Molecular Weight Macromolecules Research Articles

Scaffold-enabled high-resolution cryo-EM structure determination of RNA.

Cryo-EM structure determination of protein-free RNAs has remained difficult with most attempts yielding low to moderate resolution and lacking nucleotide-level detail. These difficulties are compounded for small RNAs as cryo-EM is inherently more difficult for lower molecular weight macromolecules. Here we present a strategy for fusing small RNAs to a group II intron that yields high resolution structures of the appended RNA, which we demonstrate with the 86-nucleotide thiamine pyrophosphate (TPP) riboswitch, and visualizing the riboswitch ligand binding pocket at 2.5 Å resolution. We also determined the structure of the ligand-free apo state and observe that the aptamer domain of the riboswitch undergoes a large-scale conformational change upon ligand binding, illustrating how small molecule binding to an RNA can induce large effects on gene expression. This study both sets a new standard for cryo-EM riboswitch visualization and offers a versatile strategy applicable to a broad range of small to moderate-sized RNAs, which were previously intractable for high-resolution cryo-EM studies.

Humic Acid: A Promising and Green Bioorganic Catalyst in Organic Syntheses

AbstractThe growing pollution and threat to the environment demand green synthetic methods. Green chemistry mainly focuses on minimizing the waste and utilization of green solvents, energy sources, and catalysts and prefers one‐pot reactions. In this context, humic acid (HA), a natural bioorganic catalyst found in rivers, peat coal and sewage; is a high molecular weight macromolecule containing multifunctional groups, mainly contains quinone, phenolic OH, and COOH groups which make it acidic and activate carbonyl groups by protonation. Owing to its green aspect such as biodegradability, recyclability and reusability, humic acid is considered as sustainable bioorganic catalyst which meets the criteria for industrial requirements. The HA is mild acidic in nature, thus many functional groups tolerate in the HA catalyzed reactions. After few initial reports in 2001 and 2009, the HA catalyzed reactions gained much attention by the organic synthetic community from 2019 in aldol condensation, Knoevenagel condensation, Claisen‐Schmidt reaction, Michael addition, Strecker synthesis, tetrazole synthesis, Hantzsch dihydropyridine synthesis, hydrosilylation of terminal alkenes, hydrogenation, α‐aminophosphonate synthesis, cross coupling reactions such as Heck and Suzuki coupling reactions. Herein we report the comprehensive analysis on the role of HA in organic transformations providing diverse array of molecular scaffolds till date and future perspective.

Therapeutic Ultrasound for Enhanced Corneal Permeability to Macromolecules.

Topically applied macromolecules have the potential to provide vision-saving treatments for many of the leading causes of blindness in the United States. The aim of this study was to determine if ultrasound can be applied to increase transcorneal drug delivery of macromolecules without dangerously overheating surrounding ocular tissues. Dissected corneas of adult rabbits were placed in a diffusion cell between a donor compartment filled with a solution of macromolecules (40, 70 kDa, or 150 kDa) and a receiver compartment. Each cornea was exposed to the drug solution for 60 minutes, with the experimental group receiving 5 minutes of continuous ultrasound or 10 minutes of pulsed ultrasound at a 50% duty cycle (pulse repetition frequency of 500 ms on, 500 ms off) at the beginning of treatment. Unfocused circular ultrasound transducers were operated at 0.5 to 1 W/cm2 intensity and at 600 kHz frequency. The greatest increase in transcorneal drug delivery seen was 1.2 times (P < .05) with the application of pulsed ultrasound at 0.5 W/cm2 and 600 kHz for 10 minutes with 40 kDa macromolecules. Histological analysis revealed structural damage mostly in the corneal epithelium, with most damage occurring at the epithelial surface. This study suggests that ultrasound may be used for enhancing transcorneal delivery of macromolecules of lower molecular weights. Further research is needed on the long-term effects of ultrasound parameters used in this study on human ocular tissues.

A high-throughput microfluidic mechanoporation platform to enable intracellular delivery of cyclic peptides in cell-based assays.

Cyclic peptides are poised to target historically difficult to drug intracellular protein-protein interactions, however, their general cell impermeability poses a challenge for characterizing function. Recent advances in microfluidics have enabled permeabilization of the cytoplasmic membrane by physical cell deformation (i.e., mechanoporation), resulting in intracellular delivery of impermeable macromolecules in vector- and electrophoretic-free approaches. However, the number of payloads (e.g., peptides) and/or concentrations delivered via microfluidic mechanoporation is limited by having to pre-mix cells and payloads, a manually intensive process. In this work, we show that cells are momentarily permeable (t 1/2 = 1.1-2.8 min) after microfluidic vortex shedding (μVS) and that lower molecular weight macromolecules can be cytosolically delivered upon immediate exposure after cells are processed/permeabilized. To increase the ability to screen peptides, we built a system, dispensing-microfluidic vortex shedding (DμVS), that integrates a μVS chip with inline microplate-based dispensing. To do so, we synced an electronic pressure regulator, flow sensor, on/off dispense valve, and an x-y motion platform in a software-driven feedback loop. Using this system, we were able to deliver low microliter-scale volumes of transiently mechanoporated cells to hundreds of wells on microtiter plates in just several minutes (e.g., 96-well plate filled in <2.5 min). We validated the delivery of an impermeable peptide directed at MDM2, a negative regulator of the tumor suppressor p53, using a click chemistry- and NanoBRET-based cell permeability assay in 96-well format, with robust delivery across the full plate. Furthermore, we demonstrated that DμVS could be used to identify functional, low micromolar, cellular activity of otherwise cell-inactive MDM2-binding peptides using a p53 reporter cell assay in 96- and 384-well format. Overall, DμVS can be combined with downstream cell assays to investigate intracellular target engagement in a high-throughput manner, both for improving structure-activity relationship efforts and for early proof-of-biology of non-optimized peptide (or potentially other macromolecular) tools.

Temperature responsive crosslinked starch-kraft lignin macromolecule

Starch is a natural polymer with a relatively simple structure and limited solubility in water. Kraft lignin (KL) is a complex biopolymer obtained as a by-product from the delignification of wood and grasses. The present work reports developing a temperature-responsive high molecular weight macromolecule from crosslinking KL and starch (KLS). The NMR and XPS analyses quantified the changes in the aromatic and anhydroglucose units of KL and starch, observing a higher content of C-O-C bonds, which confirms the presence of glycerol ether cross-linkages between starch and KL in KLS. The rheological analysis of KLS dispersions revealed the formation of a thermo-responsive structured network. The temperature-dependent water solubility and rheological characteristics of KLS were related to the presence of hydrophilic starch chains, crosslinking degree, and physicochemical characteristics of KL. The incorporation of KL and ether crosslinks increased the thermal stability of KLS. Because of its multiple functional groups and large molecular weight (3.6–4.2 × 105 g/mol) that was arranged in an extended globular shape, KLS-5 formed a gel-like structure after a heating-cooling treatment. Overall, the results confirmed that incorporating lignin in starch would fabricate sustainable materials with potentially altered applications, such as temperature-responsive hydrogels and films.

Therapeutic ultrasound for enhanced transcorneal macromolecule delivery

Previous experiments demonstrated that ultrasound exposure at 400-600 kHz can increase transcorneal drug delivery of sodium-fluorescein. Our study aims to determine if these same methods can enhance the delivery of fluorescently labeled FITC-dextran macromolecules of similar molecular weights to clinically relevant drugs. Dissected corneas of adult rabbits were placed in a diffusion cell between a donor compartment filled with a solution of FITC-dextran macromolecules diluted with phosphate-buffered saline (PBS) to 1 mg/ml and a receiver compartment filled with PBS. Each cornea was exposed to the drug solution for 60 minutes, with the experimental group receiving 5 min of continuous ultrasound or 10 min of pulsed ultrasound at 50% duty cycle at the beginning of treatment. Unfocused circular ultrasound transducers were operated at 0.5 –1 W/cm2 intensity and at 600 kHz frequency. Macromolecule delivery was quantified by the fluorescence intensity detected in the receiver compartment. The greatest increase in transcorneal drug delivery seen was 1.2 times (p &amp;lt; 0.05) with the application of pulsed ultrasound at 0.5 W/cm2 and 600 kHz for 10 min with 40 kDa macromolecules. Gross observation of corneas after experiments demonstrated no significant damage. Ongoing microscopy and thermal-modeling studies aim to characterize any ultrasound-induced damage.

Interpenetrating Low-Molecular Weight Hyaluronic Acid in Hyaluronic Acid-Based In Situ Hydrogel Scaffold for Periodontal and Oral Wound Applications.

Tissues engineering has gained a lot of interest, since this approach has potential to restore lost tooth-supporting structures, which is one of the biggest challenges for periodontal treatment. In this study, we aimed to develop an in situ hydrogel that could conceivably support and promote the regeneration of lost periodontal tissues. The hydrogel was fabricated from methacrylated hyaluronic acid (MeHA). Fragment/short-chain hyaluronic acid (sHA) was incorporated in this hydrogel to encourage the bio-synergistic effects of two different molecular weights of hyaluronic acid. The physical properties of the hydrogel system, including gelation time, mechanical profile, swelling and degrading behavior, etc., were tested to assess the effect of incorporated sHA. Additionally, the biological properties of the hydrogels were performed in both in vitro and in vivo models. The results revealed that sHA slightly interfered with some behaviors of networking systems; however, the overall properties were not significantly changed compared to the base MeHA hydrogel. In addition, all hydrogel formulations were found to be compatible with oral tissues in both in vitro and in vivo models. Therefore, this HA-based hydrogel could be a promising delivery system for low molecular weight macromolecules. Further, this approach could be translated into the clinical applications for dental tissue regeneration.

Dually Cross-Linked Core-Shell Structure Nanohydrogel with Redox-Responsive Degradability for Intracellular Delivery.

A redox-responsive nanocarrier is a promising strategy for the intracellular drug release because it protects the payload, prevents its undesirable leakage during extracellular transport, and favors site-specific drug delivery. In this study, we developed a novel redox responsive core-shell structure nanohydrogel prepared by a water in oil nanoemulsion method using two biocompatible synthetic polymers: vinyl sulfonated poly(N-(2-hydroxypropyl) methacrylamide mono/dilactate)-polyethylene glycol-poly(N-(2-hydroxypropyl) methacrylamide mono/dilactate) triblock copolymer, and thiolated hyaluronic acid. The influence on the nanohydrogel particle size and distribution of formulation parameters was investigated by a three-level full factorial design to optimize the preparation conditions. The surface and core-shell morphology of the nanohydrogel were observed by scanning electron microscope, transmission electron microscopy, and further confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy from the standpoint of chemical composition. The redox-responsive biodegradability of the nanohydrogel in reducing environments was determined using glutathione as reducing agent. A nanohydrogel with particle size around 250 nm and polydispersity index around 0.1 is characterized by a thermosensitive shell which jellifies at body temperature and crosslinks at the interface of a redox-responsive hyaluronic acid core via the Michael addition reaction. The nanohydrogel showed good encapsulation efficiency for model macromolecules of different molecular weight (93% for cytochrome C, 47% for horseradish peroxidase, and 90% for bovine serum albumin), capacity to retain the peroxidase-like enzymatic activity (around 90%) of cytochrome C and horseradish peroxidase, and specific redox-responsive release behavior. Additionally, the nanohydrogel exhibited excellent cytocompatibility and internalization efficiency into macrophages. Therefore, the developed core-shell structure nanohydrogel can be considered a promising tool for the potential intracellular delivery of different pharmaceutical applications, including for cancer therapy.

Interaction between polychlorinated biphenyls and dissolved organic matter of different molecular weights from natural and anthropic sources

Polychlorinated biphenyls (PCBs) are compounds of significant interest due to high toxicity, persistence, long-range atmospheric transport, and bioaccumulation. These compounds can interact with components present in the environment, including dissolved organic matter (DOM) in soils and waters, thereby modifying its availability and movement. In this study, DOM was fractionated by ultrafiltration and characterized according to its hydrophobicity and hydrophilicity, then the interaction of a series of PCBs and different DOM fractions was evaluated. The DOM was collected from the surface waters of three sectors located along a river in the southern part of America. These sectors are subject to different anthropic activities, thus the DOM of sector 1, with the least anthropic influence, was mainly hydrophobic and with a high content of aromatic structures. In contrast, the DOM collected from sectors 2 and 3, where anthropic activity is highest, was slightly hydrophobic and hydrophilic, respectively. The DOM of these two sectors was mainly composed of low molecular weight macromolecules. These results revealed that more hydrophobic PCBs (i.e., 101, 118, 138, and 180) have a greater affinity to DOM with a higher molecular weight (i.e., >1 kDa). In turn, PCBs with lesser chlorination and hydrophobicity presented a greater affinity to DOM with a lower molecular weight. In conclusion, our study shows that the high molecular weight DOM is responsible for mobilizing PCBs with a high degree of chlorination.

Effect of Gamma- Irradiation on Structure, Morphology and Thermal Properties of Novel Polyamide Based Thermoset Obtained by Double Cycloaddition

Cycloaddition reactions gained prominence in macromolecular chemistry for generating macromolecules because of high yields of these reactions, which is a key tool that drives polyaddition reactions. Cycloaddition reaction plays major role in extension of polymerisation or in other words high conversions of monomers to macromolecules of high molecular weights. Until the late 1990s, the major studies regarding cycloadditions in novel polymer synthesis were related to polyaddition reactions. Since then in the field of polymer synthesis the affirmative strengths of these cycloaddition reactions have been exhibited in multi fold polymer design and headway material architecture. Future demand exists in unlatching the capacity of these novel synthetic routes for advanced applications in catalysis, separation, optoelectronics, and analytical media. Thus, we have developed an able and productive synthetic podium for the preparation of a new class of polyimide based on the double 1, 3-dipolar cycloaddition of thiasydnone with bis-maleimide. This paper reports the effect of gamma irradiation on the changes in physico-chemical properties of the polyamide based thermoset synthesised by double cycloaddition approach. The thermoset synthesized by this exclusive approach were irradiated with gamma doses in the range 10- 300 kGy. The substantial effect of gamma radiation and the structural modifications induced on the thermoset have been studied as a function of dose using different characterization techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry- thermo gravimetric analysis (DSC-TGA), Field Emission Scanning Electron Microscope (FESEM) and UV-Vis Spectroscopy.

In-situ extraction of depolymerization products by membrane filtration against lignin condensation

Catalytic depolymerization of lignin is a challenging process due to competitive repolymerization reactions. In this paper, the oxidative depolymerization of lignin was catalyzed by a commercial laccase both in a batch experiment and in a membrane bioreactor using the same catalytic conditions. The membrane bioreactor was previously optimized to reach high permeation flux (25 L.h−1.m−2) during lignin diafiltration. While the lignin was exclusively condensed in the batch experiment leading to high molecular weight macromolecules (from 9 to 16 kDa), its depolymerization was effective in the bioreactor producing fragments of less than 1 kDa thanks to the in-situ extraction of the reaction products. This paper demonstrates that the reactor configuration is playing an essential role in triggering or preventing lignin condensation. It also reports the first proof-of-concept demonstrating that in-situ membrane extraction of the reactive fragments of lignin from the bulk medium can be useful against detrimental repolymerization reactions.

The rheology of soft bodies suspended in the simple shear flow of a viscoelastic fluid

Many industrial applications involve soft suspended bodies in viscoelastic fluids. Moreover, many biological fluids contain high molecular weight macromolecules which impart viscoelasticity to the fluid, and any cells which are suspended in such fluids again form a suspension of elastic bodies in a viscoelastic fluid. For control purposes, microfluidic platforms are beginning to utilizing viscoelastic solvents to perform tasks such as cell focusing [34]. However, despite numerical studies into the kinematics of such deformable bodies in viscoelastic fluids, no studies currently consider the rheology of such systems. Due to the competing effects of the viscoelasticity of the fluid and the elasticity of the solids it is clear that there exists a non-trivial rheological behavior exhibited by such suspensions. In this study, we present simulations of dilute systems of deformable particles with viscoelastic suspending fluids. We compute the effective viscosity and the first/second normal stresses for a suspension of neoHookean particles sheared in a Giesekus suspending fluid up to modest deformations characterized by a capillary number, Ca, up to Ca = 0.3. The results indicate that the per particle extra stress that originates from the suspending fluid (the particle induced fluid stress) remains relatively constant regardless of deformation. In contrast, the component of the extra stress that arises from the stress inside the particle (the stresslet) is a strong function of both the capillary number and the Weissenberg number for the parameter space investigated. Note that we find the suspensions “thicken” and/or “thin” with increasing shear depending on the range of parameter space examined.

Molecular characterization of kerogen and its implications for determining hydrocarbon potential, organic matter sources and thermal maturity in Marcellus Shale

Organic-rich shales are a vital component of the US energy sector. Kerogen, a high molecular weight macromolecule is the largest reservoir of organic carbon on earth and serves as the starting material for the oil and gas generation in these shales. Despite its importance, kerogen structure and its evolution on maturation are still not well understood, especially for mature shales (VRo > 1). Moreover, most of the models built to determine hydrocarbon (HC) potential and thermal maturity of the source rocks have used the structural parameters of kerogen extracted from immature shales (VRo < 1). Therefore, these models might not yield accurate results for mature and over-mature shales like Marcellus. In this study, we determine the structural parameters of kerogen extracted from three Marcellus Shale cores using 13C solid-state Nuclear magnetic resonance (NMR). Samples were acquired from the upper and lower Marcellus Shale Formation from a dry gas well WV-6 (VRo > 2.5), a wet gas well WV-7 (VRo ∼ 1.4) and an oil window well BG-1 (VRo ∼ 0.81) in Monongalia, Wetzel and Brooke County, West Virginia, respectively. Our results indicate that the percentage of carbon chains such as mobile (freely rotating) and immobile alkyl without heteroatoms (with restricted rotation), and alkyl-substituted aromatic carbons decrease with increasing maturity indicating that these chains are more prone to thermal degradation and might have higher HC generating potential. However, carbon chains such as O- substituted alkyl (ether), O2 substituted alkyl (dioxy alkyl), amine, protonated aromatic carbons, O- substituted aromatic (phenol) and bridgehead aromatic carbons does not decrease directly with thermal maturity suggesting that these groups are either more refractory in nature or their carbon fraction is influenced by changing sources of OM. Our results also indicate that the previous models based on the structural parameters of kerogen derived from immature shales overestimate the HC generation potential and underestimate the thermal maturity in mature shales from the Marcellus. In addition, H, O, C ratios derived from structural parameters of kerogen can be utilized to determine the kerogen type in these mature shales where traditional pyrolysis analysis fails to characterize the kerogen.

Enhancing the Angular Sensitivity of Plasmonic Sensors Using Hyperbolic Metamaterials.

Surface plasmon resonance (SPR) sensors operate mainly on prism and grating coupling techniques, with spectral and angular scans being the two major interrogation schemes. Among them, the angular scan technique has several advantages including higher measurement precision owing to its higher signal-to-noise ratio. The currently available SPR sensor arrangements provide a maximum angular sensitivity of 500°-600° per RIU. Here, we report the study of grating coupled-hyperbolic metamaterial (GC-HMM) sensors with high angular sensitivity. The experimental studies show extraordinary angular sensitivities from visible to near infrared (NIR) wavelengths by exciting bulk plasmon polaritons associated with hyperbolic metamaterials, with a maximum of 7000° per RIU. This angular-scan plasmonic biosensor has been used for the detection of low molecular weight biomolecules such as biotin (244 Da) and high molecular weight macromolecules such as Cowpea mosaic virus (CPMV, 5.6 × 106 Da) at ultralow concentrations. The miniaturized sensing device can be integrated with microfluidic systems for the development of next-generation biosensors for lab-on-a-chip and point-of-care applications.

А new factor effecting gel strength of pectin polysaccharides

Pectin polysaccharides obtained from various raw materials have a different component composition and form gels with water, sugar and acid or calcium. In this study, an experimental approach the gelation properties of different pectin samples, varied from different sources, using new methods of hydrolysis and purification. Samples were obtained by hydrolysis of accelerated extraction of pectin and purified by diaultrfiltration, have a high gel strength. The highest gel strength have been found in series of high methoxyl (HM-) pectin samples of apple, peach, orange and low methoxyl (LM-) pectin samples of commercial citrus pectin and apple pectin obtained by new method. It is shown that in addition to the basic parameters (the content of galacturonic acid, degree of esterification, molecular weight and hidrodinamic radius macromolecule) to affect gel strength pectins aggregation of macromolecules, which is determined by the z-average molecular weight. There were observed a clear pattern of the influence of the molecular weight on hydrodynamic parameters for both HM- and LM- pectin samples on the gel strength. It were shown that a high values of molecular weight, intrinsic viscosity, and radius of gyration of pectin samples can significantly increase gel strength, while the value of Mz oppositely influenced the gel strength. As a result, a systematic analysis of this parameter and its relationship to the average molecular weight found that indeed the ratio Mz/Mw for pectin’s is an crucial to assess the quality of pectin at the study of gel strength for pectin polysaccharides.

ارزیابی خواص عملکردی موسیلاژ دانه بِه استخراج شده به کمک فراصوت

موسیلاژ دانه به از جمله هیدروکلوئیدهای بومی است که استخراج آن به علت ویسکوزیته بالا نیازمند روشی است که علاوه بر کاهش زمان و مصرف انرژی، از بازدهی بالایی نیز برخوردار باشد. استخراج به کمک فراصوت به عنوان یکی از روش‌های نوین می‌تواند در دستیابی به این هدف نقش داشته باشد. به این منظور در ابتدا شرایط استخراج رایج (زمان 45 دقیقه، دمایC˚47 و نسبت آب به دانه 1: 5/32)، با هدف تعیین بهترین شرایط هیدراسیون بهینه‌سازی گردید . در این پژوهش از فراصوت (پروب با فرکانس KHz24 و توان W400) با شدت‌ها (20،60،100 درصد) و زمان‌های مختلف صوت‌دهی (5، 15و 30 دقیقه) استفاده شد. نتایج حاکی از آن بود که طی 30 دقیقه استخراج با شدت 100 درصد، بازده نسبت به نمونه کنترل 7/42 درصد افزایش داشت. مدل هرشل بالکی بهترین مدل رئولوژیکی برای توصیف رفتار جریان نمونه‌ها انتخاب شد. به علت شکست ساختار پلی‌ساکاریدی موسیلاژ توسط امواج فراصوت، حلالیت نمونه‌ها بین 66 تا 92 درصد متغیر بود اما در مقایسه با نمونه کنترل به شدت افزایش یافت. در شدت 60 درصد نیز بالاترین پایداری نمونه‌ها مشاهده شد. پایداری کف نمونه‌ها نسبت به نمونه کنترل 31/17 درصد افزایش نشان داد. با وجود کاهش جذب آب موسیلاژهای استخراج شده طی زمان طولانی با شدت بالا، اما این پارامتر تقریبا در بسیاری از تیمارها فراتر از نمونه کنترل بود. نتایج این پژوهش نشان داد استفاده از فراصوت به دلیل تاثیر مثبت بر بسیاری از خواص علمکردی می‌تواند روش مناسبی برای استخراج موسیلاژ دانه به معرفی گردد.

Molecular based prediction of the extensional rheology of high molecular weight polystyrene dilute solutions: A hi-fidelity Brownian dynamics approach

A highly efficient Brownian dynamics algorithm for simulation of bead-spring chain micromechanical models that utilizes the Krylov framework and the semi-implicit predictor-corrector scheme is used to study the behavior of dilute solutions of high molecular weight polystyrene in uniaxial extensional flow. The influence of key parameters, namely, appropriate inclusion of hydrodynamic interactions (HI) and excluded volume (EV), the level of fine-graining, and the flow strength on the observed extensional hardening of the dilute solutions over a broad molecular weight range is considered. Specifically, it is demonstrated that the combination of HI and successive fine-graining results in very good predictions of rheological properties of solutions containing 1.95, 3.9, and 10.2 × 106 molecular weight macromolecules. However, for the highest molecular weight system, namely, 20 × 106, some level of discrepancy between experiment and the simulation results is observed. Finally, the incorporation of EV in order to predict material functions that are more consistent with the measurements for the highest molecular weight macromolecule solution is discussed.

Variation in Colloidal Organic Matter Composition and Aggregation in Coastal Waters (Gulf of Trieste, Northern Adriatic Sea)

Large volumes of seawater were sampled monthly from December 2011 to October 2012 in the southeastern part of the Gulf of Trieste (northern Adriatic Sea) in order to study the seasonal changes of colloidal organic matter (COM) concentrations, its origin and composition. Isolation of COM was performed by ultrafiltration with molecular weight cut-off membranes of 5 kDa and final desalinization by dialysis. COM was characterized using 1H NMR and FT-IR spectroscopy, elemental C and N and 13C and 15N isotope analyses and high-pressure size exclusion chromatography. COM represents about 1/4 of dissolved organic carbon (DOC) and appears to be mainly of marine origin. COM is mainly composed of polysaccharides, lipids, proteins and humics. FT-IR analysis indicated the presence of OH (carbohydrates and lipids), COOH (proteins and lipids) and NH (proteins) containing functional groups. Using the NMR technique, it was possible to semiquantitatively determine variations of four main biochemical constituents present in our COM samples. In the late spring - summer an accumulation of COM was observed, reaching up to 25 μmol L−1 Corg. and representing about 1/3 of DOC in the Gulf waters. The lipid fraction increased up to 2-fold and the polysaccharide fraction remained nearly constant while protein fraction decreased, reflected in a higher C/N (28) molar ratio. Also, higher concentrations of humics were observed in late spring – early summer probably due to local freshwater discharges in spring. An increase of lipid fraction and nearly constant polysaccharide content in late spring - early summer, in parallel with agglomeration of high molecular weight (>200 kDa) macromolecules, indicates the possible formation of macroaggregates, which has been periodically occurred in the northern Adriatic Sea in the past.

New biodegradable dextran-based hydrogels for protein delivery: Synthesis and characterization

A new derivative of dextran grafted with polyethylene glycol methacrylate through a carbonate bond (DEX–PEG–MA) has been synthesized and characterized. The photo-crosslinking reaction of DEX–PEG–MA allowed the obtainment of biodegradable networks tested for their mechanical and release properties. The new hydrogels were compared with those made of dextran methacrylate (DEX–MA), often employed as drug delivery systems of small molecules. The inclusion of PEG as a spacer created additional interactions among the polymeric chains improving the extreme fragility and lack of hardness typical of gels made of DEX–MA. Moreover, the different behavior in terms of swelling and degradability of the networks was able to affect the release of a model macromolecule over time, making DEX–PEG–MA matrices suitable candidates for the delivery of high molecular weight peptides. Interestingly, the combination of the two dextran derivatives showed intermediate ability to modulate the release of high molecular weight macromolecules.

A Chromatographic Study of Shear Stability of Poly(styrene-co-alkyl methacrylate) Viscosity Modifier for Lubricating Oils

Shear stability of styrene, dodecyl methacrylate, and octadecyl methacrylate terpolymer of various molecular weights, as the rheology modifier of improved solubility, thermal and oxidation stability in mineral base oil, was investigated. Viscosity loss of the 5 wt% solutions caused by scission of macromolecules subjected to the high shear forces ranges between 15% and 27% for weight average molecular weights from 156000 to 252000. After the shear tests the number average molecular weights of polymer increases while weight and Z-average molecular weights decrease. As macromolecules of molecular weights above 700000 fully break the molar-mass dispersity decreases significantly, from starting at 2.34–2.79 down to below 1.8. A linear dependence between viscosity loss of terpolymer solutions and molecular weights was observed. The advantage of using the size exclusion chromatography to determine the stability of the polymer against mechanical shear directly and the viscosity loss indirectly was established.