Chemistry Commons^™

Exploring Conditions For The Enhancement Of Acene Semiconductors Through The Use Of The Diels-Alder Reaction, Brittni Qualizza Qualizza

Dissertations

This dissertation demonstrates the application of SAMs to the surface of acene crystals, specifically of tetracene and rubrene, using the Diels-Alder reaction. The second chapter details preliminary reaction results and two analytical methods which were employed to confirm adsorption of the dienophile on the surface of single crystals, tetracene and rubrene. These were mass spectrometry and X-ray photoelectron spectroscopy (XPS). Mass spectrometry experiments distinguish the chemical identity of adduct on the crystals and also it discerned chemi- and physisorbed molecules from one another. XPS was used to prove face selectivity of the reaction by the detection of dichloromaleic anhydride. From …

Characterization Of Dielectric Barrier Discharge Atmospheric Air Plasma Treated Chitosan Films, Shashi Pankaj, Carmen Bueno-Ferrer, Luke O'Neill, B.K. Tiwari, Paula Bourke, Patrick J. Cullen

Articles

Dielectric barrier discharge (DBD) plasma is a novel non-thermal food decontamination technology. The effects of DBD plasma on the surface topography, chemical composition and crystal structure, film hydrophilicity, water vapor permeability and oxygen permeability of chitosan films have been examined. DBD plasma treatment increased the surface roughness of chitosan films with emergence of sharp protuberances. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy spectra confirm a significant increase in the oxygen containing groups in the chitosan film after plasma treatment. Significant increase in the film hydrophilicity was observed after plasma treatment. X-ray diffraction results showed that DBD plasma treatment do …

Development Of Protein-Polymer Core-Shell Nanoparticles (Ppcs-Nps) As Efficient Vehicles To Deliver Therapeutic Agents Across Blood Brain Barrier (Bbb), Napat Tandikul

Theses and Dissertations

Blood Brain Barrier (BBB) plays a main role as selective barrier which controls and limits access of chemicals, molecules and therapeutic agents from blood to brain. The BBB endothelial cells are connected by Tight Junctions (TJs) which close intracellular spaces between the endothelial cells and block the free diffusion of substances, therefore many potential drugs for treating human brain diseases cannot reach the brain in sufficient concentration. Recently, many studies have thrown an interest in development of nanoparticles for delivering drugs and imaging agents across BBB. Our research group has developed protein-polymer core-shell nanoparticles (PPCS-NPs) which demonstrate great potential for …

Wide Field Measurements Using A Spatial Heterodyne Raman Spectrometer For Transmission Raman Spectroscopy And Standoff Detection, Kimberly A. Fessler

Theses and Dissertations

Our group recently developed a new type of Fourier transform Raman spectrometer, the spatial heterodyne Raman spectrometer (SHRS), for planetary exploration. The SHRS is a high spectral resolution, high throughput, compact dispersive interferometer, similar in design to a Michelson interferometer, where the mirrors are replaced by stationary diffraction gratings. The SHRS has no moving parts and does not require an entrance slit, making the throughput of the system orders of magnitude larger than a typical dispersive spectrometer. The wide field-of-view (FOV) of the SHRS enables wide area measurements without loss of sensitivity or spectral resolution and offers advantages such as …

Cdk8 And Cdk19 As Novel Regulators Of Bmp4 Induced Emt In Cancer, Anne Elizabeth Serrao

Theses and Dissertations

Bone morphogenetic protein 2/4 (BMP2/4), members of the transforming growth factor β (Tgf-β) superfamily, play a dichotomous role in the progression of cancers through cell growth suppression and the enhancement of tumorigenesis in a variety of cancers. Cyclin dependent kinase 8 (CDK8), a protein kinase that regulates gene transcription, is involved in a variety of cancers including breast and pancreatic cancers as well as in mediating BMP2 signaling via its canonical Smad1 pathway. Our studies show that BMP4 induced EMT signals primarily though Smad1 and that Yap1, a transcriptional co-activator, is necessary for BMP4 induced EMT. Using a highly specific …

Investigating Structure-Activity Relationships Of Sl11 To Develop A Better Prostate Cancer Diagnostic, Rong Huang

Theses and Dissertations

Prostate cancer is now the second leading cause of cancer death in American men. Since many of the diagnostics either have high false results or risky, it’s important to have better diagnostics and earlier diagnosis of prostate cancer. Aberrant glycosylation is a hallmark of cancer. When cancer occurs, aberrant glycosylation occurs, therefore, glycosylation patterns may provide information about different cancer types and metastatic potential. In order to study and use these glycosylation patterns, the boronic acid functionalized synthetic lectins that can interact with glycans have been developed. The work described here focuses on 1) the structure activities of synthetic lectins …

Improved Systems For On-Site Raman Measurements, William Joshua Huntington

Theses and Dissertations

The need to development lightweight miniature sensors for spectrometers for use in hazardous environments such as war zones, industrial settings, and space exploration is ever growing. This thesis will present studies aimed at improving Raman instruments for such applications by reducing the size, weight, and power consumption of the instrument. The two methods described here include the utilization of a light emitting diode (LED) source for Raman spectroscopy and a new type of Raman gas sensor.

Chapter one describes a new Raman spectrometer that utilizes an LED for Raman excitation coupled to the SHRS. LEDs are highly divergent broadband , …

Mechanistic Investigation And Potential Application Of A Fatty Acid Decarboxylating Cytochrome P450 Peroxygenase, Chun H. Hsieh

Theses and Dissertations

OleT (CYP152L1) is a recently discovered cytochrome P450 that is structurally similar to peroxide dependent P450s that catalyze fatty acid hydroxylations. OleT has been shown to catalyze the cleavage of n chain length fatty acids to form n-1 alkenes through C-C bond scission of the terminal carboxylate. Using headspace GC-MS and FTIR with isotopically labeled substrates, we have confirmed that OleT metabolizes eicosanoic acid to 1-nonadecene, forming carbon dioxide (CO2) as a co-product of the reaction. No oxygen deriving from peroxide is observed in either product. In order to probe the mechanistic deviation of OleT from P450 peroxygenases, we have …

Synthesis Attempts And Plausible Applications Of Dithiolated Ortho –Carboranyl Transition Metal Complexes And Synthesis Of Bulky Terphenyls, Surendra Bahadur Karki

Theses and Dissertations

The reaction of coordination compounds of palladium, rhodium, ruthenium and nickel with thiolated ortho-carborane derivatives- 1,2-dimercapto-o-carborane (1,2-(HS)2-1,2- C2B10H10 ) and 9,12- dimercapto-o-carborane (9,12-(HS)2-1,2- C2B10H10 ) and with carbornanyl dicarboxylate has been studied. To further investigate the chemistry of o-carboranyl dithiolate, both of the reported literature dithiols have been employed to study the reactivity with some of the above mentioned transition metal coordination compounds. The 1,2-dimercapto-o-carborane reacts with bis(triphenylphosphine)palladium(II) chloride [PdCl2(PPh3)2] to form a square planar bis(triphenylphosphine)palladium(II) carboranyl dithiolate (PdC2B10S2(PPh3)2) complex. With the inspiration from the reactivity of the dithiols and versatility of carboranyldithiolate ligand in organometallic chemistry, new avenue of …

Materials Discovery By Crystal Growth: Synthesis, Structure Determination, Magnetic, And Optical Properties Of Complex Lanthanide Containing Oxides, Oxyhydroxides, And Oxyfluorides, Allison Marie Latshaw

Theses and Dissertations

Exploratory crystal growth is a versatile technique and one that can advance materials discovery. Through exploratory crystal growth, it is possible to synthesize many new materials that can have applications in many fields, including solid-state lighting. There exist many adaptations for exploratory crystal growth, including the use of alkali halide flux growth and hydroflux growth, both reported herein. By changing variants in these techniques like reactant ratios, temperature, reaction profile, and, most importantly here, the flux compositions, it is possible to change the products formed or fine tune reactions for product purity.

For solid-state lighting applications, compounds that adopt colorless …

Novel Approaches To Investigate The Oxidation Rate Of Fe(Ii) And The Role Of Fe(Ii)/Fe(Iii) Cycling On The Maintenance Of Reactive Oxygen Species In Aquatic Systems, Justin Maurice Copeland

Theses and Dissertations

The biogeochemical cycling of iron, oxygen, and organic carbon are inextricably linked through the intermediacy of Reactive Oxygen Species (ROS) brought about by the autoxidation of ferrous iron (Fe(II)). This dissertation presents laboratory and field-based studies to investigate the kinetics of Fe(II) oxidation and its role in the production of ROS at oxic/anoxic interfaces. The net oxidation of Fe(II) in natural waters is a complex process consisting of alternating cycles of Fe(II) oxidation and Fe(III) reduction processes that are ultimately terminated via precipitation as insoluble Fe(III) (oxy)hydroxides. This complicates kinetic measurements of individual reaction steps in the process.

A critical …

Physical Property Control In Core/Shell Inorganic Nanostructures For Fluorescence And Magnetic Targeting Applications, Stephen K. Roberts

Theses and Dissertations

Nanomaterials show immense promise for the future in numerous areas of application. Properties that are unique from the bulk material and are tunable allow for innovation in material design. This thesis will focus on controlling the physical properties of core/shell nanostructures to enhance the utility of the materials.

The first focus is on the impact of different solvent mixtures during the shell growth phase of SILAR based core/shell quantum dot synthesis is studied. Gaining insight into the mechanism for SILAR growth of core/shell nanoparticles allows improved synthetic yields and precursor binding, providing enhanced control to synthesis of core/shell nanoparticles. The …

Investigating The Effects Of Glutathione And Other Key Proteins On Iron Homeostasis And Subcellular Redox Balance In Yeast Model Systems, Kirsten Renee Collins

Theses and Dissertations

Iron homeostasis in Saccharomyces cerevisiae is controlled through several pathways and is important because too much iron can cause cellular damage. Iron homeostasis in yeast is primarily controlled by transcription factors Aft1 and Aft2 which bind to the iron regulon to induce iron uptake when iron levels are low. When iron levels are sufficient, Aft1 and Aft2 are bound and inhibited by monothiol glutaredoxins (Grxs) Grx3 and Grx4. These Grxs are also involved in iron trafficking in the cell and bind to and deliver iron-sulfur clusters to multiple proteins.

The first part of this thesis focuses on determining if excess …

Surface Chemistry And Transport Properties Of Ii-Vi Semiconductor Nanowires, Pravin Paudel

Theses and Dissertations

Semiconductor nanowires have been widely studied due to their unique properties such as width comparable to critical length-scales, high aspect ratio, and high carrier mobility. These unique properties make them a suitable candidate for various optical and electronic devices like photovoltaics, photodetectors, and field effect transistors. The nanowire surface plays an important role in the performance of these devices because of their high surface to volume ratio. The larger surface area of nanowires may provide better charge separation than planar heterostructures in photovoltaics by providing shorter distance to move for carrier before separation, however, presence of surface states may lead …

Building And Optimizing A Spectroelectrochemical System For The Study Of Shewanella Putrefaciens, Jonathan Muscolino

Master's Theses

Shewanellaceae are among the most widely studied electroactive microorganisms. This study reports on Shewanella putrefaciens under anaerobic conditions during applied potential while monitored by spectroscopy. The attachment of the microbe Shewanella putrefaciens onto an indium tin oxide electrode was found to occur after 2 hr of +0.2 V applied potential. Microbial detachment occurred with a 5 mV/s scan rate cyclic voltammogram from +0.2 V to -0.5 V to +0.2 V. This was confirmed through use of a spectroelectrochemical apparatus utilizing a standard 3 electrode setup with evanescent wave spectroscopy.

Liposomal Delivery Of Pde5 Inhibitors And Ut-15c To Human Erythrocytes, Elizabeth Anne Bowles

Doctoral Dissertations

"Previous studies have shown that the controlled release of adenosine triphosphate (ATP) from human erythrocytes is an important mechanism for the regulation of vascular caliber. However, erythrocytes from patients with pulmonary arterial hypertension (PAH) fail to release ATP in response to the physiological stimuli of exposure to low oxygen tension or mechanical deformation of a magnitude these cells would encounter in the pulmonary circulation. This defect could be a significant contributor to the increased pulmonary vascular resistance (PVR) that is the cause of the pathological increase in vascular pressures in humans with PAH.

One important approach to the treatment of …

พอลิเมอร์ผสมของพอลิแล็กทิกแอซิดและเซลลูโลสแอซีเทตจากผักตบชวา, กรองกาญจน์ อมตาริยกุล

Chulalongkorn University Theses and Dissertations (Chula ETD)

เซลลูโลสอะซิเทดถูกสังเคราะห์โดยใช้เซลลูโลสผักตบชวาเป็นวัตถุดิบ ซึ่งส่วนที่ใช้จะเป็นส่วนของก้านขั้นตอนแรกนำเส้นใยผักตบชวาไปกำจัดสิ่งสกปรกก้านแห้งและตามมาด้วยการฟอกสีไฮโปคลอไรเซลลูโลสให้เป็นสีขาวสีขาวแล้ว หลังจากนั้นเตรียมเซลลูโลสเจลโดยใช้โซเดียมไฮดรอกไซด์ / ยูเรีย / น้ำ (7:12:81 โดยน้ำหนัก) จากนั้นนำมาผสม ปริมาณของไวนิลอะซิเตทโดยมีอัตราส่วนต่างกันคือ 3.0, 5.0, 7.0, 9.0, 11.0% โดยน้ำหนักของเซลลูโลส หลังจากนั้นส่วนผสมที่ถูกเก็บไว้ในตู้แช่แข็งเป็นเวลา 6 ชั่วโมงเพื่อให้เกิดปฏิกิริยาแอซิทิเลชันสมบูรณ์ เซลลูโลสอะซิเตทมีความสามารถในการปรับปรุงคุณสมบัติของพอลิแล็กทิกแอซิดโดยการเปลี่ยนเป็นผลึกที่สมบัติเชิงกลและสมบัติทางความร้อน จุดมุ่งหมายของการศึกษาครั้งนี้คือการสังเคราะห์ เซลลูโลสแอซิเทดจากผักตบชวาโดยใช้พอลิไวนิลอะซิเตตสารช่วยเพิมความเข้ากันได้ (Compatiblizer) จากนั้นพอลิแล็กทิกแอซิด / เซลลูโลสอะซิเทดนำไปผสมกันโดยใช้เครื่องอัดรีดเกลียว หลังจากนั้นนำไปวิเคราะผล ดังนี้ วิเคราะห์หมู่ฟังก์ชันโดยใช้ฟูเรียทรานสฟอร์มสเปกโตรสโคปี (FTIR) วิเคราห์ความเป็นผลึกด้วยเครื่องเอกซ์เรย์ดิฟแฟรกโทรมิเตอร์(XRD) และ วิเคราะห์สัณฐานวิทยาด้วยกล้องจุลทรรศน์อิเล็กตรอนแบบส่องกราด(SEM) พบว่าพอลิแล็กทิกแอซิด / เซลลูโลสอะซิเตทโดยความเข้มข้นที่เหมาะสมที่สุดของเซลลูโลสอะซิเตทสำหรับการผสมกับพอลิแล็กทิกแอซิด เป็น 11% โดยน้ำหนักและสัดส่วนของพอลิแล็กทิกแอซิด/เซลลูโลสแอซิเทดคือ 95 : 5

A Search For Blues Brothers: X-Ray Crystallographic/Spectroscopic Characterization Of The Tetraarylbenzidine Cation Radical As A Product Of Aging Of Solid Magic Blue, Marat R. Talipov, Mohammad M. Hossain, Anitha Boddeda, Khushabu Thakur, Rajendra Rathore

Chemistry Faculty Research and Publications

Magic blue (MB⁺˙ SbCl₆⁻ salt), i.e. tris-4-bromophenylamminium cation radical, is a routinely employed one-electron oxidant that slowly decomposes in the solid state upon storage to form so called ‘blues brothers’, which often complicate the quantitative analyses of the oxidation processes. Herein, we disclose the identity of the main ‘blues brother’ as the cation radical and dication of tetrakis-(4-bromophenyl)benzidine (TAB) by a combined DFT and experimental approach, including isolation of TAB⁺˙ SbCl₆⁻ and its X-ray crystallography characterization. The formation of TAB in aged magic blue samples occurs by a Scholl-type …

Chemometric Curve Resolution For Quantitative Liquid Chromatographic Analysis, Daniel W. Cook

Theses and Dissertations

In chemical analyses, it is crucial to distinguish between chemical species. This is often accomplished via chromatographic separations. These separations are often pushed to their limits in terms of the number of analytes that can be sufficiently resolved from one another, particularly when a quantitative analysis of these compounds is needed. Very often, complicated methods or new technology is required to provide adequate separation of samples arising from a variety of fields such as metabolomics, environmental science, food analysis, etc.

An often overlooked means for improving analysis is the use of chemometric data analysis techniques. Particularly, the use of chemometric …

Probing Allosteric, Partial Inhibition Of Thrombin Using Novel Anticoagulants, Stephen S. Verespy Iii

Theses and Dissertations

Thrombin is the key protease that regulates hemostasis; the delicate balance between procoagulation and anticoagulation of blood. In clotting disorders, like deep vein thrombosis or pulmonary embolism, procoagulation is up-regulated, but propagation of clotting can be inhibited with drugs targeting the proteases involved, like thrombin. Such drugs however, have serious side effects (e.g., excessive bleeding) and some require monitoring during the course of treatment. The reason for these side effects is the mechanism by which the drugs’ act. The two major mechanisms are direct orthosteric and indirect allosteric inhibition, which will completely abolish the protease’s activity. Herein we sought an …

Versatile Synthesis Of Transition Metal Phosphides: Emerging Front-Runners For Affordable Catalysis, April C. Mattei

Theses and Dissertations

Transition metal phosphide materials have found themselves at the forefront of research revolving around energy applications. Due to the vast range of properties possessed by marginally different phase compositions, binary and ternary metal phosphides are utilized as catalysts, semi-conductors and magnetocaloric materials along with many others. These attractive properties, which are highly phase dependent, call for a versatile and cost effective synthesis route for various phosphide materials without sacrificing properties important at the nanoscale such as particle size and morphology.

The primary focus outlined in the work of this dissertation pertains to a versatile wet chemical synthesis capable of producing …

Fabrication Of Multifunctional Nanostructured Porous Materials, Ahmed A. Farghaly

Theses and Dissertations

Nanostructured porous materials generally, and nanoporous noble metals specifically, have received considerable attention due to their superior chemical and physical properties over nanoparticles and bulk counterparts. This dissertation work aims to develop well-established strategies for the preparation of multifunctional nanostructured porous materials based on the combination of inorganic-chemistry, organic-chemistry and electrochemistry. The preparation strategies involved one or more of the following processes: sol-gel synthesis, co-electrodeposition, metal ions reduction, electropolymerization and dealloying or chemical etching. The study did not stop at the preparation limits but extended to investigate the reaction mechanism behind the formation of these multifunctional nanoporous structures in order …

Interactions Of The Naphthalene Radical Cation With Polar And Unsaturated Molecules In The Gas Phase, Sean P. Platt

Theses and Dissertations

Characterizing the interactions of solvent molecules with ions is fundamental in understanding the thermodynamics of solution chemistry. These interactions are difficult to observe directly in solution because the number of solvent molecules far exceed that of ions. This lend the gas phase to be the ideal medium in the study ion-solvent interactions on a molecular level. Ionized polycyclic aromatic hydrocarbon (PAH) molecules can readily form hydrogen bonds with neutral solvent molecules in aqueous and interstellar medium. Previous research has been done for stepwise solvation of small molecules such as benzene⁺, pyridine, and phenylacetylene. The similarity in these results …

Systematic Postsynthetic Modification Of Nanoporous Organic Frameworks And Their Performance Evaluation For Selective Co2 Capture, Timur Islamoglu

Theses and Dissertations

Porous organic polymers (POPs) with high physicochemical stability have attracted significant attention from the scientific community as promising platforms for small gas separation adsorbents. Although POPs have amorphous morphology in general, with the help of organic chemistry toolbox, ultrahigh surface area materials can be synthesized. In particular, nitrogen-rich POPs have been studied intensively due to their enhanced framework-CO₂ interactions. Postsynthetic modification (PSM) of POPs has been instrumental for incorporating different functional groups into the pores of POPs which would increase the CO₂ capture properties. We have shown that functionalizing the surface of POPs with nitro and amine groups …

Measurement Of Rare Earth And Uranium Elements Using Laser-Induced Breakdown Spectroscopy (Libs) In An Aerosol System For Nuclear Safeguards Applications, Ammon N. Williams

Theses and Dissertations

The primary objective of this research is to develop an applied technology and provide an assessment for remotely measuring and analyzing the real time or near real time concentrations of used nuclear fuel (UNF) elements in electrorefiners (ER). Here, Laser-Induced Breakdown Spectroscopy (LIBS) in UNF pyroprocessing facilities was investigated. LIBS is an elemental analysis method, which is based on the emission from plasma generated by focusing a laser beam into the medium. This technology has been reported to be applicable in solids, liquids (includes molten metals), and gases for detecting elements of special nuclear materials. The advantages of applying the …

Laser Vaporization Controlled Condensation And Laser Irradiation In Solution For The Synthesis Of Supported Nanoparticle Catalysts, Vitaly Kisurin Mr.

Theses and Dissertations

Solid catalyst supports of SiOx-RGO (Reduced Graphene Oxide) and UiO-67 (Universitet i Oslo) have been successfully synthesized and were loaded with palladium nanoparticles to test for a series of heterogeneous reactions. The SiOx/RGO catalysts were synthesized through laser ablation of silicon and graphite oxide micron powder and UiO-67 metal-organic framework (MOF) was synthesized through mixing of precursors with DMF/HCl solution and washing the resultant powder from impurities. The SiOx/RGO supports were later impregnated with palladium precursors which were then subject to Microwave Irradiation (MWI). The UiO-67 framework was impregnated with palladium precursors and was irradiated with pulsed Nd:YAG 532 nm …

Hydrogen-Atom Attack On Phenol And Toluene Is Ortho-Directed, Olha Krechkivska, Callan M. Wilcox, Tyler P. Troy, Klaas Nauta, Bun Chan, Rebecca Jacob, Scott A. Reid, Leo Radom, Timothy W. Schmidt, Scott H. Kable

Chemistry Faculty Research and Publications

The reaction of H + phenol and H/D + toluene has been studied in a supersonic expansion after electric discharge. The (1 + 1′) resonance-enhanced multiphoton ionization (REMPI) spectra of the reaction products, at m/z = parent + 1, or parent + 2 amu, were measured by scanning the first (resonance) laser. The resulting spectra are highly structured. Ionization energies were measured by scanning the second (ionization) laser, while the first laser was tuned to a specific transition. Theoretical calculations, benchmarked to the well-studied H + benzene → cyclohexadienyl radical reaction, were performed. The spectrum arising from the …

A Flipped Classroom Redesign In General Chemistry, Scott A. Reid

Chemistry Faculty Research and Publications

The flipped classroom continues to attract significant attention in higher education. Building upon our recent parallel controlled study of the flipped classroom in a second-term general chemistry course (J. Chem. Educ., 2016, 93, 13–23), here we report on a redesign of the flipped course aimed at scaling up total enrollment while keeping discussion sizes small (i.e.,students), and maintaining equivalent contact hour load for faculty and workload for students. To that end, the course format featured lecture contact pushed outside of the classroom in the form of video lectures (mean duration 13 minutes) paired with online …

Reactivity Of (3-Methylpentadienyl)Iron(1+) Cation: Late-Stage Introduction Of A (3-Methyl-2z,4-Pentadien-1-Yl) Side Chain, Subhabrata Chaudhury, Shukun Li, William A. Donaldson

Chemistry Faculty Research and Publications

The 3-methyl-2Z,4-pentadien-1-yl sidechain is found in various sesquiterpenes and diterpenes. A route for the late stage introduction of this functionality was developed which relies on nucleophilic attack on the (3-methylpentadienyl)iron(1+) cation, followed by oxidative decomplexation. This methodology was applied to the synthesis of the proposed structure of heteroscyphic acid A methyl ester. Realization of this synthesis led to a correction of the proposed structure.

On Stabilization Of Scattering Resonances In Recombination Reaction That Forms Ozone, Mikhail V. Ivanov, Dmitri Babikov

Chemistry Faculty Research and Publications

Calculations of energy transfer in the recombination reaction that forms ozone are carried out within the framework of the mixed quantum/classical theory and using the dimensionally reduced 2D-model of ozone molecule, with bending motion neglected. Recombination rate coefficients are obtained at room temperature for symmetric and asymmetric isotopomers of singly and doubly substituted isotopologues. The processes of resonance formation, spontaneous decay, collisional dissociation, and stabilization by bath gas (Ar) are all characterized and taken into account within the steady-state approximation for kinetics. The focus is on stabilization step, where the mysterious isotopic η-effect was thought to originate from. Our results …