Compositional and optical characteristics of aqueous brown carbon and HULIS in the eastern Indo-Gangetic Plain using a coupled EEM PARAFAC, FT-IR and 1H NMR approach.

This study provides insights into the fluorophoric composition of aqueous brown carbon (BrCaq) and chemically-separated humic-like substances (HULIS): neutral HULIS (HULIS-n; at pH = 7) and acidic HULIS (HULIS-a; at pH = 2) on a seasonal and day-night basis in the eastern Indo-Gangetic Plain (IGP), India. A coupled approach including excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC) model, Fourier-transformed infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy was employed to understand the links between structural, compositional and fluorophoric characteristics of BrCaq and HULIS fractions. HULIS fluorophores (HULISfluoro) with varying oxidation states transported from the northwest IGP were dominant during biomass burning seasons (post-monsoon and winter), while protein-like fluorophores (PRLISfluoro) from marine emissions showed large contributions during summer. HULIS-n moieties were mostly primary in nature with higher conjugation, while HULIS-a were associated with secondarily formed and aged species with a larger contribution from degradation products. A substantial presence of tyrosine-like proteins in both chemically-separated HULIS fractions indicated that atmospheric HULIS is not entirely humic or fulvic-like in the eastern IGP. Finally, the dominance of H-C-O groups across seasons suggested consistent fossil fuel signatures along with season-specific influence of photodegradable cellulose from marine organisms in the summer and biomass burning in the post-monsoon and winter.

Optical source apportionment of aqueous brown carbon (BrC) on a daytime and nighttime basis in the eastern Indo-Gangetic Plain (IGP) and insights from 13C and 15N isotopic signatures.

This study reports day-night and seasonal variations of aqueous brown carbon (BrCaq) and constituent humic-like substances (HULIS) (neutral and acidic HULIS: HULIS-n and HULIS-a) from the eastern Indo-Gangetic Plain (IGP) of India during 2019-2020. This is followed by the application of the receptor model positive matrix factorization (PMF) for optical source apportionment of BrCaq and the use of stable isotopic ratios (δ13C and δ15N) to understand atmospheric processing. Nighttime BrCaq absorption and mass absorption efficiencies (MAE) were enhanced by 40-150 % and 50-190 %, respectively, compared to the daytime across seasons, possibly as a combined effect from daytime photobleaching, dark-phase secondary formation, and increased nighttime emissions. MAE250 nm/MAE365 nm (i.e., E2/E3) ratios and Angstrom Exponents revealed that BrCaq and HULIS-n were relatively more aromatic and conjugated during the biomass burning-dominated periods while BrCaq and HULIS-a were comprised mostly of non-conjugated aliphatic structures from secondary processes during the photochemistry-dominated summer. The relative radiative forcing of BrCaq with respect to elemental carbon (EC) was 10-12 % in the post-monsoon and winter in the 300-400 nm range. Optical source apportionment using PMF revealed that BrCaq absorption at 300, 365 and 420 nm wavelengths in the eastern IGP is mostly from biomass burning (60-75 %), followed by combined marine and fossil fuel-derived sources (24-31 %), and secondary processes (up to 10 %). Source-specific MAEs at 365 nm were estimated to be the highest for the combined marine and fossil fuel source (1.34 m2 g-1) followed by biomass burning (0.78 m2 g-1) and secondary processing (0.13 m2 g-1). Finally, δ13C and δ15N isotopic analysis confirmed the importance of summertime photochemistry and wintertime NO3--dominated chemistry in constraining BrC characteristics. Overall, the quantitative apportionment of BrCaq sources and processing reported here can be expected to lead to targeted source-specific measurements and a better understanding of BrC climate forcing in the future.

Are fireworks a significant episodic source of brown carbon?

We hypothesize that firework events involving the combustion of charcoal fuel, organic binders, metal salts, and cellulose-based wrapping material could be significant transient sources of aerosol brown carbon (BrC). To test this, we couple high time-resolution (1 min) measurements of black carbon (BC) and BrC absorption from a 7-wavelength aethalometer with time-integrated (12-24 h) measurements of filter extracts, i.e., UV-visible, fluorescence, and Fourier-transformed infrared (FT-IR) signatures of BrC, total and water-soluble organic carbon (OC and WSOC), ionic species, and firework tracer metals during a sampling campaign covering the Diwali fireworks episode in India. In sharp contrast to BC, BrC absorption shows a distinct and considerable rise of 2-4 times during the Diwali period, especially during the hours of peak firework activity, as compared to the background. Fluorescence profiles suggest enrichment of humic-like substances (HULIS) in the firework plume, while the enhancement of BrC absorption in the 400-500 nm range suggests the presence of nitroaromatic compounds (NACs). Considerable contributions of WSOC and secondary organics to OC (44.1% and 31.2%, respectively) and of the water-soluble fraction of BrC to total BrC absorption (71.0%) during the Diwali period point toward an atmospherically processed, polar signature of firework-related BrC, which is further confirmed by FT-IR profiles. This aqueous BrC exerts a short-lived but strong effect on atmospheric forcing (12.0% vis-à-vis BC in the UV spectrum), which could affect tropospheric chemistry via UV attenuation and lead to a stabilization of the post-Diwali atmosphere, resulting in enhanced pollutant build-up and exposure.

Brown carbon aerosols in the Indo-Gangetic Plain outflow: insights from excitation emission matrix (EEM) fluorescence spectroscopy.

We report the first characterization of the aerosol brown carbon (BrC) composition in the Indian context using excitation emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor (PARAFAC) analysis. We find that biomass burning (BB)-dominated wintertime aerosols in the Indo-Gangetic Plain (IGP) outflow are characterized by two humic-like (HULIS) (C1_aq and C2_aq) and one protein-like/fossil fuel-derived (C3_aq) component for aqueous-extractable BrC (BrCaq), and by one humic-like (C1_me) and one protein-like (C2_me) component for methanol-extractable BrC (BrCme). Strong correlations of the BB tracer nss-K+ with C1_aq and C2_aq (r = 0.75-0.84, p < 0.01) and C1_me (r = 0.77, p < 0.01) point towards the BB-dominated IGP outflow as the major source. This is also supported by the analysis of fluorescence indices, which suggest extensive humification of BB emissions during atmospheric transport. The HULIS components correlate significantly with BrC absorption (r = 0.85-0.94, p < 0.01), and contribute substantially to the BrC relative radiative forcing of 13-24% vis-à-vis elemental carbon (EC). There is strong evidence that the abundant BB-derived NOX leads to NO3- formation in the IGP plume and drives the formation of water-soluble nitroaromatics (NACs) that constrain BrCaq light absorption (r = 0.56, p < 0.01) to a considerable degree. Overall, the study uncovers complex atmospheric processing of the IGP outflow in winter, which has important implications for regional climate.

Sources and atmospheric processing of brown carbon and HULIS in the Indo-Gangetic Plain: Insights from compositional analysis.

We present here spectroscopic compositional analysis of brown carbon (BrC) and humic-like substances (HULIS) in the Indian context under varying conditions of source emissions and atmospheric processing. To this end, we study bulk water-soluble organic matter (WSOM), neutral- and acidic-HULIS (HULIS-n and HULIS-a), and high-polarity (HP)-WSOM collected in the eastern Indo-Gangetic Plain (IGP) with respect to UV-Vis, fluorescence, FT-IR, 1H NMR and 13C characteristics under three aerosol regimes: photochemistry-dominated summer, aged biomass burning (BB)-dominated post-monsoon, and fresh BB-dominated winter. Absorption coefficients (babs_365 nm; Mm-1) of WSOM and HULIS fractions increase by a factor of 2-9 during winter as compared to summer, with HULIS-n dominating total HULIS + HP-WSOM absorption (73-81%). Fluorophores in HULIS-n appear to contain near-similar levels of aromatic and unsaturated aliphatic conjugation across seasons, while HULIS-a exhibits distinctively smaller-chain structures in summer and post-monsoon. FT-IR spectra reveals, among others, strong signatures of aromatic phenols in winter WSOM suggesting a BB-related origin. 1H NMR-based source attribution coupled with back trajectory analysis indicate the presence of secondary and BB-related organic aerosol (SOA and BBOA) in the post-monsoon and winter, and marine-derived OA (MOA) in the summer, which is supported by 13C measurements. Overall, these observations uncover a complex interplay of emissions and atmospheric processing of carbonaceous aerosols in the IGP.

Programmable One-Pot Synthesis of Heparin Pentasaccharide Fondaparinux.

The clinically approved Fondaparinux (Arixtra) has been used for the treatment of deep vein thrombosis and acute pulmonary embolism since 2002 and is considered to be better than the low-molecular weight heparin in terms of anticoagulation response, duration of action, and biosafety. However, the synthetic methods previously developed for its manufacture are relatively complicated, thus restricting its extensive use. We report here a potentially scalable and programmable one-pot synthesis of Fondaparinux using the [1,2,2] strategy and designed thioglycosides with well-defined reactivity as building blocks.

Optical properties of aerosol brown carbon (BrC) in the eastern Indo-Gangetic Plain.

We report here measurements of aerosol black carbon (BC) and aqueous and methanol-extractable brown carbon (BrCaq and BrCme) from a receptor location in the eastern Indo-Gangetic Plain (IGP) under two aerosol regimes: the photochemistry-dominated summer and biomass burning (BB) dominated post-monsoon. We couple time-resolved measurements of BC and aerosol light absorption coefficients (babs) with time-integrated analysis of BrC UV-Vis and fluorescence characteristics, along with measurements of total and water-soluble organic carbon (OC and WSOC), and ionic species (NH4+, K+, NO3-). In the BB regime, BC and its BB-derived fraction (BCBB) increased by factors of 3-4 over summertime values. In comparison, babs_365_aq and babs_365_me (absorption coefficients of BrCaq and BrCme at 365 nm) increased by a factor of 5 (9.7 ± 7.8 vs 2.1 ± 1.4 Mm-1) and 2.5 (17.2 ± 9.0 vs 6.9 ± 2.9 Mm-1), respectively, in the BB period over summer, and were highly correlated (r = 0.82-0.87; p < 0.01) with the BB-tracer nssK+. The wavelength dependence of babs_BrC (Ångstrom exponent: 5.9-6.2) and the presence of characteristic fluorescence peaks at 420-430 nm suggested presence of humic-like substances (HULIS) in the aged BB aerosol, while significant association between BrCaq and NO3- (r = 0.73; p < 0.01) possibly indicated formation of water-soluble nitroaromatic compounds. BrCaq contributed 55% to total BrC absorption at 300-400 nm while that for the water-insoluble component (WI-BrC) increased from 41% at 340 nm to ~60% at 550 nm, suggesting formation of water-insoluble polycyclic aromatic hydrocarbons (PAHs) and/or N-PAHs. Mass absorption efficiencies at 365 nm (MAE365) of BrCaq and BrCme in the BB regime (0.95 ± 0.45 and 1.17 ± 0.78 m2 g-1, respectively) were in line with values expected from photobleaching of BB source emissions after transport to the eastern IGP. Overall, BrCaq and BrCme were significant components of light absorbing aerosol in the BB regime, with contributions of 9 ± 5% and 16 ± 7%, respectively, to radiative forcing vis-à-vis BC in the 300-400 nm range.

Spatially resolved distribution, sources and health risks of heavy metals in size-fractionated road dust from 57 sites across megacity Kolkata, India.

This work reports the first assessment of contamination levels, source contributions and health risks associated with heavy metals (HMs) in road dust from Kolkata, the second-most polluted metropolis in India. To this end, samples collected from 57 locations across 6 land-use categories: residential, roadside, traffic, railway, port and industrial areas in the city during 2018 were analyzed for 11 major and trace metals (Ca, Mg, Fe, Al, Mn, Ni, V, Cu, Zn, Cr, Pb) in three size fractions: <75 µm, 75-125 µm and 125-300 µm. Overall, Mn, Zn, Cr, Pb, V, Cu and Ni were enriched in the smallest fraction by factors of 1.2-2.7. Based on metal distribution across land-use categories, crustal dust (Fe, Al, V), construction activities (Ca, Mg), metallurgical processes (Pb), and non-exhaust abrasive emissions from brake, tire and paint wear (Cu, Zn, Cr) were found to be significant. HMs such as Cu, Zn, Cr and Pb were considerably enriched over background levels as suggested by three contamination indices: Enrichment Factor (EF; overall range: 2.4-12.0), Index of Geo-accumulation (Igeo; overall range: 1.1-3.4), and Pollution Index (PI; overall range: 3.1-15.6). Geospatial mapping identified HM contamination hotspots (integrated PI >4) in west-central and northern parts (the older sections) of the city represented by industrial, port, and traffic-congested residential areas. Using positive matrix factorization (PMF), the following sources were apportioned for the three size fractions: crustal dust (48-66%), construction activities (18-20%), vehicular abrasion (7-21%), industrial emissions (5-8%), a Cr-dominated mixed source (6%) and an unassigned source (7%). Finally, health risk assessment in the form of cumulative hazard index (HI) and incremental lifetime cancer risk (ILCR) found that children (mean HIchildren: 1.29 and ILCRchildren: 2E-04) are comparatively more vulnerable than adults (mean HIadults: 0.22 and ILCRadults: 8E-05) to HM exposure, with the ingestion exposure pathway dominating over dermal contact and inhalation.

Hierarchical and Programmable One-Pot Oligosaccharide Synthesis.

This article presents a general experimental protocol for programmable one-pot oligosaccharide synthesis and demonstrates how to use Auto-CHO software for generating potential synthetic solutions. The programmable one-pot oligosaccharide synthesis approach is designed to empower fast oligosaccharide synthesis of large amounts using thioglycoside building blocks (BBLs) with the appropriate sequential order of relative reactivity values (RRVs). Auto-CHO is a cross-platform software with a graphical user interface that provides possible synthetic solutions for programmable one-pot oligosaccharide synthesis by searching a BBL library (containing about 150 validated and >50,000 virtual BBLs) with accurately predicted RRVs by support vector regression. The algorithm for hierarchical one-pot synthesis has been implemented in Auto-CHO and uses fragments generated by one-pot reactions as new BBLs. In addition, Auto-CHO allows users to give feedback for virtual BBLs to keep valuable ones for further use. One-pot synthesis of stage-specific embryonic antigen 4 (SSEA-4), which is a pluripotent human embryonic stem cell marker, is demonstrated in this work.

An Efficient Modular One-Pot Synthesis of Heparin-Based Anticoagulant Idraparinux.

Idraparinux is a fully O-sulfated α-methyl glycoside of heparin pentasaccharide motif known to interact with the antithrombin III domain and act as anticoagulant. The current most effective synthesis of Idraparinux is complicated and nonstereoselective, requiring numerous stepwise procedures with low yields. We report here an efficient modular one-pot synthesis of Idraparinux involving the use of a glycosyl phosphate with 6- O- tert-butyl diphenyl silyl group and a d-glucuronic acid-containing disaccharide thioglycoside with 6- O-acetyl group as donor building blocks for the α-directing one-pot glycosylations with an l-iduronic acid-containing disaccharide acceptor building block. The uronic acid was incorporated in a disaccharide module used in the one-pot synthesis to avoid the complicated late-stage installation of these acidic sugars. The one-pot synthesis of Idraparinux demonstrated here is an effective strategy and should be applicable to the modular assembly of other heparan sulfates with regiodefined sulfation pattern for functional study.

Synthesis of Sialidase-Resistant Oligosaccharide and Antibody Glycoform Containing α2,6-Linked 3Fax-Neu5Ac.

Fluorinated glycosides are known to resist the glycosidase-catalyzed glycosidic bond cleavage; however, the synthesis of such glycans, especially 3-fluoro-sialic acid (3F-Neu5Ac) containing sialosides, has been a major challenge. Though the enzymatic synthesis of α-2,3-linked 3F-sialosides was reported, until recently there has not been any effective method available for the synthesis of 3F-sialosides in the α-2,6-linkage. In order to understand the biological effect of such modification, we report here a chemical synthesis of 3Fax-Neu5Ac-α2,6-Gal as a building block for the assembly of 3Fax-Neu5Ac-containing sialosides and a representative homogeneous antibody glycoform. Our results showed that the sialosides are stable under sialidase catalysis and the rituximab glycoform with a sialylated complex-type biantennary glycan terminated with 3Fax-Neu5Ac in the α-2,6-linkage (α2,6-F-SCT) has a similar binding avidity as its parent glycoform. These findings open up new opportunities for the development of therapeutic glycoproteins with improved pharmacokinetic parameters.

Hierarchical and programmable one-pot synthesis of oligosaccharides.

The programmable one-pot oligosaccharide synthesis method was designed to enable the rapid synthesis of a large number of oligosaccharides, using the software Optimer to search Building BLocks (BBLs) with defined relative reactivity values (RRVs) to be used sequentially in the one-pot reaction. However, there were only about 50 BBLs with measured RRVs in the original library and the method could only synthesize small oligosaccharides due to the RRV ordering requirement. Here, we increase the library to include 154 validated BBLs and more than 50,000 virtual BBLs with predicted RRVs by machine learning. We also develop the software Auto-CHO to accommodate more data handling and support hierarchical one-pot synthesis using fragments as BBLs generated by the one-pot synthesis. This advanced programmable one-pot method provides potential synthetic solutions for complex glycans with four successful examples demonstrated in this work.

Programmable one-pot synthesis of heparin pentasaccharides enabling access to regiodefined sulfate derivatives.

Heparin (H) and heparan sulfate (HS) belong to the glycosaminoglycan (GAG) family of oligosaccharides, and their sequences and sulfation patterns are known to regulate the functions of various proteins in biological processes. Among these, the 6-O-sulfation of HS/H contributes most significantly to the structural diversity and binding interactions. However, the synthesis of HS with defined sulfation patterns remains a major challenge. Herein, we report a highly efficient and programmable one-pot method for the synthesis of protected heparin pentasaccharides using thioglycoside building blocks with optimized relative reactivities to allow the selective deprotection and preparation of regiodefined sulfate derivatives.

Synthesis of Modular Building Blocks using Glycosyl Phosphate Donors for the Construction of Asymmetric N-Glycans.

Glycosyl phosphates are known as versatile donors for the synthesis of complex oligosaccharides both chemically and enzymatically. Herein, we report the stereoselective construction of modular building blocks for the synthesis of N-glycan using glycosyl phosphates as donors. We have synthesized four trisaccharide building blocks with orthogonal protecting groups, namely, Manß2GlcNAc(OAc)3ß6GlcNAc (9), Manß2GlcNAc-ß6GlcNAc(OAc)3 (15), Manß2GlcNAc(OAc)3ß4GlcNAc (18) and Manß2GlcNAcß4GlcNAc(OAc) (22) for further selective elongation using glycosyltransferases. The glycosylation reaction using glycosyl phosphate was found to be high yielding with shorter reaction time. Initially, The phthalimide protected glucosamine donor was exploited to ensure the formation of ß-glycosidic linkage and later converted to the N-acetyl group before the enzymatic synthesis. The selective deprotection of O-benzyl group was performed prior to enzymatic synthesis to avoid its negative interference.

Solid state structure of p-bromo phenyl 4,5,7-tri-O-benzyl-ß-D-glycero-D-talo-septanoside and an analysis of non-covalent interactions.

The solid state structure of a new seven-membered sugar oxepane derivative, namely, p-bromo phenyl 4,5,7-tri-O-benzyl-ß-D-glycero-D-talo-septanoside is discussed, as determined through single crystal X-ray structural determination and in relation to their conformational features. The molecule adopts twist-chair as the preferred conformation, with conformational descriptor (O,1)TC(2,3). The solid state packing of molecules is governed by a rich network of non-covalent bonding originating from O-H⋯O, C-H⋯π, C-H⋯Br and aromatic π⋯π interactions that stabilize the packing of molecules in the crystal.

Glycosidic bond hydrolysis in septanosides: a comparison of mono-, di-, and 2-chloro-2-deoxy-septanosides.

A kinetic study of the hydrolytic stabilities of mono-, di-, and 2-chloro-2-deoxy septanosides, under acid-catalysis, is reported herein. A comparison of mono- and diseptanosides, shows that the glycosidic bond in the disaccharide is more stable than the monosaccharide. Further the glycosidic bond at the reducing end hydrolyzes almost twice as faster than that of the non-reducing end of the disaccharide. 2-Chloro-2-deoxy septanoside is found to be the most stable and its glycosidic bond hydrolysis occurs at elevated temperatures only. The orientation of the exo-cyclic hydroxymethyl group and the inductive effect are suggested to play a role in the rates of hydrolysis.

Dense network of O-H⋯O and C-H⋯O interactions in the solid state structure of n-pentyl-2-chloro-2-deoxy-α-D-manno-sept 3-uloside.

Single crystal X-ray structural analysis of a septanoside, namely, n-pentyl-2-chloro-2-deoxy sept-3-uloside (1) provides many finer details of the molecular structure, in addition to its preferred twist-chair conformation, namely, (5,6)TC3,4 conformation. Structural analysis reveals a dense network of O-H⋯O, C-H⋯O and van der Waals interactions that stabilize interdigitized, planar bi-layer structure of the crystal lattice.

Exclusive ring opening of gem-dihalo-1,2-cyclopropanated oxyglycal to oxepines in AgOAc.

Treatment of gem-dihalo-1,2-cyclopropanated d-oxyglycal with primary, secondary, and unsaturated alcohols, in the presence of AgOAc, leads to the formation of chloro-oxepines exclusively. Reaction of the resulting 2-chloro-oxepines with excess alcohol in the presence of AgOAc, do not promote further reactions. This result is in contrast to the reactions of d-glucal derived halo-oxepine with alcohols known previously that lead to the formation of furanoses as the major product under similar reaction conditions. Observation of this study consolidates the reactivity differences of gem-dihalo-1,2-cyclopropanated oxyglycals, as compared to gem-dihalo-1,2-cyclopropanated glycals.

Branching out at C-2 of septanosides. Synthesis of 2-deoxy-2-C-alkyl/aryl septanosides from a bromo-oxepine.

This paper deals with the synthesis of 2-deoxy-2-C-alkyl/aryl septanosides. A range of such septanoside derivatives was synthesized by using a common bromo-oxepine intermediate, involving C-C bond forming organometallic reactions. Unsaturated, seven-membered septanoside vinyl bromides or bromo-oxepines, obtained through a ring expansion methodology of the cyclopropane derivatives of oxyglycals, displayed a good reactivity towards several acceptor moieties in C-C bond forming Heck, Suzuki and Sonogashira coupling reactions, thus affording 2-deoxy-2-C-alkyl/aryl septanosides. Whereas Heck and Sonogashira coupling reactions afforded 2-deoxy-2-C-alkenyl and -alkynyl derivatives, respectively, the Suzuki reaction afforded 2-deoxy-2-C-aryl septanosides. Deprotection and reduction of the 2-deoxy-2-alkenyl derivative afforded the corresponding 2-deoxy-2-C-alkyl septanoside free of protecting groups. The present study illustrates the reactivity of bromo-oxepine in the synthesis of hitherto unknown septanosides, branching out at C-2, through C-C bond formation with alkyl and aryl substituents.