User:Pseudonymonous/sandbox

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Is there such thing as high molecular mass organic gelators? maybe be explicit about the difference? What is the threshold for categorization? Low Molecular-Mass Organic Gelators (LMOGs) are a relatively new and dynamic soft material capable of numerous possible applications; LMOGs form by self-assembled fibrillar networks (SAFINs) that entrap solvent between the strands.[1] This seems to be two independent statements, maybe use two separate sentences rather than semicolon? Also, since there is no link to SAFIN, you may need explicitly explain what it is, especially since it's in the first sentence of the intro. Once solvent molecules are entrapped within the network, they are immobilized by surface tension effects. The stability of these gels is dependent on the equilibrium between the assembled network and the dissolved gelators. One characteristic of a LMOG, that demonstrates its stability, is their ability to contain an organic solvent at the boiling point of that solvent due to extensive solvent-fibrillar interactions.[2] You've got mixing of singular and plural connotation, I would change to..." One characteristic of LMOGs that demonstrate their stability is their ability to..." Gels self-assemble through non-covalent interactions such as π-stacking, hydrogen-bonding, or Van der Waals interactions to form volume-filling 3D networks. Self assembly is key to gel formation and dependent upon reversible bond formation. The propensity of a low molecular weight molecule to form LMOGs is classified by its critical gelation concentration (cgc). The cgc is the lowest possible gelator concentration needed to form a stable gel. A lower cgc is desired to minimize the amount of gelator material needed to form gels. Super gelators have a cgc of less than 1 wt%. It might be useful to state the motivations for studying these systems in the intro - allude to possible interesting applications that you may expand upon below. In the first sentence you state 'numerous possible applications', give examples? Why are these important?



Gels can be organized according to multiple characteristics. The source of the gel (natural/artificial), the gel's medium (organic/aqueous/areo/xero), the constitution of the gel (macromolecular/supramolecular), and the type of crosslinking the gel forms (physical/chemical).

History[edit]

LMOGs were first reported in the 1930's, but advances in the field were more often than not discoveries of chance; as there existed little theoretical understanding of gel formation. Comma instead of semicolon? Seems like one sentence During this time LMOGs found applications as additives? in thickening lubricants, printing inks, and napalm.[3] Interest in the field dwindled for several decades until the mid-1990s when Hanabusa, Shinkai, and Hamilton designed numerous LMOGs which form thermoreversible intermolecular amide-carbonyl hydrogen bonds.[4] Might have to explain this...maybe, "whereby application of heat to the gelator material resulted in reversible...." The LMOGs developed by Hanabusa et. al were suitable for forming hard gels, including gels with chloroform, which had been resistant to gelation prior to their discovery. These new LMOGs were rationally designed and represented the first time that scientists had been able to discover new LMOGs based on supramolecular principles. From these earliest studies and screening numerous compounds, it was determined by Hanabusa "et. al" that for thermoreversible gels based on the amide-carbonyl hydrogen bond that amino acid structure, enantiopurity, hydrophilic-lypophilic ratio, and increasing peptide substitution greatly effected the gelling ability of various new compounds. Sentence a bit awkward...Maybe something like "From these early studies of thermoreversible gels based on the amide-carbonyl hydrogen bond, Hanabusa et al reasoned that AA structure....greatly effect..."


The aforementioned principles that developed in this field's infancy have proved successful in allowing researchers to tune LMOGs for different functions. Today, LMOGs have been extensively studied for their unique properties. This newfound functional diversity has led to a wide range of possible applications for LMOGs in agriculture, drug delivery, pollutant/heavy metal remediation, luminescent devices, and chemical sensing. this sentence may be more useful in intro, but you should probably have citations for these applications

Gel Formation and Morphology[edit]

Is there any insight into the mechanism of formation of these systems? Are these linear chains of organic molecules, dendritic networks...is there a nucleation event that initiates formation? thermodynamic driving force? Maybe have a short section on suspected gelation mechanisms for different LMOGs? Also, are these systems always reversible? Is there a common failure mechanism (mechanical, thermal, photo) that limits long time use (like some polymeric materials).


Also, would a Preparation or Synthesis section be useful - or just mention briefly how these systems are prepared

A LMOG liquid mixture forming a gel upon heating and cooling.

The majority of LMOGs can be triggered to form by manipulating the systems' properties, such as the pH, solvent, exposure to light, or by introducing oxidizing or reducing reagents.[5] Researchers have proposed a set of guidelines for successful gel formation[6]

1. It is necessary to have the presence of strong self-complementary and unidirectional inter-molecular interactions that can enforce 1D self-assembly.
2. The solvent-fiber interfacial energy should be manipulated to control solubility and prevent crystallization of the LMOG.
3. Some other factor must be present that can induce the fiber cross-linking network formation.

examples of systems with the previous guidelines may be useful. what is the state-of-the-art for design of these systems? Are there subcategories of LMOGs that people work on? You mention in the history section that Hanabusa et al was able to rationally design these, is he the only one? Examples of common LMOGs with their physical properties may be useful here.

Traditionally, gel phase transitions are strictly temperature dependent. However, it has recently been shown that non-liquid crystalline gelators, composed of (R)-18-(n-alkylamino)octadecan-7-ols (HSN-n), undergo first order gel-to-gel phase transitions; leading to different morphologies of the gel in carbon tetrachloride (CCl4).[7] The uniqueness of this discovery stems from the idea that it is the solvent molecules entering and exiting the structure which leads to the different structural morphologies. All other previously known gel phase transitions have occurred as the result of temperature changes and only one previous case documents this type of solvent dependent morphological change. However, even in the case of N-isopropylacrylamide hydrogels that underwent conformational changes (folding and unfolding of their polymer chains); it occurred only via a temperature dependent process which resulted in water molecules, near the structure, entering or exiting the structure.[8] [9] [10] [11] The stability of a formed gelation matrix is dependent on the equilibrium between the assembled network and the dissolved gelator assemblies. LMOGs are functionally diverse and can be composed of both polar and non-polar regions (amphiphiles). Here you discuss a specific exception to the common T-dependent gelators, but you don't really discuss any specific 'common' gelators that do follow this Temp dependence

Is SEM the only technique for characterization? What are the other common techniques...DSC, various forms of spectroscopy, etc.? How do people study these systems? You could make a characterization category and include rheology, SEM, calorimetry, spectroscopy, etc as subcategories.

Scanning Electron Microscopy

SEM of a Low Molecular Weight Gelator

Scanning Electron Microscopy is a useful means for researchers to determine the structural properties of a low molecular-mass weight gel. These gels exhibit a wide range of structures; from fibrous strands (of various lengths) to ribbons and tubes. The structure of these gels is a key factor in their ability to gel solvents or water. Their tertiary structure determines the critical gelation concentration of the gel.

Rheological Measurements[edit]

Generally, rheology is used to study the flow of matter within a substance. In order for a substance to be considered a gel it must posses solid-like traits when characterized by rheological measurements. Rheological characterization, tests materials by applying stress to measure the material's resistance to deformation. From rheological measurements, a gel can be classified as either a "strong" or "weak" gel. This classification emphasizes the strength of the interactions between gelator molecules in a particular gel. A "weak" gel is often not considered a true gel because it does not conform to a purely solid-like material's rheological traits. Instead, "weak" gels are generally better classified as viscoelastic liquids.

As a result of this distinction, these classes of gels demonstrate different elasticity as calculated by the elastic modulus, a mathematical model for predicting the elasticity of different materials under different stressors. The shear modulus (G) of a "strong" gel exhibits a smaller dissipation of energy than "weak" gels, and the "strong" gel's G-values plateau for longer periods of time.[12]. Furthermore, rheological properties of different gels can occasionally be used to compare naturally occurring biopolymer gels with synthetic LMOGs [13].

Interactions of Gel and Solvent[edit]

Researchers have not been able to reliably predict novel LMOGs. A key aspect in predicting new gelator materials is understanding the interaction between the gel molecules and the solvent. The most common solvents for LMOGs are organic in nature and result in organogels. Much rarer are hydrogels, or gels that form with water as the solvent.[14] Several attempts have been made to quantify the gel and solvent interaction using a variety of parameters:

The single or multi-component solubility parameter (δ) of a solvent can give insight on how well-suited the solvent will be for gelation. Depending on the gelator/solvent system, a high solubility parameter can indicate high or low thermal stability of the gel.[15]
The dielectric constant (ε) reflects the bulk polarity of the solvent.[16]
The Dimroth-Reichardt parameter (ET(30)) is a measure of ionizing power of a solvent.[17]
The Kamlet-Taft solvent parameters establish solvatochromic relationships which measure separately the hydrogen bond donor (α), hydrogen bond acceptor (β), and polarizability (π*) of solvents.[18]
The Hildebrand parameter measures the energy it takes to create a cavity within a solvent.[19]

How have these metrics informed people's understanding of these systems? Maybe provide some results of studies employing these methods? Is/are there certain methods that are better fitted for prediction

Applications[edit]

Agricultural Industry[edit]

Pheromone Release Devices[20] Multiple reservoir-type controlled release devices (CRDs) have been developed to achieve the controlled release of highly volatile pheromones into an agricultural setting; whereby they could act as pesticides throughout the growing season.[21] [22] [23] There are several draw-backs associated with current CRDs because they involve multi-step preparation protocals, exhibit low pheromone-holding capacities, are not biodegradable, and exhibit leaking of the pheromones when compressed or broken. To address these functional issues a sugar alcohol-based amphiphilic super-gelator, mannitol dioctanoate (M8), has been developed that efficiently gelled the pheromones, 2-heptanone and lauryl acetate. The miticide, 2-heptanone controls the parasitic mite, varroa (Varroa destructor), that are responsible for honey bee (Apis mellifera L) colony destruction.[24] [25] The researchers further developed the application of this supergelator by developing a reservoir-type CRD that consisted of the 2-heptanone gel in a vapor-barrier-film sealed pouch which was then activated by boring a small hole through the vapor barrier. The CRD had a high loading capacity of 92% wt/wt allowing for the construction of small devices with a high biocompatibility and because, M8 is composed of mannitol and fatty acids it is also biodegradable.

Drug Delivery[edit]

Researchers have been exploring LMOGs belonging to a class of molecules called cyclohexane trisamides due to their ability to form hydrogels. By attaching functional groups to the gelator molecule, the researchers can adjust the gelation properties. The gels transition to the liquid state upon changes in temperature or pH [26] Taking it one step further, the researchers attached an amino acid and a model drug to the gel molecule and added an enzyme to the gel matrix. When the temperature or pH was changed, the gel molecules entered the liquid phase where the amino acid and drug molecule could be cleaved from the gel molecule by the enzyme. Researchers believe these LMOGs may some day be used as a fast, two-step release drug delivery system.[27]

Pollutant/Heavy Metal Remediation[edit]

In 2010 researchers developed phase-selective gelators toward the containment and treatment of oil spills. They developed a class of LMOGs that were capable of gelling diesel, gasoline, pump, mineral, and silocone oils. These LMOGs were composed of dialkanoate derivatives of the sugar alcohols, mannitol and sorbital. These sugar alcohol derivatives were ideal as they are biodegradable, inexpensive, and non-toxic. Once the oil was taken up by the gel fibers; it could then be separated from the gel by utilizing vacuum distillation and furthermore the gelator could be recycled.[28] Comma instead of semicolon

Luminescent Devices[edit]

Some gels can be used in luminescent devices such as OLED's and/or fluorescent sensors. One example of an OLED type LMOG is mono-substituted ethynyl-pyrene. This gelator forms a stable gel with DMF spell out , toluene, or cyclohexane while maintaining its luminescence. Another important characteristic of these gels is that they maintain high charge carrier mobility. This means that the gel can pass sufficient current in an electronic luminescent device.[29]

Furthermore, luminescent gels can also be utilized as sensors. These sensors operate by forming a stable luminescent gel in the presence of different analytes. One example of a luminescent gel for sensing fluoride anions is presented by Prasad and Rajamalli. This example utilizes poly(aryl ether) dendrons attached to a core aryl ether with anthracene attached. Upon forming a stable yellow gel (under normal gelation conditions), if fluoride is introduced in the presence of the gel, the gel undergoes a gel to sol transition and becomes bright red. explain sol. also, what concentration of F? Being able to visually detect a color change in the presence of a dilute analyte is a promising field application of LMOG materials.[30]

Chemical Sensing[edit]

Molecular gels can be sensitized toward an external stimuli aka light, heat, or chemicals. Also, LMOG's can be sensitized by the incorporation of a receptor unit or a spectroscopically active unit into the gelator molecule.[31] A variety of quinoxalinones were recently developed that act as a mercury sensor by forming a gel when these ligands complex to mercury.[32] A nonplaner dihydropyridine derivative was induced to gel upon oxidizing the molecule with nitric oxide and then dissolving the oxidized ligand in DMSO/water and then heating and cooling the mixture. This gel has the useful application as it can therefore act as a nitric oxide sensor.[33]

Links to include: Surface tension, self-assembly, ligand, complex, luminescent, mannitol, sorbitol, supramolecular, anthracene, analyte, charge carrier, oxidizing, DMSO, dihydropyridine, OLED, fluorescent, DMF, miticide, cyclohexane, intermolecular, hydrophilic-lipophlic balance, carbonyl, amide, cross-linking, phase transition, crystalline, non-polar, polar, tertiary structure, elasticity, soft matter, biocompatibility, fatty acids, ionizing, solvent, solubility

The diagram listing the different categorization is useful. The video seems a bit long for someone to watch the entire thing, also it shows essentially the same thing conveyed in the single image - the last 45s or so is nice because you are zoomed in on the vial and you can see the phase change. Maybe crop the video to include only that portion sped up by 10x. You could overlay a text banner that says 'heated with heat gun, gelation upon cooling' or something like that.

Check your links, there are some duplicates

See Also[edit]

Aerogel

Nanogel (insulation)mo

Gel Permeation Chromatography

Rheology


External Links[edit]

Low Molecular Mass Gelators of Organic Liquids and the Properties of Their Gels: Pierre Terech and Richard G. Weiss Review Article of LMOG's

Organic Gels and Low Molecular Mass Organic Gelators: D. J. Abdallah and Richard G. Weiss Review Article of LMOG's

A LMOG Based on Gemini Surfactants

A Novel Class of Low Molecular-Weight Organic Gels Based on Terthiophene

Ionic Conductivities of Low Molecular-Weight Organic Gels and Their Application as Electrochromic Materials

Soft Matter Scientific Journal

Journal of Materials Science

Chemical Communications Scientific Journal

Langmuir Scientific Journal

The City College of New York Department of Chemistry with George John's Soft Matter Research Group

References[edit]

  1. ^ Frkanec, L.; Zinic, M. Chiral bis(amino acid)- and bis(amino alcohol)-oxalamide Gelators. Gelation Properties, Self-Assembly Motifs and Chirality Effects” 2010 Chem. Commun. 46, 522-537.
  2. ^ Hafkamp, R. J. H.; Feiters, M. C.; Nolte, R. J. 1999 J. Org. Chem. 64, 412.
  3. ^ Esch, J. H. We Can Design Molecular Gelators, But Do We Understand Them? 2009 Langmuir 25(15), 8392-8394.
  4. ^ Hanabusa, K.; Tange, J.; Taguchi, Y.; Koyama, T.; Shirai, H.Small Molecular Gelling Agents to Harden Organic Liquids: Alkylamide of N-Benzyloxycarbonyl-L-valyl-L-valine 1993 J. Chem. Soc. Commun., 390.
  5. ^ Bai, H.; Li, C.; Wang, X.; Shi, G. A pH-Sensitive Graphene Oxide Composite Hydrogel 2010 Chem. Commun. 46, 2376-2378.
  6. ^ Esch, J. H. "We Can Design Molecular Gelators, But Do We Understand Them?" 2009 Langmuir 25(15), 8392-8394.
  7. ^ Mallia, V.A.; Butler, P. D.; Sarkar, B.; Holman, K. T.; Weiss, R. G. "Reversible Phase Transitions Within Self-Assembled Fibrillar Networks of (R)-18-(n-alkylamino)octadecan-7-ols in Their Carbon Tetrachloride Gels" 2011 J. Am. Chem. Soc. 133, 15045-15054.
  8. ^ Schild, H. G. 1992 Prog. Polym. Sci. 17, 163–249.
  9. ^ Hirokawa, Y.; Tanaka, T. J. 1984 Chem. Phys. 81, 6379–6380.
  10. ^ Zhang, X.-Z.; Xu, X.-D.; Cheng, S.-X.; Zhuo, R.-X. 2008 Soft Matter 4, 385–391.
  11. ^ Qiu, Y.; Park, K. 2001 Adv. Drug Delivery Rev. 53, 321–339.
  12. ^ Terech, P.; Weiss, R. G. Low Molecular Mass Gelators of Organic Liquids and the Properties of Their Gels "Chem. Rev." 1997, 97, 3133-3159.
  13. ^ Burchard, W.; Ross-Murphy, S. B. '"Physical Networks, Polymers and Gels'" Elsevier: London, 1990
  14. ^ Tritt-Goc, J.; Bielejewski, M.; Luboradzki, R. 2011 Tetrahedron, 67, 8170-8176
  15. ^ Hanabasu, K.; Matsumoto, M.; Kimura, M,; Kakehi, A.; Shirai, H. 1999 Colloid Interface Science, 224, 231-244
  16. ^ Bielejewski, M.; Lapinski, A.; Luboradzki, R.; Tritt-Goc, J. 2009 Langmuir, 25, 8274-8279
  17. ^ Muller P. "Glossary of Terms Used in Physical Organic Chemistry" 1994 Pure & Applied Chemistry 66(5), 1077-1184
  18. ^ Muller P. "Glossary of Terms Used in Physical Organic Chemistry" 1994 Pure & Applied Chemistry 66(5), 1077-1184
  19. ^ Muller P. "Glossary of Terms Used in Physical Organic Chemistry" 1994 Pure & Applied Chemistry 66(5), 1077-1184
  20. ^ Jadhav, S. R.; Chiou, B.; Wood, D. F.; DeGrande-Hoffman, G.; Glenn, G. M.; John, G. "Molecular Gels-Based Controlled Release Devices for Pheromones" 2011 Soft Matter 7, 864-867.
  21. ^ Shorey, H. H.; Sisk, C. B.; Gerber, R. G. 1996 Environ. Entomol. 25, 446.
  22. ^ Glenn, G. M.; Klamczynski, A. P.; Shey, J.; Chiou, B. S.; Holtmann, K. M.; Wood, D. F.; Ludvik, C.; DeGrandi-Hoffman, G.; Orts, W.; Imam, S. 2007 Polym. Adv. Technol. 18, 636.
  23. ^ Yosha, I.; Shani, A.; Magdassi, S. 2006 J. Agric. Food Chem. 56, 8045.
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  29. ^ Diring, S.; Camerel, F.; Donnio, B.; Dintzer, T.; Toffanin, S.; Capelli, R.; Muccini, M.; Ziessel, R. "Luminescent Ethynyl-Pyrene Liquid Crystals and Gels for Optoelectronic Devices", 2009, J. Am. Chem. Soc., 131, 18177-18185.
  30. ^ Rajamalli, P.; Prasad, E. "Low Molecular Weight Fluorescent Organogel for Fluoride Ion Detection", 2011, Org. Lett., 13, 3714-3717.
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  33. ^ Chen, J.; McNeil, A. J. Am. Chem. Soc. 2008, 130, 16496–16497
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