Side Chain Length Research Articles

Cyclic carbonates as building blocks for non‐isocyanate polyurethanes

AbstractThree different cyclic carbonates (ethylene, propylene, and butylene carbonate) that can be derived from CO2 were successfully polymerized with hexamethylenediamine to form non‐isocyanate polyurethanes (NIPUs) via self‐polycondensation route without the use of harmful di‐isocyanates. Three different catalysts were compared for their performance in self‐polycondensation. Increasing the side chain length in cyclic carbonate increased the amount of urea side reaction and decreased the solubility of the final product. The increased amount of urea lead to a more thermoset behavior as the melting and decomposition took place simultaneously. Furthermore, the extent of urea side reaction and melting behavior were adjustable with the selection of the catalyst or polymerization parameters. With ethylene and propylene carbonate based precursors, it was possible to obtain promising melting temperatures and lap shear strength for the NIPUs when optimized polymerization parameters and catalyst were used.

Construction of alkali-stable anion exchange membranes with hydrophilic/hydrophobic microphase separation structure by adjusting side chain length

A series of side-chains anion exchange membranes were assembled by poly (arylene ether ketone) with amino groups (Am-PAEK) which was grafted different length of side chains by Friedel-Crafts acylation and then imidazole cationic groups were introduced by bromination reaction. The side-chain membranes exhibited excellent mechanical properties, thermal stability and alkali stability. In addition, swelling ratios of side chain membranes were lower than 10% even at 100 °C. And the alkali stability of Im-AP-6 (where Am-PAEK was grafted with 6-bromohexanoyl chloride and then grafted with 1,2-dimethylimidazole.) was higher than 87% after immersing in 1 M NaOH for 168 h at 60 °C. Hydroxide conductivities of the membranes were in the range of 43.5 ∼ 49.8 mS cm−1 at 30 °C and 87.3 ∼ 126.6 mS cm−1 at 80 °C. The open circuit voltage (OCV) and peak power density of Im-AP-6 were 1.13 V and 389.71 mW cm−2 (80 °C, 100% RH), respectively. The results showed side-chain membranes have good comprehensive properties and substantially possible as AEMs.

Study on the dispersion performance and mechanism of polycarboxylate superplasticizer by the long side‐chain dicarboxyl terminated

AbstractThe steric hindrance formed by polyether side chains is the key factor determining the dispersion performance of polycarboxylate superplasticizer (PCE). While with the increase of the side chain length, the coiled conformation of side chain will prevent the dispersion ability of PCE from being further improved. In this work, the methallyl polyoxyethylene ether (HPEG) was esterified with tricarballylic acid (TA) to obtain dicarboxyl terminated macromonomer, and further used to synthesize polycarboxylate (PCETA). The fluidity tests show that compared with ordinary PCE‐B2400 with short side chain, the dispersion performance of PCETA‐2400 was slightly improved. While for the PCEs with long side chain, the dispersion ability of PCETA‐4000 was significantly improved than that of ordinary PCE‐B4000. The adsorption layer thickness of PCETA‐4000 adsorbed on the surface of SiO2 sphere measured by dynamic light scattering is 7.93 nm, which is 1.3 times that of PCE‐B4000. Due to electrostatic repulsion between the carboxylic groups, the stretching of long side‐chain forms stronger steric hindrance and enhancing the dispersion of cement particles. In addition, PCETA also shows good slump retention and clay resistance properties, and it is an excellent multi‐functional concrete admixture with great application potential.

Selective solvent vapor induced self-assembly of silicon-containing bottlebrush block copolymer thin films to generate mesoporous silicon oxide patterns

Bottlebrush block copolymers (BBCPs) are intriguing architectures that can produce various anisotropic nanostructures dictated by the composition, length of the backbone and the lengths of side-chains. Here, we develop a facial approach toward ordered inorganic silicon oxide patterns and particles on substrates by solvent vapor induced thin film self-assembly of anisotropic bottlebrush block copolymers (BBCP) containing polydimethylsiloxane (PDMS) and polystyrene (PS) side chains. The in-plane cylindrical or stripes-like, spherical, and ordered porous morphologies as well as Janus particles-like morphology were fabricated on the substrate through solvent vapor annealing (SVA). The Janus particle-like morphology consisting of PS heads inserted in PDMS heads were directed to produce meso-to macroporous silicon oxide bowls after oxygen plasma etching. The effects of the solvent vapor on the molecular geometry and morphology of the BBCPs were described, and the influence of the backbone length on the self-assembly behavior of the thin film were discussed. This work demonstrates that silicon-containing BBCPs with a native etch contrast and a large difference in solubility parameters are potential candidates to generate ordered silicon oxide templates of different geometries with periodicity 80–150 nm providing access to length scales larger than linear block copolymers.

Synthesis of Amino Acids Bearing Halodifluoromethyl Moieties and Their Application to p53-Derived Peptides Binding to Mdm2/Mdm4.

Therapeutic peptides are a significant class of drugs in the treatment of a wide range of diseases. To enhance their properties, such as stability or binding affinity, they are usually chemically modified. This includes, among other techniques, cyclization of the peptide chain by bridging, modifications to the backbone, and incorporation of unnatural amino acids. One approach previously established, is the use of halogenated aromatic amino acids. In principle, they are thereby enabled to form halogen bonds (XB). In this study, we focus on the -R-CF2X moiety (R = O, NHCO; X = Cl, Br) as an uncommon halogen bond donor. These groups enable more spatial variability in protein-protein interactions. The chosen approach via Fmoc-protected building blocks allows for the incorporation of these modified amino acids in peptides using solid-phase peptide synthesis. Using a competitive fluorescence polarization assay to monitor binding to Mdm4, we demonstrate that a p53-derived peptide with Lys24Nle(εNHCOCF2X) exhibits an improved inhibition constant Ki compared to the unmodified peptide. Decreasing Ki values observed with the increasing XB capacity of the halogen atoms (F ≪ Cl < Br) indicates the formation of a halogen bond. By reducing the side chain length of Nle(εNHCOCF2X) to Abu(γNHCOCF2X) as control experiments and through quantum mechanical calculations, we suggest that the observed affinity enhancement is related to halogen bond-induced intramolecular stabilization of the α-helical binding mode of the peptide or a direct interaction with His54 in human Mdm4.

Combined interaction of PCE chains lengths, C3A and water content in cementitious systems

In this study, the interaction of polycarboxylate ether-based water reducing admixture (PCE) molecule chain length variation with cements having different C3A contents and water content was investigated. For this purpose, a total of seven PCEs were synthesized following three different approaches, i.e., the main chain length changed at a constant side chain length, the side chain lengths varied at a constant main chain length, and both main and side chain lengths changed at a similar molecular weight. Paste and mortar mixtures were prepared with the PCEs and CEM I-42.5R type cements containing three different C3A contents (3.60%, 6.82%, 9.05%). The effects of above mentioned variables on the rheological properties and compressive strength of the paste/mortar mixtures were determined. The interaction of PCEs with cements having different C3A contents was investigated in detail by performing total organic carbon (TOC) and dynamic light scattering (DLS) analyses. The increase in the main and side chain lengths of PCE molecule up to a certain point positively affected the fresh properties of cementitious systems. Beyond a certain point (i.e. when main chain length is higher than 21 k), the increase in main chain length reduced the hydrodynamic diameter of PCE molecules (up to 32%), and decreased the dispersion performance of the admixture. The increment in side chain length (i.e. when side chain length is higher than 2100 g/mole), on the other hand, adversely affected the rheological properties, especially with high C3A cements.

Outer sidechain engineering of selenophene and thiophene-based Y-series acceptors to produce efficient indoor organic solar cells

In recent years, efficient indoor organic photovoltaics (OPVs) have emerged as promising energy harvesters to drive Internet of Nanothings (IoNT) applications. The diverse design strategies developed for non-fullerene acceptor (NFA) materials have dramatically increased the power conversion efficiency (PCE) of indoor OPVs to 31%, and progress tends to continue. In this context, the current study investigated the indoor performance of NFA-OPVs by modifying the chalcogen-containing heterocycle of the acceptor molecule to thiophene (ThTh) and selenophene (ThSe), and changing the length of the external side chain using n-hexyl (C6) and n-nonyl (C9) components. Compared with the ThSe systems, the ThTh-containing OPVs exhibited enhanced current densities (JSC) and open-circuit voltages (VOC) owing to their enhanced crystallinity and reduced degree of bimolecular recombination. Similarly, the introduction of a short side chain (i.e., C6) led to relatively reduced monomolecular recombination and a moderated planarity compared to the system modified with the long side chain (i.e., C9). Ultimately, this resulted in an enhanced JSC and improved charge transport properties. Finally, the optimized OPV exhibited a PCE of 24.6% under a 1000 lx light-emitting diode lamp.

The Effect of a Blended Polycarboxylate Superplasticizer on the Rheology of Self-Compacting Concrete Paste

High-strength-performing concretes (HSPC) have been used extensively due to new building requirements and their special properties suitable for modern cities. Superplasticizers (SPs) are essential components in the mix design of these concretes since they control their fresh properties and improve durability. In practice, superplasticizers are used to achieve a desired workability without increasing the water content by dispersing agglomerated cement particles. The aim of this research was to investigate the effectiveness of a blended polycarboxylate (PCE) superplasticizer on the rheological behavior for three different cements. It was found that two SP agents with the same molecular structure but with different weight and side-chain length provided an SP product that had a greater effect on the rheological properties of the cement paste. Yield stress values remained unaffected in the presence of blended SP with an SP fraction above 50% and with long side chains while its adsorption ability increased with the decrease in SP fraction with shorter side chains and lower molecular mass.

Different starch varieties influence the complexing state and digestibility of the resulting starch-lipid complexes

In this study, we investigated the complexing state and digestibility of complexes formed between myristic acid (MA) and several varieties of starch (maize starch, MS; waxy maize starch, WS; high amylose maize starch, HMS; rice starch, RiS; cassava starch, CS; potato starch, PS). The resistant starch (RS) content, complexing index, and degree of the structural order of HMS-MA and MS-MA complexes were significantly higher (p < 0.05) than those of the other complexes. Notably, the RS increments of MS-MA complexes were the highest (14.10%). CS-MA, MS-MA and RiS-MA complexes showed better thermal stability of starch than the other complexes. The MA molecules were primarily physically embedded outside the helical structure of starch in WS-MA and PS-MA complexes. Additionally, CS-MA complexes possessed the highest relative number of physically embedded MA molecules. Moreover, the distribution of physically embedded MA molecules in WS-MA, CS-MA, and PS-MA complexes was more homogeneous than that in the other complexes. The weight-average molecular weight of amylose, average chain length of amylopectin side chains, and the proportion of chains with a degree of polymerization of 6–12 and 25–36 greatly affected their interactions with MA molecules. These results indicated that starch types substantially influenced the digestibility of the complexes, which was closely related to their complexing state and structural order.

Diagonal Interactions between Glutamate and Arginine Analogs with Varying Side-Chain Lengths in a β-Hairpin

Cross-strand interactions are important for the stability of β-sheet structures. Accordingly, cross-strand diagonal interactions between glutamate and arginine analogs with varying side-chain lengths were studied in a series of β-hairpin peptides. The peptides were analyzed by homonuclear two-dimensional nuclear magnetic resonance methods. The fraction folded population and folding free energy of the peptides were derived from the chemical shift data. The fraction folded population trends could be rationalized using the strand propensity of the constituting residues, which was not the case for the peptides with lysine analogs, highlighting the difference between the arginine analogs and lysine analogs. Double-mutant cycle analysis was used to derive the diagonal ion-pairing interaction energetics. The most stabilizing diagonal cross-strand interaction was between the shortest residues (i.e., Asp2-Agp9), most likely due to the least side-chain conformational penalty for ion-pair formation. The diagonal interaction energetics in this study involving the arginine analogs appears to be consistent with and extend beyond our understanding of diagonal ion-pairing interactions involving lysine analogs. The results should be useful for designing β-strand-containing molecules to affect biological processes such as amyloid formation and protein-protein interactions.

Elucidating the particle concentration-dependent flow behavior of aqueous TiO2 suspensions based on polymer dispersant structures and interparticle surface distances

Flowing behavior of concentrated aqueous TiO2 suspensions was evaluated in relation to the structure of polymeric dispersants, their adlayer thickness on particle surface, and particle concentrations. Comb-type polymeric dispersants comprising polyethylene glycol-based side chains with different combinations of unit number and side chain length were investigated. Based on particle concentration–apparent viscosity curves of the suspensions with TiO2 nanoparticles saturated with dispersants, maximum packing fraction and polymer adlayer thickness were estimated through the Krieger–Dougherty model. When the steric repulsive force of polymer dispersant dominated van der Waals attractive forces, the flow curves of the suspension exhibited hysteresis characteristics as the average particle surface distance approached the adlayer thickness of polymer dispersants. Additionally, by introducing the concept of relative surface distance, which is the average particle surface distance divided by the adlayer thickness, the particle concentration dependency of the suspension viscosities with different dispersants followed a unified trend.

Application of machine learning models to predict cytotoxicity of ionic liquids using VolSurf principal properties

Ionic Liquids (ILs) are considered greener alternatives to traditional organic solvents due to their unique physical and chemical properties. Nevertheless, recent studies showed that ILs can induce toxic effects in ecosystem. Therefore, it is essential to determine the level of risk to the aquatic life to successfully use these ILs. Toxicity measurement of various ILs on a broad spectrum of conditions through experimental techniques is way demanding on time, resources, and is at times impractical. Various research works have been performed in Quantitative Property Relationship (QSAR/QSPR) for IL toxicity prediction expressed as EC50. In this study, five supervised machine learning models were trained and tested using nine Principal Properties (PPs) as descriptors to predict leukemia rat cell line (IPC-81) cytotoxicity. Then eight feature selection techniques were used to preprocess the data to improve the performance of the best machine learning model among the preliminary trained models. Analysis of the performance of the models on predicting the out-of-sample data set showed that the Extreme Gradient Boosting (XGBoost) supervised machine learning model is the best in predicting with the highest test score (R2 = 0.79). This model was the most parsimonious (minimum AIC of 46.50), consistent (minimum RMSE of 0.45), and precise (minimum MAE of 0.32) in predicting IPC-81 cytotoxicity. The feature importance attribute of XGBoost confirmed that the structural features of ILs’ cation like cationic hydrophilicity and the side chain length have significant impact on the toxicity. Nevertheless, the anionic part of IL is also important to their toxicity and needs to be considered in toxicity prediction. Among the tested feature selection techniques, the random forest technique was the best in improving model performance (i.e., the least error matrices: AIC = 41.22, MAE = 0.31 and RMSE = 0.4259 respectively) but at longer execution time. However, the wrapper methods were the most robust in improving computational efficiency (i.e, improved the model performance at the shortest execution time). Therefore, this study improves QSPR studies on toxicity prediction of new ILs with the application of machine learning and feature selection techniques.

Bio-derived lactones – Combustion and exhaust emissions of a new class of renewable fuels

The use of bioderived drop-in fuels is an essential step in the reduction in fossil fuel usage. While ethanol and biodiesel are known quantities, the use of novel biomass that does not compete with food for its production could be vital in ensuring a reliable supply. Lactones are a class of chemicals that can also be sourced from 2nd generation biomass and possess molecular attributes that, from previous investigations within the group, are believed to be effective in reducing particulate emissions relative to diesel, while maintaining high ignition propensity. In this study, a systematic investigation of the combustion and exhaust emissions of a series of lactone fuels in a compression ignition engine was undertaken. The results indicated that blended C6 lactones- ε-caprolactone, δ-hexalactone and γ-caprolactone- displayed promising ignition qualities, relative to butanol, an alcohol often employed in diesel blending experiments. Ignition delay decreased as the length of the lactone side chain increased, but combustion was seemingly more stable in both ε-caprolactone and γ-caprolactone, compared to the methyl branched δ-hexalactone, which possessed the highest CO emissions and particle number. The C10 lactone, γ-decalactone, within the diesel-butanol blend, possessed excellent ignition quality, while also reducing particle mass significantly. All blends produced lower nitrogen oxides (NOx) emissions and particle mass than unblended fossil diesel. Subsequently, two C10 and two C12 lactones were employed- based on their potential to be derived from biomass- as pure fuels in the engine. Despite significant differences in physical properties compared to diesel, stable combustion was observed, with ignition delay approximately equivalent to that of base diesel. The high carbon number and long alkyl chains of the C12 lactones meant that particulate emissions were comparable to diesel. C10 lactones showed greater alleviation of particulate emissions, likely due to a combination of lower carbon number and extended ignition delay relative to diesel, while all pure lactone fuels significantly reduced NOx emissions, suggested to be due to combustion phasing.

Toward solvent selection for the extractive removal of pyridine from fuels using ionic liquids: A QSPR study

In the present study, the distribution of pyridine between the ionic liquid (IL)-rich phase and hydrocarbon-rich phase has been predicted using the quantitative structure–property relationship (QSPR) approach. After a comprehensive survey in the literature, a large dataset including 51 ternary systems (i.e., IL (1), pyridine (2), and hydrocarbon (3)) was collected. The present dataset covers 19 cations, 14 anions, and 10 hydrocarbons. Therefore, the structural effect of each cation, anion, and hydrocarbon has been taken into account on the prediction of pyridine distribution between the IL-rich phase and hydrocarbon-rich phase. Multiple linear regression (MLR) and multi-layer perceptron (MLP) have been employed to develop the predictive/descriptive linear and non-linear models, respectively. Results showed that the final linear model (R2 = 0.9165, %AARD = 23.2722) and non-linear model (R2 = 0.9892, %AARD = 9.1936) have an acceptable prediction capability. By interpreting the selected descriptors of the QSPR model, the effect of changes in the cation, anion, and hydrocarbon structures on the extraction of pyridine was also studied. It was found that the size, branches, and cyclic or acyclic structure of hydrocarbons were important parameters affecting the pyridine distribution. Also, the size, branches, and position of the electronegative atoms (especially oxygen atoms) in the structure of anions as well as the alkyl side chain length and C-N bonds in the structure of cations could also affect the pyridine distribution.

Structure-Activity Relationships of Ligand Binding to Oxysterol-Binding Protein (OSBP) and OSBP-Related Protein 4.

Oxysterol-binding protein (OSBP) and OSBP-related protein 4 (ORP4) have emerged as potentially druggable targets in antiviral and precision cancer drug development. Multiple structurally diverse small molecules function through targeting the OSBP/ORP family of proteins, including the antiviral steroidal compounds OSW-1 and T-00127-HEV2. Here, the structure-activity relationships of oxysterols and related compound binding to human OSBP and ORP4 are characterized. Oxysterols with hydroxylation at various side chain positions (i.e., C-20, C-24, C-25, and C-27)─but not C-22─confer high affinity interactions with OSBP and ORP4. A library of 20(S)-hydroxycholesterol analogues with varying sterol side chains reveal that side chain length modifications are not well tolerated for OSBP and ORP4 interactions. This side chain requirement is contradicted by the high affinity binding of T-00127-HEV2, a steroidal compound lacking the side chain. The binding results, in combination with docking studies using homology models of OSBP and ORP4, suggest multiple modes of steroidal ligand binding to OSBP and ORP4.

Investigating Fundamental Principles of Nonequilibrium Assembly Using Temperature-Sensitive Copolymers.

Both natural biomaterials and synthetic materials benefit from complex energy landscapes that provide the foundation for structure-function relationships and environmental sensitivity. Understanding these nonequilibrium dynamics is important for the development of design principles to harness this behavior. Using a model system of poly(ethylene glycol) methacrylate-based thermoresponsive lower critical solution temperature (LCST) copolymers, we explored the impact of composition and stimulus path on nonequilibrium thermal hysteretic behavior. Through turbidimetry analysis of nonsuperimposable heat-cool cycles, we observe that LCST copolymers show clear hysteresis that varies as a function of pendent side chain length and hydrophobicity. Hysteresis is further impacted by the temperature ramp rate, as insoluble states can be kinetically trapped under optimized temperature protocols. This systematic study brings to light fundamental principles that can enable the harnessing of out-of-equilibrium effects in synthetic soft materials.

Comparison of adjuvant mechanisms of medium-chain triacylglycerol in a mouse FITC-induced contact hypersensitivity model

The number of allergy sufferers has been increasing with the increase in chemicals to which we are potentially exposed. We have discovered that tributyrin, a short-chain triacylglycerol (TAG), enhanced fluorescein isothiocyanate (FITC)-induced contact hypersensitivity in a mouse model. Medium-chain triacylglycerols (MCTs) are used in cosmetics, with which we come into direct contact frequently, to maintain skin conditions and as a thickening agent for cosmetics. In this study, we examined whether MCTs with different side chain lengths enhanced skin sensitization to FITC in the mouse model. During skin sensitization to FITC, the presence of tributyrin (side chain carbon number, 4; C4) as well as that of each MCT, tricaproin (C6), tricaprylin (C8), or tricaprin (C10), resulted in enhanced skin sensitization, whereas that of trilaurin (C12) did not. As to the mechanism underlying the enhanced sensitization, three MCTs (C6, C8 and C10) facilitated migration of FTIC-presenting CD11c+ dendritic cells to draining lymph nodes. These results indicated that not only tributyrin but also MCTs, up to side chain carbon number 10, have an adjuvant effect on FITC-induced skin hypersensitivity in mice.

Chain-Length Induced Structural Polymorphism for two-dimension self-assembly

Structural polymorphism obtained through the 2D self-assembly which was made use of the chain-ength induced, has has aroused wide concern. On the one hand, owing to its significance meaning in crystal engineering, on the other hand, it has a broad application prospect in nano science and technolog.The assembly of symmetric 2, 7-bis (n-alkoxy) -9-fluorenone(F-OCn) with varying lengths of peripheral alkyl chains dissolved in homologous acids was investigated. The size and shape of molecules and the structure and position of substituents were critical factors that regulate the equilibrium of the interaction and formation of self-assembled patterns. Useing altered the symmetry and chain-length of the molecular structure, the self-assembly morphology and cellular properties can be predicted. The self-assembled strcture displayed the assembly of F-OCn (11-14). “S” shaped and alternating phases are the thermodynamic stable states. The competition between van der Waals forces from the interdigital alkyl chains and van der Waals forces between molecule-substrate takes effect. The vdW forces between the molecule-substrate was predominant when n varies from 15 to 18. The observation of the chain-length effects and odd-even effects showed that: F-OCeven developed from a loose-and close-packed patterns to a dislocated zigzag patterns.Self-assembled morphology of F-OCodd evolved from a well-distributed trimer monolayer to the dislocated zigzag pattern.These researches offers insight into the structural diversity by regulating the alkyl side chain-length and odd-even effects on two-dimension self-assembly and the construct a new molecular materials.

Small Schiff base molecules derived from salicylaldehyde as colorimetric and fluorescent neutral-to-basic pH sensors

The development of pH sensors is very important to distinguish different pHs in several applications. In this study, we examined the change of the side chain moiety on the photophysical properties of eight pH-sensitive small Schiff bases (SBs) that can act as both, colorimetric and fluorometric probes. For that, we synthesized all SBs by condensation between salicylaldehyde with a primary amine (methyl-, ethyl-, isopropyl, propyl-, butyl-, pentyl-, cyclohexyl-, and benzyl-amine). The complete molecular structure was confirmed by 1H NMR, 13C NMR, FTIR, UV–Vis, and by GC–FID purity over 90% was confirmed for all synthesized SBs. Theoretical calculations were also performed to give support to our findings. All synthesized samples were tested as a colorimetric and fluorometric pH sensor in the range of pH 3.0–12.0. All SBs exhibited similar behavior, despite the side chain lengths. The SBs are quite long-lived in water solution, allowing their usage as pH sensor. While between pH 3.0–7.0 they are colorless due to the presence of the protonated species, HSB, above pH 7.0 they turn yellow due to the formation of SB−, indicating that the chromogenic property depends on the pH. Additionally, these SBs also exhibit fluorogenic characteristic as they show fluorescence off at acidic pH 3.0–7.0 and fluorescence on (508 nm) above pH 8.0, exhibiting a linear response between pH 7.0–9.0. The pKa value was calculated using the Henderson–Hasselbalch equation for all SBs, obtaining values from 8.20 to 8.52. All SBs act as pH-sensitive colorimetric and fluorometric probes in neutral-to-basic solutions and this process is reversible.

Systematic Molecular-Size Variants in Diphosphonate Inhibitors for Oilfield Scale Management

Organophosphorus-based scale inhibitors (SIs) have been widely used in the petroleum industry for several decades. Among them, aminomethylenephosphonates (possessing at least one −NH+–CH2–PO3H– moiety) have shown outstanding inhibition efficiency against carbonate and sulfate oilfield scales. However, one of the main drawbacks of aminomethylenephosphonate-based SIs with multiple phosphonate (−PO3H2) groups is their poor tolerance against high-calcium brines. In this work, the calcium tolerance of aminomethylenephosphonates was improved by reducing the number phosphonate groups in the inhibitor backbone to less than three and introducing a variable-length non-polar alkyl side chain while maintaining acceptable inhibitory efficiency levels. Hence, we synthesized a series of variable-length alkyl chain-based amino-di(methylenphosphonate) [(H2O3P–CH2)2–N–(X)] inhibitors, (X = methyl, ethyl, propyl, butyl, hexyl, octyl, and dodecyl). In addition, we also studied the role of the alkyl side-chain length in the diphosphonate structure backbone on the scale inhibitory activity. All newly synthesized aminomethylenediphosphonates were evaluated as SIs for calcium carbonate (calcite) and barium sulfate (barite) in brines based on the Heidrun oilfield using a high-pressure dynamic tube blocking rig at 100 °C and 80 bar. Furthermore, we investigated the calcium compatibility of all aminomethylenediphosphonate SIs at several levels of calcium stresses. The new aminoalkyldiphosphonate inhibitors possessing shorter alkyl chain lengths (X = methyl, ethyl, propyl, butyl, and hexyl) gave better calcite scale inhibition performance and outstanding calcium compatibility of up to 1000 ppm of Ca2+ compared to the commercial benchmark ATMP SI [amino-tris(methylenephosphonate)] and longer alkyl-chain diphosphonates, that is, octylamine-N,N-di(methylenephosphonate) (ODMP, C8-D) and dodecylamine-N,N-di(methylenephosphonate) (DDMP, C12-D). Moreover, we tested the thermal stability (at 130 °C for one week) of the best-performing additive (based on calcite inhibition and calcium tolerance performances), and it was found that methylamine-N,N-dimethylenephosphonate (MDMP, C1-D) was thermally stable under these harsh conditions without any loss of its inhibition performance. The Ca-C8-D “complex” was deliberately synthesized and structurally characterized. It appears that the major factor for its poor Ca tolerance is the tight packing of the octyl side-chain groups.