Publications by authors named "Sujun Wei"

12 Publications

  • Page 1 of 1

Triage and Recovery of STEM Laboratory Skills.

J Microbiol Biol Educ 2021 31;22(1). Epub 2021 Mar 31.

Department of Biological Sciences and Geology, Queensborough Community College, City University of New York, Bayside, NY 11364.

The global COVID-19 pandemic left universities with few options but to turn to remote learning. With much effort, STEM courses made this change in modality; however, many laboratory skills, such as measurement and handling equipment, are more difficult to teach in an online learning environment. A cohort of instructors who are part of the NSF RCN-UBE funded Sustainable, Transformative Engagement across a Multi-Institution/Multidisciplinary STEM (STEM) Network (a working group of faculty from two community colleges and three 4-year universities) analyzed introductory biology and chemistry courses to identify essential laboratory skills that students will need in advanced courses. Seven essential laboratory proficiencies were derived from reviewing disciplinary guiding documents such as AAAS , the American Society for Microbiology , and the American Chemical Society : data analysis, scientific writing, proper handling and disposal of laboratory materials, discipline-specific techniques, measurement, lab safety and personal protective equipment, and interpersonal and collaborative skills. Our analysis has determined that some of these skills are difficult to develop in a remote or online setting but could be recovered with appropriate interventions. Skill recovery procedures suggested include a skills "boot camp," department or college coordinated club events, and a triage course. The authors recommend that one of these three recovery mechanisms be offered to bridge this skill gap and better prepare STEM students for upper-level science courses and the real world.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/jmbe.v22i1.2565DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8083169PMC
March 2021

Enhanced coupling through π-stacking in imidazole-based molecular junctions.

Chem Sci 2019 Nov 16;10(43):9998-10002. Epub 2019 Sep 16.

Department of Chemistry , Queensborough Community College of the City University of New York , Bayside , New York 11364 , USA . Email:

We demonstrate that imidazole based π-π stacked dimers form strong and efficient conductance pathways in single-molecule junctions using the scanning-tunneling microscope-break junction (STM-BJ) technique and density functional theory-based calculations. We first characterize an imidazole-gold contact by measuring the conductance of imidazolyl-terminated alkanes (, = 3-6). We show that the conductance of these alkanes decays exponentially with increasing length, indicating that the mechanism for electron transport is through tunneling or super-exchange. We also reveal that π-π stacked dimers can be formed between imidazoles and have better coupling than through-bond tunneling. These experimental results are rationalized by calculations of molecular junction transmission using non-equilibrium Green's function formalism. This study verifies the capability of imidazole as a Au-binding ligand to form stable single- and π-stacked molecule junctions at room temperature.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9sc03760hDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6979055PMC
November 2019

Tuning the polarity of charge carriers using electron deficient thiophenes.

Chem Sci 2017 Apr 28;8(4):3254-3259. Epub 2017 Feb 28.

Department of Chemistry , Columbia University , 3000 Broadway, MC3124 , New York , NY 10027 , USA . Email:

Thiophene-1,1-dioxide (TDO) oligomers have fascinating electronic properties. We previously used thermopower measurements to show that a change in charge carrier from hole to electron occurs with increasing length of TDO oligomers when single-molecule junctions are formed between gold electrodes. In this article, we show for the first time that the dominant conducting orbitals for thiophene/TDO oligomers of fixed length can be tuned by altering the strength of the electron acceptors incorporated into the backbone. We use the scanning tunneling microscope break-junction (STM-BJ) technique and apply a recently developed method to determine the dominant transport channel in single-molecule junctions formed with these systems. Through these measurements, we find that increasing the electron affinity of thiophene derivatives, within a family of pentamers, changes the polarity of the charge carriers systematically from holes to electrons, with some systems even showing mid-gap transport characteristics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c6sc05283eDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5465950PMC
April 2017

Single-excitation dual-color coherent lasing by tuning resonance energy transfer processes in porous structured nanowires.

Nanoscale 2015 Oct;7(37):15091-8

Applied Optics Beijing Area Major Laboratory, Department of Physics, Beijing Normal University, Beijing, China100875.

Single-excitation dual-color coherent lasing was achieved in a mixed random system of a binary dye and the suspension of gold-silver porous nanowires with plenty of nanogaps. This greatly enhanced the local electromagnetic field in the visible range and guaranteed a low threshold and high Q factor (>10 000) operator for simultaneous dual-color lasing. By tuning the resonance energy transfer process in the stimulated emission, triple output modes (single chartreuse lasing, chartreuse and red dual-color lasing, and single red coherent lasing) were easily obtained. This triple-mode coherent random lasing introduces a new approach to designing multi-functional micro-optoelectronic devices for multi-color speckle-free imaging and interference.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c5nr03349gDOI Listing
October 2015

Control of single-molecule junction conductance of porphyrins via a transition-metal center.

Nano Lett 2014 Sep 15;14(9):5365-70. Epub 2014 Aug 15.

Molecular Foundry and Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.

Using scanning tunneling microscope break-junction experiments and a new first-principles approach to conductance calculations, we report and explain low-bias charge transport behavior of four types of metal-porphyrin-gold molecular junctions. A nonequilibrium Green's function approach based on self-energy corrected density functional theory and optimally tuned range-separated hybrid functionals is developed and used to understand experimental trends quantitatively. Importantly, due to the localized d states of the porphyrin molecules, hybrid functionals are essential for explaining measurements; standard semilocal functionals yield qualitatively incorrect results. Comparing directly with experiments, we show that the conductance can change by nearly a factor of 2 when different metal cations are used, counter to trends expected from gas-phase ionization energies which are relatively unchanged with the metal center. Our work explains the sensitivity of the porphyrin conductance with the metal center via a detailed and quantitative portrait of the interface electronic structure and provides a new framework for understanding transport quantitatively in complex junctions involving molecules with localized d states of relevance to light harvesting and energy conversion.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nl5025062DOI Listing
September 2014

Breakdown of interference rules in azulene, a nonalternant hydrocarbon.

Nano Lett 2014 May 22;14(5):2941-5. Epub 2014 Apr 22.

Department of Chemistry and ‡Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York 10027, United States.

We have designed and synthesized five azulene derivatives containing gold-binding groups at different points of connectivity within the azulene core to probe the effects of quantum interference through single-molecule conductance measurements. We compare conducting paths through the 5-membered ring, 7-membered ring, and across the long axis of azulene. We find that changing the points of connectivity in the azulene impacts the optical properties (as determined from UV-vis absorption spectra) and the conductivity. Importantly, we show here that simple models cannot be used to predict quantum interference characteristics of nonalternant hydrocarbons. As an exemplary case, we show that azulene derivatives that are predicted to exhibit destructive interference based on widely accepted atom-counting models show a significant conductance at low biases. Although simple models to predict the low-bias conductance do not hold with all azulene derivatives, we demonstrate that the measured conductance trend for all molecules studied actually agrees with predictions based on the more complete GW calculations for model systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/nl5010702DOI Listing
May 2014

Bandgap engineering through controlled oxidation of polythiophenes.

Angew Chem Int Ed Engl 2014 Feb 21;53(7):1832-6. Epub 2014 Jan 21.

Department of Chemistry, Columbia University, 3000 Broadway, MC3124, New York, NY 10027 (USA) http://camposgroup.chem.columbia.edu.

The use of Rozen's reagent (HOF⋅CH3 CN) to convert polythiophenes to polymers containing thiophene-1,1-dioxide (TDO) is described. The oxidation of polythiophenes can be controlled with this potent, yet orthogonal reagent under mild conditions. The oxidation of poly(3-alkylthiophenes) proceeds at room temperature in a matter of minutes, introducing up to 60 % TDO moieties in the polymer backbone. The resulting polymers have a markedly low-lying lowest unoccupied molecular orbital (LUMO), consequently exhibiting a small bandgap. This approach demonstrates that modulating the backbone electronic structure of well-defined polymers, rather than varying the monomers, is an efficient means of tuning the electronic properties of conjugated polymers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.201309398DOI Listing
February 2014

Cascade-pumped random lasers with coherent emission formed by Ag-Au porous nanowires.

Opt Lett 2014 Jan;39(1):5-8

A series of sequentially cascade-pumped random lasers is reported. It consists of three random lasers in which the Ag-Au bimetallic porous nanowires play the role of scatterers, and the gain materials are coumarin 440 (C440), coumarin 153 (C153), and rhodamine 6G (R6G), respectively. The random laser with C440 is first pumped by a 355 nm pulsed laser. The emission of C440 pumps the C153, and the emission of C153 pumps the R6G sequentially. Low-threshold coherent emissions from the three random lasers are observed. The cascade-pumped random lasers can be achieved easily with low cost and can be used in applications conveniently.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OL.39.000005DOI Listing
January 2014

Unusual molecular conformations in fluorinated, contorted hexabenzocoronenes.

Org Lett 2010 Nov;12(21):4840-3

Department of Chemical & Biological Engineering, Princeton University, Princeton, New Jersey 08544, United States.

Fluorinated, contorted hexabenzocoronenes (HBCs) have been synthesized in a facile manner via Suzuki-Miyaura coupling of fluorinated phenyl boronic acids followed by photocyclization and Scholl cyclization. In addition to the molecular conformation observed in previous HBC derivatives, close-contact fluorine-fluorine intramolecular interactions result in a metastable conformation not previously observed. Heating the metastable HBCs above 100 °C irreversibly converts them to the stable conformation, suggesting that the metastable conformation arises from a kinetically arrested state during cyclization.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ol102016mDOI Listing
November 2010

High rates and substrate selectivities in water by polyvinylimidazoles as transaminase enzyme mimics with hydrophobically bound pyridoxamine derivatives as coenzyme mimics.

J Am Chem Soc 2009 Nov;131(43):15604-5

Department of Chemistry, Columbia University, New York, New York 10027, USA.

Free-radical polymers of 4-vinylimidazole and copolymers with 1-dodecyl-4-vinylimidazole were used as enzyme mimics to transaminate pyruvic acid to alanine, phenylpyruvic acid to phenylalanine, and indole-3-pyruvic acid to tryptophan in water at pH 7.5 and 20 degrees C using pyridoxamines carrying hydrophobic side chains as coenzyme mimics. The best enzyme mimic accelerated the transamination of indole-3-pyruvic acid by a factor of 4 million relative to the rate without the polymer, a higher rate ratio than we had previously achieved with a polyaziridine-based enzyme mimic. The properties of various polyvinylimidazoles were compared, including those prepared with the RAFT modification of the polymerization process.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/ja9072589DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2794039PMC
November 2009

Dendrimers in solution can have their remote catalytic groups folded back into the core: enantioselective transaminations by dendritic enzyme mimics-II.

Bioorg Med Chem Lett 2009 Oct 21;19(19):5543-6. Epub 2009 Aug 21.

Columbia University, Department of Chemistry, 3000 Broadway, New York, NY 10027, USA.

PAMAM dendrimers with double thioether arms have been synthesized with a pyridoxamine core and terminal chiral amino groups. Transamination to afford natural isomers of phenylalanine and alanine induced enantioselectivity by the peripheral chiral caps, supporting a computer model that indicates folding of dendrimer chains back into the core.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.bmcl.2009.08.061DOI Listing
October 2009

Enantioselective Transaminations by Dendrimeric Enzyme Mimics.

Tetrahedron 2007 Jul;63(27):6317-6321

Department of Chemistry, Columbia University, New York NY 10027.

PAMAM dendrimers have been constructed with a pyridoxamine core, and chiral capping amino groups. Transamination to form phenylalanine and alanine from their related ketoacids produced enantioselectivities induced by the formally remote chiral caps, supporting computer models that indicate folding of the dendrimer chains back into the core region.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.tet.2007.02.052DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2031867PMC
July 2007
-->