Pharmaceutical Crystals (Volume II)

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (15 November 2021) | Viewed by 29910

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Guest Editor
School of Pharmacy and Pharmaceutical Sciences, Hoshi University, Tokyo 142-8501, Japan
Interests: physicochemimcal properties; physical property analysis; crystal form; polymorph prediction
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Guest Editor
Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan
Interests: crystallography; structure analysis; pharmaceutical crystals; phase transition
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are delighted to invite you to submit an article for the “Pharmaceutical Crystals (Volume II)” Special Issue of Crystals. The 1st Special Issue attracted much attention and successfully published ten high-quality articles, and it will be available as a printed book in 2020. This significant success of the 1st issue strongly indicates that the Pharmaceutical Crystals field is quite attractive for many researchers. In light of this, we have decided to launch a 2nd Special Issue in Crystals on “Pharmaceutical Crystals”.

Needless to say, the crystalline state is the most used and the most important form of solid active pharmaceutical ingredients (APIs). The characterization of pharmaceutical crystals encompasses numerous scientific disciplines, and its center is crystal structure analysis, which reveals the molecular structure of important pharmaceutical compounds and also affords key structural information that relates to the broadly variable physicochemical properties of the APIs, e.g., solubility, stability, tablet ability, color, and hygroscopicity.

The Special Issue on “Pharmaceutical Crystals” aims to publish novel molecular and crystal structures of pharmaceutical compounds. We especially encourage the submission of works of new crystal structures of APIs, including polymorphs and solvate crystals, and of multicomponent crystals of APIs, including co-crystals and salts, which would be related to changes in the physicochemical properties of pharmaceutical crystals.

This Special Issue demonstrates the importance of crystal structure information in many sectors of pharmaceutical science and engineering, and thus, contributions from both industry and academia are welcome.

Prof. Etsuo Yonemochi
Prof. Hidehiro Uekusa
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Pharmaceutical crystals
  • Co-crystals
  • Salts
  • Solvates
  • Physicochemical properties
  • Crystal engineering

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Published Papers (10 papers)

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Research

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15 pages, 5266 KiB  
Article
Solid-State Dehydration Mechanism of Diclofenac Sodium Salt Hydrates
by Hironaga Oyama, Takashi Miyamoto, Akiko Sekine, Ilma Nugrahani and Hidehiro Uekusa
Crystals 2021, 11(4), 412; https://doi.org/10.3390/cryst11040412 - 12 Apr 2021
Cited by 1 | Viewed by 4228
Abstract
Salt formation is a useful technique for improving the solubility of active pharmaceutical ingredients (APIs). For instance, a nonsteroidal anti-inflammatory drug, diclofenac (DIC), is used in a sodium salt form, and it has been reported to form several hydrate forms. However, the crystal [...] Read more.
Salt formation is a useful technique for improving the solubility of active pharmaceutical ingredients (APIs). For instance, a nonsteroidal anti-inflammatory drug, diclofenac (DIC), is used in a sodium salt form, and it has been reported to form several hydrate forms. However, the crystal structure of the anhydrous form of diclofenac sodium (DIC-Na) and the structural relationship among the anhydrate and hydrated forms have not yet been revealed. In this study, DIC-Na anhydrate was analyzed using single-crystal X-ray diffraction (XRD). To determine the solid-state dehydration/hydration mechanism of DIC-Na hydrates based on both the present and previously reported crystal structures (4.75-hydrate and 3.5-hydrate), additional experiments including simultaneous powder XRD and differential scanning calorimetry, thermogravimetry, dynamic vapor sorption measurements, and a comparison of the crystal structures were performed. The dehydration of the 4.75-hydrate form was found to occur in two steps. During the first step, only water molecules that were not coordinated to Na+ ions were lost, which led to the formation of the 3.5-hydrate while retaining alternating layered structures. The subsequent dehydration step into the anhydrous phase accompanied a substantial structural reconstruction. This study elucidated the complete landscape of the dehydration/hydration transformation of DIC-Na for the first time through a crystal structure investigation. These findings contribute to understanding the mechanism underlying these dehydration/hydration phenomena and the physicochemical properties of pharmaceutical crystals. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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19 pages, 5693 KiB  
Article
Crystal Structures of Antiarrhythmic Drug Disopyramide and Its Salt with Phthalic Acid
by Majid Ismail Tamboli, Yushi Okamoto, Yohei Utsumi, Takayuki Furuishi, Siran Wang, Daiki Umeda, Okky Dwichandra Putra, Kaori Fukuzawa, Hidehiro Uekusa and Etsuo Yonemochi
Crystals 2021, 11(4), 379; https://doi.org/10.3390/cryst11040379 - 6 Apr 2021
Cited by 1 | Viewed by 2942
Abstract
Disopyramide (DPA) is as a class IA antiarrhythmic drug and its crystallization from cyclohexane at ambient condition yields lower melting form crystals which belong to the monoclinic centrosymmetric space group P21/n, having two molecules in an asymmetric unit. [...] Read more.
Disopyramide (DPA) is as a class IA antiarrhythmic drug and its crystallization from cyclohexane at ambient condition yields lower melting form crystals which belong to the monoclinic centrosymmetric space group P21/n, having two molecules in an asymmetric unit. Crystal structure analysis of pure DPA revealed closely associated DPA molecules aggregates via amide–amide dimer synthon through the N–H∙∙∙O hydrogen bond whereas the second amide hydrogen N–H engaged in an intramolecular N–H∙∙∙N hydrogen bond with N-nitrogen of 2-pyridine moieties. Crystallization of DPA and phthalic acid (PA) in 1: 1 stoichiometric molar ratio from acetone at ambient condition yielded block shape crystals of 1:1 DPA_PA salt. Its X-ray single crystal structure revealed the formation of salt by transfer of acidic proton from one of the carboxylic acidic groups of PA to the tertiary amino group of chain moiety (N3-nitrogen atom) of DPA molecules. DPA_PA salt crystals belong to the monoclinic centrosymmetric space group P21/n, comprising one protonated DPA and one PA¯ anion (hydrogen phthalate counterion) in an asymmetric unit and linked by N–H∙∙∙O and C–H∙∙∙O hydrogen bonds. Pure DPA and DPA_PA salt were further characterized by differential calorimetric analysis, thermal gravimetric analysis, powder x-ray diffraction and infrared spectroscopy. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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11 pages, 14772 KiB  
Article
Crystal Structure of Novel Terephthalate Salt of Antiarrhythmic Drug Disopyramide
by Majid Ismail Tamboli, Yohei Utusmi, Takayuki Furuishi, Kaori Fukuzawa and Etsuo Yonemochi
Crystals 2021, 11(4), 368; https://doi.org/10.3390/cryst11040368 - 31 Mar 2021
Cited by 2 | Viewed by 1911
Abstract
1:1 salt of Disopyramide (DPA) with Terephthalic acid (TA) was obtained by the slow solvent evaporation and the slurry crystallization methods. X-ray single crystal diffraction of DPA:TA confirmed the formation of salt by the transfer of an acidic proton from one of the [...] Read more.
1:1 salt of Disopyramide (DPA) with Terephthalic acid (TA) was obtained by the slow solvent evaporation and the slurry crystallization methods. X-ray single crystal diffraction of DPA:TA confirmed the formation of salt by the transfer of an acidic proton from one of the carboxylic acidic groups of TA to the tertiary amino group of the chain moiety (N3-nitrogen atom) of the DPA molecules. DPA:TA salt crystals crystalize in the triclinic system with space group P-1. The asymmetric unit, comprising one protonated DPA and one TA anion, are linked by a strong charge assisted N+–H∙∙∙O¯ hydrogen bond and a C–H∙∙∙O¯ hydrogen bond. Moreover, structural characterization of DPA:TA salt was carried out using Fourier transform infrared spectroscopy, differential scanning calorimeter, thermogravimetric analysis, and powder X-ray diffraction techniques Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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16 pages, 4985 KiB  
Article
Crystal Structure and Solid-State Conformational Analysis of Active Pharmaceutical Ingredient Venetoclax
by Franc Perdih, Nina Žigart and Zdenko Časar
Crystals 2021, 11(3), 261; https://doi.org/10.3390/cryst11030261 - 7 Mar 2021
Cited by 2 | Viewed by 3044
Abstract
Venetoclax is an orally bioavailable, B-cell lymphoma-2 selective inhibitor used for the treatment of chronic lymphocytic leukemia, small lymphocytic lymphoma, and acute myeloid leukemia. Venetoclax’s crystal structure was until now determined only when it was bound to a B-cell lymphoma-2 (BCL-2) protein, while [...] Read more.
Venetoclax is an orally bioavailable, B-cell lymphoma-2 selective inhibitor used for the treatment of chronic lymphocytic leukemia, small lymphocytic lymphoma, and acute myeloid leukemia. Venetoclax’s crystal structure was until now determined only when it was bound to a B-cell lymphoma-2 (BCL-2) protein, while the crystal structure of this active pharmaceutical ingredient alone has not been reported yet. Herein, we present the first successful crystallization, which provided crystals of venetoclax suitable for X-ray diffraction analysis. The crystal structure of venetoclax hydrate was successfully determined. The asymmetric unit is composed of two crystallographically independent molecules of venetoclax and two molecules of interstitial water. Intramolecular N–H⋯O hydrogen bonding is present in both molecules, and a molecular overlay shows differences in their molecular conformations, which is also observed in respect to venetoclax molecules from known crystal structures of BCL-2:venetoclax complexes. A supramolecular structure is achieved through various N–H⋯N, O–H⋯O, C–H⋯O, C–H⋯π, C–Cl⋯π, ONO⋯π, and π⋯π interactions. The obtained crystals were additionally characterized with spectroscopic techniques, such as IR and Raman, as well as with thermal analysis. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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15 pages, 4925 KiB  
Article
Single Crystal X-Ray Structure for the Disordered Two Independent Molecules of Novel Isoflavone: Synthesis, Hirshfeld Surface Analysis, Inhibition and Docking Studies on IKKβ of 3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-6,7-dimethoxy-4H-chromen-4-one
by Soon Young Shin, Young Han Lee, Yoongho Lim, Ha Jin Lee, Ji Hye Lee, Miri Yoo, Seunghyun Ahn and Dongsoo Koh
Crystals 2020, 10(10), 911; https://doi.org/10.3390/cryst10100911 - 9 Oct 2020
Cited by 5 | Viewed by 2352
Abstract
The structure of the isoflavone compound, 3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-6,7-dimethoxy-4H-chromen-4-one (5), was elucidated by 2D-NMR spectra, mass spectrum and single crystal X-ray crystallography. Compound 5, C19H16O6, was crystallized in the monoclinic space group P21/c [...] Read more.
The structure of the isoflavone compound, 3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-6,7-dimethoxy-4H-chromen-4-one (5), was elucidated by 2D-NMR spectra, mass spectrum and single crystal X-ray crystallography. Compound 5, C19H16O6, was crystallized in the monoclinic space group P21/c with the cell parameters; a = 12.0654(5) Å, b =11.0666(5) Å, c = 23.9550(11) Å, β = 101.3757(16)°, V = 3135.7(2) Å3, and Z = 8. The asymmetric unit of compound 5 consists of two independent molecules 5I and 5II. Both molecules exhibit the disorder of each methylene group present in their 1,4-dioxane rings with relative occupancies of 0.599(10) (5I) and 0.812(9) (5II) for the major component A, and 0.401(10) (5I) and 0.188(9) (5II) for the minor component B, respectively. Each independent molecule revealed remarkable discrepancies in bond lengths, bond angles and dihedral angles in the disordered regions of 1,4-dioxane rings. The common feature of the molecules 5I and 5II are a chromone ring and a benzodioxin ring, which are more tilted towards each other in 5I than in 5II. An additional difference between the molecules is seen in the relative disposition of two methoxy substituents. In the crystal, the molecule 5II forms inversion dimers which are linked into chains along an a-axis direction by intermolecular C–H⋯O interactions. Additional C–H⋯O hydrogen bonds connected the molecules 5I and 5II each other to form a three-dimensional network. Hirshfeld surface analysis evaluated the relative intermolecular interactions which contribute to each crystal structure 5I and 5II. Western blot analysis demonstrated that compound 5 inhibited the TNFα-induced phosphorylation of IKKα/β, resulting in attenuating further downstream NF-κB signaling. A molecular docking study predicted the possible binding of compound 5 to the active site of IKKβ. Compound 5 showed an inhibitory effect on the clonogenicity of HCT116 human colon cancer cells. These results suggest that compound 5 can be used as a platform for the development of an anti-cancer agent targeting IKKα/β. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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11 pages, 2967 KiB  
Article
Synthesis, Crystal Structure and Solid State Transformation of 1,2-Bis[(1-methyl-1H-imidazole-2-yl)thio]ethane
by Leo Štefan, Dubravka Matković-Čalogović, Darko Filić and Miljenko Dumić
Crystals 2020, 10(8), 667; https://doi.org/10.3390/cryst10080667 - 3 Aug 2020
Cited by 1 | Viewed by 2471
Abstract
The spontaneous S-alkylation of the thyreostatic drug methimazole (1-methyl-1,3-dihydro-1H-imidazole-2-thione, 1) with 1,2-dichloroethane at room temperature, in dark or light conditions, led to the formation of its related substance 1,2-bis[(1-methyl-1H-imidazole-2-yl)thio]ethane, C10H14N4S2 [...] Read more.
The spontaneous S-alkylation of the thyreostatic drug methimazole (1-methyl-1,3-dihydro-1H-imidazole-2-thione, 1) with 1,2-dichloroethane at room temperature, in dark or light conditions, led to the formation of its related substance 1,2-bis[(1-methyl-1H-imidazole-2-yl)thio]ethane, C10H14N4S2 (2a), primarily isolated in the form of dihydrochloride tetrahydrate [C10H16N4S2]Cl2·4(H2O) (2b), which crystallized in the monoclinic P21/c space group. Neutralization of 2b, followed by crystallization from the acetone/water mixture, produced dihydrate C10H14N4S2·2(H2O) (2c), which crystallized in the trigonal R-3 space group. Six water molecules in 2c are H-bonded mutually and to the nitrogen atoms of six molecules of 2a. DSC and TGA showed that 2c melts at 65 °C and loses water up to 120 °C. By cooling to room temperature, anhydrous 2a was obtained. Single crystals of 2a that are suitable for X-ray structure analysis were obtained by neutralization of 2b, followed by crystallization from dry dichloromethane. Anhydrous 2a crystallizes in the monoclinic P21/c space group. The dehydration of 2c led to the formation of the anhydrous product 2a, which is identical to the one obtained by crystallization, as was found by complementary solid-state techniques. No intermediate monohydrate or hemihydrate phases were detected. Powder diffraction showed the same pattern of 2c via both preparation procedures. The structures of all the forms were elucidated by spectroscopy, microscopy and thermal methods and confirmed by single crystal X-ray analysis. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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18 pages, 4146 KiB  
Article
Pharmaceutical Salts of Enrofloxacin with Organic Acids
by Hong Pang, Yu-Bin Sun, Jun-Wen Zhou, Meng-Juan Xie, Hao Lin, Yan Yong, Liang-Zhu Chen and Bing-Hu Fang
Crystals 2020, 10(8), 646; https://doi.org/10.3390/cryst10080646 - 27 Jul 2020
Cited by 11 | Viewed by 4060
Abstract
Enrofloxacin is a poorly soluble antibacterial drug of the fluoroquinolones class used in veterinary medicine. The main purpose of this work was to investigate the structural and pharmaceutical properties of new enrofloxacin salts. Enrofloxacin anhydrate and its organic salts with tartaric acid, nicotinic [...] Read more.
Enrofloxacin is a poorly soluble antibacterial drug of the fluoroquinolones class used in veterinary medicine. The main purpose of this work was to investigate the structural and pharmaceutical properties of new enrofloxacin salts. Enrofloxacin anhydrate and its organic salts with tartaric acid, nicotinic acid and suberic acid formed as pure crystalline anhydrous solids. All the crystals were grown from a mixed solution by slow evaporation at room temperature. These products were then characterized by field-emission scanning electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry. Further, X-ray single crystal diffraction analysis was used to study the crystal structure. The intermolecular interactions and packing arrangements in the crystal structures were studied, and the solubility of these salts in water was determined using high-performance liquid chromatography. The results show that the new salts of enrofloxacin developed in this study exhibited excellent water solubility. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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12 pages, 2260 KiB  
Article
Design, Synthesis, Crystal Structure, and Fungicidal Activity of Two Fenclorim Derivatives
by Ke-Jie Xiong and Feng-Pei Du
Crystals 2020, 10(7), 587; https://doi.org/10.3390/cryst10070587 - 7 Jul 2020
Cited by 2 | Viewed by 2459
Abstract
Two fenclorim derivatives (compounds 6 and 7) were synthesized by linking active sub-structures using fenclorim as the lead compound. The chemical structures of the two compounds were confirmed by NMR spectroscopy, high resolution mass spectrometry, and X-ray diffraction analysis. Their fungicidal activity [...] Read more.
Two fenclorim derivatives (compounds 6 and 7) were synthesized by linking active sub-structures using fenclorim as the lead compound. The chemical structures of the two compounds were confirmed by NMR spectroscopy, high resolution mass spectrometry, and X-ray diffraction analysis. Their fungicidal activity against six plant fungal strains was tested. Compounds 6 and 7 both crystallized in the monoclinic system, with a P21/c space group (a = 8.4842(6) Å, b = 24.457(2) Å, c = 8.9940(6) Å, V = 1855.0(2) Å3, Z = 4) and Cc space group (a = 10.2347(7) Å, b = 18.3224(10) Å, c = 7.2447(4) Å, V = 1357.50(14) Å3, Z = 4), respectively. The crystal structure of compound 6 was stabilized by C–H···N and C–H···O hydrogen bonding interactions and N–H···N hydrogen bonds linked the neighboring molecules of compound 7 to form a three-dimensional framework. Compound 6 displayed the most excellent activity, which is much better than that of pyrimethanil against Botrytis cinerea in vivo. Additionally, compound 6 exhibited greater in vitro activity against Pseudoperonospora cubensis compared to that of pyrimethanil. Moreover, compound 7 exhibited strong fungicidal activity against Erysiphe cichoracearum at 50 mg/L in vitro, while pyrimethanil did not. Compounds 6 and 7 could be used as new pyrimidine fungicides in the future. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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13 pages, 2163 KiB  
Article
New Crystal Forms for Biologically Active Compounds. Part 2: Anastrozole as N-Substituted 1,2,4-Triazole in Halogen Bonding and Lp-π Interactions with 1,4-Diiodotetrafluorobenzene
by Mariya A. Kryukova, Alexander V. Sapegin, Alexander S. Novikov, Mikhail Krasavin and Daniil M. Ivanov
Crystals 2020, 10(5), 371; https://doi.org/10.3390/cryst10050371 - 5 May 2020
Cited by 17 | Viewed by 2530
Abstract
For an active pharmaceutical ingredient, it is important to stabilize its specific crystal polymorph. If the potential interconversion of various polymorphs is not carefully controlled, it may lead to deterioration of the drug’s physicochemical profile and, ultimately, its therapeutic efficacy. The desired polymorph [...] Read more.
For an active pharmaceutical ingredient, it is important to stabilize its specific crystal polymorph. If the potential interconversion of various polymorphs is not carefully controlled, it may lead to deterioration of the drug’s physicochemical profile and, ultimately, its therapeutic efficacy. The desired polymorph stabilization can be achieved via co-crystallization with appropriate crystallophoric excipients. In this work, we identified an opportunity for co-crystallization of anastrozole (ASZ), a well-known aromatase inhibitor useful in second-line therapy of estrogen-dependent breast cancer, with a classical XB donor, 1,2,4,5-tetrafluoro-3,6-diiodobenzene (1,4-FIB). In the X-ray structures of ASZ·1.5 (1,4-FIB) co-crystal, different non-covalent interactions involving hydrogen and halogen atoms were detected and studied by quantum chemical calculations and QTAIM analysis at the ωB97XD/DZP-DKH level of theory. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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Review

Jump to: Research

25 pages, 962 KiB  
Review
Application of Fundamental Techniques for Physicochemical Characterizations to Understand Post-Formulation Performance of Pharmaceutical Nanocrystalline Materials
by Bwalya A. Witika, Marique Aucamp, Larry L. Mweetwa and Pedzisai A. Makoni
Crystals 2021, 11(3), 310; https://doi.org/10.3390/cryst11030310 - 21 Mar 2021
Cited by 4 | Viewed by 2934
Abstract
Nanocrystalline materials (NCM, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from drug delivery and electronics to optics. Drug nanocrystals (NC) and nano co-crystals (NCC) are examples of NCM with fascinating physicochemical properties and have [...] Read more.
Nanocrystalline materials (NCM, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from drug delivery and electronics to optics. Drug nanocrystals (NC) and nano co-crystals (NCC) are examples of NCM with fascinating physicochemical properties and have attracted significant attention in drug delivery. NCM are categorized by advantageous properties, such as high drug-loading efficiency, good long-term physical stability, steady and predictable drug release, and long systemic circulation time. These properties make them excellent formulations for the efficient delivery of a variety of active pharmaceutical ingredients (API). In this review, we summarize the recent advances in drug NCM-based therapy options. Currently, there are three main methods to synthesize drug NCM, including top-down, bottom-up, and combination methods. The fundamental characterization methods of drug NCM are elaborated. Furthermore, the applications of these characterizations and their implications on the post-formulation performance of NCM are introduced. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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