Side-chain Substitution Research Articles

Local Structure-Induced Selective Interactions Enables High-Performance and Burn-in-Free Organic Photovoltaics.

Oligomeric acceptors (OAs) have attracted considerable attention in the organic photovoltaics (OPV) field owing to their capacity in balancing the merits from both monomeric and polymeric acceptors. A delicate control over the distortion between blocks of OAs usually determines the performance and stability of relevant OPV devices. However, it imposes great complexity to realize a controllable degree of distortion by tuning the skeleton of blocks and the position of linker between blocks. Herein, we developed a facile strategy to rationally control the geometry distortion of OAs via a straightforward substitution of alkoxy side-chains on their blocks. This helps elucidate the integrated influences of molecular distortion and non-bonded contacts on the selective interactions between OA molecules and between OA and host acceptor in ternary blend. We demonstrate the alkoxy-OA molecules having stronger self-interactions would mitigate their interactions with host acceptor, therefore alleviating the kinetic diffusion and excessive aggregation of total acceptors. Combining with a composite-interlayer strategy by introducing a phenyl-substituted self-assembled monolayer to enhance the doping with polyoxometalate, an impressive efficiency of 20.1% is achieved accompanied by a negligible burn-in loss against physical aging. This study demonstrates the validation of tuning of selective interactions towards high-performance and burn-in-free OPV.

A scalable, chromatography-free, biocatalytic method to produce the xyloglucan heptasaccharide XXXG

Xyloglucan oligosaccharides (XyGOs) are highly branched, complex carbohydrates with a variety of chemical and biotechnological applications. Due to the regular repeating pattern of sidechain substitution of the xyloglucan backbone, well-defined XyGOs are readily accessed for analytical and preparative purposes by specific hydrolysis of the polysaccharide with endo-glucanases. To broaden the application potential of XyGOs, we present here an optimized, scalable method to access large quantities of galactosylated XyGOs by treatment of the bulk agricultural by-product, tamarind kernel powder (TKP), with a highly specific endo-xyloglucanase at high-solids content. Subsequent β-galactosidase treatment reduced XyGO complexity to produce exclusively the branched heptasaccharide XXXG (Xyl3Glc4: [α-D-Xylp-(1 → 6)]-β-D-Glcp-(1 → 4)-[α-D-Xylp-(1 → 6)]-β-D-Glcp-(1 → 4)-[α-D-Xylp-(1 → 6)]-β-D-Glcp-(1 → 4)-D-Glcp). The challenge of removing the co-product galactose was overcome by fermentation with baker’s yeast, thereby avoiding chromatography and other fractionation steps to yield highly pure XXXG. This simplified approach employs many of the core concepts of green chemistry and engineering, enables facile production of 100 g quantities of XyGOs and XXXG for laboratory use, and serves as a guide to further production scale-up for applications, including as prebiotics, plant growth effectors and elicitors, and building blocks for glycoconjugate synthesis.

Identification of glycosyltransferases mediating 2-O-arabinopyranosyl and 2-O-galactosyl substitutions ofglucuronosyl side chains of xylan.

Xylan is one of the major hemicelluloses in plant cell walls and its xylosyl backbone is often decorated at O-2 with glucuronic acid (GlcA) and/or methylglucuronic acid (MeGlcA) residues. The GlcA/MeGlcA side chains may be further substituted with 2-O-arabinopyranose (Arap) or 2-O-galactopyranose (Gal) residues in some plant species, but the enzymes responsible for these substitutions remain unknown. During our endeavor to investigate the enzymatic activities of Arabidopsis MUR3-clade members of the GT47 glycosyltransferase family, we found that one of them was able to transfer Arap from UDP-Arap onto O-2 of GlcA side chains of xylan, and thus it was named xylan 2-O-arabinopyranosyltransferase 1 (AtXAPT1). The function of AtXAPT1 was verified in planta by its T-DNA knockout mutation showing a loss of the Arap substitution on xylan GlcA side chains. Further biochemical characterization of XAPT close homologs from other plant species demonstrated that while the poplar ones had the same catalytic activity as AtXAPT1, those from Eucalyptus, lemon-scented gum, sea apple, 'Ohi'a lehua, duckweed and purple yam were capable of catalyzing both 2-O-Arap and 2-O-Gal substitutions of xylan GlcA side chains albeit with differential activities. Sequential reactions with XAPTs and glucuronoxylan methyltransferase 3 (GXM3) showed that XAPTs acted poorly on MeGlcA side chains, whereas GXM3 could efficiently methylate arabinosylated or galactosylated GlcA side chains of xylan. Furthermore, molecular docking and site-directed mutagenesis analyses of Eucalyptus XAPT1 revealed critical roles of several amino acid residues at the putative active site in its activity. Together, these findings establish that XAPTs residing in the MUR3 clade of family GT47 are responsible for 2-O-arabinopyranosylation and 2-O-galactosylation of GlcA side chains of xylan.

X-Ray-Sensitizers: Organic Pharmaceutical Drug Intermediates Activated Directly by X-Rays to Efficiently Populate Triplet Excitons for Cancer Treatment

Radiotherapy is an important treatment for cancer, but it is associated with major side effects due to the high dose of radiation (generally more than 50 Gy). Because radiation’s low acute and late toxicity, many tumors are treated with fractionated radiation in small doses (< 2 Gy). Scintillator X-ray-induced photodynamic therapy is an efficient methodology for cancer management that employs small doses of X-ray irradiation (< 2 Gy) in a complex process. Here we screened pharmaceutical drug intermediates that are derivatives of thioxanthone (TX) and investigated TX-derived organic pharmaceutical molecules that efficiently undergo X-ray-sensitization to populate triplet excitons (singlet oxygen) for cancer therapy when exposed to low-dose X-ray irradiation. By modifying alkoxy side chain substitutions at the 2-position to tune the molecular packing and intermolecular interactions, the fluorescence and room-temperature phosphorescence of a series of TX derivatives were assessed under X-ray irradiation. The ability of these derivatives to generate singlet oxygen and their potential for treating tumors provide new opportunities for developing organic molecules with simple chemical structures, in which large numbers of triplets can be populated directly under ultralow-dose X-ray irradiation.

6-Strand to Stable 10/12 Helix Conformational Switch by Incorporating Flexible β-hGly in the Homooligomers of Camphor Derived β-Amino Acid: NMR and X-Ray Crystallographic Evidence.

Rational design of unnatural amino acid building blocks capable of stabilizing predictable secondary structures similar to protein fragments is pivotal for foldamer chemistry/catalysis. Here, we introduce novel β-amino acid building blocks: [1S,2R,4R]exoCDA and [1S,2S,4R]endoCDA, derived from the abundantly available R(+)-camphor, which is traditionally known for its medicinal value. Further, we demonstrate that the homooligomers of exoCDA adopt 6-strand conformation, which switches to a robust 10/12-helix simply by inserting flexible β-hGly spacer at alternate positions (1 : 1 β-hGly/exoCDA heterooligomers), as evident by DFT-calculations, solution-state NMR spectroscopy and X-ray crystallography. To the best of our knowledge, this is the first example of crystalline-state structure of left-handed 10/12-mixed helix, that is free from the conventional approach of employing β-amino acids of either alternate chirality or alternate β2/β3 substitutions, to access the 10/12-helix. The results also show that the homooligomers of heterochiral exoCDA don't adopt helical fold, instead exhibit banana-shaped strands, whereas the homodimers of the other diastereomer endoCDA, nucleate 8-membered turns. Furthermore, the homo-exoCDA and hetero-[β-hGly-exoCDA] oligomers are found to exhibit self-association properties with distinct morphological features. Overall, the results offer new possibilties of constructing discrete stable secondary and tertiary structures based on CDAs, which can accommodate flexible residues with desired side-chain substitutions.

Small molecule donor third component incorporating thieno[3,2-b]thiophene unit enables 19.18% efficiency ternary organic solar cells with improved operational stability

The rational design of the third component to enhance the efficiency and stability of organic solar cell (OSC) is a critical and challenge. Herein, a thieno[3,2-b]thiophene (TT) substituted wide-bandgap small molecule donor BTTC, was designed, synthesized and incorporated into the state-of-the-art PM6:L8-BO binary to construct ternary OSC. The rigid side chain and planar molecule skeleton enables strong crystallinity and complementary absorption with binary system. The introduction of BTTC enhanced the molecular packing, fibril-like film and preferred vertical phase separation, yielding balanced and higher charge transport, more efficient exciton dissociation and suppressed charge recombination. Besides, lower energy loss was attained and thus leading to higher open-circuit voltage (VOC). Consequently, the introduction of BTTC achieved the highest efficiency of 18.8% along with extended operational stability. Furthermore, replacing L8-BO to BTP-eC9 further boosted the ternary PCE to 19.18%, standing one of the best charge management in ternary OSC. This work presents efficient rigid side chain substitution strategy to construct the third component of small molecule donor for high performance ternary OSCs with comprehensively improved photovoltaic parameters. This strategy broadens the selection of guest materials toward realizing the actual commercial application of OSCs.

Tailoring the Position of Ester Group on N-Alkyl Chains of Benzotriazole-based Small Molecule Acceptors for High-Performance Organic Solar Cells.

Side chain engineering plays a vital role in exploring high-performance small molecule acceptors (SMAs) for organic solar cells (OSCs). In this work, we designed and synthesized a series of A-DA'D-A type SMAs by introducing different N-substituted alkyl and ester alkyl side chains on benzotriazole (BZ) central unit and aimed to investigate the effect of different ester substitution positions on photovoltaic performances. All the new SMAs with ester groups exhibit lower the lowest unoccupied molecular orbital (LUMO) energy levels and more blue-shifted absorption, but relatively higher absorption coefficients than alkyl chain counterpart. After blending with the donor PM6, the ester side chain-based devices demonstrate enhanced charge mobility, reduced amorphous intermixing domain size and long-lived charge transfer state compared to the alkyl chain counterpart, which are beneficial to achieve higher short-circuit current density (Jsc ) and fill factor (FF), simultaneously. Thereinto, the PM6 : BZ-E31 based device achieves a higher power conversion efficiency (PCE) of 18.33 %, which is the highest PCE among the OSCs based on the SMAs with BZ-core. Our work demonstrated the strategy of ester substituted side chain is a feasible and effective approach to develop more efficient SMAs for OSCs.

Tailoring the Position of Ester Group on N‐Alkyl Chains of Benzotriazole‐based Small Molecule Acceptors for High‐Performance Organic Solar Cells

Side chain engineering plays a vital role in exploring high‐performance small molecule acceptors (SMAs) for organic solar cells (OSCs). In this work, we designed and synthesized a series of A‐DA’D‐A type SMAs by introducing different N‐substituted alkyl and ester alkyl side chains on benzotriazole (BZ) central unit and aimed to investigate the effect of different ester substitution positions on photovoltaic performances. All the new SMAs with ester groups exhibit lower the lowest unoccupied molecular orbital (LUMO) energy levels and more blue‐shifted absorption, but relatively higher absorption coefficients than alkyl chain counterpart. After blending with the donor PM6, the ester side chain‐based devices demonstrate enhanced charge mobility, reduced amorphous intermixing domain size and long‐lived charge transfer state compared to the alkyl chain counterpart, which are beneficial to achieve higher short‐circuit current density (JSC) and fill factor (FF), simultaneously. Thereinto, the PM6:BZ‐E31 based device achieves a higher power conversion efficiency (PCE) of 18.33%, which is the highest PCE among the OSCs based on the SMAs with BZ‐core. Our work demonstrated the strategy of ester substituted side chain is a feasible and effective approach to develop more efficient SMAs for OSCs.

Extraction of citrus pectin using pressurized carbon dioxide and production of its oligosaccharides

In this study, we utilized pressurized carbon dioxide (pCO2) for pectin extraction from citrus residues because of its potential to produce acid without chemicals, that is non-toxic, green technology for humans and the environment. The pCO2 was performed at 2.5 MPa and 90 °C for 90 min, while the conventional method (CM) for pectin extraction using HCl was performed under atmospheric pressure at 90 °C for 90 min. Pectin extraction yields with pCO2 depended on the type of citrus fruit and were lower than those obtained with the CM. However, pCO2-extracted pectin (pCO2-pectin) provided a higher degree of esterification (DE), neutral sugar side-chain substitution on the pectate backbone, and greater molecular size than those of pectin extracted using the conventional method (CM-pectin). Pectin oligosaccharide (POS) was prepared from CM-pectin and pCO2-pectin using viscozyme L hydrolysis under optimum conditions. These POSs were then designated as CM-POS and pCO2-POS, respectively. Both pCO2-POS and CM-POS stimulated the growth of Lactobacillus and Bifidobacterium species, and induced them to produce short-chain fatty acids, and slightly suppressed immunoglobulin E production in U266 cells. Furthermore, pCO2-POS had higher angiotensin-converting enzyme inhibitory activity compared to CM-POS. This study suggests that pCO2 is a novel method for extracting pectin with unique molecular properties affecting POS functionality in vitro.

Influence of the substituent in the benzene ring on the structure and properties of two isostructural crystals

This work provides a successful case of constructing single-component isostructural crystals with similar luminescence behavior using side-chain group substitution.

Elucidating the effects of the sidechain substitution direction on the optoelectronic properties of isomeric diketopyrrolopyrrole-based conjugated polymers for near-infrared organic phototransistors

Compared to P3BT-out, P3BT-in with sidechains in the inner way has better molecular planarity, narrower bandgap, and stronger light absorption ability, resulting in an increased electron mobility and higher near-infrared photoresponsivity.

C-reactive protein binds to short phosphoglycan repeats of Leishmania secreted proteophosphoglycans and activates complement.

Human C-reactive protein (CRP) binds to lipophosphoglycan (LPG), a virulence factor of Leishmania spp., through the repeating phosphodisaccharide region. We report here that both major components of promastigote secretory gel (PSG), the filamentous proteophosphoglycan (fPPG) and the secreted acid phosphatase (ScAP), are also ligands. CRP binding was mainly associated with the flagellar pocket when LPG deficient Leishmania mexicana parasites were examined by fluorescent microscopy, consistent with binding to secreted material. ScAP is a major ligand in purified fPPG from parasite culture as demonstrated by much reduced binding to a ScAP deficient mutant fPPG in plate binding assays and ligand blotting. Nevertheless, in sandfly derived PSG fPPG is a major component and the major CRP binding component. Previously we showed high avidity of CRP for LPG ligand required multiple disaccharide repeats. ScAP and fPPG only have short repeats but they retain high avidity for CRP revealed by surface plasmon resonance because they are found in multiple copies on the phosphoglycan. The fPPG from many species such as L. donovani and L. mexicana bound CRP strongly but L. tropica and L. amazonensis had low amounts of binding. The extent of side chain substitution of [-PO4-6Galβ1-4Manα1-] disaccharides correlates inversely with binding of CRP. The ligand for the CRP on different species all had similar binding avidity as the half maximal binding concentration was similar. Since the PSG is injected with the parasites into host blood pools and phosphoglycans (PG) are known to deplete complement, we showed that CRP makes a significant contribution to the activation of complement by PSG using serum from naive donors.

Manipulation of the spacing between the donor and acceptor by gradual side-chain modification to reduce energy loss of the organic solar cells

As one of the simple but effective molecular modify strategies, the side chain engineering based on siloxane-terminated alkyl side chain has been proved to be a promising design strategy for facilitating the formation of optimal film morphology, and further improving the photovoltaic performance of organic solar cells (OSCs). Herein, two polymer donors named 2FP-1EH-1Si and 2FP-2Si with symmetrical and asymmetrical siloxane-terminated alkyl side chain substitution were designed and synthesized. The results demonstrate that compared with the alkyl side chain substituted polymer 2FP-2EH, the introduction of siloxane-terminated alkyl side chain not only regulates the miscibility between the polymer donor and small molecular acceptor (SMA), but also affects the spacing between the donor (D) and the acceptor (A) molecules. As a result, the asymmetrical and symmetrical siloxane-terminated alkyl side chain substituted polymer 2FP-1EH-1Si and 2FP-2Si exhibit lower surface energy, stronger self-aggregation ability and higher hole mobility. More importantly, the OSCs based on 2FP-1EH-1Si:IT-4F and 2FP-2Si:IT-4F exhibited gradually decreased energy loss, which is suppressed by controlling the D-A spacing, along with the increased open-circuit voltage (VOC) from 0.77 V to 0.80 V and then to 0.86 V. This work further reveals the regulation mechanism of siloxane-terminated alkyl chain on the photovoltaic performance of active layer materials for efficient OSCs with enhanced stability.

I‐Indigo‐Based Self‐assembled Microparticles and Their Conversion to Nanoparticles

AbstractMicroscopic particles (MPs) are used to scatter and reflect UV light. It is well established that inorganic MPs such as TiO2 and ZnO produce carcinogens. Therefore, organic MPs are explored for UV absorption. Conjugated chromophores with differing lipophilicity usually self‐assemble into nanoscopic structures. In our previous experiments, unsymmetrical i‐Indigo was found to self‐assemble into 500 nm particles. We hypothesized that the size of the self‐assembled particles can be increased by increasing the lipophilicity difference between the side chains. Toward this objective, we have chosen the i‐Indigo core with TEG and alkyl chains as side chains. As a result, the i‐Indigo molecules were found to self‐assemble into 3 μ spheres in solution. By substituting side chains with different lipophilicity, i‐Indigo microparticles with the size of 5 μ are prepared. A careful analysis showed that the spheres are similar to a soccer ball, and they deflate upon drying on the substrate surface. The judiciously chosen side chain binds with a metal‐ion (Cs+) and forms nanoscopic assemblies. After Cs+ binding, the size of the particles is decreased drastically to 100 nm. The simple addition of ions converts microscopic assemblies into nanoscopic assemblies.

CHANGES IN HEMICELLULOSE STRUCTURE ASSOCIATED WITH THE TRANSITION FROM EARLYWOOD TO LATEWOOD AT JUVENILE WOOD IN CRYPTOMERIA JAPONICA

The chemical composition and variations in chemical structure of hemicellulose in earlywood (EW) and latewood (LW) of two individual Japanese cedar trees (C-Boka and T-Boka) were investigated. The trees were cultivated under different growth conditions: C-Boka grew slowly in a forest, while T-Boka grew rapidly in a location rich in nutrients and sunshine. For the chemical structure of hemicellulose, arabinoglucuronoxylan (AGX) showed varied side-chain substitution rates with glucuronic acid and different molecular weights in the transition between EW and LW. In contrast, the fundamental composition of glucomannan/galactoglucomannan (GM/GGM) was relatively unchanged between EW and LW. The modification of AGX and GM/GGM from EW to LW differed between C-Boka and T-Boka and might be influenced by the growth rate of the trees.

One-pot synthesis of cellulose ester–graft–polylactide copolymers in an ionic liquid and the effect of graft-chain composition on their thermoplasticities and enzymatic degradabilities

With the aim of developing polymers having controlled thermoplasticities and biodegradabilities, a series of cellulose ester–graft–polylactide copolymers was synthesized using a homogeneous one-pot system in which the reaction medium was the ionic liquid 1-ethyl-3-methylimidazolium diethylphosphate (EmimDEP). The structures and compositions of the copolymers were controlled by varying the feed ratio of the carboxylic anhydride (acetic (C2), propionic (C3), or hexanoic (C6)) and L-lactide. In terms of side-chain substitution, the copolymers exhibited DSAcyl values of 0.7–2.7 and MSPLA values of 3.2–14.2. With increasing DSAcyl, the copolymers presented enhanced thermal stability and thermoplasticity due to the intermolecular interactions between the acyl groups and polylactide side-chains. The effect of graft-chain composition on mechanical properties and biodegradability was investigated using homogeneous cast films prepared with the copolymers. The mechanical properties were found to be affected by the carbon number of the acyl group (C2–C6), with higher carbon numbers imparting better plasticization. To investigate biodegradability, a two-step enzymatic degradation was performed using proteinase K and then cellulase. The copolymers with DSAcyl values below 1.3 exhibited enzymatic biodegradability with weight losses in the range 15.2%–34.6% (cf. 58.4% for polylactide).

Revealing intermolecular coupling effects on vibrational spectra with infrared-reflectance absorbance analysis of perylene diimide thin films

Intermolecular interactions govern the optical and electronic properties of organic semiconductor thin films. Optimizing the function of molecular devices such as organic solar cells and light emitting diodes relies on understanding structural effects in a heterogeneous film environment. Because organic thin films are typically more disordered than inorganic crystalline semiconductors, advanced techniques are often needed to sufficiently characterize these materials. However, polarized infrared reflectance measurements are a benchtop method that can provide well-resolved vibrational spectra with specificity in their molecular orientation. By using infrared reflectance-absorbance spectroscopy (IRRAS) we relate the effects of intermolecular packing geometry on thin film vibrational spectra of perylene diimide (PDI), a prototypical molecular semiconductor. We analyze a suite of PDIs with differing sidechain substitutions, which adopt distinct crystal packing arrangements in thin films, by comparison of the reflectance spectra to isotropic KBr mixtures. We observe differences in the degree of Davydov splitting as a function of displacement along the short and long molecular axes and the π-π stacking distance that are evident in either the symmetric or anti-symmetric CO stretching frequencies of the solid. The four PDIs also display changes in relative intensity between the two modes that indicate different average molecular orientations.

Organic nanoparticles with tunable AIE derived from amino acids appended naphthalenediimide based amphiphiles

Fluorescent organic nanoparticles (FONPs) are unique cooperative manifestations of supramolecular self-aggregates and luminescent nanoparticles. In this work, we developed naphthalenediimide (NDI) based amphiphiles (NDI-1-9) having amino acids substitution from L-alanine to L-phenyl alanine to 3-(2-naphthyl)-L-alanine in absence and presence of alkyl spacer (C-6, C-11). Formation of self-aggregated spherical organic nanoparticles of ∼50 nm took place at and above 50 vol% water or methyl cyclohexane (MCH) in different binary solvent systems (DMSO/DMF-water, CHCl3-MCH) via J-aggregation. In case of NDI-1-3 (amino acids are directly connected to the NDI) self-assembled FONPs (MCH in CHCl3) exhibited aggregation-induced emission (AIE) through excimer formation. Red shift in the emission maxima were observed from 484 nm to 495 nm, and 590 nm, respectively with increasing π electron cloud at substituted donor from NDI-1 to NDI-3. Alongside, in case of aromatic amino acids substitution, FONPs of 6-amino caproic acid spacer containing NDI derivatives (NDI-5 and NDI-6) showed AIE at 505 nm and 545 nm (water in DMF/DMSO). Corresponding 11-amino undecanoic acid containing analogues (NDI-8 and NDI-9) showed AIE at 480 nm and 585 nm in CHCl3-MCH and DMF/DMSO-water. The multi colour emission from blue-green to yellow-orange with enrichment of π-electron cloud density in the side chain substitution of NDI was observed possibly due to the facilitated electron transfer at a lesser energy to the electron deficient NDI core that resulted in red shifted emission maxima. This was further clarified by regulating the availability of π-electrons of phenyl ring of NDI-2 by including electron withdrawing –NO2 and donating -OMe groups at the molecular backbone (NDI-2a and NDI-2b) that showed blue shifted (475 nm) and red shifted (570 nm) emission maxima with respect to NDI-2 (495 nm). However, increase in alkyl spacer length between side chain substitution and NDI core yielded relatively lower quantum yield presumably due to the impeded electron transfer.

Effect of bulky side groups on photophysical properties and electroluminescent performance of oligo(styryl)benzenes

The rational design of electroluminescent compounds has been recognized as a promising strategy to maximize the efficiency of electronic devices. In this work, we analyze the impact of the substitution of n-alkyl and n-alkoxy side chains by bulkier side groups (tert-butyl and tert-butoxy) on the photophysics of the two model fluorophores 1,3,5-tris(styryl)benzene and 1,2,4,5-tetra(styryl)benzene. We found that the bulky side groups have a significant contribution to the vibrational normal modes associated with the non-radiative deactivation. The aggregation-induced enhanced emission phenomenon observed in some cases was attributed to the blocking of the trans→cis photoisomerization and the restriction of intramolecular vibrations. In the solid state, the bulky side groups have demonstrated to play a determining role in the supramolecular structure and photophysical properties, particularly in the case of the tetra(styryl)benzenes. In light-emitting devices, we found that the incorporation of the bulky side groups in oligo(styryl)benzenes could reduce the electromer formation and improve the device performance. The tetra(styryl)benzenes, and particularly the tert-butyl derivative, showed better device performance, with lower turn-on voltage, higher current density and electroluminescent intensity.

Experimental and simulated distribution and interaction of water in cellulose esters with alkyl chain substitutions

This study investigated the effect of the average length of substituted side chains in different cellulose esters on water sorption and the water association mechanism. For this purpose, a set of esters with a similar total degree of substitution was selected: cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate. Dynamic vapor sorption was used to determine the effect of the side chain length on sorption, desorption, and the occurrence of water clustering. Since water association in the structure was of interest, molecular dynamics simulations were performed on cellulose acetate and cellulose acetate propionate. This study showed that cellulose acetate appears to be water-sensitive and experiences hysteresis upon water sorption, which was attributed to structural changes. The simulations also showed that water is screened out by the side chains and forms intermolecular hydrogen bonds, primarily to the carbonyl oxygen rather than the residual hydroxyl groups.