phase.</a> Science. 342 (6162), 1084-1186 (2013).</li><li>D&#246;rner, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cold+Target+Recoil+Ion+Momentum+Spectroscopy:+a+'momentum+microscope'+to+view+atomic+collision+dynamics.">Cold Target Recoil Ion Momentum Spectroscopy: a 'momentum microscope' to view atomic collision dynamics.</a> Physics Reports. 330, 95-192 (2000).</li><li>Ullrich, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recoil-ion+and+electron+momentum+spectroscopy:+reaction-microscopes.">Recoil-ion and electron momentum spectroscopy: reaction-microscopes.</a> Rep. 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Phys. 66 (9), 1463-1545 (2003).</li><li>Jagutzki, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+Hit+Readout+of+a+Microchannel+Plate+Detector+With+a+Three-Layer+Delay-Line+Anode.">Multiple Hit Readout of a Microchannel Plate Detector With a Three-Layer Delay-Line Anode.</a> IEEE Trans Nucl Sci. 49 (5), 2477-2483 (2002).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> RoentDek GmbH MCP Delay Line Detector Manual. , (2017).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> RoentDek GmbH The RoentDek Constant Fraction Discriminators CFD8c, CFD7x, CFD4c, CFD1c and CFD1x. , (2017).</li><li>Zeller, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+the+He2+quantum+halo+state+using+a+free+electron+laser.">Imaging the He2 quantum halo state using a free electron laser.</a> PNAS. 113 (51), 14651-14655 (2016).</li><li>Pitzer, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stereochemical+configuration+and+selective+excitation+of+the+chiral+molecule+halothane.">Stereochemical configuration and selective excitation of the chiral molecule halothane.</a> J. Phys. B.: At. Mol. Opt. Phys. 49 (23), 234001 (2016).</li><li>Hine, J., Dowell, A. M., Singley, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carbon+Dihalides+as+Intermediates+in+the+Basic+Hydrolysis+of+Haloforms:+IV+Relative+Reactivities+of+Haloforms.">Carbon Dihalides as Intermediates in the Basic Hydrolysis of Haloforms: IV Relative Reactivities of Haloforms.</a> J. Am. Soc. Chem. 78, 479-482 (1956).</li><li>Wales, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+coincidence+detection+algorithm+for+improving+detection+rates+in+coulomb+explosion+imaging.">A coincidence detection algorithm for improving detection rates in coulomb explosion imaging.</a> Nucl. Instr. Meth. in Phys. Res. A. 667, 11-15 (2012).</li><li>Kastirke, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Konstruktion und Aufbau einer UHV-tauglichen COLTRIMS-Kammer. , (2014).</li><li>Calegari, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Charge+migration+induced+by+attosecond+pulses+in+bio-relevant+molecules.">Charge migration induced by attosecond pulses in bio-relevant molecules.</a> J. Phys. B.: At. Mol. Opt. Phys. 49 (14), 142001 (2016).</li><li>Gaie-Levrel, F., Garcia, G. A., Schwell, M., Nahon, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=VUV+state-selected+photoionization+of+thermally-desorbed+biomolecules+by+coupling+an+aerosol+source+to+an+imaging+photoelectron/photoion+coincidence+spectrometer:+case+of+the+amino+acids+tryptophan+and+phenylalanine.">VUV state-selected photoionization of thermally-desorbed biomolecules by coupling an aerosol source to an imaging photoelectron/photoion coincidence spectrometer: case of the amino acids tryptophan and phenylalanine.</a> Phys. Chem. Chem. Phys. 13, 7024-7036 (2010).</li><li>Ablikim, U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+absolute+geometries+of+cis+and+trans+molecular+isomers+by+Coulomb+Explosion+Imaging.">Identification of absolute geometries of cis and trans molecular isomers by Coulomb Explosion Imaging.</a> Sci. Rep. 6, 38202 (2016).</li></ol>

Yazarlar hiçbir rakip ilgi bildirin.

Bileşenleri çeşitli nedeniyle, özellikle vakum tekniği, parçacık algılama, hızlı elektronik ve veri analizi alanlarında teknik uzmanlık oldukça yüksek düzeyde bir COLTRIMS kurulum gerektirir. Kur tarafından performans ve diatomic veya triatomic türler üzerinde bir ölçüm analiz örneğin düzgün çalışıyorsa, karmaşık türler soruşturma açmadan önce bu nedenle iyice kontrol edilmelidir.
Yoğunluk ve lazer bakliyat ve moleküler jet ile örtüşme süresi o...

Sembolik büyüleyici araştırmacılar 150 yıldan fazla oldu bizim doğanın bir özelliktir. 19th yüzyıl, Pasteur, van't Hoff ve diğer moleküller süper-bizim sol ve sağ ellerini gibi imposable - olmayan iki ayna görüntüsü yapıları meydana gelebilir keşfetti. Bu özellik 'kiral', 'el' için Yunanca kelime olarak adlandırdığı oldu.
Şimdiye kadar hiçbir fark termodinamik özellikleri veya sol ve sağ el formları (iki ' enantiomers') enerji seviyeleri tespit edilmiştir. Belirli bir örnek el kullanımı çözümlemek amacıyla ve enantiomers ayırmak için kiral diğer molekülleri ile etkileşimi, örneğin çeşitli chromatographical yaklaşımlar yapılır gibi kullanılabilir. 1 Chiroptical yöntemleri (titreşim) dairesel dichroism, (V) CD ve optik çevirme dağılım, ORD, gibi düzenli olarak enantiomers arasında ayırt etmek için istihdam edilmektedir. 2
Bu mikroskobik yapısı belirlenmesi gelince, bu tekniklerin ek bilgiler, örneğin kuantum kimyasal hesaplamalar yer gerektirir. Doğrudan mutlak yapılandırması belirlemek için yaygın olarak kabul edilen tek anormal x-ışını kırınım tekniğidir. 3
Son zamanlarda basit kiral türlerin mutlak yapılandırma Coulomb patlama Imaging tarafından belirlenebilir gösterilmiştir. 4 , 5 bu yaklaşım, gaz aşamasında moleküller vardır çarpma iyonize kalan çekirdek güçlü her diğer püskürtmek böylece. Bu itme moleküller hızlı parçalanma ('patlama') yol açar. Yönü ve parça momenta ilişkili – küçük moleküller için molekül yapısını büyüklüğü ivme yön şaşırtıcı derecede iyi bond eksenleri karşılık gelir. Coulomb patlama moleküler yapısı tayini için moleküler iyon kirişler Hızlandırıcı üzerinden kullanarak öncülük. 6 bu ışın folyo tekniği son zamanlarda da be kiral tanıma için uygulanan. 7
Aksine anormal x-ışını kırınım, kristal ama gaz aşamasında sağlanan örnek olmamalıdır. Bu uçucu türler için ideal ve böylece x-ışını kırınımı için tamamlayıcı Coulomb patlama yaklaşım sağlar. Belirli durumlarda, el kullanımı için bireysel moleküllerin bile belirlenebilir.
Uygulamada, moleküler yapısı tam olarak yeniden inşası metan türevleri, örneğin merkezi bir karbon ve farklı ornatıklarla moleküller için bile zor kanıtlamıştır. Bu gerçeği parçaları arasındaki etkileşimi tam olarak Coulombic değil ve tüm bağlarını aynı anda koparmak için atfedilir. Özellikle enantiomers arasında ayırt edilebilmesi için stereochemical bilgi elde etmek için bu yeniden yapılanma Neyse ki gerekli değildir. Bunun yerine, farklı parçalarının ivme vektörel çizimler sol ve sağ el molekülleri için ayrı bir miktar vermeye ilişkili olabilir. Güvenilir sonuçlar elde etmek için en az dört parça momenta kaydedilmesi gerekiyor.
Bu ivme bilgi ölçmek için bir- ve sadece bir-moleküler ayrılık parçalardan bir tek ölçüm adımda tespit gerekir. Bu durum genellikle 'çakışık algılama' denir. Buna ek olarak, emisyon yönergeleri analiz edilecek tutarları zaman ve parçanın konumunu kaydetmek için pratik bir liste modu veri biçiminde etkisi var.
Atomik ve moleküler fizik Elektrostatik Spektrometreler yığın ayırma ve zaman ve pozisyon duyarlı çok isabet dedektörleri için istihdam ederek bu yaklaşım ölçü uygulayan teknikleri geliştirilmiştir. COLTRIMS (soğuk hedef geri tepme iyon Momentum spektroskopisi) kurulum-olarak da bilinen tepki mikroskop en önemli örnektir. 8 , 9 bir kroki böyle bir deney için şekil 1' de verilmiştir. Elektron de kaydedebilirsiniz bir standart COLTRIMS aksine, Coulomb patlama Imaging yalnızca iyon detektörü gerektirir.
Spektrometre ve Dedektör ultra yüksek vakum altında monte edilmiştir (&#60; 1 x 10-9 inç) iyonları arta kalan gaz üzerinden oluşturulmasını önlemek için. Örnek tek molekülleri gaz halinde olan yakıtlar ücretsiz moleküler jet süpersonik genişleme tarafından oluşturulan aracılığıyla sağlanır: buhar basıncı sayesinde molekülleri küçük bir başlık (yaklaşık 50 µm çapı) vakum içine genişletin. Bu deneyin, kaynak odası parçası etkileşim bölgesinden genellikle iki kevgir ve differentially pompalanan aşamaları tarafından ayrılır. Ek bir bölüm differentially pompalı gaz jet dökümü ve böylece arka plan gaz etkileşim bölgesi önlemek için etkileşim bölgesi arkasında yer alır.
İyonizan radyasyon moleküler jet altında 90 ° ile kesişiyor. Sinkrotron radyasyon, hızlı iyonları veya elektron etkisi olmasına rağmen 'Coulomb patlama ikna etmek mümkün mermi' çoğu laboratuvarları femtosecond lazer bakliyat, günümüzde kullanın.
Aşağıdaki iletişim kuralı kurulumunu çalıştırarak iyonları ve femtosecond lazer çakışık görüntüleme için laboratuar ortamında kullanılabilir varsayımı yapar. Coulomb patlama dört bes bile parçalara ikna etmek için gerekli en yüksek yoğunluk 6 x 1014 sırasına W/cm2olması gerekir. Son derece uzun ölçümleri önlemek için lazer tekrarlama oranı 10 kHz veya daha fazla olmalıdır. Parçalanma lazer odak için olasılık önemli ölçüde lazer darbe (ideal olarak fazla % 10) başına 1 aşağıda ise bir yandan çakışık algılama yalnızca tespit edilebilir çünkü bu önemlidir. Çünkü ilgili multifragmentation yolları payı genellikle az 10-4toplam parçalanma hızı, öte yandan, bir kaç kHz düşük olmamalıdır. Kadar cesaret verici aslında, ilke bir tek parçalanma olayı bir enantiopure örnek yapılandırma tanımlamak için yeterli zaten ve enantiomers içinde bolluk belirlemek için bir kaç yüz tespiti sağlar belirtilmelidir bir Bilinmeyen enantiomeric kompozisyon örneği.

<table><tbody><tr><td>CHBrCl2</td><td>SigmaAldrich</td><td>139181-10G</td><td>or other suitable sample</td></tr><tr><td>femtosecond laser system</td><td>KMLabs</td><td>Wyvern500</td><td></td></tr><tr><td>High-reflective mirrors</td><td>EKSMA</td><td>042-0800</td><td></td></tr><tr><td>mirror mounts</td><td>Newport</td><td>U100-A-LH-2K&amp;nbsp;&amp;nbsp;</td><td></td></tr><tr><td>focusing mirror (protected silver, f = 75 mm)</td><td>Thorlabs&amp;nbsp;</td><td>CM254-075-P01</td><td>(if available: f = 60 mm)</td></tr><tr><td>COLTRIMS spectrometer, including electronics and data acquisition system</td><td>RoentDek</td><td>custom</td><td>contrary to the standard COLTRIMS, only one detector is needed</td></tr></tbody></table>

coulomb explosion imaging as a tool to distinguish between stereoisomers

Bu makalede nasıl COLTRIMS (soğuk hedef geri tepme iyon Momentum spektroskopisi) veya "tepki mikroskop" tekniği enantiomers (hipoglisemi) bireysel moleküllerin düzeyde basit kiral türlerin ayırt etmek için kullanılabileceğini gösterir. Bu yaklaşımda, gaz halinde olan yakıtlar moleküler jet örnek bir vakum odasına genişletir ve (fs) femtosecond lazer bakliyat ile kesişiyor. Bakliyat yüksek yoğunluklu birkaç Katyonik (pozitif yüklü) parçaları üreten sözde bir Coulomb patlama tutuşabilme birden fazla iyonlaşma hızlı yol açar. Bir elektrostatik alan zaman ve pozisyon duyarlı dedektörler üzerine bu özellikler size yol gösterir. Benzer şekilde bir uçuş zaman Kütle Spektrometre, her iyon varış saati kütlesi hakkında bilgi verir. Bir fazlalık Elektrostatik alan emisyon yön ve parçalanma sonra kinetik enerji çeşitleri için uçuş zaman ve etkisi konumda Dedektör üzerinde kurşun bir şekilde ayarlanır.
Her iyon etkisi bir elektronik sinyal dedektörü oluşturur; Bu sinyali yüksek frekanslı elektronik tarafından tedavi ve bu olay tarafından bir bilgisayar tarafından kaydedildi. Kayıtlı veri etkisi kez ve pozisyonlar için karşılık gelir. Bu veriler ile enerji ve her parça emisyon yönünü hesaplanabilir. Bu değerler soruşturma, yani bağ uzunlukları ve atomlar molekül molekül tarafından el kullanımı basit kiral tür ve isomeric diğer özellikleri belirlemek için izin, göreli konumları altında molekülünün yapısal özellikleri ile ilgili.

Bu bölümde, halomethanes için elde edilen sonuçlar gösterir. Bu tür kanıt prensibi deneyler basitlik ve yüksek buhar basıncı nedeniyle için idealdir. Bu arada, daha karmaşık türler halotan birden fazla iyonlaşma ikna etmek için bir sinkrotron kaynaktan tek yumuşak-x-ışını fotonlar kullanarak araştırmış. 14
CHBrClF
Bromoc...

Watch this Scientific Journal Video about Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers at JoVE.com

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

Hipoglisemi arasında ayırt etmek için bir araç olarak Coulomb patlama görüntüleme

Küçük kiral türler için patlama Coulomb Imaging bireysel moleküllerin el kullanımı belirlemek için yeni bir yaklaşım sağlar.

This article shows how the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) or the "reaction microscope" technique can be used to distinguish ...

coulomb-explosion-imaging-as-tool-to-distinguish-between

Universidad San Sebastian

Education

Research

JoVE Core

JoVE Journal

Organic Chemistry

Chemistry

Unit 1

Transition Metals and Coordination Complexes

Stereoisomerism

SCIENTISTS IN ACTION

9.0K Görüntüleme.  Goethe-Universität Frankfurt am Main. Küçük kiral türler için patlama Coulomb Imaging bireysel moleküllerin el kullanımı belirlemek için yeni bir yaklaşım sağlar.

Video: Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

Moleküler Konformatörlerin ve Kümelerin Mekansal Ayrımı

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Mühendislik

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb explosion imaging setup in which a hitherto-impractical camera angle is realized. In our imaging technique, diatomic molecules are irradiated with a circularly polarized strong laser pulse. The ejected atomic ions are accelerated perpendicularly to the laser propagation. The ions lying in the laser polarization plane are selected through the use of a mechanical slit and imaged with a high-throughput, 2-dimensional detector installed parallel to the polarization plane. Because a circularly polarized (isotropic) Coulomb exploding pulse is used, the observed angular distribution of the ejected ions directly corresponds to the squared rotational wave function at the time of the pulse irradiation. To create a real-time movie of molecular rotation, the present imaging technique is combined with a femtosecond pump-probe optical setup in which the pump pulses create unidirectionally rotating molecular ensembles. Due to the high image throughput of our detection system, the pump-probe experimental condition can be easily optimized by monitoring a real-time snapshot. As a result, the quality of the observed movie is sufficiently high for visualizing the detailed wave nature of motion. We also note that the present technique can be implemented in existing standard ion imaging setups, offering a new camera angle or viewpoint for the molecular systems without the need for extensive modification.

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

Lazer güdümlü Ultrafast Moleküler Rotasyon Doğrudan Görüntüleme

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

Kimya

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F&#8722;

Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound electrons with neutral molecules/atoms. State-of-the-art in vacuo anion generation techniques allow application to a broad range of atomic, molecular, and cluster anion systems. These are separated and selected using time-of-flight mass spectrometry. Electrons are removed by linearly polarized photons (photo detachment) using table-top laser sources which provide ready access to excitation energies from the infra-red to the near ultraviolet. Detecting the photoelectrons with a velocity mapped imaging lens and position sensitive detector means that, in principle, every photoelectron reaches the detector and the detection efficiency is uniform for all kinetic energies. Photoelectron spectra extracted from the images via mathematical reconstruction using an inverse Abel transformation reveal details of the anion internal energy state distribution and the resultant neutral energy states. At low electron kinetic energy, typical resolution is sufficient to reveal energy level differences on the order of a few millielectron-volts, i.e., different vibrational levels for molecular species or spin-orbit splitting in atoms. Photoelectron angular distributions extracted from the inverse Abel transformation represent the signatures of the bound electron orbital, allowing more detailed probing of electronic structure. The spectra and angular distributions also encode details of the interactions between the outgoing electron and the residual neutral species subsequent to excitation. The technique is illustrated by the application to an atomic anion (F&#8722;), but it can also be applied to the measurement of molecular anion spectroscopy, the study of low lying anion resonances (as an alternative to scattering experiments) and femtosecond (fs) time resolved studies of the dynamic evolution of anions.

Here, we present a protocol for photoelectron imaging of anionic species. Anions generated in vacuo and separated by mass spectrometry are probed using velocity mapped photoelectron imaging, providing details of anion and neutral energy levels, anion and neutral structure and the nature of the anion electronic state.

F− 310 Nm dekolmanı tarafından resimli anyon photoelectron görüntüleme

Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound ...

Direct Comparison of Hyperspectral Stimulated Raman Scattering and Coherent Anti-Stokes Raman Scattering Microscopy for Chemical Imaging

Stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) microscopy are the most widely used coherent Raman scattering imaging technologies. Hyperspectral SRS and CARS imaging offer Raman spectral information at every pixel, which enables better separation of different chemical compositions. Although both techniques require two excitation lasers, their signal detection schemes and spectral properties are quite different. The goal of this protocol is to perform both hyperspectral SRS and CARS imaging on a single platform and compare the two microscopy techniques for imaging different biological samples. The spectral focusing method is employed to acquire spectral information using femtosecond lasers. By using standard chemical samples, the sensitivity, spatial resolution, and spectral resolution of SRS and CARS in the same excitation conditions (i.e., power at the sample, pixel dwell time, objective lens, pulse energy) are compared. The imaging contrasts of CARS and SRS for biological samples are juxtaposed and compared. The direct comparison of CARS and SRS performances would allow for optimal selection of the modality for chemical imaging.

This paper directly compares the resolution, sensitivity, and imaging contrasts of stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) integrated into the same microscope platform. The results show that CARS has a better spatial resolution, SRS gives better contrasts and spectral resolution, and both methods have similar sensitivity.

Kimyasal Görüntüleme için Hiperspektral Uyarılmış Raman Saçılması ve Tutarlı Anti-Stokes Raman Saçılma Mikroskobunun Doğrudan Karşılaştırılması

Stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS) microscopy are the most widely used coherent Raman scattering imaging ...

Differential Imaging of Biological Structures with Doubly-resonant Coherent Anti-stokes Raman Scattering (CARS)

Coherent Raman imaging techniques have seen a dramatic increase in activity over the past decade due to their promise to enable label-free optical imaging with high molecular specificity 1. The sensitivity of these techniques, however, is many orders of magnitude weaker than fluorescence, requiring milli-molar molecular concentrations 1,2. Here, we describe a technique that can enable the detection of weak or low concentrations of Raman-active molecules by amplifying their signal with that obtained from strong or abundant Raman scatterers. The interaction of short pulsed lasers in a biological sample generates a variety of coherent Raman scattering signals, each of which carry unique chemical information about the sample. Typically, only one of these signals, e.g. Coherent Anti-stokes Raman scattering (CARS), is used to generate an image while the others are discarded. However, when these other signals, including 3-color CARS and four-wave mixing (FWM), are collected and compared to the CARS signal, otherwise difficult to detect information can be extracted 3. For example, doubly-resonant CARS (DR-CARS) is the result of the constructive interference between two resonant signals 4. We demonstrate how tuning of the three lasers required to produce DR-CARS signals to the 2845 cm-1 CH stretch vibration in lipids and the 2120 cm-1 CD stretching vibration of a deuterated molecule (e.g. deuterated sugars, fatty acids, etc.) can be utilized to probe both Raman resonances simultaneously. Under these conditions, in addition to CARS signals from each resonance, a combined DR-CARS signal probing both is also generated. We demonstrate how detecting the difference between the DR-CARS signal and the amplifying signal from an abundant molecule's vibration can be used to enhance the sensitivity for the weaker signal. We further demonstrate that this approach even extends to applications where both signals are generated from different molecules, such that e.g. using the strong Raman signal of a solvent can enhance the weak Raman signal of a dilute solute.

Differential Imaging of Biological Structures with Doubly-resonant Coherent Anti-stokes Raman Scattering CARS

A combination of three single wavelength short-pulsed lasers is used to generate coherent anti-Stokes Raman scattering (CARS) and doubly-resonant CARS (DR-CARS). The difference between these signals provides enhanced sensitivity for otherwise difficult to detect coherent Raman signals, enabling imaging of weak Raman scatterers.

Çifte rezonans Tutarlı Anti-Stokes Raman saçılımı (CARS) Biyolojik Yapıların Diferansiyel Görüntüleme

Coherent Raman imaging techniques have seen a dramatic increase in activity over the past decade due to their promise to enable label-free optical imaging ...

Biyoloji

Multimodal, Hızlı, Hiperspektral Kimyasal Analiz için VSFG Mikroskobu Kullanma

Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy

Vibrational sum-frequency generation (VSFG), a second-order nonlinear optical signal, has traditionally been used to study molecules at interfaces as a spectroscopy technique with a spatial resolution of ~100 &#181;m. However, the spectroscopy is not sensitive to the heterogeneity of a sample. To study mesoscopically heterogeneous samples, we, along with others, pushed the resolution limit of VSFG spectroscopy down to ~1 &#181;m level and constructed the VSFG microscope. This imaging technique not only can resolve sample morphologies through imaging, but also record a broadband VSFG spectrum at every pixel of the images. Being a second-order nonlinear optical technique, its selection rule enables the visualization of non-centrosymmetric or chiral self-assembled structures commonly found in biology, materials science, and bioengineering, among others. In this article, the audience will be guided through an inverted transmission design that allows for imaging unfixed samples. This work also showcases that VSFG microscopy can resolve chemical-specific geometric information of individual self-assembled sheets by combining it with a neural network function solver. Lastly, the images obtained under brightfield, SHG, and VSFG configurations of various samples briefly discuss the unique information revealed by VSFG imaging.

Yazar Spot Işığı: VSFG Mikroskobunun Mezoskopik Olarak Heterojen Kendinden Montajlı Yapıların İncelenme Potansiyelini Ortaya Çıkarmak 

A multimodal, rapid hyperspectral imaging framework was developed to obtain broadband vibrational sum-frequency generation (VSFG) images, along with brightfield, second harmonic generation (SHG) imaging modalities. Due to the infrared frequency being resonant with molecular vibrations, microscopic structural and mesoscopic morphology knowledge is revealed of symmetry-allowed samples.

Çizgi Taramalı Titreşimli Toplam Frekans Oluşturma Mikroskobu Kullanılarak Multimodal Doğrusal Olmayan Hiperspektral Kimyasal Görüntüleme

Vibrational sum-frequency generation (VSFG), a second-order nonlinear optical signal, has traditionally been used to study molecules at interfaces as a ...

Stereoisomers

On the basis of mirror symmetry, stereoisomers of an organic molecule can be further classified into diastereomers and enantiomers. Diastereomers are stereoisomers that are not mirror images of each other. Substituted alkenes, such as the cis and trans isomers of 2-butene, are diastereomers, as these molecules exhibit different spatial orientations of their constituent atoms, are not mirror images of each other,&#160;and do not interconvert. Here, the interconversion is suppressed due to restricted rotation around the &#960; bond. Another class of diastereomers &#8212; those without &#960; bonds &#8212; are molecules that have non-superposable spatial orientations and exhibit different configurations of their substituent groups at some, but not all, stereocenters. For example, cis-1,2-dimethylcyclohexane and trans-1,2-dimethylcyclohexane are diastereomers, as these molecules are not superposable and have a different configuration of the methyl and hydrogen groups at only one out of their two stereocenters.
Enantiomers are stereoisomers that are mirror images of each other. As only chiral molecules can have non-superposable mirror images, enantiomers are chiral molecules. For example, the chiral molecule 2-butanol and its mirror image are enantiomers, as these molecules exhibit non-superposable spatial orientations of their constituent atoms and are mirror images of each other. A chiral molecule and its mirror image are collectively referred to as an enantiomeric pair, or a pair of enantiomers. The enantiomer of a chiral molecule can be drawn by taking its mirror image from any position or&#160;exchanging the positions of two of the substituents at each stereocenter of the molecule.

Stereoisomers: Diastereomers and Enantiomers

Stereoizomerler

On the basis of mirror symmetry, stereoisomers of an organic molecule can be further classified into diastereomers and enantiomers. Diastereomers are ...

Organik Kimya

Stereoizomerizm

KEY TERMS AND CONCEPTS

<h3>Isomerism in Complexes</h3>
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis configuration, the two chloride ligands are adjacent to each other. The other isomer, the trans configuration, has the two chloride ligands directly across from one another.
<img alt="Image1" src="/files/ftp_upload/11459/11459_Image1.svg" style="text-align: center; height: 200px;" />
Figure 1. The cis and trans isomers of [Co(H2O)4Cl2]+ contain the same ligands attached to the same metal ion, but the spatial arrangement causes these two compounds to have very different properties.
Different geometric isomers of a substance are different chemical compounds. They exhibit different properties, even though they have the same formula. For example, the two isomers of [Co(NH3)4Cl2]NO3 differ in color; the cis form is violet, and the trans form is green. Furthermore, these isomers have different dipole moments, solubilities, and reactivities. As an example of how the arrangement in space can influence the molecular properties, consider the polarity of the two [Co(NH3)4Cl2]NO3 isomers. Remember that the polarity of a molecule or ion is determined by the bond dipoles (which are due to the difference in electronegativity of the bonding atoms) and their arrangement in space. In one isomer, cis chloride ligands cause more electron density on one side of the molecule than on the other, making it polar. For the trans isomer, each ligand is directly across from an identical ligand, so the bond dipoles cancel out, and the molecule is nonpolar.
Another important type of isomers are optical isomers, or enantiomers, in which two objects are exact mirror images of each other but cannot be lined up so that all parts match. This means that optical isomers are non-superposable mirror images. A classic example of this is a pair of hands, in which the right and left hand are mirror images of one another but cannot be superposed. Optical isomers are very important in organic and biochemistry because living systems often incorporate one specific optical isomer and not the other. Unlike geometric isomers, pairs of optical isomers have nearly identical properties (boiling point, polarity, solubility, etc.). Optical isomers differ only in the way they affect polarized light and how they react with other optical isomers. For coordination complexes, many coordination compounds such as [M(en)3]n+ [in which Mn+ is a central metal ion such as iron(III) or cobalt(II)] form enantiomers, as shown in Figure 2. These two isomers will react differently with other optical isomers. For example, DNA helices are optical isomers, and the form that occurs in nature (right-handed DNA) will bind to only one isomer of [M(en)3]n+ and not the other.
<img alt="Image2" src="/files/ftp_upload/11459/11459_Image_2.svg" style="text-align: center; height: 200px;" />
Figure 2. The complex [M(en)3]n+ (Mn+ = a metal ion, en = ethylenediamine) has a non-superposable mirror image.
The [Co(en)2Cl2]+ ion exhibits geometric isomerism (cis/trans), and its cis isomer exists as a pair of optical isomers (Figure 3).
<img alt="Image3" src="/files/ftp_upload/11459/11459_Image_3.svg" style="text-align: center; height: 200px;" />
Figure 3. Three isomeric forms of [Co(en)2Cl2]+ exist. The trans isomer, formed when the chlorines are positioned at a 180&#176; angle, has very different properties from the cis isomers. The mirror images of the cis isomer form a pair of optical isomers, which have identical behavior except when reacting with other enantiomers.
This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/19-2-coordination-chemistry-of-transition-metals">Openstax, Chemistry 2e, Chapter 19.2 Coordination Chemistry of Transition Metals.</a>

Stereoisomerism: Geometric &amp; Optical Isomers

Stereoizomizm

Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric ...

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Özet

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Stereoizomerler

Stereoizomizm