Raman Spectroscopic and Quantum Chemical Investigation of the Pyridine-Borane Complex and the Effects of Dative Bonding on the Normal Modes of Pyridine

The pyridine-borane (PyBH3) complex was analyzed by Raman vibrational spectroscopy and density functional theory to elucidate its structural and vibrational properties and to compare these with those for neat pyridine (Py). The borane-nitrogen (BN) bond length, the BN dative bond stretching frequency, and the effects of dative-bonded complex formation on Py are presented. Rather than having a single isolated stretching motion, the complex exhibits multiple BN dative bond stretches that are coupled to Py\u27s vibrations. These modes exhibit large shifts that are higher in energy relative to neat Py, similar to previous observations of Py/water mixtures. However, significantly higher charge transfer was observed in the dative-bonded complex when compared to the hydrogen-bonded complex with water. A linear relationship between charge transfer and shifts to higher frequencies of pyridine\u27s vibrational modes agrees well with earlier observations. The present work is of interest to those seeking a stronger relationship between charge-transfer events and concomitant changes in molecular properties

Tracking the Amide I and αCOO− Terminal ν(C=O) Raman Bands in a Family of L-Glutamic Acid-Containing Peptide Fragments: A Raman and DFT Study

The E-hook of β-tubulin plays instrumental roles in cytoskeletal regulation and function. The last six C-terminal residues of the βII isotype, a peptide of amino acid sequence EGEDEA, extend from the microtubule surface and have eluded characterization with classic X-ray crystallographic techniques. The band position of the characteristic amide I vibration of small peptide fragments is heavily dependent on the length of the peptide chain, the extent of intramolecular hydrogen bonding, and the overall polarity of the fragment. The dependence of the E residue’s amide I ν(C=O) and the αCOO− terminal ν(C=O) bands on the neighboring side chain, the length of the peptide fragment, and the extent of intramolecular hydrogen bonding in the structure are investigated here via the EGEDEA peptide. The hexapeptide is broken down into fragments increasing in size from dipeptides to hexapeptides, including EG, ED, EA, EGE, EDE, DEA, EGED, EDEA, EGEDE, GEDEA, and, finally, EGEDEA, which are investigated with experimental Raman spectroscopy and density functional theory (DFT) computations to model the zwitterionic crystalline solids (in vacuo). The molecular geometries and Boltzmann sum of the simulated Raman spectra for a set of energetic minima corresponding to each peptide fragment are computed with full geometry optimizations and corresponding harmonic vibrational frequency computations at the B3LYP/6-311++G(2df,2pd) level of theory. In absence of the crystal structure, geometry sampling is performed to approximate solid phase behavior. Natural bond order (NBO) analyses are performed on each energetic minimum to quantify the magnitude of the intramolecular hydrogen bonds. The extent of the intramolecular charge transfer is dependent on the overall polarity of the fragment considered, with larger and more polar fragments exhibiting the greatest extent of intramolecular charge transfer. A steady blue shift arises when considering the amide I band position moving linearly from ED to EDE to EDEA to GEDEA and, finally, to EGEDEA. However, little variation is observed in the αCOO− ν(C=O) band position in this family of fragments

Taking “Fun and Games” Seriously: Proposing the Hedonic-Motivation System Adoption Model (HMSAM)

Hedonic-motivation systems (HMS)—systems used primarily to fulfill users’ intrinsic motivations—are the elephant in the room for IS research. Growth in HMS sales has outperformed utilitarian-motivation systems (UMS) sales for more than a decade, generating billions in revenue annually; yet IS research focuses mostly on UMS. In this study, we explain the role of intrinsic motivations in systems use and propose the hedonic-motivation system adoption model (HMSAM) to improve the understanding of HMS adoption. Instead of a minor, general TAM extension, HMSAM is an HMS-specific system acceptance model based on an alternative theoretical perspective, which is in turn grounded in flow-based cognitive absorption (CA). The HMSAM extends van der Heijden’s (2004) model of hedonic system adoption by including CA as a key mediator of perceived ease of use (PEOU) and of behavioral intentions to use (BIU) hedonic-motivation systems. Results from experiments involving 665 participants confirm that, in a hedonic context, CA is a more powerful and appropriate predictor of BIU than PEOU or joy, and that the effect of PEOU on BIU is fully mediated by CA sub-constructs. This study lays a foundation, provides guidance, and opens up avenues for future HMS, UMS, and mixed-motivation system research

Effect of Pyrolysis Temperature on PhysicoChemical Properties and Acoustic-Based Amination of Biochar for Efficient CO\u3csub\u3e2\u3c/sub\u3e Adsorption

© Copyright © 2020 Chatterjee, Sajjadi, Chen, Mattern, Hammer, Raman and Dorris. The present study examined the effect of pyrolysis temperature on the physicochemical properties of biochar, activation process and carbon capture. Two different categories of biochars were synthesized from herbaceous (miscanthus and switchgrass) and agro-industrial (corn stover and sugarcane bagasse) feedstock under four different pyrolysis temperatures −500, 600, 700, and 800°C. The synthesized biochars underwent sono-amination activation comprising low-frequency acoustic treatment followed by amine functionalization to prepare adsorbents for CO2 capture. The highest increment (200%) of CO2 capture capacity was observed for sono-aminated samples prepared at 600 and 700°C (maximum improvement for miscanthus), while biochars synthesized at 500 and 800°C demonstrated comparatively lesser increment in adsorption capacities that falls in the range of 115–151 and 127–159%, respectively compared to 600 and 700°C. The elevated pyrolysis temperature (particularly 600 and 700°C) resulted in increased %C and %ash contents and reduced %N contents with enhancement of micro surface area and pore volume. Thus, the superior adsorption capacity of miscanthus (at 600 and 700°C) can be attributed to their large surface areas (303–325 m2/g), high carbon contents (82–84%), and low ash contents (4–5%), as well as %N contents after sono-amination that was twice that of raw char

Proposing the Interactivity-Stimulus-Attention Model (ISAM) to Explain and Predict the Enjoyment, Immersion, and Adoption of Purely Hedonic Systems

Traditional TAM research primarily focuses on utilitarian systems where extrinsic motivations chiefly explain and predict acceptance. We propose a theoretical model, ISAM, which explains the role of intrinsic motivations in building the user attention that leads to hedonic system acceptance. ISAM combines several theories with TAM to explain how interactivity acts as a stimulus in hedonic contexts—fostering curiosity, enjoyment, and the full immersion of cognitive resources. Two experiments involving over 700 participants validated ISAM as a useful model for explaining and predicting hedonic system acceptance. Immersion and PE are shown to be the primary predictors of behavioral intention to use hedonic systems. Unlike traditional utilitarian adoption research, PEOU does not directly impact BIU, and extrinsic motivations are virtually non-existent. The implications of this study extend beyond hedonic contexts, as users of utilitarian systems continue to demand more hedonic features and enjoyment is often more important than PEOU

Early initiation of antiretroviral therapy and associated reduction in mortality, morbidity and defaulting in a nurse-managed, community cohort in Lesotho.

INTRODUCTION: The latest WHO guidelines recommend initiating antiretroviral therapy (ART) at CD4 cell counts less than 350 cells/μl. However, donors and national governments are reluctant to support implementation owing to uncertainty regarding feasibility and relative benefit. Lesotho has supported earlier initiation since 2008. We assessed outcomes comparing early (CD4 cell counts >200 cells/μl) and late (CD4 cell counts ≤200 cells/μl) initiation. METHODS: We describe survival probability among patients initiating ART at CD4 cell counts 200 or less and more than 200 cells/μl and assess associations between baseline CD4 cell counts and mortality, morbidity, loss to follow-up and hospitalization using Cox regression adjusting for confounders identified a priori. RESULTS: Our analysis included 1177 patients; median age was 38 years and the majority (67%) were women. Median time on ART for the overall cohort was 506 days (interquartile range 396-608). Five hundred and thirty eight patients initiated ART at a CD4 cell count 200 cells/μl or less (interquartile range 54-160) and 639 patients initiated at CD4 cell count more than 200 cells/μl (interquartile range 238-321). In multivariate analysis, we found that patients initiating at CD4 cell count more than 200 cells/μl were 68% less likely to die (adjusted hazard ratio 0.32, 95% confidence interval 0.20-0.50), and 39% less likely to be lost to follow-up (adjusted hazard ratio 0.61, 95% confidence interval 0.43-0.87). Initiating ART at CD4 cell count more than 200 cells/μl was also associated with a 27% reduction in the rate of incident morbidity (adjusted hazard ratio 0.73, 95% confidence interval 0.65-0.82) and a 63% decreased rate of hospitalization (adjusted hazard ratio 0.37, 95% confidence interval 0.19-0.73). CONCLUSION: Earlier initiation is feasible in a low resource, high HIV prevalence setting, and provides important benefits in terms of reduced mortality, morbidity, retention and hospitalization. Donors should fully support the implementation of the latest WHO recommendations

Urea functionalization of ultrasound-treated biochar: A feasible strategy for enhancing heavy metal adsorption capacity

© 2018 Elsevier B.V. The main objective of a series of our researches is to develop a novel acoustic-based method for activation of biochar. This study investigates the capability of biochar in adsorbing Ni(II) as a hazardous contaminant and aims at enhancing its adsorption capacity by the addition of extra nitrogen and most probably phosphorous and oxygen containing sites using an ultrasono-chemical modification mechanism. To reach this objective, biochar physically modified by low-frequency ultrasound waves (USB) was chemically treated by phosphoric acid (H3PO4) and then functionalized by urea (CO(NH2)2). Cavitation induced by ultrasound waves exfoliates and breaks apart the regular shape of graphitic oxide layers of biochar, cleans smooth surfaces, and increases the porosity and permeability of biochar\u27s carbonaceous structure. These phenomena synergistically combined with urea functionalization to attach the amine groups onto the biochar surface and remarkably increased the adsorption of Ni(II). It was found that the modified biochar could remove \u3e 99% of 100 mg Ni(II)/L in only six hours, while the raw biochar removed only 73.5% of Ni(II) in twelve hours. It should be noted that physical treatment of biochar with ultrasound energy, which can be applied at room temperature for a very short duration, followed by chemical functionalization is an economical and efficient method of biochar modification compared with traditional methods, which are usually applied in a very severe temperature (\u3e873 K) for a long duration. Such modified biochars can help protect human health from metal-ion corrosion of degrading piping in cities with aging infrastructure

A Raman spectroscopic and computational study of new aromatic pyrimidine-based halogen bond acceptors

© 2019 by the authors. Two new aromatic pyrimidine-based derivatives designed specifically for halogen bond directed self-assembly are investigated through a combination of high-resolution Raman spectroscopy, X-ray crystallography, and computational quantum chemistry. The vibrational frequencies of these new molecular building blocks, pyrimidine capped with furan (PrmF) and thiophene (PrmT), are compared to those previously assigned for pyrimidine (Prm). The modifications affect only a select few of the normal modes of Prm, most noticeably its signature ring breathing mode, ν1. Structural analyses afforded by X-ray crystallography, and computed interaction energies from density functional theory computations indicate that, although weak hydrogen bonding (C-H...O or C-H...N interactions) is present in these pyrimidine-based solid-state co-crystals, halogen bonding and π-stacking interactions play more dominant roles in driving their molecular-assembly

Heteroacene-Based Amphiphile as a Molecular Scaffold for Bioimaging Probes

The challenges faced with current fluorescence imaging agents have motivated us to study two nanostructures based on a hydrophobic dye, 6H-pyrrolo[3,2-b:4,5-b’]bis [1,4]benzothiazine (TRPZ). TRPZ is a heteroacene with a rigid, pi-conjugated structure, multiple reactive sites, and unique spectroscopic properties. Here we coupled TRPZ to a tert-butyl carbamate (BOC) protected 2,2-bis(hydroxymethyl)propanoic acid (bisMPA) dendron via azide-alkyne Huisgen cycloaddition. Deprotection of the protected amine groups on the dendron afforded a cationic terminated amphiphile, TRPZ-bisMPA. TRPZ-bisMPA was nanoprecipitated into water to obtain nanoparticles (NPs) with a hydrodynamic radius that was \u3c150 nm. For comparison, TRPZ-PG was encapsulated in pluronic-F127 (Mw = 12 kD), a polymer surfactant to afford NPs almost twice as large as those formed by TRPZ-bisMPA. Size and stability studies confirm the suitability of the TRPZ-bisMPA NPs for biomedical applications. The photophysical properties of the TRPZ-bisMPA NPs show a quantum yield of 49%, a Stokes shift of 201 nm (0.72 eV) and a lifetime of 6.3 ns in water. Further evidence was provided by cell viability and cellular uptake studies confirming the low cytotoxicity of TRPZ-bisMPA NPs and their potential in bioimaging

SWIR Emissive RosIndolizine Dyes With Nanoencapsulation In Water Soluble Dendrimers

Shortwave infrared (SWIR) emission has great potential for deep-tissue in vivo biological imaging with high resolution. In this article, the synthesis and characterization of two new xanthene-based RosIndolizine dyes coded PhRosIndz and tolRosIndz is presented. The dyes are characterized via femtosecond transient absorption spectroscopy as well as steady-state absorption and emission spectroscopies. The emission of these dyes is shown in the SWIR region with peak emission at 1097 nm. TolRosIndz was encapsulated with an amphiphilic linear dendritic block co-polymer (LDBC) coded 10-PhPCL-G3 with high uptake yield. Further, cellular toxicity was examined in vitro using HEK (human embryonic kidney) cells where a \u3e90% cell viability was observed at practical concentrations of the encapsulated dye which indicates low toxicity and reasonable biocompatibility