Characterization of Cassava Starch and Its Structural Changes Resulting of Thermal Stress by Functionally-Enhanced Derivative Spectroscopy (FEDS)

Two-dimensional Covalent organic frameworks (2D COFs) are periodic, permanently porous, and lightweight solids that are polymerized from topologically designed monomers. The predictable design and structural modularity of these materials make them promising candidates for applications including catalysis, environmental remediation, chemical separations, and organic electronics, many of which will require stability to mechanical and thermal stress. Based on their reinforced structures and high degradation temperatures as determined by thermal gravimetric analysis (TGA), many reports have claimed that COFs have excellent thermal stability. However, their stability to heat and pressure has not been probed using methods that report on structural changes rather than the loss of volatile compounds. Here we explore two structurally analogous 2D COFs with different polymerization chemistries using in operando X-ray diffraction, which demonstrates the loss of crystallinity at lower temperatures than the degradation temperatures measured by TGA. Density functional theory calculations suggest that an asymmetric buckling of the COF lattice is responsible for the observed loss of crystallinity. In addition to their thermal stability, x-ray diffraction of the 2D COFs under gas pressures up to 100 bar showed no loss in crystallinity or structural changes, indicating that these materials are robust to mechanical stress by applied pressure. We expect that these results will encourage further exploration of COF stability as a function of framework design and isolated form, which will guide the design of frameworks that withstand demanding application-relevant conditions.

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Effect of Drying Temperature in Biopolymeric Films of Cassava Starch and its Effect on Wettability, Water Vapor Barrier and Mechanical Properties

Materials Science Forum ◽

10.4028/www.scientific.net/msf.930.270 ◽

2018 ◽

Vol 930 ◽

pp. 270-275 ◽

Cited By ~ 1

Author(s):

Victor Rafael Leal Oliveira ◽

M.K.S. Monteiro ◽

F.K.G. Santos ◽

R.H.L. Leite ◽

E.M.M. Aroucha

Keyword(s):

Mechanical Properties ◽

Water Vapor ◽

Structural Changes ◽

High Efficiency ◽

Low Cost ◽

Water Vapor Permeability ◽

Cassava Starch ◽

Life Extension ◽

Vapor Permeability ◽

Drying Time

Coating technologies with biopolymeric films of low cost and high efficiency are effective in maintaining the chemical and sensory characteristics and shelf-life extension of several fruits.Films of cassava starch/glycerol were synthesized at different temperature and time conditions (25oC / 60h, 40oC / 5h, 60oC / 3h and 80oC / 2h) in order to decrease the drying time of the filmogenic solutions.SEM analysis (scanning electron microscopy), WVP (water vapor permeability), wettability and mechanical properties were evaluated in order to identify morphological and structural changes in the polymeric matrix in different conditions.Changes in temperature and drying time significantly reduced the roughness and affected the barrier characteristics, effectively improving tensile strength. A reduction of more than 90% in the drying time was identified.

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Natural and Chemically Modified Post-Mining Clays—Structural and Surface Properties and Preliminary Tests on Copper Sorption

Minerals ◽

10.3390/min9110704 ◽

2019 ◽

Vol 9 (11) ◽

pp. 704

Author(s):

Beata Jabłońska ◽

Mark Busch ◽

Andriy V. Kityk ◽

Patrick Huber

Keyword(s):

Structural Properties ◽

Surface Properties ◽

Structural Changes ◽

Low Cost ◽

Fractal Dimensions ◽

Nitrogen Adsorption ◽

Raw Material ◽

Water Pretreatment ◽

Maximum Sorption ◽

Nitrogen Adsorption Isotherms

The structural and surface properties of natural and modified Pliocene clays from lignite mining are investigated in the paper. Chemical modifications are made using hydrofluoric acid (HF), sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid (HNO3), sodium hydroxide (NaOH), and hydrogen peroxide (H2O2), at a concentration of 1 mol/dm3. Scanning electron microscopy is used to detect the morphology of the samples. Nitrogen adsorption isotherms were recorded to determine the specific surface area (SSA), mesoporosity, microporosity, and fractal dimensions. The raw clay has an SSA of 66 m2/g. The most promising changes in the structural properties are caused by modifications with HF or H2SO4 (e.g., the SSA increased by about 60%). In addition, the raw and modified clays are used in preliminary tests with Cu(II) sorption, which were performed in batch static method at initial Cu(II) concentrations of 25, 50, 80, 100, 200, 300, and 500 mg/dm3 in 1% aqueous suspensions of the clayey material. The maximum sorption of Cu(II) on the raw material was 15 mg/g. The structural changes after the modifications roughly reflect the capabilities of the adsorbents for Cu(II) adsorption. The modifications with HF and H2SO4 bring a similar improvement in Cu(II) adsorption, which is around 20–25% greater than for the raw material. The structural properties of investigated clays and their adsorptive capabilities indicate they could be used as low-cost adsorbents (e.g., for industrial water pretreatment).

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Molecular Recognition via Hydrogen Bonding in Supramolecular Complexes: A Fourier Transform Infrared Spectroscopy Study

Molecules ◽

10.3390/molecules23092278 ◽

2018 ◽

Vol 23 (9) ◽

pp. 2278 ◽

Cited By ~ 9

Author(s):

Alfonso Martinez-Felipe ◽

Fraser Brebner ◽

Daniel Zaton ◽

Alberto Concellon ◽

Sara Ahmadi ◽

...

Keyword(s):

Hydrogen Bonding ◽

Fourier Transform ◽

Infrared Spectroscopy ◽

Molecular Recognition ◽

Fourier Transform Infrared Spectroscopy ◽

Density Functional ◽

Fourier Transform Infrared ◽

Supramolecular Complexes ◽

Spectroscopic Techniques ◽

Temperature Dependent

We assess the assembly of supramolecular complexes by hydrogen bonding between azocompounds and a diacylaminopyridine monomer by temperature-dependent Fourier transform infrared spectroscopy (FT-IR) and density functional theory (DFT) calculations. The electronic delocalisation in the supramolecular rings formed by multiple hydrogen bonds stabilises the complexes, which coexist with dimeric species in temperature-dependent equilibria. We show how the application of readily available molecular modelling and spectroscopic techniques can predict the stability of new supramolecular entities coexisting in equilibria, ultimately assessing the success of molecular recognition.

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Application of Spectroscopy in Additive Manufacturing

Materials ◽

10.3390/ma14010203 ◽

2021 ◽

Vol 14 (1) ◽

pp. 203

Author(s):

Jingjunjiao Long ◽

Ashveen Nand ◽

Sudip Ray

Keyword(s):

Additive Manufacturing ◽

Material Selection ◽

Low Cost ◽

Raw Material ◽

Spectroscopic Techniques ◽

Processing Defects ◽

Product Assessment ◽

Raw Material Selection ◽

Am Processes

Additive manufacturing (AM) is a rapidly expanding material production technique that brings new opportunities in various fields as it enables fast and low-cost prototyping as well as easy customisation. However, it is still hindered by raw material selection, processing defects and final product assessment/adjustment in pre-, in- and post-processing stages. Spectroscopic techniques offer suitable inspection, diagnosis and product trouble-shooting at each stage of AM processing. This review outlines the limitations in AM processes and the prospective role of spectroscopy in addressing these challenges. An overview on the principles and applications of AM techniques is presented, followed by the principles of spectroscopic techniques involved in AM and their applications in assessing additively manufactured parts.

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Buckling of Two-Dimensional Covalent Organic Frameworks Under Thermal Stress

10.26434/chemrxiv.7831727 ◽

2019 ◽

Author(s):

Austin Evans ◽

Matthew Ryder ◽

Nathan C. Flanders ◽

Edon Vitaku ◽

Lin Chen ◽

...

Keyword(s):

Thermal Stability ◽

Thermal Stress ◽

Density Functional ◽

Structural Changes ◽

Gravimetric Analysis ◽

Two Dimensional ◽

Covalent Organic Frameworks ◽

X Ray Diffraction ◽

Excellent Thermal Stability ◽

X Ray

Two-dimensional Covalent organic frameworks (2D COFs) are periodic, permanently porous, and lightweight solids that are polymerized from topologically designed monomers. The predictable design and structural modularity of these materials make them promising candidates for applications including catalysis, environmental remediation, chemical separations, and organic electronics, many of which will require stability to mechanical and thermal stress. Based on their reinforced structures and high degradation temperatures as determined by thermal gravimetric analysis (TGA), many reports have claimed that COFs have excellent thermal stability. However, their stability to heat and pressure has not been probed using methods that report on structural changes rather than the loss of volatile compounds. Here we explore two structurally analogous 2D COFs with different polymerization chemistries using in operando X-ray diffraction, which demonstrates the loss of crystallinity at lower temperatures than the degradation temperatures measured by TGA. Density functional theory calculations suggest that an asymmetric buckling of the COF lattice is responsible for the observed loss of crystallinity. In addition to their thermal stability, x-ray diffraction of the 2D COFs under gas pressures up to 100 bar showed no loss in crystallinity or structural changes, indicating that these materials are robust to mechanical stress by applied pressure. We expect that these results will encourage further exploration of COF stability as a function of framework design and isolated form, which will guide the design of frameworks that withstand demanding application-relevant conditions.

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2,2’-Dipyridylamine as Organic Molecular Electrocatalyst for Hydrogen Evolution Reaction in Acidic Electrolytes

10.26434/chemrxiv.8273627.v1 ◽

2019 ◽

Cited By ~ 1

Author(s):

Xi Yin ◽

Ling Lin ◽

Hoon T. Chung ◽

Ulises Martinez ◽

Andrew M. Baker ◽

...

Keyword(s):

Hydrogen Evolution ◽

Hydrogen Evolution Reaction ◽

Density Functional ◽

Low Cost ◽

Membrane Electrode Assembly ◽

Carbon Surface ◽

Membrane Electrode ◽

Durability Test ◽

Onset Potential ◽

Precious Metal Catalysts

Finding a low-cost and stable electrocatalyst for hydrogen evolution reaction (HER) as a replacement for scarce and expensive precious metal catalysts has attracted significant interest from chemical and materials research communities. Here, we demonstrate an organic catalyst based on 2,2’-dipyridylamine (dpa) molecules adsorbed on carbon surface, which shows remarkable hydrogen evolution activity and performance durability in strongly acidic polymer electrolytes without involving any metal. The HER onset potential at dpa adsorbed on carbon has been found to be less than 50 mV in sulfuric acid and in a Nafion-based membrane electrode assembly (MEA). At the same time, this catalyst has shown no performance loss in a 60-hour durability test. The HER reaction mechanisms and the low onset overpotential in this system are revealed based on electrochemical study. Density functional theory (DFT) calculations suggest that the pyridyl-N functions as the active site for H adsorption with a free energy of -0.13 eV, in agreement with the unusually low onset overpotential for an organic molecular catalyst.<br>

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2,2’-Dipyridylamine as Organic Molecular Electrocatalyst for Hydrogen Evolution Reaction in Acidic Electrolytes

10.26434/chemrxiv.8273627 ◽

2019 ◽

Author(s):

Xi Yin ◽

Ling Lin ◽

Hoon T. Chung ◽

Ulises Martinez ◽

Andrew M. Baker ◽

...

Keyword(s):

Hydrogen Evolution ◽

Hydrogen Evolution Reaction ◽

Density Functional ◽

Low Cost ◽

Membrane Electrode Assembly ◽

Carbon Surface ◽

Membrane Electrode ◽

Durability Test ◽

Onset Potential ◽

Precious Metal Catalysts

Finding a low-cost and stable electrocatalyst for hydrogen evolution reaction (HER) as a replacement for scarce and expensive precious metal catalysts has attracted significant interest from chemical and materials research communities. Here, we demonstrate an organic catalyst based on 2,2’-dipyridylamine (dpa) molecules adsorbed on carbon surface, which shows remarkable hydrogen evolution activity and performance durability in strongly acidic polymer electrolytes without involving any metal. The HER onset potential at dpa adsorbed on carbon has been found to be less than 50 mV in sulfuric acid and in a Nafion-based membrane electrode assembly (MEA). At the same time, this catalyst has shown no performance loss in a 60-hour durability test. The HER reaction mechanisms and the low onset overpotential in this system are revealed based on electrochemical study. Density functional theory (DFT) calculations suggest that the pyridyl-N functions as the active site for H adsorption with a free energy of -0.13 eV, in agreement with the unusually low onset overpotential for an organic molecular catalyst.<br>

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Influence of Ascorbic Acid on the Structure and Function of Alpha-2- macroglobulin: Investigations using Spectroscopic and Thermodynamic Techniques

Protein and Peptide Letters ◽

10.2174/0929866526666191002113525 ◽

2020 ◽

Vol 27 (3) ◽

pp. 201-209

Author(s):

Syed Saqib Ali ◽

Mohammad Khalid Zia ◽

Tooba Siddiqui ◽

Haseeb Ahsan ◽

Fahim Halim Khan

Keyword(s):

Ascorbic Acid ◽

Conformational Changes ◽

Structural Changes ◽

The Body ◽

Titration Calorimetry ◽

Spectroscopic Techniques ◽

Human Beings ◽

Plasma Ascorbic Acid ◽

Dietary Antioxidant ◽

And Function

Background: Ascorbic acid is a classic dietary antioxidant which plays an important role in the body of human beings. It is commonly found in various foods as well as taken as dietary supplement. Objective: The plasma ascorbic acid concentration may range from low, as in chronic or acute oxidative stress to high if delivered intravenously during cancer treatment. Sheep alpha-2- macroglobulin (α2M), a human α2M homologue is a large tetrameric glycoprotein of 630 kDa with antiproteinase activity, found in sheep’s blood. Methods: In the present study, the interaction of ascorbic acid with alpha-2-macroglobulin was explored in the presence of visible light by utilizing various spectroscopic techniques and isothermal titration calorimetry (ITC). Results: UV-vis and fluorescence spectroscopy suggests the formation of a complex between ascorbic acid and α2M apparent by increased absorbance and decreased fluorescence. Secondary structural changes in the α2M were investigated by CD and FT-IR spectroscopy. Our findings suggest the induction of subtle conformational changes in α2M induced by ascorbic acid. Thermodynamics signatures of ascorbic acid and α2M interaction indicate that the binding is an enthalpy-driven process. Conclusion: It is possible that ascorbic acid binds and compromises antiproteinase activity of α2M by inducing changes in the secondary structure of the protein.

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