Nucleic acids, proteins, and polysaccharides are the most important classes of biopolymers. The inherent properties of biomacromolecules are contrary to those of well-defined small molecules consequently raising a number of specific challenges which become particularly apparent if biomacromolecules are treated as objects in quantitative analysis. At the same time, their specific functional ability of molecular recognition and self-organization (e.g., enzymes, antibodies, DNA) enables us to make biomacromolecules serving as molecular tools in biochemistry and molecular biology, or as precisely controllable dimensional platforms for nanometrological applications. Given the complexity of biomacromolecules, quantitative analysis is not limited to the measurement of their concentration but also involves the determination of numerous descriptors related to structure, interaction, activity, and function. Among the biomacromolecules, glycans set examples that quantitative characterization is not necessarily directed to the measurement of amount-of-substance concentration but instead involves the determination of relative proportions (molar ratios) of structural features for comparison with theoretical models. This article addresses current activities to combine optical techniques such as Raman spectroscopy with isotope dilution approaches to realize reference measurement procedures for the quantification of protein biomarkers as an alternative to mass spectrometry-based techniques. Furthermore, it is explored how established ID-MS protocols are being modified to make them applicable for quantifying virus proteins to measure the HIV viral load in blood samples. As an example from the class of carbohydrates, the challenges in accurate determination of substitution patterns are outlined and discussed. Finally, it is presented that biomacromolecules can also serve as tools in quantitative measurements of dimensions with an example of DNA origami to generate defined dimensional standards to be used for calibration in super-resolution fluorescence microscopy. Graphical abstractQuantitative analysis of biomacromolecules is accompanied with special challenges different from low molecular weight compounds. In addition, they are not only objects but also tools applicable for quantitative measurements

Multi-block glucans comprising permethylated and partially methylated blocks are compounds of interest. In order to monitor their formation by transglycosylation of corresponding starting glucans, a method has been developed and applied to model compounds. This method allows determining the average length of the blocks and the progress of incorporation of methyl blocks in partially methylated sequences with a random distribution. The method, comprising liquid chromatography mass spectrometry (LC-MS) and electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS n ) measurements of two types of peralkylated glucans representing derivatives of the target compounds, is comprehensively described and discussed. ESI-MS n allows looking into the sequences of oligomeric domains. In addition, transglycosylation is followed by attenuated total reflection FTIR and NMR spectroscopy.

The complexity of the substituent distribution in polysaccharide derivatives is discussed and defined. The challenges regarding analytical characterization that results from various interrelated categories of distributions, including molecular weight, chemical composition, and microstructure, are outlined. Due to these convoluted levels of complexity, results should always be interpreted with carefulness. Various analytical approaches which have been applied to starch and cellulose derivatives are recapped, including enzymatic, mass spectrometric, and chromatographic methods. The relation of heterogeneities of first and second order among and along the polysaccharide chains is addressed. Finally, examples of own analytical work on cellulose ethers are presented, including the MS analysis of methyl cellulose (MC) blends and fractionation studies of fully esterified MC, especially its 4-methoxybenzoates by gradient HPLC on normal phase. Preparative fractionation according to the degree of substitution (DS) allows follow-up analysis in order to get more detailed information on the substituent distribution in such sub-fractions.

Transition metal carbides and nitrides (MXenes) are an emerging class of 2D materials, which are attracting ever-growing attention due to their remarkable physicochemical properties. The presence of various surface functional groups on MXenes' surface, e.g., -F, -O, -OH, -Cl, opens the possibility to tune their properties through chemical functionalization approaches. However, only a few methods have been explored for the covalent functionalization of MXenes and include diazonium salt grafting and silylation reactions. Here, an unprecedented two-step functionalization of Ti 3 C 2 T x MXenes is reported, where (3-aminopropyl)triethoxysilane is covalently tethered to Ti 3 C 2 T x and serves as an anchoring unit for subsequent attachment of various organic bromides via the formation of C-N bonds. Thin films of Ti 3 C 2 T x functionalized with linear chains possessing increased hydrophilicity are employed for the fabrication of chemiresistive humidity sensors. The devices exhibit a broad operation range (0-100% relative humidity), high sensitivity (0.777 or 3.035), a fast response/recovery time (0.24/0.40 s 𝚫H −1 , respectively), and high selectivity to water in the presence of saturated vapors of organic compounds. Importantly, our Ti 3 C 2 T x -based sensors display the largest operating range and a sensitivity beyond the state of the art of MXenes-based humidity sensors. Such outstanding performance makes the sensors suitable for real-time monitoring applications.

The anion-intercalation chemistries of graphite have the potential to construct batteries with promising energy and power breakthroughs. Here, we report the use of an ultrathin, positively charged two-dimensional poly(pyridinium salt) membrane (C2DP) as the graphite electrode skin to overcome the critical durability problem. Large-area C2DP enables the conformal coating on the graphite electrode, remarkably alleviating the electrolyte. Meanwhile, the dense face-on oriented single crystals with ultrathin thickness and cationic backbones allow C2DP with high anion-transport capability and selectivity. Such desirable anion-transport properties of C2DP prevent the cation/solvent co-intercalation into the graphite electrode and suppress the consequent structure collapse. An impressive PF6−-intercalation durability is demonstrated for the C2DP-covered graphite electrode, with capacity retention of 92.8% after 1000 cycles at 1 C and Coulombic efficiencies of > 99%. The feasibility of constructing artificial ion-regulating electrode skins with precisely customized two-dimensional polymers offers viable means to promote problematic battery chemistries.

The reversible gelation of aqueous methylcellulose (MC) solutions at high temperature is followed stepwise with low-field time-domain nuclear magnetic resonance (LF-TD-NMR). The gel transition does not influence the self-diffusion coefficient of water but is associated with a decrease of proton transverse relaxation times 1H T 2 by more than 60%. The effect of molecular weight and concentration of polysaccharide chains on transition temperature and gel strength is probed on several MCs with the same degree of substitution. The measured trends connect the NMR relaxation with macroscopic observables and agree with literature results from more demanding techniques like small-angle X-ray and neutron scattering (SAXS and SANS). These findings support the idea of a network structure of disorderly arranged fibrils, with an inhomogeneous mesh size at least on the order of tens of microns, which is in accord with the opaque appearance of these hydrogels. Magic sandwich echo (MSE) NMR measurements performed at 80 °C by substituting water with D2O also reveal the appearance with thermogelation of a rigid fraction involving about 25% of MC. This is consistent with the formation of fibrils mostly constituted by an amorphous matrix strongly permeated by water and strengthened by well-dispersed MC crystallites.

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